A new technique to characterize mono-molecular micelles in random ethylene–propylene copolymers

A new technique to investigate the nano-structure of ethylene–propylene (EP) random copolymers has been developed. It consists in the measurement of the turbidity which develops at a lower critical solution temperature (LCST) in pentane solutions. The information on the solution comes from different types of turbidity obtained during a step-by-step temperature increase. The transient turbidity (h_i) is associated with random coils (I) and structured coils (II) while the stable turbidity comes from aggregates (III). The proportion of (I), (II) and (III) depends on the solution history and on the solvent. The M_w distribution can be obtained from the set h_i (T_i) of (I). Turbidity (II) has an unexpected gap in the h_i (T_i) trace. The gap (10–20 K) is explained by the presence of two entities in solution. Their temperatures of phase separation permit their identification as monomolecular micelles, whose outer core is either E-rich or P-rich. This nano-structure is thought to exist in the solid and also in solution as a metastable state. The technique can differentiate between mobile chains in solutions (I, II) and attached chains in a network (III) through the sedimentation behaviour of the concentrated phase. Three samples with a similar (EP) content (0.75) made with different catalysts have been analysed by LCST and slow calorimetry.     

Synthesis and solution properties of poly(trans-5-ethylproline). A slow mutarotating substituted polyproline

An optically active polypeptide, poly(trans-5-ethylproline) (PT5EP) was synthesized and its solution properties were observed to investigate the conformational changes with various conditions. The trans-5-ethyl substitution on polyproline showed noticeable perturbed effects on the conformations of the polypeptide as well as mutarotation of the polypeptide in solution. Circular dichroism (CD) spectra suggested that the polypeptide existed in a poly(L -proline) form-I-type helix and mutarotated slowly to an intermediate conformation in which some of the amide bonds had rotated to a trans conformation. In trifluoroethanol (TFE) solution the polymer took more than 20 days to change from a form-I-type helix conformation, in which CD bands for D -PT5EP are at 199.5 ± 1.0 (positive), 115.5 ± 0.5 (negative), and around 238 nm (positive), to an intermediate conformation. Upon addition of trifluoroacetic acid (TFA) to a TFE solution, the polymer was transformed to form-II-type polymers. Even a greater change in conformation was observed in a solution of TFA or in LiClO₄-TFE. The overall change of the intensity ratio R_CD of positive to negative CD bands of D -PT5EP was from 0.6–0.7 to 30. Reverse mutarotation toward the original form I was observed when n-butyl alcohol, water, or THF was added to a solution containing the form II polymer. A blue shift of the UV spectra and a change in the NMR spectrum also supported the concept of this conformational change.     

Reclassifying exciton-phonon coupling in molecular aggregates: evidence of strong nonadiabatic coupling in oligothiophene crystals

Exciton-phonon (EP) coupling in molecular aggregates is reexamined in cases where extended intermolecular interactions result in low-energy excitons with high effective masses. The analysis is based on a single intramolecular vibrational mode with frequency omega0 and Huang-Rhys factor lambda2. When the curvature Jc at the exciton band bottom is much smaller than the free-exciton Davydov splitting W, the strength of the EP coupling is determined by comparing the nuclear relaxation energy lambda2omega0 with the curvature. In this way, weak (lambda2omega0<4piJc), intermediate I (lambda2omega0 approximately 4piJc), and strong I (lambda2omega0>4piJc) coupling regimes are introduced. The conventional intermediate (lambda2omega0 approximately W) and strong (lambda2omega0>W) EP coupling regimes originally defined by Simpson and Peterson [J. Chem. Phys. 26, 588 (1957)] are based solely on the Davydov splitting and are referred to here as intermediate II and strong II regimes, respectively. Within the intermediate I and strong I regimes the near degeneracy of the low-energy excitons allows efficient nonadiabatic coupling, resulting in a spectral splitting between the b- and ac-polarized first replicas in the vibronic progression characterizing optical absorption. Such spectral signatures are clearly observed in OT4 thin films and crystals, where splittings for the lowest energy mode with omega0=161 cm(-1) are as large as 30 cm(-1) with a small variation due to sample disorder. Numerical calculations using a multiphonon BO basis set and a Hamiltonian including linear EP coupling yield excellent agreement with experiment.     

STATE I-STATE II TRANSITIONS IN THE THERMOPHILIC BLUE-GREEN ALGA (CYANOBACTERIUM) Synechococcus lividus*

Time courses of state I-state II transitions were measured in the thermophilic blue-green alga (Cyanobacterium), Synechococcus lividus, that was grown at 55°C. The rate of the state I–II transition using light II illumination was the same as that in the dark, and the dark state was identified to be state II. Therefore, light regulation attained by state transitions is produced by the state II–I transition induced by system I light. The redox level of plastoquinone did not affect this dark state II. Arrhenius plots of the state transitions showed a break point around 43°C that corresponded to the phase transition temperature of this alga. Since both the state I–II and II–I transitions were very much temperature-independent, we could keep the alga in either state for a long time at a “low” temperature such as room temperature. Activities of both photosystems I and II in states I and II were also measured. After a state II–I transition, the system II activity increased about 16% and at the same time, svstem I activity decreased about 30%.     

4‐Vinyl­benzoic acid and 9‐vinyl­anthracene

The crystal structures of two styrene analogues, 4‐vinyl­benzoic acid, C₉H₈O₂, (I), and 9‐vinyl­anthracene, C₁₆H₁₂, (II), were determined by X‐ray analyses at 108 and 293 K for (I) and at 123 and 293 K for (II). In (I), a pair of mol­ecules around an inversion center form a dimer connected by two carboxyl groups. The anthracene planes of two mol­ecules in (II) are antiparallel to each other around an inversion center. The vinyl group of (I) is almost coplanar with the phenyl ring, whereas the vinyl group of (II) is nearly perpendicular to the anthracene plane. In (I), the bond length of the vinyl group at 293 K is significantly shorter than that at 108 K [1.288 (2) versus 1.3248 (14) Å] suggesting a bias of the thermal motion, whereas the bond lengths are not so different between the two temperatures in (II) [1.3266 (15) versus 1.310 (2) Å].     

Synthesis,Structure, Magnetic and Optical Properties of Ternary Thio‐germanates: Ln4(GeS4)3 (Ln = Ce,Nd)

Single crystals of two ternary thio‐germanates containing rare‐earth metals, Ln₄(GeS₄)₃ (Ln = Ce ( I ), Nd ( II )), have been isolated from the reaction of anhydrous rare‐earth trichloride (LnCl₃) and ternary sodium thio‐germanate (Na₂GeS₃) in evacuated quartz ampoules. We have determined the crystal structure of the compounds, which are isostructural to La₄(GeS₄)₃ and crystallize in trigonal system in the space group R3c with the cell dimensions: I , a = b = 19.375(3) Å, c = 8.028(2) Å, Z = 6; II , a = b = 19.250(3) Å, c = 7.949(2) Å, Z = 6. The structure is built with the complex network of two independent tricapped trigonal prisms of CeS₉, in which Ge atoms occupy tetrahedral holes of sulfur atoms. The bulk synthesis of the two compounds has also been achieved by the stoichiometric combination of the elements. The magnetic and optical properties of the compounds have been investigated. The magnetic moments of 2.32 and 3.49 μ_B for I and II , respectively, are in good agreement with the theoretical magnetic moments of Ce and Nd in the +3 oxidation state. The optical band gap of I is found to be located around 2.3 eV, while the optical band gap of II lies around 2.62 eV. In addition, Raman spectroscopic characterizations have also been performed for I , II , and La₄(GeS₄)₃.     

Excited state dipole moments and polarizabilities of centrosymmetric and dimeric molecules. I. Model study of a bichromophoric molecule

Refractometric, dielectric and electro-optical absorption measurements are reported for 1-dimethylamino-2,6-dicyano-4-methyl-benzene (I) and 1,4-bis(4′-dimethylamino-3′,5′-dicyanophenyl)bicyclo[2.2.2]octane (II). The evaluation leads to dipole moments and polarizabilities of the ground state as well as the first dipole allowed singlet state. The experimental res excellently substantiate the method of electro-optical absorption measurements in solution. It is shown that the excited dimer wavefunctions of the bichromophoric molecule II localize by solvent induced local site perturbations.     

4-Alkoxy-2-hydroxy-4′-vinylbenzophenones,ultraviolet-absorbing monomers

2,4-Dihydroxy-4′-vinylbenzophenone (I) and its 4-alkyl ethers (II), Me, Et, n-Bu, n-Oct, and n-dodecyl, were prepared in three steps by Hoesch synthesis, starting with p-(2-bromoethyl) benzonitrile and resorcinol and its monoalkyl ethers. I and its precursor 2,4-dihydroxy-4′-(2-bromoethyl) benzophenone were also converted into their 4-alkyl ethers with alkyl halides in dimethylformamide (DMF) in the presence of sodium hydrogen carbonate. Copolymerizations of I and II with styrene took place smoothly with satisfactory conversions to yield copolymers with ε-values around 10⁴ L/mol cm^?1 per benzophenone unit over the ultraviolet (UV) range of 235–340nm.     

(1R,8R,11R)‐3,3,11‐Tri­methyl‐6,6‐ethyl­ene­dioxy­bi­cyclo­[6.3.0]­undecan‐2‐one and (1R,2R,8R,11R)‐3,3,11‐tri­methyl‐6,6‐ethylenedioxybicyclo[6.3.0]undecan‐2‐ol

The reduction of (1R,8R,11R)‐3,3,11‐tri­methyl‐6,6‐ethyl­ene­dioxy­bi­cyclo­[6.3.0]­undecan‐2‐one, C₁₆H₂₆O₃, (I), gave exclusively an alcohol, C₁₆H₂₈O₃, (II). The stereochemistry of the hydroxyl group in (II) was shown as R. The conformation around the eight‐membered carbocycle in (I) differs markedly from that in (II).     

Polymerization and conformational studies of poly(trans-3-ethyl-D and L-proline)

Poly(L -trans-3-ethylproline), L -PT3EP, and poly(D -trans-3-ethylproline), D -PT3EP, were prepared by ring opening polymerization of the corresponding N-carboxyanhydrides (NCA) using triethylamine as an initiator. Using circular dichroism spectroscopy, it was shown that the incorporation of an ethyl group at the 3 position of the pyrrolidine ring caused a noticeable change in the conformational behavior of the polymer in solution. The ethyl group limited to some extent rotation of the polymer chain around the C_? ? CO bond and prevented the mutarotation between the two forms found in poly-L -proline polymers.     

Microencapsulated ammonium polyphosphate with epoxy resin shell: preparation,characterization, and application in EP system

Microencapsulated ammonium polyphosphate with an epoxy resin (EP) shell (MCAPP) was prepared by in situ method, and was characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), and thermgravimetric analysis (TGA). Compared to ammonium polyphosphate (APP), MCAPP has smaller particle sizes and lower water solubility. The effect of MCAPP on the fire performance of EP was studied by using limiting oxygen index (LOI) and UL‐94 tests. When the same loading levels of APP or MCAPP were added into EP, the LOI and UL‐94 tests show similar results. Tensile, bending, and impact strengths of the EP/APP and EP/MCAPP composites were also evaluated, and the results indicate that MCAPP has much less negative influence on the mechanical properties than APP. Copyright © 2010 John Wiley & Sons, Ltd.     

N‐band Hubbard models. III. Boson–fermion and interaction–boson models for high‐Tc superconductivity

In this series of articles (I, II), N‐band Hubbard models have been considered for strongly correlated electron systems, which are realized in d–p, π–d, π–R, and σ–R conjugated systems. The magnetism and superconductivity of these systems have been elucidated in terms of effective exchange integrals (J), which are calculated by first‐principle methods. In part III of this series, the BCS–BEC crossover theory, has been introduced to elucidate the physical foundation of our J and JP model for the high‐T_c superconductivity (HTSC). The boson–fermion (BF) model for this theory is found useful for a reasonable explanation of the experimental phase diagrams of HTSC. The underlying physics of the BF model is different from that of the slave boson field‐theoretical model assuming spinon–holon condensations in the low dimension. The interaction boson model (IBM) for nuclear matter is also employed to describe the cooperative mechanisms of electron–phonon (EP), spin fluctuation (SF), charge fluctuation (CF), and many‐bands (MB) effects. This phenomenological model is useful for pictorial understanding and for the theoretical explanation of the cooperative mechanisms: (EP + SF), (SF + CF), (EP + SF + MB), etc. These are also investigated in analogy to BF model of fermionic gases, where the Feshbach resonance between boson and fermion is responsible for their coupling. The implications of these theoretical results are discussed in relation to recent ALPES and STM experiments for HTSC, which suggest the contributions of SF (J) and EP (P) interactions. The recently discovered superconductivity of boron‐doped diamond is examined as an example of two‐band sigma‐radical (σ–R) conjugated systems. Finally, the bipolaron model is briefly discussed in relation to boson–fermion model via EP interaction to superconductivity. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Molecular symmetry. IV. The coupled perturbed Hartree–Fock method

Symmetry methods employed in the ab initio polyatomic program HONDO are extended to the coupled perturbed Hartree–Fock (CPHF) formalism, a key step in the analytical computation of energy first derivatives for configuration interaction (CI) wavefunctions, and energy second derivatives for Hartree–Fock (HF) wavefunctions. One possible computational strategy is to construct Fock-like matrices for each nuclear coordinate in which the one- and two-electron integrals of the usual Fock matrix are replaced by the integral first derivatives. “Skeleton” matrices are constructed from the unique blocks of electron-repulsion integral derivatives. The correct matrices are generated by applying a symmetrization operator. The analysis is valid for many wavefunctions, including closed- or open-shell spin-restricted and spin-unrestricted HF wavefunctions. To illustrate the method, we compare the computer time required for setting up the coupled perturbed HF equations for eclipsed ethane using D_3h symmetry point group and various subgroups of D_3h. Computational times are roughly inversely proportional to the order of the point group.     

Synthesis, crystal structure, spectroscopic and electrochemical characterization of the dinuclear complex {tetra-μ-[(±)-2-(p-methoxyphenoxy)-propionato-O,O′]bis(aqua)dicopper(II)}

Structural, electrochemical and spectroscopic data of a new dinuclear copper(II) complex with (±)-2-(p-methoxyphenoxy)propionic acid are reported. The complex {tetra-μ-[(±)-2-(p-methoxyphenoxy)propionato-O,O′]-bis(aqua)dicopper(II)} crystallizes in the monoclinic system, space group P2₁/n with a = 14.149(1) ?, b = 7.495(1) ?, c = 19.827(1) ?, β = 90.62(1) and Z = 4. X-ray diffraction data show that the two copper(II) ions are held together through four carboxylate bridges, coordinated as equatorial ligands in square pyramidal geometry. The coordination sphere around each copper ion is completed by two water molecules as axial ligands. Thermogravimetric data are consistent with such results. The ligand has an “L” type shape due to the angle formed by the β-carbon of the propionic chain and the linked p-methoxyphenoxy group. This conformation contributes to the occurrence of a peculiar structure of the complex. The complex retains its dinuclear nature when dissolved in acetonitrile, but it decomposes into the corresponding mononuclear species if dissolved in ethanol, according to the EPR measurements. Further, cyclic voltammograms of the complex in acetonitrile show that the dinuclear species maintains the same structure, in agreement with the EPR data in this solvent. The voltammogram shows two irreversible reduction waves at E _pc = −0.73 and −1.04 V vs. Ag/AgCl assigned to the Cu(II)/Cu(I) and Cu(I)/Cu° redox couples, respectively, and two successive oxidation waves at E _pa =− 0.01 and +1.41 V vs. Ag/AgCl, assigned to the Cu°/Cu(I) and Cu(I)/Cu(II) redox couples, respectively, in addition to the oxidation waves of the carboxylate ligand.     

p‐Phenylenediamine and its dihydrate: two‐dimensional isomorphism and mechanism of the dehydration process,and N—H...N and N—H...π interactions

p‐Phenylenediamine can be obtained as the dihydrate, C₆H₈N₂·2H₂O, (I), and in its anhydrous form, C₆H₈N₂, (II). The asymmetric unit of (I) contains one half of the p‐phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p‐phenylenediamine molecules are arranged in layers stabilized by N—H...π interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in‐plane rotation of every fourth p‐phenylenediamine molecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.     

A mononuclear nickel(II) complex based on polypyridyl ligand: synthesis,characterization, and biological activity

[Ni(acac)₂(o-NPIP)](CH₃OH)₃ (acac = acetylacetonate), based on the polypyridyl ligand 2-(2-nitrophenyl)imidazo[4,5-f]1,10-phenanthroline) (o-NPIP), has been synthesized and characterized by single-crystal analysis, IR and electronic spectra. In the structure of Ni(II) complex, the coordination sphere around Ni(II) is distorted octahedral with one o-NPIP and two acetylacetonates. DNA binding and human serum albumin (HSA) interactions with the Ni(II) complex have been investigated by electronic absorption and fluorescence measurements, revealing that the Ni(II) complex binds with DNA via intercalative binding. The quenching constants verified a dynamic quenching mechanism between HSA and the Ni complex by fluorescence quenching. ΔG, ΔH, and ΔS at different temperatures (288, 298, and 310 K) indicated that hydrophobic interactions play a major role. Synchronous fluorescence spectral experiments revealed that the Ni(II) complex affected the microenvironment around the tryptophan residue of HSA.     

Integral Hellmann-Feynman investigations oftrans bent acetylene

The integral Hellmann-Feynman (IHF) theorem has been applied to various wavefunctions representing the¹ A _u state of acetylene with a view to testing traditional explanations of the excited state geometry. When LCAOSCF wavefunctions are used, the electronic energy changes associated with the individual corresponding orbitals (CMG's) are in sympathy with the trend in orbital (i.e. MO) energies suggested by Walsh. However, when LMO wavefunctions based on hybrid AO's are employed, the IHF results are against all experience; and imply that a change in hybridisation, fromsp tosp ², is not a viable model for the change in geometry.     

Synthesis,spectroscopic exploration,biocidal activities,and crystal structures of 3‐(3‐fluorophenyl)‐2‐phenylpropenoic acid and trimethyltin(IV) complex

The ligand, 3‐(3‐fluorophenyl)‐2‐phenylpropenoic acid, [C₁₅H₁₁FO₂] ( I ) was prepared by reacting equimolar amount of phenyl acetic acid with 3‐fluorobenzaldehyde (1:1) using Perkin condensation method. The trimethyltin(IV) carboxylate, [Me₃SnO₂FH₁₀C₁₅] ( II ) was synthesized by refluxing an equimolar (1:1) mixture of trimethyltin chloride and silver salt of the ligand acid, [C₁₅H₁₀FO₂Ag] ( Ia ). The ligand and complex both were characterized by elemental analysis, IR, mass, ¹H NMR, and X‐ray crystallographic data. On the basis of ¹H NMR data, (²J[^117/119Sn, ¹H] and C Sn C bond angle), it is concluded that the environment around the tin atom in solution is tetrahedral. The Infrared spectroscopic results showed that trimethyltin(IV) derivative has 5‐coordinated polymeric structure with bridging carboxylate groups in the solid state, which has been confirmed by the X‐ray crystallographic data. The crystal of ligand acid ( I ) is triclinic with space group Pbar1. However, the crystal of the complex ( II ) is monoclinic with space group C_2/c. The geometry around the tin atom is distorted trigonal bipyramid with O(1) and O(2) atoms in apical positions. The ligand ( I ) and complex ( II ) were also tested for their biocidal activities. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:398–406, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20032     

Synthesis and characterization of a new Schiff base derived from 2,3-diaminopyridine and 5-methoxysalicylaldehyde and its Ni(II), Cu(II) and Zn(II) complexes. Electrochemical and electrocatalytical studies

We describe the synthesis and characterization of a new tetradentate Schiff base ligand obtained from 2,3-diaminopyridine and 5-methoxysalicylaldehyde. This ligand (H₂L) reacted with nickel(II), copper(II), and zinc(II) acetates to give complexes. The ligand and its metal complexes were characterized using analytical, spectral data (UV–vis, IR, and mass spectroscopy), and cyclic voltammetry (CV). The crystal structure of the copper complex was elucidated by X-ray diffraction studies. The electrochemical behavior of these compounds, using CV, revealed that metal centers were distinguished by their intrinsic redox systems, e.g. Ni(II)/Ni(I), Cu(II)/Cu(I), and Zn(II)/Zn(I). Moreover, the electrocatalytic reactions of Ni(II) and Cu(II) complexes catalyze the oxidation of methanol and benzylic alcohol.