Interaction Of Electron Acceptors Research Articles

Structurally divergent dynamic combinatorial chemistry on racemic mixtures

Structurally Divergent Reactions on Racemic Mixtures are atypical processes in Nature. The few examples reported in the literature take place in organic solvents and are driven by the reagents’ interaction with bulky chiral catalysts. Herein, we describe a dynamic combinatorial approach to generate structural divergence from racemic building blocks. The divergence is due to a stereospecific electron-donor – electron-acceptor interaction of diastereomeric macrocycles, leading to structurally distinct pseudorotaxanes. The equilibrated dynamic combinatorial library contains, amongst various macrocycles, two different types of [2]catenanes that are non-isomeric. The formation of these [2]catenanes is due to a spontaneous stereo and structurally divergent assembly of the building blocks.

Structural Based Investigation of Artificial Electron Acceptor Interaction of Fungus Derived Flavin Adenine Dinucleotide Dependent Glucose Dehydrogenase

[Introduction]Self-monitoring of blood glucose (SMBG) is inevitable for the glycemic control of the diabetic patients, and plays an indispensable role in the current diabetes management. The current most popular principle for the sensor for SMBG is based on the so-called “second generation” type that are the use of the dye mediated dehydrogenase reactions. The principle employs the artificial electron acceptor and monitoring the concentration/quantity of thus reacted (reduced) artificial electron acceptor on the electrode. Fungi-derived flavin adenine dinucleotide dependent glucose dehydrogenases (FADGDHs) have recently been paid significant attention, focusing its narrow specificity, especially as the enzyme not active toward maltose. However, interaction between FADGDHs and artificial electron acceptor has not yet been investigated. Recently, we have reported on the first 3D structures of FADGDH, using Aspergillus flavus derived FADGDH (AfGDH). Here we report the investigation of interaction between mediator and enzyme by elucidating the 3D structure of AfGDH complex with potassium ferricyanide. Mutagenesis studies were also carried out to investigate the role of residues elucidated to interact with ferricyanide. [Methods]The structural gene of AfGDH was inserted into an expression vector and the enzyme was recombinantly expressed using E. coli BL21 (DE3). Soluble AfGDH was harvested and purified by hydrophobic interaction chromatography and anion exchange chromatography. Purified protein was concentrated, and crystallized by sitting-drop vapor-diffusion method. In order to obtain a ternary complex structure with FAD and ferricyanide, a single crystal was soaked in the potassium ferricyanide solution. X-ray diffraction data were collected and structure was determined. Based on the 3D structure, several mutants were constructed by site-directed mutagenesis and evaluated GDH activity, which was determined using either phenazine methosulphate/2,6-dichlorophenol indophenol (PMS/DCIP) or potassium ferricyanide as the electron acceptors. [Results & Discussion] A ternary complex structure of AfGDH with FAD and ferricyanide complex was obtained. Two potassium ferricyanide molecules were observed in the protein structure. One potassium ferricyanide interacted with one lysine residue, whereas the other molecules interacted with two lysine residues. In order to elucidate the role of these lysine residues, mutant AfGDHs were constructed by substituting lysine residues with alanine. The structural gene of AfGDH mutants were inserted into an expression vector and the enzyme was recombinantly prepared using E. coli BL21 (DE3). All mutants were expressed at soluble fraction. These mutants were subjected for anion exchange chromatography for purification. Interestingly, the mutant enzymes were eluted at different salt concentration than those eluted in the purification of wild type enzyme, suggesting that surface net charge was significantly changed by these mutations. Some of the mutant AfGDH showed unique property in the specificity toward electron acceptors. The GDH activities were compared by using either PMS/DCIP or ferricyanide as the electron acceptor, for both wild type and mutant enzymes. Although the alanine substitutions to these lysine residues did not significantly influenced PMS/DCIP based dye mediated GDH activity, but some mutation affected the ratio of dye mediated GDH activities of those using PMS/DCIP and of using ferricyanide. These results, together with the results of the change in the elution properties during anion exchange chromatography, suggested the lysine residues, we focused, play important role in the affinity toward ferricyanide during oxidative half reaction. (1) K. Mori, et al., Biotechnol Lett. 33(11) 2255-63(2011) (2) G. Sakai, et al., Biotechnol Lett. 37(5) 1091-99(2015) (3) H. Yoshida, et al. Sci. Rep. 5:13498. doi:10.1038/srep13498 (2015)

Charge-transfer interactions of metoclopramide nausea drug against six kind of π-acceptors: Spectral and thermal discussions

The target of this paper is aimed to discuss the fast and newly techniques in order to assessment the metoclopramide (Mcp) nausea drug in pure form in solid and solution shape with different kind of π-acceptors upon charge transfer interactions. Charge-transfer complexes (CTC) of metoclopramide with picric acid (PA), 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), m-dinitrobenzene (DNB), p-nitrobenzoic acid (p-NBA) and tetrachloro-p-quinon (p-CL) have been studied spectrophotometrically in absolute methanol at room temperature. The stoichiometries of the complexes were found to be 1:1 ratio by the spectrophotometric titration between metoclopramide and represented π-acceptors. The equilibrium constants, molar extinction coefficient (εCT) and spectroscopic-physical parameters (standard free energy (ΔG°), oscillator strength (ƒ), transition dipole moment (μ), resonance energy (RN) and ionization potential (ID)) of the complexes were determined upon the modified Benesi-Hildebrand equation. The results indicate that the formation constants for the complexes depend on the nature of electron acceptors and configuration of drug donor, and also the spectral studies of the complexes were determined by (infrared, Raman, and 1H NMR) spectra and X-ray powder diffraction (XRD). The charge-transfer complexes are formed during the interaction of electron-acceptors and electron-donors as result of partial or complete transfer of a negative charge from (D+−A−).

Aliphatic–aromatic polyimide blends for H 2 separation

In this work the synthesis of a semi aliphatic BTDA-DAH polyimide and their blends with BTDA-ODA and BTDA-DDS polyimides was carried out in order to improve the H 2 permselective properties of polyimides. The syntheses were made using the well-known two steps method and the silylation method. The prepared films were characterized by FTIR, DSC, thermal stability and fluorescence spectroscopy. Intercatenary distances (d-spacing) and gas separation properties were also investigated. PI blend membranes presented only one glass transition temperature (Tg) intermediate between those of the neat polyimides. Fluorescence spectra were a useful tool to recognize electron-donor and electron-acceptor interactions indicating intermolecular charge-transfer complex (CTC) formation which were confirmed by UV–Vis absorptions. As a result, a decrease in the intercatenary distances and a shift for both IR and fluorescence bands of polyimide blends were measured. PI blend membranes showed a permeability decrease with respect to the neat ones, while the selectivity increased according to X-ray diffraction results. To analyze the polyimide blend permselectivities, H 2/CH 4, H 2/CO 2, H 2/O 2 and H 2/N 2 systems were chosen. As a result, H 2/CH 4 separation factor of PI blends was among the highest reported by other authors using traditional membrane materials.

Surface free energy of polypropylene and polycarbonate solidifying at different solid surfaces

Advancing and receding contact angles of water, formamide, glycerol and diiodomethane were measured on polypropylene (PP) and polycarbonate (PC) sample surfaces which solidified at Teflon, glass or stainless steel as matrix surfaces. Then from the contact angle hystereses (CAH) the apparent free energies γ s tot of the surfaces were evaluated. The original PP surface is practically nonpolar, possessing small electron donor interaction ( γ s − = 1.91 mJ/ m 2 ), as determined from the advancing contact angles of these liquids. It may result from impurities of the polymerization process. However, it increases up to 8–10 mJ/m 2 for PP surfaces contacted with the solids. The PC surfaces both original and modified show practically the same γ s − = 6.5 6.7 mJ/ m 2 . No electron acceptor interaction is found on the surfaces. The γ s tot of modified PP and PC surfaces depend on the kind of probe liquid and contacted solid surface. The modified PP γ s tot values determined from CAH of polar liquids are greater than that of original surface and they increase in the sequence: Teflon, glass, stainless steel surface, at which they solidified. No clear dependence is observed between γ s tot and dielectric constant or dipole moment of the polar probe liquids. The changes in γ s tot of the polymer surfaces are due to the polymer nature and changes in its surface structure caused by the structure and force field of the contacting solid. It has been confirmed by AFM images.

Fullerene architectures made to order; biomimetic motifs — design and features

This article highlights the progress made in the design, synthesis and study of supramolecular fullerene architectures that are based upon biomimetic organization principles. In particular, an overview of hydrogen-bonding, π–π stacking, metal-mediated complexation and electrostatic motifs is given, which have been used to incorporate fullerenes into well-ordered arrays. Owing to the presence of fullerenes, as an integrative building block, the majority of the presented molecular assemblies exhibit unique and remarkable features. Issues relevant to electron-donor–electron-acceptor interactions are considered.

Investigation of alumina/(+)-catechin system properties. Part II: ζ-potential and surface free energy changes of alumina

The effects of (+)-catechin adsorption to the alumina surface were studied by ζ-potential and surface free energy determination. The presence of catechin causes essential changes in the alumina ζ-potential, which at the concentration slightly higher than 10 −5 M reverses from the positive into negative one. At constant concentration of catechin (10 −3 M), the effect on ζ-potential of alumina as a function of pH appears in a drastic shift of the isoelectric point, from pH 8.4 to 4.6, and the equilibrium is established practically within 2 h. This is probably due to relatively low p K a=4.6 for catechin 3′-OH group deprotonation. At high alkaline environment (pH≥10), even in the presence of catechin in the solution, the hydroxyl OH − ions play principal role in the surface charge formation for the alumina. At such pH catechin molecule is double negatively charged and hence its adsorption on highly negatively charged alumina surface is rather restricted. Nevertheless, various dimeric forms of catechin, which are formed at the alkaline pH, probably adsorb on the alumina surface. This appears in small increase in apolar surface free energy component at natural and alkaline pH. On the other hand, at acidic pH 3 small increase of the electron acceptor interaction is observed. This may result from increased number of hydroxyl groups on the alumina surface originating from the adsorbed molecules of catechin, which are mostly undissociated at this pH. The interactions of catechin with alumina surface seems to be also of some specific nature, because neither changes in the ultraviolet–visible (UV–vis) absorbance (Part I) nor in the ζ-potentials had occurred in the silica suspensions in which also catechin was present.

Effect of Tannic Acid on the Surface Free Energy of Cotton Fabric Dyed with a Cationic Dye

The effect of tannic acid and/or Rhodamine B on the surface free energy components of bleached cotton was studied. The zeta potential of cotton fabric was also measured in 10−6–10−2M tannic acid solutions and in the presence of 10−3M NaCl. It was found that the zeta potential of cotton is negative and that its absolute value decreases with increasing concentration of tannic acid. In the presence of NaCl the potential is more negative than in the tannic acid solutions alone. One may conclude that both H+and Cl−are potential-determining ions for the cotton surface. The surface is practically monopolar Lewis basic with an electron donor, γ−S, interaction of 50.1 mJ/m2, while its electron acceptor interaction, γ+S, equals only 0.92 mJ/m2. This polar character of the surface results from the presence of carboxyl end-groups. The apolar Lifshitz–van der Waals interaction, γLWS, amounts 45.0 mJ/m2. The cotton surface with adsorbed tannic acid from 10−3or 10−2M solutions, or Rhodamine B from 10−3M solutions, as well the surface dyed with Rhodamine after adsorption of tannic acid, shows different values of the surface free energy components. The changes are within ca. 14 mJ/m2for apolar γLWScomponent and within ca. 13 mJ/m2for polar γ−Scomponent. It is believed they result from the presence of the above mentioned polar end groups of bleached cotton, phenolic hydroxy groups in the tannic acid molecule, and two amine groups and one carboxyl group in the Rhodamine B molecule. The adsorption processes occurring in the systems are due to both electrostatic interaction and hydrogen bonding between the polar groups. It appeared that the thin-layer wicking technique adapted to the fabric materials is very useful for the surface free energy study, especially because the contact angle method cannot be applied for such materials.

Persistence of Molecular Orientation in Adsorbed Ethylene−Vinyl Acetate Copolymer Nanofilm Studied by Fourier Transform Infrared Reflectance Spectroscopy

FTIR reflectance experiments have been performed on thin ethylene−vinyl acetate (EVA) copolymer layers deposited on aluminum mirrors in order to determine the orientation of polymer functional groups at the interface. This was accomplished by using various reflection angles under p-polarization states of the incident IR wave. Film thickness is estimated by ellipsometric experiments. Kramers−Kronig analysis is first applied to the external infrared reflection spectrum from a single copolymer surface measured near the normal incidence angle. Absorption spectra, k(ν), are then deduced and used to calculate specular reflectance intensities of the functional groups of interest, as a function of reflection angle, polarization state, and film thickness. The calculated values are compared to the experimental ones. An original layer model was developed and allows us to determine the persistence length of the molecular orientation of EVA carbonyl groups at the interface. This approach is based on the fact that molecular orientation persists only over a given distance from the geometrical interface. This distance is called the “persistence length of molecular orientation”. We then suppose that the nanofilm adsorbed is stratified and consists of an oriented layer (in the near interface region) plus an isotropic one. It seems that only carbonyl groups involved in specific electron donor−electron acceptor interactions at the interface are subjected to specific orientation.

The Influence of Thermal Treatment of Silica Gel on Surface–Molecule Interactions: I. Finite Coverage Region

Adsorption isotherms ofn-octane, benzene, toluene, and chloroform were determined by a gas chromatographic method on the surface of silica gel heated at 200, 400, and 800°C. From the isotherms, the film pressure of the adsorbates was determined, and then the components of silica surface free energy were calculated. It was determined that the thermal treatment provided almost no changes in nonspecific interactions and a considerable decrease in acid–base ones; however, electron–acceptor interactions were always stronger than electron–donor ones. Based on these data, the surface concentration of adsorption sites was estimated. The adsorption energy distribution function (χ) was also determined for silica gels according to the asymptotically corrected condensation approximation method. The influence of the thermal treatment on distribution of adsorption sites was demonstrated for adsorbates possessing various types of interactions.

On the Consistency of Surface Free Energy Components as Calculated from Contact Angles of Different Liquids: An Application to the Cholesterol Surface

Contact angles of diiodomethane, bromoform, water, formamide, and glycerol were measured on cholesterol surfaces both bare and precontacted with bile salts (sodium cholate, sodium deoxycholate, and sodium chenodeoxycholate). Ten different sets of the measured contact angles were used for the calculation of the surface free energy components, Lifshitz-van der Waals, γ LW s, electron acceptor, γ + s, and electron donor, γ - s. Additionally, contact angles of the same liquids were measured on the pellets of the bile salts. From the calculated values of the components it results that in the case of a bare surface, almost any of the liquid triplets can be used for determination of the surface free energy components. The lowest confidence level can be put to the values obtained from contact angles of the liquid set, including two weakly monopolar liquids (diiodomethane and bromoform), and also that including two liquids with similar strong electron donor and relatively weak electron acceptor interactions (glycerol and formamide). The situation is much more complicated in the case of precontacted surfaces, especially when micelles of bile salts were formed in the solutions in which the cholesterol surface was dipped. The results were very scattered and dependent on the triplet used for the calculations. However, an explanation can be found for such scattered values, based on calculations of the surface free energy of bile salt surface, and on the assumption of the presence of hydrating water molecules around bile salt ones.

Surface free energy of cholesterol and bile salts from contact angles

Measurements of contact angles for water, ethylene glycol, diiodomethane, and bromoform on cholesterol, and water, diiodomethane, and bromoform on bile salts pellets were conducted. Using the values of the contact angles, total surface free energy of cholesterol and bile salts and components of the energy resulting from different kinds of intermolecular interactions were calculated. For this purpose, various approaches to the solid—liquid interfacial free energy have been considered, though some older ones were criticized. Thus, it was found that the surface free energy of cholesterol originates mainly from the Lifshitz—van der Waals interactions, while that of bile salts is due to apolar Lifshitz—van der Waals, and to a great extent to the polar (Lewis acid—base) electron-donor and electron-acceptor interactions. It was found that all the tested approaches to the solid—liquid interfacial energies may be useful; however, the one describing the surface free energy of a solid and a liquid in terms of apolar Lifshitz—van der Waals and polar acid—base interactions gives more information about properties of the cholesterol and bile salts surfaces. Using values of the Lifshitz—van der Waals, electron-donor, and electron-acceptor components of the surface free energy of cholesterol, bile salts, and water, the free energy of interaction between two particles of cholesterol in water, and of cholesterol—bile salt and of bile salt—bile salt immersed in water was calculated. From these calculations it appears that bile salts adsorbed on cholesterol surfaces cause the free energy of interaction between the cholesterol particles immersed in water to be positive. As a result, the cholesterol dispersions should be stable (unflocculated). However, no electrostatic interactions due to the surface electric charge were taken into account.

A study of the activity of chemical groups on carbonaceous and model surfaces by infinite dilution chromatography

Surface properties of activated carbons and carbon fibers subjected to oxidation processes are investigated by means of inverse gas chromatography (IGC). A general correlation between surface density of acidic groups and the empirical parameter eπ related to electron acceptor interactions is established. Model adsorbents based on benzene derivatives with known numbers of functional groups are also studied by IGC to examine the effect of surface geometry in relationship to the eπ results from the carbons.

Solid surface free energy components determination by the thin-layer wicking technique

A thin-layer wicking technique [1] and van Oss et al.'s [2] approach to interfacial free energy interactions were tested to determine the solid surface free energy components: apolar Lifshitz-van der Waals, yl,w y; and polar, electron donor, γ- y, and electron acceptor, γ+ y. For this purpose, the penetration rates of n-alkanes, diiodomethane, water, formamide, toluene and chloroform were measured. For these studies, silica, used for thin-layer chromatography, and α-Al2O3 were used as the model solids. It was found that both are strongly polar, electron donor solids with weak electron acceptor interactions. It is concluded that van Oss, Good et al.'S [2] approach to the interfacial free energy interactions and the thin-layer wicking technique are very useful for cxplaining many interfacial phenomena taking place in the dispersed systems. However, more experimental work using different systems is needed.

An N.M.R. Study of Electron Donor-Electron Acceptor Interaction Between Aromatic Hydrocarbons and Diazines

Equilibrium constants have been measured by n.m.r , spectroscopy for the electron donor- electron acceptor interaction between a number of aromatic hydrocarbons and diazines . The values obtained have shown that the interaction is weak, and that the aromatic hydrocarbon acts as the electron donor and the diazine as the electron acceptor in the systems studied. Chemical-shift data have provided evidence for the relative positioning of the donor and acceptor components within the various complexes. The effect of temperature on the equilibrium constant for complex formation between (1H6)benzene and pyrazine has shown that the enthalpy of formation is close to zero.

Interaction of electron acceptors with thylakoids from halophytic and non-halophytic species

Thylakoid membranes isolated from halophytic species showed differences in their interactions with ionic and lipophilic electron acceptors when compared to thylakoids from non-halophytes. FeCN was considerably less efficient as electron acceptor with halophyte thylakoids, supporting much lower rates of O2 evolution and having a lower affinity. FeCN accepted electrons at a different, DMMIB insensitive, site with these thylakoids. 1,4-Benzo-quinones with less positive midpoint potentials were less effective in accepting electrons from halophyte thylakoids compared to nonhalophyte thylakoids, also reflected in lower rates of O2 evolution and lower affinity. Considering the lipolphilic nature and the fact that there was no apparent change in the site donating electrons to the quinones, an alteration in the midpoint potential of this site by about +100mV is postulated for the halophyte thylakoids.

Interaction of electron acceptors with the excited triplet state of Zn cytochrome c

The decay rate of the excited triplet state of Zn cytochrome c was enhanced by electron acceptors including methyl viologen and ferric complexes of cyanide, oxalate, EDTA and cytochrome c at room temperature. Ferrous compounds were several orders of magnitude less effective than the respective ferric form in quenching the phosphorescence. In the presence of ferricytochrome c and ferricyanide the semilogarithmic plots of the decay curve showed an anomalous decay profile in which the rate of interaction appeared to accelerate after excitation. One explanation is that the quenching process was accelerated by a conformational change of the polypeptide chain around the excited triplet state porphyrin. Another explanation is that quenching occurs via an intermediate. Cytochrome c Excited triplet state Electron acceptor Phosphorescence lifetime

Relationships between Chemical Structure and Inhibition of Human Placental Choline Acetyltransferase by Keto Analogs of Acetylcholine

Seven keto analogs of acetylcholine were synthesized and evaluated as inhihitors of human placental choline acetyltransferase. Their potencies for inhibition of horse serum cholinesterase and stimulation of cholinergic receptors in the longitudinal ileal muscle of the guinea pig were investigated. The most potent and selective inhibitor of choline acetyltransferase was (2-benzoylethyl)trimethylammonium chloride with an I50 of 3 × 10–6M. It exhibited considerably low activities at muscarinic and nicotinic receptors and cholinesterases. Its high potency for inhibiting choline acetyltransferase was attributed to: (a) its cationic terminal, a site for an electron acceptor interaction; (b) an aryl moiety for hydrophobic and electron donor contributions; and (c) a positive charge on the carbon atom adjacent to the benzene ring due to the presence of the carbonyl group, which interacts with the nucleophilic residue on the enzyme.

Desorption of carbonium ions from zeolite surfaces; A comparison of reactive surface ionization with field ionization

In comparison with field ionization on platinum the thermal desorption of surface carbonium ions from zeolite surfaces has been investigated mass spectrometrically. CaY-zeolites — forming carbonium ions — were supported by Pt filaments or Pt emitter tips where hydrocarbons are chemisorbed in a non-ionic form. Thermal ion desorption at very low external fields has been observed with stable carbonium ions of triphenylmethyl compounds Ph 3 C-X. This ion desorption was achieved on CaY zeolite surfaces and occurred in the order X  Br > X  Cl > X  OH; however, no ions could be obtained with X  H and X  COOH up to 825°K. On Pt surfaces high fields were required for desorbing molecular ions. The ion desorption from the zeolite and the field desorption from platinum could be distinguished by an energy analysis of desorbed ions. Those ions originating from the dielectric grains of CaY-zeolite suffer field dependent energy losses and therefore a virtual shift in the mass scale. Thermal desorption (a) and field desorption (b) differ in principle: (1) in the kind of ions formed, (a) carbonium ions from zeolite surfaces, (b) parent molecular ions from platinum; (2) in the temperature dependence of ion currents, in (a) a positive temperature function with necessary minimum temperature, in (b) no minimum temperature, and negative temperature coefficients have been observed; (3) in the field dependence of ion currents (a) very low fields < 10 5 V cm were sufficient, and Schottky-line dependences of intensities have been found, in (b) a minimum field > 10 7 V cm was required. Ion formation on zeolite surfaces is facilitated by an intra-molecular substitution of Ph 3CX, which polarizes the C δ+−X δ- bond, and as well by an intermolecular interaction of electron acceptors, for instance by [(CN) 2-C  C-(CN) 2]. Experimental results are discussed with respect of surface fields on zeolite structures, Brönsted- or Lewis acid sites, and the formation of charge-transfer complexes. In conclusion, acidic surface sites are most likely responsible for the carbonium ion desorption in this investigation.

Interaction of electron acceptors with bases—XXI : Further studies of the proton magnetic resonance spectra of meisenheimer-like compounds

The structures of σ-complexes formed by the reaction of methoxide ion or acetonate ion with various nitroaromatic compounds are confirmed or established from observations of their PMR. The substrates include: 1-x-2,4-dinitrobenzenes; 1-x-2,6-dinitrobenzenes; 1-x-2,4,6-trinitrobenzenes; 1-x-2,4-dinitronaphthalenes; and 9-x-10-nitroanthracenes.