Search

The tautomerism of curcumin has been investigated in ethanol/water binary mixtures by using UV-Vis spectroscopy and advanced quantum-chemical calculations. The spectral changes were processed by using advanced chemometric procedure, based on resolution of overlapping bands technique. As a result, molar fractions of the tautomers and their individual spectra have been estimated. It has been shown that in ethanol the enol-keto tautomer only is presented. The addition of water leads to appearance of a new spectral band, which was assigned to the diketo tautomeric form. The results show that in 90% water/10% ethanol the diketo form is dominating. The observed shift in the equilibrium is explained by the quantum chemical calculations, which show that water molecules stabilize diketo tautomer through formation of stable complexes. To our best knowledge we report for the first time quantitative data for the tautomerism of curcumin and the effect of the water., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The tremendous therapeutic potential of curcumin as a chemopreventive, antineoplastic and chemosensitizing agent has failed to progress towards clinical development and commercialization due to its unfavorable physicochemical properties, low aqueous solubility, chemical instability, and pharmacokinetics. The present contribution is focused on the feasibility of using PEGylated calixarene, in particular polyoxyethylene-derivatized tert-butylcalix[4]arene, to prepare various platforms for delivery of curcumin such as inclusion complex, supramolecular aggregates, and hybrid liposomal systems. The inclusion complex is characterized by UV-vis and FT-IR spectroscopy as well as thermal gravimetrical analysis and differential scanning calorimetry. At concentrations exceeding the critical micellization concentration of PEGylated calixarene, the tremendous solubility enhancement of curcumin is attributed to additional solubilization and hydrophobic non-covalent interactions of the drug with supramolecular aggregates. A hybrid liposomal system is created via encapsulation of the inclusion complex in dipalmitoylphosphatidylcholine:cholesterol liposomes. Bare and liposomal curcumin:BEC-X inclusion complexes, as well as free curcumin were additionally investigated for cytotoxicity and apoptogenic activity against human tumor cell lines., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The ability of the acetylcholinesterase reactivator obidoxime (H2L(2+)) to bind palladium(II) cations was evaluated spectrophotometrically at different reaction conditions (pH, reaction time, metal-to-ligand molar ratio). The results showed that immediately after mixing the reagents, pH 7.4, complex species of composition [PdHL](3+) existed predominantly with a value of conditional stability constant lgβ'=6.52. The reaction was completed within 24 hours affording the formation of species [Pd2L](4+) with significantly increased stability (lgβ'=9.34). The spectral data suggest that obidoxime coordinates metal(II) ions through the oximate functional groups. The in vitro reactivation assay of paraoxon-inhibited rat brain acetylcholinesterase revealed that the new complex species were much less active than the non-coordinated obidoxime. The lack of reactivation ability could be explained by the considerable stability of complexes in solution as well as by the deprotonation of oxime groups essential for recovery of the enzymatic activity.

Tautomerization energies of a series of isomeric [(4-R-phenyl)azo]naphthols and the analogous Schiff bases (R = N(CH3)2, OCH3, H, CN, NO2) are calculated by LPNO-CEPA/1-CBS using the def2-TZVPP and def2-QZVPP basis sets for extrapolation. The performance of various density functionals (B3LYP, M06-2X, PW6B95, B2PLYP, mPW2PLYP, PWPB95) as well as MP2 and SCS-MP2 is evaluated against these results. M06-2X and SCS-MP2 yield results close to the LPNO-CEPA/1-CBS values. Solvent effects (CCl4, CHCl3, CH3CN, and CH3OH) are treated by a variety of bulk solvation models (SM8, IEFPCM, COSMO, PBF, and SMD) as well as explicit solvation (Monte Carlo free energy perturbation using the OPLSAA force field).

Yariv phenylglycosides [1,3,5-tri(p-glycosyloxyphenylazo)-2,4,6-trihydroxybenzene] are a group of chemical compounds that selectively bind to arabinogalactan proteins (AGPs), a type of plant proteoglycan. Yariv phenylglycosides are widely used as cytochemical reagents to perturb the molecular functions of AGPs as well as for the detection, quantification, purification, and staining of AGPs. However, the target structure in AGPs to which Yariv phenylglycosides bind has not been determined. Here, we identify the structural element of AGPs required for the interaction with Yariv phenylglycosides by stepwise trimming of the arabinogalactan moieties using combinations of specific glycoside hydrolases. Whereas the precipitation with Yariv phenylglycosides (Yariv reactivity) of radish (Raphanus sativus) root AGP was not reduced after enzyme treatment to remove α-l-arabinofuranosyl and β-glucuronosyl residues and β-1,6-galactan side chains, it was completely lost after degradation of the β-1,3-galactan main chains. In addition, Yariv reactivity of gum arabic, a commercial product of acacia (Acacia senegal) AGPs, increased rather than decreased during the repeated degradation of β-1,6-galactan side chains by Smith degradation. Among various oligosaccharides corresponding to partial structures of AGPs, β-1,3-galactooligosaccharides longer than β-1,3-galactoheptaose exhibited significant precipitation with Yariv in a radial diffusion assay on agar. A pull-down assay using oligosaccharides cross linked to hydrazine beads detected an interaction of β-1,3-galactooligosaccharides longer than β-1,3-galactopentaose with Yariv phenylglycoside. To the contrary, no interaction with Yariv was detected for β-1,6-galactooligosaccharides of any length. Therefore, we conclude that Yariv phenylglycosides should be considered specific binding reagents for β-1,3-galactan chains longer than five residues, and seven residues are sufficient for cross linking, leading to precipitation of the Yariv phenylglycosides.

Background: The title compound belongs to the class of bis-azomethine pigments. On the basis of comparative studies on similar structures, insight into the complex excited state dynamics of such compounds has been gained. It has been shown, for example, that only compounds that possess hydroxyl groups are fluorescent, and that the possibility for cis-trans isomerisation and/or bending motions of the central bis-azomethine fragment allows for different non-radiative decay pathways., Results: The compound, 4,4'-dihydroxy-1,1'-naphthaldazine (1) was synthesized and characterized by means of spectroscopic and quantum chemical methods. The tautomerism of 1 was studied in details by steady state UV-Vis spectroscopy and time resolved flash photolysis. The composite shape of the absorption bands was computationally resolved into individual subbands. Thus, the molar fraction of each component and the corresponding tautomeric constants were estimated from the temperature dependent spectra in ethanol., Conclusions: According to the spectroscopic data the prevalent tautomer is the diol form, which is in agreement with the theoretical (HF and DFT) predictions. The experimental data show, however, that all three tautomers coexist in solution even at room temperature. Relevant theoretical results were obtained after taking into account the solvent effect by the so-called supermolecule-PCM approach. The TD-DFT B3LYP/6-31 G** calculated excitation energies confirm the assignment of the individual bands obtained from the derivative spectroscopy.

The title compound, C(21)H(16)N(2)O, has an E-conformation about the diazene N=N bond. It is reasonably planar with the phenyl ring being inclined to the mean plane of the anthracene moiety [planar to within 0.077 (3) Å] by 6.43 (10)°. The crystal structure is stabilized by C-H⋯π and weak π-π inter-actions [centroid-centroid distances of 3.7192 (16) and 3.8382 (15) Å], leading to the formation of two-dimensional networks stacking along [001] and lying parallel to (110).

The keto-enol tautomeric equilibrium in two newly developed molecular switches was studied by using various mass spectral techniques. In these two compounds, namely 4-(phenyldiazenyl)-2-(piperidin-1- ylmethyl)naphthalen-1-ol and 2-[(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl]-4- (phenyldiazenyl)naphthalen-1-ol, the switching on/off states are achieved by a controlled shift of the tautomeric equilibrium. In the first compound, electron impact-mass spectrometry confirms that the unprotonated dye exists as an enol tautomer, while the electrospray ionization tandem mass spectrometry (ESI-MS/MS) experiment proves the clear shift to the keto tautomeric form under switching with acid addition. In the second compound, the addition of the alkali metal ions causes transition of the tautomeric equilibrium from the pure enol to the pure keto form. The ESI-MS study demonstrated better sensitivity towards lithium ions.

Two-photon absorption (TPA) properties of newly synthesized conjugated ketone derivatives that include nonalternant azulenyl moieties in the pi-conjugation system, alpha,alpha'-bis(1-azulenylidene)cyclopentanone (1Az), alpha,alpha'-bis(2-azulenylidene)cyclopentanone (2Az), and alpha,alpha'-bis(6-azulenylidene)cyclopentanone (6Az) are reported. TPA spectra of these azulenyl compounds were measured using the open-aperture Z-scan method with a femtosecond laser. The TPA cross section at the peak position (sigma(2)peak) of 1Az was found to be the largest among the three azulenyl compounds, which is almost 7 times larger than that of the alpha,alpha'-bis(1-naphthylidene)cyclopentanone (1Nph), an alternant isomer of 1Az with the same number of pi-electrons. The small detuning energies of the azulenyl compounds compared to those of 1Nph were responsible for the large TPA cross sections. We report that a compound having an azulenyl moiety can be a promising TPA material.

Two-photon absorption (TPA) properties of two trefoil-shaped compounds with different edge linkages--tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)--and three asterisk-shaped compounds having no edge-linkage--hexakis(phenylethynyl)benzenes--are investigated experimentally by the open-aperture Z-scan and TPA-induced fluorescence methods with wavelength tuneable femtosecond pulses. The compound with ethynylene edge-linkage exhibits the most intense TPA (the maximal TPA cross section is 1300+/-170 GM at 572 nm where 1 GM=10(-50) cm(4) s molecule(-1) photon(-1)). The TPA activity of the compounds is primarily explained in terms of the planarity of the molecules in relation with the type of edge-linkage.

Two-photon absorption (TPA) properties of noncentrosymmetric pi-conjugated stilbenoid molecules with D-pi-A structures, TPA spectra of which have been reported [L. Antonov et al., Phys. Chem. Chem. Phys. 5, 1193 (2003)], have been investigated theoretically by ab initio molecular orbital methods. The difference in the observed one-photon absorption and TPA spectra among compounds with the same donor (D) and acceptor (A) units is well reproduced by the present calculations, although the calculated excitation energies are overestimated by the configuration interaction with single excitation method used. It was found that the spectral differences among the compounds were mainly due to the deviation from the planar structure by intramolecular rotation around the N[Single Bond]C (phenyl) bond of the N-benzilideneanilines having the C[Double Bond]N linkage as the central pi bridge. Substitution of the end donor or acceptor groups with weaker ones leads to a decrease in the TPA intensity of the lowest pi-pi(*) TPA states, resulting mainly from the decrease in the dipole moment of the excited states. The total TPA cross section spectra have been separated into contributions of the dipolar term, which appear only in noncentrosymmetric systems, and the three-state term, which appear in any systems irrespective of symmetry. The dipolar term predominates only for the lowest pi-pi(*) state, while for the higher excited states the three-state terms become predominant. An analysis employing the index R(f) defined with the transition polarizability shows that the TPA properties of the higher excited states are well described by the three-state approximation mediated by the lowest pi-pi(*) state. The differences found between the centrosymmetric and dipolar molecules in the enhancement mechanism of the TPA intensity by substituting the end groups with strong donors are discussed by comparison with the TPA properties of azobenzenes symmetrically substituted with the same donors.

Phenyl-substituted 1-arylazo-2-naphthols (AAN) display ...HN-N=C-C=O... <==>...N=N-C=C-OH... ketohydrazone-azoenol tautomerism and can form intramolecular resonance-assisted H-bonds from pure N-H...O to pure N...H-O through tautomeric and dynamically disordered N-H...O <==>N...H-O bonds according to the electronic properties of their substituents. Three compounds of this series (m-OCH(3)-AAN = mOM; p-Cl-AAN = pCl; and p-NMe(2)-AAN = pNM2) have been studied by X-ray crystallography at four temperatures (100-295 K), showing that the remarkably short H-bonds formed (2.53 < or = d(N...O) < or = 2.55 A) are a pure N-H...O in mOM, a dynamically disordered mixture in pCl (N-H...O:N...H-O = 69:31 at 100 K), and a statically disordered mixture in pNM2 (N-H...O:N...H-O = 21:79 at 100 K). These compounds, integrated by the p-H-, p-NO(2)-, p-F-, and p-O(-)-substituted derivatives, have been emulated by DFT methods (B3LYP/6-31+G(d,p) level) with full geometry optimization of the stationary points along the proton-transfer (PT) pathway: N-H...O and N...H-O ground states and N...H...O transition state. Analysis of DFT-calculated energies and geometries by the methods of the rate-equilibrium Marcus theory shows that all H-bond features (stability and tautomerism, as well as position and height of the PT barrier) can be coherently interpreted in the frame of the transition-state (or activated-complex) theory by considering the bond as a chemical reaction N-H...O <==> N...H...O <==> N...H-O which is bimolecular in both directions and proceeds via the N...H...O PT transition state (the activated complex).

An approach for quantitative analysis of mixtures with unknown individual responses of the components is discussed. Although it is based on a resolution of overlapping bands technique, the main emphasis is not given to the computational facets of curve fitting. A logical procedure is described, allowing estimation of the unknown concentrations in the mixture, and both the number of overlapping bands and their assignment to the components in the solution to be determined automatically. A general conclusion about the precision of the method cannot be defined, because it depends on the extent of overlapping of the individual spectra of the components and their complexity. Using this procedure a complicated three-component acid-base equilibrium of a halochromic dye in solution is studied.

Two cDNA clones, specifically expressed in Nicotiana sylvestris anthers during uninucleate microspore development, were isolated using a subtractive hybridization approach. Sequence analysis showed that one of them, NSCHSLK, displayed a high level of similarity to several anther-specific chalcone synthase-like (CHSLK) proteins and an ORF from chromosome I of Arabidopsis thaliana. A lower, but significant, similarity to chalcone synthases and closely related enzymes (CHSRE) was also detected. The structure of the nschslk gene was found to be typical of the chalcone (chs)/stilbene (sts) synthase family. Expression of NSCHSLK mRNA was confined to microspores and tapetal cells. UV-irradiation or infection with Phytophthora parasitica var. nicotianae of transgenic Nicotiana benthamiana plants carrying a chimeric nschslk/GUS gene indicated that the nschslk promoter exhibits the same anther-specific, developmentally regulated expression pattern. Comparison of CHSRE and CHSLK polypeptide sequences revealed some important similarities and differences between the two groups. The data presented in this study, suggest that the anther-specific chslk genes represent a separate sub-family of plant polyketide synthases related to chs/sts in terms of gene structure, polypeptide sequence and the possible catalytic mechanism, but differing in substrate/product specificity. The putative role of CHSLK enzymes in anther development and particularly in exine synthesis is discussed.

A new processed pseudogene (rpL32-5C) that belongs to the mouse rpL32 multigene family has been sequenced and compared to previously characterised mammalian rpL32 family members. rpL32-5C has intact direct terminal repeats of 13 nt, a poly A tail of 10 nt and it does not contain conserved promoter elements at its 5' end. The comparison with the L32 cDNA and 4A processed pseudogene shows a deletion of 25 nt in rpL32-5C as well as several nt substitutions that lead to frameshifts and interruption of the ORF. Most of the consistent substitutions occur in the third codon position lending support to the suggestion that all rpL32 processed pseudogenes have been derived from transcripts of the functional gene.