1 00:00:00,030 --> 00:00:02,400 The following content is provided under a Creative 2 00:00:02,400 --> 00:00:03,780 Commons license. 3 00:00:03,780 --> 00:00:06,020 Your support will help MIT OpenCourseWare 4 00:00:06,020 --> 00:00:10,090 continue to offer high quality educational resources for free. 5 00:00:10,090 --> 00:00:12,670 To make a donation or to view additional materials 6 00:00:12,670 --> 00:00:16,580 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:16,580 --> 00:00:17,560 at ocw.mit.edu. 8 00:00:26,630 --> 00:00:29,970 CATHERINE DRENNAN: So if we switch to today's lecture 9 00:00:29,970 --> 00:00:33,910 notes, we're going to talk today about applying 10 00:00:33,910 --> 00:00:36,700 some of the chemistry knowledge, with clicker questions 11 00:00:36,700 --> 00:00:39,880 and a clicker championship, to the issue 12 00:00:39,880 --> 00:00:43,200 of using CO2 to make biofuels. 13 00:00:43,200 --> 00:00:44,980 So first I just want to briefly review 14 00:00:44,980 --> 00:00:48,440 the course objectives, what I was hoping people would get out 15 00:00:48,440 --> 00:00:50,170 of this course. 16 00:00:50,170 --> 00:00:54,379 So I was hoping that you would know enough chemistry, 17 00:00:54,379 --> 00:00:55,920 have enough basic chemistry knowledge 18 00:00:55,920 --> 00:00:57,586 to do a UROP in the Chemistry Department 19 00:00:57,586 --> 00:01:00,700 without taking any other chemistry classes; that in UROP 20 00:01:00,700 --> 00:01:03,790 positions in other departments you would be using chemistry 21 00:01:03,790 --> 00:01:08,090 in your research; that you could also appreciate how chemistry 22 00:01:08,090 --> 00:01:10,550 is used to solve real world problems like we're talking 23 00:01:10,550 --> 00:01:12,980 about today, make informed decisions 24 00:01:12,980 --> 00:01:15,480 about your own health, the health of your family, 25 00:01:15,480 --> 00:01:19,250 environmental issues, energy issues, a lot 26 00:01:19,250 --> 00:01:21,860 of political decisions that are going on-- there's 27 00:01:21,860 --> 00:01:24,590 a lot of science actually in the news these days; 28 00:01:24,590 --> 00:01:26,580 and hopefully, make the world a better 29 00:01:26,580 --> 00:01:29,770 place by applying chemical principles to problems 30 00:01:29,770 --> 00:01:31,330 in science and engineering. 31 00:01:31,330 --> 00:01:32,840 So those are my goals. 32 00:01:32,840 --> 00:01:35,320 And then if we just kind of look at the material 33 00:01:35,320 --> 00:01:36,370 that we've covered. 34 00:01:36,370 --> 00:01:39,520 The first half of the course, which 35 00:01:39,520 --> 00:01:42,810 will be Exam One, Exam Two material-- 36 00:01:42,810 --> 00:01:44,650 talked about the basic properties 37 00:01:44,650 --> 00:01:47,860 of matter, atomic theory, periodic table, bonding 38 00:01:47,860 --> 00:01:49,510 structures of molecules. 39 00:01:49,510 --> 00:01:53,480 And then thermodynamics kind of transitioned us 40 00:01:53,480 --> 00:01:55,490 from thinking about basic properties 41 00:01:55,490 --> 00:01:57,340 to thinking more about reactivity 42 00:01:57,340 --> 00:01:59,490 and how that material that we learned 43 00:01:59,490 --> 00:02:01,950 about in the first half, how those elements could 44 00:02:01,950 --> 00:02:04,260 come together and react to form molecules. 45 00:02:04,260 --> 00:02:05,910 And to think about how things react, 46 00:02:05,910 --> 00:02:07,493 we usually think about thermodynamics. 47 00:02:07,493 --> 00:02:10,389 We need to think about chemical equilibrium, acid base, 48 00:02:10,389 --> 00:02:13,440 oxidation, and sometimes, transition metals, 49 00:02:13,440 --> 00:02:16,160 because they are-- that middle part of the periodic table 50 00:02:16,160 --> 00:02:19,950 can do amazing chemistry-- and also kinetics and solubility. 51 00:02:19,950 --> 00:02:23,600 So all of these things are about how material reacts. 52 00:02:23,600 --> 00:02:25,940 So we can't review everything. 53 00:02:25,940 --> 00:02:29,810 But I thought we would stick with this sort of carbon 54 00:02:29,810 --> 00:02:33,162 dioxide biofuels theme. 55 00:02:33,162 --> 00:02:35,620 And see how some of the things we've learned in this course 56 00:02:35,620 --> 00:02:37,699 would help us understand how we could 57 00:02:37,699 --> 00:02:39,240 approach this problem, how people are 58 00:02:39,240 --> 00:02:41,070 trying to solve this problem. 59 00:02:41,070 --> 00:02:42,610 So what is the problem again? 60 00:02:42,610 --> 00:02:46,310 And Jingnan brought this up, CO2 is a waste product 61 00:02:46,310 --> 00:02:48,070 of combustion of fossil fuels. 62 00:02:48,070 --> 00:02:50,230 We want to remove it from our environment. 63 00:02:50,230 --> 00:02:51,470 It's a greenhouse gas. 64 00:02:51,470 --> 00:02:54,620 It's also leading to the acidification of the oceans. 65 00:02:54,620 --> 00:02:57,120 This is not a molecule we want around 66 00:02:57,120 --> 00:02:59,470 in the kind of quantities that it is around. 67 00:02:59,470 --> 00:03:03,220 And I am personally very concerned about climate change. 68 00:03:03,220 --> 00:03:05,940 And after those of you who are freshman experience 69 00:03:05,940 --> 00:03:08,790 this winter, I think you will also be very concerned 70 00:03:08,790 --> 00:03:10,230 about climate change. 71 00:03:10,230 --> 00:03:11,820 So this is a problem. 72 00:03:11,820 --> 00:03:13,010 What is the approach? 73 00:03:13,010 --> 00:03:15,460 Well, the idea, I think, is really great-- 74 00:03:15,460 --> 00:03:18,180 that you can take CO2 and not just get rid of it, 75 00:03:18,180 --> 00:03:20,200 but convert it into something we want, 76 00:03:20,200 --> 00:03:22,800 which is alternative fuels, like biofuels. 77 00:03:22,800 --> 00:03:24,740 So I think this is a really great thing. 78 00:03:24,740 --> 00:03:27,430 So there are a few ways that one could do it. 79 00:03:27,430 --> 00:03:30,340 You could think about designing small molecule catalysts 80 00:03:30,340 --> 00:03:31,180 to do this. 81 00:03:31,180 --> 00:03:32,740 This is one thing people are doing. 82 00:03:32,740 --> 00:03:34,660 But there's really been a lot of energy 83 00:03:34,660 --> 00:03:37,290 on looking at how nature does things. 84 00:03:37,290 --> 00:03:40,030 So a lot of people are interested in nature, 85 00:03:40,030 --> 00:03:43,380 thinking about biological pathways that already do this. 86 00:03:43,380 --> 00:03:47,560 They already remove CO2 from our environment and fix it. 87 00:03:47,560 --> 00:03:50,390 Form carbon carbon bonds and make it 88 00:03:50,390 --> 00:03:54,170 into multicarbon chains that can be used as biofuels. 89 00:03:54,170 --> 00:03:59,170 So but before we do any of this, before we can go and think 90 00:03:59,170 --> 00:04:01,380 about any of these solutions, we need 91 00:04:01,380 --> 00:04:04,090 to understand the basic properties of CO2, 92 00:04:04,090 --> 00:04:07,790 it's reactivity, and more about these pathways. 93 00:04:07,790 --> 00:04:11,180 So let's talk about carbon dioxide, 94 00:04:11,180 --> 00:04:15,750 and let's think about how carbon and oxygen are bonded together. 95 00:04:15,750 --> 00:04:19,720 And we can use Lewis structures to predict 96 00:04:19,720 --> 00:04:23,160 what the Lewis structure of this should be, 97 00:04:23,160 --> 00:04:24,540 what the bonding will be. 98 00:04:24,540 --> 00:04:29,830 So let's go ahead with our first, our clicker question, 99 00:04:29,830 --> 00:04:32,894 and predict which of these, and we 100 00:04:32,894 --> 00:04:34,560 have a little bit of the periodic table, 101 00:04:34,560 --> 00:04:36,525 is the correct Lewis structure for CO2. 102 00:04:54,230 --> 00:04:55,280 OK. 103 00:04:55,280 --> 00:04:56,060 10 more seconds. 104 00:05:12,920 --> 00:05:13,970 All right. 105 00:05:13,970 --> 00:05:15,540 So we're going to go through and just 106 00:05:15,540 --> 00:05:17,623 look at what's wrong with some of these structures 107 00:05:17,623 --> 00:05:18,320 as a review. 108 00:05:18,320 --> 00:05:22,220 But first, can someone tell me for a t-shirt, what is 109 00:05:22,220 --> 00:05:23,960 the equation for formal charge? 110 00:05:23,960 --> 00:05:25,665 And Alaina will bring you the mic. 111 00:05:33,250 --> 00:05:36,660 AUDIENCE: One half the number of bonds 112 00:05:36,660 --> 00:05:41,149 that are going on plus the number of loan pair electrons. 113 00:05:41,149 --> 00:05:42,190 CATHERINE DRENNAN: Right. 114 00:05:42,190 --> 00:05:46,540 So I think we're missing one thing-- so formal charge, 115 00:05:46,540 --> 00:05:47,940 or maybe I didn't hear it. 116 00:05:47,940 --> 00:05:52,820 We have the number of valence electrons that we have, 117 00:05:52,820 --> 00:05:54,415 which for carbon was what? 118 00:05:58,220 --> 00:05:59,350 Four. 119 00:05:59,350 --> 00:06:03,970 So for carbon was four, and for oxygen is six, right. 120 00:06:03,970 --> 00:06:09,240 So minus the number of lone pair and then half of the bonding 121 00:06:09,240 --> 00:06:10,620 electrons. 122 00:06:10,620 --> 00:06:12,680 So this is how we're going to do this. 123 00:06:12,680 --> 00:06:15,490 The first structure has zero formal charges. 124 00:06:15,490 --> 00:06:16,380 It's good. 125 00:06:16,380 --> 00:06:18,950 And that is, in fact, the correct structure. 126 00:06:18,950 --> 00:06:21,770 The second structure here, if we do it out 127 00:06:21,770 --> 00:06:31,640 we have oxygen in the middle and we have carbon on the end. 128 00:06:31,640 --> 00:06:36,810 And here we should have a formal charge of minus 2 129 00:06:36,810 --> 00:06:41,310 on that carbon and plus 2 on the middle oxygen. 130 00:06:41,310 --> 00:06:47,130 So it's not good, because it has charges, which is not good. 131 00:06:47,130 --> 00:06:50,840 But it's also not good because the negative charge 132 00:06:50,840 --> 00:06:53,780 should be on what type of atom? 133 00:06:53,780 --> 00:06:56,710 A more electronegative, so that's not true here. 134 00:06:56,710 --> 00:07:00,000 So that structure is not good for a variety of reasons. 135 00:07:00,000 --> 00:07:02,370 OK, so if we look at the next structure, 136 00:07:02,370 --> 00:07:06,610 we have six valence electrons around one of the oxygens. 137 00:07:06,610 --> 00:07:11,600 We have two bonds to carbon and two lone pairs. 138 00:07:11,600 --> 00:07:14,430 And we have-- oh, actually we have the six 139 00:07:14,430 --> 00:07:18,190 around the other one as well. 140 00:07:18,190 --> 00:07:20,630 So first off, if you counted, there's 141 00:07:20,630 --> 00:07:24,160 more valence electrons used here than you had. 142 00:07:24,160 --> 00:07:25,780 So that's not good. 143 00:07:25,780 --> 00:07:30,570 And if you look at the charges, it's minus 1, minus 2, 144 00:07:30,570 --> 00:07:32,070 and minus 1. 145 00:07:32,070 --> 00:07:34,570 So that's a lot of charge, but also, 146 00:07:34,570 --> 00:07:35,950 what else is wrong with that? 147 00:07:39,780 --> 00:07:42,920 It should add up to 0, which it does not. 148 00:07:42,920 --> 00:07:45,350 And it doesn't add up to 0, because I 149 00:07:45,350 --> 00:07:49,440 put extra valence electrons in there that do not exist. 150 00:07:49,440 --> 00:07:51,920 So this structure is bad for a lot of reasons. 151 00:07:51,920 --> 00:07:54,020 Also the higher negative charge is not 152 00:07:54,020 --> 00:07:55,760 on the most electronegative atom. 153 00:07:55,760 --> 00:07:59,630 So this has many things wrong with it. 154 00:07:59,630 --> 00:08:04,870 So then if we looked at number four-- 155 00:08:04,870 --> 00:08:08,130 so we have an oxygen with six around it, 156 00:08:08,130 --> 00:08:12,930 a carbon that has two lone pairs double 157 00:08:12,930 --> 00:08:16,290 bonded to an oxygen with two lone pairs. 158 00:08:16,290 --> 00:08:20,380 And this has minus 1 and also minus 1. 159 00:08:20,380 --> 00:08:22,720 So again charges don't add up. 160 00:08:22,720 --> 00:08:25,330 It has the wrong number of valence electrons. 161 00:08:25,330 --> 00:08:27,790 So that's bad. 162 00:08:27,790 --> 00:08:33,309 And then the last one-- we have an oxygen with six lone pair 163 00:08:33,309 --> 00:08:38,490 electrons, a carbon with three bonds, no lone pair electrons, 164 00:08:38,490 --> 00:08:40,539 and an oxygen with two double bonds, 165 00:08:40,539 --> 00:08:45,270 two loan pair electrons, minus 1, plus 1. 166 00:08:45,270 --> 00:08:48,300 So this is not zero like that one is up there. 167 00:08:48,300 --> 00:08:50,280 But also something else is wrong. 168 00:08:50,280 --> 00:08:53,092 What else is wrong with that structure? 169 00:08:53,092 --> 00:08:54,300 What's wrong with the carbon? 170 00:08:58,024 --> 00:09:00,980 AUDIENCE: Doesn't add up to 8. 171 00:09:00,980 --> 00:09:04,600 CATHERINE DRENNAN: Right, so it has an complete octet. 172 00:09:04,600 --> 00:09:08,200 And so sometimes you can have an incomplete octet. 173 00:09:08,200 --> 00:09:11,730 Does anybody remember what two elements we mentioned 174 00:09:11,730 --> 00:09:13,395 are happy with an incomplete octet? 175 00:09:13,395 --> 00:09:15,430 AUDIENCE: Boron. 176 00:09:15,430 --> 00:09:18,960 CATHERINE DRENNAN: Boron and aluminum, right. 177 00:09:18,960 --> 00:09:21,230 And then some of them are happy with an expanded 178 00:09:21,230 --> 00:09:23,700 octet, but to be expanded you have 179 00:09:23,700 --> 00:09:27,000 to have an n number of what? 180 00:09:27,000 --> 00:09:28,380 Three or above. 181 00:09:28,380 --> 00:09:32,460 So carbon does not want to have a deficient octet 182 00:09:32,460 --> 00:09:34,200 or an expanded octet. 183 00:09:34,200 --> 00:09:37,860 So many of these other ones had a lot of things wrong. 184 00:09:37,860 --> 00:09:42,069 And so this is something that could be useful to review. 185 00:09:42,069 --> 00:09:44,360 And again, Lewis structure is one thing that people go, 186 00:09:44,360 --> 00:09:45,609 oh, yeah, I know how to do it. 187 00:09:45,609 --> 00:09:48,560 But it's good to review the rules right before an exam. 188 00:09:48,560 --> 00:09:52,870 OK, so here with our correct Lewis structure. 189 00:09:52,870 --> 00:09:54,740 And that Lewis structure stood well. 190 00:09:54,740 --> 00:09:55,780 That's a good structure. 191 00:09:55,780 --> 00:10:00,130 OK, so now that we know the Lewis structure, 192 00:10:00,130 --> 00:10:03,700 we can think about the geometry of the molecule, what 193 00:10:03,700 --> 00:10:07,100 its angles are, what it looks like in 3D. 194 00:10:07,100 --> 00:10:12,110 And we can use our friend, the Valence Shell Electron Pair 195 00:10:12,110 --> 00:10:15,060 Repulsion theory and Valence Bond Theory 196 00:10:15,060 --> 00:10:18,765 to predict things about this structure. 197 00:10:18,765 --> 00:10:21,140 So why don't you tell me which ones of these are correct? 198 00:10:21,140 --> 00:10:34,462 [CLASSROOM CHATTER] 199 00:10:34,462 --> 00:10:35,670 CATHERINE DRENNAN: All right. 200 00:10:35,670 --> 00:10:36,559 10 more seconds. 201 00:10:36,559 --> 00:10:51,640 [CLASSROOM CHATTER] 202 00:10:51,640 --> 00:10:53,440 CATHERINE DRENNAN: All right? 203 00:10:53,440 --> 00:10:57,220 OK, so let's take a look at that. 204 00:10:57,220 --> 00:11:02,080 So valence shell electron pair repulsion theory-- 205 00:11:02,080 --> 00:11:06,800 the AX, no AXE nomenclature. 206 00:11:06,800 --> 00:11:10,630 So X is the number of atoms bonded, and there are two here. 207 00:11:10,630 --> 00:11:12,500 So it's AX2. 208 00:11:12,500 --> 00:11:14,660 If there had been lone pairs, which they're not 209 00:11:14,660 --> 00:11:17,230 on the carbon, we would have added an E 210 00:11:17,230 --> 00:11:19,070 to indicate the lone pair. 211 00:11:19,070 --> 00:11:21,620 And AX2 molecules are linear. 212 00:11:21,620 --> 00:11:23,685 So here we have our carbon monoxide. 213 00:11:23,685 --> 00:11:25,190 It just has a single bond. 214 00:11:25,190 --> 00:11:27,010 This model kit doesn't have double bonds, 215 00:11:27,010 --> 00:11:30,930 but we have a linear molecule there. 216 00:11:30,930 --> 00:11:34,290 And again valence shell theory is really just 217 00:11:34,290 --> 00:11:37,300 about minimizing the repulsion between things. 218 00:11:37,300 --> 00:11:39,850 So the atoms, and especially those lone pairs 219 00:11:39,850 --> 00:11:41,470 that really take up a lot of room, 220 00:11:41,470 --> 00:11:43,930 try to position themselves around the central atom 221 00:11:43,930 --> 00:11:46,250 so it's the least repulsive. 222 00:11:46,250 --> 00:11:51,660 So in valence bond theory leads to the idea of hybrid orbitals. 223 00:11:51,660 --> 00:11:53,830 This idea that the valence electrons 224 00:11:53,830 --> 00:11:55,910 are available for bonding. 225 00:11:55,910 --> 00:11:59,367 And that you're not really just having s orbitals 226 00:11:59,367 --> 00:12:00,950 and p orbitals separate, you're really 227 00:12:00,950 --> 00:12:03,540 forming these hybrid orbitals, which 228 00:12:03,540 --> 00:12:06,680 tell you about the geometry around individual atoms. 229 00:12:06,680 --> 00:12:09,020 So the number of hybrid orbitals is 230 00:12:09,020 --> 00:12:12,780 the number of bonded atoms and the number of lone pairs. 231 00:12:12,780 --> 00:12:15,460 So carbon has two bonded atoms. 232 00:12:15,460 --> 00:12:19,476 So it's sp, and n equals 2, so it's 2sp. 233 00:12:19,476 --> 00:12:23,260 And oxygen has one atom and two lone pairs. 234 00:12:23,260 --> 00:12:25,790 Again the number of bonds doesn't matter here. 235 00:12:25,790 --> 00:12:31,120 So it has one plus two or three, so its sp2 and again 236 00:12:31,120 --> 00:12:32,290 n equals 2. 237 00:12:32,290 --> 00:12:34,670 So 2sp2. 238 00:12:34,670 --> 00:12:37,339 And then we can also have questions about the geometries, 239 00:12:37,339 --> 00:12:39,130 what are the angles for the different types 240 00:12:39,130 --> 00:12:40,430 of hybridization? 241 00:12:40,430 --> 00:12:45,240 So this really gets at what the geometry at every atom 242 00:12:45,240 --> 00:12:47,500 is like, whereas the vesper is really 243 00:12:47,500 --> 00:12:51,920 thinking about the overall shape of the molecule 244 00:12:51,920 --> 00:12:54,660 around the central atom and not so much 245 00:12:54,660 --> 00:12:57,080 about the individual atoms. 246 00:12:57,080 --> 00:12:59,330 All right, and remember that if we 247 00:12:59,330 --> 00:13:02,510 have a singly-bonded terminal atom, it's not hybridized. 248 00:13:02,510 --> 00:13:05,550 But this is not singly-bonded. 249 00:13:05,550 --> 00:13:12,960 OK, so now we can also ask what is 250 00:13:12,960 --> 00:13:15,690 the polarity of this molecule, and that's 251 00:13:15,690 --> 00:13:16,890 one more clicker question. 252 00:13:30,490 --> 00:13:31,763 All right 10 more seconds. 253 00:13:46,310 --> 00:13:47,920 All right. 254 00:13:47,920 --> 00:13:49,794 So if the polar bear t-shirt had won, 255 00:13:49,794 --> 00:13:50,960 it would have given it away. 256 00:13:50,960 --> 00:13:53,730 But it didn't matter, you still remembered. 257 00:13:53,730 --> 00:13:56,280 So, yeah, it does have polar bonds. 258 00:13:56,280 --> 00:13:59,050 Electronegativity difference greater than 0.4 259 00:13:59,050 --> 00:14:01,510 does make it a polar bond, but because it is 260 00:14:01,510 --> 00:14:03,510 linear there's no net dipole. 261 00:14:03,510 --> 00:14:09,350 So the polar bond-- this cancels each other out 262 00:14:09,350 --> 00:14:11,150 with this linear geometry. 263 00:14:11,150 --> 00:14:13,650 Great. 264 00:14:13,650 --> 00:14:18,620 So non-polar molecule, even though it has polar bonds. 265 00:14:18,620 --> 00:14:20,270 So it's not just about the property 266 00:14:20,270 --> 00:14:21,550 of the bonds that's important. 267 00:14:21,550 --> 00:14:24,540 It's also about the overall shape of the molecule. 268 00:14:24,540 --> 00:14:30,730 OK, so we have looked at some of the basic properties of CO2 269 00:14:30,730 --> 00:14:32,400 now, which is the top part. 270 00:14:32,400 --> 00:14:37,100 And now let's move in to think about the reactivity of the CO2 271 00:14:37,100 --> 00:14:38,310 molecule. 272 00:14:38,310 --> 00:14:42,870 So when we're thinking about reactivity we want to say 273 00:14:42,870 --> 00:14:46,690 is CO2 a stable or an unstable molecule 274 00:14:46,690 --> 00:14:48,640 compared to its elements? 275 00:14:48,640 --> 00:14:50,580 And this is not a clicker question. 276 00:14:50,580 --> 00:14:51,830 So you can just tell me. 277 00:14:51,830 --> 00:14:55,030 To answer this question about stability of a molecule 278 00:14:55,030 --> 00:14:57,460 compared to its elements, what is 279 00:14:57,460 --> 00:15:00,745 the thing I want to know about? 280 00:15:00,745 --> 00:15:04,980 Yeah, I want to know about delta G. In particular, I 281 00:15:04,980 --> 00:15:09,360 want to know about the delta G of formation of this molecule. 282 00:15:09,360 --> 00:15:11,850 But if you said delta G, that would be very good. 283 00:15:11,850 --> 00:15:17,930 So here the delta G of formation of CO2 is a negative number. 284 00:15:17,930 --> 00:15:19,720 It's a fairly big negative number 285 00:15:19,720 --> 00:15:23,830 minus 394 kilojoules per mol. 286 00:15:23,830 --> 00:15:27,330 So is CO2 stable or unstable? 287 00:15:27,330 --> 00:15:30,580 And you can just yell this out? 288 00:15:30,580 --> 00:15:32,110 It's stable, right. 289 00:15:32,110 --> 00:15:35,090 So the way we're thinking about this is with a delta G that's 290 00:15:35,090 --> 00:15:38,680 negative, it's spontaneous in the forward direction, 291 00:15:38,680 --> 00:15:41,960 which means it's not spontaneous in the reverse direction. 292 00:15:41,960 --> 00:15:47,530 So CO2 decomposing into its elements is not spontaneous. 293 00:15:47,530 --> 00:15:50,810 So that makes it a stable molecule. 294 00:15:50,810 --> 00:15:53,370 All right, so let's kind of put all these things together 295 00:15:53,370 --> 00:15:55,310 about CO2 now. 296 00:15:55,310 --> 00:16:01,030 So according to the Lewis structure, it has double bonds. 297 00:16:01,030 --> 00:16:03,930 And usually a double bond means that it's harder 298 00:16:03,930 --> 00:16:07,830 to disassociate a big bond dissociation energy. 299 00:16:07,830 --> 00:16:09,530 And you don't need to know these, 300 00:16:09,530 --> 00:16:11,650 but in case you're interested, when 301 00:16:11,650 --> 00:16:14,160 you have carbon double bonded to oxygen, 302 00:16:14,160 --> 00:16:17,810 you have a bond dissociation energy of about 805 kilojoules 303 00:16:17,810 --> 00:16:18,560 per mol. 304 00:16:18,560 --> 00:16:21,010 And it depends a little on the molecule in question, 305 00:16:21,010 --> 00:16:25,630 but a single bond is more like 358. 306 00:16:25,630 --> 00:16:29,920 And so double bond, it's hard to disassociate that. 307 00:16:29,920 --> 00:16:32,900 And it's also linear, non-polar, and stable. 308 00:16:32,900 --> 00:16:33,400 All right. 309 00:16:33,400 --> 00:16:36,520 So we want to take CO2 and turn it into other stuff. 310 00:16:36,520 --> 00:16:39,630 We want to make biofuels and solve the energy problem. 311 00:16:39,630 --> 00:16:44,400 But this is a non-polar molecule, and it's very stable. 312 00:16:44,400 --> 00:16:46,570 It has strong bonds. 313 00:16:46,570 --> 00:16:48,330 This is a hard challenge. 314 00:16:48,330 --> 00:16:49,900 And if it were an easy challenge, 315 00:16:49,900 --> 00:16:50,870 we would have figured this out. 316 00:16:50,870 --> 00:16:52,286 But this is not an easy challenge. 317 00:16:52,286 --> 00:16:54,620 It's a hard challenge, which is why 318 00:16:54,620 --> 00:16:58,100 it is a big area of research right now. 319 00:16:58,100 --> 00:17:02,480 So fixing CO2, i.e., putting these 1 carbon units together 320 00:17:02,480 --> 00:17:04,310 to make these long chain carbons like you 321 00:17:04,310 --> 00:17:08,490 saw in Jingnan's video, when she talked about these multichain 322 00:17:08,490 --> 00:17:11,720 carbons being used as biofuels. 323 00:17:11,720 --> 00:17:13,119 This is hard. 324 00:17:13,119 --> 00:17:15,280 All right, so when things are hard, 325 00:17:15,280 --> 00:17:18,720 first thing that scientists often like to do is say, 326 00:17:18,720 --> 00:17:20,819 can someone solve this problem and can we 327 00:17:20,819 --> 00:17:23,374 steal an idea from them? 328 00:17:23,374 --> 00:17:24,540 Honestly, that's what we do. 329 00:17:24,540 --> 00:17:27,589 But it's OK when the people we want to steal from 330 00:17:27,589 --> 00:17:29,990 are not really people, but Mother Nature. 331 00:17:29,990 --> 00:17:31,770 And so we look to Mother Nature and we 332 00:17:31,770 --> 00:17:35,640 look to some of the most intelligent life forms I know, 333 00:17:35,640 --> 00:17:37,990 which are microbes and bacteria. 334 00:17:37,990 --> 00:17:41,150 Oh man, can they do amazing chemistry that we cannot do. 335 00:17:41,150 --> 00:17:44,440 They are fantastic chemists, these little microbes. 336 00:17:44,440 --> 00:17:48,280 So one approach is to look at a microbe that does 337 00:17:48,280 --> 00:17:50,680 a process called acetogenesis. 338 00:17:50,680 --> 00:17:55,680 And that is one of the six known pathways of CO2 fixation. 339 00:17:55,680 --> 00:18:01,170 So acetogenesis makes acetate, or what's known as Acetyl-CoA. 340 00:18:01,170 --> 00:18:02,280 That's Coenzyme A. 341 00:18:02,280 --> 00:18:07,780 And this is considered the most ancient pathway 342 00:18:07,780 --> 00:18:11,890 of carbon fixation before origins 343 00:18:11,890 --> 00:18:16,450 of life kind of times, high CO2 environment, 344 00:18:16,450 --> 00:18:19,710 that maybe this was one of the first reactions that sort 345 00:18:19,710 --> 00:18:23,390 of generated metabolic fuel. 346 00:18:23,390 --> 00:18:26,130 And so here you have two molecules of CO2, one in blue, 347 00:18:26,130 --> 00:18:31,430 one in red, that are both converted to other carbons 348 00:18:31,430 --> 00:18:34,500 units that are then combined with Coenzyme A 349 00:18:34,500 --> 00:18:38,900 to make Acetyl-CoA, which then can go on to make biofuels. 350 00:18:38,900 --> 00:18:41,880 So this is what we want to understand, 351 00:18:41,880 --> 00:18:48,260 and we want to use this and turn our CO2 into biofuels. 352 00:18:48,260 --> 00:18:49,870 So but before we do this again, we 353 00:18:49,870 --> 00:18:52,180 must understand how it works. 354 00:18:52,180 --> 00:18:54,980 And we can ask the following questions. 355 00:18:54,980 --> 00:18:57,560 Are there redox reactions involved? 356 00:18:57,560 --> 00:18:58,580 Yes, there are. 357 00:18:58,580 --> 00:19:00,830 Is there acid-base catalysis? 358 00:19:00,830 --> 00:19:02,950 Why, yes, of course, there is. 359 00:19:02,950 --> 00:19:05,120 Are there transition metals involved? 360 00:19:05,120 --> 00:19:06,580 Is this hard chemistry? 361 00:19:06,580 --> 00:19:09,560 Yes, therefore pretty much guaranteed they'll 362 00:19:09,560 --> 00:19:12,270 be transition metals involved. 363 00:19:12,270 --> 00:19:14,210 Are there challenging rate-limiting steps? 364 00:19:14,210 --> 00:19:16,760 Oh, there's always, something's always rate-limiting, 365 00:19:16,760 --> 00:19:17,840 absolutely. 366 00:19:17,840 --> 00:19:19,550 And what about the chemical equilibrium? 367 00:19:19,550 --> 00:19:21,200 What about our [INAUDIBLE]? 368 00:19:21,200 --> 00:19:22,950 All right, so let's review the second half 369 00:19:22,950 --> 00:19:27,420 material thinking about the process of acetogenesis. 370 00:19:27,420 --> 00:19:30,480 First, oxidation reduction-- so you 371 00:19:30,480 --> 00:19:33,780 can tell me with a clicker question what 372 00:19:33,780 --> 00:19:36,170 is happening to CO2? 373 00:19:36,170 --> 00:19:38,120 And what's happening to blue CO2, 374 00:19:38,120 --> 00:19:40,510 and what's happening to red CO2? 375 00:19:40,510 --> 00:19:42,668 Are they being reduced or oxidized? 376 00:20:03,140 --> 00:20:03,640 All right. 377 00:20:03,640 --> 00:20:04,438 10 more seconds. 378 00:20:19,130 --> 00:20:20,390 Great. 379 00:20:20,390 --> 00:20:25,850 OK, so let's take a look at that. 380 00:20:25,850 --> 00:20:28,890 So that is right, the top reaction. 381 00:20:28,890 --> 00:20:30,390 So both of these are plus 4. 382 00:20:30,390 --> 00:20:32,390 It's the same molecule. 383 00:20:32,390 --> 00:20:34,970 And so in one case you're going to minus 2. 384 00:20:34,970 --> 00:20:37,290 So it's a 6 electron process. 385 00:20:37,290 --> 00:20:39,500 And in the other, you're going to plus 2. 386 00:20:39,500 --> 00:20:41,790 But both of them are being reduced. 387 00:20:41,790 --> 00:20:45,090 And so that is what's happening in a lot of these carbon 388 00:20:45,090 --> 00:20:46,130 fixation pathways. 389 00:20:46,130 --> 00:20:49,570 You're reducing carbon dioxide and making it 390 00:20:49,570 --> 00:20:53,080 into hydrocarbons, which can be used for biofuel. 391 00:20:53,080 --> 00:20:57,870 And the precursor here is the reduced form of this 2 carbon 392 00:20:57,870 --> 00:20:59,600 molecule, this Acetyl-CoA. 393 00:20:59,600 --> 00:21:02,260 All right, so it's being reduced. 394 00:21:02,260 --> 00:21:04,830 Now this is a fairly large reduction. 395 00:21:04,830 --> 00:21:06,550 Six electrons is a lot. 396 00:21:06,550 --> 00:21:11,000 Most of the reagents in nature that do reduction chemistry 397 00:21:11,000 --> 00:21:12,900 do one or two electron processes. 398 00:21:12,900 --> 00:21:14,130 So six is a lot. 399 00:21:14,130 --> 00:21:17,690 And in fact, it requires five different enzymes 400 00:21:17,690 --> 00:21:19,920 to do this six electron reduction. 401 00:21:19,920 --> 00:21:21,460 So it's not just one enzyme, it's 402 00:21:21,460 --> 00:21:24,260 multiple enzymes that need to do this. 403 00:21:24,260 --> 00:21:27,160 So this raises a question then. 404 00:21:27,160 --> 00:21:30,795 How are these carbon units, if you take one, you reduce it. 405 00:21:30,795 --> 00:21:33,170 Then you reduce it again and remove it to another enzyme, 406 00:21:33,170 --> 00:21:34,690 reduce it again and remove it to another enzyme, 407 00:21:34,690 --> 00:21:36,680 and reduce it again, move it to another enzyme. 408 00:21:36,680 --> 00:21:38,530 How does that happen? 409 00:21:38,530 --> 00:21:40,890 How do the enzymes kind of pass things along? 410 00:21:40,890 --> 00:21:43,460 And I think about this as a problem like kindergarten 411 00:21:43,460 --> 00:21:44,330 soccer. 412 00:21:44,330 --> 00:21:46,430 So we have a bunch of enzymes. 413 00:21:46,430 --> 00:21:49,610 And we have a bunch of one carbon units. 414 00:21:49,610 --> 00:21:52,670 But the one carbon units do not get passed from enzyme 415 00:21:52,670 --> 00:21:54,970 to enzyme in an organized fashion. 416 00:21:54,970 --> 00:21:58,250 And in fact, sometimes the enzymes 417 00:21:58,250 --> 00:22:01,101 don't really have control of those 1 carbon units. 418 00:22:01,101 --> 00:22:02,600 They can't grab it with their hands. 419 00:22:02,600 --> 00:22:03,540 That's not allowed. 420 00:22:03,540 --> 00:22:06,000 And we know enzymes do not have hands as such. 421 00:22:06,000 --> 00:22:10,550 So how do the enzymes grab onto these one carbon units 422 00:22:10,550 --> 00:22:13,600 and how does an enzyme bring it from one enzyme to the next. 423 00:22:13,600 --> 00:22:17,720 And why-- you know it takes energy to reduce CO2. 424 00:22:17,720 --> 00:22:20,550 So you don't want to just reduce it and kind of pass it 425 00:22:20,550 --> 00:22:23,101 along, and then who knows what happens to that reduced 426 00:22:23,101 --> 00:22:23,600 molecule. 427 00:22:23,600 --> 00:22:25,808 You want to go to the next enzyme and the next enzyme 428 00:22:25,808 --> 00:22:26,810 and the next enzyme. 429 00:22:26,810 --> 00:22:28,680 You want to make your Acetyl-CoA. 430 00:22:28,680 --> 00:22:30,110 So how does nature do it? 431 00:22:30,110 --> 00:22:33,200 It has a solution to the kindergarten soccer problem, 432 00:22:33,200 --> 00:22:36,260 and its solution is a B vitamin folic acid, 433 00:22:36,260 --> 00:22:37,750 also known as folate. 434 00:22:37,750 --> 00:22:39,504 And we talked about this before. 435 00:22:39,504 --> 00:22:40,920 This is why some people might want 436 00:22:40,920 --> 00:22:43,510 to drink Norwegian beer, lots of folic acid in it, 437 00:22:43,510 --> 00:22:47,990 or orange juice, or eat leafy green vegetables. 438 00:22:47,990 --> 00:22:50,580 So here's folic acid in its large form. 439 00:22:50,580 --> 00:22:53,360 In your notes, it just has an R. This entire thing 440 00:22:53,360 --> 00:22:58,940 is abbreviated as R. And what these enzymes do is 441 00:22:58,940 --> 00:23:02,510 they grab onto R, to that arm. 442 00:23:02,510 --> 00:23:05,920 And they hold onto it and they bind their one carbon unit over 443 00:23:05,920 --> 00:23:06,910 here. 444 00:23:06,910 --> 00:23:09,380 And then one enzyme does a reduction. 445 00:23:09,380 --> 00:23:12,280 And then it releases it, attached to folic acid. 446 00:23:12,280 --> 00:23:16,340 The next enzyme grabs onto the folate acid by the R group, 447 00:23:16,340 --> 00:23:18,980 reduces it again, lets go of it. 448 00:23:18,980 --> 00:23:22,820 The next enzyme grabs onto the folic acid by the R, 449 00:23:22,820 --> 00:23:26,070 reduces it again and this works. 450 00:23:26,070 --> 00:23:27,240 This is a great thing. 451 00:23:27,240 --> 00:23:28,630 You have something small. 452 00:23:28,630 --> 00:23:31,700 You don't want it just fre floating in the cell, 453 00:23:31,700 --> 00:23:34,660 especially if it's not really all that soluble. 454 00:23:34,660 --> 00:23:37,020 So you use something else to hold onto it. 455 00:23:37,020 --> 00:23:40,020 You use a vitamin to hold onto it this is great. 456 00:23:40,020 --> 00:23:42,530 But there's a problem. 457 00:23:42,530 --> 00:23:44,960 Well, first let's say, it holds onto it really well. 458 00:23:44,960 --> 00:23:46,610 You can pass it really well. 459 00:23:46,610 --> 00:23:47,920 This is great. 460 00:23:47,920 --> 00:23:51,000 But then when you get to the end, 461 00:23:51,000 --> 00:23:53,170 you're holding onto it really tight. 462 00:23:53,170 --> 00:23:56,310 You get to the end-- how do you get the methyl 463 00:23:56,310 --> 00:23:59,220 group off the folic acid? 464 00:23:59,220 --> 00:24:02,210 Great vehicle, but you need a final step. 465 00:24:02,210 --> 00:24:04,350 You need to remove it when you're done. 466 00:24:04,350 --> 00:24:07,290 So when the enzymes are done, how 467 00:24:07,290 --> 00:24:11,480 is this methyl group, CH3 group removed? 468 00:24:11,480 --> 00:24:17,000 And now we need to think about acid-base chemistry. 469 00:24:17,000 --> 00:24:20,710 So it turns out that the deprotonated form 470 00:24:20,710 --> 00:24:24,460 of folic acid, very hard to remove the methyl group. 471 00:24:24,460 --> 00:24:28,600 Whereas the protonated form of folic acid here, 472 00:24:28,600 --> 00:24:33,420 with the proton H in red, it's much easier 473 00:24:33,420 --> 00:24:36,200 to remove the methyl group. 474 00:24:36,200 --> 00:24:44,710 So if the pKa of folic acid is 4.8, how much of folic acid 475 00:24:44,710 --> 00:24:50,020 will be deprotonated compared to protonated at physiological pH? 476 00:25:07,070 --> 00:25:07,570 All right. 477 00:25:07,570 --> 00:25:08,492 10 more seconds. 478 00:25:29,420 --> 00:25:29,920 Yeah. 479 00:25:34,160 --> 00:25:36,060 Yeah. 480 00:25:36,060 --> 00:25:40,410 So sometimes these things move around. 481 00:25:40,410 --> 00:25:42,330 The fonts change. 482 00:25:42,330 --> 00:25:45,110 So more will be deprotonated. 483 00:25:45,110 --> 00:25:47,700 I see that people are paying attention. 484 00:25:47,700 --> 00:25:53,416 And we can look at exactly how much more. 485 00:25:53,416 --> 00:25:55,540 So if we're going to look at exactly how much more, 486 00:25:55,540 --> 00:25:59,170 what equation do I want to haul out? 487 00:25:59,170 --> 00:26:00,662 And Henderson-Hasselbalch. 488 00:26:00,662 --> 00:26:02,370 I should have a little approximate there, 489 00:26:02,370 --> 00:26:06,800 but still, there it is. 490 00:26:06,800 --> 00:26:12,150 So we have pH of 7.4. 491 00:26:12,150 --> 00:26:14,870 pKa of 4.8. 492 00:26:14,870 --> 00:26:21,080 And if we solve this, we have much more that is deprotonated. 493 00:26:21,080 --> 00:26:26,490 And again, the deprotonated form is nonreactive. 494 00:26:26,490 --> 00:26:30,225 So this is true off the enzyme, just a folic acid. 495 00:26:30,225 --> 00:26:33,530 It is not in a state that's going to react very well. 496 00:26:33,530 --> 00:26:37,260 You're not going to get that methyl group off very easily. 497 00:26:37,260 --> 00:26:40,290 Most of it will be deprotonated and nonreactive. 498 00:26:40,290 --> 00:26:42,800 That's fine if you're just transporting it, 499 00:26:42,800 --> 00:26:43,580 and that's great. 500 00:26:43,580 --> 00:26:44,680 Your body does this. 501 00:26:44,680 --> 00:26:48,140 You have methyl tetrahydrofolate in your blood right now. 502 00:26:48,140 --> 00:26:51,260 And you have an enzyme that takes off the methyl group. 503 00:26:51,260 --> 00:26:53,090 And you need an enzyme to catalyze it, 504 00:26:53,090 --> 00:26:56,090 because it needs to be a catalyzed reaction. 505 00:26:56,090 --> 00:26:58,010 It's not going to go on its own. 506 00:26:58,010 --> 00:27:03,180 So again, just to remember our little pretty pictures. 507 00:27:03,180 --> 00:27:08,300 When the pH equals the pKa, you have equal number of moles 508 00:27:08,300 --> 00:27:10,830 of protonated and deprotonated. 509 00:27:10,830 --> 00:27:14,660 At pH's below the pKa, it's more protonated. 510 00:27:14,660 --> 00:27:19,850 And a pH's above the pKa, it's more deprotonated. 511 00:27:19,850 --> 00:27:23,130 OK, so again we have the problem here 512 00:27:23,130 --> 00:27:26,510 that the removal of this methyl group is challenging, 513 00:27:26,510 --> 00:27:29,830 this is in fact a very challenging reaction 514 00:27:29,830 --> 00:27:32,570 both for humans and microbes. 515 00:27:32,570 --> 00:27:38,870 And so the solution, of course, transition metal and an enzyme. 516 00:27:38,870 --> 00:27:41,680 So you need both the transition metal, Vitamin B-12, 517 00:27:41,680 --> 00:27:44,170 bound to an enzyme to be able to do this really 518 00:27:44,170 --> 00:27:45,130 challenging chemistry. 519 00:27:45,130 --> 00:27:48,360 So this is one of the hard steps in this pathway. 520 00:27:48,360 --> 00:27:51,890 So Vitamin B-12 we have talked about before. 521 00:27:51,890 --> 00:27:56,000 It's an example of a naturally occurring metal chelate. 522 00:27:56,000 --> 00:27:59,830 You have cobalt in the middle of this core and ring system. 523 00:27:59,830 --> 00:28:02,900 And you have cobalt in the plus 1 oxidation 524 00:28:02,900 --> 00:28:08,010 state is very reactive and it's capable of removing that methyl 525 00:28:08,010 --> 00:28:12,770 group from the folic acid and transferring it to itself, 526 00:28:12,770 --> 00:28:16,940 forming a methyl cobalt 3 species. 527 00:28:16,940 --> 00:28:19,760 And here's the little methyl group on top. 528 00:28:19,760 --> 00:28:23,130 So we know about transition metals as well, 529 00:28:23,130 --> 00:28:25,520 and we can figure out the d-count. 530 00:28:25,520 --> 00:28:27,760 So we can look at the periodic table. 531 00:28:27,760 --> 00:28:29,694 And remember what about cobalt? 532 00:28:29,694 --> 00:28:31,110 What do we need to know from this? 533 00:28:33,630 --> 00:28:35,710 And so our d-count would be what then? 534 00:28:35,710 --> 00:28:39,420 You can just yell it out , it's not a clicker question. 535 00:28:39,420 --> 00:28:43,360 So it was group 9? 536 00:28:43,360 --> 00:28:46,200 So we have 9 minus 1, or 8 d8. 537 00:28:46,200 --> 00:28:50,570 And over here we have 9 minus 3 equals 8? 538 00:28:50,570 --> 00:28:55,280 No, d6-- yes, there's a typo. 539 00:28:55,280 --> 00:28:59,380 d6 is right, the other math is incorrect, d6 system. 540 00:28:59,380 --> 00:29:02,470 OK, I was doing this at 3:00 in the morning. 541 00:29:02,470 --> 00:29:06,530 OK, geometry around the central metal. 542 00:29:06,530 --> 00:29:09,800 And it's a little hard to see from this, 543 00:29:09,800 --> 00:29:11,750 so I'm going to help you out. 544 00:29:11,750 --> 00:29:15,650 So here there are no upper or lower ligands 545 00:29:15,650 --> 00:29:17,440 in the code one state. 546 00:29:17,440 --> 00:29:20,080 So you just have the ring system. 547 00:29:20,080 --> 00:29:23,420 So what is this geometry? 548 00:29:23,420 --> 00:29:26,890 Yeah, so we have square planar geometry. 549 00:29:26,890 --> 00:29:29,080 And then in the code three state, 550 00:29:29,080 --> 00:29:31,080 you have a methyl group above. 551 00:29:31,080 --> 00:29:35,060 And now you're also interacting with this lower ligand. 552 00:29:35,060 --> 00:29:37,250 So now our geometry is what? 553 00:29:42,230 --> 00:29:46,030 And what do we call this core and ring that 554 00:29:46,030 --> 00:29:50,120 has four points of attachment? 555 00:29:50,120 --> 00:29:52,090 Tetradentate. 556 00:29:52,090 --> 00:29:53,010 Right? 557 00:29:53,010 --> 00:29:57,360 Dent from teeth like claws grabbing onto your metal. 558 00:29:57,360 --> 00:30:01,790 OK so before we do our last chemical equilibrium, 559 00:30:01,790 --> 00:30:03,630 do we have a winner? 560 00:30:03,630 --> 00:30:05,742 We have a winner. 561 00:30:05,742 --> 00:30:06,450 We have a winner. 562 00:30:06,450 --> 00:30:07,790 We do not need a tie breaker. 563 00:30:07,790 --> 00:30:09,549 OK, we'll announce that at the end. 564 00:30:09,549 --> 00:30:11,090 And if you're the winning recitation, 565 00:30:11,090 --> 00:30:13,830 please come down to collect your t-shirts. 566 00:30:13,830 --> 00:30:20,550 OK so very briefly then, chemical equilibrium. 567 00:30:20,550 --> 00:30:24,330 So this B-12 enzyme which catalyzes the reaction, 568 00:30:24,330 --> 00:30:28,680 it not only uses this transition metal, but it also 569 00:30:28,680 --> 00:30:33,700 hydrogen bonds to the folic acid and lowers that transition 570 00:30:33,700 --> 00:30:35,540 state energy. 571 00:30:35,540 --> 00:30:37,080 And so here is the enzyme. 572 00:30:37,080 --> 00:30:40,750 And this enzyme exists in multiple confirmations. 573 00:30:40,750 --> 00:30:43,410 So we can think about chemical equilibrium 574 00:30:43,410 --> 00:30:45,450 in terms of enzyme structure. 575 00:30:45,450 --> 00:30:49,710 Chemical equilibrium applies to so many processes, not just 576 00:30:49,710 --> 00:30:52,420 a plus b equals c plus d. 577 00:30:52,420 --> 00:30:56,970 So here we have our B-12 enzyme, the B-12 is bound here. 578 00:30:56,970 --> 00:30:58,710 And this is the state, it's closed. 579 00:30:58,710 --> 00:31:02,280 B-12 is highly reactive, so it needs to be protected. 580 00:31:02,280 --> 00:31:06,280 When you bind the enzyme that binds the folic acid, 581 00:31:06,280 --> 00:31:07,440 it opens a little. 582 00:31:07,440 --> 00:31:10,220 When you bind the folic acid, it opens a lot 583 00:31:10,220 --> 00:31:12,990 and it's able to do the methyl transfer reaction. 584 00:31:12,990 --> 00:31:16,890 Then it needs to close up again to protect the methyl group. 585 00:31:16,890 --> 00:31:20,640 And then it needs to go on to transfer that methyl 586 00:31:20,640 --> 00:31:23,310 group to the enzyme that makes Acetyl-CoA. 587 00:31:23,310 --> 00:31:25,810 So you have all of these equilibrium, which 588 00:31:25,810 --> 00:31:28,440 are shifted by the binding of various things, 589 00:31:28,440 --> 00:31:31,740 the binding of the other enzymes or the binding of substrates. 590 00:31:31,740 --> 00:31:35,320 So the important point is that enzymes are dynamic. 591 00:31:35,320 --> 00:31:38,090 Chemistry is dynamic. 592 00:31:38,090 --> 00:31:41,910 This is not about just chemistry in the solid state. 593 00:31:41,910 --> 00:31:44,370 Chemistry in solution is cool! 594 00:31:44,370 --> 00:31:47,660 And chemistry in solution can save the planet. 595 00:31:47,660 --> 00:31:59,885 [APPLAUSE] 596 00:31:59,885 --> 00:32:02,820 [MUSIC PLAYING] 597 00:32:02,820 --> 00:32:05,245 CATHERINE DRENNAN: So if you appreciate this, 598 00:32:05,245 --> 00:32:09,810 this is how we're going to make biofuels and save the planet. 599 00:32:15,720 --> 00:32:17,300 All right. 600 00:32:17,300 --> 00:32:22,180 We have what I would consider as a bit of an upset. 601 00:32:22,180 --> 00:32:29,530 The winner of the 2014 t-shirt clicker competition 602 00:32:29,530 --> 00:32:33,370 is Jay's Recitation. 603 00:32:33,370 --> 00:32:41,700 In second place, we have Lisa's recitation in second place. 604 00:32:41,700 --> 00:32:45,160 And in third place, which will also have a prize, 605 00:32:45,160 --> 00:32:48,780 we have Odin's Recitation. 606 00:32:48,780 --> 00:32:51,910 So good luck on the final. 607 00:32:51,910 --> 00:32:53,950 It's been a pleasure.