H-bonded Complexes Research Articles

Similarities and Differences of Hydridic and Protonic Hydrogen Bonding.

Ab initio calculations were employed to investigate the interactions between selected electron-donating groups, characterized by M-H bonds (where M represents a transition metal and H denotes a hydridic hydrogen), and electron-accepting groups featuring both σ- and π-holes. The study utilized the ωB97X-D3BJ/def2-TZVPPD level of theory. Hydridic hydrogen complexes were found in all complexes with σ- and π-holes. A comparative analysis was conducted on the properties hydridic H-bond complexes, presented here and those studied previously, alongside an extended set of protonic H-bonds complexes. While the stabilization energies changes in M-H bond lengths, vibrational frequencies, intensities of the spectral bands, and charge transfer for these complexes are comparable, the nature of hydridic and protonic H-bonds fundamentally differ. In protonic H-bond complexes, the main stabilization forces arise from electrostatic contributions, while in hydridic H-bond complexes, dispersion energy, is the primary stabilization factor due to the excess of electrons and thus larger polarizability at hydridic H. The finding represents an important characteristic that distinguishes hydridic H-bonding from protonic H-bonds.

A neutron diffraction study of the hydrous borate inderborite, CaMg[B3O3(OH)5]2(H2O)4·2H2O

Abstract The crystal chemistry of inderborite, a B-rich mineral (B2O3 ~41 wt%) with ideal formula CaMg[B3O3(OH)5]2·6H2O or CaMg[B3O3(OH)5]2(H2O)4·2H2O from the Inder Deposit, Kazakhstan, was re-investigated by a multi-methodological approach (single-crystal X-ray and neutron diffraction, electron probe micro-analysis in wavelength-dispersive mode, laser ablation multi-collector inductively mass spectrometry). The experimental findings show that the real chemical formula of inderborite from the Inder Deposit is virtually identical to the ideal one: the fraction of potential isomorphic substituents is insignificant. Boron is, therefore, the only industrially relevant element occurring in this mineral. The in situ B isotope composition of the Inder inderborite shows enrichment in the heavy 11B isotope, giving a weighted mean δ11BNIST951 of +35.15 ± 0.49 ‰ (2σ, N = 6). Such a positive δ11B value falls within the range of values in which the source of boron is ascribable to marine reservoirs rather than to terrestrial ones. X-ray (at 293 K) and neutron (at 20 K) structure refinements confirm that the principal building block unit of the structure is a [B3O3(OH)5]2– ring, consisting of two BO2(OH)2 tetrahedra (B-ion in sp3 electronic configuration) and one planar-triangular BO2OH group (B-ion in sp2 electronic configuration). In the [B3O3(OH)5]2– ring, all the oxygen atoms that are not shared between two boron atoms are protonated. The building units share corners with the CaO2(OH)4(OH2)2 polyhedra and Mg(OH)4(OH2)2 octahedra, forming hetero-polyhedral sheets parallel to (100). Subsequent hetero-polyhedral sheets are mutually connected only by H-bonding interactions, even mediated by the zeolitic (“interstitial”) H2O molecules. Ten out of 11 independent oxygen sites in the structure of inderborite are involved in H-bonds as donors or acceptors, and this reflects the pervasive effect of the H-bonding network. The role played by the complex H-bond network is expected to be substantial on the stability of the crystalline edifice, having effects within the single hetero-polyhedral sheet, between subsequent sheets, and in the bonding with the interstitial zeolitic H2O molecules. Finally, the potential utilizations of inderborite, as a B-bearing mineral, are discussed.

IR absorption band of weak H-Bonded systems: Showcasing the signature of the quantum indirect damping within the framework of a new approach using non-Hermitean Hamiltonian formalism

Herein, we investigate the effects of the irreversible action of the medium on the theoretical elucidation of the IR spectrum of weakly H-bonded systems, a prototypical model which provides a rigorous treatment of the relaxation mechanisms impacts on the IR spectral density. The attention will be focused particularly on the effect of indirect damping on the IRυS(X−H⃗) spectrum beyond the harmonic and adiabatic approximations. The ultimate objective of the present investigation is the treatment of the action of the surrounding of the intermonomer modes of H-bonded systems, which must induce a broadening of the Dirac delta peaks, the nature of which, as shown by Maréchal and Witkowski theory, is a Franck–Condon progression. The quantum treatment of the IR absorption band reveals that quantum relaxation of the intermonomer mode of H-bonded complexes could be successfully approached by a non-Hermitian Hamiltonian formalism. Motivated by development of a second method that will be able to validate the first approach, a computationally efficient algorithm was proposed for elucidating the quantum indirect relaxation using Hermitean Hamiltonians. The real eigenvalues, corresponding to different energies of the system are considered to be complex by adjunction of the imaginary parts, which reflects the action of the indirect irreversible action of the medium. These two crude approaches may pave the way for the incorporation of the mechanism of indirect relaxation in more physical and complex situations dealing, particularly, with tunnelling effects in strong H-bonded species, Fermi resonances, and Davydov coupling for cyclic H-bonds dimers beyond the harmonic and adiabatic assumptions.

A systematic study on interplay between intermolecular hydrogen bonding and aromaticity

In this study, the interplay between aromaticity and intermolecular hydrogen bonding was investigated in some heterocyclic compounds using quantum mechanical calculations. The NH … O intermolecular hydrogen bonds between formamide and NH and CO functional groups of the selected compounds enhance the delocalisation of the six-membered ring electron cloud, resulting in an increase in the aromaticity of the ring. The contribution of various factors to the binding energy, including the stabilisation energy of the interplay between aromaticity and H-bonding, was estimated using two model systems. The relative binding energies and the estimated stabilisation energies of the aforementioned interplay can be explained by the weights of resonance structures calculated using the natural resonance theory (NRT) analysis with the natural bond orbitals (NBO) method. These weights reflect the tendency of ring nitrogen lone pairs to contribute to the π electron cloud of the ring. The results of the topological analysis of electron charge densities using the atoms in molecules (AIM) method were used to estimate the aromaticity of the ring. Aromaticity indices, particularly nucleus-independent chemical shifts (NICS) calculated one angstrom above the ring plane, are in good linear correlation with the estimated stabilisation energies and electron density at the H-bond critical points. The sum of the total nuclear spin–spin coupling 1J of adjacent atoms of the ring (Σ1J), and the J values of H-bond donor and H-bond acceptor atoms, 1HJNO, which are in good agreement with the energy data and aromaticity indices, can be used as measures of the interplay between aromaticity and H-bonding. The interplay between H-bonding and the aromaticity of the ring is clearly evident from the changes in the pattern of the molecular electrostatic potential (MEP) contour maps at 1.7 Å above the plane of the molecule upon H-bond complexation.

Uracil-water interaction revisited - in search of single H-bonded secondary minima.

Monohydrated uracil (UW) complexes are stabilized by both O⋯HO and NH⋯O hydrogen bonds (H-bonds), simultaneously participating in forming three stable cyclic structures. The role and contribution of these individual H-bonds (O⋯HO and NH⋯O) to the stability of the three UW complexes are still not understood, because of the technical problems in obtaining their optimized structures by standard geometry optimization. The present study explores a non-standard approach to identify three single H-bonded local minima structures without imaginary frequency using DFT (M06-2X, B3LYP and B3LYP-D3), MP2 and CCSD(T) theories and Dunning's correlation-consistent aug-cc-pVTZ basis set, in both vacuum and aqueous media (CPCM method). The results reveal that these new structures are very shallow secondary minima between two deep wells or next to a deep well of primary minima (double H-bonded structures) in the potential energy surface. The H-bond energy of these single H-bonded complexes is found to be less sensitive to a wide range (about 15-20 degrees) of O⋯HO and NH⋯O angles, and the linearity is preferred in the stable three single H-bonded structures. The technical method used to locate such a shallow minimum is described in detail and may be useful for identifying local minima in other cases where consecutive multiple H-bonded structures are global minima. Energy decomposition (using symmetry adapted perturbation theory (SAPT)) of interaction energy, electron redistribution, and relevant vibrational modes are discussed.

Tailoring Chiral Discotic Liquid Crystals: Mesophase Engineering through Alternative Approaches and Chain Lengths.

Hydrogen (H)-bonding is crucial in constructing superstructures in chemical (such as chiral discotic liquid crystals (DLCs)) as well as in biological systems due to its specific and directional nature. In this context, we achieved the successful synthesis of two branches of heptazine-based H-bonded complexes using distinct strategies. Hpz*-Es-Cn , we incorporated chiral alkyl tails (Hpz-chiral) onto the central C3 symmetric heptazine core, connected to achiral benzoic acid derivatives (Es-Cn acid) through H-bonding. In Hpz-Es-Cn -acid*, we used an achiral heptazine derivative (Hpz-Es-Cn ) linked to a chiral acid via H-bonding. On the other hand, based on the DSC results, we observed that Hpz*-Es-Cn complexes exhibited three distinct phases, whereas Hpz-Es-Cn -acid* complexes displayed only a single mesophase. In polarized optical microscopy (POM) observations, all the complexes displayed birefringence at room temperature, with the color of the POM images changing as the temperature varied. X-ray diffraction (XRD) studies at lower temperatures confirmed that Hpz*-Es-C8 exhibited the columnar rectangular (Colr ) phase, while Hpz*-Es-C10/12 exhibited the columnar oblique (Colob ) phase. However, all the H-bonded complexes exhibited the columnar hexagonal (Colh ) phase at higher temperatures. The chiroptical spectra recorded by Circular dichroism (CD) highlight the specific observations in the columnar phase of two complexes, Hpz*-Es-C10 and Hpz*-Es-C12 . This behavior has potential applications in various fields, including sensors, displays, and responsive materials.

Solvation Plays a Key Role in Antioxidant-Mediated Attenuation of Elevated Creatinine Level: An In Vitro Spectroscopic Investigation.

An elevated level of creatinine (CRN) is a mark of kidney ailment, and prolonged retention of such condition could lead to renal failure, associated with severe ischemia. Antioxidants are clinically known to excrete CRN from the body through urine, thereby reducing its level in blood. The molecular mechanism of such an exclusion process is still illusive. As the excretion channel is urine, solvation of the solute is expected to play a pivotal role. Here, we report a detailed time-domain and frequency-domain terahertz (THz) spectroscopic investigation to understand the solvation of CRN in the presence of two model antioxidants, mostly used to treat elevated CRN level: N-Acetyl-l-cysteine (NAC) and ascorbic acid (ASC). FTIR spectroscopy in the mid-infrared region and UV absorption spectroscopy measurements coupled with quantum chemical calculations [at the B3LYP/6-311G++(d,p) level] reveal that both NAC and ASC form HBonded complexes with CRN and rapidly undergo a barrier-less proton transfer process to form creatinium ions. THz measurements provide explicit evidence of the formation of highly solvated complexes compared with bare CRN, which eventually enables its excretion through urine. These observations could provide a foundation for designing more beneficial drugs to resolve kidney diseases..

Hydrogen Bonding with Hydridic Hydrogen–Experimental Low-Temperature IR and Computational Study: Is a Revised Definition of Hydrogen Bonding Appropriate?

Spectroscopic characteristics of Me3Si-H···Y complexes (Y = ICF3, BrCN, and HCN) containing a hydridic hydrogen were determined experimentally by low-temperature IR experiments based on the direct spectral measurement of supersonically expanded intermediates on a cold substrate or by the technique of argon-matrix isolation as well as computationally at harmonic and one-dimensional anharmonic levels. The computations were based on DFT-D, MP2, MP2-F12, and CCSD(T)-F12 levels using various extended AO basis sets. The formation of all complexes related to the redshift of the Si-H stretching frequency upon complex formation was accompanied by an increase in its intensity. Similar results were obtained for another 10 electron acceptors of different types, positive σ-, π-, and p-holes and cations. The formation of HBe-H···Y complexes, studied only computationally and again containing a hydridic hydrogen, was characterized by the blueshift of the Be-H stretching frequency upon complexation accompanied by an increase in its intensity. The spectral shifts and stabilization energies obtained for all presently studied hydridic H-bonded complexes were comparable to those in protonic H-bonded complexes, which has prompted us to propose a modification of the existing IUPAC definition of H-bonding that covers, besides the classical protonic form, the non-classical hydridic and dihydrogen forms.

Atomic-level understanding on conformational flexibility of neochlorogenic and chlorogenic acids and their inclusion complexation with β-cyclodextrin

Neochlorogenic acid (NCA) and chlorogenic acid (CGA) are positional isomers, abundant in plums and prunes. Their limited bioavailability due to instability under ambient conditions can be overcome by cyclodexrin (CD) encapsulation. Here, single-crystal X-ray diffraction combined with density functional theory (DFT) calculation has been carried out on NCA in free form (1) and in complex with β-CD (2), providing atomic-level insights into the structural flexibility and the inclusion complexation with β-CD of CGA isomers. X-ray analysis revealed that the two symmetry-independent s-cis-NCA and 0.3 water molecules form elaborated H-bond networks (1). Upon β-CD encapsulation, complex H-bond patterns are disrupted and the converted s-trans-NCA is almost entirely enclosed in the asymmetric capsular β-CD dimer (2). On the contrary, the twofold symmetry-related β-CD–s-cis-CGA dimer forms a rare [4]pseudorotaxane reported previously. DFT full-geometry optimization disclosed that both the 2:1 and 1:1 trimodal β-CD–s-trans-NCA inclusion complexes are energetically stable, as the reported s-cis-CGA complex. Furthermore, the three-dimension potential energy surface (3D PES) profiles and all the DFT-fully optimized NCA and CGA structures existing in different lattice environments showed that both the s-cis and s-trans conformers are thermodynamically stable. This study not only presents crystallographic evidence for the distinct NCA and CGA conformers, unequivocally differentiating and resolving the long-time confusing CGA nomenclature for the first time, but also highlights the prime role of CGA conformational flexibility in their pharmacological functions.

The adsorption of arsenate and p-arsanilic acid onto ferrihydrite and subsequent desorption by sulfate and artificial seawater: Future implications of sea level rise

Sea level rise (SLR) is estimated to impact 25% of the world's population along coastal areas leading to an increase in saltwater intrusion. Consequently, changes in the soil biogeochemistry of currently non-saline and/or well-drained soils due to saltwater intrusion are of major concern. Saltwater intrusion is expected to affect farmland across large broiler producer regions, where large amounts of manure containing organic arsenicals were applied over the past decades. To determine how SLR may impact the speciation and mobility of adsorbed inorganic and organic As, we used in situ real-time attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) to determine the adsorption and desorption mechanisms of As(V) and 4-aminophenylarsonic (p-ASA, a poultry feed additive) on ferrihydrite (Fh) in the presence of sulfate at varying pH. The adsorption of As(V) and p-ASA increased at lower pH, with As(V) showing IR features consistent with the formation of inner-sphere of As-Fh surface complexes, while p-ASA also formed others structures as H-bonded As-surface complexes, likely mediated by outer-sphere complexes, based on our FTIR and batch experiments data. No observable As(V) or p-ASA desorption from the Fh surface was promoted by sulfate, however sulfate adsorption on the Fh surface was remarkably larger for p-ASA than for As(V). Complimentary, we carried out batch studies of As(V) and p-ASA desorption by Fh, using artificial seawater (ASW) at varying concentrations. The 1% ASW desorbed ∼10% of initially sorbed p-ASA, while at 100% ASW desorbed ∼40%. However, <1% of As(V) was desorbed by 1% ASW solution and only ∼7.9% were desorbed at 100% ASW. The spectroscopic data support the more extensive desorption of p-ASA compared to As(V) observed in batch experiments, suggesting that organoarsenicals may be easily desorbed and, after conversion to inorganic forms, pose a risk to water supplies.

A Proton-Coupled Electron Transfer Strategy to the Redox-Neutral Photocatalytic CO2 Fixation.

Herein, we report our study on the design and development of a novel photocarboxylation method. We have used an organic photoredox catalyst (PC, 4CzIPN) and differently substituted dihydropyridines (DHPs) in combination with an organic base (1,5,7-triazabicyclodec-5-ene, TBD) to access a proton-coupled electron transfer (PCET) based manifold. In depth mechanistic investigations merging experimental analysis (NMR, IR, cyclic voltammetry) and density-functional theory (DFT) calculations reveal the key activity of a H-bonding complex between the DHP and the base. The thermodynamic and kinetic benefits of the PCET mechanism allowed the implementation of a redox-neutral fixation process leading to synthetically relevant carboxylic acids (18 examples with isolated yields up to 75%) under very mild reaction conditions. Finally, diverse product manipulations were performed to demonstrate the synthetic versatility of the obtained products.

Synergistic Effect of 4A Molecular Sieve on Intumescent Ternary H-Bonded Complex in Flame-Retarding of Polypropylene

In this study, a ternary hydrogen (H)-bonded complex intumescent flame retardant (TH-IFR) of melamine (ME) · phosphoric acid (PA)…pentaerythritol (PER) was synthesized through hydrothermal reaction. The combination of the synthesized TH-IFR with 4A molecular sieve as the synergist was used for the first time to improve the flame retardancy of polypropylene (PP). The involved structure, morphology, flame retardancy, flame-retarding mechanism and mechanical properties of the prepared PP composites were systematically investigated. The results show that incorporation of 1 wt% synergist 4A shows the optimum synergistic effect, and the flame retardancy and mechanical properties of the flame-retarded (FR) PP composites are significantly improved. Incorporation of 4A could change the pyrolysis process of the entire system and promote the char-forming chemical interaction, thereby further enhancing the flame retardancy of FR PP composite. The synergistically flame-retarding mechanism of 4A is explained by the significantly improved quality and quantity of the solid-phase char layer, which is formed through generation of SiO2 and Al2O3 substances, and also participation of PP macromolecular chains in the final char layer formation during burning. Furthermore, the improved dispersion and compatibility of TH-IFR in the composite is largely beneficial to the improvement of flame retardancy and mechanical properties.

Theoretical Studies on OH−+NH2Cl Reaction: Nucleophilic Substitution at Neutral Nitrogen

The SN2 and proton transfer (PT) pathways for [Formula: see text]Cl reaction are represented by employing various electronic structure computations. Both back-side SN2 and PT channels are exothermic and stationary points of PESs are below the reactant asymptote. Overall, the PES is similar to the C-centered SN2 reactions. Conversely, ion-dipole complex was not found for [Formula: see text]Cl system. The N–HOH/NH–Cl hydrogen bond characterizes on either side of the reaction barrier of nitrogen complexes. Moreover, a halogen-bonded complex (HO−–ClNH2) and two types of H-bond complexes (HONH2–Cl− and Cl−–HONH2) were described, predicting an important role in dynamics. The PT pathway may be the major channel in the title system, which is contradictory to [Formula: see text]Cl and [Formula: see text]Cl reactions. Here, MP2, B3LYP and CAM-B3LYP methods show overall excellent consistency with CCSD(T)/CBS energies and are recommended to carry out dynamics simulations.

Structural elucidation of N-amidothiourea derived from nicotinic acid hydrazide: A detailed study of its application as selective anion sensor

A novelN-amidothiourea receptor (1), synthesized by the reaction of nicotinic acid hydrazide with phenyl isothiocyanate, was evaluated for the detection of fluoride, acetate, and hydroxide ions selectively over other anions. Receptor1was characterized by various spectroscopic methods, and further structural elucidation of it was done by Single Crystal X-ray diffraction analysis. The efficacy of receptor1as a colorimetric sensor for fluoride ions was observed by an instant colour change from colourless to light yellow, which can be attributed to the H-bonding complex formation between receptor1and anion. The binding characteristics of the thiourea receptor with fluoride ion (F−) showed 1:1 binding stoichiometry at a lower concentration, whereas at a higher concentration, the binding stoichiometry increased to 1:2. The receptor, when treated with acetate and hydroxide ion, showed 1:2 and 1:1 binding stoichiometry, respectively. The binding affinity of receptor1was found to be following the Brønsted acidity order, i.e., OH− > AcO− > F−. Detailed quantum chemical calculations also supported the experimental findings.

Atmospheric breakdown chemistry of the new “green” solvent 2,2,5,5-tetramethyloxolane via gas-phase reactions with OH and Cl radicals

Abstract. The atmospheric chemistry of 2,2,5,5-tetramethyloxolane (TMO), a promising “green” solvent replacement for toluene, was investigated in laboratory-based experiments and computational calculations. Results from both absolute and relative rate studies demonstrated that the reaction OH + TMO (Reaction R1) proceeds with a rate coefficient k1(296 K) = (3.1±0.4) ×10-12 cm3 molecule−1 s−1, a factor of 3 smaller than predicted by recent structure–activity relationships. Quantum chemical calculations (CBS-QB3 and G4) demonstrated that the reaction pathway via the lowest-energy transition state was characterised by a hydrogen-bonded pre-reaction complex, leading to thermodynamically less favoured products. Steric hindrance from the four methyl substituents in TMO prevents formation of such H-bonded complexes on the pathways to thermodynamically favoured products, a likely explanation for the anomalous slow rate of Reaction (R1). Further evidence for a complex mechanism was provided by k1(294–502 K), characterised by a local minimum at around T=340 K. An estimated atmospheric lifetime of τ1≈3 d was calculated for TMO, approximately 50 % longer than toluene, indicating that any air pollution impacts from TMO emission would be less localised. An estimated photochemical ozone creation potential (POCPE) of 18 was calculated for TMO in north-western Europe conditions, less than half the equivalent value for toluene. Relative rate experiments were used to determine a rate coefficient of k2(296 K) = (1.2±0.1) ×10-10 cm3 molecule−1 s−1 for Cl + TMO (Reaction R2); together with Reaction (R1), which is slow, this may indicate an additional contribution to TMO removal in regions impacted by high levels of atmospheric chlorine. All results from this work indicate that TMO is a less problematic volatile organic compound (VOC) than toluene.

Unexpected Strengthening of the H-Bond Complexes in a Polar Solvent Due to a More Efficient Solvation of the Complex Compared to Isolated Monomers.

It is generally assumed that hydrogen-bonded complexes are less stable in solvents than in the gas phase and that their stability decreases with increasing solvent polarity. This assumption is based on the size of the area available to the solvent, which is always smaller in the complex compared to the subsystems, thereby reducing the solvation energy. This reduction prevails over the amplification of the electrostatic hydrogen bond by the polar solvent. In this work, we show, using experimental IR spectroscopy and DFT calculations, that there are hydrogen-bonded complexes whose stability becomes greater with increasing solvent polarity. The explanation for this surprising stabilization is based on the analysis of the charge redistribution in the complex leading to increase of its dipole moment and solvation energy. Constrained DFT calculations have shown a dominant role of charge transfer over polarization effects for dipole moment and solvation energy.

Experimental and DFT investigation on the role of aromaticity on the stability of hydrogen bonded complexes of cyclohexanone with amines and hydroxyl compounds

The existence of intermolecular hydrogen bonded interaction between four structurally hydroxyl and amino compounds namely, phenol (PHE), aniline (ANI), cyclohexanol (CHL) and cyclohexylamine (CHA) with cyclohexanone (CHE) was investigated in n-hexane medium at 303 K by experimental methods (ultrasonic, UV–Visible, IR spectral analysis) and theoretical (DFT, NCI) methods. From the acoustical and excess thermo-acoustical parameters, strong solute–solute interactions of hydrogen bonded type between the solutes were established. The formation of 1:1complexes between cyclohexanone and hydroxyl, amino compounds was confirmed by UV–visible spectral method and the presence of hydrogen bonding in these complexes was proved by IR spectrum. The stability constant of the four hydrogen bonded complexes was calculated by both ultrasonic and UV–Visible spectroscopic methods. Interestingly, it was found that the order of strength of hydrogen bonding between CHE and hydroxyl as well as amino compounds is in the order CHE-PHE > CHE-ANI > CHE-CHL > CHE-CHA. DFT calculations, NBO analysis and NCI plots were also made to quantify the nature of stabilizing interactions between CHE and hydroxyl and amino compounds. Our computed results are in good agreement with the experimental observations. It is observed that aromatic moiety adjacent to hydrogen donor influences significantly the stability of the H-bonded complexes.

Tuning the course of the oxygen reduction reaction at a carbon electrode using alkaline electrolytes based on binary DMSO–water solvent mixtures

We studied the oxygen reduction reaction (ORR) at a glassy carbon electrode in KOH electrolytes based on DMSO–water solvent mixtures of various compositions (ranging from 0.0 to 93.3 vol% DMSO). The results of RDE (rotating disk electrode) experiments show that by changing the composition ofthe DMSO–water solvent mixture, one can control the course of oxygen electroreduction. Specifically, in the absence of dimethyl sulfoxide, the ORR at −1.5 V vs. Hg/HgO proceeds mainly as a two-electron process (n = 2.28 at 400 rpm), whereas with increasing DMSO content the ORR shifts gradually towards complete four-electron reduction. This tendency continues until the maximum electron transfer number is reached (n = 3.70 at 400 rpm) in an alkaline electrolyte based on a 1:1 H2O:DMSO (v/v) solvent mixture. The effect of DMSO addition on the course of the ORR process at the carbon electrode is thought to arise from the unique physicochemical properties of DMSO–water systems, i.e. their high viscosity and polarity as a result of H-bonded intermolecular complexes formed between water and DMSO molecules.

Anion Recognition by Benzoxaborole.

The binding types (H-bonding or coordinate) and stability constants for complexes of 11 mono- and di-anions with benzoxaborole (1) were determined by 1H and 11B NMR titrations in DMSO or MeCN. Compared to phenylboronic acid (PBA), 1 is a stronger Lewis acid and a poorer H-bond donor with only one B-OH group, which is expected therefore to recognize anions mostly through the coordinate bonding. This is the case however only with F-, HPO42-, and PhPO32- anions, which are coordinately bonded to 1, and partially with SO42-, which forms only the H-bonded complex with PBA, but both H-bonded and coordinate complexes with 1. The majority of tested anions (AcO-, PhPO3H-, (PhO)2PO2-, Cl-, and Br-) form H-bonded complexes with both 1 and PBA, whereas H2PO4- changes the binding mode from coordinate for PBA to H-bonded for 1. The preferable binding type for each anion is confirmed by calculations of DFT-optimized structures of the anion complexes of 1. The preferable binding type can be rationalized considering the effects of the steric hindrance, more significant for the coordinate bonding, and of increased anion basicity, which is favorable for both binding types, but enhances the strength of coordinate bonding more significantly than the strength of H-bonding.

In situ PEGylation of polyamide network of thin film composite membrane by inter-polymer H-bond complex formation

Fouling propensity of membranes is a bottleneck problem. PEGylation is an effective approach to improve the antifouling property of a polyamide (PA) thin film composite (TFC) membrane. However, reactive PEG involves in the covalent network formation with PA leading to the increase of network pore size and lowers the rejection efficiency of the membranes. Post-surface modification by reactive PEG leads to lowering of permeates flux. End-functional (reactive) PEG samples are costly and prepared by multi-step process. Herein, the high pKa value of the fraction of –COOH groups of PA network is utilized for the formation of stable complex with PEG. Addition of linear PEG into the aqueous solution of m-phenylenediamine during interfacial polymerization leads to grafting of polyamide network by PEG through the formation of interpolymer H-bond complex of ether oxygen of PEG and –COOH groups of cross-linked PA network. PEG in the PA network increases the hydrophilicity, permeate flux, rejection efficacy and antifouling property of the membranes. The PEG chains remain stable in the PA network in the pH window of acidic to ≤8 as confirmed by the ATR-IR, wetting behavior, model spectroscopic experiments and X-Ray photoelectron spectroscopy. A PEGylated membrane prepared by the in situ addition of PEG (molecular weight 2000 g mol−1, 1% w v−1) into the MPD solution shows 20–30% higher permeate water flux, superior salt rejection efficiency and fouling resistant property than that of a pristine membrane. This approach is simple, cost-effective and easy to implicate.