Unmasking latent thioesters under hydrophobic-compatible conditions.

Hydrophobic latent C-terminal thioesters were converted into thioesters, and were also coupled with cysteine in one-pot reactions, using conditions generally compatible with hydrophobic materials. The reaction conditions (ethanethiol and triethylamine in a mixture of DMF and THF) are compatible with acid-labile protecting groups (Boc/t-Bu) that are standard in Fmoc peptide synthesis.

Morphology evolution and gelation mechanism of alkali induced konjac glucomannan hydrogel.

A molecular-level mechanism of alkali induced konjac glucomannan (KGM) hydrogel gelation processing is considered with the application of nuclear magnetic resonance (NMR) spectroscopy and atomic force microscopy (AFM) as complementary methods to diffusive wave spectroscopy (DWS) microrheology and thermoanalysis. It is shown that deacetylation of KGM chains occurs immediately upon mixing with Na2CO3, inducing self-packaging. Partial unfolding of the packed loose structure of dehydrated KGM is observed upon heating. The configuration transition from random coils to self-assembling filament networks takes place before KGM aggregating to form large irreversible bundles with a lower degree of cross-linking. The gelation is not fulfilled until the temperature is increased to above 70 °C when the significant agglomeration is initiated among transitional fibrils to form junction zones essentially composed of acetyl-free portions. This suggests the intermolecular aggregation of KGM chains not simply regarding to hydrogen bonds, but essentially relating to hydrophobic interactions.

Synergistic Enhancement of Electrocatalytic CO2 Reduction with Gold Nanoparticles Embedded in Functional Graphene Nanoribbon Composite Electrodes.

Regulating the complex environment accounting for the stability, selectivity, and activity of catalytic metal nanoparticle interfaces represents a challenge to heterogeneous catalyst design. Here we demonstrate the intrinsic performance enhancement of a composite material composed of gold nanoparticles (AuNPs) embedded in a bottom-up synthesized graphene nanoribbon (GNR) matrix for the electrocatalytic reduction of CO2. Electrochemical studies reveal that the structural and electronic properties of the GNR composite matrix increase the AuNP electrochemically active surface area (ECSA), lower the requisite CO2 reduction overpotential by hundreds of millivolts (catalytic onset > -0.2 V versus reversible hydrogen electrode (RHE)), increase the Faraday efficiency (>90%), markedly improve stability (catalytic performance sustained over >24 h), and increase the total catalytic output (>100-fold improvement over traditional amorphous carbon AuNP supports). The inherent structural and electronic tunability of bottom-up synthesized GNR-AuNP composites affords an unrivaled degree of control over the catalytic environment, providing a means for such profound effects as shifting the rate-determining step in the electrocatalytic reduction of CO2 to CO, and thereby altering the electrocatalytic mechanism at the nanoparticle surface.

Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization.

Molybdenum carbyne complexes [RC≡Mo(OC(CH3)(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene, to yield fully conjugated poly(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesC≡Mo(OC(CH3)(CF3)2)3] exclusively yields linear poly(o-phenylene ethynylene), polymerization initiated by [EtC≡Mo(OC(CH3)(CF3)2)3] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtC≡Mo(OC(CH3)(CF3)2)3] undergoes a highly selective intramolecular backbiting into the butynyl end-group.