GC and Mass-Spectrometric Comparison of Organo Sulfur Compounds in Two Varieties of Iranian Garlic

Abstract

Garlic antibiotic action is well known; it is reputed to offer protection against coronary thrombosis and atherosclerosis exhibiting antioxidant and anticancer effects. ^1,2 In this work ¹ H NMR and gas chromatography in conjunction with mass spectrometry have been used for the identification and determination of these compounds in two varieties of Iranian garlic [Allium sativum var. sativum (I) and Allium sativum var. holmense (II)]. The organosulfur compounds in (I) exhibiting a concentration higher than 1% are diallyl sulfide (1.3%), diallyl disulfide (8%), methyl allyl disulfide (19%), methyl allyl trisulfide (3.2%), diallyl trisulfide (5.5%), diallyl tetrasulfide (2%), 2,3-dimethyl thiophen (1.8%), 5-methyl-1,2,3-thiadiazol (5%), and 1,2-ditiolan-3-carboxilic acid (1.5%). The amount of organosulfur compounds in (II) are diallyl disulfide (2%), methyl allyl trisulfide (6.3%), diallyl tetrasulfide (5%), and cyclopentanthiol (2.5%).     

A simple synthetic protocol for oxidation of alkyl-arenes into ketones using a combination of HBr-H2O2

A wide variety of alkyl- and cycloalkyl-arenes undergo benzylic C-H oxidation by employing a combination of 48% hydrogen bromide and 30% hydrogen peroxide in dichloromethane at room temperature. In addition, a chemoselective oxidation at the benzylic position is feasible by deactivating the aromatic ring using the same combination.     

Analysis of amplification properties of a photonic crystal fiber

In this work, effects of geometrical parameters and dopant concentration on amplification performance of Yb doped photonic crystal fiber amplifiers (YDPCFAs) are investigated. To this end, numerical results obtained from fully vectorial effective index method, are combined with conventional rate equations. The variation of the normalized frequency of the photonic crystal fiber with respect to air filling factor for different air hole spacing are depicted. Using obtained results, the single-mode region at signal and pump wavelengths are determined. In addition, the influence of dopant concentration on the maximum gain and optimum length are investigated. It is shown that by changing photonic crystal fiber cross-section parameters such as pitch and air filling factor, rather than increasing dopant concentration, one can obtain a higher gain at shorter optimum length. These results are useful for the design of YDPCFAs with less nonlinearity effects such as cooperative up conversion and Yb³⁺ ion quenching.     

Application of 13C N.M.R. in a re-examination of the isopropylidenation of D-ribose diethyldithioacetal and erythritol

The di-$\text{O}$-isopropylidene acetals resulting from the reaction of $\text{D}$-ribose diethyldithioacetal and erythritol with acidic acetone have been shown to contain 5- and 7- but not 6-membered rings.     

Matrix effects in biological reference materials used in the standardization of cholesterol measurements

Summary The precise and accurate laboratory measurement of blood cholesterol has become a national public health priority in the diagnosis and management of patients at risk for coronary heart disease. Unreliable measurements can hamper the national program to control heart disease. The National Cholesterol Education Program (NCEP) recommends that manufacturers and clinical laboratories achieve traceability to the National Reference System for Cholesterol in order to reliably classify patients according to the NCEP guidelines for assessing coronary heart disease risk. Documenting the accuracy of certain clinical analytical systems for the measurement of cholesterol has been complicated by the occurrence of fluid matrix effects. The major difficulty is that some processed materials (including calibrators, controls, proficiency survey samples, and reference materials) may not be reliable and may result in inaccurate measurement of patient specimens. Similarly, use of such material in accuracy assessment or proficiency testing may yield erroneous conclusions regarding system accuracy. Here, we will review the problem of matrix effects in cholesterol materials and present the results of several studies evaluating sources of matrix error. An alternate approach to documenting accuracy, to be used until commutable materials free of matrix effects are available, will also be discussed.     

Recent advances in C-heteroatom bond forming by asymmetric Michael addition

In this review, we try to highlight the recently reported stereoselective Michael conjugate additions of heteroatom nucleophiles to electron-deficient alkenes. The topic is divided based on the nature of the nucleophile employed (nitrogen-, oxygen-, sulfur-, or phosphorus-centered) and then subdivided to distinguish between catalyst-controlled and substrate/reagent-controlled methods which is necessary to achieve asymmetric synthesis.     

Opals: Status and Prospects

The beauty of opals results from a densely packed, highly ordered arrangement of silica spheres with a diameter of several hundred nanometers. Such ordered nanostructures are typical examples of materials called photonic crystals, which can be formed by known microstructuring methods and by self‐assembly. Opals represent a self‐assembly approach to these structured media; such an approach can lead to novel materials for photonics, photocatalysis, and other areas. Although self‐assembly leads to many types of defects, resulting in the surprising and very individual appearance of natural opals, it causes also difficulties in technological applications of opal systems.     

Optical spectra and angular dependence of the visible light emitted by metal-insulator-metal tunnel junctions

Optical spectra and angular dependence of electromagnetic emission from Al-Al oxide-Ag and Al-Al oxide-Au tunnel junctions are reported. Data from Ag junctions are consistent with the assumption of roughness induced decoupling of surface polaritons, while data from Au junctions suggest that the emission results from direct coupling of current fluctuations in the junction to the external radiation fields.     

Aromatic substitution. The effect of alcoholic solvents on the reaction of phenyltriethyltin with mercury (II) salts

Second-order rate constants are reported for the cleavage of the phenyltin bond of phenyltriethyltin by mercury(II) salts in ethanol. propan-1-ol, propan2-ol and butan-1-ol. It is shown that the reactivity order for the mercury(II) salts is HgI₃^? << HgI₂ < HgCl₂. Activation parameters are reported, and on the basis of the low values of activation enthalpies the presence of an intermediate π-complex is suggested for the reactions.     

CeCl3·7H2O: an efficient and reusable catalyst for the preparation of β-acetamido carbonyl compounds by multi-component reactions (MCRs)

A convenient method for the preparation of β-acetamido carbonyl compounds is described by multi-component reactions of aromatic aldehydes, enolizable ketones or β-keto esters and acetonitrile in the presence of acetyl chloride and 10 mol % CeCl₃·7H₂O at room temperature.