Alternative preparation and characterization of platinum(II) organometallic dinuclear complexes and oligomers with 3,8-diethynylphenanthroline derivatives

Novel platinum(II) organometallic dinuclear complexes and oligomers with two types of phenanthroline ligands, namely 3,8-diethynylphenanthroline (L1) and 3,8-bis-(4-ethynyl-phenylethynyl)-1,10-phenanthroline (L2), were synthesized from trans-Pt(PBu₃)₂(1-ethynyl-4-methyl-benzene)Cl and trans-Pt(PBu₃)₂Cl₂ by transmetalation of copper ion. The alternative procedure targeted platinum oligomer termination selection of either chloride or respective phenanthrolines and was successfully performed with different purifications by extraction and column chromatography. The structural formulae of these platinum complexes and oligomers were revealed with by analysis of both ³¹P{¹H}-NMR and ¹H-NMR spectral data. Alternative preparations of platinum oligomers with two types between chloride and respective phenanthroline termination are very useful for the selective synthesis for hybrid polymers with the coupling reaction with two different platinum oligomers with different diethynylaryl ligands. The platinum organometallic compounds showed similar absorption bands in the UV–Vis region. Those prepared with L1 had a strong absorption band at around 400 nm, assignable to the lowest energy metal-perturbed ¹[π–π*] transitions, while in compounds prepared with L2, the strong band appeared around 410 nm, because L2 has an extended π conjugation relative to L1. No distinct differences were observed in the absorption spectra of these platinum oligomers between the different terminal structures, chloride or various phenanthrolines. The luminescence spectra of the platinum compounds prepared with either L1 or L2, however, showed a distinct difference. Those with L1 showed only a phosphorescence assignable to a typical metal-perturbed ³[π–π*] transition with vibronic progressions centered at around 530 nm in deoxygenated CH₂Cl₂ at room temperature, while those with L2 showed weak dual emissions assignable to a mixture of typical metal-perturbed ¹[π–π*] and ³[π–π*] transitions in the visible region.     

Spontaneous vesicle formation of mixtures of double-chain cationic surfactants with a different counterion

Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.     

Wetting and freezing of hexadecane on an aqueous surfactant solution: triple point in a 2-D film

Wetting of water by hexadecane has been investigated by ellipsometry as a function of the concentration of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) in the aqueous phase and temperature. Three phases are identified: a 2-D gas of hexadecane molecules and DTAB molecules, a 2-D liquid comprising a mixed monolayer of hexadecane and DTAB, and a 2-D 'solid' phase. Evidence is presented to support the hypothesis that the liquid-solid phase transition is actually a wetting transition in which a surface-frozen layer of pure hexadecane wets the liquid-like mixed monolayer of hexadecane and DTAB. The triple point, at which the three phases coexist, is located at a temperature of 17.3 degrees C and DTAB concentration of 0.75 mmol kg (-1). The slopes of the three phase boundaries are analyzed thermodynamically.     

A Solid‐State Fluorescent Host System with a 21‐Helical Column Consisting of Chiral (1R,2S)‐2‐Amino‐1,2‐diphenylethanol and Fluorescent 1‐Pyrenecarboxylic Acid

A solid‐state fluorescent host system was created by self‐assembly of a 2₁‐helical columnar organic fluorophore composed of (1R,2S)‐2‐amino‐1,2‐diphenylethanol and fluorescent 1‐pyrenecarboxylic acid. This host system has a characteristic 2₁‐helical columnar hydrogen‐ and ionic‐bonded network. Channel‐like cavities are formed by self‐assembly of this column, and various guest molecules can be included by tuning the packing of this column. Moreover, the solid‐state fluorescence of this host system can change according to the included guest molecules. This occurs because of the change in the relative arrangement of the pyrene rings as they adjust to the tuning of the packing of the shared 2₁‐helical column, according to the size of the included guest molecules. Therefore, this host system can recognize slight differences in molecular size and shape.     

Cyclopropanation of alkenes with CH2I2/Et3Al by the phase-vanishing method based on fluorous phase screen

Phase-vanishing (PV) method using perfluorohexanes as a screen phase was applied to cyclopropanation reactions with CH₂I₂/Et₂Zn and CH₂I₂/Et₃Al. When Et₃Al was used as a carbenoid generator, the reaction proceeded smoothly and desired cyclopropane derivatives were obtained in high yield. The PV cyclopropanation took 2 or 3 days to complete, however, reduction of reaction time by a factor of 2-3 was also achieved by vigorous stirring after the bottom CH₂I₂ layer disappeared.     

An ESR and ENDOR study of irradiated 6Li-formate

Lithium formate ((6)LiOOCH.H(2)O), 95% (6)Li enrichment, combined with an exchange of crystallization water with D(2)O was investigated. The ESR spectrum of the radiation induced free radicals stable at room temperature consists of a singlet with a narrow line width, 0.92mT. (6)Li has smaller magnetic moment and nuclear spin, which resulted in the narrower line width accompanied with an increase in peak amplitude. In comparison with lithium formate with natural isotopic composition, (6)Li (7.5%, I=1) and (7)Li (92.5%, I=3/2), the sensitivity was increased by a factor of two. With optimised spectrometer settings (6)Li formate had seven times higher sensitivity compared to alanine. Therefore this material is proposed as a dosimeter material in a dose range down to 0.1Gy. The g and the (13)C-hyperfine (hf) tensors of the CO(2)(-) radical anion, major paramagnetic products, were evaluated to be g=(2.0037, 1.9975, 2.0017), and A((13)C)=(465.5, 447.5, 581.3) MHz for polycrystalline samples at room temperature. Furthermore, the (1)H-hf and (6)Li-hf tensors observed for the surroundings of CO(2)(-) by ENDOR technique were in fairly good agreement with DFT calculations. The CO(2)(-) radicals are found to be so stable that the formate is applicable to the ESR dosimetry, because of fully relaxing in a fully relaxed geometrical structure of the CO(2)(-) component and remaining tight binding with the surroundings after the H atom detachment from HCO(2)(-).     

Spontaneous vesicle formation of single chain and double chain cationic surfactant mixtures

The concentration vs composition diagram of aggregate formation of the dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) mixture in aqueous solution at rather dilute region was constructed by analyzing the surface tension, turbidity, and electrical conductivity data and inspected by cryo-TEM images and dynamic light scattering data. Although the aqueous solution of DTAB forms only micelles, the transition from monomer to small aggregates and then to vesicle was found at 0.1 < X2 相似文献   

Dissecting the proline effect: dissociations of proline radicals formed by electron transfer to protonated Pro-Gly and Gly-Pro dipeptides in the gas phase

We report a combined experimental and computational study of the proline effect in model dipeptides Pro-Gly and Gly-Pro. Gas-phase protonated peptide ions were discharged by glancing collisions with potassium or cesium atoms at 3 keV collision energies, and the peptide radical intermediates and their dissociation products were analyzed following collisional ionization to anions. The charge reversal (+CR-) mass spectra of (Pro-Gly + H)+(1a+) and (Gly-Pro + H)+ (2a+) showed dramatic differences and thus provided a sensitive probe of ion structure. Whereas 1a+ completely dissociated upon charge inversion, 2a+ gave a nondissociated anion as the most abundant product. Ab initio and density functional theory calculations provided structures and vertical recombination energies (REvert) for 1a+ and 2a+. The recombination energies, REvert = 3.07 and 3.36 eV for 1a+ and 2a+, respectively, were lower than the alkali metal ionization energies and indicated that the collisional electron transfer to the peptide ions was endoergic. Radical 1a* was found to exist in a very shallow local energy minimum, with transition state energies for loss and migration of H indicating very facile dissociation. In contrast, radical 2a* was calculated to spontaneously isomerize upon electron capture to a stable dihydroxycarbinyl isomer (2e*) that can undergo consecutive and competitive isomerizations by proline ring opening and intramolecular hydrogen atom transfers to yield stable radical isomers. Radical 2e* and its stable isomers were calculated to have substantial electron affinities and thus can form the stable anions that were observed in the +CR- mass spectra. The calculated TS energies and RRKM kinetic analysis indicated that peptide N-C alpha bond dissociations compete with pyrrolidine ring openings triggered by radical sites at both the N-terminal and C-terminal sides of the proline residue. Open-ring intermediates were found in which loss of an H atom was energetically preferred over backbone dissociations. This provided an explanation for the proline effect causing low incidence of electron capture dissociations of N-C alpha bonds adjacent to proline residues in tryptic peptides and also for some peculiar behavior of proline-containing protein cation-radicals.     

Ab initio ONIOM-molecular dynamics (MD) study on the deamination reaction by cytidine deaminase

We applied the ONIOM-molecular dynamics (MD) method to the hydrolytic deamination of cytidine by cytidine deaminase, which is an essential step of the activation process of the anticancer drug inside the human body. The direct MD simulations were performed for the realistic model of cytidine deaminase by calculating the energy and its gradient by the ab initio ONIOM method on the fly. The ONIOM-MD calculations including the thermal motion show that the neighboring amino acid residue is an important factor of the environmental effects and significantly affects not only the geometry and energy of the substrate trapped in the pocket of the active site but also the elementary step of the catalytic reaction. We successfully simulate the second half of the catalytic cycle, which has been considered to involve the rate-determining step, and reveal that the rate-determining step is the release of the NH3 molecule.