Side chain-directed assembly of triangular molecular panels into a tetrahedron vs. open cone

Despite their structural similarity, triangular tetradentate ligands 2b and 2c experience different assembly pathways on complexation with (en)Pd(NO3)2 to give M8L4 tetrahedral (3) and open cone (4) structures, respectively, due to steric restriction by side chains at the corner or on the edge of the ligands.     

New Proof of the Fukui Conjecture by the Functional Asymptotic Linearity Theorem

The present article provides a new proof of the Fukui conjecture concerning the additivity problem of the zero-point vibrational energies of hydrocarbons. This conjecture played a prominent role in the initial development of the repeat space theory (RST), and continues to be of vital significance in the recent development of the theory of the generalized repeat space X _r (q,d). The new proof of the Fukui conjecture has been given here by establishing the functional version of the Asymptotic Linearity Theorem (ALT), the Functional ALT. This enhanced version of the ALT directly implies the validity of the Fukui conjecture; it easily unifies, in a broad perspective, a variety of additivity phenomena in physico-chemical network systems having many identical moieties, and efficiently solves some interpretational problems of the empirical additivity formulae from experimental chemistry. The proof of the functional version of the ALT is based on a new method transferable to the extended theoretical framework of the generalized repeat space X _r (q,d).     

ESTABLISHMENT and CHARACTERIZATION OF A MONOCLONAL ANTIBODY RECOGNIZING THE DEWAR ISOMERS OF(6–4)PHOTOPRODUCTS

Abstract— We established a monoclonal antibody(DEM–1) that recognizes UV-induced DNA damage other than cyclobutane pyrimidine dimers or(6–4)photoproducts. The binding ofDEM–1 antibody to 254 nm UV-irradiated DNA increased with subsequent exposure to UV wavelengths longer than 310 nm, whereas that of the 64M-2 antibody specific for the(6–4)photoproduct decreased with this treatment. Furthermore, the increase inDEM–1 binding was inhibited by the presence of the 64M-2 antibody during the exposure. We concluded that theDEM–1 antibody specifically recognized the Dewar photoproduct, which is the isomeric form of the(6–4)photoproduct. TheDEM–1 antibody, however, also bound to DNA irradiated with high fluences of 254 nm UV, suggesting that 254 nm UV could induce Dewar photoproducts without subsequent exposure to longer wavelengths of UV. Furthermore, an action spectral study demonstrated that 254 nm was the most efficient wavelength for Dewar photoproduct induction in the region from 254 to 365 nm, as well as cyclobutane dimers and(6–4)photoproducts, although the action spectrum values in the U V-B region were significantly higher compared with those for cyclobutane dimer and(6–4)photoproduct induction.     

Direct chiral resolution of tartaric acid by ion-pair capillary electrophoresis using an aqueous background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane as a chiral counterion

Chiral resolution of native DL-tartaric acid was achieved by ion-pair capillary electrophoresis (CE) using an aqueous-ethanol background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane (R-DACH) as a chiral counterion. Factors affecting chiral resolution and migration time of tartaric acid were studied. By increasing the viscosity of the background electrolyte and the ion-pair formation, using organic solvents with a lower relative dielectric constant, resulted in a longer migration time. The optimum conditions for both high resolution and short migration time of tartaric acid were found to be a mixture of 65% v/v ethanol and 35% v/v aqueous solution containing 30 mM R-DACH and 75 mM phosphoric acid (pH 5.1) with an applied voltage of -30 kV at 25 degrees C, using direct detection at 200 nm. By using this system, the resolution (Rs) of racemic tartaric acid was approximately 1. The electrophoretic patterns of tartaric and malic acids suggest that two carboxyl groups and two hydroxyl groups of tartaric acid are associated with the enantioseparation of tartaric acid by the proposed CE method.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMSI effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO?H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

Polyhydrazides. III. N-methylated polyhydrazides by ring-opening of poly-p-phenylene-1,3,4-oxadiazole

A new ring-opening reaction of 1,3,4-oxadiazole by methylating reagents was developed in fuming sulfuric acid or polyphosphoric acid and then, by applying this reaction to poly-p-phenylene-1,3,4-oxadiazole, a high molecular weight poly-N-methylterephthalylhydrazide was obtained. Various methylating reagents were investigated as ring-opening reagents. The degrees of ring-opening in polymers were estimated and related to the properties of the polymers.     

Interaction between peroxide ion and phenol group which are coordinated to the same iron(III) ion

We have prepared several new iron(III) complexes with ligands which contain a phenol group; these are tetradentate [(X-phpy)H, X and H(phpy) represent the substituents on the phenol ring and N,N-bis(2-pyridylmethyl)-N-(2-hydroxybenzyl)amine, respectively] and pentadentate ligands [(R-enph-X)H; R=ethyl(Et) or methyl(Me) derivative and H(Me-enph) denotes N,N-bis(2-pyridylmethyl)-N″-methyl-N″-(2″-hydroxyl-benzylamine)ethylenediamine] and have determined the crystal structures of Fe(phpy)Cl₂, Fe(5-NO₂-phpy)Cl₂, and Fe(Me-enph)ClPF₆, which are of a mononuclear six-coordinate iron(III) complex with coordination of one or two chloride ion(s). These compounds are highly colored (dark violet) due to the coordination of phenol group to an iron(III) atom. When hydrogen peroxide was added to the solution of the iron(III) complex, a color change occurs with bleaching of the violet color, indicating that oxidative degradation of the phenol moiety occurred in the ligand system. The bleaching of the violet color was also observed by the addition of t-butylhydroperoxide. The rate of the disappearance of the violet color is highly dependent on the substituent on the phenol ring; introduction of an electron-withdrawing group in the phenol ring decreases the rate of bleaching, suggesting that disappearance of the violet band should be due to a chemical reaction between the phenol group and a peroxide adduct of the iron(III) species with an η¹-coordination mode and that in this reaction the peroxide adduct acts as an electrophile towards phenol ring. The intramolecular interaction between the phenol moiety and an iron(III)-peroxide adduct may induce activation of the peroxide ion, and this was supported by several facts that the solution containing an iron(III) complex and hydrogen peroxide exhibits high activities for degradation of nucleosides and albumin.     

Quartz crystal microbalance immunosensor for highly sensitive 2,3,7,8-tetrachlorodibenzo-p-dioxin detection in fly ash from municipal solid waste incinerators

A quartz crystal microbalance (QCM) immunosensor was developed for the detection of 2,3,7,8-tetrachlorodibenzo-p-dioxins (TCDD) in environmental pollutants. An anti-TCDD antibody was immobilized on the gold surface of the QCM via chemical coupling, and its immunologic activity was then maintained by treatment with an artificial stabilizing reagent such as poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate). A competitive immunoreaction with TCDD conjugated ovalbumin (TCDD-ovalbumin) was used to detect TCDD. A calibration curve was obtained through the competitive immunoreaction, and linearity was shown from 100 ng mL(-1) to 0.1 ng mL(-1). Also, the cross-reactivities of the anti-TCDD monoclonal antibody were thoroughly evaluated with several TCDD derivatives. The relationships between GC-MS, ELISA, and QCM were compared using fly ash samples from a municipal solid waste, which were prepared using an accelerated solvent extractor. For 23 samples, the experimental relationship between the TCDD concentration by QCM vs. the TCDD concentration by ELISA was y= 1.07x + 2.70, r= 0.99, and the TCDD concentration by QCM vs. the toxic equivalent quantity (TEQ) value by GC-MS was y= 2.46x - 14.98, r= 0.89.     

Sensitive and high-throughput analyses of purine metabolites by dynamic pH junction multiplexed capillary electrophoresis: a new tool for metabolomic studies.

On-line sample preconcentration by a dynamic pH junction in conjunction with multiplexed capillary electrophoresis (CE) and UV detection represents a sensitive and high-throughput format for future metabolomic research, such as purine analysis. The optimization of purine focusing can be rapidly assessed by systematically altering the sample matrix properties, such as the buffer co-ion, pH and ionic strength using a 96-capillary array format. This method permits focusing of large sample injection volumes, resulting in over a 50-fold improvement in the concentration sensitivity. The limit of detection (S/N = 3) for purine metabolites was less than 8.0 x 10(-8) M under optimum conditions when using UV absorbance. Dynamic pH junction multiplexed CE demonstrated excellent linearity over a hundred-fold concentration range, as well as low inter-capillary precision in terms of normalized migration times and peak areas. The potential for clinically relevant high-throughput analyses of micromolar amounts of purine metabolites in urine was also demonstrated.     

High-sensitivity analyses of metabolites in biological samples by capillary electrophoresis using dynamic pH junction-sweeping

Emerging fields of biochemical research, such as metabolomics, present challenges to current separation technologies because of the large number of metabolites present in a cell and their often low (submicromolar) concentration. Although capillary electrophoresis (CE) holds great promise as the method of choice for high-resolution separations of biological samples, it suffers from poor concentration sensitivity, especially with the use of UV detection. In CE, sweeping and dynamic pH junction represent two complementary on-line focusing techniques that have been used for sensitivity enhancement of hydrophobic and weakly acidic analytes, respectively. However, the application of either the sweeping or dynamic pH junction technique alone might, in some cases, be less effective for the analysis of certain sample mixtures. Recent work in the development of a hyphenated dynamic pH junction-sweeping technique is presented as an effective on-line method of preconcentration suitable for both hydrophilic (anionic) and hydrophobic (neutral) analytes. Sensitive analyses of flavin metabolites by CE with laser-induced fluorescence (LIF) detection is demonstrated in various biological matrixes, including cell extracts of Bacillus subtilis, pooled human plasma, as well as heat-deproteinized flavoenzymes. Enhanced analyte band narrowing and improved sensitivity is achieved for flavins using dynamic pH junction-sweeping compared to either sweeping or dynamic pH junction alone. This results in over a 1200-fold improvement in sensitivity relative to conventional injection methods, giving a limit of detection (LOD, defined as S/N = 3) of about 4.0 x 10(-12) M. Strategies for sensitive and more comprehensive analyses of other cell metabolites, including nucleotides, coenzymes, and steroids, are also discussed when using on-line focusing techniques in conjunction with multiplexed CE and UV detection.