Mark Rozenberg

An empirical correlation between stretching vibration redshift and hydrogen bond length

A correlation is found between the magnitude of the redshift (Δν=20 to 2500 cm−1 relative to the free molecule) of the stretching mode of H-bonded A–H groups in an A–H···B complex, and the length of the H-bond (rH···B=0.28 to 0.12 nm). The correlation is based on both new spectral data for narrow decoupled H-bands in cold isotopically diluted carbohydrate crystals with known H-bond distances and on literature spectral and structural data from a total of 36 systems. Once established, additional data for H-bonded crystals (hydrates, acid salts of carboxylic acids) and for gas phase dimer systems also fit this correlation quite well. Hydrogen bond enthalpies in the range of −ΔH=10–80 kJ mol−1 correlate with the inverse third power of the H-bond length. Literature experimental data on −ΔH and rH···B of ten gas phase dimers confirm this relationship.

A correlation between the proton stretching vibration red shift and the hydrogen bond length in polycrystalline amino acids and peptides.

The FTIR spectra of pure and isotopically diluted (H/D and D/H) polycrystalline L-glutamine, L-hystidine, L-tyrosine, DL-serine, L-threonine, di-, tri-glycine and di-glycine x HCl x H2O salt were measured in the range 4000-2000 cm(-1) at temperatures from 300 to 10 K. The frequencies of decoupled proton stretching mode bands upsilon1, which can be observed only at low temperature, were used for estimation of the of upsilon1-bands red shift, which occurs upon formation of H-bonds involving ionized NH3+ and/or peptide HN-CO groups. The empirical correlation between the red shift and H-bond length, which was found previously for binary gas phase H-bonded complexes, carbohydrates and nucleosides [M. Rozenberg, A. Loewenschuss and Y. Marcus, Phys. Chem. Chem. Phys., 2000, 2, 2699-2702; M. Rozenberg, C. Jung and G. Shoham, Phys. Chem. Chem. Phys., 2003, 5, 1533-1535], was now extended to H-bonded networks in polycrystalline amino acids and peptides. The energies of the different H-bonds present in the crystalline structures could also be successfully estimated from the well-established empirical correlation [A. V. Iogansen, Spectrochim. Acta, 1999, A55, 1585-1612] between this property and the red shifts of the corresponding upsilon1 mode bands.

IR spectra and hydration of short-chain polyethyleneglycols

Abstract IR spectra of pure polyethyleneglycol PEG-200, PEG-400, monomethylether of PEG-350, dimethyl ether of PEG-250, several related compounds and water solutions in PEG-200 were recorded in the range of the skeletal band at 1100 cm −1 . The observed structured band in pure liquid PEGs and solutions was deconvoluted into five components shown to be due to non-interacting vibrations. The component near 1068 cm −1 is mainly due to the (C–OH) group and the 1104 and 1127 cm −1 components to the (C–O–C) groups. Of these the former is free or in the trans conformation and the latter is involved in an intramolecular H-bond or gauche conformation relative to the C–C bond. The changes band component parameters in PEG-200, on addition of small amounts of water, are ascribed to the attachment of the first water molecules to the terminal OH-group hydrogen bond system of the PEG molecule.

The manifestation of hydrogen bonding in the IR spectra of dl-threitol and erythritol (300–20 K)

Abstract The infrared (4000–400 cm −1 ) and, in part, Raman spectra were recorded for the two isomeric polycrystalline sugar alcohols, dl -threitol and erythritol. Samples were pure substances and isotopically diluted OH/OD compounds. IR spectra were recorded in the 300–20 K range. Assignment of hydrogen bond structure sensitive out-of-plane bending vibrational modes for OH/OD-groups of different H-bond systems is based on isotope exchange and temperature variations. At least seven bands for threitol and two for erythritol correspond to differently H-bonded OH/OD-groups. Relative strengths and quantity of different H-bonds were evaluated. Unlike erythritol, threitol contains over 5% of weak H-bonds. The formation from the melt of a crystalline racemate as a molecular compound of d - and l -forms is suggested. Comparisons with previous neutron scattering results are discussed. In solution, all four OH-groups of both tetritols form H-bonds of equal strength in accord with the basicity of the solvent.

Trimethylamine/Sulfuric Acid/Water Clusters: A Matrix Isolation Infrared Study

In continuation of our studies of sulfuric acid H-bonded complexes of atmospheric relevance we report the infrared spectra of the matrix isolated complexes formed between trimethylamine and sulfuric acid. Evidence for proton transfer was anticipated for the present system, as trimethylamine ((CH3)3N) is of strong basic nature. However, the spectra of this system are complicated by the inevitable presence water in the vapor and in the matrix, resulting in matrix layers containing three species capable of forming H-bonded complexes. The complex formed between trimethylamine and sulfuric acid is of ionic character due to proton transfer of the H(+) proton from sulfuric acid to (CH3)3N to form a new N-H bond and the replacement of the intramolecular O-H bond in H2SO4 by a strong intermolecular N-H···O hydrogen bond. The complex is further stabilized by hydration. The skeletal modes show clear bisulfate related bands and are only slightly affected by hydration. The ν(OH) region shows a rich band scheme, best explained by a structure involving (at least) three H2O molecules. A broad spectral feature spanning the 1700-500 cm(-1) is assigned, in analogy to previous studies to a double-well potential quasi-symmetric, Zundel-like, ionic species with a (CH3)3-N···H(+)···N-(CH3)3 configuration. A band in the skeletal S═O stretch spectral region may be assigned to hydrated sulfate as its counterion.

Infrared spectra and hydrogen bonding of pentitols and pyranosides at 20 to 300 K

Infrared spectra in the range 400-4000 cm(-1) of three pentitols--ribitol, xylitol, D-arabinitol, and of three pyranosides--methyl alpha-D-manno-, methyl alpha-D-gluco- and methyl beta-D-galactopyranoside, as polycrystalline solids of both the pure OH and > 90% isotopically substituted OD compounds, were recorded at 20-300 K. In the low temperature spectra of the OH substances, at least three isolated narrow bands in the stretching mode and about ten narrow bands in the out-of-plane-bending mode range (< 1000 cm(-1)) are affected by cooling. Almost all have counterparts in the respective OD spectra with frequency ratios of 1.30-1.40. On this basis, they are assigned to OH groups bonded in H-bonds of different strengths (from 10 to 50 kJ mol(-1)). The average number of the OH...O hydrogen bonds is found to be two to three times larger than indicated by the stretching mode only or by structural data. The newly measured peak frequencies of the very narrow decoupled stretching mode bands show a correlation between the red shift (delta nu) and the H-bond length. As previously found for tetritols, the presence of weak H-bonds (bond energy < 14 kJ mol(-1)) is related to the different water sorption capabilities of the pentitols.

Structural and IR-spectroscopic evidence of S–H···Ph hydrogen bonding in the solid state

Structural and IR spetroscopic evidence is given for S–H···Ph hydrogen bonding in the solid state, an effect previously only known in solution. In the crystalline thiol N-(o-hydroxyphenyl)-3-sulfanylmethylpyrrolidin-2-one, hydrogen bond energies based on red shifts of the infrared S–H stretching marks are estimated as slightly below 0.5 (in benzene) and 1.0 (solid state) kcal mol-1.

Photoinduced Structural Changes in Poly(4-Vinyl Pyridine): A Luminescence Study

In the present work we show a way of controlling photoluminescence (PL) properties through photoinduced quasi-crystal formation in a system based on poly(4-vinyl pyridine) (P4VPy). Under UV irradiation at 380 nm, concentrated solutions of P4VPy in pyridine turn into gel. This phase transition results in changes in the optical properties of this polymer. The position of the PL maximum can be changed continuously from 440 to 480 nm during irradiation. After several minutes of UV irradiation a new red-shifted PL at 492 nm appears upon excitation by light of a wavelength corresponding to that of the initial PL maximum, which is also red-shifted during irradiation. Solutions of P4VPy in pyrimidine show similar behavior, but those in pyridazine do not exhibit such behavior. We have found that the reason for the observed changes in the electronic properties is a photoinduced directional ordering of polymer molecules in a special quasi-crystal formation. The process originates from a structural change in the side chain of P4VPy, namely, protonation of the polymeric pyridine after solvation. During irradiation, the polymeric pyridinium ion interacts with neutral polymeric pyridine molecules. Interchain interaction through hydrogen bonds lead to an electronic property change. We observed that the process of photoinduced sol-gel transformation is reversible. Mechanical perturbation or heating can convert the gel back to a fluid solution. The red-shifted PL is not observed, and the initial PL is blue-shifted to 450 nm and stays there.

H-Bonded Clusters in the Trimethylamine/Water System: A Matrix Isolation and Computational Study

The environmentally important interaction products of trimethylamine (TMA) and water molecules have been observed by Matrix Isolation Fourier Transform Infrared Spectroscopy (MIS-FTIR). Infrared spectra of solid argon matrix layers, in which both TMA and H(2)O molecules were entrapped as impurities, were analyzed for bands in the ν(O-H) region, not seen in matrix layers containing either of the parent molecules alone. Results were interpreted on the basis of the emergence of several spectral band pairs and their red shifts from the position of the matrix isolated H(2)O monomers as compared to semiempirically scaled frequencies from the B3LYP/aug-cc-pVTZ calculations and empirical correlations with a large body of data on H-bonded complexes. Bands were assigned to a complex cluster of two TMA molecules flanking a closed ring of four H-bonded H(2)O molecules. The formation of this cluster is argued to be formed in the vapor phase (as opposed to being a result of diffusion of the trapped species) and is related to its large stabilization energy (enthalpy) because of strong cooperative effects in its H-bond system.

Ordered and disordered hydrogen bonds in adenosine, cytidine and uridine studied by low temperature FT infrared spectroscopy

FTIR study in the range below 1000 cm−1 revealed the presence of more hydrogen bond contacts of OH- and NH-groups in the nucleoside (and nucleobase) crystals, which are supposed to arise from disorder, when compared to the well-known ordered H-bonds determined by structural methods data. The energies of both types of H-bonds are estimated.