Stepwise solvation enthalpies of protonated water clusters: collision-induced dissociation as an alternative to equilibrium studies

The sodium cation affinities of six commonly used MALDI matrices are determined here using guided ion beam tandem mass spectrometry techniques. The collision-induced dissociation behavior of six sodium cationized MALDI matrices, Na + (MALDI), with Xe is studied as a function of kinetic energy. The MALDI matrices examined here include: nicotinic acid, quinoline, 3-aminoquinoline, 4-nitroaniline, picolinic acid, and 3-hydroxypicolinic acid. In all cases, the primary dissociation pathway corresponds to endothermic loss of the intact MALDI matrix. The cross section thresholds are interpreted to yield zero and 298 K Na + −MALDI bond dissociation energies (BDEs), or sodium cation affinities, after accounting for the effects of multiple ionneutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G* and MP2(full)/6-311+G(2d,2p)//B3LYP/6-31G* levels of theory are used to characterized the structures and energetics for these systems. The calculated BDEs exhibit very good agreement with the measured values for most systems. The experimental and theoretical Na + −MALDI BDEs determined here are compared with those previously measured by cation transfer equilibrium methods.

Section: Thermochemical Analysismentioning

confidence: 99%

Sodium Cation Affinities of Commonly Used MALDI Matrices Determined by Guided Ion Beam Tandem Mass Spectrometry

Chinthaka¹,

Rodgers²

2012

“…Therefore, loss of scattered reactant and product ions in the octopole region is almost entirely eliminated [34 -36]. Xe is used here, and in general for all of our CID measurements, because it is heavy and polarizable and therefore leads to more efficient kinetic to internal energy-transfer in the CID process [37][38][39]. Product and unreacted beam ions drift to the end of the octopole, where they are focused into a quadrupole mass filter for mass analysis, and subsequently detected with a secondary electron scintillation detector and standard pulse counting techniques.…”

Section: General Proceduresmentioning

confidence: 99%

“…All energy available is treated statistically because the ro-vibrational energy of the reactants is redistributed throughout the M ϩ (TMP) complex upon impact with the Xe atom. Because the CID processes examined here are simple noncovalent bond cleavage reactions, the E 0 (PSL) values determined by analysis with eq 1 can be equated to 0 K BDEs [37,55].…”

Section: Thermochemical Analysismentioning

confidence: 99%

A simple model for metal cation-phosphate interactions in nucleic acids in the gas phase: Alkali metal cations and trimethyl phosphate

Ruan

Huang

Rodgers

2008

Threshold collision-induced dissociation techniques are employed to determine the bond dissociation energies (BDEs) of complexes of alkali metal cations to trimethyl phosphate, TMP. Endothermic loss of the intact TMP ligand is the only dissociation pathway observed for all complexes. Theoretical calculations at the B3LYP/6-31G* level of theory are used to determine the structures, vibrational frequencies, and rotational constants of neutral TMP and the M ϩ (TMP) complexes. Theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311ϩG(2d,2p) level using the B3LYP/6-31G* optimized geometries. The agreement between theory and experiment is reasonably good for all complexes except Li ϩ (TMP hosphate esters are integral parts of many biologically active molecules ranging from nucleic acids, lipids, and ATP to pesticides and nerve agents [1][2][3]. Serving as link components in nucleic acids, phosphate esters connect thousands of base pairs to form large molecules that contain the genetic information. These phosphate groups are deprotonated under physiological conditions. The resulting negative charges along the phosphate backbone are stabilized and neutralized by the binding of metal cations. Metal cations can and often do exert a significant influence on nucleic acid structure and genetic information transfer [4]. Metal cation binding reduces the repulsion between neighboring nucleotide units, and therefore influences the stabilization and structural dynamics of nucleic acids and lipids in membranes. For example, alkali and alkaline earth metal cations, including the most biologically important of these cations, Na ϩ and Mg 2ϩ , prefer to bind to a phosphate group rather than to the nucleobases or sugar moieties [5]. Mg 2ϩ is found to increase the melting temperature of DNA [6]. Metal cations may also be involved in the functioning of nucleic acids, e.g., metal cations are required for the proper functioning of all ribozymes [7]. Metal cation-nucleic acid interactions are currently of great interest because metal cations and metal cation-ligand complexes bind to DNA and regulate gene expression, act as drugs, or can be used as tools for molecular biology studies [8]. Hendry and Sargeson studied metal cation-promoted phosphate ester hydrolysis and found that the rate of hydrolysis is modulated by the size of the metal cation and the ease of formation of a four-membered chelate ring [9]. Dempcy and Bruice found a pentacoordinate intermediate for the catalysis of alkyl phosphate diesters [10]. Schneider and Kabelac et al. [11] studied the distribution of five metal cations (i.e., Na, and Zn 2ϩ ) and water around a negatively charged phosphate group from various crystal structures, and found that all of the cations prefer asymmetric monodentate coordination over bidentate coordination. Their ab initio calculations suggest that bidentate binding of these metal cations to an isolated phosphate group is preferred, but that the presence of even a single water molecule alters this preference. Ab...

“…Experimentally determined threshold dissociation energies (E o ) were converted into binding enthalpies (⌬H) using eq 1 [61,65,66],…”

Section: Bet⅐limentioning

confidence: 99%

Binding energies of water to lithiated valine: Formation of solution-phase structure in vacuo

Lemoff

Williams

2004

100

Dissociation kinetics for loss of a water molecule from hydrated ions of lithiated valine, alanine ethyl ester and betaine are determined using blackbody infrared radiative dissociation at temperatures between Ϫ60 and 110°C. From master equation modeling of these data, values of the threshold dissociation energy are obtained for clusters containing one through three water molecules. By comparing the values for valine with its two isomers, one a model for the nonzwitterion structure, the other a model for the zwitterion structure, information about the structure of valine in these hydrated clusters is inferred. Structures, relative energies, and water binding energies for these ions are also calculated at the B3LYP/6-31ϩϩG** level of theory. With one water molecule, both experiment and theory indicate that valine is not a zwitterion and that the lithium ion coordinates with the amino nitrogen and the carbonyl oxygen (NO coordinated) and the water molecule interacts directly with the lithium ion. With two water molecules, the zwitterion and nonzwitterion structures are nearly isoenergetic, but the experiment clearly indicates a NO-coordinated nonzwitterion structure. With three water molecules, both the experimental data and theory indicate that the lithium ion binds to the carboxylate group of valine, i.e., valine is zwitterionic with three water molecules. The agreement between the experimentally determined and calculated binding energies is good for all the clusters, with deviations of Յ 0.12 eV. M olecular structure in solution depends on both the intrinsic properties of the molecule and on the effects of the surrounding solvent molecules. Exclusion of water from the interior of proteins influences protein folding and conformation. Similarly, lipid bilayer formation is due to differences in water interaction with the polar and hydrophobic ends of the lipid molecules. Gas-phase experiments make possible investigation of the intrinsic properties of the molecule. Differences between gas-phase and solution-phase structure can be attributed to solvent effects. Studies of gas-phase peptides indicate that ␣-helices can be stable in the absence of water and indicate that the propensity for helix formation for some amino acids differs in the gas phase and in solution [1,2]. For example, peptides with high valine content have a higher helix-forming propensity than their alanine analogues in the gas phase, but just the opposite is observed in aqueous solution [1].In the condensed phase, specific water molecules can play an important role in molecular structure. Such specific water molecules are often observed in crystal structures of proteins and other molecules. Evidence for specific water has been reported by Jarrold and coworkers for the molecule BPTI which tightly binds one water molecule in the gas phase [3,4]. Magic hydration numbers for gramicidin S at 8, 11, and 14 water molecules suggest stable solvation shells around the doubly protonated gas-phase ion [5], while a magic hydration number of 40 water molecules h...