Marianny Y. Combariza

Gas-Phase Ion-Molecule Reactions of Transition Metal Complexes: The Effect of Different Coordination Spheres on Complex Reactivity

Using a modified quadrupole ion trap mass spectrometer, a series of metal complex ions have been reacted with acetonitrile in the gas phase. Careful control of the coordination number and the type of coordinating functionality in diethylenetriamine-substituted ligands enable the effects of the coordination sphere on metal complex reactivity to be examined. The association reaction kinetics of acetonitrile with these pentacoordinate complexes are followed in order to obtain information about the starting complexes and the reaction dynamics. The kinetics and thermodynamics of acetonitrile addition to the metal complex ions are strongly affected by the chemical environment around the metal center such that significant differences in reactivity are observed for Co(II) and Cu(II) complexes with various coordination spheres. When thiophene, furan, or benzene moieties are present in the coordination sphere of the complex, addition of two acetonitrile molecules is readily observed. In contrast, ligands with better σ donors react mainly to add one acetonitrile molecule. Among the ligands with good σ donors, a clear trend in reactivity is observed in which complexes with nitrogen-containing ligands are the least reactive, sulfur-containing complexes are more reactive, and oxygen-containing complexes are the most reactive. In general, equilibrium and reaction rate constants seem to be consistent with the hard and soft acid and base (HSAB) principle. Interestingly, the presence of certain groups (e.g., pyridine and imidazole) in the coordination sphere clearly can change the acid character of the metal as seen by their effect on the binding properties of other functional groups in the same ligand. Finally, we conclude that because complexes with different coordination spheres react to noticeably different extents, ion-molecule (I-M) reactions may be potentially useful for obtaining coordination structure information for transition metal complexes.

The utility of ion–molecule reactions in a quadrupole ion trap mass spectrometer for analyzing metal complex coordination structure

Gas-phase ion–molecule reactions of metal complex ions with acetonitrile in a quadrupole ion trap mass spectrometer are shown to have some potential for determining the number and types of functional groups bound to a metal. Metal complexes with varying coordination spheres show significant differences in their gas-phase reactivity with acetonitrile. The relative product ion intensities observed in the mass spectrum after a given reaction time provide the appropriate data to distinguish complexes with different coordination spheres. Experimental parameters suspected to have an effect on the reproducibility of these intensities are examined in order to understand better which factors need to be most closely controlled to maximize precision. Ni(II) and Cu(II) complex ions of the pentadentate ligands 1,9-bis(2-imidazolyl)-2,5,8-triazanonane (DIEN-(imi)2) and 1,9-bis(2-tetrahydrofuranyl)-2,5,8-triazanonane (DIEN-(THF)2) are reacted in the gas-phase at different temperatures, pressures of acetonitrile, and pressures of buffer gas (helium) in a modified quadrupole ion trap mass spectrometer. The effects of such experimental variations on the product ion intensities are measured and analyzed. Under conditions where the precision is maximized, the temperature and acetonitrile pressure seem to have the biggest impact on the reproducibility of the resulting product ion intensity with the acetonitrile level being slightly more important. The reproducibility of ion intensities for the reactions of the Ni(II) complexes are the lowest due to their higher reactivity, while the measurements for the Cu(II) complexes have a higher degree of precision. In general, with careful control of the temperature and reagent gas pressure, ion–molecule (I–M) reactions seem to be a promising method for providing a rapid and sensitive analysis of the functional groups bound to a metal in a given complex.

A comparison of the gas, solution, and solid state coordination environments for the Ni(II) complexes of a series of linear penta- and hexadentate aminopyridine ligands with accessible Ni(III) oxidation states

Abstract The synthesis and characterization of the nickel(II) complexes of a series of pentadentate and hexadentate aminopyridine ligands that contain ethylenediamine and/or propylenediamine groups are described. The ligands include: 1,12-bis(2-pyridyl)-2,5,8,11-tetraazadodecane, TRIEN-pyr; 1,13-bis(2-pyridyl)-2,5,9,12-tetraazatridecane, DIEN-PN-pyr; 1,14-bis(2-pyridyl)-2,6,9,13-tetraazatetradecane, DIPN-EN-pyr; 1,15-bis(2-pyridyl)-2,6,10,14-tetraazapentadecane, TRIPN-pyr; 1,9-bis(2-pyridyl)-2,5,8-triazanonane, DIEN-pyr; and 1,11-bis(2-pyridyl)-2,6,10-triazaundecane, DIPN-pyr. The following methods were used to determine the binding geometries of the nickel(II) complexes in the solid, solution, and gas phases: magnetic susceptibility measurements, absorption spectroscopy, EPR spectroscopy, electrochemistry, and electrospray ionization mass spectrometry. All of the ligands form 6-coordinate compounds in the solid, liquid, and gas states, with the exception of the TRIEN-pyr, DIEN-PN-pyr(partially), DIPN-pyr, and DIEN-pyr ligands which form 5-coordinate species in the gas state. All of the complexes could be oxidized to Ni(III) species electrochemically, although the Ni(III) complexes of TRIPN-pyr and DIPN-pyr were much less stable than the other four ligands. EPR spectra of the frozen solutions showed the low spin d7 Ni(III) complexes of TRIEN-pyr and DIPN-EN-pyr to be similar to those that have been found for poly-aza macrocyclic compounds.

Exploring the composition of raw and delignified Colombian fique fibers, tow and pulp

As worldwide agricultural production rises, agro-industrial biomass becomes an abundant raw source for uses in energy and materials production. In Colombia fique plants (Furcraea spp.) are traditionally used to extract hard cellulosic fibers using mechanical decortication. Juice, pulp and tow, the by-products of this process, represent almost 95% of the fique leaf weight and are produced in large quantities. Data on these materials is scarce and greatly needed to guide and fuel fique agro-industrial development in Colombia. In this contribution we study the physicochemical properties of fique fibers and by-products (tow and pulp), before and after alkaline hydrogen peroxide treatment (AHP), using spectroscopic and microscopic techniques. Raw/clean fique tow is similar in structure and composition to fique fibers with average cellulose, hemicellulose and lignin contents of 52.3, 23.8 and 23.9%; in this by-product cellulose exists as a highly ordered structure with crystallinity index of 57%. Raw/clean fique pulp, composed of cellulose filaments from secondary cell walls and leaf epidermis, has average cellulose, hemicellulose and lignin contents of 30.5, 29.7 and 9.6%, with cellulose exhibiting an amorphous structure with a crystallinity index of 35%. The AHP treatment of these by-products effectively removed non-cellulosic compounds such as hemicellulose and lignin. After AHP lignin content in fique tow decreases to 2.8% while cellulose crystallinity increases up to 73%, Likewise, fique pulp shows a reduction in lignin to 2.1% and an increase in cellulose crystallinity up to 47%. IR spectroscopic analysis, after AHP, show a decrease of signals attributed to hemicellulose and lignin and FESEM images show a disruption of the lamellar structure in the macro fiber by the removal of hemicellulose, lignin and ground tissue, leaving cellulose fibrils exposed. As the first in-depth report on fique by-products characterization, our results indicate that pulp and tow are interesting lignocellulosic materials due to their significant content of crystalline and amorphous cellulose.

Oligo p-Phenylenevinylene Derivatives as Electron Transfer Matrices for UV-MALDI

AbstractPhenylenevinylene oligomers (PVs) have outstanding photophysical characteristics for applications in the growing field of organic electronics. Yet, PVs are also versatile molecules, the optical and physicochemical properties of which can be tuned by manipulation of their structure. We report the synthesis, photophysical, and MS characterization of eight PV derivatives with potential value as electron transfer (ET) matrices for UV-MALDI. UV-vis analysis show the presence of strong characteristic absorption bands in the UV region and molar absorptivities at 355 nm similar or higher than those of traditional proton (CHCA) and ET (DCTB) MALDI matrices. Most of the PVs exhibit non-radiative quantum yields (φ) above 0.5, indicating favorable thermal decay. Ionization potential values (IP) for PVs, calculated by the Electron Propagator Theory (EPT), range from 6.88 to 7.96 eV, making these oligomers good candidates as matrices for ET ionization. LDI analysis of PVs shows only the presence of radical cations (M+.) in positive ion mode and absence of clusters, adducts, or protonated species; in addition, M+. threshold energies for PVs are lower than for DCTB. We also tested the performance of four selected PVs as ET MALDI matrices for analytes ranging from porphyrins and phthalocyanines to polyaromatic compounds. Two of the four PVs show S/N enhancement of 1961% to 304% in comparison to LDI, and laser energy thresholds from 0.17 μJ to 0.47 μJ compared to 0.58 μJ for DCTB. The use of PV matrices also results in lower LODs (low fmol range) whereas LDI LODs range from pmol to nmol. Graphical Abstractᅟ

Spontaneous assembly of a hydrogen-bonded tetrahedron

Triphenylamine ortho-tricarboxylic acid (1) has been synthesized and the crystal structure reported. This molecule is shown to spontaneously self-assemble into a hydrogen-bonded tetrahedron. Furthermore, Electrospray Ionization Mass Spectroscopy shows evidence for the stability of such aggregates from an ethanol/water solution.