稀土化合物增强ZA—27合金耐磨性的研究

对稀土化合物增强ＺＡ－２７合金的组织及耐磨性做了研究。试验发现,由于在ＺＡ－２７合金中加入一定量的ＥＲ和Ｓｉ元素,组织中出现一些颗粒状第二相;这些物相分布在晶界及枝晶间,阻止了晶粒长大。通过航向电镜能谱分析发现,该物相是一种含有Ｚｎ、Ａｌ、Ｓｉ及ＲＥ元素的复杂化合物。经测试,这种物相的显微硬度要比基体高得多。耐磨性等性能试验结果表明,这种合金的耐磨性要比ＺＡ－２７合金高４倍,比Ｓｉ相增强合金也高,     

Traceability to units

On the grounds that clear and direct communication is required of us today, it is proposed that traceability be regarded as the ability to demonstrate that measurements are what they are purported to be and that traceability is thus to measurement units rather than reference values per se. It is suggested that such an approach may give greater flexibility in the establishment, maintenance and propagation of traceability, and that accreditation practices are becoming central to the practical establishment of traceability for chemical and biological measurement.     

On the reality of residual entropies of glasses and disordered crystals

We show that the hypothesis that the configurational entropy of a liquid disappears when it is kinetically frozen into a single glass state implies a spontaneous decrease of entropy. We show further that this is not an innocuous exception to the second law that requires a slight modification of that law, but rather implies directly the possibility of an uncompensated conversion of heat to work. We also note that the number of microstates visited in the course of a measurement does not determine the entropy, but rather that this number is always an inconceivably small fraction of the accessible microstates. Various experimental and computational tests of the possible vanishing of configurational entropy on kinetic arrest (e.g., from studies of glass vapor pressure and solubilities, and the coexistence curve between a disordered crystal and the liquid), with the exception of one questionable case, are consistent with the view that it does not vanish. We then show that this result is actually required by the second law. These considerations apply equally to the residual entropy of disordered crystals.     

Simulation studies of protein folding/unfolding equilibrium under polar and nonpolar confinement

We study the equilibrium folding/unfolding thermodynamics of a small globular miniprotein, the Trp cage, that is confined to the interior of a 2 nm radius fullerene ball. The interactions of the fullerene surface are changed from nonpolar to polar to mimic the interior of the GroEL/ES chaperonin that assists proteins to fold in vivo. We find that nonpolar confinement stabilizes the folded state of the protein due to the effects of volume reduction that destabilize the unfolded state and also due to interactions with the fullerene surface. For the Trp cage, polar confinement has a net destabilizing effect that results from the stabilizing confinement and the competitive exclusion effect that keeps the protein away from the surface hydration shell and stronger interactions between charged side chains in the protein and the polar surface that compete against the formation of an ion pair that stabilizes the protein folded state. We show that confinement effects due to volume reduction can be overcome by sequence-specific interactions of the protein side chains with the encapsulating surface. This study shows that there is a complex balance among many competing effects that determine the mechanism of GroEL chaperonin in enhancing the folding rate of polypeptide inside its cavity.     

Lone pair-pi and pi-pi interactions play an important role in proton-coupled electron transfer reactions

Proton-coupled electron transfer (PCET), a class of formal hydrogen atom transfer (HAT) reactions, is of widespread interest because it is implicated in a broad range of chemical and biochemical processes. PCET is typically differentiated from HAT by the fact that it occurs when a proton and electron are transferred between different sets of molecular orbitals. Previous theoretical work predicted that hydrogen bonding between reactants is a necessary but not sufficient condition for H exchanges to take place by PCET. This implies that HAT is the only mechanism for H exchange between two carbon atoms. In this work, we present computational results that show that the H exchange in the tert-butylperoxyl/phenol couple, a prototypical antioxidant exchange reaction, occurs by PCET and that the transfer of the electron can occur via an oxygen lone pair-ring pi overlap. We then show that the H exchange in a model for the tyrosyl/tyrosine couple, which is implicated in ribonucleotide reductase chemistry, occurs via PCET and that one path for the electron transfer is provided by a strong pi-stacking interaction. Finally, we show that a pi-stacking interaction in the benzyl/toluene couple, a system in which there is no H-bonding, can result in this exchange occurring via PCET to some extent. Collectively, these results indicate that PCET reactions are not unique to systems that can engage in H-bonding and that lone pair-pi and pi-pi interactions in these systems may be more important than previously understood.     

Systematic coarse-graining of potential energy landscapes and dynamics in liquids

Recent efforts have shown that the dynamic properties of a wide class of liquids can be mapped onto semi-universal scaling laws and constitutive relations that are motivated by thermodynamic analyses of much simpler models. In particular, it has been found that many systems exhibit dynamics whose behavior in state space closely follows that of soft-sphere particles interacting through an inverse power repulsion. In the present work, we show that a recently developed coarse-graining theory provides a natural way to understand how arbitrary liquids can be mapped onto effective soft-sphere models and hence how one might potentially be able to extract underlying dynamical scaling laws. The theory is based on the relative entropy, an information metric that quantifies how well a soft-sphere approximation to a liquid's multidimensional potential energy landscape performs. We show that optimization of the relative entropy not only enables one to extract effective soft-sphere potentials that suggest an inherent scaling of thermodynamic and dynamic properties in temperature-density space, but that also has rather interesting connections to excess entropy based theories of liquid dynamics. We apply the approach to a binary mixture of Lennard-Jones particles, and show that it gives effective soft-sphere scaling laws that well-describe the behavior of the diffusion constants. Our results suggest that the relative entropy formalism may be useful for "perturbative" type theories of dynamics, offering a general strategy for systematically connecting complex energy landscapes to simpler reference ones with better understood dynamic behavior.     

催化裂解CH4或CO制碳纳米管结构性能的谱学表征

利用TEM、HRTEM、XRD、XPS和TPO等方法对CH₄或CO催化分解生成的碳纳米管结构和性能进行了表征.结果表明,所得产物是管径15～20nm的均匀碳纳米管.其XRD谱图与石墨的相近,但特征衍射峰稍宽化,表明其长程有序度较石墨的低.由CH₄制备的碳纳米管系由多层具有类石墨片状结构的同心、等径及中空圆锥形面叠合而成,类石墨层面取向与管轴倾斜;而由CO制备的碳纳米管系由多层具有类石墨片状结构的圆柱形面围叠而成,类石墨层面取向与管轴平行.碳纳米管中C_1s的电子结合能比石墨的下降约0.5eV.TPO试验结果显示所制备的两种产物中无定形碳含量都很低,其整体结构石墨化程度较高;由CH₄制得的碳纳米管与O₂反应的起燃温度比由CO制得的约高100K.     

Tethered dimer inhibitors of NAD synthetase: parallel synthesis of an aryl-substituted SAR library

We previously reported that tethered dimers containing indoles on one end and a permanent positive charge on the other, using a 6-9 carbon polymethylene tether, provided NAD synthetase inhibitors with impressive antibacterial activities against Gram-positives. Here, we report that the phenyl ring is a good substitute for indole, and we utilize solution-phase parallel synthesis to explore structure-activity relationships for substituents on that ring. General conclusions are that nonpolar substituents are more effective than polar ones and that different positional isomers often have very different enzyme inhibition activities. This latter observation reveals that enzyme activity is sensitive to minor structural changes and suggests that nonspecific detergent actions are not important for the observed effects.     

A new turn structure for the formation of beta-hairpins in peptides

Previous studies by Gellman and co-workers have elegantly shown that mirror-image beta-turns based upon d-Pro-Gly are especially good at stabilizing beta-hairpins and have demonstrated that peptide 1 [Arg-Trp-Gln-Tyr-Val-d-Pro-Gly-Lys-Phe-Thr-Val-Gln-NH2] folds into a well-defined beta-hairpin [Espinosa, J. F.; Gellman, S. H. Angew. Chem., Int. Ed. 2000, 39, 2330-2333]. The present study establishes that the amino acid ornithine (Orn) also forms a turn structure that is excellent at stabilizing beta-hairpins when linked through the delta-amino group and that this turn is comparable to d-Pro-Gly in ability to induce beta-hairpin formation. Thus, 1H NMR chemical shift and NOE studies establish that Orn-containing analogue 2 [Arg-Trp-Gln-Tyr-Val-deltaOrn-Lys-Phe-Thr-Val-Gln-NH2] is comparable in structure to peptide 1. The present study also establishes that the Orn turn is superior to Asn-Gly turns and that replacement of the deltaOrn with epsilonLys or d-deltaOrn generates structures that do not fold significantly.     

不同取代基的噻碳菁和吲哚碳菁染料对其在溴化银微晶上吸附能力及形成J-聚集体尺寸分布的影响

本文研究了5-位不同取代基的噻碳菁和吲哚碳菁染料对其在立方型颗粒和T-颗粒溴化银微晶上吸附能力的影响,并采用ACFEM(Analytical Color Fluore scence Electron Microscopy)研究了上述结构染料对其吸附在溴化银微晶所形成的J-聚集体尺寸分布的影响。实验结果表明,对吲哚碳菁染料来说,立方体溴化银微晶表面的吸附能力较T-颗粒溴化银微晶表面的吸附能力强;但对噻碳菁染料来说则相反,它们在T-颗粒溴化银微晶表面的吸附能力较立方体溴化银微晶表面的吸附能力强。另外,对5-位不同取代基的噻碳菁染料而言,无论是在立方型颗粒或T-颗粒溴化银微晶上的吸附能力来说,含取代基(无论4-取代基是吸电子型还是推电子型)的噻碳菁染料较未取代的噻碳菁染料强;而5-位取代基是吸电子型的噻碳菁染料更有利于其吸附在T-颗粒溴化银微晶表面。此外,本文还进一步证明了溴化银微晶表面上染料J-聚集体的生长过程是符合奥斯瓦尔特成熟过程的。吲哚碳菁染料在T-颗粒溴化银微晶上形成的J-聚集体的平均尺寸明显大于在立方体溴化银微晶上形成的J-聚集体的平均尺寸。吸附在立方体溴化银微晶上的5-不同取代基的噻碳菁染料对其形成J-聚集体尺寸分布的影响的研究结果表明,含取代基(-CH₃,-Ph,-Cl)的噻碳菁染料形成的J-聚集体的尺寸分布几乎相同,但与未取代的噻碳菁染料形成的J-聚集体的尺寸分布明显不同;5-位含取代基的噻碳菁染料形成的J-聚集体平均尺寸大于未取代的噻碳菁染料的。     

五彩湾煤镜质组与惰质组在热解中的相互作用

以五彩湾煤镜质组、惰质组为研究对象,建立两种不同的体系,镜质组与惰质组无相互作用体系(A)和相互作用体系(B)。利用热重技术(TG)和傅里叶变换红外技术(FT-IR),将两体系的热解固体产物进行红外分析。结果表明,在300~450℃,体系B的脂肪氢含量高于体系A,表明镜质组与惰质组之间发生了烷基自由基转移反应,芳氢的含量也是体系B多于体系A,这说明镜质组与惰质组之间同时发生了芳构化作用,随温度升高,镜质组生成少量氢自由基与惰质组发生侧链取代反应;在500~700℃,体系B的脂肪氢含量和芳氢含量均低于体系A,表明此时镜质组与惰质组之间发生缩聚反应及缩合反应;750~800℃时,脂肪氢和芳香氢含量均为体系B大于体系A,说明体系B中,镜质组产生较多的氢自由基与惰质组大分子芳香结构发生氢化反应,同时与惰质组发生侧链取代反应;850~900℃时,镜质组与惰质组之间进一步发生多环芳香缩合反应。     

Peptide‐Guided Assembly of Repeat Protein Fragments

Herein, we present the peptide‐guided assembly of complementary fragments of designed armadillo repeat proteins (dArmRPs) to create proteins that bind peptides not only with high affinity but also with good selectivity. We recently demonstrated that complementary N‐ and C‐terminal fragments of dArmRPs form high‐affinity complexes that resemble the structure of the full‐length protein, and that these complexes bind their target peptides. We now demonstrate that dArmRPs can be split such that the fragments assemble only in the presence of a templating peptide, and that fragment mixtures enrich the combination with the highest affinity for this peptide. The enriched fragment combination discriminates single amino acid variations in the target peptide with high specificity. Our results suggest novel opportunities for the generation of new peptide binders by selection from dArmRP fragment mixtures.     

Mechanistic implications of the equality of compensation temperatures in chromatography

A common interpretation of the observation that two processes exhibit similar compensation temperatures in an enthalpy-entropy plot is that the two processes occur via the same "mechanism". We show that this interpretation is not rigorously allowed. In fact, the only thing that can be concluded from the observation of identical compensation temperatures is that the relative contributions of enthalpy and entropy to the overall free energy are the same in the two processes. Since it is possible that two processes occur via different mechanisms that, by chance, result in the same relative blends of enthalpy and entropy, the observation of identical compensation temperatures cannot be used as evidence for mechanistic identity. If two processes exhibit different compensation temperatures, however, it can logically be concluded that the two processes are mechanistically distinct.     

Mass spectrometric characteristics and kinetics of iron release in visceral mass of Saccostrea cucullata

Ferritins with electrophoretic homogeneity were prepared from the visceral mass of Saccostrea cucullata in batch. The native PAGE approach showed similar electrophoretic mobility among pig pancreatic ferritin, liver ferritin of Dasyatis akajei, and visceral mass ferritin of Saccostrea cucullata. SDS-PAGE indicated that the Saccostrea cucullata visceral ferritin (SCVF) consisted of a single subunit type and had a molecular weight (MW) of approximately 20 kDa, suggesting that the protein shell in SCVF was composed of a single subunit. In addition, peptide mass fingerprinting and transmission electron microscopy were used to identify SCVF further, and to observe its molecular structure. We found that the molecular structure in SCVF was similar to that of most mammalian ferritins, which are composed of a protein shell and an iron core. The results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry under the assistance of an acidic matrix, sinapic acid, also showed that SCVF was composed of a single subunit type and its subunit MW was calculated to be 19871.042 Da in the absence of heme. Kinetics analysis revealed that the complete process of iron release fitted the law of a first-order reaction, which is similar to that of most ferritins in mammals. Similar to bacterial ferritin, studies indicated that the shell consisted of a single subunit type and showed similar kinetics of iron release, suggesting that this subunit plays two important roles in iron release and storage, and that it shows different stability and intensity of interaction in carrying out its physiological functions in SCVF.     

Do commercially available metal salts mediate calixarene formation via hydrogen-bonded dimers?

In this article we report the first example of a Lewis acid promoted, one-pot, Br?nsted acid free, high-yielding synthesis of the calixarene macrocycle from the "monomer" p-tert-butylphenol. We report that when a commercially available metal salt (Lewis acid) is incorporated within the calixarene-forming reaction, a certain amount of control over the size of the calixarenes produced can be gained. Although a detailed mechanistic rationale on how the macrocycle is assembled is unclear, what is evident from this work is that the metal cation, the counteranion, and the oxidation state of the salt employed are all important contributors to the outcome of the reaction process. Indeed, evidence to date suggests that a subtle "symbiotic" relationship exists between the metal cation, its oxidation state, and the anion that allows the efficient transformation of the "monomeric" p-tert-butylphenol into linear oligomers and, ultimately, into macrocyclic calixarenes. Athough the metal salt mediated process described herein is efficient and high-yielding, what is also fundamentally important is that a comprehensive mechanistic understanding of how the calixarenes are assembled be accrued. Searching for possible indicators or clues, we propose that oligomeric methylene-linked phenolic entities are initially formed and that these, we tentatively suggest, generate metal and/or anion hydrogen-bonded supramolecular intermediates. It is possible that the preorganization of the linear polyphenolic oligomers allows the formation of hydrogen-bonded structures which, critically, result in the formation of supramolecular assemblies that are subsequently "stitched" together, generating the p-tert-butylcalix[n]arenes (n = 4-9) in excellent yields. Substantiating the possibility that hydrogen-bonded entities are generated (and that these subsequently afford metal-templated assemblies), we make reference to a seldom cited 1962 Nature publication that reported the propensity of polyphenolic linear oligomers to form "well-defined intramolecularly hydrogen-bonded conformations".     

The molecular underpinnings of a solute-pump/solvent-probe spectroscopy: the theory of polarizability response spectra and an application to preferential solvation

Recent ultrafast experiments on liquids have made clear that it is possible to go beyond light scattering techniques such as optical Kerr spectroscopy that look at the dynamics of a liquid as a whole. It is now possible to measure something far more conceptually manageable: how that liquid dynamics (and that light scattering) can be modified by electronically exciting a solute. Resonant-pump polarizability-response spectra (RP-PORS) in particular, seem to show that different solvents respond in noticeably distinct ways to such solute perturbations. This paper is a theoretical attempt at understanding the kinds of molecular information that can be revealed by experiments of this sort. After developing the general classical statistical mechanical linear response theory for these spectra, we show that the experimentally interesting limit of long solute-pump/solvent-probe delays corresponds to measuring the differences in 4-wave-mixing spectra between solutions with equilibrated ground- and excited-state solutes-meaning that the spectra are essentially probes of how changing liquid structure affects intermolecular liquid vibrations and librations. We examine the spectra in this limit for the special case of an atomic solute dissolved in an atomic-liquid mixture, a preferential solvation problem, and show that, as with the experimental spectra, different solvents can lead to spectra with different magnitudes and even different signs. Our molecular-level analysis of these results points out that solvents can also differ in how local a portion of the solvent dynamics is accessed by this spectroscopy.     

Techniques for the calculation of three-dimensional structural similarity using inter-atomic distances

Summary This paper reports a comparison of several methods for measuring the degree of similarity between pairs of 3-D chemical structures that are represented by inter-atomic distance matrices. The methods that have been tested use the distance information in very different ways and have very different computational requirements. Experiments with 10 small datasets, for which both structural and biological activity data are available, suggest that the most cost-effective technique is based on a mapping procedure that tries to match pairs of atoms, one from each of the molecules that are being compared, that have neighbouring atoms at approximately the same distances.     

AEG3482 is an antiapoptotic compound that inhibits Jun kinase activity and cell death through induced expression of heat shock protein 70

We describe a group of small-molecule inhibitors of Jun kinase (JNK)-dependent apoptosis. AEG3482, the parental compound, was identified in a screening effort designed to detect compounds that reduce apoptosis of neonatal sympathetic neurons after NGF withdrawal. We show that AEG3482 blocks apoptosis induced by the p75 neurotrophin receptor (p75NTR) or its cytosolic interactor, NRAGE, and demonstrate that AEG3482 blocks proapoptotic JNK activity. We show that AEG3482 induces production of heat shock protein 70 (HSP70), an endogenous inhibitor of JNK, and establish that HSP70 accumulation is required for the AEG3482-induced JNK blockade. We show that AEG3482 binds HSP90 and induces HSF1-dependent HSP70 mRNA expression and find that AEG3482 facilitates HSP70 production while retaining HSP90 chaperone activity. These studies establish that AEG3482 inhibits JNK activation and apoptosis by a mechanism involving induced expression of HSP proteins.     

Assembly of antibodies in lipid membranes for biosensor development

An investigation of the incorporation of antibody in lipid films of a composition that has been used for biosensor preparation is reported. IgG that is incorporated into lipid monolayers prepared from 7:3 mixtures of dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidic acid is edge-active, and enters and penetrates the fluid region of the mixed-phase system when monolayers are held at low pressure (< 20 mN/m). It was found that there is an “exclusion pressure” observed in pressure-area (π-A) curves that are collected for monolayers that contain antibody. This term refers to a specific threshold of lateral pressure (which is reached by monolayer compression) that can cause explusion of antibody from the interior of a membrane. Microscopic images of monolayers containing the fluorescent phospholipid nitrobenzoxadiazole dipalmitoyl phosphatidylethanolamine (NBD-PE), or antibody labeled with tetramethylrhodamine isothiocyanate (TRITC), were used to determine the structure of membranes, and the location of effects on structure caused by IgG. Ellipsometric measurements of lipid monolayers that were cast onto silicon wafers by the LangmuirBlodgett method were used to study the thickness of monolayers and to investigate the structural changes that occurred at the “exclusion pressure.” Both the use of fluorescent antigen and ellipsometry indicated that antibody binding activity was present and was dependent on compression pressure. The effects of pH and ionic strength of subphase, antibody concentration, incubation time, and lateral pressure have been examined. The results may indicate the conditions that can be used to improve the incorporation of active IgG for preparation of biosensors that are based on lipid membranes.     

REGULATION OF NITRATE REDUCTASE ACTIVITY IN RICE

The properties of NR from rice varieties Yuanfengzao and Jingyin 127 are the same in molecular weight of native enzyme and subunit, optimum pH, K_m value for substrates NO_3~- and NADH, stability in vitro and immunological characteristics. The decay rate in vitro of the activity of the partially purified NR from Yuanfengzao is 20％ lower than that from Jingyin 127. The results from antiserum titration and rocket immunoelectrophoresis indicated that the amount of NR in Yuanfengzao is about 1.5 times more than that in Jingyin 127. Further study on in vivo incorporation of ~3H-labeled amino acids into NR revealed that the rate of NR synthesis in Yuanfengzao is obviously higher than that in Jingyin 127. In vitro translation of mRNA showed that the products of NR-mRNA per unit of total mRNA of Yuanfengzao is much more than that of Jingyin 127. It is concluded that, therefore, NR activity in rice is regulated through NR synthesis and NR-inhibitory protein(s) system, the former is further controlled at the lev