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Hemp (Cannabis sativa L.), traditionally cultivated for industrial use and harvested for fibers and seeds, has raised much interest as a sustainable crop in the last years. Recently, hemp seeds and derived oil have started to be used in a variety of food products. Hemp-based food products are considered less allergenic than those from other edible seeds, although this statement has never been experimentally verified. In this study high purity grade hemp flour (HF) and hemp protein isolate (HPI) were obtained through a fast and cheap process starting from defatted hemp cakes, a residue of hempseed oil extraction. HPI resulted enriched at nearly 86% protein, mainly constituted by the storage protein edestin (accounting for 70% total protein). In vitro protein digestibility was determined using a static model of gastrointestinal digestion (GID), which included a final step with purified brush border membrane (BBM) enzyme preparations. HF and HPI showed a high degree of digestibility. The survival of potential bioactive and/or allergenic peptide sequences in digests was investigated by peptidomic analysis. Only a limited number of sequences survived GID. Among them, fragments from 12 seed proteins. These fragments were precursors of sequences with potential bioactive peptides, which might justify the bioactivity of HPI hydrolysates, reported in previous studies. More importantly, all known hemp allergens, including the major thaumatin-like protein and LTP, were entirely eliminated by the HPI production process, neither fragments of the proteins were present after GID. These data support the use of HPI as an ingredient for hypoallergenic foods.

A detailed study of the conformational landscape of chloromethyl-oxirane and chloromethyl-thiirane is here reported. The equilibrium of the three different conformers of the two molecules was assessed, using a joint approach of experimental and theoretical methods. High quality infrared spectroscopy measurements of the liquid and of the crystalline phases were interpreted with the aid of ab initio Molecular Dynamics (AIMD) simulations, anharmonic frequencies and free energy calculations, obtaining a very good reproduction of the experimental data. The modulation of the conformational equilibrium upon the addition of polar and non-polar solvents was computationally evaluated and results found a confirmation in experimental measures.

The binary mixtures of the ionic liquid ethylammonium nitrate with acetonitrile have been studied by means of wide- and small-angle X-ray scattering and via two different computational methods, namely, classical molecular dynamics and DFT. The recently debated odd feature in the extreme low q region of some ionic liquid-based binary mixtures is linked to density fluctuations within the system. We show how the "low q excess" is due to some nanoscopic objects which are formed at certain compositions. These structures have different density with respect to the surrounding, thus generating the feature observed. Our results also show how the local arrangement is directly linked to the long-range structure. Moreover, we found once again a similarity in the physicochemical behavior of ethylammonium nitrate and water.

Barrelene, H–C(CH=CH)3C–H, is an unsaturated polycyclic hydrocarbon containing three isolated double bonds in a non-planar arrangement. We have studied the transmission of field effects through the barrelene framework by analyzing the small structural changes occurring in the phenyl group of many Ph–C(CH=CH)3C–X molecules, where X is a variable substituent. Molecular geometries have been determined by quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Comparison with the results obtained for the corresponding saturated molecules, the bicyclo[2.2.2]octane derivatives Ph–C(CH2–CH2)3C–X, reveals a small, but significant, field-induced π-polarization of the barrelene cage, especially when the remote substituent is a charged group. Additional evidence of π-polarization is obtained by comparing the electric dipole moments of the two sets of uncharged molecules. The structural variation of the barrelene cage caused by the variable substituent in Ph–C(CH=CH)3C–X molecules has also been investigated. It is much larger than that of the phenyl group and depends primarily on the electronegativity of the substituent. Particularly pronounced is the concerted variation of the non-bonded distance between the bridgehead carbons of the cage, r(C···C) 1 BARR , and the average of the three C–C–C angles at the cage carbon bonded to the variable substituent, α 1 BARR . A scattergram of r(C···C) 1 BARR versus the corresponding parameter for bicyclo[2.2.2]octane derivatives, r(C···C) 1 BCO , shows that the variation of r(C···C) 1 BARR becomes gradually less pronounced than that of r(C···C) 1 BCO as the electronegativity of the substituent increases.

We explore the structure of two ionic liquids based on the choline cation and the monoanion of the maleic acid. We consider two isomers of the anion (H-maleate, the cis-isomer and H-fumarate, the trans-isomer) having different physical chemical properties. H-maleate assumes a closed structure and forms a strong intramolecular hydrogen bond whereas H-fumarate has an open structure. X-ray diffraction, infrared and Raman spectroscopy and molecular dynamics have been used to provide a reliable picture of the interactions which characterize the structure of the fluids. All calculations indicate that the choline cation prefers to connect mainly to the carboxylate group through OH⋯O interactions in both the compounds and orient the charged head N(CH3)3+ toward the negative portion of the anion. However, the different structure of the two anions affects the distribution of the ionic components in the fluid. The trans conformation of H-fumarate allows further interactions between anions through COOH and CO2&minus, groups whereas intramolecular hydrogen bonding in H-maleate prevents this association. Our theoretical findings have been validated by comparing them with experimental X-ray data and infrared and Raman spectra.

The hyperlithiated species Lik+1Fk (k=1, 2, 3, and 4) have been studied by quantum mechanical (QM) methods. Different structures have been localized for each molecule by the CBS-QB3 composite method: all the isomers show superalkali properties and strong tendency to donate an electron to carbon dioxide forming stable Lik+1Fk···CO2 complexes. With the aim to find molecular systems able to stabilize superalkalis, geometries of complexes between superalkalis and pyridine and superalkalis and graphene surfaces doped with a pyridinic vacancy were calculated. The pyridinic graphene sheets were modeled with two finite molecular systems C69 H21 N3 and C117 H27 N3 . The interaction with one pyridine molecule is quite weak and the superalkali maintains its structure and electron properties. The affinity for graphene sheets is instead stronger and the superalkalis tend to deform their geometry to better interact with the graphene surface. However, the superalkalis continue to show the tendency to transfer electrons to carbon dioxide reducing CO2 , as found in graphene absence.

In this work, the EDXD/molecular dynamics approach to the study of molecular liquids, is applied to cyclohexane and two substituted analogues, piperidine and morpholine. The Structure Functions and Radial Distribution Functions obtained from EDXD (Energy Dispersive X-ray Diffraction) scattered intensity data are interpreted with the same theoretical model recently used for unsaturated liquids. The agreement obtained is satisfactory, although a bit lower in this case. The models are then refined through least-squares fitting to experimental data.

The local structure of the hydration of pyrazole has been analysed through static and dynamical microsolvation models described by quantum mechanical methods. Then, a reliable classical force field of pyrazole has been obtained on the basis of the quantum mechanical results and the dynamical properties of aqueous pyrazole solutions have been studied by molecular dynamics simulations. Finally, the structure of pyrazole-water solutions at different concentrations has been investigated by energy dispersive X-ray diffraction and experimental results have been compared to calculations. This comparison provides both a tool for interpretation of experiments and a way to validate the computational protocol.

We present an analysis of gas-phase structures of small clusters of n-alkylammonium nitrates (ethyl, propyl, and butyl) together with vibrational Raman spectroscopy of their respective liquid phases. The assignment and interpretation of the resonant frequencies have been performed by comparison with high-quality ab initio (DFT) computations. The theoretical spectra are in excellent agreement with the measured ones and allow the interpretation and assignment of almost all the spectral features. A careful analysis of the vibrational frequencies and of the electronic structure of the compounds has provided additional information on various structural features and on the rather complex hydrogen bonding network that exists in such compounds. A geometric structure of the short-range local arrangement in the bulk phases is also proposed.

Using microsolvation models and mixed quantum/classical ab initio molecular dynamics simulations, we investigate the vibrational properties of two azoles in water solution: pyrazole and oxazole. The effects of the water-azole hydrogen bonding are rationalized by an extensive comparison between structural parameters and harmonic frequencies obtained by microsolvation models. Following the effective normal-mode analysis introduced by Martinez et al. [Martinez et al., J. Chem. Phys. 2006, 125, 144106], we identify the vibrational frequencies of the solutes using the decomposition of the vibrational density of states of the gas phase and solution dynamics. The calculated shifts from gas phase to solution are fairly in agreement with the available experimental data.

Background Compared with the Taxus® stent, the non-polymeric paclitaxel-eluting Amazonia® PAX stent shows no differences in the occurrence of coronary restenosis or clinical events after four months of follow-up. However, the performance of the Amazonia® PAX stent in more complex cases and with longer angiographic follow-up has not been demonstrated. Methods The PAX-B study was a prospective, non-randomised, multicentre study assessing the long-term follow-up of patients treated with the Amazonia® PAX stent. The primary outcome was late in-stent lumen loss. Results The study included 103 patients with a mean age of 61.3 ± 11.4 years; 26.2% were diabetics, 24.3% had acute coronary syndromes, and 71.6% had type B2/C lesions. Multiple stents were implanted in 4.7% of the patients, and angiographic success was achieved in 100% of the cases. During hospitalisation, the periprocedural acute myocardial infarction rate was 3.9%, and one of these events led to target-lesion revascularisation (TLR). At the nine-month angiographic follow-up, the median late in-stent lumen loss was 0.91 [0.50; 1.21] mm. The cumulative rates of major adverse cardiac events at the six-month, nine-month, and 12-month follow-ups were 7.8%, 18.5%, and 21.3%, respectively, mostly due to TLR. There were no deaths or stent thromboses at 12 months. Conclusions The Amazonia® PAX stent showed excellent immediate results and a good safety profile. However, angiographic recurrence rates were relatively high because of the low efficacy of neointimal hyperplasia inhibition.

We present an analysis of the structure of the monomethylammonium nitrate (MMAN) compound. Vibrational Raman spectroscopy and X-ray powder diffraction have been used to characterize the bulk phases of MMAN, and assignment of the resonant frequencies has been performed by ab initio (DFT) computations on small clusters of the compound. The theoretical spectra are in excellent agreement with the experimental ones and provide a means by which an interpretation of the hydrogen-bonding network that exists in such compound can be analyzed. In particular, we found that the spectrum of one of the solid phases is structurally very similar to that of the liquid. We present experimental evidence for the existence of such phase both from X-ray data and Raman spectra which, in turn, is easily interpreted with a one-to-one correspondence with the ab initio simulation of the small clusters. A geometric structure of the short-range local arrangement in these two bulk phases is therefore proposed.

Electronic substituent effects in 4-substituted 1-phenylcubane derivatives, Ph–C8H6–X, have been investigated from the structural changes caused by the substituent X. The molecular structures of 34 derivatives with charged or dipolar substituents have been determined from quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Geometrical variations caused by substitution appear both in the cubane framework and in the benzene ring, but the two kinds of changes show no correlation. The rather small changes in the benzene ring geometry are caused by long-range polar effects (field effects), while the larger changes in the cubane cage are controlled primarily by electronegativity effects. A structural parameter measuring the long-range polar effect of the substituent, S F CUB , has been derived from the geometry of the phenyl group acting as a probe. This parameter correlates well with the calculated gas-phase acidities of 4-substituted cubane-1-carboxylic acids, HOOC–C8H6–X, and with other indicators of long-range polar effects obtained from bicyclo[2.2.2]octane derivatives. The correlations can further be improved by introducing a resonance parameter as an additional explanatory variable. This indicates that the electron delocalization resulting from hyperconjugative interactions between substituent and cage modifies the long-range polar effect of the substituent. Strong hyperconjugative interactions between some charged substituents and the cubane cage result in remarkable variations in the cage geometry, superimposed onto those ascribed to electronegativity effects.

The molecular structure of triphenylsilane has been investigated by gas-phase electron diffraction and theoretical calculations. The electron diffraction intensities from a previous study (Rozsondai B, Hargittai I, J Organomet Chem 334:269, 1987) have been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from calculations. The free molecule has a chiral, propeller-like equilibrium conformation of C 3 symmetry, with a twist angle of the phenyl groups τ = 39° ± 3°; the two enantiomeric conformers easily interconvert via three possible pathways. The low-frequency vibrational modes indicate that the three phenyl groups undergo large-amplitude torsional and out-of-plane bending vibrations about their respective Si–C bonds. Least-squares refinement of a model accounting for the bending vibrations gives the following bond distances and angles with estimated total errors: r g(Si–C) = 1.874 ± 0.004 A, 〈r g(C–C)〉 = 1.402 ± 0.003 A, 〈r g(C–H)〉 = 1.102 ± 0.003 A, and ∠aC–Si–H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si–C bonds in H4−n SiPh n molecules (n = 1–4) increase gradually with n, due to π → σ*(Si–C) delocalization. They also show that the mean lengths of the ring C–C bonds are about 0.003 A larger than in unsubstituted benzene, due to a one hundredth angstrom lengthening of the Cipso–Cortho bonds caused by silicon substitution. A small increase of r(Si–H) and decrease of the ipso angle with increasing number of phenyl groups is also revealed by the calculations.

The molecular structures of cyanobenzene, p-dicyanobenzene, and 1,2,4,5-tetracyanobenzene have been accurately determined by gas-phase electron diffraction and ab initio/DFT MO calculations. The equilibrium structures of these molecules are planar, but their average geometries in the gaseous phase are nonplanar because of large-amplitude vibrational motions of the substituents out of the plane of the benzene ring. The use of nonplanar models in electron diffraction analysis is necessary to yield ring angles consistent with the results of MO calculations. The angular deformation of the benzene ring in the three molecules is found to be much smaller than obtained from previous electron diffraction studies, as well as from microwave spectroscopy studies of cyanobenzene. While the deformation of the ring CC bonds and CCC angles in p-dicyanobenzene is well interpreted as arising from the superposition of independent effects from each substituent, considerable deviation from additivity occurs in 1,2,4,5-tetracyanobenzene. The changes in the ring geometry and C ipso-C cyano bond lengths in this molecule indicate an enhanced ability of the cyano group to withdraw pi-electrons from the benzene ring, compared with cyanobenzene and p-dicyanobenzene. In particular, gas-phase electron diffraction and MP2 or B3LYP calculations show a small but consistent increase in the mean length of the ring CC bonds for each cyano group and a further increase in 1,2,4,5-tetracyanobenzene. Comparison with accurate results from X-ray and neutron crystallography indicates that in p-dicyanobenzene the internal ring angle at the place of substitution opens slightly as the molecule is frozen in the crystal. The small geometrical change, about 0.6 degrees , is shown to be real and to originate from intermolecular C identical withN...HC interactions in the solid state.

We report here a combined experimental and theoretical study on the bio-compatible salicylate choline ionic liquid. The liquid structure has been investigated by X-ray diffraction and vibrational (IR and Raman) spectroscopy. Local structure has been obtained from ab initio calculations on static ion pairs and from dynamic simulations of a small portion of the liquid. The theoretical models indicate that salicylate is connected by hydrogen bonding to choline mainly through the carboxylate group and forms stable ion pairs. A strong intramolecular interaction hinders internal rotations of the OH group of salicylate and competes with the hydrogen bonding with choline. When the liquid has been simulated by classical force fields we found a good agreement with the X-ray experimental features, comparable to that obtained from AIMD simulations. Important insights on hydrogen bonding between carboxylate and choline have been also derived from the analysis of the CO stretching modes of carboxylate measured in the Raman and IR spectra and calculated from VDOS-Wannier centers procedures.

The free energy profile and the (classical) kinetics of chemical reactions in (soft) condensed phase are modeled theoretically by means of molecular dynamics simulations, the Perturbed Matrix Method (PMM) and the quasi Gaussian entropy (QGE) theory. In this paper we describe the theoretical framework and apply the model to the intramolecular proton transfer reaction of aqueous malonaldehyde. Although in the present application we disregard the quantum effects for the proton dynamics along the reaction coordinate (i.e., tunneling), the classical-like view of the proton transition over the reaction free energy surface seems to properly describe the kinetic process and shows that water acts lowering the reaction free energy barrier. Moreover, a weak temperature dependence of the free energy surface is obtained, implying small entropy variations in the transition. Interestingly the activation entropy, as provided by the QGE model, is negative in the whole temperature range considered, thus indicating an entropy reduction at the transition structure. Finally, by comparing our results with theoretical and experimental literature data, we critically address the actual role of tunneling in this reaction and discuss the emerging kinetic scheme. Copyright (c) 2006 John Wiley & Sons, Ltd.

A series of microclusters containing up to eigtht C2 symmetry urea molecules was studied at the B3LYP density functional theory level. The equilibrium structures of each aggregate and the respective theoretical infrared spectra were determined from B3LYP/6-311++G** calculations. Relative stability considerations and binding energy of each species were obtained from MP2/6-311++G**//B3LYP/6-311++G** single point calculations, including basis set superposition error (BSSE) and zero-point energy (ZPE) corrections. Further single point energy calculations at the MP2/6-311++G(3df,3pd)//B3LYP/6-311++G** level were made for all dimers and trimers. The theoretical study of these aggregates was integrated with FT-IR spectroscopy measurements in low temperature argon matrixes.

We propose a new scale of group electronegativities, derived from benzene ring deformations in Ph−X molecules. A recent analysis of such deformations (Campanelli, A. R.; Domenicano, A.; Ramondo, F....

We report a X-ray diffraction and molecular dynamics study on three choline-based bio-ionic liquids, choline formate, [Ch] [For], choline propanoate, [Ch][Pro], and choline butanoate, [Ch][But]. For the first time, this class of ionic liquids has been investigated by X-ray diffraction. Experimental and theoretical structure factors have been compared for each term of the series. Local structural organization has been obtained from ab initio calculations through static models of isolated ion pairs and dynamic simulations of small portions of liquids through twelve, ten, and nine ion pairs for [Ch][For], [Ch][Pro], and [Ch][But], respectively. All the theoretical models indicate that cations and anions are connected by strong hydrogen bonding and form stable ion pairs in the liquid that are reminiscent of the static ab initio ion pairs. Different structural aspects may affect the radial distribution function, like the local structure of ion pairs and the conformation of choline. When small portions of liquids have been simulated by dynamic quantum chemical methods, some key structural features of the X-ray radial distribution function were well reproduced whereas the classical force fields here applied did not entirely reproduce all the observed structural features.

Density functional theory and vibrational spectroscopy are used to investigate a class of bioionic liquids consisting of a choline cation and carboxylate anions. Through quantum mechanical studies of motionless ion pairs and molecular dynamics of small portions of the liquid, we have characterized important structural features of the ionic liquid. Hydrogen bonding produces stable ion pairs in the liquid and induces vibrational features of the carboxylate groups comparable with experimental results. Infrared and Raman spectra of liquids have been measured, and main bands have been assigned on the basis of theoretical spectra.

The effects of intermolecular hydrogen bonding on the vibrational frequencies of uracil are discussed on the basis of ab initio calculations. DFT methods are applied to calculated vibrational frequencies of various uracil dimers, namely six cyclic structures and four T-shaped arrangements, as well as eight uracil–water complexes. Frequency shifts experienced by some normal modes in the dimerisation are clearly correlated with acidity or basicity of the interaction sites. Interaction energies and frequency changes indicate that cooperativity plays a fundamental role in a self-association process. Moreover the cooperative effects increase their contribution with the strength of hydrogen bonding. The theoretical IR spectra of all the hydrogen bonded uracils considered here are compared with the FT-IR spectra of uracil and thymine measured in an N2 matrix at different concentrations.

The present electron diffraction study of the molecular structure of tetramethylsilane, augmented with theoretical calculations, answers the need for accurate and detailed information on the most fundamental molecules containing silicon. The Si—C bond length is r g = 1.877 ± 0.004 A, in perfect agreement with a previous study (Beagley, B.; Monaghan, J. J.; Hewitt, T. G. J. Mol. Struct. 1971 8 401). The C—H bond length is r g= 1.110 ± 0.003 A and the Si—C—H angle is 111.0 ± 0.2°. The experimental data are consistent with a model of T d symmetry and staggered methyl conformation. The barrier to methyl rotation is estimated to be 5.7 ± 2.0 kJ mol−1 on the basis of the experimentally observed average torsion of the methyl groups.

A dual RAIR (reflection–absorption infrared) spectroscopy and ab initio study of the interaction between molecular bromine and water-ice has been performed. The spectra were measured in the temperature range 85 to 180 K and the results compared to theoretical models of Br–H2O clusters and hydrated H2OX+ and X2OH− ions. Particular theoretical attention was paid to the possibility that the interacting molecules modify their properties (geometry, partial atomic charge and vibrational frequencies) with the size of the water clusters i.e. Br2···(H2O)n. Additionally, ab initio methods were employed to investigate the actual mechanism of the bromine hydrolysis by evaluating the stability of possible reaction intermediates such as [H2OBr]+ in the gas-phase as well as upon solvation. The chemical structures and vibrational frequencies of the hydrated ion-pairs were also examined. The theoretical treatments employed show that the bromine and water molecules can form a weakly bonded binary complex with interaction between the Br- and O-atoms. Furthermore, the experimental evidence obtained for bromine hydrolysis occurring via an [H2OBr]+ ion on water-ice is investigated by the energy calculations, which show that the route is competitive with that occurring via an H3O+ ion. The vibrational frequencies calculated for a hydrated H2OBr+ Br− ion pair satisfactorily reproduce the set of RAIR spectroscopy experiments preformed at 180 K.

The effect of water solvation on the structure and stability of cyclic dimers of urea has been investigated with the aid of density functional theory at the B3LYP/6-311++G** level. Several hydration models have been discussed. Specific solvent effects have been simulated through single and multiple water-urea interactions involving all the hydration sites of urea. The bulk solvent effects have been estimated through polarised continuum models. Under all the hydration patterns cyclic dimers continue to be stable structures although the solvent weakens the urea-urea interaction. Single and multiple specific urea-water interactions are competitive with urea dimerisation. The anticooperative nature of the two intermolecular interactions is largely due to the changes on sigma- and pi-electron density of urea caused by hydrogen bonding with water. The stability of the dimer is however, lost within a few ps when the hydrated dimer is described by a quantum mechanical molecular dynamics approach (ADMP). The cyclic dimer evolves towards structures where urea molecules are linked not more directly but through water molecules which have a bridge function.

The structure of Furan and thiophene neat liquids is discussed. Energy dispersive X-ray diffraction spectra were successfully inter- preted with molecular dynamics models. A detailed description of liquids at molecular level is obtainable, provided that a suitable and complete all-atom force field is employed.

In this work, a coupled experimental–theoretical protocol for the study of molecular liquids is reported. Energy dispersive X-ray diffraction results are successfully interpreted with molecular dynamics. Several models, differing for geometry and force field are presented; their behavior in reproducing experimental data is discussed.

The molecular structure and conformation of p-bis(trimethylsilyl)benzene have been investigated by gas-phase electron diffraction, ab initio MO calculations at the HF/6-31G*, MP2(f.c.)/6-31G*, and B3LYP/6-31G* levels, and MM3 molecular mechanics calculations. The calculations indicate the syn- and anti-coplanar conformations, with two $${\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{Me}}$$ bonds in the plane of the benzene ring, to be energy minima. The perpendicular conformations, with two $${\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{Me}}$$ bonds in a plane orthogonal to the ring plane, are transition states. The two coplanar conformers have nearly the same energy with a low interconversion barrier, 0.3–0.5 kJ mol−1. The calculated lengths of the $${\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{Me}}$$ and $${\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{Ph}}$$ bonds differ by only a few thousandths of an angstrom, in agreement with electron diffraction results from molecules containing either $${\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{Me}}$$ or $${\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{Ph}}$$ bonds. The geometrical distortion of the benzene ring in p-bis(trimethylsilyl)-benzene may be described by superimposing independent distortions from each of the two SiMe3 groups. The electron diffraction intensities from a previous study (Rozsondai, B.; Zelei, B.; Hargittai, I. J. Mol. Struct. 1982, 95, 187) have been reanalyzed, imposing constraints from the theoretical calculations, and using a model based on a 1:1 mixture of the two coplanar conformers. The effective torsion angles of the SiMe3 groups may indicate nearly free rotation. Important geometrical parameters from the present electron diffraction analysis are $$\langle r_g {\text{(C}}{\kern 1pt} - {\kern 1pt} {\text{C)}}\rangle {\text{ }} = {\text{ 1}}{\text{.407 }} \pm {\text{ 0}}{\text{.003 }}{\AA}{\text{, }}\langle r_g ({\text{Si}}{\kern 1pt} - {\kern 1pt} {\text{C}})\rangle = {\text{ 1}}{\text{.881 }} \pm {\text{ 0}}{\text{.004 }}{\AA}{\text{, }}\langle r_g ({\text{C}}{\kern 1pt} - {\kern 1pt} {\text{H}})\rangle = 1.108{\text{ }} \pm {\text{ 0}}{\text{.003 }}{\AA}{\text{ }}$$ , and $$\angle {\text{C}}_{{\text{ortho}}} {\kern 1pt} - {\kern 1pt} {\text{C}}_{{\text{ipso}}} {\kern 1pt} - {\kern 1pt} {\text{C}}_{{\text{ortho}}} = 117.2{\text{ }} \pm {\text{ 0}}{\text{.3}}^\circ $$ . While the mean bond lengths are virtually the same from the previous and present analyses, the new ipso angle is in better agreement with the MO calculations [HF, 116.9° MP2(f.c.), 117.1° B3LYP, 116.9°].

The molecular structure of phenylsilane has been determined accurately by gas-phase electron diffraction and ab initio MO calculations at the MP2(f.c.)/6-31G* level. The calculations indicate that the perpendicular conformation of the molecule, with a Si–H bond in a plane orthogonal to the plane of the benzene ring, is the potential energy minimum. The coplanar conformation, with a Si–H bond in the plane of the ring, corresponds to a rotational transition state. However, the difference in energy is very small, 0.13 kJ mol−1, implying free rotation of the substituent at the temperature of the electron diffraction experiment (301 K). Important bond lengths from electron diffraction are: =1.403±0.003 A, rg(Si–C)=1.870±0.004 A, and rg(Si–H)=1.497±0.007 A. The calculations indicate that the Cipso–Cortho bonds are 0.010 A longer than the other C–C bonds. The internal ring angle at the ipso position is 118.1±0.2° from electron diffraction and 118.0° from calculations. This confirms the more than 40-year old suggestion of a possible angular deformation of the ring in phenylsilane, in an early electron diffraction study by F.A. Keidel, S.H. Bauer, J. Chem. Phys. 25 (1956) 1218.

The presence of myocardial injury during non-surgical coronary revascularization has been evaluated by means of highly specific and sensitive biochemical markers. Troponin T, creatine kinase-MB isoenzyme mass concentration, and creatine kinase MB2/MB1 isoform ratio have been determined in 80 patients who underwent coronary revascularization with percutaneous transluminal coronary angioplasty (PTCA). Forty-five patients underwent balloon angioplasty, 15 rotational atherectomy, 10 directional atherectomy, and 10 elective coronary stenting. Serum concentration of the evaluated markers did not increase significantly after 57 uncomplicated revascularization procedures, including 15 rotablation procedures, nor after 8 PTCAs complicated by localized coronary type B and C dissections. Significant elevation of all markers above the upper limits of the reference interval (P0.05) was detected after occlusion of small side branches (0.5 mm diameter) in 5 patients. Creatine kinase MB2/MB1 isoform ratio was the earliest marker to increase. After recanalization of occluded vessels in 8/10 patients with 6-60 days old myocardial infarction only troponin T concentrations increased from a baseline of 0.28 microgram/l to a median peak of 0.80 microgram/l. This increase was statistically not significant (P = 0.12). In conclusion, myocardial damage was not detected following uncomplicated non-surgical revascularization obtained with different techniques. Markers of myocardial injury provide high sensitivity after small side branch occlusion.

The FTIR spectrum of N,N′-diformohydrazide isolated in argon and nitrogen matrices is presented and discussed in terms of normal modes predicted by ab initio calculations. MP2/6-31G* and BLYP/6-31G* methods are applied to calculate vibrational frequencies, IR intensities and isotopic shifts of different structures of the molecule. The number of absorption bands and their frequencies for the isolated molecule differ significantly from those of N,N′-diformohydrazide in the solid state. The conformation of the undistorted molecule is different from the planar structure adopted by the molecule in the crystal and such a conformation change is proposed as the reason for the spectral differences. Ab initio calculations support this assignment and predict the vapour of N,N′-diformohydrazide to be a mixture of conformers.

Germanium monocarbonyl has been prepared by high-temperature vaporization of Ge with excess carbon powder or CO co-condensation and trapped in various matrices at 12 K. Fourier transform infrared spectra, ab initio (MP2 and CISD) and density function (Becke3LYP) calculations suggested a linear species with the formula GeCO. A weak feature appearing only in annealed N 2 and CO matrices containing GeCO has tentatively been assigned to germanium dicarbonyl on grounds of isotopic substitution and theoretical calculations. SCF and CI methods predict a bent structure for this complex.

Geometries of guanidine and eight of its N-imino derivatives (CH3, SiH3, OH, CN, F, Cl, CHO, and NO2) were calculated using ab initio molecular orbital techniques. MP2, MP4, and CISD geometries indicate that the guanidine molecule is pyramidal at amino groups and π-conjugation through the amidine skeleton is modest. MP2 structures of the eight N-imino guanidines reveal that substituting the hydrogen atom of the imino nitrogen by a functional group leads to a concerted variation of the CN bond distances. Topological electron density analyses indicate that the structural changes calculated upon N-imino substitution are largely due to changes of conjugation onto the amidine π-skeleton. Intermolecular hydrogen bonding involving the imino and amino groups is also found to affect the amidine geometry. Special attention has been paid in the work of 2-cyanoguanidine. The centrosymmetric dimer and a more extended hydrogen-bonded complex have been proposed as simulation of the crystal environment and the respective...

The molecular structure of p-diethynylbenzene has been determined by gas-phase electron diffraction and ab initio MO calculations at the HF/6-31G* and MP2/6-31G*(fc) levels. The two ethynyl groups undergo large-amplitude bending motions, making the equilibrium D2h model inadequate to describe the average structure from electron diffraction. Based on spectroscopic information on low-frequency modes, the electron diffraction data were approximated by a model consisting of a mixture of rigid conformers, differing only in the extent of the symmetric out-of-plane bending of the substituents. This gave the following geometrical parameters: ∠Cortho−Cipso−Cortho = 119.2 ± 0.2°, 〈rg(C−C)〉 = 1.402 ± 0.003 A, rg(Cring−Csp) = 1.431 ± 0.003 A, and rg(C⋮C) = 1.211 ± 0.003 A. The computed re values (MP2) are 119.2°, 1.401 A, 1.430 A, and 1.223 A, respectively, with the Cipso−Cortho bond 0.016 A longer than the central C−C bond. The HF/6-31G* geometries of ethynylbenzene and p-diethynylbenzene indicate that the interact...

The vaporization of DyBr3(s) was investigated in the temperature range between 803 and 1053 K by Knudsen effusion mass spectrometry. The ions Dy+, DyBr+, DyBr+2, DyBr+3, Dy2Br+5, and Br+ were detected and their appearance potentials determined leading to an upper bound for the atomization energy of DyBr3(g). The species DyBr3(g) and (DyBr3)2(g) were identified in the vapor and their partial pressures determined using quantitative vaporization. Enthalpies and entropies of sublimation resulted according to the second‐law and third‐law methods. The enthalpy and entropy changes of the dissociation reaction (DyBr3)2(g) = 2 DyBr3(g) were obtained as ΔdH0298=220.8±6.6 kJ mol−1 and ΔdS0298=163.7±8.5 J mol−1 K−1.

The effect of intermolecular O-H ⋯ O hydrogen bonding on the molecular structure of phenol has been studied by SCF ab initio MO calculations at the HF/6-31G * level. The systems investigated are eight phenol-water complexes and the dimer and trimer of phenol. Optimized geometries show that hydrogen bond formation causes a consistent pattern of changes in the structure of the molecule. When phenol acts as a proton donor, the expected increase ofr (O-H) is accompanied by a slight decrease ofr(C-O) and of the internal ring angles at theipso andpara positions, and by an increase ofr(Cipso©ortho). These changes suggest that the relative contribution of polar canonical forms to the electronic structure of the molecule increases upon hydrogen bond formation, since this enhances the strength of the interaction. The opposite changes occur when phenol acts as a proton acceptor, except forr(O-H), which is the same as in the free molecule. If phenol acts as a proton donorand as a proton acceptor, the two hydrogen bonds become stronger due to a synergic effect. In this case, however, the structural deformation of the molecule is less pronounced than in the previous cases, due to the opposite effect of the two hydrogen bonds. The available experimental evidence on gas-crystal structural differences for phenol is critically reviewed, also in the light of the present results on gas-phase complexes.

The molecular structure of glutamic acid in the non-zwitterionic form has been optimized by using the semiempirical MNDO and AMI methods and an ab initio calculation at the 4–31G level. The results were compared with previous reported data for other amino acids. The ab initio optimized structure was used as the starting point for a further force field calculation, and vibrational frequencies and theoretical assignments were thus obtained. In order to compare these results with experiments, the FT-IR spectrum of glutamic acid in an argon matrix was recorded and the measured frequencies were successfully compared with theoretical values, which were previously scaled by using a set of scaling factors.

The molecular conformation of N,N′-diformohydrazide has been studied by ab initio molecular orbital calculations including electron correlation corrections up to the MP4/6-31 G*//MP2/6-31G* level. The calculations indicate that the stable structures of the molecule are non-planar at nitrogen and show twisted conformation about the N–N bond. Structures and rotational barrier heights have been compared with those of N,N′-dimethylhydrazine, calculated at uniform levels of theory. A simulation of the crystal field has been proposed to investigate the effects of intermolecular hydrogen bonding on the structural properties of N,N′-diformohydrazide. Our crystal model, studied by HF/4-31G* calculations, shows that hydrogen bonding causes not only a concerted change in the length of the C–N, CO and N–H bonds, but also a significant conformational change. In agreement with the neutron diffraction structure, the crystal molecule of our model is predicted to be planar. The overall geometrical perturbations due to self association reveal an increase of π-conjugation between the nitrogen and carbonyl groups which can rationalize the conformational change. The effect of intermolecular hydrogen bonding on the vibrational spectrum is also discussed.

The transmission of substituent effects through a benzene framework has been studied by a novel approach, based on the structural variation of the Ph group in p-Ph-C(6)H(4)-X molecules. The molecular structures of many 4-substituted biphenyls were determined from MO calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. The twist angle between the phenyl probe (ring B) and the benzene framework carrying the substituent (ring A) was set at 90° to prevent π-electron transfer from one ring to the other and at 0° to maximize it. The structural variation of the probe is best represented by a linear combination of the internal ring angles, termed S(F)(BIPH(o)) and S(F)(BIPH(c)) for the orthogonal and coplanar conformations of the molecules, respectively. Regression analysis of these parameters using appropriate explanatory variables reveals a composite field effect, a substantial proportion of which is originated by resonance-induced π-charges on the carbon atoms of ring A. Field-induced polarization of the π-system of ring A also contributes to the structural variation of the probe. Thus, the S(F)(BIPH(o)) parameter is very well reproduced by a linear combination of the π-charges on the ortho, meta, and para carbons of ring A, an uncommon example of a quantitative relationship between molecular geometry and electron density distribution. Comparison of S(F)(BIPH(o)) with the gas-phase acidities of para-substituted benzoic acids shows that, while the deprotonating carboxylic probe is more sensitive to π-electron withdrawal than donation, the phenyl probe is equally sensitive to both. While the ability of the orthogonal biphenyl system to exchange π-electrons with the para substituent is the same as that of the benzene ring in Ph-X molecules, an increase by about 18% occurs when the conformation is changed from orthogonal to coplanar. The structural variation of the probe becomes more complicated, however. This is due to π-electron transfer from one ring to the other, which is shown to introduce quadratic terms in the regressions.

In this study, the molecular structure of p-diisocyanobenzene has been determined by gas-phase electron diffraction and quantum chemical calculations. The electron diffraction intensities from a previous study by Colapietro et al. (J Mol Struct 125:19–32, 1984) have been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from computations. The equilibrium structure of the molecule has D 2h symmetry, whereas the average geometry in the gaseous phase is best described by a non-planar model of C 2v symmetry. The lowering of symmetry is due to large-amplitude motion of the substituents out of the plane of the benzene ring. The non-planar model has an internal ring angle at the ipso position, ∠aC2–C1–C6 = 120.6 ± 0.2°, about 1° smaller than that from the previous study, but consistent with the quantum chemical calculations. The mean length of the ring C–C bonds and the length of the triple bond are accurately determined as 〈r g(C–C)〉 = 1.398 ± 0.003 A and r g(N≡C) = 1.177 ± 0.002 A, respectively. Comparison with the gaseous isoelectronic molecules p-diethynylbenzene and p-dicyanobenzene shows that the differences in the mean lengths of the ring C–C bonds and in the lengths of the triple bonds determined by electron diffraction are equal or closely similar to the corresponding differences from quantum chemical calculations. The present experimental value of the ipso angle in free p-diisocyanobenzene is slightly, but significantly smaller than that obtained by X-ray crystallography. The difference is confirmed by computational modeling of the crystal structure and appears to be due to –N≡C···H–C intermolecular interactions in the crystal.

The solvation of glycine in two ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium acetate, [C(1)C(4)Im][OAc], and 1-butyl-3-methylimidazolium trifluoroacetate, [C(1)C(4)Im][TFA], was studied by a combination of experimental and theoretical methods. The solubility of glycine in both ILs was determined at 333.15 K to be (8.1±0.5) and (1.0±0.5) wt % in [C(1)C(4)Im][OAc] and [C(1)C(4)Im][TFA], respectively. By IR spectroscopy it was found that, when dissolved in the ILs, glycine was mainly present in its zwitterionic form. Structural and energetic aspects of the solvation of glycine in the ILs and in mixtures of ILs and water were investigated by ab initio calculations and molecular dynamic simulations. It was observed that the firstly solvation shell around glycine consisted predominantly of acetate or trifluoroacetate anions, which formed hydrogen bonds either with the carboxylic group of neutral glycine or with the protonated ammonium group of the zwitterionic form. When water is present in the solutions, hydrogen bonds between water and the anion prevail. The overall energy of the system was decomposed into its components between pairs of species. It was established that the dominant contribution to the interaction energy between glycine and the IL was due to hydrogen bonds with the anions and the statistics of hydrogen bonds were analysed.

We report a joined X-ray diffraction and molecular dynamics study on the series of 1-ethyl-3-methylimidazolium alkyl sulfates (alkyl = ethyl, butyl, hexyl, octyl) ionic liquids. A general good agreement between experimental and theoretical structure functions has been found for each term of the series in all ranges of q values. Once the quality of the employed force field in reproducing structural data was tested, we used dynamics simulations to access information on morphology and properties of these systems. The series of ionic liquids presents nanoscale structural heterogeneity, whose size depends on the anion alkyl chain size. Analyzing our simulation data on the basis of alkyl chain length, we propose a structural model consistent with the presence of low q peaks.

The structural properties and intramolecular hydrogen bonding of a series of structures of naphthazarin molecule were investigated by ab initio HF-SCF methods. The geometries of theC 2v ,C 2h ,D 2h , andC s symmetry structures were optimized using split-valence basis sets. MP2/6-31G*// HF/6-31G single-point energy calculations indicate that theC 2v isomer (5,8-dihydroxy-1,4-naphthoquinone) is the lowest energy structure of the molecule and that theC 2h symmetry one (4,8-dihydroxy-1,5-naphthoquinone), lying 37 kJ/mol above theC 2v form, is the other stable isomer of naphthazarin. At the HF/6-31G level, the intramolecular proton exchange between two equivalentC 2v structures is a two-step process where each proton can be independently transferred through an unsymmetrical potential having a 1,5-quinone intermediate, theC 2h symmetry structure, and two equivalent transition states ofC s symmetry, with a barrier height equal to 38 kJ/ mol (MP2/6-31G*//HF/6-31G). The study of naphthazarin molecule is flanked by a theoretical investigation on theC 2v andC 2h isomers of the parent naphthoquinone and dihydroxynaphthalene molecules. The SCF vibrational spectrum of the ground state of naphthazarin, harmonic frequencies, and infrared and Raman band intensities were computed at the HF/6-31G level. The results of the calculations are compared with the matrix isolation FT-IR spectroscopy measurements and with the infrared and Raman spectra of the crystal molecule.