Degradation induced variation of LC transition of poly(n-undecyl isocyanate)

The first-order thermal transitions including side-chain melting, crystal-LC, biphasic chimney-like, and isotropic transitions of poly(n-undecyl isocyanate) (PUDIC) were investigated by varying its thermal history. After annealing at 140 °C for different periods of time, it leads to different degrees of backbiting degradation into n-undecyl isocyanurate trimer which behaves as a solvent for the rest non-degraded/rigid PUDIC to change into a lyotropic LC from thermotropic transition. Based on the degree of degradation, various amounts of trimers are present and the PUDIC demonstrates different types of thermal transitions found in DSC thermograms due to the variation of the non-degraded PUDIC concentration in solvent trimers. Finally, a phase diagram includes all types of crystallines, LC, and isotropic regions can be drawn according to the DSC thermograms.     

How light affects 5,10,15-tris(pentafluorophenyl)corrole

5,10,15-Tris(pentafluorophenyl)corrole slowly undergoes oligomerization when left in solution at room temperature, under air and ambient light. This transformation was studied in different solvents (chloroform, dichloromethane, and toluene) and the main resulting products were identified as the 3,3′-corrole dimer 2a and the 3,3′,17′,3′′-corrole trimer 3a.     

The acclimative response of the main light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) to elevated irradiances at the level of trimeric subunits

The changes in structural organization of the major light-harvesting chlorophyll a/b–protein complex of photosystem II (LHC II) at the level of trimeric subcomplexes were studied in spinach plants grown under low light conditions (50 μmol quanta m⁻² s⁻¹) and then acclimated to elevated irradiances. By monitoring photochemical quenching of fluorescence yield (q_P), photosystem II (PS II) functional status was assessed in leaves of plants acclimated to a range of elevated irradiances. Three separate acclimative irradiances were selected for the experiments, reflecting: limiting light conditions (150 μmol quanta m⁻² s⁻¹), near to the inflexion point on the irradiance curve conditions (300 μmol quanta m⁻² s⁻¹) and an excessive light, causing a moderate stress in the form of down regulation of PS II (450 μmol quanta m⁻² s⁻¹). An immunoblot analysis showed that there was a clear decline in an abundance on chlorophyll basis of Lhcb1-3 apoproteins as an acclimative irradiance increased from 50 to 450 μmol quanta m⁻² s⁻¹, with Lhcb1 decreasing to a lesser extent than Lhcb2 and Lhcb3 (only at excessive irradiance). When analyzed by non-denaturing isoelectric focusing BBY membrane fragments (PSII-enriched, stacked thylakoid membranes) isolated from low light-grown plants were resolved into nine fractions, seven of which (labelled 3–9) were established by us previously [Jackowski and Pielucha, J. Photochem. Photobiol. B: Biol. 64 (2001) 45] to be LHC II subcomplexes representing mixed populations of closely similar trimers, comprising permutations of Lhcb1 and Lhcb2 (subcomplexes 3–7) or Lhcb1-3 (subcomplexes 8 and 9). A heterogeneity with regard to accumulation behaviour of LHC II subcomplexes in response to elevated irradiances was revealed. The subcomplexes 5 and 6 were accumulating at similar level, regardless of the light irradiance experienced. Another group consisting of the subcomplexes 3 and 4 (the most basic ones) showed a progressive increase in relative abundance with increasing an irradiance intensity whereas the subcomplexes 7–9 (the most acidic ones) exhibited a progressive decline in their relative abundance during an acclimation of spinach plants to elevated irradiances thus they may collectively represent an elevated irradiance-responsive subunit of LHCII.     

Reactivity studies of [Pd2(μ-X)2(PBu3)2] (X = Br, I) with CNR (R = 2,6-dimethylphenyl), H2 and alkynes

Improved syntheses for the dimeric compounds [Pd₂(μ-X)₂(PBu^t₃)₂] (X = Br, I) have been developed and the X-ray crystal structure for the dimer with X = 1 is reported. The reactions of these dimers with CNR (R = 2,6-dimethylphenyl), H₂ and a series of terminal and substituted alkynes are also reported. The dimer with X = Br is an initiator for the catalytic polymerisation of phenylacetylene. The product of the dimers with disubstituted alkynes results in the synthesis of trimeric species with formula [Pd₃(μ-X){ν²-C₄(CO₂R)₄}₂][PBu^t₃)Me]₂ (X = Br, I; R = Me, Et). The X-ray crystal structure of one of these compounds (when R = Et and X = I) is presented, demonstrating that the palladium dimers assist the C---C coupling of the alkynes.     

Synthesis,characterisation and crystal structures of three trinuclear cadmium(II) complexes with multidentate Schiff base ligands

Three novel Schiff base Cd(II) trimeric complexes, [Cd₃(L¹)₂(SCN)₂(CF₃COO)₂] (1), [Cd₃(L¹)₂(SCN)₂(HCONMe₂)] (2) and [Cd₃(L²)₂{N(CN)₂}₂] (3) have been prepared from two different symmetrical Schiff bases H₂L¹ and H₂L² (where H₂L¹ = N¹,N³-bis(salicylideneimino)diethylenetriamine, a potentially pentadentate Schiff base with a N₃O₂ donor set, and H₂L² = N¹,N³-bis(3-methoxysalicylideneimino)diethylenetriamine, a potentially heptadentate Schiff base with a N₃O₄ donor set). All the complexes have been synthesised under similar synthetic procedures and their crystal structures have been established by single crystal X-ray diffraction methods. The ligands and their metal complexes have been characterised by analytical and spectroscopic techniques. Among the three complexes, 1 and 3 are linear whereas 2 is a cyclic trimer. In 1 and 3, all the doubly phenoxo bridged Cd(II) metal centres are in a distorted octahedral environment. In complex 2, two of the three Cd(II) centres reside in a distorted octahedral environment and the remaining one enjoys a monocapped octahedral geometry. Altogether the variety in the bridging mode of two new salen-type ligands has been established through these complexes.     

A polyoxoniobate based on dimeric hexanionbate: [Cu(en)2]4{[Nb6O19H2]K(H2O)5}2 · (H2en) · 17H2O

A polyoxoniobate, [Cu(en)₂]₄{[Nb₆O₁₉H₂]K(H₂O)₅}₂ ? (H₂en) ? 17H₂O (en = ethylenediamine) (1), has been synthesized and characterized by elemental analysis, IR, XPS, TGA, and single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P 1, with a = 12.3533(16) Å, b = 12.7188(16) Å, c = 29.626(4) Å, α = 93.235(2)°, β = 96.094(1)°, γ = 106.098(2)°, V = 4429.0(10) ų, Z = 2. The polyoxoanion is composed of a Lindqvist-type [Nb₆O₁₉H₂]^6? dimer bi-bridged via two K⁺. K⁺ is 10-coordinate with 10 oxygens, three from one [Nb₆O₁₉H₂]^6?, one from a terminal oxygen of another [Nb₆O₁₉H₂]^6? moiety, and the other six from water molecule. Adjacent dimeric polyoxoanions are linked to form an infinite 1-D chain via O–H ··· O hydrogen-bonding interactions which exist between the two water trimers and the dimeric polyoxoanions.     

Two-dimensional gel permeation chromatography (2D GPC) correlation studies of the aggregate-aggregate interactions in acid-catalyzed triethoxysilyl-terminated polystyrene systems. The effect of specific catalysts on growth process

A set of time resolved gel-permeation chromatography (GPC) profiles, for the reaction mixture of a well-defined polymeric silane coupling agent, triethoxysilyl-terminated polystyrene with molecular weight equal to 8000 (TESi-PS (8000)), catalyzed by HCl (0.1 mol/kg) in tetrahydrofuran (THF), was measured over a long time scale (1–768 h). The GPC profiles were then converted to two-dimensional (2D) correlation spectra. The 2D GPC correlation spectra were compared with those for the CH₃SO₃H (0.1 mol/kg)-catalyzed TESi-PS (8000)-THF system. It has been demonstrated that predominant production of less-reactive oligomers in the HCl-catalyzed system hinders further growth of the oligomer, while formation of reactive oligomers leads to further growth of polymeric precursors in the CH₃SO₃H-catalyzed system.     

Anticancer activity and DNA binding property of the trimers of triphenylethylene-coumarin hybrids

Novel trimers of triphenylethylene-coumarin hybrid containing two amino side chains(5a-d and 6a-d)were designed and synthesized by the condensation of 1,3,5-benzenetricarboxylic acid with the varied amino monomeric hybrids catalyzed by HATU and DIPEA at room temperature.The extended trimeric compound 6a(R = piperidinyl) exhibited significant anti-proliferative activity against three cancer cells at IC_(50) of near 10μmol/L UV-vis,fluorescence(lifetime) and thermal denaturation exhibited that 6a had significant interaction with Ct-DNA by the intercalative mode of binding.The order of their antiproliferative activities was 6(a,d) 5(a,d) and(5-6)a (5-6)d,respectively,in accordance with that of their DNA binding properties,which suggested that the prolonged linker(six carbons) and piperidinyl group on the side chains are beneficial to DNA binding and the anti-tumor activity.     

New Phosphorus Chemistry Leads to Unnatural Aminoacid Trimers

Unnatural or modified amino acids have become important biochemical vectors because of their potential utility in diagnostic or therapeutic medicine. Our ongoing research in hydroxymethyl phosphine chemistry has provided unique reaction pathways to produce unnatural aminoacid. The reaction of tris(hydroxymethyl)phosphine (THP) with chiral aminoacid L-alanine produced trimeric alanine in excellent yields. The X-ray crystal structure of 1 shows an unusual layered structure with water molecules sandwiched between the layers. Implications of this new chemistry in such emerging areas as chiral technology and drug discovery will be presented.