Energetics Of Complex Formation Research Articles

Exceptional Hydrogen Uptake in Crystalline InxGa1-xN Semiconductors.

The irradiation of InN and InxGa1-xN samples with low-energy H ions results in exceptionally high hydrogen uptake in a crystalline semiconductor. This phenomenon is attributed to specific In-H complex formation. By exploiting spectral fingerprints of the In-H complexes observable in In L3-edge X-ray absorption spectroscopy, we provide direct evidence of complex formation. Density functional theory calculations assist in interpreting the X-ray absorption spectra and offer insights into the energetics of complex formation. We quantify the total amount of reversibly incorporated hydrogen in these semiconductors and discuss their strengths and weaknesses as innovative materials for hydrogen storage.

PROBING αIIbβ3: LIGAND INTERACTIONS BY DYNAMIC FORCE SPECTROSCOPY AND SURFACE PLASMON RESONANCE

The interaction between platelet integrin αIIbβ3 and fibrin(ogen) plays a key role in blood clot formation and stability. Integrin antagonists, a class of pharmaceuticals used to prevent and treat cardiovascular disease, are designed to competitively interfere with this process. However, the energetics of the integrin-drug binding are not fully understood, potentially hampering further development of this class of pharmaceuticals. We integrated dynamic force spectroscopy (DFS) and surface plasmon resonance (SPR) to probe the energetics of complex formation between αIIbβ3 and cHarGD, a cyclic peptide integrin antagonist. Analysis of αIIbβ3:cHarGD DFS rupture force data at pulling rates of 14 000 pN/s, 42 000 pN/s and 70 000 pN/s yielded koff = 0.02-0.09 s-1, a dissociation energy barrier [Formula: see text] = 22-29 kJ/mol, and a potential well width x-1 = 0.5-0.8 nm. SPR kinetic data yielded an association rate constant kon = 7 × 103 L/mol-s and a dissociation rate constant koff = 10-2 s-1, followed by a slower stabilization step (τ ~ 400 s). Both DFS and SPR detected minimal interactions between αIIbβ3 and cHarGA demonstrating a key role for electrostatic interactions between the ligand aspartate and the integrin metal ion-dependent adhesion site (MIDAS). Our work provides new insights into the energy landscape of αIIbβ3's interactions with pharmacological and physiological ligands.

Analysis of supramolecular complex energetics in artificial replicators

The energetics of complex formation in a number of artificial self-replicating systems has been studied by density functional theory calculations. Complex stabilities were dissected into stabilizing contributions from hydrogen bonding, dispersion, electrostatics, and destabilizing distortions of monomers from their optimum geometries. Strong cooperative effects were identified in all systems, and dispersion and electrostatics contribute more to the overall energies of complex formation than hydrogen bonding in some systems.

Contribution of enthalpy to the energetics of complex formation of aromatic ligands with DNA

The energy contributions of electrostatic, van der Waals interactions, hydrogen bonds, and interactions of charge transfer type to the enthalpy of complex formation of the double-stand DNA with the antitumor antibiotics daunomycin, nogalamycin, and novantron, as well as the mutagens ethidium bromide and proflavine have been calculated. According to the calculations, the van der Waals component (except for nogalamycin) is energetically favorable during complex formation of the antibiotics with DNA, and the contributions of H bonds and electrostatic interactions are unfavorable, with the probability of charge transfer in the complexes being low. It has been shown that the relatively low value of the experimental enthalpy of binding is the sum of components greater in absolute value and different in the sign, which is the cause of large errors in estimating the total enthalpy of complex formation of aromatic ligands with DNA.

Comparative study of semiempirical methods for calculating interactions between large molecules with an application to the actinomycin-Guanine complex

A comparison of semiempirical variational and perturbation calculations of intermolecular interactions is presented. The results are compared with ab initio rhf calculations, ab initio perturbation calculations, and with experiments for systems representing hydrogen bonding, electron donor-acceptor complexes, incipient chemical reactions, and π-π stacking interactions. The failure of CNDO supermolecule calculations is discussed. Various approaches to a perturbation scheme using CNDO wave functions are investigated and an optimal method is suggested. The calculation of the stacking interactions in the deoxyguanosine actinomycin D complex suggests that a dual charge-transfer complex is formed. The experimental observation of two inequivalent binding sites on the actinomycin chromophore is interpreted in terms of the calculated energetics of complex formation.