180
L. Mammino
suitable option to highlight differences depending on the entire molecular structure,
because the ion does not come close to other parts of the molecule.
The lowest natural charges are observed when the ion binds only to a π bond,
although this is the third preferred binding site only for HPJA, while it falls in the
high-relative-energy region for the other molecules. This points to great reducing
ability of the π bond and is consistent with the importance of the presence of a π
bond in a substituent for the antioxidant activity of polyhydroxybenzenes [14, 16].
The distances of the ion from its binding site/s in the lowest energy complex of
the four molecules are comparable (somewhat longer for FNGB). The distances in
the other complexes selected for comparison are fairly similar.
The length of the first IHB increases considerably when the ion binds to O14 and
the red shift in the vibrational frequency of the donor OH decreases sharply (both
phenomena indicating considerable weakening of the first IHB); the decrease for
HPGB and FNGB is more than double with respect to the decrease for HPJA and
ARZ. As for the other IHBs, they often weaken, although to a much less extent than
the first IHB. There are also complexes where the length of some IHBs decreases
and the corresponding red shift increases (indicating strengthening of the given IHB).
The greatest noted increases in the red shift concern O8–H15 for all these molecules,
but correspond to different binding sites of the ion in different molecules.
The ranges of the free energy of solvation are basically comparable for the
complexes of all these molecules in the same solvent.
Table S21 summarises the same features considered in table S20, for a molecule
(1-[3-geranyl-2,4,6-trihydroxyphenyl]-2-methylpropan-1-one, GTM [58]), that does
not have additional OH groups or O atoms, and differs from HPJA only because R
has
the two π bonds typical of a geranyl chain, does not have the additional OH present
in HPJA, but maintains the methyl at C18. The values of the considered features are
comparable with those of the complexes of HPJA, ARZ, HPGB and FNGB. The main
differences relate to the absence of the additional OH and the presence of two π bonds
in R
; for instance, the three lowest energy complexes involve simultaneous binding
to both π bonds (the two lowest energy ones also entailing additional simultaneous
binding to either O8 or O10).
The results for the complexes of FNGB with a Cu
2+ ion presented here add to those
obtained for the complexes of other ACPLs with substantially different molecular
structures [6–8, 58, 59]. Altogether, the results highlight a number of similarities
in the behaviour of ACPLs on complexation with a Cu
2+ ion, thus contributing
information both about ACPLs and about the effects of complexation with a metal
ion in general.
References
1. Singh IP, Bharate SB (2006) Nat Prod Rep 23:558–591
2. Heilmann J, Winkelmann K, Sticher O (2003) Planta Med 69:202–206
3. Winkelmann K, Heilmann J, Zerbe O, Rali T, Sticher O (2000) J Nat Prod 63:104–108
L. Mammino
suitable option to highlight differences depending on the entire molecular structure,
because the ion does not come close to other parts of the molecule.
The lowest natural charges are observed when the ion binds only to a π bond,
although this is the third preferred binding site only for HPJA, while it falls in the
high-relative-energy region for the other molecules. This points to great reducing
ability of the π bond and is consistent with the importance of the presence of a π
bond in a substituent for the antioxidant activity of polyhydroxybenzenes [14, 16].
The distances of the ion from its binding site/s in the lowest energy complex of
the four molecules are comparable (somewhat longer for FNGB). The distances in
the other complexes selected for comparison are fairly similar.
The length of the first IHB increases considerably when the ion binds to O14 and
the red shift in the vibrational frequency of the donor OH decreases sharply (both
phenomena indicating considerable weakening of the first IHB); the decrease for
HPGB and FNGB is more than double with respect to the decrease for HPJA and
ARZ. As for the other IHBs, they often weaken, although to a much less extent than
the first IHB. There are also complexes where the length of some IHBs decreases
and the corresponding red shift increases (indicating strengthening of the given IHB).
The greatest noted increases in the red shift concern O8–H15 for all these molecules,
but correspond to different binding sites of the ion in different molecules.
The ranges of the free energy of solvation are basically comparable for the
complexes of all these molecules in the same solvent.
Table S21 summarises the same features considered in table S20, for a molecule
(1-[3-geranyl-2,4,6-trihydroxyphenyl]-2-methylpropan-1-one, GTM [58]), that does
not have additional OH groups or O atoms, and differs from HPJA only because R
has
the two π bonds typical of a geranyl chain, does not have the additional OH present
in HPJA, but maintains the methyl at C18. The values of the considered features are
comparable with those of the complexes of HPJA, ARZ, HPGB and FNGB. The main
differences relate to the absence of the additional OH and the presence of two π bonds
in R
; for instance, the three lowest energy complexes involve simultaneous binding
to both π bonds (the two lowest energy ones also entailing additional simultaneous
binding to either O8 or O10).
The results for the complexes of FNGB with a Cu
2+ ion presented here add to those
obtained for the complexes of other ACPLs with substantially different molecular
structures [6–8, 58, 59]. Altogether, the results highlight a number of similarities
in the behaviour of ACPLs on complexation with a Cu
2+ ion, thus contributing
information both about ACPLs and about the effects of complexation with a metal
ion in general.
References
1. Singh IP, Bharate SB (2006) Nat Prod Rep 23:558–591
2. Heilmann J, Winkelmann K, Sticher O (2003) Planta Med 69:202–206
3. Winkelmann K, Heilmann J, Zerbe O, Rali T, Sticher O (2000) J Nat Prod 63:104–108