Preparation and Characterization of New Optically Active Poly(amide-imide)s from N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic)-bis-L-isoleucine and Aromatic Diamines

Five new optically active aromatic poly(amide-imide)s (PAIs) 5a–e were prepared from a direct polycondensation reaction of a new diacid of N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic)-bis-L-isoleucine 3 with various aromatic diamines 4a–e in a medium consisting of triphenyl phosphite (TPP), calcium chloride (CaCl₂), pyridine (Py) and N-methyl-2-pyrrolidone (NMP). The polycondensation reaction produced a series of novel poly(amid-imide)s 5a–e in quantitative yields with inherent viscosities of 0.39–0.51 dL/g. The resulting polymers were fully characterized by means of ¹H-NMR, FT-IR spectroscopy, elemental analyses, inherent viscosity, solubility test, specific rotation and thermal properties of them were investigated using TGA/DTG and differential scanning calorimeter (DSC). The diacid 4 was synthesized by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6- tetracarboxylic dianhydride 1 with L-isoleucine 2 in acetic acid solution.     

Syntheses of Optically Active Polyacrylates

ABSTRACT

Different secondary alcohols were resolved by lipase catalyzed transesterification using 2,3-butanedione monoxime acrylate as acrylating agent. The results showed that the reaction rates were the fastest among reactions reported until now. The effect of solvent on the transesterification rate was studied. The enantiomeric excess (ee) and enantiomeric purity (E value) of all the acrylate monomers were determined. The synthesized optically active acrylate monomers were polymerized by free radical polymerization technique.     

Simultaneously Probing Two Ultrafast Condensed‐Phase Molecular Symmetry Breaking Events by Two‐Dimensional Infrared Spectroscopy

In condensed phases, a highly symmetric gas‐phase molecule lowers its symmetry under perturbation of the solvent, which is vital to a variety of structural chemistry related processes. However, the dynamical aspects of solvent‐mediated symmetry‐breaking events remain largely unknown. Herein, direct evidence for two types of solvent‐mediated symmetry‐breaking events that coexist on the picosecond timescale in a highly symmetric anion, namely, hexacyanocobaltate, is presented: 1) an equilibrium symmetry‐breaking event in which a solvent‐bound species having lowered symmetry undergoes a population exchange reaction with the symmetry‐retaining species; 2) a dynamic symmetry‐breaking event that is composed of many dynamic population‐exchange reactions under fluctuating solvent interactions. Ultrafast two‐dimensional infrared spectroscopy is used to simultaneously observe and dynamically characterize these two events. This work opens a new window into molecular symmetry and structural dynamics under equilibrium and non‐equilibrium conditions.     

Stereospecific radical polymerization of optically active (S)-N-(2-hydroxy-1-phenylethyl) methacrylamide catalyzed by Lewis acids

The effects of Lewis acids, namely, rare earth metal trifluoromethanesulfonates, on the radical polymerization of (S)-N-(2-hydroxy-1-phenylethyl) methacrylamide were examined under various conditions. In the absence of Lewis acids, syndiotactic-rich polymers (r = 84%) were obtained, whereas in the presence of a catalytic amount of Lewis acids, the polymerization proceeded in an isotactic-specific manner (m up to 64%). Polymerization solvents strongly influenced the effect of the Lewis acids. The polymerization in n-butyl alcohol showed the highest isotactic selectivity, whereas the polymerization in DMSO showed no isotacticity-enhancing effect. Further increases in the Lewis acid concentration and the polymerization temperature did not produce clear effects on the tacticity of the polymers. The interaction between the monomer and Lewis acids was investigated, and the plausible mechanism of stereocontrol in the radical polymerization of (S)-HPEMA was analyzed based on the Lewis acid-monomer interaction.     

Phase Transfer Catalyzed Alkylation: An Efficient Protection of Acid Labile Hemiketals

The reaction of hemiketals (1–6) with sodium hydroxide and methyl iodide in the presence of TBAI as a catalyst furnished methoxy hemiketals (7–10) in more than 90% yield.     

Albumin-mediated asymmetric nitroaldol reaction of aromatic aldehydes with nitromethane in water

We succeeded in the asymmetric nitroaldol (Henry) reaction of aromatic aldehydes with nitromethane using human serum albumin (HSA) in water at neutral pH. The reaction of 4-nitrobenzaldehyde smoothly proceeded for 24 h at 30 °C to afford the corresponding (R)-2-nitro-1-(4-nitrophenyl)ethanol (27% ee). Lowering the reaction temperature to 0 °C improved the enantioselectivity (53% ee). Although the denatured HSA also catalyzed the coupling reaction, no enantioselectivity was observed. The reaction was also applicable to other substrates bearing various substitutions on the benzene ring, and the ee of (R)-1-(biphenyl-4-yl)-2-nitroethanol was up to 79% ee.     

Rate constant measurements for initial addition reactions of radicals at the propagation step of photo‐polymerization as studied by pulsed EPR spectroscopy

Pulsed EPR spectroscopy was employed to determine reaction rate constants at an early stage of addition reactions in radical polymerizations triggered by four initiator radicals, which were generated by photodissociation of four parent molecules. Two monomers (tert‐butylacrylate and tert‐butylmethacrylate) were examined as reactant. Stern–Volmer analysis on the measured decay time of electron spin echo intensity of reacting radicals provides rate constants for addition reactions. We focused on rate constants for the second step reaction between monomer and adduct radical that is produced by the first step addition reaction between initiator radical and monomer. The rate constant measured by pulsed EPR was evaluated by theoretical calculations in the light of (1) enthalpy difference between product radical and reactants and (2) charge transfer interaction between reacting radical and monomer. Copyright © 2016 John Wiley & Sons, Ltd.     

New optically active poly(amide–imide)s from N-trimellitylimido-l-amino acid and 1,2-bis[4-aminophenoxy]ethane in the main chain: Synthesis and characterization

Six new optically active poly(amide–imide)s (PAIs) with good inherent viscosities were synthesized from the direct polycondensation reaction of N-trimellitylimido-l-amino acids with 1,2-bis[4-aminophenoxy]ethane by direct polycondensation in a medium consisting of N-methyl-2-pyrrolidone (NMP)/triphenyl phosphite (TPP)/calcium chloride (CaCl₂)/pyridine (py). Diamine was synthesized by using a two-step reaction. At first 1,2-bis[4-nitrophenoxy]ethane was prepared from the reaction of two equimolars 4-nitrophenol and one equimolar 1,2-dibromo ethane and the dinitro compound was reduced by using Pd/C. Also N-trimellitylimido-l-amino acids were synthesized by the condensation reaction of trimellitic anhydride with two equimolars of various l-amino acids in acetic acid solution. The polymerization reactions produced a series of optically active PAIs with a high yield and good inherent viscosity. The resulted polymers were fully characterized by means of FTIR and ¹H NMR spectroscopy, elemental analyses, inherent viscosity, specific rotation, solubility tests, thermogravimetric analysis (TGA), and a derivative of thermogravimetric (DTG) analysis.     

Mechanism of Back Electron Transfer in an Intermolecular Photoinduced Electron Transfer Reaction: Solvent as a Charge Mediator

Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine the BET reaction of pyrene (Py) and 1,4‐dicyanobenzene (DCB) in acetonitrile (ACN) by using time‐resolved near‐ and mid‐IR spectroscopy. The Py dimer radical cation (Py₂^.+) and DCB radical anion (DCB^.?) generated after photoexcitation of Py show asynchronous decay kinetics. To account for this observation, we propose a reaction mechanism that involves electron transfer from DCB^.? to the solvent and charge recombination between the resulting ACN dimer anion and Py₂^.+. The unique role of ACN as a charge mediator revealed herein could have implications for strategies that retard charge recombination in dye‐sensitized solar cells.