Production of a positron microprobe using a transmission remoderator.

A production method for a positron microprobe using a beta+-decay radioisotope (22Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was mounted at the focal point of the magnetic lens and was used as a remoderator for brightness enhancement in a transmission geometry. The remoderated positrons were accelerated by an electrostatic lens and focused on the target by an objective magnetic lens. As a result, a 4-mm-diameter positron beam could be transformed into a microprobe of 60 microm or less with 4.2% total efficiency. The S parameter profile obtained by a single-line scan of a test specimen coincided well with the defect distribution. This technique for a positron microprobe is available to an accelerator-based high-intensity positron source and allows 3-dimensional vacancy-type defect analysis and a positron source for a transmission positron microscope.     

In situ observation of the formation of Si clathrate Ba8Si46 at high pressures and high temperatures

X-ray diffraction measurements at high pressures and high temperatures revealed that Si clathrate Ba 8Si 46 is formed by a solid-phase reaction of an 8:30 molar mixture of SrSi 2-phase BaSi 2 and Si after BaSi 2 undergoes the BaSi 2-to-EuGe 2 and the EuGe 2-to-SrSi 2 transitions. The volume reduction during the formation of Ba 8Si 46 is the largest, 7.6%, among the observed transitions. On the other hand, an 8:30 molar mixture of SrSi 2-phase SrSi 2 and Si does not result in the formation of Sr 8Si 46 at high pressures and high temperatures; only SrSi 2 transforms from the SrSi 2 phase into the alpha-ThSi 2 phase, and Si remains in the diamond phase.     

Development of Donor-π-Acceptor-Type Fluorinated Tolanes as Compact Condensed Phase Luminophores and Applications in Photoluminescent Liquid-Crystalline Molecules

Fluorinated tolanes, produced by introducing fluorine atoms into one of the aromatic rings of tolane, emitted almost no fluorescence in a solution state, but the fluorescence intensity increased dramatically in the crystalline state because of intermolecular H⋅⋅⋅F hydrogen bonds. The photoluminescent (PL) colors depend on the molecular orbitals, dipole moments, and molecular aggregated structures can be varied by controlling terminal substituents along the major molecular axis. The introduction of a long alkoxy or semifluoroalkoxy unit as a flexible chain into the terminal positions along the major molecular axis induced the formation of a liquid-crystalline (LC) phase; fluorinated tolanes act both as luminophores and as mesogens, leading to the molecular design of new photoluminescent LC molecules (PLLCs). The results also indicated that a fluorinated tolane dimer, which consists of two fluorinated tolanes linked by a flexible alkylene spacer, also becomes a novel PLLC.     

On the functional properties of the confluent hypergeometric zeta-function

A zeta-function associated with Kummer’s confluent hypergeometric function is introduced as a classical Dirichlet series. An integral representation, a transformation formula, and relation formulas between contiguous functions and one generalization of Ramanujan’s formula are given. The inverse Laplace transform of confluent hypergeometric functions is essentially used to derive the integral representation.     

Metallosupramolecular Structures Derived from a Series of Diphosphine‐bridged Digold(I) Metalloligands with Terminal d‐Penicillamine

In this report, we describe our recent work on the development of a new family of chiral heteroleptic digold(I) metalloligands with mixed diphosphine and d ‐penicillaminate (d ‐pen), [Au₂(dppx)(d ‐pen‐S)₂]^2– (dppx = PPh₂(CH₂)_nPPh₂, n = 1–5) and their application for the construction of chiral multinuclear and metallosupramolecular structures. The reactions of the metalloligands with 3d metal ions produce a variety of chiral heterobimetallic structures retaining the digold(I) metalloligand structure, ranging from discrete trinuclear to infinite helix structures that depend on the type of dppx. In addition, monophosphine and triphosphine analogues of the metalloligands were designed, and their coordination behavior is discussed to show the essential properties and potential extensibility of this class of metalloligands.     

Catalytic enantioselective amination of silyl enol ethers using chiral dirhodium(II) carboxylates: asymmetric formal synthesis of (-)-metazocine

Dirhodium(II) tetrakis[N-tetrafluorophthaloyl-(S)-tert-leucinate], Rh2(S-TFPTTL)4, is an exceptionally efficient catalyst for enantioselective aminations of silyl enol ethers derived from acyclic ketones or alpha,beta-enones with [N-(2-nitrophenylsulfonyl)imino]phenyliodinane (NsN=IPh), providing N-(2-nitrophenylsulfonyl)-alpha-amino ketones in high yields and with enantioselectivities of up to 95% ee. The effectiveness of the present catalytic protocol has been demonstrated by an asymmetric formal synthesis of (-)-metazocine.     

Microfluidic flow control on charged phospholipid polymer interface

A type of charged phospholipid polymer biointerface was constructed on a quartz microfluidic chip to control the electroosmotic flow (EOF) and to suppress non-specific protein adsorption through one-step modification. A negatively charged phospholipid copolymer containing 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate (BMA), potassium 3-methacryloyloxypropyl sulfonate (PMPS) and 3-methacryloxypropyl trimethoxysilane (MPTMSi) moieties (referred to as PMBSSi) was synthesized to introduce such phosphorylcholine segments as well as surface charges onto the silica-based microchannels via chemical bonding. At neutral pH, the homogenous microchannel surface modified with 0.3 wt% PMBSSi in alcoholic solution, retained a significant cathodic EOF ((1.0 +/- 0.1) x 10(-4) cm(2) V(-1) s(-1)) with approximately one-half of the EOF of the unmodified microchannel ((1.9 +/- 0.1) x 10(-4) cm(2) V(-1) s(-1)). Along with another non-charged copolymer (poly(MPC-co-MPTMSi), PMSi), the regulation of the surface charge density can be realized by adjusting the concentration of PMBSSi or PMSi initial solutions for modification. Coincidently, the zeta-potential and the EOF mobility at neutral pH showed a monotonically descending trend with the decrease in the charge densities on the surfaces. This provides a simple but feasible approach to controlling the EOF, especially with regard to satisfying the requisites of miniaturized systems for biological applications requiring neutral buffer conditions. In addition, the EOF in microchannels modified with PMBSSi and PMSi could maintain stability for a long time at neutral pH. In contrast to the EOF in the unmodified microchannel, the EOF in the modified microchannel was only slightly affected by the change in pH (from 1 to 10). Most importantly, although PMBSSi possesses negative charges, the non-specific adsorptions of both anionic and cationic proteins (considering albumin and cytochrome c, respectively, as examples) were effectively suppressed to a level of 0.15 microg cm(-2) and lesser in the case of the 0.3 wt% PMBSSi modification. Consequently, the variation in the EOF mobility resulting from the protein adsorption was also suppressed simultaneously. To facilitate easy EOF control with compatibility to biomolecules delivered in the microfluidic devices, the charged interface described could provide a promising option.     

Criteria for determining the hydrogen-bond structures of a tyrosine side chain by fourier transform infrared spectroscopy: density functional theory analyses of model hydrogen-bonded complexes of p-cresol

Fourier transform infrared (FTIR) spectroscopy is a powerful method to investigate the structures of key Tyr residues involved in various protein reactions. In this study, we have performed density functional theory (DFT) calculations for various hydrogen-bonded complexes of p-cresol, a simple model of a Tyr side chain, in different hydrogen-bond forms to develop explicit criteria for determining the hydrogen-bond structures of Tyr using FTIR spectroscopy. The CO stretching (nuCO) and COH bending (deltaCOH) vibrations were focused as markers and calculated results were compared with experimental data of p-cresol and Tyr. The calculated and experimental nuCO frequencies appeared at 1280-1260, 1260-1250, 1255-1235, and 1240-1220 cm-(1) in the hydrogen-bond donor, free, donor-acceptor, and acceptor forms, respectively. These frequencies, which showed little overlap between the individual hydrogen-bond forms, had a negative linear correlation with the CO lengths in optimized geometries. The deltaCOH frequencies were found at 1255-1210 cm-(1) in the donor form, while the free and acceptor forms showed relatively low deltaCOH frequencies at 1185-1165 and 1190-1160 cm-(1), respectively. In the donor-acceptor form, the vibrational mode with a considerable deltaCOH contribution was found at 1280-1255 cm-(1) with a weak IR intensity. This frequency and the nuCO frequency in the donor-acceptor form are similar to the nuCO and deltaCOH frequencies, respectively, of the donor form, making it difficult to discriminate the two forms. These two forms can be clearly distinguished by detecting a strong nuCO(D) band in p-cresol-OD or Tyr-OD, in which the deltaCOD vibration largely downshifts to approximately 1000 cm-(1). The nuCO(D) frequency of the donor-acceptor form was found at 1260-1240 cm-(1), while that of the donor form was at 1270-1255 cm-(1). Practically, plotting the frequency of the lower-frequency strong IR band (nuCO of the donor-acceptor form or deltaCOH of the donor form) of undeuterated species against the nuCO(D) frequency is convenient for accurate discrimination. Because the donor form shows a positive linear correlation between deltaCOH and nuCO(D) frequencies, the two forms exhibited distinct areas in this plot. The effects of hydrogen-bond interactions on other potential IR and Raman markers are also discussed.