Recent Publications

Jorge Kohanoff

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  1. Title: Multiple proton translocation in biomolecular systems: concerted to stepwise transition in a simple model

    Author(s): Kohanoff J.J., Cachau R.E.

    Molecular Physics, 102, No. 9-10, pp. 1007-1014 (MAY 10 2004)

    doi: 10.1080/00268970410001725738

    In this paper we study a simple model potential energy surface (PES) useful for describing multiple proton translocation mechanisms. The approach presented is relevant to the study of more complex biomolecular systems like enzymes. In this model, at low temperatures, proton tunnelling favours a concerted proton transport mechanism, while at higher temperatures there is a crossover from concerted to stepwise mechanisms; the crossover temperature depends on the energetic features of the PES. We illustrate these ideas by calculating the crossover temperature using energies taken from ab initio calculations on specific systems. Interestingly, typical crossover temperatures lie around room temperature; thus both concerted and stepwise reaction mechanisms should play an important role in biological systems, and one can be easily turned into another by external means such as modifying the temperature or the pH, thus establishing a general mechanism for modulation of the biomolecular function by external effectors.

  2. Title: Ab-initio investigations of pressure effects on the ferroelectric instabilities in KDP and DKDP

    Author(s): Colizzi G., Kohanoff J., Lasave J., Koval S., Migoni R.L.

    Ferroelectrics, 301, pp. 61-64 (2004)

    doi: 10.1080/00150190490454991

    Results of first-principles calculations are reported for KDP and DKDP as a junction of pressure. The global energy barrier between the two stable (oppositely polarized) equilibrium configurations, and the separation between the corresponding positions of the H-atoms in the O-H-O bridges, are analyzed in terms of a previously proposed, self-consistent double-well model. We argue that the experimentally observed similarity of the H(D) off-centering distance in KDP and DKDP at the transition temperature call be explained only by means of important geometric isotope effects.