Chemical Physics Letters (v.602, #C)

Contents (iii-vii).

Display OmittedA theoretical Density Functional Theory study was performed for a benzene molecule in water cages. Two DFT functionals (B3LYP and BLYP) were employed. The optimized geometries of the studied clusters were used to calculate the aromaticity of benzene in a condensed phase using the aromaticity indices: HOMA, NICS, PDI, and H. The results were compared with aromaticity of a single benzene molecule in the gas phase and in the solvent environment provided by the PCM continuum model. It is argued that high aromaticity of benzene in the gas phase is retained in the water environment.

Controlling mobility via rapidly oscillating time-periodic stimulus by Prasun Sarkar; Alok Kumar Maity; Anindita Shit; Sudip Chattopadhyay; Jyotipratim Ray Chaudhuri; Suman K. Banik (4-9).
We focus on the simulation of the dynamics of a Brownian particle on a periodic symmetric substrate under high-frequency periodic forcing in Kapitza–Landau stratified media through the computation of mobility.Display OmittedTo address the dynamics of a Brownian particle on a periodic symmetric substrate under high-frequency periodic forcing with a vanishing time average, we construct an effective Langevin dynamics by invoking Kapitza–Landau time window. Our result is then exploited to simulate the mobility both for original and effective dynamics which are in good agreement with theoretical predictions. This close agreement and the enhancement of mobility are very robust against the tailoring of amplitude-to-frequency ratio which substantiates the correctness of our calculation. Present results may be illuminating for understanding the dynamics of cold atoms in electromagnetic fields.

Polyol synthesis of silver nanostructures: Inducing the growth of nanowires by a heat-up process by Guh-Hwan Lim; Seong Jun Lee; Insung Han; Shingyu Bok; Jung Heon Lee; Jaewook Nam; Jeong Ho Cho; Byungkwon Lim (10-15).
The polyol synthesis of silver (Ag) nanostructures typically involves the rapid injection of Ag precursor to a preheated, ethylene glycol solution containing polymeric stabilizers and other additives. Here we report that Ag nanowires can be synthesized in high yields by applying a heat-up process in the polyol synthesis. Electron microscopy studies revealed that multiple-twinned Ag seeds were generated preferentially during the heat-up procedure, and then grew into nanowires. We also demonstrate that these Ag nanowires can be applied as electrode materials for the fabrication of flexible and transparent organic field-effect transistors with a reasonably high hole-mobility.

Display OmittedThe interaction between chloroacetylene (C2HCl) and substituted benzenes has been investigated using density functional theory (DFT), MP2, and CCSD(T)/CBS methods. The results derived from these calculations revealed predominant non-covalent π…ClC2H interactions in all cases. The predicted interaction energies for substituted benzene/ClC2H complexes span a narrow range from −1.61 to −3.96 kcal/mol, indicating that the π…ClC2H interaction is comparable in strength to well-documented C–H…π interactions. The trend for interaction energies was found to be hexafluorobenzene–ClC2H < sym-tetrafluorobenzene–ClC2H < sym-trifluorobenzene–ClC2H < sym-difluorobenzene–ClC2H < benzene–ClC2H < sym-dimethylbenzene–ClC2H < sym-trimethylbenzene–ClC2H < sym-tetramethylbenzene–ClC2H < hexamethylbenzene–ClC2H. We have shown that electron-withdrawing groups weaken the complex, whereas electron-donating groups strengthen the interaction energy of the complex.

Protein aggregation and partial globular state in aqueous 1-alkyl-3-methylimidazolium nitrate solutions by Takahiro Takekiyo; Keisuke Fukudome; Kumiko Yamazaki; Hiroshi Abe; Yukihiro Yoshimura (22-27).
Display OmittedWe have investigated the relationship between protein size and the structural modification in concentrated aqueous solutions of ionic liquids (ILs) 1-alkyl-3-methylimidazolium nitrate ([C n mim][NO3] (n  = 2, 4)). Proteins with the radii of gyration (R g) above ∼20 Å form amorphous aggregates in an aqueous [C4mim][NO3] solution at X (mol% IL) = 20, whereas those with R g values below ∼20 Å assume partial globular states. Remarkably, a decrease in the alkyl-chain length causes an increase in the protein size at which protein aggregation occurs. Concentrated [C n mim][NO3] (n  = 2, 4) solutions might control a boundary between the protein aggregation and partial globular states.

Molecular dynamics and free volume in organic glass-formers: A series of oligomer and polymer 1,4-poly(isoprene)s by J. Bartoš; H. Švajdlenková; M. Lukešová; Y. Yu; R. Krause-Rehberg (28-33).
Display OmittedWe present a combined study of the rotational dynamics and free volume in a series of 1,4-poly(isoprene)s using ESR and PALS, respectively. The spectral parameter of mobility, 2A zz′, of the spin probe TEMPO is related to the annihilation of the ortho-positronium (o-Ps) probe. The o-Ps lifetime τ 3(T 50G) ≅ const.1 and τ 3( T x 1 fast ) ≅ const.2 rules are valid independent of chain length and moreover, the T 50G’s coincides with the bend effect at T b 1 L ’s. Finally, the new finding is that the first acceleration at T x 1 slow agrees with a change in the o-Ps lifetime width parameter, σ 3, below the glass transition temperature.

Theoretical study of low-lying excited states of HSX (X = F, Cl, Br, I) by Hengjie Chen; Ajith Perera; Thomas Watson; Rodney J. Bartlett (34-39).
Display OmittedThe twelve electronic excited states of HSX (X = F, Cl, Br, I) are determined using the equation-of-motion coupled-cluster singles, doubles and with non-iterative triple excitations (EOM-CCSD(T)) method. Comparisons have been made with the two most popular multi-reference methods and detailed assignments are performed. The results show that most excitations of those species originate from the two highest occupied molecular orbitals (n  →  σ or n  → Rydberg transitions), valence like, and predominantly single excitation states. A number of Rydberg states have also been predicted. It is confirmed that the benchmark EOM-CCSD(T) results are in excellent agreement with other theoretical methods.

Display OmittedThe RES-TOCSY experiment for accurate determination of heteronuclear nJ HF is reported. The main feature of the proposed technique is the accurate measurement of magnitudes of heteronuclear couplings from the displacement of cross sections of the 2D spectrum and their relative signs from the slopes of their displacement vectors. The experiment is highly advantageous as the couplings of smaller magnitudes hidden within line widths could also be accurately determined, and also in situations when the spectrum does not display any coupling fine structures. The efficient utility of the developed pulse sequence is unambiguously established on fluorine containing aromatic and aliphatic molecules.

On the preferred structure of dicoumarol and implications for enzyme binding: A quantum chemical analysis by Bilal M. Hussain; Kassam Hassam; Qing-Xi Ooi; Richard A. Bryce (45-51).
Display OmittedDicoumarol and related coumarin compounds are potent inhibitors of oxidoreductase NQO1, an enzyme overexpressed in several types of solid tumour. Using density function theory, we study dicoumarol conformation in various tautomeric and ionisation states, in the gas phase and low and high dielectric environments. In aqueous solution, where the monoanionic form of dicoumarol is predominant, we predict a syn rotamer as favoured, which is the conformation crystallographically observed bound to NQO1. Comparison of internal distortion energies and protein docking calculations rationalise why only the syn form is found bound to NQO1.

Display OmittedPhotoreaction pathways of salicylic acid have been investigated by the low-temperature matrix-isolation infrared spectroscopy with an aid of the density-functional-theory calculations. Only the most stable E form existed in an argon matrix. The second stable R form and the fourth stable H form were produced by UV irradiation (λ  > 290 nm). The third stable O form was assumed to return immediately to E form even if it was produced. Ketoketene–water complex was yielded from R form by dissociation of the H and OH parts interacting through intramolecular hydrogen bonding upon prolonged UV irradiation.

Reaction dynamics and relative yields of the H- and CH3-displacement channels in the O + CH3CCH reaction by Nadia Balucani; Francesca Leonori; Vaclav Nevrly; Stefano Falcinelli; Astrid Bergeat; Domenico Stranges; Piergiorgio Casavecchia (58-62).
Display OmittedThe O + CH3CCH reaction has been investigated in crossed molecular beam experiments at a collision energy of 38.7 kJ mol−1. Product angular and translational energy distributions have been measured for the H- and CH3-displacement channels and their relative branching ratio has been determined. The CH3-displacement channel is more important (by a factor of 3) than the H-displacement channel. This is not explained by a preference for the addition on the substituted acetylenic carbon atom, but rather by the different tendencies of the two addition intermediates CH3CCOH and CH3COCH to undergo intersystem crossing to the underlying singlet potential energy surface.

Microwave frequency modulation to enhance Dissolution Dynamic Nuclear Polarization by Aurélien Bornet; Jonas Milani; Basile Vuichoud; Angel J. Perez Linde; Geoffrey Bodenhausen; Sami Jannin (63-67).
Display OmittedHyperpolarization by Dissolution Dynamic Nuclear Polarization is usually achieved by monochromatic microwave irradiation of the ESR spectrum of free radicals embedded in glasses at 1.2 K and 3.35 T. Hovav et al. (2014) have recently shown that by using frequency-modulated (rather than monochromatic) microwave irradiation one can improve DNP at 3.35 T in the temperature range 10–50 K. We show in this Letter that this is also true under Dissolution-DNP conditions at 1.2 K and 6.7 T. We demonstrate the many virtues of using frequency-modulated microwave irradiation: higher polarizations, faster build-up rates, lower radical concentrations, less paramagnetic broadening, more efficient cross-polarization, and less critical frequency adjustments.

Reactions of OH and Cl with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate by Y.J. Zhang; P. Liang; Z.H. Jiang; M. Cazaunau; V. Daële; Y.J. Mu; A. Mellouki (68-74).
Relative rate data for the OH and Cl reactions with the studied esters at 296 K and atmospheric pressure using pentane as reference compound for OH reactions and ethane for Cl reactions with isopropyl formate and isobutyl formate and propane for n-propyl isobutyrate and isopropyl isobutyrate.The rate coefficients for the reactions of OH with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate have been determined using both absolute and relative methods. The relative rate method has been also used to measure the room temperature rate coefficient for the reaction of Cl with the same esters. In addition, a series of runs conducted on the OH-initiated oxidation of isopropyl formate, isobutyl formate and n-propyl isobutyrate showed the formation of acetone from the three reactions. The formation of propanal was also observed for n-propyl isobutyrate.

Roles of allene-group in an intramolecular charge transfer character of a short fucoxanthin homolog as revealed by femtosecond pump-probe spectroscopy by Daisuke Kosumi; Takayuki Kajikawa; Koki Yano; Satoshi Okumura; Mitsuru Sugisaki; Kazuhiko Sakaguchi; Shigeo Katsumura; Hideki Hashimoto (75-79).
Display OmittedUltrafast excited state dynamics of the short fucoxanthin homolog with four conjugated double bonds and its allene-modified analog in various solvents have been studied by femtosecond pump-probe spectroscopy. The results clarified that the short fucoxanthin homolog exhibits a strong intramolecular charge transfer character in an excited manifold even in a nonpolar solvent. Then, the data show that a modification of the allene-group induced the lifetime shortening of the lowest singlet state of the short fucoxanthin homolog. This implies that the allene-group enhances the ICT character of the short fucoxanthin homolog.

A designed fluorescent anthracene derivative: Theory, calculation, synthesis, and characterization by Motoyuki Uejima; Tohru Sato; Masahiro Detani; Atsushi Wakamiya; Furitsu Suzuki; Hajime Suzuki; Tatsuya Fukushima; Kazuyoshi Tanaka; Yasujiro Murata; Chihaya Adachi; Hironori Kaji (80-83).
Display Omitted5,11-Bis(phenylethynyl)benzo[1,2-f:4,5-f]diisoindole-1,3,7,9(2H,8H)-tetraone 1H was designed as an application of the theoretical design principle for fluorescent molecules which is derived from the vibronic coupling density analysis. For solubility reasons, tertiary-butylated 1H, 2,8-di-tert-butyl-5,11-bis(phenylethynyl)benzo[1,2-f:4,5-f]diisoindole-1,3,7,9(2H,8H)-tetraone 1 was synthesized and its fluorescence properties were measured. It is found that the photoluminescence quantum yield of 1 was 96%. We discuss the rationale for designing 1H as a highly efficient fluorescent molecule, and compare the theoretical calculations for 1 with the observed absorption and photoluminescence spectra.