Kinetic and Morphological Investigation on the Magnesium Ethoxide-Based Ziegler-Natta Catalyst for Propylene Polymerization Using Typical External Donors

Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂-supported Ziegler-Natta catalyst synthesized from a Mg(OEt)₂ precursor in the presence and absence of two different external donors are investigated. The kinetic profiles show similar trend in presence and absence of donors. The Mg(OEt)₂-based catalyst show a mild activation and a long-standing activity with good replication of the catalyst particles. The results show that synthesized Mg(OEt)₂-based Ziegler-Natta catalyst presents a highly stable polymerization activity and good replication due to the uniform Ti distribution all over the catalyst particles.     

Synthesis of a protected ribonucleoside phosphoramidite-linked spin label via an alkynyl chain at the 5′ position of uridine

New, spin-labeled nucleosides, and an efficient synthetic route for a modified uridine amidite, were developed. The spin-labeled part was the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group, which was linked via an alkynyl chain at the 5 position of uridine. Three typical protecting groups, the t-butyldimethylsilyl (TBDMS) group at 2′, the dimethoxytrityl (DMTr) group at 5′, and the phosphoramidite group at 3′, were introduced to produce an automated nucleic acid synthesizer. The TEMPO group at the 5 position in the uridine structure affected introduction of bulky protecting groups, such as the DMTr group at the 5′ position and the TBDMS group at the 2′ position. The electron paramagnetic resonance (EPR) data revealed a nitroxyl radical in the structure of synthetic nucleoside compounds; however, RNA produced by automated synthesis using a TEMPO-linked uridine phosphoramidite building block was EPR silent.     

Ab initio GB study of prebiotic synthesis of purine precursors from aqueous hydrogen cyanide: dimerization reaction of HCN in aqueous solution

Ab initio MO GB theory which includes the continuum model of solvent effect using generalized Born formula has been applied to the dimerization reaction of HCN in aqueous solution which is the starting step in prebiotic synthesis of purine precursors from aqueous hydrogen cyanide. Three steps considered were: (i) the reaction of HCN and H₂O to produce the CN⁻ anion, (ii) the reaction of CN⁻ with HCN to give the NC–CH=N⁻ anion, and (iii) the addition of a proton to the anion to give iminoacetonitrile. The formation of CN⁻ ion from HCN in aqueous solution requires 15.1 kcal/mol (the experimental value estimated from the dissociation constant of HCN in water is 14.8 kcal/mol). The reaction of CN⁻ with HCN requires the activation energy of 32.2 kcal/mol (MP2/6-31++G^**//HF/6-31++G^**) to give the dimer. This barrier height is reduced to 26.1 kcal/mol when HCN is associated with H₃O⁺. In the presence of NH₃ in aqueous solution, CN⁻ is produced easily by the reaction of HCN and NH₃ with a low activation energy of 4.3 kcal/mol. It was shown that the formation of CN⁻ becomes easier in ammoniacal solution, and the dimerization occurs efficiently in aqueous solutions which contain NH₃.     

Energy and photoinduced electron transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex

Functional mimics of a photosynthetic antenna-reaction center complex comprising five bis(phenylethynyl)anthracene antenna moieties and a porphyrin-fullerene dyad organized by a central hexaphenylbenzene core have been prepared and studied spectroscopically. The molecules successfully integrate singlet-singlet energy transfer and photoinduced electron transfer. Energy transfer from the five antennas to the porphyrin occurs on the picosecond time scale with a quantum yield of 1.0. Comparisons with model compounds and theory suggest that the F?rster mechanism plays a major role in the extremely rapid energy transfer, which occurs at rates comparable to those seen in some photosynthetic antenna systems. A through-bond, electron exchange mechanism also contributes. The porphyrin first excited singlet state donates an electron to the attached fullerene to yield a P(*+)-C(60)(*-) charge-separated state, which has a lifetime of several nanoseconds. The quantum yield of charge separation based on light absorbed by the antenna chromophores is 80% for the free base molecule and 96% for the zinc analogue.     

Semipermeable polymer vesicle (PICsome) self-assembled in aqueous medium from a pair of oppositely charged block copolymers: physiologically stable micro-/nanocontainers of water-soluble macromolecules

A new entity of polymer vesicle with a polyion complex (PIC) membrane, a PICsome, was prepared by simple mixing of a pair of oppositely charged block copolymers, composed of biocompatible PEG and poly(amino acid)s, in an aqueous medium. Flow particle image analysis revealed the formation of spherical particles with a size range up to 10 mum. Observation by dark-field and confocal laser scanning microscopes clearly confirmed that the PICsome has a hollow structure with an inner-water phase, in which FITC-dextran emitting green fluorescence was successfully encapsulated simply by the simultaneous mixing with the block copolymers. Confocal laser scanning microscopic observation and spectral analysis revealed the smooth penetration of a low molecular weight fluorescent dye (TRITC; MW = 443.5) emitting red fluorescence into the FITC-dextran encapsulated PICsome to give the PICsome image with a merged color of yellows, indicating the semipermeable nature of the PICsome membrane. The PICsomes showed appreciable physiological stability even in the presence of serum proteins, suggesting their feasibility in biomedical fields such as carriers of therapeutic compounds and compartments for diagnostic enzymes.     

Specific inclusion mode of guest compounds in the amylose complex analyzed by solid state NMR spectroscopy

The inclusion compound formation between linear amylose of molecular weight 102500 (AS100) and p-aminobenzoic acid (PA) during the sealed-heating process was investigated by powder X-ray diffractometry, infrared spectroscopy and solid state NMR spectroscopy. Sealed-heating of AS100 and PA at 100 degrees C for 6 h provided an inclusion compound with 6(1)-helix structure, while a 7(1)-helix structure was found when sealed-heating was carried out at 150 degrees C for 1 h. The formation of an inclusion compound was not observed when sealed-heating was performed at 50 degrees C for 6 h. The 7(1)-helix inclusion compound maintained its structure even during storage at high temperature while the 6(1)-helix inclusion compound decomposed and returned to the original V(a)-amylose upon heating to 180 degrees C. Quantitative determination revealed that one PA molecule could be included per one helical turn of AS100 for both 6(1)-helix and 7(1)-helix inclusion compounds. Solid state NMR spectroscopy suggested that PA molecules were included in the amylose helix core in the 7(1)-helix inclusion compound, while in the case of 6(1)-helix inclusion compound, PA molecules were accommodated in the interstices between amylose helices. Moreover, the inclusion compound formation by sealed-heating of AS100 was also observed when using PA analogues as guest compounds. The binding ratio of AS100 and PA analogues varied depending on the size of guest molecules.     

Quantum control of a chiral molecular motor driven by laser pulses

"Molecular motors or machines" are one of the hot subjects in chemistry because they play an important role in molecular devices. We have theoretically demonstrated that unidirectional rotations of a chiral molecular motor can be driven by using tailored linearly polarized laser pulses. The findings obtained here serve as a theoretical basis for control of functions such as gearing or acceleration of molecular motors.     

A sub-second, time-resolved, linear dichroism measurement system for visible attenuated total reflection spectroscopy with a slab optical waveguide

A sub-second, time-resolved, linear dichroism (LD) measurement system was constructed, fitted with a slab optical waveguide (SOWG), and utilized to observe the adsorption process of methylene blue (MB) onto silica surfaces. In the system, a semiconductor laser (670 nm) was used as the light source and the out-coupled beam from the SOWG was split by a polarizing beam splitter into two polarized beams (TE and TM modes) to allow sequential linear dichroic ratio data to be obtained; the acquisition rate was 11 data sets per second. For an MB solution that contained no sodium dodecylbenzenesulfonate (DBS), in contact with a bare silica surface, a clear decrease occurred in the average orientation angle of adsorbed MB in the initial stages of the adsorption process. This result may correspond to a change in the chemical form of MB from monomer to dimer.     

Selective recognition of dihydrogen phosphate by receptors bearing pyridyl moieties as hydrogen bond acceptors

Dihydrogen phosphate anion is selectively recognized by amide-based receptors bearing pyridyl moieties as hydrogen bond acceptors in 0.5% DMSO-acetonitrile.     

Single-cell growth and division dynamics showing epigenetic correlations

The emergence of variation and subsequent inheritance of the emergent characteristics in a clonal population of bacteria is considered as evidence for epigenetic processes in the cell. We report here the results of experiments in which we quantitatively examined variations in single Escherichia coli cells with an identical genetic endowment in order to establish whether certain characteristics of single cells were inherited by their descendants maintained in a uniform environment. Significantly large variations of interdivision time, initial length, and final length were observed from generation to generation. Comparing the generations shows that interdivision time had no correlation with that of the consecutive generations, whereas those of initial length and final length were positively correlated with those of neighbouring generations.