Yoshinori Nibu

Effect of headgroup type on the miscibility of homologous phospholipids with different acyl chain lengths in hydrated bilayer

The miscibility of homologous phosphatidylcholines with different acyl chain lengths in hydrated bilayer was examined through the binary phase diagram constructed by differential scanning calorimetry. By analyzing the phase diagram according to a thermodynamic model based on the Bragg-Williams approximation to evaluate the excess free energy of mixing, the non-ideality parameter of mixing, rho(0), was estimated, which allows one to interpret the mixing behavior of the two lipid components in terms of the difference in the pair-interaction energies between like-pairs and mixed-pairs formed in the mixture. By summarizing the rho(0) values obtained previously for other classes of phospholipids, it was found that rho(0) increases in the order of phosphatidylglycerol (PG) approximately phosphatidylcholine (PC) < phosphatidylethanolamine (PE) < phosphatidic acid (PA). Since the difference in the pair-interaction energies is considered to be determined by the relative contribution of inter-headgroup interaction to the overall intermolecular interaction, this sequence of rho(0) value suggests that the headgroup interaction in hydrated bilayer increases in the order of PA < PE < PC approximately PG.

Comparable Strength of OH–O versus OH−π Hydrogen Bonds in Hydrogen-Bonded 2,3-Benzofuran Clusters with Water and Methanol

Two different types of hydrogen bond, which are classified into a familiar OH-O and a relatively weak OH-π one, have been compared in the 1:1 hydrogen-bonded 2,3-benzofuran clusters with water and methanol molecules. By applying fluorescence-detected infrared spectroscopy and dispersed fluorescence spectroscopy, two isomers having different types of hydrogen bonds are distinguished. From the calculated stabilization energy as well as the frequency shift of the OH stretching vibration in each cluster, these two isomers are almost equally stable, although that of OH-π type is usually thought to be relatively weak. It is suggested that the origin of the weak OH-O hydrogen bond is derived from the lower availability for a hydrogen bond acceptor on the oxygen atom of a heteroaromatic ring, which is attributed to the larger furan aromaticity.

Raman spectroscopic study on photochromic reaction of a diarylethene derivative

Abstract Photochromic reaction of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene has been studied by FT-Raman spectroscopy. The Raman bands in the 1300–1700 cm −1 region of the open-ring isomer of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene are clearly distinguished from those of the closed-ring isomer. The vibrational assignment has been made by measuring the polarized Raman spectrum and density functional theory calculations at the B3LYP/6-31G** level.

Conformation of 2,2,2-trifluoroethanol and the solvation structure of its 2-fluoropyridine clusters.

The conformation of 2,2,2-trifluoroethanol (TFE) in the 2-fluoropyridine-(TFE)(m)-(H(2)O)(n) clusters in a supersonic jet has been investigated with fluorescence-detected infrared spectroscopy and quantum chemical calculations. It is common to the observed clusters that they form chain structures containing the weak interaction of the pyridyl CH with the fluorine or oxygen atom in the terminal TFE. The detectable conformation of TFE is gauche only even in the case of the existence of the strong base such as 2-fluoropyridine. This result is explained by the change in hyperconjugation among several dominant orbitals. The preference of the terminal TFE in the mixed clusters with TFE and water solvents is observed, which is ascribed to the stronger cooperative effect of TFE than water.

Radio frequency magnetic field effects on molecular dynamics and iron uptake in cage proteins

The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2 x 10(-6) m(3) kg(-1) and its Néel relaxation time at about 10(-10) s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30 microT at 1 MHz, as measured via Raman spectroscopy. After 2 h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale.

Effects of organometallic compounds introduced to plasma on diamond synthesis

Volatile organometallic compounds were introduced to feed gas (CH4/H2) during the synthesis of diamond by microwave plasma chemical vapor deposition. Addition of Si(CH3)4, Sn(CH3)4, Sn(CH3)4, Fe(AA)3, TiO(AA)2 or Zr(AA)4 increased nucleation density of diamond particles to 2-10 times that without additives. Addition of Zr(AA)4 and TiO(AA)2 made the grain sizes smaller. Most additives lowered atomic hydrogen temperature, increased concentration of C2 in plasma and seemed therefore to degrade the crystallinity of the diamonds. Some additives shifted the A band cathodoluminescence to a higher energy region. In the case of Si(CH3)4, the GR-1 center cathodoluminescence was observed as well as the A-band, and adhesion of the diamond film was markedly improved.

Phase behavior of hydrated bilayer of binary phospholipid mixtures composed of 1,2-distearoylphosphatidylcholine and 1-stearoyl-2-oleoylphosphatidylcholine or 1-oleoyl-2-stearoylphosphatidylcholine

Abstract Phase behavior of hydrated bilayer of binary phospholipid mixtures composed of 1,2-distearoylphosphatidylcholine (DSPC) and 1-stearoyl-2-oleoylphosphatidylcholine (SOPC), and DSPC and 1-oleoyl-2-stearoylphosphatidylcholine (OSPC) was examined in terms of a pseudo-binary phase diagram. The phase boundaries determined by differential scanning calorimetry (DSC) were analyzed based on a thermodynamic model applying the Bragg–Williams approximation for non-ideality of mixing. The interchange energy parameters derived from this approach for liquid-crystalline and solid-like gel phases were ρ0(L)=2.0 kJ mol−1 and ρ0(S)=5.4 kJ mol−1 for SOPC/DSPC mixture and ρ0(L)=1.9 kJ mol−1 and ρ0(S)=5.5 kJ mol−1 for OSPC/DSPC mixture. These values for both mixture systems are close to each other, and also close to those obtained for dimyristoylphosphatidylcholine (DMPC)/DSPC mixture. This suggests that the effect of introducing a cis-unsaturated acyl chain into a diacylphosphatidylcholine on the mixing behavior with homologous phospholipid with two identical saturated acyl chains is comparable to that of shortening the length of saturated acyl chain by four methylene units.

MISCIBILITY OF BINARY PHOSPHOLIPID MIXTURES UNDER HYDRATED AND NON-HYDRATED CONDITIONS. III: REINVESTIGATION OF PHOSPHATIDIC ACIDS WITH DIFFERENT ACYL CHAIN LENGTH

Abstract Our previous study on the miscibility property of phosphatidic acids with different acyl chain length under hydrated and non-hydrated conditions (Inoue et al. (1992) Chem. Phys. Lipids 63, 203–212) was reinvestigated using an improved procedure to prepare the lipid samples for differential scanning calorimetric (DSC) measurements. The phospholipid species examined were dimyristoyl-, dipalmitoyl-, and distearoylphosphatidic acids (DMPA, DPPA and DSPA, respectively). Phase diagrams of binary mixtures among these phospholipids were constructed based on the DSC thermograms. The phase diagrams obtained for hydrated mixtures revealed that DMPA and DPPA are mutually miscible in both liquid-crystalline and gel bilayers, whereas DMPA and DSPA exhibit a partial phase separation in the gel phase although they are miscible in the liquid-crystalline bilayer. These mixing behaviors are quite different from those reported in the previous paper, where the occurrence of partial and complete demixing was concluded in liquid-crystalline and gel bilayers, respectively. A thermodynamic model was applied to analyze the phase diagrams obtained in the present reinvestigation for hydrated PA mixtures, and discussed on the basis of the non-ideality parameter of mixing derived by this approach.

Phase behavior of hydrated lipid bilayer composed of binary mixture of phospholipids with different head groups

Abstract Phase behavior of hydrated lipid bilayer was investigated for the mixtures of two phospholipid species chosen from phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) with the same acyl chains. The pseudo-binary phase diagrams constructed by a differential scanning calorimetry (DSC) were analyzed based on a thermodynamic model applying the Bragg–Williams approximation for non-ideality of mixing. The interchange energy parameters, ρ0, derived from this approach were positive for all mixture systems in both gel and liquid–crystalline phase bilayers, and increased in the order PG/PE

Dispersed phosphorescence spectra in a supersonic free jet by electric discharge excitation

Abstract Pyrazine and benzophenone were excited into the lowest triplet state by electric discharge and their dispersed phosphorescence spectra in a supersonic free jet were observed. The bandwidth of the spectrum of pyrazine is narrower than that of the spectra obtained with laser excitation. The experiment shows that electric discharge excitation is an efficient technique for creating a triplet state molecule under collision free conditions.