Interactions of NAs with Small Molecules

Adsorption enthalpies and vibrational frequencies of small molecules adsorbed on cation sites in zeolites are often related to acidity (either Bronsted or Lewis acidity of H+ and alkali metal cations, respectively) of particular sites. It is now well accepted that the local environment of the cation (the way it is coordinated with the framework oxygen atoms) affects both, vibrational dynamics and adsorption enthalpies of adsorbed molecules. Only recently it has been demonstrated that in addition to the interaction of one end of the molecule with the cation (effect from the bottom) also the interaction of the other end of the molecule with a second cation or with the zeolite framework (effect from the top) has a substantial effect on vibrational frequencies of the adsorbed molecule [1,2]. The effect from bottom mainly reflects the coordination of the metal cation with the framework - the tighter is the cation-framework coordination the lower is the ability of that cation to bind molecules and the smaller is the effect on the vibrational frequencies of adsorbed molecules. This effect is most prominent for Li+ cations [3-6], In this contribution we focus on the discussion of the effect from top. The interaction of acetonitrile (AN) and carbon monoxide with sodium exchanged zeolites Na-A (Si/AM) andNa-FER (Si/Al= 8.5 and 27) is investigated. 

In the absence of Ca2+e, a-LTX only binds to LPH1 and PTPc. Ca2+-independent exocytosis requires the presence of Mg2+ and toxin insertion into the plasma membrane, but these conditions also induce formation of a-LTX channels. Influx of Na+ and efflux of K+ through these channels and associated efflux of small molecules and influx/efflux of water may cause secretion. In addition, transmitter release can be caused by membrane perturbation or direct interaction with secretory machinery. Some secretion may be nonvesicular. Receptor-mediated signaling can cause the activation of PKC in some cells. However, Ca2+-independent release is blocked by La3+, indicating that toxin pores play a crucial role in this release. 

This technique has widely been applied in a series of papers by Clementi and coworkers for the description of the solvation of amino acids, peptides as well as of RNA, DNA and their constituents (for reviews see 161 l62>). The interactions of some cations with these types of molecules were also described 163 166>. Pair potentials between small model molecules and the cations Li+ 62), Na+ 167), K+ l68), NII4+ I68), Mg2+ 98> and Ca2 + 98) were developed in order to describe ion-ionophore interactions169>. 

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