NOPR Collection:

Solubilization of n-decane into n-decyl-polyoxyethylene surfactants: A cavity forming free energy based model

2017-04-24T09:30:34Z

Title: Solubilization of n-decane into n-decyl-polyoxyethylene surfactants: A cavity forming free energy based model Authors: Nandi, Nilashis Abstract: The present paper reports the results of a theoretical study of the forces and factors driving the solubilization of n-alkane solubilizates into the micellar core of some non-ionic surfactants, based on a micellar model which· includes the cavity forming free energy as a component of micellization. The solubiIizate is n-decane and the non-ionic surfactants considered are n-decyl-polyoxyethylene surfactants. The extent of solubilization, i.e. the mole fraction of the solubilizate within the core has been calculated. The results indicate that the incorporated solubilizate has more translational and rotational degrees of freedom as compared to those of the tail parts of the surfactants present in the core. This drives the total free energy of aggregation after solubilization into a more favourable direction. The results are in fair agreement with the experimental results. Page(s): 625-628

Density functional study of the reaction paths of formamidine

2017-04-24T09:28:11Z

Title: Density functional study of the reaction paths of formamidine Authors: Kaushik, R; Rastogi, R C; Ray, N K Abstract: Density functional theory (DFT) is used to study the reaction paths of formamidine. The E conformer of formamidine is predicted to be more stable (1.4 kcal mol^-1) than the Z. The energy of activation is estimated to be 26.7 kcal mol^-1 for the E Z isomerization. The E isomer can undergo 1,3-sigmatropic shift and the energy barrier is estimated to be 47.6 kcal mol ^-1 Unimolecular decomposition of the Z isomer to HCN and NH₃ is predicted to have a barrier height of 66.8 kcal mol^-1. The predicted barrier heights are significantly lower than those obtained from Hartree-Fock estimates particularly for 1,3-sigmatropic shift and decomposition reaction of formamidine. Results of second order Moller-Plesset (MP2) studies also lead to the conclusion that inclusion of electron correlation decreases the barrier heights significantly for 1,3-sigmatropic shift and unimolecular decomposition of formamidine. Calculated equilibrium geometries, harmonic vibrational frequencies and relative energies are in excellent agreement with the results of MP2 studies. Page(s): 629-632

Spectroscopic properties and fluorescence quenching of luminol in aqueous medium

2017-04-24T07:02:15Z

Title: Spectroscopic properties and fluorescence quenching of luminol in aqueous medium Authors: Bhattacharjee, U; Mitra, S; Das, R; Mukherjee, S Abstract: The interaction of 3-aminophthalhydrazide (luminol) with aqueous solution of NaOH and H₂SO₄ has been studied employing steady-state fluorescence quenching measurements and time-correlated single photon counting technique. From nanosecond lifetime measurements and quantum yields of fluorescence, the radiative and nonradiative decay rate constants are calculated at different pH. It is shown that both the fluorescence quantum yield and rate constants are pH dependent. The quenching of luminol fluorescence is analyzed by using simple Stern-Volmer equation. It is proposed that quenching is due to some exciplex type of hydrogen bonding interaction. Page(s): 633-638

Formation constants and molecular modelling studies of metal ion-tetracycline complexes

2017-04-24T06:58:28Z

Title: Formation constants and molecular modelling studies of metal ion-tetracycline complexes Authors: Sharma, R K; Joseph, Sherly Abstract: Formation and proton association constants have been determined using BEST and PKAS programs. Species distributions are plotted using program BEST in order to see the presence of M-tetracycline species in biological fluids. Formation constants and species distribution curves indicate the strong interaction of Ca, Mg, Cu, Ni, Co and Fe with tetracycline and the predominant species at biological pH value is of MHL type. Action of tetracycline is explained on the basis of strong chelation behaviour with Mg. Molecular mechanics calculations show that the chelating sites are 010-011 for Cu-tetracycline complex. Page(s): 639-642