Marcin Leda

Coupled oscillations in a 1D emulsion of Belousov–Zhabotinsky droplets

We experimentally and computationally study the dynamics of interacting oscillating Belousov–Zhabotinsky (BZ) droplets of ∼120 µm diameter separated by perfluorinated oil and arranged in a one-dimensional array (1D). The coupling between BZ droplets is dominated by inhibition and is strongest at low concentrations of malonic acid (MA) and small droplet separations. A microfluidic chip is used for mixing the BZ reactants, forming monodisperse droplets by flow-focusing and directing them into a hydrophobized 100 µm diameter capillary. For samples composed of many drops and in the absence of well defined initial conditions, the anti-phase attractor, in which adjacent droplets oscillate 180° out-of-phase, is observed for strong coupling. When the coupling strength is reduced the initial transients in the phase difference between neighboring droplets persist until the BZ reactants are exhausted. In order to make quantitative comparison with theory, we use photosensitive Ru(bipy)32+-catalyzed BZ droplets and set both boundary and initial conditions of arrays of small numbers of oscillating BZ droplets with a programmable illumination source. In these small collections of droplets, transient patterns decay rapidly and we observe several more complex attractors, including ones in which some adjacent droplets are in-phase. Excellent agreement between experiment and numerical simulations is achieved.

Experimental and Model Investigation of the Oscillatory Transenantiomerization of L-α-Phenylalanine

Abstract In an earlier study, we obtained experimental evidence of the oscillatory transenantiomerization of selected profen drugs (e.g., S-(+)-ibuprofen, S-(+)-naproxen, and S-(+) and R-(−)-flurbiprofen) dissolved in aqueous, aqueous-organic, and purely organic liquid media. This process was apparently catalyzed by basic or amphiprotic environments and involved keto-enol tautomerism, and the self-organization of molecules in the solution via association of the carboxylic functional group of profens through hydrogen bonding to form mixed H-bonded associates with the remaining constituents of the solution. A model of the oscillatory transenantiomerization of profens was also developed by adapting an earlier oscillatory model, the Templator. Our new model comprises two linked Templators. The essence of the Templator model adapted to the oscillatory transenantiomerization of profens is the assumption that the H-bonded profen homodimer acts as a template, able to generate new dimers having the same steric configuration as their respective monomeric units. As profens belong to the class of 2-arylpropionic acids (2-APAs), we concluded that the phenomenon of oscillatory transenantiomerization may occur in other 2-APAs as well, among them those amino acids whose molecular structure can formally be derived from propionic acid. Thus, in this study, we focus our attention on L-α-phenylalanine (LPA; one of the nine amino acids essential for humans). Using thin layer chromatography (TLC) and polarimetry, we demonstrate the ability of LPA to undergo oscillatory transenantiomerization analogous to that observed with profens. The self-organization of molecules in a 70% ethanol solution of LPA is confirmed with photographs taken in UV light (λ = 254 nm). Finally, we propose a skeleton molecular mechanism for the transenantiomerization of LPA and simulate the oscillatory interconversion of its L and D forms with two linked Templators.

High-Frequency Oscillations in the Belousov-Zhabotinsky Reaction

Chemical oscillations in the classic Belousov-Zhabotinsky (BZ) system typically have a period of a few minutes, which can be increased significantly by changing the organic substrate. Here we show that by changing the temperature and concentrations, an increase of 3-4 orders of magnitude in the frequency of BZ oscillations can be obtained. At elevated temperatures, in high concentration mixtures, the cerium-catalyzed reaction exhibits sinusoidal oscillations with frequencies of 10 Hz or greater. We report the effect of temperature on the frequency and shape of oscillations in experiments under batch conditions and in a four-variable model. We show that our simple model accurately captures the complex temporal behavior of the system and suggests paths toward even higher frequencies.

Condensation oscillations in the peptidization of phenylglycine

In earlier studies, we showed that certain low-molecular-weight carboxylic acids (profens, amino acids, hydroxy acids) can undergo spontaneous in vitro chiral conversion accompanied by condensation to from oligomers, and we proposed two simple models to describe these processes. Here, we present the results of investigations using non-chiral high-performance liquid chromatography with diode array detector (HPLC-DAD) and mass spectrometry (MS) on the dynamics of peptidization of S-, R-, and rac-phenylglycine dissolved in 70% aqueous ethanol and stored for times up to one year. The experimental results demonstrate that peptidization of phenylglycine can occur in an oscillatory fashion. We also describe, and carry out simulations with, three models that capture key aspects of the oscillatory condensation and chiral conversion processes.

Small-Amplitude and Mixed-Mode pH Oscillations in the Bromate#Sulfite#Ferrocyanide#Aluminum(III) System

The BrO(3)(-)-SO(3)(2-)-Fe(CN)(6)(4-) (BSF) pH-oscillatory system is coupled to the Al(OH)(3) precipitation equilibrium (BSFA system) and studied in a stirred flow reactor. The dynamic behavior of the BSFA system differs significantly from that of the BSF system. In addition to the large-amplitude pH oscillations found in the BSF system, new small-amplitude and mixed-mode oscillations occur. A detailed mechanism of the BSFA system is developed and investigated.

In vitro Chiral Conversion, Phase Separation, and Wave Propagation in Aged Profen Solutions

Abstract We have shown, earlier, that profens, i.e., 2-arylpropionic acids can undergo oscillatory in vitro chiral conversion, exhibiting oscillatory changes in the chromatographic retention parameter (R F) and the specific rotation ([α]D) for periods of up to two weeks after preparation of the solutions in aqueous ethanol. Here, we examine the oscillatory chiral conversion of S-(+)-ibuprofen and S,R-(±)-ketoprofen dissolved in 70% aqueous ethanol and stored in tightly closed colorless glass vials for one year. During that time, each initially homogenous, transparent profen solution separates into two immiscible layers, one clear and the other turbid. Employing chiral thin layer chromatography, high performance liquid chromatography with diode-array detection, gas chromatography, and Raman spectroscopy, we find that both samples undergo chiral conversion to yield a strong predominance of the R-(−) antimer. Additionally, microscopy reveals characteristic spatial patterns in both layers of the demixed ibuprofen and ketoprofen solutions. We use a model proposed earlier for the homogeneous oscillatory interconversion of the S and R profens involving two linked templators to simulate microscopic spatial patterns analogous to those observed in the solutions investigated here.