Polar Azo Dyes Research Articles

Goethite Hinders Azo Dye Bioreduction by Blocking Terminal Reductive Sites on the Outer Membrane of Shewanella decolorationis S12.

Iron (hydr)oxides are the most ubiquitous Fe(III)-containing minerals in the near-surface environments and can regulate organic pollutant biotransformation by participating in bacterial extracellular electron transfer under anaerobic conditions. Mechanisms described so far are based on their redox properties in bacterial extracellular respiration. Here, we find that goethite, a typical iron (hydr)oxide, inhibits the bioreduction of different polar azo dyes by Shewanella decolorationis S12 not through electron competition, but by the contact of its surface Fe(III) with the bacterial outer surface. Through the combined results of attenuated total reflectance (ATR) Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, and confocal laser scanning microscope, we found that the outer membrane proteins MtrC and OmcA of strain S12 are key binding sites for goethite surface. Meanwhile, they were identified as the important reductive terminals for azo dyes. These results suggest that goethite may block the terminal reductive sites of azo dyes on the bacterial outer membrane to inhibit their bioreduction. This discovered role of goethite in bioreduction provides new insight into the microbial transformation processes of organic pollutants in iron (hydr)oxide-containing environments.

Induction of the vector polyphotochromism in side-chain azopolymers

The phenomenon of vector photochromism was observed in some high-efficient polarization-sensitive materials depending on the radiant exposure of the inducing linearly polarized actinic light. When radiant exposure exceed certain value specific to each material, a sharp change in the transmission spectrum of the probing linearly polarized nonactinic beam is observed after analyzer. While probing with unpolarized light the transmission spectrum is practically unchanged and does not depend on the magnitude of the radiant exposure. The mechanism of this phenomenon is discussed. The effect is an interference nature and depends on the path difference between the ordinary and extraordinary rays in material with photo-induced anisotropy. It is shown that the kinetics of this effect depends on the photosensitive layer thickness and the concentration of the chromophore.The beams with a wavelength away from the absorption band of the material were used as a probing. It is shown that in this case birefringence has made the main contribution in photoanisotropy. The experiments were carried out for polarization-sensitive materials with varying degrees of components integration, in particular, two synthesized side-chain azopolymers obtained by immobilization of polar azo dyes on polymethylmethacrylate backbone. It is shown that the maximum value of the birefringence Δn=0.162 achieved in azopolymers with covalently bonded components. In this case a third order of interference of the probing beam is observed.

Transcriptional analysis of Escherichia coli during Acid Red 18 decolorization

To comprehensively understand the bio-decolorization process of azo dyes at the molecular level, the transcriptional response of Escherichia coli K-12 to a highly polar azo dye, Acid Red 18 (AR 18), was investigated in this study using whole-genome DNA microarrays. The results showed that genes involved in the reductive decolorization of AR 18 displayed significant upregulation; they were followed by stress response genes. This result indicated that the former genes play more important roles in increasing the AR 18 resistance of E. coli. Moreover, mutants deficient in the functions of yqhD, fdhF, nrfABCD, frdBCD and dmsABC showed lower abilities of decolorizing AR 18 compared with wild type strain, indicating that these genes play important roles in AR 18 decolorization. The above findings reveal that a network of genes is involved in AR 18 decolorization.

Synthesis, Characterization and Some Optical Properties of Poly(hexa-2,4-diynylene-1,6-dioxy)dinaphthoates Containing Polar Azo Dye

In order to study the effect of main-chain conformation on the second-order non-linear optical properties, two novel isomeric polymers, consisting of hexa-2,4-diynylene-1,6-dioxydinaphthoates main-chains containing a polar azo dye, Disperse Red 19, were synthesized and characterized. The 1,2- and 3,2-polymers had a T g of 134 and 143°C, respectively. Their spin-coated films were exposed to corona poling, and the orientation behavior was studied. The order parameters of the two polymers were similar, around 0.2. The 3,2-polymer underwent cross-linking during poling. Neither polymer did cross-link when irradiated by UV light during poling, indicating that their chemical structures are not apt to cross-link.

Effects of main chains on the second order nonlinear optical susceptibility of poled poly(dipropargyloxybenzoates) containing 2-[4-(2-chloro-4-nitrophenylazo)- N-ethyl-phenylamino]ethanol ( Disperse Red 13)

A series of isomeric polymers containing hexa-2,4-diynylene-1,6-dioxybenzoate group as the main chain and a polar azo dye ( Disperse Red 13) as in the side chain were synthesized, and their second order nonlinear optical responses were studied. The second order nonlinear coefficients, d 33 were found to be in the range of 50–90 pm/V. The nonlinear response ( d 33) with respect to the positions of main chain was found to be in the order; 3,5-( meta) > 3,4-( ortho) > 2,5- ( para) > 2,4-( meta), but the order of values d 33/ d 31 was 3,5-( meta) > 2,4-( meta) > 2,5- ( para) > 3,4 ( ortho). The higher response of the 3,5-polymer may be attributed to the symmetric substitution on the benzene ring, permitting the main chain conformation with less flexibility, as well as a higher Tg.

Synthesis and characterization of poly(dipropargyloxynaphtoates) containing polar Azo dyes

In order to study the relationships between the chemical structures of polymer main chains and second order nonlinear optical properties, novel polymers with hexa-2,4-diynylene-1,6-dioxynaphthoate as a main chain and common azo dyes (Disperse Red 1 and 13) in the side chains, were synthesized and characterized. The polymers were soluble in common organic solvents such as chloroform, dimethylformamide, N-methylpyrrolidone, etc, and gave films with excellent optical quality by spin coating. Apparent orientation parameters of around 0.25 were observed by the absorption decrease by Corona poling. The steric effect of chlorine atom of the dye on poling was not observed. On heating at 100 °C after poling the order parameters did not return to zero but reached a constant. It is thought that some of the chromophores remain orientated permanently.

Diacetylene-Containing Polymers XIV: Poly(octa-3,5-diynylene-1,8-dicarboxyalates) containing some polar azo dyes

A series of novel polymers having polar azo dyes were synthesized and characterized. Although their chromophore contents are very high, their second order nonlinear (2-NLO) response was very poor. The poor 2-NLO responses are thought to be due to poor orientation because of their improper main chain conformations, as well as their low glass transition temperatures. They undergo slow cross-linking on standing at room temperature, and rapidly on heating at temperalures above 150°C, through the diacetylene units of the main chains. Nevertheless, these polymers are interesting materials as azo-polymers because of their very high concentration of azo dyes, which are distributed homogeneously in the polymers. Synthesis and characterization are described, and the most important factor for the 2-NLO polymers is discussed.

A novel flow-through disk-based solid-phase extraction diffuse reflectance optrode. Application to preconcentration and determination of trace levels of nitrite

A novel, versatile and sensitive flow-through optical fiber diffuse reflectance sensor to implement disk-based solid-phase extraction in a flow injection analysis (FIA) system is presented. Nitrite optosensing at trace levels is chosen as a model of chemistry to demonstrate its applicability. The methodology is based on on-line nitrite derivatization with Shinn reagent to form a moderately polar azo dye, whose preconcentration on to octadecyl covalently bonded silica gel particles tightly bound to an inert matrix (C18 disk) is continuously monitored using a plug-in diode-array spectrophotometer. After the analytical signal has been recorded, fast sensor regeneration is achieved with a methanolic eluent, rendering the system ready for the next extraction. Selection of the solid disk support and the suitable flow-through cell configuration to reduce back-pressure effects are discussed in detail. By matching the illumination and retention zones, concentrations of nitrite as low as 1 ng ml−1 are easily determined using 2.5 ml of sample. A detection limit (3σblank) of 0.1 ng ml−1 of nitrite, repeatability and reproducibility better than 3.2%, an analytical throughput of 11 h−1 and an enrichment factor of 140 are the figures of merit of the proposed optrode. The utility of the flow-through optosensing system, wherein minimization of additive matrix interferences is feasible, was testified by the satisfactory results obtained in its application to tap, ground, harbor and aquarium water samples.

Light-induced orientation in a high glass transition temperature polyimide with polar azo dyes in the side chain

We report on both polar and nonpolar light-induced orientation of a polyimide of high glass transition temperature (Tg ≈ 210 °C) with nonlinear optical azo dye molecules in the side chain. This photoinduced orientation is shown to occur at room temperature, i.e., at least 190 °C below the Tg value of the polymer, which indicates that the photoisomerization-induced movement of the nonlinear optical chromophores induces, in turn, a movement of the polyimide main chain. This allows for an efficient orientation of the dye molecules in spite of the stiffness of the polyimide main chain. A nonpolar orientation is induced by polarized light irradiation alone, whereas polar orientation is achieved by application of a dc field during the photoisomerization process. Further light irradiation in the absence of a dc field destroys the previously induced stable polar order. A detailed theoretical study of this light-induced depoling process is also presented.

Creation of second-order nonlinear optical effects by photoisomerization of polar azo dyes in polymeric films: theoretical study of steady-state and transient properties

It was shown recently that the application of a dc field across a polymer film containing polar azo dye chromophores at a temperature far below that of its glass transition leads to an appreciable polar order when the azo dyes undergo cis ⇔ trans isomerization. We present a detailed theoretical study of this phenomenon based on the enhanced mobility of the azo chromophores during the isomerization process. The equations representing this phenomenological theory are solved by recurrence relations of Legendre polynomials, and both the steady state and the dynamics are investigated. Analytical expressions are derived for the photoinduced polar order and its related anisotropy for both cis and trans molecular distributions.

Room-Temperature Photoinduced Poling and Thermal Poling of a Rigid Main-Chain Polymer with Polar Azo Dyes in the Side Chain

Room-Temperature Photoinduced Poling and Thermal Poling of a Rigid Main-Chain Polymer with Polar Azo Dyes in the Side Chain