A microwave spectroscopic and quantum chemical study of propa-1,2-dienyl selenocyanate (H(2)==C==CHSeC[triple bond]N) and cyclopropyl selenocyanate (C(3)H(5)SeC[triple bond]N)

The microwave spectra of propa-1,2-dienyl selenocyanate, H(2)C==C==CHSeC[triple bond]N, and cyclopropyl selenocyanate, C(3)H(5)SeC[triple bond]N, are reported. The spectra of the ground and two vibrationally excited states of the (80)Se isotopologue and the spectrum of the ground state of the (78)Se isotopologue were assigned for one rotameric form of H(2)C==C[double bond, length as m-dash]CHSeC[triple bond]N. This conformer is characterized by a C-C-Se-C dihedral angle of 129(5) degrees from synperiplanar (0 degrees ) and is shown to be the global minimum of H(2)C[double bond, length as m-dash]C[double bond, length as m-dash]CHSeC[triple bond]N. The spectra of the ground and of three vibrationally excited states of the (80)Se isotopologue, as well as of the ground state of the (78)Se isotopologue of one rotamer of C(3)H(5)SeC[triple bond]N were assigned. This conformer has a H-C-Se-C dihedral angle of 80(4) degrees from synperiplanar and is at least 3 kJ mol(-1) more stable than any other form of the molecule. The microwave study has been augmented by quantum chemical calculations at the B3LYP/6-311+ +G(3df,3pd) and MP2/6-311+ +G(3df,3pd) levels of theory.     

Volumetric properties of the glycyl group of proteins in aqueous solution at high pressures

Sound speeds have been measured for aqueous solutions of alanine and the peptides alanylglycine (alagly), alanylglycylglycine (ala(gly)(2)), alanylglycylglycylglycine (ala(gly)(3)) and alanylglycylglycylglycylglycine (ala(gly)(4)) at T=298.15 K and at the pressures p=0.1, 5.0, 10.0, 20.0, 40.0, 60.0, 80.0 and 100.0 MPa. A method is described whereby reliable partial molar volumes at infinite dilution, Vo2, partial molar isentropic compressions at infinite dilution, Ko(S,2), and partial molar isothermal compressions at infinite dilution, Ko(T,2), for the solutes can be derived from the sound speed data. These results were used to obtain partial molar volumes, isentropic and isothermal compressions for the backbone glycyl group of proteins, CH(2)CONH, over the pressure range p=0.1 to 100.0 MPa. The variations of these properties with pressure are discussed in terms of the likely glycyl-group-water interactions.     

Influence of substrate treatment on self-organized pattern formation by langmuir-blodgett transfer

Mesoscopic stripe patterns can be obtained by Langmuir-Blodgett (LB) transfer of l-alpha-dipalmitoylphosphatidylcholine (DPPC) onto solid substrates. In order to investigate the influence of substrates on the pattern formation, silicon slides treated by different cleaning processes were taken as model systems. A shift in the transfer pressure range for patterning was observed between plasma- and RCA-treated silicon. This can be explained with a model of equivalent states and taking into account the influence of microscale water films on the substrates.     

Distinguishing chromophore structures of photocycle intermediates of the photoreceptor PYP by transient fluorescence and energy transfer

The cinnamoyl chromophore is the light-activated switch of the photoreceptor photoactive yellow protein (PYP) and isomerizes during the functional cycle. The fluorescence of W119, the only tryptophan of PYP, is quenched by energy transfer to the chromophore. This depends on the chromophore's transition dipole moment orientation and spectrum, both of which change during the photocycle. The transient fluorescence of W119 thus serves as a sensitive kinetic monitor of the chromophore's structure and orientation and was used for the first time to investigate the photocycle kinetics. From these data and measurements of the ps-fluorescence decay with background illumination (470 nm) we determined the fluorescence lifetimes of W119 in the I(1) and I (1') intermediates. Two coexisting distinct chromophore structures were proposed for the I(1) photointermediate from time-resolved X-ray diffraction ( Ihee, H., et al. Proc. Natl. Acad. Sci. U.S.A., 2005, 102, 7145 ): one with two hydrogen bonds to E46 and Y42, and a second with only one H-bond to Y42 and a different orientation. Only for the first of these is the calculated fluorescence lifetime of 0.22 ns in good agreement with the observed one of 0.26 ns. The second structure has a predicted lifetime of 0.71 ns. Thus, we conclude that in solution only the first I(1) structure occurs. The high resolution structure of the I(1') intermediate, the decay product of I(1) at alkaline pH, is still unknown. We predict from the observed lifetime of 1.3 ns that the chromophore structure of I(1') is quite similar to that of the I(2) intermediate, and I(1') should thus be considered as the alkaline (deprotonated) form of I(2).     

A Triply [5]Helicene-Bridged (1,3,5)Cyclophane

A rigid propeller-shaped conjugated triple macrocycle consisting of two nearly perfectly stacked benzene rings and three linking [5]helicene moieties has been synthesized using a glyoxylic Perkin approach. Analysis of the electron delocalization in this atypical aromatic molecule revealed global aromaticity and a 78 π-electron circuit along the edge of its triple loop, to the detriment of the two 6 π-electron circuits in the two stacked benzene rings.     

Electrochemical and complexation behavior of neptunium in aqueous perchlorate and nitrate solutions

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption, and Np L(III)-edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo structural rearrangement from spherical coordinating ions (Np(3+) and Np(4+)) to transdioxoneptunyl ions (NpO2(n+), n = 1 for Np(V) and 2 for Np(VI)). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate and nitrate solutions. A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10](4+) in 1.0 M HClO4, while Np(V) and Np(VI) exist dominantly as pentaaquoneptunyl complexes, [NpO2(H2O)5](n+) (n = 1 for Np(V) and 2 for Np(VI)). A systematic change is observed on the Fourier transforms of the EXAFS spectra for all of the Np oxidation states as the nitrate concentration is increased in the sample, revealing that the hydrate water molecules are replaced by bidentate-coordinating nitrate ions on the primary coordination sphere of Np.     

Complex polarization propagator calculations of magnetic circular dichroism spectra

It is demonstrated that the employment of the nonlinear complex polarization propagator enables the calculation of the complete magnetic circular dichroism spectra of closed-shell molecules, including at the same time both the so-called Faraday A and B terms. In this approach, the differential absorption of right and left circularly polarized light in the presence of a static magnetic field is determined from the real part of the magnetic field-perturbed electric dipole polarizability. The introduction of the finite lifetimes of the electronically excited states into the theory results in response functions that are well behaved in the entire spectral region, i.e., the divergencies that are found in conventional response theory approaches at the transition energies of the system are not present. The applicability of the approach is demonstrated by calculations of the ultraviolet magnetic circular dichroism spectra of para-benzoquinone, tetrachloro-para-benzoquinone, and cyclopropane. The present results are obtained with the complex polarization propagator approach in conjunction with Kohn-Sham density functional theory and the standard adiabatic density functionals B3LYP, CAM-B3LYP, and BHLYP.     

Enamino derivatives of 1,3-dioxoindane-2-carboxylic acid

Although 1,3-dioxoindane-2-carboxylic acid is highly unstable, its enamino derivatives can be isolated by careful hydrolysis of their esters with 2,4-dihydroxy-1,4-naphthoquinone. Crystal structure determination reveals the formation of two intramolecular hydrogen bonds, offering thus a possible explanation for the stability of these acids.