Biomass- and Carbon Dioxide-Derived Polyurethane Networks for Thermal Interface Material Applications.

Recent environmental concerns have increased demand for renewable polymers and sustainable green resource usage, such as biomass-derived components and carbon dioxide (CO2). Herein, we present crosslinked polyurethanes (CPUs) fabricated from CO2- and biomass-derived monomers via a facile solvent-free ball milling process. Furan-containing bis(cyclic carbonate)s were synthesized through CO2 fixation and further transformed to tetraols, denoted FCTs, by aminolysis and utilized in CPU synthesis. Highly dispersed polyurethane-based hybrid composites (CPU-Ag) were also manufactured using a similar ball milling process. Due to the malleability of the CPU matrix, enabled by transcarbamoylation (dynamic covalent chemistry), CPU-based composites are expected to present very low interfacial thermal resistance between the heat sink and heat source. The characteristics of the dynamic covalent bond (i.e., urethane exchange reaction) were confirmed by the results of dynamic mechanical thermal analysis and stress relaxation analysis. Importantly, the high thermal conductivity of the CPU-based hybrid material was confirmed using laser flash analysis (up to 51.1 W/m·K). Our mechanochemical approach enables the facile preparation of sustainable polymers and hybrid composites for functional application.

Fe-Catalyzed C-H Alkenylation of Dialkyl Anilines with Disulfonylethenes.

The oxidative alkenylation reaction of α-aminoalkyl C(sp3)-H bonds has been investigated with (E)-1,2-bis(sulfonyl)ethenes. The catalytic process of iron-polypyridyl complexes drives the single-electron oxidation of dialkyl anilines, resulting in the formation of α-aminoalkyl radical species. Subsequent cascades of radical addition and elimination reactions ensue, ultimately leading to the generation of sulfonylated allylic amine products. The utility of these products extends further, enabling the synthesis of multisubstituted heterocycles like pyrroles, pyrazines, and triazoles.

Iron Catalysis of C(sp3)-H Azidation Using a Heteroarene Radical Cation Strategy.

The FeIII(phen)3 catalysis of the benzylic C(sp3)-H azidation of indoles has been investigated. The Fe(III) complex can selectively oxidize indoles to form arene radical cations, which are transformed into benzylic C(sp3) radical intermediates. This strategy exhibits a difference in reactivity between N-heteroarenes and benzene, which is difficult to achieve via direct hydrogen abstraction approaches. Various biorelevant azide precursors were constructed, highlighting the utility of this mild first-row transition-metal catalyst system.

Redox-Selective Iron Catalysis for α-Amino C-H Bond Functionalization via Aerobic Oxidation.

Single-electron oxidation and α-deprotonation of tertiary anilines using Fe(phen)3(PF6)3 afford α-aminoalkyl radicals, which can be coupled with electrophilic partners to afford various tetrahydroquinolines. Mechanistically, the Fe(phen)n2+/3+ catalytic cycle is maintained by O2 or a TBHP oxidant, and the presence of the oxygen bound iron complex, Fe(III)-OO(H), was elucidated by electron paramagnetic resonance and electrospray ionization mass spectrometry. This redox-selective nonheme iron catalyst behaves similarly to bioinspired heme iron catalysts.

Single-Electron-Transfer Strategy for Reductive Radical Cyclization: Fe(CO)5 and Phenanthroline System.

An electron-transfer strategy using low-valent iron pentacarbonyl [Fe(CO)5] to generate radical species from alkyl iodides was achieved. A range of pyrrolidines, tetrahydrofurans, and carbocycles were synthesized via 5-exo cyclization reactions of alkyl radical intermediates generated by electron transfer from a system involving Fe(CO)5, 1,10-phenanthroline, and diisopropylamine. Moreover, tandem addition reactions with Michael acceptors were also explored. Photophysical and electrochemical studies support a mechanism that involves electron transfer from the low-valent Fe reductant to alkyl iodide.

Computational selection, identification and structural analysis of ω-aminotransferases with various substrate specificities from the genome sequence of Mesorhizobium loti MAFF303099.

ω-Aminotransferase (ω-AT) is an important class of enzymes for the synthesis of chiral amines or ß-amino acids. Family profile analysis was applied to screen putative ω-ATs from Mesorhizobium loti MAFF303099, a nitrogen fixation bacterium that has a larger number of ATs than other microorganisms. By family profile analysis, we selected 10 putative ω-ATs according to E-value. The functions of the putative ω-ATs were investigated by examining activities towards amines and/or ß-amino acids. 10 putative proteins were found to have ω-AT activity with narrow or broad substrate specificity. Structure analysis using crystal structure of mll7127 and homology models of mll1632 and mll3663 indicated that the structures of active sites of the enzymes were very similar and highly conserved, but their substrate specificities appeared to be determined by residues positioned at the entrance region of the active site binding pockets.

Simultaneous synthesis of 2-phenylethanol and L-homophenylalanine using aromatic transaminase with yeast Ehrlich pathway.

2-Phenylethanol is a widely used aroma compound with rose-like fragrance and L-homophenylalanine is a building block of angiotensin-converting enzyme (ACE) inhibitor. 2-phenylethanol and L-homophenylalanine were synthesized simultaneously with high yield from 2-oxo-4-phenylbutyric acid and L-phenylalanine, respectively. A recombinant Escherichia coli harboring a coupled reaction pathway comprising of aromatic transaminase, phenylpyruvate decarboxylase, carbonyl reductase, and glucose dehydrogenase (GDH) was constructed. In the coupled reaction pathway, the transaminase reaction was coupled with the Ehrlich pathway of yeast; (1) a phenylpyruvate decarboxylase (YDR380W) as the enzyme to generate the substrate for the carbonyl reductase from phenylpyruvate (i.e., byproduct of the transaminase reaction) and to shift the reaction equilibrium of the transaminase reaction, and (2) a carbonyl reductase (YGL157W) to produce the 2-phenylethanol. Selecting the right carbonyl reductase showing the highest activity on phenylacetaldehyde with narrow substrate specificity was the key to success of the constructing the coupling reaction. In addition, NADPH regeneration was achieved by incorporating the GDH from Bacillus subtilis in the coupled reaction pathway. Based on 40 mM of L-phenylalanine used, about 96% final product conversion yield of 2-phenylethanol was achieved using the recombinant E. coli.