Electrochemical behaviors of native and thermally denatured fish DNA in the presence of cytosine derivatives and porphyrin by cyclic voltammetry using boron-doped diamond electrode

The electrochemical behaviors of native and thermally denatured fish DNA was investigated using boron-doped diamond (BDD) film electrode by cyclic voltammetry. The BDD electrode afforded us to measure weak current less than muA for the DNA solution in 100 microl. The mixture of acetic acid and sodium acetate solution (0.2 M) was used as a supporting electrolyte. Two oxidation peaks were observed at about +1.1 V and +1.3 V at pH 4.6 for thermally denatured fish DNA. This is due to the oxidation of guanine and adenine in the denatured fish DNA, respectively. In contrast, the native fish DNA showed ill-defined peaks at +1.1 V. Furthermore, the electrochemical behaviors of thermally denatured fish DNA were studied in the presence of cytosine, cytidine, cytidine-5-monophosphate, tetrakis(1-methypyridinium-4-yl)porphyrin (H(2)(TMPyP)(4+)) and Ru(II)(TMPyP)(4+). The oxidation peak intensity at +1.1 V gradually decreased with the increase of the concentrations of the above compounds. Based on the above studies, electrochemical behaviors of the thermally denatured fish DNA at BDD electrode is discussed.     

Hydrogen generation from weak acids: electrochemical and computational studies of a diiron hydrogenase mimic

Extended investigation of electrocatalytic generation of dihydrogen using [(mu-1,2-benzenedithiolato)][Fe(CO)3]2 has revealed that weak acids, such as acetic acid, can be used. The catalytic reduction producing dihydrogen occurs at approximately -2 V for several carboxylic acids and phenols resulting in overpotentials of only -0.44 to -0.71 V depending on the weak acid used. This unusual catalytic reduction occurs at a potential at which the starting material, in the absence of a proton source, does not show a reduction peak. The mechanism for this process and structures for the intermediates have been discerned by electrochemical and computational analysis. These studies reveal that the catalyst is the monoanion of the starting material and an ECEC mechanism occurs.     

Statistical solution to the capacity problem in direct-sequence code-division multiple-access communication systems

Tohru Kohda Department of Computer Science and Communication Engineering, Kyushu University, Fukuoka 812-8581, Japan Minoru Tabata Department of Mathematical Sciences, Osaka Prefecture University, Osaka 599-8531, Japan Email: eshima{at}med.oita-u.ac.jp Received on September 21, 2005; Accepted on May 2, 2006 Capacity in the direct-sequence code-division multiple-access(DS/CDMA) communication system was considered according to thecode acquisition performance with the conventional serial-searchmethod, because code acquisition needs a difficult operation.Since capacity in DS/CDMA systems is defined by the maximumnumber of users that can simultaneously transmit their signalswith the same carrier frequencies, assuring a larger capacityis very important in DS/CDMA systems with respect to the economyof frequency source. This paper reconsiders the capacity problemthrough a statistical approach to code acquisition. First, aDS/CDMA system model is reviewed. Second, properties of thecounting method for code acquisition are discussed. It is provedthat the method can acquire the target user's code under anynumber of interference users that simultaneously transmit theirsignals, and that the method can guarantee a considerable precisionin code acquisition. Third, an observation time necessary forcode acquisition is given from a statistical discussion, andthe original counting method is modified into a simpler one.It is concluded that the capacity of the DS/CDMA communicationsystem can be set by the ‘bit error-rate-based capacityor signal-to-noise ratio-based capacity’, i.e. ‘post-acquisition-basedcriterion’, rather than the ‘acquisition-based capacity’.     

An attempt to discriminate between the hydrophobic and aromatic pi-pi interactions in the copper(II) ternary complexes CuLA with L=1,10-phenanthroline or 2,2'-bipyridyl and A=para-X-substituted phenylalaninates

For the title complexes, the value of formation constant K(CuL+A) is higher than that of K1(CuA2). According to the mechanistic consideration, log K(CuL+A) is calculated for regular Cu(II) complexes with neither special enhancement nor diminution of the stability constant. Then, the difference of log K(CuL+A)(obs)-log K(CuL+)(calc) represents extrastabilization due to the hydrophobic interactions and the aromatic pi-pi interactions. The former has been found to be proportional to the free energy of the transfer of side chains of aminocarboxylates A. The discrimination between the hydrophobic and the aromatic pi-pi interactions has been attempted.     

Mechanism of Homogeneous Liquid-Liquid Extraction

Extraction mechanism and solvent structure were studied for the solvent extraction of cationic porphyrin (5,10,15,20-tetrakis(l-methyl-pyridinium-4-yl) porphyrin; H2(tmpyp)⁴⁺, and its metalloporphyrins (MP^(n+2)+-) into an acetonitrile phase separated from a 1:1 (v/v) mixture of acetonitrile with water by addition of sodium chloride, where Mⁿ⁺ denotes Zn²⁺, Cu²⁺,Co³⁺, Fe³⁺, and Mn³⁺, and H₂P⁴⁺ is the free base form of H₂tmpyp⁴⁺. The separated acetonitrile phase contains a lot of water (4.53 mol dm^-3) and sodium chloride (2.49×10^-2 mol dm^-3) that afford to extract the highly charged chemical species of the above porphyrin or metalloporphyrins with perchlorate ion (X^-). The extracted chemical species dissociate in the acetonitrile phase.     

Separation and Transport of Lithium of 10-5 M in the Presence of Sodium Chloride Higher than 0.1 M

Lithium is an important element for lithium battery and clinical treatment of manic depression. Thus,rapid and accurate methods for the determination of lithium and its separation and collection of lithium in recycle are receiving a great concern. Because of the high concentrations of Na⁺ in sea water and blood, very high Li⁺/Na⁺ selectivity is required for the separation and determination of Li⁺ at concentration less than 10^-4 M (700 ppb) in a large excess of Na⁺. We report here the methods of separation, transport and determination of lithium as low as 10^-5 M (M=mol dm^-3) in the presence of Na⁺ more than 0.1 M by using a water-soluble octabromoporphyrin; H₂P^4-) synthesized in our laboratory.     

Synthesis of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] and anomalous proton conductivities of the thin films

New proton-conductive polyamide oligomers, oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thin films. The obtained oligomers were characterized by the X-ray diffraction, FT-IR spectra, ¹H NMR, Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrum, and electrical conductivity measurements. The bulk proton conductivity is 3.0 × 10^? 4 S cm^? 1 at the relative humidity (RH) of 80%. The proton conductivity of thin film is relatively higher than that of bulk sample. Thickness dependence of the proton conductivity was observed in these thin films. The maximum proton conductivity of the thin film is 4.0 × 10^? 3 S cm^? 1 at the relative humidity (RH) of 80%, which is higher one order magnitude than that of the bulk sample. The activation energies of bulk and 200 nm thick film are 1.0 and 0.69 eV at the RH of 60%, respectively.     

One-pot concise syntheses of benzimidazo[2,1-a]isoquinolines by a microwave-accelerated tandem process

Direct, efficient syntheses of the benzimidazo[2,1-a]isoquinoline ring system have been achieved with 2-bromoarylaldehydes, terminal alkynes, and 1,2-phenylenediamines by a microwave-accelerated tandem process in which a Sonogashira coupling, 5-endo cyclization, oxidative aromatization, and 6-endo cyclization can be performed in a single synthetic operation.