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Theoretical investigation on growth kinetics and thermodynamic properties of pyridine-2-carboxylic acid crystals

100%

Manopradha N. , Rama S. , Gowri S. , Kirubavathi K. , Selvaraju K.

Mechanics and Mechanical Engineering

2019

tom Vol. 23, nr 1

23--27

This work illustrates the significance of kinetic parameters of nucleation and thermal decomposition for Pyridine-2-carboxylic acid crystals. In the interest of maximizing the growth condition for the production of single crystals, nucleation parameters such as interfacial energy (σ), volume free energy (ΔGv), critical energy barrier for nucleation (ΔG*), radius of the critical nucleus (r*) and nucleation rate (J) were determined from the classical nucleation theory of solubility-enthalpy relation. The optimized geometry of the compound was computed from the DFTB3LYP gradient calculations employing 6-31G(d,p) basis set and its vibrational frequencies were evaluated. Based on the vibrational analysis, the thermodynamic parameters were obtained and the correlative equations between these thermodynamic properties and variation in temperatures were also reported.

Presynaptic voltage facilitation of synaptic transmission between CA3-CA3 pyramidal neurons

86%

Bialowas A. , Rama S. , Zbili M. , Fronzaroli-Molinieres L. , Ankiri N. , Carlier E. , Debanne D.

Acta Neurobiologiae Experimentalis

2012

tom 72

nr 2

Synaptic transmission in the brain generally depends on action potentials. However, subthreshold variation in presynaptic membrane potential also determines spike-evoked transmission. We show here that excitatory synaptic transmission at CA3–CA3 connections depends on the membrane potential of the presynaptic neuron. Connected CA3 pyramidal neurons were recorded and synaptic transmission was tested when the presynaptic neurone was held at −61 mV, −77 mV or −48 mV. The presynaptic voltage facilitation (PVF) of synaptic transmission quantified by normalizing the postsynaptic responses obtained at −48 mV to those measured at −77 mV amounted to 135 ± 14% (n=13). PVF was associated with a decrease in the paired-pulse ratio and was totally occluded by bath application of the Kv1 channel blocker dendrotoxin (DTX). Using confocal laser scanning microscopy, we measured calcium transients evoked by the propagated spike in axons (50–250 µm from the soma) of CA3 neurons loaded with Fluo-4. Depolarization of the cell body from −75 to −50 mV enhanced spike-evoked calcium transients by ~17%. We conclude that PVF is a short-term plasticity at excitatory CA3–CA3 synapses resulting from the increase in spike-evoked calcium transients in the axon caused by voltage-inactivation of Kv1 channels.