Intramolecular hydrogen bonds and hydrogen-bonded systems in di-Schiff bases of 4-methyl-isophthalaldehyde with 4-substituted anilines

Three di-Schiff bases of 2-hydroxy-5-methyl-isophthalaldehyde with 4-R-anilines (R=H, CH₃, OCH₃) and their 1:1 complexes with HClO₄ were studied by FT-IR, ¹H, and ¹³C NMR spectroscopy in acetonitrile and [²H₃]acetonitrile solutions, respectively. In di-Schiff bases intramolecular OH…N hydrogen bonds have been detected; however, they show no proton polarizability. Hydrogen-bonded systems with fast proton fluctuation and large proton polarizability have been found in the 1:1 complexes of di-Schiff bases with HClO₄.     

Time-resolved enzymatic determination of glucose using a fluorescent europium probe for hydrogen peroxide

An enzymatic assay for glucose based on the use of the fluorescent probe for hydrogen peroxide, europium(III) tetracycline (EuTc), is described. The weakly fluorescent EuTc and enzymatically generated H₂O₂ form a strongly fluorescent complex (EuTc–H₂O₂) whose fluorescence decay profile is significantly different. Since the decay time of EuTc–H₂O₂ is in the microseconds time domain, fluorescence can be detected in the time-resolved mode, thus enabling substantial reduction of background fluorescence. The scheme represents the first H₂O₂-based time-resolved fluorescence assay for glucose not requiring the presence of a peroxidase. The time-resolved assay (with a delay time of 60 s and using endpoint detection) enables glucose to be determined at levels as low as 2.2 mol L^–1, with a dynamic range of 2.2–100 mol L^–1. The method also was adapted to a kinetic assay in order to cover higher glucose levels (mmol L^–1 range). The latter was validated by analyzing spiked serum samples and gave a good linear relationship for glucose levels from 2.5 to 55.5 mmol L^–1. Noteworthy features of the assay include easy accessibility of the probe, large Stokes shift, a line-like fluorescence peaking at 616 nm, stability towards oxygen, a working pH of approximately 7, and its suitability for both kinetic and endpoint determination.     

Structure and vibrational spectra of the bis(betaine)-selenic acid molecular crystal

The crystal structure of bis(betaine)-selenic acid has been determined by X-ray diffraction as orthorhombic, space group Pbca, with a = 11.591(2), b = 22.930(5), c = 12.045(2) Å and Z = 8. The crystal comprises hydrogen selenate ions, HSeO⁻₄, and two distinct betaine molecules, which are held together into a complex by short hydrogen bonds. One of the betaine molecules is present as the zwitterion form (CH₃)₃N⁺---CH₂---COO⁻ and the second occurs as the protonated form (CH₃)₃N⁺---CH₂---COOH. Powder FTIR and Raman spectra were measured. An assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the hydrogen selenate ion and the betaine molecules is proposed.     

超临界状态下炭基材料的储氢

评介了目前各种储氢方法，指出了炭基材料作为储氢材料的优势，综述了近年来纳米炭材料在储氢方面的进展，详细探讨了超临界状态下氢气在纳米孔隙中的吸附机理，并在此基础上提出了研究中的问题及进一步的研究方向。     

Specific and non-specific interactions of hydropseudohalic acids with water and organic solvents

Partition coefficients P of the HNCS, HNCO and HN₃ hydropseudohalic acids between a number of organic solvents and water were determined. It has been found that log P increases with pKa of the acid and with the basicity of the solvent, but the effect of pKa on P is the smaller the more basic is the solvent. The relationships have been explained in terms of hydrogen bond formation between undissociated acid and solvent molecules. H-bonding between the pseudohalic acids and organic solvents has been confirmed by IR spectra on the example of HN₃ in benzene. Association constants for H-bonding between the three acids and water, benzene, dibutyl ether and tri-n-butyl phosphate were determined from partition data. It has been found that H-bonding increases with the strength of the acid, whereas the contribution to partition from non-specific interactions with water and organic solvents depends on the molecular surface area of the acid molecule.     

Structure and Magnetic Properties of a Novel Two‐Dimensional Complex from 1, 3, 5‐Benzenetricarboxylate and Neodymium(III) — {[Nd(1, 3, 5‐benzenetricarboxylate)(H2O)4] · H2O}n

A unique neodymium(III) complex, {[Nd(BTC)(H₂O)₄] · H₂O}_n (BTC = 1, 3, 5‐benzenetricarboxylate), was obtained from the reaction between Nd(ClO₄)₃ · xH₂O and Na₃BTC. Coordination bonds, hydrogen bonds, and π‐π stacking form a supramolecular structure with a novel, two‐dimensional framework. The temperature‐dependent magnetic susceptibilities were analyzed by the Curie‐Weiss law; the following values were found C = 1.32, θ = —18.3 K, respectively.     

Ammonium hexafluorosilicate salts

The preparation and characterization of the ammonium hexafluorosilicate salts, 2[R]⁺ [SiF₆]²⁻ (where R=piperidinium (2), methylammonium (3), quinolinium (4), acridinium (5), 2,2,6,6-tetramethylpiperidinium (6), and propylammonium (7)) is described.The salts were prepared from the reaction of the corresponding alkylammonium fluoride with silica gel. The compounds were characterized by NMR, IR, mass spectrometry and in the case of 1 (piperidinium fluoride), 2-4 by X-ray crystallography. Compounds 1-3 crystallize in the orthorhombic crystal system (space groups Iba2, Fdd2, and Pnnm, respectively), with Z=8, 14, and 4, respectively. Compound 4 crystallizes in the triclinic space group P-1, with Z=2. Compounds 1-4 exhibit hydrogen bonding.     

Automatic sequential determination of the hydrogen peroxide scavenging activity and evaluation of the antioxidant potential by the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation assay in wines by sequential injection analysis

An automatic system that performs two analytical procedures, allowing the evaluation of the relative antioxidant capacity of wine samples, was developed. Automation was carried out using a sequential injection analysis (SIA) system that allowed, thanks to its versatility, the development of two methodologies. One is based on the decolorization assay of the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical, using a spectrophotometric detector. A second methodology allowed the evaluation of the hydrogen peroxide scavenging activity by measuring the oxidation of homovanylic acid (HVA) to its fluorescent dimer, using a fluorescent detector.The developed automatic methodologies were evaluated using trolox as standard and subsequently using other antioxidant substances as gallic acid, caffeic acid, ascorbic acid, catechin and taxifolin which are abundant in wine and whose antioxidant activities were compared to that shown by trolox. The spectrophotometric and fluorimetric assays showed linearity intervals between 0.001 and 0.01 mM, and 0.001 and 0.008 mM of trolox, respectively.The evaluation of the antioxidant power of 20 white and red wine samples, from different Portuguese wine producing regions, was carried out sequentially, in the automatic system. The results were expressed in trolox equivalent antioxidant capacity (TEAC) and presented, for the ABTS and hydrogen peroxide scavenging activity methodologies, detection limits of 8.4 × 10⁻⁷ and 1.4 × 10⁻⁴ mM and relative standard deviation (R.S.D. (%)) in the range 0.6-2.4 and 1-1.8, respectively.     

Hydrogen peroxide-generating nanomedicine for enhanced chemodynamic therapy

Chemodynamic therapy(CDT) is an emerging endogenous stimulation activated tumor treatment approach that exploiting iron-containing nanomedicine as catalyst to convert hydrogen peroxide(H_2O_2)into toxic hydroxyl radical(·OH) through Fenton reaction.Due to the unique characteristics(weak acidity and the high H_2O_2 level) of the tumor microenvironment,CDT has advantages of high selectivity and low side effect.However,as an important substrate of Fenton reaction,the endogenous H_2O_2 in tumor is still insufficient,which may be an important factor limiting the efficacy of CDT.In order to optimize CDT,various H_2O_2-generating nanomedicines that can promote the production of H_2O_2 in tumor have been designed and developed for enhanced CDT.In this review,we summarize recently developed nanomedicines based on catalytic enzymes,nanozymes,drugs,metal peroxides and bacteria.Finally,the challenges and possible development directions for further enhancing CDT are prospected.     

过氧化氢氧化酸碱滴定法测定苯甲醛的含量

本文提出和建立了一种分析醛类化合物的方法，并用此方法测定了分析纯苯甲醛的含量为９９．４％，相对标准偏差为０．２１％，实验苯甲醛中所带的寻质苯甲醇以及乙醇，甲醇均不干扰测定，苯甲酸的干扰可以扣除，本法操作简单，终点易于掌握，推广应用方便。