Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces

Investigation into nanostructured organic films has served many purposes, including the design of functionalized surfaces that may be applied in biomedical devices and tissue engineering and for studying physiological processes depending on the interaction with cell membranes. Of particular relevance are Langmuir monolayers, Langmuir–Blodgett (LB) and layer-by-layer (LbL) films used to simulate biological interfaces. In this review, we shall focus on the use of vibrational spectroscopy methods to probe molecular-level interactions at biomimetic interfaces, with special emphasis on three surface-specific techniques, namely sum frequency generation (SFG), polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and surface-enhanced Raman scattering (SERS). The two types of systems selected for exemplifying the potential of the methods are the cell membrane models and the functionalized surfaces with biomolecules. Examples will be given on how SFG and PM-IRRAS can be combined to determine the effects from biomolecules on cell membrane models, which include determination of the orientation and preservation of secondary structure. Crucial information for the action of biomolecules on model membranes has also been obtained with PM-IRRAS, as is the case of chitosan removing proteins from the membrane. SERS will be shown as promising for enabling detection limits down to the single-molecule level. The strengths and limitations of these methods will also be discussed, in addition to the prospects for the near future.     

Detection and quantitative analysis of carbendazim herbicide on Ag nanoparticles via surface‐enhanced Raman scattering

Carbendazim (MBC) is a fungicide widely used in agriculture, and there are serious concerns regarding the health risks that could be caused by this fungicide. Here, we explore its ultrasensitive detection by surface‐enhanced Raman scattering (SERS). First, to obtain maximum SERS signal, the adsorption of the target molecule onto metallic surface is essential. Therefore, we study the adsorption of the MBC onto the nanoparticle surface by SERS under different experimental conditions, such as different synthesis methods of nanoparticle, variable excitation wavelength, and fungicide concentration with the aim to detect MBC at low concentrations. Experiments are carried out with three kinds of colloidal nanoparticles: Ag and Au reduced by citrate and Ag reduced by hydroxylamine. However, mainly Ag colloids are highly efficient in the SERS detection of MBC. In addition, theoretical calculations of MBC Raman spectrum and that of the surface complex are used to help with the understanding the mechanisms responsible for the interaction between MBC and Ag. Ultraviolet–visible absorption spectroscopy showed displacement to the red of the plasmon resonance of Ag colloid in the presence of MBC. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis of Substituted γ-Butyrolactones: β-Hydroxymethyl-, β-Methylene and Cyclopropane Derivatives

A β-hydroxymethyl-γ-butyrolactone, which is a useful intermediate for the synthesis of several natural products with biological activity, was synthesized with good yield and a reduced number of steps from simple commercially available starting materials. Model compounds of natural products containing the unsaturated γ-butyrolactone unit, such as butenolides and β-methylene-γ-butyrolactones, were also conveniently synthesized from this hydroxymethyl-lactone.     

An Approach to the Synthesis of Bakkenolide A

Bakkenolide A 1 is the simplest member of a new class of eremophilane sesquiterpenes isolated a few years ago from Petasites japonicus. ² A recent synthesis of 1 ³ prompts us to disclose our preliminary results which, in a model system, provide an alternative approach to the construction of the novel β-methylene-γ-spirolactone system present in the bakkenolide series.     

A Short Synthesis of Symmetrical Betweenanemes

In the course of studies on the synthesis and chemistry of betweenanenes¹ we have devised a short route (Chart I) to symmetrical members of the family (e.g., 4) which we disclose herewith.     

Fluxes of cosmic rays: a delicately balanced stationary state

The analysis of cosmic rays fluxes as a function of energy reveals a knee slightly below 10¹⁶ eV and an ankle close to 10¹⁹ eV. Their physical origins remain up to now quite enigmatic; in particular, no elementary process is known which occurs at energies close to 10¹⁶ eV. We propose a phenomenological approach along the lines of nonextensive statistical mechanics, a formalism which contains Boltzmann–Gibbs statistical mechanics as a particular case. The knee then appears as a crossover between two fractal-like thermal regimes, the crossover being caused by process occurring at energies ten million times lower than that of the knee, in the region of the quark hadron transition (10⁹ eV). This opens the door to an unexpected standpoint for further clarifying the phenomenon.     

A polyhedral approach to a production planning problem

Production planning in manufacturing industries is concerned with the determination of the production quantities (lot sizes) of some items over a time horizon, in order to satisfy the demand with minimum cost, subject to some production constraints. In general, production planning problems become harder when different types of constraints are present, such as capacity constraints, minimum lot sizes, changeover times, among others. Models incorporating some of these constraints yield, in general, NP-hard problems. We consider a single-machine, multi-item lot-sizing problem, with those difficult characteristics. There is a natural mixed integer programming formulation for this problem. However, the bounds given by linear relaxation are in general weak, so solving this problem by LP based branch and bound is inefficient. In order to improve the LP bounds, we strengthen the formulation by adding cutting planes. Several families of valid inequalities for the set of feasible solutions are derived, and the corresponding separation problems are addressed. The result is a branch and cut algorithm, which is able to solve some real life instances with 5 items and up to 36 periods. This revised version was published online in June 2006 with corrections to the Cover Date.     

Calcul differentiel exterieur de degre arbitraire

LetX and V be F-modules. For every integer t, it is developed an algebraic formalism which generates, by an analogous procedure of construction of the exterior de rivation in the usual sense, couples formed by a deriva tion of degree t of A_F(X,F), an endomorphism of degree t of the graded additive group A_F(X,V), and satisfying a rule of derivation of degree t. This formalism is the most general ifX is projective of finite type. If t is odd, the curvature, and ifX - V, the torsion, are discussed at some lenght. If t=1, the differen tial calculus associated to Lie modules, linear connexions and fields of endomorphisms, are special cases.

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Ce travail a été financé par le Conselho Nacio nal de Pesquisas (Brésil), contract TC 8233.     

Structural assignment of Diels-Alder adducts: an experimental and theoretical approach

A detailed NMR analysis with total assignment of (1)H and (13)C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by (1)H and (13)C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311 + g(2d, p) from optimized structures at the B3LYP/6-31g(d) level.     

Numerical solution of the poisson-boltzmann equation for a spherical cavity

The Poisson-Boltzmann equation is numerically solved for a spherical cavity filled with a charged electrolyte solution. The network method used makes it possible to solve the problem in the most general case: the electrolyte solution can have any number of ion types with valences having any value. Furthermore, no a priori assumption concerning electroneutrality at the center of the cavity is required. Electric potential and ion concentration profiles, as well as the total potential drop in the cavity, are calculated for different system parameter values. These results are discussed and compared to the corresponding results obtained for suspended particles. Important differences arise, except for very thin double layers. For instance, the usual definition of the Debye length can no longer be used, since the electrolyte solution is nonneutral in the whole volume of the cavity. Furthermore, the charge density at the center of the cavity cannot be assigned any arbitrary value, since the charge density and the ion densities are no longer independent quantities.