Replacement Of Hydroxyl Groups Research Articles

Structural modifications of apelin-12 molecule differently affect cardiac function

Purpose: Apelin-12, the short active fragment of natural apelin-77, and its synthetic analog apelin-12-2 have been shown to exert beneficial effects in experimental heart failure. The aim of this study was to explore effects of other analogs of apelin-12 molecule. Methods: The cardiac function of ketamine-anesthetized Wistar rats has been studied using catheterization of the left ventricle (LV) with Millar micromanometer and thoracic electrical impedance. Electric and pressure signals were sent to a computer via an analog-to-digital converter. Bolus injections of apelins were applied with subsequently increasing rate (0.05-5.0 mg/kg) at 10-min intervals. Results: Substitution of methionine in apelin-12 molecule on norleucine (apelin-12-1 analog) shortened duration of hypotensive effect due to more rapid recovery of LV systolic pressure and LV dP/dtmax associated with an increase dP/dtmax/P index and the shortening of duration of preejection time. Further modifications were made on the basis of apelin-12-1 molecule. Replacement of arginine at N-end on methylarginine (apelin-12-2 analog) was associated with removal of hypotensive effect, increased enddiastolic and systolic LV pressures as well as the rate of increment of impedance signal suggesting increased ejection speed. Replacement of hydroxyl group at C-end of this molecule by amide group (apelin-12-3 analog) reduced the extent of positive inotropic effect, but increased the relaxation constant. Finally, replacement in the latter molecule of methylarginine at the N-end by nitroarginine (apelin-12-4 analog) while retaining relaxation acceleration, exerted hypotensive effect with a reduction of LV systolic pressure, but slightly increased ejection speed and dP/dtmax/P index. Conclusions: Hypotensive effect of apelin analogs is associated with the presence of arginine and not methylarginine at N-end of molecule. The combination of methylarginine at N-end and OH-group at C-end facilitate positive inotropic effect of an analog. The presence of NH2-group instead of OH-group at C-end results in fastened relaxation. Thus, these modifications are capable to influence different targets in myocardial and vascular cells.

Electrochemical behaviour of an austenitic stainless steel reinforced concrete in the presence of starch and cellulose admixtures

The electrochemical behaviour of an austenitic stainless steel embedded in concrete containing various proportions (5%, 10%, 15%, 20% and 25%) of starch and cellulose admixtures in contact with one molar solution of sodium chloride was studied. The electrode potential measurements were determined using a digital voltmeter with zinc rod reference electrode. Surface passivation was observed at 10–20% starch content, while 5–10% cellulose admixture was required to enhance surface passivation of the reinforced austenitic stainless steel. The synergetic effect of the two admixtures occurred at 5% starch and 15% cellulose, and produced good film stability. These deductions were attributed to the alteration in the composition of the concrete medium, which was brought about by the replacement of hydroxyl group in the structures of the admixtures by the aggressive chloride ions. There was an excess hydroxyl group released into the concrete medium, which created an excess alkaline and passivating environment for the reinforcing austenitic stainless steel (ASS) within the concrete.

Simultaneous removal of arsenate and arsenite by a nanostructured zirconium–manganese binary hydrous oxide: Behavior and mechanism

Arsenate and arsenite typically co-exist in groundwater. Arsenite is more toxic than arsenate, while it is more difficult to be removed than arsenate. In order to effectively remove arsenate and arsenite simultaneously from water solution, a nanostructured zirconium–manganese binary hydrous oxide was successfully developed in this study. The amorphous sorbent was aggregate of nanoparticles with a high surface area of 213m2g−1. Our sorption experiments showed that the nano-scale particles could effectively oxidize As(III) to As(V) and greatly remove both As(V) and As(III). The maximal adsorption capacities of As(V) and As(III) were 80 and 104mgg−1 at pH 5.0, respectively. As(V) uptake may be mainly achieved through replacement of hydroxyl groups and sulfate anions on the surface of the oxide and formation of inner complexes. The As(III) removal was essentially due to a sorption coupled with oxidation process; the MnO2 was mainly responsible for oxidization of As(III) to As(V) that was subsequently adsorbed onto ZrO2.

Antioxidant activity in aluminium oxide – poly(ethylene-co-butyl acrylate) nanocomposites

The antioxidant activity of Irganox 1010 (0.2wt%) in aluminium oxide (2–12wt%) – poly(ethylene-co-butyl acrylate) nanocomposites was studied. The aluminium oxide nanoparticles were in three different forms: uncoated and coated with either octyltriethoxysilane or aminopropyltriethoxysilane. The activity of the stabilizer in the nanocomposites was assessed by determining the oxidation induction time (OIT) using DSC. Composites with untreated aluminium oxide nanoparticles showed a much shorter OIT than the pristine polymer with the same overall antioxidant concentration indicating adsorption of the antioxidant onto the nanoparticle surfaces. The adsorption of antioxidant onto both uncoated and coated nanoparticles was confirmed by X-ray photoelectron spectroscopy. Composites containing coated nanoparticle fillers showed a significantly smaller depression of the OIT, indicating that the replacement of hydroxyl groups with organic silane tails decreased the concentration of available adsorption sites on the particle surfaces. Composites with a filler coated with a silane having terminal aliphatic amine groups showed an increased OIT with respect to that of the pristine polymer suggesting a synergistic on the stability effect between the antioxidant and the amine groups. The long-term activity of the stabilizer was assessed by measuring the OIT on samples after ageing in air at 90°C for 720h. The decrease in OIT with increasing ageing time of the nanocomposites was slower than for the unfilled polymer. A possible interpretation of these data is that the antioxidant was slowly released from the adsorption sites on extended ageing.

Room temperature chemical synthesis of highly oriented PbSe nanotubes based on negative free energy of formation

The sacrificial template free chemical synthesis of PbSe nanotubes at room temperature has been performed by lead hydroxination from cadmium hydroxide nanowires. This process was based on the ion exchange reaction to replace Cd 2+ with Pb 2+ ions from hydroxyl group followed by replacement of hydroxyl group with selenium ions. The reaction kinetics was accomplished due to more negative free energy of formation and thus the difference in the solubility products. The formed nanotubes were inclusive of Pb and Se with proper inter-chemical bonds with preferred orientations having diameter in tens of nanometer. These nanotubes can have future applications in electronic, optoelectronics and photovoltaic's as well.

Thiolated hydroxyethylcellulose: Synthesis and in vitro evaluation

In recent years, thiomers have received considerable interest due to advantageous characteristics, such as improved mucoadhesive and permeation enhancing properties. Thiolated polymers, however, are characterized by an ionic charge which represents for various applications a great limitation. The aim of this study was therefore to synthesize a novel thiolated polymer not exhibiting ionizable groups. Hydroxyethylcellulose (HEC) was chosen as polymer backbone. The chemical modification was achieved by the replacement of hydroxyl groups on the carbohydrate structure with thiol moieties, using thiourea as thiolating reagent. The resulting thiolated hydroxyethylcellulose (HEC-SH) was characterized in vitro regarding its gelling properties, swelling behaviour, mucoadhesion on freshly excised porcine intestinal mucosa and permeation enhancing effect across rat intestinal mucosa. The new thiomer displayed up to 131.58 ± 11.17 μmol thiol groups per gram polymer, which are responsible for the observed in situ gelling capacity. The swelling behaviour and the mucoadhesive properties of tablets based on HEC-SH were 1.5-fold and 4-fold improved compared with unmodified HEC, respectively. The permeation enhancing effect of 0.5% (m/v) HEC-SH on rhodamine 123 (Rho-123) transport was 1.9-fold improved compared with buffer only. According to these results, HEC-SH seems to represent a promising tool for the development of in situ gelling, mucoadhesive delivery systems with permeation enhancing properties.

Determination of critical micellar concentrations of cholic acid and its keto derivatives

The critical micellar concentration (CMC) values of keto derivatives of cholic acid (3α,12α-dihydroxy-7-oxo-5β-cholanoic acid, 3α,7α-dihydroxy-12-oxo-5β-cholanoic acid, 12α-hydroxy-3,7-dioxo-5β-cholanoic acid, 3α-hydroxy-7,12-dioxo-5β-cholanoic acid, 3,7,12-triketo-5β-cholanoic acid) and cholic acid itself, were determined. Replacement of hydroxyl groups in cholic acid molecule with keto groups yields the derivatives whose CMC values increase with increase in the number of keto groups introduced. The CMCs of derivatives with the same number of keto groups but at different positions do not differ significantly. The relationship between the number of keto groups in the molecule of cholic acid keto derivatives and CMC value can be described by the following equation: CMC = 43 number of keto groups + 14.667. The effect of NaCl concentration on CMC increases with increase in the number of keto groups.

Origin of the slow photoresponse in an individual sol-gel synthesized ZnO nanowire

Photocurrent of a single ZnO nanowire synthesized by a sol-gel route was investigated. In vacuum, the dark current was bigger but the photoresponse was slower than that in air, attributed to the release of the available charge carriers by the desorption of water molecules and the decrease of the exchange rates of molecular ions. Under the steady radiation of the ultraviolet light (λ=325nm), a gradual decrease of the photocurrent was noticeable, which can be explained in terms of the annihilation of the carriers by the replacement of hydroxyl groups (OH−) by O2−, resulting in the decrease of charge carriers.

Density improvement of the sol–gel dip-coated SnO 2 films by chemical surface modification

We compare the effect of organic (Tiron ®) and inorganic (Mn(II)) additives on the low temperature (<600 °C) densification of the sol–gel dip-coated SnO 2 films. The structural and compositional properties of the samples were investigated by X-ray reflectometry (XRR), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The results suggest that the replacement of hydroxyl groups at the particle surface by Tiron ® reduces the level of agglomeration of the sol, increasing the particles packing and the apparent density of the coatings. Undoped and Mn-doped films drawn from a Tiron ® containing suspension show after firing at 500 °C a porosity reduction of 12 and 8.6%, respectively. The porosity decrease is less pronounced (4.3%) for the film without additives. Both XAS and XPS data show the presence of trivalent manganese. The formation of a non-homogeneous solid solution characterised by the presence of Mn(III) replacing tin atom near to the crystallite surface was evidenced by XAS. Additionally, XPS results reveal the presence of metallic Sn at the surface of films containing Tiron ®.

Preferential target is mitochondria in α-mangostin-induced apoptosis in human leukemia HL60 cells

Our previous study has shown that α-mangostin, a xanthone from the pericarps of mangosteen, induces caspase-3-dependent apoptosis in HL60 cells. In the current study, we investigated the mechanism of apoptosis induced by α-mangostin in HL60 cells. α-Mangostin-treated HL60 cells demonstrated caspase-9 and -3 activation but not -8, which leads us to assume that α-mangostin may mediate the mitochondrial pathway in the apoptosis. Parameters of mitochondrial dysfunction including swelling, loss of membrane potential (Δ Ψm), decrease in intracellular ATP, ROS accumulation, and cytochrome c/AIF release, were observed within 1 or 2 h after the treatment. On the other hand, α-mangostin-treatment did not affect expression of bcl-2 family proteins and activation of MAP kinases. These findings indicate that α-mangostin preferentially targets mitochondria in the early phase, resulting in indication of apoptosis in HL60 cells. Furthermore, we examined the structure–activity relationship between xanthone derivatives including α-mangostin and the potency of Δ Ψm-loss in HL60 cells. Interestingly, replacement of hydroxyl group by methoxy group remarkably decreased its potency. It was also shown that the cytotoxicity substantially correlated with Δ Ψm decrease. These results indicate that α-mangostin and its analogs would be candidates for preventive and therapeutic application for cancer treatment.

Sintered hydroxyfluorapatites. Part II: Mechanical properties of solid solutions determined by microindentation

Fluoride substitution within hydroxyapatite is an important occurrence for biological apatites and is a promising approach for the chemical modification of synthetic hydroxyapatite. Limited information on the influence of fluoride substitution for hydroxyl groups on the mechanical properties has provided the rationale for this study. Hydroxyfluorapatites with 0%, 20%, 40%, 60%, 80% and 100% replacement of hydroxyl groups with fluoride ions were assessed for hardness, elastic modulus, fracture toughness and brittleness using microindentation of sintered pellets. The production of samples with a similar grain size and density allowed the influence of fluoride on mechanical properties to be determined. It was found that the hardness remains unaffected until 80% replacement of hydroxyl groups with fluoride, after which the hardness rapidly increases. The elastic modulus increases linearly with fluoride content. Fracture toughness is improved with fluoride incorporation into the lattice and reaches a peak of 1.8 for a 95% dense sintered pellet with a 60% fluoride replacement, followed by a rapid decrease at higher fluoride concentrations. The brittleness index is lowered to a minimum at 60%, after which a rapid increase occurs. High fluoride levels are unfavourable from a mechanical perspective, are not recommended for biomaterials, and can lead to a higher incidence of fracture where sodium fluoride, for treatment of osteoporosis, may produce a highly fluoridated hydroxyapatite.

In-situ XAFS Analysis of Y Zeolite-Supported Rh Catalysts during High-Pressure Hydrogenation of CO2

In-situ XAFS (X-ray absorption fine structure) analysis under high-pressure, high-temperature reaction conditions was done to clarify the effect of Li doping on the structures of Rh species in Rh ion-exchanged NaY zeolite catalysts (RhY). The analysis showed that Rh species in RhY were reduced at a lower temperature than those in Li-doped RhY (Li/RhY). The reduction of Rh in RhY at a lower temperature was related to the formation of amorphous Rh oxide species during the initial stage of reduction, which was not observed in Li/RhY catalysts. The average particle size of metallic Rh species formed under the reaction conditions was 1.3 nm for RhY catalysts and 0.8 nm for Li/RhY catalysts. During exposure to either CO or air, the metallic Rh species in RhY were more easily subject to structural changes than the metallic Rh species in Li/RhY. These differences in the properties of Rh species between the RhY and Li/RhY catalysts resulted from the replacement of hydroxyl groups on the zeolite surface by O–Li compounds, and caused different catalytic activities during CO2 hydrogenation.

Luteolin, a flavone, does not suppress postprandial glucose absorption through an inhibition of alpha-glucosidase action.

In order to clarify the postprandial glucose suppression via alpha-glucosidase (AGH) inhibitory action by natural compounds, flavonoids were examined in this study. Among the flavonoids (luteolin, kaempferol, chrysin, and galangin), luteolin showed the potent maltase inhibitory activity with the IC50 of 2.3 mM, while less inhibitions were observed against sucrase. In addition, the effects of maltase inhibition by flavonoids were observed in the descending order of potency of luteolin > kaempferol > chrysin > galangin. Apparently, the AGH inhibition power greatly increased with the replacement of hydroxyl groups at 3' and 4'-position of the B-ring. However, the inhibitory power of luteolin was poorer than a therapeutic drug (acarbose: IC50; 430 nM). As a result of a single oral administration of maltose or sucrose (2 g/kg) in SD rats, no significant change in blood glucose level with the doses of 100 and 200 mg/kg of luteolin was observed. These findings strongly suggested that luteolin given at less than 200 mg/kg did not possess the ability to suppress the glucose production from carbohydrates through the inhibition of AGH action in the gut.

AM1 study on infra-red spectra of silica clusters modified by fluorine

AM1 molecular orbital (MO) calculations were made for various cluster models of silica and for fluorinated silica. Calculations were made on clusters containing up to 12SiO 4 units. On the basis of the relative position and relative intensity of the theoretical vibrational spectra of fluorine-free silica clusters with different sizes and fluorinated silica clusters, the effects of the replacement of OH groups by fluorine on the vibrational spectra of the silica clusters were established. In ring-type silica clusters the absorption around 640–720 cm −1, assignable to the ring vibration within the ring plane, could be seen in the three-membered ring. The intensity of absorption around 500–600 cm −1, assignable to the O–Si–O bending vibration, decreased with increasing size of rings and by the replacement of hydroxyl groups (OH −) by fluorine (F −). In block-type silica clusters all absorption peaks shifted to higher frequencies than those in ring-type silica clusters. The absorption peaks in AM1 calculated vibrational spectra correlated with the experimental IR spectra except for the stretching vibration of Si–F bonds.

Fluorination of Secondary and Primary Alcohols by Thermal Decomposition of Electrochemically Generated Alkoxy Triphenylphosphonium Tetrafluoroborates.

Replacement of hydroxyl groups in secondary and primary alcohols (1) with a fluorine atom arising from tetrafluorobote anion has been performed by the electrochemical formation of alkoxy triphenylphosphonium tetrafluoroborarates (2) from 1, followed by their thermal decomposition. The procedure is quite simple, involving : (1) constant-current electrolysis of a mixture of 1, Ph3P, and Ph3PH·BF4 in CH2Cl2 in an undivided cell; (2) refluxing a tetrahydrofuran or dioxane solution of the residue afforded by evaporation of the solvent in vacuo after the electrolysis. Cyclic secondary alcohols such as 3β-hydroxy steroids and 2-adamantanol are transformed into the corresponding fluorides in satisfactory yields when the geometry of the leaving group in 2 is suitable for the substitution or an elimination process for 2 to give an alkene is stereochemically forbidden. The fluorination of steroidal alcohols and 4-phenyl-1-cyclohexanol proceeded with complete inversion, demonstrating that a fluorine atom from the tetrafluoroborate anion attacks from the side opposite to the phosphonium moiety in 2 via an SN2 mechanism rather than as SN1 mechanism. The fluorination of acyclic secondary and primary alcohols was performed by the present method in reasonable yields, although the reaction for the latter required more forcing conditions, such as refluxing in dioxane.

Synthesis and characterization of highly substituted deoxyfluorocellulose acetate

Deoxyfluorocellulose acetates were prepared from cellulose acetate (CA, degree of substitution by acetyl groups: 2.2 and 1.7) by using diethylaminosulfur trifluoride (DAST) in 1,4-dioxane or diglyme. The maximum degree of substitution of fluorine of the products was ∼ 0.60, and depolymerization was not significant during fluorination. The replacement of hydroxyl groups by fluorine atoms occurred exclusively at C-6, as confirmed by carbon-13 NMR spectroscopy. In the presence of pyridine, an N-pyridinium derivative of CA was obtained instead of a deoxyfluoro derivative of cellulose.

Inhibition of protein-tyrosine kinase activity by flavanoids and related compounds.

A series of 22 flavanoids and related compounds were tested for their ability to inhibit the activity of a protein-tyrosine kinase purified from bovine thymocytes (p40). Flavones or flavanols with hydroxyl groups at C-5 and C-7 or with three hydroxyl groups on the phenyl ring were potent inhibitors of p40. The replacement of hydroxyl groups with methoxyl groups led to a substantial loss of inhibitory activity. The presence of methoxyl or rhamnosyl substituents at C-3 also abolished inhibitory activity. Kinetic analyses indicated that the flavone apigenin [2] was a competitive inhibitor of p40 with respect to ATP. Flavanones and isoflavones were relatively inactive as protein-tyrosine kinase inhibitors. The isoflavone genistein [17], which has been reported as a potent inhibitor of both pp60(v=src) and the epidermal growth factor receptor, was not an inhibitor of p40.

Specificity of an Na+ -dependent taurocholate transport site in isolated rat hepatocytes.

The structural specificity of the taurocholate uptake mechanism was studied by determining the ability of 100 microM structural analogues of taurocholate to inhibit the uptake of 5 microM [14C]-taurocholate into freshly isolated rat hepatocytes. Taurocholate was a more potent inhibitor than cholate. The fewer the number of hydroxyl groups, the more potent the inhibitors. Neither hydroxyl group orientation (alpha or beta) nor esterification with formic acid strongly influenced inhibitory potency. Replacement of hydroxyl groups with keto groups, however, diminished inhibitory potency. These facts suggested that distortion of the sterol backbone may be an important factor in diminishing inhibitory potency. Charge on the nonsteroid moiety affected potency. Both neutral and negatively charged compounds inhibited more strongly than positively charged compounds. As important as charge, however, was length of the nonsteroidal moiety. Inhibitory potency increased progressively as length beyond C-17 increased up to 11 A. Inhibitory potency was reduced again, however, with an extremely long end group of 18 A. The inhibitors do not act as cytotoxins since cellular oxygen consumption was not diminished by any of them. Furthermore, inhibition was specific for the taurocholate uptake mechanism. The three most potent inhibitory compounds inhibited L-alanine uptake little or not at all. The kinetics of inhibition, determined for three selected compounds, were consistent with competitive inhibition. The structural specificity of the rat hepatocyte sodium-dependent taurocholate uptake site is similar to that of the guinea pig ileum uptake site.

ChemInform Abstract: Replacement of Alcoholic Hydroxyl Groups by Halogens and Other Nucleophiles via Oxyphosphonium Intermediates

The Michaelis–Arbuzov reaction involves the formation of dialkyl alkylphosphonates by heating alkyl halides with trialkyl phosphites, via an intermediate phosphonium salt. In recent years it has been found that phosphonium salts can be formed by reaction of a variety of trivalent phosphorus compounds with oxidizing electrophiles, and that the resulting phosphonium intermediates can be trapped with an alcohol to form alkoxyphosphonium cations. These cations can then undergo nucleophilic displacements, either with their own counterions or with added nucleophiles. This chapter is limited to species formed in situ from trivalent phosphorus compounds and various oxidants. The most commonly used trivalent phosphorus compounds are triphenyl phosphite, triphenylphosphine, and tris(dimethylamino)phosphine. The most commonly used oxidants are molecular halogens, alkyl halides, carbon tetrahalides, N-haloamides, N-haloamines, and diethyl azodicarboxylate (DEAD). Other oxidants that have been used include mercuric salts, peroxides, dithioesters, and sulfenamides. The more common combinations of phosphorus(III) compounds and oxidants are summarized. The replacement of hydroxyl groups by halogen, the most common use of oxyphosphonium intermediates, is the principal subject of this chapter. However, the replacement of hydroxyl groups by oxygen, nitrogen, sulfur, and carbon nucleophiles is also discussed. This review is restricted to alcoholic hydroxyl groups, and does not include a discussion of carboxylic hydroxyl groups. The principal combinations covered are triphenylphosphine–diethyl azodicarboxylate, triphenyl phosphite–methiodide, triphenylphosphine–halogen, triphenylphosphine–tetrahalomethane, triphenylphosphine–N-haloimide, and tris(dimethylamino)phosphine–tetrahalomethane. Some of these combinations have been discussed in recent reviews. Keywords: replacements; alcoholic hydroxyl groups; halogens; oxyphosphonium intermediates; triphenylphosphine; carbon tetrachloride; diethyl azodicarboxylate; carbonnitrogen bonds; esters; ethers; alcohol dehydration; scope; limitations; phosphoranes; halosuccinimide reagent; tris(dimethylamino)phosphine; anomeric position; tetrahalomethanes; haloamide; carbohydrates; selectivity; experimental procedures

Radiation‐induced ionic polymerization of styrene: effects of additives

When styrene in dichloromethane solution was irradiated at -78 deg C, the resulting polymerization occurred via an ionic mechanism. It was previously shown that the yields in this reaction can be greatly enhanced by the addition of finely divided solids such as Aerosil. Additives studied included a number of silica powders whose surfaces were modified by the replacement of hydroxyl groups by alkyl, allyl, and aryl groups. It was found that the catalytic power'' of these silicas can be correlated with the nature and number of substituted groups. Although the polymerization is cationic in character, the presence of excess electron trapping material (tetracyanoethylene) caused a diminution of yield. Electrical conductivity measurements on the polymerizing solution, in the presence and absence of additives, were made to clarify the proposed reaction mechanism.