The dynamics of a mode locked and frequency-doubled laser

The theory for the transient build-up of mode locked pulses in a mode-locked and frequency-doubled laser is presented. The time required for the mode-locked pulsewidth to reach a steady-state value is computed. It is found that steady-state is reached faster in the presence of internal frequency doubling because of the broadening effect of the doubling crystal. The effects of different conversion efficiencies and modulation depths on the mode-locked pulsewidth are investigated and the results are graphically presented.     

Palladium-mediated synthesis of 5-substituted 4-alkynylthieno[2,3-c]pyran-7-ones

We describe here, the first palladium-mediated tandem C-C bond forming reaction between 3-iodothiophene-2-carboxylic acid and terminal alkynes to afford the unexpected 5-substituted 4-alkynylthieno[2,3-c]pyran-7-ones in good yields.     

The use of driver inserts to reduce non-ideal pressure variations behind reflected shock waves

Non-ideal shock tube facility effects, such as incident shock wave attenuation, can cause variations in the pressure histories seen in reflected shock wave experiments. These variations can be reduced, and in some cases eliminated, by the use of driver inserts. Driver inserts, when designed properly, act as sources of expansion waves which can counteract or compensate for gradual increases in reflected shock pressure profiles. An algorithm for the design of these inserts is provided, and example pressure measurements are presented that demonstrate the success of this approach. When these driver inserts are employed, near- ideal, constant-volume performance in reflected shock wave experiments can be achieved, even at long test times. This near-ideal behavior simplifies the interpretation of shock tube chemical kinetics experiments, particularly in experiments which are highly sensitive to temperature and pressure changes, such as measurements of ignition delay time of exothermic reactions.     

Influence of the double bond position in combustion chemistry of methyl butene isomers: A shock tube and laser absorption study

Shock tube experiments have been carried out on 2-methyl-1-butene (2M1B), 2-methyl-2-butene (2M2B), and 3-methyl-1-butene (3M1B)—the three isomers of methyl butene compound. Carbon monoxide (CO) time-histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350-1630 K and pressures of 8.3-10.5 atm with stoichiometric mixtures of 0.075% fuel in O₂/Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time-resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C₃H₃ + O₂ = CH₂CO + HCO reaction are suggested based on the current investigation.     

Copper nanoparticles entrapped in SWCNT-PPy nanocomposite on Pt electrode as NOx electrochemical sensor

A highly sensitive NO_x sensor was designed and developed by electrochemical incorporation of copper nanoparticles (CuNP) on single-walled carbon nanotubes (SWCNT)-polypyrrole (PPy) nanocomposite modified Pt electrode. The modified electrodes were characterized by scanning electron microscopy and energy dispersive X-ray analysis. Further, the electrochemical behavior of the CuNP-SWCNT-PPy-Pt electrode was investigated by cyclic voltammetry. It exhibited the characteristic CuNP reversible redox peaks at −0.15 V and −0.3 V vs. Ag/AgCl respectively. The electrocatalytic activity of the CuNP-SWCNT-PPy-Pt electrode towards NO_x is four-fold than the CuNP-PPy-Pt electrode. These results clearly revealed that the SWCNT-PPy nanocomposite facilitated the electron transfer from CuNP to Pt electrode and provided an electrochemical approach for the determination of NO_x. A linear dependence (r² = 0.9946) on the NO_x concentrations ranging from 0.7 to 2000 μM, with a sensitivity of 0.22 ± 0.002 μA μM⁻¹ cm⁻² and detection limit of 0.7 μM was observed for the CuNP-SWCNT-PPy-Pt electrode. In addition, the sensor exhibited good reproducibility and retained stability over a period of one month.     

An efficient one-pot synthesis of functionally diverse 2-aminothiazoles from isothiocyanates,amidines/guanidines and halomethylenes

An efficient one-pot method for the synthesis of 2-aminothiazoles using simple starting materials like isothiocyanates, amidines/guanidines and various halomethylenes is reported. The synthesis of 2-aminothiazoles involves reactions such as nucleophilic addition, S-alkylation and intramolecular nucleophilic substitution in which amines departs as the leaving group.     

Cloning, Expression and Characterization of NADP-Dependent Isocitrate Dehydrogenase from Staphylococcus aureus

The Krebs cycle dictates oxidative and reductive conditions in Staphylococcus aureus and is mainly regulated by isocitrate dehydrogenase (IDH) which plays pivotal role in the growth and pathogenesis of the bacteria. In the present study, IDH gene from S. aureus ATCC12600 was cloned in the Sma I site of pQE 30 vector; the resultant clone was named as UVIDH1. The insert in the clone was sequenced (accession number HM067707), and the sequence showed complete homology with IDH sequence of other S. aureus strains reported in the database indicating presence of single enzyme in S. aureus, and considerable sequence homology with other bacteria was observed; however, only 24 % homology was found with NADP-dependent human IDH. Phylogenetically, the S. aureus IDH showed close identity with Bacillus subtilis and high degree of variability with other bacteria and human IDH. The expression of IDH in the clone UVIDH1 was induced with 1 mM IPTG, and the recombinant IDH was purified by passing through nickel metal chelate column; the purified recombinant IDH showed a single band in SDS–PAGE with a molecular weight of 40 kDa; K _m and V _max for isocitrate are 8.2?±?0.28 and 525?±?25 μM NADPH/mg/min, respectively, and for cofactor NADP 67.5?±?2.82?μM and V _max 50.5?±?2.12 μM NADPH/mg/min.     

1-[(Pyridine-2-ylamino)methyl]pyrrolidine-2,5-dione: Supramolecular Aggregation via Cooperative H-bonded Network of N–H···N and C–H···O Interactions

Abstract  

In the crystal structure of the title compound, C₁₀H₁₁N₃O₂, the pyrrolidine ring adopts a puckered envelope conformation. The supramolecular architecture is dictated by the cooperative H-bonded network of centrosymmetric dimers of N–H···N and C–H···O interactions. Two edge to face C–H···π interactions involving the centroid of the pyrrolidine ring contribute to the supramolecular aggregation.     

Chemical composition and antibacterial activity of essential oil from Salvia mukerjeei

The composition of steam volatile oil from aerial parts of Salvia mukerjeei Bennet & Raizada (Lamiaceae) was analyzed by capillary GC and GC-MS. The oil was rich in sesquiterpene hydrocarbons (67.3%). Among 71 identified constituents representing 91.7% of the oil, beta-caryophyllene (28.7%), gamma-muurolene (15.5%) and dehydro-aromadendrane (9.5%), were the principal constituents. The oil was tested against ten bacterial strains and was active against Enterococcus faecalis, Erwinia chrysanthemi and Agrobacterium tumefaciens.