The mechanism of the hantzsch pyridine synthesis: A study by 15N and 13C NMR spectroscopy

The mechanism of the reactions of ammonia and benzaldehyde with three different beta-dicarbonyl compounds to form the corresponding dihyropyridines has been followed by NMR. In each case the pathway is shown to involve the reaction of benzaldehyde with one molecule of beta-dicarbonyl to give chalcone, and of the ammonia with a second molecule of beta-dicarbonyl to give an enamine. The rate determining stage is shown to be the Michael addition of the chalcone to the enamine.     

A redox combined photocatalysis: New method of N-alkylation of ammonia by TiO2/Pt suspended in alcohols

Ammonia was efficiently N-alkylated into tertiary amines by room-temperature photoirradiation at > 300 nm in the presence of platinized titanium dioxide suspended in alcohols, such as methanol, ethanol, and ethylene glycol. A couple of processes, photocatalytic dehydrogenation of alcohols and thermal hydrogenation of an imine intermediate, account for the ammonia N-alkylation.     

Enhancement origin of SERS from pyridine adsorbed on AgCl colloids

SERS of pyridine molecules adsorbed on AgCl colloids are recorded. The enhancement origins are discussed by studying the effects of illumination, thiosulfate, hydrogen peroxide and ferricyanide on SERS of pyridine on AgCl colloids. In addition to an important contribution of local field enhancement on photolytic Ag particles in AgCl colloid, the surface Ag⁺ complexes on AgCl colloids as the SERS-active sites also make an important contribution to SERS of pyridine on AgCl colloid.     

Growth rate and some physiological features of Deleya halophila CCM 3662 at different salt concentrations

The growth rate of the type strain of the new, moderately halophilic species Deleya halophila (Deleya halophila CCM 3662) at different salt concentrations was determined and its optimal marine salt concentration for growth was established. Oxygen uptake and some cellular chemical composition characteristics of cells grown at their optimal salt concentration (7.5 % w/v) and at a higher concentration (15 % w/v) were compared, showing that both protein and carbohydrate intracellular contents decreased when the external medium salt concentration was increased, with the carbohydrate content reaching 50 % of the value presented by cells cultured at optimal salinity conditions. Oxygen uptake and poly-β-hydroxybutyric acid content were not significantly affected by changes in external salinity.     

Phenoxyaluminium compounds: VI. Complex and reaction mechanism of methylaluminium compounds with anisole

The reactions of anisole with organoaluminium compounds Me_nAlX_3−n have been investigated.The formation of a complex is the first reaction step, followed by cleavage and elimination of the gases MeX and small amounts of hydrocarbons. The yield of the gases and the cleavage rate decreases in the order: AlCl₃ >/ MeAlCl₂ > Me₂AlCl > Me₃Al and Me₂AlI > Me₂AlCl > Me₂AlBr. For most of the investigated reactions a marked decrease in gas evolution was observed after a short period of time. This is explained by the formation of an almost inactive mixed dimer (I) which at the

reaction temperature is more stable than the Me₂(Cl)Al : O(Me)Ph complex. It is suggested that dimer I is formed after the intramolecular reaction of the 2 : 1 complex II after elimination of MeX.

     

A novel double deprotection-peptide cyclisation procedure and its application to the synthesis of analogues of the cyclic tetrapeptide HC-toxin.

A hydroxide-mediated Fmoc/methyl ester double deprotection procedure followed by an improved bis(2-oxo-3-oxazolidinyl)phosphinic chloride (BOP-Cl) cyclisation reaction are reported. This novel methodology was applied to the synthesis of three new HC-toxin analogues.     

Phosphorus compounds with unusual coordination - 201. 1,2,3,4- triazaphospholes by [3+2]-cycloaddition of azides to a stable phosphaalkyne

The azides 2a-i undergo regiospecific [3+2]-cycloaddition with the phospha-alkyne 1 to form the l,2,3,4-triazaphospholes 3a-i; in the case of the reaction with 2J, an additional silyl shift occurs resulting in the formation of 4j. The latter product can by hydrolyzed to 6 which has also been prepared independently from 1 and hydrazoic acid(7). Flash vacuum pyrolyses of the 1,2,3,4-triazaphospholes 3c and 3e produce mixtures of the isomers 13a,b and 14a,b, respectively, from which the 1,2-azaphospholes 14 can be isolated as the major reaction products.     

Anionic surfactant selective electrode for the titrimetric determination of anionic surfactant

The construction and characteristic performance of a PVC membrane electrode responsive for sodium dodecylsulfate (SDS) are described in this paper. The electrode based on CTA⁺DS^? ion pair as ionophore in PVC membrane displays a Nernstian slope of ?58.8 ± 0.7 mV/decade in a 1.32 × 10^?6 to 3.75 × 10^?3 mol L^?1 concentration range and a limit of detection of 1.13 × 10^?6 mol L^?1. The electrode can be used for 3 months without showing significant changes in the value of slope or working range. The electrode has been utilized as an end point indicator electrode for potentiometric titration involving Hyamine as titrant. More than 100 titrations were carried out for the evaluation of the electrode parameters: the standard deviations of the equivalent volume and the equivalent potential, the height of the potential jump and the number of faulty titrations. The behavior of the electrode was assessed with regard to their usefulness in routine analysis.     

Vibrational spectroscopic study of poly(dimethylsiloxane)-ZnO nanocomposites

A series of poly(dimethylsiloxane)-zinc oxide (PDMS-ZnO) nanocomposites having different concentrations of ZnO nanoparticles (0, 1, 5, 10 and 20 wt%) have been prepared. Raman and FTIR-ATR spectroscopic analysis was performed in order to determine the interaction between the ZnO nanoparticles and PDMS polymer matrix. Density functional theory (DFT) using the (B3-LYP)/6-311++G(2df,2p) method was used to investigate the vibrational spectra of PDMS. A complete vibrational assignment is supported by the normal coordinate analysis, calculated Raman activities as well as IR intensities.The presence of ZnO nanoparticles in PDMS gives rise to significant differences in relative intensities of the characteristic vibrational bands with respect to the cross-linked polymer. The changes in relative intensities of Raman bands, as well as swelling measurements, were used to explain the effect of ZnO nanoparticles on the cross-linked structure of PDMS nanocomposites. It is established that ZnO nanoparticles influence the cross-linking density of the polymer matrix.     

Raman spectroscopic study on classification of cervical cell specimens

Cervix-cancer is the third most common female cancer worldwide. Papanicolaou (Pap) test, a well-recognized screening tool, is labor intensive, time consuming and prone to subjective interpretations. Optical spectroscopic methods, sensitive to molecular changes are being pursued as potential diagnostics tool. In this study we have explored Raman spectroscopic approach to differentiate exfoliated cell pellets using 94 cervical cell specimens (45-normal and 49-abnormal specimens). Study was carried out by two approaches. In the first approach, spectral data from 37 cell specimens were acquired and analyzed by Principal Component-Linear Discriminant Analysis (PC-LDA), which yielded classification efficiencies of 86% and 84% for normal and abnormal specimens, respectively. Mean and difference spectra suggest presence of blood in abnormal specimen as a major cause of discrimination. However, as tumor is vascular, bleeding was observed during abnormal sample collection. Hence, spectra of abnormal specimens show heme and fibrin features, and this can lead to false interpretations, as bleeding also occur in several non-cancerous conditions. Therefore, remaining 57 specimens were treated with Red Blood Corpuscles (RBC) lysis buffer in order to remove the RBC influence. PC-LDA resulted classification efficiency of about 79% and 78% for normal and abnormal smear, respectively – comparable to Pap test. Thus finding of the study suggests feasibility of Raman spectroscopic classification of normal and cancerous exfoliated cervical cell specimens.