Using Dissipative Particle Dynamics to Model Effects of Chemical Reactions Occurring within Hydrogels

Computational models that reveal the structural response of polymer gels to changing, dissolved reactive chemical species would provide useful information about dynamically evolving environments. However, it remains challenging to devise one computational approach that can capture all the interconnected chemical events and responsive structural changes involved in this multi-stage, multi-component process. Here, we augment the dissipative particle dynamics (DPD) method to simulate the reaction of a gel with diffusing, dissolved chemicals to form kinetically stable complexes, which in turn cause concentration-dependent deformation of the gel. Using this model, we also examine how the addition of new chemical stimuli and subsequent reactions cause the gel to exhibit additional concentration-dependent structural changes. Through these DPD simulations, we show that the gel forms multiple latent states (not just the “on/off”) that indicate changes in the chemical composition of the fluidic environment. Hence, the gel can actuate a range of motion within the system, not just movements corresponding to the equilibrated swollen or collapsed states. Moreover, the system can be used as a sensor, since the structure of the layer effectively indicates the presence of chemical stimuli.

High success perfect transmission of 1-qubit information using purposefully delayed sharing of non-maximally entangled 2-qubit resource and repeated generalized Bell-state measurements

We propose a new scheme in which perfect transmission of 1-qubit information is achieved with high success using purposefully delayed sharing of non-maximally entangled 2-qubit resource and repeated generalized Bell-state measurements (GBSM). Alice possesses initially all qubits and she makes repeated GBSM on the pair of qubits, consisting of (1) the qubit of information state and (2) one of the two entangled resource qubits (taken alternately) until transmission with perfect fidelity is indicated. Alice then sends to Bob, the qubit not used in the last GBSM and also the result of this GBSM and Bob applies a suitable unitary transformation to replicate exactly the information state. Continued probabilistic transmission with unit fidelity is achieved by changing continuously the generalized Bell basis and also the pair of measured qubits of the collapsed states. We calculate the success probability up to the third repeated attempt of GBSM and plot it with concurrence of the entangled resource state. We also discuss the maximal average fidelity.

The final phase of state collapse : the trap of playing chess

How do states destroy themselves and become "collapsed states" or "bankrupt states"? After having observed and analyzed the devolution of some countries towards collapse, we took note of at least two factors which are not well documented in literature but which are nevertheless decisive in the collapse of a state.

Colloidal Probes of PNIPAM-Grafted SiO2 in Studying the Microrheology of Thermally Sensitive Microgel Suspensions

The complex rheology and the phase behavior of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels have been investigated in both the swollen and collapsed states by using microrheology. To avoid the interactions between the tracer probes and the PNIPAM microgels, such as the adsorption or the depletion effect, the probes of silica (SiO2) particles have been grafted with PNIPAM chains (SiO2-PNIPAM) and characterized with Fourier transform infrared spectroscopy (FTIR). The successful preparation of SiO2-PNIPAM has also been proved by the investigation of the particle size and morphology with dynamic light scattering (DLS) and transmission electron microscope (TEM) below and beyond the phase transition temperature of PNIPAM. The microrheology of the PNIPAM microgel suspension has been investigated by using the prepared SiO2-PNIPAM particles as microrheological probes, and the results show that the diffusive coefficient of the probes in the swollen state is one-fifth of that in the collapsed state, and the viscosity of the PNIPAM microgel suspension in the swollen state is four times higher than that in the collapsed state, indicating SiO2-PNIPAM is a good probe in the microrheological study of PNIPAM microgel suspensions.

AFM images of open and collapsed states of yeast condensin suggest a scrunching model for DNA loop extrusion

SUMMARYStructural Maintenance of Chromosome (SMC) protein complexes are the key organizers of the spatiotemporal structure of chromosomes. The condensin SMC complex, which compacts DNA during mitosis, was recently shown to be a molecular motor that extrudes large loops of DNA. The mechanism of this unique motor, which takes large steps along DNA at low ATP consumption, remains elusive however. Here, we use Atomic Force Microscopy (AFM) to visualize the structure of yeast condensin and condensin-DNA complexes. Condensin is found to exhibit mainly open ‘O’ shapes and collapsed ‘B’ shapes, and it cycles dynamically between these two states over time. Condensin binds double-stranded DNA via a HEAT subunit and, surprisingly, also via the hinge domain. On extruded DNA loops, we observe a single condensin complex at the loop stem, where the neck size of the DNA loop correlates with the width of the condensin complex. Our results suggest that condensin extrudes DNA by a fast cyclic switching of its conformation between O and B shapes, consistent with a scrunching model.

Electrochemical characterization of the stimuli-response of surface-immobilized elastin-like polymers

The stimuli-responsive behavior of surface-immobilized ELPs, corresponding to proposed extended and collapsed states, was characterized using electrochemical impedance spectroscopy.