#Amino functional group free
In particular, improved derivatization was obtained with the troublesome histidine and tyrosine: exclusively monosubstituted histidine, and disubstituted tyrosine were formed, and eluted as free peaks in the chromatogram. During this long reaction time, all amino acids gave stable derivatives. Recently, an improved method for the quantitative derivatization of AAs with FMOC was proposed, using borate buffer at pH 11.4 for 40 min, at ambient temperature. They involve applying various quenching reagents such as 1-aminoadamantane.HCl, hydoxylamine in alkaline media, or heptylamine. Instead of the time-consuming and incomplete extraction by hexane or pentane, other method for elimination of the excess reagent are preferred. Thus, an additional step in the derivatization procedure is necessary for removing excess of reagent. The disadvantages of this method are the fluorescence of the FMOC itself and of hydolysis products such as 9-fluorenylmethanol. Primary and secondary amino groups react very fast (2 min) with FMOC, in slightly alkaline solution, to give the corresponding fluorescent 9-fluorenylmethyl carbamates, which exhibit high stability (48 h, at room temperature) and very sensitive fluorescence detectability. In the case of the amino-azines, the small blue shifts observed may be due to differential stabilization of the excited state in hydroxylic solvent which outweighs the hydrogen-bonding stabilization of the ground state.
![amino functional group amino functional group](https://patentimages.storage.googleapis.com/WO2009029341A2/imgf000013_0001.png)
We discussed above the explanation for the latter phenomenon in terms of solvation stabilization which implies that we accept the view that the p-electrons of oxygen are active in the first two electronic transitions of the hydroxy-azines and we are measuring the extent of hydrogen-bonding by the solvent shift. In sharp contrast, the corresponding hydroxypyridines show red shifts of nearly 30 m μ for the change EtOH → hexane. The change from ethanol to hexane gives a blue shift of 7 m μ in the spectrum of 4-aminopyridine. 2-Aminopyridine has λ max229, 287 m μ in water and 231, 288 m μ in cyclohexane. It is instructive to compare the shifts of the maxima of the aminoazines on change from hydroxylic to hydrocarbon solvent with the corresponding hydroxy-azine shift. This is not the order predicted by the charge-transfer model but has been explained in terms of a benzyl anion model. It is also found that for a particular class of pyridine derivative, the long wave bands lie in the order 3 > 2 > 4-substituted pyridine. (XLVIII) show again the wavelength order (for a given band) zwitterion > cation > neutral form.