13 research outputs found
Selective Enzymatic Oxidation of Silanes to Silanols
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wildâtype cytochrome P450 monooxygenase (P450_(BM3) from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this nonânative activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves CâH bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native CâH hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire
Selective Enzymatic Oxidation of Silanes to Silanols
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wildâtype cytochrome P450 monooxygenase (P450_(BM3) from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this nonânative activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves CâH bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native CâH hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire
Political travel across the âIron Curtainâ and Communist youth identities in West Germany and Greece in the 1970s and 1980s
This article explores tours through the Iron Curtain arranged by West German and Greek pro-Soviet Communist youth groups, in an attempt to shed light on the transformation of European youth cultures beyond the âAmericanisationâ story. It argues that the concept of the âblack boxâ, employed by Rob Kroes to describe the influence of American cultural patterns on Western European youth, also applies to the reception of Eastern Bloc policies and norms by the Communists under study. Such selective reception was part of these groupsâ efforts to devise a modernity alternative to the âcapitalistâ one, an alternative modernity which tours across the Iron Curtain would help establish. Nevertheless, the organisers did not wish such travel to help eliminate American/Western influences on youth lifestyles entirely: the article analyses the excursionsâ aims with regard to two core components of youth lifestyles in Western Europe since the 1960s, which have been affected by intra-Western flows, the spirit of âdoing oneâs own thingâ and transformations of sexual practices. The article also addresses the experience of the travellers in question, showing that they felt an unresolved tension: the tours neither served as a means of Sovietisation nor as an impulse to develop an openly anti-Soviet stance.PostprintPeer reviewe
Synthesis of SiCl<sub>4</sub> via the Chloride Salt-Catalyzed Reaction of Orthosilicates with SOCl<sub>2</sub>
This paper details a method to chlorinate
tetraalkyl orthosilicates
in the presence of a catalyst using SOCl<sub>2</sub> as the chloride
source/deoxygenating agent. Several inexpensive catalysts were screened,
and it was found that soluble chloride salts performed better than
Lewis base catalysts. The optimized reaction employed a widely used
and commercially available soluble chloride salt catalyst (e.g., NBu<sub>4</sub>Cl, 0.4 equiv), 16 equiv of SOCl<sub>2</sub>, and afforded
quantitative yield of SiCl<sub>4</sub> after 3 h. As the bulk of the
orthosilicate substrate increased, the yield of SiCl<sub>4</sub> decreased.
A reaction mechanism has been proposed
Synthesis of SiCl<sub>4</sub> via the Chloride Salt-Catalyzed Reaction of Orthosilicates with SOCl<sub>2</sub>
This paper details a method to chlorinate
tetraalkyl orthosilicates
in the presence of a catalyst using SOCl<sub>2</sub> as the chloride
source/deoxygenating agent. Several inexpensive catalysts were screened,
and it was found that soluble chloride salts performed better than
Lewis base catalysts. The optimized reaction employed a widely used
and commercially available soluble chloride salt catalyst (e.g., NBu<sub>4</sub>Cl, 0.4 equiv), 16 equiv of SOCl<sub>2</sub>, and afforded
quantitative yield of SiCl<sub>4</sub> after 3 h. As the bulk of the
orthosilicate substrate increased, the yield of SiCl<sub>4</sub> decreased.
A reaction mechanism has been proposed
Selective Enzymatic Oxidation of Silanes to Silanols
Compared to the biological worldâs rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild-type cytochrome P450 monooxygenase (P450BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to make silanols. Directed evolution enhanced this non-native activity and created a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as terminal oxidant. The evolved enzyme does not touch CâH bonds also present in the silane substrates, nor does this biotransformation lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the P450âs native CâH hydroxylation mechanism. Enzymatic silane oxidation now extends Natureâs already impressive catalytic repertoire