CBS-QB3 Model Chemistry Research Articles

Benchmarking model chemistry composite calculations for vertical ionization potential of molecular systems

In chemical science, the vertical ionization potential (VIP) is a crucial metric for understanding the electronegativity, hardness and softness of chemical material systems as well as the electronic structure and stability of molecules. Ever since the last century, the model chemistry composite methods have witnessed tremendous developments in computing the thermodynamic properties as well as the barrier heights. However, their performance in realm of the vertical electron processes of molecular systems has been rarely explored. In this study, we for the first time benchmarked the model chemistry composite methods (e.g., CBS-QB3, G4 and W1BD) in comparison with the commonly used Koopmans's theorem (KT), electron propagator theory (e.g., OVGF, D2, P3 and P3+) and CCSD(T) methods in calculating the VIP for up to 613 molecular systems with available experimental measurements. The large-scale test calculations strongly showed that the CBS-QB3 model chemistry composite technique can be well recommended to calculate VIP from the perspectives of accuracy, economy and applicability. Notably, the VIP values of up to 7 molecules were identified to have the absolute errors of larger than 0.3 eV at all calculation levels, which have strong hints that their VIP experimental values should be re-investigated.

A comprehensive model for the role of water and silanols in the amine catalyzed aldol reaction

The experimentally observed effects of water, and the effects of silanol groups, on the liquid-phase amine-catalyzed aldol reaction of acetone with 4-nitrobenzaldehyde have been elucidated with a comprehensive theoretical model describing the reaction kinetics. The CBS-QB3 model chemistry is used, with bulk solvent effects accounted for according to COSMO-RS theory, and water molecules explicitly considered. Two promoting water molecules were found to be optimal in reducing the Gibbs free energy barriers for reactions involving a proton transfer, i.e., the carbinolamine and enamine formation steps, and the aldol product liberation step. The presence of one water molecule in the carbon-carbon coupling step was already sufficient to prevent the formation of a site-blocking enamine species, which would otherwise lead to deactivation of the amine. Compared to a single water molecule, isolated silanol groups were found to assist the amine in a similar and slightly more pronounced manner, resulting in overall lower barriers for all transition states. Promotion by two vicinal silanols resulted in even lower barriers. The effect of water was found to be more pronounced in apolar hexane as compared to DMSO, i.e., resulting in a less pronounced deactivation of the amine, and lower barriers for reactions where water is assisting in the transition state.

Rational design of nucleophilic amine sites via computational probing of steric and electronic effects

Accessibility of the nucleophilic site in organocatalysts is essential to ensure adequate catalytic activity. Gas-phase trimethylborane (TMB) Lewis basicity and Brønsted proton basicity of several amine based organocatalysts have been calculated using the CBS-QB3 model chemistry. This TMB basicity scale can, as opposed to the proton basicity scale, account for steric effects encountered in the initial nucleophilic attack of the nitrogen free electron pair on a substrate. Since such a step is the first one in several amine catalyzed reactions, severe steric hindrance of the nucleophilic center would render the catalyst ineffective. Comparing the TMB basicity and proton basicity with the experimentally observed catalytic activity of both homogeneous and heterogeneously supported amine sites found in literature for the aldol reaction of acetone with 4-nitrobenzaldehyde showed that, due to the inclusion of these steric effects, the TMB basicity scale is a much better predictor of catalytic activity than the proton basicity. According to this computational Lewis basicity scale, potential steric hindrance in alternative nitrogen containing active sites was probed. This resulted in 3-propylpyrrolidine being proposed among the most promising monofunctional amine groups and 1-(methylamino)propan-2-ol among the most promising bifunctional amine-hydroxyl groups for heterogeneous aldol reaction catalysts.

Generation and Dissociation of RCOOCaCl2 - and other Carboxylate-Substituted Superhalogens: CO2 Capture and Implications for Structure Analysis.

Carboxylate-substituted superhalogens of the type RCOOMX2 - (M=Mg, Ca, Sr, Ba, Mn, Co, Ni, Zn; X=Cl, Br) are easily accessible in the gas phase by electrospray ionisation. Their collision-induced dissociation (CID) characteristics have been probed by using ion-trap and triple-quadrupole mass analysers with particular emphasis on the behaviour of RCOOCaCl2 - -type ions. In the ion trap these appear to react readily with residual water to yield HOCaCl2 - as the hydrolysis product. In the absence of water, a collision-induced McLafferty-type rearrangement takes over to produce HCaCl2 - with the expulsion of an olefin and CO2 . A brief computational analysis using the CBS-QB3 model chemistry provides a satisfactory rationale for these observations. If complexed with MX2 (M=Mg, Ca, Sr, Ba), long-chain unsaturated aliphatic carboxylate anions undergo various backbone cleavages upon collision. These lead to structure-diagnostic olefin losses because the position of the double bonds remains intact. Such cleavages are absent in the bare ion RCOO- . The long-chain ions RCOOMX2 - also produce the intriguing species [CO2 ]MX2 -. . These have been characterised by CID experiments, and theory indicates that they may be viewed as a CO2 molecule captured by the salt anion MX2 -. . Finally, it is shown that the CID spectra of RCOOCaCl2 - ions derived from all-trans retinoic acid, a compound of current interest in biochemistry and medicine, show a unique structure-diagnostic dissociation that may greatly aid its qualitative and quantitative analysis.

The hydrogen-bridged radical cation [NH2C[dbnd]O⋯H⋯O[dbnd]CHCH3][rad]+ and its dissociation by proton-transport catalysis

The title ion (HBRC-1) is an easily accessible hydrogen-bridged radical cation when generated by the decarbonylation of ionized ethyl oxamate, NH2COCOOC2H5.Tandem mass spectrometry experiments and CBS-QB3 model chemistry calculations agree that HBRC-1 dissociates into HC(OH)NH2++CH3CO by proton-transport catalysis. Its CH3CHO component catalyzes the isomerization NH2–C–OH+→NH2C(O)H+ and the ensuing intermediate [NH2C(O)H⋯OCHCH3]+ loses CH3CO by a facile proton transfer.In support of this, lactamide ions ND2C(O)CH(OD)CH3+ dissociate into DC(OH)ND2++CH3CO via the HBRC-1 isotopologue [ND2CO⋯D⋯OCHCH3]+. HBRC-1 also plays a key role in the decarbonylation of its isomer ionized urethan, NH2COOC2H5.

The double hydrogen transfer in the 1-methoxy-2-propanol molecular ion: Loss of CH3CO[rad] by proton-transport catalysis

The previously proposed mechanism of the double hydrogen transfer in the molecular ion of 1-methoxy-2-propanol, which yields protonated dimethyl ether and a C2H3O radical [1], has been re-examined. To obtain a more refined picture of the structures of the intermediates and transition states as well as the energetics of this reaction, calculations using the CBS-QB3 model chemistry have been performed. In addition, collision-induced dissociative ionization (CIDI) experiments have been carried out which show that the eliminated C2H3O radical is solely the acetyl radical.Theory predicts that hydrogen-bridged radical cations (HBRCs) play a pivotal role in the reaction and that the lowest energy route involves loss of a CH3CO radical, by proton transport catalysis.Our mechanistic study also accounts for the minor H/D exchange observed in the DO-analogue of 1-methoxy-2-propanol and it proposes a revision of the energetics of the mechanisms of the earlier study [1].

The dissociation chemistry of low-energy N-formylethanolamine ions: Hydrogen-bridged radical cations as key intermediates

Tandem mass spectrometry experiments show that N-formylethanolamine molecular ions HOCH2CH2NHC(H)O+ (FE1) lose C2H3O, CH2O and H2O to yield m/z 46 ions HC(OH)NH2+, m/z 59 ions CH2N(H)CHOH+, and m/z 71 N-vinylformamide ions CH2C(H)N(H)CHO+.A detailed mechanistic study using the CBS-QB3 model chemistry reveals that the readily generated 1,5-H shift isomer HOCHCH2N(H)C(H)OH+ (FE2) and hydrogen-bridged radical cations (HBRCs) act as key intermediates in a ‘McLafferty+1′ type rearrangement that yields the m/z 46 ions. The co-generated C2H3O neutrals are predicted to be vinyloxy radicals CH2CHO in admixture with CH3CO generated by quid-pro-quo (QPQ) catalysis.A competing C−C bond cleavage in FE1 leads to HBRC [CH2N(H)C(H)O-⋯H⋯OCH2]+, which serves as the direct precursor for CH2O loss.In addition, ion FE2 also communicates with a myriad of ion–molecule complexes of vinyl alcohol and formimidic acid whose components may recombine to form distonic ion FE3, HOCH(CH2)N(H)C(H)OH+, which loses H2O after undergoing a 1,5-H shift. Further support for these proposals comes from experiments with D- and 18O-labelled isotopologues.Previously reported proposals for the H2O and CO losses from protonated N-formylethanolamine are briefly re-examined.

A mechanistic study of the prominent loss of H 2O from ionized 2-hydroxyaminoethanol

Tandem mass spectrometry experiments on the HCl salt of 2-hydroxyaminoethanol reveal that low-energy ions HOCH 2CH 2NHOH + dissociate by loss of H 2O with remarkable efficiency ( c. 10%). Analysis of its high energy collision-induced dissociation (CID) mass spectrum leaves little doubt that the resulting m/ z 59 ion is the cyclic 1,2-oxazetidine ion, whose elusive neutral counterpart has not yet been identified by experiment. A mechanistic analysis using the CBS-QB3 model chemistry indicates that the dissociation chemistry of HOCH 2CH 2NHOH + is entirely different from that of the structurally related ions HOCH 2CH 2ONH 2 + and HOCH 2CH 2OH +. It involves a 1,5-H transfer in one of its stable conformers that leads to a hydrogen-bridged radical cation of the 1,2-oxazetidine ion and a water molecule. In support of this proposal the isotopologues DOCH 2CH 2NDOD·DCl and HOCH 2CD 2NHOH·HCl, upon ionization (almost) exclusively lose D 2O and H 2O, respectively.

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

The CBS-4M, CBS-QB3, G2, G2(MP2), G3 and G3(MP2) model chemistry methods have been used to calculate proton and electron affinities for a set of molecular and atomic systems. Agreement with the experimental value for these electronic properties is quite good considering the uncertainty in the experimental data. A comparison among the six theories using statistical analysis (average value, standard deviation and root-mean-square) showed a better performance of CBS-QB3 to obtain these properties.

The reaction of the acrylonitrile ion CH 2[dbnd]CH−C [tbnd]N [rad]+ with HCN: Proton-transport catalysis vs formation of ionized pyrimidine

The CBS-QB3 model chemistry predicts that the title ion–molecule reaction, of potential interest in astrochemistry, yields a stable head-to-tail dimer, [HC N−CH 2C(H)C N] + ( D1). Cyclization of D1 into ionized pyrimidine seems possible, but the initiating 1,2-H shift is close in energy to back-dissociation into CH 2 C(H)CN + ( AN) + HCN. Less energy demanding is formation of the H-bridged isomers [CH 2 C(CN)H--N CH] + and [HC N--HC(H) C(H)CN] +, whose HCN component may catalyze isomerization of AN into CH 2 C C NH + ( AN1) and CH C(H)C NH + ( AN2) respectively. Tandem mass spectrometry based experiments using 15N/ 13C labelling show that cyclization of D1 does not occur and that AN1 is the predominant reaction product instead.

Accurate Reaction Enthalpies and Sources of Error in DFT Thermochemistry for Aldol, Mannich, and α-Aminoxylation Reactions

Enthalpies for bond-forming reactions that are subject to organocatalysis have been predicted using the high-accuracy CBS-QB3 model chemistry and six DFT functionals. Reaction enthalpies were decomposed into contributions from changes in bonding and other intramolecular effects via the hierarchy of homodesmotic reactions. The order of the reaction exothermicities (aldol < Mannich approximately alpha-aminoxylation) arises primarily from changes in formal bond types mediated by contributions from secondary intramolecular interactions. In each of these reaction types, methyl substitution at the beta- and gamma-positions stabilizes the products relative to the unsubstituted case. The performance of six DFT functionals (B3LYP, B3PW91, B1B95, MPW1PW91, PBE1PBE, and M06-2X), MP2, and SCS-MP2 has been assessed for the prediction of these reaction enthalpies. Even though the PBE1PBE and M06-2X functionals perform well for the aldol and Mannich reactions, errors roughly double when these functionals are applied to the alpha-aminoxylation reactions. B3PW91 and B1B95, which offer modest accuracy for the aldol and Mannich reactions, yield reliable predictions for the two alpha-aminoxylation reactions. The excellent performance of the M06-2X and PBE1PBE functionals for aldol and Mannich reactions stems from the cancellation of sizable errors arising from inadequate descriptions of the underlying bond transformations and intramolecular interactions. SCS-MP2/cc-pVTZ performs most consistently across these three classes of reactions, although the reaction exothermicities are systematically underestimated by 1-3 kcal mol(-1). Conventional MP2, when paired with the cc-pVTZ basis set, performs somewhat better than SCS-MP2 for some of these reactions, particularly the alpha-aminoxylations. Finally, the merits of benchmarking DFT functionals for the set of simple chemically meaningful transformations underlying all bond-forming reactions are discussed.

On the interaction of peptides with calcium ions as studied by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry: Towards peptide fishing using metal ion baits

In a previous report [J.W. de Beukelaar, J.W. Gratama, P.A. Sillevis Smitt, G.M. Verjans, J. Kraan, Th.M. Luider, P.C. Burgers, Rapid Commun. Mass Spectrom. 21 (2007) 1282] on the quality assessment of synthetic peptides used in protein-spanning peptide pools by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) we noted that certain peptides showed remarkably intense signals for their calcium-containing analogues. Here we report on a detailed mass spectrometric study of the unimolecular chemistry of these calcium-containing peptides. By integration of the experimental findings with computational results derived from DFT and the CBS-QB3 model chemistry, we have traced the processes induced by Ca 2+ attachment in the peptide ions. Key to our analysis is the observation that all of the studied calcium-bound peptides containing a threonine or serine residue show prominent losses of CH 3CH O (from threonine) and/or CH 2 O (from serine) in both the positive and the negative ion mode. In the first step, Ca 2+ attaches itself to a negatively charged in-chain carboxylate group. Next, electrophilic attack of the calcium ion on the CH(R)OH group of threonine (R CH 3) or serine (R H) releases the hydroxyl proton which can then move to a suitable acceptor site, viz. a peptide bond. This leads to the formation of a very stable ionic bidentate structure. Upon collisional activation (MS/MS), this bidentate opens up leading to the loss of the exposed acetaldehyde or formaldehyde molecule, to yield another bidentate structure. MS/MS spectra of selected peptides interacting with other metal ions have also been investigated and it is found that only divalent ions follow the Ca 2+-induced transformations.

The remarkable dissociation chemistry of 2-aminoxyethanol ions NH 2OCH 2CH 2OH [rad]+studied by experiment and theory

Low-energy 2-aminoxyethanol molecular ions NH 2OCH 2CH 2OH + exhibit a surprisingly rich gas-phase ion chemistry. They spontaneously undergo five major dissociations in the microsecond timeframe, yielding ions of m/ z 61, 60, 46, 32 and 18. Our tandem mass spectrometry experiments indicate that these reactions correspond to the generation of HOCH 2CH(OH) + (protonated glycolaldehyde), HOCH 2C( O)H + (ionized glycolaldehyde), HC(OH)NH 2 + (protonated formamide), CH 2OH 2 + (the methylene oxonium ion) and NH 4 +. A mechanistic analysis of these processes using the CBS-QB3 model chemistry shows that the molecular ions undergo a 1,4- H shift followed by a facile isomerization into the ion–molecule complex [HOCH 2C( O)H +]⋯[NH 3] which acts as the reacting configuration for the five exothermic dissociation processes. Analysis of the D-labelled isotopomer ND 2OCH 2CH 2OD +, in conjunction with our computational results, shows that proton-transport catalysis may be responsible for the partial conversion of the m/ z 60 glycolaldehyde ions into the more stable 1,2-dihydroxyethene isomer HOC(H) C(H)OH +.

Loss of DN [tbnd]C from ionized 4-hydroxypyridine-OD: An intriguing reaction unravelled by theory and experiment

Low energy 4-hydroxypyridine ions ( HP- 1) decarbonylate but also readily lose hydrogen ( iso)cyanide. Surprisingly, this reaction leads to a specific loss of the label from the OD-labelled isotopomer. Our tandem mass spectrometry experiments show that ionized vinylketene, CH 2 CHCH C O + ( 1), is the product ion. This ion is also generated by the decarbonylation of 4-cyclopentene-1,3-dione ions ( CP- 1) and a computational analysis using the CBS-QB3 model chemistry indicates that these seemingly unrelated ionic systems share similar dissociation mechanisms. In this study, a mechanism is presented for the decarbonylation of metastable ions CP- 1 that satisfies the energy requirement dictated by its appearance energy. Our computational analysis further shows that ions HP- 1 may isomerize into the ( iso)imino analogues of CP- 1, by consecutive H-shift, ring-opening and cyclization steps. The CP- 1 analogues serve as the immediate precursors for the specific loss of DNC (rather than DCN) from OD-labelled HP- 1 and also its decarbonylation into the vinyl( iso)ketenimine ions CH 2 CHCH N CH + ( 3) and CH 2 CHCH C NH + ( 4).

Theoretical Reinvestigation of the O(3P) + C6H6 Reaction: Quantum Chemical and Statistical Rate Calculations

The lowest-lying triplet and singlet potential energy surfaces for the O(3P) + C6H6 reaction were theoretically characterized using the "complete basis set" CBS-QB3 model chemistry. The primary product distributions for the multistate multiwell reactions on the individual surfaces were then determined by RRKM statistical rate theory and weak-collision master equation analysis using the exact stochastic simulation method. It is newly found that electrophilic O-addition onto a carbon atom in benzene can occur in parallel on two triplet surfaces, 3A' and 3A' '; the results predict O-addition to be dominant up to combustion temperatures. Major expected end-products of the addition routes include phenoxy radical + H*, phenol and/or benzene oxide/oxepin, in agreement with the experimental evidence. While c-C6H5O* + H* are nearly exclusively formed via a spin-conservation mechanism on the lowest-lying triplet surface, phenol and/or benzene oxide/oxepin are mainly generated from the lowest-lying singlet surface after inter-system crossing from the initial triplet surface. CO + c-C5H6 are predicted to be minor products in flame conditions, with a yield < or = 5%. The O + C6H6 --> c-C5H5* + *CHO channel is found to be unimportant under all relevant combustion conditions, in contrast with previous theoretical conclusions (J. Phys. Chem. A 2001, 105, 4316). Efficient H-abstraction pathways are newly identified, occurring on two different electronic state surfaces, 3B1 and 3B2, resulting in hydroxyl plus phenyl radicals; they are predicted to play an important role at higher temperatures in hydrocarbon combustion, with estimated contributions of ca. 50% at 2000 K. The overall thermal rate coefficient k(O + C6H6) at 300-800 K was computed using multistate transition state theory: k(T) = 3.7 x 10-16 x T 1.66 x exp(-1830 K/T) cm(3) molecule(-1) s(-1), in good agreement with the experimental data available.

The loss of NH 2O [rad] from the N-hydroxyacetamide radical cation CH 3C( [dbnd]O)NHOH [rad]+: An ion-catalysed rearrangement

A previous study [Ch. Lifshitz, P.J.A. Ruttink, G. Schaftenaar, J.K. Terlouw, Rapid Commun. Mass Spectrom. 1 (1987) 61] shows that metastable N-hydroxyacetamide ions CH 3C( O)NHOH + ( HA-1) do not dissociate into CH 3C O + + NHOH by direct bond cleavage but rather yield CH 3C O + + NH 2O . The tandem mass spectrometry based experiments of the present study on the isotopologue CH 3C( O)NDOD + reveal that the majority of the metastable ions lose the NH 2O radical as NHDO rather than ND 2O . A mechanistic analysis using the CBS-QB3 model chemistry shows that the molecular ions HA-1 rearrange into hydrogen-bridged radical cations [O C C(H 2) H⋯N(H)OH] + whose acetyl cation component then catalyses the transformation NHOH → NH 2O prior to dissociation. The high barrier for the unassisted 1,2-H shift in the free radical, 43 kcal mol −1, is reduced to a mere 7 kcal mol −1 for the catalysed transformation which can be viewed as a quid-pro-quo reaction involving two proton transfers.

CBS-QB3 calculation of quantum chemical molecular descriptors of isomeric thiadiazoles

The results of the calculation of several molecular descriptors of isomeric thiadiazoles through the CBS-QB3 model chemistry are presented in this work. The results could be useful in quantitative structure–activity relationship (QSAR) or quantitative structure–property relationship (QSPR) studies of derivatives of the nitrogen-containing analogs of thiophene.

Formaldehyde mediated proton-transport catalysis in the ketene–water radical cation CH 2[dbnd]C( [dbnd]O)OH 2[rad

Previous studies have shown that the solitary ketene–water ion CH 2 C( O)OH 2 + ( 1) does not isomerize into CH 2 C(OH) 2 + ( 2), its more stable hydrogen shift isomer. Tandem mass spectrometry based collision experiments reveal that this isomerization does take place in the CH 2 O loss from low- energy 1,3-dihydroxyacetone ions (HOCH 2) 2C O +. A mechanistic analysis using the CBS-QB3 model chemistry shows that such molecular ions rearrange into hydrogen-bridged radical cations [CH 2C( O)O(H)–H⋯OCH 2] + in which the CH 2O molecule catalyzes the transformation 1 → 2 prior to dissociation. The barrier for the unassisted reaction, 29 kcal mol −1, is reduced to a mere 0.6 kcal mol −1 for the catalysed transformation. Formaldehyde is an efficient catalyst because its proton affinity meets the criterion for facile proton-transport catalysis.

Dissociation of protonated oxalic acid [HOOC-C(OH) 2] + into H 3O + + CO + CO 2: An experimental and CBS-QB3 computational study

The predominant dissociation process observed for metastable protonated oxalic acid ions HOOC-C(OH) 2 + (generated by self-protonation) leads to H 3O ++ CO + CO 2. We have traced the mechanism of this intriguing reaction using the CBS-QB3 model chemistry. Our calculations show that a unique ter-body complex, O C O⋯H 3O +⋯CO, plays a key role in the rearrangement process. This complex can also dissociate to the proton bound dimers [H 2O⋯H⋯O C O] + and [H 2O⋯H⋯CO] + which are minor processes observed in the metastable ion mass spectrum. A further minor process leads to the proton bound dimer O C O⋯H +⋯CO which is formed by water extrusion from the ter-body complex. Arguments are provided that the ter-body complex is also generated in the ion source by the collision encounter between neutral and ionized oxalic acid.

Effect of Metal Ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and Water Coordination on the Structure of Glycine and Zwitterionic Glycine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.