Contribution to the study of the mechanism of curing of unsaturated polyester resins

The mechanism of copolymerization of monomethyl and dimethyl maleates and fumarates with styrene was studied by analysis of the conformation of the acid units of the resulting copolymers. The absorption bands for C?O stretching and OH stretching in the spectra of the copolymers are fully identical. They are quite different from the spectra of the copolymers obtained from maleic anhydride and styrene that are subsequently treated with absolute methanol to give the monoester which is then esterified with diazomethane to give the diester. The acid units of the copolymers derived from maleic anhydride exist in a gauche configuration; copolymers derived from fumaric units exist in a trans conformation. The identity of copolymers derived from maleic units with those derived from fumaric units but not with those derived from maleic anhydride indicates that the first step in the copolymerization of the maleic units is an isomerization to fumaric units, which are actually the genuine comonomers.     

Applications of counter-current chromatography in organic synthesis purification of heterocyclic derivatives of lapachol

This work describes the application of counter-current chromatography (CCC) as a useful, fast and economic alternative for the isolation and purification of heterocyclic derivatives from lapachol and beta-lapachone, two naturally occurring compounds from Tabebuia species, and nor-beta-lapachone, a synthetic congener of lapachol. The discussed data comprise four examples of purification of synthetic reactions with different solvent systems - the mixture of the oxazole and the imidazole from beta-lapachone; the quinoxaline from nor-beta-lapachone; and the purification of the N-oxides from the quinoxaline and the phenazine from nor-beta-lapachone from their respective not fully reacted substrates by means of aqueous reversed- and normal-phase elution modes and non-aqueous solvent systems. Traditional purification of these reaction products by silica gel column chromatography demanded a large amount of solvent and time and, in some cases, serious degradation of the products occurred, leading to low yield of the reaction. High-speed counter-current chromatography (HSCCC) was used as an alternative to optimize the process and raise the yield of the reactions.     

ESR studies of aqueous suspensions of zinc oxide

Results are presented from a technique which allows reproducible ESR spectra to be obtained from circulating aqueous suspensions of various zinc oxides. Singlet ESR signals with g ≈ 1.96 were observed in the dark from In-ZnO and from several zinc oxides under UV illumination. Fast and slow components of the photoinduced ESR signal are attributed respectively to surface and bulk electrons produced initially from photogenerated electron—hole pairs.     

Calculation of cryoscopic data

The accuracies of determinations of purity and freezing point based upon cryometric freezes suffer from the scatter of data, from the failure of systems ever to recover from the effects of supercooling, and from complex phenomena that elevate temperature during the later parts of runs. Methods are here proposed for decreasing the errors caused by scatter of data and failure to recover from supercooling. These methods utilize the optical projection of calculated curves upon the actual data and involve a new interpretation of the nature of recovery from supercooling.     

Influence of the structure of the hydrophobe on the ideality of mixing in micelles in binary mixtures of amphiphilic tricyclic drugs

The composition of the micelles in binary mixtures of the cationic amphiphilic antidepressant drugs nortriptyline, amitriptyline, and doxepin has been determined from an analysis of the variation of the critical micelle concentration from conductivity measurements, as a function of solution composition. Assessment of the nonideality of mixing in terms of the interaction parameter from the regular solution approximation showed small deviations from ideal mixing, with negative interaction parameters for nortriptyline/amitriptyline systems and positive interaction parameters for mixtures of nortriptyline and doxepin. These differences in nonideality have been attributed to differences in the packing of the drugs in the mixed micelles arising from differences in the structure of the hydrophobe.     

Equation of state of aqueous NaCl solutions over a wide range of temperatures, pressures and concentrations

This work describes an equation of state for calculating the density of aqueous, liquid-phase NaCl solutions, based on an analytical equation for a mixture of hard-sphere ions and dipoles in the mean spherical approximation. The equation gives reasonable accuracy at temperatures from 273 to 973 K, pressures from 0.1 to 1000 MPa, concentrations from 0 to 50 wt.%, and densities higher than 650 kg m⁻³. The observed data of Hilbert (1979), Rogers and Pitzer (1982) and Urusova (1975) are fitted with only 10 empirically adjusted parameters plus the two water molecule parameters (diameter and dipole moment) which were determined from the density and dielectric properties of water. A comparison of the calculated and observed density data is presented. Errors in the calculated values vary from 0.5 to 1.5% over the whole range of temperature, pressure and concentration. A table of densities at temperatures from 273 to 973 K, pressures from 0.1 to 1000 MPa and concentrations from 0 to 50 wt.% is presented.     

Terpenoids of the needles of Picea abies

The composition of the terpenoids of the neutral petroleum-ether-soluble substances from an isopropanol extract of the needles of the Norway spruce has been studied. The main components of the extractive substances are polyprenol acetates, alcohols with the labdane type of structure, and epimanool and epitorulosol. It has been shown that the terpenoids from the needles differ in composition from the extractive substances of the trunk part of the tree and those from the oleoresins of the sprucesPicea abies, P. ajanensis, andP. obovata.S. M. Kirov Leningrad Academy of Wood Technology. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 168–176, March–April, 1986.     

Structural Analysis of the Condensation Products of Xylan with Organotin Halides

Physical characterization of the products resulting from condensation of xylan with organostannanes halides is consistent with a tin-modified product. Results from elemental analysis shows the presence of tin consistent with the presence of the tin moiety. Results from control reactions are consistent with the product containing portions derived from both reactants. The presence of the Sn–O–R ether linkage is found by infrared spectroscopy. The presence of portions derived from both reactants is indicated by mass and infrared spectral results.     

Preparation and unequivocal identification of the regioisomers of nitrocatechol monobenzyl ether

The four positional isomers of nitrocatechol monobenzyl ether were prepared as intermediates to nitrobenzodioxanes directly from 2-benzyloxyphenol or, through two-four steps, from catechol. These preparations addressed the issue of the certain identification of the nitration products prescinding from chemical correlation to the synthetic precursors because the positional isomers are very similar for some properties and analytical data available from the literature are largely incomplete and not conclusive. The here provided NMR, DSC, and acidity data unequivocally distinguish each nitrocatechol monobenzyl ether from its regioisomers.     

Evolution of emission manners of organic light-emitting diodes: From emission of singlet exciton to emission of doublet exciton

The emission manners of organic light-emitting diodes(OLEDs) have experienced almost three-decade evolution.In this review,we briefly summarized the emission manners of OLEDs including:(ⅰ) emission from singlet exciton;(ⅱ) emission from triplet exciton;(ⅲ) emission from singlet exciton converted from triplet exciton.Then we introduced a new type of OLEDs with the emission from doublet exciton,wherein organic neutral radicals are used as emitters.Due to the spin-allowed transition of doublet excitons,using neutral radicals as emitters is believed to be a new way to break the 25%upper limit of internal quantum efficiency of OLEDs.The progress of emissive stable neutral radicals is also shortly reviewed.     

Electric Conductivity of Sandwich Structures with Films of Poly-N-epoxypropylcarbazole Doped with Organic Dyes of Various Ionicity

The conducting characteristics of samples of a sandwich structure with films based on the photoconducting polymer poly-N-epoxypropylcarbazole doped with cationic, anionic, cationic–anionic, neutral, and bipolar organic dyes were investigated. It was shown that the conductivity of the samples is caused by ion drift, thermofield generation of holes from uncontrollable impurity centers, thermofield generation of electrons and holes from the dopant molecules, and thermofield injection of electrons and holes from the electric contacts. The contribution from the injection currents of the charge carriers increases in the transition from a cationic dye to anionic, cationic–anionic, and intraionic dyes.     

The chemistry of the surface of modified detonation nanodiamonds of different types

The influence of standard chemical treatment used to extract interstellar nanodiamonds from meteorites on the chemical composition of the surface of synthetic nanodiamonds with substantially different properties was studied by thermal desorption mass spectrometry and IR spectroscopy. The chemistry of the surface of nanodiamonds after treatment was substantially different from that of initial particles. The suggestion was made that the chemical structure of the surface of diamond particles in the interstellar space could be reconstructed from the data on meteorite diamonds. Mass spectrometric studies also gave information about possible mechanisms of the release of noble gases from meteorite diamonds at various temperatures.     

Headspace constituents of the tree remain of Cinnamomum camphora

The volatile ingredients isolated from a fresh tree of Cinnamomum camphora (camphor tree) and from a tree remain of C. camphora were collected by using headspace techniques and analyzed by means of gas chromatography/mass spectrometry (GC/MS). 99.77% of the constituents consisting 23 components from the fresh tree, 98.68% of the constituents consisting 24 components from the tree remain were identified. Of these ingredients, camphor was obtained as the most abundant component.     

Solution crystallization of nylon 6

Electron microscopy and x-ray diffraction data have been obtained on nylon 6 which has been crystallized from solutions in 1,6-hexanediol and 1,2,6-hexanetriol. Lamellar single crystals and spherulites of the γ form are obtained by crystallization from 1,2,6-hexanetriol. The morphology of the single crystals is different from that obtained from glycerine solutions. The spherulites of the γ form are composed of larger lamellae. Sheaflike crystals of the α form are obtained from both solvents. α-form and γ-form crystals both grow from 1,2,6-hexanetriol at appropriate crystallization temperatures. α-form crystals alone are obtained from 1,6-hexanediol solution at every crystallization temperature. The long periods measured by small-angle x-ray diffraction for the solution-grown crystals are in the range 56 to 66 Å. The melting behavior of the solution-grown crystals is examined and discussed. Effects of solvent on growth of the two crystalline forms from solution are investigated.     

Diagnostic value of different antigenic fractions of hydatid cyst fluid from camel and sheep in Kingdom of Saudi Arabia

Hydatid cyst fluids (HCF) crude extracts from camels and sheep slaughtered in Riyadh region, KSA were subjected to Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis (SDS–PAGE) and Western blot analysis. Sera from 17 confirmed human cases of hydatidosis, 25 patients with other parasitic infections and 10 clinically healthy subjects were used to evaluate the diagnostic value of the different antigenic fractions of these extracts. Immunoblotting results revealed that, at least 11 major discrete protein fractions (110–8 kDa) were recognized by sera from hydatidosis patients, sera from patients with other parasitic diseases showed cross-reactivity with few of these bands. The cluster of bands (38–35 kDa) that may be a breakdown of “Arc 5” antigen (39–38 kDa) was detected by 100% and 94% of sera from hydatidosis cases with HCF extracts from camel and sheep, respectively. This cluster showed also some cross reactivity (20% and 8%) with control sera from patients with other parasitic infections with camel and sheep HCF extracts, respectively. Polypeptides at 24–22, 16 and 8 kDa which may probably correspond to antigen B subunits were also identified by all samples from hydatidosis patients with sheep HCF extracts and by 100%, 65% and 74% with camel HCF extracts respectively. Sera from control subjects did not react with any of these polypeptides (24–22, 16 and 8 kDa). According to our results, the identified molecular weight bands (16 and 8 kDa using HCF crude extracts from sheep and 24–22 kDa using HCF crude extracts either from camel or sheep) represent good candidates for immunodiagnosis of hydatidosis.     

Experimental and modeling study of the oxidation of toluene

This paper describes an experimental and modeling study of the oxidation of toluene. The low‐temperature oxidation was studied in a continuous flow stirred tank reactor with carbon‐containing products analyzed by gas chromatography under the following experimental conditions: temperature from 873 to 923 K, 1 bar, fuel equivalence ratios from 0.45 to 0.91, concentrations of toluene from 1.4 to 1.7%, and residence times ranging from 2 to 13 s corresponding to toluene conversion from 5 to 85%. The ignition delays of toluene–oxygen–argon mixtures with fuel equivalence ratios from 0.5 to 3 were measured behind reflected shock waves for temperatures from 1305 to 1795 K and at a pressure of 8.7 ± 0.7 bar. A detailed kinetic mechanism has been proposed to reproduce our experimental results, as well as some literature data obtained in other shock tubes and in a plug flow reactor. The main reaction paths have been determined by sensitivity and flux analyses. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 25–49, 2005     

Neutron activation analysis of ivory of African elephants

Instrumental neutron activation analysis was applied to 80 samples from various African countries and 81 samples from the Kruger National Park in the Republic of South Africa. Twelve elements such as Br, Ca, Cl, Co, Cs, Fe, Mg, Mn, Na, Sc, Sr, and Zn, were determined in all samples. The factor scores of each sample were calculated from those elemental concentrations for the first and second factors to clarify the differences of samples from various African countries with those from Kruger Park. The results were compared with those by stable isotope analysis (¹³C and¹⁵N).     

Cation-exchange separation of metals in dimethyl sulphoxide-aqueous hydrochloric acid media

The behaviour of bismuth, cadmium, copper, lead, silver, tin and zinc on a cation-exchange resin in a solvent system consisting of dimethyl sulphoxide, hydrochloric acid and water was studied. The distribution coefficients of these metal ions between liquid and resin were determined as functions of the concentration of dimethyl sulphoxide and of hydrochloric acid. On the basis of the distribution coefficients found, predictions were made as to the possibilities of separating these metals from mixtures. Such separations were confirmed experimentally for bismuth from lead, bismuth from copper, zinc from lead, lead from cadmium, silver from copper, silver from lead, lead from cadmium from zinc, bismuth from lead from zinc, and bismuth from zinc from copper.     

Estimation of cellulose nanofibre aspect ratio from measurements of fibre suspension gel point

Cellulose nanofibre aspect ratio controls the properties of sheets made from nanofibres and processing conditions, but aspect ratio is very difficult to measure. In this paper, aspect ratio was estimated from the gel point of a cellulose nanofibre suspension, the solids concentration at which the transition from a dilute to a semi-dilute suspension occurs. Four batches of cellulose nanofibres were tested. Two were produced from softwood fibres using ball milling. Commercially produced microfibrillated cellulose material was also used, both in as supplied form and after removal of the larger fibres by filtering. The average diameter measured from SEM images of fibres ranged from 33 to 73 nm. One sample was too heavily treated and an average dimension could not be measured. The gel-point was measured both from the height of a layer of cellulose nanofibres sedimented from a dilute suspension or from the lowest solids concentration at which a yield stress could be measured using a vane rheometer. The two methods were closely in agreement for all samples. Aspect ratio was then calculated using either the effective medium (EMT) or crowding number (CN) theories. Aspect ratio calculated with an assumed fibre density of 1,500 kg/m³, using the CN theory ranged from 155 to 60. Use of the EMT theory reduced the calculated aspect ratio by between 11 and 23 %. Reducing the assumed density in suspension from 1,500 to 1,166 kg/m³ reduced the calculated aspect ratio by 12–14 %. The heavily treated sample had by far the lowest aspect ratio.     

尿液中纳米微晶的团聚促进泌尿系结石的形成

采用纳米粒度仪和透射电子显微镜(TEM)比较研究了尿石症患者与健康对照者尿液中纳米微晶的尺寸、粒度分布、聚集状态、自相关函数和ξ电位随放置时间的变化. 患者尿样放置3 h后, 其尿微晶平均粒径(D_a)由506 nm增至958 nm, 粒度分布范围变宽, 自相关时间由1.84 s延长到3.93 s, ξ电位由-1.34 mV降低至-3.89 mV; 而健康对照者尿微晶的D_a仅由330 nm增加至416 nm, 自相关时间由1.44 s延长至2.10 s, ξ电位由-8.35 mV降低至-8.90 mV. 此结果表明, 尿石症患者和健康对照者尿液中的纳米微晶不但在尺寸、粒度分布、聚集、自相关函数和ξ电位等方面存在明显的差异, 而且患者尿微晶的稳定性比对照者的差; 随着时间的延长, 患者尿液中的纳米微晶会逐渐团聚, 而对照者尿微晶的团聚要轻微得多. 从两类尿液中尿大分子和小分子抑制剂的浓度、尿微晶表面形成双电层的稳定性等方面进行了分析, 结果表明, 尿微晶的聚集是泌尿系结石生长的关键因素.