Cβ-H stretching vibration as a new probe for conformation of n-propanol in gaseous and liquid states.

The development of potential probes to identify molecular conformation is essential in organic and biological chemistry. In this work, we investigated a site-specific C-H stretching vibration as a conformational probe for a model compound, 1,1,3,3,3-deuterated n-propanol (CD3CH2CD2OH), using stimulated photoacoustic Raman spectroscopy in the gas phase and conventional spontaneous Raman spectroscopy in the liquid state. Along with quantum chemistry calculations, the experiment shows that the CH2 symmetric stretching mode at the β-carbon position is very sensitive to the conformational structure of n-propanol and can serve as a new probe for all five of its conformers. Compared with the O-H stretching vibration, a well-established conformational sensor for n-propanol, the Cβ-H stretching vibration presented here shows better conformational resolution in the liquid state. Furthermore, using this probe, we investigated the conformational preference of n-propanol in pure liquid and in dilute water solution. It is revealed that in pure liquid, n-propanol molecules prefer the trans-OH conformation, and in dilute water solution, this preference is enhanced, indicating that the water molecules play a role of further stabilizing the trans-OH n-propanol conformers. This leads to conformational evolution that n-propanol molecules with gauche-OH structure are transferred to the trans-OH structure upon diluting with water. These results not only provide important information on structures of n-propanol in different environments, but also demonstrate the potential of the C-H stretching vibration as a new tool for conformational analysis. This is especially important when considering that hydrocarbon chains are structural units in organic and biological molecules.

[1]  A. C. Tam,et al.  Optoacoustic Raman gain spectroscopy of liquids , 1979 .

[2]  Michael J. Berry,et al.  Photoacoustic Raman spectroscopy (PARS) using cw laser sources , 1979 .

[3]  Yi Luo,et al.  The microscopic structure of liquid methanol from Raman spectroscopy. , 2010, The journal of physical chemistry. B.

[4]  D. Patterson,et al.  Enantiomer-specific detection of chiral molecules via microwave spectroscopy , 2013, Nature.

[5]  Ilana Bar,et al.  Ionization-loss stimulated Raman spectroscopy for conformational probing of flexible molecules. , 2011, Physical chemistry chemical physics : PCCP.

[6]  Kenji Watanabe,et al.  Structure of 1-Propanol–Water Mixtures Investigated by Large-Angle X-ray Scattering Technique , 2004 .

[7]  T. Korter,et al.  Tryptamine in the gas phase. A high resolution laser study of the structural and dynamic properties of its ground and electronically excited states , 2005 .

[8]  S. Corcelli,et al.  Carbon-deuterium vibrational probes of peptide conformation: alanine dipeptide and glycine dipeptide. , 2009, The Journal of chemical physics.

[9]  W. J. van der Zande,et al.  A conformation-selective IR-UV study of the dipeptides Ac-Phe-Ser-NH2 and Ac-Phe-Cys-NH2: probing the SH···O and OH···O hydrogen bond interactions. , 2014, Physical chemistry chemical physics : PCCP.

[10]  R. G. Snyder,et al.  Carbon-hydrogen stretching modes and the structure of n-alkyl chains. 1. Long, disordered chains , 1982 .

[11]  Yuanqin Yu,et al.  Overlapping spectral features and new assignment of 2‐propanol in the C–H stretching region , 2014 .

[12]  Yuanqin Yu,et al.  New C-H Stretching Vibrational Spectral Features in the Raman Spectra of Gaseous and Liquid Ethanol † , 2007 .

[13]  V. Barone,et al.  Fully anharmonic IR and Raman spectra of medium-size molecular systems: accuracy and interpretation. , 2014, Physical chemistry chemical physics : PCCP.

[14]  J. Reid,et al.  Observation of conformational changes in 1-propanol-water complexes by FTIR spectroscopy. , 2010, The journal of physical chemistry. A.

[15]  T. Zwier,et al.  The Infrared and Ultraviolet Spectra of Individual Conformational Isomers of Biomolecules: Tryptamine , 2000 .

[16]  Timothy S Zwier,et al.  A first-principles model of Fermi resonance in the alkyl CH stretch region: application to hydronaphthalenes, indanes, and cyclohexane. , 2014, The journal of physical chemistry. B.

[17]  Yang Song,et al.  Hydrogen bonds and conformations in ethylene glycol under pressure. , 2012, The journal of physical chemistry. B.

[18]  Yuanqin Yu,et al.  Precise measurement of the depolarization ratio from photoacoustic Raman spectroscopy , 2007 .

[19]  T. Zwier,et al.  Infrared and ultraviolet spectral signatures and conformational preferences of jet-cooled serotonin. , 2007, Journal of the American Chemical Society.

[20]  E. Sibert.  Dressed local mode Hamiltonians for CH stretch vibrations , 2013 .

[21]  Yuanqin Yu,et al.  Accurate Measurement of Raman Depolarization Ratio in Gaseous CO2 , 2015 .

[22]  D. Pratt,et al.  Permanent electric dipole moments of four tryptamine conformers in the gas phase: a new diagnostic of structure and dynamics. , 2006, The Journal of chemical physics.

[23]  Yuanqin Yu,et al.  Complete Raman spectral assignment of methanol in the C-H stretching region. , 2013, The journal of physical chemistry. A.

[24]  K. Jordan,et al.  Direct measurement of the energy thresholds to conformational isomerization in tryptamine: experiment and theory. , 2005, The Journal of chemical physics.

[25]  S. Krimm,et al.  Conformation dependence of the CαDα stretch mode in peptides. II. Explicitly hydrated alanine peptide structures , 2009, Biopolymers.

[26]  Evan G. Buchanan,et al.  Towards a first-principles model of Fermi resonance in the alkyl CH stretch region: application to 1,2-diphenylethane and 2,2,2-paracyclophane. , 2013, The Journal of chemical physics.

[27]  William F. Murphy,et al.  Isolated C–H stretching vibrations of n‐alkanes: Assignments and relation to structure , 1984 .

[28]  I. Bar,et al.  Simultaneous Ionization-Detected Stimulated Raman and Visible-Visible-Ultraviolet Hole-Burning Spectra of Two Tryptamine Conformers. , 2012, The journal of physical chemistry letters.

[29]  W. Gan,et al.  C-H stretching vibrations of methyl, methylene and methine groups at the vapor/alcohol (N = 1-8) interfaces. , 2005, The journal of physical chemistry. B.

[30]  M. Suhm,et al.  Isomerization around C–C and C–O bonds in 1-propanol: Collisional relaxation in supersonic jets and selective IR photo-isomerization in cryogenic matrices , 2012 .

[31]  Saeed Amirjalayer,et al.  Conformational heterogeneity of methyl 4-hydroxycinnamate: a gas-phase UV-IR spectroscopic study. , 2013, The journal of physical chemistry. B.

[32]  A. Sahoo,et al.  The probable molecular association in liquid D-1-propanol through neutron diffraction. , 2009, The journal of physical chemistry. A.

[33]  Yi Luo,et al.  Reorientation dynamics in liquid alcohols from Raman spectroscopy , 2012 .

[34]  B. Drouin,et al.  Determination of precise relative energies of conformers of n-propanol by rotational spectroscopy. , 2010, Physical chemistry chemical physics : PCCP.

[35]  C. Ning,et al.  Electron momentum spectroscopy study of a conformationally versatile molecule: n-propanol , 2009 .

[36]  Timothy S Zwier,et al.  Ground state conformational preferences and CH stretch-bend coupling in a model alkoxy chain: 1,2-diphenoxyethane. , 2013, The journal of physical chemistry. A.

[37]  S. Krimm,et al.  Conformation dependence of the CalphaDalpha stretch mode in peptides. 1. Isolated alanine peptide structures. , 2007, The journal of physical chemistry. A.

[38]  C. Medcraft,et al.  Rotational spectroscopy and three-wave mixing of 4-carvomenthenol: A technical guide to measuring chirality in the microwave regime. , 2015, The Journal of chemical physics.

[39]  Prasad L. Polavarapu,et al.  Ab initio vibrational Raman and Raman optical activity spectra , 1990 .

[40]  R. G. Snyder,et al.  C-H stretching modes and the structure of n-alkyl chains. II: Long, all-trans chains , 1984 .

[41]  F. Bermejo,et al.  Glassy dynamics in supercooled-liquid and glassy ethanol: A molecular dynamics study , 2000 .

[42]  S. Rosenwaks,et al.  Revealing the hot bands in the regions of the N-H and C-H stretch fundamentals of pyrrole. , 2013, The journal of physical chemistry. A.

[43]  Ke Lin,et al.  Populations of Ethanol Conformers in Liquid CCl4 and CS2 by Raman Spectra in OH Stretching Region , 2015 .

[44]  S. Chervenkov,et al.  Identification of conformational structures of 2-phenylethanol and its singly hydrated complex by mass selective high-resolution spectroscopy and ab initio calculations. , 2008, The journal of physical chemistry. A.

[45]  P. J. Krueger,et al.  SPECTROSCOPIC STUDIES OF ALCOHOLS: IV. CONFORMATIONAL HETEROGENEITY OF 1-PROPANOL IN DILUTE CCl4 SOLUTION , 1964 .

[46]  T. Row,et al.  Conformation-changing aggregation in hydroxyacetone: a combined low-temperature FTIR, jet, and crystallographic study. , 2011, Journal of the American Chemical Society.

[47]  A. Matic,et al.  The temperature dependent structure of liquid 1-propanol as studied by neutron diffraction and EPSR simulations. , 2013, The Journal of chemical physics.

[48]  M. Suhm,et al.  Ethanol monomers and dimers revisited: a Raman study of conformational preferences and argon nanocoating effects. , 2010, The journal of physical chemistry. A.

[49]  Timothy J. Johnson,et al.  Relative Raman Intensities in C6H6, C6D6, and C6F6: A Comparison of Different Computational Methods , 2007 .

[50]  R. G. Snyder,et al.  Carbon-hydrogen stretching modes and the structure of n-alkyl chains. 2. Long, all-trans chains , 1984 .

[51]  M. Suhm,et al.  Structural preferences, argon nanocoating, and dimerization of n-alkanols as revealed by OH stretching spectroscopy in supersonic jets. , 2007, The journal of physical chemistry. A.

[52]  U. Schmitt,et al.  FTIR-spectroscopy of molecular clusters in pulsed supersonic slit-jet expansions , 1999 .

[53]  Yi Luo,et al.  Identification of alcohol conformers by Raman spectra in the C-H stretching region. , 2015, The journal of physical chemistry. A.

[54]  Samuel Krimm,et al.  Conformation dependence of the DαDα stretch mode in peptides: Side-chain influence in dipeptide structures. , 2010, Biopolymers.

[55]  I. Bar,et al.  Vibrational and vibronic spectra of tryptamine conformers. , 2013, The Journal of chemical physics.

[56]  T. C. Bruice,et al.  Focal-point conformational analysis of ethanol, propanol, and isopropanol. , 2005, Chemphyschem : a European journal of chemical physics and physical chemistry.

[57]  M. Suhm,et al.  Concerted proton motion in hydrogen-bonded trimers: a spontaneous Raman scattering perspective. , 2006, Physical chemistry chemical physics : PCCP.

[58]  S. Sarkar,et al.  Molecular conformation and structural correlations of liquid D-1-propanol through neutron diffraction , 2008 .

[59]  S. Rosenwaks,et al.  Raman spectral signatures as conformational probes of gas phase flexible molecules. , 2009, The Journal of chemical physics.

[60]  N. Maiti,et al.  Calpha-H bond-stretching frequency in alcohols as a probe of hydrogen-bonding strength: a combined vibrational spectroscopic and theoretical study of n-[1-D]propanol. , 2005, The journal of physical chemistry. A.