Hypoxanthine sensor based on an amorphous silicon field-effect transistor

The pH response of an a-ISFET with xanthine oxidase immobilized on a ca. 20-μm thick poly(vinyl butyral) membrane over the gate insulator, is used to detect the uric acid produced by enzyme-catalyzed oxidation of hypoxanthine. The pH sensitivity between pH 5.0 and 10.0 is ca 48 mV/pH at 32°C in 10 mM phosphate buffer. The change in the output gate voltage 1 min after sample injection, is linearly related to the logarithm of the hypoxanthine concentration in the range 0.02–0.1 mM. The optimum buffer pH is 7.5. The system can be used for 2 weeks with 30% loss of enzymatic activity.     

Organic and organometallic derivatives of dihydrogen-encapsulated [60]fullerene

Regioselective multi-addition reaction of organocopper and amine compounds onto dihydrogen-encapsulated [60]fullerene, H2@C60, produced a variety of organic and organometallic derivatives of H2@C60. The X-ray crystallographic analysis of dihydrogen-encapsulated bucky ferrocene, Fe(H2@C60Ph5)C5H5, showed the presence of the dihydrogen molecule located almost in the center but slightly away from the ferrocene moiety. The 1H NMR chemical shift values for the encapsulated molecular hydrogen indicated that these values are susceptible to the magnetic environment of the inside as well as the outside of the fullerene cage.     

Selective allylic hydroxylation of octahydronaphthalene derivatives with a bridgehead double bond using electrochemical method with iron picolinate complexes

The combination of electrolysis and the Fe(III)(PA)3/O2/CH3CN system was investigated for allylic hydroxylation of octahydronaphthalene derivatives. Substrates with a bridgehead double bond gave the allylic alcohol with alpha-preference, while non-bridgehead olefin did not react smoothly. This system is a useful tool for alpha-selective allylic hydroxylation of octahydronaphthalene derivatives with a bridgehead double bond as model compounds for the AB fused ring of cholesterols.     

Alternating polyampholytes prepared by hydrolysis of copolymer of maleic anhydride and N-vinylsuccinimide

Alternating polyampholytes (MA-VA) containing two acidic groups and one basic group were prepared by the copolymerization of maleic anhydride (M₁) and N-vinylsuccinimide (M₂) at 60°C with AIBN as the initiator, followed by acid hydrolysis with 1N hydrochloric acid at 140°C for 24 hr. The monomer reactivity ratios r₁ and r₂ are 0.025 and 0.06, respectively. The structure of polymers was discussed on the basis of the data of their elementary, infrared (IR), and thermal analyses and the binding ability of heavy metal ion. Polyampholytes were soluble in strong acidic and basic media but were precipitated in the pH range 3–4. An isoelectric point at pH 3 was determined by potentiometric titration and the turbidimetric method. By thermal treatment above 205°C the polyampholyte turned quantitatively into a cyclized lactam. This suggests that the polyampholyte MA–VA has an intramolecular hydrogen bond between the amino and γ-carboxyl groups. The binding of Cu²⁺ and Hg²⁺ by the polyelectrolyte was evaluated by equilibrium dialysis.     

On the structural change of some TCNB complexes in the excited singlet state

The absorption spectra of the TCNB-toluene complex in the fluorescent state at 4.2°K were observed. On the basis of the results of excited singlet-singlet absorption spectra of some TCNB complexes at various temperatures, available fluorescence spectral data were re-interpreted. Instead of the model of so-called structural change, an alternative explanation in terms of the triple complex (D₂⁺A^?) in the excited state is proposed.     

A new synthetic method of 3-acyltetronic acid derivatives and its application to the synthesis of isoaspertetronin a (isogregatin A)

A new synthetic method of 3-acyltetronic acid derivatives from the corresponding 3-bromo compound via lithiation with n-BuLi followed either by acylation with acid chloride or better by first reacting with aldehyde and then subsequent oxidation with active MnO₂ is described. A revised structure $\text{10}$ for aspertetronin A(gregatin A) was presented based on the synthesis of the proposed structure $\text{8}$ and spectral comparison of a model compound $\text{12}$ with the natural product.     

Apparent anomalous behavior of polar substituents on the benzene ring in the regioselectivity of di-π-methane rearrangement of 5,6-benzo-2-azabicyclo[2.2.2]octadienones

Polar substituent effects on the aromatic ring emerge in the regioselectivity of the di-π-methane rearrangement of the title compounds when they possess the structural feature of including the bridgehead carbon in a saturated ring; the importance of the environment at the bridgehead carbon is pointed out.     

Enantioselective synthesis of alpha-substituted ketones by asymmetric addition of chiral zinc enamides to 1-alkenes

A zinc enamide of a chiral imine derived from a ketone and (S)-valinol or (S)-t-leucinol undergoes addition to 1-alkene to generate a gamma-zincioimine intermediate, which reacts with a carbon electrophile to give upon hydrolysis an optically active alpha-substituted ketone in good yield. The stereoselectivity of the addition reaction may reach 99% for the reaction of a cyclohexanone imine with ethylene.     

Phosphate ion-sensitive coated-wire/field-effect transistor electrode based on cobalt phthalocyanine with poly(vinyl chloride) as the membrane matrix

An ion-selective coated-wire/field-effect transistor electrode responding to dihydrogenphosphate is described. The device consists of a coated-platinum wire electrode connected to the gate of a conventional field-effect transistor. Cobalt phthalocyanine is used as ion-exchange electroactive substance and poly(vinyl chloride) as the membrane matrix. The characteristics of the device are investigated and its response is studied by two methods, the linear dependence of the square root of the drain current in the saturated region on the logarithm of ion activity for sodium dihydrogenphosphate, and the dependence of the gate-source potential on the logarithm of ion activity of the same ion. A linear response is obtained in the range of ion activity 10^?5-10^?1 mol dm^?3 and the response slope is 45 mV per decade change of H₂PO₄^? ion activity; the selectivity coefficients are discussed.     

Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions

Two fluorescent ligands, N-(2-(5-cyanopyridyl))cyclen (L5) and N-(2-pyridyl)cyclen (L6) (cyclen = 1,4,7,10-tetraazacyclododecane), were designed and synthesized to control twisted intramolecular charge transfer (TICT) by metal chelation in aqueous solution. By complexation with Zn(2+), L6 exhibited TICT emissions at 430 nm (excitation at 270 nm) in 10 mM HEPES (pH 7.0) with I = 0.1 (NaNO(3)) at 25 degrees C due to the perpendicular conformation of a pyridine ring with respect to a dialkylamino group, which was fixed by Zn(2+)-N(pyridine) coordination, as proven by potentiometric pH, UV, and fluorescence titrations and X-ray crystal structure analysis. We further describe that the 1:1 complexation of ZnL6 with guests such as succinimide, phosphates, thiolates, and dicarboxylates, which compete with a nitrogen in the pyridine ring for Zn(2+) in ZnL6, induces considerable emission shift from TICT emissions (at 430 nm) to locally excited emissions (at ca. 350 nm) in neutral aqueous solution at 25 degrees C.