Acceptor Reaction Research Articles

Enantioselective Syntheses of 3,4-Dihydropyrans Employing Isochalcogenourea-Catalyzed Formal (4+2)-Cycloadditions of Allenoates.

We herein successfully demonstrate the use of chiral isochalcogenoureas as Lewis Base catalysts for a variety of (4+2)-cycloaddition reactions of allenoates and different Michael acceptors. In all cases the same structural key-motive, a dihydropyran with a (Z)-configurated exocyclic double bond could be accessed as the major regio- and diastereoisomer in an enantioselective manner. Furthermore, these chiral dihydropyrans were successfully engaged in different follow-up transformations.

Diastereoselective (3 + 3)-Annulations of Trisubstituted Michael Acceptors for Access to Polyfunctional Cyclohexanones.

Michael-aldol domino reactions are powerful tools for rapidly assembling carbocyclic scaffolds. We herein disclose a base-catalyzed Michael-aldol domino reaction of trisubstituted Michael acceptors with β-keto ester nucleophiles. The cyclohexanone products are obtained in excellent diastereoselectivity (up to >20:1 dr) and good yields (up to 84%). An attractive practical consideration is that pure products are isolated directly via filtration of the unpurified reaction mixtures. Further functionalization of the cyclohexanones is achieved without perturbation of stereocenters installed through the preceding annulation.

Engineering an annular donor–acceptor reaction chamber with spontaneous feedstock collection for boosting CO2 photoreduction

The interaction between methyl and phosphorus atoms constructs a porous reaction chamber and an annular electron donor–acceptor structure in g-C3N4, inducing a spontaneous collection mechanism of feedstock to enhance photoreduction of CO2 to CO.

Utilisation of an active branching sucrase from Lactobacillus kunkeei AP-37 to produce techno-functional poly-oligosaccharides

Glucansucrase AP-37 was extracted from the culture supernatant of Lactobacillus kunkeei AP-37 and characteristics of the glucan produced by the active glucansucrase in terms of structural and functional roles were determined in this study. A molecular weight around 300 kDa was observed for glucansucrase AP-37 and its acceptor reactions with maltose, melibiose and mannose were also conducted to unveil the prebiotic potential of the poly-oligosaccharides formed via these reactions. The core structure of glucan AP-37 was determined by 1H and 13C NMR and GC/MS analysis which revealed that glucan AP-37 was a highly branched dextran composing of high levels of (1 → 3)-linked α-d-glucose units with low levels of (1 → 2)-linked α-d-glucose units. The structural features of the glucan formed, demonstrated that glucansucrase AP-37 was an α-(1 → 3) branching sucrase. Dextran AP-37 was further characterised by FTIR analysis and XRD analysis demonstrated its amorphous nature. A fibrous compact morphology was observed for dextran AP-37 with SEM analysis whereas TGA and DSC analysis revealed its high stability as no degradation was observed up to 312 °C. Finally, the prebiotic potential of the dextran AP-37 and the gluco-oligosaccharides produced with the acceptor reaction of α-(1 → 3) branching sucrase AP-37 were determined and promising results were found for the gluco-oligosaccharides to act as prebiotics.

Thermodynamic performance of coupled enzymatic reactions: A chemical kinetics model for analyzing cotransporters, ion pumps, and ATP synthases

Previous research has suggested that molecular energy converters such as ATP synthases, ion pumps, and cotransporters operate via spatially separate pathways for free energy donor and acceptor reactions linked by a protein molecule. We present a chemical kinetics model based on these works, with the basic assumption that all molecular energy converters can be thought of as linked enzymatic reactions, one running downhill the chemical potential gradient and driving the other uphill. To develop the model we first look at how an enzyme process can be forced to go backwards using a basic kinetic model. We then use these findings to suggest a thermodynamically consistent method of linking two enzymatic reactions. Finally, in the context of the aforementioned energy converters, the thermodynamic performance of the resulting model is thoroughly investigated and the obtained results are contrasted with experimental data.

Degradation of phenol in the bio-cathode of a microbial desalination cell with power generation and salt removal

In this study, the performance of a three-chamber microbial desalination cell (MDC) was assessed to simultaneously remove salt (35 g.L-1) from water and degrade phenol as a hazardous compound. Two parallel MDCs with the same configurations were run using glucose as the chemical oxygen demand (COD) at an initial concentration of 1.5 g.L-1 as the anolyte. MDC#1 operated with 10 mM phosphate buffer solution (PBS), while MDC#2 operated with bio-cathode as the catholyte for the degradation of 100 mg.L-1 of phenol. The use of MDC#1 resulted in a power density, desalination efficiency, and COD removal of 366.2 mW.m−2, 50.3 ± 4.0 %, and 79.3 ± 2.2 %, respectively. All performance parameters were improved in MDC#2 with bio-cathode so that power density, desalination efficiency, and COD removal reached 660.1 mW.m−2, 72.1 ± 3.0 %, and 92.6 ± 2.4 %, respectively. Also, more than 96 % of phenol was degraded using bio-cathode within 7 h of operation. Bio-cathode could enhance the performance of the MDC reactor through catalyzing the final reactions of electron acceptors compared to MDC#1 with a chemical cathode. In general, the results indicated that heterotrophic microorganisms, able to grow alongside autotrophic bacteria, could effectively extend the applications of MDC reactors to degrade hazardous compounds in cathode chambers.

Intermolecular charge-transfer complexes between chlorothiazide antihypertensive drug against iodine sigma and picric acid pi acceptors: DFT and molecular docking interaction study with Covid-19 protease

The interaction of chlorothiazide (CH) as donor (D) with picric acid (PA) and iodine (I2) as π- and σ-acceptors (A), respectively, gives charge-transfer (CT) complexes as a final products. The reaction of donor and acceptors were studied spectrophotometrically. The complexes are generally of the n-π* and n-σ* types, with the ground state wave function primarily characterized by the non-bonding structure. For the micro determination of chlorothiazide using picric acid and iodine as acceptors, the ideal conditions encouraging the formation of complexes are thoroughly explored. It was discovered that the stoichiometry of the molecular structure is 1:1 (D:A). The equilibrium constant and the molar extinction coefficient were calculated using Benesi-Hildebrand and its modifications. DFT/TD-DFT calculations with B3LYP/LanL2DZ and 6-311G++ level of theory were used to provide comparable theoretical data along with electronic energy gap of HOMO→LUMO. Molecular docking calculations have been performed between CT complexes and Covid-19 protease (6LU7) to study the interaction between them and their inhibitory effect.

The Main Models of Change Management in Kurt Lewin's Thinking

The early and end steps of the change acceptor reaction model have been studied. Kurt Lewin's concept of change management thinking is something that has to be revisited. This research focuses on the intermediate phases of change rather than the pre-change antecedents or consequences of change. The act of altering the antecedent as well as the explicit response to change. Investigate the attitudes and reactions of followers to change from the standpoint of the change process. Researchers do so by using the notion of change evaluation to investigate cognitive and behavioral development. Unlike most change research, which focuses on the negative aspects of change, the notion of specific evaluation follows the development of positive attitudes toward change, manager attitudes, and behavioral changes relating to routines and processes, work practices, and traditions. This research focuses solely on the opinions and views of followers. Followers, on the other hand, are not merely beneficiaries of change; they also have an impact on the process and its outcomes. The application of management in Kurt Lewin's own theory is related to change management, which is always utilized as a reference point to examine a stigma.

Reactions introducing 4-cyano-5-dicyanomethylene-2-oxo-3-pyrrolin-3-yl group to 4-ethynyl-N,N-dialkylaniline derivatives and characterization of the resulting dyes

Electrophilic reactions of a strong acceptor, 3-chloro-1-butyl-4-cyano-5-dicyanomethylene-2-oxo-3-pyrroline, with 4-ethynylaniline derivatives were investigated. The major products were found to be the cis- or trans-monoadducts of the pyrroline-type acceptor, i.e., 4-(dialkylamino)phenylethene derivatives in which the ethene moiety is substituted by chlorine and 1-butyl-4-cyano-5-dicyanomethylene-2-oxo-3-pyrrolin-3-yl group. Their stereostructures depended on the substituent attached to the ethynyl group on the opposite side of aminophenyl group. The adducts with a chloroethylene linkage were able to convert to the ethynylene derivatives by triethylamine. Among the obtained D-π-A molecules, the cis-compounds respect to the donor and acceptor groups showed the absorption maximum at longer wavelengths compared with the corresponding trans-compound. The calculation results suggested more polarized structures in the cis-forms, resulting in their bathochromic shift of the absorption.

A facile depolymerization reaction enables efficient feedstock recycling of polymerized small molecule acceptors in all-polymer solar cells

A facile depolymerization reaction of polymerized small molecule acceptors (PSMAs) is developed for efficiently recovering the polymeric monomers in various circumstances, showing potential on decreasing the cost of PSMA-based all-PSCs.

Synthesis and characterization of cellobiose-derived oligosaccharides with Bifidogenic activity by glucansucrase E81

Cellobiose-derived oligosaccharides were produced from acceptor reactions with glucansucrase E81 and their prebiotic potentials were determined in this study. The major product was a mixture of trisaccharides formed by the addition of an α-linked glucose to cellobiose at either the 2-O position of the reducing end (86%) glucose or the 6-O position of the non-reducing end glucose (11%) demonstrated by NMR spectroscopy and LC-MS-LTQ analysis. The purified DP 3 cellobiose-derived oligosaccharides were then tested for in vitro human gastric juice and α-amylase digestion and no digestion was observed during the 6 h digestion period. Importantly, DP 3 cellobiose-derived oligosaccharides promoted the growth of Bifidobacteria at high levels demonstrating a Bifidogenic effect and a mild level of proliferation was observed for Lactobacilli suggesting the prebiotic roles of cellobiose-derived oligosaccharides.

Construction of Entropically Favored Supramolecular Metal–Ligand Trimeric Assemblies Supported by Flexible Pyridylaminophosphorus(V) Scaffolds

The self-assembly reactions of tetratopic metal acceptors with the flexible bidentate ligands are known to yield self-assembled molecular squares of the type [M4L8], triangles of composition [M3L6], or a mixture of these two. In this work, we demonstrate the preferential formation of a trimeric cage assembly of the formula [Pd3(L1)6·(BF4)6] (1a) over the tetrameric cage [Pd4(L1)8·(BF4)8] (1b) by employing a flexible dipodal phosphoramide ligand, [PhPO(NH(3-Py))2] (L1; 3-Py = 3-aminopyridine), in a reaction with [Pd(CH3CN)4·(BF4)2]. The entropically favored trimeric self-assembly of 1a is the predominant species in the solution [dimethyl sulfoxide (DMSO)-d6] at room temperature. In fact, at higher temperatures, 1a was found to be the only product, as observed from the disappearance of the peak due to 1b in the 31P NMR spectrum. However, in a 1:1 mixture of acetonitrile (MeCN)-d3 and DMSO-d6, the tetrameric species 1b is the preferred species, as revealed by the 31P NMR and electrospray ionization mass spectral analyses. The structure of the molecular trimer 1a has been established in the solid state by using single-crystal X-ray diffraction analysis. Interestingly, treatment of an another flexible ligand, [MePO(NH(3-Py))2] (L2), with the same Pd(II) acceptor resulted in exclusive formation of the trimeric cage [Pd3(L2)6·(BF4)6] (2).

Synthesis and characterization of Bifidogenic raffinose-derived oligosaccharides via acceptor reactions of glucansucrase E81

Glucansucrases can perform acceptor reactions with different sugars to produce distinct oligosaccharides which can potentially act as prebiotics depending on their characteristics. Using cheap substrate sucrose and under mild and environmentally friendly conditions, glucansucrase-derived oligosaccharides can be produced with high yields. In this study, raffinose-derived oligosaccharides up to degree of polymerization (DP) 7 produced by glucansucrase E81 were characterized and their prebiotic functions were evaluated. The main product was a DP 4 oligosaccharide containing two products formed by the transfer of the glucose to raffinose at either the 3- (81%) or 4-O (19%) position of its galactose residue confirmed by NMR spectroscopy and LC-MS-LTQ analysis. The purified DP 4 raffinose-derived oligosaccharides were subjected to in vitro human gastric fluid and α-amylase digestion tests and no digestion was observed under both cases. Finally, prebiotic potential of DP 4 raffinose-derived oligosaccharides was tested with probiotic and pathogenic strains and only growth of Bifidobacteria promoted, thus supported the Bifidogenic activity of DP 4 raffinose-derived oligosaccharides.

Heteroleptic Ruthenium(II) Complexes with 2,2'-Bipyridines Having Carbonitriles as Anchoring Groups for ZnO Surfaces: Syntheses, Physicochemical Properties, and Applications in Organic Solar Cells.

Heteroleptic ruthenium (II) complexes were used for sensitizing ZnO surfaces in organic solar cells (OSCs) as mediators with photoactive layers. The complexes [Ru(4,4'-X2-bpy)(Mebpy-CN)2]2+ (with X = -CH3, -OCH3 and -N(CH3)2; bpy = 2,2'-bipyridine; Mebpy-CN = 4-methyl-2,2'-bipyridine-4'-carbonitrile) were synthesized and studied by analytical and spectroscopical techniques. Spectroscopic, photophysical, and electrochemical properties were tuned by changing the electron-donating ability of the -X substituents at the 4,4'-positions of the bpy ring and rationalized by quantum mechanical calculations. These complexes were attached through nitrile groups to ZnO as interfacial layer in an OSC device with a PBDB-T:ITIC photoactive layer. This modified inorganic electron transport layer generates enhancement in photoconversion of the solar cells, reaching up to a 23% increase with respect to the unsensitized OSCs. The introduction of these dyes suppresses some degradative reactions of the nonfullerene acceptor due to the photocatalytic activity of zinc oxide, which was maintained stable for about 11 months. Improving OSC efficiencies and stabilities can thus be achieved by a judicious combination of new inorganic and organic materials.

Unravelling Regioselectivity of Leuconostoc citreum ABK-1 Alternansucrase by Acceptor Site Engineering.

Alternansucrase (ALT, EC 2.4.1.140) is a glucansucrase that can generate α-(1,3/1,6)-linked glucan from sucrose. Previously, the crystal structure of the first alternansucrase from Leuconostoc citreum NRRL B-1355 was successfully elucidated; it showed that alternansucrase might have two acceptor subsites (W675 and W543) responsible for the formation of alternating linked glucan. This work aimed to investigate the primary acceptor subsite (W675) by saturated mutagenesis using Leuconostoc citreum ABK-1 alternansucrase (LcALT). The substitution of other residues led to loss of overall activity, and formation of an alternan polymer with a nanoglucan was maintained when W675 was replaced with other aromatic residues. Conversely, substitution by nonaromatic residues led to the synthesis of oligosaccharides. Mutations at W675 could potentially cause LcALT to lose control of the acceptor molecule binding via maltose–acceptor reaction—as demonstrated by results from molecular dynamics simulations of the W675A variant. The formation of α-(1,2), α-(1,3), α-(1,4), and α-(1,6) linkages were detected from products of the W675A mutant. In contrast, the wild-type enzyme strictly synthesized α-(1,6) linkage on the maltose acceptor. This study examined the importance of W675 for transglycosylation, processivity, and regioselectivity of glucansucrases. Engineering glucansucrase active sites is one of the essential approaches to green tools for carbohydrate modification.

Biosynthesis, structural characteristics and prebiotic properties of maltitol-based acceptor products

To obtain novel prebiotic candidates, maltitol derivatives were obtained through alternansucrase-catalyzed reaction between sucrose and maltitol and their structural characteristics and in vitro fermentation were investigated. The reaction parameters, including the ratio of sucrose to maltitol, substrate concentration and reaction time, were optimized with the yield of 44.9% as well as 89.6 mg/mL of maltitol derivatives. These maltitol derivatives included α-D-Glcp-(1 → 6)-α-D-Glcp-(1 → 4)-D-Gol (DP3-H), α-D-Glcp-(1 → 3)-α-D-Glcp- (1 → 6)-α-D-Glcp-(1 → 4)-D-Gol (DP4-H) and α-D-Glcp-(1 → 6)-α-D-Glcp-(1 → 3)-α- D-Glcp-(1 → 6)-α-D-Glcp-(1 → 4)-D-Gol (DP5-H). Similar to fructooligosaccharides, they showed the prebiotic activity. Specifically, the highest increase of Bifidobacteria was observed in the cultures supplemented with both DP4-H and DP5-H, whereas the most significant proliferation of Lactobacillus occurred in the culture supplemented with DP3-H. Moreover, fermentation of DP4-H resulted in the highest contents of butyrate and total short-chain fatty acids, which might be related to the highest α-(1 → 3) bond content. These results suggested that the maltitol-receptor products via alternansucrase-catalyzed acceptor reaction were the prebiotic ingredient candidates and the prebiotic activity of maltitol derivatives depended on the type of the glycosidic bond.

Experimental and theoretical study of the O3/O4 regioselectivity of glycosylation reactions of glucopyranosyl acceptors

The knowledge of the regioselectivity between different hydroxyl groups of glycosyl acceptors is valuable in planning simple strategies for the synthesis of oligosaccharides, minimizing the use of protecting groups. With the aim of obtaining deeper knowledge on this subject, we analyzed the relative reactivity of the OH-3 and OH-4 groups of 2,6-di-O-protected methyl α- and β-glucopyranosides in glycosylation reactions. The glycosyl acceptors were prepared by simple procedures, and galacto-pyranosyl and furanosyl trichloroacetimidates were evaluated as glycosyl donors. Experimental results were contrasted with those obtained by a molecular modeling approach. A fair agreement of the molecular modeling and experimental results was obtained. It has been shown, that by choosing the right anomer and protecting group, either the 1 → 3 or 1 → 4 linkage can selectively be installed using the appropriate glucosyl acceptor.

Production of lactose derivative hetero-oligosaccharides from whey by glucansucrase E81 and determination of prebiotic functions

Bioactive oligosaccharides are important compounds for development of functional foods and ingredients. In this study, lactose derivative hetero-oligosaccharides were produced by acceptor reaction of glucansucrase E81 with whey. The synthesis of oligosaccharides was monitored by Thin Layer Chromatography (TLC) analysis followed by 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy analysis which demonstrated the glycosylation of lactose with α-(1 → 2), α-(1 → 3) and α-(1 → 4) linkages. Liquid chromatography–mass spectrometry (LC-MS) analysis demonstrated the formation of DP 7 oligosaccharides from whey. The synthesized oligosaccharides were not digested under in vitro human gastric juice and α-amylase conditions. The prebiotic effect of lactose derivative hetero-oligosaccharides was tested and no growth in pathogenic strains was observed whereas certain probiotic strains utilised lactose derivative hetero-oligosaccharides as Carbon source and their growth was promoted. These findings can be important to reveal the potential of glucansucrases to produce functional oligosaccharides from different sources including waste materials.

A new electrochemical strategy for the synthesis of a new type of sulfonamide derivatives

This study is the first report of electrochemical generation of hydroxyimino-cyclohexa-dien-ylidene haloniums and their application in the synthesis of new halo-N-hydroxysulfonamide derivatives. These compounds were obtained in a one-pot process based on the reaction of halonium acceptors with arylsulfinic acids. The method is easy to carry out, as it is performed using the carbon electrodes in a simple undivided cell. The protocol has a broad substrate scope with a tolerance for a variety of functional groups. The proposed mechanism is a ping-pong type reaction mechanism, which in its first stage the halonitroarene is reduced at the cathode to related hydroxylamine and in the second stage the cathodically generated hydroxylamine by oxidation at the anode and participating in disproportionation reaction is converted to the halonium acceptor.

Efficient production of inulin and oligosaccharides using thermostable inulosucrase from Lactobacillus jensenii

Fructan, inulin and levan, have been applied in many industrial fields because of their versatile properties and functions. Recently, microbial fructan has attracted much attention. In this study, a novel inulosucrase from Lactobacillus jensenii JV-V16 was constructed by truncating partial sequence. The truncated inulosucrase was overexpressed, purified and identified. The optimized pH and temperature for transfructosylation were pH 6.0 and 45 °C, respectively. The inulosucrase showed high thermostability and the half-life at 60 °C was 14.5 h. It also exhibited high transfructosylation capability, resulting in a high ratio of transfructosylation activity to hydrolysis activity. After optimizing the conditions of inulin production, 278.4 g/L inulin was obtained from 600 g/L sucrose with an approximately 46% conversion rate from sucrose to inulin. Additionally, acceptor reaction was attempted to explore the transfructosylation capability of the enzyme and some novel saccharides were detected, indicating the potential application in the synthesis of prebiotics.