Hydrogen Donor Ability Research Articles

Structure-Chiral Selectivity Relationships of Various Mandelic Acid Derivatives on Octakis 2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-gamma-cyclodextrin Containing Gas Chromatographic Stationary.

Frequently, a good chiral separation is the result of long trial and error processes. The three-point interaction mechanisms require the fair geometrical fitting and functional group compatibility of the interacting groups. Structure-chiral selectivity correlations are guidelines that can be established via trough systematic studies using model compounds. The enantiorecognition of the test compounds was studied on an octakis 2,3-Di-O-acetyl-6-O-tert-butyldimethylsilyl-gamma-cyclodextrin (TBDMSDAGCD) chiral selector. In our work, mandelic acid and its variously substituted compounds were used as model compounds to establish adaptable rules for other enantiomeric pairs. The mandelic acid and its modified compounds were altered at both their carboxyl and hydroxyl positions to test the key interaction forces of the chiral recognition processes. Ring- and alkyl-substituted mandelic acid derivatives were also used in our experiments. The chiral selectivity values of 20 test compounds were measured and extrapolated to 100 °C. The hydrogen donor abilities of test compounds improved their chiral selectivities. The inclusion phenomenon also played a role in chiral recognition processes in several cases. Enantiomer elution reversals were observed for different derivatives of hydroxyl groups, providing evidence for the multimodal character of the selector. The results of our research can serve as guidelines to achieve appropriate chiral separation for other enantiomeric pairs.

Microwave synthesis of carbon dots in ten choline chloride-based deep eutectic solvents: Effect of solvent molecular structure on carbon dots fluorescence and sensing properties

Deep eutectic solvents (DESs) have showed great interest in carbon dots synthesis. Surface and optical characteristics of carbon dots (CDs) can be influenced by solvent during the synthesis. In this study, microwave method was used for CDs synthesis in ten choline chloride based DESs. Glucose was used as a cheap carbon source. Surface functional groups, optical and fluorescence properties of ten CDs were compared. Quantum yield (QY) of the prepared CDs in choline chloride/urea, choline chloride/glycerol and choline chloride/thiourea DESs were 41.3, 38.7 and 35.5%, respectively. Doping of nitrogen and sulfur atoms in the CDsDES1, CDsDES2 and CDsDES4 enhanced the photoluminescence performance. TEM, FT-IR, EDXS and fluorescence spectroscopy were used for CDs characterization. Results showed that molecular structure of hydrogen bond donor (HBD) had important influence on the CDs properties and doping. The hydrogen bond strength and hydrogen donor ability of DES reduce by the increase of carbon chain length of HBD. DESs with short carbon chain and high content of –NH2 and –OH produce CDs with higher QYs. Some of these CDs were also used as fluorescent nano-probes.

Thermokinetic parameters of the primary coal tars destruction in the presence of catalysts and polymeric materials

The hydrogen-donor abilities of polymers and the activity of catalysts in the process of thermal destruction of the organic mass of primary coal tar (PCT) are studied by non-isothermal kinetics methods. PCT,magnetic microspheres, nickel-deposited chrysotilechrysotile and Fe3O4nanocatalysts were used as initial raw materials. Рolymers such as polyethylene (PE), polystyrene(PS) and polyethylene glycol (PEG) were selected as a hy-drogen donor. The phases Mg3[OH]4{Si2O5} and NiO were determined by X-ray phase analysis (XRD) in the obtained catalyst (nickel-deposited chrysotile), and the presence of highly dispersed nickel oxide particles on the surface and inside the nanotubes was shown by the transmission electron microscope (TEM). Nickel oxide particles of 8–11 nmand 30–37 nmwere evenly distributed on the surface and inside the chrysotile nanotubes. The kinetic parameters of the thermal destruction of a mixture of PCT, catalyst and polymer material were determined on the basis of thermogravimetric analysis using the integral method and the method for determin-ing the thermokinetic parameters by the inflection point on the thermogravimetric curve(TG). The change in the activation energy, rate constant and pre-exponential factor with an increase in the degree of destruction of the organic mass of the PCT is established. It was shown that the nature of polymers and catalysts significantly affects the value of the rate constant and the activation energy. The calculated activation energies of the thermal destruction of a mixture of coal tar with PS and PE in the presence of a catalyst (nickel-deposited chrysotile) by the first method are 47.6 kJ/mol and 40.4 kJ/mol, and by the second method are 47.3 kJ/mol and 86.5kJ/mol respectively.

Enhanced Proton Conductivity of Imidazole-Doped Thiophene-Based Covalent Organic Frameworks via Subtle Hydrogen Bonding Modulation.

Anhydrous proton-conductive materials have attracted great attention in recent years. Doping imidazole as a proton carrier in porous materials, especially pure organic crystalline covalent organic frameworks (COFs), is a promising solution. However, the influence of the hydrogen donor ability of imine functional groups inCOFs on the proton conduction has largely been unexplored. Herein, a series of iso-reticular thiophene-based COFs has been synthesized with a similar pore structure and surface area. Different amounts of imidazole were infiltrated to the COFs by vapor diffusion in a highly controlled manner. The introduction of thiophene rings increases the hydrogen bonding donation ability of the imine linker, which resulted in an enhanced proton conductivity of the imidazole-doped COFs by one order of magnitude. The formation of hydrogen bonding between the imine group and imidazole was demonstrated by Fourier transform infrared spectroscopy and density functional theory calculations.

Investigating reaction pathways for formic acid and lignin at HTL conditions using 13C-labeled formic acid and 13C NMR

The lignin to liquid (LtL) solvolysis is a type of hydrothermal liquefaction (HTL) that utilizes formic acid to facilitate the desired hydrodeoxygenation process to depolymerize lignin. Formic acid has been chosen due to its hydrogen donor ability, and it has proven to be a more efficient hydrogen donor than hydrogen gas and isopropanol. Based on previous experiments where the amount of carbon in the solid phase and organic phase together exceeded 100% relative to carbon in the lignin starting material, we set up experiments with 13C-labeled formic acid in order to investigate where the carbon form formic acid is incorporated. All the experiments were performed in duplicates, one with 13C-labeled formic acid and one with standard formic acid. The bio-oils from the experiments were analyzed by Nuclear Magnetic Resonance (NMR) and the spectra were compared. The 13C NMR spectra showed significant differences between oils made with standard formic acid and oils made with 13C-labeled formic acid, located in the section between δ 170 ppm and δ 180 ppm in the NMR spectra. The signal in this range arise from carbonyl bonds and shows that the carbon from formic acid ends up in the carbonyl structures of the bio-oil in compounds such as aromatic acids. This paper has also shown that the amount of formic acid plays a minor role in product composition compared to reaction temperature, which influences the product composition on a functional group level.

Cotransformations of n-Hexadecane, Hexene-1, and Cyclohexane over Dual-Zeolite Cracking Catalysts

Characteristic features of the conversion of n-hexadecane, hexene-1, cyclohexane, and their mixtures over dual-zeolite catalysts for co-cracking of light and heavy fractions are considered. The maximum yield of olefins (the yield of C2–C4 olefins reaches 66.8 wt %) is achieved in the case of the use of hexene-1 possessing maximum reactivity under cracking conditions as a feedstock. Cotransformation of n-hexadecane and hexene-1 do not indicate the presence of any significant interaction between the components. The presence of cyclohexane in the feedstock has substantial influence on the transformation of n-hexadecane, which is due to the high hydrogen donor ability of naphthenes. It is found that the ratio of HREEY and P/HZSM-5 zeolites in the composition of the catalyst has substantial influence on the value of the interaction between the components of the feedstock. The use of hydrocarbons containing “labeled” hydrogen atoms (deuterium) makes it possible to estimate the distribution of the naphthene hydrogen between the main gaseous products.

Helical Multi-Coordination Anion-Binding Catalysts for the Highly Enantioselective Dearomatization of Pyrylium Derivatives.

A general and highly enantioselective synthesis of oxygen heterocycles from readily available in situ generated pyrylium derivatives has been realized by embracing a multi‐coordination approach with helical anion‐binding tetrakistriazole catalysts. The high activity of the tetrakistriazole (TetraTri) catalysts, with distinct confined anion‐binding pockets, allows for remarkably low catalyst loadings (down to 0.05 mol %), while providing a simple access to chiral chromanones and dihydropyrones in high enantioselectivities (up to 98:2 e.r.). Moreover, experimental and theoretical studies provide new insights into the hydrogen‐donor ability and key binding interactions of the TetraTri catalysts and its host:guest complexes, suggesting the formation of a 1:3 species.

Reductive Radical Cascades Triggered by Alkoxyl Radicals in the β-Cyclodextrin Framework.

The generation and fate of 2I-VII,3I-VII,6II-VII-icosa- O-methyl-β-cyclomaltoheptaos-6I- O-yl radical under reductive conditions is described. Two radical cascade reactions are involved: the main one is triggered by a 1,8-HAT of the hydrogen at 5VIIC. The radical can reach the anomeric hydrogen at 1VC three sugar units ahead using a six-step sequence. The different hydrogen donor ability of the group 14 hydrides permits one to selectively stop the cascade at 5VIIC, 2VIC, and 4VIC to obtain β-CD with a β-l-Ido p unit, acyclic hepta-, and hexa-saccharide structures, respectively.

Study on the thermal liquefaction of Xilinguole lignite in solvent at high temperature

In this paper, thermal liquefaction (TL) of Xilinguole lignite (XL) in the range of 400–540 °C have been carried out in toluene, tetralin (THN) and their mixed solvent, respectively. Results indicated that the conversion of XL primarily depends on the hydrogen donor ability of solvent. The highest conversions of XL in toluene and THN were obtained at 480 °C, which are 25.8% and 98.6%, respectively. The condensation of pyrolytic free radicals dominates the TL in toluene solvent but there is hardly obvious coking occurred in THN at below 510 °C. In toluene and THN mixed solvent, the conversion of XL increases with the THN content. The products of TL in toluene mainly consist of oil and gas (O + G) fraction, but the asphaltene (AS) and preasphaltene (PA) factions prevail in the products of TL in THN. Hydrogen donor solvent has obvious improvement on the deoxygenation in the TL process. Therefore, TL in hydrogen donor solvent is a potential conversion technology of XL due to low reaction pressure and without H2 and catalyst used.

Upgrading of petroleum vacuum residue using a hydrogen-donor solvent with acid-treated carbon

Hydrocarbon/carbon systems can be used to perform the hydrogen transfer reaction in heavy oil upgrading, as alternatives to metal catalysts and molecular hydrogen. In this study, a system comprising a hydrogen-donor solvent (tetralin) and acid-treated activated carbon was established to evaluate its ability as a hydrogen transfer agent to upgrade a vacuum residue (VR). The use of tetralin substantially decreased coke formation from 32.7 wt% to a negligible amount in VR upgrading at 450 °C because the solvent could act as a hydrogen donor and diluent for the coke precursors. The acid-treated activated carbon accelerated dehydrogenation of tetralin through hydrogen transfer in the upgrading, resulting in a higher residue conversion and moderate coke formation. In view of the phase behavior, the hydrogen transfer reaction could also be promoted by increasing the contact between the hydrogen acceptor and donor in the supercritical medium. In the VR upgrading using the activated carbon in supercritical tetralin, complete residue conversion was achieved with 47 wt% light fractions (gas and light oil) and 6 wt% coke at 450 °C and 5.33 MPa. The results indicate that the streams available in oil refinery processes, which are rich in hydrocarbons with hydrogen-donor abilities, have great potential for use in heavy oil upgrading.

Metal free green protocol for the synthesis of bis-spiro piperidine and pyrimidine derivatives

A highly efficient one-pot three-component synthesis of bis-spiro piperidine and pyrimidine derivatives has been reported by performing the reaction of formaldehyde, aromatic aniline and 1,3-dicarbonyl compounds. This reaction was carried out at room temperature in 2,2,2-trifluoroethanol (TFE) as a recyclable reaction medium under the metal free condition. The strong hydrogen donor ability and acidic property of TFE plays a key role in accelerating the rate of reaction and initiates the reaction smoothly. The advantageous features of this method are a mild reaction condition, no column chromatographic purification, and high yield of products and recyclability of TFE.

Cover Feature: The Dual Roles of Phenylenediamines: Using their Voltammetric Behavior to Measure the Hydrogen Donor and Acceptor Abilities of Alcohols in Acetonitrile (ChemPhysChem 24/2017)

Cover Feature: The Dual Roles of Phenylenediamines: Using their Voltammetric Behavior to Measure the Hydrogen Donor and Acceptor Abilities of Alcohols in Acetonitrile (ChemPhysChem 24/2017)

The Dual Roles of Phenylenediamines: Using their Voltammetric Behavior to Measure the Hydrogen Donor and Acceptor Abilities of Alcohols in Acetonitrile.

Cyclic voltammetry experiments on 2,3,5,6-tetramethyl-1,4-phenylenediamine (P) in acetonitrile in the presence of varying concentrations of alcohols indicate that the oxidized forms of the compound (P.+ and P2+ ) interact with the alcohols through a hydrogen-bonding mechanism where P.+ and P2+ act as the hydrogen donor and the alcohols act as acceptors. However, the neutral form (P) largely acts as a hydrogen acceptor but only for strong hydrogen donors that do not undergo proton-transfer reactions with the phenylenediamine. These results were ascertained based on measuring the difference in potential of the two one-electron transfer reactions (ΔEPox(1, 2) =|EPox(1) -EPox(2) |) in the oxidative electrochemistry of P, which thereby allows a simple measure of relative hydrogen bonding strengths.

Hepatoprotective liposomal glycyrrhizin in alcoholic liver injury

IntroductionLicorice root (Glycyrrhiza glabra L.) extract and its main active component glycyrrhizin, as well as derivates are well known hepatoprotective and gastroprotective agents. Liposomal applications of these compounds may prevent low bioavailability and side-effects, e.g. pseudoaldosteronism and has further benefits, because the nanoparticles with glycyrrhizin and glycyrrhetinic acid have enhanced uptake into the liver. Our aim was to study the hepatoprotective effect of liposomal glycyrrhizin treatment during long-term alcohol consumption in rats. MethodsHarlan-Wistar (175–200g) rats were randomly allocated into three groups: control, alcoholic, ethanol and liposomal glycyrrhizin-treated. The redox status of the liver was studied with the measurement of free sulfhydryl-group concentration and hydrogen-donor ability. Transmethylation capacity was measured in dimedone adduct form. Histological examination was carried out as well. ResultsData showed mild elevation in the hydrogen-donor ability and slightly lowered free sulfhydryl level, although transmethylation capacity was significantly lowered (p<0,05) in the alcoholic group. Liposomal glycyrrhizin caused no marked histological changes. Effect of the treatment on the redox homeostasis and transmethylation capacity was beneficial. ConclusionsLiposomal glycyrrhizin treatment moderated the alcohol-related negative changes, therefore glycyrrhizin and/or its derivatives may have further impact in the treatment of alcoholic liver diseases.

Study of Supercritical Coal Extraction in Toluene Containing Fluids

The conversion of brown coals and sapropelic coal in toluene containing mixtures with co-solvents (water, ethanol and tetralin) was studied under sub- and supercritical conditions within the temperature range of 375-550°C and at pressures from 7 to 40 MPa. It was found that the extent of coal extraction in the toluene solvent medium, at 400°C, was significantly increased by the addition of small amounts of hydrogen-donor tetralin or ethanol co-solvents. The extract yield from sapropelic coal reached 79-83%, with the gas yield being small. The effect of process variables on extract yields under sub- and supercritical conditions was monitored. Coal extraction in the toluene-tetralin mixtures was found to depend mainly on the hydrogen donor ability of the tetralin co-solvent irrespective of sub-or supercritical toluene states. According to the composition, the bitumen extracted from coals can be used as a feedstock for pitch production. In the water containing mediums, aside from coal liquefaction, coal methanation, hydrolysis and oxidation reactions occurred resulting in the generation of large amounts of methane, hydrogen and carbon dioxide.

Role of intersystem crossing in the fluorescence quenching of 2-aminopurine 2’-deoxyriboside in solution

2-Aminopurine is a fluorescent probe widely used to study local dynamics as well as charge and energy transfer reactions in DNA/RNA. Despite its broad utilization, the nonradiative relaxation pathways responsible for the variation in its fluorescence quantum yield and fluorescence lifetime in different solvents are still under scrutiny. In this work we use steady-state absorption and emission spectroscopy and broad-band transient absorption covering the time scale from femtoseconds to microseconds to investigate the excited-state dynamics of 2-aminopurine 2'-deoxyriboside (2APdr) in acetonitrile, ethanol, and aqueous buffer solution at pH 7. It is shown that up to ~40% of the initial excited-state population decays by intersystem crossing to the triplet state depending on the solvent used, thus competing effectively with fluorescence emission. Furthermore, the rate of formation and yield of the triplet state depend sensitively on the hydrogen-donor ability and polarity of the solvent.

Hypoglycemic effect of oral crude tea flower polysaccharides on alloxan modeling Sprague–Dawley rats and the possible mechanism

This article mainly focused on the hypoglycemic effects of green tea flower polysaccharides (TFPS) and their possible mechanisms about regulating concentration of blood glucose. An alloxan-induced Sprague–Dawley (SD) rat model was used to observe the change in blood glucose. Inhibition rate of α-amylase and α-glucosidase, and antioxidant ability of TFPS were also tested to explain the possible mechanism. The results showed that TFPS could reduce blood glucose in alloxan-treated rats. TFPS had strong hydrogen donor ability and could protect cell membrane from overoxidation. TFPS could also inhibit the activity of α-amylase and α-glucosidase in vitro. But the inhibition of α-amylase by TFPS was comparatively low. It suggested that TFPS could protect against rapid blood glucose rise in alloxan-induced SD rats. The possible mechanism was that TFPS not only could donate hydrogen to protect SD rats from oxidative damage, but also inhibit digestive enzymes activities.

Modelling heterocyclic azo dye affinities for cellulose fibres by computational approaches

Textile dyeing has economical and ecological implications. Our application of QSAR techniques to dye–cellulose binding is based on the hypothesis of specific dye–fibre interactions. As an alternative to classical QSAR studies, comparative molecular field analysis was previously used to predict technical dye adsorption properties. This paper presents a structure-affinity study of heterocyclic azo dye adsorption on cellulose fibre by multiple linear regression (MLR), comparative molecular field (CoMFA) and comparative molecular similarity index (CoMSIA) analysis. Structural descriptors, derived from the minimum energy conformers, obtained by molecular mechanics and semiempirical level quantum chemical calculations, were correlated with dye affinity for cellulose by MLR. Models with predictive power were obtained. Despite these good results 3D-QSAR CoMFA and CoMSIA approaches gave a deeper insight into dye–cellulose interactions. Dye conformers obtained by the AM1 and ab initio approaches were aligned using atom per atom superposition of a common frame. A comparative analysis on statistic performances and predictive model power was performed for the AM1 and DFT variants of CoMFA and CoMSIA models. Statistically significant models were established for 16 molecules and validated by an external test set of 5 compounds, yielding the best predictive DFT CoMFA model [r2 = 0.960, with 4 components, q2 = 0.707 and SEE = 1.12] and several CoMSIA models for AM1 and ab initio cases [r2 = 0.935 ÷ 0.947, q2 = 0.688 ÷ 0.739 and SEE = 1.32 ÷ 1.46]. The contour maps obtained from 3D-QSAR studies were appraised for affinity trends for the investigated dye molecules. Results indicate a predominant hydrogen donor ability of the dye molecules for both AM1 and ab initio variants to play a significant role in dye binding to cellulose. Electrostatic interactions derived from DFT charges bring an important contribution to dye affinity, too. The information obtained from both CoMFA and CoMSIA 3D contour maps may be used in the design of new heterocyclic azo dyes.

Brønsted Acid Catalyzed Reductive Amination with Benzothiazoline as a Highly Efficient Hydrogen Donor

Reductive amination of aldehyde and amine proceeded smoothly in the presence of benzothiazoline as efficient hydrogen source by means of 20 mol% trifluoroacetic acid to give the corresponding amines in excellent yields. Hydrogen-donor abilities of benzothiazoline, benzimidazoline, and benzoxazoline were compared.

Studies on antioxidant effects of the red grapes seed extract fromVitis Vinifera, Burgund Mare, Recaşin pregnant rats

To estimate the effects of hydroethanolic red grapes seeds extract obtained from Vitis vinifera, Burgund Mare variety, Recaş , Romania (BMR) on oxidant-antioxidant ballance, as compared to ascorbic acid, during pregnancy in rats. Thirty Wistar female rats were assigned to three groups (n=10) which were administered by gavage: Group I, 3 x 100 mg/kg body weight saline, Group II - BMR 3 x 30 mg gallic acid equivalents/kg body weight; Group III - vitamin C 3 x 100 mg/kg body weight on days 1, 7 and 14 of pregnancy. On day 21 blood samples were collected. Malon dyaldehyde, lipid peroxides, protein carbonyls, nitric oxide (as oxidative stress parameters) and hydrogen donor ability and total thiol groups (as antioxidant parameters) serum concentrations were measured. Vitamin C significantly enhanced the antioxidant capacity of plasma (hydrogen donor ability, p=0.0001; thiol groups, p=0.0001), as well as nitric oxide levels (p=0.001). The extract increased the plasma antioxidant capacity (hydrogen donor ability, p=0.001; thiol groups p=0.001) and did not elevate the nitric oxide plasma levels in pregnant rats.In conclusion, in the chosen dose, the red grapes seed extract enhanced the plasma antioxidant capacity and did not influence the nitric oxide levels in pregnant rats.