Effect of the Composition of the Aqueous Organic Solvent on the Kinetics of N-Acylation of α-Amino Acids with 4-Nitrophenyl 4-Nitrobenzoate

Equations relating the N-acylation rate constants of glycine, L--alanine, DL-threonine, and L-proline with 4-nitrophenyl 4-nitrobenzoate in water-acetonitrile, water-2-propanol, and water-2-methyl-2-propanol solvents to the composition of the medium were obtained, and reaction rate constants in water were calculated.     

Acylation of piperidine and morpholine with phenyl benzoates in the mixtures water-2-propanol and water-dioxane

Kinetics of acylation of piperidine and morpholine with 4-nitro- and 2,6-dinitrophenyl benzoates was studied in binary systems water-2-propanol and water-dioxane. Structural and energy characteristics of solvate complexes of morpholine and piperidine with the components of the mixed solvents were calculated. Kinetic regularities of acylation are considered from the viewpoint of specific solvation of amines.     

Cavity enhanced wavelength modulation spectrometry for application in chemical analysis

A simple and robust absorption technique is developed which combines cavity enhanced absorption spectroscopy and wavelength modulation spectroscopy and measures the integrated output of unlocked cavities. The detection power of the technique is affected by peculiarities of the laser injection into a cavity causing excess noise which exceeds the shot noise. The noise and ways for its reduction are discussed. The new method is demonstrated by absorption measurements of excited carbon atoms in a microwave induced plasma. Preliminary detection limits equivalent to optical depths below 10^-6 were obtained. PACS 42.55.Px; 42.62.Fi; 42.60.Mi     

Optical detection of an electric field in a GaAs/AlGaAs <Emphasis Type="Italic">n</Emphasis>-<Emphasis Type="Italic">i</Emphasis>-<Emphasis Type="Italic">n</Emphasis> heterostructure with double quantum wells

Processes occurring when a static transverse electric field is applied to a GaAs/AlGaAs n-i-n heterostructure with single quantum wells and asymmetric tunnel-coupled double quantum wells have been investigated by optical methods. The difference between the energies of exciton transitions for quantum wells of different widths makes it possible to attribute the observed photoluminescence peaks to particular pairs of wells or particular single quantum wells. The local electric field for each quantum well has been determined in terms of the Stark shift and splitting of exciton lines in a wide range of external voltage. A qualitative model has been proposed to explain the nonmonotonic distribution of the electric field over the depth of the heterostructure.     

Reactivity of α-Amino Acids in the Reaction with Esters in Aqueous–1,4-Dioxane Media

The kinetics of the reaction of a series of α-amino acids with 4-nitrophenyl acetate, 4-nitrophenyl benzoate, and 2,4,6-trinitrophenyl benzoate in aqueous 1,4-dioxane medium has been studied. Kinetics of the reactions involving 4-nitrophenyl acetate and 2,4,6-trinitrophenyl benzoate has complied with the Brønsted dependence and revealed linear correlation between rate constant logarithm and the energy difference of the frontier orbitals of α-amino acids anions.     

Theory of a laser-plasma method for detecting terahertz radiation

A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation.     

Measurements of the temperature and water vapor concentration in a hot zone by tunable diode laser absorption spectrometry

A tunable diode laser absorption spectroscopy (TDLAS) technique and appropriate instrumentation was developed for the measurement of temperature and water vapor concentrations in heated gases. The technique is based on the detection of the spectra of H₂O absorption lines with different energies of low levels. The following absorption lines of H₂O were used: 7189.344 cm⁻¹ (E″=142 cm⁻¹), 7189.541 cm⁻¹ (E″=1255 cm⁻¹), 7189.715 cm⁻¹ (E″=2005 cm⁻¹). Spectra were recorded using fast frequency scanning of a single distributed feedback (DFB) laser. A unique differential scheme for the recording of the absorption spectra was developed. An optimal technique for fitting the experimental spectra was developed.     

Influence of pH of an aqueous-organic solvent on the kinetics of N-acylation of α-amino acids with benzoic acid esters

The pH dependence of the apparent rate constants and activation parameters (enthalpy, entropy) of N-acylation of α-amino acids with benzoic acid esters in water-2-propanol solvent was studied.