Electrode kinetic phenomena of solid state ionic devices

With the development of functional materials with high ionic and combined ionicelectronic conductivity, the engineering of interfaces became prerequisite. Technological applications demand combinations of materials with different electrical properties to form junctions. The occurring kinetic electrode phenomena play a significant role to the overall performance and may be rate determining. We show here the significance of the equilibration between platinum and the solid electrolyte with respect to the response time in potentiometric oxygen sensors. Fundamental aspects of voltage generation are discussed as well, and the response time is correlated to the equilibration along the contact zone between platinum and the electrolyte. A common problem of potentiometric devices for gas sensing applications is the cross sensitivity to species other than those under detection. The proposed kinetic method based on the theta concept is investigated for selective detection in the presence of a multiple number of complex gases by employing a single electrochemical cell. Information from current-voltage plots is converted to generate complex plane plot for the Fourier coefficients. The various polarizations under the applied electric perturbation are modelled and compared to experimental data for the determination of the rate determining processes.     

Scaffold topologies. 1. Exhaustive enumeration up to eight rings

Mapping the chemical space of small organic molecules is approached from a theoretical graph theory viewpoint, in an effort to begin the systematic exploration of molecular topologies. We present an algorithm for exhaustive generation of scaffold topologies with up to eight rings and an efficient comparison method for graphs within this class. This method uses the return index, a topological invariant derived from the adjacency matrix of the graph. Furthermore, we describe an algorithm that verifies the adequacy of the comparison method. Applications of this method for chemical space exploration in the context of drug discovery are discussed. The key result is a unique characterization of scaffold topologies, which may lead to more efficient ways to query large chemical databases.     

1H NMR determination of hypericin and pseudohypericin in complex natural mixtures by the use of strongly deshielded OH groups

The ¹H NMR spectra of the commercially available compounds hypericin and its derivative pseudohypericin in CD₃OH solutions indicate significantly deshielded signals in the region of 14-15 ppm. These resonances are attributed to the peri hydroxyl protons OH(6), OH(8) and OH(1), OH(13) of hypericins which participate in a strong six-membered ring intramolecular hydrogen bond with CO(7) and CO(14), respectively, and therefore, they are strongly deshielded. In the present work, we demonstrate that one-dimensional ¹H NMR spectra of hypericin and pseudohypericin, in Hypericum perforatum extracts show important differences in the chemical shifts of the hydroxyl groups with excellent resolution in the region of 14-15 ppm. The facile identification and quantification of hypericin and its derivative compound pseudohypericin was achieved, without prior HPLC separation, for two H. perforatum extracts from Greek cultivars and two commercial extracts: a dietary supplement, and an antidepressant medicine. The results were compared with those obtained from UV-vis and LC/MS measurements.     

Plasma Nanotextured Polymeric Surfaces for Controlling Cell Attachment and Proliferation: A Short Review

Plasma etching has evolved in an important technology for rapid and cost-effective generation of random or quasi-ordered nanostructures in large areas and in a repeatable manner, if properly controlled. It simultaneously affects the chemical composition of etched surfaces. Thus, plasma etching finds numerous applications in the areas of biomaterials and biomicrosystems, since surface chemistry and topography are proven to influence strongly cell–substrate interactions. Herein, we briefly review published studies addressing cell–surface interactions, especially those focusing on optimal surface properties favoring cell adhesion and proliferation. We show that plasma-based micro- and nano-texturing of polymeric surfaces provides a unique, simple and yet versatile tool for tuning the physicochemical properties of polymeric surfaces to those favoring cell cultures. Plasma etching and nanotexturing is proven indispensable also for the patterning on the same substrate of different chemical and/or topographical areas to induce preferential cell adhesion in predefined areas. In this respect, the implementation of surfaces with extreme wettabilities (superhydrophobic/superhydrophilic patterns) is highly valued and when integrated inside microchannels can add new potential to the current archery of microanalytical devices. The paper concludes with the authors’ view to the future outlook of the niche area of plasma nanotextured polymer surfaces.     

Are Two‐Station Biased Random Walkers Always Potential Molecular Motors?

The short answer to the title question is no. Despite their tremendous complexity, many nanomachines are simply one‐dimensional systems undergoing a biased, that is, unidirectional, walk on a two‐minima potential energy curve. The initially prepared state, or station, is higher in energy than the final equilibrium state that is reached after overcoming an energy barrier. All chemical reactions comply with this scheme, which does not necessarily imply that a generic chemical reaction is a potential molecular motor. If the barrier is low, the system may walk back and the motion will have a large purely Brownian component. Alternatively, a large distance from the barrier of either of the two stations may introduce a Brownian component. Starting from a general inequality that leverages on the idea that the amount of heat dissipated along the potential energy curve is a good indication of the effectiveness of the biased walk, we provide guidelines for the selection of the features of artificial molecular motors.     

Robust and sensitive high-performance liquid chromatographic-UV detection technique for the determination of tigecycline in rabbit plasma

An isocratic HPLC method with detection at 248 nm was developed and fully validated for the determination of tigecycline in rabbit plasma. Minocycline was used as an internal standard. A Hypersil BDS RP-C18 column (250 x 4.6 mm, 5 microm particle size) was used with the mobile phase phosphate buffer (pH 7.10, 0.070 M)-acetonitrile (76 + 24, v/v) at a flow rate of 1.0 mL/min. The elution time of tigecycline and minocycline was approximately 8.1 and 9.9 min, respectively. Calibration curves of tigecycline were linear in the concentration range of 0.021-3.15 microg/mL in plasma. The LOD and LOQ in plasma were estimated as 7 and 21 ng/mL, respectively. The intraday and interday precision values of the method were in the range of 5.0-7.1 and 5.6-9.1%, while the corresponding accuracy values were in the ranges of 92.8-111.1 and 97.6-102.3%, respectively. At the LOQ, the intraday precision was 18.7%, while intraday and interday accuracy values were 97.3 and 98.0%, respectively. Robustness of the proposed method was studied using a Plackett-Burman experimental design. A pharmacokinetic profile is presented for confirmation of the applicability of the method to pharmacokinetic studies.     

Synthesis and in vivo biological activity of large-ringed calixarenes against Mycobacterium tuberculosis

A series of large-ringed calix[6,7,8]arene analogues have been synthesised and their affect against Mycobacterium tuberculosis in vivo established. In general, when p-phenylcalixarenes and tert-butylcalixarenes were not functionalised at the lower rim, low biological activities were observed. However on going from partially to fully lower rim pegylated calixarenes the anti-mycobacterial properties improved. The addition of cyanopropoxy groups at the lower rim gave rise to low activities, whereas the addition of acetate moieties interestingly had pro-TB effects. Two upper rim sulfonated calixarenes showed promising properties. In the course of this work, a high yielding procedure to synthesise p-phenylcalix[7]arene was also established.     

A Density Functional Theory Study of Secondary Reactions in n‐Butyl Acrylate Free Radical Polymerization

In this work, secondary reactions involved in the free radical polymerization of butyl acrylate are investigated using quantum chemistry. First, various backbiting reactions are studied by adopting a simplified molecular model suitable for treating long polymer chains. The predicted reaction kinetics suggest the possibility of a radical migration along the poly(butyl acrylate) (PBA) chain as a consequence of subsequent j:j + 4 hydrogen abstractions, which are characterized by a low activation energy. Moreover, branching propagation and β‐scission reactions originating from mid‐chain radicals are investigated using a complete PBA model composed of five monomer units. The reaction kinetics involving short‐branch radicals are also examined, and a novel backbiting step leading to the formation of short branches is proposed.

     

How to gamble if you're in a hurry

The beautiful theory of statistical gambling, started by Dubins and Savage (for subfair games) and continued by Kelly and Breiman (for superfair games), has mostly been studied under the unrealistic assumption that we live in a continuous world, that money is indefinitely divisible and that our life is indefinitely long. Here, we study these fascinating problems from a purely discrete, finitistic and computational viewpoint, using both symbol-crunching and number-crunching (and simulation just for checking purposes).