Spectroscopic investigations of Nd(3+)-doped alkali chloroborophosphate glasses

Optical absorption spectra were studied in wavelength region 400-900 nm for the Nd(3+)-doped alkali (R = Li, Na and K) chloroborophosphate glasses at room temperature. The energy level scheme of the 4f(3) electron configuration was deduced from the observed energy level data using a parametrized Hamiltonian (H(F1)) model which includes 20 free-ion interaction parameters. Reasonable correlation was obtained between the experimental and calculated energy levels. The Judd-Ofelt model for the intensity analysis of induced electric dipole transitions has been applied to the measured oscillator strengths of the absorption bands to determine the three phenomenological intensity parameters Omega(2), Omega(4) and Omega(6) for each glass. Using these parameters, the total radiative transition rates (A(T)), non-radiative relaxation rates (W(NR)), branching ratios (beta(R)), integrated cross-sections for the stimulated emission (Sigma), excited state emission intensities (f(ESE)) and excited state absorption intensities (f(ESA)) have been theoretically calculated for certain excited Nd(3+) fluorescent levels. From the results obtained, the conclusion is made about the possibility of using these glasses as laser media.     

Synthesis and characterization of the aqueous solution chemistry of the food-derived carcinogen model N-acetoxy-N-(1-methyl-5H-pyrido[4,5-b]indol-3-yl)acetamide and its N-pivaloyloxy analogue

We report the synthesis of N-acetoxy-N-(1-methyl-5H-pyrido[4,5-b]indol-3-yl)acetamide, 7, its N-pivaloyloxy analogue, 9, and improved synthesis of indole-2-acetonitrile, 3 (70% in five steps from indole-2-carboxylic acid), the carcinogenic amine Trp-P-2, 4 (40% from 3), and the nitro compound, 5 (40% from 4 by oxidation with H₂O₂ using Mo(CO)₆ catalyst). In aqueous solution at neutral pH, 7 primarily undergoes C-O bond cleavage to yield the hydroxamic acid, 8, but under the same conditions the sterically hindered 9 decomposes predominately by N-O bond cleavage with a pH independent rate constant that is 7.5-fold smaller than that for 7. In the pH range 0.5-7.0 three different processes for the decomposition of 9 were detected by kinetics. Only the process that dominates at neutral pH generates a nitrenium species that can be trapped by N₃⁻.     

Radiolysis of resist polymers. IV. Poly(p-substituted-α-methylstyrene)s

The effect of parasubstituents on the radiation chemistry of poly(α-methylstyrene) (PMS) was compared for the fluoro (PFMS), chloro (PCMS), bromo (PBMS), isopropyl (PiPMS), and methoxy (PMeOM) derivatives. Radiolysis yields, ESR spectra, and GC? MS analysis of products were obtained. PMS and PFMS have similar low radiolysis yields, products, and product distributions. Only main-chain radicals which persist to 200° were observed. PCMS has increased values of G_s, G_x, and G_r. The product analysis results suggest that the presence of chlorine contributes to the primary process by dissociative electron capture and enhances the cleavage of α-methyl group. Irradiation of PBMS caused crosslinking and yielded few volatile products. PMeOMS and PiPMS gel readily by γ-irradiation and may be useful as negative radiation resists.     

Copolymerizations of alkyl methacrylates with vinyltriacetoxysilane

Copolymerizations of methyl methacrylate (MMA) and butyl methacrylate (BMA) with vinyltriacetoxysilane (VTAS) have been carried out in bulk at 70°. The compositions of the copolymers were determined from their silicon contents; the reactivity ratios were calculated by the Kelen-Tüdős method. For MMA/VTAS, r₁ = 7.75 ± 0.31 and for BMA/VTAS, r₁ = 4.62 ± 0.15; in both systems, r₂ is zero, indicating that VTAS does not homopolymerize under the experimental conditions. The influence of the silicon comonomer on properties of the copolymers, such as solubility annd thermal behaviour, was studied.     

Effect of isomeric butanols on the temperature corresponding to the adiabatic compressibility minimum of water

The effect of isomeric butanols on the temperature corresponding to the adiabatic compressibility minimum of water (T _β) was studied using a variablepath interferometer working at 3 MHz. The structural contribution to the shift inT _β, [ΔT _βstr]_exp, was found to be positive and to increase with concentration to a maximum atX ₂?0.0193, 0.0100, and 0.0090 fort-butanol, sec-butanol, and isobutanol, respectively. The results have been explained on the basis of stabilization of water structure at low concentrations of alcohol. The quantity [ΔT _βstr]_exp forn-butanol is practically zero at low concentrations, while at high concentrations it is negative, indicating rupture of the hydrogen-bonded structure of water by this solute. At any given concentration,t-butanol > sec-butanol > isobutanol >n-butanol is the order of increasing structural contribution to the shift inT _β. Theoretical values of the structural contribution to the shift inT _β are in good agreement with the experimental data.     

Study of phase transition and volume thermal expansion in a rare-earth (RE) oxyfluoride system by high-temperature XRD (RE=La, Nd, Sm, Eu and Gd)

Volume thermal expansion behaviour of a number of rare-earth oxyfluorides (REOF) have been studied using high-temperature X-Ray diffractometry (HT-XRD) in the 298–1075 K range in air. The studies revealed an anomalous expansion for each compound associated with phase transition. The phase transition temperature and the coefficient of volume thermal expansion of five compounds in REOF series determined by this method are reported and compared with our earlier results obtained by dilatometry.     

Synthesis of peptides employing Fmoc-amino acid chlorides and commercial zinc dust

Coupling of Fmoc-amino acid chlorides mediated by activated commercial zinc dust for the synthesis of peptides is described. The reaction is carried out in an organic medium. The necessity of using an inorganic base like NaHCO₃/Na₂CO₃ or an organic base like DIEA/NMM/TEA/pyridine is circumvented. The coupling is reasonably fast, clean, racemization free and high yielding.