Oxidation-Induced Structural Alterations and Its Effect on Chaperone Function of Rat Lens α-Crystallin

An ascorbate-FeCl₃-EDTA-H₂O₂ system was used to oxidize rat lens α-crystallins. Under this oxidative insult, the chaperone activity of α-crystallin toward γ-crystallin was shown to decrease significantly, which is quite different from the result reported by Wang and Spector. (Invest. Ophthalmol. Vis. Sci. 1995 , 36, 311-321.) Fluorescence spectroscopy and circular dichroism were employed to characterize the structural changes of oxidized α-crystallin. It was found that fluorescence intensity of l-anilinonaphthalene-8-sul-phonate (ANS) bound to oxidized α-crystallin increased comparing to that bound to normal α-crystallin, suggesting oxidation causes the exposure of more hydrophobic regions. Further, α-crystallin's fluorescence intensity in response to tryptophan residues showed a pseudo first order decline. Amino acid analysis of normal versus oxidized α-crystallin confirmed actual decline in tryptophan levels, showing about 80% of tryptophan being modified after 10-hour oxidation. Circular dichroism showed both changes in the secondary and tertiary structures of oxidized α-crystallin, characterized by a large loss of aromatic-type amino acid interactions and a large loss of β-sheet structure. In conclusion, modified tryptophan, secondary and tertiary structural changes of α-crystallin correlate best with the reduction of chaperone function, the curves all showing a linear slope for 10 hours, then plateauing. These results indicate that the decrease of α-crystallin chaperone activity is attributed to the structural changes.     

3—Mercaptopropionic Acid Capped Gold Nanoclusters：Quantized Capacitance in Aquesous Media

3-Mercaptopropionic acid monolayer protected gold nanoclusters (MPA-MPCs) were synthesized and characterized by transmission electorn microscopy,UV-Vis spectroscopy,X-ray photoelectron spectroscopy and Fourler transform infrared spectroscopy.The exact value of quantized double-layer capacitance of MPCs in aqueous media was obtained by differential pulse voltammograms.     

298.1 K时脂肪酸钠盐对定组成水溶液中非水组分活度系数的影响

本文报告了298.1 K下甲酸钠(C_1), 乙酸钠(C_2)、丙酸钠(C_3)、丁酸钠(C_4)、戊酸钠(C_5)、已酸钠(C_6)和庚酸钠(C_7)七个盐对水溶液中乙醇、丙酮和乙腈三个溶质的活度系数的影响。实验方法是, 固定水溶液中乙醇、丙酮和乙腈的浓度(摩尔分数约为0.05), 用气相色谱法检测不同盐浓度下平衡气相中溶质分压的变化, 从而得出溶质的盐效应活度系数γ。本文给出了一个可以连续取样的气液平衡装置的设计。由实验结果可见, 不同碳链大小的脂肪酸根离子的盐效应作用差别很大。C_1、C_2的盐效应主要由于静电作用; 对C_3、C_4盐, 除静电作用外,它们的疏水基与溶质疏水基的相互作用对盐效应有显著影响; C_5、C_6和C_7的盐效应则反映了疏水离子的特色, 疏水水化、疏水相互作用、疏水离子形成的聚集体与不同官能团的特定相互作用等几项因素, 导致儿个溶质盐效应的差异。     

NiOxHy薄膜的电致变色特性和机理

运用循环伏安和阶跃电位方法研究了Ni（OH）2粉末靶直流溅射沉积的NiOxHy薄膜电致变色特性．结合实时的光透射-时间变化，发现着色后的薄膜在零外电势下有一自发的消色过程，该过程可能对应着Li 的自发注入。着色没有自发过程，获取了着消色状态Ni2p3／2和O1s的XPS谱，表明在着色态镍被氧化，消色态镍被还原，相应地氧的化学环境发生改变．     

9,9‐Dimethoxy‐7,11‐diphenyl‐2,4‐diazaspiro[5.5]undecane‐1,3,5‐trione monohydrate

Due to steric repulsions, the cyclo­hexane ring in the title compound, C₂₃H₂₄N₂O₅·H₂O, shows some bond‐length abnormalities and adopts a chair conformation. The pyrimidine and cyclo­hexane rings are approximately perpendicular to each other, and the phenyl rings are equatorial. C—H?π and N—H?O intermolecular interactions, as well as C—H?O inter‐ and intramolecular interactions, occur between the mol­ecules. In addition to van der Waals interactions, the water mol­ecule interacts with the pyrimidine­trione ring to stabilize the structure.     

2‐Hydro­xy‐3‐(4,5,6,7‐tetra­hydro‐1H‐imidazo­[4,5‐c]­pyridin‐5‐ium‐4‐yl)­benzoate monohydrate

The title mol­ecule, C₁₃H₁₃N₃O₃·H₂O, is in the form of a mono­hydrated zwitterion. The tetra­hydro­pyridinium ring adopts an envelope conformation and is nearly coplanar with the plane of the imidazoline ring. The water solvate mol­ecule plays an important role as a bridge between zwitterions, forming molecular chains running along the c direction, which are interconnected by N—H?O hydrogen bonds into molecular ribbons. The crystal packing is further stabilized by another N—H?O and one O—H?N hydrogen bond, which interconnect the molecular ribbons.     

NMR Conformational Analysis and Theoretical Calculations for 2‐Aryl‐ 1,3‐dihydroxy‐4,4,5,5‐tetramethylimidazolidines

Conformational studies of 1,3‐dihydroxy‐4,4,5,5‐tetramethyl‐2‐(pyridin‐1‐yl)imidazolidine ( 1a ) and 1,3‐dihydroxy‐4,4,5,5‐tetramethyl‐2‐(pyridin‐3‐yl)imidazolidine ( 1b ), carried out by using 1D ¹H‐ and ¹³C‐NMR and 2D HMQC, HMBC, and NOESY experiments and with the aid of theoretical calculations, indicate that the OH groups are trans to the pyridinyl substituent. Because the two ¹H‐NMR signals of the Me groups are distinguishable and do not change between 290 and 380 K, it is proposed that 1a and 1b have each only one conformation in this temperature range. This behavior was not found with 1,3‐dihydroxy‐4,4,5,5‐tetramethyl‐2‐(pyridin‐2‐yl)imidazolidine ( 1c ) because its Me ¹H‐NMR signals cross over at 300 K. Hence, more than one conformation must be present, beyond those produced by simple inversions. Theoretical calculations including temperature and solvent effects were performed to provide further information on the conformational analysis and to help to assign the NMR data. The combination of NMR measurements and quantum‐chemical calculations is shown to be a very promising strategy for conformational analysis studies in solution.     

Synthesis and Characterization of Base‐catalyzed Phenyl Modified PDMS/PHMS Copolymers

A series of phenyl modified polydimethylsiloxane (PDMS) / polyhydrogenmethylsiloxane (PHMS) random copolymers containing both internal Si‐H and terminal SiH₂ and T (MeSiO_3/2) units was synthesized in one step through n‐BuLi‐catalyzed ring‐opening polymerization of cyclic comonomers and characterized by GPC, IR and ¹H and ²⁹Si NMR. Sequential microstructures of these copolymers were determined by ²⁹Si‐NMR spectroscopy. Epoxy‐modified polysiloxanes were prepared and used as comparable standards for the assignment of the NMR spectra. A hydride‐transfer mechanism has been proposed to account for the formation of terminal Si‐H and T group. Detailed sequential analyses and chemical shifts of ²⁹Si‐NMR for various siloxane units are reported for the first time.     

Analysis of Seven Herbicides by Gas-Liquid Chromatography

Simutaneous analysis of seven commonly used herbicides, 2,4-D methyl ester, 2,4-D methyl ester, 2,4,5-T methyl ester, silvex methyl ester, ramrod, CIPC and DEF, by gas-liquid chromatography with an electron capture detector was attempted. Two packed columns (which are generally used for the analysis of chlorinated pesticides) and two chemically bonded fused silica capillary columns were used for the analysis. When the packed columns were used, ramrod always interfered with the analysis of 2,4-D methyl ester and/or silvex methyl ester. Complete separation with reasonable analysis time can be achieved using one of the chemically bonded fused silica capillary columns.     

Sodium 5‐nitro‐2‐pyridonate trihydrate

The title compound, alternatively sodium pyridin‐2‐olate trihydrate, Na⁺·C₅H₃N₂O₃^?·3H₂O, crystallizes in the P space group. It is made up of edge‐shared chains of NaO₆ octahedra with five water mol­ecules and one 5‐nitro‐2‐pyridonate anion. Four of these water mol­ecules are bicoordinating, involved in connecting the adjacent octahedra, and the fifth is coordinated to only one octahedron. The crystal structure is stabilized by a network of strong O—H?O and O—H?N interactions. The organic moieties occupy the space between the chains with an antiparallel alignment.