The volume and compressibility change for the formation of transition metal sulfate ion pairs at 25°C

The apparent molal volume and adiabatic compressibilities of some transition metal (Mn²⁺, Co²⁺ Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) sulfates have been determined at 25°C. Values of to 11.4 cm³-mole^–1 and to 31.3 × 10^–4cm³-mole^–1-bar^–1 at 1 atm were found for the formation of the transition metal sulfate ion pairs. These results are in good agreement with the values obtained from the high-pressure conductance measurements of Fisher et al., Shimizu et al., and Taniguchi et al. The volume and compressibility data indicate that 3.1±0.7 water molecules are lost when transition metals form ion pairs with SO ₄ ^2– . The fractions of inner-sphere ion pairs (20%) estimated in this study are in good agreement with the values obtained from ultrasonic measurements.     

聚丙烯腈的加压水解

定型纤维状或无定型的聚丙烯腈在高温压力下均可用水水解,且产物中含有酰胺、酰亚胺、羧酸铵盐,经减压干燥后,铵盐部分分解成羧酸,最后的平均相对组成为:羧酸∶铵盐∶酰胺∶酰亚胺≈13∶36∶18∶33。 在我们的反应条件下,聚丙烯腈产生严重的断链现象,分子量大为降低,特别是未经喷丝成型的浆块更严重。 用阳离子交换树脂交换之后再进行分析的方法,一方面避免了滴定两种不同羧基(游离羧基、铵盐的羧基)之间的干扰,同时亦避免了通常方法测定铵盐时酰胺的干扰,因而数据更为可靠。     

Intramolecular [2 + 2]-photocycloaddition/thermal fragmentation approach toward 5-8-5 ring systems

[reaction: see text]. An intramolecular [2 + 2]-photocycloaddition is used to provide a photoadduct, which upon fragmentation, lactone cleavage, and subsequent Cope rearrangement provides a dicyclopenta[a,d]cyclooctene ring system with substituents in place (e.g., C3 and C11) to access several 5-8-5 diterpene and sesterterpene natural products.     

Determination of mercury in human urine by neutron activation analysis,with lead diethyldithiocarbamate as a preconcentration agent

Lead diethyldithiocarbamate is an effective reagent for preconcentration of mercury in urine for neutron activation analysis. Sodium and bromine are removed from the sample by this procedure. As lead diethyldithiocarbamate is insensitive to neutron activation, radiochemical separation is not needed after neutron irradiation. Results from the analysis of urine collected from workers in caustic soda manufacturing plants are discussed.     

Spectrophotometric determination of zinc in copper-base alloys with TAN

TAN reacts with zinc(II) forming a red complex with composition 1:2 Zn(II)-TAN and absorption maximum at 582 nm. Zinc can be determined with this reagent in the presence of Triton X-100, in the pH range 6.20-8.00 with a molar absorptivity of 4.5×10⁴ l/mol/cm Beer's Law was obeyed up to least 1.55 g/ml. Copper interference was eliminated with a mixture of thiosulfate and ascorbic acid and nickel separated by precipitation with dimethylglyoxime. The proposed method was used for zinc determination in several copper-base alloys and the results of analysis in comparison with certified values indicated that the procedure was accurate and precise. A derivative procedure is also proposed, allowing zinc determination with high sensitivity (5-400 ng/ml).     

Imino acids and collagen triple helix stability: characterization of collagen-like polypeptides containing Hyp-Hyp-Gly sequence repeats

The analysis of factors contributing to the stability of proteins is a subject of intense debate. Particularly challenging is the study of structural proteins, since their function is their structure. Among these is collagen, the key structural component of bones, skin, cartilage, tendons, and other connecting tissues. It is well established that the collagen triple helix is characterized by the presence of hydroxyproline, whose content modulates triple helix thermal stability according to the requirement of the host organism. Because of the complexity and the fibrous nature of collagen, data on the stability and structure of this protein have been mainly obtained by the use of collagen-like polypeptides. On the basis of CD characterization of collagen-like polypeptides we here show that the presence of Hyp at the X position of repeating triplets Hyp-Hyp-Gly stabilizes the triple helix significantly. This extra-stabilization has been ascribed, by using molecular modeling, to the formation of a hydrogen bond between Hyp residues belonging to the X and the Y positions of adjacent chains. This communication also provides a comprehensive interpretation of the ensemble of available data on polypeptides containing proline derivatives.     

Cellulose microfibrils from banana farming residues: isolation and characterization

Cellulose microfibrils have been prepared from banana rachis using a combination of chemical and mechanical treatments. The morphology and structure of the samples were characterized using transmission electron microscopy, atomic force microscopy, and X-ray diffraction. Fourier-transformed infrared spectroscopy (FTIR) was used to characterize the chemical modifications of the samples after each treatment. Suspensions of bundled or individualized 5-nm-wide microfibrils were obtained after homogenization (PH) whereas an organosolv (PO) treatment resulted in shorter aggregates of parallel cellulose microcrystallites. The sharper rings in the X-ray diffraction pattern of the PO-treated sample suggest a higher crystallinity due to a more efficient removal of hemicelluloses and dissolution of amorphous zones by the acid treatment. Both microfibrils and microcrystals prepared by both methods can be used as reinforcing filler in nanocomposite materials.     

Gas chromatographic study of the urinary codeine-to-morphine ratios in controlled codeine consumption and in mass screening for opiate drugs

The urinary codeine-to-morphine ratios in fifteen volunteers administered codeine tablets at intervals were studied by gas chromatography (GC) and compared with one month's GC results for enzyme multiplied immunoassay technique (EMIT)-screened urine specimens in a mass-screening programme for abuse of opiate drugs, particularly heroin. It appears that when M less than 2 and C/M greater than 0 or when M greater than 2 and C/M greater than 0.5, where C and M are codeine and morphine concentrations in micrograms per 10 ml of urine, codeine consumption has to be presumed.