Structures and energetics of hydrated oxygen anion clusters

Hydration of the atomic oxygen radical anion is studied with computational electronic structure methods, considering (O(-))(H(2)O)(n) clusters and related proton-transferred (OH(-))(OH)(H(2)O)(n)(-)(1) clusters having n = 1-5. A total of 67 distinct local-minimum structures having various interesting hydrogen bonding motifs are obtained and analyzed. On the basis of the most stable form of each type, (O(-))(H(2)O)(n)) clusters are energetically favored, although for n > or = 3, there is considerable overlap in energy between other members of the (O(-))(H(2)O)(n) family and various members of the (OH(-))(OH)(H(2)O)(n)(-)(1) family. In the lower-energy (O(-))(H(2)O)(n) clusters, the hydrogen bonding arrangement about the oxygen anion center tends to be planar, leaving the oxygen anion p-like orbital containing the unpaired electron uninvolved in hydrogen bonding with any water molecule. In (OH(-))(OH)(H(2)O)(n)(-)(1) clusters, on the other hand, nonplanar arrangements are the rule about the anionic oxygen center that accepts hydrogen bonds. No instances are found of OH(-) acting as a hydrogen bond donor. Those OH bonds that form hydrogen bonds to an anionic O(-) or OH(-) center are significantly stretched from their equilibrium value in isolated water or hydroxyl. A quantitative inverse correlation is established for all hydrogen bonds between the amount of the OH bond stretch and the distance to the other oxygen involved in the hydrogen bond.     

Selective Vesicle Formation from Calixarenes by Self‐Assembly

Amphiphilic polyhydroxy macrocycles self‐assemble in water to form vesicles selectively. These vesicles are uniform in size (50–200 nm; see representation) and stable both in aqueous solution and in dried form. The selective mode of aggregation can be correlated with structural characteristics of the phenolic amphiphiles, in particular, the macrocyclic moiety and intra‐ and intermolecular hydrogen bonds between the phenolic OH groups.     

Infrared photodissociation spectroscopy of Al(+)(CH(3)OH)(n) (n = 1-4)

Infrared photodissociation spectra of Al(+)(CH(3)OH)(n) (n = 1-4) and Al(+)(CH(3)OH)(n)-Ar (n = 1-3) were measured in the OH stretching region, 3000-3800 cm(-1). For n = 1 and 2, sharp absorption bands were observed in the free OH stretching region, all of which were well reproduced by the spectra calculated for the solvated-type geometry with no hydrogen bond. For n = 3 and 4, there were broad vibrational bands in the energy region of hydrogen-bonded OH stretching vibrations, 3000-3500 cm(-1). Energies of possible isomers for the Al(+)(CH(3)OH)(3),4 ions with hydrogen bonds were calculated in order to assign these bands. It was found that the third and fourth methanol molecules form hydrogen bonds with methanol molecules in the first solvation shell, rather than a direct bonding with the Al(+) ion. For the Al(+)(CH(3)OH)(n) clusters with n = 1-4, we obtained no evidence of the insertion reaction, which occurs in Al(+)(H(2)O)(n). One possible explanation of the difference between these two systems is that the potential energy barriers between the solvated and inserted isomers in the Al(+)(CH(3)OH)(n) system is too high to form the inserted-type isomers.     

First Total Synthesis of (±)‐Latifolin and Its Antioxidant Mechanism

The first total synthesis of (±)‐latifolin has been accomplished in six steps and 47.8% overall yield. To understand the relative importance of phenolic O? H and benzhydryl C? H hydrogen on the antioxidant activity of latifolin, 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging assay and density functional theory (DFT) studies were carried out. On scavenging DPPH radical in ethanol, the activity of latifolin ( 1 ) bearing phenolic hydrogen is remarkably higher than analogue 10 bearing no phenolic hydrogen. Therefore, Phenolic hydrogen is responsible for latifolin's antioxidant activity rather than benzhydryl C? H hydrogen. Furthermore, the 5‐OH BDE is lower than 2′‐OH and 7‐CH BDEs by a DFT calculation, respectively. Based on theoretical results it is definitely concluded that the phenolic 5‐OH plays a major role in the antioxidant activity of latifolin.     

Vibrational analysis of sodium α-, β- and γ-hydroxybutyrates. Inter- and intramolecular hydrogen bonds

The infrared and Raman spectra of sodium α-, β- and γ-hydroxybutyrates and their deuterated analogues are examined in the 4000-100 cm⁻¹ range and an assignment of the fundamental vibrations is given. Based on the localization of the asymmetric stretching vibrations ν_asOH and the out-of-plane vibration γOH, inter- and/or intramolecularly hydrogen-bonded forms are proposed: the low frequencies of ν_asOH (<3200 cm⁻¹) and high frequencies of γOH (≈800 cm⁻¹) argue in favour of the existence of intramolecular hydrogen bonding. Sodium α-hydroxybutyrate exhibits as a chelate ring with an intramolecular hydrogen bond between hydroxyl and carboxyl groups, whereas sodium, β-hydroxybutyrate has the two association forms with inter- and intramolecular hydrogen bonds. Sodium γ-hydroxybutyrate exists as a hydrogen-bonded polymer, with an intermolecular hydrogen bond between the hydroxyl groups and between the hydroxyl and carbonyl groups. At a crystallization temperature above 50°C, only the α- salt showed a structural change indicating the existence of intra- and intermolecular hydrogen bonds. This result is confirmed by differential scanning analysis.     

Synthesis, spectral characterisation of 2-(5-methyl-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols and their complexes with zinc(II) ion, and solvent effect on complexation

2-(5-Methyl-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols (HLBr and HLNO2) and their Zn(II) complexes with ZnX2 (X = Cl, I, NO3) were synthesized and characterized by elemental analysis, molar conductivity, IR, 1H and 13C NMR spectra. The OH proton appears near the NH protons in the 1H NMR spectra of the ligands because of the strong intramolecular hydrogen bonding between the OH hydrogen and the C=N nitrogen atoms. The complexation is investigated in ethanol and isopropanol and it is observed that isopropanol is a better solvent than ethanol for the complex forming. HLBr gives harder complexation reaction with Zn(II) according to HLNO2 because of the stronger intramolecular hydrogen bonding in HLBr, and the both ligands react easier with Zn(NO3)2 than ZnCl2 and ZnI2. The Zn(II) complexes of HLBr have 1:1 M:L ratio and ionic character, however, HLNO2 give a non-ionic complex that has 1:2 M:L ratio. In the complexes the phenolic hydrogen is eliminated and a chelate structure is formed.     

Computational Study of Hydrogen Bonding in Substituted Phenol‐Acetonitrile‐Water Clusters

The calculations for a water‐acetonitrile‐substituted phenols system and the comparison with the experimental parameters will be given. Here we study change in the nature of the interactions into the system with donor and acceptor electron substituents on the phenolic ring, the structures, relative energies and harmonic frequencies. The conformers showed a significant difference in the OH and CN band shift depending on the type of the hydrogen bond formed and the position of the substituent on the phenolic ring. The cyclical hydrogen bonds between water‐acetonitrile and substituted phenol OH are important evidence of the relative stability in the system under study.     

Classical molecular-dynamics simulation of the hydroxyl radical in water

We have studied the hydration and diffusion of the hydroxyl radical OH0 in water using classical molecular dynamics. We report the atomic radial distribution functions, hydrogen-bond distributions, angular distribution functions, and lifetimes of the hydration structures. The most frequent hydration structure in the OH0 has one water molecule bound to the OH0 oxygen (57% of the time), and one water molecule bound to the OH0 hydrogen (88% of the time). In the hydrogen bonds between the OH0 and the water that surrounds it the OH0 acts mainly as proton donor. These hydrogen bonds take place in a low percentage, indicating little adaptability of the molecule to the structure of the solvent. All hydration structures of the OH0 have shorter lifetimes than those corresponding to the hydration structures of the water molecule. The value of the diffusion coefficient of the OH0 obtained from the simulation was 7.1x10(-9) m2 s(-1), which is higher than those of the water and the OH-.     

Theoretical study of the symmetry of the (OH...O)- hydrogen bonds in vinyl alcohol-vinyl alcoholate systems

The interactions between substituted vinyl alcohols and vinyl alcoholates (X = NH(2), H, F, Cl, CN) are studied at the B3LYP/6-311++G(d,p) level of theory. In a first step, the conformation of the monomers is investigated and the proton affinities (PA(A(-))) of the enolates are calculated. The enols and enolates are held together by strong (OH...O)(-) hydrogen bonds, the hydrogen bond energies ranging from 19.1 to 34.6 kcal mol(-1). The optimized O...O distances are between 2.414 and 2.549 A and the corresponding OH distances from 1.134 and 1.023 A. The other geometry parameters such as C[double bond]C or CO distances also indicate that, in the minimum energy configuration, the hydrogen bonds are characterized by a double well potential. The Mulliken charges on the different atoms of the proton donors and proton acceptors and the frequencies of the nu(OH) stretching vibrations agree with this statement. All the data indicate that the hydrogen bonds are the strongest in the homomolecular complexes. The transition state for hydrogen transfer is located with the transition barrier estimated to be about zero. Upon addition of the zero-point vibration energies to the total potential energy, the barrier vanishes. This is a characteristic feature of low-barrier hydrogen bonds (LBHBs). The hydrogen bond energies are correlated to the difference 1.5 PA(AH) - PA(A(-)). The correlation predicts different energies for homomolecular hydrogen bonds, in agreement with the theoretical calculations. Our results suggest that a PA (or pK(a)) match is not a necessary condition for forming LBHBs in agreement with recent data on the intramolecular hydrogen bond in the enol form of benzoylacetone (J. Am. Chem. Soc. 1998, 120, 12117).     

Lattice vibration spectra. Part XCV. Infrared spectroscopic studies on the iron oxide hydroxides goethite (α), akaganéite (β), lepidocrocite (γ), and feroxyhite (δ)

Infrared spectra (IR, FIR, DRIFT, 90 and 295 K) and DSC measurements of the various polymorphs of iron oxide hydroxide, viz. goethite (α), akaganéite (β), lepidocrocite (γ), and feroxyhite (δ), and of deuterated specimens are reported. They are discussed with respect to the crystal structures proposed in the literature, the hydrogen bonds present, the energies of the OH stretching, OH bending (librational), and translational modes, and their thermal decomposition. From the two space groups proposed for β- and γ-FeO(OH), the groups I4/m and Cmc2₁, respectively, seem to be more reliable. The disorder of the OH⁻ ions of γ-FeO(OH) has not been confirmed in contrast to that of δ-FeO(OH). The intraionic O(H,D) distances of γ- and δ-FeO(OH) derived from neutron powder diffraction studies have to be doubted. The greater strength of the OHOH hydrogen bonds of lepidocrocite, for example, compared to that of the OHO hydrogen bonds of goethite despite the larger hydrogen bond acceptor capability of O²⁻ is due to the strong cooperativity of the hydrogen bonds of the γ-polymorph. The extremely different strength of the hydrogen bonds of isostructural α-AlO(OH) (v_OH = 2950 cm⁻¹, 295 K), α-MnO(OH) (v_OH = 2686 cm⁻¹), and α-FeO(OH) (v_OH = 3130 cm⁻¹) is caused by the different synergetic effect of the metal ions involved, especially that of Mn³⁺ due to its Jahn-Teller behaviour. The decomposition temperatures and heats of the various FeO(OH) modifications as well as the halfwidths of the DSC peaks evidence a much faster decomposition rate of akaganéite than those of the other polymorphs. This is obviously due to the Cl⁻ ion impurities present in this compound.     

Syntheses and Crystal Structures of Four New Complexes [Mn(4,4''-bip)2(OH2)4](DBA)·4H2O and [M(OH2)(HDPA)2]·3H2O (M = Mn, Co, Ni)

Four new transition metal complexes, [Mn(4,4'-bip)2(OH2)4](DBA)·4H2O 1(4,4'-bip = 4,4'-bipyridine, H2DBA = benzene-1,3-dicarboxylic acid) and [M(OH2)(HDPA)2]·3H2O (M = Mn 2, M = Co 3, M = Ni 4,H2DPA = 2,6-pyridine-dicarboxylic acid), have been prepared from the reaction of transition metals and carboxylic acids, and characterized by X-ray and elemental analyses. For compound 1, the packing diagram shows that a three-dimensional network is formed via hydrogen bonds and strong π-π interactions. For compounds 2, 3 and 4,a double-helical chain is formed through hydrogen bonds. Moreover, a three-dimensional network is constructed from chains via complicated hydrogen bonds between crystal water molecules and oxygen atoms of HDPA-.     

Infrared spectroscopy of acetone-water liquid mixtures. II. Molecular model

In aqueous acetone solutions, the strong bathochromic shifts observed on the OH and CO stretch infrared (IR) bands are due to hydrogen bonds between these groups. These shifts were evaluated by factor analysis (FA) that separated the band components from which five water and five acetone principal factors were retrieved [J. Chem. Phys. 119, 5632 (2003)]. However, these factors were abstract making them difficult to interpret. To render them real an organization model of molecules is here developed whose abundances are compared to the experimental ones. The model considers that the molecules are randomly organized limited by the hydrogen bond network formed between the water hydrogen atoms and the acetone or water oxygen atoms, indifferently. Because the oxygen of water has two covalent hydrogen atoms which are hydrogen-bonded and may receive up to two hydrogen atoms from neighbor molecules hydrogen-bonded to it, three types of water molecules are found: OH2, OH3, and OH4 (covalent and hydrogen bonds). In the OH stretch region these molecules generate three absorption regimes composed of nu3, nu1, and their satellites. The strength of the H-bond given increases with the number of H-bonds accepted by the oxygen atom of the water H-bond donor, producing nine water situations. Since FA cannot separate those species that evolve concomitantly the nine water situations are regrouped into five factors, the abundance of which compared exactly to that retrieved by FA. From the factors' real spectra the OH stretch absorption are simulated to, respectively, give for the nu3 and nu1 components the mean values for OH2, 3608, 3508; OH3, 3473, 3282 and OH4, 3391, 3223 cm(-1). The mean separations from the gas-phase position which are respectively about 150, 330, and 400 cm(-1) are related to the vacancy of the oxygen electron doublets: two, one, and zero, respectively. No acetone hydrate that sequesters water molecules is formed. Similarly, acetone produces ten species, two of which evolve concomitantly. Spectral similarities further reduce these to five principal IR factors, the abundance of which compared adequately to the experimental results obtained from FA. The band assignment of the five-acetone spectra is given.     

Syntheses and Crystal Structures of Four New Complexes [Mn(4,4′-bip)_2(OH_2)_4](DBA)·4H_2O and [M(OH_2)(HDPA)_2]·3H_2O (M = Mn,Co,Ni)

1 INTRODUCTION During the past years, dicarboxylic acids have been widely used as one polydentate ligand invo- lved in various metal chelation reactions to form transition or rare earth metal complexes with inter- esting properties in material science[1] and biological systems[2]. For example, Kim Y and his coworkers focused on the synthesis of copper(II) complexes containing malonate and pyrazine ligands to study their magnetic property and electronic conducti- vity[3]. The importance o…     

Two new "onium" fluorosilicates, the products of interaction of fluorosilicic acid with 12-membered macrocycles: structures and spectroscopic properties

Two novel compounds, (L(1)H)(2)[SiF(6)] x 2H(2)O (1) and (L(2)H)(2)[SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of [SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), and two water molecules, all components being bound in the layer through a system of NH[...]F, NH[...]O and OH[...]F hydrogen bonds. The [SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OH[dot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the [SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., [SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH[...]F, NH[...]O, OH[...]F, OH[dot dot dot]O hydrogen bonds. In a way similar to 1, the [SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH[...]F and OH[...]O interactions.     

Dynamics of the intermolecular hydrogen bonds in the polymorphs of paracetamol in relation to crystal packing and conformational transitions: a variable-temperature polarized Raman spectroscopy study

The properties of the intermolecular hydrogen bonds in the monoclinic (Form I) and the orthorhombic (Form II) polymorphs of paracetamol, C(8)H(9)NO(2), have been studied by single crystal polarized Raman spectroscopy (40 to 3700 cm(-1)) in a wide temperature range (5 K < T < 300 K) in relation to the dynamics of methyl-groups of the two forms. A detailed analysis of the temperature dependence of the wavenumbers, bandwidths and integral intensities of the spectral bands has revealed an essential difference between the two polymorphs in the strength and ordering of OH···O and NH···O hydrogen bonds. The compression of intermolecular hydrogen bonds is interrelated with crystal packing and the dynamics of methyl-groups. On structural compression of the orthorhombic polymorph on cooling, a compromise is to be sought between the shortening of OH···O and NH···O bonds, attractive CH···O and repulsive CH···H contacts in the crystal structure. As a result of a steric conflict at temperatures below 100 K, N-H···O hydrogen bonds become significantly disordered, and an extended intramolecular transition from the conformation "staggered" with respect to the C=O bond to the one "staggered" with respect to the NH bond is observed. In most of the studied crystals this transition was only about 60% complete even at 5 K, but in some of the crystals the orientation of all the methyl-groups became staggered with respect to the NH bond at low temperatures. This complete transition was coupled to a sharp shortening of the OH···O and NH···O hydrogen bonds at <100 K, the appearance of new additional positions of the protons in these H-bonds, and a slight strengthening of the C-HO bonds formed by methyl-groups. The same conformational transition has been observed also in the monoclinic polymorph at T < 80 K. The crystal packing in Form I prevents the O-H···O hydrogen bonds from adopting the optimum geometry, and they are significantly disordered at all the temperatures, especially at ≤200 K. The packing of molecules in Form I is also not favourable to form C-H···O hydrogen bonds involving methyl-groups. One can conclude from the comparison of diffraction and spectroscopic data that the higher stability of Form I results not from a larger strength of individual OH···O and NH···O hydrogen bonds, but is a cumulative effect: all the hydrogen bonds together stabilize the structure of the monoclinic polymorph more than that of the orthorhombic polymorph.     

Vibrational spectra and structure of some oxalic acid/substituted pyridine (methyl-, amino-, and dihalogeno-) complexes: Hydrogen bond features

The Raman and infrared spectra of some polycrystalline substituted pyridine/oxalic acid complexes have been investigated and assignments in terms of group frequencies are given. Various hydrogen bonds (NH?O, OH?O, OH?N) are distinguished and crystal structures are proposed. For the stronger bases (methyl- or aminopyridines with pk_a ≈ 6) proton transfer occurs. The 1/1 complex contains infinite chains of hydrogen oxalate ions linked by strong OH?O hydrogen bonds with vOH between 2000 and 800 cm⁻¹. R_OH?O distances are 2.47–2.62 Å). The substituted pyridinium cations are linked to the chain backbone by medium NH?O hydrogen bonds with NH?O lengths of 2.71–2.81 Å. The 3,5-dichloropyridine forms a 2/1 adduct without proton transfer, in accordance with its pk_a (0.6), and strong OH?N hydrogen bonds occur (vOH about 2000 cm⁻¹ and ). Finally, the 2,6-dihalogenopyridine derivatives do not form complex with oxalic acid, presumably because of steric hindrance.     

Quantifying the relative contribution of hydrogen bonding and hydrophobic environments, and coordinating groups, in the zinc(II)-water acidity by synthetic modelling chemistry

Ligands derived from the tripodal N4 ligand tris(pyridylmethyl)amine ((pyCH2)3N, tpa) of general formula (6-RNHpyCH2)nN(CH2py)(3-n)(R = H, n= 1-3 L(1-3); R = neopentyl, n= 1-3 L'(1-3)) were used to elucidate and quantify the magnitude of the effects exerted by hydrogen bonding and hydrophobic environments in the zinc-water acidity of their complexes. The pKa of the zinc-bound water molecule of [(L(1-3))Zn(OH2)]2+ and [(L'(1-3))Zn(OH2)]2+ 1'-3' was determined by potentiometric pH titrations in water (1-3) or water-ethanol (1:1) (1'-3'). The zinc(II) water acidity gradually increases as the number of -NH2 hydrogen bonding groups adjacent to the water molecule increases. Thus, the zinc-bound water of [(L3)Zn(OH2)]2+ and [(tpa)Zn(OH2)]2+ deprotonate with pKa values of 6.0 and 8.0, respectively. The pKa of the water molecule, however, is only raised from 8.0 in [(tpa)Zn(OH2)]2+ to 9.1 in [(bpg)Zn(OH2)]+ (bpa =(pyCH2)2N(CH2COO-)). Moreover, the acidity of the zinc-bound water of several of the five-coordinate zinc(II) complexes with the hydrogen bonding groups is greater than that of four-coordinate [((12)aneN3)Zn(OH2)]2+ (pKa = 7.0). This result shows that the magnitude of the effect exerted by the hydrogen bonding groups can be larger than that induced by changing one neutral by one anionic ligand, and/or even by changing the coordination number of the zinc(II) centre. The X-ray structure of [(L'2)Zn(OH)]ClO4 2' and [(L'3)Zn(OH)]ClO4.CH3CN 3'.CH3CN is reported, and show the neopentylamino groups forming N-H...O hydrogen bonds with the zinc-bound hydroxide. Although, which have hydrogen bonding and hydrophobic groups, have a zinc-bound water more acidic than [(tpa)Zn(OH2)]2+, their pKa is not always lower than that of 1-3. This result suggests that a hydrogen bonding microenvironment may be more effective than a hydrophobic one to increase the zinc-water acidity.     

The structure of water in p-sulfonatocalix[4]arene

Tetrasodium p-sulfonatocalix[4]arene exists as a hydrate with approximately 14 water molecules and has three polymorphic modifications, all of which contain a water molecule in the molecular cavity that is engaged in OH···π interactions. Single-crystal neutron structures are reported for two of these three forms and reveal a "compressed" water molecule with short OH bonds. Partial atomic charges and hardness analysis (PACHA) calculations based on the neutron coordinates give an OH···π interaction energy of 6.9-7.5 kJ mol(-1). The PACHA analysis also reveals the dominance of the charge-assisted hydrogen bonds from the Na(+)-coordinated water molecules. The instability of the crystal towards dehydration can be traced to an uncoordinated lattice water site. The remarkable calixarene-Na(+)-hydrate motif is conserved almost unchanged across all three polymorphs. A single-crystal neutron structure is also reported for pentasodium p-sulfonatocalix[4]arene·12H(2)O, which exhibits an intracavity water molecule that is engaged in both OH···π and OH···O hydrogen bonding. The shorter covalent bond to the hydrogen atom that forms the interaction with the aromatic ring is again apparent.     

Combined NMR and quantum chemical studies on the interaction between trehalose and dienes relevant to the antioxidant function of trehalose

In a previous study (Oku, K.; Watanabe, H.; Kubota, M.; Fukuda, S.; Kurimoto, M.; Tujisaka, Y.; Komori, M.; Inoue, Y.; Sakurai, M. J. Am. Chem. Soc. 2003, 125, 12739), we investigated the mechanism of the antioxidant function of trehalose against unsaturated fatty acids (UFAs) and revealed that the key factor relevant to the function is the formation of OH...pi and CH...O hydrogen bonds between trehalose and the cis double bonds of the UFA. Here, we investigate whether such intriguing interactions also occur between this sugar and cis double bonds in other unsaturated compounds. For this purpose, we selected various diene compounds (1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, and 2,5-heptadiene) as interaction partners. All NMR experiments performed, including 1H-1H NOESY measurements, indicated that trehalose selectively interacts with the cis-olefin proton pair in the above diene with a 1:1 stoichiometry, and the C-3 (C-3') and C-6' (C-6) sites of the sugar are responsible for the interaction. Similar interactions were not observed for the mixtures of the diene and other saccharides (neotrehalose, kojibiose, nigerose, maltose, isomaltose, sucrose, maltitol, and sorbitol). Quantum chemical calculations revealed that the OH-3 and OH-6 groups bind to the olefin double bonds of the diene through OH...pi and CH...O types of hydrogen bonds, respectively, and the stabilization energy of the resulting complex is 5-6 kcal mol(-1). These results strongly support the above NMR results. Finally, the activation energies were calculated for the hydrogen abstraction reactions from the activated methylene group of heptadiene. In particular, when the reaction was initiated by a methyl radical, the activation energy was only 10 kcal mol(-1) for the free heptadiene, but on complexation with trehalose it drastically increased to ca. 40 kcal mol(-1). This indicates that trehalose has a significant depression effect on the oxidation of the diene compounds. These results strongly support the antioxidant mechanism deduced in the previous study and indicate that the formation of unique multiple hydrogen bonds between trehalose and cis-olefin bonds is rather a general event not confined to the case of UFA.     

Infrared-optical double resonance spectroscopic investigation of trifluoromethylphenols and their water complexes

The hydrogen bonding behavior of trifluoromethylphenols and their water complexes were investigated using IR-UV double resonance spectroscopy. Both ortho- and meta-trifluoromethylphenols exist in the syn conformer, which is the global minimum in both the cases. The IR spectrum in the O-H stretching region reveals the absence of an intramolecular O-H···F hydrogen bond in the syn-o-trifluoromethylphenol, which is in contrast to the results reported in the literature. The water complexes of both o-trifluoromethylphenol and m-trifluoromethylphenol are characterized by formation of O-H···O hydrogen bonds between the donor phenolic OH group and the acceptor water molecule. In addition, the o-trifluoromethylphenol-(water)(2) complex was also observed.