Iterative lineshape fitting of MAS NMR spectra: a tool to investigate homonuclear J coupling in isolated spin pairs

Possibilities and limitations of iterative lineshape fitting procedures of MAS NMR spectra of isolated homonuclear spin pairs, aiming at determination of magnitudes and orientations of the various interaction tensors, are explored. Requirements regarding experimental MAS NMR spectra as well as simulation and fitting procedures are discussed. Our examples chosen are the isolated 31P spin pairs in solid Na4P2O7. 10H2O, (1), and Cd(NO3)2. 2PPh3, (2). In both cases the two 31P chemical shielding tensors in the molecular unit are related by C2 symmetry, and determination of the orientations of these two tensors in the molecular frame is possible. In addition, aspects of homonuclear J coupling will be addressed. For 1, both magnitude and sign of 2Jiso(31P, 31P) (Jiso = -19.5 +/- 2.5 Hz) are obtained; for 2, (Jiso = +139 +/- 3 Hz) anisotropy of J with an orientation of the J-coupling tensor collinear, or nearly collinear, with the dipolar coupling tensor can be excluded, while absence or presence of anisotropy of J with any other relative orientation of the J-coupling tensor cannot be determined.     

Different NMR approaches to the chiral analysis of trisubstituted allenes devoid of polar functional groups and aromatic hydrocarbons

The use of permethylated beta-cyclodextrin as chiral solvating agent for NMR spectroscopy allowed us to determine the enantiomeric purity of chiral aromatic hydrocarbons as well as the enantiomeric purity and absolute configuration of chiral trisubstituted allenes devoid of polar functional groups. The enantiomeric excesses of the trisubstituted allenes have been also determined by 195Pt NMR spectroscopy of the diastereoisomeric trans-dichloro[(S)-alpha-phenylethyl-amine](allene)Pt(II) complexes.     

Effect of cytarabine on the NMR structure of a model okazaki fragment from the SV40 genome

Okazaki fragments occur as intermediates during lagging strand DNA replication. Alterations in Okazaki fragment structure may contribute to the anticancer activities of nucleoside analogues such as cytarabine, a potent anti-leukemic agent that inhibits lagging strand replication. We have determined the solution structures for two model Okazaki fragments, [OKA] and [ARAC]. These sequences are derived from a frequent initiation site for primase during replication of the SV-40 viral genome. The sequence of [ARAC] differs from [OKA] only by substitution of cytarabine for one deoxycytidine. The structure of each model Okazaki fragment was elucidated using NMR spectroscopy and restrained molecular dynamics simulations. The solution structures of [OKA] and [ARAC] each consist of two distinct domains: a DNA duplex region (DDR) and an RNA-DNA hybrid duplex region (HDR). The DDR of [OKA] adopts geometry similar to B-form except for variations in helical parameters, especially twist and roll, which occur in the purine tract, increasing base overlap among the five consecutive purines. The helical axes for the DDR and HDR of [OKA] are bent 22 degrees relative to one another. Although the local structures for the DDR and HDR of [ARAC] are similar to those in [OKA] (root-mean-square deviation (rmsd) approximately 0.8, 1.7 A), the bending at the junction is different (41 degrees for [ARAC] vs 22 degrees for [OKA]). Increased helical bending of cytarabine-substituted Okazaki fragments may contribute to the propensity of cytarabine to inhibit elongation of the lagging strand during DNA replication, and in effecting anticancer activity.     

熔融钒渣直接氧化提钒方法节能减排初步分析

为了分析熔融钒渣直接氧化提钒方法在节能减排方面的效果,计算对比了该方法与现行钒渣焙烧提钒工艺能耗,结果显示熔融钒渣直接氧化提钒方法比现行钒渣焙烧提钒工艺节能2.09×106kJ/t（钒渣）,相当于减排CO2 178.00kg/t（钒渣）。该方法可为钒渣提钒工业的节能减排作出巨大的贡献。     

A thermodynamic model for the extraction of lithium from chloride brines containing aluminium and magnesium

The equilibrium constants for the extraction of lithium chloride, magnesium chloride and aluminium chloride by 1-hexanol and isopentyl alcohol were determined. For the joint distribution of the three salts between aqueous and organic solutions, a computer calculation based on a thermodynamic multicomponent electrolyte solution approach was applied. The coextraction of water was also taken into account. Predictions for the selective extraction of lithium were tested against experimental data, and reasonable agreement was found at low concentrations. The discrepancies observed at high chloride concentrations were ascribed to ion-pairing in the organic phase and to water co-extraction, possibly also to cation—cation interactions on the organicphase.     

Hormonal and gestational parameters in female rats submitted to the pilocarpine model of epilepsy

Endocrine and reproductive alterations are frequently reported to occur in women with temporal lobe epilepsy as well as in female rats in different experimental models of limbic seizures. As previously reported, women with epilepsy have lower fertility rates than women without epilepsy (Tanganelli, P., Regesta, G., 1992. Neurology (suppl.) 42 (5), 89-93; Cummings, L.N., Guidice, L., Morrel, M.J., 1995. Epilepsia 36, 355-359). In order to investigate the possible substrate of endocrine alterations in epilepsy, hormonal and gestational parameters were studied in female rats submitted to the pilocarpine model of epilepsy. The results demonstrated that the oestrus cycle is altered following pilocarpine-induced status epilepticus and such alteration lasted for several weeks. Progesterone, LH and FSH levels decreased and estradiol levels increased significantly during the period of spontaneous and recurrent seizures. The frequency of seizures during pregnancy and lactation decreased. These results document that significant changes in gonadal, hypophyseal and hypothalamic hormones, as well as in sexual behaviour, occur following status epilepticus induced by pilocarpine administration.     

Use of a mathematical model to establish normal serum parameters characterizing the function of the fetoplacental complex

Based on the author, data on the content of alpha-fetoprotein, trophoblastic beta-1-glycoprotein, and nonconjugated estriol in the blood serum of 278 somatically healthy women in various periods of normal gestation, the author proposes an approach to the definition of normal range of values. Using mathematical simulation methods, the values of normal concentrations of the fetoplacental complex products were calculated for every week of gestation, this permitting a different representation of laboratory findings and a dynamic follow-up of the course of gestation.     

Hormonal regulation of sex differentiated parameters in liver nodules from rats treated in the resistant hepatocyte model

Sex differentiation of liver functions has been shown to be attenuated in preneoplastic rat liver nodules. The present study was performed to investigate whether nodules from male rats are to some extent withdrawn from the normal growth hormone (GH) regulation of these functions. Male and female Wistar rats were treated according to a modified resistant hepatocyte model (RH-model), with diethylnitrosamine initiation and promotion with intragastric administration of 2-acetylaminofluorene (2-AAF) combined with partial hepatectomy (PH). Eleven months post-initiation male rats were treated with either human (hGH) or bovine growth hormone (bGH) or ovine prolactin (oPRL) by continuous infusion for 1 week. The mRNA expression of a number of genes known to be sex differentiated in liver from adult control rats was compared in nodular and surrounding tissue from nodule-bearing male, female and hormone-treated male rats. The basal mRNA expression of the female-predominant cytochrome P4502C12 (CYP2C12) was increased and the male-predominant CYP2C11 was decreased in liver nodules from male rats compared with the surrounding liver. Expression of the prolactin receptor (PRL-r; female > male) and the steroid 5 alpha-reductase (female > male) genes was decreased in male nodules, whereas no difference was observed with respect to GH-receptor (GH-r; female > male) expression in nodules versus surrounding tissue. Early nodules obtained from males treated according to the original RH-model (dietary 2-AAF, 0.02%) and isolated 2 weeks after completion of the 2-AAF/PH treatment showed significantly lower GH-r mRNA levels than the total liver tissue. In hepatocellular carcinomas from hormonally unmanipulated males 11 months post-initiation the decrease in PRL-r expression was even more pronounced than in the nodules and a significant decrease in GH-r expression was seen. In female nodules the only significant difference with respect to the sex differentiated parameters was a lower 5 alpha-reductase expression than in the surrounding tissue. Continuous infusion of both hGH and bGH feminized the expression of all the sex differentiated genes in male tissues and eliminated the previously detected differences between nodules and surrounding tissue. oPRL also eliminated the differences between nodules and surrounding tissue in males and partly feminized the expression of both the 5 alpha-reductase and the PRL-r genes.(ABSTRACT TRUNCATED AT 400 WORDS)     

A modified couchy distribution model for the extraction of copper by hydroxyoximes from very dilute acidic sulphate solutions

A modified Couchy distribution was used to model the influence of the equilibrium pH of the aqueous phase upon the extraction of copper by means of hydroxyoximes. Statistical analysis of the derived models and the approximation errors are given. The values of pH_0.5 calculated by means of the derived models are in agreement with those obtained by the use of the graphical method.The position and the structure of the alkyl group in the hydroxyoximes does not significantly influence the extraction of copper. 2-Hydroxy-5-alkylbenzaldehyde oximes can extract copper from more acidic solutions than 1-(2′-hydroxy-5′-alkylphenyl)-alkan-1-one oximes and alkyl derivatives of 2-hydroxybenzophenone oximes.