A tetraalkylated pyrene building block for the synthesis of pyrene-fused azaacenes with enhanced solubility

The synthesis and characterisation of a soluble pyrene-fused tetraazaoctacene derivative has been achieved by developing a key pyrene-based building block with four solubilising groups.     

Characterization of an unprecedented organomercury adduct via Hg(II)-mediated cyclization of N9-propargylguanine

This communication describes mercury(II)-mediated cyclization of N9-propargylguanine under hydrothermal conditions. The structural investigations reported here confirm cyclization and reveal simultaneous formation of a unique organomercury adduct of a tricyclic guanine derivative.     

Hamming weight distributions of multi-twisted codes over finite fields

Designs, Codes and Cryptography - Let $${\mathbb {F}}_q$$ denote the finite field of order q,  and let $$n = m_1+m_2+\cdots +m_\ell ,$$ where $$m_1,m_2,\ldots ,m_\ell $$ are arbitrary...     

Pb（NO3）2 Mediated Synthesis of Pyrazine

Lead nitrate was used as an efficient catalyst in the oxidation and condensation reaction of hydroxy ketone with diamine leading to the formation of pyrazine derivatives in excellent yields.     

Biosynthesis of (+)-,(-)- and (±)-tetrahydropalmatines

Specific incorporation of didehydroreticuline and reticuline into (±)- (+)-, and (-)-tetrahydropalmatines in Cocculus laurifolius and of (R)- and (S)-reticulines into (R)- and (S)-tetrahydropalmatines respectively has been demonstrated. Feeding of[l-³H, 4'-methoxy-¹⁴C]reticuline suggested that reticuline was not converted in the plants into didehydroreticuline and racemisation of optically active forms of tetrahydropalmatine did not take place via dehydrotetrahydropalmatine     

Spectrophotometric determination of vanadium after extraction as vanadium(III) picolinate

Vanadium(V) is conveniently reduced by sodium dithionite to vanadium(III) which is extracted as its picolinate complex into chloroform. Vanadium is determined spectrophotometrically by measuring the absorbance of the complex at 385 nm against a reagent blank, Beer's law being obeyed over the range 1-50 microg/ml. The method is one of the most selective, being free from interference by relatively high concentrations of almost all the important elements, titanium, chromium, manganese, iron, cobalt, nickel, zinc, copper, aluminium, molybdenum, tungsten and uranium, found in industrial alloys. Only bismuth interferes. The method is quite simple and rapid. It has been successfully applied for the analysis of vanadium in a variety of samples.     

Fourier-transform infrared spectroscopic studies of dithia tetraphenylporphine

We present here infrared absorption spectra of dithia tetraphenylporphine and its cation in the 450–1600 and 2900–3400 cm⁻¹ regions. Most of the allowed IR bands are observed in pairs due to overallD _2h point group symmetry of the molecule. The observed bands have been assigned to the porphyrin skeleton and phenyl ring modes. Some weak bands, which are forbidden underD _2h , also appear in the spectra due to the distortion of the molecule from planarity-caused by the out-of-plane positioned N and S atoms. Increased intensity of some phenyl ring bands compared to free-base tetraphenylporphine is explained on the basis of rotation of phenyl rings towards the mean molecular plane. Contrary to the point group symmetry of cation of dithia tetraphenylporphine, certain bands are observed to be degenerate due to identical bonding arrangements in pyrrole rings of the cation     

Biosynthesis of tetrahydropalmatine and palmatine

The incorporation of (±)-norlaudanosoline, norprotosinomenine, nororientaline, norlaudanidine, reticuline and laudanosine into tetrahydropalmatine and palmatine has been studied, and specific utilization of reticuline demonstrated. Feeding of (±)-[N-methyl-¹⁴C] reticuline showed that C atom 8 of tetrahydropalmatine and palmatine are formed by oxidative cyclisation of the N-Me group of reticuline. Parallel experiments with (R)-; and (S)-, reticulines demonstrated specific incorporation of (R)- isomer into these bases. Feeding experiments also revealed that the plants can convert tetrahydropalmatine into palmatine with high efficiency.     

Microscopic optical fields and mixing coefficients of x-ray and optical frequencies in solids

Simple approximation schemes are developed to calculate induced optical fields and local field corrections to the linear optical dielectric function in metals like aluminium and in insulators like germanium. In these calculations, the unperturbed electronic states in Ge are described within the framework of the bonding orbital approach, whereas the nearly-free-electron approximation is used for Al. As expected, explicit numerical calculations show that the contribution to secondary longitudinal induced fields is more appreciable in Ge. The second order susceptibility describing the non-linear mixing of an optical frequency with an x-ray frequency, which depends upon the magnitude of the microscopic induced optical charge density, is also calculated for these solids. For most relevant wavevectors of secondary optical fields, it is found to be of the order of 10^?12 esu in Ge and 10^?14 esu in Al.     

Deposition of aluminide and silicide based protective coatings on niobium

We compare aluminide and alumino-silicide composite coatings on niobium using halide activated pack cementation (HAPC) technique for improving its oxidation resistance. The coated samples are characterized by SEM, EDS, EPMA and hardness measurements. We observe formation of NbAl₃ in aluminide coating of Nb, though the alumino-silicide coating leads to formation primarily of NbSi₂ in the inner layer and a ternary compound of Nb-Si-Al in the outer layer, as reported earlier (Majumdar et al. [11]). Formation of niobium silicide is preferred over niobium aluminide during alumino-silicide coating experiments, indicating Si is more strongly bonded to Nb than Al, although equivalent quantities of aluminium and silicon powders were used in the pack chemistry. We also employ first-principles density functional pseudopotential-based calculations to calculate the relative stability of these intermediate phases and the adhesion strength of the Al/Nb and Si/Nb interfaces. NbSi₂ exhibits much stronger covalent character as compared to NbAl₃. The ideal work of adhesion for the relaxed Al/Nb and Si/Nb interfaces are calculated to be 3226 mJ/m² and 3545 mJ/m², respectively, indicating stronger Nb-Si bonding across the interface.