Degree Of Hydroxylation Research Articles

The use of $$O_2^{\begin{array}{*{20}c}--\\\cdot \\ \end{array} } $$ radical anions as spin probes for testing nanostructured materials based on zirconium oxide

The conditions of formation of $$O_2^{\begin{array}{*{20}c}--\\\cdot \\ \end{array} } $$ radical anions on the surface of zirconium oxide systems including nanostructured pillared clays, in interaction with hydrogen peroxide and an NO + O2 mixture of gases were studied by the EPR method. The special features of the formation of these radicals depending on the phase composition, structure, and degree of hydroxylation of the surface are discussed.

Effect of humidity on structure and electrochromic properties of sol–gel-derived tungsten oxide films

The influence of varying relative humidity (RH∼55 and 75%) during thin film deposition from an oxalato-acetylated peroxotungstic acid sol by dip coating, on the microstructure and electrochromic properties of pristine tungsten oxide (WO3) films obtained upon annealing is presented. The films fabricated under a relative humidity of 55% are amorphous whereas the ones cast under a substantially humid atmosphere (RH∼75%) are characterized by interconnected nanocrystallites with a triclinic phase and a nanoporous surface morphology as well. Upon lithium insertion, larger integrated values of transmission modulation and coloration efficiency are observed over the photopic and solar regions, for the films prepared under a RH∼75% as compared to that observed for the films deposited under a RH of 55%. Functional improvements are due to the larger surface area of nanocrystallites and a porous microstructure, a consequence of a higher degree of hydration and hydroxylation in the former films in contrast to the non-porous and a rather featureless structure of the latter films. Faster switching kinetics between the clear and blue states, a greater current density for lithium intercalation, a higher diffusion coefficient for lithium and a superior cycling stability, again shown by the film fabricated under a 75% RH confirm that the WO3 film microstructure is most conducive for a more facile ion insertion–extraction process, which hints at its potential for electrochromic window applications.

1H MAS NMR study of the coordination of hydroxyl groups generated upon adsorption of H 2O and CD 3OH on clean MgO surfaces

The coordination of OH groups on MgO has been characterized by 1H MAS NMR after appropriate pre-treatment conditions to obtain surfaces free from carbonates and with a controlled degree of hydroxylation. On MgO-sol–gel sample treated at 1023 K under flowing nitrogen, hydroxylated with water and evacuated at 673 K for 2 h, at least six lines have been identified at 1.2, 0.7, 0.0, −0.4, −0.7 and −1.8 ppm. Upon dehydroxylation at higher temperature, the signals become sharper and a relative decrease of intensity of the lines at δ ≥ −0.4 and at −1.8 ppm is observed. After adsorption of CD 3OH and further desorption at 473 K, an OH signal with two main lines at 0.4 and 0.0 ppm and a broad contribution around 1.0 ppm are observed. Thus deuterated methanol dissociation generates only OH groups at high chemical shift. These observations are related to the coordination of the oxygen atom of the OH groups. It is thus suggested that, when water dissociates on the surface, the OH groups coming from protonation of O 2− ions and being the more coordinated, give a signal at a higher chemical shift than the OH groups formed by coordination of a hydroxide ion to a Mg 2+. The link with the acido-basic properties is then discussed on the basis of literature data.

Liquid chromatography on porous graphitic carbon with atmospheric pressure photoionization mass spectrometry and tandem mass spectrometry for the analysis of glycosphingolipids

The study of several structural variations (the length, the degree of unsaturation and hydroxylation of the alkyl chains, the number and nature of osidic residues) helped understand the behaviour of neutral glycosphingolipids (GSLs) on porous graphitic carbon stationary phase (PGC). Atmospheric pressure photoionization mass spectrometry (APPI) and tandem mass spectrometry were used to perform the detection and the identification of molecular species in positive mode where [M + H] + and [M − H 2O + H] + ions provided structural information on the fatty acid and the sphingoid base. The retention of GSLs increased with the hydrocarboneous volume of their alkyl chains and with the number of osidic residues in agreement with hydrophobic properties and polar retention effect of graphite, respectively. The presence of polar groups, such as OH-group or double bond within alkyl chains, decreased their retention. The coupling of chromatography on PGC with APPI tandem mass spectrometry detection appeared a powerful technique to discriminate isobaric molecules. Isobaric solutes differing by the position of two double bonds or by the repartition of hydrocarboneous skeleton were discriminated according to their chromatographic comportment or their mass spectrum, respectively. Among isobaric molecules, only few structures differing by the nature of osidic residue were not discriminated (i.e. glucosylceramide and galactosylceramide with similar ceramide skeleton were co-eluted and no difference in mass spectra was observed).

An easy approach to hydroxyethylated SWNTs and the high thermal stability of the innergrafted hydroxyethyl groups

A new approach to hydroxyethylated single-walled carbon nanotubes (SWNTs) is reported.Treating SWNTs with sec-butyllithium and subsequently with epoxy ethane leads toSWNTs functionalized with both butyl and hydroxyethyl groups. The functionalizedSWNTs were characterized by Raman and FT-IR spectroscopy, thermogravimetric analysis(TGA) and atomic force microscopy. The degree of hydroxylation was estimated to be atleast one hydroxyl group for every 31 nanotube carbon atoms from the TGA dataand the resultant SWNTs can be stably dispersed in water at a concentration of0.5 mg ml−1. It was also found that the functional groups encapsulated in the channels of SWNTspossess a high thermal stability during the TGA procedure.

Molecular dynamics simulations of spontaneous bile salt aggregation

Bile salts are surfactants in bile that facilitate digestion, adsorption and excretion of various compounds. They have planar hydrophobic and hydrophilic faces and therefore exhibit some unusual properties; including the shape and size of the micelles that they form. Molecular dynamics simulations of the spontaneous aggregation of six bile salts (cholate (CHD), glycocholate (GCH), taurocholate (TCH), glycochenodeoxycholate (GCD), glycodeoxycholate (GDX) and glycolithocholate (GLC)) were performed in an aqueous phase to gain insight into their micellar structure. The aggregates that formed spontaneously from a random distribution of molecules ranged in size from 8 to 17 molecules. The structures are highly dynamic in nature and are on average oblate, but can vary from oblate, to spherical or prolate. Intermolecular hydrogen bonding within the micelles was found to be an important factor in determining the micelle size, structure and dynamics. The molecular arrangement within the micelles maximises the hydration of the hydrophilic chains and some favourable orientations for adjacent molecules were acquired. The dynamics of the micelles were investigated using the hydrogen-bond lifetime autocorrelation function correlation time, which exhibited a relationship with the degree of hydroxylation. Comparison of the proposed model to the three literature models showed some features of the disk shaped models of Cary and Small [M.C. Cary, D.M. Small, Arch. Intern. Med. 130 (1972) 506–527] and Kawamura et al. [H. Kawamura, Y. Murata, T. Yamaguchi, H. Igimi, M. Tanaka, G. Sugihara, J.P. Kratohvil, J. Phys. Chem. 93 (1989) 3321–3326], whereas the third, inverted helix model of Giglio et al. [E. Giglio, S. Loreti, N.V. Pavel, J. Phys. Chem. 92 (1988) 2858–2862] can be discounted. The proposed model is better than the existing models, which assumed a rigid and structured molecular arrangement.

Hydroxyl-bearing poly(α-hydroxy acid)-type aliphatic degradable polyesters prepared by ring opening (co)polymerization of dilactones based on glycolic, gluconic and l-lactic acids

The synthesis of HO-protected poly(glycolic acid- co-gluconic acid) and poly( l-lactic acid- co-glycolic acid- co-gluconic acid) by copolymerisation of l-lactide and 3-(1,2-3,4-tetraoxobutyl-diisopropylidene)-1,4-dioxane-2,5-dione (DIPAGYL) is reported. The resulting polymers were characterized by size exclusion chromatography, FT Infrared, nuclear magnetic resonance, differential scanning calorimetry and X-ray diffractometry. The composition of reaction media and the reactivity ratios of the two cyclic monomers were determined at low conversion and indicated random distributions of lactyl and gluconoglycolyl constitutive units. X-ray diffraction data showed semi-crystalline morphology, as observed for poly (lactide) stereocopolymers containing more than 90% of l-enantiomer. Deprotection of the isopropylidene-protected side chain OH was possible under acidic conditions and yielded copolymers with various degrees of hydroxylation. Deprotection of the 5–6 OH groups was fast and complete whereas that of 3–4 ones was partial and occurred at the expenses of partial degradation of the aliphatic polyester chains. T g increased with the number of hydroxyl functions, a feature attributed to the formation of hydrogen bonds. Comparison is made with features reported previously for analogs derived from dl-lactide.

Assessing the antioxidant and pro-oxidant activity of phenolic compounds by means of their copper reducing activity

The antioxidant or pro-oxidant activity of some dietary phenolic compounds has been determined by their reducing activity over Fe3+ and Cu2+. The FRAP method has shown that phenolic acids exert a high reducing activity that give rise to a decrease in linoleic acid oxidation mediated by Fe3+, measured as TBARS. However, the reducing activity of phenolic compounds over Cu2+ leads to linoleic acid oxidation. Reducing capability against copper has been measured by a new approach called CRAI (Copper Reducing Activity Index), and results agreed with the degree of hydroxylation of the studied compounds. Sensibility and reproducibility of the method have been checked by measuring the inter-day and intra-day variation (1.08 and 1.89%, respectively). Possible pro-oxidant activity of phenolic compounds should be considered when the overall antioxidant activity in Cu naturally rich or Cu-enriched foodstuffs for dietetic purposes has to be evaluated.

Cleanability of Stainless Steel Surfaces as Influenced by Heat Treatment

The cleanability of heat-treated 316L stainless steel particles treated at various temperatures of 100 to 500 degrees C was studied in a plug-flow column fed by a 0.1M NaOH solution. Bovine Serum albumin (BSA) was used as the model fouling agent. Heat treatment resulted in the enrichment of iron in passive films on stainless steel particles depending on temperature. The degree of surface hydroxylation and the apparent surface charge density (sigma(app)) of stainless steel particles decreased markedly with increasing heating temperatures. The saturation amounts of BSA adsorbed (gamma(sat)) were larger on the particles heated at higher temperatures. No correlation was observed between the gamma(sat) and sigma(app) values. With increasing heating temperatures, the rate of BSA desorption from stainless steel particles decreased gradually in the initial and later stages of cleaning, resulting in larger amounts of BSA remaining on the particles at the end of 120-min of cleaning. The susceptibility to BSA adsorption and the cleanability were found to be correlated with the iron content of the passive films on stainless steel particles. It could be suggested that the decrease in the cleanability was probably due to the formation of iron-enriched passive films with lower degrees of surface hydroxylation of stainless steel particles due to heat treatment.

Asymmetric total synthesis of B-ring modified (−)-epicatechin gallate analogues and their modulation of β-lactam resistance in Staphylococcus aureus

Two enantiomerically pure B-ring modified analogues of (−)-epicatechin gallate were synthesised and their modulation of β-lactam resistance using three strains of methicillin resistant Staphylococcus aureus (BB 568, EMRSA-15 and EMRSA-16) evaluated. Sub-inhibitory concentrations (12.5 and 25 mg/L) of the two analogues fully sensitised each of the three MRSA strains to oxacillin, reducing the MIC to less than 0.5 mg/L, identical to levels achieved with ECg. Lower concentrations demonstrated that the position and degree of hydroxylation of the B-ring is important for activity.

Natural and newly synthesized hydroxy-1-aryl-isochromans: A class of potential antioxidants and radical scavengers

We investigated the antioxidant and radical scavenging activity of polyphenolic isochromans. To assess the relation between structure and scavenging properties the natural occurring 1-(3′-methoxy-4′-hydroxy)phenyl-6,7-dihydroxy-isochroman (ISO-3, three OH groups) was compared with three newly synthesized derivatives that differ in their degree of hydroxylation by substitution with methoxy-groups (ISO-4: four OH groups; ISO-2: two OH groups and ISO-0: fully methoxylated). We found that ISO-4 is a 2-fold better scavenger for the artificial radical 1,1-diphenyl-2-picrylhydrazyl (DPPH, 100 μM) with an EC50=10.3 μM compared to the natural ISO-3 (EC50=22.4 μM) and to ISO-2 (EC50=25.1 μM), while ISO-0 did not react with DPPH. The scavenging capacity for superoxide enzymatically generated in a hypoxanthin-xanthinoxidase reaction was the highest for ISO-4 (EC50=34.3 μM) compared to those of ISO-3 (EC50=84.0 μM) and ISO-2 (EC50=91.8 μM), while ISO-0 was inactive. In analogy, ISO-4 scavenged peroxynitrite (ONOO−, EC25=23.0 μM) more effective than ISO-3, ISO-2 and ISO-0.When C6 rat glioma cells loaded with the reactive oxygen/nitrogen (ROS/RNS)-sensitive fluorochrome 2,7-dichlorodihydrofluorescein, were exposed to hydrogen peroxide, the lowest stress level as indicated by the fluorescence signal was detected when the cells were pretreated with ISO-4 or ISO-2 but to a much lesser extent with ISO-3, while ISO-0 did not show any effect. All tested hydroxyisochromans superceded the scavenging effect of trolox.The excellent radical and ROS/RNS scavenging features of the hydroxy-1-aryl isochromans and their simple synthesis let these compounds appear to be interesting candidates for pharmaceutical interventions that protect against the deleterious action of ROS/RNS.

Water adsorption on plasma sprayed transition metal oxides

The aim of this study was to characterize water adsorption on plasma sprayed chromia and titania coatings. Both materials are widely used in industry as wear and corrosion resistant coatings. During plasma spraying both materials become oxygen deficient so that high concentrations of oxygen vacancies are formed. Vapor adsorption experiments were performed using microcalorimetry and isothermal gas adsorption experiments. Studies were performed to samples of two or three different degree of surface hydroxylation. The surface hydroxide content was controlled using heat treatments at 100, 200 or 400 °C. All experiments were repeated to plasma sprayed coating samples, which were pre-heat-treated (12 h at 1000 °C). It was found that behavior of water adsorption is sensitive to both temperature of dehydroxylation and initial concentration of surface defects especially for TiO 2 samples.

Liquid Chromatography–Tandem Mass Spectrometry Quantification of Globotriaosylceramide in Plasma for Long-Term Monitoring of Fabry Patients Treated with Enzyme Replacement Therapy

Fabry disease is a rare X-linked lysosomal storage disorder resulting from a deficiency in the α-galactosidase A enzyme. Deficiency in the activity of this enzyme causes an accumulation of neutral glycosphingolipids, predominantly globotriaosylceramide (GL-3), in most nonneural tissues and in body fluids (1). Recent clinical studies indicate that tissue and plasma GL-3 concentrations in Fabry patients can be significantly reduced by enzyme replacement therapy (2)(3)(4)(5). GL-3 (see Fig. 1 in the Data Supplement that accompanies the online version of this Technical Brief at http://www.clinchem.org/content/vol51/issue1/) exists as a mixture of structural isoforms containing acyl chains ranging from 16 to 24 carbons in length with various degrees of saturation and hydroxylation. These variations make the extraction and quantification of GL-3 challenging (6)(7). Moreover, no well-characterized reference standards of known purity are available. GL-3 in tissues and plasma has been measured by thin-layer chromatography (8)(9), liquid chromatography (LC) (10)(11)(12)(13)(14)(15), and gas chromatography(16), but the methods are labor-intensive and slow. An enzyme-linked immunosorbent assay (17) requires recombinant verotoxin B and polyclonal rabbit anti-verotoxin B. To date, the most rapid quantitative assays for total GL-3 have used flow-injection tandem mass spectrometry (MS/MS) (18)(19). We now report the development and use of a rapid LC/MS/MS method for the quantitative determination of total plasma GL-3. Porcine GL-3 and porcine globotriaosylsphingosine A ( lyso -GL-3), from Matreya, were ≥98% pure by thin-layer chromatographic analysis. C16:0-GL-3 and C17:0-GL-3 were enzymatically synthesized from lyso -GL-3 at Genzyme Pharmaceuticals (18). C16:0-enriched GL-3 was prepared by gravimetrically combining C16:0-GL-3 and porcine GL-3 in a 9:25 g/g mass ratio. Methanol, water, and chloroform were HPLC grade. Normal heparin-plasma samples from 104 men and 101 women were obtained from Interstate Blood …

Crystal-Chemical Characteristics of Silicon−Neodymium Substituted Hydroxyapatites Studied by Combined X-ray and Neutron Powder Diffraction

Neodymium−silicon britholites, Ca10-xNdx(PO4)6-x(SiO4)x(OH)2, have been synthesized by the ceramic method. These materials can be used as host matrixes for actinides immobilization and Nd models the actinide. The crystal-chemistry evolution as a function of the Si and Nd content has been studied by combined neutron and X-ray Rietveld refinement. The SiO44- substitution for PO43- does not lead to significant changes in the PO4 tetrahedrons. The Nd3+ cations substitute for Ca2+ and are placed at the Ca(2) sites, getting closer to the hydroxyl sites. The local increase of positive charge around hydroxyls leads to the O2- stabilization in 4e Wyckoff position. Since neutrons are sensitive to the H atoms, the hydroxylation degree has been calculated. Finally, the scattering density Fourier difference maps suggest the presence of HPO42- groups, which partially substitute for PO43- to keep the electric balance of these compounds.

Effects of Triblock Copolymer Architecture and the Degree of Functionalization on the Organoclay Dispersion and Rheology of Nanocomposites

The effects of triblock copolymer architecture (ABA-type vs ABC-type) and the degree of functionalization on the organoclay dispersion in nanocomposites were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and linear dynamic viscoelasticity. For the study, a lamella-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and a homogeneous polyisoprene-block-polystyrene-block-polybutadiene (ISB triblock) copolymer were synthesized via sequential anionic polymerization. Subsequently, the polyisoprene block of the SIS triblock copolymer was hydroxylated yielding an SIOHS triblock copolymer, and the polybutadiene block of the ISB triblock copolymer was hydroxylated yielding an ISBOH triblock copolymer. The degree of hydroxylation in both SIOHS and ISBOH triblock copolymers was varied. Both the unfunctionalized (SIS and ISB) and functionalized (SIOHS and ISBOH) triblock copolymers were used to prepare nanocomposites with two different types of organ...

Specific interactions of quercetin and other flavonoids with target proteins are revealed by elicited fluorescence

The fluorogenic properties of quercetin and similar flavonoids common in plants were exploited to analyse their interaction with target proteins. Quercetin produced a strong fluorescent signal upon binding to bovine serum albumin (BSA) and insulin. The fluorescent signal showed saturation kinetics with increasing flavonoid concentrations indicating the presence of defined peptide binding motifs. Other tested proteins showed no fluorescence with the flavonoids. In a comparative study including 22 flavonoids the compounds with fluorogenic properties were identified using our model proteins BSA and insulin and the structural requirements for the fluorogenic property were defined. Only flavones with a high degree of hydroxylation were able to elicit fluorescence. The emitted fluorescence was strongly enhanced at alkaline pH. Finally, an attempt was made to identify intracellular target molecules in live cells. Drosophila follicles showed a distinct staining pattern thus giving evidence that high concentrations of quercetin binding proteins are present in the nuclei and are associated with the ring canals. The presented biochemical and cytological data show that the interaction of the studied flavonoids with target proteins is specific and this finding opens up new experimental possibilities to systematically identify the cellular proteins with specific binding motifs for quercetin or other fluorogenic compounds of medical interest.

Permeability characteristics and membrane affinity of flavonoids and alkyl gallates in Caco-2 cells and in phospholipid vesicles

Biomembrane interactions of flavonoids and alkyl gallates were investigated using transport studies on Caco-2 cells and membrane affinity experiments in phospholipid vesicles. Flavone was rapidly absorbed across the cell monolayer ( P app,380×10 −6 cm/s), whereas efficient uptake but no apical to basolateral transport was observed with the flavonoids with higher degree of hydroxylation (e.g., quercetin and luteolin). The transport of alkyl gallates was governed by the length of the alkyl chain, i.e., methyl and propyl gallate were absorbed while octyl gallate showed cellular uptake but no transport. Flavonoids with several hydroxyl groups exhibited highest affinity for vesicle membranes, partition coefficients being 7.1 and 7.5 μM for luteolin and quercetin, respectively. In conclusion, the degree of hydroxylation, molecular configuration, and length of the side chain of flavonoids and alkyl gallates seem to have a highly important impact on their membrane affinity as well as on their permeability characteristics in Caco-2 cells.

Effect of the Interfacial Chemical Environment on In-Plane Electronic Conduction of Indium Tin Oxide: Role of Surface Charge, Dipole Magnitude, and Carrier Injection

Reaction of the indium tin oxide (ITO) surface with Brønsted acids (bases) leads to increases (decreases) in its in-plane conductance as measured by a four-point probe configuration. The conductance varies monotonically with pH, suggesting that the degree of surface protonation or hydroxylation controls the surface charge density, which in turn affects the width of the n-type depletion layer and ultimately the in-plane conductance. Measurements at constant pH with a series of tetraalkylammonium hydroxide species of varying cation size indicate that surface dipoles also affect ITO conductance by modulating the magnitude of the surface polarization. Modulating the double layer with varying aqueous salt solutions also affects ITO conductance, though not to the same degree as strong Brønsted acids and bases. Solvents of varying dielectric constant and proton donating ability (ethanol, dimethylformamide) decrease ITO conductance relative to H2O. In addition, changing solvent gives rise to thermally derived conductance transients, which result from exothermic solvent mixing. The self-assembly of alkanethiols at the surface increases the conductance of ITO films, most likely through carrier population effects. In all cases examined the combined effects of surface charge, adsorbed dipole layer magnitude, and carrier injection are responsible for altering the ITO conductance. Besides being directly applicable to the control of electronic properties, these results also point to the use of four-point probe resistance measurements in condensed phase sensing applications.

Relevance of posttranslational modifications for the arthritogenicity of type II collagen.

To establish the role of posttranslational modification in modulating the immune response to collagen, recombinant human type II collagen (rCII) was produced using a yeast expression system (rCII(pic)) and a baculovirus expression system (rCII(bac)). The biosynthesis of CII requires extensive posttranslational modification including the hydroxylation of prolyl and lysyl residues and glycosylation of selected hydroxylysyl residues. Amino acid analyses indicated that the rCII(bac) was adequately hydroxylated at prolyl residues but underhydroxylated at lysyl residues and underglycosylated compared with tissue-derived CII, whereas rCII(pic) was adequately hydroxylated at prolyl residues but unhydroxylated at lysyl residues and had no glycosylation. When DBA/1 mice were immunized with rCII, rCII(pic) induced a lower incidence of arthritis than tissue-derived CII, whereas rCII(bac) induced an intermediate level of arthritis. The severity of the arthritis was significantly lower in mice immunized with rCII(pic) compared with mice immunized with tissue-derived CII, whereas that of rCII(bac) was intermediate. These data indicate that the degree of lysine hydroxylation and glycosylation plays a role in the induction of arthritis. The recombinant collagens were then compared with tissue-derived CII when given as i.v. or oral tolerogens to suppress arthritis. Both recombinant collagens were less potent than tissue-derived CII, and this decrease in arthritis was associated with a decrease in Ab response to CII. These data suggest that the degree of glysosylation affects the immune response to CII, so that underglycosylated CII is less effective in the induction of arthritis and in its ability to suppress collagen-induced arthritis.

Simulating the atomic layer deposition of alumina from first principles

Atomic Layer Deposition (ALD) is a chemical vapour deposition technique that is suitable for the controlled growth of thin, conformal oxide films. Insulating layers of alumina (Al2O3) are fabricated by ALD for electroluminescent flat-screen-displays, memory capacitors and read/write heads. Successful precursors for alumina ALD are trimethylaluminium (TMA) and water. Various models for the mechanism of alumina ALD have been proposed but definitive evidence for the surface intermediates is lacking. We therefore use density functional theory to investigate the atomic-scale structure and reactivity of bare and hydroxylated alumina surfaces with respect to TMA. The competition between dissociative chemisorption and molecular desorption is quantified. The calculations show that TMA adsorbs and dissociates at both O and OH sites on the surface, but that these lead to different ALD efficiencies. In this way we clarify how the degree of surface hydroxylation and hence the substrate temperature affects the ALD growth rate.