Preparation of Polystyrenylphosphonous Acid of Low Polymerization Degree and Influence of Initiators upon the Free Radical Reaction Mechanism

Organophosphorus chemistry plays an important role in chemical engineering, pesticide, medicine and catalysis1,2. In recent years, after extensive research and widespread application, synthesis and preparation of new organophosphorus compounds have attracted increasing research interest. Polystyrene is a very important and versatile matrix or precursor of various kinds of functional polymer. Usually, introducing of phosphonic PO3H2 or phosphinic PO2H2 group into polystyrene matrix through…     

Preparation of Polystryenylphosphonous Acid of Low Polymerization Degree and Influence of Initiators upon the Free Radical Reaction Mechanism

The polystyrenylphosphonous acid (PSPA) of low polymerization degress was prepared with one step reaction. The reaction mechanism was changed with different initiators. For the reaction with AIBN or BPO as the initiator, therer are 2 or 3 serives of radical reaction chains and 5 or 9 series of polystyrenyl products. The main products are PSPA without or with the fragment of the initiator H[CH(C6H5)-CH2]n-PO2H2 and C6H5CO2-[CH2CH(C6H5)]n-PO2H2 respectively.     

Low Temperature Sol-Gel Preparation of β-Al2TiO5 Thin Films: Spectroscopic Analysis of the Precursors

Two sol-gel syntheses allowed the preparation of -Al₂TiO₅ thin films on silicon substrates at 700°C, reacting aluminum and titanium alkoxides with and without acetylacetone as a chelating agent. Nuclear magnetic resonance (NMR) and mass spectra of the sols allowed identification of the intermediate species formed and to show the formation of an Al-Ti containing polymer establishing that the synthesis without acetylacetone leads to the most extensive polymerization. The formation of -Al₂TiO₅ at low temperatures is attributed to diffusion-limited crystallization process, which takes place in the conditions of high homogeneity at molecular level reached in the sol-gel synthesis. The crystallization of the films was studied as a function of the firing time and temperature and confirmed that -Al₂TiO₅ with better thermal stability was obtained with the synthesis without chelating agent.     

Flow Injection Chemiluminescence Analysis of Low Level Concentration of Hydrazine

IntroductionHydrazine is often used as high-energy propellant in space shuttle program, and it is an important precursor in polymer industry, pesticides, and pharmaceuticals1,2. However, owing to its intensive mammalian toxicity, the monitoring of hydrazine residues in environment matrices has become a priority field in industrial laboratories. Siontorou et al.3,4 and Marrazza et al.5 recently designed a kind of DNA biosensor for monitoring pollutant including hydrazine. Some electrochemical…     

Low temperature heat capacity of the system “silica gel–calcium chloride–water”

Heat capacity was measured for two composite systems based on silica gel KSK and calcium chloride confined to its pores. One corresponds to an anhydrous state, while another contains water bound with the salt to give the composition of CaCl₂·2.04H₂O. The measurements were performed in the temperature range of 6–300 K with a vacuum adiabatic calorimeter. The smoothed experimental curves C _p (T) were used for calculating the calorimetric entropy and the enthalpy increment for both studied systems as well as the effective heat capacity associated only with water in the hydrated composite. The heat capacities C _p (298.15 K) of both composites were compared with those calculated as a linear addition of the heat capacities of silica gel and bulk calcium chloride (or its dihydrate) with appropriate weight coefficients.     

Study on the Interferation of the Concentration of Free Calcium in Peripheral Human Lymphocyte by Low Dose Penicillin, Using Fura-2 as Fluorescent Probe

Penicillin and other β-lactams antibiotics are used widely to treat infection in clinic to prevent bacterial contamination of tissue culture. Fura-2 method is one of the most accurate method for measurement of intracellular free Ca2 in active mammalian …     

Interaction Between the Low Molecular Mass Components of Blood Serum and the Vanadium(III)–2,2′-Bipyridine System

The complex species formed between vanadium(III)?C2,2??-bipyridine (Bipy) and the small blood serum bioligands lactic (HLac), oxalic (H₂Ox), citric (H₃Cit) and phosphoric (H₃PO₄) acids were studied in aqueous solution by means of electromotive forces measurements emf(H) at 25?°C and 3.0?mol?dm^?3 KCl as the ionic medium. The data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic products of vanadium(III) and the binary complexes formed. Formation of the complexes [V(Bipy)(Lac)]²⁺, [V(Bipy)(Lac)₂]⁺, [V(OH)₂(Bipy)(Lac)] and [V₂O(Bipy)₂(Lac)₂]^? were observed in the vanadium(III)?CBipy?CHLac system. Also, the species [V(Bipy)(HOx)]²⁺, [V(Bipy)(Ox)]⁺, [V(OH)(Bipy)(Ox)], [V(OH)₂(Bipy)(Ox)]^? and [V(OH)₃(Bipy)(Ox)]^2? were found in the vanadium(III)?CBipy?CH₂Ox system, the complexes [V(Bipy)(HCit)]⁺, [V(Bipy)(Cit)], [V(OH)(Bipy)(Cit)]^? and [V(OH)₂(Bipy)(Cit)]^2? were found in the vanadium(III)?CBipy?CH₃Cit system, and the species [V(Bipy)(H₂PO₄)]²⁺ and [V(Bipy)(HPO₄)]⁺ were detected in the vanadium(III)?CBipy?CH₃PO₄ system. The stability constants of these complexes were determined.     

Direct Electrochemical Oxidation of NADPH at a Low Potential on the Carbon Nanotube Modified Glassy Carbon Electrode

Introduction Because of its novel structural and electronic proper-ties, high chemical stability, and extremely high me-chanical strength and modulus,1 carbon nanotube (CNT), which has become a major subject of many experimen-tal and theoretical investigations, has a wide potential application from structural materials to nanoelectronic components2-12 since its initial discovery by Iijima13 in 1991 and the subsequent report about the synthesis of large quantities of CNT by Ebbesen and cowork…     

How Low Can You Go? Low Densities of Poly(ethylene glycol) Surfactants Attract Stealth Proteins

It is now well‐established that the surface chemistry and “stealth” surface functionalities such as poly(ethylene glycol) (PEG) chains of nanocarriers play an important role to decrease unspecific protein adsorption of opsonizing proteins, to increase the enrichment of specific stealth proteins, and to prolong the circulation times of the nanocarriers. At the same time, PEG chains are used to provide colloidal stability for the nanoparticles. However, it is not clear how the chain length and density influence the unspecific and specific protein adsorption keeping at the same time the stability of the nanoparticles in a biological environment. Therefore, this study aims at characterizing the protein adsorption patterns depending on PEG chain length and density to define limits for the amount of PEG needed for a stealth effect by selective protein adsorption as well as colloidal stability during cell experiments. PEG chains are introduced using the PEGylated Lutensol AT surfactants, which allow easy modification of the nanoparticle surface. These findings indicate that a specific enrichment of stealth proteins already occurs at low PEG concentrations; for the decrease of unspecific protein adsorption and finally the colloidal stability a full surface coverage is advised.     

Calorimetric Behaviour of Anhydrous β-Cyclodextrin at Very Low Temperature

Heat capacities of anhydrous -cyclodextrin were measured between 10 K to 300 K using an adiabatic low-temperature calorimeter. Two distinct types of thermal behaviour were observed in the temperature range 50–130 K, depending on the way the sample was cooled. In the absence of hydration water molecules, we assumed that the two types of thermal behaviour could be attributed to freezing in more or less ordered states of the hydroxyl groups engaged in the intramolecular interglucose flip-flop-type interactions.     

A Review on Complete Oxidation of Methane at Low Temperatures

This paper reviews recent developments in complete oxidation of methane at low temperatures over noble metal catalysts in the past 20 years. The Pd/A1203 catalyst system is fully discussed. The review mainly focuses on the kinetic aspects of methane oxidation over this catalyst, and methane activation behavior over Pd and PdO phases (the form of PdO on the surface, transient behavior, the nature of the active sites, the influence of metal particle size and their structure sensitivities, and so on). Some Pd catalysts supported on other oxides besides the Al2O3 support are briefly discussed. Possible routes of non-noble metal catalysts as substitutes for the Pd catalyst are also proposed.     

Effect of Low Energy Electron Exposure on Ion Scattering Spectroscopy

The effect of low energy electron (LEE) exposure on ISS, including on the sputter peak and scatter peak as well as on ion neutralization, has been investigated for different samples. Some new results are discussed.     

Characteristics of Analyte Ionization in Low Power Microwave Plasma Torch

The ionization characteristics of the analytes in a low power Ar microwave plasma torch (MPT) was studied. The influence of forward microwave power, the flow rate of carrier gas and matrix element on the degree of ionization were observed. The axial profiles of the degree of the ionization of some elements were determined. The experimental results are very important for developing the new analytical source——microwave plasma torch (MPT).     

Construction of the Skeleton of Phthalascidin, Mechanism of the Formation of the Key Tricyclic Lactam Intermediate

Phthalascidin is a structurally simplified version of Et-743, which is a potent anti-tumor marine natural product isolated from Ecteinascidia turbinata. Its antiproliferative activity is greater than that of the agents taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude. An elegant synthesis of Et-743 and phthalascidin has been reported by E. J. Corey and co-workers1,2. As part of our continuing program, we have also engaged in dev…     

Synthesis of two peptides of α-bungarotoxin and the participation of the amino acid residue Trp-28 of the neurotoxin in the antigenicity of the molecule

Using the method of solid-phase peptide synthesis, two peptides have been synthesized, one of which corresponds to the central ring structure of -bungarotoxin (-BTX), while the second has in position 28 a Gly residue in place of the Trp in the first peptide, and their interrelationship with antitoxin antibodies has been investigated. It has been shown that the amino acid residue Trp-28 of -BTX, which is the contact residue in binding with the acetylcholine receptor, also participates directly in binding with the active centers of antibodies to -BTX.Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 628–631, July–August, 1997.     

Studies of the dissociation and the protonation of TB-chlorosulphophenol

The dissociation constant of each step for TB-chlorosulphophenol has been determined by potentiometric method, and the thermodynamic constants, △G°, △H° and △S°, of the dissociation process have been calculated. The protonation constants were measured by the spectrophotometric method. The pH values of various forms of anions of the chromogenic reagent at their concentrations were also calculated.     

Low Density Ionic Liquid-Based Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction for the Preconcentration of Trace Aromatic Amines in Waters

Journal of Analytical Chemistry - Low density ionic liquid-based ultrasound-assisted dispersive liquid?liquid microextraction for the preconcentration of aromatic amines in river waters and...     

Preparation of ZnSe Nanoparticles via Low‐Temperature Solid Phase Process

ZnSe nanoparticles were prepared from ZnCl₂, Se and KBH₄ in the presence of cetyltrimethyl ammonium bromide (CTAB) through a room temperature solid phase process. The products were characterized with x‐ray diffraction (XRD), transmission electron microscope (TEM), and energy dispersive analysis of x‐ray (EDAX). The results show that the cubic zincblende phase ZnSe nanoparticles can be obtained using this simple method. The size of nanoparticles was evaluated to be from 8 to 30 nm.     

Reactions of β-Dioxo Compounds with Hydrogen Peroxide at Low Temperatures

The paper presents the results obtained for the malonic aldehyde—hydrogen peroxide and β-oxobutanal—hydrogen peroxide systems. The systems were studied by IR spectroscopy in xenon matrices. The potential energy surfaces and vibrational spectra of the molecules that could occur in these systems were calculated quantum-chemically. As distinct from similar systems with monoaldehydes and α-dioxo compounds, the first stage of the reactions that occurred in the systems under consideration involved the decomposition of hydrogen peroxide with the formation of atomic oxygen, whose secondary reactions determined the set of reaction products.