Les propriétés topologiques des flots riemanniens retrouvées à l'aide du théorème des variétés presque plates

Sans résumé     

Isotopic thermal diffusion factors of the noble gases

A new set of isotopic thermal diffusion factors for Ar, Kr and Xe is reported. The data have been obtained from thermal diffusion column measurements in a column previously calibrated with Ne gas, and complete the α_T data for the binary mixtures of noble gases given previously. The results lead to the conclusion that the thermal diffusion properties of the noble gases and their mixtures are well described by the law of corresponding states first proposed by Kestin, Ro and Wakeham. It is also concluded that the calibration technique used makes the thermal diffusion column a valuable instrument for the determination of the thermal diffusion factors of isotopic and non-isotopic dilute gas mixtures.     

ICP-AES法测定内蒙古地区六种沙生木本植物中金属元素

采用ICP-AES法分别对内蒙古地区梭梭、小叶锦鸡儿、沙冬青、红柳、沙枣和沙柳等六种沙生木本植物中金属元素进行了测定和分析。该方法的加标回收率为94.98％～120.25％,RSD＜3.4％,具有良好的准确度和精密度。结果表明,常量元素Ca,K,Mg,Na,Al及植物生命活动所必需的微量元素Fe,Mn,Cu,Zn在六种沙生木本植物中表现为不同的含量顺序,且Fe,Mn,Cu,Zn四种元素的含量均低于陆生高等植物的平均含量。该测定结果为改善西部地区生态环境,选择优良防风固沙树种提供可靠的数据和理论依据。     

1H and 13C NMR spectral assignment of N,N′‐disubstituted thiourea and urea derivatives active against nitric oxide synthase

The ¹H and ¹³C NMR resonances of seventeen N‐alkyl and aryl‐N′‐[3‐hydroxy‐3‐(2‐nitro‐5‐substitutedphenyl)propyl]‐thioureas and ureas ( 1–17 ), and seventeen N‐alkyl or aryl‐N′‐[3‐(2‐amino‐5‐substitutedphenyl)‐3‐hydroxypropyl]‐thioureas and ureas ( 18–34 ), designed as NOS inhibitors, were assigned completely using the concerted application of one‐ and two‐dimensional experiments (DEPT, HSQC and HMBC). NOESY studies confirm the preferred conformation of these compounds. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterization of 4,5‐Dihydro‐1H‐Pyrazole Derivatives by 13C NMR Spectroscopy

The ¹³ C NMR resonances of 19 1‐acyl‐3‐(2‐nitro‐5‐substitutedphenyl)‐4,5‐dihydro‐1H‐pyrazoles, and 19 1‐acyl‐3‐(2‐amino‐5‐substituted)‐4,5‐dihydro‐1H‐pyrazoles, were completely assigned using the concerted application of one‐ and two‐dimensional NMR experiments (DEPT, gs‐HSQC and gs‐HMBC). Copyright © 2012 John Wiley & Sons, Ltd.     

Ionic liquids based microwave-assisted extraction of lichen compounds with quantitative spectrophotodensitometry analysis

Ionic liquids based extraction method has been applied to the effective extraction of norstictic acid, a common depsidone isolated from Pertusaria pseudocorallina, a crustose lichen. Five 1-alkyl-3-methylimidazolium ionic liquids (ILs) differing in composition of alkyl chain and anion were investigated for extraction efficiency. The extraction amount of norstictic acid was determined after recovery on HPTLC with a spectrophotodensitometer. The proposed approaches (IL-MAE and IL-heat extraction (IL-HE)) have been evaluated in comparison with usual solvents such as tetrahydrofuran in heat-reflux extraction and microwave-assisted extraction (MAE). The results indicated that both the characteristics of the alkyl chain and anion influenced the extraction of polyphenolic compounds. The sulfate-based ILs [C(1)mim][MSO(4)] and [C(2)mim][ESO(4)] presented the best extraction efficiency of norstictic acid. The reduction of the extraction times between HE and MAE (2 h-5 min) and a non-negligible ratio of norstictic acid in total extract (28%) supports the suitability of the proposed method. This approach was successfully applied to obtain additional compounds from other crustose lichens (Pertusaria amara and Ochrolechia parella).     

13C2]-Acetaldehyde promotes unequivocal formation of 1,N2-propano-2'-deoxyguanosine in human cells

Acetaldehyde is an environmentally widespread genotoxic aldehyde present in tobacco smoke, vehicle exhaust and several food products. Endogenously, acetaldehyde is produced by the metabolic oxidation of ethanol by hepatic NAD-dependent alcohol dehydrogenase and during threonine catabolism. The formation of DNA adducts has been regarded as a critical factor in the mechanisms of acetaldehyde mutagenicity and carcinogenesis. Acetaldehyde reacts with 2'-deoxyguanosine in DNA to form primarily N(2)-ethylidene-2'-deoxyguanosine. The subsequent reaction of N(2)-ethylidenedGuo with another molecule of acetaldehyde gives rise to 1,N(2)-propano-2'-deoxyguanosine (1,N(2)-propanodGuo), an adduct also found as a product of the crotonaldehyde reaction with dGuo. However, adducts resulting from the reaction of more than one molecule of acetaldehyde in vivo are still controversial. In this study, the unequivocal formation of 1,N(2)-propanodGuo by acetaldehyde was assessed in human cells via treatment with [(13)C(2)]-acetaldehyde. Detection of labeled 1,N(2)-propanodGuo was performed by HPLC/MS/MS. Upon acetaldehyde exposure (703 μM), increased levels of both 1,N(2)-etheno-2'-deoxyguanosine (1,N(2)-εdGuo), which is produced from α,β-unsaturated aldehydes formed during the lipid peroxidation process, and 1,N(2)-propanodGuo were observed. The unequivocal formation of 1,N(2)-propanodGuo in cells exposed to this aldehyde can be used to elucidate the mechanisms associated with acetaldehyde exposure and cancer risk.     

Stereoselective synthesis and Diels-Alder reactions of bis-Ether 1,3 Dienes. A further test for cooperativity during cycloaddition reactions.

A stereoselective synthesis of dienes $\text{1a}$ and $\text{1b}$, using butadiene-iron tricarbonyl complexes, is described. Higher diastereoselectivity is observed during Diels-Alder reaction of $\text{1a}$ as compared with $\text{1c}$, affording good evidence for cooperativity in these cycloadditions.