Phase guanidinium cations

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. 

A thermodynamic datum that could be of interest for comparison with data for other cations is the enthalpy of hydration of the guanidinium cation, Ahy //°(GuH+). For its calculation are needed the enthalpy of formation of the gaseous cation, Af//°(GuH+,g) and that of the aqueous one, Af//°(GuH+,aq). For obtaining the former, its formation from guanidine by protonation in the gas phase ... 

The (Guanidinium Cl )iO salt at the interface and in the pure liquids Guanidinium cations are surface active and tend to stack in the aqueous phase. 

As expected for lipophilic guanidinium cations/ both 13 and 14 extract carboxylates from aqueous into organic phases, presumably exchanging for chloride. As hoped, this can happen with significant enantioselectivity for amino acid derivatives. Table 4 summarises the results from a series of experiments employing A -acetyl a-amino carboxylates 15. The selectivities are not exceptional, but are close to the best previously reported for extractions of amino acid derivatives. Considering the variations possible on the theme of 12, we can reasonably hope for improved performance in future, more refined versions of the system. 

Fig. 13 Diversity-oriented synthesis of-guanidinium-based cationic lipids by divergent solid-phase assembly [158]...

Bipyridinium cation 9 [58], phosphonium [59-62], guanidinium [63], and vina-midinium [64] cations were used to form thermotropic ionic liquid crystals. For example, the mixture of diheptyl and dioctyl viologens 9 (20 80 by wt%) with TFSI anion forms a smectic A phase between 22° and 132°C. It was reported that the viologens show fluorescence in both non-polar and polar organic solvents, which can be useful for the development of biological and chemical sensors [65]. 

Oligonucleotide complex stability has also been enhanced with cationic deoxynucleic and ribonucleic guanidine backbones (DNG and RNG) (Figure 127), which are electrostatically attracted to the anionic phosphodiester backbone of natural chains within a complex (substituted guanidinium linkages have also been investigated715). Through both solution-716-718 and solid-phase synthesis,719 722 pentameric DNG T... 

Lu et al. used calix[4]arene derivatives with two ammonium (25) or guanidinium functionalities (26) at opposite sides of the lower rim to form stable monolayers. Inside the layer the amphiphiles are orientated orthogonal to the air-water interface (Fig. 24.10). With their cationic moieties immersed in the water phase the calixarene derivatives are able to recognize nucleotides in the subphase. The properties of the monolayer along with the recognition potential for 5 -AMP and 5 -GMP were analyzed at the film balance by means of surface pressure-area tz-A) isotherms and relaxation experiments as well as UV, CD, TR-IR spectra and X-ray photoelectron spectra. Due to their strong molecular interactions nucleotides can even be transferred onto solid substrates along with the monolayers. The... 

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