Donor Arrangement Research Articles

A Hybrid Organic–Inorganic Conductor κ′-BETS2FeCl4, BETS = Bis(ethylenedithio)tetraselenafulvalene

A hybrid organic–inorganic conductor κ′-BETS2FeCl4 is obtained by an electrocrystallization method from BETS and (Me4N)3Fe(C2O4)3 dissolved in a mixture of C6H5Cl and C2H5OH under 2.0 V for 4 weeks. It belongs to the monoclinic space group C2/c, with cell parameters a = 37.783(9), b = 11.207(3), c = 8.530(2) Å, β = 94.835(1)°, V = 3598.8(1.4) Å3, and Z = 4. The donor arrangement resembles the κ-phase but is different to that of the previously reported antiferromagnetic superconductor κ-BETS2FeCl4, which is orthorhombic and has been studied for 10 years. The inorganic anion exists in two opposite configurations in the anion sheet of κ′-BETS2FeCl4, and its crystal structure and electronic structure are different from those of the polymorphs λ-BETS2FeCl4 and κ-BETS2FeCl4.

Signalling states of photoactivated rhodopsin.

In microseconds after photoexcitation, rhodopsin forms the Meta I intermediate from lumirhodopsin. In this conversion, contacts between retinal and the apoprotein are formed, which result in a defined arrangement of donor and acceptor groups for proton translocations. A system of protonation-dependent coupled equilibria is now adopted, comprising Meta intermediates I, II and III, and their isospectral subforms. Some Meta states were identified as signalling states, in which the receptor interacts with transducin (Gt), rhodopsin kinase (RK) and arrestin. The binding of Gt or arrestin shifts the equilibrium to Meta II, while RK does not, indicating exposure of the RK binding site(s) before Meta II is formed. On contact with the activated receptor, each signalling protein responds with a conformational change, which transforms it into a functionally active state. The bell-shaped pH/rate profiles which are seen for the activation of both the G protein and the receptor kinase, indicate the necessary protonation and deprotonation of groups with different pKa. The right wing of the profile reflects the formation of the protonated subconformation (termed MIIb) of Meta II. For the interaction with Gt, recent work suggests a 'sequential fit' mechanism, involving the recognition of the C-terminal peptide of the Gt alpha subunit and of the farnesylated C-terminus of the gamma subunit. Isolated peptides derived from these portions of the G protein mimic the left wing of the pH/rate profile. We discuss the sequential fit as a time-ordered sequence of microscopic recognition and conformational interlocking in the interaction with the G protein.

Pollen-mediated intraspecific gene flow from herbicide resistant oilseed rape (Brassica napus L.)

The cultivation of genetically modified (GM) herbicide resistant oilseed rape (Brassica napus) has increased over the past few years. The transfer of herbicide resistance genes via pollen (gene flow) from GM crops to non-GM crops is of relevance for the realisation of co-existence of different agricultural cultivation forms as well as for weed management. Therefore the likelihood of pollen-mediated gene flow has been investigated in numerous studies. Despite the difficulty to compare different experiments with varying levels of outcrossing, we performed a literature search for world-wide studies on cross-fertilisation in fully fertile oilseed rape. The occurrence and frequency of pollen-mediated intraspecific gene flow (outcrossing rate) can vary according to cultivar, experimental design, local topography and environmental conditions. The outcrossing rate from one field to another depends also on the size and arrangement of donor and recipient populations and on the ratio between donor and recipient plot size. The outcrossing levels specified in the presented studies are derived mostly from experiments where the recipient field is either surrounding the donor field (continuous design) or is located as a patch at different distances from the donor field (discontinuous design). Reports of gene flow in Brassica napus generally show that the amount of cross-fertilisation decreases as the distance from the pollen source increases. The evidence given in various studies reveals that the bulk of GM cross-fertilisation occurs within the first 10 m of the recipient field. The removal of the first 10 m of a non-transgenic field facing a GM crop might therefore be more efficient for reducing the total level of cross-fertilisation in a recipient sink population than to recommend separation distances. Future experiments should investigate cross-fertilisation with multiple adjacent donor fields at the landscape level under different spatial distributions of rapeseed cultivars and different cropping systems. The level of cross-fertilisation occurring over the whole field is mainly important for co-existence and has not been investigated in agricultural scale experiments until now. Potential problems with herbicide resistant oilseed rape volunteers arising from intraspecific gene flow can be largely solved by the choice of suitable cultivars and herbicides as well as by soil management.

Dimethyl 2,2′-bipyridine-6,6′-dicarboxylate and bis(dimethyl 2,2′-bipyridine-6,6′-dicarboxylato-κ2N,N′)copper(I) tetrafluoroborate

The single-crystal X-ray structures of dimethyl 2,2'-bipyridine-6,6'-dicarboxylate, C(14)H(12)N(2)O(4), and the copper(I) coordination complex bis(dimethyl 2,2'-bipyridine-6,6'-dicarboxylato-kappa(2)N,N')copper(I) tetrafluoroborate, [Cu(C(14)H(12)N(2)O(4))(2)]BF(4), are reported. The uncoordinated ligand crystallizes across an inversion centre and adopts the anticipated anti pyridyl arrangement with coplanar pyridyl rings. In contrast, upon coordination of copper(I), the ligand adopts an arrangement of pyridyl donors facilitating chelating metal coordination and an increased inter-pyridyl twisting within each ligand. The distortion of each ligand contrasts with comparable copper(I) complexes of unfunctionalized 2,2'-bipyridine.

Molecular Complexes Based on Tetrathiafulvalene and Dialkylviologens

Three kinds of molecular complexes based on tetrathiafulvalene (TTF) and dialkylviologens were prepared and their crystal structures elucidated. While TTF-dimethylviologen complex forms a mixed stack arrangement of donors and acceptors in its crystal structure, TTF donors aggregate with long alkyl groups by CH/pi and/or van der Waals interactions in a couple of TTF-heptylviologen complexes.

Quantum Calculations on Hydrogen Bonds in Certain Water Clusters Show Cooperative Effects

Water molecules in clefts and small clusters are in a significantly different environment than in bulk water. We have carried out ab initio calculations that demonstrate this in a series of clusters, showing that cooperative effects must be taken into account in the treatment of hydrogen bonds and water clusters in such bounded systems. Hydrogen bonds between water molecules in simulations are treated most frequently by using point charge water potentials, such as TIP3P or SPC, sometimes with a polarizable extension. These produce excellent results in bulk water, for which they are calibrated. Clefts are different from bulk; it is necessary to look at smaller systems, and investigate the effect of limited numbers of neighbors. We start with a study of isolated clusters of water with varying numbers of neighbors of a hydrogen bonded pair of water molecules. The cluster as a whole is in vacuum. The clusters are defined so as to provide the possible arrangements of nearest neighbors of a central hydrogen bonded pair of water molecules. We then scan the length and angles of the central hydrogen bond of the clusters, using density functional theory, for each possible arrangement of donor and acceptor hydrogen bonds on the central hydrogen bonding pair; the potential of interaction of two water molecules varies with the number of donor and of acceptor neighbors. This also involves changes in charge on the water molecules as a function of bond length, and changes in energy and length as a function of number of neighboring donor and acceptor molecules. Energy varies by approximately 6 k(B)T near room temperature from the highest to the lowest energy when bond length alone is varied, enough to seriously affect simulations.

Functional Characterization of PmHS1, a Pasteurella multocida Heparosan Synthase

Heparosan synthase 1 (PmHS1) from Pasteurella multocida Type D is a dual action glycosyltransferase enzyme that transfers monosaccharide units from uridine diphospho (UDP) sugar precursors to form the polysaccharide heparosan (N-acetylheparosan), which is composed of alternating (-alpha4-GlcNAc-beta1,4-GlcUA-1-) repeats. We have used molecular genetic means to remove regions nonessential for catalytic activity from the amino- and the carboxyl-terminal regions as well as characterized the functional regions involved in GlcUA-transferase activity and in GlcNAc-transferase activity. Mutation of either one of the two regions containing aspartate-X-aspartate (DXD) residue-containing motifs resulted in complete or substantial loss of heparosan polymerizing activity. However, certain mutant proteins retained only GlcUA-transferase activity while some constructs possessed only GlcNAc-transferase activity. Therefore, it appears that the PmHS1 polypeptide is composed of two types of glycosyltransferases in a single polypeptide as was found for the Pasteurella multocida Type A PmHAS, the hyaluronan synthase that makes the alternating (-beta3-GlcNAc-beta1,4-GlcUA-1-) polymer. However, there is low amino acid similarity between the PmHAS and PmHS1 enzymes, and the relative placement of the GlcUA-transferase and GlcNAc-transferase domains within the two polypeptides is reversed. Even though the monosaccharide compositions of hyaluronan and heparosan are identical, such differences in the sequences of the catalysts are expected because the PmHAS employs only inverting sugar transfer mechanisms whereas PmHS1 requires both retaining and inverting mechanisms.

Interaction of cationic 5,10,15,20-tetrakis(4-N-methyl pyridyl) porphyrin with mono-and polynucleotides: A study by picosecond fluorescence spectroscopy

The interaction of water-soluble cationic 5,10,15,20-tetrakis(4-N-methyl pyridyl) porphyrin (H2TMPyP4) with some mono-and polynucleotides is studied by time-resolved and steady-state fluorescence spectroscopy, as well as by steady-state absorption spectroscopy. The fluorescence decay kinetics are analyzed by reconstructing the decay time distributions, which made it possible to describe in more detail than previously the complexes formed due to the interaction. The main effect of binding of H2TMPyP4 adenosine 5′-monophosphate and to poly(dA-dT)2 is shown to be an increase in the fluorescence lifetime from 4.6 ns in the solution to 8.3 and 12.3 ns, respectively. This effect is explained by a less polar (in comparison with water) environment of porphyrin in complexes, which leads to a decrease in the quenching action of the intramolecular charge transfer state between the porphyrin macrocycle and methyl pyridyl groups. In the case of complex formation with guanine-containing nucleotides (guanosine 5′-monophosphate and poly(dG-dC)2), the effect of decrease in the quenching action of the intramolecular charge transfer state caused by a decrease in the medium polarity is superimposed by a stronger effect of decrease in the fluorescence lifetime of porphyrin as a result of intermolecular electron transfer from guanine to excited porphyrin. A high sensitivity of this intermolecular quenching to the mutual arrangement of the electron donor and the electron acceptor makes it possible to reveal four types of complexes between H2TMPyP4 and guanosine 5′-monophosphate, which differ in the positions of four broad peaks in the porphyrin fluorescence decay time distribution (0.1, 0.7, 2.4, and 6.1 ns). For the complex with poly(dG-dC)2, a narrow peak at 2.8 ns prevails in the fluorescence decay time distribution, with the contributions from two additional narrow peaks at 1.0 and 6.2 ns being small.

Crystal structures and conductivities of new hydrogen-bonded system: CnDT-EDO-TTF and BzDT-EDO-TTF

A new series of RDT-EDO-TTF [ R = C5, C6, C7, C8; (cis-l,2-cycloalkylene-l,2-dithio)ethylenedioxytetrathiafulvalene and R = Bz; (benzodithio)ethylenedioxytetrathiafulvalene] donors containing cycloalkylene or benzene, and ethylenedioxy groups as a source of the steric hindrance and the intermolecular hydrogen bonds has been synthesized. The charge transfer (CT) salts, β″-(RDT-EDO-TTF) 2(PF 6) x ( R = C5, C6, C7, C8, and Bz), have the similar β″-type donor arrangement due to the intermolecular hydrogen-bonded network (CH …O) in the two-dimensional (2D) plane. The C6DT-EDO-TTF molecule containing the flexible cyclohexylene group affords the 2:1 salts, which shows the metallic behaviors down to 1.3 K with a variety of resistivities at room temperature, 3.0 × 10 −3∼5.0 × 10 −2 ohm cm. On the other hand, the BzDT-EDO-TTF donor with the fixed functional benzo group gives the non-stoichiometry complexes, which exhibit the similar metallic behavior down to 1.3 K with the largest RRR = 40∼115 among the RDT-EDO-TTF salts.

Metal “Capture” by a Heterotrimetalloligand, Heterometallic d10−d10 Interactions, and Unexpected Iron-to-Platinum Silyl Ligand Migration: a Combined Experimental and Theoretical Study

The heterotrinuclear chain complex Hg[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)](2) (dppm = Ph(2)PCH(2)PPh(2)) 1 which has a transoid arrangement of the phosphine donors was used as a versatile chelating metallodiphosphine ligand owing to the easy rotation of its metal core about the Fe-Hg sigma-bonds. Its reaction with the labile Pt(0) olefin complex [Pt(C(7)H(10))(3)] yielded [HgPt{Si(OMe)(3)}Fe(2)(CO)(6){Si(OMe)(3)}(mu-dppm)(2)] 5 which resulted, after coordination of the dangling phosphine donors to Pt, from an unprecedented intramolecular rearrangement involving a very rare example of silyl ligand migration between two different metal centers, and the first one in metal cluster chemistry. The major structural differences observed between the heterometallic complexes obtained from 1 and d(10) Cu(I), Pd(0), or Pt(0) precursors have been established by X-ray diffraction. The bonding situation in the silyl migrated Pt complex 5 was analyzed and compared to those in the isoelectronic, but structurally distinct complexes obtained from Cu(I) and Pd(0) precursors, [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Cu](+) (2) and [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Pd] (4), respectively, by means of extended Hückel interaction diagrams. DFT calculations then allowed the energy minima associated with the three structures to be compared for 2, 4, and 5. All three minima are in close competition for the Pd complex 4, but silyl migration is favored by approximately 10 kcal mol(-)(1) for 5, mainly due to the more electronegative character of Pt with respect to Pd.

Structural, Electrical, and Magnetic Properties of α-(ET)7[MnCl4]2·(1,1,2-C2H3Cl3)2 (ET = Bis(ethylenedithio)tetrathiafulvalene)

Abstract A new charge-transfer salt of ET with a chloromanganate(II) complex anion has been synthesized and characterized by X-ray structural analysis, resistivity measurements, magnetic susceptibility, electron spin resonance (ESR), and an extended Hückel tight biding (EHTB) band calculation. The crystal has a sheet structure comprised of an α-type two-dimensional (2D) donor arrangement in the bc-plane and insulating sheets of discrete [MnCl4]2− anions and 1,1,2-C2H3Cl3 (TCE) molecules. Its conducting property exhibits considerable anisotropy, which is of effectively metallic along the b-axis down to 1.2 K under 2.9 kbar and higher pressure. The magnetic susceptibility is approximately reproduced by the Curie–Weiss law with a Weiss temperature of θ = −(1.35 ± 0.07) K from 2–300 K. ESR measurements revealed that the π-electron system in this salt exhibits Pauli paramagnetism at least at 3.6 to ∼50 K. The band calculation suggests that the HOMO (the highest occupied molecular orbital) band has very small dispersion, almost solely along the b*-axis.

Anion induced conformational switch of a macrocyclic amide receptor

Isophthalic acid-based macrocyclic tetraamide 4 shows considerable conformational change during anion binding. In the solid state and in solution the free receptor exists in nonbonding, closed conformation stabilized by two intramolecular hydrogen bonds. Upon anion complexation, the receptor switches to a conformation with convergent arrangement of hydrogen bond donors. The conformational switch is evidenced by 2D NMR and X-ray analyses of the free ligand and its Cl − complex.

Photoinduced Multistep Electron Transfer in an Oligoaniline−Oligo(p-phenylene Vinylene)−Perylene Diimide Molecular Array

Photoinduced multistep electron transfer has been studied in two symmetrical oligoaniline−oligo(p-phenylene vinylene)−perylene diimide−oligo(p-phenylene vinylene)−oligoaniline (OAn−OPV−PERY−OPV−OAn) multichromophore arrays with fluorescence and transient absorption spectroscopy in the femtosecond and nanosecond time domains. The arrays consist of a symmetrical donor(2)−donor(1)−acceptor−donor(1)−donor(2) arrangement, with two OAn−OPV segments coupled to a central PERY unit via a direct linkage (1) or a saturated spacer (2). Photoexcitation gives the OAn−OPV+•−PERY-•−OPV−OAn as the primary charge-separated state. For 1 the transfer is extremely fast (kCS > 1000 ns-1) in polar and apolar solvents, while the rate constants for recombination differ and are significantly higher in polar solvents than in apolar solvents because recombination occurs in the Marcus inverted region. Charge separation and charge recombination are slower in 2, because the saturated spacer reduces the electronic coupling between OPV d...

Control of electronic state in the 2D hydrogen-bonded system: β″-(CnDT-EDO-TTF) 2(PF 6) x ( n = 5, 6, 7, 8)

A new series of CnDT-EDO-TTF [ n=5, 6, 7, 8; ( cis-1,2-cycloalkylene-1,2-dithio)ethylenedioxytetrathiafulvalene] donors containing cycloalkylene and ethylenedioxy groups as a source of intermolecular hydrogen bonds and the steric hindrance has been synthesized. The charge transfer (CT) salts, β″-(CnDT-EDO-TTF) 2(PF 6) x ( n=5, 6, 7, 8), have the similar β″-type donor arrangements owing to the intermolecular hydrogen-bonded network (CH⋯O) in the two-dimensional (2D) plane. The steric hindrance of cycloalkylene groups enlarges the intermolecular distance in the order from n=5, 6, 7, to 8 salt. The calculated bandwidth, however, decreases in the different order from n=8, 5, 7, to 6 salt in consideration of the 2D interactions. All salts, β″-(CnDT-EDO-TTF) 2(PF 6) x , show a metallic feature down to 1.5 K, and the temperature dependences indicate the negative chemical pressure effect from n=8, 5, 7, to 6 salt in the same order of the calculated bandwidth.

Crystal structures and electrical conductivities controlled by CH/n interactions

A series of new TTF derivatives, CnDT-EDO-TTF (n= 5,6), CnDT-EDT-TTF (n= 5,6), and CnDTP-TTF (n= 5,6) have been synthesized. As for the CnDT-EDO-TTF salts, the intermolecular CH...O interactions construct the pseudo-2D electronic state, which stabilizes the metallic character down to 1.3 K. The sulfur based C5DT-EDT-TTF salts preferred the dimeric β'-type structure, which could be Mott insulators. The pyrazino-fused donor C5DTP-TTF afford a variety of donor arrangements by the S...N interaction and the steric hindrance: κ-(C5DTP-TTF) 2 X (X= AsF6, SbF 6 ) are semiconductors, whereas β-(C5DTP-TTF) 2 TaF 6 reveal the metallic down to 150 K.

Fluorescence Polarization Studies of B‐Phycoerythrin Oriented in Polymer Film¶

ABSTRACTPolarized 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.

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.

Family members as gamete donors and surrogates

Family members as gamete donors and surrogates

Theoretical studies on magnetic interactions in many types of organic donor salts: BEDT-TTF, BETS, TMTTF and TMTSF

Intermolecular magnetic interaction of some donors, i.e. BEDT-TTF, BETS, TMTTF and TMTSF, in some organic superconductive crystals were studied theoretically by using ab initio MO and DFT methods. In addition, donor arrangements in both κ- and λ-phases crystals are also focused. For this purpose we employed κ-BETS2FeCl4 and λ-BETS2FeCl4 crystals for BETS salts; κ-(BEDT-TTF)2Cu[N(CN)2]X (X=Cl, Br and I) and κ-(BEDT-TTF)2Cu(NCS)2 crystals for BEDT-TTF salts; TMTTF2PF6 and TMTSF2PF6 crystals for TMTTF and TMTSF salts. For these systems all the effective exchange integral (Jab) values between two donors and between donor and counter anions were successfully evaluated. In addition the other effective parameters (tab, Ueff) were also obtained. Finally relationship between integral pair (J, J′) and transition temperature (TSC) was discussed. The two- and one-dimensional magnetic networks are essential for these crystals.

A New Packing Pattern of the Conducting BEDO-TTF Complexes

The crystal structure of (BEDO-TTF) 4 Pd(CN) 4 (H 2 O) x (x 1) showed the exceptional donor arrangement as a conductive BEDO-TTF complex. The crystal structure is understood as a modified I 3 -type, which is the most common packing pattern of the metallic complexes based on this donor molecule. Also, the title complex showed the abnormal EPR line width broadening on cooling despite of trivial metallic behaviors in the conductivity and static magnetic susceptibility.