Binding molecular entity with

Second, since the small number of atoms bind firmly to the underlying support, it may be more appropriate to regard the nanocluster as a molecular entity with its activity and selectivity being more like that of multinuclear single-site catalysts, such as that found in many metalloenzymes, e.g., hydrogenases, than of a bulk metal or alloy. 

The requisite research issues essential to the creation of fluorescent chemosensors are (1) how can one bind a molecular entity with selectivity (preferably from water), (2) what molecular changes result in fluorescence changes, and (3) what mechanisms for binding and fluorescence signal transduction intersect. 

Binding a Molecular Entity with Selectivity. While much of organic chemistry focusses on the selective creation of covalent bonds, such irreversible associations of potential analytes yield chemodosimeters (designed for cumulative assay) in contrast to chemosensors (designed for real-time assay). Thus, sensing applications require the existence of receptors (hosts) that associate with analytes (guests) selectively and reversibly. 

The binding, reaction, or interception of a reactive molecular entity or transitory intermediate in a reaction pathway to convert the substance to a more stable form and/or remove that substance from the system. Trapping may involve binding or reaction with another molecular entity or involve the alteration of some parameter (e.g., thermal trapping) ... 

It is very likely an inaccuracy to call the D-l dopamine receptor an enzyme. Because of the effects of guanine nucleotides on dopamine-stimulated adenylate cyclase, it is likely by analogy with other receptors (i.e. the 3 receptor) that the D-l receptor is a distinct molecular entity which is coupled to adenylate cyclase by a guanine nucleotide binding subunit. Proof of this point, of course, will require physical separation of these entities. 

Upon reaction with an adsorptive in aqueous solution (which then becomes an adsorbate), surface functional groups can engage in adsorption complexes, which are immobilized molecular entities comprising the adsorbate and the surface functional group to which it is bound closely [18]. A further classification of adsorption complexes can be made into inner-sphere and outer-sphere surface complexes [19]. An inner-sphere surface complex has no water molecule interposed between the surface functional group and the small ion or molecule it binds, whereas an outer-sphere surface complex has at least one such interposed water molecule. Outer-sphere surface complexes always contain solvated adsorbate ions or molecules. Ions adsorbed in surface complexes are to be distinguished from those adsorbed in the diffuse layer [18] because the former species remain immobilized on a clay mineral surface over time scales that are long when compared, e.g., with the 4-10 ps required for a diffusive step by a solvated free ion in aqueous solution [20]. Outer-sphere surface complexes formed in the interlayers of montmorillonite by Ca2+ or Mg2+ are immobile on the molecular time scale... 

Host — A - molecular entity that forms an -> inclusion complex with organic or inorganic -> guests, or a - chemical species that can accommodate guests within cavities of its crystal structure. Examples include cryptands and crowns (where there are -> ion-dipole interactions between heteroatoms and positive ions), hydrogen-bonded molecules that form clathrates (e.g., hydroquinone and water), and host molecules of inclusion compounds (e.g., urea or thiourea). The - van der Waals forces and hydrophobic interactions (- hydrophobic effect) bind the guest to the host molecule in clathrates and inclusion compounds. 

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