Incorporation of Ag nanoparticles into membrane mimetic systems composed by phospholipid layer‐by‐layer (LbL) films to achieve surface‐enhanced Raman scattering as a tool in drug interaction studies

The synergistic effect produced by nanoparticles when incorporated into different systems used as analytical tools represents a growing research field nowadays. On the other hand, the study of interactions involving pharmacological drugs and biological membranes using phospholipids as mimetic systems is a research field already well established. Here, we combine both the anionic phospholipid dipalmitoyl phosphatidyl glycerol (DPPG) and negative Ag nanoparticles (AgNP) to form layer‐by‐layer (LbL) multilayered films using the cationic polymer poly(allylamine hydrochloride) (PAH) as the supporting polyelectrolyte, which were further investigated in the presence of a phenothiazine compound (methylene blue—MB). The molecular architecture of the LbL films in terms of controlled growth, morphology with micro and nanometer spatial resolutions, and dispersion of both AgNP and MB within the DPPG matrix was determined combining spectroscopy [ultraviolet–visible (UV–Vis) absorption and micro‐Raman spectroscopy] and microscopy [scanning electron microscopy (SEM) and atomic force microscopy (AFM)]. The results showed that the LbL films can be grown in a controlled way at nanometer thickness scale with the surface morphology susceptible to the presence of both AgNP and MB. The surface‐enhanced phenomenon was applied to investigate the LbL films taking the advantage of the strong surface‐enhanced resonance Raman scattering (SERRS) signal presented by the MB molecules. Besides, as MB is a pharmacological drug of interest, its molecular arrangements when dispersed in LbL films containing DPPG, which is the biological membrane mimetic system here, were investigated. In this case, the AgNP played a key role in achieving the MB SERRS signal. Copyright © 2009 John Wiley & Sons, Ltd.     

Detection of trace levels of atrazine using surface-enhanced Raman scattering and information visualization

The detection of trace amounts of pesticides is essential for the quality control of waters, particularly with their inevitable increasing use with the growing demand for food. In this study, we report on the detection of atrazine, a highly toxic herbicide, down to 5?×?10^?12 M, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations. Such detection was performed with surface-enhanced Raman scattering (SERS) in atrazine incorporated into silver nanoparticles (AgNPs) colloids, with the SERS spectra being treated with Sammon’s mapping, an information visualization technique. In addition to providing a fingerprint of the atrazine molecules, SERS is advantageous in comparison with impedance spectroscopy and cyclic voltammetry applied to a sensor array of units made with layer-by-layer (LbL) films containing AgNPs and AuNPs. The combined use of SERS and information visualization methods is promising for monitoring water quality with regard to other pesticides, which may even approach single molecule detection.     

A Novel Asymmetric Total Synthesis of (+)-Artemisinin

A 12-step synthesis of the natural product (+)-Artemisinin, very active against malaria, is described. (-)-Isopulegol, which already contains two of the asymmetric centers of (+)-Artemisinin in the correct absolute configuration, was used as starting material.     

Bionanocomposites of Cassava Starch and Synthetic Clay

Starch-based biofilms containing synthetic Laponite clay and glycerol were prepared using a solvent casting technique. Electron microscopy images showed predominance of the exfoliated type of nanocomposite. Dynamic mechanical analysis revealed a larger influence of glycerol content on the polymer β relaxation and T _g than the clay content. Gas barrier properties were influenced by clay particles and plasticizer content. An increase of clay content led to lower gas permeability values. Although both glycerol and Laponite are hydrophilic, no significant changes were observed on the water sorption by starch films at different relative humidity values. Mechanical properties are kept similar after the inorganic filler incorporation.     

Weak chaos and metastability in a symplectic system of many long-range-coupled standard maps

We introduce, and numerically study, a system of N symplectically and globally coupled standard maps localized in a d=1 lattice array. The global coupling is modulated through a factor r^-α, being r the distance between maps. Thus, interactions are long-range (nonintegrable) when 0≤α≤1, and short-range (integrable) when α>1. We verify that the largest Lyapunov exponent λ_M scales as λ_M ∝ N^-κ(α), where κ(α) is positive when interactions are long-range, yielding weak chaos in the thermodynamic limit N↦∞ (hence λ_M→0). In the short-range case, κ(α) appears to vanish, and the behaviour corresponds to strong chaos. We show that, for certain values of the control parameters of the system, long-lasting metastable states can be present. Their duration t_c scales as t_c ∝N^β(α), where β(α) appears to be numerically in agreement with the following behavior: β>0 for 0 ≤α< 1, and zero for α≥1. These results are consistent with features typically found in nonextensive statistical mechanics. Moreover, they exhibit strong similarity between the present discrete-time system, and the α-XY Hamiltonian ferromagnetic model.     

Sensitivity to initial conditions, entropy production, and escape rate at the onset of chaos

We analytically link three properties of nonlinear dynamical systems, namely sensitivity to initial conditions, entropy production, and escape rate, in z-logistic maps for both positive and zero Lyapunov exponents. We unify these relations at chaos, where the Lyapunov exponent is positive, and at its onset, where it vanishes. Our result unifies, in particular, two already known cases, namely (i) the standard entropy rate in the presence of escape, valid for exponential functionality rates with strong chaos, and (ii) the Pesin-like identity with no escape, valid for the power-law behavior present at points such as the Feigenbaum one.     

Poisson-Boltzmann description of the electrical double layer including ion size effects

The electrical double layer is examined using a generalized Poisson-Boltzmann equation that takes into account the finite ion size by modeling the aqueous electrolyte solution as a suspension of polarizable insulating spheres in water. We find that this model greatly amplifies the steric effects predicted by the usual modified Poisson-Boltzmann equation, which imposes only a restriction on the ability of ions to approach one another. This amplification should allow for an interpretation of the experimental results using reasonable effective ionic radii (close to their well-known hydrated values).     

New insights on integer-programming models for the kidney exchange problem

In recent years several countries have set up policies that allow exchange of kidneys between two or more incompatible patient–donor pairs. These policies lead to what is commonly known as kidney exchange programs.     

News and Views: About Complexity and Why to Care

What is nowadays ubiquitously referred to as complexity emerges in a wide variety of natural, artificial, and social systems. This very rich concept is nontrivial to understand and is therefore hard to operationally define. Consequently, along the years, many intertwined characterizations have been proposed in the literature. Among those, a powerful and practical one consists in focusing on the entropic and statistical mechanical aspects of the system. We attempt here to put this active line of research into a contemporary perspective.     

Nonadditive entropy: The concept and its use

The thermodynamical concept of entropy was introduced by Clausius in 1865 in order to construct the exact differential dS = Q/T , where Q is the heat transfer and the absolute temperature T its integrating factor. A few years later, in the period 1872-1877, it was shown by Boltzmann that this quantity can be expressed in terms of the probabilities associated with the microscopic configurations of the system. We refer to this fundamental connection as the Boltzmann-Gibbs (BG) entropy, namely (in its discrete form) , where k is the Boltzmann constant, and {p _i} the probabilities corresponding to the W microscopic configurations (hence ∑^W _i=1 p _i = 1 . This entropic form, further discussed by Gibbs, von Neumann and Shannon, and constituting the basis of the celebrated BG statistical mechanics, is additive. Indeed, if we consider a system composed by any two probabilistically independent subsystems A and B (i.e., , we verify that . If a system is constituted by N equal elements which are either independent or quasi-independent (i.e., not too strongly correlated, in some specific nonlocal sense), this additivity guarantees S_BG to be extensive in the thermodynamical sense, i.e., that in the N ≫ 1 limit. If, on the contrary, the correlations between the N elements are strong enough, then the extensivity of S_BG is lost, being therefore incompatible with classical thermodynamics. In such a case, the many and precious relations described in textbooks of thermodynamics become invalid. Along a line which will be shown to overcome this difficulty, and which consistently enables the generalization of BG statistical mechanics, it was proposed in 1988 the entropy . In the context of cybernetics and information theory, this and similar forms have in fact been repeatedly introduced before 1988. The entropic form S_q is, for any q 1 , nonadditive. Indeed, for two probabilistically independent subsystems, it satisfies . This form will turn out to be extensive for an important class of nonlocal correlations, if q is set equal to a special value different from unity, noted q_ent (where ent stands for entropy . In other words, for such systems, we verify that , thus legitimating the use of the classical thermodynamical relations. Standard systems, for which S_BG is extensive, obviously correspond to q _ent = 1 . Quite complex systems exist in the sense that, for them, no value of q exists such that S_q is extensive. Such systems are out of the present scope: they might need forms of entropy different from S_q, or perhaps --more plainly-- they are just not susceptible at all for some sort of thermostatistical approach. Consistently with the results associated with S_q, the q -generalizations of the Central Limit Theorem and of its extended Lévy-Gnedenko form have been achieved. These recent theorems could of course be the cause of the ubiquity of q -exponentials, q -Gaussians and related mathematical forms in natural, artificial and social systems. All of the above, as well as presently available experimental, observational and computational confirmations --in high-energy physics and elsewhere-- are briefly reviewed. Finally, we address a confusion which is quite common in the literature, namely referring to distinct physical mechanisms versus distinct regimes of a single physical mechanism. This paper is part of the Topical Issue Statistical Power Law Tails in High-Energy Phenomena.