Recognition ligand systems

Electrochemical recognition, 39 80 anions, macrocyclic and acyclic polycobalti-cinium ligand systems, 39 134-140 cations, 39 81-133 ammonium cation, 39 128-133 crown ether and bis crow ether ligands containing bipyridyl transition metal recognition sites, 39 111 crown ether dithiocarbamate and dithi-olene complexes, 39 123-124 di-h-cyclopentadienyl-molybdenum(IV) and -tungsten(IV) crown ether complexes, 39 107-108... 

Guanidinium and imidazolium ions are also recognized by the appropriate ligand system.22 230 These planar ions are surrounded by suitably sized macrocycles which are capable of circular recognition as shown in (60). The size of the [27]crown-9 is structurally ideal for complexation of... 

Abstract Carbohydrates have been investigated and developed as delivery vehicles for shuttling nucleic acids into cells. In this review, we present the state of the art in carbohydrate-based polymeric vehicles for nucleic acid delivery, with the focus on the recent successes in preclinical models, both in vitro and in vivo. Polymeric scaffolds based on the natural polysaccharides chitosan, hyaluronan, pullulan, dextran, and schizophyllan each have unique properties and potential for modification, and these results are discussed with the focus on facile synthetic routes and favorable performance in biological systems. Many of these carbohydrates have been used to develop alternative types of biomaterials for nucleic acid delivery to typical polyplexes, and these novel materials are discussed. Also presented are polymeric vehicles that incorporate copolymerized carbohydrates into polymer backbones based on polyethylenimine and polylysine and their effect on transfection and biocompatibility. Unique scaffolds, such as clusters and polymers based on cyclodextrin (CD), are also discussed, with the focus on recent successes in vivo and in the clinic. These results are presented with the emphasis on the role of carbohydrate and charge on transfection. Use of carbohydrates as molecular recognition ligands for cell-type specific dehvery is also briefly... 

The nature of the solvent can also have a profound effect on the electrochemical recognition process. All of the redox-responsive ligand systems cited in this review give examples of guest cation/anion redox couple perturbations in organic solvents such as dichloromethane and acetonitile. The next challenge will be to demonstrate analogous redox-responsive behavior in the aqueous environment. 

Systemic administration of drugs in the form of nanoparticulates intravenously has been widely studied. Currently, there are some liposomal anticancer and antifungal medications in clinical use. These products show relative increase in drug bioavailability in the target sites. They are not, however, active targeting systems with recognition ligands on the surface. 

And then there is finally - besides the artificial evolutions of selecting functional nucleic acids for specific interactions with cooperative mates, high-affinic recognitions, and catalytic activities fiom random pools - the evolution of an individual scientific life s work [50], which itself follows decisive stages of the grand process the exploration of early chemical requirements, the development of prebiotic ligand systems, the fixation into the ordered structures of informational inorganic matrix patterns... 

The use of ligand systems, which allow for synergetic action of the metal centers, provides a valuable tool to study such delicate mechanisms as the binding and activation of small molecules on dinuclear metal sites. Systematic ligand variation can reveal effects of active site environment on substrate recognition and binding. The knowledge how O2 can be activated forms a basis for the development of new catalysts for mild and selective oxidation processes. 

Early examples of enantioselective extractions are the resolution of a-aminoalco-hol salts, such as norephedrine, with lipophilic anions (hexafluorophosphate ion) [184-186] by partition between aqueous and lipophilic phases containing esters of tartaric acid [184-188]. Alkyl derivatives of proline and hydroxyproline with cupric ions showed chiral discrimination abilities for the resolution of neutral amino acid enantiomers in n-butanol/water systems [121, 178, 189-192]. On the other hand, chiral crown ethers are classical selectors utilized for enantioseparations, due to their interesting recognition abilities [171, 178]. However, the large number of steps often required for their synthesis [182] and, consequently, their cost as well as their limited loadability makes them not very suitable for preparative purposes. Examples of ligand-exchange [193] or anion-exchange selectors [183] able to discriminate amino acid derivatives have also been described. 

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