REACTIONS OF 1,3-OXAZOLIDINE-2-THIONE WITH ZINC(II), CADMIUM(II) AND MERCURY(II) HALIDES

Abstract

The reactivity of 1,3-oxazolidine-2-thione towards II B group metals is considered. Cadmium halides, mercury chloride and bromide react to give coordination compounds, whose stereochemistry is tentatively assigned by their i.r. spectra.

Otherwise zinc halides and mercury iodide induce a ring opening.     

邻氨基噻唑偶氮类试剂质子化机理的研究

邻氨基噻唑偶氮类试剂［１～３］在不同酸度下呈现不同的颜色,关于其质子化发生的位置以及先后次序至今尚未见文献报道．本文通过量子化学计算,结合分光光度法对这类试剂质子化行为进行了研究．１实验方法１．１吸收光谱测定移取１．０ｍＬ１．０×１０－３ｍｏｌ／ＬＴ...     

Morphological transition of nanostructures of self-assembled block copolymers by stimuli-induced conformational changes in the hydrophilic block

The morphological control of nanostructures created by the self-assembly of macromolecular building blocks in solution has practical importance because the structural parameters of nanostructures greatly affect their physical and chemical behavior in solution, for example, pharmacokinetics. Herein, we report that the stimuli-induced changes to the conformation of the hydrophilic polymer block of a block copolymer (BCP), in this case branched-linear poly(ethylene glycol)-b-poly(styrene) BCPs, are translated to changes in the morphology of the BCP self-assemblies in solution. Specifically, the cone angle between the poly(ethylene glycol) arms in the tri-arm hydrophilic block equipped with pyridyl units in the scaffold can be changed by varying the self-assembly conditions, thus affecting the packing parameter (p) of the BCP. Upon increasing the cone angle by protonating the pyridyl units, the self-assembled BCP structures underwent changes consistent with a reduction in the p value. In contrast, the chelation of zinc metal cations (Zn²⁺) to the pyridyl groups resulted in the conformation of the hydrophilic block taking on a closed form, resulting in an apparent increase in the p value of the BCP. Our results could be applied to stimuli-dependent morphological transitions of other self-assembled BCP nanostructures in solution.     

Anhydrous Silicophosphoric Acid Glass: Thermal Properties and Proton Conductivity

Anhydrous silicophosphoric acid glass with an approximate composition of H₅Si₂P₉O₂₉ was synthesized and its thermal and proton-conducting properties were characterized. Despite exhibiting a glass transition at 192 °C, the supercooled liquid could be handled as a solid up to 280 °C owing to its high viscosity. The glass and its melt exhibited proton conduction with a proton transport number of ∼1. Although covalent O−H bonds were weakened by relatively strong hydrogen bonding, the proton conductivity (4×10⁻⁴ S cm⁻¹ at 276 °C) was considerably lower than that of phosphoric acid. The high viscosity of the melt was due to the tight cross-linking of phosphate ion chains by six-fold-coordinated Si atoms. The low proton conductivity was attributed to the trapping of positively charged proton carriers around anionic SiO₆ units (expressed as (SiO_6/2)²⁻) to compensate for the negative charges.     

Excited-state relaxation of protonated adenine.

The excited state dynamics of protonated adenine in the gas phase were investigated by femtosecond pump-probe transient mass spectroscopy. Adenine was protonated in an electrospray ionization source and transferred to a Paul trap. Two femtosecond laser pulses at 266 nm and 800 nm excited the lowest electronic pipi* state and probed the excited-state dynamics by monitoring ion fragment formation. The measured excited state decay is monoexponential with a lifetime shorter than 161 fs. This agrees with a theoretical prediction of very fast internal conversion via a conical intersection with the ground state.     

Protonation of 18-crown-6 by dichloropicric acid in anhydrous and in water saturated 1,2-dichloroethane. Homoconjugation of dichloropicric acid

From conductometric and UV-VIS spectrophotometric studies of the reaction between 18-crown-6 (L) and dichloropicric acid (HA) in dry and water saturated 1,2-dichloroethane, it has been concluded that formation of a 1:1 homoconjugate HA ₂ ^– accompanies the simple protonation of L, viz, L+HALH⁺A^– and L+2HALH⁺HA ₂ ^– . The electrolytes LH⁺A^– and LH⁺HA ₂ ^– are extensively, or practically completely dissociated in both solvents under the experimental conditions. The specie LH⁺A^– appears to be a contact ion pair in DCE. The stability constant of HA ₂ ^– in the dry solvent, 5.7×10³ mol^–1-cm³, is some 10^2.4 times that in propylene carbonate reflecting the difference in H-bond accepting capacity of the two solvents. Hydration of HA, A^– and HA ₂ ^– in wet dichloroethane is negligible or slight. As expected, LH⁺ is rather strongly hydrated, the ratio of the hydration constants of LH⁺ and L being about 1×10¹.     

Absorption spectra of thin film of polyaniline

The absorption spectra of thin film of polyaniline (PANI) on slide glass coated by a spin coater were measured as a function of the protonation state of PANI, the concentration of solution of PANI in NMP, drying temperature, and atmosphere. The absorbance value of the 950 nm peak and the ratio of the absorbance value at 950 nm to that of the 630 nm peak increases with increasing the protonation state of PANI. This is consistent with the observation of varying the conductivity with the protonation state. A modified molecular structure of PANI is proposed: where y and x are defined as the oxidation and the protonation states of PANI, respectively.     

量热分析化学放大方法及技术

该文从提高选择性、灵敏度和分析性能的角度,在富集、缓冲液放大、非水溶液体系、级联反应等方面评述了量热分析化学热焓放大的原理、方法以及关键技术,其中,富集是通过集聚提升待测物浓度来提高反应焓变;缓冲液放大利用缓冲液的质子焓变增强反应焓变;非水溶液体系可从热容量的角度提升量热灵敏度;级联反应由系列反应或循环完成,最终焓变是系列反应焓变的叠加,达到热焓放大目的。通过结合最新的研究成果和应用进一步阐明化学放大方法实现热焓放大能有效改善和提高量热分析系统的信噪比和降低检出限,并大大加强量热分析方法在现场、实际试样分析测试中的固有应用优势。同时,对当前存在的问题、挑战及未来的研究方向进行了探讨,并展望了其发展趋势和前景。     

Acid‐Induced Shift of Intramolecular Hydrogen Bonding Responsible for Excited‐State Intramolecular Proton Transfer

The significant progress recently achieved in designing smart acid‐responsive materials based on intramolecular charge transfer inspired us to utilize excited‐state intramolecular proton transfer (ESIPT) for developing a turn‐on acid‐responsive fluorescent system with an exceedingly large Stokes shift. Two ESIPT‐active fluorophores, 2‐(2‐hydroxyphenyl)pyridine (HPP) and 2‐(2‐hydroxyphenyl)benzothiazole (HBT), were fused into a novel dye (HBT‐HPP) fluorescent only in the protonated state. Moreover, we also synthesized three structurally relevant control compounds to compare their steady‐state fluorescence spectra and optimized geometric structures in neutral and acidic media. The results suggest that the fluorescence turn‐on was caused by the acid‐induced shift of the ESIPT‐responsible intramolecular hydrogen bond from the HPP to HBT moiety. This work presents a systematic comparison of the emission efficiencies and basicity of HBT and HPP for the first time, thereby utilizing their differences to construct an acid‐responsive smart organic fluorescent material. As a practical application, red fluorescent letters can be written using the acid as an ink on polymer film.     

Quantum chemical prediction for complex organic molecules

Numerous types of quantum chemical calculations and protocols have been successfully applied to computing of small, uncomplicated organic molecules. Here, we argue for the need to shift attention to more challenging molecules that are marked by an interplay of complicating factors such as conformational, tautomeric, steric, and other effects. The challenge is not in choosing the right quantum chemical method and solvation model but in combining the existing methods to simultaneously and accurately describe the breadth of chemical and physical phenomena that give rise to the experimentally observed . The complexity of the phenomena that must be considered begs for the need for a greater automation of prediction workflows. We review our experience with these challenges and outline paths for future progress in the direction of tackling prediction of complex organic molecules.