Conformation and electrochemical reduction of myoglobin in PEO oligomers

Horse-heart myoglobin (Mb) was modified with poly(ethylene oxide) (PEO) to solubilize it in PEO oligomers. PEO-modified Mb (PEO–Mb) showed a quasi-reversible electrochemical redox reaction in PEO₂₀₀ (molar mass of 200 g). PEO–Mbs, modified with lower molecular weight of PEO chains, were soluble in PEO oligomers with wider range of molecular weight. A conformation of PEO–Mb was studied with circular dichroism spectroscopy in phosphate buffer solution (PBS) or PEO oligomers. The α-helix content of PEO–Mb, determined by the molar ellipticity at 222 nm, decreased from 71% to about 58% after PEO modification. However, the degree of PEO modification did not affect the α-helix content of PEO–Mbs. On the other hand, the α-helix content of PEO–Mbs was reduced by lowering the molecular weight of the modified PEO chains. Since the α-helix content of PEO–Mb in PBS and that in the PEO oligomers were almost identical, the conformation of PEO–Mb in PBS was considered to be maintained even in PEO oligomers. Although the reduction rate constant of PEO–Mb in PEO oligomers depended on the total molecular weight of the PEO–Mbs, their relation did not obey the Stokes–Einstein equation. The reduction of the PEO–Mb was probably affected by the interfacial electron transfer process at the electrode surface rather than by diffusion in the PEO oligomer.     

Time-dependent density functional theory investigation of electric field effects on absorption spectra of meso-meso-linked zinc porphyrin arrays: Role of charge-transfer States

By using time-dependent density functional theory, we calculated the transition energies of a zinc porphyrin monomer and its meso-meso-linked arrays. In line with the prediction of the molecular exciton model, the calculated splitting energy of the Soret band increased as the number of linked porphyrins increased. We then examined how the transition energies of the dimer array were shifted by an applied electric field. For reproduction of an electroabsorption spectrum (EA), i.e., the field-induced change in absorption intensity, a model Hamiltonian constructed from five states is proposed. It is concluded for the dimer that the field-induced coupling between the lower-energy Soret band Se and the lower-lying ionic character (charge-transfer) states is responsible for the experimentally observed blue shift of Se as well as the second-derivative profile in the EA spectrum.     

Molecular alignment in a liquid induced by a nonresonant laser field: Molecular dynamics simulation

We carried out molecular dynamics (MD) simulations for a dilute aqueous solution of pyrimidine in order to investigate the mechanisms of field-induced molecular alignment in a liquid phase. An anisotopically polarizable molecule can be aligned in a liquid phase by the interaction with a nonresonant intense laser field. We derived the effective forces induced by a nonresonant field on the basis of the concept of the average of the total potential over one optical cycle. The results of MD simulations show that a pyrimidine molecule is aligned in an aqueous solution by a linearly polarized field of light intensity I approximately 10(13) W/cm2 and wavelength lambda = 800 nm. The temporal behavior of field-induced alignment is adequately reproduced by the solution of the Fokker-Planck equation for a model system in which environmental fluctuations are represented by Gaussian white noise. From this analysis, we have revealed that the time required for alignment in a liquid phase is in the order of the reciprocals of rotational diffusion coefficients of a solute molecule. The degree of alignment is determined by the anisotropy of the polarizability of a molecule, light intensity, and temperature. We also discuss differences between the mechanisms of optical alignment in a gas phase and a liquid phase.     

Supramolecular complex formation by beta-cyclodextrin and ferrocenylnaphthalene diimide-intercalated double stranded DNA and improved electrochemical gene detection

Ferrocenylnaphthalene diimide 1 can bind to double stranded DNA (dsDNA) by the threading intercalation mode and the resulting complex was stabilized further by beta- cyclodextrin (CD) by forming a supramolecular complex. These complex formation processes were studied by spectroscopic, viscometric, and electrochemical means in the absence or presence of beta-CD. Quantitative analysis by quartz crystal microbalance (QCM) and electrochemical experiments strongly suggested a 2:1 binding stoichiometry for beta-CD to 1 threading-intercalated to the dsDNA-immobilized electrode. Owing to this supramolecular complex formation, electrochemical DNA detection based on 1 was improved considerably.     

Design, synthesis, and structure-activity relationships of 3,4-dihydropyridopyrimidin-2(1H)-one derivatives as a novel class of sodium/calcium exchanger inhibitor

Design, synthesis, and structure-activity relationships for 3,4-dihydropyridopyrimidin-2(1H)-one derivatives, which are aza-3,4-dihydro-2(1H)-quinazolinone derivatives, as the sodium/calcium (Na+/Ca2+) exchanger inhibitors are discussed. These studies based on 3,4-dihydro-2(1H)-quinazolinone derivatives led to the discovery of a structurally novel and potent Na+/Ca2+ exchanger inhibitor, 3,4-dihydropyridopyrimidin-2(1H)-one derivative (26), with an IC30 value of 0.02 microM. Compound 26 directly inhibited the Na+-dependent Ca2+ influx via the Na+/Ca2+ exchanger after Na+-free treatment in cardiomyocytes.     

Long-range stereocontrol in the self-assembly of two-nanometer-dimensioned triple-stranded dinuclear helicates

A series of bisimine-bridged dicatechol ligands 2-H(4)-5-H(4) were synthesized and were used to prepare triple-stranded dinuclear helicate-type complexes with a length of up to more than 2 nm. X-ray structural analyses of Na(4)[(2)(3)V(2)], Na(4)[(3)(3)Ti(2)], Na(4)[(4)(3)Ti(2)], and Na(4)[(5)(3)Ti(2)], as well as temperature-dependent NMR investigations of Na(4)[(4)(3)Ti(2)] and Na(4)[(5)(3)Ti(2)] show that, in the case of the rigid linear ligands 2 and 3, and of the ligand 5, which possesses C(2h) symmetry in its idealized structure, homochiral helicates are diastereoselectively formed. Ligand 4, on the other hand, with idealized C(2v) symmetry, leads with surprisingly high selectivity to the formation of the heterochiral meso-helicate. This is attributed to the ability of ligand 4 to adopt a less-restricted conformation in the meso compound than in the helical complex. NMR investigations indicate that both complex units of Na(4)[(4)(3)Ti(2)] invert (LambdaDelta-->DeltaLambda) simultaneously, while in the case of Na(4)[(5)(3)Ti(2)] a stepwise racemization proceeds.     

Modulation of Energy Conversion Processes in Carbonaceous Molecular Bearings

The energetics and photodynamics of carbonaceous molecular bearings with discrete molecular structures were investigated. A series of supramolecular bearings comprising belt‐persistent tubular cycloarylene and fullerene molecules accepted photonic stimuli to afford charge‐separated species via a photoinduced electron transfer process. The energy conversion processes associated with the photoexcitation, however, differed depending on the molecular structure. A π‐lengthened tubular molecule allowed for the emergence of an intermediary triplet excited state at the bearing, which should lead to an energy conversion to thermal energy. On the other hand, low‐lying charge‐separated species induced by an endohedral lithium ion in fullerene enabled back electron transfer processes to occur without involving triplet excited species. The structure–photodynamics relationship was analyzed in terms of the Marcus theory to reveal a large electronic coupling in this dynamic supramolecular system.     

High-Speed voltammetry of Mn-doped LiCoO2 using a microelectrode technique

The microelectrode technique was applied to investigate the electrochemical properties of LiCo_{1- x} Mn _x O₂ (x=0, 0.01, 0.05, 0.2, or 0.5) synthesized using the citrate process. From the X-ray diffraction measurements, an expansion of the c-axis and a decrease in the crystal size of the materials were observed on substitution of Mn into LiCoO₂. In the electrochemical measurements, the high-speed cyclic voltammogram for the Mn-substituted materials gave one set of peaks at 3.9 V vs. Li/Li⁺. The apparent chemical diffusion constant (D _app) of LiCo_0.8Mn_0.2O₂ obtained from the potential step experiment was 6.4 × 10⁻⁸ cm²/s, which is larger than that of LiCoO₂. The increase in D _app is attributable to the expansion of the c-axis and/or the decrease in the crystal size. In addition, the increase in Mn substitution up to 20% lead to an improvement in the kinetic reversibility and the cycle stability of LiCoO₂. Received: 7 June 1999 / Accepted: 25 June 1999     

Hydrodynamics and boiling phenomena of water droplets impinging on hot solid

The collision of single water droplets with a hot Inconel 625 alloy surface was investigated by a two-directional flash photography technique using two digital still cameras and three flash units. The experiments were conducted under the following conditions: the pre-impact diameters of the droplets ranged from 0.53 to 0.60 mm, the impact velocities ranged from 1.7 m/s to 4.1 m/s, and the solid surface temperatures ranged from 170 °C to 500 °C. When a droplet impacted onto the solid at a temperature of 170 °C, weak boiling was observed at the liquid/solid interface. At temperatures of 200 or 300 °C, numerous vapor bubbles were formed. Numerous secondary droplets then jetted upward from the deforming droplet due to the blowout of the vapor bubbles into the atmosphere. No secondary droplets were observed for a surface temperature of 500 °C at the low-impact Weber numbers (∼30) associated with the impact inertia of the droplets. Experiments using 2.5-mm-diameter droplets were also conducted. The dimensionless collision behaviors of large and small droplets were compared under the same Weber number conditions. At temperatures of less than or equal to 300 °C, the blowout of vapor bubbles occurred at early stages for a large droplet. At a surface temperature of 500 °C, the two dimensionless deformation behaviors of the droplets were very similar to each other.