Calorimetry and cryo-transmission electron microscopic studies of PEG2000-grafted liposomes

The phase behavior of poly(ethylene glycol) grafted liposomes (PEG-liposomes) was investigated by differential scanning calorimetry (DSC), dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM). PEG-liposomes were prepared from mixtures of dipalmitoyl phosphatidylcholine (DPPC) and distearoyl phosphatidylethanolamine with a covalently attached PEG molecular weight of 2000 (DSPE-PEG2000). From the results of DLS measurements, the coexistence of PEG-liposomes and small molecular assemblies were confirmed at mole fractions of DSPE-PEG2000 above about 0.1. Moreover, it was confirmed that small molecular assemblies were disk micelles by cryo-TEM. However, the phase transition enthalpies of PEG-liposomes were hardly changed according to the DSC measurement, though the mole fraction of the PEG lipid increased. From these results, it was suggested that the phase transition enthalpies hardly changed despite mixed micelles being formed because the bilayer structure of the disk micelle maintains high cooperativity between the DPPC molecules.     

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin,Chlorin, and Bacteriochlorin π‐Systems

Zinc complex of pyropheophorbide‐b, a derivative of chlorophyll‐b, was covalently dimerized through ethylene glycol diester. The synthetic homo‐dyad was axially ligated with two methanol molecules from the β‐face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto‐carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, ¹H NMR and IR spectra. All the synthetic zinc chlorin homo‐ and hetero‐dyads consisting of pyropheophorbides‐a, b and/or d took the above methanol‐locked and π–π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo‐dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo‐dyads partially took such supramolecules. The J‐type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads.     

Synthesis and characterization of charged polystyrene-acrylic acid latex particles

Novel, monodisperse charged colloidal particles of polystyrene cross linked with divinylbenzene and surface-grafted with acrylic acid were synthesized by emulsion polymerization and were characterized by estimating the dissociable surface charge by conductivity titration, the particle effective charge by conductivity verses particle concentration, and the particle size by dynamic light scattering and atomic force microscopy. The structural ordering and dynamics were investigated as a function of the volume fraction of the particles using static and dynamic light scattering, respectively. Furthermore, from the electrophoresis measurements, these particles are found to have a high salt tolerance due to increases in charge as a function of salt concentration.     

Efficient H2 adsorption by nanopores of high-purity double-walled carbon nanotubes

DWNT buckypaper adsorbed much more hydrogen than did a SWNT bundle. XRD measurements and GCMC simulation results suggested that the DWNT bundle is loosely packed into an hexagonal array with interstitial pores which can efficiently adsorb H2 molecules.     

Novel Thermo‐Responsive Formation of a Hydrogel by Stereo‐Complexation between PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA Block Copolymers

Gel formation was discovered in an aqueous mixture of enantiomeric triblock copolymers, PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA. This system is characteristic in that an interesting sol–gel transition was induced by the stereo‐complexation of the PLLA and PDLA segments of the block copolymers around 37°C. The process of gel formation was clearly monitored by the rheological change, and the responsibility of the stereo‐complex formation for the gelation was confirmed by wide‐angle X‐ray scattering. The mechanism of this gel formation is discussed in relation to its potential applications.     

Preparation and characterization of ruthenium(II), rhodium(III) and iridium(III) complexes of isocyanide bearing the azo group

Reactions of [(η⁶-arene)RuCl₂]₂ (1) (η⁶-arene=p-cymene (1a), 1,3,5-Me₃C₆H₃ (1b), 1,2,3-Me₃C₆H₃ (1c) 1,2,3,4-Me₄C₆H₂(1d), 1,2,3,5-Me₄C₆H₂ (1e) and C₆Me₆ (1f)) or [Cp*MCl₂]₂ (M=Rh (2), Ir (3); Cp*=C₅Me₅) with 4-isocyanoazobenzene (RNC) and 4,4′-diisocyanoazobenzene (CN–R–NC) gave mononuclear and dinuclear complexes, [(η⁶-arene)Ru(CNC₆H₄N=NC₆H₅)Cl₂] (4a–f), [Cp*M(CNC₆H₄N=NC₆H₅)Cl₂] (5: M=Rh; 6: M=Ir)_, [{(η⁶-arene)RuCl₂}₂{μ-CNC₆H₄N=NC₆H₄NC}] (8a–f) and [(Cp*MCl₂)₂(μ-CNC₆H₄N=NC₆H₄NC)}] (9: M=Rh; 10: M=Ir)_, respectively. It was confirmed by X-ray analyses of 4a and 5 that these complexes have trans-forms for the ---N=N--- moieties. Reaction of [Cp*Rh(dppf)(MeCN)](PF₆)₂ (dppf=1,1′-bis (diphenylphosphino)ferrocene) with 4-isocyanoazobenzene gave [Cp*Rh(dppf)(CNC₆H₄N=NC₆H₅)](PF₆)₂ (7), confirmed by X-ray analysis. Complex 8b reacted with Ag(CF₃SO₃), giving a rectangular tetranuclear complex 11b, [{(η⁶-1,3,5-Me₃C₆H₃)Ru(μ-Cl}₄(μ-CNC₆H₄N=NC₆H₄NC)₂](CF₃SO₃)₄ bridged by four Cl atoms and two μ-diisocyanoazobenzene ligands. Photochemical reactions of the ruthenium complexes (4 and 8) led to the decomposition of the complexes, whereas those of 5, 7, 9 and 10 underwent a trans-to-cis isomerization. In the electrochemical reactions the reductive waves about −1.50 V for 4 and −1.44 V for 8 are due to the reduction of azo group, [---N=N---]→[---N=N---]²⁻. The irreversible oxidative waves at ca. 0.87 V for the 4 and at ca. 0.85 V for 8 came from the oxidation of Ru(II)→Ru(III).     

Excited-state intramolecular proton transfer (ESIPT) fluorescence from 3-amidophthalimides displaying RGBY emission in the solid state

Fluorescence properties of phthalimide derivatives (1) incorporating sulfonamide and acetamide functionalities at the 3-position were investigated both in solution and in the solid states to reveal the effects of the amide functionalities on the fluorescence properties. In the solid state, sulfonamides 1a and 1b, respectively, gave off red (λ^F_max 595?nm) and green (λ^F_max 537?nm) emission through an ESIPT process. Acetamides 1c and 1d, respectively displayed blue (λ^F_max 432?nm) and yellow (λ^F_max 560?nm) emission. Through simply modifying the amide functionality, phthalimide 1 displayed multicolor RGBY emission in the solid state.     

Supercritical fluid chromatography with post-column addition of supporting electrolyte solution for electrochemical determination of tocopherol and tocotrienol isomers

A supercritical fluid chromatography with electrochemical detection system was developed for the simultaneous determination of tocopherol and tocotrienol isomers. The supercritical fluid chromatography with electrochemical detection system was connected with an additional pump to create a flow path to add a supporting electrolyte solution. The supporting electrolyte solution was mixed with a mobile phase in a post-column fashion, enabling the independent control of the separation and detection. After optimization of the measurement conditions, vitamin E isomers and an internal standard substance (2,2,5,7,8-pentamethyl-6-hydroxychroman) were separated within 30 min using a mixture of supercritical carbon dioxide and methanol (99:1, v/v) as a mobile phase and a cyanopropyl column (4.6 mm inner diameter × 250 mm length, 5 μm). For the electrochemical detection, methanol containing 1.0 mol/L ammonium acetate was used as a supporting electrolyte solution, and the applied potential was set at +0.8 V. This analytical method showed good linearity (5–100 μg/mL) and repeatability (less than 2.5% relative standard deviation, n = 6) and was applicable to the determination of tocopherol and tocotrienol isomers in nutrition supplements.     

Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged {HAT ⋅ (FeIICl2)3}n (n=2- and 3-) Assemblies of Hexaazatriphenylenes (HAT)

Hexaazatrianthracene (HATA) and hexaazatriphenylenehexacarbonitrile {HAT(CN)₆} are reduced by metallic iron in the presence of crystal violet (CV⁺)(Cl⁻). Anionic ligands are produced, which simultaneously coordinate three Fe^IICl₂ to form (CV⁺)₂{HATA ⋅ (Fe^IICl₂)₃}²⁻ ⋅ 3 C₆H₄Cl₂ ( 1 ) and (CV⁺)₃{HAT(CN)_6. (Fe^IICl₂)₃}³⁻ ⋅ 0.5CVCl ⋅ 2.5 C₆H₄Cl₂ ( 2 ). High-spin (S=2) Fe^II atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between Fe^II in {HATA ⋅ (Fe^IICl₂)₃}²⁻ ( 1 ) with a Weiss temperature (Θ) of −80 K, the PHI estimated exchange interaction (J) is −4.7 cm⁻¹. The {HAT(CN)₆ ⋅ (Fe^IICl₂)₃}³⁻ assembly is obtained in 2 . The formation of HAT(CN)₆^.3− is supported by the appearance of an intense EPR signal with g=2.0037. The magnetic behavior of 2 is described by a strong antiferromagnetic coupling between the Fe^II and HAT(CN)₆^.3− spins with J₁=−164 cm⁻¹ (−2 J formalism) and by a weaker antiferromagnetic coupling between the Fe^II spins with J₂=−15.4 cm⁻¹. The stronger coupling results in the spins of the three Fe^IICl₂ units to be aligned parallel to each other in the assembly. As a result, an increase of the χ_MT values is observed with the decrease of temperature from 9.82 at 300 K up to 15.06 emu ⋅ K/mol at 6 K, and the Weiss temperature is also positive being at +23 K. Thus, a change in the charge and spin state of the HAT-type ligand to ⋅3⁻ results in ferromagnetic alignment of the Fe^II spins, yielding a high-spin (S=11/2) system. DFT calculations showed that, due to the high symmetry and nearly degenerated LUMO of both HATA and HAT(CN)₆, their complexes with Fe^IICl₂ have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.     

Crystalline Rhodium-Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

Crystalline {Cryptand(Na⁺)}[(COD)Rh^ICl⋅Sn^II(Pc³⁻)]⁻⋅2C₆H₄Cl₂ ( 1 ) and {Cryptand(Cs⁺)}[(COD)Rh^I⋅Sn^II(Pc⁴⁻)]⁻⋅C₆H₅CH₃ ( 2 ) complexes were obtained via the interaction of [Sn^II(Pc³⁻)]⁻ and [Sn^II(Pc⁴⁻)]²⁻, respectively, with organometallic {(COD)RhCl}₂ dimer (COD is 1,5-cyclooctadiene). Dissociation of {(COD)RhCl}₂ followed by the Rh−Sn binding is observed at the formation of 1 . Elimination of the chlorine atom at the rhodium atom is observed in 2 , and rhodium is additionally coordinated to the imine nitrogen atom of Pc⁴⁻. The complexes contain mono- Pc⋅³⁻ and doubly reduced Pc⁴⁻ species, respectively, that is supported by the data of XRD analysis as well as optical and magnetic properties of 1 and 2 . There is an alternation of C-N_imine bonds in the macrocycles, which gradually increases with increasing negative charge on the macrocycle. The difference between shorter and longer bonds increases from 0.051 Å in Pc³⁻ to 0.075 Å in Pc⁴⁻. The formation of 1 is accompanied by an essential blue shift of the Q-band of starting SnPc and the appearance of a new intense band at 1031 nm. The even stronger shift of the Q-band is observed in the spectrum of 2 , but the band in the near-IR range becomes weaker. The value of effective magnetic moment of 1 is 1.76 μ_B at 300 K corresponding the contribution of the Pc³⁻ radical trianions (S=1/2). Only weak magnetic coupling with the Weise temperature of −3 K is observed in 1 due to weak π–π interaction between the macrocycles in the chains. Paramagnetic Pc³⁻ species additionally monitored by EPR spectroscopy show a strong temperature dependence of g-factor and linewidth of the EPR signal. Complex 2 is diamagnetic and EPR silent.