Reverse Solvatochromism of Imine Dyes Comprised of 5-Nitrofuran-2-yl or 5-Nitrothiophen-2-yl as Electron Acceptor and Phenolate as Electron Donor.

Eight compounds with phenols as electron-donating groups and 5-nitrothiophen-2-yl or 5-nitrofuran-2-yl acceptor moieties in their molecular structures were synthesized. The crystalline structures of six compounds were obtained. Their corresponding phenolate dyes were studied in 29 solvents and the data showed that in all cases a reverse solvatochromism occurred. The results are explained in terms of the ability of the medium to stabilize the electronic ground and excited states of the probes to different extents. The frontier molecular orbitals were analyzed for the protonated and deprotonated forms of the compounds. The calculated geometries are in agreement with the X-ray structures determined for the compounds and it was verified that after their deprotonation an increase in the electron delocalization occurs. Radial distribution functions were calculated for the dyes in water and n-hexane to analyze different solvation patterns resulting from the interaction of the solvents with the dyes. Data obtained by using the Catalán multiparameter equation revealed that the medium acidity is responsible for hypsochromic shifts, whereas the solvent basicity, polarizability, and dipolarity contributed to bathochromic shifts of the solvatochromic band of these dyes. Two model "hybrid cyanine" dyes were used in the design of simple experiments to demonstrate that the solvatochromic behavior of these dyes in solution can be tuned with careful consideration of the properties of the medium.

Structure-behavior study of a family of "hybrid cyanine" dyes which exhibit inverted solvatochromism.

The inverted solvatochromism of twenty dyes containing an electron-donor phenolate conjugated with an electron-withdrawing nitro-substituted phenyl ring was analyzed in terms of the dye structure and substituents. Structural factors that increased the difference between the electrophilicities of the donor and acceptor moieties, or the donor-acceptor strength of the phenolate dyes, also increased the sensitivity of the dyes to solvent-polarity changes and red-shifted their solvatochromic absorption bands.

Reverse solvatochromism in solvent binary mixtures: a case study using a 4-(nitrostyryl)phenolate as a probe.

A 4-(nitrostyryl)phenolate was synthesized and its use in pure solvents revealed a reversion in solvatochromism. Solutions of a dye in binary solvent mixtures, using as components the solvents in the region of the occurrence of the reversion, provided the first case in the literature of reverse solvatochromism in a binary mixture.

Antibacterial properties of 3 H-spiro[1-benzofuran-2,1'-cyclohexane] derivatives from Heliotropium filifolium.

A re-examination of cuticular components of Heliotropium filifolium allowed the isolation of four new compounds: 3'-hydroxy-2',2',6'-trimethyl-3H-spiro[1-benzo-furan-2,1'-cyclohexane]-5-carboxylic acid(2), methyl 3'-acetyloxy-2',2',6'-trimethyl-3H-spiro[1-benzofuran-2,1'-cyclohexane]-5-carboxylate (3), methyl 3'-isopentanoyloxy-2',2',6'-trimethyl-3H-spiro[1-benzofuran-2,1'-cyclohexane]-5-carboxylate (4) and methyl 3'-benzoyloxy-2',2',6'-trimethyl-3H-spiro[1-benzofuran-2,1'-cyclohexane]-5-carboxylate (5).Compounds 2-5 were identified by their spectroscopic analogies with filifolinol (1), and their structures confirmed by chemical correlation with 1. The antimicrobial properties of the compounds were tested against Gram positive and Gram negative bacteria. Some of them proved to be active against Gram positive, but inactive against Gram negative bacteria. In searching for structure-activity relationships from the obtained MIC values, lipophilicity was shown to be an important variable.

A structure-activity study of antibacterial diterpenoids.

An analysis of the antibacterial activities of 15 terpenoids, eleven of which were previously described by us and four were extracted from the literature, suggested two structural requirements for activity of these and related compounds: a hydrophobic moiety,consisting of a substituted decalin skeleton, and a hydrophilic region possessing one hydrogen-bond-donor group. These structural requirements are responsible for an optimal insertion of these and related compounds into cell membranes, as suggested by the results of docking some of these compounds into a model phospholipid bilayer.

Supramolecular structures of five 5-(arylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-triones: isolated molecules, hydrogen-bonded chains and chains of fused hydrogen-bonded rings.

In each of the five title compounds, namely 5-benzylidene-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C13H12N2O3, (I), 5-(3-methoxybenzylidene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C14H14N2O4, (II), 5-(4-methoxybenzylidene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C14H14N2O4, (III), 5-[4-(dimethylamino)benzylidene]-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C15H17N3O3, (IV), and 5-(3,5-di-tert-butyl-4-hydroxybenzylidene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C21H28N2O4, (V), which crystallizes with Z' = 2 in P-1, there is a very wide C-C-C angle at the methine C atom linking the two rings, ranging from 137.1 (2) degrees in (I) to 139.14 (14) degrees in (III). There is evidence for intramolecular charge separation in (IV) and, to a lesser degree, in (III). The molecules of (I)-(III) are linked by pairs of C-H...O hydrogen bonds into chains of edge-fused rings, with alternating R(2)2(14) and R(2)2(16) rings in (I), alternating R(2)2(14) and R(4)4(20) rings in (II), with two types of R(2)2(16) rings alternating in (III). The molecules in (IV) are linked by a single C-H...O hydrogen bond into simple C(8) chains, but there are no direction-specific intermolecular interactions in (V).