Blue-shifting Hydrogen Bonds Research Articles

Exploring fundamental differences between red- and blue-shifted intramolecular hydrogen bonds using FAMSEC, FALDI, IQA and QTAIM

We have discovered, using developed by us recently FALDI and FAMSEC computational techniques, fundamentally distinct mechanisms of intramolecular red- and blue-shifted H-bond formation that occurred in different conformers of the same molecule (amino-acid β-alanine) involving the same heteroatoms (O–H⋅⋅⋅N and N–H⋅⋅⋅O). Quantitative topological, geometric and energetic data of both H-bonds obtained with well-known QTAIM and IQA methodologies agree with what is known regarding H-bonding in general. However, the FALDI charge and decomposition scheme for calculating in real space 3D conformational deformation densities provided clear evidence that the process of electron density redistribution taking place on the formation of the stronger red-shifted H-bond is fundamentally distinct from the weaker blue-shifted H-bond. Contributions made by atoms of the X–H⋅⋅⋅Y–Z fragment (IUPAC notation) as well as distinct atoms on the H-bond formation were fully explored. The FAMSEC energy decomposition approach showed that the atoms involved in formation of the red-shifted H-bond interact in a fundamentally different fashion, both locally and with the remainder of the molecule, as compared with those of the blue-shifted H-bond. Excellent correlations of trends obtained with QTAIM, IQA, FAMSEC and FALDI techniques were obtained. Commentary regarding IUPAC recommended definition of an H-bond and validity of observed AILs (or bond paths) of the two H-bond kinds is also discussed.

Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.

Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes.

The structures and vibrational spectra of the methyl halide dimers. An ab initio study

Four homodimers and six heterodimers of the methyl halides, CH3X (X = F, Cl, Br, I), have been examined by means of ab initio calculations at the second order level of Møller-Plesset perturbation theory and with an augmented correlation-consistent polarized valence triple-zeta basis set. Three families of dimers have been found. All four homodimers optimize as both cyclic doubly hydrogen-bonded CH … X species and as non-hydrogen-bonded van der Waals C … X aggregates. All six heterodimers also optimize with cyclic doubly bonded structures; in addition, three of them are non-hydrogen-bonded with C … X linkages, and the three containing CH3I are singly bonded, with a CH … I interaction. The properties normally regarded as distinguishing features separating red-shifted from blue-shifted hydrogen bond interactions (CH bond length changes, shifts of the CH stretching wavenumbers and infrared CH stretching band intensity ratios) have been determined, and their variations with respect to the structures of the adducts have been rationalized.

A Study of the Solvation Structure of L-Leucine in Alcohol-Water Binary Solvents through Molecular Dynamics Simulations and FTIR and NMR Spectroscopy.

The solvation structures of l-leucine (Leu) in aliphatic-alcohol-water and fluorinated-alcohol-water solvents are elucidated for various alcohol contents by using molecular dynamics (MD) simulations and IR, and (1) H and (13) C NMR spectroscopy. The aliphatic alcohols included methanol, ethanol, and 2-propanol, whereas the fluorinated alcohols were 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol. The MD results show that the hydrophobic alkyl moiety of Leu is surrounded by the alkyl or fluoroalkyl groups of the alcohol molecules. In particular, TFE and HFIP significantly solvate the alkyl group of Leu. IR spectra reveal that the Leu C-H stretching vibration blueshifts in fluorinated alcohol solutions with increasing alcohol content, whereas the vibration redshifts in aliphatic alcohol solutions. When the C-H stretching vibration blueshifts in the fluorinated alcohol solutions, the hydrogen and carbon atoms of the Leu alkyl group are magnetically shielded. Consequently, TFE and HFIP molecules may solvate the Leu alkyl group through the blue-shifting hydrogen bonds.

Hydrogen bonds and ionic forms versus polymerization of imidazole at high pressures.

Imidazole (C3H4N2) is an important biomaterial for material research and applications. Our high-pressure Raman spectroscopic investigations combined with ab initio calculations on crystalline imidazole suggest that C-H---X (X = N, π) and N-H---N intermolecular hydrogen bonding interactions largely influence the nature of its structural and polymeric transformations under pressure. At pressures around ∼10 GPa, the reduction in the N---N distances close to the symmetrization limit and the emergence of the spectral features of the cationic form indicate the onset of proton disorder. The pressure-induced strengthening of the "blue-shifting hydrogen bonds" C-H---X (X = N, π) in this compound is revealed by the Raman spectra and the ab initio calculations. No polymer phase was retrieved on release from the highest pressure of 20 GPa in this study.

On the Nature of Blueshifting Hydrogen Bonds

The block-localized wave function (BLW) method can derive the energetic, geometrical, and spectral changes with the deactivation of electron delocalization, and thus provide a unique way to elucidate the origin of improper, blueshifting hydrogen bonds versus proper, redshifting hydrogen bonds. A detailed analysis of the interactions of F(3)CH with NH(3) and OH(2) shows that blueshifting is a long-range phenomenon. Since among the various energy components contributing to hydrogen bonds, only the electrostatic interaction has long-range characteristics, we conclude that the contraction and blueshifting of a hydrogen bond is largely caused by electrostatic interactions. On the other hand, lengthening and redshifting is primarily due to the short-range n(Y)→σ*(X-H) hyperconjugation. The competition between these two opposing factors determines the final frequency change direction, for example, redshifting in F(3)CH⋅⋅⋅NH(3) and blueshifting in F(3)CH⋅⋅⋅OH(2). This mechanism works well in the series F(n)Cl(3)-n CH⋅⋅⋅Y (n=0-3, Y=NH(3), OH(2), SH(2)) and other systems. One exception is the complex of water and benzene. We observe the lengthening and redshifting of the O-H bond of water even with the electron transfer between benzene and water completely quenched. A distance-dependent analysis for this system reveals that the long-range electrostatic interaction is again responsible for the initial lengthening and redshifting.

Interplay between molecule–molecule and molecule–substrate interactions: first-principles study of fluoroform aggregates on a hexagonal ice (0001) surface

The adsorption of fluoroform molecules on a hexagonal ice (0001) surface was studied using static density functional theory (DFT) calculations and Car-Parrinello molecular dynamics (CP-MD) simulations. Extending our previous work on isolated molecules we focus in the present study on the interplay between molecule-molecule and molecule-substrate interactions. Coverages of up to a full monolayer were modeled by introducing two, three and four fluoroform molecules per unit cell of the ice (0001) substrate. Lowest-energy structures of fluoroform aggregates on the ice surface were determined in a systematic search by performing geometry optimizations from a large set of initial configurations chosen by chemical intuition and from snapshots taken from CP-MD simulations. In the vibrational analysis of the optimized geometries both conventional red- and unusual blue-shifting hydrogen bonds were found. The finite temperature stability of the lowest-energy configurations was probed by CP-MD simulations and conformational changes were analyzed in terms of transformations between the global and local minima structures.

The gas phase FTIR studies of chloroform + B and halothane + B (B = TMA, FCD3) mixtures

An infrared and ab initio (MP2/6-311++G(2d,2p)) study of complexes of chloroform (Cl3CH(D)) and halothane (CHClBrCF3) with weak – methyl fluoride (FCD3) and strong – trimethylamine (N(CH(D)3)3 TMA) proton acceptors in the gas phase near the room temperature is presented. The so called blue shifting hydrogen bond has been identified in the former case and the formation of conventional H-bond with the red frequency shift of CH stretching vibration of the proton donors was observed in the latter case. An attempt of temperature spectroscopic measurements has been made for the systems studied to estimate the formation energy. In the case of Cl3CD…N(CH3)3 complex this value equals −23(2)kJ/mol. The results obtained in ab inito calculations generally agree with those obtained in IR spectroscopic measurements, however they overestimate the frequency shift caused by the complex formation, especially in the case of the red-shifting H-bonds. Possible origin of such overestimation is discussed shortly.

Triplex Blue-shifting Hydrogen Bonds of ClO4–···H–C in the Nanointerlayer of Montmorillonite Complexed with Cetyltrimethylammonium Cation from Hydrophilic to Hydrophobic Properties

In this study, molecular interactions of perchlorate (ClO4(-)), an emerging pollutant, with cetyltrimethylammonium(CTMA(+)) complexed in the nanointerlayer of negatively charged montmorillonite were characterized using the zeta potentials, FTIR, Raman, and XRD spectroscopy and quantified using quantum mechanical calculations and sorption experiments. We found that blue-shifting hydrogen bonds assisted in the uptake of ClO4(-) from water into the nanointerlayer spacing of CTMA(+)-montmorillonite and were tunable according to CTMA(+) loading. FTIR spectra presented an obvious 47 cm(-1) blue shift in the C-H vibration coming from the N-terminal methyl group of CTMA(+) when ClO4(-) was absorbed. Quantum mechanical calculations based on density functional theory demonstrated that triplex blue-shifting hydrogen bonds of C-H···O were formed between the three terminal methyl groups of CTMA(+) and three oxygen atoms of ClO4(-). The contribution of blue-shifting hydrogen bonds to perchlorate uptake switched from a ClO4(-)/CTMA(+) ratio of 0.0453 at low CTMA(+) loadings to a ClO4(-)/CTMA(+) ratio of 0.2563 (5.6-fold) at high CTMA(+) loadings, which can be ascribed to the evolution of the nanointerlayer microenvironments from hydrophilic properties to hydrophobic properties. The blue-shifting hydrogen bond of C-H···O that is tunable with the hydrophobic nature of the organic phase should be recognized to elucidate the biochemical behavior of perchlorate in organisms.

Nucleotide insertion initiated by van der Waals interaction during polymerase beta DNA replication

We present here an unambiguous theoretical analyses and to show that the exclusive biochemical reaction involved in a single nucleotide insertion into the DNA primer can be efficiently tracked using the renormalized van der Waals (vdW) interaction of a stronger type, the Hermansson blue-shifting hydrogen bond effect, and the Arunan composite hydrogen-vdW bond. We find that there are two biochemical steps involved to complete the insertion of a single base (cytosine) into the 3′ end of a DNA primer. First, the O3′ (from a DNA primer) initiates the nucleophilic attack on P α (from an incoming dCTP), in response, O3 α (bonded to P α ) interacts with H′ (bonded to O3′). These interactions are shown to be strongly interdependent and require the forming and breaking of P—O and H—O covalent bonds, which in turn imply that we do not need any external energy supply.

Interactions in water–THF binary mixture by contact angle, FTIR and dielectric studies

Contact angle, dielectric and IR studies of aqueous tetrahydrofuran (THF) are carried over the entire concentration range. IR studies indicate the formation of blue-shifted hydrogen bonds between water and THF molecules over the entire concentration region. On addition of small quantities of THF to water, THF molecules enter into the hydrogen bonded water network forming clathrate like complexes. Concentration dependent wetting of aqueous THF over various substrates is also reported. The effect of clathrate formation on the wetting properties of the substrate has also been explored. The clathrate structures formed are seen to influence the wetting properties on moderately hydrophobic substrates like Indium tin Oxide (ITO), Cubic Bismuth Zinc Niobate thin film on sapphire substrate (CBZN), Yttrium-stabilized zirconia (YSZ), Strontium Titanate (STO) and Si wafer. Contact angles decreases with an increase in THF concentration except in the region (0.03≤XTHF≤0.05 and 0.07≤XTHF≤0.09) where clathrate structure appears and hence no change of contact angle is seen.

Interactions of carbon dioxide with model organic molecules: A comparative theoretical study

Interaction energies obtained using CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ computations including both ZPE and BSSE corrections range from −2.9 to −14.2kJmol−1. While formic acid forms the most stable complex with CO2, formaldehyde yields the least stable complex. Lewis acid–base interaction such as C–N⋯C(CO2), CO⋯C(CO2), which overcomes C–H⋯O blue-shifting hydrogen bond, plays a significant role in stabilizing most complexes. However, the strength of (HCOOH, CO2) is mainly determined by O–H⋯O red-shifting hydrogen bond. The C–H⋯O blue-shifting hydrogen bond is revealed upon complexation of CH3OH, HCHO, HCOOH, CH3COCH3 and HCOOCH3 with CO2. Remarkably, existence of weak hydrogen bonded C–H⋯O interaction is not found in the (CH3OCH3, CO2) and (CH3NH2, CO2) pairs.

Toward understanding the role of water molecules in the uptake of nitrosyl hydride by sulfuric acid aerosols: A computational study

In the present study, the equilibrium structures, binding energies, and the nature of the coupling interactions in H2SO4⋯HNO⋯(H2O)n (n=0–2) clusters have been systematically investigated at the MP2/aug-cc-pVDZ level of theory in combination with the atoms in molecules (AIM) theory and many-body interaction energies. Particular attention is given to existence and magnitude of NH⋯O blue-shifting hydrogen bonds (H-bonds). It was found that the insert of one or two water molecules can efficiently enhance the interactions between H2SO4 and HNO, pointing the positive role of water molecules in the uptake of the HNO via sulfuric acid aerosols. Based on the energy decomposition analysis (EDA), it can be seen that the stabilities of the clusters are predicted to be attributable mainly to electrostatic and polarization effects.

A theoretical study on the red- and blue-shift hydrogen bonds of cis-trans formic acid dimer in excited states

Abstract The excited states of cis-trans formic acid dimer and its monomers have been investigated by time-dependent density functional theory (TDDFT) method. The formation of intermolecular hydrogen bonds O1-H1...O2=C2 and C2-H2...O4=C1 induces bond length lengthening of the groups related to the hydrogen bond, while that of the C2-H2 group is shortened. It is demonstrated that the red-shift hydrogen bond O1-H1...O2=C2 and blue-shift hydrogen bond C2-H2...O4=C1 are both weakened when excited to the S1 state. Moreover, it is found that the groups related to the formation of red-shift hydrogen bond O1-H1...O2=C2 are both strengthened in the S1 state, while the groups related to the blue-shift hydrogen bond C2-H2...O4=C1 are both weakened. This will provide information for the photochemistry and photophysical study of red- and blue-shift hydrogen bond.

Molecular interactions and macroscopic effects in binary mixtures of an imidazolium ionic liquid with water, methanol, and ethanol

Intermolecular interactions in mixtures of room-temperature ionic liquids (RTILs) and co-solvents define the properties of the solution. In this work, we study the mixing behavior in the binary systems [EMIM][EtSO4]/water, [EMIM][EtSO4]/methanol and [EMIM][EtSO4]/ethanol, which is governed by a change in the balance of molecular interactions present in neat [EMIM][EtSO4]. The mixing behavior and interactions are investigated at molecular level by means of Raman spectroscopy, and at macroscopic level utilizing excess data taken from the literature. The discussion of the results aims at a distinct interpretation of the spectroscopic data and at identifying the relationships between molecular phenomena and macroscopic behavior. The Raman spectra of the binary systems indicate that the balance of intermolecular interactions in the neat RTIL is dominantly distorted by solute–solvent interactions involving hydrogen atoms (IIHAs). In concert with former studies, the spectroscopic and macroscopic data suggest, that the IIHA include a combination of conventional (red-shifting) and unconventional (blue-shifting) hydrogen bonds. With increasing co-solvent concentration, the interionic bonds become successively weaker and eventually ion-co-solvent interactions even replace those between the RTIL counter ions leading to ion pair dissociation.

Theoretical study of different substituent benzenes and benzene dimers blue-shifted hydrogen bonds

Density functional theory (DFT) optimizations at M06-2X/6-31++G (d,p) level had been performed in the T-shaped structures of C6H5R (R=NO2, F, H, OH, CH3, and NH2) with benzene complexes. The interaction energies were calculated by counterpoise (CP)-corrected methods. Among the six dimers, we can see that the C–H⋯π bonded of C6H5NO2⋯benzene complex is the most stable one. Furthermore, the C–H⋯π blue-shifted hydrogen bonds in the dimers were studied. All the C–H bonds of the proton donors showed behavior of the contraction. And the different substituent groups had some effect on the contraction of the C–H bond. In addition, the natural bond orbital (NBO) and atoms in molecules (AIMs) analysis were investigated the origin of C–H⋯π blue-shifted hydrogen bond. From the NBO analysis, it was found that a negligible increase of electron density (ED) on the σ* (C–H) orbital and an increase of an s character of the C–H bond upon complexation were responsible for contraction and strengthening of this C–H bond. The AIM analysis showed that all studied dimers in this paper satisfied the indicative criteria of hydrogen bonding interactions and it was necessary to supplement those criteria with information on the changes in the electron density of the donor X–H bond occurring upon complexation to differentiate between H bonding and anti-H bonding.

Theory of electron localization and its application to blue-shifting hydrogen bonds

We propose a theory of electron localization or stabilization by electron localization through the interactions between occupied (i) and vacant (j*) orbitals under certain conditions, which have been believed so far to cause only electron delocalization. Electrons localize when the electrons redistributed by the interaction are more stable in the i-th occupied orbital than in the overlap region: h(ij*) > s(ij*)h(ii) for s(ij*) > 0. Electron delocalization occurs when h(ij*) < s(ij*)h(ii) for s(ij*) > 0. The h(ij*) and s(ij*)h(ii) terms represent the energy of the electrons in the overlap region and the energy of the redistributed electrons in the occupied orbital, respectively. The theory of electron localization is substantiated by the correlation of the C-H bond lengths of fluorinated methanes H(4-n)CF(n) (n = 1, 2, 3) to the electron population of the σ(CH) bonding orbital, and successfully applied to understanding blue-shifting hydrogen bonds in F(3)CH···X (X = CO, N(2), OC, Ne, OC(CH(3))(2)) and designing some proton donors, HCO(2)CH(3) and hypervalent molecules HPF(4) and HSF(5), for blue-shifting hydrogen bonds.

Blue and red shift hydrogen bonds in crystalline cobaltocinium complexes

Typical hydrogen-bonded cobaltocinium salts of formula [Cp2Co+][A−] [with Cp = C5H5 and A = PF6 ( 1), AsF6 ( 2), SbF6 ( 3), I ( 4), I3 ( 5), Co(CN)6 ( 6), Co(CO)4 ( 7), Br3 ( 8), FeI4 ( 9) and HCl2 ( 10)] were studied by means of a combined structural, spectroscopic (IR, Raman, solid-state NMR) and theoretical approach. The solid-state vibrational spectra show blue or red shift hydrogen bond behavior depending on the anionic species, i.e. high- or low-frequency ν(CH) shift with respect to the solution value. The crystal structure of the new complex [Cp2Co+][SbF6−], a blue-shifted system, is reported while the [Cp2Co+][I−] complex, a red-shifted system disordered at room temperature, reveals a novel ordered polymorph at 150 K. The weak interactions (C⋯H, H⋯H, H⋯X, C⋯X) between cations and anions were analyzed by means of the Hirshfeld surfaces model, which permits their clear graphic visualization. HS fingerprint plots and normalized contact distances visually describe the difference between blue- and red-shifted complexes. Chemical shift tensors and shielding anisotropy values of the Cp carbon atoms, extracted from 13C CPMAS solid-state NMR spectra, allow the evaluation of Cp rotational motions which are related to the intermolecular contact extent. Finally, a DFT computational model is able to rationalize all the experimental data. It shows that the prevalence of one between two forces, that is, the attractive polarization of C–H bonds and the repulsive effect of electronic clouds, leads to the blue or red shift phenomenon.

Blue or red ΔνXH complexation shift in X–H⋯CO2 hydrogen-bonded complexes?

The position of the ν(XH) stretching band for more than 100 proton donors (X=O,N,C,S,Se,P,Si,B,F,Cl,Br) complexed with CO2 was calculated at the MP2/6-311++G(d,p) level. Complexation energies and natural bond orbital characteristics were also determined. These calculations revealed that the direction of the ν(XH) band shift was related to the charge born by the hydrogen atom of the proton donor. X–H⋯OCO blue-shifting hydrogen bonds were found for compounds characterised by a small charge, while red-shifting was observed for those compounds with a high positive charge on the hydrogen atom.

Red- and Blue-Shifted Hydrogen Bonds: the Bent Rule from Quantum Theory of Atoms in Molecules Perspective

MP2/6-311++G(3pd,3df) calculations were performed on complexes of acetylene and fluoroform acting as the proton donating systems and different Lewis bases being the proton acceptors since these complexes are linked through C-H···Y hydrogen bonds. Quantum Theory of Atoms in Molecules (QTAIM) is applied to explain the nature of these interactions. The characteristics of bond critical points are presented for these complexes. The inter-relations between energetic and geometrical parameters as well as the parameters derived from the Natural Bond Orbital (NBO) theory are analyzed here. Red- and blue-shifted hydrogen bonds are detected for the complexes investigated and the differences between those interactions are analyzed from the QTAIM perspective. It is shown that such differences are in agreement with the Bent rule. The position of the bond critical point of the proton donating bond is connected with the nature of hydrogen bonding, that is, if it is blue- or red-shifted.