Dynamics of noncovalent interactions in all-α and all-β class proteins: implications for the stability of amyloid aggregates

A fully folded functional protein is stabilized by several noncovalent interactions. When a protein undergoes conformational motions, the existing noncovalent interactions may be maintained. They may also break or new interactions may be formed. Knowledge of the dynamical nature of the different types of noncovalent interactions is extremely important to understand the structural stability, function, and folding of a protein. There are experimental limitations to investigate the dynamics of different noncovalent interactions simultaneously in a biomolecule. We have carried out molecular dynamics simulations on four different proteins, two belonging to all-α class proteins and the other two are representatives of all-β class proteins. The dynamical nature of eight different noncovalent interactions was studied by monitoring the maximum residence time (MRT) and lifetime (LT). The conventional hydrogen bonds are the dominant interactions in all four proteins, and the majority of those formed between the main-chain atoms were maintained during most of the simulation time with MRT greater than 10 ns. Such interactions with more than 1 ns lifetime provide stability to the secondary structures, and hence they are responsible for the overall stability of the protein. The weak C-H···O hydrogen bond is the next major type of interactions. However, a large number of such interactions are observed between the main-chain atoms only in all-β proteins as interstrand interactions, and, surprisingly, they are observed during most part of the simulation although their average lifetime is only about 20 to 30 ps. The strong cation···π and salt-bridge interactions are present few in number. However, in many cases they are almost uninterrupted indicating the higher strength of these interactions. Four other interactions involving the π-electron cloud of aromatic rings are very small in number, and, in many cases, their presence is not maintained throughout the simulation. Our results clearly indicate that the weak C-H···O interactions between the main-chain atoms are the distinguishing factor between the all-α and all-β class of proteins, and these interstrand interactions can provide additional stability to all-β protein structures. Based on these results, we hypothesize that such weak C-H···O interstrand interactions could play a major role in providing stability to amyloid type of aggregates that are responsible for the pathological state of many proteins.     

SYNTHESIS AND CRYSTAL STRUCTURE OF 5, 10, 15, 20, 22, 24-HEXAHYDRO-5, 5, 10, 10, 15, 15, 20, 20-OCTAMETHYL-PORPHINE

<正> The title com pound (HHOMP) has been synthesized with the pho-toinduced condensation of acetone and pyrrole in the presence of iodoaromatic hydrocarbons, and its molecular and crystal structures have been determined by X-ray analysis. C28H36N4, Mr = 428. 63, triclinic; space group P1; a =10. 165(3), b = 10. 185(2), c=13. 012(3)(?); α=85. 41(2), β=67. 84(2), γ= 89. 75(2)°; V = 1243 (?)3; Z = 2; D = 1. 145g. cm-3; μ= 0. 635cm-1; F (000) = 464. Although the HHOMP molecule twists, it is found that the four nitrogen atoms are still in a plane.     

在小硅化物SiX^m4（X=H,He,Li,Be,O,F,Ne,Na,Mg,S,Cl,Ar;m=0,…

用从头算方法，在ＨＦ／ＳＴＯ－３Ｇ、ＨＦ／３－２１Ｇ和ＨＦ／６－３１Ｇ水平上研究了小硅化物ＳｉＸ＾ｍ４的成键倾向性。计算结果表明，所研究的分子势能曲线均有稳定的极小值（ＳｉＬｉ４除外）。与已知的稳定分子ＳｉＨ１、ＳｉＦ４和ＳｉＣｌ４比较，含惰性元素的未知分子ＳｉＨｅ＾４＋４、ＳｉＮｅ＾４＋４和ＳｉＡｒ＾４＋４比含碱金属和碱土金属的未知分子ＳｉＬＩ４、ＳｉＮａ４、ＳｉＢｅ＾４＋４和ＳｉＭｇ＾４＋４有     

Theoretical Study on the Structure and Stability of Si5X （X = Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl） Clusters

1 INTRODUCTION In the later 60s of last century, silicon substituted for germanium to present as mainstream in semicon- ductor. The semi-conductive devices made by silicon have many advantages, for example, refractory pro- perty, high radioresistance, simple and stable process- ing technic, high machinability and low cost. So it was widely used to manufacture large power appara- tuses, for instance, digit and linear integrated circuit, large scale integrated circuit (LSI), etc. Thus, th…     

Über die verbreitung ternärer komplexnitride mit Perowskitstruktur in SE-Al-N-systemen (SE ≡ La,Ce, Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er, Tm,Yb, Lu)

The existence of complex nitrides in the RE-Al-N (RE ≡ rare earth) ternaries is investigated. In the systems containing lanthanum, cerium, praseodymium, neodymium and samarium either ternary phases (RE)₃AlN_x with a perovskite-type structure or alternatively almost complete filling of the octahedral voids by nitrogen in (RE)₃Al phases with an L1₂-type structure are found. An isothermal section for Pr-Al-N at 600 °C is presented. In the systems RE-A1-N (RE ≡ Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) no ternary phase is observed.     

急性心肌梗塞患者血清硒,锌,铜,钙,镁,铁,锶含量的测定

分别对２９例急性心肌梗塞（ＡＭＩ）病人和４０例健康人进行血清中七种微量、常量元素含量测定，结果表明，ＡＭＩ患者血清Ｓｅ、Ｚｎ、Ｃａ较正常对照组明显降低；血清Ｃｕ显著增高，血清Ｆｅ、Ｍｇ较对照组低，差异不显著；血清Ｓｒ两组无差异。对ＡＭＩ患者与血清硒及各元素间相互关系进行了探讨，指出调整人体微量、常量元素的不平衡状况，对冠心病和ＡＭＩ的发生、发展和康复有一定的临床意义。     

硫酸镍中Ca,Mg,Cu,Fe,Pb,Zn的光谱测定

用发射光谱法测定结晶硫酸镍中Ｃａ,Ｍｇ,Ｃｕ,Ｆｅ,Ｐｂ,Ｚｎ等杂质元素,加入ＮａＣｌ为缓冲剂改善杂质元素的激发行为,以提高分析的灵敏度。用交流电弧激发,以镍为内标,一次摄谱,可同时测定上述六种元素。此法快速、准确,满足实际需要。     

Die extraktive Abtrennung von Metallspuren (Hg, Ag, Pb, Cu, M, Co, Zn, Cd, Bi, Mn) in Silicatmineralien mit Natriumdi?thyldithiocarbamidat

Ohne Zusammenfassung     

ICP—AES法测定钢铁样中硅,磷,锰,铬,镍,铜,铝

详细地研究了钢铁样中主量铁对７种被测定元素的干扰和被测定元素间的干扰情况，并研究了不同酸分解样品的效果，确定了用电感耦合等离子体发射光谱测定钢铁样中硅、磷、锰、铬、镍、铜和铝的方法。     

Sn(Ⅱ)-X和Sn(Ⅳ)-X (X=O,S,N,C,P,As,Se,Te,F,Cl,Br,I)键价参数

基于剑桥晶体数据库中同配配合物的Sn(Ⅱ)-X和Sn(Ⅳ)-X (X=O,S,N,C,P,As,Se,Te,F,Cl,Br,I)键长数据,采用键价参数B=0.037 nm拟合得到Sn(Ⅱ)-X和Sn(Ⅳ)-X的键价参数R0,这样拟合的经验参数R0中有一些是首次推出.本文所报道的Sn(Ⅱ)-O键基于B=0.037 nm的R0值(0.1956 nm)可适用于多数Sn(Ⅱ)呈各种配位数时的氧化态指定,而文献报道的B=0.055 nm和R0=0.1859 nm主要对于低配位的情况能取得Sn(Ⅱ)原子价态指定的较好结果.本研究证明,进一步研究键价参数对键价和(BVS)计算至关重要的那些可能的因素实乃当务之急.     

X射线荧光光谱法测定锌铝镁合金中锌,铝,镁,硅,铁,钛,钙,锆和铈

通过确立仪器的测量条件并在X射线荧光仪上拟合出检测锌铝镁合金中各元素的工作曲线,建立了X射线光谱法测定锌铝镁合金中Zn,Al,Mg,Si,Fe,Ti,Zr,Ce的快速分析方法。对实际样品进行测试,相对标准偏差(RSD,n=11)在0.12%~4.8%之间。与化学分析方法比对,测试结果基本一致。方法已应用到日常锌铝镁合金样品的检测。     

STUDY ON POLYMERIZATION MECHANISM OF 3, 9,-DIALLYL-3, 9, -DIBENZYL-1, 5, 7, 11-TETRAOXASPIRO [5, 5] UNDECANE

A new monomer, 3,9-diallyl-3, 9-dibenzyl-1, 5,7,11 - tetraoxa- spiro [5,5] undecane (6) was prepared by the reaction of 2- allyl- 2' - benzyl- propanediol - 1.3 with dibutyltin oxide, and then treated with CS_2. Monomer 4 could be initiated by cationic initiators to give a viscous polymer (white powder in the case of polymerization at 0℃). Upon the NMR and IR spectra of the obtained polymer, the components and their relative amount were estimated. The polymerization mechanism was discussed.     

王玉功,倪能 ,杨发旺

采用电感耦合等离子体发射光谱法(ICP-AES)测定地表水和地下水中的全S、P、B来近似代替水中的SO42-、PO43-、H3BO3。结果表明,ICP-AES可同时测定地表水和地下水的SO42-、PO43-、H3BO3,方法检出限分别为0.0265mg/L、0.0320mg/L、0.0192mg/L。方法的精密度(RSD,n=6)为0.53﹪～6.09﹪,加标回收率为91.9﹪～102.2﹪,经与单个项目分别测定的方法比对实验,测定值无明显系统偏差。方法快速、准确,经国家标准物质验证,结果与标准值相符。