Esam A Orabi

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Proteins of the Amt/MEP family facilitate ammonium transport across the membranes of plants, fungi, and bacteria and are essential for growth in nitrogen-poor environments. Some are known to facilitate the diffusion of the neutral NH(3), while others, notably in plants, transport the positively charged NH(4)(+). On the basis of the structural data for AmtB(More)
Polarizable potential models for the interaction of Li(+), Na(+), K(+), and NH4(+) ions with benzene are parametrized based on ab initio quantum mechanical calculations. The models reproduce the ab initio complexation energies and potential energy surfaces of the cation-π dimers. They also reproduce the cooperative behavior of "stacked", cation-π-π trimers(More)
A polarizable model for ammonia is optimized based on the ab initio properties of the NH3 molecule and the NH3-NH3 and NH3-H2O dimers calculated at the MP2 level. For larger (NH3)m, NH3(H2O)n, and H2O(NH3)n clusters (m = 2-7 and n = 1-4), the model yields structural and binding energies in good agreement with ab initio calculations without further(More)
A polarizable potential model for M(+)-NH3 interactions (M(+) = Li(+), Na(+), K(+), Rb(+), Cs(+)) is optimized based on the ab initio properties of the ion-ammonia dimers calculated at the MP2 level of theory. The optimized model reproduces the ab initio binding energies of M(+)(NH3)n (n = 2-4) and M(+)(NH3)n(H2O)m (n, m = 1-3 and n + m ≤ 4) clusters and(More)
In human cells, membrane proteins of the rhesus (Rh) family excrete ammonium and play a role in pH regulation. Based on high-resolution structures, Rh proteins are generally understood to act as NH3 channels. Given that cell membranes are permeable to gases like NH3, the role of such proteins remains a paradox. Using molecular and quantum mechanical(More)
A polarizable model for hydrogen sulfide (H2S) is optimized based on the experimental properties of the monomer and of the bulk liquid. The model is characterized by rigid SH bonds but flexible HSH angle and the polarizability is based on the Drude oscillator model. Bonded parameters and atomic charges are based on the experimental properties of the gaseous(More)
  • Esam A Orabi
  • Spectrochimica acta. Part A, Molecular and…
  • 2010
The electronic absorption spectra of 3-formylsalicylic acid (3-fsa) and 5-formylsalicylic acid (5-fsa) have been studied in different pure and mixed solvents. From the pure solvent study, the Einstein transition probabilities (A(if) and B(if)), dipole moment (D(if)), oscillator strength (F(if)), life time (tau), and the molar extinction coefficient(More)
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