Hydrogen Bond Energy Research Articles

Effective Ion Charges in Ion Exchangers and Electrolyte Solutions

Structures, effective numbers of charges and molecular orbitals of ion pairs and representative fragments of a sulfocation exchanger in various ionic forms were calculated by the non-empirical quantum chemical method of LCAO MO. The effective charges of ions in accordance with the principles of the molecular orbital method were fractional values. For contact ion pairs, where the effective ion charges were experimentally measured by X-ray absorption spectroscopy, we obtained full agreement with the calculated values. The charge numbers of cations and anions differed in both hydrate-separated and ion-exchange systems due to the fact that the oxygen atoms of hydrated water molecules influenced the formation of molecular orbitals. According to the obtained values of the numbers of charges and interionic distances, the energies of the electrostatic interaction of ions were calculated using the integral form of Coulomb's law. Experimental values of the energies of chemical bonds of counterions and fixed ions were obtained using the conductometric contact-difference method when measuring the specific electrical conductivity of MK-40 cation exchange membranes in the range of 20-50oC and according to the Arrhenius equation. The coordination of experimental and calculated chemical bond energies in the ion exchanger was achieved after the addition of hydrogen bond energy to the electrostatic interaction energy. In order to be able to completely nonempirically calculate the energies of chemical bonds in an ion exchanger, we took the value of the hydrogen bond energy as the excitation energy of the first energy level of deformation vibrations of water molecules having a value of 19.4 kJ/mol. A comparison of the contribution of the electrostatic interaction to the total binding energy of alkali metal cations with a fixed ion showed its small role in ion exchange and membrane transport, so that in the first approximation we can say that the transfer of alkali metal cations is determined by the breaking of the hydrogen bond. For cations of a larger charge (calcium), the electrostatic energy already makes a significant contribution, and for trivalent ions, the energies of the Coulomb interaction and hydrogen bonding are close to each other. The soliton mechanism of translation of the energy of deformation vibrations along a chain of water molecules is considered, which allows explaining the decrease in energy when several hydrogen bonds are broken.

Theoretical and experimental approach on investigation of ethylurea-water clusters

Abstract Alkylated urea derivatives have found wide application as starting materials for the production of many drugs, including anticancer drugs, as well as in many other areas. In this work, we studied ethylurea crystalline hydrates using a complex of theoretical and experimental methods. The nature of the intermolecular interactions between ethylurea and water molecules is investigated using topological analyses such as atoms in molecules (AIM), non-covalent interaction (NCI), reduced density gradient (RDG), electron localized functions (ELF), and localized orbital locator (LOL). The hydrogen bond energy is in the range of 1.1295–14.4327 kcal/mol. Also, a highly correlated parabolic relationship between topological parameters (E HB, ρ, and ∇2 ρ) and H-bond length was determined. According to RDG data, with an increase in the number of water molecules in ethylurea clusters, the area corresponding to hydrogen bonds increases. The initial ethylurea and its crystalline hydrate were studied by FTIR spectroscopy and X-ray diffraction. The introduction of water molecules into the ethylurea crystal was proved by IR spectroscopy by the appearance of the corresponding absorption bands. X-ray diffraction showed that the initial ethylurea has intense peaks at 11.2, 16.8, 21.4, 22.24, 25.06, 25.78° 2Ɵ, the intensity of which changes when water molecules are introduced into the crystal.

Spatial structure of soymorphin-6 molecule

By the method of the theoretic conformational analysis the conformational capabilities of the soymorphin-6 (Tyr1-Pro2-Phe3-Val4-Val5-Asn6-NH2) molecule were studied. The potential energy of this molecule is given as the sum of nonvalent, electrostatic and torsional interactions and the energy of hydrogen bonds. Low-energy conformations of the soymorphin-6 molecule, the values of the dihedral angles of the main and side chains of amino acid residues that make up the molecules are found, the energy of intra- and inter-residual interactions is estimated. It is shown that the spatial structure of the soymorphin-6 molecule can be represented by eight conformations. The results obtained can be used to study the structure and structural-functional organization of the soymorphin molecules.

Ab initio Modeling of Hydrogen Bonding of Remdesivir and Adenosine with Uridine.

Remdesivir (RDV) emerged as an effective drug against the SARS-CoV-2 virus pandemic. One of the crucial steps in the mechanism of action of RDV is its incorporation into the growing RNA strand. RDV, an adenosine analogue, forms Watson-Crick (WC) type hydrogen bonds with uridine in the complementary strand and the strength of this interaction will control efficacy of RDV. While there is a plethora of structural and energetic information available about WC H-bonds in natural base pairs, the interaction of RDV with uridine has not been studied yet at the atomic level. In this article, we aim to bridge this gap, to understand RDV and its hydrogen bonding interactions, by employing density functional theory (DFT) at the M06-2X/cc-pVDZ level. The interaction energy, QTAIM analysis, NBO and SAPT2 are performed for RDV, adenosine, and their complex with uridine to gain insights into the nature of hydrogen bonding. The computations show that RDV has similar geometry, energetic, molecular orbitals, and aromaticity as adenosine, suggesting that RDV is an effective adenosine analogue. The important geometrical parameters, such as bond distances and red-shift in the stretching vibrational modes of adenosine, RDV and uridine identify two WC-type H-bonds. The relative strength of these two H-bonds is computed using QTAIM parameters and the computed hydrogen bond energy. Finally, the SAPT2 study is performed at the minima and at non-equilibrium base pair distances to understand the dominant intermolecular physical force. This study, based on a thorough analysis of a variety of computations, suggests that both adenosine and RDV have similar structure, energetic, and hydrogen bonding behaviour.

Interface‐Guided Computational Protein Design Reveals Bebtelovimab‐Resistance Mutations in SARS‐CoV‐2 RBD: Correlation with Global Viral Genomes and Bebtelovimab‐Escape Mutations

AbstractThe emergence of novel mutations in the SARS‐CoV‐2 spike protein challenges monoclonal antibody (mAb) effectiveness. Comprehending resistance mutations and pinpointing vulnerable spike protein residues is vital for enhanced antibody design. To address this issue, we employed an interface‐guided computational protein design (CPD) approach to decode bebtelovimab‐resistance mutations and uncover susceptible residues within the receptor‐binding domain (RBD). Utilizing structural‐modeling and high‐throughput techniques, we mapped the bebtelovimab‐RBD interface, identifying critical resistance mutations through analysis of binding energetics and residue interactions. Our design protocol integrated stability predictions, side‐chain conformational sampling, and binding affinity calculations to prioritize substitutions that restore antibody recognition and neutralization. Previously unexplored susceptible RBD residues were also discovered, offering new therapeutic avenues. Comparative analysis with COVID‐19 patient data validated the predicted resistance mutations (69 %–100 % correlation, based on different MinProp cut‐offs). Precision and recall values, calculated by comparing our predictions with experimentally reported bebtelovimab‐escape mutants, demonstrated the performance and accuracy of our predictions. Investigation of intermolecular interactions highlighted the importance of van der Waals forces, hydrogen bond energy, and electrostatic contributions in bebtelovimab‐RBD binding affinity. This computational design empowers the decoding of resistance mutations and the development of next‐generation antibodies against viral variants, strengthening our response to SARS‐CoV‐2 and related coronaviruses.

Synergistic mechanism of dodecylamine/octanol mixtures enhancing lepidolite flotation from the self-aggregation behaviors at the air/liquid interface

Surface tension measurements and molecular dynamics (MD) simulations were used to explore the flotation foam properties and self-aggregation behaviors of dodecylamine (DDA)/octanol (OCT) mixtures formed with different mole ratios at the air/liquid interface. Based on the surface and thermodynamic parameters, the DDA/OCT mixtures exhibited greater interfacial activities and adsorption capacities than their individual components. The MD simulations showed that DDA and OCT were aggregated through hydrogen bonding, coulombic forces and hydrophobic association. OCT was inserted into the DDA adsorption layer, causing the alkyl chains of both DDA and OCT to extend from water to air at varying heights and angles. The addition of OCT improved the hydration of the amino groups and reduced the overall number of hydrogen bonds. The stability of the flotation foam decreased, and the high viscosity and difficult defoaming of the DDA flotation foam were significantly improved. When the DDA/OCT mole ratio was 2:1, the included angle formed between the alkyl chains and the interface was maximized, leading to enhanced compatibility among the alkyl chains, and the hydrogen bond energy was relatively large, which showed a strong synergistic effect. The MD simulation findings were consistent with the results obtained from the lepidolite flotation and surface tension experiments conducted in this study; our results could provide a theoretical foundation for the selection of superior mixed collectors and frothers.

Theoretical and experimental study of resonance-assisted hydrogen bond in o-hydroxyl diaryl schiff bases

In this paper, the intramolecular hydrogen bond (IMHB) energies (EHB) in fifty 2-OH-XArCH=NArY (2-OH-XBAY) compounds containing resonance-assisted hydrogen bond (RAHB) system and fourteen XArCH=NAr-2′-OH (XBA-2′-OH) compounds without RAHB system were estimated by molecular tailoring approach (MTA) and cis-trans method (CTM) at the theoretical level of DFT B3LYP/6–311++G(d, p). The above compounds were synthesized and their 1H NMR and 13C NMR spectra were determined, then the chemical shifts of H δH on OH and chemical shifts of C δC on CH=N were assigned. The relationship between the δH of the bridged hydrogen atom on OH, the δC of the carbon atom on the CH=N bond in the RAHB ring and the estimated EHB was investigated. The results show that: (1) There is a good linear relationship between the IMHB energy calculated by CTM and that calculated by MTA. (2) There is a good linear relationship between the calculated O-H bond length dO-H and the N···H distance dN···H. (3) For 2-OH-XBAY compounds with fixed X and changing Y, the chemical shift of the bridge hydrogen atom δH(OH) has a good linear relationship with the IMHB energy ECTM, but when both X and Y change, the linear relationship is not good. (4) There is no good linear relationship between the chemical shift of C on CH=N δC(CH=N) and the IMHB energy ECTM. (5) The IMHB energy ECTM of 2-OH-XBAY cannot be expressed by only employing δH(OH), and it is necessary to employ both δH(OH) and δC(CH=N) for expressing their ECTM. (6) As a comparison, there is no RAHB in XBA-2′-OH, and in such case, it is unsuitable to use δH(OH) to express the EHB.

The Influence Mechanism of Interfacial Characteristics between CSH and Montmorillonite on the Strength Properties of Cement-Stabilized Montmorillonite Soil.

To elucidate the impact mechanism of the interfacial characteristics of Calcium Silicate Hydrate gel (CSH)-Montmorillonite (MMT) at the nanoscale on the strength of cement-stabilized montmorillonite soil, this paper begins by examining the interfacial energy. Through Molecular Dynamics (MD) simulation methods, the energy at the MMT and CSH binding interface is quantitatively calculated, and the correlation between the interfacial energy and macroscopic strength is determined in conjunction with grey relational analysis. Finally, based on the characterization results from X-ray diffraction (XRD), the accuracy and sources of deviation in the MD simulation results are discussed. The study shows the CSH-MMT interfacial energy is composed of van der Waals forces, hydrogen bond energy, and electrostatic interactions, which are influenced by the migration of cations; there is a good consistency between the CSH-MMT interfacial energy and the unconfined compressive strength (UCS) of cement-stabilized soil (cemented soil), with the interfacial energy decreasing as the number of water molecules increases and first decreasing then increasing as the number of MMT layers grows; by adjusting the mix proportions, the magnitude of the CSH-MMT interfacial energy can be altered, thereby optimizing the strength of the cemented soil.

Exploring the excited state multi-proton transfer path and the associated photophysical properties of P-TNS molecule by DFT and TDDFT theory

Recently, Chen et al. designed and synthesized a new multi-purpose dye probe P-TNS with bifunctional groups, which has an ultra-fast excited state intramolecular proton transfer characteristic (ESIPT) (Spectrochim Acta A Mol Biomol Spectrosc., 2021, 262: 120084.). The P-TNS molecules are very sensitive to hydrazine (N2H4) and cyanide (CN-), which makes it have a good practical application prospect in the field of probe detection. However, the corresponding optical properties and the related mechanisms have not been systematically investigated in experiments. In the present work, the proton transfer pathways as well as the photophysical properties changes in the transfer path of P-TNS with three intramolecular hydrogen bonds (HB1, HB2 and HB3) are revealed for the first time. First, the analysis of potential energy surface and potential energy curve determined the stable conformation of P-TNS molecule and its isomer structure, and clarified the reaction mechanism of ESIPT process. Subsequently, the analysis of the frontier molecular orbitals reveal that the charge difference is the driving force required for the proton transfer process from the microscopic level, which led to the determination that the HB1 structure without the charge difference could not complete the ESIPT process. Finally, the variation of hydrogen bond strength and the path of proton transfer are demonstrated from several perspectives of hydrogen bond parameters, hydrogen bond energy, infrared vibrational frequency (IR) and reduced density gradient (RDG) surface. This study essentially explains the photophysical properties and proton transfer pathways of a new multipurpose dye probes for organic luminescence with bifunctional groups, which are important for the fields of spectroscopy and measurement technology, and also provides ideas for the design and synthesis of new fluorescent probes.

Crystal Structure, Hirshfeld Surface Analysis, and Biological Activities of Schiff-Base Derivatives of 4-Aminoantipyrine.

Eight Schiff bases, synthesized by the reaction of 4-aminoantipyrine with different cinnamaldehydes, were studied in the solid state by using vibrational spectroscopy (IR) and X-ray diffraction techniques. The analysis was extended to the solution phase through ultraviolet-vis, fluorescence spectroscopy, and cyclic voltammetry. Finally, the crystal structures of four compounds (3b, 3d, 3g, and 3h) were determined and studied. In addition to the experimental study, theoretical calculations using the semiempirical method PM6/ZDO were performed to understand better the compound's molecular properties, UV-vis, and infrared spectra. The primary difference is the angular conformation of the terminal phenyl rings around the corresponding linking C-N and C-C σ-bonds. Furthermore, as a result of extended bonding, the > C=N- azomethine group-containing Cpyr-N=(CH)-(CR)=(CH)-Cbz chain (with R=H for 3b, 3d, and 3h, and R=CH3 for 3g) is planar, nearly coplanar, with the mean plane of the pyrazole ring. Hirshfeld surface (HS) analysis was used to investigate the crystal packing and intermolecular interactions, which revealed that intermolecular C-H···O and C-H···N hydrogen bonds, π···π stacking, and C-H···π and C=O···π interactions stabilize the compounds. The energy contributions to the lattice energies of potential hydrogen bonds were primarily dispersive and repulsive. All derivatives were tested in vitro on LPS-stimulated mouse macrophages to assess their ability to suppress the LPS-induced inflammatory responses. Only a slight reduction in the level of NO production was found in activated macrophages treated with 3h. Additionally, the derivatives were tested for antimicrobial activity against several clinical bacteria and fungi strains, including three biofilm-forming microorganisms. Nevertheless, only Schiff base 3f showed interesting antibacterial activities with minimum inhibitory concentration (MIC) values as low as 15.6 μM against Enterobacter gergoviae. On the other hand, Schiff base 3f and, to a lesser extent, 3b and 3h showed antifungal activity against clinical isolates of Candida. The lowest MIC value was for 3f against Candida albicans (15.6 μM). It is interesting to note that the same Schiff bases exhibit the highest activity in both biological evaluations.

Crystal structure, Hirshfeld surface and crystal void analysis, inter-molecular inter-action energies, DFT calculations and energy frameworks of 2H-benzo[b][1,4]thia-zin-3(4H)-one 1,1-dioxide.

In the title mol-ecule, C8H7NO3S, the nitro-gen atom has a planar environment, and the thia-zine ring exhibits a screw-boat conformation. In the crystal, corrugated layers of mol-ecules parallel to the ab plane are formed by N-H⋯O and C-H⋯O hydrogen bonds together with C-H⋯π(ring) and S=O⋯π(ring) inter-actions. The layers are connected by additional C-H⋯O hydrogen bonds and π-stacking inter-actions. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H⋯O/O⋯H (49.4%), H⋯H (23.0%) and H⋯C/C⋯H (14.1%) inter-actions. The volume of the crystal voids and the percentage of free space were calculated as 75.4 Å3 and 9.3%. Density functional theory (DFT) computations revealed N-H⋯O and C-H⋯O hydrogen-bonding energies of 43.3, 34.7 and 34.4 kJ mol-1, respectively. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via the electrostatic energy contribution. Moreover, the DFT-optimized structure at the B3LYP/ 6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap.

Atomic insights into hydrogen peroxide decomposition on the surface of pure and pre-treated silver: A reactive molecular dynamics simulation study

Based on ReaxFF molecular dynamics simulation, H2O2 decomposition on pure and pre-treated silver catalyst is studied at a microscopic level. The pretreatment undergoes a surface annealing with redundant H2O2 on top of catalyst. The simulation results indicate that H2O2 decomposition can be drastically accelerated by elevating temperature. The extent of decomposition is closely related to bond, hydrogen bond, and potential energy of simulation system. It is found that H2O2 decomposition follows a four-stage HOOH bond break mechanism while it needs three times longer for pre-treated silver catalyst than pure silver catalyst. The activation energy of pre-treated silver catalyst is about 50 % lower than pure silver catalyst. However, the overall reaction rate of pre-treated silver catalyst is about an order of magnitude slower than pure silver catalyst, which owes to the much smaller pre-factor. It is believed that although the pretreatment causes silver oxide to be formed on the surface, it leads to more hydrogen and oxygen atoms deposited so that most active sites for catalytic reaction are blocked for further decomposition. This may be helpful to understand the inherent mechanism of H2O2 decomposition on silver-based catalyst and provide instructional advice for further catalyst modification design.

Three-Dimensional Noncovalent Interaction Network within [NpO2Cl4]2- Coordination Compounds: Influence on Thermochemical and Vibrational Properties.

Noncovalent interactions (NCIs) can influence the stability and chemical properties of pentavalent and hexavalent actinyl (AnO2+/2+) compounds. In this work, the impact of NCIs (actinyl-hydrogen and actinyl-cation interactions) on the enthalpy of formation (ΔHf) and vibrational features was evaluated using Np(VI) tetrachloro compounds as the model system. We calculated the ΔHf values of these solid-state compounds through density functional theory+ thermodynamics (DFT+ T) and validated the results against experimental ΔHf values obtained through isothermal acid calorimetry. Three structural descriptors were evaluated to develop predictors for ΔHf, finding a strong link between ΔHf and hydrogen bond energy (EHtotal) for neptunyl-hydrogen interactions and total electrostatic attraction energy (Eelectrostatictotal) for neptunyl-cation interactions. Finally, we used Raman spectroscopy together with bond order analysis to probe Np=O bond perturbation due to NCIs. Our results showed a strong correlation between the degree of NCIs by axial oxygen and red-shifting of Np=O symmetrical stretch (ν1) wavenumbers and quantitatively demonstrated that NCIs can weaken the Np=O bond. These properties were then compared to those of related U(VI) and Np(V) phases to evaluate the effects of subtle differences in the NCIs and overall properties. In general, the outcomes of our study demonstrated the role of NCIs in stabilizing actinyl solid materials, which consequently governs their thermochemical behaviors and vibrational signatures.

Selective production of levoglucosenone from catalytic pyrolysis of regenerated cellulose from a H3PO4-H2O system

A series of regenerated cellulose (RC) were prepared by a H3PO4-H2O system with different H3PO4 concentrations. The effects of H3PO4 concentrations on the physicochemical properties of RCs were studied, including crystallinity index (CrI), hydrogen bond energy (EH), accessibility, and degree of polymerization (DP). The catalytic pyrolysis experiments of RCs were executed with a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) instrument and a lab-scale device, to investigate the regulatory function of cellulose structure on the LGO formation. The results indicated that the H3PO4-H2O system could transform the cellulose crystal form from Ⅰ to amorphous form, reduce its CrI and EH significantly, improve its accessibility, while had slight effects on the DP. These changes made RC more appropriate for the selective preparation of LGO, and the corresponding optimal catalyst loading and pyrolytic temperature were also decreased significantly. With phosphoric acid activated carbon as the catalyst, the highest yield of LGO from RC in Py-GC/MS experiments reached 21.50 wt% at catalyst/cellulose (Cat/Cel) ratio of 1/5 and 270 °C, which was much higher than the 18.16 wt% of LGO gained from untreated cellulose at Cat/Cel ratio of 1/3 and 300 °C. In the lab-scale device, the maximum LGO yield from RC was 17.09 wt% at 270 °C and Cat/Cel ratio of 1/6.

Hydrogen bond energy estimation (H-BEE) in large molecular clusters: A Python program for quantum chemical investigations.

A procedure, derived from the fragmentation-based molecular tailoring approach (MTA), has been proposed and extensively applied by Deshmukh and Gadre for directly estimating the individual hydrogen bond (HB) energies and cooperativity contributions in molecular clusters. However, the manual fragmentation and high computational cost of correlated quantum chemical methods make the application of this method to large molecular clusters quite formidable. In this article, we report an in-house developed software for automated hydrogen bond energy estimation (H-BEE) in large molecular clusters. This user-friendly software is essentially written in Python and executed on a Linux platform with the Gaussian package at the backend. Two approximations to the MTA-based procedure, viz. the first spherical shell (SS1) and the Fragments-in-Fragments (Frags-in-Frags), enabling cost-effective, automated evaluation of HB energies and cooperativity contributions, are also implemented in this software. The software has been extensively tested on a variety of molecular clusters and is expected to be of immense use, especially in conjunction with correlated methods such as MP2, CCSD(T), and so forth.

Enhancing the hemocompatibility of polyethersulfone (PES) hemodialysis membranes using synthesized pseudo zwittronic polymers with various orientations

The incompatibility of membrane materials with blood in the dialysis process has resulted in extensive number of side effects as well as undesired mortality rates for end-stage renal disease (ESRD) patients. Recent attention has been directed at enhancing the hemocompatibility of dialysis membranes. This study synthesized polyether sulfone (PES) mixed matrix membranes (MMMs) containing modified silica nanoparticles (SiO2 NPs) using the phase inversion technique. SiO2 NPs were modified with pseudo-zwitterionic (pZW) coatings of different structures. The modification of SiO2 NPs and their presence in casted MMMs were confirmed using Fourier-transform infrared (FTIR) spectroscopy. Molecular dynamics (MD) simulations were used to compute the quantity and energy of hydrogen bonds, which serve as a metric of hemocompatibility. Surface charge measurements were used to confirm the neutralization of the modified membrane surface charge. Atomic force microscopy (AFM) analysis revealed the influence of the structure of the SiO2 NPs on casted MMM surface roughness. The influence of the pZW coating structure on MMM hemocompatibility was examined in vitro using patient serum to investigate the inflammatory biomarkers released (C5a, IL-1α, IL-1β, IL-6, properdin, C5b-9). The clinicalex-vivo studies showed improvement of hemocompatibility in terms of IL-1α, IL-1β, Properdin, and C59-9. 5 % lower secretion of complement factor and interleukins reflected an improvement of hemocompatibility. Comparing MMM-1 to the other samples, the hemocompatibility profile was better. MD results were in agreement with the clinical outcomes as MMM-1 had the highest number of hydrogen bonds (8) and hydrogen bonding energy value (0.72 kcal/mol), indicating greater water interaction.

Pseudocatalytic acceleration of hydrothermal leaching of amylose from starch in acidic media

Kinetic studies were conducted at 60–700C using buffer solutions with pH 3–5 to establish the effect of solution acidity on the efficiency of amylose leaching from starch. It was shown that the kinetic data are well described by the Kruger-Ziegler model. It was established that as the pH of the solutions decreases from 5.0 to 3.0, the activation energy of amylose leaching process decreases from 185 to 22 kJ/mol, and its dependence on hydrogen ion concentration is described by two linear segments within the pH ranges of 3.0–3.3 and 3.6–5.0. The effect of reducing the hydrogen bond energy upon addition of an additional proton to the water molecule was demonstrated through quantum-chemical modeling using the Gaussian 09 software. It was shown that protonation of the water molecule leads to a decrease in the effective charge on the oxygen atom from –0.626 to –0.142 unit of electron charge. At the same time, the linearity of the hydrogen bond along the –ОН–О– atoms is violated, the length of the hydrogen bond increases from 1.856 to 2.370 Å, and the binding energy decreases by 4.6 times. Thus, hydrogen ions can be considered as a kind of pseudo-catalyst for the process of amylose leaching from starch grains, since in their presence the activation energy of the process decreases and its rate increases. It was concluded that the process of hydrothermal leaching of amylose from starch can be intensified by carrying it out in acidic media without additional heating of starch suspensions.

Role of the amide group in the design of the superbases constructed upon bicyclo[2.2.2]octane framework. Intra- vs. intermolecular hydrogen bonding

A series of bicyclo[2.2.2]octanes (BCO) and 1–methylenebicyclo[2.2.2]octanes (MBCO) containing superbasic subunits supplemented with amide functionality were modeled using the DFT approach. The gas phase basicities (GB) for all modeled bases span the range of 1025–1128 kJ mol−1, and their pKa are mostly above 26, going up to 33–35 for N–heterocyclic carbenes. The energies of the intramolecular hydrogen bonds (IHB) are compared with those in the flexible analogs. Increasing rigidity by switching from the MBCO to the BCO system only slightly affects IHB and substrate binding. The additional amide group strongly increases the energy of substrate binding (ΔGsb), reaching values of −45 kJ mol−1. Solvation removes the effect of the IHB even in the protonated forms, indicating minimal competition between the intramolecular and intermolecular hydrogen bonding. Calculated data suggest that most of the modeled bicyclic bases are promising candidates as the new base organocatalysts for aldol and similar reactions.

Paying Comprehensive Attention to the Temperature-Dependent Dual-Channel Excited-State Intramolecular Proton Transfer Mechanism of Fluorescence Ratio Probe BZ-DAM.

The mechanism of fluorescence detection of diethyl chlorophosphate (DCP) based on 2-substituted benzothiazole (BZ-DAM) was studied by a theoretical calculation method. It should not be ignored that both the BZ-DAM and the detection product BZ-CHO have two excited-state intramolecular proton transfer (ESIPT) channels. Density functional theory (DFT) and time-dependent DFT (TDDFT) theory were used to study the photophysical mechanism of two compounds in two channels in (acetonitrile) ACN solvent, and the temperature dependence of the two channels was given. Channel 1 is more likely to exist at low temperatures and channel 2 is more likely to exist at high temperatures. By theoretical analysis of the constructed potential energy curve, the hydrogen bond energy and electron-hole analysis, we confirmed that both molecules undergo ESIPT and intramolecular charge transfer (ICT) processes in channel 1 and ESIPT and twisted intramolecular charge transfer (TICT) coupling processes in channel 2. The formation of product BZ-CHO molecules led to a significant fluorescence blue-shift phenomenon and inhibited the ICT process, which confirmed that BZ-DAM could be used as a fluorescence probe for fluorescence detection. We sincerely hope that this work will not only help to clarify the excited-state dynamics behavior of the BZ-DAM probe but also provide a new idea for designing and optimizing a new chemical dosimeter.

Effect of the Weber number on the coalescence of relatively moving droplets in an electric field: A molecular dynamics study

Herein, the movement of two non-centric droplets in hexane was studied using a molecular dynamics method to understand the microscopic coalescence mechanism of droplets with an initial velocity in an electric field. Unlike previous studies, this study overcame the limitations in experimental conditions and conventional analytical tools to understand the mechanism of droplet coalescence under the coupling effect of electric and velocity fields at the molecular level. This has implications for the development of inkjet printing technology and microfluidics. The analysis of droplet trajectories and centroid distances revealed that the Weber number can be divided into three ranges according to the three modes of droplet behaviour: incomplete coalescence, complete coalescence and non-coalescence. At a low Weber number (We < 1), the inhomogeneous distribution of ions in droplets causes the fragmentation of droplets that are not completely coalesced. The interaction energy and weak interaction analysis shows that hydrogen bonds between water molecules are the strongest, followed by van der Waals interactions, which is very prominent in the first and second coordination layers. Hexane and water molecules exhibit van der Waals interactions. As the Weber number increases from 0 to 5, the total interaction energy between two droplets increases, and the number of hydrogen bonds increases. A decrease in the total interaction energy, number of hydrogen bonds, radial distribution function and coordination number in a single droplet shows that increasing the Weber number loosens the single droplet and simultaneously promotes the coalescence of two droplets. However, when We > 5, the total interaction energy and number of hydrogen bonds between droplets are zero, and the two droplets do not merge. This is because the angle between the electric field and centreline of the droplets is so large that the electric field cannot horizontally act upon the droplets. This study provides a fundamental guide for studying the mechanism of droplet coalescence under the coupling effect of electric and flow fields.