13C NMR Substituent Parameters of Dithioacetal Groups in Benzene Derivatives. The σp+ Values of Cyclic Dithioacetals

The ¹³C NMR spectra of forty-six cyclic dithioacetals and their derivatives have been studied. A set of shift parameters was established for each of these heterocycles as substituent. Based on the Hammett type correlation for substituted benzenes, the σ_P ⁺values of cyclic dithioacetal groups have been determined.     

Oligonucleotide-stabilized Ag nanocluster fluorophores

Single-stranded oligonucleotides stabilize highly fluorescent Ag nanoclusters, with emission colors tunable via DNA sequence. We utilized DNA microarrays to optimize these scaffold sequences for creating nearly spectrally pure Ag nanocluster fluorophores that are highly photostable and exhibit great buffer stability. Five different nanocluster emitters have been created with tunable emission from the blue to the near-IR and excellent photophysical properties. Ensemble and single molecule fluorescence studies show that oligonucleotide encapsulated Ag nanoclusters exhibit significantly greater photostability and higher emission rates than commonly used cyanine dyes.     

Optical Resolution of 5‐Oxo‐1‐Phenyl‐Pyrazolidine‐3‐Carboxylic Acid as a New Organocatalyst for Organic Reactions

Optical resolution of racemic 5‐oxo‐1‐phenyl‐pyrazolidine‐3‐carboxylic acid 2 with L‐amino acid methyl ester via the diastereomers formation was investigated. Treatment of racemic 5‐oxo‐1‐phenyl‐pyrazolidine‐3‐carboxylic acid 2 with L‐valine methyl ester gave diastereomers with a total yield of 86%. The diastereomeric dipeptides can be easily separated by flash column chromatography. Acidic cleavage of the derived diastereomers gave both the optically pure (+)‐(R)‐ and (‐)‐(S)‐5‐oxo‐1‐phenyl‐pyrazolidine‐3‐carboxylic acid ((+)‐(R)‐ 2 and (‐)‐(S)‐ 2 ) with a total yield of 94% and 95%, respectively.     

Single-walled carbon nanotubes displaying multivalent ligands for capturing pathogens

A single-walled carbon nanotube was exploited for its semi-flexible pseudo-one-dimensional nanostructure as a unique scaffold to display multivalent carbohydrate ligands, with a specific demonstration showing that galactosylated carbon nanotubes were effective in the capturing of pathogenic Escherichia coli in solution.     

Synthesis and Antimycobacterial Evaluation on Arylsulfonyl and Arylcarbonyl Derivatives of Ofloxacin

Four ofloxacin derivatives 3, 5, 6 , and 11 were found to exhibit > 90% inhibition on the growth of M. tuberculosis at a concentration of 6.25 μg/mL. Compounds 3, 5 and 11 have also exhibited a broad spectrum of antibacterial activities while 8‐fluoro‐3‐methyl‐9‐[4‐(4‐nitrophenylsulfonyl)piperazin‐1‐yl)‐6‐oxo‐2,3‐dihydro‐6H‐1‐oxo‐3a‐azaphenalene‐5‐carboxylic acid ( 6 ), which exhibited potent activity against the growth of TB with the MIC of 2.23 μg/mL and a selectivity index (SI) of > 14.80, was inactive against the growth of G(+)‐ and G(‐)‐bacteria. Selective anti‐TB activity was achieved by the introduction of an arylsulfonyl group at C‐7 piperazin‐4‐yl of N‐demethyl ofloxacin. Compound 6 is species‐specific, exhibiting no significant activity against the growth of bacterial species other than M. tuberculosis, which implied the possibility of developing new specific anti‐TB drug candidates without inducing cross resistance with other currently used antibacterial drugs. Structural optimization of 6 is on‐going.     

Using a Fuzzy Piecewise Regression Analysis to Predict the Nonlinear Time-Series of Turbulent Flows with Automatic Change-Point Detection

Research has already shown that turbulent flow consists of some coherent time- and space-organized vortical structures. Some dynamic systems and experimental models are employed to understand the turbulent generation mechanism. However, these approaches still cannot provide a good nonlinear analysis of turbulent time-series. In the real turbulent flow, very complicated nonlinear behaviors, which are affected by many vague factors are present. Based on the nonlinear behavior and the results of from this traditional research, we introduce multivariate statistical analysis of an experimental study to explain practical phenomenon. In this paper, a new approach of fuzzy piecewise regression analysis with automatic change-point detection is proposed to predict the nonlinear time-series of turbulent flows. In order to show the practicality and usefulness of this model, we present an example of predicting the near-wall turbulence time-series as a verifiable model. The results of practical applications show that the proposed method is appropriate and appears to be useful in nonlinear analysis and in fuzzy environments to predict the turbulence time-series. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reversible Phase Transformation and Luminescence of Cadmium(II)–Dipyridylamide‐Based Coordination Frameworks

We have synthesized a series of 1D double‐zigzag ({[Cd(paps)₂(H₂O)₂](ClO₄)₂}_n ( 1 ), {[Cd(papo)₂(H₂O)₂](ClO₄)₂}_n ( 3 ), and {[Cd(papc)₂(H₂O)₂](ClO₄)₂}_n ( 5 )) and 2D polyrotaxane frameworks ([Cd(papc)₂(ClO₄)₂]_n ( 6 )) by the reaction of Cd(ClO₄)₂ with dipyridylamide ligands N,N′‐bis(pyridylcarbonyl)‐4,4′‐diaminodiphenyl thioether (paps), N,N′‐bis(pyridylcarbonyl)‐4,4′‐diaminodiphenyl ether (papo), and N,N′‐(methylenedi‐p‐phenylene)bispyridine‐4‐carboxamide (papc), respectively, where their molecular structures have been determined by X‐ray diffraction studies. Based on the powder X‐ray data (PXRD) of compound 3 and its Zn^II analogue, heating the double‐zigzag framework of compound 3 can give the polyrotaxane framework of [Cd(papo)₂(ClO₄)₂]_n ( 4 ) and grinding this powder sample in the presence of moisture resulted in its complete conversion back into the pure double‐zigzag framework. In addition, heating the double‐zigzag frameworks of compounds 1 and 5 can induce structural transformation into their respective polyrotaxanes, whereas grinding these solid samples in the presence of moisture did not lead to the formation of the double zigzags. Herein, we investigated the effect of the metal (from Zn^II to Cd^II) on the assembly process and luminescence properties, as well as on the particularly intriguing structural transformation of a series of papx‐based frameworks. In fact, the assembly behavior and luminescence properties of the Cd^II? papx and Zn^II? papx frameworks were really similar. However, both Zn^II? papx (x=s, o) frameworks can perform reversible structural transformation, but only the Cd^II? papo framework can do it. Therefore, a delicate metal effect on such a new structural transformation can be observed.     

Highly Sensitive Quantitative Analysis of 1-[3-(Furo[3,2-c]quinolin-4-ylamino)phenyl]ethanone Oxime, a New Antitumor Agent, in Rat Plasma by LC with Electrochemical Detection

1-[3-(Furo[3,2-c]quinolin-4-ylamino)phenyl]ethanone oxime (CCK2) is an antitumor agent which was especially active against the growth of the renal cancer cell UO-31 (GI₅₀ = 0.03 μm) and the two melanoma cancer cells UACC-257 (GI₅₀ < 0.01 μm) and UACC-62 (GI₅₀ < 0.01 μm) in cytotoxicity evaluation of NCI’s full panel of 60 human cancer cell lines. From structure–activity relationships for amsacrine and CCK2, CCK2 is, moreover, expected to have a longer half-life than amsacrine in plasma. A sensitive high-performance liquid chromatographic method with electrochemical detection has therefore been developed and validated for determination of the pharmacokinetics of CCK2 in rats. Plasma samples were spiked with 2-naphthol as internal standard and extracted with dichloromethane. The analytes were separated on a C₁₈ reversed-phase column (55 × 4 mm) with 20% acetonitrile, 5% tetrahydrofuran, and 75% pH 3.0 McIlvaine buffer as mobile phase at a flow rate of 1.0 mL min^?1. Electrochemical detection of CCK2 was performed at 1.0 V and 20 nA. Intra-day and inter-day precision and accuracy were acceptable down to the limit of quantification of 10 ng mL^?1. The lower limit of detection was 5 ng mL^?1. In an in vivo study pharmacokinetic data were determined for CCK2 in rat after intravenous administration of 6, 12, and 24 μmol kg^?1. The apparent volume of distribution, elimination half-life, and clearance were not significantly different among the three doses. The area under the plasma concentration–time curve increased in proportion to increasing dose. The elimination half-life of CCK2 was 3.4 times that of amsacrine. CCK2 might, therefore, have the potential to be tested clinically. The results also showed that this selective, sensitive, and reproducible LC method could be successfully applied to investigation of the pharmacokinetics of CCK2.