Ab Initio and DFT Computational Study …
223
in vacuo and in the three solvents; however, the difference with the second lowestenergy conformer is so small as to be below experimental errors. The parameters of
the first IHB (Tables S48–S50; Figs. S43–S45) show some changes in solution with
respect to in vacuo. Both the H15···O14 and the H17···O14 lengths are slightly smaller
in chloroform than in vacuo, slightly smaller in acetonitrile than in chloroform, and
the same in acetonitrile and water, for nearly all conformers. A similar trend appears
for the O···O distance. The O ˆ
HO bond angle increases slightly as the medium polarity increases. The distance between the H atom of the donor OH and the closest C
atom in the acceptor aromatic B ring for the O–H···π IHBs (H15···C23 or H16···C23,
Tables S51–S53; Figs. S46–S48) decreases slightly from vacuum to chloroform to
acetonitrile for the first four lowest energy conformers and increases slightly for
higher energy conformers, with the only exception of cis-DBPO-s-w-ε-q-a; the values in acetonitrile and in water are the same. The dipole moment of the conformers (Tables S54–S56; Figs. S49–S51) increases as the medium polarity increases,
consistently with commonly observed trends; the difference between the values in
acetonitrile and in water is small. The HOMO-LUMO energy gap (Tables S57–S59;
Figs. S52–S54) slightly decreases as the medium polarity increases; the minimum
and maximum HOMO-LUMO energy gaps in solution occur for the same conformers
despite the different permittivities of the solvents.
Tables S60–S74 and Figs. S55–S69 compare the same properties in the four
media for the conformers with different geometries of R and the same geometry
of ABDE: conformers’ relative energies (Tables S60–S62; Figs. S55–S57); parameters of the H15···O14 first IHB (Tables S63–S65; Fig. S58–S60); H16···C23 distance for the H16···π interaction (Tables S66–S68; Figs. S61–S63); dipole moment
of the conformers (Tables S69–S71; Figs. S64–S66); and HOMO-LUMO energy
gap (Tables S72–S74; Figs. S67–S69). The relative energies decrease slightly as
the medium polarity increases. The H16···C23 distance for the H16···π interaction
decreases slightly from vacuum to chloroform to acetonitrile and has the same value
in acetonitrile and in water. The trends of the other quantities (parameters of the
H15···O14 first IHB, dipole moment, HOMO-LUMO energy gap) are similar to
those of the conformers with the same geometry of R and different geometries of
ABDE. The values of these quantities in acetonitrile and in water are nearly always
so close that their curves overlap in the graphs highlighting trends, for both the conformers with the same geometry of R and different geometries of ABDE and the
conformers with different geometries of R and the same geometry of ABDE.
The solvent effect (free energy of solvation, G solv , Tables S75–S80; Figs. S70–
S75) is positive in acetonitrile and negative in chloroform and water for all the
three molecules, with the magnitude of G solv being considerably greater in water
than in chloroform. This is consistent with the other findings for ACPLs [14, 15].
A quick evaluation of the octanol/water partition coefficients [38] yields 8.30663
for MYRA and 8.88063 for both c-DBPO and t-DBPO, which suggests very poor
solubility in water; this can be related to the bulk and to the high molecular mass of the
molecules. The negative values of G solv in water are likely related to the presence of
five OH groups, which favour interactions with water molecules; they also suggest
the possibility of some presence of these molecules in the aqueous medium in a
223
in vacuo and in the three solvents; however, the difference with the second lowestenergy conformer is so small as to be below experimental errors. The parameters of
the first IHB (Tables S48–S50; Figs. S43–S45) show some changes in solution with
respect to in vacuo. Both the H15···O14 and the H17···O14 lengths are slightly smaller
in chloroform than in vacuo, slightly smaller in acetonitrile than in chloroform, and
the same in acetonitrile and water, for nearly all conformers. A similar trend appears
for the O···O distance. The O ˆ
HO bond angle increases slightly as the medium polarity increases. The distance between the H atom of the donor OH and the closest C
atom in the acceptor aromatic B ring for the O–H···π IHBs (H15···C23 or H16···C23,
Tables S51–S53; Figs. S46–S48) decreases slightly from vacuum to chloroform to
acetonitrile for the first four lowest energy conformers and increases slightly for
higher energy conformers, with the only exception of cis-DBPO-s-w-ε-q-a; the values in acetonitrile and in water are the same. The dipole moment of the conformers (Tables S54–S56; Figs. S49–S51) increases as the medium polarity increases,
consistently with commonly observed trends; the difference between the values in
acetonitrile and in water is small. The HOMO-LUMO energy gap (Tables S57–S59;
Figs. S52–S54) slightly decreases as the medium polarity increases; the minimum
and maximum HOMO-LUMO energy gaps in solution occur for the same conformers
despite the different permittivities of the solvents.
Tables S60–S74 and Figs. S55–S69 compare the same properties in the four
media for the conformers with different geometries of R and the same geometry
of ABDE: conformers’ relative energies (Tables S60–S62; Figs. S55–S57); parameters of the H15···O14 first IHB (Tables S63–S65; Fig. S58–S60); H16···C23 distance for the H16···π interaction (Tables S66–S68; Figs. S61–S63); dipole moment
of the conformers (Tables S69–S71; Figs. S64–S66); and HOMO-LUMO energy
gap (Tables S72–S74; Figs. S67–S69). The relative energies decrease slightly as
the medium polarity increases. The H16···C23 distance for the H16···π interaction
decreases slightly from vacuum to chloroform to acetonitrile and has the same value
in acetonitrile and in water. The trends of the other quantities (parameters of the
H15···O14 first IHB, dipole moment, HOMO-LUMO energy gap) are similar to
those of the conformers with the same geometry of R and different geometries of
ABDE. The values of these quantities in acetonitrile and in water are nearly always
so close that their curves overlap in the graphs highlighting trends, for both the conformers with the same geometry of R and different geometries of ABDE and the
conformers with different geometries of R and the same geometry of ABDE.
The solvent effect (free energy of solvation, G solv , Tables S75–S80; Figs. S70–
S75) is positive in acetonitrile and negative in chloroform and water for all the
three molecules, with the magnitude of G solv being considerably greater in water
than in chloroform. This is consistent with the other findings for ACPLs [14, 15].
A quick evaluation of the octanol/water partition coefficients [38] yields 8.30663
for MYRA and 8.88063 for both c-DBPO and t-DBPO, which suggests very poor
solubility in water; this can be related to the bulk and to the high molecular mass of the
molecules. The negative values of G solv in water are likely related to the presence of
five OH groups, which favour interactions with water molecules; they also suggest
the possibility of some presence of these molecules in the aqueous medium in a