Crystal structure of 3-diethylaminomethyl-2,2′-biphenol

Crystals of 3-diethylaminomethyl-2,2′-biphenol were examined using X-ray diffraction and FT-IR spectroscopy. Their space group is P2₁/c with a=7.305(1), b=13.816(2), c=29.232(4) Å, β=92.411(3)° and Z=8. The unit cell contains two symmetry-independent zwitterions. The hydrogen atom of the protonated diethylaminomethyl group is linked to the negatively charged phenolate oxygen atom, which in turn is linked to the hydroxyl group by a short hydrogen bond (molecule a: NO=2.604(3), OO=2.512(3) Å; molecule b: NO=2.593(4), OO=2.489(4) Å). The OHO⁻H⁺N bifurcated intramolecular hydrogen bonds are crystallographically asymmetric. The IR spectrum of the crystals confirms very well the results obtained by the X-ray study. Instead of continuous absorption, only broad bands are found indicating relatively low proton polarisability in the two types of intramolecular hydrogen bonds.     

Fluorescence polarization studies of B-phycoerythrin oriented in polymer film

Polarized steady-state fluorescence and fluorescence excitation spectra as well as time-resolved fluorescence for B-phycoerythrin (B-PE) from red algae, Porphyridium cruentum, embedded in polyvinyl stretched films were measured. The lifetimes of polarized fluorescence were analyzed using exponential components and fractal models. The interactions between various chromophores of the pigment-protein complexes investigated were discussed. The anisotropy of fluorescence excitation spectra differs from the anisotropy of absorption spectra and depends on the wavelength of observation. This shows that differently oriented chromophores take part in various paths of excitation energy transfer (ET) or change their excitation into heat with various efficiencies (or both). Also, analysis of time-resolved fluorescence measured in various spectral regions gives different polarized components of emission. Fractal analysis of lifetimes, done under supposition of the Foerster resonance ET mechanism, suggests different arrangements of energy donors and acceptors for molecules absorbing in different spectral regions. It shows that several fractions of differently oriented "forms" of chromophores exhibiting different spectral properties occur in B-PE complexes. Small changes in the orientation of the chromophores can be followed by modification of the path of excitation energy migration. Based on the results obtained a new reorientational mechanism of the State 1 --> State 2 transition was proposed: Even small conformational modifications of biliproteins, which could be caused in vivo by the change in the conditions of preillumination of bacteria, are able to modify the path of excitation ET. Such a reorientation may be responsible for the change in the partition of biliprotein excitation energy between photosystem II (PSII) and PSI (State 1 --> State 2 transition). The proposed mechanism needs further verification by the investigation of whole bacteria cells.     

Screening of intramolecular hydrogen bonds in monosalts of diols and IR continuum

Solutions of salts of the diols o-xylidenedicarbinol, o-xylidenetetraethyldicarbinol and o-xylidenetetrahexyldicarbinol were studied by IR and NMR spectroscopy. Within this series the IR continuum caused by intramolecular OH…O^? ? ^?O…HO bonds vanishes, a band at 1950 cm^?1 being observed. Thus occurence of the continuum requires interaction of the hydrogen bonds with great proton polarizability with their solvent environments.     

Pair potential for helium from symmetry-adapted perturbation theory calculations and from supermolecular data

Symmetry-adapted perturbation theory (SAPT) was applied to the helium dimer for interatomic separations R from 3 to 12 bohrs. The first-order interaction energy and the bulk of the second-order contribution were obtained using Gaussian geminal basis sets and are converged to about 0.1 mK near the minimum and for larger R. The remaining second-order contributions available in the SAPT suite of codes were computed using very large orbital basis sets, up to septuple-zeta quality, augmented by diffuse and midbond functions. The accuracy reached at this level was better than 1 mK in the same region. All the remaining components of the interaction energy were computed using the full configuration interaction method in bases up to sextuple-zeta quality. The latter components, although contributing only 1% near the minimum, have the largest uncertainty of about 10 mK in this region. The total interaction energy at R=5.6 bohrs is -11.000+/-0.011 K. For R< or =6.5 bohrs, the supermolecular (SM) interaction energies computed by us recently turned out to be slightly more accurate. Therefore, we have combined the SM results for R< or =6.5 bohrs with the SAPT results from 7.0 to 12 bohrs to fit analytic functions for the potential and for its error bars. The potential fit uses the best available van der Waals constants C(6) through C(16), including C(11), C(13), and C(15), and is believed to be the best current representation of the Born-Oppenheimer (BO) potential for helium. Using these fits, we found that the BO potential for the helium dimer exhibits the well depth D(e)=11.006+/-0.004 K, the equilibrium distance R(e)=5.608+/-0.012 bohrs, and supports one bound state for (4)He(2) with the dissociation energy D(0)=1.73+/-0.04 mK, and the average interatomic separation R=45.6+/-0.5 A.     

CP/MAS spectroscopy in the determination of the tautomeric forms of gossypol, its Schiff bases and hydrazones in the solid state

New Schiff bases and new hydrazones were synthesized and studied by (13)C and (15)N CP/MAS spectroscopy and by (1)H--(1)H COSY, (1)H--(13)C HMBC, (1)H--(13)C HSQC, (1)H--(15)N HMQC and (1)H--(15)N HSQC correlations. The CP/MAS investigation of gossypol has demonstrated that in the solid state it exists exclusively in the aldehyde-aldehyde tautomeric form. In contrast, CP/MAS studies of hydrazones and Schiff bases reveal that these compounds occur in the solid state in the N-imine-N-imine and enamine-enamine tautomeric forms, respectively. It is shown that the (13)C resonances of C-6, C-7 and C-11 carbon atoms are suitable for distinguishing between the tautomeric forms of aza-derivatives of gossypol in the solid state. Furthermore, we have proved that the (15)N CP/MAS spectra can be used to identify these tautomeric forms.     

Tryptophan Fluorescence Yields and Lifetimes as a Probe of Conformational Changes in Human Glucokinase

Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.1) including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the entire protein. While the fluorescence quantum yield changes upon glucose binding, the enzyme’s absorption spectra, emission spectra and fluorescence lifetimes change very little. These results are consistent with the existence of a dark complex for excited state Trp. Addition of glycerol, L-glucose, sucrose, or trehalose increases the binding affinity of glucose to the enzyme and increases fluorescence intensity. The effect of these osmolytes is thought to shift the protein conformation to a condensed, high affinity form. Based upon these results, we consider the nature of quenching of the Trp excited state. Amide groups are known to quench indole fluorescence and amides of the polypeptide chain make interact with excited state Trp in the relatively unstructured, glucose-free enzyme. Also, removal of water around the aromatic ring by addition of glucose substrate or osmolyte may reduce the quenching.     

Completeness criteria for explicitly correlated Gaussian geminal bases of axial symmetry

The completeness criteria for the basis set of explicitly correlated Gaussian-type geminals adapted to C_∞v symmetry are given. Specifically, we show that any pair function of Σ⁺ symmetry can be expanded in terms of products involving two spherical Gaussian orbitals located on the internuclear axis and a Gaussian correlating factor with a positive exponent. Pair functions corresponding to other irreducible representations of C_∞v can be expressed as linear combinations of products of a σ⁺ function and an angular factor depending on the azimuthal angles. The minimal set of the angular factors needed for completeness is given. These factors are relevant also for other explicitly correlated bases. © 1997 John Wiley & Sons, Inc.     

Towards synthetic diatoms: The Phaeodactylum tricornutum Pt-syn 1.0 project

Synthetic genomics is an emerging field where large-scale DNA engineering is used to study and produce organisms of interest. Here we propose the marine diatom, Phaeodactylum tricornutum, as a candidate for a synthetic genome project and describe some of the strategies to bring this design, termed Pt-syn1.0, to life. This project is fueled by the emergence of a completed genome assembly, powerful methods for manipulating large-scale DNA, and effective DNA delivery methods. We propose that a recombination-deficient strain be created as a prerequisite to downstream genome manipulation to preserve any genetic modifications. In addition, the synthetic genome will be split between 50 chromosomes of approximately 500 kbp each to allow for easy construction and delivery. The establishment of a Pt-syn1.0 strain will lay the foundation for a streamlined engineering platform for P. tricornutum, alleviating many of the current constraints, and would drive diatom research and biotechnology into the next era.     

Unexpected α,β-unsaturated products of reductive amination of the macrolide antibiotic josamycin

Reductive amination of the macrolide antibiotic josamycin with alkyl amines, using three different reducing agents: NaBH₃CN, NaBH₄ and NaBH(OAc)₃, yields surprisingly different major products which are identified as either Lewis complexes, aminoalkyl derivatives or α,β-unsaturated derivatives of josamycin by ¹H and ¹³C NMR, FT-IR and ESI MS methods.     

Selective Esterification of Gossypol by Copper Acetate in Acetonitrile-Spectroscopic Studies

Gossypol and its 1: 1 complexes with copper acetate in acetonitrile were studied by FTIR and UV-visible spectroscopy. With the complexation with Cu cation the tautomeric equilibrium of gossypol is completely shifted from the aldehyde-aldehyde to the lactol-lactol tautomer. The acidic character of O₁₁H group in the gossypol-Cu complex led to the selective esterification of the lactol form of gossypol by the acetate group.