Intramolecular photocycloaddition of β-stilbazoles tethered by silyl chains

Intramolecular (2+2) photocycloaddition of β-stilbazoles tethered by silyl chains took place with high efficiency. Complexation with dicarboxylic acid or catechol further enhanced both the efficiency and stereoselectivity.     

Ion-transfer voltammetry at a polarized room-temperature molten salt/water interface.

Tetraoctylammonium cation forms a room-temperature molten salt (RTMS) with 2,4,6-trinitrophenolate anion. The RTMS is immiscible with water (W) and forms a stable RTMS/W interface. It has been shown that the RTMS/W interface can be electrochemically polarized. A well-defined voltammetric wave due to the transfer of thiocyanate ion across the RTMS/W interface was observed within the potential window. This is the first example of a polarized RTMS/W interface.     

Rapid and sensitive determination of the conversion of UV-cured acrylic ester resins by pyrolysis-gas chromatography in the presence of an organic alkali.

The double-bond conversion of UV-cured resins prepared from pentaerythritol triacrylate (PETA) was determined by pyrolysis-gas chromatography in the presence of an organic alkali, tetramethylammonium hydroxide (TMAH). The pyrogram of the uncured prepolymer compound, consisting of PETA and a photoinitiator, 2,2-dimethoxy-2-phenylacetophenone, contained specific products reflecting the original acrylate structure, such as methyl acrylate (MA) and methyl ethers of pentaerithritol. Meanwhile, in pyrograms of the UV-cured PETA, the yields of MA considerably decreased. The double-bond conversions of the cured resins, irradiated with various UV dosages, were calculated based on the relative yields of MA among specific products in the pyrograms. The conversions determined by this approach were analyzed by comparing them with those estimated by Fourier-transform infrared spectroscopy.     

Polymorphy in the stereostructure of periodic polymer backbones

We theoretically investigated the polymorphy of the stereostructures of a periodic polymer. Using the polymer's internal conformation parameters of bond lengths, bond angles, and internal rotation angles, we extended the mathematical treatment for designing polymer backbones. We considered those periodic polymers whose unit cell consists of one (m = 1), two (m = 2), or three (m = 3) kinds of atoms. Moreover, for these three types of polymers, we supposed two catenation types for the skeleton atoms; one is a “homorotatory” sequence and the other is a “heterorotatory” one. To specify the backbone's stereostructure, we introduced several conformation parameters such as the helical pitch number n, the translation distance d, and the inclination angle of the skeleton plane Θ. By combining these parameters, we can systematically understand the variety and the possible polymorphy in the stereostructure of a periodic polymer backbone. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2829–2849, 2003     

Mechanisms of ATPases--a multi-disciplinary approach

ATPases are important molecular machines that convert the chemical energies stored in ATP to mechanical actions within the cell. ATPases are among the most abundant proteins with diverse functions involved in almost every cellular pathway. The well characterised ATPases include the various motor proteins responsible for cargo transfers, cell motilities, and muscle contractions; the protein degradation machinery - the proteasome; the ATP synthase, F-ATPase; and the chaperone systems. Other ATPases include DNA helicases and DNA replication complex; proteins responsible for protein/complex disassembly; and certain gene regulators. It is beyond the scope of this review to cover the complete range of ATPases. Instead, we will focus on a few representative ATPases, chosen based on their diverse mechanisms and properties. Furthermore, this review is by no means trying to cover comprehensively the literature for each ATPase nor the historical aspects in each field. We will focus on describing the various techniques being employed to derive the mechanisms and properties of the chosen ATPases. Among them, high and low resolution structural studies combined with biochemical assays seem to be the dominant technical advances adapted to reveal mechanisms for most of the ATPases except the bacterial sigma54 activators, whose mechanism of action is mostly derived from large amount of biochemical studies. A number of them, especially the F-ATPase and motor proteins, have been studied successfully by various single molecule and imaging techniques. We will therefore discuss them in greater details in order to describe the wide range techniques being utilised.     

Solid sampling technique for direct detection of condensed tannins in bark by matrix-assisted laser desorption/ionization mass spectrometry

A novel method for the direct analysis of condensed tannin components in bark was developed on the basis of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with a simple solid sampling technique. The MALDI mass spectra obtained from the wood (bark) powder sample clearly showed a series of peaks corresponding to the sodium ion adducts of condensed tannin oligomers up to around m/z 3000. The results indicate that the condensed tannins in the bark sample used in this work mostly consist of combinations of flavan-3-ol units such as profisetinidin (PF), prorobinetinidin (PR) and prodelphinidin (PD), at least up to 10-mers (m/z approximately 3000).     

Novel synthesis of heterocyclic spirans by tandem cycloaddition to sulfur-containing heterocumulenes

Novel Ni(C0)₄-promoted tandem cycloadditions of diphenylcyclo- propenone to isothiocyanates and to CS₂ were found to provide new heterocyclic spirans, pyrroline-2-one-5-spiro-5′-thiolene-4′-ones and a thiolene-2-one-5-spiro-5′-thiolene-4′-one, respectively, in moderate yields.     

Design and synthesis of highly sensitive and selective fluorescein-derived magnesium fluorescent probes and application to intracellular 3D Mg2+ imaging

The role of intracellular magnesium ions is of high interest in the fields of pharmacology and cellular biology. To accomplish the dynamic and three-dimensional imaging of intracellular Mg2+, there is a strong desire for the development of optimized Mg2+ fluorescent probes. In this paper we describe the design, synthesis, and cellular application of the three novel Mg2+ fluorescent probes KMG-101, -103, and -104. The compounds of this series feature a charged beta-diketone as a binding site specific for Mg2+ and a fluorescein residue as the fluorophore that can be excited with an Ar+ laser such as is widely used in confocal scanning microscopy. This molecular design leads to an intensive off-on-type fluorescent response toward Mg2+ ions. The two fluorescent probes KMG-103 and -104 showed suitable dissociation constants (Kd,Mg2+ = 2 mM) and nearly a 10-fold fluorescence enhancement over the intracellular magnesium ion concentration range (0.1-6 mM), allowing high-contrast, sensitive, and selective Mg2+ measurements. For intracellular applications, the membrane-permeable probe KMG-104AM was synthesized and successfully incorporated into PC12 cells. Upon application of the mitochondria uncoupler FCCP to the probe-incorporated cells, the resulting increase in the free magnesium ion concentration could be followed over time. By using a confocal microscope, the intracellular 3D magnesium ion concentration distributions were satisfactorily observed.     

The counterion releasing effect and the partition coefficient of branched alkanols in ionic micellar solution

In the micellar solution of SDS, the partition coefficient (K_x) of following branched alkanols at infinite dilution was determined by applying a differential conductivity method: the alkanols used were i-C_mH_2m+1OH (m=4-9, i=1-5) in which the position of OH group (i) shifts from an end to the center of a hydrocarbon chain. The method provides two significant quantities, d!/dX_am and dC_sf/dC_af in addition to K_x. The following results have been obtained. (1) The dependence of K_x on i indicates that the hydrophobicity of alkanol is weakened with increasing i, whereas the increase in m strengthens the hydrophobicity. (2) The degree of counterion disossiation of micelles (!) is accelerated by the solubilized alkanols in micelles (mole fraction: X_am) and the acceleration rate, d!/dX_am (=0.17), depends on neither m nor i. (3) In the bulk water, the monomerically dissolved alkanols (concentration: C_af) depresses the concentration of free monomer surfactant (C_sf), and the depressing rate, dC_sf/dC_af, in micellar solution is identical with the corresponding quantity, ((CMC/(C_a)_o at CMC.