Higher Degree Of Hydroxylation Research Articles

DFT study on Mo-stabilized passive films: Hydroxylation effects on chromium and iron oxide surfaces

Hydrous Cr2O3 and Fe2O3 surfaces without and with substitutional molybdenum were simulated by DFT modelling to investigate at the atomic scale the role of Mo in improving the corrosion resistance of passive films on stainless steels. The surface structures most energetically favoured were determined in the conditions of interest. For surfaces with a high degree of hydroxylation, the preferential location of substitutional Mo is just under the hydroxyl groups, in agreement with the experimental observations. The substitution by Mo is exothermic and Mo preferentially substitutes in Fe- than in Cr-rich zone of the inner barrier layer of passive films.

Preparation of Antioxidative MXene by Deep Eutectic Solvent-Assisted Electrochemical Ultrasonic Composite Exfoliation and Its Application in Flexible Solid-State Supercapacitors

In this work, we achieved a novel preparation of Ti3C2 MXene (MXene–DES) with few layers and a high degree of hydroxylation by a deep eutectic solvent (DES)-assisted electrochemical ultrasonic composite exfoliation method which is easy to scale up. The electrochemical process used a mixture of low-cost DES (choline chloride–urea) and water as the electrolyte, in which DES acts as a triple role of intercalation, interlayer expansion, and anti-oxidation. DES attached to the surface and interlayer of layered Ti3C2 formed an antioxidative protective cover, resulting in the layered Ti3C2 being grafted with hydroxyl functional groups instead of forming TiO2 in water during the entire exfoliation process. The prepared MXene–DES exhibits fewer layers, larger interlayer spacing, higher degree of hydroxylation, and stronger oxidation resistance than the MXene prepared by traditional ultrasound in a nitrogen atmosphere (MXene–N2). The symmetric flexible solid-state supercapacitor based on an activated carbon electrode and the composite gel polymer electrolyte composed of MXene–DES, DES, and polyvinyl alcohol exhibits good mechanical properties, a wide voltage window of 2.3 V, and a high specific capacitance of 133.7 F·g–1 (0.1 A·g–1). Our strategy paved a simple, low-cost, and relatively environmentally friendly way to the scalable preparation and application of antioxidative high-quality MXene.

New Atomistic Insights on the Chemical Mechanical Polishing of Silica Glass with Ceria Nanoparticles.

Reactive molecular dynamics simulations have been used to simulate the chemical mechanical polishing (CMP) process of silica glass surfaces with the ceria (111) and (100) surfaces, which are predominantly found in ceria nanoparticles. Since it is known that an alteration layer is formed at the glass surface as a consequence of the chemical interactions with the slurry solutions used for polishing, we have created several glass surface models with different degrees of hydroxylation and porosity for investigating their morphology and chemistry after the interaction with acidic, neutral, and basic water solutions and the ceria surfaces. Both the chemical and mechanical effects under different pressure and temperature conditions have been studied and clarified. According to the simulation results, we have found that the silica slab with a higher degree of hydroxylation (thicker alteration layer) is more reactive, suggesting that proper chemical treatment is fundamental to augment the polishing efficiency. The reactivity between the silica and ceria (111) surfaces is higher at neutral pH since more OH groups present at the two surfaces increased the Si-O-Ce bonds formed at the interface. Usually, an outermost tetrahedral silicate unit connected to the rest of the silicate network through a single bond was removed during the polishing simulations. We observed that higher pressure and temperature accelerated the removal of more SiO4 units. However, excessively high pressure was found to be detrimental since the heterogeneous detachment of SiO4 units led to rougher surfaces and breakage of the Si-O-Si bond, even in the bulk of the glass. Despite the lower concentration of Ce ions at the surface resulting in the lower amount of Si-O-Ce formed, the (100) ceria surface was intrinsically more reactive than (111). The different atomic-scale mechanisms of silica removal at the two ceria surfaces were described and discussed.

Adsorption of Epoxy Oligomers on Iron Oxide Surfaces: The Importance of Surface Treatment and the Role of Entropy.

Epoxy-based coatings are widely used in a range of industries as protective coatings. The performance of the final solid-polymer system is dependent on the physicochemical properties of the interface and the interaction between the polymer and the solid substrate. In this study, we perform atomistic molecular dynamics simulations to investigate the binding of a common component in epoxy resins, diglycidyl ether of bisphenol A (DGEBA), on two iron oxide surfaces, hematite (0001) and magnetite (100), and investigate the effect of surface hydroxylation on the binding energy. We show that adsorption of DGEBA on hematite is more favorable than on magnetite and that the adsorbed molecules are highly localized on the pristine hematite surface but mobile on highly hydroxylated hematite surfaces and magnetite surfaces irregardless of surface hydroxylation fraction. A high degree of hydroxylation significantly reduces the binding energy of DGEBA on hematite but not on magnetite. The free-energy calculations confirm the trends observed upon hydroxylation, but the magnitude of the potential of mean force is lower than the binding energy due to the entropic contributions. Therefore, it can be suggested that DGEBA will adsorb more strongly on a surface containing a higher content of hematite than magnetite and that the presence of hydroxyl groups will weaken this adsorption. The presence of hydroxyl groups increases mobility of the chains, which can affect the coating rigidity.

Quantitative structure–activity relationship between antioxidant capacity of phenolic compounds and the plasmonic properties of silver nanoparticles

Plasmonic response of silver nanoparticles (AgNPs) reduced with phenolic compounds were evaluated and correlated with the antioxidant capacities of corresponding phenolic compounds and their relative chemical structures. The reference methods including DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging assays were used for the measurement of antioxidant capacity of phenolic compounds which was positively correlated with redox characteristics of these compounds against the formation of AgNPs. It is found that the higher plasmonic response of AgNPs corresponds to the highest antioxidant capacity of phenolic acids, which in turn depends on chemical structures and degree of hydroxylation. The higher degree of hydroxylation in chemical structures of phenolic compounds demonstrated the higher radical scavenging capacity and higher tendency to reduce Ag+ to AgNPs. The influence of reaction time and temperature on reducing efficiency of the tested phenolic compounds is found to be different. Some phenolic compounds such as quercetin, rutin and gallic acid reacted fast (< 1.0 min) while others were found slow reacting. This study establishes the relationship between the antioxidant capacity of phenolic acids and corresponding optical response by means of plamonics, which can be used as an innovative antioxidant detection assay for samples rich in phenolic compounds.

Hot-melt extrusion of polyvinyl alcohol for oral immediate release applications

The primary purpose of this study was to process partially hydrolyzed PVOH grades (degree of hydroxylation (DH): 33–88%) via HME and to evaluate them as carrier for oral immediate release dosage forms in order to improve the release rate of poorly water soluble drugs (i.e., HCT and CEL) via the formulation of solid dispersions. PVOH grades (DH >70%) were able to solubilize HCT and CEL up to 15%, but required higher extrusion temperature, due to the crystalline nature of PVOH. The highest drug release rate was observed from hot-melt extruded PVOH samples with a high DH. While drug release from extrudates consisting of PVOH with a low DH was affected by ionic strength, there was no influence of pH and ionic strength on HCT release from PVOH samples with a higher DH. However, PVOH (DH >70%) required higher extrusion temperatures, which could hamper its application for thermosensitive drugs. Therefore, the secondary purpose was to investigate the effect of sorbitol, a water-soluble plasticizer, on the thermal properties of hot-melt extruded PVOH (DH >70%). The melting of PVOH/sorbitol mixture was required to establish molecular interactions between PVOH and sorbitol. These molecular interactions were reflected in the HME behavior: whereas an extrusion temperature of 180°C was necessary to process physical mixtures of PVOH (DH >70%) and sorbitol, only 140°C was necessary during re-extrusion (after quench cooling and cryomilling) of the PVOH/sorbitol mixture. In addition, the in vitro and in vivo dug release of plasticized PVOH was examined; whereas the CEL/PVO/sorbitol system was able to maintain supersaturation during in vitro dissolution (0.1N HCl) compared to Celebrex®, the in vivo pharmacokinetic parameters (AUC0–24h, Cmax and Tmax) were highly comparable.

Adrenal hormonal imbalance in acute intermittent porphyria patients: results of a case control study.

BackgroundAcute Intermittent Porphyria (AIP) is a rare disease that results from a deficiency of hydroxymethylbilane synthase, the third enzyme of the heme biosynthetic pathway. AIP carriers are at risk of presenting acute life-threatening neurovisceral attacks. The disease induces overproduction of heme precursors in the liver and long-lasting deregulation of metabolic networks. The clinical history of AIP suggests a strong endocrine influence, being neurovisceral attacks more common in women than in men and very rare before puberty. To asses the hypothesis that steroidogenesis may be modified in AIP patients with biochemically active disease, we undertook a comprehensive analysis of the urinary steroid metabolome.MethodsA case–control study was performed by collecting spot morning urine from 24 AIP patients and 24 healthy controls. Steroids in urine were quantified by liquid chromatography-tandem mass spectrometry. Parent steroids (17-hydroxyprogesterone; deoxycorticosterone; corticoesterone; 11-dehydrocorticosterone; cortisol and cortisone) and a large number of metabolites (N = 55) were investigated. Correlations between the different steroids analyzed and biomarkers of porphyria biochemical status (urinary heme precursors) were also evaluated. The Mann–Whitney U test and Spearman’s correlation with a two tailed test were used for statistical analyses.ResultsForty-one steroids were found to be decreased in the urine of AIP patients (P < 0.05), the decrease being more significant for steroids with a high degree of hydroxylation. Remarkably, 13 cortisol metabolites presented lower concentrations among AIP patients (P < 0.01) whereas no significant differences were found in the main metabolites of cortisol precursors. Nine cortisol metabolites showed a significant negative correlation with heme precursors (p < 0.05). Ratios between the main metabolites of 17-hydroxyprogesterone and cortisol showed positive correlations with heme-precursors (correlation coefficient > 0.51, P < 0.01).ConclusionsComprehensive study of the urinary steroid metabolome showed that AIP patients present an imbalance in adrenal steroidogenesis, affecting the biosynthesis of cortisol and resulting in decreased out-put of cortisol and metabolites. This may result from alterations of central origin and/or may originate in specific decreased enzymatic activity in the adrenal gland. An imbalance in steroidogenesis may be related to the maintenance of an active disease state among AIP patients.

Carboxymethylated-κ-casein: A convenient tool for the identification of polyphenolic inhibitors of amyloid fibril formation

Reduced and carboxymethylated-κ-casein (RCM-κ-CN) is a milk-derived amyloidogenic protein that readily undergoes nucleation-dependent aggregation and amyloid fibril formation via a similar pathway to disease-specific amyloidogenic peptides like amyloid beta (Aβ), which is associated with Alzheimer’s disease. In this study, a series of flavonoids, many known to be inhibitors of Aβ fibril formation, were screened for their ability to inhibit RCM-κ-CN fibrilisation, and the results were compared with literature data on Aβ inhibition. Flavonoids that had a high degree of hydroxylation and molecular planarity gave good inhibition of RCM-κ-CN fibril formation. IC 50 values were between 10- and 200-fold higher with RCM-κ-CN than literature results for Aβ fibril inhibition, however, with few exceptions, they showed a similar trend in potency. The convenience and reproducibility of the RCM-κ-CN assay make it an economic alternative first screen for Aβ inhibitory activity, especially for use with large compound libraries.

Cultivar differences of total anthocyanins and anthocyanidins in red and purple-fleshed potatoes and their relation to antioxidant activity

Total anthocyanins (TAC) and individual anthocyanidins (AN) after hydrolysis were measured in 15 red and purple-fleshed potato cultivars produced in five different locations in the Czech Republic and a new cultivar Blaue St. Galler from Switzerland. It was found that TAC, expressed as cyanidin content, varied between 0.7 mg 100 g −1 FW (cv. Blue Congo) and 74.3 mg 100 g −1 FW (cv. Blaue Ludiano). Major differences in cultivars were found for AN relative abundance. For cv. Highland Burgundy Red a high proportion of pelargonidin (98.7%) was characteristic, whereas cv. British Columbia Blue contained almost exclusively cyanidin. Cultivars Violette and Vitelotte showed a relatively high content of malvidin. Cultivar Shetland Black differed from others with its higher content of peonidin (on average 36.7%). High petunidin abundance in the cultivars Valfi, Blue Congo, Salad Blue, Blaue St. Galler, Blaue Hindel Bank, Blaue Ludiano, Blaue Schweden, Farbe Kartoffel and Salad Red was found. TAC and AN contents highly corresponded with antioxidant activity (AA) determined with the ABTS, FRAP and DPPH assays in vitro. High AA was shown by the cultivars Vitelotte, Violette, Blaue Ludiano, Hafija, and Highland Burgundy Red. Increased height above sea level, higher annual sum of precipitation, and lower annual average temperatures caused higher AA and TAC. A high degree of hydroxylation and/or methoxylation of individual anthocyanidins could contribute in conjunction with other phenolics to high AA (peonidin, delphinidin and malvidin in the cultivars Blue Congo, Highland Burgundy Red and Shetland Black). Consequently, new red and purple-fleshed cultivars with high TAC and highly methoxylated and/or hydroxylated AN could be a promising source of favourable antioxidants in human nutrition.

Stability of Ba,K/CeO 2 catalyst during diesel soot combustion: Effect of temperature, water, and sulfur dioxide

In this work we study the stability of Ba,K/CeO 2 catalysts, which have been shown to be very active for soot combustion. The effects of high-temperature treatments and the presence of water or sulfur dioxide on the catalytic properties for soot oxidation are studied. Fresh and deactivated catalysts are characterized by XPS, FTIR, XRD, and high-frequency CO 2 pulses, and the activity is measured by TPO. Barium has only a minor effect on the activity for soot combustion, whereas potassium has a pronounced effect in decreasing the temperature needed to burn soot. In the case of Ba,K/CeO 2, optimum activity as a function of potassium content of around 7 wt% is found. The optimum, which is very smooth, is due to the synergistic effect between K and CeO 2. This catalyst is thermally stable up to 830 °C and does not deactivate even after 30 h at 800 °C. At higher temperatures, a decrease in the K/Ce surface ratio and formation of the BaCeO 3 perovskite, indicated by the XPS analyses, are the causes of activity loss. In these cases, there is a decrease in the level of interaction with CO 2. The presence of water at 400 °C does not lead to any significant modification of catalytic activity. However, the presence of water at 800 °C leads to both a drastic decrease in activity and a change in surface composition as indicated by XPS, with a high degree of hydroxylation and probably a spreading of BaO on the ceria surface. The presence of SO 2 (1000 ppm in air) at 400 °C deactivates the catalyst for soot oxidation even after rather short times (32 h). Under these conditions, FTIR and XPS analyses show that barium, potassium, and cerium sulfates are formed. Consequently, the activity for soot oxidation is lost, and there is no interaction between the catalyst and the CO 2. This type of catalyst has good thermal stability and very good tolerance to water at low temperatures (e.g., 400 °C). However, high concentrations of SO 2 lead to rapid deactivation. This should not be a major drawback, because in the near future a much lower level of sulfur in diesel fuel is expected.

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.

Tannin diagenesis in mangrove leaves from a tropical estuary: a novel molecular approach

Molecular-level condensed tannin analyses were conducted on a series of mangrove (Rhizophora mangle) leaves at various stages of decomposition in a tropical estuary. Total molecular tannin yields ranged from 0.5% ash-free dry weight (AFDW) in the most highly degraded black leaves (6–7 weeks in the water) up to >7% AFDW in fresh leaves (<1 week in the water). Total tannin exhibits an intermediate lability in these leaves relative to other measured biochemicals. Leaching is an important mechanism in tannin removal from leaves as indicated by the 30% loss of measurable tannin during a leaching experiment. Condensed tannin was >80% procyanidin (PC) with the remainder being prodelphinidin (PD). PD tannin, with its higher degree of hydroxylation, proved to be more labile than PC tannin. Average chain length of condensed tannin (degree of polymerization) exhibited an initial increase in response to leaching, but later decreased in the subsequent shift toward abiotic or microbially mediated chemical reactions. Several trends point toward a possible condensation reaction in which tannin plays a role in nitrogen immobilization. These include an apparent inverse correlation between molecular tannin and nitrogen, a positive correlation between molecular tannin and percent basic amino acids, 13C-NMR data indicating transformation of tannin as opposed to remineralization, and 13C-NMR data showing loss of condensed tannin B-ring phenolic carbons coupled with preservation of A-ring phenolic carbon. In addition to condensed tannin, the molecular method used also yielded several triterpenoids. Triterpenoids accounted for up to 3.5% AFDW of the leaf material and exhibited a threefold increase between yellow senescent leaves entering the estuary and black leaves. This trend is likely due to the weakening of protective cuticular membranes during leaf decomposition, which leads to increased yields in the acidic conditions used for tannin analyses.

Tin oxide surfaces. Part 18.—Infrared study of the adsorption of very low levels (20–50 ppm) of carbon monoxide in air on to tin (IV) oxide gel

Three major types of surface species, unidentate carbonate, bidentate carbonate and carboxylate, are formed when tin(IV) oxide is exposed to dry air containing very low levels of CO(20–50 ppm). All three types appear to be formed immediately and simultaneously upon exposure to the CO–air mixtures, and the abundance of each continues to increase during the period of exposure. Little adsorption occurs at low oxide calcination temperatures when the surface retains a relatively high degree of hydroxylation, but abundances of the three surface species increase markedly at temperatures > 570 K, and appear to reach a maximum at calcination temperatures of ca. 590–610 K, declining thereafter. Although quite stable at lower temperatures, the surface bidentate carbonate and carboxylate slowly transform into surface unidentate carbonate at temperatures ca. 400 K under an atmosphere of dry air.

Comparative studies on collagen glycosylation in chick skin and bone

Glycosiylation has been examined in Type I collagens from chick skin and bone in situations where the amount of hydroxylysine in these collagens is known to vary. The following observations were made. 1. 1. The age-dependent decrease in the hydroxylation of lysine known to occur in both α1- and α2-chains, mostly in the immediate post-embroyonic peiod, was found to coincide with a reduction in these chains in the level of glycosylation which fell from approximately nine glycosylated residues per molecule in skin and seven in bone to a relatively constant value, in each, approaching four. 2. 2. The ratio of glucosylgalactosyl- to galatocylhydroxylysine remained generally in the region of two in bone but declined with age to a value of unity or less in skin. 3. 3. Increased hydroxylation in bone collagen in calium deficiency equivalent to 5–6 residues of hydroxylysine per chain, was accompanied by an increase in glycosylation amounting only to about one-half residue per chain. There was no change in the ratio of di- to monosaccharide substitution. 4. 4. The relatively high degree of hydroxylation in embryonic collagens of the lysyl residue located in the N-terminal, non-helical telopeptide region of the α1 (I)-chain was associated with only minimal glycosylation. The significance of these findings is discussed and in particular it is concluded that there is no readily-discernible, tissue-dependent pattern of glycosylation that could indicate a role for the latter in calcification for example.

Hydroxylysine in the N-terminal regions of the 1 - and 2 -chains of various collagens.

The degree of hydroxylation of the lysine residue located in both alpha(1)- and alpha(2)-chains of collagen in the N-terminal, non-helical telopeptide region of the molecule has been determined in collagen from various sources after isolation of the peptides (alpha(1)- and alpha(2)-CB1) that contain the lysine residue in question and are obtained by cyanogen bromide cleavage of collagen alpha(1)- and alpha(2)-chains respectively. As with collagen from chick tibia, bone collagens from rat tibia and femur and embryonic chick frontal bone, have a high degree of hydroxylation (approx. 50% or more) of the lysine residue in both alpha(1)- and alpha(2)-CB1 peptides. This is in contrast with the lack of hydroxylation of this residue in both alpha(1)- and alpha(2)-chains of all skin collagens so far examined. The presence of hydroxylysine in alpha(1)- and alpha(2)-CB1 peptides from tendon collagen is also indicated. In rat tail tendon collagen the amount of hydroxylation is only slight but in the much less soluble tendon collagen from embryonic chick leg tendons, approximately one-third of the lysine is hydroxylated.

Research on Modified Rubbers. Part VI. The Oxidation of Rubber Solutions with Gaseous Oxygen in Presence of Catalysts

Abstract In a previous study of the oxidation of rubber, the oxidative action of peracetic acid, or mixtures behaving substantially as such, was examined (Bloomfield and Farmer, J. Soc. Chem Ind., 53, 121T(1934)). The results then obtained pointed to a course of reaction characterized by (a) additive attack at the unsaturated centers of the rubber molecules, resulting in the production of a high degree of hydroxylation, and (b) extensive molecular degradation with liberation of carbon dioxide (see also Mair and Todd, J. Chem. Soc., 1932, 386). In an extension of this work, attempts have been made to prepare peracetic acid by means other than the interaction of hydrogen peroxide with acetic acid or anhydride, and among other methods the autoxidation of acetaldehyde at low temperatures in the presence of cobalt acetate as catalyst (G P. 269,937; U.S.P. 1,179,121) was tried. Though peracetic acid was successfully obtained in this way in fair yield, an attempt to prepare it on a larger scale resulted in a violent explosion. In order to eliminate the danger arising from an accumulation of peracetic acid, oxygen was led into a chloroform solution of rubber containing a cobalt acetate catalyst together with acetaldehyde, with the hope that in this way peracetic acid might be formed in situ; at low temperatures (−20° to 0°) no reaction occurred, but on submitting such a solution to the action of oxygen at temperatures above 30° a very rapid reduction of viscosity set in, and the solution yielded a viscous gum containing a little oxygen. Now Stevens and his co-workers have recently shown that rubber solutions readily undergo oxidation by gaseous oxygen when certain catalysts (notably the heavy metal salts of organic acids) are present. It immediately became apparent that the oxidation phenomenon just described affords the basis for a greatly accelerated process of this type, the acceleration being due to the presence of acetaldehyde. It was thought desirable at this stage to investigate broadly the entire subject of oxidation of rubber solutions in the presence of catalysts of this nature, and a study has accordingly been made of the oxygen absorption of rubber solutions containing different catalysts, the oxygen intake being measured by the contraction occurring in a closed system containing oxygen, the latter being kept constantly circulating by means of a pump of the pattern designed by Finch (J. Chem. Soc., 1925, 2464). Since it was found that a considerable quantity of carbon dioxide was formed during oxidations of this type, the circulating gases were passed through a trap containing baryta water, and at any stage of the oxidation the amount of carbon dioxide formed could be ascertained by removing the contents of the trap, filtering off the precipitated barium carbonate, and determining the barium as sulfate.