Guanidium groups

So far we have discussed only the nucleic acid portion of nucleoproteins. There is evidence that in one nucleoprotein (found in fish perm), a polyarginine chain lies in one of the grooves of the double helix, held by electrostatic forces between the negative phosphate groups of the polynucleotide (which face the outside of the helix) and the positive guanidium groups of the arginine residues. 

Since PYP is one of the most well-characterized photosensors it has attracted a lot of attention from computational chemists. Robb et al. have used a QM/MM molecular dynamics strategy to examine the complete photocycle of PYP [12]. By comparing the behavior of the chromophore in vacuo with that of the chromophore within the protein they were able to determine the chemical role of the protein cavity. They found that CTI of the chromophore does not occur in vacuo, however in the protein the isomerization is facilitated by electrostatic stabilization of the chromophore s excited state with the guanidium group of Arg52 that lies just above the negatively charged phenolate of the chromophore. 

Bocchi et al. [5] pointed out that while the tetraacetate of p-/ T/-butyl calix[4]arene fails to form complexes with guanidium ions or Cs, the octa-(3,6-dioxaheptyl)-ether of p-/cr/-butyl calix[8]arene forms strong complexes with these cations. The Parma group [6] later showed that the hexa-(3-oxabutyl)ether of p-tert-hu y calix[6]arene also forms complexes with these ions. 

Solid state analysis of crystals obtained of receptor with acetate from water/methanol solutions reveal that once again the guanidiniocarbonylpyrrole cation exists in an extended conformation however in contrast to the proposed solution state model, the pyrrole NH points away from the guanidium NHs with the acetate anions bound by two separate receptor groups with solvent molecules helping to create a series of 2D arrays (figure 23c). 

IR spectrometry is the analytical technique for determination of functional groups of TTX. IR spectra of TTX are measured in a KBr pellet, using a JASCO model IR-S spectrophotometer (Tokyo) (Onoue et ah, 1984). Figure 11 represents an IR spectrum of puffer toxin, showing characteristic absorption in 3360 (OH), 3200,1660 (guanidium), 1610 (COO", and 1075 cm ... 

As already highlighted in the partial list of Scheme 20, various groups of compounds may act as precursors alkali metals alkali metal hydrides, oxides, hydroxides, alkoxides, halides, carbonates alkali metal salts of organic acids alkyl aluminums alkali aluminum hydrides and their alkoxides quaternary ammonium salts guanidium salts of lactams, etc. 

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