Synthesis of water‐soluble perylenediimide‐functionalized polymer through esterification with poly(vinyl alcohol)

A new material has been prepared by covalent attachment of a perylene derivative, N‐(carboxyphenyl)‐N′‐(8‐pentadecyl)perylene‐3,4:9,10‐bis(dicarboximide) (PDI‐COOH), to poly(vinyl alcohol) (PVA) by esterification. The perylenediimide (PDI)‐modified PVA polymers are soluble in water and dimethylsulfoxide (DMSO). This solubility is conferred to the insoluble perylene derivative by the water‐soluble polymer. The materials have been characterized by hydrogen‐nuclear magnetic resonance, Fourier transform infrared spectra, X‐ray diffraction, and X‐ray photoelectron spectroscopy confirming the covalent attachment of the PDI to the polymer chains. The significant changes in the crystalline parameters and the thermal stability observed for the polymer after the esterification also confirm the covalent linkage with PDI. In addition, the PDI‐modified PVA shows good fluorescence both in solution (quantum yield ～0.2–0.25) and in solid suggesting that the PDI retains largely its photochemical and photophysical properties after immobilization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3613–3622, 2010     

An oxime-carbapalladacycle complex covalently anchored to silica as an active and reusable heterogeneous catalyst for Suzuki cross-coupling in water

A preformed oxime-carbapalladacycle complex covalently anchored onto mercaptopropyl modified silica is highly active (> 99%) for the Suzuki reaction of p-chloroacetophenone and phenylboronic acid in water; no leaching occurs and the same catalyst sample was reused eight times without decreased activity.     

Design, construction and testing of a system for detection of toxic gases based on piezoelectric crystals

A system for static operation of toxic gas sensors based on piezoelectric crystals was constructed as a preliminary step in the development of this type of sensor. The sensing part of the setup consists of a twin oscillating circuit assembled from commercially available electronic parts mounted on a motherboard. The oscillating circuits can accommodate two piezoelectric crystals, of which one or both can be coated with different materials, or a single one, as required. The sensing assembly (crystals plus oscillating circuits) is placed in a customized test chamber that allows one to control and reproduce its internal environment. Once assembled and fine-tuned, the proposed setup was used to test a commercially available piezoelectric crystal for sensing formaldehyde in order to expand available information on this type of sensor.     

Dielectric behavior of polyaniline synthesized by different techniques

Polyaniline doped with dodecylbenzenesulfonic acid (Pani.DBSA) was synthesized by different procedures: by a dedoping-redoping process, by one step inverted emulsion polymerization and by one step aqueous dispersion polymerization. The effect of these different techniques on the electric properties (dielectric constant, dielectric losses, and complex electric modulus) of the corresponding emeraldine base has been studied by thermal dielectric analyzer (DETA) in the temperature range −130 °C to 200 °C and in frequency range 0.03-10⁵ Hz. It was found that the preparation technique has significant influence on the dielectric properties of Pani. The different synthetic routes give rise to polyaniline with different distribution of electric relaxation process, indicating different chain structure. Emeraldine base from Pani.DBSA prepared by one step aqueous dispersion polymerization exhibits one single relaxation peak with narrow distribution whereas that prepared by inverted emulsion polymerization exhibits two relaxation peaks, indicating two-phase structure as indicated by a bimodal distribution of relaxation process. Emeraldine base from Pani.DBSA prepared by dedoping-redoping process presents an intermediary behavior. Percentage crystallinity of Pani.DBSA samples has also been investigated using wide-angle X-ray diffraction analysis. Pani.DBSA prepared by aqueous dispersion exhibited higher crystallinity degree, which agrees with the higher conductivity.     

Kinetic parameters relevant to repetitive determinations via transient signals in flow-through systems : Part I. Direct Sample Injection into the Detection Chamber with application to the determination of some phenothiazines by a transient redox effect

The effect of rate proportionality constants on three fundamental parameters, which limit sensitivity as well as determination rate in sample injection (for repetitive determinations) into unsegmented (single-phase) flow-through systems, is discussed. Under first order or pseudo-first order conditions, the individual values and ratios of the rate constants for the two consecutive processes leading to the transient signal control the three parameters; namely : (1) the ratio of peak height to theoretical steady-state signal, (2) the time to reach the maximum (or minimum) signal value, and (3) the time to return to baseline. A simple way of extracting the values of the rate constants from the signal profiles when the two processes cannot be isolated is presented. Application to the determination of some phenothiazines based on the transient redox effect observed in their oxidation with cerium(IV) is also illustrated. The discussion and application are limited to the case of direct sample injection into the detection chamber.     

Stereoselective addition of the titanium enolate of N-acetyl (4S)-isopropyl-1,3-thiazolidine-2-thione to five-membered N-acyl iminium ions

[reaction: see text] Addition of the chlorotitanium enolate of N-acetyl 4-isopropyl-1,3-thiazolidine-2-thione to five-membered, N-substituted N-acyl iminium ions furnished the corresponding Mannich-type addition products with good diastereoselectivity and in good yields. The synthetic utility of the addition product 8 was demonstrated in a chemospecific anti-aldol reaction with cinnamaldehyde. By using this strategy, we constructed three contiguous chiral centers with high stereocontrol employing the same chiral auxiliary. X-Ray crystallographic analysis of addition product 2 and aldol product 14 revealed their absolute stereochemistry.     

Spectrophotometric cell comprising parallel rotating and stationary bioreactors: Application to the determination of glucose in serum samples

A spectrophotometric cell comprising parallel bioreactors facing each other and containing immobilized enzyme preparations is described. The lower reactor rotates to minimize diffusional constraints, and the upper reactor is fixed to provide an integrated design for the realization of coupled enzyme-catalyzed reactions. The operating characteristics of the cell are illustrated with the determination of glucose using glucose oxidase [EC 1.1.3.4] and horseradish peroxidase [EC 1.11.1.7] as immobilized enzymes (horseradish peroxidase on the rotating reactor and glucose oxidase on the stationary one). The H₂O₂ produced in the dissolved-oxygen oxidation of β- -glucose enters into oxidative coupling in a reaction with N,N-dimethylaniline and 4-aminophenazone which is catalyzed by horseradish peroxidase; the absorbance of the colored complex formed provides the basis for monitoring. The cell was incorporated into a continuous-flow/stopped-flow/continuous-flow operation, and the determination was based on the rate of response under stopped-flow conditions. The overall approach was applied to the determination of glucose in standards of human serum and samples of bovine blood serum.     

Study of Frozen Waves’ theory through a continuous superposition of Bessel beams

This paper presents a study of a recent solution to Maxwell's equation, the so-called “Frozen Waves”, whose main characteristics are to remain static in space, and to keep an arbitrary longitudinal field pattern previously chosen. These waves could be obtained by an adequate, but discrete, superposition of monochromatic Bessel beams. Contrary to that, we have here proposed a new way to get these waves through a continuous superposition of Bessel beams, and discussed some physical aspects and then exemplified for both loss and lossless media.     

Sub‐ppm determination of Hg and Cr in water: Cr speciation

A sensitive and alternative analytical procedure for the determination of chromium and mercury content in natural waters by coprecipitation with APDC and determination using an absolute thin layer EDXRF method is described. The use of ¹⁰⁹Cd and ²³⁸Pu annular radioisotope sources, the influence of the chromium oxidation states and the elemental concentration were studied. At pH 4, 100% recovery was found for mercury. The coprecipitation of Cr(VI) was not quantitative (75%) but constant for the selected concentration range (5–100 µg/l). On the other hand, Cr(III) did not precipitate at the same pH. The relative standard deviations (RSD) were lower than 9.0% for mercury (10 µg/l) and 5.0% for chromium (50 µg/l). The detection limits (DLs) for mercury and chromium were 0.4 and 0.6 µg/l when the ²³⁸Pu source was employed. Nevertheless, higher DL values were achieved using ¹⁰⁹Cd (0.6 and 3.3 µg/l). The proposed method was applied to the analysis of surface water samples. An alternative and simple chromium speciation procedure without chemical separation of Cr species is recommended. Copyright © 2007 John Wiley & Sons, Ltd.     

In phase and antiphase synchronization of coupled homoclinic chaotic oscillators

We numerically investigate the dynamics of a closed chain of unidirectionally coupled oscillators in a regime of homoclinic chaos. The emerging synchronization regimes show analogies with the experimental behavior of a single chaotic laser subjected to a delayed feedback.