Precise control and consecutive modulation of spin transition temperature using chemical migration in porous coordination polymers

Precise control of spin transition temperature (T(c)) is one of the most important challenges in molecular magnetism. A Hofmann-type porous coordination polymer {Fe(pz)[Pt(II)(CN)(4)]} (1; pz = pyrazine) exhibited cooperative spin transition near room temperature (T(c)(up) = 304 K and T(c)(down) = 284 K) and its iodine adduct {Fe(pz)[Pt(II/IV)(CN)(4)(I)]} (1-I), prepared by oxidative addition of iodine to the open metal sites of Pt(II), raised the T(c) by 100 K. DSC and microscopic Raman spectra of a solid mixture of 1-I and 1 revealed that iodine migrated from 1-I to 1 through the grain boundary after heating above 398 K. We have succeeded in precisely controlling the iodine content of {Fe(pz)[Pt(CN)(4)(I)(n)]} (1-In; n = 0.0-1.0), which resulted in consecutive modulation of T(c) in the range 300-400 K while maintaining the hysteresis width. Furthermore, it was demonstrated that iodine migration in the solid mixture was triggered by the spin transition of 1-I. The magnetically bistable porous framework decorating guest interactive open-metal-site in the pore surface makes it possible to modulate T(c) ad arbitrium through unique postsynthetic method using iodine migration.     

Semiconducting behavior of type-I Si clathrate K8Ga8Si38

A ternary type-I Si clathrate K(8)Ga(8)Si(38) has been revealed to be an indirect band gap semiconducting material with an energy gap (E(g)) of approximately 0.10 eV, which is much smaller than the calculated E(g) value that is 0.15 eV wider than E(g) of elemental Si with the diamond-type structure.     

Synthesis and Pyrolysis of Fullerenol-stabilized Pt Nanocolloids as a unique Approach to Pt-doped Carbon

An aqueous colloidal dispersion of Pt nanoparticles (NPs) stabilized by fullerenol C₆₀(OH)₁₂ (Pt:C₆₀(OH)₁₂) was successfully synthesized via liquid-phase chemical reduction. The subsequent pyrolysis of Pt:C₆₀(OH)₁₂ at different temperatures was conducted to afford Pt-doped carbon with different chemical compositions (Pt:C60ⁿ). X-ray absorption spectroscopy (XAS) and Infrared (IR) absorption spectroscopy and thermogravimetric measurements revealed that the thus-prepared nanocomposite consists of Pt NPs and high valent Pt-C₆₀(OH)₁₂ complex. One distinct feature of C₆₀(OH)₁₂ matrix as catalyst support is the suppression of size growth of Pt NPs during the pyrolysis up to 300 °C. Electrochemical experiments using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were performed to find that Pt:C60³⁰⁰ (pyrolyzed at 300 °C) exhibited higher activity than others, that was attributed to the π-extended feature of the as-obtained carbon.     

Synthesis of functionalized porphyrins as oxygen ligand receptors

Oxophilic synthetic receptors were designed and synthesized using a porphyrin scaffold, with the aim of constructing a preorganized complementary binding site for phenols and carbohydrates. We pursued three strategies for phenol recognition: (1) Lewis acid/Lewis base combinations serving as a hydrogen bond donor and acceptor for the OH group, (2) Lewis base/pi-pi stacking, targeting both the OH group and the aromatic moiety of phenols, and (3) exchange of the axial hydroxyl ligand on a trivalent and oxophilic metal center of aluminum porphyrin. For the recognition of acidic phenols, the most promising recognition motif was Lewis base/pi-pi stacking, which can bind to phenols with a hydrogen bond and pi-pi stacking interactions. [5-(8-Quinolyl)-10,15,20-triphenylporphyrinato]zinc binds to p-nitrophenol with a binding constant of 540 M(-)(1) in CHCl(3) at 25 degrees C. For carbohydrate recognition, we designed the metalloporphyrin receptor having 8-quinolyl groups and o-carbomethoxymethoxyphenyl groups, where these Lewis basic parts serve as the cooperative hydrogen bonding sites for the hydroxyl groups of glucoside. The receptor binds to beta-octyl glucoside with a binding constant of 7.35 x 10(4) M(-)(1) in CHCl(3) at 15 degrees C, demonstrating importance of formation of a highly ordered hydrogen bonding network between the receptor and the guest. These binding features have significant implications for the rational design of oxophilic artificial receptors.     

Analysis of carbohydrates in glycoproteins by high-performance liquid chromatography and high-performance capillary electrophoresis

We describe two methods for the analysis of oligosaccharide chains in glycoproteins by high-performance liquid chromatography (HPLC) and high-performance capillary electrophoresis (HPCE).O-andN-glycosidically linked oligosaccharides released from glycoproteins can be identified as their borohydride-reduced forms by anion-exchange HPLC with pulsed amperometric detection.N-Glycosidically linked oligosaccharides can also be analyzed as 2-aminopyridine derivatives by HPCE in direct zone electrophoresis mode in an acidic phosphate buffer and zone electrophoresis mode as borate complexes in an alkaline buffer. We also present a convenient procedure for the analysis of the constituent monosaccharides of these oligosaccharides chains by HPLC based on reversed-phase partition mode as 1-phenyl-3-methyl-5-pyrazolone derivatives.     

Specific isolation of N-terminal fragments from proteins and their high-fidelity de novo sequencing

A new method to determine N-terminal amino acid sequences of multiple proteins at low pmol level by a parallel processing has been developed. The method contains the following five steps: (1) reduction, S-alkylation and guanidination for targeted proteins; (2) coupling with sulfosucccimidyl-2-(biotinamido)ethyl-1,3-dithiopropionate(sulfo-NHS-SS-biotin) to N(alpha)-amino groups of proteins; (3) digestion of the modified proteins by an appropriate protease; (4) specific isolation of N-terminal fragments of proteins by affinity capture using the biotin-avidin system; (5) de novo sequence analysis of peptides by MALDI-TOF-/MALDI-TOF-PSD mass spectrometry with effective utilization of the CAF (chemically assisted fragmentation) method.1 This method is also effective for N-terminal sequencing of each protein in a mixture of several proteins, and for sequencing components of a multiprotein complex. It is expected to become an essential proteomics tool for identifying proteins, especially when used in combination with a C-terminal sequencing method.     

Elution behaviour and environmental impact of heavy metals and rare-earth elements from volcanic ashes of Mt. Oyama,Miyake Island

To obtain information on the environmental impact of materials eluted from volcanic ashes of Mt. Oyama, Miyake Island, which erupted in July 2000, the dissolution behaviours of heavy metals and rare-earth elements from the volcanic ashes were examined. The most important characteristic of the Mt. Oyama eruption is that sulphur dioxide (SO₂) gas has been continuously released, and all persons living on Miyake Island have been required to evacuate. To estimate in terms of the volcanic eruption using SO₂ gas, the ash nature in Mt. Usu, Hokkaido, was also examined and compared with that in Mt. Oyama. When rain water mixed the ashes, the water from the ashes of Mt. Oyama became acidic because of the sulphuric acid. Therefore, SO₂ gas in Mt. Oyama can accelerate the dissolution of protons and heavy metals in the ashes, whereas the rain water in Mt. Usu was not acidic and the dissolution of the heavy metals was not so evident compared with that in the case of Mt. Oyama. With this sulphuric acid, heavy metals such as As, Cd, Pb and Hg in the ashes in Mt. Oyama easily dissolved owing to the low pH. The ashes in Mt. Oyama had been released for eight years and the amount of fallen ashes was estimated to be 33 billion tons. The weights of the harmful heavy metals in the volcanic ashes, such as As, Cd, Pb and Hg, were estimated to be 3.8?×?10², 1.3?×?10³, 1.1?×?10³ and 29?kg, respectively, and these heavy metals were dissolved and diluted in seawater. Therefore, the concentration and species (chemical form) of these metals should be carefully monitored in the future. Moreover, SO₂ gas, which has a direct effect on human health and has been monitored continuously, causes other effects, such as facilitation of metal ion elution and rock aeration.     

Heterocyclic effect for optical properties of naphthoquinone-based pigment: 2-methyl-3-heteroarylthio-1,4-naphthalenedione

Three novel naphthoquinone-based heterocyclic pigments, 2-methyl-3-[(1-methyl-1H-imidazol-2-yl)thio-1,4-naphthalenedione, (4-methyl-4H-1,2,4-triazol-3-yl)thio-1,4-naphthalenedione, and (1-methyl-1H-tetrazol-5-yl)thio]-1,4-naphthalenedione, are synthesized, and their optical properties in both solution and solid states are investigated. Depending on the heteroarylthio ring in the pigment, variation in optical properties is observed, e.g. characteristic colours for each pigment in the solution and solid states. The achiral pigment containing the 1-methyl-1H-tetrazol-5-yl ring exhibits a chiral space group and a CD signal in the solid state.     

Structural and Physical Properties of New Conducting Cation Radical Salts with Te-Based Counteranions, Tetraiodotellurate(II) and Hexaiododitellurate(II)

This article reports preparation, structure, and conducting property of several cation radical salts of organic donors tetramethyltetrathiafulvalene (TMTTF), ethylenedithiotetrathiafulvalene (EDT-TTF), bis(ethylenedithio)tetrathiafulvalene (ET), bis(ethylenedithio)tetraselenafulvalene (BETS) and hexamethylenetetraselenafulvalene (HMTSF) with two novel planar Te-based dianions, TeI₄²⁻ and Te₂I₆²⁻. (ET)₅Te₂I₆ 1 and (BETS)₅Te₂I₆ 2 are isostructural. In these Te₂I₆²⁻ salts, intermolecular short I···I contacts form a supramolecular corrugated anion sheet. Donor arrangement is similar to the θ-type. With lowering temperature, the resistivity of 1 shows a gradual increase followed by a sharp upturn at 110 K. 2 is metallic down to 120 K and shows a gradual increase of the resistivity followed by a clear transition to an insulating state around 60 K. Crystal structure of (ET)₄TeI₄ 3 is based on the “herring bone” arrangement of ET molecules similar to the α-type. 3 shows a semiconductive behavior around room temperature followed by a transition to an insulating state at 210 K. (EDT-TTF)₄TeI₄ 4, a semiconductor, exhibits a unique two-dimensional arrangement of dimerized EDT-TTF molecules.     

Nucleic acid related compounds. 116. Nonaqueous diazotization of aminopurine nucleosides. Mechanistic considerations and efficient procedures with tert-butyl nitrite or sodium nitrite

Nonaqueous diazotization-dediazoniation of two types of aminopurine nucleoside derivatives has been investigated. Treatment of 9-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)-2-amino-6-chloropurine (1) with SbCl(3)/CH(2)Cl(2) was examined with benzyltriethylammonium (BTEA) chloride as a soluble halide source and tert-butyl nitrite (TBN) or sodium nitrite as the diazotization reagent. Optimized yields (>80%) of the 2,6-dichloropurine derivative were obtained with SbCl(3). Combinations with SbBr(3)/CH(2)Br(2) gave the 2-bromo-6-chloropurine product (>60%), and SbI(3)/CH(2)I(2)/THF gave the 2-iodo-6-chloropurine derivative (>45%). Antimony trihalide catalysis was highly beneficial. Mixed combinations (SbX(3)/CH(2)X'(2); X/X' = Br/Cl) gave mixtures of 2-(bromo, chloro, and hydro)-6-chloropurine derivatives that were dependent on reaction conditions. Addition of iodoacetic acid (IAA) resulted in diversion of purine radical species into a 2-iodo-6-chloropurine derivative with commensurate loss of other radical-derived products. This allowed evaluation of the efficiency of SbX(3)-promoted cation-derived dediazoniations relative to radical-derived reactions. Efficient conversions of adenosine, 2'-deoxyadenosine, and related adenine nucleosides into 6-halopurine derivatives of current interest were developed with analogous combinations.