Absolute configuration of (+)‐(S)‐2‐(5‐fluoro‐2‐methoxy‐1,4‐benzodioxan‐2‐yl)­imidazolinium bromide

The title compound, C₁₂H₁₄FN₂O₃⁺·Br^?, crystallizes in the non‐centrosymmetric P2₁2₁2₁ space group. The absolute configuration of the pharmacologically active mol­ecule could be resolved in the hydro­bromide salt, the structure of which is reported. The mol­ecule of the title compound has the S configuration. The molecular packing in the crystal is stabilized by weak N—H?Br [N?Br = 3.240 (4) and 3.302 (4) Å] hydrogen bonding.     

Multimedia Tools for Learning Fluorescence: A Spectrofluorometer Simulator

A new teaching method, using multimedia software, is in progress at our university. Running on a PC computer, it allows self-formation in molecular spectroscopy. A new software package devoted to photoluminescence (ISPL) is currently in progress. The concepts are introduced by using numerous graphs, animations, and simulations. The software allows electronic book facilities (search function, glossary, and bookmarks, for instance) and self-assessment. Tedious and time-consuming training is always necessary to acquire experimental skill. This is particularly true in the case of luminescence because numerous artifacts are possible and the number of parameters to be optimized is very large. In this view, a spectrofluorometer simulator appears to be a valuable tool that makes this training easy and fast: after choosing a set of experimental parameters, the computer displays immediately the corresponding spectrum. The influence of every experimental parameter is simulated: monochromator slit width, excitation or emission wavelengths, xenon source type, photomultiplier tube high-voltage, etc. The nature of solvents, with first- and second-order Rayleigh and Raman scattering, is managed. Sample geometry and concentration, with a corresponding inner filter, are also simulated. Obviously, there is no risk of damaging the virtual photomultiplier tube.     

Superconductivity in high Debye temperature material

The theoretical upper limit of the critical temperature of superconducting materials is discussed. It is concluded that a metal that does not have a high Debye temperature (as do metallic H, B, Be or their alloys) cannot become a high Tc superconductor. Various attempts at enhancing the Tc of Be by quench condensing with various elements, by coevaporation with Li and by treatment in an alloyed form : Be₂₂Re, are presented. Probably for metallurgical reasons, we were unable to approach the predicted maximum critical temperature but believe we have somewhat clarified the question and the field remains promising.     

Water dynamics in silica nanopores: the self-intermediate scattering functions

The dynamics of water molecules confined in approximately cylindrical silica nanopores is investigated using molecular simulation. The model systems are pores of diameter varying between 20 and 40 ? containing water at room temperature and at full hydration, prepared using grand canonical Monte Carlo simulation. Water dynamics in these systems is studied via molecular dynamics simulation. The results of the basic characterization of these systems have been reported in A. A. Milischuk and B. M. Ladanyi [J. Chem. Phys. 135, 174709 (2011)]. The main focus of the present study is the self-intermediate scattering function (ISF), F(S)(Q, t), of water hydrogens, the observable in quasi-elastic neutron scattering experiments. We investigate how F(S)(Q, t) depends on the pore diameter, the direction and magnitude of the momentum transfer Q, and the proximity of water molecules to the silica surface. We also study the contributions to F(S)(Q, t) from rotational and translational motions of water molecules and the extent of rotation-translation coupling present in F(S)(Q, t). We find that F(S)(Q, t) depends strongly on the pore diameter and that this dependence is due mainly to the contributions to the ISF from water translational motion and can be attributed to the decreased mobility of water molecules near the silica surface. The relaxation rate depends on the direction of Q and is faster for Q in the axial than in the radial direction. As the magnitude of Q increases, this difference diminishes but does not disappear. We find that its source is mainly the anisotropy in translational diffusion at low Q and in molecular reorientation at higher Q values.     

Non-Covalent Binding of Tripeptides-Containing Tryptophan to Polynucleotides and Photochemical Deamination of Modified Tyrosine to Quinone Methide Leading to Covalent Attachment

A series of tripeptides TrpTrpPhe (1), TrpTrpTyr (2), and TrpTrpTyr[CH₂N(CH₃)₂] (3) were synthesized, and their photophysical properties and non-covalent binding to polynucleotides were investigated. Fluorescent Trp residues (quantum yield in aqueous solvent Φ_F = 0.03–0.06), allowed for the fluorometric study of non-covalent binding to DNA and RNA. Moreover, high and similar affinities of 2×HCl and 3×HCl to all studied double stranded (ds)-polynucleotides were found (logK_a = 6.0–6.8). However, the fluorescence spectral responses were strongly dependent on base pair composition: the GC-containing polynucleotides efficiently quenched Trp emission, at variance to AT- or AU-polynucleotides, which induced bisignate response. Namely, addition of AT(U) polynucleotides at excess over studied peptide induced the quenching (attributed to aggregation in the grooves of polynucleotides), whereas at excess of DNA/RNA over peptide the fluorescence increase of Trp was observed. The thermal denaturation and circular dichroism (CD) experiments supported peptides binding within the grooves of polynucleotides. The photogenerated quinone methide (QM) reacts with nucleophiles giving adducts, as demonstrated by the photomethanolysis (quantum yield Φ_R = 0.11–0.13). Furthermore, we have demonstrated photoalkylation of AT oligonucleotides by QM, at variance to previous reports describing the highest reactivity of QMs with the GC reach regions of polynucleotides. Our investigations show a proof of principle that QM precursor can be imbedded into a peptide and used as a photochemical switch to enable alkylation of polynucleotides, enabling further applications in chemistry and biology.     

Structure and equilibrium optical properties of liquid CS2

Equilibrium optical properties of liquid carbon disulphide (CS₂), i.e. its refractive index, Kerr constant and depolarized light scattering intensity are calculated using two models of optical response of the fluid. The first one, the point polarizability approximation (PPA) assumes that a point dipole, proportional to the total polarizability, is induced in each molecule. The second one, the point atomic polarizability approximation (PAPA) assumes that point dipoles are induced in individual atomic sites.

The symmetry components of the intermolecular pair distribution function needed to calculate optical properties of the fluid are obtained by Monte Carlo computer simulation on a hard triatomic model of CS₂ as well as by two approximate approaches using this same model. The approximations are both based on the use of the site superposition approximation (SSA) for the intermolecular pair distribution function. In the first approach, the SSA pair distribution is obtained using the Monte Carlo site-site functions and in the second using the site-site functions calculated using the reference interaction site model (RISM) equations.

Extensive comparisons are carried out between the Monte Carlo results and the two approximations in order to examine the influence of the SSA and the RISM equations on optical properties of CS₂. We conclude that, while these approximations, especially the SSA, have a substantial effect on individual symmetry components of the pair distribution, they predict measurable optical properties with satisfactory accuracy.     

Halogen-halogen interactions in halomethanes

We report the study of the electronic structure of CHFI(2), CHBrI(2), CHBr(2)I, CHClI(2), and CHCl(2)I using VUV photoelectron spectroscopy (UPS). The lone pair orbital interactions are discussed on the basis of experimental results and comparisons with other halomethanes.