Frequency shift on the potential-dependent surface-enhanced Raman scattering of pyridine: simplified models for metal and solvent effects

The electronic structure of adsorbates is altered when it interacts with a surface, modifying the properties of both entities and giving rise to interesting phenomena related to heterogeneous catalysis or molecular electronics. If such surface is a metallic substrate, the electrode potential can be used to tune this interaction. Potential-dependent Surface-Enhanced Raman Scattering (SERS) is a particularly useful technique to study the induced effects on the molecule when the metal-adsorbate surface complex is formed, as the observed frequency shifts of the vibrational modes can provide information about it. However, from the computational point of view, these systems are difficult to model, because the macroscopic metal cannot be modelled easily using quantum mechanics. As an approach, we propose a simple model using silver atomic wires with different size and charge bonded to the molecule (AgnPyq, n = 2,3,5,7 and q = 0 and ±1 for n even and odd, respectively) which has been developed by the group and provides a good description of the effect of the electrode potential on the chemical enhancement mechanism of SERS.1-3 Electronic calculations were performed using Density Functional Theory (DFT). In order to study the frequency shifts, solvent effects have been taken into account by using the Polarizable Continuum Model (PCM). We have used three different functionals (B3LYP, PW91 and M06HF) and two basis sets (LANL2DZ for all atoms and LANL2DZ for Ag and 6-31G(d) for C,N,H) and, in all cases, a good agreement is achieved in terms of amplitude and trend of the frequency shift for most of the vibrational modes, especially when solvent interactions are included. The method was extended to other metals and solvents giving results in agreement with the available experimental data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Charge Transfer mechanism in the Surface Enhanced Raman Scattering of 2,2'-bipyridine recorded on a silver electrode

Nowadays, Surface Enhanced Raman Spectroscopy (SERS) has become a powerful technique to investigate the electronic structure of surface-molecule hybrid systems due to the huge enhancement of the Raman signal. It is established that the origin of this enhancement has two main contributions; the electromagnetic (EM), related to surface plasmons, and the chemical mechanism, due to resonant charge transfer (CT) processes between the adsorbate and the metal. With the aim to investigate the SERS-CT of bipyridine and to identify charge transfer process, the spectra were recorded on silver electrode by using three different wavelengths (473, 532 and 785 nm) in a range from 0.0 up to -1.4 V electrode potential. The electrode potential was modelled in the calculations with atomic silver wires of different size and charge attached to the BPy molecule (AgnBPyq, with q = 0 for n = 2 and q = ±1 for n = 3, 5, 7) and were computed with Density Functional Theory (DFT). Although BPy shows a trans conformation in solution, a cis conformation was chosen for its chelating properties. The results indicate that the intensification of the ~1550 cm-1 band at negative potentials is due the Franck-Condon factors related to the resonant CT process from the metal to the BPy molecule.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

An MS-CASPT2 Study of the Photodecomposition of 4- Methoxyphenyl Azide. Role of Internal Conversion and Intersystem Crossing

Aryl azides photochemistry is strongly dependent on the substituent relative position, as has been studied by time resolved resonant Raman (TR3) spectroscopy for 4-methoxyphenyl azide and its isomer 3-methoxyphenyl azide. When irradiated at 266 nm, the former results in 4,4’-dimethoxyazobenzene whereas the latter forms 1,2-didehydroazepine. It is proposed that the key step of the reactions is the formation of a nitrene derivative. Recently, it has been proposed by us that nitrenes might have a relevant role in the Surface-Enhanced Raman Scattering (SERS) of p-aminothiophenol, however, the molecular mechanism is not well known in neither of these cases. Therefore, we studied the photodecomposition of 4-methoxyphenyl azide using multiconfigurational self-consistent field methods (MC-SCF) with the CAS-SCF and MS-CASPT2 approximations and calculated the resonant Raman spectra of the relevant species using a multi-state version of Albrecht’s vibronic theory. The results propose that the reaction follows a two steps sequence after irradiation at 266 nm: an intersystem crossing 21A’/23A’’ which decays through a 21A’/21A’’ conical intersection producing molecular nitrogen and triplet 4-methoxyphenyl nitrene in its ground state.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Modeling the effect of the electrode potential in SERS by electronic structure calculations.

Surface Enhanced Raman Spectroscopy (SERS), due to the ability of greatly intensify the weak Raman signal of molecules adsorbed to metal surfaces, has proven to be a very useful tool to investigate changes in the electronic structure of metal-molecule surface complex. A deep knowledge of the electronic structure of these metal-molecule hybrid systems is key in electrochemistry, catalysis, plasmonics, molecular electronics, and in the development of selective and ultra-sensitive analytical sensors. The origin of this huge enhancement in SERS is due to two contributions: the electromagnetic (EM), related to surface plasmons, and the chemical mechanism, due to resonant charge transfer (CT) process between the adsorbate and the metal (CTSERS). Unfortunately, the SERS implies very complex phenomena where the molecule and the metal nanoparticle are involved. This fact makes challenging to build realistic theoretical models that take into account both the metal and the molecule at quantum level. We propose a methodology, based on DFT and ab initio electronic calculations, to simulate the effect of the electrode potential on the absorption, on the charge transfer states energies, and on the electronic excitations in metal-molecule hybrid systems from a microscopic point of view. This methodology consists on the prediction of Raman intensities from ab initio calculations of the geometries or the energy gradients at the excited states Franck-Condon point, bringing the possibility to predict the intensities in CTSERS as well as in resonance Raman without the need to know the excited state geometries, not always feasible to compute. The microscopic model adopted to mimic the effect of the interphase electric potential consist in a molecule adsorbed to a linear silver cluster [Agn-Adsorbate]q, were n is the number of silver atoms, and the total charge of the system (q) is zero for n=2 and q=±1 for n=1, 3 and 7.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Selection rules of surface-enhanced Raman scattering: the role of the out-of-plane vibrations

The electromagnetic/plasmonic (SERS-PL) and the chemical (usually involving resonant photoinduced metal-adsorbate (M-A) charge transfer processes (SERS-CT:M-A+hn-->M+-A-)) mechanisms are recognized as the two main contributions to the enhancement of a particular band in a SERS record. The key problem is to know which mechanism dominates the spectrum and to apply the corresponding selection rules. Many spectra have been analyzed according to the so-called “SERS propensity rules” of the PL mechanism. In this way, it would be possible to get information about the perpendicular/parallel orientation of the adsorbate on the nanoparticle if in-plane/out-of-plane vibrations of planar aromatic molecules show relative enhancement. The SERS of pyridazine (Pdz) on a silver electrode (Figure 1) is a very special case where the relative intensities are tuned by the electrode potential. Three different types of spectra are recorded showing no selective intensification (0 V) or in-plane (-0.5 V) and out-of-plane (-0.75 V) enhancements. The relative activity of both in-plane (8a and 19b modes) and out-of-plane (16b mode) vibrations can be explained under the same resonant SERS-CT chemical mechanism due to Franck-Condon factors related to differences between the equilibrium geometries (A1 vibrations, DQ≠0) and gradients (B1 vibrations, Dn≠0 and DQ≠0), respectively, of the potential energy surfaces of the involved ground and photoinduced CT electronic states. Therefore, it is not necessary to resort to any change in the orientation of the adsorbate, which is the standard explanation based on the propensity rules of the SERS-PL mechanism. This conclusion is supported on the basis of electronic structure calculations of the properties of Ag2-Pdz clusters in the ground (S0;A1) and excited states with CT characteristics (CT0;A2 and CT1;B1).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Comparative study of different theoretical approaches for modeling the dependence of the SERS vibrational wavenumbers on the electrode potential

Surface-enhanced Raman scattering (SERS) is a powerful technique to study the electronic structure of charged metal-molecule interfaces, which are relevant in many fields like electrochemistry, heterogeneous catalysis or molecular electronics. When electrochemical SERS experiments are carried out two main features are observed: a selective enhancement of the intensity of some bands and a shift of the vibrational wavenumbers. Both characteristics are very often dependent on the applied electrode potential. The first of them has been widely discussed and is related to different SERS enhancement mechanisms,1,2 while the second one reflects changes of the electronic structure of the adsorbate in the ground electronic state. The theoretical modelling of the effect of the electrode potential in electronic structure calculations is a challenge due to the large number of factors to be considered such as the adsorption on a particular site of the metal surface, the way to take into account the role of the electrode potential on the calculations or the electrolyte or solvent effects. In this work we discuss two different approaches to compute the wavenumber dependence of the vibrational modes of pyridine adsorbed on silver at different electrode potentials (Figure 1). On the one hand, the effect of the electrode potential has been modelled by means of simple linear metal-pyridine complexes3 [AgnPy]q where the metal cluster has variable size (n) and charge (q) what allows for defining the qeff = q/n parameter, which quantifies the mean density of charge of the cluster (Figure 1A). On the other hand, an external electric dipole field has been applied on the [Ag2Py]0 neutral complex as an alternative model for simulating the effect of the electrode potential (Figure 1B). The calculations were performed using Density Functional Theory (DFT) and several variables have been considered like the level of theory, solvent effects and the size or shape of the metal cluster.Universidad de Málaga. Campus de Excelencia Internacional Andalucia Tech

Mice carrying an epithelial deletion of the glucocorticoid receptor NR3C1 develop a higher tumor load in experimental colitis associated cancer

The glucocorticoid receptor NR3C1 is expressed in multiple cell types in the gut and elsewhere. Intestinal epithelial cells both produce and respond to glucocorticoids in different physiological and pathological contexts. In experimental colitis glucocorticoids have been shown to exert a dual role, dampening inflammation while producing a deterioration in animal status, including death. Mice with tamoxifen inducible, intestinal epithelial specific deletion of NR3C1 (NR3C1IEC mice) are protected against experimental colitis, suggesting glucocorticoid epithelial actions are deleterious. Since glucocorticoids modulate epithelial proliferation it follows that they may affect the development of colon cancer. In this study we set out to test this hypothesis using the dextran sulfate sodium - azoxymethane model of colitis-associated cancer. KO mice were found to exhibit a 2-fold higher tumor load but similar incidence and tumor size. Tumors had a higher trend to extend to the submucosal layer (36% vs. 0%) in NR3C1IEC mice, and overexpressed Lgr5, Egfr and Myc, consistent with increased proliferation and neoplastic transformation. Snai1 and Snai2 were upregulated specifically in tumors of NR3C1ΔIEC mice, suggesting enhanced epithelial to mesenchymal transition in the absence of the intestinal epithelial GC receptor. We conclude that endogenous GC epithelial signaling is involved in colitis associated cancer.This work was supported by funds from the Ministry of Economy and Competitivity, partly with Fondo Europeo de Desarrollo Regional (FEDER) funds [SAF2017-88457-R, AGL2017-85270-R, BFU2014-57736-P, AGL2014-58883-R] and by Junta de Andalucía [CTS235, CTS164]. MA and CJA were supported by the University of Granada (Contrato Puente Program - Plan Propio) and the Ministry of Education [Spain], respectively. CIBERehd is funded by Instituto de Salud Carlos III

Immunoregulatory Effects of Porcine Plasma Protein Concentrates on Rat Intestinal Epithelial Cells and Splenocytes

This study was funded by APC Europe and the Ministry of Economy and Competitivity, partly with Fondo Europeo de Desarrollo Regional FEDER funds [SAF2017-88457-R, AGL2017-85270- R, BFU2014-57736-P, AGL2014-58883-R], and by Junta de Andalucía [CTS235, CTS164]. CHC, CJA and BO were supported by the University of Granada (Contrato Puente Program-Plan Propio) and the Ministry of Education [Spain], respectively. CIBERehd is funded by Instituto de Salud Carlos III.Blood contains proteins which have interest as products that may regulate immune function. For this reason some protein-based products are currently used as nutritional supplements for animals, for instance two porcine concentrates, spray dried serum (SDS), and an immunoglobulin concentrate (IC). These products have shown to protect against colonic inflammation in rodents. In the present study we characterize the ability of these products to modulate immune function in isolated cells, namely intestinal epithelial cells (IEC18 cells) and rat spleen cells. Our data indicate that both porcine protein concentrates indeed alter immune cell function, based on the secretion of the modulators known as cytokines. In intestinal epithelial IEC18 cells they promoted the secretion of GRO alpha and MCP-1 cytokines. In spleen cells they mainly inhibited the production of TNF, a key proinflammatory cytokine. In addition, the IC product augmented the release of IL-10, an anti-inflammatory cytokine. Taken together, our data indicate that the immunomodulatory effects observed in vivo are consistent with the direct actions of the protein concentrates on epithelial cells, T lymphocytes, and monocytes. Serum protein concentrates have been shown to exert in vivo anti-inflammatory effects. Specific effects on different cell types and their mechanism of action remain unraveled. We aimed to characterize the immunomodulatory effect of two porcine plasma protein concentrates, spray dried serum (SDS) and an immunoglobulin concentrate (IC), currently used as animal nutritional supplements with established in vivo immunomodulatory properties. Cytokine production by the intestinal epithelial cell line IEC18 and by primary cultures of rat splenocytes was studied. The molecular pathways involved were explored with specific inhibitors and gene knockdown. Our results indicate that both products induced GRO alpha and MCP-1 production in IEC18 cells by a MyD88/NF-kappa B-dependent mechanism. Inhibition of TNF production was observed in rat primary splenocyte cultures. The immunoglobulin concentrate induced IL-10 expression in primary splenocytes and lymphocytes. The effect on TNF was independent of IL-10 production or the stimulation of NF-kB, MAPKs, AKT, or RAGE. In conclusion, SDS and IC directly regulate intestinal and systemic immune response in murine intestinal epithelial cells and in T lymphocytes and monocytes.APC EuropeMinistry of Economy and CompetitivityEuropean Commission SAF2017-88457-R AGL2017-85270R BFU2014-57736-P AGL2014-58883-RJunta de Andalucia CTS235 CTS164University of Granada (Contrato Puente Program-Plan Propio)Ministry of Education [Spain]Instituto de Salud Carlos IIIEuropean Commissio

A new methodology for the in vivo estimation of the elastic constants that characterize the patient-specific biomechanical behavior of the human cornea

This work presents a methodology for the in vivo characterization of the complete biomechanical behavior of the human cornea of each patient. Specifically, the elastic constants of a hyperelastic, second-order Ogden model were estimated for 24 corneas corresponding to 12 patients. The finite element method was applied to simulate the deformation of human corneas due to non-contact tonometry, and an iterative search controlled by a genetic heuristic was used to estimate the elastic parameters that most closely approximates the simulated deformation to the real one. The results from a synthetic experiment showed that these parameters can be estimated with an error of about 5%. The results of 24 in vivo corneas showed an overlap of about 90% between simulation and real deformed cornea and a modified Hausdorff distance of 25 mu m, which indicates the great accuracy of the proposed methodology. (C) 2014 Elsevier Ltd. All rights reserved.This project has been partially funded by MECD (reference AP2009-2414) and MINECO (INNPACTO, IPT-2012-0495-300000).Lago, MA.; Rupérez Moreno, MJ.; Martínez Martínez, F.; Monserrat Aranda, C.; Larra, E.; Gueell, JL.; Peris-Martinez, C. (2015). A new methodology for the in vivo estimation of the elastic constants that characterize the patient-specific biomechanical behavior of the human cornea. Journal of Biomechanics. 48(1):38-43. https://doi.org/10.1016/j.jbiomech.2014.11.009S384348