1 00:00:00,000 --> 00:00:00,024 The following content is provided under a Creative 2 00:00:00,024 --> 00:00:00,033 Commons license. 3 00:00:00,033 --> 00:00:00,057 Your support will help MIT OpenCourseWare continue to 4 00:00:00,057 --> 00:00:00,081 offer high quality educational resources for free. 5 00:00:00,081 --> 00:00:00,108 To make a donation or view additional materials from 6 00:00:00,108 --> 00:00:00,132 hundreds of MIT courses, visit MIT OpenCourseWare at 7 00:00:00,132 --> 00:00:00,150 ocw.mit.edu. 8 00:00:00,150 --> 00:00:25,120 PROFESSOR: OK, we have the clicker question up. 9 00:00:25,120 --> 00:00:28,510 We're going to have another clicker competition today. 10 00:00:28,510 --> 00:00:37,180 The defending champs, there's Darcy's recitation. 11 00:00:37,180 --> 00:01:44,720 So, OK, let's just take 10 more seconds on this. 12 00:01:44,720 --> 00:01:50,960 OK, not too bad, 74%. 13 00:01:50,960 --> 00:01:53,520 So, in this problem, the trick was just to look at the 14 00:01:53,520 --> 00:01:58,620 equation and figure out what's going on -- which element is 15 00:01:58,620 --> 00:02:01,990 being reduced, and which one is being oxidized. 16 00:02:01,990 --> 00:02:04,970 So this is something that you will be seeing on 17 00:02:04,970 --> 00:02:06,600 the upcoming exam. 18 00:02:06,600 --> 00:02:09,330 So we're going to talk about that in a few minutes, but 19 00:02:09,330 --> 00:02:13,550 first I want to answer the question from last time. 20 00:02:13,550 --> 00:02:18,130 So, first, let's just, I know you've all been wondering 21 00:02:18,130 --> 00:02:26,960 about how vitamin B12 is reduced in the body. 22 00:02:26,960 --> 00:02:28,840 So, let's take a look at this now. 23 00:02:28,840 --> 00:02:38,080 So, if everyone can quiet down, let's get started. 24 00:02:38,080 --> 00:02:43,250 So, vitamin B12 is reduced by a protein that's called 25 00:02:43,250 --> 00:02:43,530 flavodoxin. 26 00:02:43,530 --> 00:02:46,920 And flavodoxin is a protein that has a cofactor which is a 27 00:02:46,920 --> 00:02:53,110 flavin, and that's also a vitamin B, as it turns out, 28 00:02:53,110 --> 00:02:56,010 they're both vitamin B's. 29 00:02:56,010 --> 00:03:03,240 So, vitamin B12 has a redox potential or a standard 30 00:03:03,240 --> 00:03:05,720 reduction potential of minus 0 . 31 00:03:05,720 --> 00:03:11,180 5 2 6 volts, and that is a very low number for a 32 00:03:11,180 --> 00:03:13,290 biological system. 33 00:03:13,290 --> 00:03:16,435 And flavodoxin has a potential of minus 0. 34 00:03:16,435 --> 00:03:19,180 2 3 volts. 35 00:03:19,180 --> 00:03:31,210 So, which of these things is a better reducing agent? 36 00:03:31,210 --> 00:03:34,530 So, which thing, you want to think about reducing agent, 37 00:03:34,530 --> 00:03:37,390 which thing would prefer to be oxidized and 38 00:03:37,390 --> 00:03:42,850 reduce something else? 39 00:03:42,850 --> 00:03:46,660 So, with the low negative number, B12 is a better 40 00:03:46,660 --> 00:03:50,170 reducing agent than flavodoxin, and just based on 41 00:03:50,170 --> 00:03:54,650 these numbers, vitamin B12 should be reducing flavodoxin, 42 00:03:54,650 --> 00:03:58,790 not the other way around. 43 00:03:58,790 --> 00:04:01,160 So, how does this work then? 44 00:04:01,160 --> 00:04:05,940 So, in your body right now, you have a version of a 45 00:04:05,940 --> 00:04:10,490 flavodoxin protein, and you of vitamin B12 attached to an 46 00:04:10,490 --> 00:04:14,370 enzyme, methionine synthase, and for that to be activated, 47 00:04:14,370 --> 00:04:15,540 it needs to be reduced. 48 00:04:15,540 --> 00:04:18,630 So how is this happening? 49 00:04:18,630 --> 00:04:23,860 So, let's consider whether the reduction of B12 by flavodoxin 50 00:04:23,860 --> 00:04:25,060 is spontaneous. 51 00:04:25,060 --> 00:04:27,990 It happens in your body so one might think that it is. 52 00:04:27,990 --> 00:04:30,600 But let's look at that. 53 00:04:30,600 --> 00:04:33,680 So, we can look at it the same way you've looked at all the 54 00:04:33,680 --> 00:04:38,790 other systems, we're talking about batteries, electric 55 00:04:38,790 --> 00:04:42,080 chemical cells -- you can use the same equations if it's a 56 00:04:42,080 --> 00:04:45,830 biological system as you can for any other system. 57 00:04:45,830 --> 00:04:47,470 So we've seen this equation before. 58 00:04:47,470 --> 00:04:51,040 We've calculated changes in the standard reduction 59 00:04:51,040 --> 00:04:54,620 potential for a cell, and we talked about e nought for 60 00:04:54,620 --> 00:04:58,900 reduction minus the e nought for oxidation, and we can use 61 00:04:58,900 --> 00:05:01,000 that same equation. 62 00:05:01,000 --> 00:05:04,590 So we can put it in in the biological context. 63 00:05:04,590 --> 00:05:07,610 The vitamin B12 is the thing that's being reduced, and the 64 00:05:07,610 --> 00:05:11,060 flavodoxin is the thing that's being oxidized, that's the 65 00:05:11,060 --> 00:05:12,580 reaction that happens. 66 00:05:12,580 --> 00:05:16,260 So, we can plug those values in. 67 00:05:16,260 --> 00:05:18,140 So we have minus 0 . 68 00:05:18,140 --> 00:05:21,720 5 2 6 volts, minus a negative 0 . 69 00:05:21,720 --> 00:05:24,970 2 3 volts, and if you put those together, 70 00:05:24,970 --> 00:05:26,350 you get minus 0 . 71 00:05:26,350 --> 00:05:29,590 2 9 6 volts. 72 00:05:29,590 --> 00:05:34,080 So is that going to be a spontaneous reaction? 73 00:05:34,080 --> 00:05:36,180 No, it's not going to be. 74 00:05:36,180 --> 00:05:40,100 Your value for the e is negative, which means what is 75 00:05:40,100 --> 00:05:43,180 true about delta g? 76 00:05:43,180 --> 00:05:47,630 Positive, so it won't be spontaneous. 77 00:05:47,630 --> 00:05:52,170 So, let's figure out how not spontaneous it's going to be. 78 00:05:52,170 --> 00:05:54,860 How much trouble are we all in? 79 00:05:54,860 --> 00:05:58,340 So we can use again, the same equation that we used for 80 00:05:58,340 --> 00:06:01,060 batteries that we've used in this course -- just because 81 00:06:01,060 --> 00:06:03,270 it's a biological system, doesn't mean the equation 82 00:06:03,270 --> 00:06:04,980 doesn't hold. 83 00:06:04,980 --> 00:06:08,230 So our equation for delta g nought minus n, the number of 84 00:06:08,230 --> 00:06:12,350 moles of electrons times Faraday's constant times the 85 00:06:12,350 --> 00:06:15,060 change in the standard potential. 86 00:06:15,060 --> 00:06:16,270 So we can plug it in. 87 00:06:16,270 --> 00:06:19,330 I can tell you it's a one electron process -- flavodoxin 88 00:06:19,330 --> 00:06:23,610 puts one electron into vitamin B12, so we have minus 1 times 89 00:06:23,610 --> 00:06:27,020 Faraday's constant times the cell potential difference you 90 00:06:27,020 --> 00:06:29,120 just measured, which is minus 0 . 91 00:06:29,120 --> 00:06:35,400 2 9 6, and if you multiply those out, then you get 28 . 92 00:06:35,400 --> 00:06:38,270 6 kilojoules per mole positive. 93 00:06:38,270 --> 00:06:41,470 That is a very big value -- that's not spontaneous and 94 00:06:41,470 --> 00:06:46,270 it's not a small number for a biological system. 95 00:06:46,270 --> 00:06:49,000 So, why don't we all have heart disease and 96 00:06:49,000 --> 00:06:49,320 megaloblastic anemia? 97 00:06:49,320 --> 00:06:53,890 Those are problems associated when this particular enzyme is 98 00:06:53,890 --> 00:06:58,280 not functioning. 99 00:06:58,280 --> 00:07:00,990 So, what happens in this system is what happens in a 100 00:07:00,990 --> 00:07:05,290 number of biological systems. How do you drive something 101 00:07:05,290 --> 00:07:07,580 forward that is not spontaneous? 102 00:07:07,580 --> 00:07:11,450 And what you can do is put energy into the system to 103 00:07:11,450 --> 00:07:14,380 drive that non-spontaneous reaction. 104 00:07:14,380 --> 00:07:17,790 And in this case, the energy that's put into the system is 105 00:07:17,790 --> 00:07:18,760 from a molecule called s adenosylmethionine. 106 00:07:18,760 --> 00:07:22,550 And the cleavage of s adenosylmethionine has a delta 107 00:07:22,550 --> 00:07:28,380 g nought of negative 37 . 108 00:07:28,380 --> 00:07:30,480 6 kilojoules per mole. 109 00:07:30,480 --> 00:07:34,350 So it's more favorable than the reduction of B12 is 110 00:07:34,350 --> 00:07:38,410 unfavorable, and so this drives this system. 111 00:07:38,410 --> 00:07:43,050 So, s adenosylmethionine is your friend, it helps in the 112 00:07:43,050 --> 00:07:46,100 body for B12 to be reduced so that you can 113 00:07:46,100 --> 00:07:49,070 function and be healthy. 114 00:07:49,070 --> 00:07:52,240 So, many biological systems work like this. 115 00:07:52,240 --> 00:07:56,580 So what have we been calling something, a cell, in which an 116 00:07:56,580 --> 00:08:00,290 unfavorable reaction is driven by applying some kind of 117 00:08:00,290 --> 00:08:11,400 energy or current, what do we call that? 118 00:08:11,400 --> 00:08:13,450 Two types of cells we mentioned. 119 00:08:13,450 --> 00:08:18,470 One that has a favorable, it has a spontaneous reaction. 120 00:08:18,470 --> 00:08:22,070 A cell that has a spontaneous reaction is called what? 121 00:08:22,070 --> 00:08:22,780 Galvanic. 122 00:08:22,780 --> 00:08:26,780 And the other kind is called? 123 00:08:26,780 --> 00:08:27,050 Yup. 124 00:08:27,050 --> 00:08:28,500 So, electrolitic cell. 125 00:08:28,500 --> 00:08:30,900 So this is sort of the biological equivalent of an 126 00:08:30,900 --> 00:08:33,310 electrolitic cell where you have s adenosylmethionine 127 00:08:33,310 --> 00:08:38,340 cleavage coupled to an unfavorable reaction to drive 128 00:08:38,340 --> 00:08:41,480 that reduction of B12 by flavodoxin. 129 00:08:41,480 --> 00:08:45,360 And B12 has such a low potential, that there really 130 00:08:45,360 --> 00:08:47,640 isn't anything else that can reduce it. 131 00:08:47,640 --> 00:08:49,740 It has one of the lowest potentials known in a 132 00:08:49,740 --> 00:08:53,720 biological system, so nature said, OK, well, we're not 133 00:08:53,720 --> 00:08:56,110 going to make something with a lower potential to do this 134 00:08:56,110 --> 00:08:58,640 chemistry, we'll have something else with a higher 135 00:08:58,640 --> 00:09:01,680 potential, but will drive the reaction because it's going to 136 00:09:01,680 --> 00:09:03,740 be non-spontaneous. 137 00:09:03,740 --> 00:09:07,320 So that's how this works. 138 00:09:07,320 --> 00:09:10,500 So, today there's a long list of topics, all of these are 139 00:09:10,500 --> 00:09:14,730 pretty short and basically constitute the introductory 140 00:09:14,730 --> 00:09:16,830 material in this unit. 141 00:09:16,830 --> 00:09:21,190 And we've jumped ahead, this is in chapter 16. 142 00:09:21,190 --> 00:09:26,840 So, I really like transition metals, because I am a fan of 143 00:09:26,840 --> 00:09:32,260 metals that are involved in biological systems. So, I just 144 00:09:32,260 --> 00:09:36,670 thought as part of chemistry, I just want to sort of review 145 00:09:36,670 --> 00:09:39,260 the kind of basic areas of chemistry for a minute. 146 00:09:39,260 --> 00:09:42,150 This is not in your handout, but just so you sort of think 147 00:09:42,150 --> 00:09:45,720 about what are all parts of chemistry. 148 00:09:45,720 --> 00:09:49,600 There is organic chemistry -- does anyone know what organic 149 00:09:49,600 --> 00:09:52,300 chemistry concerns itself with? 150 00:09:52,300 --> 00:09:56,100 Carbon. 151 00:09:56,100 --> 00:10:02,470 And then what we have known as inorganic chemistry. 152 00:10:02,470 --> 00:10:07,080 Anyone know what that is? 153 00:10:07,080 --> 00:10:11,910 Not carbon. 154 00:10:11,910 --> 00:10:14,570 So, a lot of people who are inorganic chemists study 155 00:10:14,570 --> 00:10:18,590 transition metals, but it's basically other 156 00:10:18,590 --> 00:10:20,220 things besides carbon. 157 00:10:20,220 --> 00:10:25,480 And then one of the areas that I like is bioinorganic 158 00:10:25,480 --> 00:10:28,930 chemistry, and these are people who 159 00:10:28,930 --> 00:10:31,690 study metals in biology. 160 00:10:31,690 --> 00:10:40,800 So, people who study metals in biology, and we're also kind 161 00:10:40,800 --> 00:10:45,680 of referred to as, we're sort of in a club, 162 00:10:45,680 --> 00:10:50,070 which we call the MIB. 163 00:10:50,070 --> 00:10:53,150 So, some of you -- and Will Smith did a disservice -- 164 00:10:53,150 --> 00:10:58,020 people now associate this with hunting aliens, but in fact, 165 00:10:58,020 --> 00:11:02,040 people who are in MIB are associated with hunting for 166 00:11:02,040 --> 00:11:04,640 metal ions in biological cells. 167 00:11:04,640 --> 00:11:09,460 So this is sort of the true MIB. 168 00:11:09,460 --> 00:11:12,510 And in an honor of this discussion today, I am wearing 169 00:11:12,510 --> 00:11:14,630 a teeshirt from one of our meetings. 170 00:11:14,630 --> 00:11:18,440 This is from the International Congress on Bioinorganic 171 00:11:18,440 --> 00:11:22,040 Chemistry, which we refer to as ICBIC. 172 00:11:22,040 --> 00:11:26,160 And you notice that the clever people who made this teeshirt 173 00:11:26,160 --> 00:11:31,090 used the B from the bioinorganic to make B12, 174 00:11:31,090 --> 00:11:33,540 which is a very popular vitamin in the 175 00:11:33,540 --> 00:11:38,770 bioinorganic community. 176 00:11:38,770 --> 00:11:42,890 So, metals in biology. 177 00:11:42,890 --> 00:11:46,810 Carbon, carbon's a good thing, amino acids are 178 00:11:46,810 --> 00:11:48,970 good, I like proteins. 179 00:11:48,970 --> 00:11:51,990 But often, when you take a metal and attach it to a 180 00:11:51,990 --> 00:11:55,570 protein, that protein can do really cool chemistry -- 181 00:11:55,570 --> 00:11:58,490 really need oxidation reduction chemistry. 182 00:11:58,490 --> 00:12:02,430 So, here is part of the periodic table that includes 183 00:12:02,430 --> 00:12:04,990 many of these transition metals that we're going to be 184 00:12:04,990 --> 00:12:06,190 talking about. 185 00:12:06,190 --> 00:12:10,010 And things that are in orange here are metals that are very 186 00:12:10,010 --> 00:12:12,070 important biologically. 187 00:12:12,070 --> 00:12:15,750 Some of the things that are in grey here are metals that are 188 00:12:15,750 --> 00:12:20,780 used as probes or as drugs in biological systems, and some 189 00:12:20,780 --> 00:12:22,670 could be both. 190 00:12:22,670 --> 00:12:26,640 So, when you add a metal to a protein you can do cool stuff. 191 00:12:26,640 --> 00:12:27,460 What can you do? 192 00:12:27,460 --> 00:12:29,330 Well, you can split nitrogen. 193 00:12:29,330 --> 00:12:32,290 You learned that the triple bond of nitrogen is pretty 194 00:12:32,290 --> 00:12:39,020 hard to break, but metals in proteins can do it. 195 00:12:39,020 --> 00:12:42,140 You've heard of hydrogen fuel cells and things like that. 196 00:12:42,140 --> 00:12:46,090 There's a protein called hydrogenase that uses metals 197 00:12:46,090 --> 00:12:48,230 to do chemistry with hydrogen. 198 00:12:48,230 --> 00:12:50,220 You could you radical based chemistry. 199 00:12:50,220 --> 00:12:52,600 You can do a lot of really great things when you have a 200 00:12:52,600 --> 00:12:57,200 protein that has a metal in it. 201 00:12:57,200 --> 00:13:00,690 So, let me introduce you to some of the concepts and 202 00:13:00,690 --> 00:13:04,010 terminology involved in this, so we're going to have a metal 203 00:13:04,010 --> 00:13:07,000 and the metal's going to be bound to stuff. 204 00:13:07,000 --> 00:13:10,440 So, one of the great features of transition metals is their 205 00:13:10,440 --> 00:13:15,520 ability to form complexes with small molecules or ions. 206 00:13:15,520 --> 00:13:19,130 They also, this applies to a protein system in the case 207 00:13:19,130 --> 00:13:22,220 that instead of small molecules, you have amino 208 00:13:22,220 --> 00:13:27,490 acids of proteins it can also form complexes with. 209 00:13:27,490 --> 00:13:32,210 So, the way that they do this is metals have often, they can 210 00:13:32,210 --> 00:13:35,880 attract electron density, usually a lone pair of 211 00:13:35,880 --> 00:13:39,010 electrons from another atom, and so they can form what are 212 00:13:39,010 --> 00:13:44,480 called these coordination complexes. 213 00:13:44,480 --> 00:13:47,890 So, now we're going to review for a minute, donor atoms, 214 00:13:47,890 --> 00:13:52,550 they're called ligands, and we can think about something that 215 00:13:52,550 --> 00:13:55,180 we learned when we talked about acids and bases, our 216 00:13:55,180 --> 00:13:57,290 more broad definition. 217 00:13:57,290 --> 00:14:01,390 So, donor atoms are ligands, and ligands are what? 218 00:14:01,390 --> 00:14:04,020 Lewis acids or Lewis bases, and what do they do? 219 00:14:04,020 --> 00:14:43,690 OK, let's just take 10 more seconds. 220 00:14:43,690 --> 00:14:48,000 So most of you thought donor atoms -- the answers that had 221 00:14:48,000 --> 00:14:52,800 donate electrons did better, so that was good reading of 222 00:14:52,800 --> 00:14:58,950 the question, but they are Lewis bases. 223 00:14:58,950 --> 00:15:02,860 So Lewis bases donate electron pairs. 224 00:15:02,860 --> 00:15:06,250 So, here's some examples that you will see of ligands that 225 00:15:06,250 --> 00:15:08,520 we'll be talking about in this unit. 226 00:15:08,520 --> 00:15:12,530 You will become very familiar with some of these as you work 227 00:15:12,530 --> 00:15:16,420 problems. So they're typically donating one 228 00:15:16,420 --> 00:15:21,140 lone pair of electrons. 229 00:15:21,140 --> 00:15:25,380 So, acceptor atoms are the transition metals themselves, 230 00:15:25,380 --> 00:15:29,570 and so the transition metals are acting as Lewis acids, and 231 00:15:29,570 --> 00:15:32,620 so then they would be accepting those 232 00:15:32,620 --> 00:15:34,410 lone pairs of electrons. 233 00:15:34,410 --> 00:15:37,270 So, you can think about coordination complexes as 234 00:15:37,270 --> 00:15:41,110 Lewis acids and Lewis bases, or acceptor atoms and donor 235 00:15:41,110 --> 00:15:48,580 ligands or donor atoms. So here are some examples of 236 00:15:48,580 --> 00:15:51,070 transition metals that we're going to see, so it's that 237 00:15:51,070 --> 00:15:54,180 sort of d-block of the periodic table that we'll 238 00:15:54,180 --> 00:15:59,690 become very familiar with in this unit. 239 00:15:59,690 --> 00:16:03,110 So, then when you take your acceptor atom and your donor 240 00:16:03,110 --> 00:16:05,800 atom and you put them together, you get what is 241 00:16:05,800 --> 00:16:08,220 known as coordination complexes. 242 00:16:08,220 --> 00:16:11,210 So, coordination complex is just the metal or the Lewis 243 00:16:11,210 --> 00:16:14,520 acid surrounded by the ligands, or the Lewis bases or 244 00:16:14,520 --> 00:16:17,840 the donor atoms. 245 00:16:17,840 --> 00:16:20,850 And here is an example of a coordination complex. 246 00:16:20,850 --> 00:16:23,830 We have metal, we have cobalt in the middle, and it's 247 00:16:23,830 --> 00:16:27,000 surrounded by a series of ligands, and 248 00:16:27,000 --> 00:16:30,130 these are n h 3 ligands. 249 00:16:30,130 --> 00:16:34,100 And so then our cobalt in the center, our metal, is the 250 00:16:34,100 --> 00:16:38,720 Lewis acid, and it's going to be the acceptor atom. 251 00:16:38,720 --> 00:16:42,150 And the n h 3 groups are our Lewis bases, they're donor 252 00:16:42,150 --> 00:16:46,240 atoms, see it's written with those two electrons there, 253 00:16:46,240 --> 00:16:50,340 that they're sharing their electrons with the cobalt 254 00:16:50,340 --> 00:16:52,600 forming this coordination complex. 255 00:16:52,600 --> 00:16:55,730 And in this scheme, we have the bonds are just these 256 00:16:55,730 --> 00:16:58,940 straight lines are in the plane, the thick bonds coming 257 00:16:58,940 --> 00:17:01,690 out are coming out toward you, and the dashed lines going 258 00:17:01,690 --> 00:17:06,800 back are going back into the screen here. 259 00:17:06,800 --> 00:17:11,110 So, let's talk about a couple of definitions here. 260 00:17:11,110 --> 00:17:14,340 We have something called coordination number or CN 261 00:17:14,340 --> 00:17:17,440 number, and this is simply the number of ligands 262 00:17:17,440 --> 00:17:19,010 bonded to the metal. 263 00:17:19,010 --> 00:17:22,920 So the number is six, there is six ligands. 264 00:17:22,920 --> 00:17:25,780 Typically, the numbers will range for these coordination 265 00:17:25,780 --> 00:17:33,440 complexes to two to 12, with six being the most common. 266 00:17:33,440 --> 00:17:36,050 So, here is some notation. 267 00:17:36,050 --> 00:17:38,810 If you see this picture, you should be able to write a 268 00:17:38,810 --> 00:17:40,530 notation for it. 269 00:17:40,530 --> 00:17:44,490 And within a bracket, you would write cobalt, and then 270 00:17:44,490 --> 00:17:47,700 you have your n h 3, six of them, so you put that in a 271 00:17:47,700 --> 00:17:50,880 bracket and indicate that there's six n h 3 groups. 272 00:17:50,880 --> 00:17:53,830 Then you have this overall bracket here 273 00:17:53,830 --> 00:17:55,550 with a charge up above. 274 00:17:55,550 --> 00:17:59,000 And so over here, we have this little bracket plus 3, that 275 00:17:59,000 --> 00:18:01,610 means that this whole coordination complex has a 276 00:18:01,610 --> 00:18:03,940 charge of plus 3. 277 00:18:03,940 --> 00:18:06,980 Because it has a positive charge, sometimes coordination 278 00:18:06,980 --> 00:18:09,860 complexes are associated with counter ions. 279 00:18:09,860 --> 00:18:13,090 So, you might see three chloride minus 1 ions around 280 00:18:13,090 --> 00:18:15,110 to counter that charge. 281 00:18:15,110 --> 00:18:18,310 And if you did, you would see the three chlorides on the 282 00:18:18,310 --> 00:18:19,790 outside of the bracket. 283 00:18:19,790 --> 00:18:22,290 So things inside of the bracket are actually 284 00:18:22,290 --> 00:18:25,870 coordinated to the metal, things outside the bracket are 285 00:18:25,870 --> 00:18:27,580 counter ions. 286 00:18:27,580 --> 00:18:30,720 And so that would be how you would translate that 287 00:18:30,720 --> 00:18:35,360 particular notation. 288 00:18:35,360 --> 00:18:38,580 All right, so, we're back to geometry again. 289 00:18:38,580 --> 00:18:40,880 As I said, everything you learn in this course, we're 290 00:18:40,880 --> 00:18:42,430 going to use again. 291 00:18:42,430 --> 00:18:47,970 So, if you're forgetting some material from units 1 and 2, 292 00:18:47,970 --> 00:18:50,630 this would be a good time to review those. 293 00:18:50,630 --> 00:18:53,940 So, if we have this coordination number of six 294 00:18:53,940 --> 00:19:14,400 things around, what kind of geometry are we going to have? 295 00:19:14,400 --> 00:19:28,740 All right, 10 seconds. 296 00:19:28,740 --> 00:19:32,980 Yup, so we have octahedral geometry. 297 00:19:32,980 --> 00:19:37,230 And here is an example of our octahedral geometry. 298 00:19:37,230 --> 00:19:39,790 So, let's just quickly run through the rest of these. 299 00:19:39,790 --> 00:19:43,040 You can yell out the answers, either looking at your handout 300 00:19:43,040 --> 00:19:45,030 or not looking at your handout. 301 00:19:45,030 --> 00:19:51,170 The next one over here, what is it? 302 00:19:51,170 --> 00:19:51,810 Right, trigonal bipyramidal. 303 00:19:51,810 --> 00:19:56,800 For a c n number of five, we have another option shown over 304 00:19:56,800 --> 00:20:00,130 here, what's that one called? 305 00:20:00,130 --> 00:20:01,520 Square pyramidal. 306 00:20:01,520 --> 00:20:04,310 For c n numbers of four, there's two things that you'll 307 00:20:04,310 --> 00:20:07,690 commonly see, what's the first one called? 308 00:20:07,690 --> 00:20:08,530 Square planar. 309 00:20:08,530 --> 00:20:10,210 The second one? 310 00:20:10,210 --> 00:20:10,500 Tetrahedral. 311 00:20:10,500 --> 00:20:15,900 For c n number of three, what's that geometry called? 312 00:20:15,900 --> 00:20:16,960 Trigonal planar. 313 00:20:16,960 --> 00:20:20,290 And c n of two, only one option. 314 00:20:20,290 --> 00:20:20,490 Linear. 315 00:20:20,490 --> 00:20:23,930 All right, so let's just review the angles as well, 316 00:20:23,930 --> 00:20:26,200 those are not in your handouts, but you can yell 317 00:20:26,200 --> 00:20:28,850 those out as well. 318 00:20:28,850 --> 00:20:33,040 So what angle do we have in an octahedral system? 319 00:20:33,040 --> 00:20:34,700 90. 320 00:20:34,700 --> 00:20:37,180 There are two angles involved if we have trigonal 321 00:20:37,180 --> 00:20:38,850 bipyramidal. 322 00:20:38,850 --> 00:20:42,110 What's the angle from the axial to the equatorial? 323 00:20:42,110 --> 00:20:43,410 STUDENT: 90. 324 00:20:43,410 --> 00:20:45,380 PROFESSOR: And what's the angle from one equatorial atom 325 00:20:45,380 --> 00:20:47,110 to another equatorial atom? 326 00:20:47,110 --> 00:20:53,990 So, we have 90 and 120. 327 00:20:53,990 --> 00:20:58,080 What about in our square pyramidal system, what are the 328 00:20:58,080 --> 00:21:00,250 angles here? 329 00:21:00,250 --> 00:21:03,890 90. 330 00:21:03,890 --> 00:21:10,060 What about square planar? 331 00:21:10,060 --> 00:21:10,840 90. 332 00:21:10,840 --> 00:21:16,650 Tetrahedral? 333 00:21:16,650 --> 00:21:21,390 Let's try that again with more enthusiasm. 334 00:21:21,390 --> 00:21:22,750 Awesome, 109 . 335 00:21:22,750 --> 00:21:24,910 5. 336 00:21:24,910 --> 00:21:25,250 Trigonal planar? 337 00:21:25,250 --> 00:21:29,320 120. 338 00:21:29,320 --> 00:21:31,840 And finally, linear. 339 00:21:31,840 --> 00:21:37,360 180. 340 00:21:37,360 --> 00:21:39,640 So, we're going to use this information again in this 341 00:21:39,640 --> 00:21:42,950 unit, and of course, it'll be on the final when we're 342 00:21:42,950 --> 00:21:47,040 talking about Lewis structures and hybridization and other 343 00:21:47,040 --> 00:21:47,850 things as well. 344 00:21:47,850 --> 00:21:52,920 So this comes back in several times, vsper theory, you have 345 00:21:52,920 --> 00:21:55,580 this several times. 346 00:21:55,580 --> 00:21:58,860 OK. 347 00:21:58,860 --> 00:22:02,520 So, another term that you hear a lot when people are talking 348 00:22:02,520 --> 00:22:05,180 about coordination complexes is what's 349 00:22:05,180 --> 00:22:07,930 called the chelate effect. 350 00:22:07,930 --> 00:22:11,880 So, ligands that bind to a metal at one point are called 351 00:22:11,880 --> 00:22:17,980 unidentate or monodentate, and that's from dent, which is 352 00:22:17,980 --> 00:22:21,350 tooth, so one tooth. 353 00:22:21,350 --> 00:22:26,780 Now, if a ligand attaches with two or more points of 354 00:22:26,780 --> 00:22:30,260 attachment, it can be called a chelating ligand. 355 00:22:30,260 --> 00:22:34,200 And this comes from the Greek, chele is claw. 356 00:22:34,200 --> 00:22:37,540 So, if it's attaching with more than one point of 357 00:22:37,540 --> 00:22:41,670 attachment, if the ligand is grabbing on, it's like a claw 358 00:22:41,670 --> 00:22:45,940 and that's called a chelate. 359 00:22:45,940 --> 00:22:49,050 So, if you have two points of attachment, 360 00:22:49,050 --> 00:22:51,750 that's called bidentate. 361 00:22:51,750 --> 00:22:55,270 And even if you've never had a unit on transition metals 362 00:22:55,270 --> 00:22:59,030 before, I bet that you can answer this without me even 363 00:22:59,030 --> 00:23:00,440 telling you. 364 00:23:00,440 --> 00:23:05,230 What do you think tridentate might be? 365 00:23:05,230 --> 00:23:06,420 Three. 366 00:23:06,420 --> 00:23:08,180 Tetradentate? 367 00:23:08,180 --> 00:23:08,870 Four. 368 00:23:08,870 --> 00:23:10,330 Hexadentate? 369 00:23:10,330 --> 00:23:11,180 Six. 370 00:23:11,180 --> 00:23:14,380 So sometimes this would be a little question on the final. 371 00:23:14,380 --> 00:23:17,520 Please don't get this wrong, this is my gift to you, right, 372 00:23:17,520 --> 00:23:19,250 you knew it even before I taught it. 373 00:23:19,250 --> 00:23:22,090 So, this should be something that you can definitely get a 374 00:23:22,090 --> 00:23:24,880 couple extra points on on the final. 375 00:23:24,880 --> 00:23:29,970 All right, so, chelates bind with more than one point of 376 00:23:29,970 --> 00:23:35,320 attachment, and metal chelates are unusually stable. 377 00:23:35,320 --> 00:23:40,330 And this property is due to favorable and tropic factor, 378 00:23:40,330 --> 00:23:43,520 so we're back to entropy, we're back to thermodynamics. 379 00:23:43,520 --> 00:23:46,050 And this has to do with the fact that when a chelate binds 380 00:23:46,050 --> 00:23:49,990 a metal, it releases a lot of water, and that makes the 381 00:23:49,990 --> 00:23:53,440 chelate pretty stable. 382 00:23:53,440 --> 00:23:56,090 So, let me give you some examples of chelates, and then 383 00:23:56,090 --> 00:23:57,830 we're going to come back and think about the 384 00:23:57,830 --> 00:23:59,810 chelate effect again. 385 00:23:59,810 --> 00:24:05,680 Of course, you knew it, vitamin B12 has a chelating 386 00:24:05,680 --> 00:24:11,410 ligand associated with it. 387 00:24:11,410 --> 00:24:16,870 So, cobalt is in the middle of vitamin B12, and it has a ring 388 00:24:16,870 --> 00:24:19,410 system around it. 389 00:24:19,410 --> 00:24:22,550 And the ring system has these nitrogens, the nitrogens are 390 00:24:22,550 --> 00:24:25,880 the donor ligands to the cobalt, and so this ring 391 00:24:25,880 --> 00:24:29,530 system is attaching at four points, so it's a 392 00:24:29,530 --> 00:24:31,260 tetradentate ligand. 393 00:24:31,260 --> 00:24:34,500 There's also two other ligands attached to vitamin B12, 394 00:24:34,500 --> 00:24:37,810 there's an upper ligand shown here, which is 5 prime 395 00:24:37,810 --> 00:24:42,400 deoxyadenosine, and a bottom ligand, which is a 396 00:24:42,400 --> 00:24:42,980 dimethylbenzamitisol ligand. 397 00:24:42,980 --> 00:24:49,200 So, let's take a look, this is the cartoon, but let's look at 398 00:24:49,200 --> 00:24:51,780 another model for this here. 399 00:24:51,780 --> 00:24:56,360 So, we have a ring system, we have this upper ligand, and 400 00:24:56,360 --> 00:24:58,490 then a lower ligand down here. 401 00:24:58,490 --> 00:25:03,090 And so, the middle ring system is a tetradentate chelate. 402 00:25:03,090 --> 00:25:07,300 Overall, at the cobalt metal, what is the 403 00:25:07,300 --> 00:25:11,110 geometry of this system? 404 00:25:11,110 --> 00:25:12,710 It's octahedral, right. 405 00:25:12,710 --> 00:25:15,220 So we have this sort of square, the middle part is 406 00:25:15,220 --> 00:25:17,680 square planar, but the two upper and lower ligands make 407 00:25:17,680 --> 00:25:21,640 the whole thing an octahedral system. 408 00:25:21,640 --> 00:25:23,980 So this is an example of a naturally 409 00:25:23,980 --> 00:25:28,200 occurring chelated complex. 410 00:25:28,200 --> 00:25:30,110 So, this structure is actually fairly 411 00:25:30,110 --> 00:25:31,730 complicated for a vitamin. 412 00:25:31,730 --> 00:25:35,410 It's one of the most complex vitamins that's known, and I 413 00:25:35,410 --> 00:25:38,830 thought I'd just mention just a moment of history. 414 00:25:38,830 --> 00:25:42,530 So, this structure was determined by Dorothy Hodgkin 415 00:25:42,530 --> 00:25:45,230 who was a crystalographer in England. 416 00:25:45,230 --> 00:25:49,290 And she started working on this in the late 1940's, and 417 00:25:49,290 --> 00:25:53,010 people told her she was crazy, that something this large 418 00:25:53,010 --> 00:25:56,850 could never be solved by these x-ray defraction techniques. 419 00:25:56,850 --> 00:25:59,510 And, of course, now people are solving today's structures of 420 00:25:59,510 --> 00:26:00,720 things like the ribosomes. 421 00:26:00,720 --> 00:26:03,530 So, we've come a long way with crystallography. 422 00:26:03,530 --> 00:26:06,540 But she was one of the first true believers that x-ray 423 00:26:06,540 --> 00:26:08,980 crystallography was a powerful technique. 424 00:26:08,980 --> 00:26:11,790 And so, she went ahead, despite what everyone said, 425 00:26:11,790 --> 00:26:14,060 and determined this structure. 426 00:26:14,060 --> 00:26:16,670 And for this work and for some other things, she was awarded 427 00:26:16,670 --> 00:26:17,920 a Nobel Prize. 428 00:26:17,920 --> 00:26:20,460 So, this was a really significant contribution in 429 00:26:20,460 --> 00:26:24,440 the early 1950's and late 1940's. 430 00:26:24,440 --> 00:26:28,270 She had graduate students that she inspired. 431 00:26:28,270 --> 00:26:31,710 Some of them went on to become famous crystalographers. 432 00:26:31,710 --> 00:26:33,750 Other ones were not so successful -- 433 00:26:33,750 --> 00:26:37,310 crystallography's hard and it's not for everyone. 434 00:26:37,310 --> 00:26:41,235 She was actually known also, Dorothy was, for her work in 435 00:26:41,235 --> 00:26:43,910 the third world and her liberal politics, but one of 436 00:26:43,910 --> 00:26:47,080 her graduate students did not agree with her politics, but 437 00:26:47,080 --> 00:26:49,220 they were still friends. 438 00:26:49,220 --> 00:26:54,050 So this is just a message that as you go through your career, 439 00:26:54,050 --> 00:26:56,590 Margaret Thatcher who is a graduate student of Dorothy 440 00:26:56,590 --> 00:27:00,350 Hodgkins, couldn't quite cut it as a crystalographer, but 441 00:27:00,350 --> 00:27:03,540 for some people, you haven't found your true thing, and she 442 00:27:03,540 --> 00:27:06,690 was able to find another job, so I'm told. 443 00:27:06,690 --> 00:27:10,000 So, just remember that if you're not good at one thing, 444 00:27:10,000 --> 00:27:11,520 there's something else out there that you 445 00:27:11,520 --> 00:27:17,360 might be good at. 446 00:27:17,360 --> 00:27:22,130 So, let me give you a second example of a chelate. 447 00:27:22,130 --> 00:27:26,380 This molecule is known as EDTA. 448 00:27:26,380 --> 00:27:31,480 So this ligand has six points that it can attach to a metal. 449 00:27:31,480 --> 00:27:35,340 So, it is six atoms the can serve as these donor ligands. 450 00:27:35,340 --> 00:27:37,860 So, we have one up here, have the little electrons and the 451 00:27:37,860 --> 00:27:41,920 oxygen, another oxygen down here, nitrogen, nitrogen, 452 00:27:41,920 --> 00:27:44,110 another oxygen, another oxygen. 453 00:27:44,110 --> 00:27:49,790 So all of those six points can coordinate to a metal. 454 00:27:49,790 --> 00:27:54,320 So here again is the free EDTA, and here's a structure 455 00:27:54,320 --> 00:27:59,930 of EDTA bound to a metal, the metal is abbreviated m. 456 00:27:59,930 --> 00:28:24,720 So, why don't you tell me what the geometry is of that metal? 457 00:28:24,720 --> 00:28:39,260 All right, let's take only 10 more seconds. 458 00:28:39,260 --> 00:28:41,680 Hoping for 90, we're getting close, maybe 459 00:28:41,680 --> 00:28:42,780 by the end of today. 460 00:28:42,780 --> 00:28:46,070 All right, yeah, so it's octahedral geometry. 461 00:28:46,070 --> 00:28:50,430 So we have upper ligands and a lower ligand, two ligands 462 00:28:50,430 --> 00:28:55,190 coming out, two ligands going back, and it's also a 463 00:28:55,190 --> 00:28:57,680 hexadentate complex. 464 00:28:57,680 --> 00:28:59,800 So we see we're coordinated with the oxygen in red, 465 00:28:59,800 --> 00:29:02,570 nitrogen in blue, around to the other nitrogen in blue, 466 00:29:02,570 --> 00:29:05,780 another nitrogen in purple, another nitrogen up here in 467 00:29:05,780 --> 00:29:09,380 green and in blue. 468 00:29:09,380 --> 00:29:16,260 So, EDTA, when EDTA binds to a metal, it forms a very stable 469 00:29:16,260 --> 00:29:17,450 metal complex. 470 00:29:17,450 --> 00:29:19,460 And the reason for this is that chelate 471 00:29:19,460 --> 00:29:21,770 effect, and it's entropy. 472 00:29:21,770 --> 00:29:25,090 So if we look, metals are often coordinated by waters if 473 00:29:25,090 --> 00:29:26,750 they're just is solution. 474 00:29:26,750 --> 00:29:30,910 But if you bind one molecule of EDTA to the metal, it'll 475 00:29:30,910 --> 00:29:33,930 take all of those six sites, displacing all 476 00:29:33,930 --> 00:29:35,650 of these six waters. 477 00:29:35,650 --> 00:29:38,650 So here, on this side, you have one thing free in 478 00:29:38,650 --> 00:29:42,350 solution, and over here you have six things that are free. 479 00:29:42,350 --> 00:29:45,240 So that's entrotropically favorable, you have more 480 00:29:45,240 --> 00:29:47,620 entropy when you have lots of more free 481 00:29:47,620 --> 00:29:49,160 things floating around. 482 00:29:49,160 --> 00:29:51,290 So this has greater entropy. 483 00:29:51,290 --> 00:29:56,680 So, the chelate effect, then, has to do with entropic 484 00:29:56,680 --> 00:30:00,430 effect, that when you're binding a metal with multiple 485 00:30:00,430 --> 00:30:02,910 points of attachments, it's releasing water. 486 00:30:02,910 --> 00:30:04,860 So these are very stable. 487 00:30:04,860 --> 00:30:08,780 And so, because of this stability, they have a lot of 488 00:30:08,780 --> 00:30:11,240 important uses. 489 00:30:11,240 --> 00:30:14,870 What is one use you can think of that you might have for 490 00:30:14,870 --> 00:30:15,480 such a thing? 491 00:30:15,480 --> 00:30:20,050 When might you want to chelate a metal out -- get metal out 492 00:30:20,050 --> 00:30:21,450 of something pretty quickly. 493 00:30:21,450 --> 00:30:23,400 Yeah. 494 00:30:23,400 --> 00:30:28,820 Yeah, you can purify out a metal out of water with this. 495 00:30:28,820 --> 00:30:34,880 What about rushing to the emergency room with something? 496 00:30:34,880 --> 00:30:37,700 Yeah, lead poisoning, yup. 497 00:30:37,700 --> 00:30:40,430 So, sometimes you might want to just purify your water, you 498 00:30:40,430 --> 00:30:42,640 might be happy with that, other times you might really 499 00:30:42,640 --> 00:30:45,280 want to have that metal out. 500 00:30:45,280 --> 00:30:49,180 So, every emergency room in the United States, and 501 00:30:49,180 --> 00:30:53,690 probably mostly around the world, will have EDTA on hand 502 00:30:53,690 --> 00:30:57,050 in case someone comes in with lead poisoning. 503 00:30:57,050 --> 00:31:01,560 Do you know who's at the most risk for lead poisoning, at 504 00:31:01,560 --> 00:31:03,970 least in this country? 505 00:31:03,970 --> 00:31:04,700 Kids. 506 00:31:04,700 --> 00:31:07,560 And what do they do they gives them lead poisoning? 507 00:31:07,560 --> 00:31:08,630 Lead paint, yeah. 508 00:31:08,630 --> 00:31:11,910 So, I don't know, most of you are probably living on campus, 509 00:31:11,910 --> 00:31:15,040 but if any of you move off campus, and some people who 510 00:31:15,040 --> 00:31:17,800 are living maybe across the river in fraternity houses, 511 00:31:17,800 --> 00:31:21,010 those buildings are old and they have had lead paint in at 512 00:31:21,010 --> 00:31:22,320 some point or another. 513 00:31:22,320 --> 00:31:25,790 So this is a big problem, actually, in the Boston area. 514 00:31:25,790 --> 00:31:28,570 So, if you have any toddlers visiting you, you might want 515 00:31:28,570 --> 00:31:31,710 to make sure they're not eating paint chips off any 516 00:31:31,710 --> 00:31:33,610 window sill or anything like that. 517 00:31:33,610 --> 00:31:38,520 Or if you do, have some EDTA on hand. 518 00:31:38,520 --> 00:31:41,860 All right, one other thing, some of you, once you start 519 00:31:41,860 --> 00:31:46,330 studying chemistry, it's always fun/scary to start 520 00:31:46,330 --> 00:31:49,710 reading the ingredients on food packages. 521 00:31:49,710 --> 00:31:53,220 But you will discover that some food that you eat will 522 00:31:53,220 --> 00:31:57,690 say as an ingredient EDTA added for freshness. 523 00:31:57,690 --> 00:32:02,060 So, bacteria and fungi and things like that need metals 524 00:32:02,060 --> 00:32:05,270 for growth, metals are very important for life, and so you 525 00:32:05,270 --> 00:32:09,510 add a little EDTA and it prevents things from growing 526 00:32:09,510 --> 00:32:10,630 on your food. 527 00:32:10,630 --> 00:32:14,330 So that's added for freshness. 528 00:32:14,330 --> 00:32:16,880 So you'll see it in food. 529 00:32:16,880 --> 00:32:21,280 Another use that occasionally I find MIT students are not as 530 00:32:21,280 --> 00:32:27,760 familiar with is in cleaning bathtubs, so you want to 531 00:32:27,760 --> 00:32:31,740 chelate out the calcium in tub scum, and that's a 532 00:32:31,740 --> 00:32:34,380 good use for EDTA. 533 00:32:34,380 --> 00:32:37,520 So, I always like to mention how freshman chemistry 534 00:32:37,520 --> 00:32:40,080 information can make you a lot of money. 535 00:32:40,080 --> 00:32:43,540 So, I thought I'd tell you a little story about a man named 536 00:32:43,540 --> 00:32:45,640 Robert Black. 537 00:32:45,640 --> 00:32:48,020 So one day, I think it might have been a little before 538 00:32:48,020 --> 00:32:51,750 Thanksgiving, Mrs. Robert Black, I don't know her first 539 00:32:51,750 --> 00:32:55,870 name, said to her husband, "We're having company, how 540 00:32:55,870 --> 00:33:01,790 about you go clean the bathtub?" Apparently, Robert 541 00:33:01,790 --> 00:33:04,400 Black's wife had never mentioned this to him before, 542 00:33:04,400 --> 00:33:07,530 and he had, in fact, never cleaned a bathtub. 543 00:33:07,530 --> 00:33:11,790 Also, I think that Robert Black's wife was tired of 544 00:33:11,790 --> 00:33:14,700 cleaning the bathtub, and perhaps, had not done it for, 545 00:33:14,700 --> 00:33:17,470 say, a very long time. 546 00:33:17,470 --> 00:33:21,055 So, Robert Black went in there and tried to scrub off the 547 00:33:21,055 --> 00:33:23,450 scum, and it was actually really challenging and he was 548 00:33:23,450 --> 00:33:27,290 very frustrating, and he said, "I never want to do that 549 00:33:27,290 --> 00:33:28,600 again." 550 00:33:28,600 --> 00:33:33,490 So, he went and developed a product, a shower cleaner, 551 00:33:33,490 --> 00:33:35,960 that had all the ingredients of the shower cleaners he was 552 00:33:35,960 --> 00:33:38,450 using, except that he advertised it slightly 553 00:33:38,450 --> 00:33:42,990 differently, and he said "Every time you shower, just 554 00:33:42,990 --> 00:33:46,330 spray a little bit on and you'll never have to really 555 00:33:46,330 --> 00:33:49,350 scrub again." because this will take care of it and avoid 556 00:33:49,350 --> 00:33:51,980 scrubbing in the future, so a little bit of spraying after 557 00:33:51,980 --> 00:33:56,050 each shower avoids these problems. And the ingredients 558 00:33:56,050 --> 00:33:58,900 he had in were all typical ingredients, including 559 00:33:58,900 --> 00:34:00,700 chelating agents. 560 00:34:00,700 --> 00:34:04,310 You need a surfactant to break up the water beads, and 561 00:34:04,310 --> 00:34:08,100 alcohol to get rid of the oily stuff, and the chelating agent 562 00:34:08,100 --> 00:34:09,990 for the calcium in the tub scum. 563 00:34:09,990 --> 00:34:14,230 And the one he actually used is EDTA. 564 00:34:14,230 --> 00:34:18,970 So, as a result of a wife saying to her husband, it's 565 00:34:18,970 --> 00:34:22,490 your turn to clean the tub, they now make $70 million 566 00:34:22,490 --> 00:34:24,390 dollars annually. 567 00:34:24,390 --> 00:34:29,190 So, I think this is a lesson that we can learn in many ways 568 00:34:29,190 --> 00:34:32,210 that cleaning the tub is something that everyone should 569 00:34:32,210 --> 00:34:36,420 do at some point in their life, and that the simple 570 00:34:36,420 --> 00:34:39,570 things you learn in freshman chemistry can, if applied 571 00:34:39,570 --> 00:34:42,030 correctly, make you a lot of money. 572 00:34:42,030 --> 00:34:44,640 And I just want to encourage you, again, that anything that 573 00:34:44,640 --> 00:34:47,460 I teach you that you use to make a lot of money, I'll 574 00:34:47,460 --> 00:34:49,860 remind you that I am perfectly willing to have a 575 00:34:49,860 --> 00:34:51,460 cut of any of that. 576 00:34:51,460 --> 00:34:55,580 So, just something to keep in mind. 577 00:34:55,580 --> 00:35:00,880 So, one more thing that you might have heard for EDTA. 578 00:35:00,880 --> 00:35:04,700 Have any of you heard, perhaps, maybe watching 579 00:35:04,700 --> 00:35:14,170 television or a movie, about a use for EDTA? 580 00:35:14,170 --> 00:35:20,290 Have any of you, perhaps, seen a movie called Blade? 581 00:35:20,290 --> 00:35:23,090 How many of you have seen this? 582 00:35:23,090 --> 00:35:25,040 Not very many people. 583 00:35:25,040 --> 00:35:28,930 Hmm, I think we're going to have a separate course in 584 00:35:28,930 --> 00:35:37,950 vampire movies and TV. Anyway, Blade fights vampires, and 585 00:35:37,950 --> 00:35:41,360 they have a special gun, and the special gun has cartridges 586 00:35:41,360 --> 00:35:44,240 -- cartridges are shown here. 587 00:35:44,240 --> 00:35:47,970 And the cartridges have in them -- anyone want to guess? 588 00:35:47,970 --> 00:35:49,630 EDTA, yes. 589 00:35:49,630 --> 00:35:53,370 And the idea behind it, if you shoot at a vampire, the 590 00:35:53,370 --> 00:35:58,040 vampire turns instantaneously to dust, and the idea behind 591 00:35:58,040 --> 00:36:02,960 it is that vampires drink blood, blood has what in it? 592 00:36:02,960 --> 00:36:04,150 Iron. 593 00:36:04,150 --> 00:36:04,970 What chelates iron? 594 00:36:04,970 --> 00:36:06,610 EDTA. 595 00:36:06,610 --> 00:36:10,250 And, therefore, if you chelate the iron out of blood, and a 596 00:36:10,250 --> 00:36:13,970 vampire's mostly blood, it just instantaneously turns to 597 00:36:13,970 --> 00:36:19,920 dust. So, actually, as chemistry goes, it's kind of 598 00:36:19,920 --> 00:36:21,300 cool, yeah. 599 00:36:21,300 --> 00:36:25,490 So, that's the final use that I am aware of for EDTA. 600 00:36:25,490 --> 00:36:30,600 Some of you may encounter some more. 601 00:36:30,600 --> 00:36:36,080 All right, so coordination complexes. 602 00:36:36,080 --> 00:36:39,200 Some of them can have isomers. 603 00:36:39,200 --> 00:36:42,510 They can have geometric isomers. 604 00:36:42,510 --> 00:36:46,860 And geometric isomers can have vastly different properties. 605 00:36:46,860 --> 00:36:49,650 And if you're interested in biochemistry, this is 606 00:36:49,650 --> 00:36:53,920 something that you'll be interested in, because this 607 00:36:53,920 --> 00:36:57,390 can be very important in biological systems. 608 00:36:57,390 --> 00:37:01,850 So, let me tell you about a coordination complex that has 609 00:37:01,850 --> 00:37:06,970 platinum at the center, it has two ammonia ligands and two 610 00:37:06,970 --> 00:37:12,860 chloride ligands, and it has two ways that you can do it. 611 00:37:12,860 --> 00:37:16,800 So, you can either put the ammonia ligands on different 612 00:37:16,800 --> 00:37:19,990 sides or you can put them on the same side. 613 00:37:19,990 --> 00:37:24,300 So, here we have two nitrogen ligands over here, and I have 614 00:37:24,300 --> 00:37:25,700 these here. 615 00:37:25,700 --> 00:37:30,830 So, on one side, you have the two nitrogen ligands, on the 616 00:37:30,830 --> 00:37:36,630 other side two chlorides, or we can have a transarrangement 617 00:37:36,630 --> 00:37:38,810 where they're across from each other. 618 00:37:38,810 --> 00:37:40,700 So you see, there's 2 different ways to do it, on 619 00:37:40,700 --> 00:37:43,060 the same side or sort of across. 620 00:37:43,060 --> 00:37:45,030 So, cis or trans. 621 00:37:45,030 --> 00:37:52,060 Cisplatin is a potent anti-cancer drug, transplatin 622 00:37:52,060 --> 00:37:55,160 has no use that anyone's been able to detect. 623 00:37:55,160 --> 00:37:58,230 So it's the exact same composition, but a different 624 00:37:58,230 --> 00:38:01,120 arrangement of the atoms coordinated 625 00:38:01,120 --> 00:38:02,910 to the central metal. 626 00:38:02,910 --> 00:38:05,930 So, why should it make a difference, they have the same 627 00:38:05,930 --> 00:38:10,880 ingredients, why should one be a potent anti-cancer drug and 628 00:38:10,880 --> 00:38:12,450 the other one be useless? 629 00:38:12,450 --> 00:38:16,820 Well, it's because of how it interacts in the body. 630 00:38:16,820 --> 00:38:20,150 And so, one of the people who have spent a lot of their 631 00:38:20,150 --> 00:38:24,110 career studying cisplatin is Professor Steve Lippard, who's 632 00:38:24,110 --> 00:38:27,990 in the Chemistry Department here, and he has determined 633 00:38:27,990 --> 00:38:30,750 x-ray structures looking at this, and done a number of 634 00:38:30,750 --> 00:38:31,780 other studies. 635 00:38:31,780 --> 00:38:35,930 And so, here is a little cartoon of cisplatin bound to 636 00:38:35,930 --> 00:38:39,730 DNA, so the chlorides are displaced when it binds, and 637 00:38:39,730 --> 00:38:42,640 so they need to be on the same side, otherwise it's 638 00:38:42,640 --> 00:38:44,980 not going to work. 639 00:38:44,980 --> 00:38:50,960 And when cisplatin binds to DNA, then this will act to 640 00:38:50,960 --> 00:38:54,820 kill the cancer cells. 641 00:38:54,820 --> 00:38:58,950 So, the chlorides both need to be on the same side so a 642 00:38:58,950 --> 00:38:59,940 combined DNA. 643 00:38:59,940 --> 00:39:02,490 If they're on other sides, that's not going to interact 644 00:39:02,490 --> 00:39:06,190 with DNA, and so it doesn't have any known function. 645 00:39:06,190 --> 00:39:11,560 So, geometric isomers, same composition, but in different 646 00:39:11,560 --> 00:39:18,120 arrangements can have vastly different properties. 647 00:39:18,120 --> 00:39:21,140 So you can have what are called optical isomers or 648 00:39:21,140 --> 00:39:25,100 enantiomers, and so these can our mirror images of each 649 00:39:25,100 --> 00:39:27,160 other, but they're not superimposable. 650 00:39:27,160 --> 00:39:30,680 And so, when you have a mirror image like this, it's called a 651 00:39:30,680 --> 00:39:34,750 chiral molecule, and this is a term that you'll hear a lot 652 00:39:34,750 --> 00:39:37,000 when you take organic chemistry. 653 00:39:37,000 --> 00:39:41,170 So, I have two mirror images up here, so these are mirror 654 00:39:41,170 --> 00:39:45,280 images, so the mirror plane is between these molecules. 655 00:39:45,280 --> 00:39:48,340 But these molecules may look the same in the mirror, but 656 00:39:48,340 --> 00:39:49,070 they're non-superimposable. 657 00:39:49,070 --> 00:39:54,970 So, they are, in fact, different molecules, and they 658 00:39:54,970 --> 00:39:59,860 can have different properties in a chiral environment. 659 00:39:59,860 --> 00:40:02,580 What do I mean by a chiral environment? 660 00:40:02,580 --> 00:40:05,670 Well, the human body, for example, is a chiral 661 00:40:05,670 --> 00:40:08,180 environment. 662 00:40:08,180 --> 00:40:11,710 So that's why a lot of drugs, people are wanting to make 663 00:40:11,710 --> 00:40:14,600 just one enantimer of the drug and not the other, one 664 00:40:14,600 --> 00:40:16,690 enantiomer can have good properties, the 665 00:40:16,690 --> 00:40:19,670 other one may not. 666 00:40:19,670 --> 00:40:24,100 All right, so let's do some d-electron counting. 667 00:40:24,100 --> 00:40:26,120 This is the final thing we need to talk about in 668 00:40:26,120 --> 00:40:31,490 coordination complexes. 669 00:40:31,490 --> 00:40:35,110 So we're going to refer to a thing called the d-electron 670 00:40:35,110 --> 00:40:39,510 count of the metal, which just has to do with a group number 671 00:40:39,510 --> 00:40:43,470 from the periodic table minus the oxidation number of the 672 00:40:43,470 --> 00:40:46,710 metal, is going to tell us the d-electron count. 673 00:40:46,710 --> 00:40:50,330 So, if you haven't learned how to do oxidation numbers yet, 674 00:40:50,330 --> 00:40:53,340 you need to know that for exam 3, and you need to know that 675 00:40:53,340 --> 00:40:55,190 for this unit. 676 00:40:55,190 --> 00:40:58,520 So, let's look at a few examples of this, and we'll 677 00:40:58,520 --> 00:41:02,780 put up our friend, the periodic table. 678 00:41:02,780 --> 00:41:07,030 So let's look at the complex that we saw on the first page 679 00:41:07,030 --> 00:41:10,420 where we had -- in the beginning of today's lecture 680 00:41:10,420 --> 00:41:15,800 where we had cobalts with six n h 3 ligands in a 681 00:41:15,800 --> 00:41:20,820 coordination complex that had a charge of plus 3. 682 00:41:20,820 --> 00:41:24,240 So here, we need to figure out the oxidation number of the 683 00:41:24,240 --> 00:41:29,260 cobalt, and for this particular group, the overall 684 00:41:29,260 --> 00:41:30,950 charge of that is 0. 685 00:41:30,950 --> 00:41:35,680 We have three hydrogens at plus 1, and we also have a 686 00:41:35,680 --> 00:41:38,400 nitrogen at minus 1. 687 00:41:38,400 --> 00:41:41,550 And so, overall that charge is 0. 688 00:41:41,550 --> 00:41:46,990 So we have six things of 0, and what does that leave for 689 00:41:46,990 --> 00:41:49,680 our cobalt charge? 690 00:41:49,680 --> 00:41:51,020 Plus 3. 691 00:41:51,020 --> 00:41:55,520 Because overall, it now has to equal plus 3. 692 00:41:55,520 --> 00:42:00,870 So, then our d count for our electrons is going to be the 693 00:42:00,870 --> 00:42:02,080 group number. 694 00:42:02,080 --> 00:42:05,840 And for cobalt, what's the group number? 695 00:42:05,840 --> 00:42:07,670 9. 696 00:42:07,670 --> 00:42:14,630 So minus 3 is 6, so this cobalt in this complex is 697 00:42:14,630 --> 00:42:21,290 what's called a d 6 system. 698 00:42:21,290 --> 00:42:31,090 All right, let's look at a couple other examples here. 699 00:42:31,090 --> 00:42:35,820 Let's look at nickel with carbon monoxide 700 00:42:35,820 --> 00:42:40,800 ligands, four of them. 701 00:42:40,800 --> 00:42:47,300 What would nickel be in this case? 702 00:42:47,300 --> 00:42:48,770 Someone said zero. 703 00:42:48,770 --> 00:42:49,900 That's right. 704 00:42:49,900 --> 00:42:54,330 So this is zero, and nickel is zero, the 705 00:42:54,330 --> 00:42:56,270 overall charge is zero. 706 00:42:56,270 --> 00:43:03,950 So, our oxidation number here is 0. 707 00:43:03,950 --> 00:43:09,170 So, our d count here, what's the group number for nickel? 708 00:43:09,170 --> 00:43:10,630 10. 709 00:43:10,630 --> 00:43:14,290 10 minus 0 is 10. 710 00:43:14,290 --> 00:43:20,860 So we have a d 10 system. 711 00:43:20,860 --> 00:43:24,310 So, I'm going to write another example down and you're going 712 00:43:24,310 --> 00:43:28,050 to tell me the answer to this one as a clicker question. 713 00:43:28,050 --> 00:43:42,340 So we have cobalt, two waters -- three waters -- that's 714 00:43:42,340 --> 00:43:43,670 actually a mistake. 715 00:43:43,670 --> 00:43:45,940 It should be two. 716 00:43:45,940 --> 00:43:50,020 Two waters, because it's going to be six things -- this is 717 00:43:50,020 --> 00:43:54,340 not some kind of bizzaro seven complex. 718 00:43:54,340 --> 00:43:58,980 So here's the correct, cobalt, two waters, one ammonia, and 719 00:43:58,980 --> 00:44:32,040 three chlorides with an overall charge of minus 1. 720 00:44:32,040 --> 00:44:34,370 All right, let's just take 10 seconds, since we're running 721 00:44:34,370 --> 00:44:49,260 out of time. 722 00:44:49,260 --> 00:44:53,670 So that's right, we should have a charge of plus 2 here. 723 00:44:53,670 --> 00:45:00,380 This is zero, 0 minus 3, overall minus 1, so we have a 724 00:45:00,380 --> 00:45:01,990 plus 2 state. 725 00:45:01,990 --> 00:45:07,890 We have 9 minus 2, which is 7, and it's a d 7 system.