Synthesis of a “memory tripeptide” (Arg—Glu—Arg,RER) and the Kabachnik—Fields reaction with di- and tripeptides as a method for the synthesis of phosphorus-containing peptide analogs

Methods for the synthesis of potential “twin-drugs” containing fragments of the glutamate receptor antagonist and cognitive function enhancing oligopeptides were developed. The “memory tripeptide” Arg—Glu—Arg (RER) containing the tripeptide sequence of a protein APP_328–330, a gB-amyloid precursor, was synthesized. A method for the synthesis of gA-aminophosphonates with oligopeptides as the amine component of the one-pot three-component Kabachnik—Fields reaction was developed. A method for the synthesis of phosphonopeptides by the introduction of gA-aminophosphonates into the peptide chain was proposed.     

A novel strategy for oligopeptide synthesis using a polymer-supported ammonium fluoride

A novel method for the preparation of oligopeptides with a PS-ammonium fluoride in the solution phase is reported. The synthesis of lipid II pentapeptide is efficiently synthesized via a PS-ammonium fluoride without chromatographic purifications. The method reported here is very convenient to synthesize a relatively large amount of oligopeptides with abundantly available Fmoc-protected amino acids in a time efficient manner.     

Some Cyclic Oligopeptide with S2n Symmetry

Some cyclic oligopeptides formed by an equal number of alternating D- and L-amino-acid residues have been synthesized by using the hydrochloride of the open-chain peptide acid as precursor and the mixed-anhydride condensation method. The cyclic oligopeptides (tetra-, hexa-, and octavaline, hexaleucine, and hexaphenylalanine) form very stable H-bonded structures (IR-amide band at 3270–3290 cm^?1) which are insoluble in common organic solvents. In CF₃COOH/CDCI₃ (25°), they yield ¹H-NMR spectra snowing the expected equivalency of the various amino-acid residues.     

Preparation of nanocrystalline CuAlO<Subscript>2</Subscript> through sol–gel route

Nanocrystalline powders of CuAlO₂ were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used a new set of precursor materials for the synthesis of CuAlO₂ through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration. The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase pure CuAlO₂ were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best possible combinations for obtaining phase pure CuAlO₂ at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO₂.     

Novel Synthesis of CeO2 Nanoparticles Within Formamide/Tri(ethyleneglycol)monododecyl Ether/n-Octane Nonaqueous Microemulsion Systems

The present study evaluates a new method to prepare Cerium oxide (CeO₂) nanoparticles by formamide/tri(ethyleneglycol)monododecyl ether (C₁₂E₃)/n-octane oil-continuous nonaqueous microemulsion. The effect of the polar phase (formamide/water) on the phase behavior, drop size, and conductivity behavior of the reverse microemulsion were investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase and morphology of synthesized CeO₂ nanoparticles. It was found that the CeO₂ powders synthesized within nonaqueous microemulsions and aqueous microemulisons had an average particle size of 30–50 nm and 15–40 nm, respectively. The experimental results indicate the formation mechanism of CeO₂ nanoparticles in formamide nonaqueous microemulsion and aqueous microemulsion is similar, and the formamide nonaqueous microemulsion can be used as nanoreactors for preparation of nanoparticles.     

A sol–gel combustion synthesis method for TiO<Subscript>2</Subscript> powders with enhanced photocatalytic activity

TiO₂ photocatalytic powders were synthesized by a sol–gel combustion synthesis method in which urea was used as the fuel and titanyl nitrate was used as the oxidizer. Various fuel-to-oxidizer ratios were studied for their effects on the combustion phenomena and the properties of the synthesized TiO₂. The fuel-to-oxidizer ratio was found to determine the maximum combustion temperature, which in turn affects the specific surface area, crystallite size, and weight fraction of anatase phase of the synthesized TiO₂. The synthesized TiO₂ all contain carbonaceous species and are either pure anatase or anatase–rutile mixed phase in crystalline structure. The photocatalytic activity of the TiO₂ was found to correlate to a certain degree with the specific surface area, crystallite size, weight fraction of anatase phase, and visible and IR absorbances. The mixed phase TiO₂ shows a higher photocatalytic activity than the pure anatase phase TiO₂ when containing a small fraction (<~25 wt%) of rutile phase but a lower phoyocatalytic activity when containing a large fraction (>~25 wt%) of rutile phase. The synthesized TiO₂ all show higher photocatalytic activity than Degussa P25 TiO₂. The enhanced photocatalytic activity was attributed mainly to sensitization by the carbonaceous species and larger amounts of hydroxyl group adsorbed on the TiO₂ surface.     

Selection of New Sequence‐Selective Unnatural Peptides Binding to Double‐Stranded Deoxyribonucleic Acids (dsDNA) by Means of a Gel‐Retardation Experiment for Library Analysis

Previously, we developed a methodology for the solid‐phase screening of peptide libraries for interaction with double‐stranded deoxyribonucleic acids (dsDNA). In the search for new and more‐potent DNA ligands, we investigated the strategy of solution‐phase screening of chemical libraries consisting of unnatural oligopeptides. After synthesis of the selected amino acid building blocks, libraries were constructed with the general structure Ac‐Arg‐Ual‐Sar‐X¹‐X²‐X³‐Arg‐NH₂, where X represents each of twelve unnatural or natural amino acids. Optimization of the sequence of binding peptides was performed with an iterative deconvolution procedure. Selection of interacting peptides was carried out in solution by means of gel‐retardation experiments, starting with libraries of 144 compounds. A 14‐base‐pair double‐stranded DNA fragment was chosen as the target. After several cycles of synthesis and screening of libraries and individual peptides, an oligopeptide was selected with an apparent dissociation constant of 9⋅10⁻⁵ M , as determined by gel‐retardation experiments. This peptide was studied by NMR spectroscopy. A certain degree of conformational pre‐organization of the peptides was shown by temperature‐dependent circular‐dichroism experiments. Finally, DNase‐I‐footprinting studies indicated a preferential interaction with a 6‐base‐pair mixed sequence 5′‐CTGCAT‐3′. This study demonstrates that gel‐shift experiments can be used for the solution‐phase screening of library mixtures of peptides against dsDNA. In general, this technique allows the selection of new sequence‐selective dsDNA‐interacting molecules. Furthermore, novel dsDNA‐binding unnatural oligopeptides were developed with affinities in the 0.1 mM range.     

Palladium(II)‐Catalyzed Site‐Selective C(sp3)−H Alkynylation of Oligopeptides: A Linchpin Approach for Oligopeptide–Drug Conjugation

The palladium(II)‐catalyzed C(sp³)−H alkynylation of oligopeptides was developed with tetrabutylammonium acetate as a key additive. Through molecular design, the acetylene motif served as a linchpin to introduce a broad range of carbonyl‐containing pharmacophores onto oligopeptides, thus providing a chemical tool for the synthesis and modification of novel oligopeptide–pharmacophore conjugates by C−H functionalization. Dipeptide conjugates with coprostanol and estradiol were synthesized by this method for potential application in targeted drug delivery to tumor cells with overexpressed nuclear hormone receptors.     

Novel immonium type peptide coupling reagent: 5‐(1H‐benzotriazol‐1‐yloxy)‐3,4‐dihydro‐1‐methyl 2H‐pyrrolium hexachloroantimonate (BDMP® )

A novel immonium type coupling reagent, 5‐(1H‐benzotriazol‐1‐yloxy)‐3,4‐dihydro‐1‐methyl 2H‐pyrrolium hexachloroantimonate (BDMP) has been designed, synthesized and utilized to synthesize oligopeptides and biologically active peptide both in solution and solid phase with satisfactory yield, low racemization and fast reaction rate. The estimation of racemization and the influence of several reaction parameters were studied by HPLC method using the model reaction: Z‐Gly‐Phe‐OH + Val‐OMe·HCl·Z‐Gly‐D/L‐Phe‐Val‐OMe. It was shown that the reactivity of BDMP was much higher and the racemization was much lower than those of HOBt‐based ‘onium’ reagents, even though its analogues BOMI. To further verified me effectiveness of BDMP, Leu‐enkephalin was synthesized both in solution and solid phase using BDMP as coupling reagent. The proposed mechanism was also speculated.     

Synthesis of non-porous poly(glycidylmethacrylate-co-ethylenedimethacrylate) beads and their application in separation of biopolymers

The monodisperse, 5.0 μm non-porous poly(glycidylmethacrylate-co-ethylenedimethacrylate) (P_GMA/EDMA) beads were prepared by a single-step swelling and polymerization method. The seed particles prepared by dispersion polymerization exhibited good absorption of the monomer phase. Based on this media, a weak cation exchange (WCX) stationary phase for high performance liquid chromatography (HPLC) was synthesized by a new chemical modification method. The prepared resin has advantages of biopolymer separation, high column efficiency, low column backpressure, high protein mass recovery and good resolution for proteins. The measured bioactivity recovery for lysozyme was 97 ± 5%. The dynamic protein loading capacity of the synthesized WCX packings was 20.5 mg/g. Four proteins were completely separated in 3.0 min using the synthesized WCX stationary phase. The experimental results show that the obtained WCX resin has very weak hydrophobicity. The WCX resin was also used for the rapid separation and purification of lysozyme from egg white in 3.0 min with only one step. The purity and specific bioactivity of the purified lysozyme was found more than 95% and 70.264 IU/mg, respectively.     

Characterization of brookite and a new corundum-like titania phase synthesized under hydrothermal conditions

Brookite rich samples were synthesized under hydrothermal conditions by using TiCl₃ as precursor. They also contained a new titanium oxide phase that has the same crystalline structure as Ti₂O₃, and is stable after annealing in air. Samples were characterized with X-ray powder diffraction, transmission electron microscopy and thermogravimetry. Crystalline phases were refined by using the Rietveld method, from which phase concentrations and atomic bond lengths were obtained as a function of sample annealing temperature. Samples contained brookite, anatase, rutile and the new corundum-like phase: Brookite's concentration was larger than 50 wt%, while the one of the corundum-like phase reached 20(6) wt%. The local symmetry and the atomic bond lengths of these two phases depended on the crystallite size; for both, there is a correlation between the evolution of the atomic bond lengths with temperature and their transformation into another phase. The hydrothermal conditions stabilized brookite, anatase, and the corundum-like phase at high temperature: This last phase was stable in air, even at 900°C.     

Synthesis of peptides related to immunoglobulin E (IgE) and the examination of their pharmacological activity

Five kinds of oligopeptides H-Asp-Ser-Asp-OH (1), H-Asp-Gly-Lys-OH (2), H-Ser-Asp-Gly-Lys-OH (3), H-Asp-Ser-Asp-Gly-Lys-OH (4), and H-Ala-Asp-Ser-Asp-Gly-Lys-OH (5) related to immunoglobulin E (IgE) were synthesized by the conventional solution method with the objective of obtaining a new type of antiallergic agent. Their pharmacological activity was examined by measuring the inhibition of the production of IgE and relaxation of the smooth muscle contraction of rabbit aorta. H-Ala-Asp-Ser-Asp-Gly-Lys-OH (5) displayed potent inhibition against the production of IgE antibody (69.6%) and relaxation against the contraction of rabbit aorta.     

Reactions of difluorosilylene with cyclic alkenes: Cyclopentadiene and cycloheptatriene

The reactions of difluorosilylene with cyclopentadiene and cycloheptatriene were studied both in the gas phase and by the cocondensation method. Several new organosilicon compounds were synthesized and their structures characterized. In the cycloheptatriene reaction the comparison between the results from the gas phase and cocondensation experiments provides the first solid evidence which makes it possible to differentiate between the silirane mechanism and the ·SiF₂SiF₂· diradical mechanism in the “addition reactions” of difluorosilylene.     

Synthesis,magnetic properties and X-ray analysis of Zn0.97X0.03O nanoparticles (X = Mn,Ni, and Co) using Scherrer and size–strain plot methods

Un-doped and doped ZnO nanoparticles (Zn_0.97X_0.03O-NPs, X = Mn, Co, and Ni) were synthesized from a metal acetate precursor and acetic acid by a modified sol–gel combustion method. The compounds were synthesized at calcination temperatures of 650 °C for 1 h. The synthesized un-doped/doped ZnO-NPs were characterized by X-ray diffraction analysis (XRD) and high-magnification transmission electron microscopy (TEM). The XRD results revealed that the sample product was crystalline with a hexagonal wurtzite phase. The TEM showed ZnO-NPs nearly spherical shapes and a non-uniform shape for doped ZnO-NPs. The crystalline development in the ZnO-NPs was investigated by X-ray peak broadening. The size–strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the un-doped and doped ZnO-NPs. Physical parameters such as strain, stress and energy density values were calculated more precisely for all reflection peaks of XRD corresponding to the wurtzite hexagonal phase of ZnO lying in the range of 20–80° from the SSP results. The vibrating sample magnetometer (VSM) was also used to study the magnetic behavior of the samples in the ceramic form. The obtained results showed that strain play an important role in peak broadening; moreover, the mean crystalline size of the un-doped and doped ZnO-NPs estimated from the TEM and the SSP method were highly inter-correlated.     

Au/γ-MnO2催化剂催化无溶剂条件下甲苯氧化反应

采用氧化还原法制备了α, δ, γ-MnO₂载体, 采用原位还原法制备了Au负载量为0.5%-3.0%的Au/γ-MnO₂催化剂, 并采用X射线衍射、扫描电镜、透射电镜和N₂物理吸附等手段对其进行了表征. 透射电镜照片表明Au/γ-MnO₂催化剂中Au颗粒的大小约为10 nm. 采用无溶剂存在下的甲苯氧化反应测试所制备样品的催化活性. 结果表明, 甲苯转化率随着Au负载量的增加而增大. 这是由于Au颗粒数量增多, 尺寸减小的缘故. 同时, 负载Au颗粒对苯甲醛具有较高的选择性. Au/γ-MnO₂催化剂具有良好的重复使用性.     

Sequence dependence of secondary-structure formation part IV Helix-forming potential of amphiphilic oligopeptides containing aib residues

The conformational properties of Aib-containing oligopeptides having the propensity to adopt amphiphilic helical conformations were investigated by CD spectroscopy in solution. The peptides CF₃COOH.H-Pro-Glu-[Ala-Aib-Glu-Aib-]₄Gly-OH ( I ), HCl.H-Pro-Ala-Aib-[Gul-Ala-Ala-Aib-]₂Glu-Ala-Aib-Gly-PEGM ( II ), and CF₃COOH.H-Ala-Aib-[Glu-Glu-Ala-Aib-]₃PEGM ( III ) were synthesized according to the general principles of the liquid-phase method for peptide synthesis. Peptides I-III exhibit helical conformations in CF₃CH₂OH, MeOH, and in H₂O at acidic pH; however, at pH 7, only II forms a stable helix, whereas I and III are predominantly in an unordered conformation. Some general features for the construction of amphiphilic helices are discussed in the light of the experimental data.     

Bisphosphine‐Functionalized Cyclic Decapeptides Based on the Natural Product Gramicidin S: A Potential Scaffold for Transition‐Metal Coordination

The natural product Gramicidin S is a promising scaffold for novel oligopeptide‐based bisphosphine ligands, combining the advantageous rigid chiral backbone with the close proximity of phosphine substituents. The required unnatural, phosphine‐containing, amino acid building blocks were synthesized by means of a novel protocol that involves the enantioselective alkylation of a chiral nickel Schiff base template. Three Ni complexes were prepared with different alkyl chains between the phosphine group and the α‐carbon atom of the incorporated glycine; the absolute stereochemistry of two of them was determined by single‐crystal X‐ray structure analysis. By detaching the template, enantiopure L ‐phosphine amino acids resulted enabling the solid‐phase, stepwise construction of a linear sequence of the phosphine‐modified oligopeptides. On cyclization three bisphosphine‐substituted Gramicidin S analogues resulted, differing only in the size and shape of the linkage between the phosphine groups and the oligopeptides backbone. Their crystal structures suggest these species to have potential as chelating ligands.     

Silica-based ionic liquid coating for 96-blade system for extraction of aminoacids from complex matrixes

1-Vinyl-3-octadecylimidazolium bromide ionic liquid [C₁₈VIm]Br was prepared and used for the modification of mercaptopropyl-functionalized silica (Si-MPS) through surface radical chain-transfer addition. The synthesized octadecylimidazolium-modified silica (SiImC₁₈) was characterized by thermogravimetric analysis (TGA), infrared spectroscopy (IR), ¹³C NMR and ²⁹Si NMR spectroscopy and used as an extraction phase for the automated 96-blade solid phase microextraction (SPME) system with thin-film geometry using polyacrylonitrile (PAN) glue. The new proposed extraction phase was applied for extraction of aminoacids from grape pulp, and LC–MS–MS method was developed for separation of model compounds. Extraction efficiency, reusability, linearity, limit of detection, limit of quantitation and matrix effect were evaluated. The whole process of sample preparation for the proposed method requires 270 min for 96 samples simultaneously (60 min preconditioning, 90 min extraction, 60 min desorption and 60 min for carryover step) using 96-blade SPME system.     

Nonlinear Migration Dynamics of Excess Electrons along Linear Oligopeptides Controlled by an Applied Electric Field

Migration of an excess electron along linear oligopeptides governed by the external electric field (E_ex) which is against the inner dipole electric field is theoretically investigated, including the effects of E_ex on the structural and electronic properties of electron migration. Two structural properties including electron-binding ability and the dipole moment of linear oligopeptides are sensitive to the E_ex values and can be largely modulated by E_ex due to the competition of E_ex and the inner electric field and electron transfer caused by E_ex. In the case of low E_ex values, two structural properties decrease slightly_, while for high E_ex values, the electron-binding ability continually increases strongly, with dipole moments firstly increasing significantly and then increasing more slowly at higher E_ex. Additionally, linear oligopeptides of different chain lengths influence the modulation extent of E_ex and the longer the chain length is, the more sensitive modulation of E_ex is. In addition, electronic properties represented by electron spin densities and singly occupied molecular orbital distributions vary with E_ex intensities, leading to an unusual electron migration behavior. As E_ex increases, an excess electron transfers from the N-terminus to the C-terminus and jumps over a neighboring dipole unit of two termini to other units, respectively, instead of transferring by means of a one-by-one dipole unit hopping mechanism. These findings not only promote a deeper understanding of the connection between E_ex and structural and electronic properties of electron transfer behavior in peptides, but also provide a new insight into the modulation of electron migration along the oligopeptides.     

Effect of the composition of (Mo,Nb, V,Ti)/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> surface oxide structures on the oxidative dehydrogenation of ethane to ethylene

Molecular layering method was used to synthesize on the surface of γ-Al₂O₃ vanadium-titanium oxide structures of varied composition and structure from the gas phase and niobium- and molybdenum-containing additives from the liquid phase. The resulting composites and the starting aluminum oxide were studied by X-ray diffraction analysis and chemical-analytical and adsorption methods. The catalytic properties of the synthesized products were examined in the oxidative dehydrogenation of ethane. It was shown that the activity of the samples is affected not only by the composition and structure of surface structures, but also by the relative amounts of components in mechanical mixing of vanadium-titanium oxide and niobium oxide supported systems.