Eiko Mochizuki

Enantioselective Single-Crystal-to-Single-Crystal Photodimerization of Coumarin and Thiocoumarin in Inclusion Complexes with Chiral Host Compounds.

An intermolecular enantioselective photoreaction by a single-crystal-to-single-crystal transformation has been carried out for the first time, as is evident from X-ray structure analysis and X-ray powder diffractometric studies. This reaction, the dimerization of the title compound to cyclobutane derivative 1 (X=O, S), provides a good example for studying the mechanism of topochemical reactions in the crystal.

Single-Crystal-to-Single-Crystal Enantioselective [2+2] Photodimerization of Coumarin, Thiocoumarin and Cyclohex-2-enone in the Inclusion Complexes with Chiral Host Compounds

Abstract Single-crystal-to-single-crystal enantioselective [2+2] photodimerization reactions of coumarin (1a), thiocoumarin (1b) and cyclohex-2-enone (2) were found to proceed efficiently in inclusion complexes with (R,R)-(−)-trans-bis(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxacyclopentane (3a), (R,R)-(−)-trans-2,3-bis(hydroxydiphenylmethyl)-1,4-dioxaspiro[4.4]nonane (3b), and (−)-1,4-bis[3-(o-chlorophenyl)-3-hydroxy-3-phenylprop-1-ynyl]benzene (4), respectively. Through these reactions, (−)-anti-head-to-head dimer 6a, (+)-anti-head-to-head dimer 6b and (−)-syn-trans dimer 10 were obtained in 100, 100 and 48% ee, respectively.

SEM Observation of Wet Biological Specimens Pretreated with Room‐Temperature Ionic Liquid

A facile pretreatment process for SEM: The use of room temperature ionic liquids (RTILs) provides an interesting method for SEM of biological specimens. We used a novel and concise method of pretreatment, excluding fixation or Au sputtering steps. Fine and smooth-textured SEM images of a wide variety of biological specimens treated in this way were observed without artefacts.

Chromosome observation by scanning electron microscopy using ionic liquid

Electron microscopy has been used to visualize chromosome since it has high resolution and magnification. However, biological samples need to be dehydrated and coated with metal or carbon before observation. Ionic liquid is a class of ionic solvent that possesses advantageous properties of current interest in a variety of interdisciplinary areas of science. By using ionic liquid, biological samples need not be dehydrated or metal‐coated, because ionic liquid behaves as the electronically conducting material for electron microscopy. The authors have investigated chromosome using ionic liquid in conjunction with electron microscopy and evaluated the factors that affect chromosome visualization. Experimental conditions used in the previous studies were further optimized. As a result, prewarmed, well‐mixed, and low concentration (0.5∼1.0%) ionic liquid provides well‐contrasted images, especially when the more hydrophilic and the higher purity ionic liquid is used. Image contrast and resolution are enhanced by the combination of ionic liquid and platinum blue staining, the use of an indium tin oxide membrane, osmium tetroxide‐coated coverslip, or aluminum foil as substrate, and the adjustment of electron acceleration voltage. The authors conclude that the ionic‐liquid method is useful for the visualization of chromosome by scanning electron microscopy without dehydration or metal coating. Microsc. Res. Tech. 75:1113–1118, 2012.

Cadmium-free sugar-chain-immobilized fluorescent nanoparticles containing low-toxicity ZnS-AgInS2 cores for probing lectin and cells.

Sugar chains play a significant role in various biological processes through sugar chain-protein and sugar chain-sugar chain interactions. To date, various tools for analyzing sugar chains biofunctions have been developed. Fluorescent nanoparticles (FNPs) functionalized with carbohydrate, such as quantum dots (QDs), are an attractive imaging tool for analyzing carbohydrate biofunctions in vitro and in vivo. Most FNPs, however, consist of highly toxic elements such as cadmium, tellurium, selenium, and so on, causing problems in long-term bioimaging because of their cytotoxicity. In this study, we developed cadmium-free sugar-chain-immobilized fluorescent nanoparticles (SFNPs) using ZnS-AgInS2 (ZAIS) solid solution nanoparticles (NPs) of low or negligible toxicity as core components, and investigated their bioavailability and cytotoxicity. SFNPs were prepared by mixing our originally developed sugar-chain-ligand conjugates with ZAIS/ZnS core/shell NPs. In binding experiments with lectin, the obtained ZAIS/ZnS SFNPs interacted with an appropriate lectin to give specific aggregates, and their binding interaction was visually and/or spectroscopically detected. In addition, these SFNPs were successfully utilized for cytometry analysis and cellular imaging in which the cell was found to possess different sugar-binding properties. The results of the cytotoxicity assay indicated that SFNPs containing ZAIS/ZnS have much lower toxicity than those containing cadmium. These data strongly suggest that our designed SFNPs can be widely utilized in various biosensing applications involved in carbohydrates.

Synthesis and Nonlinear Properties of Poly[1,4‐bis(4‐methylpyridinium)butadiyne triflate)]

1,4-Bis(4-methylpyridinium)butadiyne triflate (1), which was prepared from the reaction of 1,4-bis(4-pyridyl)butadiyne with methyl trifluoromethanesulfonate, was found to be piled up along the c axis with two triflates as counter anions. The UV irradiation and thermal treatment of 1 gave rise to 1,4-topochemical polymerization to yield poly[1,4-bis(4-methylpyridinium) butadiyne triflate)]. The third-order nonlinear optical susceptibility (X (3) ) of the polymer was determined by the degenerate four wave mixing (DFWM) method to exhibit the remarkable high value of 2.2 x 10 -10 esu.

Enantioselektive Einkristall-zu-Einkristall-Photodimerisierung von Cumarin und Thiocumarin in Einschlußkomplexen mit chiralen Wirtverbindungen

Eine intermolekulare enantioselektive Photoreaktion, die uber eine Einkristall-zu-Einkristall-Umwandlung erfolgt, wurde erstmals durchgefuhrt; Belege hierfur wurden durch Rontgenstrukturanalyse und Rontgenpulverdiffraktometrie erbracht. Diese Reaktion, die Dimerisierung der Titelverbindungen zu Cyclobutanderivaten 1 (X=O, S), liefert ein gutes Beispiel zur Untersuchung des Mechanismus von topochemischen Reaktionen im Kristall.

The Effect of Hydrophilic Ionic Liquids 1-Ethyl-3- Methylimidazolium Lactate and Choline Lactate on Lipid Vesicle Fusion

Ionic liquids (ILs) are room-temperature molten salts that have applications in both physical sciences and more recently in the purification of proteins and lipids, gene transfection and sample preparation for electron microscopy (EM) studies. Transfection of genes into cells requires membrane fusion between the cell membrane and the transfection reagent, thus, ILs may be induce a membrane fusion event. To clarify the behavior of ILs with cell membranes the effect of ILs on model membranes, i.e., liposomes, were investigated. We used two standard ILs, 1-ethyl-3-methylimidazolium lactate ([EMI][Lac]) and choline lactate ([Ch][Lac]), and focused on whether these ILs can induce lipid vesicle fusion. Fluorescence resonance energy transfer and dynamic light scattering were employed to determine whether the ILs induced vesicle fusion. Vesicle solutions at low IL concentrations showed negligible fusion when compared with the controls in the absence of ILs. At concentrations of 30% (v/v), both types of ILs induced vesicle fusion up to 1.3 and 1.6 times the fluorescence intensity of the control in the presence of [Ch][Lac] and [EMI][Lac], respectively. This is the first demonstration that [EMI][Lac] and [Ch][Lac] induce vesicle fusion at high IL concentrations and this observation should have a significant influence on basic biophysical studies. Conversely, the ability to avoid vesicle fusion at low IL concentrations is clearly advantageous for EM studies of lipid samples and cells. This new information describing IL-lipid membrane interactions should impact EM observations examining cell morphology.

Nucleic Acid Analogs: Their Specific Interaction and Applicability

A variety of poly(amino acid) and poly (ethyleneimine) derivatives, having pendant nucleic acid bases and nucleosides, were prepared using polymer modification reactions. The conformation of the polymers was studied by CD and ORD measurements. Further study about the polymer complex formation between complementary polymers revealed that the complexes were formed by specific base pairing between pendant bases, retaining their helical conformation in the case of poly (amino acid) type polymers.

SEM observation of hydrous superabsorbent polymer pretreated with room-temperature ionic liquids.

Room-temperature ionic liquid (RTIL), which is a liquid salt at or below room temperature, shows peculiar physicochemical properties such as negligible vapor pressure and relatively-high ionic conductivity. In this investigation, we used six types of RTILs as a liquid material in the pretreatment process for scanning electron microscope (SEM) observation of hydrous superabsorbent polymer (SAP) particles. Very clear SEM images of the hydrous SAP particles were obtained if the neat RTILs were used for the pretreatment process. Of them, tri-n-butylmethylphosphonium dimethylphosphate ([P4, 4, 4, 1][DMP]) provided the best result. On the other hand, the surface morphology of the hydrous SAP particles pretreated with 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) was damaged. The results of SEM observation and thermogravimetry analysis of the hydrous SAP pretreated with the RTILs strongly suggested that most water in the SAP particles are replaced with RTIL during the pretreatment process.