New supramolecular liquid crystals induced by hydrogen bonding between pyridyl‐1,2,4‐oxadiazole derivatives and 2,5‐thiophene dicarboxylic acid

Supramolecular liquid crystalline complexes were obtained from binary mixtures of 3‐(4‐pyridyl)‐5‐(4‐n‐alkoxy)phenyl‐1,2,4‐oxadiazoles and 2,5‐thiophene dicarboxylic acid. Although the oxadiazole derivatives and the dicarboxylic acid are non‐mesomorphic, the H‐bonded complexes exhibit mesomorphism. Their liquid crystalline properties were investigated by differential scanning calorimetry and polarizing optical microscopy. The complexes exhibit enantiotropic nematic phases. A structural study involving AM1 semi‐empirical calculations is also described.     

Solvent effects on the molecular stability,intramolecular hydrogen bond,and π-electron delocalization in the simple RAHB systems with different donors and acceptors: a quantum chemical study

Structural Chemistry - In the present study, solvent effects on the molecular stability, intramolecular hydrogen bond (IMHB), and π-electron delocalization (π-ED) in some of the simple...     

Infrared study of hydrogen bonds involving 2,2′-bipyridine and 2,2′-bipyrimidine. Influence of equivalent nitrogen atoms on the hydrogen bond strength

Hydrogen bonding between proton donors (phenols and water) and 2,2′-bipyridine (BPR) or 2,2′-bipyrimidine (BPM) has been investigated by infrared and FT-infrared techniques. The thermodynamic parameters (K, - ΔH, - ΔS°) and the frequency shifts of the ν_OH stretching vibrations have been determined in carbon tetrachloride solution. The spectroscopic results suggest that the complexes formed between phenols covering a large pK_a range (10.3–3.50) and BPR or BPM are of the normal OH⋯N type. The thermodynamic and spectroscopic properties of the BPR and BPM complexes are compared with those previously reported for the interaction between the same proton donors and the model molecules pyridine and pyrimidine. The BPR and pyridine complexes belong to the same series. The behaviours of BPM and pyrimidine are in complete contrast, the thermodynamic parameters and the related proton affinity being much higher for BPM than for pyrimidine. The results are probably ascribable to the presence of two equivalent neighbouring nitrogen atoms, the approach of a hydroxylic proton donor being greatly favoured in this electron-rich region. This effect does not exist in BPR, owing to its transoid configuration in solvents of weak polarity.     

When are two hydrogen bonds better than one? Accurate first-principles models explain the balance of hydrogen bond donors and acceptors found in proteins

Hydrogen bonds (HBs) play an essential role in the structure and catalytic action of enzymes, but a complete understanding of HBs in proteins challenges the resolution of modern structural (i.e., X-ray diffraction) techniques and mandates computationally demanding electronic structure methods from correlated wavefunction theory for predictive accuracy. Numerous amino acid sidechains contain functional groups (e.g., hydroxyls in Ser/Thr or Tyr and amides in Asn/Gln) that can act as either HB acceptors or donors (HBA/HBD) and even form simultaneous, ambifunctional HB interactions. To understand the relative energetic benefit of each interaction, we characterize the potential energy surfaces of representative model systems with accurate coupled cluster theory calculations. To reveal the relationship of these energetics to the balance of these interactions in proteins, we curate a set of 4000 HBs, of which >500 are ambifunctional HBs, in high-resolution protein structures. We show that our model systems accurately predict the favored HB structural properties. Differences are apparent in HBA/HBD preference for aromatic Tyr versus aliphatic Ser/Thr hydroxyls because Tyr forms significantly stronger O–H⋯O HBs than N–H⋯O HBs in contrast to comparable strengths of the two for Ser/Thr. Despite this residue-specific distinction, all models of residue pairs indicate an energetic benefit for simultaneous HBA and HBD interactions in an ambifunctional HB. Although the stabilization is less than the additive maximum due both to geometric constraints and many-body electronic effects, a wide range of ambifunctional HB geometries are more favorable than any single HB interaction.

Correlated wavefunction theory predicts and high-resolution crystal structure analysis confirms the important, stabilizing effect of simultaneous hydrogen bond donor and acceptor interactions in proteins.     

Spectroscopic study of hydrogen bonding in the enol form of β-diketones—I. Vibrational assignment and strength of the bond

The i.r. and Raman spectra of the trans-enol form of some β-diketones and their deuterated analogues in α position are examined in the 4000-50cm⁻¹ range and an approximate assignment is given for the fundamental vibrations. The ν_as(OH) and ν(CO) values suggest that the intramolecular H-bond strength increases in the order: hexafluoroacetylacetone < trifluoroacetylacetone < acetylacetone < α - Cl - acetylacetone < benzoylacetone < dibenzoylmethane < tetraacetylethane.The observed relative Raman intensities of the ν(CC) and ν(CC) bands also support this feature. The spectroscopic results show a great change in the internal modes of the β-diketones upon deuteration; this behaviour indicates a greater localization of the π-electron system of the chelate ring and a weakening of the H-bond on deuteration. The ν_s(OH) vibration seems to be involved in one of the in-plane ring deformational modes.     

A path integral molecular dynamics study on intermolecular hydrogen bond of acetic acid–arsenic acid anion and acetic acid–phosphoric acid anion clusters

We apply ab initio path integral molecular dynamics simulation employing ωB97XD as the quantum chemical calculation method to acetic acid–arsenic acid anion and acetic acid–phosphoric acid anion clusters to investigate the difference of the hydrogen bond structure and its fluctuation such as proton transfer. We found that the nuclear quantum effect enhanced the fluctuation of the hydrogen bond structure and proton transfer, which shows treatment of the nuclear quantum effect was essential to investigate these systems. The hydrogen bond in acetic acid–arsenic acid anion cluster showed characters related to low-barrier hydrogen bonds, while acetic acid–phosphoric acid anion cluster did not. We found non-negligible distinction between these two systems, which could not be found in conventional calculations. We suggest that the difference in amount of atomic charge of the atoms consisting the hydrogen bond is the origin of the difference between acetic acid–arsenic acid and acetic acid–phosphoric acid anion cluster. © 2018 Wiley Periodicals, Inc.     

Synthesis and ferroelectric properties of new chiral liquid crystals derived from (S)‐lactic acid with alkoxyethanols

A homologous series of chiral materials derived from (S)‐lactic acid with alkoxyethanols has been synthesized and their mesomorphic properties investigated. The mesophases and their corresponding transition temperatures were identified by differential scanning calorimetry and polarizing optical microscopy. The spontaneous polarization and electro‐optical response of ferroelectric SmC* phase are measured and reported.     

Studies on the E7 liquid crystal orientations confined to perfluorinated carboxylic acid‐treated cylindrical cavities of Anodisc membranes by FTIR spectroscopy

The orientation of E7 liquid crystal (LC) confined within 200 nm diameter cylindrical cavities of Anodisc membranes are investigated by FTIR dichroism techniques. The cavity walls of the confining pores were chemically modified with different length perfluorinated carboxylic acids (PCAs, C _n F_2n+1COOH, n = 3, 4, 5, 6) at 1, 3 and 5 mM concentrations. From the FTIR spectra of PCA‐treated alumina Anodsic membranes, we found salt formation between the –COOH group of the PCAs and the Anodisc membranes. From the FTIR spectra of LC‐filled Anodisc membranes, we found an abrupt alignment direction change, from parallel to perpendicular, of the LC molecules along the long axis of the cavities between n = 4 and n = 5 for the 1 mM concentration of PCA. However, for the 5 mM concentration of PCA, the parallel‐to‐perpendicular alignment direction of LC molecules changed between n = 3 and n = 4. These LC orientation changes for PCA‐treated Anodisc membranes occurred at shorter length than for hydrocarbon carboxylic acid (HCA, C _n H_2n+1COOH)‐treated Anodisc membranes. This change may be caused by the lower surface energy of the –(CF₂) _n CF₃ chain of PCA than that of the –(CH₂) _n CH₃ chain of HCA.     

Infrared and microwave spectra of the acetylene-ammonia and carbonyl sulfide-ammonia complexes: a comparative study of a weak C-H···N hydrogen bond and an S···N bond

We report a combined high resolution infrared and microwave spectroscopic investigation of the acetylene-ammonia and carbonyl sulfide-ammonia complexes using a pulsed slit-nozzle multipass absorption spectrometer based on a quantum cascade laser and a pulsed nozzle beam Fourier transform microwave spectrometer, respectively. The ro-vibrational transitions of the acetylene-ammonia complex have been measured at 6 μm in the vicinity of the ν(4) band of ammonia for the first time. The previously reported pure rotational transitions have been extended to higher J and K values with (14)N nuclear quadrupole hyperfine components detected and analyzed. The spectral analysis reveals that acetylene binds to ammonia through a C-H···N weak hydrogen bond to form a C(3v) symmetric top, consistent with the previous microwave [Fraser et al., J. Chem. Phys., 1984, 80, 1423] and infrared spectroscopic study at 3 μm [Hilpert et al., J. Chem. Phys., 1996, 105, 6183]. A parallel study has also been carried out for the carbonyl sulfide-ammonia complex whose pure rotational and ro-vibrational spectra at 6 μm have been detected and analyzed for the first time. The spectral and the subsequent structural analyses, in conjunction with the corresponding ab initio calculation, indicate that the OCS-NH(3) complex assumes C(3v) symmetry with S pointing to N of NH(3), in contrast to the T-shaped geometries obtained for the isoelectronic N(2)O-NH(3) and CO(2)-NH(3) complexes.     

Small heterocyclics as hydrogen bond acceptors and donors: the case of the C2H3XS···NH3 complexes (X = H, F and CH3)

B3LYP/6-311++G(d,p) calculations were employed in order to examine the molecular parameters of the C₂H₃XS···NH₃ heterocyclic hydrogen-bonded complexes with X = H, F and CH₃. Intermolecular criteria were taken into account when studying the formation of these hydrogen-bonded complexes, such as geometry analysis, charge density quantification and interpretation of the harmonic vibrational spectrum, in which case the appearance of red-shift and blue-shift effects was discussed. It was assumed from the outset that many hydrogen bond types may exist in these systems, and these were investigated using the results of topological integrations from the quantum theory of atoms in molecules (QTAIM) and intermolecular charge transfer calculations using the ChelpG scheme. The proton donor/acceptor behavior of C₂H₃XS was interpreted in terms of hydrogen bond energies, whose values were corrected using the basis sets superposition error (BSSE) and zero point energy (ZPE). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

MO investigations on lignin model compounds: IX. A PCILO study of the hydrogen bond O-H…O and O-H…N type formed by phenol with some proton acceptors

A systematic PCILO study has been carried out on the intermolecular hydrogen bond formed by phenol with proton acceptors such as acetone, ether, p-benzoquinone, N,N-dimethylformamide, trimethylamine, pyridine, acetonitrile and acrylonitrile. The complexes studied form hydrogen bonds with energy intervals of 20 − 45 kJ mol⁻¹ at distances R_O…Y = 0.265 − 0.300 nm (Y=N,0). For the system phenol-pyridine both the 1:1 complex PhPy and the 2:1 complex Ph₂Py were also studied. The calculated hydrogen bond energies are compared and discussed with experimental data from the literature. The calculated hydrogen bond and O-H stretching force constants are in range expected.     

Effect of ZnO on the interfacial bonding between Na2O–B2O3–SiO2 vitrified bond and diamond

Diamond composites were prepared by sintering diamond grains with low melting Na₂O–B₂O₃–SiO₂ vitrified bonds in air. The influence of ZnO on the wettability and flowing ability of Na₂O–B₂O₃–SiO₂ vitrified bonds was characterized by wetting angle, the interfacial bonding states between diamond grains and the vitrified bonds were observed by scanning electron microscope (SEM), and the micro-scale bonding mechanism in the interfaces was investigated by means of energy-dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The experimental results showed that ZnO facilitated the dissociation of boron/silicon–oxygen polyhedra and the formation of larger amount of non-bridging oxygen in the glass network, which resulted in the increase of the vitrified bonds' wettability and the formation of –CO, –O–H and –C–H bonds on the surface of diamond grains. B and Si diffused from the vitrified bonds to the interface, and C–C, C–O, CO and C–B bond formed on the surface of sintered diamond grains during sintering process, by which the interfacial bonding between diamond grains and the vitrified bonds was strengthened.     

Calorimetric study of the reaction between formic acid and N,N,N′,N′-tetramethylethylenediamine from the aspect of thermal energy storage

The attack by formic acid on the nitrogen electron pairs of N,N,N,N-tetramethylethylenediamine leads to the stoichiometric salt or to many other complexes with different molar fractions. Physical and thermodynamic parameters of two adducts, obtained by calorimetric study, are discussed in terms of their use as potential phase change materials in thermal energy storage because of their large heat of fusion between 288 and 333 K.

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Zusammenfassung Bei der Einwirkung von Ameisensäure auf die Elektronenpaare von N,N,N,N-Tetramethylethylendiamin entsteht ein stöchiometrisches Salz oder mehrere andere Komplexe mit unterschiedlichem Molenbruch. Es werden physikalische und thermodynamische Parameter zweier bei der kalorimetrischen Untersuchung erhaltenen Addukte hinsichtlich ihrer Verwendung als potentielle Phasenwechselsubstanzen bei der thermischen Energiespeicherung diskutiert, da sie im Bereich 288–333 K eine große Schmelz-wärme besitzen.

     

Application of Schrödinger equation to study the tunnelling dynamics of proton transfer in the hydrogen bond of 2,5-dinitrobenzoic acid: proton T1 T1rho, and deuteron T1 relaxation methods

Temperature measurements of proton T1 (24.7 MHz), deuteron (deuterated hydroxyl group) T1 (55.2 MHz), and proton T1(rho) (B1 = 9 G) spin-lattice relaxation times of 2,5-dinitrobenzoic acid have been performed. An analysis of present experimental data together with previously published proton T1 (55.2 MHz) data has revealed the following molecular motions: proton/deuteron transfer in the hydrogen bond and two-site hopping of the whole dimer. It is shown that the proton-transfer dynamics are characterized by two correlation times tau(ov) and tau(tu), describing two fundamentally different motional processes, namely, thermally activated jumps over the barrier and tunneling through the barrier. The temperature dependence of 1/tau(tu) is the solution of Schr?dinger's equation, which also yields the temperature T(tun), where begins the tunnel pathway for proton transfer. A new equation for the spectral density function of complex motion consisting of the three motions is derived. The third motion (two-site hopping of the whole dimer characterized by tau(lib) correlation time) is responsible for a proton T1(rho) minimum in high temperatures, just below the melting point. Such a minimum is not reached by T1 temperature dependencies. The minimum of T1(rho) assigned to the classical hopping of a hydrogen-bonded proton occurs in the same low-temperature regime in which the flattening of the temperature dependencies of T1 points to the dominance of incoherent tunneling. This experimental fact denies the known theories predicting the intermediate temperature regime where a smooth transition between classical and quantum tunneling dynamics is expected. The fit of the derived theoretical equations to the experimental data T1(rho) and T1 is satisfactory. The correlation times obtained for deuterons indicate deuteron-transfer dynamics much slower than proton-transfer dynamics. It is concluded that the classical proton transfer takes place over the whole temperature regime, while the incoherent tunneling occurs below 46.5 (hydrogen) or 87.2 K (deuterium) only.     

A polymer inclusion membrane based on the ionic liquid trihexyl(tetradecyl)phosphonium chloride and PVC for solid–liquid extraction of Zn(II) from hydrochloric acid solution

Abstract  

Extraction of Zn(II) from aqueous solution using polymer inclusion membranes based on poly(vinyl chloride) containing the phosphonium-based ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos^? IL 101) is described. Zn(II) could efficiently be extracted from 5 M hydrochloric acid solution with membranes containing 30 wt% Cyphos IL 101, whereas back-extraction was successfully achieved with 1 M sulfuric acid. Prepared membranes were evaluated in terms of stability in air as well as in terms of leaching of the ionic liquid from the membranes in aqueous solution.     

A comparative study of interplay effects between the cation-π and intramolecular hydrogen bond interactions in the various complexes of methyl salicylate with Mn+, Fe2+, Co+, Ni2+, Cu+, and Zn2+ cations

Structural Chemistry - The interplay among two important noncovalent interactions involving aromatic ring is studied by means of density functional theory (DFT) calculations on complexes of methyl...     

Studies on the phase properties of lyotropic liquid crystals of Brij35/sodium oleate/oleic acid/water system:By means of polarizing microscope,SAXS,~2H-NMR and rheological methods

The pseudo-quaternary phase diagram of Brij35/sodium oleate/oleic acid/water systems has been investigated, and the liquid crystal area has been identified, which covers about two thirds of the whole phase diagram. The liquid crystal structure and behavior have been also studied by using polarizing texture, small angle X-ray scattering, 2H-NMR and rheometer etc. The result shows that when the composition of the system changes along the line of AA′ in this large liquid crystal region, the structural change is cubic→cubic/lamellar→lamellar→lamellar/hexagonal→hexagonal. Meanwhile, we made the first attempt of systematic study of the rheological properties of the above system. The lattice constants of cubic and hexagonal liquid crystals are 10.53 and 5.68 nm, respectively.     

Copper coordinated-poly(α-amino acid) decorated on magnetite graphene oxide as an efficient heterogeneous magnetically recoverable catalyst for the selective synthesis of 5- and 1-substituted tetrazoles from various sources: A comparative study

In this work, poly(α-amino acid)-Cu(II) complex immobilized on magnetite graphene oxide (GO/Fe₃O₄@PAA-Cu-complex) was prepared via a multistep synthesis and employed as an efficient, heterogeneous, magnetically recyclable nanocatalyst for one-pot, three component synthesis of 5- and 1-substituted tetrazoles using different substrates including benzaldehydes, benzonitriles, and anilines in mild conditions. The different approaches were mechanically investigated and compared. The catalyst was fully characterized by Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma (ICP), FE-SEM and TEM analyses. The magnetic nanocatalyst could be readily separated from the reaction mixture by an external magnet and reused for several times without significant loss of catalytic activity. Also, the spectroscopic analysis revealed the stability and durability of the catalyst. Finally, the chemoselectivity of the method was investigated by the various combinations of aldehyde, nitrile, and oxime.