A Synthetic Approach for Oxadiazole-Decorated Azobenzene Photoswitches.

This work reports the design and synthesis of novel oxadiazole-decorated azobenzenes, structural analysis of the resulting compounds and behavior under light irradiation. The synthetic strategy involved constructing amino functionalized heterocyclic key intermediates which were used either to yield electrophilic diazonium salts able to react with phenol moieties or as nucleophilic partners in Bayer-Mills reaction with nitroso-substituted derivatives. The amino-derived oxadiazole intermediates were investigated by absorption and emission spectroscopy providing blue and green emitted light. The target oxadiazole-decorated azobenzenes were structurally characterized, including solid-state structures, and subsequently used in irradiation experiments in order to take advantage of the azo group known to provide photoswitching abilities. We noticed quenching of the emissive properties in presence of the azo group; however, all compounds were very stable to repeated cycles of light irradiation. In addition, according to structural diversification we could obtain half-lives of the meta stable isomers within hours to hundreds of hours range. The experimental results were very well correlated with DFT calculations.

Synthesis, Characterization, DFT Study and Antifungal Activities of Some Novel 2-(Phenyldiazenyl)phenol Based Azo Dyes.

In recent decades, there has been an increased interest in azo compounds with special optical and biological properties. In this work, we report the preparation of novel azo-compounds with two and three -N=N- double bonds, using the classical method of synthesis, diazotization and coupling. The compounds were characterized by 1H-NMR, 13C-NMR, FTIR, UV-VIS and fluorescence spectra. DFT calculations were employed for determining the optical parameters, polarizability α, the total static dipole moment µtot, the quadrupole moment Q and the mean first polarizability ßtot. All azo derivatives show strong fluorescence emission in solutions. The antioxidant and antifungal activities were determined and the influence of the number of azo bonds was discussed. The synthesized compounds exhibit remarkable efficiency in the growth reduction of standard and clinical isolated Candida strains, suggesting future applications as novel antifungal.

Exploring Arylazo-3,5-Bis(trifluoromethyl)pyrazole Switches.

Arylazopyrazoles stand out among the azoheteroarene photoswitches due to their excellent properties in terms of stability of the least stable isomer and conversion between isomers, leading to their use in several interesting applications. We report herein the synthesis of arylazo-trifluoromethyl-substituted pyrazoles and their switching behavior under light irradiation. UV-vis and NMR experiments showed that arylazo-1H-3,5-bis(trifluoromethyl)pyrazoles displayed very long half-lives in DMSO (days), along with reasonable values of other parameters that characterize a photoswitch. Inclusion of naphthyl moieties as aryl counterparts of the arylazopyrazoles is beneficial only in combination with trifluoromethyl groups, while extending the conjugation by grafting the pyrazole moiety with electron-donating or -withdrawing substituents positively affects the photoswitching behavior, in terms of isomerization yield and half-lives of the least stable isomer. The experimental values were correlated with theoretical calculations indicating the valuable influence of the trifluoromethyl groups onto the photoswitching behavior.

Bioactive Low Molecular Weight Keratin Hydrolysates for Improving Skin Wound Healing.

Keratin biomaterials with high molecular weights were intensively investigated but few are marketed due to complex methods of extraction and preparation and limited understanding of their influence on cells behavior. In this context the aim of this research was to elucidate decisive molecular factors for skin homeostasis restoration induced by two low molecular weight keratin hydrolysates extracted and conditioned through a simple and green method. Two keratin hydrolysates with molecular weights of 3758 and 12,400 Da were physico-chemically characterized and their structure was assessed by circular dichroism (CD) and FTIR spectroscopy in view of bioactive potential identification. Other investigations were focused on several molecular factors: α1, α2 and ß1 integrin mediated signals, cell cycle progression in pro-inflammatory conditions (TNFα/LPS stimulated keratinocytes and fibroblasts) and ICAM-1/VCAM-1 inhibition in human vascular endothelial cells. Flow cytometry techniques demonstrated a distinctive pattern of efficacy: keratin hydrolysates over-expressed α1 and α2 subunits, responsible for tight bounds between fibroblasts and collagen or laminin 1; both actives stimulated the epidermal turn-over and inhibited VCAM over-expression in pro-inflammatory conditions associated with bacterial infections. Our results offer mechanistic insights in wound healing signaling factors modulated by the two low molecular weight keratin hydrolysates which still preserve bioactive secondary structure.

New Nanofibers Based on Protein By-Products with Bioactive Potential for Tissue Engineering.

Concentrated collagen hydrolysate (HC10CC), rabbit collagen glue (RCG), and keratin hydrolysate (KH) were investigated in terms of their extraction from mammalian by-products and processing by electrospinning. The electrospun nanofibers were characterized by scanning electron microscopy coupled with the energy dispersive X-ray spectroscopy (SEM/EDS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), and indentation tests. The cytotoxicity of the electrospun nanofibers was conducted on L929 fibroblast cells using MTT and LDH assays and cell morphology observations. The electrospun RCG and KH nanofibers morphology showed an average size of nanofibers ranging between 44 and 410 nm, while the electrospun HC10CC nanofibers exhibited higher sizes. The ATR-FTIR spectra performed both on extracted proteins and electrospun nanofibers showed that the triple helix structure of collagen is partially preserved. The results were in agreement with the circular dichroism analysis for protein extracts. Furthermore, the viscoelastic properties of electrospun KH nanofibers were superior to those of electrospun RCG nanofibers. Based on both in vitro quantitative and qualitative analysis, the electrospun nanofibers were not cytotoxic, inducing a healthy cellular response. The results of new electrospun protein-based nanofibers may be useful for further research on bioactive properties of these nanofibers for tissue engineering.

Theoretical ECD calculations--a useful tool for estimating the conformational change of a ligand in the binding pocket of proteins.

The correlation of experimentally induced circular dichroism (ICD) spectra recorded from (a)chiral ligands during their binding to proteins with simulated electronic circular dichroism (ECD) spectra via time-dependent density functional theory calculations was used for obtaining structural information on the ligands in the protein binding sites. A three step procedure is reported, involving the optimization of the most relevant conformers of the different ligand species presumed to be present in the system, the calculation of their ECD spectra and the comparison of the theoretical spectra with the experimental ones. This approach was exemplified for several model systems that can yield ICD signals through steric hindrance of a degree of freedom in the protein pocket. The method was found to be suitable to identify the bound form(s) for flexible molecular systems in which several species can coexist in solution. The effect of several functional/basis set combinations was tested, aiming to establish which one gives the most reliable results.

New insights on flavonoid-serum albumin interactions from concerted spectroscopic methods and molecular modeling.

The paper offers a survey on literature data on the very wide subject concerning the interaction of a particular class of polyphenols, flavonoids, with plasma proteins. Recent developments in applying fluorescence (steady-state, time-resolved, synchronous techniques), circular dichroism and vibrational (FTIR and Raman) spectroscopies for obtaining relevant parameters (binding constant, K, number of binding sites, thermodynamic effects) are presented. Attention is paid to the modifications occurring upon the interaction process in the secondary and tertiary protein structure, as well as in the ligand conformation. In this case, we underline the significant role played by analyzing the induced dichroic signals of the ligand forced to adopt a restricted conformation in the protein pocket. In order to better understand the molecular aspects of the binding process, the differences in experimental data are discussed in terms of the structural elements of flavonoids, namely the number and position of the OH groups, the presence of methoxy and glycosidic residues and the character of the C2-C3 bond in the A ring. Some correlations of logK with parameters such as the hydrophobicity, hydrogen bond donor and acceptor character, and polar surface are also discussed. In the last section we present the representative theoretical results obtained insofar on both isolated ligands (by DFT and TDDFT methods) and supramolecular ligand-protein systems (by molecular mechanics and dynamics).

Experimental and theoretical study of the inclusion complexes of 3-carboxycoumarin acid with ß- and 2-hydroxypropyl-ß-cyclodextrins.

The association process of a host-guest system, cyclodextrins (CyD) - 3-carboxycoumarin acid (3CCA) was followed by means of UV-vis, circular dichroism and steady-state fluorescence spectroscopies in buffer solution at pH=1. The experimental data were analyzed in order to get information on the stoichiometry, the equilibrium constants and the geometry of the inclusion complexes. In the circular dichroism spectra, a positive induced signal was obtained reflecting that the guest penetrates the cavity in such a way that the transition moment of the electronic band is quasi parallel to the host main axis. The experimental data are supported by the DFT and TDDFT (B3LYP/6-31G) calculations performed on the isolated ligand and by TDDFT (ZINDO) calculations carried out on the supramolecular ligand-cyclodextrin system.

Experimental and theoretical study of the interaction of 3-carboxy-5,6-benzocoumarin with some 1,2,3,4,5,6,7,8-octahydroacridines and the corresponding N-oxides.

The interaction of 3-carboxy-5,6-benzocoumarin (BzCum) with 1,2,3,4,5,6,7,8-octahydroacridine (OHA), 9-amino-1,2,3,4,5,6,7,8-octahydroacridine (H(2)N-OHA) and the corresponding N-oxides (OHA-NO and H(2)N-OHA-NO) was studied by fluorescence (steady state, time resolved) and absorption spectroscopy. The analysis of the fluorescence data in terms of Stern-Volmer plots indicated a predominant dynamic quenching for OHA and OHA-NO, and a more complex process for H(2)N-OHA and H(2)N-OHA-NO. The dynamic process was assigned to a photoinduced electron transfer (PET) from the acridine derivatives to the excited state of BzCum. The application of the Rehm-Weller-Marcus theory leads to a good agreement with literature data and allows for the estimation of the solvent organization energy. The presence of the PET mechanism was also supported by DFT results. The absorption spectra evidence the formation of a ground state complex assigned to a hydrogen bond complex involving the carboxylic hydrogen of BzCum.

Theoretical and experimental study of the inclusion complexes of the 3-carboxy-5,6-benzocoumarinic acid with cyclodextrins.

The 3-carboxy-5,6-benzocoumarinic acid (BzCum) presents important emission properties that could make it suitable to be used as a fluorescence marker for proteins. Since the guest-cyclodextrin interaction can be used as a model for the ligand-protein interaction, the host-guest complexes of BzCum with alpha-, beta-, gamma-, 2-hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD) and 2-hydroxypropyl-gamma-cyclodextrin (2-HP-gamma-CD) were investigated by means of steady-state fluorescence measurements. As the guest may exist either in anionic or in neutral form, the experiments were performed at two different pH values, 9.48 and 2.11. The association constants and the stoichiometry of the complexes were estimated by non-linear regression analysis. A theoretical study of the complexes was made using molecular mechanics (MM) calculation methods. The electrostatic and van der Waals contributions to the energy were estimated and a discussion was made on this basis.