On the complexation of Trolox with methyl-β-cyclodextrin: characterization, molecular modelling and photostabilizing properties

Exposure to UV radiations could reduce the efficiency of some antioxidants like Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a water-soluble vitamin E analogue largely employed in cosmetic products. Accordingly, in this paper we examined the possibility of increasing the stability of Trolox towards UVB irradiation by its complexation with methyl-β-cyclodextrin. Formation of the inclusion complex was confirmed by solubility diagrams, differential scanning calorimetry (DSC), and diffusion study through hydrophilic membrane. The stability constants and docking results suggested that the complexation phenomenon was related to the pH of the medium. The photodegradation studies were carried out in different topical formulations (gel, O/W emulsion, and W/O/W emulsion) containing Trolox free or complexed with methyl-β-cyclodextrin. Results showed that in all the cases Trolox degraded following pseudo-zero order kinetics. Moreover, the host molecule increased Trolox photostability also in the presence of TiO₂, a physical sunscreen well-known as photocatalyzer.     

Oxidation of Methyl 4,6-O-Isopropylidene-α-d-glucopyranoside as a Model Compound for Starch

Abstract

The oxidation of methyl 4,6-O-isopropylidene-α-d-glucopyranoside (1) via various routes to the dicarboxylate 2 is described. This reaction is used as a model for the oxidation of starch to dicarboxylic starch, a material with very promising properties as a cobuilder in detergents. The best oxidant found for C₂-C₃ cleavage was RuO₄, prepared in situ by oxidation of a catalytic amount of Ru^III with NaOCl.     

Some Aspects of the Reaction of Methyl 4,6-O-benzylidene-α-D-glucopyranoside 2,3-Carbonate with 1-Dodecanol: Novel Non-Ionic Surfactants

Abstract

The reaction of methyl 4, 6-0-benzylidene-α-D-glucopyranoside 2, 3-cyclic carbonate (2) with 1-dodecanol in the presence of a catalytic amount of triethylamine to yield the 2-O-and the 3-O-alkoxycarbonyl esters 5 and 6 is described. Catalytic hydrogenation of 5 and 6 gave the deprotected mono-esters 3 and 4 which are of interest as potential non-ionic surfactants. The corresponding ethoxycarbonyl esters 7 and 8 were also prepared and their possible role as intermediates in the formation of 2 is discussed.     

A study of the physicochemical properties and structure of moxifloxacin complex with methyl-β-cyclodextrin

The physicochemical properties and structure of moxifloxacin?methyl-β-cyclodextrin complex have been studied by UV spectroscopy, FTIR spectroscopy, and computer simulation. The optimal conditions for the formation of the complex have been determined, and the dissociation constant of the complex in acidic media (K _dis = (5.0 ± 0.3) × 10^–5 М) has been obtained. It has been found that complexation significantly slows down the release of the drug in acidic media. Experimental results are in good agreement with computer simulation data. The following mechanism of complex formation has been proposed: the incorporation of the aromatic fragment of moxifloxacin into the cavity of methyl-β-cyclodextrin is followed by additional stabilization of the complex via multiple hydrophobic interactions and hydrogen bonding.     

On the complexation of quercetin with methyl-??-cyclodextrin: photostability and antioxidant studies

Quercetin, a plant-derived flavonoid, has been extensively investigated for a wide range of potential health benefits linked to its antioxidant properties. Unfortunately the topical administration of this molecule is restricted by its fast photodegradation. In the attempt to overcome this limitation the inclusion complex between quercetin (Q) and methyl-??-cyclodextrin (Me-??-CD) was prepared and previously investigated by a molecular modelling study, a solubility diagram and a DSC analysis. Successively the kinetics of photodegradation, the antiradical, metal chelating and anti-lipoperoxidative activities were studied by comparing the complex with free Q. In addition the accumulation of Q in porcine skin was evaluated after in vitro topical application by means of vertical Franz cells. The complex formation resulted useful in enhancing the solubility of Q without significantly reducing its antioxidant ability. A modest improvement in the photostability was also observed.     

Effects of gamma irradiation on the physical and structural properties of β-glucan

This study was carried out to evaluate the effect of gamma irradiation on the physical and structural properties of β-glucan. β-Glucan solution (10%, w/v) was exposed to a cobalt-60 source (10, 30, and 50 kGy). Gel permeation chromatography data showed that the average molecular weight of irradiated β-glucan significantly decreased as the irradiation dose increased. In addition, gamma irradiation improved the solubility and decreased the viscosity of β-glucan by the radiolysis of the glycosidic bonds, and this effect was dependent upon the absorbed dose. Fourier transform infrared spectroscopy results showed that the functional groups of β-glucan were not significantly affected by gamma irradiation. Scanning electron microscopy results showed that the irradiated β-glucan was deformed into smaller granules. Therefore, gamma irradiation could be used in commercial processes as an effective method to resolve the physical problems involved in the use of β-glucan with high viscosity and low solubility.     

C2 hydroxyl group governs the difference in hydrolysis rates of methyl-α-D-glycero-D-guloseptanoside and methyl-β-D-glycero-D-guloseptanoside

A computational investigation into the hydrolysis of two methyl septanosides, methyl-α-D-glycero-D-guloseptanoside and methyl-β-D-glycero-D-guloseptanoside was undertaken. These septanosides were chosen as model compounds for comparison to methyl pyranosides and allowed direct comparison of α versus β hydrolysis rates for a specific septanoside isomer. Results suggest that hydrolysis takes place without proceeding through a transition state, an observation that was suggested in previous computational studies on exocyclic bond cleavage of carbohydrates. A conformational analysis of α- and β-anomers 1 and 2 and their corresponding oxocarbenium 3, coupled with relaxed potential energy surface (PES) scans (M06-2X/6-311+G**, implicit methanol), indicated that hydrolysis of the α-anomer is favored by 1-2 kcal/mol over the β-anomer, consistent with experiment. Model systems revealed that the lowest energy conformations of the septanoside ring system destabilize the β-anomer by 2-3 kcal/mol relative to the α-anomer, and the addition of a single hydroxyl group at the C2-position on a minimal oxepane acetal can reproduce the PES for the septanoside 1. These results suggest that the C2 hydroxyl plays a unique role in the hydrolysis mechanism, destabilizing the septanoside via its proximity to the anomeric carbon and also through its interaction with the departing methanol from the α-anomer via hydrogen-bonding interactions.     

On the validity of the correlation – Belda equation for some physical and chemical properties in 1,4-dioxane + water mixtures

Knowledge and prediction of physicochemical properties of binary mixtures is of great importance in understanding intermolecular interactions. The literature shows that most such systems exhibit non-linear behaviour. In this frame, a correlating equation was recently proposed by Belda and tested with success on 50 binary systems for density, viscosity, surface tension and refractive index. In order to assess the validity of the proposed equation, it has been applied to 1,4-dioxane + water mixtures at 298.15?K for nine physicochemical properties. These mixtures exhibit strong interactions. The results were fitted and compared with the Redlich–Kister (R–K) equation of the same number of parameters. The equation seems to offer better results for some properties than those of R–K with two free parameters.     

On the Mössbauer parameters of barium stannate

The Mössbauer parameters of barium stannate(IV) (BaSnO₃) have been studied in the temperature range 80 to 300°K and show that this material provides a suitable source matrix for ¹¹⁹Sn spectroscopy. The zero-thickness line width for BaSnO₃ absorbers at 295°K is 0·33 mm/sec. The recoil-free absorption fraction is 0·58 ± 0·02 calculated from line width measurements at 295°K and 0·53 ± 0·02 calculated from temperature dependence measurements. The room temperature isomer shift of BaSnO₃ is identical (within the experimental error of ±0·03 mm/sec) to that of SnO₂. No chemical after-effects of the 65 keV isomeric transition in ¹¹⁹Sn have been observed using these sources.     

Influence of solvent on the thermal stability and organization of self-assembling fibrillar networks in methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside gels

Sugar based low-molecular-mass organogelator (LMOG) methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside, is a unique gelator because its small and weakly-interacting molecules can form large supramolecular structures in nonpolar, but also in polar, solvents and cause their gelation. The self-assembling properties of the gelator were studied in selected nonpolar and polar solvents. It was shown that the driving forces for both types of solvent are the intermolecular hydrogen bond interaction. The effect of the nature of the solvent on the thermal stability of the gels and on the three-dimensional network organization was determined. Different solvent parameters, such as dielectric constant, one-component solubility parameter, the polarity parameter and the Kamlet-Taft parameters were considered to quantify solvent effects on the gelation. Some correlation between these parameters and the gel stability, microstructure and the enthalpy of the phase transition were established. The effort to correlate the Kamlet-Taft parameters to the thermal stability and gelation ability is also possible but applies only to the studied gelator.     

Effect of glycerol on the optical and physical properties of sol–gel glass matrices

Glass samples are prepared with different amount of glycerol as drying control chemical additive (DCCA) via acid catalysed sol–gel method. These samples are given solvent treatment namely rinse and dip with methanol while drying of the sample. In rinse treatment solid sample is rinsed with small amount of methanol while in dip treatment sample is dipped for 5 h in methanol. Comparative studies of these treated samples containing varied DCCA concentration are carried out by measuring optical transmission, mechanical strength and bulk density. Various instrumental techniques used for analysis are FTIR, DTA-TGA, XRD, SEM and TEM. The untreated samples take long time to dry up and to come out of the cuvette and show very less transmission in UV region which is much enhanced by solvent treatment. On the basis of this study, the solvent treated glass samples with DCCA amount 8 ml in the composition used are found to have the maximum UV transmission, good mechanical strength and may be useful as silica gel host matrices for solid state dye lasers and other applications. The UV transmission reported in the present studies is 90% in 337 nm region, which is the wavelength of N₂ laser pumping.     

Synthesis and physical properties of π-conjugated metallacycle polymers of cobalt and ruthenium

Recent studies on two types of π-conjugated metallacylce polymers are reviewed. Reaction of CpCo(PPh₃)₂ with conjugated diacetylenes afford poly(arylene cobaltacyclopentadienylene) and that of CpRuBr(cod) does poly(arylene ruthenacyclopentrienylene)s in ambient conditions. Regioselectivity of the former metallacycling reacion is not perfect (at most 80% of the 2,5-diaryl selectivity) but that of the latter is satisfactory (∼100% of the 2,5-diaryl selectivity) for the formation of π-conjugated structure. Electrochemical oxidation of the cobaltacyclopentadiene polymer and reduction of the ruthenacycle polymer occur facilely and quasi-reversibly by the contribution of metal d-orbitals. Physical properties in undoped (neutral) and doped (charged) sates show the behavior of electronic band structure derived from the organic π-conjugated main chain strongly coupled with the metal d-orbitals. This affords, for example, photoconductivity in the neutral form of the cobaltacylopentadiene polymer and ferromagnetic interaction in the reduced form of the ruthenacyclopentatriene polymer.     

On the Correlation between the Blue Shift of Hydrogen Bonding and the Proton Donor-Proton Acceptor Distance

It is demonstrated that in all types of hydrogen bonds (X—H…Y) there is a balance between the long-range attractive orbital interactions and short-range Pauli/nucleus repulsions. When the proton acceptor approaches the proton donor from distance, the hydrogen bonding energy becomes more negative at relatively large distance, goes through a minimum, and then starts to become less negative when the short-range repulsive forces come into effect.Meanwhile, the X--H bond length increases at relatively large distances, goes through a maximum and starts to shorten when the short-range repulsive forces come into effect. Whether the hydrogen bond is red or blue shifted is dictated by the energy minimum position. If at the energy minimum position the X—H bond length is shorter than that for the free monomer, the hydrogen bond is blue shifted and vice versa. Further studies demonstrate that the recent report about the correlation of C—H bond lengths with proton donor-acceptor distance in F3C—H…OH2 and F3C—H…Cl^- is not fully correct because the authors conducted an inappropriate comparison. Furthermore, it is shown for the first time that the Pauli/nucleus repulsion theory is applicable to the blue-shifted hydrogen bonds in the X—H…π complexes and the blue-shifted lithium bonds in the X—Li…Y complexes.     

Relationship between the structure and thermal properties of 4-n-alkyl-4’-cyanobiphenyls

The relationship between the molecular structure and thermal properties in the homologous series nCB with n = 5–10 is investigated by the Monte Carlo and atom — atomic potential methods by dividing the thermodynamic properties of liquid crystal systems into inter- and intramolecular increments. An explicit even-odd correlation between the intermolecular term of the inner configuration energy U^inter, heat capacity C _v ^inter , and the anisotropy of the geometrical form (Σ/Σ) of nCB molecules is established. It is shown that internal degrees of freedom are responsible to a certain extent for the even-odd effect of some physicochemical properties of nCB. The major contribution to the heat capacity Cy is made by the vibrational motion.     

On the excess thermodynamic properties of aqueous electrolyte solutions—I: Free energies including excess solvent isotope effects

A new approximate formulation describing the electrostatic contribution to the excess free energy of electrolyte solutions is presented. The final equation contains only one parameter and reduces to the Debye-Huckel limiting law at low enough concentrations. It represents the experimental data nicely for the series of alkali metal halides out to quite high concentration, and clarifies certain difficulties in interpretation of solvent isotope effect data with extended theories now in widespread use.     

Relationship between the analytical properties of lanthanide(III) βdiketonates and the nature of ligands

The effect of the nature of β-diketones on the spectrochemical-luminescence properties of lanthanide complexes used as analytical forms for the highly sensitive determination of some rare-earth elements was examined. NMR spectroscopy, molecular mechanics, calculations, and an experimental evaluation of the hydrophobicity of the test β-diketones indicated that an increase in the intensity, quantum yield, and lifetime of luminescence of lanthanide (Ln) β-diketonates depends on the charge distribution in the chelate ring, on the spatial structure, and on the hydrophobicity of the coordinated ligand. These factors determine the efficiency of energy transfer from the β-diketone to the Ln⁺³ ion and the decrease in energy losses caused by the quenching action of water molecules.     

Structures and physical properties of rigid polyurethane foams with water as the sole blowing agent

Polyurethane rigid foams have been used for many applications such as pipelines insulation materials, automotive parts, solar water heater and construction materials[1,2], due to their desirable physical properties. Traditional rigid foam is made by the reaction of a polyol and 4,4′-diphenylmethane diisocyanate (MDI) with chlorofluorocarbons (CFCs), in particular tri- chlorofluoromethane (CFC-11) and/or HCFC-141b as blowing agents. However, the CFCs blowing agents contain halogens, whic…     

Optical basicity—IV: Influence of electronegativity on the Lewis basicity and solvent properties of molten oxyanion salts and glasses

The Lewis basicity of oxide (expressed in terms of the optical basicity, Λ) is reduced by highly polarizing cations such as S⁶⁺, P⁵⁺, Si⁴⁺, etc. Λ is shown to be dependent upon the stoichiometry of the medium or compound, the oxidation numbers of the cations and upon a newly defined “basicity moderating” parameter, γ, which is related to the Pauling electronegativity. It is thus possible to calculate ‘theoretical’ optical basicities of various oxyanion media, and these are shown to agree well with experimentally determined optical basicities. It is suggested that such calculations may prove useful in various systems, for example in glasses and in steel-making slags, where u.v. opaqueness prevents experimental measurement of optical basicity. The contrasting solvent properties of various molten salts are explicable in terms of the values of Λ and γ, and the competitive reactions which involve both the Lux-Flood and Lewis acid-base concepts.