The kinetics and thermodynamics of the 2,6-bis(2-hydroxybenzilidene)cyclohexanone chemical reactions network was studied at different pH values using NMR, UV-vis, continuous irradiation, and flash photolysis. The chemical behavior of the system partially resembles anthocyanins and their analogue compounds. 2,6-Bis(2-hydroxybenzilidene)cyclohexanone exhibits a slow color change from yellow to red styrylflavylium under extreme acidic conditions. The rate constant for this process (5 × 10(-5) s(-1)) is pH independent and controlled by the cis-trans isomerization barrier. However, the interesting feature is the appearance of the colorless compound, 7,8-dihydro-6H-chromeno[3,2-d]xanthene, isolated from solutions of acid to neutral range, characterized by (1)H NMR and single crystal X-ray diffraction. Light absorption by 2,6-bis(2-hydroxybenzilidene)cyclohexanone solutions immediately after preparation exclusively results in cis-isomer as photoproduct, which via hemiketal formation yields (i) red styrylflavylium by dehydration under extremely acidic solutions (pH < 1) and (ii) colorless 7,8-dihydro-6H-chromeno[3,2-d]xanthene by cyclization in solutions of acid to neutral range.
The chemistry of 2,2'-spirobis[chromene] derivatives is intimately related to the one of anthocyanins and similar compounds. The 2,2'-spirobis[chromene] species plays a central role in the network of chemical reactions connecting two different flavylium-based multistate systems. In the present work, a new asymmetric 2,2'-spirobis[chromene] intermediate possessing a constrained propylenic bridge between carbons 3 and 3' was isolated and its role as a pivot in the anthocyanins-type multistate of chemical reactions was investigated by the conjugation of absorption spectroscopy, stopped-flow, NMR, and X-ray crystallography. It was confirmed that the propylenic bridge is essential to stabilize the spirobis[chromene] species. Furthermore, under acidic conditions, two cis-trans styrylflavylium isomers were identified, which could be interconverted directly into one another with light. This is the first report of styrylflavylium cations with photoisomerization on the styryl moiety.
Glycopolymers are polymers with sugar moieties which display biodegradable and/or biocompatible character. They have emerged as an environmentally-friendly solution to classical synthetic polymers and have attracted significant research interest in the past years. Herein, we present the synthesis of a D-mannose based glycopolymer with biodegradable features. The glycopolymer was synthesized by radical copolymerization between a D-mannose oligomer bearing polymerizable double bonds and 2-hydroxypropyl acrylate, in a weight ratio of 1:2. The copolymerization kinetics was investigated by differential scanning calorimetry (DSC) and the activation energy of the process was comparatively assessed by Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods. The obtained glycopolymer displayed good thermal behavior, fact proven by thermogravimetrical (TG) analysis and it was submitted to biodegradation inside a bioreactor fed with water from the Bega River as the source of microbial inoculum. The glycopolymer sample degraded by approximately 60% in just 23 days. The biodegradation pattern of the glycopolymer was successfully fitted against a modified sigmoidal exponential function. The kinetic model coefficients and its accuracy were calculated using Matlab and the correlation coefficient is more than promising. The changes inside glycopolymer structure after biodegradation were studied using TG and FTIR analyses, which revealed that the sugar moiety is firstly attacked by the microbial consortia as nutrient source for proliferation.
This paper presents the synthesis and characterization of two oligomers based on monosaccharides (D-glucose and D-mannose). The oligomers were obtained by the polycondensation of two diacids derived from monosaccharides (3-O-benzyl-5,6-(bis(maleyloxy))-1,2-O-isopropylideneglucofuranose and 1-O-benzyl-5,6-(bis(maleyloxy))-2,3-O-isopropylidenemannofuranose, respectively), with propane-1,3-diol in the presence of p-toluenesulfonic acid. The oligomers were characterized using FTIR and NMR spectroscopy, HPLC-MS and DSC. The copolymerization of the oligomers with 2-hydroxy-propyl acrylate was studied by DSC to evaluate the possibility of obtaining cross-linked copolymers.
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