Bacterial carotenoids. XLVIII. Total syntheses of carotenes of the 1,2-dihydro series.

The total syntheses of 1,2,7,8,1',2',7',8'-octahydro-psi,psi-carotene (1), 1,2,7,8-tetrahydro-psi,psi-carotene (2), 1,2,1',2'-tetradehydro-psi,psi-carotene (3), 1,2-dihydro-psi,psi-carotene (4), 1,2-dihydor-3,4-didehydro-psi,psi-carotene (5), and 1,2,1',2'-tetrahydro-3,4,3',4'-tetrahydro-psi,psi-carotene (6) are described. The properties of products and intermediates, including the three new apocarotenals 1,2,7,8-tetrahydro-12'-apo-psi-caroten-12'-al (20), 1,2-dihydro-8'-apo-pse-caroten-8'-al (25), and 1,2-dihydro-3,4-didehydro-8'-apo-psi-carotene-8'-al (32), are reported. A fragment ion at M68 on electron impact appears to be characteristic for carotenoids with a 1,2,7,8-tetrahydro end-group.     

Electron- and energy-transfer properties of hydrophilic carotenoids

The antioxidant activities-expressed as the electron-donating properties-of five hydrophilic carotenoids (carotenoid surfactants) and three related hydrophobic carotenoids were investigated by flash photolysis. The electron-transfer rates of the carotenoids to the triplet state of the sensitizer 2-nitronaphthalene and the energy transfer rates of triplet 2-nitronaphthalene to the carotenoids were determined. The results demonstrate that the electron-donating effects of the hydrophilic and hydrophobic carotenoids were comparable when evaluated in acetonitrile. In the presence of water, however, electron transfer (i.e., antioxidant efficiency) was enhanced by a factor of four for the hydrophilic carotenoids. The increased hydrophilicity of carotenoids, therefore, could expand their antioxidant properties, thus facilitating their use as aqueous-phase radical scavengers. At the same time, it was shown that supramolecular assembly ("aggregation") of the amphiphilic carotenoids prevented electron transfer, thus deactivating the antioxidant function. Modulation of the biophysical properties of carotenoids through synthetic modification is capable of increasing the biological and medical utility of this natural class of predominantly hydrophobic antioxidant compound.     

Symmetric anionic polymethine dyes derived from fluorene and its derivatives with electron-acceptor substituents: synthesis and spectral properties

Novel anionic polymethine dyes were synthesized from 2,7-bis(phenoxysulfonyl)-, 2,7-dinitro-, and 2,4,5,7-tetranitrofluorenes. The reasons for the complicated shape of their absorption spectra were analyzed: the formation of contact ion pairs, associates, and conformational isomers and electronic effects of substituents. The quantum chemical calculations by the Pariser??Parr??Pople method and nonempirical DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set revealed that the orbitals of the nitro groups, unlike the orbitals of the SO₂OPh groups, are efficiently conjugated with the common chromophore system inducing additional electron transitions.     

Electrochemical synthesis of Cu-containing polyheteroarylenes and study of their catalytic properties

Method of electrochemical synthesis of new Cu-containing polyheteroarylenes that have biquinolyl units in their main chain is developed on the base of the soluble anode technique. The study of electrochemical properties of thus obtained Cu-containing polymer and the corresponding monomer complex revealed existence of two types of coordination environment: (1) copper Cu(I) in the tetrahedral surrounding of two biquinolyl ligands and (2) copper Cu(I) bound with only one biquinolyl fragment. The complexes with one biquinolyl polymer ligand showed high activity as catalysts for O₂ reduction in the presence of hydroquinone that is converted to quinone in the course of the reaction.     

Quinonoid oligothiophenes as electron-donor and electron-acceptor materials. A spectroelectrochemical and theoretical study

Two quinonoid bis(dicyanomethylene) oligothiophenes, terthiophene and quaterthiophene analogues of TCNQ, have been investigated by spectroelectrochemical experiments and density functional theory calculations. Electrochemical data show that the molecules can be both reduced and oxidized at relatively low potentials, and that the quaterthiophene derivative forms four stable redox species, the dianion, neutral, cation radical, and dication. The neutral oligomers are characterized by a strong electronic absorption in the red or near-infrared region and can be viewed as structural and electronic analogues of aromatic oligothiophenes in the dication or bipolaron state. Upon reduction, dianions, not anion radicals, are formed which absorb in the visible region. The theoretical calculations show that the dianions have aromatic oligothiophene moieties with two anionic dicyanomethylene groups. The transition from a quinonoid to an aromatic structure is fully supported by UV-vis-near-IR and vibrational spectroscopic data. Oxidation, generating cation radicals and dications, occurs at rather low potentials similar to those reported for oligothiophenes. The electronic spectra of these cations are understood from the calculations, which suggest that the oxidized species are stabilized by the partial aromatization of the oligothiophene backbone. IR spectra of the species, especially the CN stretching frequencies, confirm the structural conclusions and allow comparison with TCNQ and the TCNQ dianion.     

Environmental effects on vibrational properties of carotenoids: experiments and calculations on peridinin

Carotenoids are employed in light-harvesting complexes of dinoflagellates with the two-fold aim to extend the spectral range of the antenna and to protect it from radiation damage. We have studied the effect of the environment on the vibrational properties of the carotenoid peridinin in different solvents by means of vibrational spectroscopies and QM/MM molecular dynamics simulations. Three prototypical solvents were considered: cyclohexane (an apolar/aprotic solvent), deuterated acetonitrile (a polar/aprotic solvent) and methanol (a polar/protic solvent). Thanks to effective normal mode analysis, we were able to assign the experimental Raman and IR bands and to clarify the effect of the solvent on band shifts. In the 1500-1650 cm(-1) region, seven vibrational modes of the polyene chain were identified and assigned to specific molecular vibrations. In the 1700-1800 cm(-1) region a strong progressive down-shift of the lactonic carbonyl frequency is observed passing from cyclohexane to methanol solutions. This has been rationalized here in terms of solvent polarity and solute-solvent hydrogen bond interactions. On the basis of our data we propose a classification of non-equivalent peridinins in the Peridinin-Chlorophyll-Proteins, light-harvesting complexes of dinoflagellates.     

C(60)-based triads with improved electron-acceptor properties: pyrazolylpyrazolino[60]fullerenes.

A series of triad pyrazolylpyrazolino[60]fullerenes has been prepared in one pot from suitably functionalized hydrazones by 1,3-dipolar cycloaddition reactions under microwave irradiation. The electrochemical properties of the compounds obtained were investigated by cyclic voltammmetry, and they show better electron acceptor character than the parent C(60) in all cases. Fluorescence experiments and time-resolved transition spectroscopy indicate the existence of photoinduced charge-transfer processes with the C(60) triplet acting as the acceptor.     

Electrochemical properties of stoichiometric RuN film prepared by rf-magnetron sputtering: A preliminary study

The electrochemical properties and stability of ruthenium mononitride (RuN) thin films were studied. Coatings of RuN were synthesized on electropolished titanium supports by rf-magnetron sputtering. RuN electrodes appear rather stable against dissolution, independently of pH, but show to possess the greatest stability only in alkaline environment. Under hydrogen evolution conditions the films show relevant catalytic properties, comparable with Pt, Pd and Ru/Ir derivatives; a significant coverage by adsorbed reaction intermediates is involved. These electrodes are of potential application in energetics and sensoring.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The chloromethylation of 2-acetothienone and 2-formylthiophene with , -bischloromethyl ether in 60–100% sulfuric acid was studied. An increase in the acidity of the medium promotes the formation of 4-substituted products, which, as in nitration and bromination, is explained by protonation of the carbonyl group, leading to intensification of its electron-acceptor capacity.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1353–1357, October, 1971.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The composition of the products formed in the bromination of complexes of furfural with AlCl₃ and methyl furan-2-carboxylate with AlBr₃ in chloroform and dichloroethane was studied by PMR spectroscopy and gas-liquid chromatography. Some literature data pertaining to these reactions are refined and corrected. The pathways for the formation of chloro derivatives under the examined conditions are discussed.     

Electron-donor/acceptor properties of carbynes,carbenes, vinylidenes,allenylidenes and alkynyls as measured by electrochemical ligand parameters

The bases of the main redox potential parameterization approaches and their extensions are reviewed with the methods to estimate the corresponding electrochemical ligand and metal center parameters. They are applied, in most cases for the first time, to series of carbyne, vinylidene, allenylidine and alkynyl complexes, allowing the estimate of the Pickett’s P_L and Lever’s E_L ligand parameters for quite a significant number (ca. 135) of ligands of these types which can then be ordered according to their net π-electron acceptor minus σ-donor character and compared with other ligands. The dependence of such parameters on the electronic properties of various groups and their transmission along the carbon skeleton of those ligands are illustrated and limitations and scopes of the parameterization approaches are discussed.     

Theoretical study of the enthalpies of formation for C40H56 carotenes

Theoretical study of the enthalpies of formation (DeltaHf) for polyenes up to nine ethylene units and for several C40H56 carotenes including beta-carotene, alpha-carotene, lycopene, and prolycopene is presented. For polyenes and small branched alkenes, we used G2, G3, and G3MP2B3 theories, and the DeltaHf values were evaluated with the atomization, isodesmic bond separation, and homodesmic schemes. The applicability of six DFT functionals were evaluated by comparing their predictions with those obtained using G3 theory within the atomization scheme. Additivity approaches, including atom equivalents and group equivalents using DFT and semiempirical theories, were explored. We found that group equivalents associated with isodesmic reactions are able to provide the most accurate predictions within the test set. The predictions from the six functionals are in good agreement with the G3 results. Among them, B3LYP performs the best, with an average absolute deviation of only 0.30 kcal/mol. The application of DFT in the prediction for the DeltaHf value of C40H56 carotenes is promising.     

Electrochemical properties of uranium in lactones: Kinetics and electrodeposition

The electrochemical reductions of hexavalent and tetravalent uranium are reported in -butyrolactone, -valerolactone, -octanoiclactone and in the mixed solvent -butyrolactone/tetrahydrofuran. The transient techniques foresee either the formation of uranium dioxide or uranium metal according to a two-step reduction but the presence of these cathodic products is difficult to ascertain in controlled potential electrolysis. While mixing a lactone with tetrahydrofuran, the reversibility of the electrode reactions increases. The conducting salt noticeably determines the current yield of uranium deposition. As additional kinetic phenomena are made clear, we found that sampled polarography is the best method to gain a full understanding of the electrode mechanisms.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

The specificity of the nitration and bromination of dimethyl(2-thienyl)sulfonium salts was studied. It was found that, in contrast to methyl 2-thienyl sulfide, which reacts to form 3- and 5-substituted derivatives, the sulfonium salts give a mixture of 4- and 5-substituted products. Total suppression of the activity of the position under the influence of the sulfonium grouping is not observed.See [1] for communication VIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 310–314, March, 1972.     

Photoprotective nanoemulsions containing microbial carotenoids and buriti oil: Efficacy and safety study

Photoprotective nanoemulsions are able to attenuate skin damage from overexposure to the sun, thus avoiding the immediate effects caused by ultraviolet radiation. The global cosmetics market understands that there is a demand and greater acceptance by consumers for formulations containing natural products compatible with the skin. Consequently, there is an increasingly need to develop such products that are safe and effective. Furthermore, there is a growing interest in nanoemulsions (NE) in the pharmaceutical industry, due the versatility of incorporating lipophilic substances into cosmetic formulations. In the present work, oil-in-water photoprotective nanoemulsions containing microbial carotenoids, buriti oil and chemical filters were developed and characterized. The essential physical properties of the droplets, the transmission electronic microscopy (TEM), the sun protection factor (SPF) as well as the stability of the formulations were determined. In vitro phototoxicity was evaluated using Balb 3 T3 with relative cell viability estimated by Neutral Red Uptake, with the Photo Irritation Factor (PIF) and the Medium Photo Effect Factor (MPF) as the measurement parameters. Nanoemulsion 3 (NE3) showed spherical morphology with an average droplet size of 142.11 ± 0.92 nm and polydispersity index (PDI) of 0.198 ± 0.017. This nanoemulsion containing microbial carotenoids and buriti oil exhibited a SPF of 36 ± 1.5. Neutral Red Uptake revealed that the cells kept their viability even after irradiation and those nanoemulsions containing the microbial carotenoids and buriti oil were not phototoxic. The addition of microbial carotenoids and buriti oil in nanoemulsions was positive in increasing the mean SPF values compared to the control formulation.     

Reactions of aromatic and heteroaromatic compounds containing electron-acceptor substituents

A method was developed for the preparation of 4-chloromethyl-2-acylthiophenes and m-(chloromethyl)acylbenzenes in up to 65% yields by the action of paraformaldehyde and anhydrous aluminum chloride on the corresponding carbonyl compounds. The reaction mechanism is discussed.See [1] for communication XXII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1474–1476, November, 1978.     

Electrochemical synthesis and properties of gold nanomaterials

Approximately two decades ago, gold catalyst opened up a new view of their properties when they are introduced in the form of nanomaterials, since at that time, many approaches to preparation and use of gold nanoparticles started to be used in many practical applications. Today, the research activity relating to gold nanomaterials is becoming systematic and goes further to make connections between their surface structure, chemical and physical properties, and possible applications. Since electrodeposition is one of the most controllable methods used to prepare nanoparticles, nanowires, and nanoclusters of gold, the present review gives preference on their electrochemical synthesis. The relationship between catalytic activity, size, morphology and stability of gold nanomaterials is discussed in detail. Based on the properties of the prepared gold nanocatalysts, their new applications in chemical, photochemical, and electrochemical reactions have been observed.