Diastereo‐ and Regioselective Addition of Thioamide Dianions to Imines and Aziridines: Synthesis of N‐Thioacyl‐1,2‐diamines and N‐Thioacyl‐1,3‐diamines

Addition reactions of thioamide dianions that were derived from N‐arylmethyl thioamides to imines and aziridines were carried out. The reactions of imines gave the addition products of N‐thioacyl‐1,2‐diamines in a highly diastereoselective manner in good‐to‐excellent yields. The diastereomeric purity of these N‐thioacyl‐1,2‐diamines could be enriched by simple recrystallization. The reduction of N‐thioacyl‐1,2‐diamines with LiAlH₄ gave their corresponding 1,2‐diamines in moderate‐to‐good yields with retention of their stereochemistry. The oxidative‐desulfurization/cyclization of an N‐thioacyl‐1,2‐diamine in CuCl₂/O₂ and I₂/pyridine systems gave the cyclized product in moderate yield and the trans isomer was obtained as the sole product. On the other hand, a similar cyclization reaction with antiformin (aq. NaClO) as an oxidant gave the cis isomer as the major product. The reactions of N‐tosylaziridines gave the addition products of N‐thioacyl‐1,3‐diamines with low diastereoselectivity but high regioselectivity and in good‐to‐excellent yields. The use of AlMe₃ as an additive improved the efficiency and regioselectivity of the reaction. The stereochemistry of the obtained products was determined by X‐ray diffraction.     

Partial crystalline transformation of solvated cellulose IIII crystals, reproduced by theoretical calculations

In hot-water molecular dynamics simulation at 370 K, four cellulose III_I crystal models, with different lattice planes and dimensions, exhibited partial crystalline transformations of (1 ?1 0) chain sheets, in which hydroxymethyl groups were irreversibly rotated from gt into tg conformations, accompanied by hydrogen-bond exchange from the original O3–O6 to cellulose-I-like O2–O6 bonds. The final hydrogen-bond exchange ratio was about 95 % for some of the crystal models after 50 ns simulation. The corrugated (1 ?1 0) chain sheet was converted to a cellulose-I-like flat chain sheet with a slightly right-handed twist. The 3D structures of the three types of isolated chain sheet models were optimized using density functional theory calculations to compare their stabilities without crystal packing forces. The cellulose Iβ (1 0 0) models were more stable than the cellulose III_I (1 ?1 0) models. The optimized structure of cellulose III_I (1 0 0) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose III_I to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis.     

Synthesis and Characterization of Aminoporphyrin‐End‐Functionalized Poly(N‐isopropylacrylamide) with Photodynamic and Thermoresponsive Effects

The novel aminoporphyrin‐end‐functionalized poly(N‐isopropylacrylamide) (PNIPAM) polymer H₂N‐TPP‐PNIPAM (TPP=5,10,15,20‐tetraphenyl‐21H,23H‐porphyrin) behaves as a multifunctional platform that displays a photodynamic effect, thermosensitivity, and fluorescence properties. The polymer was designed by using an asymmetrical aminoporphyrin (i.e., H₂N‐TPP‐Cl) as the initiator for the atom‐transfer radical polymerization of N‐isopropylacrylamide (NIPAM). The polydispersity index (PDI) obtained by gel‐permeation chromatography indicated that the molecular‐weight distribution was narrow (1.09<PDI<1.27). The lower critical solution temperatures of H₂N‐TPP‐PNIPAM showed a decreasing trend as the molecular weight was increased as a result of the incorporation of the porphyrin group at the end of the chain. The fluorescence spectra revealed the luminescent properties of the materials. The results of confocal laser scanning microscopy showed that the polymer could enter the cytoplasm through endocytosis. In addition, the multifunctional platform exhibited low toxicity against normal cells (L929) and cancer cells (Hela) and enhanced photodynamic activity towards HeLa cells, without significant necrocytosis towards L929 cells; as a result this material may be useful in the future for practical photodynamic therapy.     

Extended ensemble molecular dynamics study of cellulose I–ethylenediamine complex crystal models: atomistic picture of desorption behaviors of ethylenediamine

Cellulose - Cellulose I crystals swell on exposure to ethylenediamine (EDA) molecules to form a cellulose I–EDA complex, and successive extraction of EDA molecules converts the complex...     

Cellulose-synthesizing machinery in bacteria

Cellulose - Cellulose is produced by all plants and a number of other organisms, including bacteria. The most representative cellulose-producing bacterial species is Gluconacetobacter xylinus, an...     

Practical Synthesis of 2-Iodosobenzoic Acid (IBA) without Contamination by Hazardous 2-Iodoxybenzoic Acid (IBX) under Mild Conditions

We report a convenient and practical method for the preparation of nonexplosive cyclic hypervalent iodine(III) oxidants as efficient organocatalysts and reagents for various reactions using Oxone^® in aqueous solution under mild conditions at room temperature. The thus obtained 2-iodosobenzoic acids (IBAs) could be used as precursors of other cyclic organoiodine(III) derivatives by the solvolytic derivatization of the hydroxy group under mild conditions of 80 °C or lower temperature. These sequential procedures are highly reliable to selectively afford cyclic hypervalent iodine compounds in excellent yields without contamination by hazardous pentavalent iodine(III) compound.     

Dual Catalysis with Copper and Rhenium for Trifluoromethylation of Propargylic Alcohols: Efficient Synthesis of α‐Trifluoromethylated Enones

Trifluoromethylation of propargylic alcohols to provide (Z)‐α‐trifluoromethylated enones and β‐unsubstituted α‐trifluoromethylated enones proceeded with high yield and selectivity in the presence of CuI/Re₂O₇. The Z isomer was formed under kinetic control, though it is less stable than the E isomer in terms of steric repulsion.     

Prediction of cellulose nanotube models through density functional theory calculations

We report the generation of a nano-scale tubular structure of cellulose molecules (CelNT), through density functional theory (DFT) calculations. When a cellulose III_I (1 0 0) chain sheet model is optimized by DFT calculations, the sheet models spontaneously roll into tubes. The oligomers arrange in a right-handed, four-fold helix with one-quarter chain staggering, oriented with parallel polarity similar to the original crystal structure. Based on a one-quarter chain staggering relationship, six large CelNT models, consisting of 16 cellulose chains with DP = 80, are constructed by combinations of two types of chain polarities and three types of symmetry operations to generate a circular arrangement of molecular chains. All six CelNT models are examined by molecular dynamics (MD) calculations in chloroform. While four CelNT models retain a tubular form throughout MD calculations, the remaining two deform. 3D-RISM theory model is used to estimate the solvation free energies of the four CelNT models. The results suggest that the CelNT model with a chain arrangement of parallel polarity and right-handed helical symmetry forms the most stable tube structure.