Influence Of Hydrogen Bond Formation Research Articles

Small Physical Cross-Linker Facilitates Hyaluronan Hydrogels.

In this study, we demonstrate that small charged molecules (NH4+, GluA+, dHA+) can form physical cross-links between hyaluronan chains, facilitating polymerization reactions between synthetically introduced thiol groups (HA-DTPH). These hybrid hydrogels can be obtained under physiological conditions ideally suited for 3D cell culture systems. The type and concentration of a physical crosslinker can be adjusted to precisely tune mechanical properties as well as degradability of the desired hydrogel system. We analyze the influence of hydrogen bond formation, concentration and additional ionic interactions on the polymerization reaction of HA-DTPH hydrogels and characterize the resulting hydrogels in regard to mechanical and biocompatibility aspects.

Guanine Nucleobase Adducts Formed by [Pt(di-(2-picolyl)amine)Cl]Cl: Evidence That a Tridentate Ligand with Only in-Plane Bulk Can Slow Guanine Base Rotation

Pt(II) complexes bind preferentially at N7 of G residues of DNA, causing DNA structural distortions associated with anticancer activity. Some distortions induced by difunctional cisplatin are also found for monofunctional Pt(II) complexes with carrier ligands having bulk projecting toward the guanine base. This ligand bulk can be correlated with impeded rotation about the Pt-N7(guanine) bond. Pt(N(H)dpa)(G) adducts (N(H)dpa = di-(2-picolyl)amine, G = 5'-GMP, 5'-GDP, 5'-GTP, guanosine, 9-EtG, and 5'-IMP) were used to assess whether a tridentate carrier ligand having bulk concentrated in the coordination plane can impede guanine nucleobase rotation. Because the Pt(N(H)dpa) moiety contains a mirror plane but is unsymmetrical with respect to the coordination plane, Pt(N(H)dpa)(G) adducts can form anti or syn rotamers with the guanine O6 and the central N-H of N(H)dpa on the opposite or the same side of the coordination plane, respectively. The observation of two sharp, comparably intense guanine H8 NMR signals provided evidence that these Pt(N(H)dpa)(G) adducts exist as mixtures of syn and anti rotamers, that rotational interchange is impeded by N(H)dpa, and that the key interactions involves steric repulsions between the pyridyl and guanine rings. The relative proximity of the guanine H8 to the anisotropic pyridyl rings allowed us to conclude that the syn rotamer was usually more abundant. However, the anti rotamer was more abundant for the Pt(N(H)dpa)(5'-GTP) adduct, in which a hydrogen bond between the 5'-GTP γ-phosphate group and the N(H)dpa central N-H is geometrically possible. In all previous examples of the influence of hydrogen bond formation on rotamer abundance in Pt(II) guanine adducts, these hydrogen bonding interactions occurred between ligand groups in cis positions. Thus, the role of a trans ligand group in influencing rotamer abundance, as found here, is unusual.

The influence of hydrogen bond formation and the proton transfer on the structure of complexes of phenols with N-methylmorpholine

Structural and energetic consequences of forming the hydrogen bonded complexes between six selected phenols and N-methylmorpholine are discussed on the basis of results of B3LYP/6-31G(d,p) calculations. Dependences of various structural parameters on the degree of proton transfer were established. The progress of the proton transfer was characterized by the O–H (d(OH)) distance, d(CO) distance and X PT. The last one was derived from the dependence of calculated dipole moment on d(OH). It was established, that dependences received at use of d(OH) scale reveal the sigmoid character, while for d(CO) and X PT scales more linear dependences were found. Especially strong influence of substituents on the dependences on d(CO) was stated. The structures with the shortest hydrogen bonds, were characterized in detail, also with the use of the formulations going from the valence conservation rule in hydrogen bond. By comparison with our earlier results, the specific properties of such “critical” structures for the complexes with pyridine were pointed out. It can be treated as evidence on resonance interactions in hydrogen bond formed between aromatic acids and bases.

The influence of hydrogen bond formation on the dual luminescence of n-phenyl-2,3-naphthalimide derivatives

The influence of hydrogen bond formation on the spectroscopic properties of dual luminescent naphthalimides was examined in n-hexane using fluorinated alcohols as hydrogen bond donors. Complex formation causes considerable red shift of the dominant intramolecular charge transfer (ICT) fluorescence maxima.

Influence of Hydrogen Bond Formation on the Photophysics of N-(2,6-Dimethylphenyl)-2,3-naphthalimide

The photophysics of N-(2,6-dimethylphenyl)-2,3-naphthalimide (DMPN) has been investigated in the presence of methanol or fluorinated aliphatic alcohols in n-hexane and carbon tetrachloride solvents. Consecutive two-step hydrogen bonded complex formation is observed in the presence of alcohols. Equilibrium constants are determined for the formation of singly and doubly complexed species. The UV absorption and fluorescence spectra for the singly and doubly complexed DMPN are derived from the measured absorption and fluorescence spectra, respectively, by means of the equilibrium constants. It is concluded from the results that the spectroscopic properties (singlet excitation energy and Stokes shift) of the complexed species are significantly influenced by the Gibbs energy change in the complexation reaction. Quantitatively, a linear relationship is found between the difference of singlet excitation energy of the complexed and uncomplexed species on one hand and the Gibbs energy change in the complexation rea...

Comprehensive ab initio studies of nuclear magnetic resonance shielding and coupling constants in XH⋯O hydrogen-bonded complexes of simple organic molecules

The influence of hydrogen-bond formation on the scalar spin–spin coupling constants and NMR shielding constants in CH2O–H2O, C2H2–H2O, CH3OH–H2O, and (HCOOH)2 complexes has been calculated using correlated MO (MCSCF and MP2) methods. The hydrogen-bond transmitted spin–spin coupling constants are also reported. The iso- and anisotropic H1 shielding constants are found to be the most general parameters of the hydrogen bond. The changes in J1(XH) coupling in the proton donor also correlate with the XH⋯Y hydrogen bond strength. A similar correlation is found in the intermolecular J1h(HY) and J2h(XY) couplings. These couplings are substantial and dominated by the Fermi-contact term in contrast to the longer-range hydrogen-bond transmitted couplings where the noncontact terms prevail.

Stability of the (H2O)2 dimer in the ground and lowest-lying excited electronic states

A theoretical study of the (H2O)2 dimer has been carried out in which the lowest S1 and T1 excited electronic states of the dimer complex, the influence of hydrogen bond formation on the shift in the maximum of the absorption band, and the stability of the dimer complex in the ground and excited states have been examined. It was found that there is only a single global maximum for the system — a nonplanar dimer complex formed by a linear hydrogen bond. Cyclic and bifurcated structures are transition states which do not form stable configurations when electronically excited. For the structure having a minimum in the ground electronic state, two nondissociating S1 and T1 states were found with bond energies of 2.0 and 4.4 kcal/mole, respectively. Formation of hydrogen bonds leads to a shift in the absorption maximum to the blue region with respect to the monomer. The hydrogen bond was found to weaken in the excited electronic states of the dimer.

Fourier transform infrared spectrometric study of the interaction between hexa-2,4-dienylideneisopropylamine and 3-phenylprop-2-enylideneisopropylamine with model proton donors Part I. Thermodynamic parameters, ?C==N and ?OH stretching vibrations

The interaction of hexa-2,4-dienylideneisopropylamine and 3-phenylprop-2-enylideneisopropylamine with phenol derivatives (pKa = 10.30−0.4) was investigated in solution by Fourier transform IR spectrometry. The influence of hydrogen bond formation on the frequency and intensity of the CN stretching vibration is discussed. The thermodynamic parameters for the normal hydrogen bonds and for the proton transfer complexes were determined; 50% proton transfer is achieved for ΔpKa values of about 2 for both imine systems. The lowest OH stretching frequencies corresponding to a delocalized proton are observed at about the same ΔpKa values.

Fourier transform infrared spectrometric study of the interaction between hexa-2,4-dienylideneisopropylamine and 3-phenylprop-2-enylideneisopropylamine with model proton donors Part I. Thermodynamic parameters, CN and OH stretching vibrations

The interaction of hexa-2,4-dienylideneisopropylamine and 3-phenylprop-2-enylideneisopropylamine with phenol derivatives (p K a = 10.30−0.4) was investigated in solution by Fourier transform IR spectrometry. The influence of hydrogen bond formation on the frequency and intensity of the ▪ CN stretching vibration is discussed. The thermodynamic parameters for the normal hydrogen bonds and for the proton transfer complexes were determined; 50% proton transfer is achieved for Δp K a values of about 2 for both imine systems. The lowest ▪ OH stretching frequencies corresponding to a delocalized proton are observed at about the same Δp K a values.

Proton kinetics and thermodynamics of carboxylic acid crown ethers. Influence of hydrogen bond formation in water, 80% (w/w) methanol-water, and chloroform-d

On determine les vitesses de protonation-deprotonation des acides crown carboxymethoxy dibenzo-16-crown-5 et carboxy pentaoxa [15] metacyclophane

13C NMR investigations of phenol–triethylamine complexes: Influence of hydrogen bond interaction on the electronic structure of the aliphatic chain

AbstractThe influence of hydrogen bond formation on 13C chemical shifts at the α and β positions of triethylamine and tri‐n‐butylamine has been investigated by dipole moment measurements and CNDO/2 calculations. It has been shown that a hydrogen bridge dipole moment occurs during complexation. Moreover, the change observed in the C‐αC‐β bond dipole moment is proportional to the hydrogen bridge dipole moment, but is approximately 100 times smaller. This change has been related to differences between the 13C chemical shifts at the α and β positions of amines.

Infrared and Raman study of the interaction between methyl acetate and phenol derivatives

Abstract In previous publications [1–3], we have been concerned with the influence of hydrogen bond formation on the Raman intensity of the carbonyl stretching vibration. It has been shown that hydrogen bond association of simple carbonyl bases (cyclohexanone, acetone, acetophenone) with proton donors such as phenol derivatives, hydrochlorid or hydrobromic acid brings about an intensity increase of the ν CO Raman band; moreover, the intensity enhancement is linearly related to the enthalpy of complex formation. In the present work, these measurements are extended to the complexes formed between methyl acetate (MeAc) and phenol derivatives. As suggested by the frequency lowering of the ν CO vibration and the frequency increase of the ν CO band, complex formation in solution takes place on the carbonyl function. From NMR [4–5] and UV data [6] it can also be concluded that protonation via hydrogen-bonded attachment occurs in solution predominantly at the carbonyl oxygen atom. Literature data for the thermodynamic quantities referring to esters with hydroxylic compounds are scarce. Consequently in this work, we have determined the equilibrium constants and the enthalpy of formation for complexes between MeAc and phenol derivatives. We also report the absolute intensity of the ν CO Raman band in the free ester molecule and in the complexes, all measurements been made in a solvent of low polarity : carbontetrachloride.

13C NMR investigations of phenol–triethylamine complexes: The influence of hydrogen bond interaction on the electronic structure of phenols

AbstractThe influence of hydrogen bond formation on the screening at the C‐1 carbon of phenols is investigated, both experimentally and theoretically. Qualitatively good agreement between experimental and predicted data, obtained by means of calculations based on the CNDO/2 method and the Karplus–Pople theory, is observed. The main factors determining the chemical shift changes in the series of complexes are discussed.