Grafting of polymers onto graphene oxide by cationic and anionic polymerization initiated by the surface-initiating groups

The grafting of polymers onto graphene oxide (GO) was achieved by two process: (1) cationic polymerization initiated by carboxyl (COOH) groups on GO and (2) anionic alternating copolymerization of epoxides with cyclic acid anhydrides initiated by potassium carboxylate (COOK) groups on GO. The cationic polymerizations of isobutyl vinyl ether and N-vinylcarbazole were successfully initiated by COOH groups on GO to give the corresponding polymer-grafted GO. The cationic polymerization was considered to be initiated by proton addition from COOH groups to monomer and propagation of polymer cation proceeds with carboxylate anion as a counter ion. It was found that the corresponding polymer was successfully grafted onto GO based on the termination reaction of growing polymer cation and surface counter carboxylate anion. On the other hand, the anionic ring-opening alternating copolymerization of epoxide and cyclic acid anhydrides were also initiated by COOK groups on GO, which were previously introduced onto GO by the neutralization of COOH groups with KOH. During the anionic ring-opening copolymerization of styrene oxide (SO) with phthalic anhydride (PAn) and maleic anhydride (MAn), the corresponding polyesters, poly(SO-alt-PAn) and poly(SO-alt-MAn), were successfully grafted onto GO, based on the propagation of the polyesters from COOK groups. The grafting of polymers onto GO during the above cationic and anionic polymerizations was confirmed by thermal decomposition gas chromatogram/mass spectrum. The untreated GO in THF was immediately precipitated within 15 min. On the contrary, these polymer-grafted GOs gave stable dispersions in THF and no precipitation of polymer-grafted GOs was observed even after one week.     

Preparation of carboxyl‐functionalized polyhedral oligomeric silsesquioxane by a structural transformation reaction from soluble rod‐like polysilsesquioxane

Carboxyl‐functionalized polyhedral oligomeric silsesquioxane (SQ; POSS‐COOH ) was successfully prepared by a structural transformation reaction, that is, a process of heating and concentrating soluble carboxyl‐functionalized rod‐like polySQ (PolySQ ‐COOH ) using the aqueous superacid trifluoromethanesulfonic acid (HOTf) as the catalyst and solvent. The obtained POSS‐COOH was a mixture of a cage‐like decamer (T₁₀‐POSS), which was the main product, and an octamer (T₈‐POSS) and a dodecamer (T₁₂‐POSS), which were the minor products. The product obtained by heating and concentrating PolySQ‐COOH using aqueous hydrochloric acid (HCl) as the catalyst and solvent was soluble polySQ rather than POSS. For comparison, heating and concentrating POSS‐COOH in aqueous HOTf and HCl were performed, which yielded POSS‐COOH and PolySQ‐COOH , respectively. Based on these results, the process of heating and concentrating each starting material ( PolySQ‐COOH and POSS‐COOH ) in aqueous HOTf afforded POSS‐COOH , and a similar process in aqueous HCl yielded PolySQ‐COOH . © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2511–2518     

Phenanthroline method for quantitative determination of surface carboxyl groups on carboxylated polystyrene particles with high sensitivity

This study developed a phenanthroline method for quantitative determination of surface carboxyl groups on carboxylated polystyrene (PS‐COOH) particles based on the coordination between the carboxyl groups and Fe²⁺. The ratio of the carboxyl groups, which is determined by conductometric titration method, to Fe²⁺ coordinated with the particles, which is determined by phenanthroline method, is 4.7, i.e. n_COOH = 4.7 × Δn_Fe²⁺. The Lambert–Beer law is obeyed in the range of 0–60 × 10^?9 mol/ml for the amount of surface carboxyl on the particles. The detection limit of the method is 2 nmol COOH/ml. The average standard deviation of the experiments is 4.4%. The relative deviation of the data obtained with this method is lower than 7% compared with that obtained with the conductometric titration method. The weight of the sample necessary for phenanthroline method is only about 0.1% of that necessary for conductometric titration method. It has been demonstrated that the phenanthroline method is suitable for quantitative determination of low amount of surface carboxyl groups on PS‐COOH particles due to its high sensitivity. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemical Syntheses and Chemical Biology of Carboxyl Polyether Ionophores: Recent Highlights

A central goal of chemical biology is to develop molecular probes that enable fundamental studies of cellular systems. In the hierarchy of bioactive molecules, the so‐called ionophore class occupies an unflattering position in the lower branches, with typical labels being “non‐specific” and “toxic”. In fact, the mere possibility that a candidate molecule possesses “ionophore activity” typically prompts its removal from further studies; ionophores—from a chemical genetics perspective—are molecular outlaws. In stark contrast to this overall poor reputation of ionophores, synthetic chemistry owes some of its most amazing achievements to studies of ionophore natural products, in particular the carboxyl polyethers renowned for their intricate molecular structures. These compounds have for decades been academic battlegrounds where new synthetic methodology is tested and retrosynthetic tactics perfected. Herein, we review the most exciting recent advances in carboxyl polyether ionophore (CPI) synthesis and in addition discuss the burgeoning field of CPI chemical biology.     

Influence of Reaction Pressure on Semibatch Esterification Process of Poly(ethylene terephthalate) Synthesis

Summary: Influence of esterification pressure on oligomeric properties was studied by using a semibatch reactor. Esterification model for semibatch process was further improved by considering EG reflux in the column. It was observed that increasing the reaction pressure decreases EG/water ratio in the column while increasing the EG/TPA feed ratio increases EG/water ratio in the column. By controlling the EG reflux in a semibatch reactor, it is possible to generate oligomers with similar oligomeric properties observed at different stages of continuous process.     

取代基对PPC/聚苯醚羧酸酯共混体系相容性的影响

由二氧化碳活化并与环氧丙烷共聚而成的脂肪族聚碳酸酯(PPC)是一类有发展前途的新型高分子弹性体。研究它与其它高聚物的混容性及混容机制对于开拓这一新材料的应用领域具有十分重要的意义。本文合成了一系列不同取代度和不同链长酯基的聚苯醚羧酸酯[E(x)-C^yPPO]^[3],探索了PPC与各聚苯醚狡酸醋的混容性,讨论了聚苯醚梭酸酷的取代度及侧基链长对PPC/E(x)-C^yPPO共混体系混容性的影响。     

Comparison of Aqueous and Non-Aqueous Treatments of Cellulose to Reduce Copper-Catalyzed Oxidation Processes

Summary. The present paper examines oxidative degradation of cellulose catalyzed by presence of Cu¹⁺and Cu²⁺ ions in the context of historic paper conservation treatments. Aqueous treatments of degraded papers further spread transition metal ions, such as copper, across the fibre matrix, and therefore augment the detrimental effect of these ions. In the paper industry, the inhibiting effects of magnesium ions on metal-catalyzed degradation of cellulose contaminated with metal impurities have been observed. Also, magnesium compounds dissolved in alcoholic or aqueous solutions are generally used in paper conservation as deacidification agents. Paper samples with artificially produced copper corrosion served as mock-ups for examination and comparison of different treatments which focused on the inhibiting effect of magnesium and antioxidants. Analytical examination of molecular weight distribution, carbonyl content, carboxyl content, and surface pH was performed. Results show an inhibiting effect of magnesium on copper-catalyzed cellulose degradation, although less pronounced than expected.     

一些含桥羧基配体的羰基钼(Ⅰ)化合物的NMR研究

化合物(1)[(CO)₄Mo(SPh)₂Mo(CO)₄]同羧酸L反应得到桥羧基配体的羰基钼(Ⅰ)化合物[Bu₄N][(CO)₃Mo(SPh)₂LMo(CO₃)](L=CF₃COO,HCOO,CH₃COO,C₂H₅COO,OOCCH₂CH₂COO,Me₃COO),在室温下测定了它们的¹H,¹³C,⁹⁵MoNMR谱,由于配位基团、对称性及Mo-Mo键长等结构的变化,两者的谱线差别很大,特别是⁹⁵MoNMR更为敏感,即使是不同的羧基也会影响它的化学位移和线宽,其屏蔽和线宽的顺序是Me₃COO^-1 > C₂H₅COO^-1 > CH₃COO^-1 > HCOO^-1 > F3COO^-1。     

Sodium Carboxyl Methyl Cellulose for Improvement of the Determination of Polyethylene Glycol Modified Carbon Nanotubes by Raman Spectroscopy

Single-walled carbon nanotubes (SWNTs) have shown great potential in various areas of biomedicine. However, few research studies have focused on in vivo carbon nanotube detection by Raman spectroscopy. In this work, SWNTs were functionalized with polyethylene glycol (PEG) to form PEG-o-SWNTs to improve the biocompatibility and dispersibility. A novel application of Raman scattering was used to detect the PEG-o-SWNTs. Compared to the traditional assay method, the recovery rate was improved from 84.2% to 102.7%, the correlation coefficient of the standard curve increased from 0.7315 to 0.9872, and the degree of precision decreased from 4.4% to 3.1%. Large errors in the measured results were found the cryopreserved blood and organ samples in which the reticular sediments separated, on which the nanotubes generally concentrate. It was determined that by achieving a final concentration of 0.5% through the addition of sodium carboxyl methyl cellulose (CMC-Na), the homogeneity of the tested sample can be greatly enhanced, thus boosting the accuracy of the analyses. This work offers methods with higher accuracy for determining the presence of PEG-o-SWNTs in blood and organs using Raman spectroscopy.     

Possible Role of Carboxyl and Imidazole Groups in the Catalysis of Pummelo Limonoid Glucosyltransferase

 Limonoid bitterness is a serious problem in the citrus industry worldwide. Limonoid glucosyltransferase is an enzyme that catalyzes the conversion of bitter limonoid into non-bitter limonoid glucoside while retaining the health benefit of limonoids in the juice. The immobilization of this enzyme in a column can solve the juice bitterness problem. More information about the catalytic residues of the en-zyme is needed in this immobilization process. Glutamate/aspartate, histidine, lysine, tryptophan, serine, and cysteine residues were chemi-cally modified to investigate their roles in the catalytic function of limonoid glucosyltransferase. Inactivation of the enzyme following modi-fication of carboxyl and imidazole moieties was a consequence of a loss in substrate binding and catalysis in the glucosyltransfer reaction. The modification of a single histidine residue completely destroyed the ability of limonoid glucosyltransferase to transfer the D-glucopyranosyl unit. Tryptophan seemed to have some role in maintaining the active conformation of the catalytic site. Lysine also seemed to have some direct or indirect role in this catalysis but the modification of serine and cysteine did not have any effect on catalysis. There-fore, we conclude that the carboxyl and imidazole groups contain amino acids are responsible for the catalytic action of the enzyme.