Dynamics of silicate exchange in highly alkaline potassium silicate solutions

Article Abstract:

Measuring kinetics of Si exchange in aqueous silicate species by 29Si NMR has been a problem. Using selective inversion-recovery (SIR) and a data-fitting program gave rate constants independent of the source of KOH in the very alkaline potassium silicate solution and at least an order of magnitude smaller than those from line-shape analysis (LSA) for measuring kinetics of silicate exchange between aqueous silicate species. Reactivities of monomer, M, dimer, D, linear trimer, L, and cyclic trimer, C, in Si-O-Si link formation or dissociation were all fairly comparable. Ignoring the presence of L made good fits and reliable rate constants for the M-D exchange possible.

Analysis, Nuclear magnetic resonance, Chemical reaction, Rate of, Chemical kinetics, Silicates

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The conformational equilibrium of N,N'-bis((S)-1-phenylethyl)-thiourea and its solvent dependence, studied by NMR and CD spectra and by X-ray crystallography

Article Abstract:

Empirical force-field calculations have been used to predict favored conformations of N,N'-bis((S)-1-phenylethyl)-thiourea. Corresponding rotational strengths for near-UV-region important transitions have been determined. Experimental studies using NMR and CD spectroscopy and X-ray crystallography make it possible to give a conformation labeled E,Za to the conformer found most in nonpolar solvents. Hydroxylic solvents favor the so-called Z,Za conformation. The E,Za conformer is predicted to be the more stable one, based on the calculations.

Observations, Nuclear magnetic resonance spectroscopy, Conformational analysis, X-ray crystallography, Solution (Chemistry), Solutions (Chemistry), Amides, Circular dichroism

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Structure and dynamics of azapropazone derivatives studied by crystallography and nuclear magnetic resonance

Article Abstract:

The azapropazone derivative 3-dimethylamino-7-methyl-1,2,4-benzotriazine, lacking the pyrazolidine ring of its parent compound, is planar. The nonsteroidal anti-inflammatory drug azapropazone, a nonplanar molecule, has an enthalpy of activation of 36 kJ/mol and a negative entropy of activation, while the derivative has an enthalpy of activation of 48 kJ/mol and a near-zero entropy of activation.

Drugs, Nonsteroidal anti-inflammatory drugs, Nonsteroidal anti-inflammatory agents, Structure-activity relationships (Pharmacology), Enthalpy, Prolixin (Medication)

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