Noncovalent interactions of Zn+ with N-donor ligands (pyridine, 4,4'-dipyridyl, 2,2'-dipyridyl, and 1,10-phenanthroline): collision-induced dissociation and theoretical studies.

The binding interactions in complexes of Zn(+) with nitrogen donor ligands, (N-L) = pyridine (x = 1-4), 4,4'-dipyridyl (x = 1-3), 2,2'-dipyridyl (x = 1-2), and 1,10-phenanthroline (x = 1-2), are examined in detail. The bond dissociation energies (BDEs) for loss of an intact ligand from the Zn(+)(N-L)(x) complexes are reported. Experimental BDEs are obtained from thermochemical analyses of the threshold regions of the collision-induced dissociation cross sections of Zn(+)(N-L)(x) complexes. Density functional theory calculations at the B3LYP/6-31G* level of theory are performed to determine stable structures of these species and to provide molecular parameters needed for the thermochemical analysis of experimental data. Relative stabilities of the various conformations of these N-donor ligands and their complexes to Zn(+) as well as theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) and M06/6-311+G(2d,2p) levels of theory using the B3LYP/6-31G* optimized geometries. The experimental BDEs for the Zn(+)(N-L)(x) complexes are in reasonably good agreement with values derived from density functional theory calculations. BDEs derived from M06 calculations provide better agreement with the measured values than those based on B3LYP calculations. Trends in the sequential BDEs are explained in terms of sp polarization of Zn(+) and repulsive ligand-ligand interactions. Comparisons are made to the analogous Cu(+)(N-L)(x) and Ni(+)(N-L)(x) complexes previously studied.

Noncovalent interactions of Ni+ with N-donor ligands (pyridine, 4,4'-dipyridyl, 2,2'-dipyridyl, and 1,10-phenanthroline): collision-induced dissociation and theoretical studies.

Kinetic-energy-dependent collision-induced dissociation (CID) of complexes of a variety of N-donor ligands (N-L) with Ni(+), Ni(+)(N-L)(x), is studied using guided ion beam tandem mass spectrometry. The N-donor ligands investigated include: pyridine, 4,4'-dipyridyl, 2,2'-dipyridyl, and 1,10-phenanthroline. For most of the Ni(+)(N-L)(x) complexes, CID results in endothermic loss of a single neutral N-L ligand as the primary dissociation pathway. Sequential dissociation of additional N-L ligands is observed at elevated energies for the pyridine and 4,4'-dipyridyl complexes containing more than one ligand. The cross-section thresholds for the primary dissociation pathways are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) of the Ni(+)(N-L)(x) complexes after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and their lifetimes for dissociation. Density functional theory calculations at the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G* level are performed to obtain model structures, molecular parameters, and energetics for the neutral N-L ligands and the Ni(+)(N-L)(x) complexes. In general, theory is found to overestimate the strength of binding to the first N-L ligand, and underestimate the strength of binding to additional ligands. Trends in the sequential BDEs of the Ni(+)(N-L)(x) complexes are examined and compared to complexes of Ni(+), to several other ligands previously investigated. The trends in the sequential BDEs are primarily determined by the valence electronic configuration and the effects of sd-hybridization of Ni(+) but are also influenced by repulsive ligand-ligand interactions. Natural bond orbital analyses indicate that the binding in these complexes is primarily noncovalent.

Synthesis, redox, and amphiphilic properties of responsive salycilaldimine-copper(II) soft materials.

Hydrolysis of the asymmetric pyridine- and phenol-containing ligand HL (1) (2-hydroxy-4-6-di- tert-butylbenzyl-2-pyridylmethyl)imine) led to the use of bis-(3,5-di -tert-butyl-2-phenolato-benzaldehyde)copper(II), [Cu (II)(L (SAL)) 2] ( 1) as a precursor for bis-(2,4-di- tert-butyl-6-octadecyliminomethyl-phenolato)copper(II), [Cu (II)(L (2)) 2] ( 3), bis-(2,4-di- tert-butyl-6-octadecyl aminomethyl-phenolato)copper(II), [Cu (II)(L (2A)) 2] ( 3'), and bis-(2,4-di- tert-butyl-6-[(3,4,5-tris-dodecyloxy-phenylimino)-methyl]-phenolato)copper(II), [Cu (II)(L (3)) 2] ( 4). These complexes exhibit hydrophilic copper-containing head groups, hydrophobic alkyl and alkoxo tails, and present potential as precursors for redox-responsive Langmuir-Blodgett films. All systems were characterized by means of elemental, spectrometric, spectroscopic, and electrochemical techniques, and their amphiphilic properties were probed by means of compression isotherms and Brewster angle microscopy. Good redox activity was observed for 3 with two phenoxyl radical processes between 0.5 and 0.8 V vs Fc (+)/Fc, but this complex lacks amphiphilic behavior. To attain good balance between redox response and amphiphilicity, increased core flexibility in 3' and incorporation of alkoxy chains in 4 were attempted. Film formation with collapse at 14 mN.m (-1) was observed for the alkoxy-derivative but redox-response was seriously compromised. Core flexibility improved Langmuir film formation with a higher formal collapse and showed excellent cyclability of the ligand-based processes.

Bond dissociation energies and equilibrium structures of Cu+(MeOH)x, x = 1-6, in the gas phase: competition between solvation of the metal ion and hydrogen-bonding interactions.

The solvation of Cu+ by methanol (MeOH) was studied via examination of the kinetic energy dependence of the collision-induced dissociation of Cu+(MeOH)x complexes, where x = 1-6, with Xe in a guided ion beam tandem mass spectrometer. In all cases, the primary and lowest-energy dissociation channel observed is the endothermic loss of a single MeOH molecule. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple ion-neutral collisions, kinetic and internal energy distributions of the reactants, and lifetimes for dissociation. Density functional theory calculations at the B3LYP/6-31G* level are performed to obtain model structures, vibrational frequencies, and rotational constants for the Cu+(MeOH)x complexes and their dissociation products. The relative stabilities of various conformations and theoretical BDEs are determined from single-point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using B3LYP/6-31G*-optimized geometries. The relative stabilities of the various conformations of the Cu+(MeOH)x complexes and the trends in the sequential BDEs are explained in terms of stabilization gained from sd hybridization, hydrogen-bonding interactions, electron donor-acceptor natural bond orbital stabilizing interactions, and destabilization arising from ligand-ligand repulsion.

Noncovalent interactions of Cu+ with N-donor ligands (pyridine, 4,4-dipyridyl, 2,2-dipyridyl, and 1,10-phenanthroline): collision-induced dissociation and theoretical studies.

Collision-induced dissociation of complexes of Cu+ bound to a variety of N-donor ligands (N-L) with Xe is studied using guided ion beam tandem mass spectrometry. The N-L ligands examined include pyridine, 4,4-dipyridyl, 2,2-dipyridyl, and 1,10-phenanthroline. In all cases, the primary and lowest-energy dissociation channel observed corresponds to the endothermic loss of a single intact N-L ligand. Sequential dissociation of additional N-L ligands is observed at elevated energies for the pyridine and 4,4-dipyridyl complexes containing more than one ligand. Ligand exchange processes to produce Cu+Xe are also observed as minor reaction pathways in several systems. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level are performed to obtain model structures, vibrational frequencies, and rotational constants for the neutral N-L ligands and the Cu+(N-L)x complexes. The relative stabilities of the various conformations of these N-L ligands and Cu+(N-L)x complexes as well as theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using B3LYP/6-31G* optimized geometries. Excellent agreement between theory and experiment is observed for all complexes containing one or two N-L ligands, while theory systematically underestimates the strength of binding for complexes containing more than two N-L ligands. The ground-state structures of these complexes and the trends in the sequential BDEs are explained in terms of stabilization gained from sd-hybridization and repulsive ligand-ligand interactions. The nature of the binding interactions in the Cu+(N-L)x complexes are examined via natural bond orbital analyses.

Sodium cation affinities of MALDI matrices determined by guided ion beam tandem mass spectrometry: application to benzoic acid derivatives.

Threshold collision-induced dissociation of Na(+)(xBA) complexes with Xe is studied using guided ion beam mass spectrometry. The xBA ligands studied include benzoic acid and all of the mono- and dihydroxy-substituted benzoic acids: 2-, 3-, and 4-hydroxybenzoic acid and 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dihydroxybenzoic acid. In all cases, the primary product corresponds to endothermic loss of the intact xBA ligand. The cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) for Na(+)-xBA after accounting for the effects of multiple ion-neutral collisions, internal and kinetic energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes and provide the molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical BDEs are determined at the B3LYP/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) levels using the B3LYP/6-31G* optimized geometries. The trends in the measured BDEs suggest two very different binding modes for the Na(+)(xBA) complexes, while theory finds four. In general, the most stable binding conformation involves the formation of a six-membered chelation ring via interaction with the carbonyl and 2-hydroxyl oxygen atoms. The ground state geometries of the Na(+)(xBA) complexes in which the ligand does not possess a 2-hydroxyl group generally involve binding of Na(+) to either the carbonyl oxygen atom or to both oxygen atoms of the carboxylic acid group. These binding modes tend to be competitive because the enhancement in binding associated with the chelation interactions in the latter is mediated by steric repulsion between the hydroxyl and ortho hydrogen atoms. When possible, hydrogen bonding interactions with the ring hydroxyl group(s) enhance the stability of these complexes. The agreement between the theoretical and experimental BDEs is quite good for B3LYP and somewhat less satisfactory for MP2(full).

Solvation of copper ions by imidazole: structures and sequential binding energies of Cu+(imidazole)x, x = 1-4. Competition between ion solvation and hydrogen bonding.

The sequential bond dissociation energies of Cu+(imidazole)x, where x = 1-4 are determined by analysis of the kinetic energy dependence of the collision-induced dissociation with Xe in a guided ion beam tandem mass spectrometer. In all cases, the primary and lowest energy dissociation channel observed is the endothermic loss of an intact imidazole molecule. The primary cross section thresholds are interpreted to yield 0 K and 298 K bond dissociation energies after accounting for the effects of multiple ion-neutral collisions, kinetic and internal energy distributions of the reactants, and dissociation lifetimes. To obtain model structures, vibrational frequencies, rotational constants and energetics for the Cu+(imidazole)x complexes and their dissociation products, density functional theory calculations at the B3LYP/6-31G* level are performed. Theoretical bond dissociation energies are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using the B3LYP/6-31G* optimized geometries. Excellent agreement between theory and experiment is observed for the Cu+(imidazole)x complexes, where x = 1, 2 and 4. In contrast, theory systematically underestimates the strength of the binding in the Cu+(imidazole)3 complex. The ground state structures of the Cu+(imidazole), complexes and the trends in the sequential bond dissociation energies are explained in terms of stabilization gained from sd hybridization and hydrogen bonding interactions and destabilization arising from ligand-ligand repulsion. The trends in the binding of these complexes are also examined to provide insight into the structural and functional roles that histidine and other ligands play in the behavior of metalloproteins and metalloenzymes.