Raman spectroscopy is applied in this work to study the adsorption of poly(ethyleneimine) (PEI) on Ag nanoparticles obtained by reduction with citrate, as well as to the study of the interaction between PEI and a plasmid. The surface-enhanced Raman spectroscopy (SERS) affords important information about the interaction and orientation of the polymer on the particles. In particular we have found that this polymer interacts with the surface through their amino groups in an interaction which also involves a change in the protonation state of amino groups as well as an increase of the chain order. This interaction implies a charge-transfer effect as deduced from the strong resonant effect in Raman spectra obtained at different excitation wavelengths. The complex formed by PEI and a plasmid, obtained by encoding the HBV (hepatitis B virus) genome inside the EcoRI restriction site of pGEM vector, was also studied by SERS. The interaction between both polymers leads to a conformational change affecting both macromolecules that can be detected by Raman at different excitation wavelengths. PEI undergoes a change to a more disordered structure as well as an increase of the number of protonated amino groups. The plasmid undergoes a structural change from A-DNA structure to B-DNA, along with a change in the superhelicity resulting in a more lineal structure when the plasmid interacts with PEI.

The stabilization of all-trans-lycopene from tomato by encapsulation using a-, b-and c-cyclodextrins (CDs) was evaluated. To that end, two different encapsulation methods were comparatively studied: a conventional method and a supercritical fluid extraction (SFE) process. An optimization procedure considering distinct molar ratios of CD/lycopene (1/0.0026, 1/0.005 and 1/0.05) as well as the type of cyclodextrin to be used was accomplished. The encapsulation was determined by using micro-Raman spectroscopy. All-trans-lycopene employed was obtained by SFE with a purity around 90-95%. As a result, a molar ratio CD/lycopene of 1/0.0026 was selected as it provided the best complexation yields (93.8%) whilst b-CD seemed to be the most favorable to be used to stabilize lycopene. A comparison of the two methods studied reflected higher encapsulation yields from the conventional method. However, the supercritical fluid approach offers numerous advantages such as the possibility of performing the extraction, fractionation and encapsulation of lycopene from tomato in one step, shortening notably the overall procedure time and minimizing the sample handling.

The interaction between adsorbates of different nature and plasmonic nanoparticles is reviewed here on the basis of the work done in our laboratory in the past few years. The paper is structured for analyzing the interaction of adsorbates with metal nanoparticles as function of the interacting atom (O, N, or S) and the adsorbate conformation. In the study of the adsorption of molecular species on metals, it is necessary to take into account that different interaction mechanisms are possible, leading to the existence of different molecular forms (isomers or conformers). These forms can be evidenced by changing the excitation wavelength, due to a resonant selection of these wavelengths. Charge-transfer complexes and electrostatic interactions are the usual driving forces involved in the interaction of adsorbates on metal surfaces when these metallic systems are used in wet conditions. The understanding of the metal-adsorbate interaction is crucial in the surface functionalization of metal surfaces, which has a growing importance in the development of sensing systems or optoelectronic devices. In relation to this, special attention is paid in this work to the study of the adsorption of calixarene host molecules on plasmonic nanoparticles.

Molecular modeling of the cholesteric liquid crystal polyester poly-[oxy(1,2 -dodecane)oxycarbonyl -1,4 -phenyleneoxycarbonyl -1,4-phenylenecarbonyloxy-1,4-phenylenecarbonyl] (PTOBDME), [C 34 H 36 O 8 ] n , synthesized in our laboratory and thermally characterized by differential scanning calorimetry (DSC), was performed to explain both its cholesteric mesophase and 3D crystalline structure. Conformational analysis (CA) was run for the monomer both by systematic search and with molecular dynamics (MD) simulations. Minima energy conformers were "polymerized" with Cerius 2 and helical, cholesteric molecules were obtained in all cases. Our models agree with the chiral behavior observed by X-ray diffraction (XRD), thermooptical analysis (TOA) and circular dichroism (CD) experiments. Crystal packing of the polymer molecules were simulated in cells with parameters a and b obtained from experimental powder X-ray diffraction patterns and c calculated from the translational repetitive unit during the theoretical polymerization. Recalculated X-ray powder diffraction patterns of our models matched the ob-