Marcelo Campos-Vallette

Complexes of macrocycles with pendant arms as models for biological molecules

Abstract Recent literature results on inorganic models related to metalloenzymes which transport electrons or activate small molecules are discussed in this review. The molecular systems are essentially restricted to macrocyclic or polydentate ligands preferentially containing nitrogen atoms and pendant arms. The discussion is mainly concerned with aspects such as spectroscopic, electrochemical and chemical characterization of the systems and electro- or photo-activation of small molecules.

SERS and theoretical studies of arginine.

Arginine amino acid (Arg) has been vibrationally studied through its infrared, Raman and surface-enhanced Raman scattering (SERS) spectra, and theoretical calculations. Net charge is used to predict the possibility to obtain the SERS spectrum of Arg in colloidal solution. The interpretation of the SERS spectral data suggests that the Arg-Ag nanoparticles interaction in a colloidal solution and in the case of the Arg coated by Ag is mainly verified through the guanidinium moiety. Theoretical calculations performed by using extended Hückel theory method for a model of Arg interacting with an Ag cluster support the observed SERS experimental result.

Functionalization of Ag nanoparticles with the bis-acridinium lucigenin as a chemical assembler in the detection of persistent organic pollutants by surface-enhanced Raman scattering.

Organochlorine pesticide endosulfan has been detected for the first time by using surface-enhanced Raman scattering (SERS) at trace concentrations. The bis-acridinium dication lucigenine was successfully used as a molecular assembler in the functionalization of metal nanoparticles to facilitate the approach of the pesticide to the metal surface. From the SERS spectra valuable information about the interaction mechanism between the pesticide and lucigenin can be deduced. In fact, endosulfan undergoes an isomerization upon adsorption onto the metal, while the viologen undergoes a rotation of the acridinium planes to better accommodate the pesticide molecule. An interaction between the N atom of the central acridinium ring and the pesticide Cl-CC-Cl fragment is verified through a charge-transfer complex. The present study affords important information which can be applied to the design of chemical sensor systems of persistent organic pollutants based on the optical detection on functionalized metal nanoparticle.

Theoretical surface-enhanced Raman spectra study of substituted benzenes: I. Density functional theoretical SERS modelling of benzene and benzonitrile

This paper reports a DFT modelling of SERS spectra for benzene and benzonitrile on the basis of a simple noncoordinate substrate-adsorbate model. Assignment of normal modes was obtained from internal force constants and potential energy distribution matrices and used to identify, according the SERS selection rules, the orientation of the optimized molecules on the metallic surface. Calculated band enhancements are in good agreement with experimental observations. The optimized geometry parameters of the molecule-Ag system, changes of HOMO-LUMO energies are discussed to give insight in the different SERS mechanisms for both molecules.

Infrared spectrum of the bis-(1,10-phenanthroline) Cu(I) and Cu(II) perchlorate complexes

Abstract FT-IR spectra of the title compounds and derivatives were measured in the range 4000–120 cm −1 . A complete experimental spectral assignment has been performed. A simplified normal coordinate treatment orientates some assignment of frequencies in the low energy region. Bands at ca. 420 and 300 cm −1 are ascribed to the v Cu-N modes. A stability order of the Cu(I) complexes is proposed on the basis of their Cu-N frequency values.

Surface-enhanced Raman scattering and theoretical studies of the C-terminal peptide of the β-subunit human chorionic gonadotropin without linked carbohydrates.

Raman and surface-enhanced Raman scattering (SERS) spectra of the synthetic carboxy terminal peptide of human chorionic gonadatropin β-subunit free of carbohydrate moieties(P37) are reported. The spectral analysis is performed on the basis of our reported Raman spectrum and SERS data of oligopeptides displaying selected amino acids sequences MRKDV, ADEDRDA, and LGRGISL. SERS samples of P37 were prepared by coating the solid peptide with metal colloids on a quartz slide. This treatment makes possible to obtain high spectral batch to batch reproducibility. Amino acids components of P37 display net charges and hydrophobic characteristics, which are related to particular structural aspects of the adsorbate-substrate interaction. The spectroscopic results are supported by quantum chemical calculations performed by using extended Hückel theory method for a model of P37 interacting with an Ag surface. The P37-metal interaction is drove by positively charged fragments of selected amino acids,mainly threonine 109, lysine 122, and arginine in positions 114 and 133. Data here reported intend to contribute to the knowledge about the antigen-antibody interaction and to the drugs delivery research area

Immunodominant role of CCHA subunit of Concholepas hemocyanin is associated with unique biochemical properties.

Hemocyanin, the oxygen transporter metallo-glycoprotein from mollusks, shows strong relationship between its notable structural features and intrinsic immunomodulatory effects. Here we investigated the individual contribution of CCHA and CCHB subunits from Concholepas hemocyanin (CCH) to in vivo humoral immune response and their pre-clinical evaluation as immunotherapeutic agent in a mice bladder cancer model, in relation to their biochemical properties. To this end, subunits were purified and well characterized. Homogeneous subunits were obtained by anionic exchange chromatography, and its purity assessed by electrophoretic and immunochemical methods. While each CCH subunit contains eight functional units showing partial cross reaction, the vibrational spectral analysis showed several spectral differences, suggesting structural differences between them. In addition, we demonstrated differences in the carbohydrate content: CCHA had a 3.6% w/w sugar with both N- and O-linked moieties. In turn, CCHB had a 2.5% w/w sugar with N-linked, while O-linked moieties were nearly absent. Considering these differences, it was not possible to predict a priori whether the immunogenic and immunotherapeutic properties of subunits might be similar. Surprisingly, both subunits by itself induced a humoral response, and showed an antitumor effect in the bladder carcinoma cell line MBT-2. However, when immunologic parameters were analyzed, CCHA showed better efficiency than CCHB. No allergic reactions or any toxic effects were observed in mice treated with CCHA, sustaining its potential therapeutic use. Our study supports that CCHA subunit accounts for the most important features involved in the immunogenicity of CCH, such as better hydrophilicity and higher content of carbohydrates.

Crystal structure and vibrational spectra of polyamine-copper(II) complexes

The structures of [Cu(en)(H2O)2]SO4 (I), [Cu(en)2](NO3)2 (II) and [Cu(trien)I]I (III) have been determined by single crystal X-ray diffraction. ComplexI is monoclinic, space group C2/c, with unit cell parametera=7.232(1),b=11.725(2),c=9.768(1), β=105.50(1)°, andZ=4. ComplexII is also monoclinic, space group P21/a, witha=7.978(2),b=9.982(4),c=8.218(3), β=111.11(2)°, andZ=2. ComplexIII is orthorhombic, space group P212121, witha=8.098(1),b=11.902(1),c=13.682(2), andZ=4. The structures were solved by direct methods and refined by full-matrix least-squares to finalR values of 0.031, 0.043 and 0.036 for complexesI, II, andIII, respectively. ComplexesI andII show an octahedral coordination geometry. ComplexIII shows a square pyramidal coordination geometry. ComplexI forms infinite monodimensional chains where the SO42− ions acts as a bridge between two neighboringen molecules. The vibrational spectra of these complexes agree well with their crystal structures. Structure and stability of seven other related Cu(II) complexes of (trien), (dien)2, (en)2 and (en) are inferred in this study.

Vibrational study of N-phenyl-substituted hydroxynaphthylaldiminate copper(II) complexes

Abstract The infrared spectra of seven bis( N -phenyl-substituted hydroxynaphthylaldiminate) complexes of Cu(II) were scanned from 4000 to 100 cm −1 . Particular emphasis is given to the low-energy region. The assignment of the chelate normal modes is supported by an approximate normal coordinate analysis based on a simplified general valence force field, and the geometrical parameters of the bis( N -phenylsalicylaldiminate)Cu(II) complex. The bands near 390 and 285 cm −1 are assigned to the CuO and CuN stretching vibrations, respectively. The corresponding force constants are estimated to be 1.37 and 0.88 mdyn A −1 . Influence of the nature of the different ligands on the structure of complexes is discussed. Similarity of the vibrational spectra for all the complexes suggests that they possess the same type of structure.

Vibrational spectra and rotational isomerism in short chain n-perfluoroalkanes

Abstract Raman and infrared spectra of n-perfluorobutane, n-perfluorohexane and n-perfluorooctane show the existence of conformational equilibria in the gaseous and liquid states and in some solid phases of n-perfluorooctane. In the low temperature solid phase, only one isomer is present: an all- trans one, slightly distorted from planarity in C 6 and C 6 compounds. Temperature and pressure dependence of IR and Raman band intensities in the gas or liquid phases leads to the determination of enthalpy and molar volume differences between the isomers present at the equilibria. The results agree qualitatively with the predictions of a statistical mechanics model of overlapping hard spheres, but do not verify some quantitative conclusions from this model. Solid—solid phase changes of different types are found: n-perfluorobutane and n-perfluorohexane crystals present a solid—solid transition which involves a very weak thermal effect and is not related to internal rotations. Three crystalline modifications exist in n-perfluorooctane; the two highest temperature ones present a conformational disorder.