Moisture induced solid phase degradation of l-ascorbic acid part 2, separation and characterization of the major degradation products

The influence of moisture in the presence and absence of air on the solid state degradation of l-ascorbic acid has been investigated previously [1]. Reaction kinetics were studied using tristimulus colorimetry and a quantitative high performance liquid chromatographic assay for both total l-ascorbic acid and dehydroascorbic acid. The degradation gave rise to a discolouration of the samples, the most severely degraded samples were almost black in appearance although over 68% w/w of the l-ascorbic acid remained. The samples were analyzed for the presence of carbonyl compounds, furan related compounds, compounds responsible for the discolouration and evolution of carbon dioxide. No 2,4-dinitrophenylhydrazine (2,4-DNP) derivatives of carbonyl compounds or furan related compounds were detected by HPLC. An HPLC screening procedure was developed which was used to monitor for compounds responsible for the discolouration, at least eight unknown compounds were resolved and a relative response factor of 5.47 was assigned to them with respect to l-ascorbic acid at 280 nm. One mole of carbon dioxide was evolved per mole of l-ascorbic acid. This paper describes the investigation into the identity of the degradation products.     

Stereoselective synthesis of the hydroxy amino acid moiety of Al-77-B,a gastroprotective substance from Bacillus pumilus Al-77

The hydroxy amino acid moiety of Al-77-B (1) has been prepared as its protected form 2 from the (R)-glyceric acid derivative 3 in an efficiently stereoselective manner through the direct C-acylation using diphenyl phosphorazidate and the hydroxy-directed hydrogenation.     

Preparation and thermal degradation of methyl methacrylate-methacrylic acid copolymers

Copolymers of methyl methacrylate with methacrylic acid, with the mole fraction of methacrylic acid units from 0.21 to 0.73, were prepared by radical copolymerization in the bulk. The influence of the composition of the copolymers on the features of their thermal degradation was examined by combined thermal analysis involving differential scanning calorimetry and thermogravimetry.     

Studies on alkaline protease produced by Bacillus sp. NG312

An alkalophilic hyperproducer of alkaline protease, Bacillus sp. NG312, was isolated, and the enzyme showed maximum activity at pH 11.0 and 60°C. The temperature optimum was increased by 10°C in presence of Ca²⁺. The crudeenzyme was found to have half-life of 11 d at 37°C and maximum stability at pH 9.0–10.0. It also exhibited very good stability in presence of detergent components and some locally available commericial detergent powders.     

Synthesis of multivalent Streptococcus suis adhesion inhibitors by enzymatic cleavage of polygalacturonic acid and 'click' conjugation

A galabiose disaccharide building block was synthesized by an efficient pectinase cleavage of polygalacturonic acid and subsequent chemical functional group transformations. Besides the disaccharide, the corresponding trisaccharide was also obtained and modified. The compounds were subsequently conjugated to dendrimers with up to eight end groups using 'click' chemistry. The compounds were evaluated as inhibitors of adhesion of the pathogen Streptococcus suis in a hemagglutination assay and strong inhibition was observed for the tetra- and octavalent galabiose compound with MIC values in the low nanomolar range. The corresponding octavalent trisaccharide was a ca. 20-fold weaker inhibitor.     

Quantitative determination of saturated oligogalacturonic acids in enzymatic digests of polygalacturonic acid,pectin and carrot pomace by on-line LC-ESI-MS

A method for the quantitative determination of oligogalacturonic acids (OGAs) by on-line high-performance liquid chromatographic (HPLC) separation and mass spectrometric detection via an electrospray interface (ESI-MS) without additional desalting steps was developed. Saturated OGAs up to a degree of polymerization (dp) of 3 were quantified by comparison with reference compounds. The calibration plots showed high linearity (R²>0.99), and the detection limits for dp 1, 2, and 3 were 11, 28, and 6 ng per injection, respectively. Non- and partially methyl-esterified OGAs with a dp of 3 and 4 were calculated semi-quantitatively as dp 3. The analytical system was used for the quantification of OGAs of digests obtained by incubation of polygalacturonic acid, pectin, and carrot pomace with commercial enzyme preparations. Furthermore, methyl-esterified OGAs up to a dp of 12 containing up to 4 methyl esters were detected in a pectin digest.     

Preparation and degradation of salts of poly(methacrylic acid). I. Lithium,sodium, potassium,and caesium salts

The polymers of lithium, sodium, potassium, and caesium salts of methacrylic acid have been prepared by free radical polymerization of the respective monomers in methanol solution. The degradation behavior of the polymers has been investigated by thermal volatilization analysis, thermogravimetry, and product analysis. These materials are stable to about 350°C under programmed heating at 10°C/min in vacuo. The principal degradation products are monomer, the corresponding isobutyrate, carbonate, oxide, carbon dioxide, and a fraction of liquid volatiles that is complex and contains a variety of aldehydes and ketones. The mechanism of degradation is discussed in detail.     

Isolation and purification of lithocholic acid metabolites produced by the intestinal microflora.

Lithocholic acid metabolites produced by the intestinal microflora of rats can be isolated from other endogenous lipids using Sephadex LH-20 column chromatography. Analyses of individual metabolites collected from the column by silica gel coated glass fiber paper chromatography result in the resolution of epimeric 3-hydroxy derivatives. In addition, glass fiber paper chromatography is more sensitive and requires less development time than conventional glass-coated thin-layer plates. Further confirmation of the identity of metabolites is achieved by gas-liquid chromatography, which separates both methyl and ethyl esters of lithocholic and isolithocholic acids.     

Qualitative and quantitative analysis of the light hydrocarbons produced by radiation degradation of N,N-diethylhydroxylamine

This paper reports on the qualitative and quantitative analyses of light hydrocarbons produced by radiation degradation of N,N-diethylhydroxylamine. The results show that when the absorbed doses are between 10 and 1000 kGy, the main light hydrocarbons are methane, ethane, ethene, propane and n-butane. Their volume fractions are increased with the increase of the dose. The volume fraction of ethene is also increased at low doses with the increase of the dose, but it is decreased with the increase of dose at high doses. This revised version was published online in July 2006 with corrections to the Cover Date.     

酸性离子液体降解纤维素制备5-羟甲基糠醛的研究

以离子液体氯化1-烯丙基-3-甲基咪唑鎓([Amim]Cl)为溶剂,以咪唑类酸功能离子液体[Cnmim]HSO4(n=2,4,6,8)和Cr Cl3·6H2O为复合催化剂,在微波辅助加热条件下降解纤维素制备5-羟甲基糠醛(5-HMF),考察了催化剂加入量、反应温度、催化剂种类、反应时间、加水量等反应条件对纤维素降解反应的影响。结果表明,当[C2mim]HSO4的加入量为0.02g、微晶纤维素(MCC)和Cr Cl3·6H2O的摩尔比为10∶1、反应温度为160℃、反应时间为30min、加水量为50μL时,微晶纤维素转化率为100%,总还原糖收率为87.2%,5-HMF产率最高可达到50%。     

Narrow molecular weight distribution poly(styrenesulfonic acid). Part I. Preparation,solution properties,and phase separation

A method is described for the conversion of polystyrene to poly(styrenesulfonic acid) without change in the molecular weight distribution; the reaction is performed at room temperature in 100% H₂SO₄ and uses Ag⁺ catalyst. The resulting polyelectrolyte has solubility and other characteristics significantly different from those of previously investigated poly(vinylsulfonic acid). This permits a study of the influence of the aromatic group on the local and long range interactions in solution. The barium salt of poly(styrenesulfonic acid) is unusual in showing both upper and lower consolute temperatures in solution.     

Study on hydrogen and carbon monoxide produced by radiation degradation of N,N-dimethylhydroxylamine

This paper reports the study of hydrogen and carbon monoxide produced by radiation degradation of N, N-dimethylhydroxylamine (DMHA). The results show that when the concentration of DMHA is between 0.1M–0.5M and the dose is between 10–1000 kGy, the volume fraction of hydrogen is very high and increases with the dose. The volume fraction of hydrogen is little dependent on the concentration of DMHA at lower dose but increases with increasing concentration of DMHA at higher dose. The volume fraction of carbon monoxide is very low.     

59Ni and 63Ni separation from boric acid concentrates produced at NPP

Procedure for direct separation of radionickel from boric acid concentrate was developed. Quantitative separation from 100 mL of real concentrate on the column filled with 3 mL of PAN-DMG composite material was achieved. PAN-DMG material (dimethylglyoxime in porous beads of polyacrylonitrile) was compared with Ni Resin and DMG-PAN material exhibited higher sorption capacity for nickel than Ni Resin.     

Gas chromatographic separation of PCB and OCP by photocatalytic degradation

A photocatalytic degradation method was developed for polychlorobiphenyl (PCB) and organochloride pesticide (OCP) discrimination and quantification. A mixture of Aroclor 1260 and p,p′-DDT was irradiated at 254 nm by UV lamp (40 W) in the presence of TiO₂ (30 mg mL⁻¹ non-aqueous solution). Comparison of gas chromatograms showed that p,p′-DDT signals decreased significantly after irradiation, while Aroclor 1260s chromatograms did not show any difference before and after irradiation. Detection limits were 0.30 mg L⁻¹ and 0.15 mg L⁻¹ for p,p′-DDT and Aroclor 1260, respectively. The method was applied to spiked egg samples, the recoveries were found as 72% for DDT and 82.01% for Aroclor 1260.     

The thermal degradation of polyoxymethylene produced by solid-state polymerization

The thermal degradation of polyoxymethylene produced by the solid-state polymerization of trioxane crystals has been studied. Changes in small-angle and wide-angle x-ray patterns, weight loss, and density have been measured in specimens heated in air at 175°C, 185°C, and 195°C. The polyoxymethylene contained material in two different crystallographic orientations, which behaved differently. Material in the so-called “twin” orientation melted preferentially at 185°C and 195°C, and at 185°C resolidified on cooling in parallel to the main orientation, in a lamellar structure. At 195°C, randomly oriented material was produced on resolidification. At 175°C, there was no evidence of melting or the formation of a lamellar structure, but the twin material was preferentially degraded so that only material in the main orientation remained after a time of 1500 min. The more rapid loss by degradation of the twin material was attributed to its having a lower molecular weight than the material in the main orientation.