a b s t r a c tThe bacterial translation factor RF3 promotes translation termination by recycling the tRNA-mimicking release factors, RF1 and RF2, after mature polypeptide release. RF3 also enhances the premature peptidyl-tRNA drop-off reaction in the presence of RRF and EF-G. Despite the recently resolved X-ray crystal structure of RF3, the molecular details of the bimodal functionality of RF3 remain obscure. In this report, we demonstrate a novel class of RF3 mutations specifically defective in the tRNA drop-off reaction. These mutations suggest differential molecular pathways closely related to the guanine nucleotide modes of RF3.

A cyclic carbonate with an ammonium carboxylate residue was found to serve as a nucleophile for esterification with alkyl bromides via the SN2 mechanism.

We have developed multiblock aromatic/aliphatic condensation polymers, comprising side-chain biofunctionalized aliphatic oligocarbonates and biobased aromatic ester triad mesogens up to 17 wt %. Nanosegregation of the aromatic mesogen-rich domains with diameters of approximately 10 nm from the soft aliphatic polymer matrix is suggested by atomic force microscopy. The polymers exhibit rubberlike properties, unlike the corresponding aliphatic polycarbonate forming viscous liquid. These properties support the interchain interactions between the aromatic mesogens, which can serve as physical cross-linking. The aromatic ester triad mesogens in the multiblock polymers significantly bolster the tolerance to organocatalytic hydrolysis and methanolysis of the polymer chains but are eventually degraded. The multiblock polymers show degradation behavior slightly faster than poly(L-lactide), whereas poly(ethylene terephthalate) remains intact under the same condition. The present study demonstrates the efficacy of aromatic ester triad mesogens incorporated into the sequences of biodegradable aliphatic polycarbonates to enhance their physical properties while retaining degradability.

Aliphatic polycarbonates have attracted attention as degradable and sustainable materials contributing to the circular plastic economy. Their chemical recycling has not been sufficiently studied. In this study, the efficacy of organocatalysts for depolymerization of poly(trimethylene carbonate) (PTMC), a representative aliphatic polycarbonate, is investigated using several organic acids and bases. The hydrolysis of PTMC produces the water‐soluble degradates propane‐1,3‐diol (PD) and CO2. A phosphazene base P2‐t‐Bu shows high activity for the hydrolysis, yielding up to 31% and 89% of PD in the homogeneous reaction at around 27°C and the inhomogeneous reaction under the reflux condition, respectively. By contrast, 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) exhibits exceptionally high catalytic activity for the methanolysis of PTMC, producing PD and dimethyl carbonate. This is because of dual hydrogen‐bonding activation, which completes the inhomogeneous reaction in a few hours at around 27°C while yielding more than 90% of PD. The reaction rate of the TBD‐catalyzed methanolysis depends on the concentration of the nucleophile and catalyst, and the ratio of the nucleophile to the substrate affects the PD yield. These results provide a highly promising standard for chemical recycling of functionalized aliphatic polycarbonates that could potentially be applied to sustainable materials in the future.

No abstract