Protein secondary structure and stability determined by combining exoproteolysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In the post-genomic era, several projects focused on the massive experimental resolution of the three-dimensional structures of all the proteins of different organisms have been initiated. Simultaneously, significant progress has been made in the ab initio prediction of protein three-dimensional structure. One of the keys to the success of such a prediction is the use of local information (i.e. secondary structure). Here we describe a new limited proteolysis methodology, based on the use of unspecific exoproteases coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), to map quickly secondary structure elements of a protein from both ends, the N- and C-termini. We show that the proteolytic patterns (mass spectra series) obtained can be interpreted in the light of the conformation and local stability of the analyzed proteins, a direct correlation being observed between the predicted and the experimentally derived protein secondary structure. Further, this methodology can be easily applied to check rapidly the folding state of a protein and characterize mutational effects on protein conformation and stability. Moreover, given global stability information, this methodology allows one to locate the protein regions of increased or decreased conformational stability. All of this can be done with a small fraction of the amount of protein required by most of the other methods for conformational analysis. Thus limited exoproteolysis, together with MALDI-TOF MS, can be a useful tool to achieve quickly the elucidation of protein structure and stability.     

热处理对聚乙烯／炭黑导电复合体系形态结构及PTC特性的影响

借助ＷＡＸＤ、ＳＡＸＤ和ＤＳＣ等手段研究了炭黑与聚乙烯复合体系在不同热处理条件下的结晶行为及聚集态结构的大尺寸效应对ＰＴＣ特性的影响。由此提出，不仅结晶度大小，而且聚集大尺寸效应性能对ＰＴＣ行性有重要影响的新观点。     

Fraktionierte Kristallisation von Ammonium- und Magnesiumdoppelnitraten der Ceriterden; Bestimmung der Trennfaktoren und Vergleich der Trennwirkung

Summary The Separation Factors for Pr/La, Nd/Pr, and Sm/Nd, characterizing the crystallization of ammonium and magnesium double nitrates under practical conditions, were determined analytically and are discussed. They confirm that La and Pr can be separated better by fractional crystallization of ammonium double nitrates, whereas in the presence of Sm the magnesium double nitrates are preferable.

     

Volume and heat capacity of model non-aqueous self-assembly systems

Blends of immiscible polymers are often stabilized by block copolymers which can form non-aqueous micelles and microemulsions in the liquid polymers. The phase diagrans, apparent volumes and apparent heat capacities of model non-aqueous binary and ternary systems were studied in order to investigate the conditions under which such self-assembly systems could form. 1,2-Hexanediol, which can cosolubilize hexane and ethyleneglycol, forms inverse micelles in hexane and weak microaggregates in ethyleneglycol. Genapol X-060, a commercial alcoholic surfactant containing on the average an aliphatic chain of 13 carbons and 6 oxyethylenes (C₁₃E₆), forms microaggregates in poly(ethyleneglycol) 400. These self-assembly systems are strengthen in the presence of a third component which has an affinity for the inner phase.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Synthesis and Characterization of Lead Sulfide Nanoparticles in Zirconia-Silica-Urethane Thin Films Prepared by the Sol-Gel Process

PbS nanocrystals (NCs) ranging between 4–8 nm were incorporated into Zirconium-Silica-Urethane (ZSUR) matrix obtained by the sol-gel method. The sizes of the particles were controlled by temperature treatment and by concentration of PbS in ZSUR matrix. The sizes of PbS NCs were determined by TEM measurements. The quantum size effect could also be extracted from optical absorption and photoluminescence spectra. The new matrix allows incorporation of up to 40% PbS forming a characteristic structure of dendrite by reacting lead acetate with ammonium thiocyanate in sol-gel matrix. The sol precursors of the matrix for Zirconium-Silica-Urethane contained zirconium oxide (ZrO₂) matrix solution, tetramethoxysilane (TMOS), 3-glycid oxypropyl trimethoxysilane (GLYMO) and polyethylene urethane silane (PEUS) synthesized separately. The ZrO₂ matrix solution was obtained from zirconium n-tetrapropoxide in propanol and acetic acid was used as a chelating agent to stabilize the zirconium oxide precursor.     

流动注射光度法同时测定铜基合金中的铝和铁

提出了同时测定铜基合金中铝和铁的流动注射分析法。以０．０４ｍｏｌ／ＬＨＣｌ作载液，铬天青Ｓ为显色剂，通过测定６２８ｎｍ处铝、铁两配合物的吸光度之和及铝配合物的吸光度，实现了两组分的同时测定。在优化的实验条件下，检测限：Ａｌ和Ｆｅ分别为１．６９×１０－３和１．７３×１０－３ｍｇ／Ｌ，Ａｌ浓度在０～０．８ｍｇ／Ｌ；Ｆｅ浓度在０～１．０ｍｇ／Ｌ时服从比耳定律。进样频率为６０样／ｈ，所拟方法用于实际样品分析，获得满意结果。     

Spectroscopic and biological studies on newly synthesized nickel(II) complexes of semicarbazones and thiosemicarbazones

Nickel(II) complexes, having the general composition Ni(L)2X2, have been synthesized [where L: isopropyl methyl ketone semicarbazone (LLA), isopropyl methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone thiosemicarbazone (LLD) and X=Cl-, 1/2SO(4)2-]. All the Ni(II) complexes reported here have been characterized by elemental analyses, magnetic moments, IR, electronic and mass spectral studies. All the complexes were found to have magnetic moments corresponding to two unpaired electrons. The possible geometries of the complexes were assigned on the basis of electronic and infrared spectral studies. Newly synthesized ligand and its nickel(II) complexes have been screened against different bacterial and fungal growth.     

Comparison of the retention behaviour of phenol derivatives on porous graphitized and octadecylsilica columns

Summary The retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH₂PO₄ mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.     

“鱼”乐圈大揭秘

This article introduces the relationship between chemistry and fish farming, fish selling, and fish food. The nitrogen cycle process in fish ponds is introduced to explain the fish farming. "Yufuling" is used as the entry point to fish selling to connect food safety with chemistry. Fishy smell is explained from a chemical perspective for fish food. This paper aims at making a scientific explanation of life phenomena, deepening the consciousness of chemical life, helping people establish a correct view of chemical science, and inspiring youth to learn to use the knowledge that they have learned to explain life phenomena. This paper also tries to show the youth that life cannot be separated from chemistry, and chemistry cannot be separated from life.     

Insights on the origin of the structural phase transition in BaV10O15 from electronic structure calculations and the effect of Ti-doping on its structure and electrical transport properties

Band structure calculations at the level of LMTO-ASA provide insight into the electronic structure of BaV₁₀O₁₅ and the origin of the structural phase transition. A crystal orbital Hamiltonian population/integrated crystal orbital Hamiltonian population analysis provides evidence that the crystallographic phase transition is driven by V-V bond formation. As well, the energy bands near the Fermi level are very narrow, <1 eV, consistent with the fact that the observed insulating behavior can be due to electron localization via either Mott-Hubbard correlation and/or Anderson disorder. The partial solid solution, BaV_10−xTi_xO₁₅, was examined to study the effect of Ti-doping at the V sites on the structure and electronic transport properties. In spite of the non-existence of “BaTi₁₀O₁₅”, the limiting x=8, as indicated by a monotonic increase in the cell volume and systematic changes in properties. This limit may be due to the difficulty of stabilizing Ti²⁺ in this structure. For x=0.5 both the first order structural phase transition and the magnetic transition at 40 K are quenched. The samples obey the Curie-Weiss law to x=3 with nearly spin only effective moments along with θ values which range from −1090 K (x=0.5) to −1629 K (x=3). For x>3 a very large, ∼2×10⁻³ emu/mol, temperature independent (TIP) contribution dominates. Conductivity measurements on sintered, polycrystalline samples show semiconducting behavior for all compositions. Activation energies for Mott hopping derived from high temperature data range from ∼0.1 eV for x=0-1 and fall to a plateau of 0.06 eV for x=3-7. Low temperature data for x=3, 5 and 7 show evidence for Mott variable range hoping (VRH) with a T^1/4 law and in one case between 5 and 17 K, a Efros-Shklovskii correlated hopping, T^1/2 law, was seen, in sharp contrast to BaV₁₀O₁₅ where only the E-S law was observed up to 75 K. Seebeck coefficients are small (<35 μV/K), positive, roughly TIP and increase with increasing x up to x=5. This may point to a Heikes hopping of holes but a simple single carrier model is impossible. The compositions for x>3 are remarkable in that local moment behavior is lost, yet a metallic state is not reached. The failure of this system to be driven metallic even at such high doping levels is not fully understood but it seems clear that disorder induced carrier localization plays a major role.