Calorimetric and spectrophotometric investigation of PLGA nanoparticles and their complex with DNA

The calorimetric investigation of non-coated and chitosan-coated PLGA nanoparticles (NP) shows that at initial temperatures of heating particle swelling takes place what results in an internal architectural change at lower than physiological temperature. It has shown that the temperature of NP tightness perturbing depends on solvent polarity: as more polar is the solvent more stable are particles. The break of existing bonds in NP shell is accompanied with heat absorption peak which undergoes significant changes depending on heating rate. In the wide pH 2–8 interval in transition temperature no changes occurred. The obtained results show that such NP could be used in acidic area for drug transfer, which gives possibility to take medicine orally. It was shown that DNA attaches only to chitosan-coated NP. The optimal ratio for DNA loading onto the NP was found to be 7:1 (W_NP/W_DNA).     

Effect of Organoclay Mixture on the Rheological Properties of ABS-Clay Nanocomposites

Summary: In this work, poly(acrylonitrile-butadiene-styrene) (ABS) and different organically modified montmorillonite clay nanocomposites were prepared by melt intercalation in a co-rotating twin screw extruder. The influence of the screw torque during processing and of the mixture of the modified organoclays in the intercalation/exfoliation of the clay in the polymeric matrix was evaluated through low angle X-ray diffraction range and capillary and parallel plate-plate rheometry.     

Infinite horizon optimal control problems with multiple thermostatic hybrid dynamics

We study an optimal control problem for a hybrid system exhibiting several internal switching variables whose discrete evolutions are governed by some delayed thermostatic laws. By the dynamic programming technique we prove that the value function is the unique viscosity solution of a system of several Hamilton-Jacobi equations, suitably coupled. The method involves a contraction principle and some suitably adapted results for exit-time problems with discontinuous exit cost.     

Chiral diamines for asymmetric synthesis: an efficient RCM construction of the ligand core of (−)- and (+)-sparteine

An efficient RCM-based approach was applied to the total asymmetric synthesis of a tricyclic diamine and, formally, of its enantiomer, widely known as efficient and versatile chiral ligands of the sparteine-like type.     

New Tetracyclic Colchicinoids from the Reaction of N‐Deacetylthiocolchicine and N‐Deacetylcolchicine with Nitrous Acid and tert‐Butyl Nitrite

Reaction of N‐deacetylthiocolchicine ( 3 ) and N‐deacetylcolchicine ( 4 ) with nitrous acid (HONO) furnished the new tetracyclic colchicinoids 5 and 6 , as well as the Demyanov‐rearrangement products 7 and 8 . Starting from 3 , the pyrazole‐containing tetracycle 9 was obtained. The novel compounds were characterized spectroscopically, and an X‐ray crystal‐structure analysis of 5 allowed us to establish the absolute configurations at the stereogenic centers.     

LIN: A new algorithm to simulate the dynamics of biomolecules by combining implicit-integration and normal mode techniques

A central goal in molecular dynamics simulations is increasing the integration time-step to allow the capturing of biomolecular motion on biochemically interesting time frames. We previously made a step in that direction by developing the Langevin/implicit–Euler scheme. Here, we present a modified Langevin/implicit–Euler formulation for molecular dynamics. The new method still maintains the major advantage of the original scheme, namely, stability over a wide range of time-steps. However, it substantially reduces the damping effect of the high-frequency modes inherent in the original implicit scheme. The new formulation involves separation of the solution into two components, one of which is solved exactly using normal-mode techniques, the other of which is solved by implicit numerical integration. In this way, the high-frequency and fast-varying components are well resolved in the analytic solution component, while the remaining components of the motion are obtained by a large time-step integration phase. Full details of the new scheme are presented, accompanied by illustrative examples for a simple pendulum system. An application to liquid butane demonstrates stability of the simulations at time-steps up to 50 fs, still with activation of the high-frequency modes. © John Wiley & Sons, Inc.     

Electrochemically patterning sol-gel structures on conducting and insulating surfaces

A new approach for the local deposition of sol-gel films on conducting and insulating surfaces using scanning electrochemical microscopy (SECM) via the feedback and direct modes is presented. Patterning is based on enhancing sol-gel condensation by altering the local pH due to water electrolysis as a result of applying negative potentials.     

Deposition of Au and Ag nanoparticles on PEDOT

The deposition of Au and Ag, locally and from bulk solution, on poly(3,4-ethylenedioxythiophene) (PEDOT) was studied. Specifically, PEDOT was electrochemically polymerized onto a glassy carbon (GC) electrode and used for bulk deposition of Au and Ag from their respective ions dissolved in the solution as well as for the local deposition of these metals using scanning electrochemical microscopy (SECM). These two sets of experiments were utilized to investigate the difference between Au and Ag electrochemical deposition on PEDOT. In particular, SECM experiments, which were conducted by the controlled anodic dissolution of Au and Ag microelectrodes close to GC/PEDOT, probed the effect of different PEDOT oxidation states on local deposition. The current-time transients recorded during the deposition, combined with scanning electron microscopy and EDX analysis provided insight into the reduction processes. AuCl(4)(-) and Ag(+) ions were electrochemically reduced at a potential equal to and more negative than the ions redox potentials (0.4 and 0.2 V, respectively) and more positive than -0.7 V, where the PEDOT starts transforming into the reduced, i.e. insulating, state. We found that the electroreduction of Ag(+) ions was diffusion-controlled and the PEDOT film served as a simple conductor. On the other hand, the reduction of AuCl(4)(-) ions was enhanced on GC/PEDOT as compared with bare GC, indicating that PEDOT catalyzes the reduction of AuCl(4)(-) to Au.     

Coherent control of molecular torsion

We propose a coherent, strong-field approach to control the torsional modes of biphenyl derivatives, and develop a numerical scheme to simulate the torsional dynamics. By choice of the field parameters, the method can be applied either to drive the torsion angle to an arbitrary configuration or to induce free internal rotation. Transient absorption spectroscopy is suggested as a probe of torsional control and the usefulness of this approach is numerically explored. Several consequences of our ability to manipulate molecular torsional motions are considered. These include a method for the inversion of molecular chirality and an ultrafast chiral switch.