On the Role of a Polymer Matrix in Enhancing Energy Transfer Efficiency Using Coumarin 6 and Rhodamine B as Donor and Acceptor Pairs.

This study investigates the critical role of polymer matrices in optimizing luminescence and energy transfer, utilizing the commercial dyes Coumarin 6 (C6) and Rhodamine B (RhB) as a donor-acceptor pair. Solution-phase experiments revealed a dependence of energy transfer efficiency on solvent dielectric constant. Furthermore, embedding the dyes within Poly(methyl methacrylate) (PMMA) or Poly(vinyl butyral) (PVB) matrices significantly enhance energy transfer due to increased molecular proximity.

Individual scale factor approach for the vibrational circular dichroism similarity-guided spectral and conformational analysis of perezone and dihydroperezone.

Evaluation of DFT calculated vibrational parameters for the IR and VCD spectra similarity of perezone (1) and dihydroperezone (2) was undertaken. Conformational sets were obtained using different search engines, and the parameters needed for spectra prediction were obtained using several combinations of commonly employed functionals and basis sets, and then weighted spectra were generated and compared with observed traces to provide infrared similarity (S ) and enantiomeric similarity index (ESI) values. These values evidenced a poor performance of the evaluated levels of theory that were overcome when using the individual scaling factors approach, providing 16% to 139% increases of the ESI values.

A Study on Perception and Exposure to Occupational Risks at Public School Food Services in Bahia, Brazil.

Food service work is hazardous due to the intense rhythm of food production, and the working conditions can cause discomfort, fatigue, and occupational accidents and illnesses. For the perception of exposure to occupational hazards, workers must participate in continuing education programs. This study aimed to verify the perception and exposure to occupational risks at school food services (SFS) in Bahia, Brazil.

Deuterium effects on the vibrational circular dichroism spectra of flavanone.

The minimum chemical modification that can be incorporated into an organic molecule is the replacement of a hydrogen atom for a deuterium atom. This change is not altering the pharmacological properties of a molecule, although it provides the possibility of making specific spectroscopic evaluations. Thus, in the present study, we explore how a stereogenic center is influenced by such an isotopic labeling.

Enantiomeric high-performance liquid chromatography resolution and absolute configuration of 6β-benzoyloxy-3α-tropanol.

The absolute configuration of the naturally occurring isomers of 6β-benzoyloxy-3α-tropanol (1) has been established by the combined use of chiral high-performance liquid chromatography with electronic circular dichroism detection and optical rotation detection. For this purpose (±)-1, prepared in two steps from racemic 6-hydroxytropinone (4), was subjected to chiral high-performance liquid chromatography with electronic circular dichroism and optical rotation detection allowing the online measurement of both chiroptical properties for each enantiomer, which in turn were compared with the corresponding values obtained from density functional theory calculations. In an independent approach, preparative high-performance liquid chromatography separation using an automatic fraction collector, yielded an enantiopure sample of OR (+)-1 whose vibrational circular dichroism spectrum allowed its absolute configuration assignment when the bands in the 1100-950 cm(-1) region were compared with those of the enantiomers of esters derived from 3α,6β-tropanediol.

Vibrational Circular Dichroism Absolute Configuration of 9,12-Cyclomulin-13-ol, a Diterpene from Azorella and Laretia Species.

The absolute configuration of the diterpenoid 9,12-cyclomulin-13-ol (1), a constituent of Azorella and Laretia species, has been established by vibrational circular dichroism spectroscopy in combination with density functional theory calculations. The obtained normal diterpene absolute configuration confirms that of azorellanol (2), which was determined by single crystal X-ray diffraction.

Stereospecific (5) JHortho,OMe couplings in methoxyindoles, methoxycoumarins, and methoxyflavones.

Long-range coupling constants (5) JHortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the -OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear (1) H-(1) H couplings were confirmed by irradiation of the -OMe signal.

Chiral resolution and absolute configuration of 3alpha,6beta-dicinnamoyloxytropane and 3alpha,6beta-di(1-ethyl-1H-pyrrol-2-ylcarbonyloxy)tropane, constituents of Erythroxylum species.

Chiral resolution of (+/-)-3alpha,6beta-dicinnamoyloxytropane (1) and (+/-)-3alpha,6beta-di(1-methyl-1H-pyrrol-2-ylcarbonyloxy)tropane (2), prepared by esterification of (+/-)-3alpha,6beta-tropanediol (3), was achieved using an amylose-derived HPLC stationary phase and normal phase conditions. The corresponding vibrational circular dichroism (VCD) spectra provided the absolute configuration of the enantiomers as (-)-(3R,6R)-1, (+)-(3S,6S)-1, (-)-(3R,6R)-2 and (+)-(3S,6S)-2. In each case, characteristic VCD bands for the absolute configuration determination of the 3alpha,6beta-tropandiol esters were observed.

Chiroptical studies of flavanone.

Chiral HPLC coupled to electronic circular dichroism and laser optical rotation detection (HPLC-ECD-OR) permitted the on-line chiroptical characterization of both enantiomers of racemic flavanone (1) as ECD(-)310-OR(-)670-flavanone and ECD(+) 310-OR(+)670-flavanone for the first and second eluted peaks, respectively. Calculation of the ECD spectrum of one enantiomer at the TD-DFT/DGTZVP level of theory yielded the (S)-ECD(-)310-OR(-)670 and (R)-ECD(+)310-OR(+)670-1 absolute configuration, in agreement with the use of empirical rules for stereochemical assignment. Vibrational circular dichroism spectra of enantiopure compounds, obtained through fraction collection during repeated HPLC runs, were recorded and compared with theoretical traces produced from DFT calculations at the B3LYP/DGDZVP and B3PW91/DGDZVP levels of theory, which further confirmed the absolute configuration obtained from the on-line chiroptical data.

Absolute configuration and 1H NMR characterization of rosmaridiphenol diacetate.

The correction of patented structure 1 of rosmaridiphenol, an antioxidant isolated from rosemary, Rosmarinus officinalis, was made recently. The correct structure is proposed as 11,12-dihydroxy-8,11,13-icetexatrien-1-one (2a) based on 2D NMR data. In order to further support the structure, this work reports the single-crystal X-ray analysis, the complete (1)H NMR assignment by full spin-spin simulation, and the absolute configuration of the diacetate 2b derived via vibrational circular dicroism measurements in comparison with density functional theory calculated data.

Stereochemical analysis of leubethanol, an anti-TB-active serrulatane, from Leucophyllum frutescens.

Bioactivity-guided fractionation of the methanolic root bark extract of Leucophyllum frutescens led to the identification of leubethanol (1), a new serrulatane-type diterpene with activity against both multi-drug-resistant and drug-sensitive strains of virulent Mycobacterium tuberculosis. Leubethanol (1) was identified by 1D/2D NMR data, as a serrulatane closely related to erogorgiane (2), and exhibited anti-TB activity with minimum inhibitory concentrations in the range 6.25-12.

Solid state structure and absolute configuration of filifolinol acetate.

Careful reevaluation of the 1H and 13C NMR spectroscopic data of filifolinol acetate (4) led to the reassignment of the C-10 and C-11 signals, as well as the gem-dimethyl signals. Single crystal X-ray analysis provided an independent structural confirmation of 4, and comparison of the experimental vibrational circular dichroism spectrum with calculations performed using density functional theory provided the absolute configuration of this 3H-spiro-1-benzofuran-2,1'-cyclohexane and related molecules.

Human cells and cell membrane molecular models are affected in vitro by the nonsteroidal anti-inflammatory drug ibuprofen.

This report presents evidence that ibuprofen interacts with red cell membranes as follows: a) in scanning electron microscopy (SEM) studies on human erythrocytes induced shape changes at a concentration as low as 10μM; b) in isolated unsealed human erythrocyte membranes (IUM) induced mild increase in the water content or in their molecular dynamics at the hydrophobic-hydrophilic interphase, while a corresponding ordering decrease at the deep phospholipids acyl chain level; c) at physiological temperature (37°C), 300μM ibuprofen induced a significant increase in the generalized polarization (GP) of dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles (LUV), an indication that ibuprofen molecules locate in the head polar group region of DMPC; d) X-ray diffraction studies showed that ibuprofen concentrations≥300μM induced increasing structural perturbation to DMPC bilayers; e) differential scanning calorimetry (DSC) data showed that ibuprofen was able to alter the cooperativity of DMPC phase transition in a concentration-dependent manner, to destabilize the gel phase and that ibuprofen did not significantly perturb the organization of the lipid hydrocarbon chains. Additionally, the effect on the viability of both human promyelocytic leukemia HL-60 and human cervical carcinoma HeLa cells was studied.

Different cell death mechanisms are induced by a hydrophobic flavin in human tumor cells after visible light irradiation.

Riboflavin (RF) is an endogenous cell component and an efficient photosensitizer that can act by both types I and II photochemical mechanisms. Human tumor cells lines cultured in vitro, were used as model to study the effect of a photosensitizer synthesized from riboflavin, the 2',3',4',5'-riboflavin-tetrabutyrate (RTB), to increase the flavin concentration in the human promyelocytic leukemia cell line HL-60 and the human epithelial cervical cancer cell line HeLa. We demonstrate that this compound, alone or with Trp, has a toxic dose-response effect evidenced by abnormal cell morphology and a decrease in the cell proliferation rate.

Inhibitory activities on mammalian central nervous system receptors and computational studies of three sesquiterpene lactones from Coriaria ruscifolia subsp. ruscifolia.

The electrophysiological characterization of sesquiterpene lactones from Coriaria ruscifolia subsp. ruscifolia has been tested on hippocampal neurons. The results for glycinergic rat hippocampal transmission and native γ-aminobutyric acid (GABA)ergic transmission on neurons (13DIV) are remarkably different for tutin, coriamyrtin, and dihydrotutin, being tutin the most potent inhibitor and dihydrotutin the least potent one.

DFT-GIAO(1)H NMR chemical shifts prediction for the spectral assignment and conformational analysis of the anticholinergic drugs (-)-scopolamine and (-)-hyoscyamine.

The relatively large chemical shift differences observed in the (1)H NMR spectra of the anticholinergic drugs (-)-scopolamine 1 and (-)-hyoscyamine 2 measured in CDCl(3) are explained using a combination of systematic/molecular mechanics force field (MMFF) conformational searches and gas-phase density functional theory (DFT) single point calculations, geometry optimizations and chemical shift calculations within the gauge including/invariant atomic orbital (GIAO) approximation. These calculations show that both molecules prefer a compact conformation in which the phenyl ring of the tropic ester is positioned under the tropane bicycle, clearly suggesting that the chemical shift differences are produced by the anisotropic effect of the aromatic ring. As the calculations fairly well predict these experimental differences, diastereotopic NMR signal assignments for the two studied molecules are proposed.

Stereostructure reassignment and absolute configuration of isoepitaondiol, a meroditerpenoid from Stypopodium flabelliforme.

Careful examination of the published NMR data for isoepitaondiol, a meroditerpenoid from Stypopodium flabelliforme, suggests that its published structure 1 must be revised. On the basis of extensive 1D and 2D NMR studies, we now propose that structure 2, with a trans-anti-trans-anti-cis arrangement fits isoepitaondiol diacetate. The relative configuration of 2 was confirmed by single-crystal X-ray diffraction, while the absolute configuration was evidenced by vibrational circular dichroism in combination with DFT B3LYP/DGDZVP calculations.

Diastereoisomeric assignment in a pacifenol derivative using vibrational circular dichroism.

The configuration of a chiral center in semisynthetic (-)-(2R,5R,5aR,8zeta,9aS)- 2,8-dibromo-2,5,9,9a-tetrahydro-5-hydroxy-5,8,10,10-tetramethyl-6H-2,5a-methano-1-benzoxepin-7(8H)-one (3 or 4), prepared in two steps from (-)-(2R,5R,5aR,7S,8S,9aS)-2, 7-dibromo-8-chloro-2,5,7,8,9,9a-hexahydro-5,8,10,10-tetramethyl-6H-2,5a-methano-1-benzoxepin-5-ol, known as pacifenol 1, has been determined using vibrational circular dichroism (VCD) measurements. The vibrational spectra (IR and VCD) of diastereoisomers 3 and 4 were calculated using density functional theory (DFT) at the B3LYP/DGDZVP level of theory for the two conformers that in each case account for the total energetic distribution found in the first 10 kcal/mol range. The DFT conformational optimization of the 8R diastereoisomer 3 indicates the cyclohexanone exists almost exclusively in a boat conformation with a beta-equatorial bromine atom and an alpha-axial methyl group at the chiral center alpha to the carbonyl group, while for the 8S diastereoisomer 4 a 5:1 conformational distribution in favor of a chair conformation with an alpha-axial bromine atom and a beta-equatorial methyl group is calculated, suggesting due to well-known chair versus boat relative stabilities that the plausible diastereoisomer would be the 8S molecule.

VCD determination of the absolute configuration of stypotriol.

The absolute configuration of the pentacyclic ichthyotoxin stypotriol, a constituent of Stypopodium zonale, was deduced to be 3S,5R,8R,9R,10S,13S,14S-(-)-1 by vibrational circular dichroism spectroscopy of the derived triacetate 2 in comparison to DFT B3LYP/DGDZVP calculations. Compound 2, C33H46O7 having 300 electrons, is the largest natural product successfully studied by VCD to date.

Absolute configuration determination and conformational analysis of (-)-(3S,6S)-3alpha,6beta-diacetoxytropane using vibrational circular dichroism and DFT techniques.

The absolute configuration of semisynthetic (-)-3alpha,6beta-acetoxytropane 1, prepared from (-)-6beta-hydroxyhyoscyamine 2, has been determined using vibrational circular dichroism (VCD) spectroscopy. The vibrational spectra (IR and VCD) were calculated using DFT at the B3LYP/DGDZVP level of theory for the eight more stable conformers which account for 99.97% of the total relative abundance in the first 10 kcal/mol range.

DFT-GIAO 1H and 13C NMR prediction of chemical shifts for the configurational assignment of 6beta-hydroxyhyoscyamine diastereoisomers.

(1)H and (13)C NMR chemical shift calculations using the density functional theory-gauge including/invariant atomic orbitals (DFT-GIAO) approximation at the B3LYP/6-311G++(d,p) level of theory have been used to assign both natural diastereoisomers of 6beta-hydroxyhyoscyamine. The theoretical chemical shifts of the (1)H and (13)C atoms in both isomers were calculated using a previously determined conformational distribution, and the theoretical and experimental values were cross-compared. For protons, the obtained average absolute differences and root mean square (rms) errors for each comparison showed that the experimental chemical shifts of dextrorotatory and levorotatory 6beta-hydroxyhyoscyamines correlated well with the theoretical values calculated for the (3R,6R,2'S) and (3S,6S,2'S) configurations, respectively, whereas for (13)C atoms the calculations were unable to differentiate between isomers.

Absolute configuration of natural diastereoisomers of 6beta-hydroxyhyoscyamine by vibrational circular dichroism.

The absolute configuration of the two natural diastereoisomers of 6beta-hydroxyhyoscyamine has been determined using vibrational circular dichroism (VCD) spectroscopy. The predicted VCD and IR spectra of (3R,6R,2'S)-6beta-hydroxyhyoscyamine (1) and (3S,6S,2'S)-6beta-hydroxyhyoscyamine (2) were calculated using density functional theory (DFT) with the B3LYP functional and 6-31G(d) basis set and considering the eight lower energy conformations of each diastereoisomer. In both cases, the first four conformers showed the N-Me group in the syn orientation, permitting the formation of a hydrogen bond between the hydroxy group at the tropane ring and the tertiary nitrogen atom.