Understanding Complexity in Biophysical Chemistry

Measurement of a Bubble-Free Chemical Oscillator Using QCMs Treated with Self-Assembled Monolayers

The oscillation of a 1,4-cyclohexanedione-bromate (CHD-bromate) system was investigated by using a quartz crystal microbalance (QCM) without or with a self-assembled monolayer (SAM), where gold and platinum were used for QCM electrodes and SAMs were composed of HS(CH2)11CH3, HS(CH2CH2O)5H, and HS(CH2CH2O)5CH3. The CHD-bromate system is well-known as a bubble-free oscillator and oscillates without or with a catalyst. In the CHD-bromate system without a catalyst, the oscillation of a resonant frequency shift (ΔF) of the QCM was observed in the Au-electrode QCMs without a SAM or with SAMs formed from HS(CH2)11CH3 and HS(CH2CH2O)5H. On the other hand, the HS(CH2CH2O)5CH3 SAM suppressed the ΔF oscillation. The results revealed that in the CHD-bromate system without a catalyst, hydrophobic CH3 terminal and helical conformation were important to prevent nonspecific adsorption of substances on a gold surface and its dissolution. In the CHD-bromate system with a catalyst (ferroin), the ΔF oscillation was observed in the Au-electrode QCM with the HS(CH2CH2O)5CH3 SAM. The results suggest evidence that the change of the solution viscosity and density led to the ΔF oscillation. These results for Au-electrode QCMs were also corroborated by those for Pt-electrode QCMs.

Reaction fronts of the autocatalytic hydrogenase reaction

We have built a model to describe the hydrogenase catalyzed, autocatalytic, reversible hydrogen oxidation reaction where one of the enzyme forms is the autocatalyst. The model not only reproduces the experimentally observed front properties, but also explains the found hydrogen ion dependence. Furthermore, by linear stability analysis, two different front types are found in good agreement with the experiments.

Nested arithmetic progressions of oscillatory phases in Olsen's enzyme reaction model

We report some regular organizations of stability phases discovered among self-sustained oscillations of a biochemical oscillator. The signature of such organizations is a nested arithmetic progression in the number of spikes of consecutive windows of periodic oscillations. In one of them, there is a main progression of windows whose consecutive number of spikes differs by one unit. Such windows are separated by a secondary progression of smaller windows whose number of spikes differs by two units. Another more complex progression involves a fan-like nested alternation of stability phases whose number of spikes seems to grow indefinitely and to accumulate methodically in cycles. Arithmetic progressions exist abundantly in several control parameter planes and can be observed by tuning just one among several possible rate constants governing the enzyme reaction.

Unpinning of scroll waves under the influence of a thermal gradient

Three-dimensional scroll waves of electrical activity are among the mechanisms believed to be responsible for the rapid, unsynchronized contraction of cardiac ventricles, thereby reducing the heart's ability to pump blood. Scroll waves can attach themselves to unexcitable obstacles, and this sometimes highly elongates their life span. Hence, the unpinning and annihilation of these vortices has attracted much attention in recent decades. In this work, we study the influence of a thermal gradient on scroll waves pinned to inert obstacles, in the Belousov-Zhabotinsky reaction. Under a temperature gradient, scroll rings were seen to unpin from these obstacles, thus strikingly reducing their lifetimes. These results were also reproduced by numerical simulations using the Barkley model.