Guanidinium cation

H a NH arginine guanidinium cation N,Nbis (adamantyl-oxycarbonyl) = Adoc pH< 10 iQA. H+... 

The strong stereoelectronic effect of vicinal nN donors is also evident in the product guanidinium cation,... 

Figure 3.70 The equilibrium guanidinium cation, (NH2)3C+, (a) side view and (b) top view. Each amino group is feathered by 12.5° with respect to the planar CN3 skeleton in the propeller-like (C3) equilibrium geometry.

Fig. 12 An example of guanidinium-sulfonate superstructures. The fundamental interaction responsible for both robustness and flexibility is the charge-assisted (+)N-H---0( ) hydrogen bonding between the guanidinium cations and the sulfonate anions, which can be varied in shape and length [44]...

Fig. 22 Hydrogen bonded ladder structure of ((NH2)3C)(CH3CN n CTV)[Co(C2B9Hn)2] 41 with N-H...OMe hydrogen bonding between guanidinium cations and CTV [90]... 

Arginine is another example of an a-amino acid in which guanidine and amine functions are separated by a chain of four carbon atoms. Raczynska and coworkers86 suggested that the strong gas-phase basicity of arginine (comparable to the GB of DBN) may be due to the internal solvation of the guanidinium cation, 48. 

The general affinity of guanidinium cations for oxoanions and the spatial direction of the two NH-protons makes the bicycloguanidinium core presented in the preceding chapters also a useful building block for the design of nucleotide receptors [96]. Besides carboxylates (see Sect. 2), bis(naphthoyl) host 12a binds several phophoesters in chloroform, for example, l,r-binaphthyl-2,2 -diyl phosphate the complex of the (S)-enantiomer is shown in formula 64. Still, despite the chiral nature of 12a, no enatioselectivity was observed [97]. 

Guanidine, H2N(G=NH)NH2, is the amidine of carbamic acid, H2N(CO)OH. Guanidine forms three types of complexes with metals cationic (in which the guanidinium cation is formed by taking up a proton), adducts with neutral molecules or coordination products with ionic salts, and substitution products. A brief account of each type is presented below. 

Fig. 2.64 Guanidinium cation as represented in chlorhexidine molecule, and one form of tautom-erism (a total of ten tautomers) to form the cation in equilibrium with other tautomer arrangements (calculated total of 10)...

Schmuck, C., How to improve guanidinium cations for oxoanion binding in aqueous solution The design of artificial peptide receptors , Coord. Chem. Rev. 2006, 250, 3053-3067. 

H NMR titrations revealed that association of 23 with acetate was so strong that accurate determination of the association constants became difficult (in DMSO-c/g/50% H20 association constant of the order of 103 M 1). A simple guanidinium cation titrated in the same conditions showed no signs of association, whilst an acetyl derived guanidinium cation produced association constants of around three times lower. 

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