Guanidyl groups

Fraenkel-Conrat H, Olcott HS. The reaction of formaldehyde with proteins. V. Cross-linking between amino and primary amide or guanidyl groups. J. Am. Chem. Soc. 1948 70 2673-2684. 

Potentiometric titration was performed in 0.1 M NaCl at 25°. Seven of the phenolic groups and a guanidyl group were not titrated. 

Compound resembling guanidyl group of arginine side chain ... 

In terms of the pK values of Table I, the alkaline end point of the titration curve is the point where all titratable groups listed in the table, except guanidyl groups, are expected to have been converted to their basic forms. 

The titration of guanidyl groups overlaps that of amino groups, so that they cannot be differentiated on inspection. 

The molecular or ionized form of benzoic acid was placed outside tbe hole and faced toward the center methyl or guanidyl group at the bottom of the pocket before starting tbe doeking as shown in Figure 3.19, then the eomplex structure was optimized to measure the direct hydrophobic and ion-ion interactions. (Me) and (GUA) indicate the center substituted groups (Me)... 

Figure 3.17 A Phase 3 GUA (C12) structure containing one guanidyl group, six methyl and 30 dodeq l groups. White, light-gray, and dark-gray balls represent hydrogen, carbon, and nitrogen, respectively.

The correlation was also very poor (r= 0.058) with nKj measured by free solution methods, even when only the most suitable values were selected. An acceptable correlation was obtained with 11K4 for acidic compounds measured using a guanidyl-group silica gel, and uRTs for basic compounds measured using a carboig l-bonded silica gel. Retention also correlated with uSTg values from ref. 57. 

Table 9.1 Capacity ratios measured on different columns. C4 represents butyl-bonded silica, SG represents guanidino-bonded silica, SA represents triethylphenylammonium-bonded silica (IXi), PG represents a guanidyl-group-bonded polyvinylalcohol copolymer (1X2), and Ph represents phenylpropyl-bonded silica. Reproduced by permission of Elsevier, ref. 36.

Log k values measured on a guanidyl-group-bonded silica gel column for acidic compounds, and on a carbo)q7l-bonded silica gel column for basic compounds correlated well with n/irs and nK4, respectively. 

---