Liquid crystalline and light emitting polyacetylenes: Synthesis and properties of biphenyl-containing poly(1-alkynes) with different functional bridges and spacer lengths

Biphenyl- (Biph-) containing 1-alkynes (3 and 4) and their polymers (1 and 2) with varying bridge groups and spacer lengths were synthesized and the effects of the structural variation on their properties, especially their mesomorphism and photoluminescence behaviors, were studied. The acetylene monomers 3(3) [HCdropC(CH2)(3)O-Biph-OCO(CH2)(10)CH3] and 4(m) [HCdropC(CH2)(m)OCO-Biph-OCO(CH2)(10)-CH3, m = 3, 4] were prepared by sequential etherization and esterification reactions of 1-alkynes. While 3(3) exhibits enantiotropic crystal E and SmB mesophases, its structural cousin 4(3) displays only a monotropic SmB phase. Enantiotropic SmA and SmB mesophases are, however, developed when the spacer length is increased to 4. Polymerizations of the monomers are effected by Mo-, W-, Rh-, and Fe-based catalysts, with the WCl6-Ph4Sn catalyst giving the best results (isolation yield up to 85% and M-w up to 59000). The polymers were characterized by IR, UV, NMR, TGA, DSC, POM, XRD, and PL analyses. Compared to 1(3), 2(3) shows a red-shifted absorption, a higher T-i, and a better packed interdigitated bilayer SmA(d) structure, while the mesophase of 2(4) involves monolayer-packing arrangements of the mesogens. Upon photoexcitation, 1(3) emits almost no light but 2(m) gives a strong ultraviolet emission (lambda(max) similar to 350 nm), whose intensity increases with the spacer length.

An improved PCR method for direct identification of Porphyra (Bangiales, Rhodophyta) using conchocelis based on a RUBISCO intergenic spacer

An improved method of PCR in which the small segment of conchocelis is amplified directly without DNA extraction was used to amplify a RUBISCO intergenic spacer DNA fragment from nine species of red algal genus Porphyra (Bangiales, Rhodophyta), including Porphyra yezoensis (Jiangsu, China), P. haitanensis (Fujian, China), P. oligospermatangia (Qingdao, China), P. katadai (Qingdao, China), P. tenera (Qingdao, China), P. suborboculata (Fujian, China), P. pseudolinearis (Kogendo, Korea), P. linearis (Devon, England), and P. fallax (Seattle, USA). Standard PCR and the method developed here were both conducted using primers specific for the RUBISCO spacer region, after which the two PCR products were sequenced. The sequencing data of the amplicons obtained using both methods were identical, suggesting that the improved PCR method was functional. These findings indicate that the method developed here may be useful for the rapid identification of species of Porphyra in a germplasm bank. In addition, a phylogenetic tree was constructed using the RUBISCO spacer and partial rbcS sequence, and the results were in concordant with possible alternative phylogenies based on traditional morphological taxonomic characteristics, indicating that the RUBISCO spacer is a useful region for phylogenetic studies.

Phylogeography of the Northern Atlantic species Chondrus crispus (Gigartinales, Rhodophyta) inferred from nuclear rDNA internal transcribed spacer sequences

Eighteen isolates of the red algae Chondrus crispus were collected from Northern Atlantic sites, together with C. ocellatus, C. yendoi and C. pinnulatus from the North Pacific. The nuclear rDNA internal transcribed spacer (ITS) was sequenced and compared, spanning both the ITS regions and the 5.8S rRNA gene. Percentage of nucleotide variation for C. crispus ranged from 0.3% to 4.0%. Phylogenetic analyses were performed using maximum parsimony (MP), neighbor-joining (NJ) and minimum evolution methods. They showed that two main clades existed within the C. crispus samples examined and that suggested C. crispus had a single Atlantic origin. The clustering however did not follow the geographic origin. We hypothesized that the current distribution of C. crispus populations might be a result of three main factors: temperature boundaries, paleoclimate and paleoceanography. ITS data exhibited abundant molecular information not only for phylogeographical investigation but also for systematics studies.

Formation of Novel Di-Nuclear Lanthanide Luminescent Sm(III), Eu(III) and Tb(III) Triple Stranded Helicates from a C2 Symmetrically 2,6-Dicarboxylic Amide based 1,3-Xylene Ligand in CH3CN

The synthesis of the C2-symmetrical ligand 1 consisting of two naphthalene units connected to two pyridine-2,6-dicarboxamide moieties linked by a xylene spacer and the formation of LnIII-based (Ln1/4 Sm, Eu, Tb, and Lu) dimetallic helicates [Ln2 · 13] in MeCN by means of a metal-directed synthesis is described. By analyzing the metal-induced changes in the absorption and the fluorescence of 1, the formation of the helicates, and the presence of a second species [Ln2 · 12] was confirmed by nonlinear- regression analysis. While significant changes were observed in the photophysical properties of 1, the most dramatic changes were observed in the metal-centred lanthanide emissions, upon excitation of the naphthalene antennae. From the changes in the lanthanide emission, we were able to demonstrate that these helicates were formed in high yields (ca. 90% after the addition of 0.6 equiv. of LnIII), with high binding constants, which matched well with that determined from the changes in the absorption spectra. The formation of the LuIII helicate, [ Lu2 · 13 ] , was also investigated for comparison purposes, as we were unable to obtain accurate binding constants from the changes in the fluorescence emission upon formation of [Sm2 · 13], [Eu2 · 13], and [Tb2 · 13].

Probing the mid-gorge of cholinesterases with spacer-modified bivalent quinazolinimines leads to highly potent and selective butyrylcholinesterase inhibitors

The spacer structure of homobivalent quinazolinimes acting as potent acetyl-(AChE)- and butyrylcholinesterase (BChE) inhibitors was chemically modified introducing tertiary amine and acyl-amide moieties, and the activities at both ChEs were evaluated. Molecular docking was applied to explain the data and probe the capacity of the mid-gorge site of both ChEs. The novel spacer structures considerably alter the biological profile of bivalent quinazolinimines with regard to both inhibitory activity and selectivity. Mutual interaction of binding to the various sites of the enzymes was further investigated by applying also different spacer lengths and ring sizes of the alicycle of the tricyclic quinazolinimines. In order to achieve selectivity toward BChE and to improve inhibitory activities, the spacer structure was optimized and identified a highly potent and selective BChE inhibitor. (C) 2010 Elsevier Ltd. All rights reserved.

Plasmon enhanced fluorescence studies from aligned gold nanorod arrays modified with SiO2 spacer layers

Here, we demonstrate that quasi self-standing Au nanorod arrays prepared with plasma polymerisation deposited SiO2 dielectric spacers support surface enhanced fluorescence (SEF) while maintaining high signal reproducibility. We show that it is possible to find a balance between enhanced radiative and non-radiative decay rates at which the fluorescent intensity is maximized. The SEF signal optimised with a 30 nm spacer layer thickness showed a 3.5-fold enhancement with a signal variance of <15% thereby keeping the integrity of the nanorod array. We also demonstrate the decreased importance of obtaining resonance conditions when localized surface plasmon resonance is positioned within the spectral region of Au interband transitions. Procedures for further increasing the SEF enhancement factor are also discussed.

Methylene spacer-regulated structural variation in cobalt(II/III) complexes with bridging acetate and Salen- or Salpn-type Schiff-base ligands

Two linear, trinuclear mixed-valence complexes, [Co-II{(mu-L-1)(mu-OAc)Co-III (OAc)}(2)] (1) and [Co-II(mu-L-2) (mu-OAc)Co-III(OAc)}(2)] (2) and two mononuclear Con' complexes [Co-III{L-3)(OAc)] (3), and [Co-III {L-4}(OAc)] (4) were prepared and the molecular structures of 1, 2 and 4 elucidated on the basis of X-ray crystallography [OAc = Acetate ion, H2L1 = H(2)Salen 1,6-bis(2-hydroxyphenyl)-2,5-diazahexa-1,5-diene, H2L2 H2Me2-Salen = 2,7-bis(2-hydroxyphenyl)-2,6-diazaocta-2,6-diene, H2L3 = H(2)Salpn = 1,7-bis(2-hydroxyphenyl)-2,6-diazahepta1,6-diene, H2L4 = H(2)Me(2)Salpn = 2,8-bis(2-hydroxyphenyl)3,7-diazanona-2,7-dienel. In complexes I and 2, the acetate groups show both monodentate and bridging bidentate coordination modes, whereas chelating bidentate acetate is present in 4. The terminal (CoN2O4)-N-III centres in 1 and 2 exhibit uniform facial arrangements of both non-bridged N2O and bridging O-3 donor sets and the Co-II centre is coordinated to six (four phenoxo and two acetato) oxygen atoms of the bridging ligands. The effective magnetic moment at room temperature corresponds to the presence of high-spin Coll in both 1 and 2. The complexes 1 and 2 are thus Co-III(S = 0)Co-II(S = 3/2)-Co-II(S = 0) trimers. Complexes 3 and 4 are monomeric and diamagnetic containing low-spin Co-III(S = 0) with chelating tetradentate Schiff base and bidentate acetate. Calculations based on DFT rationalise the formation of trinuclear or monomiclear complexes. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Syntheses and crystal structures of two new coordination polymers of Cd(II) using organic spacer and inorganic-bridging ligands

Two new cadmium (II) complexes [Cd(hmt)(dca)(2)] (n) (1) and [Cd-3(hmt)(2)(SeCN)(6)(H2O)(2)] (n) (2) (hmt=hexamethylenetetramine, dca=dicyanamide) have been synthesized and characterized by X-ray single-crystal analysis. The complex 1 is a 2D rectangular grid of octahedral cadmium (II) with CdN6 chromophore where cadmium centers are doubly bridged by dicyanamide and hmt along a-axis, which are interlinked by dicyanamide running along c-axis. Whereas, complex 2 is a 1D chain of octahedral cadmium (II) with a three-leg ladder topology running along a-axis. The Cd(II) centers are doubly bridged through SeCN (infinite rail) along a-axis and singly bridged by hmt (two-step rung) along c-axis, having cadmium centers with CdSe2N3O and CdSe2N4 chromophores. The adjacent chains through H-bonding between coordinated water and hmt, and (SeSe)-Se-... interaction are extended to 2D supramolecular architecture.

Characterization of the 23S and 5S rRNA genes and 23S-5S intergenic spacer region (ITS-2) of Photobacterium damselae

The 23S ribosomal RNA (rRNA) gene has been sequenced in strains of the fish pathogens Photobacterium damselae subsp. damselae (ATCC 33539) and subsp. piscicida (ATCC 29690), showing that 3 nucleotide positions are clearly different between subspecies. In addition, the 5S rRNA gene plus the intergenic spacer region between the 23S and 5S rRNA genes (ITS-2) were amplified, cloned and sequenced for the 2 reference strains as well as the field isolates RG91 (subsp. damselae) and DI21 (subsp. piscicida). A 100% similarity was found for the consensus 5S rRNA gene sequence in the 2 subspecies, although some microheterogeneity was detected as inter-cistronic variability within the same chromosome. Sequence analysis of the spacer region between the 23S and 5S rRNA genes revealed 2 conserved and 3 variable nucleotide sequence blocks, and 4 different modular organizations were found. The ITS-2 spacer region exhibited both inter-subspecies and inter-cistronic polymorphism, with a mosaic-like structure. The EMBL accession numbers for the 23S, 5S and ITS-2 sequences are: P. damselae subsp. piscicida 5S gene (AJ274379), P. damselae subsp. damselae 23S gene (Y18520), subsp. piscicida 23S gene (Y17901), R damselae subsp. piscicida ITS-2 (AJ250695, AJ250696), P. damselae subsp. damselae ITS-2 (AJ250697, AJ250698).

Perpendicular exchange bias in IrMn/Pt/[Co/Pt](3) multilayers with cone magnetization

The perpendicular exchange bias and magnetic anisotropy were investigated in IrMn/Pt/[Co/Pt](3) multilayers through the analysis of in-plane and out-of-plane magnetization hysteresis loops. A phenomenological model was used to simulate the in-plane curves and the effective perpendicular anisotropies were obtained employing the area method. The canted state anisotropy was introduced by taking into account the first and second uniaxial anisotropy terms of the ferromagnet with the corresponding uniaxial anisotropy direction allowed to make a nonzero angle with the film`s normal. This angle, obtained from the fittings, was of approximately 15 degrees for IrMn/[Co/Pt](3) film and decreases with the introduction of Pt in the IrMn/Pt/[Co/Pt](3) system, indicating that the Pt interlayer leads to a predominant perpendicular anisotropy. A maximum of the out-of-plane anisotropy was found between 0.5 and 0.6 nm of Pt, whereas a maximum of the perpendicular exchange bias was found at 0.3 nm. These results are very similar to those obtained for IrMn/Cu/[Co/Pt](3) system; however, the decrease of the exchange bias with the spacer thickness is more abrupt and the enhacement of the perpendicular anisotropy is higher for the case of Cu spacer as compared with that of Pt spacer. The existence of a maximum in the perpendicular exchange bias as a function of the Pt layer thickness was attributed to the predominance of the enhancement of exchange bias due to more perpendicular Co moment orientation over the exponential decrease of the ferromagnetic/antiferromagnetic exchange coupling and, consequently, of the exchange-bias field. (C) 2011 Elsevier B.V. All rights reserved.

Extension ladders - synthesis and characterisation of new spacer-bridged tetraorganodistannoxanes

Preliminary results are described on the synthesis and characterization of novel spacer-bridged tetraorganodistannoxanes, {[[R(Cl)Sn]₂(CH₂)₂]O}₄ (n = 5 – 8, 10, 12; R = CH₂SiMe₃) containing particularly long organic spacers. In the solid state, these compounds reveal typical double-ladder structures with eight tin atoms per molecule, whereas in solution a partial and reversible rearrangement takes place to form tetraorganodistannoxanes, {[[R(Cl)Sn]₂(CH₂)_n]O}₂ (n = 5 – 8, 10, 12; R = CH₂SiMe₃), having four tin atoms per molecule.

A spacer-linked molecular diorganotin oxide

The synthesis and molecular structure are reported of the first example of a diorganotin oxide, {p-[R(O)SnCH₂SiMe₂]₂C₆H₄}₃ (3) (R = (Me₃Si)₂CH), in which two six-membered Sn₃O₃ units are linked by three -CH₂Si(Me)₂C₆H₄Si(Me)₂CH₂- spacers.

Hydrolysis of dinuclear spacer-bridged diorganotin(IV) triflates. A novel cationic double ladder with supramolecular association

A series of oligomethylene-bridged diorganotin triflates R(OTf)₂Sn(CH₂)_nSn(OTf)₂R (R = CH₂SiMe₃; n = 3, 4, 8, 10) were synthesized by reaction of triflic acid with the precursor oxides R(O)Sn(CH₂)_nSn(O)R. On the basis of ¹¹⁹Sn NMR (in acetonitrile) the triflates appear to be the simple six-coordinated ionic species [(MeCN)₄(RSn(CH₂)_nSnR)(MeCN)₄]²⁺. These triflates readily undergo hydrolysis to give products, the identity of which depends on the length of the oligomethylene bridge. For n = 3 (5), the solid-state structure shows association of two dimeric units, which results in a tetracationic double ladder. Extensive hydrogen bonding gives rise to a supramolecular association. Solution ¹¹⁹Sn NMR and ES MS suggest some dissociation of 5 into dimers containing four tin atoms and possibly monomers containing two tin atoms. A rudimentary solid-state structure for n = 4 (6) indicates a linear polymer based on dimeric (four tin atoms) units. The structure of 6 also features extensive hydrogen bonding, this time effectively giving rise to alternating layers of cations and anions.

The first spacer-bridged tetraorganodistannoxanes with a mixed double ladder structure

The reaction of Me₃SiCH₂Cl₂Sn(CH₂)₃SnCl₂Ph (6) with (tBu₂SnO)₃ gave a statistical mixture of the corresponding tetraorganodistannoxanes whereas the reaction of the spacer-bridged ditin tetrachlorides RCl₂Sn(CH₂)₄SnCl₂R (3, R = Me₃CCH₂; 4, R = Me₂CHCH₂; 10, R = Me₃SiCH₂) with the polymeric spacer-bridged ditin oxides [R(O)Sn(CH₂)₄Sn(O)R]_n (7, R = Me₂CHCH₂; 8, R = Me₃CCH₂; 11, R = Me₃SiCH₂) provided the mixed double ladder compounds {[R(Cl)Sn(CH₂)₄Sn(Cl)R][R(Cl)Sn(CH₂)₄Sn(Cl)R']O₂}₂ (9, R = Me₃CCH₂, R' = Me₂CHCH₂; 12, R = Me₃CCH₂, R' = Me₃SiCH₂) in almost quantitative yield. In solution, 9 and 12 are in equilibrium with their corresponding dimers, as was evidenced by ¹¹⁹Sn NMR spectroscopy, molecular mass determination, and electrospray mass spectrometry. The molecular structures of 9 and 12 were established by single crystal X-ray diffraction.

π-Selective stationary phases: (I) Influence of the spacer chain length of phenyl type phases on the aromatic and methylene selectivity of aromatic compounds in reversed phase high performance liquid chromatography

Phenyl type stationary phases of increasing spacer chain length (phenyl, methyl phenyl, ethyl phenyl, propyl phenyl and butyl phenyl, with 0–4 carbon atoms in the spacer chain, respectively) were synthesised and packed in house to determine the impact that the spacer chain length has on the retention process. Two trends in the aromatic selectivity, q_aromatic, were observed, depending on whether the number of carbon atoms in the spacer chain is even or odd. Linear log k′ vs ϕ plots were obtained for each stationary phase and the S coefficient was determined from the gradient of these plots. For the phenyl type phases, the S vs n_c plots of the retention factors of linear polycyclic aromatic hydrocarbons vs the number of rings exhibit a distinct discontinuity that between 3 and 4 rings, which increases with increasing spacer chain length for even phases but decreases for odd phases. Accordingly, we suggest that the retention factors depend differently on the number of carbon atoms in the spacer chain depending on whether this number is even or odd and that this effect is caused by different orientations of the aromatic ring relative to the silica surface.