Application of Iodide Ion Selective Electrode to the Study of Stepwise Formation Constant and Solubility Product of Lead Iodide

Iodide ion-selective electrode were studied, prepared and applied for the complex formations and solubility product determination. The thermodynamic formation constant of PbI⁺ and the solubility product of PbI₃ were found to be 54 and 9.2 × 10^?9, respectively. The formation constant of PbNO₃⁺ was calculated to be 4.6 from the different formation constant of PbI⁺ in perchlorate and nitrate media.     

Carbon anode materials from polysiloxanes for lithium ion batteries

Three kinds of silicon-containing disordered carbons have been prepared by pyrolysis of polysiloxanes with different amounts of phenyl side groups. X-ray powder diffraction, X-ray photoelectron spectroscopy and electrochemical capacity measurements were performed to study their behaviors. Graphite crystallites, micropores, and silicon species affect their electrochemical performances. All of them present high reversible capacities, >372 mAh/g. Since the graphite crystallites are very small, they contribute very little to reversible capacity. The number of micropores produced by gas emission during the heat-treatment process decides whether they exhibit reversible capacity. Si mainly exists in the form C–Si–O and influences the irreversible capacity. There is no evident capacity fading in the first ten cycles, indicating promising properties for these disordered carbons.     

用θ-2θ型衍射仪测定溶液结构的新方法

叙述了用θ－２θ型Ｘ射线衍射仪精确测定电解质溶液结构的新实验技术。设计制作了具有恒温功能的超厚液体样品池，并建立了样品池窗口强度的校正方法。优化了液体Ｘ射线衍射数据和结构参数精细化的计算机程序，获得了非常令人满意的实验结果。由θ－２θ型Ｘ射线衍射仪精确测定的径向分布函数与θ－θ型衍射仪自由散射比较，表明ＤＲＦ分辨率有所提高。     

Thermal and autoxidation reactions of poly-3-methylenecyclobutene and poly-1-methyl-3-methylenecyclobutene

The thermal ring-opening reactions, autoxidation and hydrogenation of polymethy-lenecyclobutene (PMCB) and poly-1-methyl-3-methylenecyclobutene (PMMCB), were investigated. Both polymers were prepared by cationic polymerization and consisted almost entirely of 1,5-repeating units containing cyclobutene rings in the polymer backbone. Both polymers showed well behaved exothermic processes at elevated temperatures which apparently resulted in crosslinking. These processes were investigated by differential scanning calorimetry and interpreted to involve thermal ring-opening reactions. Autoxidation occurred very rapidly in PMCB but much more slowly in PMMCB as predicted by Bolland's rules. Attempts to hydrogenate the cyclobutene rings in both polymers resulted in the occurrence of hydrogenolysis in PMCB and little or no reaction with PMMCB for a Pd-catalyzed reaction and partial hydrogenation of the latter for a diimide reaction.     

Differentiation and quantitation of isomeric dipeptides by low-energy dissociation of copper(II)-bound complexes

Application of the kinetic method based on the dissociation of transition metal centered cluster ions is extended from chiral analysis (Tao, W. A.; Zhang, D.; Nikolaev, E. N.; Cooks, R. G. J. Am. Chem. Soc. 2000, 122, 10598) to quantitative analysis of isomeric mixtures, including those with Leu/Ile substitutions. Copper(II)-bound complexes of pairs of peptide isomers are generated by electrospray ionization mass spectrometry and the trimeric complex [CuII(ref)2(A) - H]+ (analyte A, a mixture of isomeric peptides; reference compound ref, usually a peptide) is caused to undergo collisional dissociation. Competitive loss of the neutral reference compound or the neutral analyte yields two ionic products and the ratio of rates of the two competitive dissociations, viz. the product ion branching ratio R is shown to depend strongly on the regiochemistry of the analyte in the precursor [CuII(A)(ref)2 - H]+ complex ion. Calibration curves are constructed by relating the branching ratio measured by the kinetic method, to the isomeric composition of the mixture to allow rapid quantitative isomer analysis.     

Interaction of tetrandrine with human serum albumin: a fluorescence quenching study.

The interaction of tetrandrine with human serum albumin (HSA) was studied by measuring fluorescence quenching spectra, synchronous fluorescence spectra and ultra-violet spectra. The fluorescence quenching spectra of HSA in the presence of tetrandrine showed that tetrandrine quenched the fluorescence of HSA. The quenching constants of tetrandrine on HSA were determined using the Stern-Volmer equation. Static quenching and non-radiation energy transfer were the two main reasons leading to the fluorescence quenching of HSA by tetrandrine. According to the F?rster theory of non-radiation energy transfer, the binding distances (r) and the binding constants (K(A)) were obtained. The thermodynamic parameters obtained in this study revealed that the interaction between tetrandrine and HSA was mainly driven by a hydrophobic force. The conformational changes of HSA were investigated by synchronous spectrum studies.     

What controls the melting properties of DNA-linked gold nanoparticle assemblies?

We report a series of experiments and a theoretical model designed to systematically define and evaluate the relative importance of nanoparticle, oligonucleotide, and environmental variables that contribute to the observed sharp melting transitions associated with DNA-linked nanoparticle structures. These variables include the size of the nanoparticles, the surface density of the oligonucleotides on the nanoparticles, the dielectric constant of the surrounding medium, target concentration, and the position of the nanoparticles with respect to one another within the aggregate. The experimental data may be understood in terms of a thermodynamic model that attributes the sharp melting to a cooperative mechanism that results from two key factors: the presence of multiple DNA linkers between each pair of nanoparticles and a decrease in the melting temperature as DNA strands melt due to a concomitant reduction in local salt concentration. The cooperative melting effect, originating from short-range duplex-to-duplex interactions, is independent of DNA base sequences studied and should be universal for any type of nanostructured probe that is heavily functionalized with oligonucleotides. Understanding the fundamental origins of the melting properties of DNA-linked nanoparticle aggregates (or monolayers) is of paramount importance because these properties directly impact one's ability to formulate high sensitivity and selectivity DNA detection systems and construct materials from these novel nanoparticle materials.     

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID VESICLE SYSTEMS: COMPARISON OF INSIDE-OUTSIDE ASYMMETRY BETWEEN LARGE AND SMALL UNILAMELLAR VESICLES*

Abstract— We have determined the chlorophyll triplet quenching efficiencies, the chlorophyll cation radical yields and the conversion efficiencies of chlorophyll triplet to radical in large and small unilamellar phosphatidylcholine vesicles (LUV and SUV, respectively) in the presence of electrically-charged electron acceptors (ferricyanide and oxidized cytochrome c) located in either the inner or outer aqueous compartments of the vesicles. Both types of vesicles displayed inside-outside asymmetry, although the properties were reversed. Triplet quenching in SUV was more efficient when ferricyanide was located within the vesicle interior, whereas the reverse was true in LUV. When ferricyanide was located on the outside of the vesicles, the extent of triplet quenching in LUV was about two times that in SUV and the amount of cation radical formed in LUV was about two times that in SUV. Under these conditions, the conversion efficiencies of chlorophyll triplet to radical were 12.2% for LUV and 8.5% for SUV. With cytochrome c as an electron acceptor in negatively charged vesicles (25 mol per cent dixhexadecylphosphate incorporated) similar results were obtained. Again, the triplet quenching and radical yield inside-outside asymmetry properties were reversed between the two types of vesicles, and radical formation efficiencies when cyt c was located outside the vesicles were higher in LUV (11.7%) than in SUV (4.2%). We conclude that the inside-outside asymmetric photochemical behavior of unilamellar phosphatidylcholine vesicles is influenced by factors in addition to the difference in radius of curvature between the inside and outside surfaces. It is suggested that transmembrane electrostatic potentials may be involved. Furthermore, in the present system the properties of LUV were more favorable to photochemical electron transfer product formation than those of SUV.     

Structure and stability of endohedral X@Si20H20 complexes (X = Li, Na, K, Be, Mg, Ca)

The structure and stability of endohedral X@Si₂₀H₂₀ complexes (X = Li^0/+, Na^0/+, K^0/+, Be^0/2+, Mg^0/2+, Ca^0/2+) have been studied at the B3LYP/6-31G* level of density functional theory. It is found that complexes with X = Na^0/+, K^0/+, Mg and Ca^0/2+ are energy minimum structures with X at the cage center in I_h symmetry, while those with X = Li^0/+, Be^0/2+, Mg²⁺ have off-centered structures with X towards one pentagon face in C_5v symmetry. Large electron or charge transfer between the Si₂₀H₂₀ cage and the encapsulated X has been observed.     

Determination of proanthocyanidins in fresh grapes and grape products using liquid chromatography with mass spectrometric detection

Fresh grapes and grape products, such as grape wine and grape juice, were analyzed for proanthocyanidins (PACs) using liquid chromatography with electrospray ionization mass spectrometric (MS) detection. PACs were successfully separated and analyzed on the basis of their protonated molecules, allowing the identification of PACs in different degrees of polymerization from monomers to oligomers (up to 7 units), and in various isomeric forms. Using reversed-phase high-performance liquid chromatography (HPLC) combined with MS detection, the PAC monomers, (+)-catechin (C), (-)-epicatechin (EC), (-)-catechin gallate (CG), and (-)-epicatechin gallate (ECG), were successfully quantified using selected ion monitoring (SIM) mode. Standard curves were fitted for each PAC ranging from 43.8 to 5600 ng/mL for C, from 42.2 to 5400 ng/mL for EC, from 36.7 to 4700 ng/mL for CG, and from 39.8 to 5100 ng/mL for ECG. Good linearity (r2>0.999) was achieved for each analyte. The accuracy and precision (RSD) were within 10% (n=8) at the limit of detection. This method allows direct quantification of monomeric PACs in fresh grapes and grape-derived products. Additionally, flow injection analysis (FIA) was applied to estimate the concentration levels of PAC oligomers by comparing their FIA-MS peak areas, which were well correlated (r2=0.936) to the total concentrations of PAC monomers.