Chemical Physics Letters (v.456, #4-6)
Editorial Board (IFC).
Predissociation of chlorobenzene, beyond the pseudo-diatomic model by O. Anders Borg; Daniel Karlsson; Magnus Isomäki-Krondahl; Jan Davidsson; Sten Lunell (123-126).
The predissociation of chlorobenzene has been investigated by mean of femtosecond pump–probe spectroscopy and quantum chemical calculations.Dissociation of chlorobenzene via the lowest singlet excited state has been investigated by means of pump–probe femtosecond spectroscopy and spin–orbit corrected ab initio quantum chemistry. We have found that the so far accepted model with a 1ππ∗ → 3π/nσ∗ reaction mechanism has to be amended. We suggest that the mechanism goes via a transition from 1ππ∗ to a πσ∗ state that is to 90% a singlet. Further, three nuclear degrees of freedom required to describe the dissociation have been defined.
Selective IR-induced isomerization of 1,2-dichloropropane isolated in xenon matrix by Adriana Olbert-Majkut; Igor D. Reva; Rui Fausto (127-134).
Infrared irradiation of 1,2-dichloropropane isolated in a xenon matrix at 20 K results in selective conformational isomerization from Trans (T) to Gauche+ (G+), while conformer Gauche− (G−) remains intact. Factors responsible for such selectivity are discussed. The graphics shows calculated potential energy profile (red line) of the compound in polar coordinates, as a function of the Cl−C−C−Cl dihedral angle.The conformations of monomeric 1,2-dichloropropane isolated in low temperature xenon matrix were characterized experimentally using FTIR spectroscopy. The interpretation of the experimental spectra was aided by ab initio MP2/6-311++G(3df,3pd) calculations. Relative energies of three structures, differing by the orientation of the Cl−C−C−Cl dihedral angle, fall within 0–6 kJ mol−1 range. The spectral signatures of all three conformers were identified experimentally. Infrared irradiation of the matrix isolated compound resulted in selective conversion of the most stable Trans conformer into the higher energy Gauche+ rotamer, while the Gauche− conformer remained unaffected. This result was interpreted in terms of calculated energy barriers and dipole moments.
Reaction force constant and projected force constants of vibrational modes along the path of an intramolecular proton transfer reaction by Pablo Jaque; Alejandro Toro-Labbé; Peter Politzer; Paul Geerlings (135-140).
The significance of the similarity between the reaction force constant κ(ξ) and the variation of the force constant of the reaction coordinate, κξ (ξ) , is discussed in detail for an intramolecular proton transfer reaction.We have explored the relationships between the reaction force F(ξ), the reaction force constant κ(ξ) and the projected force constants of the intramolecular proton transfer HO−N＝S → O＝N−SH along the intrinsic reaction coordinate ξ. The structural changes and energetics associated with the reaction are analyzed in terms of the three regions defined by F(ξ): reactant, transition and product. The significance of the similarity between κ(ξ) and the variation of the force constant associated to the reaction coordinate mode, kξ (ξ), is discussed in detail.
The cyclohexadienylidenemethanone radical cation is a more stable distonic isomer of ionized benzaldehyde by Robert Flammang; Noémie Dechamps; Pascal Gerbaux; Pham Cam Nam; Minh Tho Nguyen (141-145).
1,3-Cyclohexadienylidenemethanone radical cation has been detected for the first time by mass spectrometry, and this distonic C7H6O •+ isomer is found 43 kJ mol−1 more stable than ionized benzaldehyde.Quantum chemical calculations (G3B3 and B3LYP/6-311++G(d,p)) and tandem mass spectrometric experiments demonstrate the higher stability of 1,3-cyclohexadienylidenemethanone radical cation compared to ionized benzaldehyde. Characterized by a heat of formation of 833 kJ mol−1 (at 298 K), this ketene C7H6O •+ isomer is found 43 kJ mol−1 more stable. It has been generated by ion/molecule reaction between ionized benzaldehyde and neutral methanol, a new example of proton transport catalysis tautomerization. The greater stability of the ketene ion is due to the low IE of the neutral (7.49 eV).
Coulomb crystals of few particles: Closed-form expressions for equilibrium energies and geometries, and vibrational force constants by J. Cioslowski; M. Buchowiecki (146-149).
Analytical expressions for properties of clusters of few particles interacting through a pairwise potential of the form ϵ ( r ) = ( 1 / 3 ) ( r 2 + 2 r - 1 ) are derived.Analytical expressions for equilibrium energies and geometries, and the corresponding vibrational force constants are derived for clusters of between three and eight particles interacting through a pairwise potential of the form ϵ ( r ) = ( 1 / 3 ) ( r 2 + 2 r - 1 ) . In the case of five-, seven-, and eight-particle clusters, these expressions are functions of single parameters that are the larger real roots of respective twelfth-degree polynomials.
IR-photodissociation and photodetachment spectroscopy of Cl− · (NH3) x (IR: x = 1–4, PD: x = 1) by Martin Tschurl; Ulrich Boesl (150-155).
The shift of ν(sym.stretch) of chloride-ammonia clusters fits an exponential curve converging to −118 cm−1. That of condensed ammonia is between 100 and 40 cm−1.Complexes of ammonia molecules and one chloride ion have been studied by photodetachment and IR-photodissociation spectroscopy. For the smallest anionic complex, the stabilisation energy with respect to the bare chloride ion and vibrational frequencies have been determined. Two bands showed a splitting due to rotational branches, which could be represented by simulation. Rotational constants obtained by former ab initio calculations [P.S. Weiser, D.A. Wild, P.P. Wolynec, E.J. Bieske, J. Phys. Chem. A 104 (2000) 2562] are confirmed and rotational constants of a vibrationally excited state are supplied. IR-photodissociation spectra of clusters with up to four ammonia molecules per chloride ion were recorded.
Computational study on the kinetics of the reaction between Ca2+ and urea by Alvaro Cimas; José A. Gámez; Otilia Mó; Manuel Yáñez; Jean-Yves Salpin (156-161).
Statistical kinetic theory calculations on the reaction of Ca2+ with urea permit to discriminate between processes in which a neutral is lost from Coulomb explosions. The kinetically preferred products are NH3 + [CaOCNH]2+, which are the fifth products in order of stability, whereas the most stable ones, NH 4 + + [ CaOCN ] + and NH 4 + + [ CaNCO ] + , appear only in residual quantities.A computational study, in the framework of statistical kinetic theories, of the reaction of Ca2+ with urea has been carried out. The kinetically preferred products are NH3 + [CaOCNH]2+, which are the fifth products in order of stability. The second kinetically preferred products are [ CaNH 2 + ] + [ NH 2 CO ] + , followed by [ CaNH 3 ] 2 + + HNCO , whereas the most stable ones, NH 4 + + [ CaNCO ] + and NH 4 + + [ CaOCN ] + , appear only in residual quantities. These estimates are in agreement with the experimental evidence and provide a suitable mechanism to understand the competition between Coulomb explosion and neutral loss processes.
Exact statistical mechanical lattice model and classical Lindemann theory of melting of inert gas solids by Lawrence J. Dunne; John N. Murrell; George Manos (162-165).
The melting points of the heavy inert gases and other effectively spherical molecular species are proportional to the depths of their diatomic potential wells.A modified form of Lindemann’s model shows that the melting points of the heavy inert gases and other effectively spherical molecular species are proportional to the depths of their diatomic potential wells. The success of the model when compared with experiment seems to rely on the almost constant value of the ratio of the fractional volume and entropy changes during fusion. The Lindemann proposal can be incorporated into an exactly treated statistical mechanical lattice model utilising expandable clusters which reproduces the solid–liquid melting phenomenon for argon with a realistic volume change and melting line.
Unusual fluorescence anisotropy spectra of three-component donor–mediator–acceptor systems in uniaxially stretched polymer films in the presence of energy transfer by Piotr Bojarski; Michał Sadownik; Simeonika Rangełowa-Jankowska; Leszek Kułak; Katarzyna Dasiak (166-169).
Emission anisotropy spectra, three-component systems, energy migration, energy transfer, Monte-Carlo simulations.Energy transfer was studied for donor–mediator–acceptor systems in uniaxially stretched polymer films. The systems differ in the ability of mediator transition moment to orientate in the matrix. It was found that acceptor fluorescence remains polarized in the stretched matrix irrespectively of mediator. This means that information on the orientation of electric vector of the exciting light was conserved after energy transfer. In disordered system sensibilized fluorescence of mediator and acceptor is strongly depolarized. The effect of transition moments correlation on 〈κ 2〉 in the stretched matrix is presented using Monte-Carlo simulation.
Born–Oppenheimer molecular dynamics of phenol in a water cluster by Sílvia Gomes Estácio; B.J. Costa Cabral (170-175).
Born–Oppenheimer molecular dynamics for a phenol molecule in a water cluster is reported. The dynamics of the system illustrates the role played by phenol as an hydrophobic/hydrophylic probe. The HB dynamics related to water–water and phenol–water interactions exhibits some significant differences. The vibrational spectra calculated from the Fourier transform of time correlation functions are compared with experimental information on small phenol–water clusters.Born–Oppenheimer molecular dynamics for a phenol molecule in a cluster with 32 water molecules is reported. The results for the dynamics provide new theoretical informations on the role played by phenol as an hydrophobic/hydrophylic probe. Significant differences between the short-time hydrogen bond dynamics related to water–water and phenol–water interactions are observed. The vibrational spectra calculated from the Fourier transform of time correlation functions were compared with experimental data on phenol–water clusters and it was found that the average red-shift of the phenol ν OH frequency (78 ± 36 cm−1) is less important than what is observed in small phenol–water clusters at low temperatures (133–312 cm−1).
Computation of the reduction free energy of coenzyme in aqueous solution by the QM/MM-ER method by Hideaki Takahashi; Hajime Ohno; Ryohei Kishi; Masayoshi Nakano; Nobuyuki Matubayasi (176-180).
One-electron reduction free energy Δμ of flavin in aqueous solution has been computed by the QM/MM-ER method.In a recent development we proposed a quantum chemical approach to compute free energy change for chemical reactions in condensed phases by combining the QM/MM method with the theory of energy representation (QM/MM-ER). We extend in this Letter the novel approach to compute reduction free energy of isoalloxazine ring of FAD (flavin adenine dinucleotide) immersed in water within the framework of the QM/MM-ER method. The characteristic feature of our approach is that the excess electron to be attached on the FAD is identified as a solute. The reduction free energy has been obtained as −80.1 kcal/mol in the aqueous solution.
Metal–metal bonding in metal–string complexes M3(dpa)4X2 (M = Ni, Co, dpa = di(2-pyridyl)amido, and X = Cl, NCS) from resonance Raman and infrared spectroscopy by Szu-Hsueh Lai; Chung-Jen Hsiao; Jung-Wei Ling; Wen-Zhen Wang; Shie-Ming Peng; I-Chia Chen (181-185).
Infrared and Raman spectra for metal string complexes Ni3(dpa)2Cl2, Ni3(dpa)2(NCS)2, Co3(dpa)2Cl2 and Co3(dpa)2(NCS)2 are presented.Infrared and Raman spectra for metal–string complexes M3(dpa)4X2 (M = Ni, Co, dpa = di(2-pyridyl)amido, and X = Cl, NCS) are studied. We assign the Ni3 asymmetric stretching vibration to infrared lines at 304 and 311 cm−1 for Ni3(dpa)2Cl2 and Ni3(dpa)2(NCS)2, respectively. A Raman shift at 242 cm−1 is assigned to the Ni3 symmetric stretching mode. For Co3 complexes a line for the Co3 asymmetric stretching mode appears at 313 and 331 cm−1 for Co3(dpa)2Cl2 and Co3(dpa)2(NCS)2, respectively.
On the role of contact line tension and 2D defects in the formation of the water depletion layer on hydrophobic surfaces by Edward Bormashenko (186-188).
The role of line (contour) tension in formation of a depletion layer on hydrophobic surfaces is discussed.It is demonstrated that formation of nano-voids in the depletion liquid layer on the hydrophobic surfaces may be due to the phenomenon of the contact line tension. The mean radius of 2D circular void is calculated. It coincides with characteristic dimensions of nano-voids in depletion liquid layers on the hydrophobic surfaces reported experimentally.
Interaction and morphology of polyethylenimine/DNA complexes as studied by solid-state NMR spectroscopy by Min Peng; Qun Chen (189-192).
By employing 1H wide-line and 31P DD/MAS NMR, the interaction and morphology of a series polyethylenimine (PEI)/DNA complexes used as gene-delivery system were characterized on the molecular level.Solid-state 1H wide-line and 31P magic angle spinning NMR were applied to a series of PEI(polyethylenimine)/DNA complexes. The experimental results revealed that the higher the nitrogen/phosphorus (N/P) molar ratio is, the more phosphorus atoms of DNA are engaged in the electrostatic interaction with PEI. 1H spin–diffusion experiments manifested that the aggregation degree of DNA in the complexes decreases greatly when N/P ratio increases from 0.5 to 3 and changes only slightly with further increase of N/P ratio, indicating that DNA disperses in the matrix of PEI on the molecular level at higher N/P ratio.
Bi2Sn2O7 nanoparticles attached to SnO2 nanowires and used as catalysts by Hyoun Woo Kim; Seung Hyun Shim; Jong Woo Lee; Jae Young Park; Sang Sub Kim (193-197).
We report a novel method to prepare SnO2 nanowires with Bi2Sn2O7 nanoparticles attached at their tips.We introduce a simple method of synthesizing SnO2 nanowire-Bi2Sn2O7 nanoparticle composites based on the principle that SnO2 nanowires can be grown by using Bi as catalysts. A mixture of Bi and Sn powders was thermally evaporated, and the effects of growth temperature on the morphology and structure of the products were investigated. We obtained Bi2Sn2O7-tipped SnO2 nanowires at 700 °C through a vapor–liquid–solid (VLS) process, whereas particle-free SnO2 nanowires were produced at higher temperatures. We have investigated the oxygen sensing properties of the as-synthesized product.
High-performance titanium dioxide photocatalyst on ordered mesoporous carbon support by In-Soo Park; Sun Young Choi; Jeong Sook Ha (198-201).
Anatase TiO2 photocatalysts on ordered mesoporous carbon were synthesized and they showed superior photoactivity in removing Rhodamine 6G dye solution.Anatase TiO2 photocatalysts supported with the ordered mesoporous carbon, CMK-3, were synthesized by the incorporation of TiO2 into CMK-3 followed by heating at 700 °C. The structural properties of the TiO2 on CMK-3 were investigated by X-ray diffraction, nitrogen physisorption and electron microscopy techniques. In particular, TiO2 was observed both inside and the external surface of CMK-3. The photocatalytic activity of TiO2 on CMK-3 under UV-light exhibited higher efficiency in removing the Rhodamine 6G dye solution than the commercial photocatalyst P25 and TiO2 on activated carbon. It was attributed to the synergistic effect of large surface area adsorption provided by mesoporous CMK-3 and the distinctive location of TiO2 on the external surface of CMK-3.
Fabrication of Au–Cu2O core–shell nanocube heterostructures by Y.Q. Wang; K. Nikitin; D.W. McComb (202-205).
Typical HAADF images of core–shell nanocube heterostructures, showing two types of morphologies.Au–Cu2O core–shell nanocubes with edge dimensions of 15–45 nm have been produced by annealing a copper grid at 300 °C in air in the presence of tetraoctylammonium bromide-stabilized gold nanoparticles. The microstructure of these novel heterostructures, especially the interface between gold nanoparticle core and Cu2O shell, has been investigated in detail using high-resolution transmission electron microscopy (HRTEM). Chemical analyses have been performed on a single Au–Cu2O core–shell nanocube using energy dispersive X-ray spectroscopy (EDS) in the scanning transmission electron microscopy (STEM). Based on the experimental results, a growth mechanism is proposed.
Theoretical study of absorption and emission spectra of the monomer of PFBT by Jing Wang; Jiande Gu; Jerzy Leszczynski (206-210).
Conjugated polymers (CPs) have been used as highly responsive optical sensors for chemical and biological targets. The density functional theory (DFT), the time-dependent density functional theory (TDDFT) and the singly excited configuration interaction (CIS) approach were employed to simulate the absorption and emission spectra of a model monomer unit of the typical CP, poly[9,9′-bis-(6′-N,N,N-trimethylammonium)hexyl]fluorene-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT). Various basis sets were applied in the calculations and their effects on the predictions for the optical properties of FBT are discussed. The results suggest that the TD-B3LYP method with basis sets larger than 6-311G(d,p) provides a suitable approach for investigations of the studied system.Absorption and emission spectra of the monomer of PFBT have been theoretically studied by TDDFT approach.
Adsorption dynamics of O2 on Cu(1 0 0): The role of vacancies, steps and adatims in dissociative chemisorption of O2 by M. Ahonen; M. Hirsimäki; A. Puisto; S. Auvinen; M. Valden; M. Alatalo (211-214).
Adsorption dynamics and kinetics of O2 adsorption on annealed and defect-rich Cu(1 0 0) are investigated experimentally and using density functional theory.Adsorption dynamics experiments on Cu(1 0 0) at 300 K indicate that surface defects induced by 3.4 keV Ar+-ion bombardment strongly enhance the dissociative chemisorption probability of O2. Energy selective molecular beam surface scattering experiments reveal a defect induced low-barrier dissociation pathway leading to enhanced dissociation of O2 molecules with translational energy up to 60 meV. Density functional theory calculations attribute the decrease in O2 dissociation barrier to the weakening of O–O bond at Cu vacancies, thus resolving the contradiction between experimental observations and theoretical predictions of the height of the barrier to O2 dissociation on Cu(1 0 0).
Light induced excited spin state trapping in the binuclear spin crossover compound [Fe(bpym)(NCS)2]2(bpym) exhibiting a high-spin ground state by S. Mouri; N. Ould Moussa; G. Molnár; J.A. Real; A.B. Gaspar; A. Bousseksou; K. Tanaka (215-219).
We confirmed LIESST and reverse-LIESST phenomena in the binuclear spin crossover complex [Fe(bpym)2(NCS)2](bpym) whose ground state is HS–HS state.A photo-magnetic effect is evidenced using near-infrared light in the binuclear complex [Fe(bpym)(NCS)2]2(bpym). This compound has a 5T2g–5T2g ground state and exhibits no thermal spin crossover – in contrast to the analogous [Fe(bpym)(NCSe)2]2(bpym). The estimated photo-conversion ratio is ca. 30%. By means of magnetic susceptibility measurements as well as Raman and infrared absorption spectroscopies, the nature of the photo-induced phase was established as the 5T2g–1A1g state, which means that only one iron center is converted to low-spin. The photo-induced state was completely converted back to the ground state either by visible light excitation or by heating.
Photodynamic release of fullerenes from within carbon nanohorn by Eijiro Miyako; Hideya Nagata; Ken Hirano; Yoji Makita; Takahiro Hirotsu (220-222).
We have found that oxidized carbon nanohorns can exhibit laser-triggered accelerated release of encapsulated fullerenes from within their inner nanospaces.We have found that oxidized single-wall carbon nanohorns (SWNHox) can exhibit a near-infrared (NIR) laser-triggered accelerated release of encapsulated fullerenes (C60) from within their inner nanospaces. After the NIR laser irradiation of an aqueous SWNHox encapsulating C60 solution/toluene biphasic system, C60 molecules are enriched in the toluene phase. NIR laser-driven SWNHs encapsulating substrates could initiate the development of a new range of drug-delivery systems.
Dipole polarizabilities of noble gas endohedral fullerenes by Hong Yan; Shengping Yu; Xin Wang; Yang He; Wen Huang; Mingli Yang (223-226).
The induced field inside the C60 cage makes the incorporated noble gas atoms less polarized than the corresponding free atoms.First-principles calculations were performed on the polarizabilities of noble gas endohedral complexes, X@C60 (X = He–Kr). The polarizability of X@C60 increases from He–Kr, but is distinctly smaller than the sum of the X atoms and C60, unlike many other non-bonded systems for which an additive rule holds. Compared to C60, the increased polarizabilities in X@C60 are mainly from the enhanced charge transfer contribution of the cage and the local polarization of the interior X atoms, though the interior atoms are found less polarized than the corresponding free ones.
Proton exchange in hybrid sulfonated poly(ether ether ketone)–silica membranes by 1H solid-state NMR by Maria Baias; Dan E. Demco; Irene Colicchio; Bernhard Blümich; Martin Möller (227-230).
The Eyring function is used for obtaining enthalpy of activation for proton exchange in sulfonated poly(ether ether ketone)–silica membranes by NMR.Enthalpy of activation for proton exchange processes in fully hydrated hybrid sulfonated poly(ether ether ketone)–silica (SPEEK/SiO2) membranes were measured from the 1H NMR spectra under magic angle sample spinning (MAS). For the first time Eyring function is used for this purpose. Two exchange processes between different water pools were detected. The isotropic chemical shift of the 1H spectrum allows us to obtain information about the normalized enthalpy of activation characterizing the water exchange. These results show that the proton exchange membranes performances could be improved by addition of small concentrations of silica in the range of 5–10 wt.%.
Anomalous photoconductivity of cobalt-doped zinc oxide nanobelts in air by Liang Peng; Jia-Li Zhai; De-Jun Wang; Ping Wang; Yu Zhang; Shan Pang; Teng-Feng Xie (231-235).
Cobalt-doped ZnO nanobelts exhibit the negative photoconductivity to 630 nm light. This negative photoconductivity is attributed to photodesorptions the water molecules adsorbed on the surface of nanobelts.The decrease of photoconductivity from 1.3 to 0.25 μA in ambient air or in water vapor atmosphere has been observed when the cobalt-doped zinc oxide nanobelts are irradiated with 630 nm light. This kind of negative photoconductivity is attributed to the photodesorption of water molecules from nanobelts’ surface, and the mechanism was discussed. This result supplies a potential method to detect water vapor with a low concentration in environment.
The binding domain of the HMGB1 inhibitor carbenoxolone: Theory and experiment by Luca Mollica; Alessandro Curioni; Wanda Andreoni; Marco E. Bianchi; Giovanna Musco (236-242).
We present a combined computational and experimental study of the interaction of the Box A of the HMGB1 protein and carbenoxolone, an inhibitor of its pro-inflammatory activity. The computational approach consists of classical molecular dynamics (MD) simulations based on the GROMOS force field with quantum-refined (QRFF) atomic charges for the ligand. Experimental data consist of fluorescence intensities, chemical shift displacements, saturation transfer differences and intermolecular Nuclear Overhauser Enhancement signals. Good agreement is found between observations and the conformation of the ligand–protein complex resulting from QRFF–MD. In contrast, simple docking procedures and MD based on the unrefined force field provide models inconsistent with experiment. The ligand–protein binding is dominated by non-directional interactions.Classical molecular dynamics with a quantum-refined force field, NMR and fluorescence provide consistent results for the interaction of HMGB1 (Box A) and carbenoxolone.
The role of residue Thr122 of methylamine dehydrogenase on the proton transfer from the iminoquinone intermediate to residue Asp76 by Gustavo Pierdominici-Sottile; Marcelo A. Martí; Juliana Palma (243-246).
Calculations indicate that Thr122 has a deleterious effect on the proton transfer that determines the rate of the catalyzed reaction.We present the results of combined molecular dynamics and full-quantum calculations aimed at elucidating the role of residue Thr122 of the enzyme methylamine dehydrogenase. Calculations were performed on the native structure and the T122A mutant. We found that the presence of Thr122 has a deleterious effect on the proton transfer step that is proposed to determine the rate of the reaction. Besides, at the PM3 level, the substitution of Thr122 by Ala does not significantly modify the preference of the proton by atom OD2 of Asp76. Transmission coefficients obtained form MP2/6-31G(d,p)//PBE/DZP minimum energy paths show that proton tunneling is significant.
Interplay of master regulatory proteins and mRNA in gene expression: 3D Monte Carlo simulations by Vladimir P. Zhdanov (247-252).
Cross-sections of the spherical cell including the nucleus (central white area), ribosomes (plus signs), cytoplasm (peripheral white area), and mRNA (filled circles).We present 3D spatio-temporal Monte Carlo simulations of gene expression for a generic model with negative feedback between the mRNA and regulatory-protein production. The attention is focused on the role of mRNA diffusion between the nucleus and cytoplasm. For rapid diffusion, the model predicts that the fluctuations of the mRNA and protein numbers are comparable to those corresponding to the Poissonian distribution. With decreasing diffusion rate, the fluctuations become much larger. Specifically, the time dependence of the mRNA and protein numbers exhibits huge bursts.
1H homonuclear dipolar decoupling at high magic-angle spinning frequencies with rotor-synchronised symmetry sequences by Subhradip Paul; Rajendra Singh Thakur; P.K. Madhu (253-256).
Symmetry based rotor synchronised RN n ν sequences were applied to obtain high resolution 1H spectra in solid-state NMR. The experimental and simulated data shows the potential of such RN n ν sequences in obtaining high resolution spectra at high spinning speeds.We demonstrate here application of symmetry-adapted sequences of the form RN n ν to obtain high-resolution 1H spectra in solid-state nuclear magnetic resonance under high-speed magic-angle spinning. Experimental results are shown for samples of alanine and glycine for spinning speeds up to 30 kHz with radio-frequency nutation rates of around 100 kHz.
Interplay between cation-π and hydrogen bonding interactions by Daniel Escudero; Antonio Frontera; David Quiñonero; Pere M. Deyà (257-261).
The interplay between two important non-covalent interactions has been studied by means of ab initio calculations. We have found interesting synergetic effects between the cation-π and the hydrogen bonding interactions in pyrrol and indol complexes, when they interact simultaneous with cations (via cation-π) and water (via H-bonding).The interplay between two important non-covalent interactions involving aromatic rings is studied by means of ab initio calculations (MP2/6-31++G∗∗). They demonstrate that synergetic effects are present in complexes where cation-π and hydrogen bonding interactions coexist. These synergetic effects have been studied using the ‘atoms-in-molecules’ theory and the molecular interaction potential with polarization partition scheme.
Decomposition of a NMR signal comprising a single resonance in exchange with a Pake doublet: Application to the analysis of 1H NMR spectra of water molecules embedded in synthetic clays by Grégory Trausch; Daniel Canet; Pierre Turq (262-267).
NMR of water in clays include several overlapping resonances, possibly with a Pake doublet. Proportions and dipolar coupling were determined.Conventional 1H NMR spectra of water in clays generally consist of several broad overlapping resonances. However, when a type of water is partially oriented, it leads to a Pake doublet superposed to the resonances corresponding to different types of non-oriented water. With the help of a recent method based on nutation experiments, the proportions of the different kinds of water could be determined. Thus, we are able to determine interesting NMR parameters like dipolar couplings, exchange rate, and line broadening. These determinations are complemented by spin relaxation times and self-diffusion measurements which bring additional information about the dynamical behavior of water.
Inversion of the sign of the solid-state circular dichroism at low temperature by Takunori Harada; Tomohiro Sato; Reiko Kuroda (268-271).
Temperature-dependent CD spectra of Ni(H2O)6 · SeO4 single crystal (P41212) in the temperature range from 240 K to 87 K.α-Ni(H2O)6 · SO4 and its selenate derivative exhibit chirality only in the solid-state. We have observed, for the first time, a sign inversion of CD (circular dichroism) in the 3A2g → 3T1g(P) Ni(II) d–d transition at near liquid nitrogen temperatures. The novel finding was achieved by building a new cooling unit to a solid-state specialized Universal Chiroptical Spectrophotometer (UCS-1) [R. Kuroda, T. Harada, Y. Shindo, Rev. Sci. Instrum. 72 (2001) 3802.] and by formulating an analytical procedure to obtain artifact-free CD signals based on the Mueller matrix method. The sign inversion is remarkable as the crystal structure hardly changes from 300 to 100 K. The origin of the sign inversion is discussed.
Author Index (272-277).