Molecular complexes energetics

A. Latini, D. Toja, A. Giardini Guidoni, S. Piccirillo, and M. Speranza, Energetics of molecular complexes in a supersonic beam A novel spectroscopic tool for enantiomeric discrimination. Angew. Chem. Int. Ed. 38, 815 817 (1999). 

This section will focus on the stmcture and energetics of chiral molecular complexes studied with Fourier-transform IR (FT-IR), microwave, LIF, hole burning (HB), IR fluorescence dip spectroscopy, resonance-enhanced multiphoton ionization (REMPl Fig. 5), and RET spectroscopy. 

Most protein-protein binding energies are related only to a group of a few amino acids at intermolecular protein interfaces the hot spots. The characterization of the energetics of molecular complexes, especially the detection of these hot spots is essential to structure-based drug design. 

The results of FAB-MS study of the macrobicyclic boron-capped iron(II) dioximates indicated that in the gas phase the energetics of bond rupture in their molecular complexes changes compared with... 

The existence of chiral pathways in this molecule is made possible by the existence of the two independent degrees of freedom that govern internal motion, rotation, and inversion. As molecular complexity increases, the number of degrees of freedom also increases and, unless an achiral pathway is energetically much preferred, it becomes more and more likely that enantiomerization proceeds by a chiral pathway. For example, it is extremely improbable that reversal of helicity in a polymeric chain involves an achiral intermediate or transition state. There is a strong resemblance here to the stochastic achirality of ensembles of achiral molecules discussed previously. 

The physical characterization in terms of phases, crystal structures, and molecular and electronic defects presents a different picture. The inorganic azides, simple though they may be in comparison with most energetic substances, are nonetheless molecularly complex, and the elucidation of the crystal structures has been the subject of investigation for 40 years. In the last decade important refinements to the earlier knowledge have become possible through the combined advances in chemical preparation, neutron diffraction, and computational techniques. The advances are presented in Chapter 3, and their importance to azide research is well illustrated by the frequency with which the information in that chapter is utilized in the other chapters. 

As Fig. 28 and Table 9 show, the reaction of ftCuCH2 (G) and NH3 to lose D2 is less favored energetically compared with elimination of H2 or HD. Both H2 and HD channels share the intermediate 37. The intermediate 37 evolves to a dihydrogen compound 39 with a barrier of 37.6 kcal mol for the key step from 37 to 38. The molecular complex 39 requires an energy of 32.8 kcal moP to loss H2. On the contrary, the barrier of the key step from 37 to 41 for the formation of a dihydrogen compound 42 through C-H and N-H bond activations is 14.2 kcal mol and the molecular complex 42 losses HD with an endothermicity of 16.2 kcal mol The channel to HD is thus more favorable than those to D2 and H2, both energetically... 

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