In of L-tyrosine with quatenary ammonium b-cyclodextrin is drawn

In the earlier works, the task of charges in inclusion complex
formation of cyclodextrin has been investigated in terms of electrostatic
interactions, hydrogen bonding and steric effects between the host and the
guest molecules. Chosen guest molecules for investigation L- and D enantiomers
of amino acids. The latter is particularly interesting from point of view of
the applications in biological systems. In case of amino acids the stability of
the associates can be the result of various effects: the hydrophobic part can
enter the cavity, whilst the hydrated amino acid moiety remains outside of the
ring and can take part in electrostatic and hydrogen bonding interactions,
depending on the different ionization states according to the pH of solution.
On the other hand, enantiomers of these compounds permit of the investigation
of chiral recognition. Aim was to investigate the structure of some amino acid &
complex, which has higher stability constant.

Investigation of complexes of
alpha-amino acids by diverse techniques like Potentiometric method and
1H and 13C NMR spectroscopy concluded that amino
acids can be classified into three types. The
utmost stability constants have been obtained for phenylalanine, tyrosine and tryptophan, in
accordance with the expectations: the presence
of the aromatic side group is especially favourable for complex formation. Complexes of leucine have also a
considerable stability in the middle
range. The lowest stabilities are set up for the smallest or most hydrophilic compounds as threonine, and
aspartic acid, glutamic acid and histidine.
The complexes are characterized by stability constants. A
significant raise of the stability constants as compared to the native
cyclodextrin has been found only in the case of the anionic forms of tyrosine,
L-aspartic acid and L-glutamic acid with quaternary ammonium cyclodextrin. This
can be understood considering that in these cases hydrogen bonding is possible
with both rims of the cyclodextrin, in addition to the improved electrostatic
attraction. This effect can overcompensate steric hindrance of the
substituents, resulting in deeper penetration of guest moiety. The results
confirm deeper insertion of phenolate ring of tyrosine in the cyclodextrin
cavity and the stronger interaction between the functional groups of the amino
acid anion and the primary alcoholic group(s) of the cyclodextrin 515.  A probable structure of the
complex of L-tyrosine with quatenary ammonium b-cyclodextrin is drawn in the review investigation as 

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