Formation Of Intermediate Complex Research Articles

Design Optimization of a Novel Catalytic Approach for Transglucosylated Isomaltooligosaccharides into Dietary Polyols Structures by Leuconostoc mesenteroides Dextransucrase.

Polyols, or sugar alcohols, are widely used in the industry as sweeteners and food formulation ingredients, aiming to combat the incidence of diet-related Non-Communicable Diseases. Given the attractive use of Generally Regarded As Safe (GRAS) enzymes in both academia and industry, this study reports on an optimized process to achieve polyols transglucosylation using a dextransucrase enzyme derived from Leuconostoc mesenteroides. These enzyme modifications could lead to the creation of a new generation of glucosylated polyols with isomalto-oligosaccharides (IMOS) structures, potentially offering added functionalities such as prebiotic effects. These reactions were guided by a design of experiment framework, aimed at maximizing the yields of potential new sweeteners. Under the optimized conditions, dextransucrase first cleared the glycosidic bond of sucrose, releasing fructose with the formation of an enzyme-glucosyl covalent intermediate complex. Then, the acceptor substrate (i.e., polyols) is bound to the enzyme-glucosyl intermediate, resulting in the transfer of glucosyl unit to the tested polyols. Structural insights into the reaction products were obtained through nuclear maneic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analyses, which revealed the presence of linear α(1 → 6) glycosidic linkages attached to the polyols, yielding oligosaccharide structures containing from 4 to 10 glucose residues. These new polyols-based oligosaccharides hold promise as innovative prebiotic sweeteners, potentially offering valuable health benefits.

SPECTROPHOTOMETRIC INVESTIGATION OF REDOX REACTION BETWEEN NAPHTHOL GREEN B AND THIOSULPHATE ION IN AQUEOUS ACID: KINETICS AND MECHANISTIC APPROACH METHOD

The kinetics of the redox reaction of naphthol green B (here and thereafter referred to as (NGB3-) with thiosulphate ion has been studied using spectrophotometer at constant ionic strength, I = 0.50 C2mol dm-3 (NaCl), ?H+? = 1.0 ? 10-4 mol dm-3 (HCl) and T = 21 ?1?C. The redox reaction showed a stoichiometry of 2:1 and rate equation for the reaction is: -d[NGB3-]/dt = (a + b[H+])[NGB3-][S2O32-]. The rate of reaction slightly increased with increase in [H+] in the range of (0.5 – 9.0) × 10?4 mol dm?3 investigated. Changes in the ionic strength of the reaction did not affect the rate of the reaction. This showed zero BrØnsted - Debye salt effect. The reaction shows a first order dependence on [oxidant] and [reductant]. Added anion on the reaction rate does not have effect on the rate of the reaction. Michaelis – Menten’s plot of 1/k1 versus 1/ S2O32- and spectrophotometric test suggest presence of an intermediate in the rate determining step. There was evidence of gel formation by the addition of acrylamide to reaction mixture followed by excess methanol. The results obtained suggest the presence of the formation of intermediate complex. Therefore, innersphere mechanism is proposed for this reaction.

Universal Transitions between Growth and Dormancy via Intermediate Complex Formation.

A simple cell model consisting of a catalytic reaction network with intermediate complex formation is numerically studied. As nutrients are depleted, the transition from the exponential growth phase to the growth-arrested dormant phase occurs along with hysteresis and a lag time for growth recovery. This transition is caused by the accumulation of intermediate complexes, leading to the jamming of reactions and the diversification of components. These properties are generic in random reaction networks, as supported by dynamical systems analyses of corresponding mean-field models.

Reactions of CH2OO, CH3CHOO, and (CH3)2COO with Methane through the Formation of Intermediate Complex

Criegee intermediates, which are the products of the ozonolysis of alkenes, play a key role in many chemical and physical processes in the atmosphere. Their reactions with other atmospheric compounds are responsible for the formation of hydroxyl, methyl, hydrogen radicals, nitric and sulfuric acids, and others. Methane is an active greenhouse gas whose concentration has increased rapidly in the last several decades. In this work, we consider the interaction between these two important atmospheric compounds. We choose the three simple Criegee intermediate (CI) molecules: formaldehyde oxide (CH2OO), acetaldehyde oxide (CH3CHOO), and acetone oxide ((CH3)2COO). Some reactions between methane and these Cis have been studied earlier as possible pathways for deactivating methane as well as a source of methanol formation due to molecular collisions in the atmosphere. In the present study, we extend the consideration to the case when an intermediate energetically stable complex is formed after collision. We found that this complex could easily decompose to form an OH radical and another unstable fragment, which can quickly dissociate into CH3 radicals, atomic hydrogen, acetone, acetaldehyde, propaldehyde, methyl alcohol, water, and others, depending on the type of CI being reacted with. These compounds can actively interact with other atmospheric components and change their physical and chemical properties. In addition, CI with a methyl substituent is shown to have increased energy in transition states and minima, resulting in slower reaction rates.

Time-Dependent Inhibition of CYP1A2 by Stiripentol and Structurally Related Methylenedioxyphenyl Compounds via Metabolic Intermediate Complex Formation

Time-Dependent Inhibition of CYP1A2 by Stiripentol and Structurally Related Methylenedioxyphenyl Compounds via Metabolic Intermediate Complex Formation

Activation of heteroallenes by metal-substituted electron-rich tetrylenes

The metal-substituted germylene LGa(μ-Cl)GeDMP (L = HC[C(Me)NDipp]2, Dipp = 2,6-iPr2C6H3, DMP = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2) 1 reacts with CO2 with reductive decarbonylation and formation of the oxygen-bridged complex L(Cl)GaOGeDMP 2, which was also formed in the reaction of 1 with N2O. The CO2 reaction most likely proceeds via intermediate formation of a gallacarboxylate germylene complex as is observed in reactions of complex 1 with both ethyl isocyanate and N,N’-dicyclohexylcarbodiimide, yielding the corresponding heteroallenes insertion complexes L(Cl)Ga-[C(NEt)O]-GeDMP 3 and L(Cl)Ga-[C(NCy)2]-GeDMP 4. In addition, the gallanediyle stannylene adduct LGa-Sn[N(SiMe3)(Dipp)] 5 reacts with CO2 to form the gallacarboxylate tin complex L(Cl)Ga-(CO2)-Sn[N(Dipp)(SiMe3)] 6. Complexes 2–4 and 6 are characterized spectroscopically (1H, 13C, 119Sn (6), IR) and by single crystal X-ray diffraction (sc-XRD).

Spectrophotometric Study of Kinetics of Redox Reaction between Caffeine and Permanganate Ion in Aqueous Acidic Medium

The kinetics of redox reaction between caffeine (hereafter referred to as CAF) and permanganate ion [MnO4-] has been studied spectrophotometrically in aqueous sulfuric acid medium. One mole of CAF was oxidized by one mole of [MnO4-].The reaction showed first-order kinetics with respect to both [CAF] and [MnO4-]. The investigation was carried out under pseudo-first order condition atI= 0.5 mol dm–3, (Na2SO4), T = 24± 0.1℃ and [H+] = 1.0 × 10–1mol dm-3. The reaction obeys the rate law: -d[MnO4-]/dt = (a+b [H+]) [CAF ] [MnO4-]. The reaction was retarded by increased in ionic strength of the reaction medium. The rate of the reaction showed dependence on acid (in the range used).Added anions and cations were observed to catalyze the reaction rate. Spectroscopic investigation and kinetic study did not suggest intermediate complex formation. An outer–sphere mechanism is proposed for the reaction.

Lewis Acid-Assisted C(sp3)-C(sp3) Reductive Elimination at Gold.

The phosphine-borane iPr2P(o-C6H4)BFxyl2 (Fxyl = 3,5-(F3C)2C6H3) 1-Fxyl was found to promote the reductive elimination of ethane from [AuMe2(μ-Cl)]2. Nuclear magnetic resonance monitoring revealed the intermediate formation of the (1-Fxyl)AuMe2Cl complex. Density functional theory calculations identified a zwitterionic path as the lowest energy profile, with an overall activation barrier more than 10 kcal/mol lower than without borane assistance. The Lewis acid moiety first abstracts the chloride to generate a zwitterionic Au(III) complex, which then readily undergoes C(sp3)-C(sp3) coupling. The chloride is finally transferred back from boron to gold. The electronic features of this Lewis-assisted reductive elimination at gold have been deciphered by intrinsic bond orbital analyses. Sufficient Lewis acidity of boron is required for the ambiphilic ligand to trigger the C(sp3)-C(sp3) coupling, as shown by complementary studies with two other phosphine-boranes, and the addition of chlorides slows down the reductive elimination of ethane.

Electron Transfer Reaction of Theobromine and Permanganate Ion in Aqueous Acidic Media

Electron transfer reaction of theobromine (hereafter referred to as TB) and permanganate ion has been studied using spectrophotometric technique under pseudo first-order conditions at T = 24, [H+] = 3.2 × 10–1 mol dm–3and I = 1.0 mol dm–3 (Na2SO4). Stoichiometric study depicted that two moles of TB were consumed by one mole of permanganate ion. The rate of the reaction is first order in both [TB] and [MnO4-] and second order overall. It was observed that, [H+] and ionic strength respectively enhanced the rate of the reaction in the range studied. Michaelis-Mentens analysis showed no evidence of intermediate complex formation. Added anions and cations were observed to catalyze the reaction rate. The reaction conforms to the rate law as shown below: -d [MnO4-]/dt = (a+b [H+]) [TB] [MnO4-] where a = 0.041 dm3mol–1 s–1 and b= 0.028 dm3mol–1 s–1. The reaction thus occurs by an outer-sphere pathway and plausible mechanism is proposed for the reaction.

Thermodynamics of the Formation of Intermediate Complexes in the Oxidation of Citric Acid with Cerium(IV) and the Kinetics of Their Intramolecular Redox Decomposition

Thermodynamics of the Formation of Intermediate Complexes in the Oxidation of Citric Acid with Cerium(IV) and the Kinetics of Their Intramolecular Redox Decomposition

Enhancement Mechanism of Minerals on Lignite-Water Molecule Interactions.

Five coal samples were prepared by deashing Shengli lignite in distinct phases, which consisted of residual ash from spontaneous combustion. The effects of removal and introduction of inherent minerals on the water reabsorption performance of coal samples were systematically investigated in three aspects: pore structure, oxygen-containing functional groups, and lignite materials. Low-field nuclear magnetic resonance spectroscopy was employed to investigate the changes in the water molecular adsorption tendency of coal samples with the variation in the mineral content. The study elucidates that the hygroscopic performance of the coal samples is significantly reduced due to the massive removal of inherent minerals. However, the pore structure of the coal samples after HCl/HF washing becomes more developed, and the oxygen-containing functional groups on the surface are more exposed, leading to an increase in the equilibrium adsorbed moisture content (EMC) of the coal samples. The binding force between coal samples and water molecules is reduced by the removal of the inherent minerals, which weakens the interaction forces between lignite and water molecules. The oxygen-containing functional groups on the surface of lignite interact with the residual ash from spontaneous combustion to enhance the binding force between lignite and surface water molecules, thus leading to the improved tendency of lignite to adsorb water molecules. The formation of intermediate complexes between minerals and oxygen-containing functional groups, in particular, carboxyl functional groups, on the surface of lignite enhances the acting force of polar sites, which improves the interaction of lignite-water molecules.

Proteomic analyses reveal new features of the box H/ACA RNP biogenesis.

The conserved H/ACA RNPs consist of one H/ACA RNA and 4 core proteins: dyskerin, NHP2, NOP10, and GAR1. Its assembly requires several assembly factors. A pre-particle containing the nascent RNAs, dyskerin, NOP10, NHP2and NAF1 is assembled co-transcriptionally. NAF1 is later replaced by GAR1 to form mature RNPs. In this study, we explore the mechanism leading to the assembly of H/ACA RNPs. We performed the analysis of GAR1, NHP2, SHQ1and NAF1 proteomes by quantitative SILAC proteomic, and analyzed purified complexes containing these proteins by sedimentation on glycerol gradient. We propose the formation of several distinct intermediate complexes during H/ACA RNP assembly, notably the formation of early protein-only complexes containing at least the core proteins dyskerin, NOP10, and NHP2, and the assembly factors SHQ1 and NAF1. We also identified new proteins associated with GAR1, NHP2, SHQ1and NAF1, which can be important for box H/ACA assembly or function. Moreover, even though GAR1 is regulated by methylations, the nature, localization, and functions of these methylations are not well known. Our MS analysis of purified GAR1 revealed new sites of arginine methylations. Additionally, we showed that unmethylated GAR1 is correctly incorporated in H/ACA RNPs, even though with less efficiency than methylated ones.

DRUG RELEASE FROM POROUS SPHERICAL PARTICLE: DIFFUSION MODEL WITH AN INTERMEDIATE COMPLEX FORMATION

This publication proposes a new model of drug release from a spherical particle that takes into account the transfer of the drug and the porous particle into the solution by forming an intermediate complex with the bio carrier, one of the components of the solution. The mathematical model is reduced to a dimension-less form that is convenient for qualitative analysis of the process. The problem is realized numerically. The initial stage of filling a porous particle with a bio carrier and stage of drug release into environment were analyzed. Two main types of kinetic curves corresponding to diffusive and convective modes were revealed. The kinetic curves with the initial stage of drug release delay were revealed. The model was in effects (unobvious at first glance) related to the interaction of opposite factors affecting the drug release. The different types of kinetic curves obtained on its basis correspond to different observational conditions, types of particles, and properties of bio fluids. This model can be improved to describe and predict drug release kinetics not only from single porous particles, but also from containers of more complex shape.

New insights into pertinent Fe-complexes for the synthesis of iron via the instant polyol process.

Chemically synthesized iron is in demand for biomedical applications due to its large saturation magnetization compared to iron oxides. The polyol process, suitable for obtaining Co and Ni particles and their alloys, is laborious in synthesizing Fe. The reaction yields iron oxides, and the reaction pathway remains unexplored. This study shows that a vicinal polyol, such as 1,2-propanediol, is suitable for obtaining Fe rather than 1,3-propanediol owing to the formation of a reducible Fe intermediate complex. X-ray absorption spectroscopy analysis reveals the ferric octahedral geometry and tetrahedral geometry in the ferrous state of the reaction intermediates in 1,2-propanediol and 1,3-propanediol, respectively. The final product obtained using a vicinal polyol is Fe with a γ-Fe2O3 shell, while the terminal polyol is favourable for Fe3O4. The distinct Fe-Fe and Fe-O bond lengths suggest the presence of a carboxylate group and a terminal alkoxide ligand in the intermediate of 1,2-propanediol. A large Fe-Fe bond distance suggests diiron complexes with bidentate carboxylate bridges. Prominent high-spin and low-spin states indicate the possibility of transition, which favors the reduction of iron ions in the reaction using 1,2-propanediol.

Collisional losses of ultracold molecules due to intermediate complex formation

Understanding the sources of losses and chemical reactions of ultracold alkali-metal molecules is among the critical elements needed for their application in precision measurements and quantum technologies. Recent experiments with nonreactive systems have reported unexpectedly large loss rates, posing a challenge for theoretical explanation. Here, we examine the dynamics of intermediate four-atom complexes formed in bimolecular collisions. We calculate the nuclear spin--rotation, spin--spin, and quadrupole coupling constants for bialkali tetramers using ab intio quantum-chemical methods. We show that the nuclear spin--spin and quadrupole couplings are strong enough to couple different rotational manifolds to increase the density of states and lifetimes of the collision complexes, which is consistent with experimental results. We propose further experiments to confirm our predictions.

Thermodynamic variation law and influence mechanism of low-temperature oxidation of lignite samples with different moisture contents

Coal spontaneous combustion (CSC) is one of the main disasters that threaten the safe production in coal mines. Moisture, which is the main factor affecting coal oxidation, has a considerable impact on CSC. In this paper, the variation characteristics of TG-DTG and DSC-DDSC curves of two kinds of lignite during low-temperature oxidation were investigated. The following results were obtained: Oxidation-induced heat production (OHP) starts to play a leading role in the temperature range of 50–75 °C; pyrolysis-induced heat absorption (PHA) grows faster than OHP in the temperature range of 70–130 °C; and OHP is dominant in the temperature range of 130–260 °C. Furthermore, for coal samples from Shengli (SL) Coal Mine and Yuanbaoshan (YB) Coal Mine, the initial heat release temperature and the end temperature both conform to the Lorentz function T=T0+2A(B4(M−Mc)2+B2). Thermodynamic parameters reach the maximum under the moisture content of 12%–17% where the CSC is the most likely to occur. In the oxygen adsorption and weight gain stage, the activation energy decreases and gradually stabilizes with the increase in moisture content. In the accelerated oxidation stage, moisture in coal plays a chemical catalytic role in the processes of oxygen chemical adsorption and intermediate complex formation and decomposition. However, excessive moisture cannot accelerate the coal-oxygen composite reaction.

Structural and mechanistic basis for protein glutamylation by the kinase fold

The kinase domain transfers phosphate from ATP to substrates. However, the Legionella effector SidJ adopts a kinase fold yet catalyzes calmodulin (CaM)‐dependent glutamylation to inactivate the SidE ubiquitin ligases. The structural and mechanistic basis in which the kinase domain catalyzes protein glutamylation is unknown. Here we present cryo‐EM reconstructions of SidJ:CaM:SidE reaction intermediate complexes. We show that the kinase‐like active site of SidJ adenylates an active site Glu in SidE resulting in the formation of a stable reaction intermediate complex. An insertion in the catalytic loop of the kinase domain positions the donor Glu near the acyl‐adenylate for peptide bond formation. Our structural analysis led us to discover that the SidJ paralog SdjA is a glutamylase that differentially regulates the SidE‐ligases during Legionella infection. Our results uncover the structural and mechanistic basis in which the kinase fold catalyzes non‐ribosomal amino acid ligations and reveal an unappreciated level of SidE‐family regulation.

Supramolecular Salts of Fe(II)/Co(II)/Ni(II)/Cu(II)/Zn(II) 1,10‐Phenanthroline Cations and Similar Complex Tartratostannate(IV) Anions: From Structural Features to Antimicrobial Activity and Enzyme Activation

AbstractIn the present study authors establish the influence of complex cation on the structure formation, crystal packing, antimicrobial activity and enzyme activation of the previously described isostructural [M(phen)3]2[Sn2(μ‐Tart)2(H2Tart)2] complexes (M(II)=Fe(1), Co(2), Ni(3), Cu(4), Zn(5)). Despite the similarity of composition and structure, compounds 1–5 showed different level of antimicrobial activity. A certain pattern in their effectiveness – decreasing of minimal concentrations, resembles the Irving‐Williams series (Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II)) and, according to the crystal field theory, correlates with the thermodynamic stability of octahedral cations [M(phen)3]2+. Quantum chemical calculations of cations revealed the insights of the “cations‐cell membranes” interactions and allowed authors to conclude that the cations in compounds 4 and 5 are the most lipophilic, have the highest affinity to the lipophilic cell membrane and, as a result, are more bioactive. It was established that compounds 1–5 had a different influence on the activity of studied α‐L‐rhamnosidases Penicillium tardum ІMB F‐100074 and Penicillium restrictum ІMB F‐100139. Correlation of these results with the crystal voids calculations and Hirshfeld surface analysis allow authors to suggest that presence of the bigger number of water molecules, generation of the branched network of hydrogen bonds and formation of active intermediate complex “enzyme – effector – substrate”, leads to the biggest intensification of activation properties for the compounds 2 and 5.

Oxidation of iminodiethanol by Ce (IV) in microheterogeneous system: a comprehensive kinetic analysis

A comprehensive kinetic analysis of catalyzed oxidative degradation of iminodiethanol by Ce(IV) in pure aqueous and microheterogeneous or surfactant media has been reported. The oxidation reactions were first order with respect to [Ce (IV)], the dependence of rate on iminodiethanol concentration is first order, the rate constant values increased with increasing dielectric constant of the medium and the entropy of activation was negative. Kinetic information suggested that the oxidation reactions proceed through intermediate complex formation. The profile of pseudo-first order rate constant, kψ against [SDS] (sodium dodecyl sulfate) shows a maximum at about the concentration near which the randomized surfactant monomers started aggregating for the formation of micelle. To demonstrate the kinetic pattern and to evaluate the micelle-reactant binding constant values, Berezin’s model has been advanced. The transfer free energy per mole of the solute from water to the micellar phase has also been computed. Activation parameters for the oxidation reaction are obtained from the temperature dependence studies. Basing on all analytical results plausible mechanisms are proposed for the catalyzed oxidation of iminodiethanol by Ce (IV) both in aqueous and surfactant medium.

Multifaceted membrane binding head of the SARS-CoV-2 spike protein.

The SARS-CoV-2 spike protein presents a surface with enormous membrane binding potential to host tissues and organelles of infected cells. Its exposed trimeric head binds not only the angiotensin-converting enzyme 2 (ACE2), but also host phospholipids which are missing from all existing structures. Hence, the membrane interaction surfaces that mediate viral fusion, entry, assembly and egress remain unclear. Here the spike:membrane docking sites are identified based on membrane optimal docking area (MODA) analysis of 3D structures of spike proteins in closed and open conformations at endocytic and neutral pH levels as well as ligand complexes. This reveals multiple membrane binding sites in the closed spike head that together prefer convex membranes and are modulated by pH, fatty acids and post-translational modifications including glycosylation. The exposure of the various membrane interaction sites adjusts upon domain repositioning within the trimer, allowing formation of intermediate bilayer complexes that lead to the prefusion state while also enabling ACE2 receptor recognition. In contrast, all antibodies that target the spike head would block the membrane docking process that precedes ACE2 recognition. Together this illuminates the engagements of the spike protein with plasma, endocytic, ER or exocytic vesicle membranes that help to drive the cycle of viral infection, and offers novel sites for intervention.