Chirality at metal and helical ligand folding in optical isomers of chiral bis(naphthaldiminato)nickel(II) complexes

Enantiopure bis[(R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]nickel(ii) complexes Ar = C6H5 (1R or 1S), p-OMeC6H4 (2R or 2S), and p-BrC6H4 (3R or 3S) are synthesized from the reactions between (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldimine and nickel(ii) acetate. Circular-dichroism spectra and their density-functional theoretical simulation reveal the expected mirror image relationship between the enantiomeric pairs 1R/1S and 3R/3S in solution. CD spectra are dominated by the metal-centered Λ- or Δ-chirality of non-planar four-coordinated nickel, this latter being in turn dictated by the ligand chirality. Single crystal structure determination for 1R and 1S shows that there are two symmetry-independent molecules (A and B) in each asymmetric unit that give a Z′ = 2 structure. Two asymmetric and chiral bidentate N^O-chelate Schiff base ligands coordinate to the nickel atom in a distorted square planar N2O2-coordination sphere. The conformational difference between the symmetry-independent molecules arises from the "up-or-down" folding of the naphthaldiminato ligand with respect to the coordination plane, which creates right- (P) or left-handed (M) helical conformations. Overall, the combination of ligand chirality, chirality at the metal and ligand folding gives rise to discrete metal helicates of preferred helicity in a selective way. Cyclic voltammograms (CV) show an oxidation wave at ca. 1.30 V for the [Ni(L)2]/[Ni(L)2]+ couple, and a reduction wave at ca. -0.35 V for the [Ni(L)2]/[Ni(L)2]- couple in acetonitrile

The folding of a metallopeptide

We have applied solid-phase synthesis methods for the construction of tris(bipyridyl) peptidic ligands that coordinate Fe(II) ions with high affinity and fold into stable mononuclear metallopeptides. The main factors influencing the folding pathway and chiral control of the peptidic ligands around the metal ions have been studied both by experimental techniques (CD, UV-vis and NMR) and molecular modeling tools. Amongst the numerous molecular variables that have been studied, this study clearly illustrates how the chirality of a given set of aminoacids (proline in this case) of the peptide dictates the chirality of the metal center of the resulting metallopeptide. Moreover, the relatively hydrophobic peptidic models used in this work show that the most stable structures present reduced solvent contacts and, in counterpart, stabilize the cis configuration of the proline residuesWe are thankful for the support given by the Spanish grants SAF2013-41943-R, CTQ2012-31341, CTQ2011-23336 and CTQ2013-49317-EXP; the ERDF and the European Research Council (Advanced Grant 340055); the Xunta de Galicia grants GRC2013-041 and PGIDIT08CSA-047209PR and the Generalitat de Catalunya grant 2009SGR68. Support of COST Action CM1105 is kindly acknowledged. G.R. thanks the INL for his PhD fellowshipS

Circular Dichroism Spectroscopies and Hyperfine Shift in Metal Complexes and Organic Molecules

The determination of the molecular structure in solution is an important target of modern chemistry. In many fields, the knowledge of the solution structure and dynamics is a fundamental piece of information for a complete understanding of chemical processes, from catalytic mechanisms to the biological activities of biopolymers. However, there is not a general strategy to approach the problem of solving solution structures for any type of molecule. The research presented in this thesis concerns the development of new protocols of structural determination using lanthanide properties, but, at the same time, the application or upgrading of well-known experimental methodologies such as ECD (electronic circular dichroism) or VCD (vibrational circular dichroism) and the theoretical simulation of chiroptical properties by means of DFT (density functional theory) and its time-dependent version (TD-DFT). All the substances we took into consideration were chosen for their importance both in inorganic and organic chemistry. In particular, we referred: (i) A new benchmark in the pseudocontact shift (PCS) extraction, developing two different methods to achieve the Fermi Contact (or FC)/PCS separation in the analysis of paramagnetic NMR spectra of lanthanide complexes. Our methodology is based on the mathematical analysis of the chemical shift along the series with the same ligand (all-lanthanide protocol) or in an extended range of temperature (temperature-based method); (ii) Studies of the near-IR (NIR) emission of the excited states of Yb3+ (around λ=1000 nm) in three different systems. For all the presented cases, a new empirical correction to Richardson equations are introduced in order to improve the prediction of the NIR-emission profile of Yb3+, comparing each results with the experimental ones. Our results open the way to a new employment of lanthanoid luminescence imaging in vivo; (iii) Different examples of uses of ECD/TD-DFT, spanning from the study of metal-centered Λ-Δ chirality in some metal complexes with Schiff bases as ligand (Cu2+ or Ni2+), to conformational/configurational investigations in purely organic systems (i.e. two enantiomers separated by HPLC of one particular Linezolid, a specific class of new antibiotics). We also report our results on a family of chiral aryl benzyl sulfoxides with perfluorinated aryl or benzyl rings. In this example, only a detailed TD-DFT study allowed us to assign correctly ECD spectra and ultimately the absolute configuration, while a commonly employed empirical assignment of experimental ECD pattern (as reported in literature) is questionable; (iv) Interpretation of VCD signal enhancement in complexes containing metals with low-lying electronic state (or LEESs). First, we report a self-assembled multicomponent system with d-metals and α-aminoacids, where the enhanced VCD signals allow us to assign the absolute configuration (AC) of the aminoacid component with a very low amount of sample. Second, we analyze a few lanthanide complexes with unpredictable experimental VCD enhancement. Using Richardson’s model, we discuss the CF energies around the lanthanide ion, the geometrical conditions and the electronic state energy of the lanthanoid ion in these systems, in order to justify the anomalous VCD enhancement

Studio dell'effetto LIVE in alcuni complessi di leganti chirali con ioni trivalenti dei Lantanidi soggetti a fenomeni di LLESs

Sintesi di complessi chirali a base di Ioni trivalenti delle Terre rare e leganti Salen-type. Caratterizzazione strutturale tramite NMR. Calcolo dei parametri di campo cristallino. Determinazione delle proprietà chirottiche tramite spettroscopie NIR-CD, ECD e VCD

Investigation of zero-valent iron (ZVI)/H2O continuous processes using multivariate analysis and artificial neural networks

Multivariate statistical techniques and artificial neural networks (ANNs) were used for the analysis, interpretation, and modeling of the results obtained in the study of zero-valent iron (ZVI) reactive beds designed for contaminant removal. A wide range of operating conditions was evaluated through more than 120 rapid small-scale column tests (RSSCT). The production of Fe(II) and Fe(III) species, dissolved oxygen consumption, and pH variation along the reactive bed were used as response variables for evaluating the process performance. Due to the complexity of the system, and the difficulty in defining and fitting kinetic parameters, ANN models were used to simulate the system without the need for kinetic expressions. Therefore the latter were used for assessing the system behavior within the investigated experimental domain and for evaluating the relative importance of the operating factors. In addition, the application of the multivariate techniques cluster analysis (CA) and principal component analysis (PCA) revealed underlying relationships among the response variables. Moreover, although multiple physicochemical processes are involved, the results obtained through PCA indicate that the main trends can be rationalized by considering a few key reactions only. The strategy of analyzing RSSCT results with different numerical techniques provides valuable knowledge for designing real-scale ZVI-based treatments aimed at the efficient elimination of a wide range of contaminants in the aqueous phase.Fil: Berardozzi, Eliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Donadelli, Jorge Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Teixeira, Antonio C. S. C.. Universidade de Sao Paulo; BrasilFil: Guardani, Roberto. Universidade de Sao Paulo; BrasilFil: Garcia Einschlag, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Syntheses, Spectroscopy, and Structural Analyses of Dinuclear Chiral-at-Metal μ-Aqua-tetrakis[(R or S)-N-1-(Ar)ethyl-sal-icylaldiminato]di-Λ- or -Δ-nickel(II) Complexes

Enantiopure dinuclear -aqua-tetrakis[(R or S)-N-1-(Ar)ethylsalicylaldiminato]di-- or --nickel(II) [Ar = C6H5 (R-1/S-1), p-MeOC6H4 (R-2/S-2), p-ClC6H4 (R-3/S-3), p-BrC6H4 (R-4)] complexes have been synthesized from the reaction between (R or S)-N-1-(Ar)ethylsalicylaldimine and nickel(II) acetate. Their CD spectra demonstrate chirality transfer from the ligands to the metal ions and a mirror-image relationship for the enantiomeric pair R-3/S-3 in thf. DSC analyses show that the complexes exhibit an irreversible dissociation to the mononuclear species, which in turn undergo decomposition. The H-1 NMR spectra reveal the presence of four salicylaldiminates, one aqua ligand, and two molecules of methanol in each dinuclear complex. They also confirm the existence of a dinuclear-bridged aqua bis-octahedral Ni-II complex in solution. The IR spectra in CH2Cl2 show a very strong band at around 2306 cm(-1) due to the O-H of the bridged aqua ligand. The X-ray structures of R-2, S-2, R-3, and S-3 confirm the formation of dinuclear compounds comprising two nickel ions, four salicylaldiminates, and one aqua ligand with two molecules of methanol (or water in S-2). Each nickel ion is surrounded by two N,O-chelating salicylaldiminates, a bridging salicyl-O atom from the neighboring nickel ion, and a bridging aqua ligand in a distorted octahedral polyhedron. Analyses of the absolute structures reveal a diastereomeric induction of the R or S ligand giving a or configuration at the nickel atoms in R-2/3 or S-2/3 that is independent of the ligand substituents

Co(II)-induced giant vibrational CD provides a new design of methods for rapid and sensitive chirality recognition

We designed a stereodynamic system, where the chirality of the analyte serves as a template for the helicity of the first coordination sphere of Co(ii). Giant VCD bands induced by Co(ii) allow the measurement of a completely significant and conclusive VCD spectrum in only a few seconds and/or on minute quantities of the analyte. This paves the way for the development of similar protocols, overcoming the limitations due to weak VCD signals for the assignment of absolute configurations