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Chapter VI UV-Vis Spectroscopic….
form an internal salt called a zwitterion. The zwitterion has no net charge;
there is one positive (COO - ) and one negative (NH3 + ) charge. On the basis of
the nature of their side chains amino acids can be characterized as follows:
(i) Non-polar side chains (ii) Polar side chains (iii) Charged side chains
Out of three selected amino acids, viz., L-histidine, L-threonine and DL-
methionine; L-histidine (NH-CH=N-CH=C-CH2-CH (NH2)-COOH) and L-
threonine (CH3-CH (OH)-CH (NH2)-COOH) have polar and uncharged side
chains. L-histidine has heterocyclic aromatic amine group and also its
imidazole group shows some degree of pH-dependent ionization, whereas, L-
threonine has hydroxyl groups. DL- methionine (CH3-S-(CH2)2-CH (NH2)-
COOH) has non-polar larger side chains and strongly hydrophobic [34].
Figure (6.5) shows the molecular structure of these selected amino-acids.
Figure:6.5 Molecular structure of L-histidine (a), L-threonine (b) and DL-methionine (c).
In the present investigation, non linear optical property of pure and
various Wt % doped different amino acids (L-histidine, L-threonine and DL-
methionine) in KDP crystals was studied by Kurtz powder method using the
fundamental beam of 1064 nm from Nd:YAG laser.
An intense green radiation of 532 nm was observed from the pure and
different amino acids doped KDP crystals confirming the second harmonic
generation (SHG).
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