Microsolvation and hydration enthalpies of CaC2O4(H2O) n (n = 0-16) and C2O4 2-(H2O) n (n = 0-14): an ab initio study

We studied hydrated calcium oxalate and its ions at the restricted Hartree–Fock RHF/6-31G* level of theory. Performing a configurational search seems to improve the fit of the HF/6-31G* level to experimental data. The first solvation shell of calcium oxalate contains 13 water molecules, while the first solvation shell of oxalate ion is formed by 14 water molecules. The first solvation shell of Ca(II) is formed by six water molecules, while the second shell contains five. At 298.15 K, we estimate the asymptotic limits (infinite dilution) of the total standard enthalpies of hydration for Ca(II), oxalate ion and calcium oxalate as ?480.78, –302.78 and –312.73 kcal mol^?1, resp. The dissociation of hydrated calcium oxalate is an endothermic process with an asymptotic limit of +470.84 kcal mol^?1.

A novel vanadium(V) homocitrate complex: synthesis,structure, and biological relevance of [K2(H2O)5][(VO2)2(R,S-homocitrate)2]·H2O

Initial investigations into the possible roles of homocitric acid in the biosynthesis and function of the active site cofactor of nitrogenase resulted in the isolation and characterization of the dinuclear vanadium(V) species [K₂(H₂O)₅][(VO₂)₂(R,S-C₇H₈O₇)₂]·H₂O ( 1). Complex 1 represents the first synthetic structurally characterized transition metal homocitrate complex and may represent an early mobilized precursor in the biosynthesis of VFeco. Compound 1 was characterized by a variety of physical methods, including X-ray crystallography. Crystal data: space group P?* (#2), with a?=?10.292 (3)?Å, b?=?16.663 (3)?Å, c?=?8.343 (1)?Å, α?=?95.93 (1)°, β?=?105.74 (2)°, γ?=?90.86 (2)°, V?=?1386 (1)?ų, and Z?=?2. The homocitrate ligand is coordinated to the vanadium(V) atoms in a bidentate fashion via the deprotonated bridging hydroxyl group and a carboxylate donor. This unique coordination mode accurately mimics the coordination of homocitrate to the cofactor of nitrogenase.     

Catalytic effect of (H2O)n (n = 1–3) clusters on the reaction of HNO2 + HO → H2O + NO2 under tropospheric conditions

ABSTRACT

The effect of (H₂O)_n (n?=?1–3) on the HNO₂?+?HO → H₂O?+?NO₂ reaction has been investigated theoretically at the CCSD(T)/CBS//B3LYP/6-311?+?G(3df,2pd) level of theory, coupled with rate constant calculations by using variational transition state theory. Our results show that, when (H₂O)_n (n?=?1–3) was introduced into HNO₂?+?HO → H₂O?+?NO₂ reaction, the product of the reaction did not change, but the potential energy surface became quite complex, yielding two kinds of reactions, namely HNO₂···(H₂O)_n (n?=?1–3)?+?HO and HO···(H₂O)_n (n?=?1–3)?+?HNO₂. In all catalysed reactions with (H₂O)_n (n?=?1–3), the former reaction type is favourable than the latter one with its effective rate constant respectively larger by 6–1 orders of magnitude than that of latter one. Within the temperature range of 240–320?K, the relative impacts on water monomer are much more obvious than dimer and trimer. However, the effective rate constant with water is larger by 658%–17% times of magnitude, showing that the positive water effect is obvious under atmospheric conditions.     

Genomic instability induced by mutant succinate dehydrogenase subunit D (SDHD) is mediated by O2(-•) and H2O2

SDHD mutations are associated with human cancers but the mechanisms that may contribute to transformation are unknown. The hypothesis that mutations in SDHD increase levels of superoxide leading to genomic instability was tested using site-directed mutagenesis to generate a truncated SDHD cDNA that was expressed in Chinese hamster fibroblasts. Stable expression of mutant SDHD resulted in 2-fold increases in steady-state levels of superoxide that were accompanied by a significantly increased mutation rate as well as a 70-fold increase in mutation frequency at the hprt locus. Overexpression of MnSOD or treatment with polyethylene glycol conjugated (PEG)-catalase suppressed mutation frequency in SDHD mutant cells by 50% (P<0.05). Simultaneous treatment with PEG-catalase and PEG-SOD suppressed mutation frequency in SDHD mutant cells by 90% (P<0.0005). Finally, 95% depletion of glutathione using l-buthionine-[S,R]-sulfoximine (BSO) in SDHD mutant cells caused a 4-fold increase in mutation frequency (P<0.05). These results demonstrate that mutations in SDHD cause increased steady-state levels of superoxide which significantly contributed to increases in mutation rates and frequency mediated by superoxide and hydrogen peroxide. These results support the hypothesis that mutations in SDHD may contribute to carcinogenesis by increasing genomic instability mediated by increased steady-state levels of reactive oxygen species.     

Crystal structure,magnetic and thermal properties of the one-dimensional complex [Nd(pzam)3(H2O)Mo(CN)8] · H2O

The new d–f cyanido-bridged 1D assembly [Nd(pzam)₃(H₂O)Mo(CN)₈] · H₂O was prepared by self-assembly of pyrazine-2-carboxamide (pzam), Nd(NO₃) · nH₂O and (Bu₃NH)₃[Mo(CN)₈] · 4H₂O in acetonitrile. X-ray crystallographic studies indicate that the complex comprises chains of alternating, cyanido-bridged [Nd(pzam)₃(H₂O)]³⁺ and Mo(CN)₈]^3? fragments. The magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (?0.3 K). Below ≈10 K the Nd(III) moment is well approximated by an effective spin S = 1/2, with anisotropic g-tensor. The exchange coupling between the Nd(III) and the Mo(V) spins S = 1/2 along the structural chains is found to be ferromagnetic, with J/k_B = 1.8 ± 0.2 K and approximately XY (planar) anisotropy. No evidence for 3D interchain magnetic ordering is found. A comparison with magneto-structural data of other cyanido-bridged complexes involving the Nd(III) ion is presented.     

HMG盒转录因子1(HBP1)参与H2O2诱导的细胞衰老过程

为探讨HMG盒转录因子1 (HBP1)在过氧化氢（H2O2）诱导的细胞衰老中所起的作用,通过慢病毒感染得到稳定表达HBP1的MDA-MB-231细胞,以H2O2处理细胞．采用Western免疫印迹杂交试验和实时PCR检测HBP1、p16和细胞周期蛋白D1（cyclinD1）表达水平的变化．用荧光免疫试验检测H2O2对HBP1表达的影响,以及HBP1在H2O2的诱导下对于p16和细胞周期蛋白D1启动子的影响．用细胞增殖试验检测H2O2对于细胞增殖的影响． 用基因敲减实验和衰老相关β半乳糖苷酶(SA-β-Gal)染色检测在H2O2诱导的细胞衰老中HBP1所起的作用．Western和免疫荧光实验结果显示,细胞经H2O2处理后,HBP1表达增高的同时促进了p16的表达,降低了细胞周期蛋白D1的表达．细胞增殖实验结果显示,H2O2显著抑制了细胞的增殖．基因敲减实验和SA-β-Gal染色实验说明,H2O2可诱导HBP1表达正常的MDA-MB-231细胞衰老,而HBP1的敲减则抑制了H2O2诱导的细胞衰老过程．本研究结果提示,在H2O2诱导的衰老中,HBP1的表达显著增加,并通过促进衰老相关基因p16的表达和抑制生长因子cyclinD1的表达来阻碍细胞增殖,促进细胞衰老．HBP1在H2O2诱导的细胞衰老过程中起着重要作用,H2O2诱导的细胞衰老必须在HBP1存在的情况下才能发生．     

Preparation of (±)-2-(2,3-2H2)Jasmonic Acid and Its Methyl Ester,Methyl (±)-2-(2,3-2H2)Jasmonate

For use as the internal standards in a quantitative analysis of natural jasmonic acid (JA) and methyl jasmonate (JAMe) by gas chromatography-mass spectrometry-selected ion monitoring, (±)-2-(2,3–²H₂)JA and its methyl ester, (±)-2-(2,3–²H₂)JAMe, were efficiently prepared from 2-(2–pentyl)-2-cyclopentenone through catalytic semi-deuteriogenation of acetylenic intermediates with deuterium gas in pyridine.     

植物中的H2O2信号及其功能

H2O2是植物细胞的信号分子,是细胞正常代谢的产物,生物和非生物胁迫促使植物细胞产生H2O2,通过H2O2信号应答胁迫.H2O2信号调控一系列重要的植物生理生化过程,如系统获得抗性(SAR)和高度敏感抗性(HR)、细胞衰老与程序化细胞死亡(PCD)、气孔关闭、根的向地性、根的生长和不定根形成、细胞壁的发育、柱头与花粉的发育及相互关系等.Ca2+流动和可逆蛋白磷酸化作用是H2O2下游信号,通过MAPK级联作用于转录因子,最终调控基因的表达.H2O2调控多种基因的表达,包括编码抗氧化酶基因、调控程序化细胞死亡相关蛋白基因、生物与非生物胁迫应答蛋白基因等.     

Optical analysis of RE3+ (RE = Nd or Er):B2O3–P2O5–CaF2–ZnO–(Li2O/Na2O/K2O) glasses

Calcium boro fluoro zinc phosphate glasses modified using alkali oxide and doped with Nd³⁺ and Er³⁺ ions with the chemical composition of 69.5 (B₂O₃) + 10 (P₂O₅) + 10 (CaF₂) + 5 (ZnO) + 5 (Na₂O/Li₂O/K₂O) + 0.5 (Er₂O₃/Nd₂O₃) were prepared using a conventional melt quenching technique. The results of X-ray diffraction patterns indicated the amorphous nature of all the prepared glasses. The visible–near-infrared red (NIR) absorption spectra of these glasses were analyzed systematically. The NIR emission spectra of Er³⁺ and Nd³⁺:calcium boro fluoro zinc phosphate glasses showed prominent emission bands at 1536 nm (⁴I_13/2→⁴I_15/2) and 1069 nm (⁴F_3/2→⁴I_11/2) respectively with λ_exci = 514.5 nm (Ar⁺ laser) as the excitation source.     

H2O2对水稻Rubisco稳定性的影响

H2 O2 浓度低于 2 0mmol·L-1时 ,Rubisco分子稳定 ;高于 2 0mmol·L-1则Rubisco的大亚基之间发生交联 ,全酶发生聚沉。H2 O2 处理后 ,Rubisco表面巯基数目减少 ,对两种蛋白水解酶尤其是胰蛋白酶的敏感性增强 ,大亚基水解明显增加。H2 O2 处理只会增加Rubisco大亚基的水解程度 ,不会造成新的水解位点     

Determination of organophosphate flame retardant tris(2-chloroethyl)phosphine based on the luminol–H2O2 chemiluminescence system

Organophosphorus flame retardants (OPFRs) are new types of environmental pollutants, therefore the rapid and sensitive detection of OPFRs is a very important objective. A new experimental phenomenon was found in which tris(2-chloroethyl)phosphine (TCEP), a type of OPFR, could effectively enhance the signal of the luminol–H₂O₂ chemiluminescence (CL) system. Combined with the controllability of flow injection analysis, a rapid, stable, and sensitive CL method was established. The CL intensity responded linearly to the concentration of TCEP in the range 0.5–100 μg/L (R² = 0.999) with a low detection limit of 33 ng/L. Relative standard deviation (RSD) was 2.2% (n = 7, c = 100 μg/L). Water samples were labelled and recycled with RSDs of 1.1–5.7% and recoveries of 88.7–116.1%. Based on these results, this study established a new CL detection method for the environmental pollutant TCEP.     

Cadmium-induced early changes in O2 •−, H2O2 and antioxidative enzymes in soybean (Glycine max L.) leaves

Cadmium-induced initial changes in the production of reactive oxygen species (ROS) and antioxidant mechanism were investigated in soybean (Glycine max L. cv. Don Mario 4800 RR) leaves. Whole plants (WP) and plants without roots (PWR) were exposed to 0.0, 10.0 and 40.0 μM Cd for 0, 4, 6 and 24 h. Compared to PWR, a higher level of endogenous Cd in WP was associated with a lower oxidative stress measured in terms of lipid peroxidation. Furthermore, O₂ ^•− content decreased in the leaves of Cd-treated WP, whereas it increased in those of Cd-treated PWR. Although O₂ ^•− accumulation in PWR was associated with a decrease in superoxide dismutase (SOD) activity, O₂ ^•− diminution in WP leaves was not related to any increase in SOD activity. H₂O₂ content increased in the leaves of both Cd-treated WP and PWR, and it was concomitant with a corresponding decline in catalase (CAT) and ascorbate peroxidase (APX) activities. When diphenyl iodonium (DPI), an inhibitor of NADPH oxidase, was added, H₂O₂ content remained unchanged in Cd-treated WP, suggesting that NADPH oxidase does not participate in the early hours of Cd toxicity. Taken together, our results showed that early ROS evolution and oxidative damage were different in WP and PWR. This suggests that the response in soybean leaves during the early hours of Cd toxicity is probably modulated by the root.     

The luminescence of europium nitrate hexahydrate,Eu(NO3)3·6H2O

Some luminescent properties of single crystals of Eu(NO₃)₃·6H₂O are reported at temperatures down to liquid helium. The water molecules are responsible for a considerable amount of quenching of the emission. The Eu³⁺ coordination changes upon lowering the temperature. The number of ⁵D₀-⁷F₂ lines observed is higher than expected.     

Molecular dynamics study on thermal dehydration process of epsomite (MgSO4·7H2O)

Water vapour sorption in salt hydrates is one of the most promising means of compact, low loss and long-term solar heat storage in the built environment. Among all, epsomite (MgSO₄·7H₂O) excels for its high-energy storage density and vast availability. However, in practical applications, the slow kinetics and evident structural changes during hydration and dehydration significantly jeopardise the heat storage/recovery rate. A molecular dynamics (MD) study is carried out to investigate the thermal properties and structural changes in the thermal dehydration process of the epsomite. The MD simulation is carried out at 450 K and a vapour pressure of 20 mbar, in accordance with experimental heat storage conditions. The study identifies the dehydration as multiple stages from the initial quick water loss and collapse of the crystal framework to the adsorption of water molecules, which inhibits complete dehydration. Further, the anisotropic diffusion behaviour supports the important role of the porous matrix structure in the heat and mass transfer process. The enthalpy changes, partial densities, mass diffusion coefficients of water and radial distribution functions are calculated and compared with corresponding experimental data to support the conclusions.     

Crystal structures of three thiourea (tu) complexes of Pt(II): trans-[(tu)2Pt(NH3)2]Cl2, trans-[(tu)2Pt(CH3NH2)2]Cl2·3H2O and [Pt(tu)4]Cl2

The structures of three Pt(II) thiourea complexes, trans-[(tu)₂Pt(NH₃)₂]Cl₂ (1), trans-[(tu)₂Pt(CH₃NH₂)₂]Cl₂·3H₂O (2) and [Pt(tu)₄]Cl₂ (3), have been determined by X-ray diffraction and refined to R = 0.049 for 1026 reflections (1), R = 0.057 for 2547 reflections (2) and R = 0.046 for 2792 reflections (3). All the compounds crystallize in the space group P2₁/c and have cell dimensions: a = 5.437(1), b = 6.450(1), c = 17.980(3) Å, β = 96.05(2)°, Z = 2 (compound 1); a = 9.225(1), b = 15.404(2), c = 12.601(2) Å, β = 105.39(2)°, Z = 4 (compound 2); and a = 9.051(6), b = 10.203(6), c = 18.263(8) Å, β = 91.12(8)°, Z = 4 (compound 3). The unit cell of 1 and 3 contains only a single type of cation, while that of 2 is formed from two independent cations. In 1 and 2 the coordination spheres of the Pt atoms are rather similar, with angles close to 90° and coplanarity of the metal and respective donor atoms. Instead, in 3 the four sulfur atoms, which surround the Pt, display a slight distortion (0.06 Å from the mean plane) towards tetrahedral.