the present study describes the fragmentation under electron ionization (ei) of gas phase serine and threonine amino acids. ab initio methods were performed to calculate the fragmentation paths and interpret the mass spectra. the six lowest energy conformers of l-serine, l-threonine and l-allo-threonine were obtained with b3lyp, g3mp2 and mp2 methods. the adiabatic and vertical ionization energ...

wheat, cv. alvand, under late sowing condition and comparison with conventional sowing date was investigated in a field experiment in 2009-2010. the factors were seven levels of priming by sa, including control or untreated seeds, 400, 800, 1200, 1600, 2000 and 2400 µm sa and two sowing dates including conventional sowing date (23 october) and late sowing (22 november). results showed that prim...

A theoretical investigation on small silicon-doped lithium clusters Li(n)Si with n = 1-8, in both neutral and cationic states is performed using the high accuracy CCSD(T)/complete basis set (CBS) method. Location of the global minima is carried out using a stochastic search method and the growth pattern of the clusters emerges as follows: (i) the species Li(n)Si with n ≤ 6 are formed by directl...

High-level ab initio calculations have been carried out to reexamine relative stability of bowl, cage, and ring isomers of C(20) and C(20)(-). The total electronic energies of the three isomers show different energy orderings, strongly depending on the hybrid functionals selected. It is found that among three popular hybrid density-functional (DF) methods B3LYP, B3PW91, PBE1PBE, and a new hybri...

Herein, a theoretical study on the stability of some vic-dioxime complexes of Ni(II), Pd(II) and Pt(II) in gas and aqueous phases is reported. The DFT/M06/SDD and DFT/M06/6-31G+(d,p) levels of theory were adopted for the metal ions and for every other element respectively. Structural analyses of investigated complexes have revealed square planar geometries stabilized by two O–H⋯Cl hydrogen bond...

We discuss the derivation and interpretation of a generalized surface phase diagram, based on first-principles density-functional calculations. Applying the approach to hydrogenated GaN surfaces, we find that the Gibbs free energies of relevant reconstructions strongly depend on temperature and pressure. Choosing chemical potentials as variables results in a phase diagram that provides immediat...

The relative stability of the different tautomers of hydantoin has been studied through the use of DFT method. The structures and the vibrational frequencies of all stable tautomers and all the transitions states connecting between them have been calculated at the B3LYP/6-311+G(d,p) level of theory in the gas phase and selected solvents using IE-PCM model. Final energies have been obtained in s...

Structures and spectra are calculated for Si(n) and Si(n)-Gly (n = 3-5) complexes. Relative stability differences of Gly conformers are magnified by interactions with the Si(n) cluster, so that one conformer of Si(n)-Gly is stabilized. Significant charge transfer occurs from the amino group in Gly to a Si atom in the cluster. Interactions with Gly are predicted to shift the excitation energies ...

Collision cross-sections of gas-phase (CsI)n = (1-7)Cs(+) cluster ions formed by pulsed-UV laser (355 nm) desorption ionization are measured by ion mobility-mass spectrometry. Experimental collision cross-sections are compared with calculated cross sections of candidate structures generated from a search for the lowest energy structures at the DFT/B3LYP/LACV3P** and MP2/LACVP3P** levels. The re...

Glycine, Alanine and Valine are taken as amino acids with an equal polar head and with thedifference in the length of hydrocarbon chains. The structural optimizations show the results of theisolated Glycine, Alanine and Valine in the gases phase, at the Hartree-Fock level by means ofSTO-3G,3-21G, 6-31G and 6-31+G basis sets. The calculations were performed for the ten (1-10)solvents using PCM m...