Interactions n-stacking

The physicochemical properties of a molecular precursor depend on the inter-molecular forces such as van der Waals interactions, n -stacking, or hydrogen bonding, which induces an interaction of metal ion with k donor ligands by adopting a... 

Currently, such planar polyfused heterocycles with pyrrole or indole fragments capable of charge transfer, hydrogen bond formation, and interplane self-assembling via 7T-7t interaction (n-stacking) attract great interest as potential DNA-interactive... 

Pyrroles are widely employed for the synthesis of 4,4-difluoro-4-bora-3a,4a-diaza-5-indacenes (BODIPY) fluorophores [639], BODIPYs bearing sterically hindered substituents that prevent intermolecular n-electron interaction (n-stacking) attract a special attention. 

The pentafluorophenyl group imparts greater crystallinity to the complexes and as a result many complexes have been studied by X-ray crystallography. Although vith other metal centers C Fs-CaFs or CfiFs-CfiHs n-n stacking interactions are observed [21, 22], there are not many examples in gold chemistry and they have been sho vn very recently [23]. 

These structural features observed for [Fe(abpt)2(TCNQ)2] involving pronounced and extended n-n stacking interactions lead to a duality with respect to its gradual spin crossover behaviour. It has generally been accepted that extended n-n interactions may lead to the occurrence of thermal hysteresis in mononuclear Fe(II) spin crossover compounds [62-65]. Clearly, the requirements responsible for cooperative Fe(II) spin crossover behaviour are not easy to define, since obviously [Fe(abpt)2(TCNQ)2] represents an exception to this rule in spite of the pronounced TCNQ n-n stacking interactions, the Fe(II) spin crossover displays at best weak cooperativity. 

The great majority of transitions observed for iron(III) are gradual and the observation of thermal hysteresis associated with them is relatively rare. In the only instances where features indicative of significant cooperativity have been reported, extensive hydrogen-bonding networks (formed in some thiosemicarbazone compounds [111, 115,118, 119]) or n-n stacking interactions (operative in several compounds of N20 Schiff base systems [135-138, 164, 165]) have been invoked as the origin of the cooperativity. 

The forces that stabilize amyloid fibrils include specific hydrogen bonding, electrostatic interactions, n-n stacking, and hydrophobic interactions. Importantly, similar types of interactions stabilize the functional native structures of protein molecules (Anfinsen, 1973 Dill, 1990 Dobson and Karplus, 1999 Kauzmann, 1959). In this sense, the conditions that favor native protein folding might also be manipulated to facilitate the formation of amyloid fibrils. 

To estimate the dispersion interaction contribution to the overall interaction between stacked rings we studied, in parallel with the role of electrostatics in Section 27.3.2, the interaction between monosubstituted benzenes Ph-X (X = H, F, NH2, Cl, CH3, OH, CN, COOH, CHO, N02) and pyridine, a simpler case with only one H-bond accepting site [58], and cytosine (with two H-bond accepting sites). An offset parallel geometry was chosen, keeping the X group and the N atom of pyridine at maximal distance, the level used being MP2/6-31G (0.25)//MP2/6-31G with BSSE correction [68]. 

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