Coordination of a chiral tin(ii) cation bearing a bis(oxazoline) ligand with tetrahydrofuran derivatives

The reaction of SnCl(2) with the lithio derivative of a bis(oxazoline) ligand precursor afforded the enantiomeric chlorostannylene whose chloride ion can be substituted by several neutral or anionic Lewis donors. Abstraction of the chloride ion from the chlorostannylene with silver salts gave the corresponding tetrahydrofuran (THF) complexes of a chiral tin(ii) cation in 1,2-dimethoxyethane (DME) containing THF. That is, the reaction with silver hexafluoroantimonate (AgSbF(6)) afforded the THF complex without interaction with the counteranion. In contrast, reaction with silver triflate (AgOTf) gave the THF complex whose tin center had a pseudo-trigonal bipyramidal structure with two nitrogen atoms of a bidentate ligand and a lone pair at the equatorial positions and one of the oxygen atoms of triflate and an oxygen atom of THF at the apical positions in the solid state. Use of 3-methyltetrahydrofuran (3-MeTHF) instead of THF afforded the 3-MeTHF complexes, where the R-enantiomer of 3-MeTHF predominantly coordinates to the tin center. The previously reported germanium(ii) analogue of the tin(ii) cation indicated a similar enantioselectivity for the coordination of 3-MeTHF on the germanium center.     

Determination of histamine in seafood by hydrophilic interaction chromatography/tandem mass spectrometry

A simple method was developed to determine histamine, an important compound in chemical food poisoning, by extraction followed by hydrophilic interaction chromatography-tandem mass spectrometry using a hydrophilic column with sulfobetaine-type zwitterion groups. The quantitation range in seafood products was from 0.4 to 200 mg kg(-1) for 5 g food samples. Quantitative recoveries were obtained with four types of seafood product. These results agreed well with those from the more complex, conventional HPLC method, which requires sample derivatization with dansyl chloride.     

Thermodynamic and kinetic stabilities of complementary double helices utilizing amidinium-carboxylate salt bridges

A series of dimer strands consisting of m-terphenyl backbones bearing complementary chiral or achiral amidines and achiral carboxylic acid residues connected by various types of linkers, such as diacetylene, Pt(II)-acetylide, and p-diethynylbenzene linkages, were synthesized by a modular strategy, and their chiroptical properties on the complementary double helix formations were investigated by absorption, circular dichroism (CD), and (1)H NMR spectroscopies. The thermodynamic and kinetic stabilities of the complementary double helices assisted by amidinium-carboxylate salt bridges are highly dependent on their linkages, and the thermodynamic analyses of the dimer duplexes revealed that the association constants increased in the order: Pt(II)-acetylide linker < p-diethynylbenzene linker < diacetylene linker, which is in agreement with the reverse order of their bulkiness. The substituents on the amidine groups were also found to affect the stabilities on the duplexes and the association constants increased in the order: isopropyl < (R)-1-phenylethyl < cyclohexyl. In addition, the introduction of electron-donating and/or electron-withdrawing substituents at the phenyl groups of the p-diethynylbenzene linkers connecting the amidine and carboxylic acid units, respectively, tends to stabilize the complementary double helices, especially in polar solvents, such as DMSO, due to the attractive charge-transfer interactions between the aromatic linkers, although the salt bridge formation is hampered in DMSO. Furthermore, the kinetic analyses of the chain exchange reactions for the duplexes bearing diacetylene and p-diethynylbenzene linkages showed that these were slow processes with negative ΔS([symbol: see text]) values, meaning that the chain exchange reactions proceed via direct exchange pathways. In contrast, those for the duplexes bearing Pt(II)-acetylide linkages were fast processes supported by positive ΔS([symbol: see text]) values, suggesting that the chain exchange reactions proceed via dissociation-exchange ones. The helix-inversion kinetics investigated for the racemic dimer duplexes composed of achiral amidines based on variable-temperature (1)H NMR measurements indicated that the barriers for the helix-inversion increased in the order: Pt(II)-acetylide linker, p-diethynylbenzene linker < diacetylene linker.     

Microwave-assisted synthesis of organometallic complexes of ⁹⁹mTc(CO)₃ and Re(CO)₃: its application to radiopharmaceuticals

(99m)Tc-tricarbonyl [(99m)Tc(CO)(3)] complexes have been conventionally synthesized by heating [(99m)Tc(CO)(3)(H(2)O)(3)](+) and a tridentate chelating ligand under atmospheric pressure; however, this method is poor in terms of chemical yield and reproducibility. Moreover, since the half-life of (99m)Tc is very short (6 h), the development of facile and rapid methods of synthesizing (99m)Tc-labeled compounds, which could be used as radioactive tracers for single photon emission computed tomography (SPECT), is required. Thus, we initiated a study on the application of a microwave reaction to the synthesis of (99m)Tc(CO)(3)-2-picolylamine monoacetic acid (PAMA) [(99m)Tc(CO)(3)-PAMA] complexes on the basis of the fact that synthesis of metal complexes proceeds rapidly by microwave irradiation owing to an efficient exothermic phenomenon and heat conduction effect. Formation of by-products could be markedly suppressed by comparison with that in conventional methods. In the present study, rhenium (Re), an element belonging to the same group in the periodic table as technetium (Tc), and which also forms bipyramidal complexes, was first used to investigate the synthetic reaction because no stable isotopes exist for Tc. As a result, when water was used as the solvent under the irradiation of microwaves within 1 min, the Re(CO)(3)-PAMA complex could be directly synthesized from ethyl ester of PAMA (PAMAEE) and [Re(CO)(3)(H(2)O)(3)]Br in one step and with a high yield (94%). Finally, the (99m)Tc(CO)(3)-PAMA complex was successfully synthesized at a high radiochemical yield (>99%) within 1 min of reaction using (99m)Tc instead of Re under the same conditions.     

STM study of l-serine adsorption on Cu(0 0 1)

The adsorption of l-serine on Cu(0 0 1) surface at 310 K was studied by scanning tunneling microscope (STM). l-serine molecules on the Cu(0 0 1) initially formed a domain of thick lines with a order structure along the direction on the terraces regardless of the coverage of serine. The thick lines were partly replaced by thin line along the direction, and completely disappeared in 2 h. It is considered that in these structures hydrogen bonds involved in hydroxymethyl group between adsorbates play some role in addition to intermolecular hydrogen bond between a hydrogen atom of amino group and an oxygen atom of carboxy group for alanine adsorption.     

Ordering of azobenzenes by two-photon isomerization

We report on light induced orientation by two-photon isomerization of azobenzenes in films of polymer. The dynamics of isomerization and orientation by one-photon absorption and two-photon absorption (TPA) are similar, and TPA creates a degree of molecular orientation which is comparable to that achieved by single-photon isomerization, in agreement with the theoretical predictions of two-photon isomeric orientation.     

Selective recognition and electrochemical sensing of dicarboxylates with a ferrocene-based bis(o-trifluoroacetylcarboxanilide) receptor

A ferrocene-based bis(o-trifluoroacetylcarboxanilide) receptor selectively recognizes m-phenylene diacetate through cooperative binding; the receptor also displays a significant negative shift in the oxidation potential of ferrocene upon the guest binding.     

Preparation and exfoliation of layered titanium butyl phosphates

Titanium butyl phosphates (TiBP) synthesized by reacting Ti(SO₄)₂ with a mixture of mono-(C₄H₉PO₄H₂) and dibutyl phosphates ((C₄H₉)₂PO₄H) in aqueous ethanol solution at 25 °C were characterized by various conventional techniques. XRD pattern of TiBP possessed a peak at 2θ?=?5.5° and a broad hump at 2θ?=?15–30°. This fact indicated that the material was composed of a multilayer alternating bilayer of butyl groups of the phosphates and amorphous titanium phosphate phase. The TiBP was spherical particles with a size of ca. 100 nm and the chemical formula of this material was Ti((C₄H₉O)₂PO₂)_x(C₄H₉OPO₃)_y(OH)_z. The TiBP possessed a UV absorption property due to charge transfer of O^2? ? Ti⁴⁺. The layered structure of TiBP was exfoliated in ethanol at 25 °C up to TiBP concentration of 1.0?×?10⁵ ppm to form nanosheet. The nanosheet dispersing solution exhibited a UV absorption property and the property depends on nanosheet concentration.