Modeling Interactions between an Amino Acid and a Metal Dication: Cysteine-Calcium(II) Reactions in the Gas Phase (original) (raw)
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Journal of Mass Spectrometry, 2005
The structure and energetics of complexes obtained upon interaction between cysteine and Zn 2+ , Cd 2+ , Hg 2+ and Cu 2+ cations were studied using quantum chemical density functional theory calculations with the 6-311++G * * orbital basis set and relativistic pseudopotentials for the cations. Different coordination sites for metal ions on several cysteine conformers were considered. In their lowest energy complexes with the amino acid, the Zn 2+ and Cd 2+ cations appear to be three-coordinated to carbonyl oxygen, nitrogen and sulfur atoms, whereas the Cu 2+ and Hg 2+ ions are coordinated to both the carbonyl oxygen and sulfur atoms of one of the zwitterion forms of the amino acid. Bonds of metal cations with the coordination sites are mainly ionic except those established with sulfur, which show a small covalent character that become most significant when Cu 2+ and Hg 2+ are involved. The order of metal ion affinity proposed is Cu > Zn > Hg > Cd.
Structural Chemistry, 2013
In recent years, interactions of metal ions with amino acid derivatives have been studied extensively due to their immense importance in the life-supporting processes. Here, we report the synthesis of three metal (Ni 2? , Cu 2? , and Zn 2?) complexes of N-acetyl-l-cysteine (NAC) using a solvent-free solid-state method. Characterization of the complexes by elemental analyses, molar conductance, SEM, infrared and electronic absorption spectra reveals that the metal ions bind to the NAC molecules in 1:2 molar ratio (metal:ligand) via the S-atoms. Theoretical calculations are carried out using the B3LYP hybrid functional in combination with 6-31??G(d,p) and LANL2DZ basis sets to investigate the effects of metal coordination on the backbone structural features of NAC and geometry about the a-carbon atom. The molecular geometries of NAC as well as its metal complexes are fully optimized in gas phase without applying any geometrical constraint, and a second derivative analysis confirms that all the optimized geometries are true minima. TD-DFT single-point calculations are performed in aqueous phase to obtain the theoretical k max values. The gas-phase interaction enthalpies (metal ion binding affinities), Gibbs energies, HOMO/ LUMO energies as well as their energy gaps, rotational constants, dipole moments, and theoretically predicted vibrational spectra of all the reaction species are also calculated and thoroughly analyzed. Most of the experimental results are well reproduced by the B3LYP level of calculations. Metal ion coordination to NAC modifies its backbone structural features as well as the geometry about the a-carbon atom.
Structures and fragmentations of Cobalt(II)–cysteine complexes in the gas phase
Journal of Mass Spectrometry, 2007
The electronebulization of a cobalt(II)/cysteine(Cys) mixture in water/methanol (50/50) produced mainly cobalt-cationized species. Three main groups of the Co-cationized species can be distinguished in the ESI-MS spectrum: (1) the cobalt complexes including the cysteine amino acid only (they can be singly charged, for example, [Co(Cys)n− H]+ with n = 1–3 or doubly charged such as [Co + (Cys)2]2+); (2) the cobalt complexes with methanol: [Co(CH3OH)n− H]+ with n = 1–3, [Co(CH3OH)4]2+; and (3) the complexes with the two different types of ligands: [Co(Cys)(CH3OH) − H]+. Only the singly charged complexes were observed. Collision-induced dissociation (CID) products of the [Co(Cys)2]2+, [Co(Cys)2 − H]+ and [Co(Cys) − H]+ complexes were studied as a function of the collision energy, and mechanisms for the dissociation reactions are proposed. These were supported by the results of deuterium labelling experiments and by density functional theory calculations. Since [Co(Cys) − H]+ was one of the main product ions obtained upon the CID of [Co(Cys)2]2+ and of [Co(Cys)2 − H]+ under low-energy conditions, the fragmentation pathways of [Co(Cys) − H]+ and the resulting product ion structures were studied in detail. The resulting product ion structures confirmed the high affinity of cobalt(II) for the sulfur atom of cysteine. Copyright © 2007 John Wiley & Sons, Ltd.
Journal of the American Chemical Society, 2007
Hydrogen-deuterium exchange experiments were carried out on the conjugate base of cysteine with four different deuterated alcohols. Three H/D exchanges are observed to take place in each case, and a relay mechanism which requires the SH and CO2H groups to have similar acidities and subsequently proceeds through a zwitterionic intermediate is proposed. Gas-phase acidity measurements also were carried out in a quadrupole ion trap using the extended kinetic method and in a Fourier transform mass spectrometer by an equilibrium determination. The results are in excellent accord with each other and high-level ab initio and density functional theory calculations and indicate that the side-chain thiol in cysteine is more acidic than the carboxyl group by 3.1 kcal mol-1. Deprotonated cysteine is thus predicted to be a thiolate ion. A zwitterionic species also was located on the potential energy surface, but it is energetically unfavorable (+10.1 kcal mol-1).
Complexation Studies of N, N′-ethylenedi-L-cysteine with Some Metal Ions
Journal of Solution Chemistry, 2009
As part of a search for environmentally friendly metal chelating ligands, the stability constants of N, N -ethylenedi-L-cysteine (EC) complexes with Ca(II), Cu(II), Mg(II) and Mn(II) were determined by potentiometry with a glass electrode in aqueous solutions containing 0.1 mol·L −1 KCl at 25°C. Final models are proposed. For the Ca(II)-EC system, the overall stability constants are log 10 β CaHL = 14.53 ± 0.03, log 10 β CaL = 4.79 ± 0.01 and log 10 β CaL2 = 8.38 ± 0.04. For the M(II)-EC systems, where M = Cu(II) or Mg(II), the overall stability constants are log 10 β CuHL = 31.19 ± 0.02 and log 10 β CuL = 27.02 ± 0.06 for Cu(II), and are log 10 β MgHL = 14.84 ± 0.02 and log 10 β MgL = 6.164 ± 0.008 for Mg(II). For the Mn(II)-EC system, the overall stability constant is log 10 β MnL = 10.12 ± 0.01.
2013
In the work ionophoretic technique has been used for the study of Fe(III), Cu(II), Ni(II) and Co(II)-cysteine binary and Fe(III), Cu(II), Ni(II) and Co(II)-cysteine-NTA (Nitrilotriacetic acid) mixed complexes. The stability constants of metal-cysteine binary complexes are found to be 10 11.30 , 10 10.00 , 10 9.10 , 10 8.90 and the stability constants of metal-cysteine-NTA mixed complexes have been found to be 10 8.40 , 10 6.80 , 10 6.00 10 5.50 for Fe(III), Cu(II), Ni(II) and Co(II) complexes respectively at µ = 0.1 M (HClO 4) and 25 °C.
International Journal of Quantum Chemistry, 2011
The structure, relative stability, and anharmonic vibrational frequencies of the most stable complexes between glycine, serine, and cysteine with Ca 2þ have been calculated by means of DFT approaches. The global minimum of the potential energy surface for glycine-Ca 2þ complex corresponds to the salt-bridge (SB) form, whereas for serine-and cysteine-Ca 2þ complexes is a charge-solvated (CS) structure in which the metal dication is bound to the carbonyl group of the acidic function, the amino group and the OH (SH) group of the alcohol (enethiol) function. The energy gap between the CS global minimum and the SB form decreases significantly on going from serine to cysteine. Hence, for the latter both CS and SB forms could coexist in the gas phase mainly at high temperatures. Anharmonicity effects are lower than 10%, and do not affect significantly the assignment of the fundamental vibrational modes. The calculated infrared spectra of the SB and CS forms of glycine-, serine-, and cysteine-Ca 2þ complexes show very distinctive characteristics, which should permit to unambiguously characterize them by IR multiphoton dissociation (IRMPD) techniques. V
Modelling peptide–metal dication interactions: formamide–Ca2+ reactions in the gas phase
Organic & Biomolecular Chemistry, 2012
The collision induced dissociation of formamide-Ca 2+ complexes produced in the gas phase through nanoelectrospray ionization yields as main products ions [CaOH] + , [HCNH] + , [Ca(NH 2 )] + , HCO + and [Ca(NH 3 )] 2+ and possibly [Ca(H 2 O)] 2+ and [C,O,Ca] 2+ , the latter being rather minor. The mechanisms behind these fragmentation processes have been established by analyzing the topology of the potential energy surface by means of B3LYP calculations carried out with a core-correlated cc-pWCVTZ basis set. The Ca 2+ complexes formed by formamide itself and formimidic acid play a fundamental role. The former undergoes a charge separation reaction yielding [Ca(NH 2 )] + + HCO + , and the latter undergoes the most favorable Coulomb explosion yielding [Ca-OH] + + [HCNH] + and is the origin of a multistep mechanism which accounts for the observed loss of water and HCN. Conversely, the other isomer of formamide, amino(hydroxyl)carbene, does not play any significant role in the unimolecular reactivity of the doubly charged molecular cation.