Quantitative investigation of spatiotemporal chaos in the ferroin-catalyzed Belousov-Zhabotinskii reaction in a batch reactor

We have analyzed experimental data on the time dependence of the potentials of 16 platinum point-contact electrodes for spatiotemporal chaos in the Belousov-Zhabotinskii reaction. We show that the largest Lyapunov exponent is a convenient characteristic for spatiotemporal chaos. We found that in going from temporal to spatiotemporal chaos, the embedding dimension of the system increases by a factor of three. We have observed that as the largest Lyapunov exponent increases, we observe a decrease in the degree of spatial correlation of the process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 1, pp. 34–39, January–February, 1995.We would like to thank the Foundation for Basic Research of the State Science and Technology Committee of Ukraine for financial support of this work (Project 3.3/87).     

Sustained self-organizing pH patterns in hydrogen peroxide driven aqueous redox systems

Many pattern developments in nature are believed to result from the interplay between self-activated (bio)chemical processes and the diffusive transport of constituents. Though the details are difficult to work out, the relevance of reaction-diffusion processes is widely accepted in many aspects of biological development. Due to their easier manipulation and control, aqueous phase chemical reactions are commonly preferred to probe the patterning capacity of reaction-diffusion processes. Nonetheless, sustained patterns of such a type were observed only in reactions involving oxyhalogen compounds. We report on halogen free solution chemistry systems which lead to stationary or oscillatory spatiotemporal pH patterns. They are based on the acid autocatalytic oxidation of sulfite ions by hydrogen peroxide in combination with two significantly different proton consuming feedback reactions. Besides the chemical novelty, yet experimentally and even theoretically undocumented pattern dynamics are uncovered. This success, based on a well-defined method, further paves the way to the discovery of stationary patterns in delicate biochemical reactions.     

Sign patterns for chemical reaction networks

Most differential equations found in chemical reaction networks (CRNs) have the form:

Moving waves and spatiotemporal patterns due to weak thermal effects in models of catalytic oxidation

We analyze the behavior of a microkinetic model of a catalytic reaction coupled with weak enthalpy effects to show that under fixed gas-phase concentrations it can produce moving waves with an intrinsic length scale, when the underlying kinetics is oscillatory. The kinetic model incorporates dissociative oxygen adsorption, reactant adsorption and desorption, and surface reaction. Three typical patterns may emerge in a one-dimensional system (a long wire or a ring): homogeneous oscillations, a family of moving waves propagating with constant velocities, and patterns with multiple source/sink points. Pattern selection depends on the ratio of the system length to the intrinsic wave length and the governing parameters. We complement these analysis with simulations that revealed a plethora of patterned states on one- and two-dimensional systems (a disk or a cylinder). This work shows that weak long-range coupling due to high feed rates maintains such patterns, while low feed rates or strong long-range interaction can gradually suppress the emerging patterns.     

Catalytic spatiotemporal thermal patterns during CO oxidation on cylindrical surfaces: experiments and simulations

Dynamics of spatiotemporal thermal patterns during the catalytic CO oxidation over Pd supported on a glass-fiber catalytic cloth rolled into a tube of 20 mm diameter and 80 mm length has been studied in a continuous flow reactor by IR thermography. A specially designed aluminum mirror built in the reactor provided image of the entire surface of the horizontally held catalytic tube. With flow in the main axial direction and through the tube surface, we observed periodic motions of a pulse, which was born downstream and propagated upstream. The temperature pulse motion was accompanied by conversion oscillations of CO2. With flow in the main axial direction, parallel to the surface, we observed a stationary hot zone after an oscillatory transient. These patterns can be simulated with a plug-flow-reactor-like heterogeneous reactor model that incorporates previously determined kinetic and transport parameters.     

Turing patterns in the chlorine dioxide-iodine-malonic acid reaction with square spatial periodic forcing

We use the photosensitive chlorine dioxide-iodine-malonic acid reaction-diffusion system to study wavenumber locking of Turing patterns to two-dimensional "square" spatial forcing, implemented as orthogonal sets of bright bands projected onto the reaction medium. Various resonant structures emerge in a broad range of forcing wavelengths and amplitudes, including square lattices and superlattices, one-dimensional stripe patterns and oblique rectangular patterns. Numerical simulations using a model that incorporates additive two-dimensional spatially periodic forcing reproduce well the experimental observations.     

Oscillatory and stationary convective patterns in a reaction driven gravity current

Horizontally propagating chemical fronts are studied in a thin solution layer of the acid-catalyzed chlorite-tetrathionate reaction. Unusual cellular patterns develop when significant amount of autocatalyst is bound to polyelectrolyte with low mobility: both oscillatory and stationary patterns evolve as a result of the interaction between the reaction front and the superposed gravity current. The concentration of the polyelectrolyte regulating the velocity of front propagation serves as a bifurcation parameter for switching between the two basic patterns.     

The glycan patterns at the individual glycosylation sites in orosomucoid from allergic reaction patients

Summary Little is known about the alterations that have occurred at the individual glycosylation sites in allergy patients or how these glycosylation patterns may change after anti-allergy treatments. Using reverse-phase HPLC, we have quantitated the glycoforms present at the individual glycosylation sites on orosomucoid isolated from the sera of allergic reaction patients and an allergic reaction patient treated with the antihistamine Terfenadine. The glycan structures isolated from the five glycosylation sites for the individual taking Terfenadine were all within normal ranges. It is suggested that if the changes in glycosylation in OMD in the allergic state are functionally driven, then it should be possible to correlate biological activities with quantitative changes at the individual glycosylation sites, and hence further define the role of OMD in allergy and inflammation.     

Quorum activation at a distance: spatiotemporal patterns of gene regulation from diffusion of an autoinducer signal

Quorum sensing (QS) bacteria regulate gene expression collectively by exchanging diffusible signal molecules known as autoinducers. Although QS is often studied in well-stirred laboratory cultures, QS bacteria colonize many physically and chemically heterogeneous environments where signal molecules are transported primarily by diffusion. This raises questions of the effective distance range of QS and the degree to which colony behavior can be synchronized over such distances. We have combined experiments and modeling to investigate the spatiotemporal patterns of gene expression that develop in response to a diffusing autoinducer signal. We embedded a QS strain in a narrow agar lane and introduced exogenous autoinducer at one terminus of the lane. We then measured the expression of a QS reporter as a function of space and time as the autoinducer diffused along the lane. The diffusing signal readily activates the reporter over distances of ~1 cm on time scales of ~10 h. However, the patterns of activation are qualitatively unlike the familiar spreading patterns of simple diffusion, as the kinetics of response are surprisingly insensitive to the distance the signal has traveled. We were able to reproduce these patterns with a mathematical model that combines simple diffusion of the signal with logistic growth of the bacteria and cooperative activation of the reporter. In a wild-type QS strain, we also observed the propagation of a unique spatiotemporal excitation. Our results show that a chemical signal transported only by diffusion can be remarkably effective in synchronizing gene expression over macroscopic distances.     

Locking of Turing patterns in the chlorine dioxide-iodine-malonic acid reaction with one-dimensional spatial periodic forcing

We use the photosensitive chlorine dioxide-iodine-malonic acid reaction-diffusion system to study wavenumber locking of Turing patterns with spatial periodic forcing. Wavenumber-locked stripe patterns are the typical resonant structures that labyrinthine patterns exhibit in response to one-dimensional forcing by illumination when images of stripes are projected on a working medium. Our experimental results reveal that segmented oblique, hexagonal and rectangular patterns can also be obtained. However, these two-dimensional resonant structures only develop in a relatively narrow range of forcing parameters, where the unforced stripe pattern is in close proximity to the domain of hexagonal patterns. Numerical simulations based on a model that incorporates the forcing by illumination using an additive term reproduce well the experimental observations. These findings confirm that additive one-dimensional forcing can generate a two-dimensional resonant response. However, such a response is considerably less robust than the effect of multiplicative forcing.     

Systematic analysis of enzyme-catalyzed reaction patterns and prediction of microbial biodegradation pathways

The roles of chemical compounds in biological systems are now systematically analyzed by high-throughput experimental technologies. To automate the processing and interpretation of large-scale data it is necessary to develop bioinformatics methods to extract information from the chemical structures of these small molecules by considering the interactions and reactions involving proteins and other biological macromolecules. Here we focus on metabolic compounds and present a knowledge-based approach for understanding reactivity and metabolic fate in enzyme-catalyzed reactions in a given organism or group. We first constructed the KEGG RPAIR database containing chemical structure alignments and structure transformation patterns, called RDM patterns, for 7091 reactant pairs (substrate-product pairs) in 5734 known enzyme-catalyzed reactions. A total of 2205 RDM patterns were then categorized based on the KEGG PATHWAY database. The majority of RDM patterns were uniquely or preferentially found in specific classes of pathways, although some RDM patterns, such as those involving phosphorylation, were ubiquitous. The xenobiotics biodegradation pathways contained the most distinct RDM patterns, and we developed a scheme for predicting bacterial biodegradation pathways given chemical structures of, for example, environmental compounds.     

Pressure-driven spatiotemporal control of the laminar flow interface in a microfluidic network

We describe a system for dynamically adjusting the position of the laminar interface between two fluids flowing inside a microfluidic channel, with a time response of less than 0.1 s, through feedback control of the channel inlet pressure.     

Fabrication of self-supported patterns of aligned beta-FeOOH nanowires by a low-temperature solution reaction

Self-supported patterns of oriented alignment of beta-FeOOH nanowires are fabricated through a simple solution reaction from the complex [Fe(phen)(3)](2+) at 60 degrees C. The alignment of nanowires with a diameter of 40 nm and length of 6 mum is relatively uniform. HRTEM studies show that the growing direction of beta-FeOOH nanowires is perpendicular to the orientation plane of self-formed beta-FeOOH flake-like substrates. In the reaction and crystal growth process, the precursor [Fe(phen)(3)](2+) is undoubtedly vital to the formation of nanowire alignment. In detail, the formation of aligned nanowires is thought to be realized by controlling two competing reactions. Electrochemical and UV-visible measurements suggest that the product might have potential applications in lithium batteries and semiconductor electronics. This synthetic process is simple, mild, clean, reproducible, and free of any template; it provides a novel pathway for the low-temperature growth of nanowires and their simultaneous oriented alignment.     

An algorithm for the deconvolution of mass spectroscopic patterns in isotope labeling studies. Evaluation for the hydrogen-deuterium exchange reaction in ketones

An easy to use computerized algorithm for the determination of the amount of each labeled species differing in the number of incorporated isotope labels based on mass spectroscopic data is described and evaluated. Employing this algorithm, the microwave-assisted synthesis of various alpha-labeled deuterium ketones via hydrogen-deuterium exchange with deuterium oxide was optimized with respect to time, temperature, and degree of labeling. For thermally stable ketones the exchange of alpha-protons was achieved at 180 degrees C within 40-200 min. Compared to reflux conditions, the microwave-assisted protocol led to a reduction of the required reaction time from 75-94 h to 40-200 min. The alpha-labeled deuterium ketones were reduced by biocatalytic hydrogen transfer to the corresponding enantiopure chiral alcohols and the deconvolution algorithm validated by regression analysis of a mixture of labeled and unlabeled ketones/alcohols.     

An interfacial oxime reaction to immobilize ligands and cells in patterns and gradients to photoactive surfaces

We report a molecularly controlled interfacial chemoselective methodology to immobilize ligands and cells in patterns and gradients to self-assembled monolayers on gold. This strategy is based on reacting soluble ketone or aldehyde tethered ligands to surface-bound oxyamine alkeanethiols to generate a covalent oxime linkage to the surface. We characterize the kinetic behavior of the reaction on the surface with ferrocenecarboxaldehyde (FcCHO) as a model ligand. The precise extent of immobilization and therefore surface density of FcCHO on the SAM is monitored and determined by cyclic voltammetry, which shows a peudo-first-order rate constant of 0.13 min(-1). In order to generate complex surface patterns and gradients of ligands on the surface, we photoprotected the oxyamine group with nitroveratryloxycarbonyl (NVOC). We show that ultraviolet light irradiation through a patterned microfiche film reveals the oxyamine group and we characterize the rate of deprotection by immobilization of ketone containing redox active groups. Finally, we extend this strategy to show biospecific cell attachment of fibroblast cells by immobilizing ketone-GRGDS peptides in patterns. The interfacial oxime reaction is chemoselective and stable at physiological conditions (pH 7.0, 37 degrees C) and may potentially be used to install ligands on the surface in the presence of attached cells to modulate the cell microenvironment to generate dynamic surfaces for monitoring changes in cell behavior in real time.     

载银缓释型抗菌敷料

近10年来,载银缓释型抗菌敷料因其优良特性,在医药、卫生等领域引起科学家们的广泛关注。本文综述了银的抗菌机理和载银缓释型抗菌敷料的缓释机制;重点介绍了目前在国际市场上销售的代表性载银缓释型抗菌敷料的性能,并从不同的载体材料角度(如生物高分子、合成高分子、生物和合成高分子共用、有机硅材料)总结了新型载银抗菌敷料的研究进展;最后,讨论了载银抗菌医用敷料在研究和应用中需要解决的问题。     

Microwave-assisted chemoselective reaction: a divergent synthesis of pyrazolopyridine derivatives with different substituted patterns

A series of new functionalized pyrazolopyridine derivatives with different substituted patterns were synthesized via microwave-assisted multi-component divergent reactions of aldehydes, 5-aminopyrazoles, and cycloketones by controlling the reaction condition. The procedures are facile, avoiding time-consuming and costly syntheses, tedious work-up, and purifications of precursors as well as protection/deprotection of functional groups. This chemistry provides an efficient and promising synthetic strategy to construction of the pyrazolopyridine skeleton.