Experimental and computational study of the gas-phase reactivity of Lead(II) ions towards D-glucosamine, N-Ac-D-glucosamines and uronic acids

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Experimental and computational study of the gas-phase reactivity of Lead(II) ions towards D-glucosamine,

N-Ac-D-glucosamines and uronic acids Jean-Yves Salpin, Ahlam El Firdoussi, Jeanine Tortajada

To cite this version:

Jean-Yves Salpin, Ahlam El Firdoussi, Jeanine Tortajada. Experimental and computational study of the gas-phase reactivity of Lead(II) ions towards D-glucosamine, N-Ac-D-glucosamines and uronic acids. 54th American Society Mass Spectrometry Conference, 2006, Seattle, United States. 2006. �hal-00106829�

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Jean-Yves Salpin

1 _{, Ahlam El Firdoussi}

1,2

_{and Jeanine Tortajada}

1 1) Université d'Evry Val d’Essonne – 2) Université Cady Ayyad, Faculté des Sciences Semlalia de Marrakech

Experimental and computational study of the gas-phase reactivity of Lead(II) ions towards D-glucosamine, N-Ac-D-glucosamine

and uronic acids.

The bioavailability and toxicity of metals in the environment are governed by the ability of natural organic molecules to bind metal ions. Moreover, these complexation processes depend on many parameters of aqueous media, such as pH, ionic strength or metal/ligand ratio. So, in order to properly assess the influence of each of these parameters, it is of particular interest to describe in a first step the gas-phase reactivity of metallic cations. In this context, tandem mass spectrometry combined to electrospray ionization is a powerful tool for studying both the formation and the reactivity of organometallic complexes in the gas phase.

Carbohydrates are ubiquitous in nature and are mainly found as polysaccharides that are essential for both plant and animal life. These macromolecules may be easily converted to a large variety of monosaccharides, which, in turn, may complex metal ions due to their numerous functional groups. Among them, chitosan and chitin may influence the metal speciation in marine media and the present poster reports our results about the interaction of D-glucosamine and N-Acetyl-D-glucosamine (building blocks of chitosan and chitin, respectively) with Lead(II) ions, which constitute a large-scale environmental pollutant. Two uronic acids have also been considered, namely D-glucuronic and D-galatouronic acids.

Introduction

Objectives

- Characterization of the complexes generated in the gas phase

- Comparison with the reactivity observed with aldoses and ketoses.

- Determination of the best coordination sites.

Theoretical study

 B3LYP/6-31G(d,p) calculations and Stuttgart effective-core potential(1) _{for Pb for}

geometry optimization and ZPE determination.

 Single point calculations at the B3LYP/6-311+G(2df,2p) level.

 Both  and  anomeric forms considered.

 NBO(2) _{analysis of both charges and hydrogen bonds.}

Methodology

 MS/MS experiments with N₂ as collision gas (P(N₂)= 10-5 _Torr).

Experimental study

 Triple-quadrupole (API2000; Applied Biosystems/MDS Sciex) fitted with a turboionspray source.

 Pb(NO₃)₂/saccharide solutions (water or water/methanol) (10-4 _mol.L-1_/10-4 _mol.L-1_).

 Temperature of the drying gas : 373 K

Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement – UMR CNRS 8587

Bâtiment Maupertuis - Université d’Evry Val d’Essonne - Boulevard François Mitterrand - 91025 Evry Cedex - France

II- D-glucosamine

Theoretical study

Experimental study

2.235 2.482 1.932 2.371 1.393 1.524 2.061 2.362 2.065 1.536 1.449 2.497 2.241 2.253 2.370 1.419 1.529 2.206

• The elimination of 59 Daltons (C₂H₅NO) is consistent with a 0,2_{A cross-ring cleavage. This is confirmed by}

the fact that the MS/MS spectrum of the m/z 267 species is strictly equivalent to that obtained with D-glucose.(3)

•Again, the main fragmentation corresponds to a

0,2_{A cross-ring cleavage which may imply a CG}

structure, for which lead interacts with the carbonyl and a deprotonated C(3) hydroxyl. Nevertheless, the reactivity with this carbohydrate is particularly rich because additional cross-ring cleavages are observed, such as 0,2_{X (m/z 308) or}

those leading to m/z 368. Note that the m/z 308 ion may also be generated in two steps according to the following sequence : 428  368  308.

III- N-acetyl-D-glucosamine

Theoretical study

Experimental study

B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d,p)

Structure E(Hartree) ZPE

(Hartree)

E

(kJ/mol)(/) kJ/mol(Global)E

-AB -670.211107 0.201298 0.0 0.0 -AF -670.192131 0.199600 45.4 45.4 -BA -670.188686 0.199640 53.3 53.3 -BC -670.197101 0.199882 33.1 33.1 -CB -670.206829 0.201012 10.5 10.5 -CD -670.190045 0.199743 51.2 51.2 -CD2 -670.205520 0.200248 11.9 11.9 -DC -670.203096 0.200638 19.1 19.1 -ED -670.207631 0.200557 7.2 7.2 -DE -670.197856 0.200047 31.5 31.5 -EF -670.195954 0.199757 36.2 36.2 -AB -670.207263 0.200872 0.0 9.0 -BA -670188294. 0.199448 46.1 55.0 -BC -670.197180 0.199679 23.3 32.3 -CB -670.204324 0.200403 6.5 15.5 -CD -670.197429 0.199640 22.6 31.6 -DC -670.197961 0.199830 21.7 30.7 -EAF -670.202801 0.199714 8.7 17.6 -ED -670.199208 0.199800 18.3 27.3 -DE -670.191324 0.199051 37.1 46.0 -C₂H₅NO 40 80 120 160 200 240 280 320 360 400 m/z, amu 1,00e5 3,00e5 5,00e5 7,00e5 9,00e5 1,06e6 In ten sity 327 279 309 386 208,0 267 m/z 309 m/z 386 m/z 327 m/z 279 m/z 267 m/z 208

MS/MS spectrum of m/z 386 (P_N2=10-5 _{Torr, 10 eV)}

0,2_A

B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d,p)

Structure E(Hartree) ZPVE

(Hartree)

E

(kJ/mol)(/) kJ/mol(Global)E

-ABG -822.915028 0.237599 55.8 59.4 -AF -822.897431 0.237253 100.5 104.1 -BA -822.919124 0.236969 43.4 47.0 -BC -822.917787 0.237674 48.8 52.3 -CG -822.934881 0.237972 4.7 8.2 -CD -822.922418 0.237689 36.6 40.2 -DC -822.934491 0.235808 3.6 0.0 -ED -822.927603 0.238094 24.1 27.7 -EF -822.613186 0.236994 63.7 67.3 -AG -822.937869 0.237828 0.0 0.0 -AEF -822.910307 0,236306 68.4 68.4 -BC -822.908460 0.236894 74.8 74.8 -CD -822.913901 0.236703 60.0 60.0 -CG -822.929091 0.237584 22.4 22.4 -DC -822.931769 0.236053 11.4 11.4 -ED -822.924863 0.237951 34.5 34.5 -EF -822.914772 0.237247 59.1 59.1 O OH NH HO HO OH CH₃ O 327 368 368 -H, +Pb 308 -C₂H₄O₂ 0,2_A -C₂H₄O₂

MS/MSspectrum of m/z 428 (P_N2=10-5 _{Torr, 10 eV)}

200 220 240 260 280 300 320 340 360 380 400 420 440 m/z, amu 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% R el. Int. ( %) 327 428 368 308 267 ₃₅₀ ₄₁₀ 392 279 m/z 309 m/z 428 m/z 327 m/z 279 m/z 267 m/z 410 m/z 368 m/z 350 m/z 308

Conclusion

In order to get more insights in the fragmentation mechanisms, labeling experiments with either deuterium or 18_{O are currently in}

progress.

The results obtained show that these four carbohydrates, in spite of different functional groups, exhibit toward Pb2+ _{ions a similar}

reactivity, mainly characterized by a 0,2_{A cross-ring cleavage. DFT calculations demonstrate that the most stable geometries are}

characterized by a bi- or tridentate coordination of the metallic center with the functional group (amino, N-acetyl, COOH) and one or two hydroxyls, while the remaining hydroxyl group participate in a cooperative hydrogen bonding scheme. NBO analysis indicates the bonding is mainly electrostatic in nature.

- Assessment of the influence of the metal onto the geometry of the monosaccharides studied.

(G) (E) 1 2 3 4 5 6 (F) (A) (B) (C) (D) Adopted nomenclature :

I- Relative energies of the various complexes

Theoretical study

Experimental study

I- D-glucuronic acid

• Doubly-charged complexes are not observed.

200 300 400 500 600 700 800 900 1000 m/z, amu 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Rel. Int. (%) 341,1 225,1 267,0 _401,1 279,1 595,4 451,3 [Pb] =10-4_{M et [GA] =10}-4 _{M in H} 2O, cone voltage 120 V [Pb(GA)₂-H]+ [Pb(GA) -H]+

Positive-ion electrospray spectrum

200 220 240 260 280 300 320 340 360 m/z, amu 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Rel. Int . (%) 267 279 323 225 208 341 -C₂H₂O₃ -CH₂O₃ 1.418 1.539 1.526 1.524 1.540 1.433 2.130 2.363 2.449 2.030 1.215 1.940 1.417 1.432 1.536 1.535 1.251 1.551 1.538 2.164 2.467 2.582 1.873 1.297 2.320 2.068 Distances (Angström) B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d,p)

Structure E(Hartree) ZPE

(Hartree) E (kJ/mol) (/) E(kJ/mol)(Global) -AB -764.129661 0.169280 38.5 38.5 -BA -764.114076 0.168083 76.3 76.3 -BC -764.134651 0.169467 25.9 25.9 -CB -764.123415 0.168899 53.9 53.9 -CD -764.136586 0.16881 19.1 19.1 -DC -764.126868 0.169084 61.6 61.6 -ED -764.124867 0.168380 48.7 48.7 -DE -764.112021 0.16740 79.9 79.9 -DG -764.144010 0.168963 0.0 0.0 -EF -764.126647 0.168195 43.6 43.6 -EG -764.116768 0.16779 68.4 68.4 -AB -764.126308 0.168938 37.3 46.4 -BA -764.115607 0.168349 63.8 73.0 -BC -764.130162 0.168878 27.0 36.1 -CB -764.126290 0.168986 37.4 46.6 -CD -764.132734 0.168078 18.1 27.3 -DC -764.117500 0.168222 58.5 67.7 -ED -764.121858 0.167612 45.2 54.5 -DE -764.106576 0.166250 82.0 91.2 -DG -764.138683 0.168040 2.5 11.7 -EFA -764.132871 0.167552 16.4 25.5 -AFG -764.139951 0.168385 0.0 9.1

200 220 24 0 260 280 300 320 340 360 380 400 420 m/z, amu 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Rel. Int. (%) 341 401 267 279 311 383 297 -C₂H₄O₂ 0,2_A

• Formation of ions of the type [Pb(monosaccharide)_n-H]+_.

• NBO analysis : the interaction is mainly electrostatic, but a donation/backdonation process between the metal and the ligand is observed

•Structures are characterized by bi- or tridentate interactions and by numerous

intramolecular hydrogen bonds.

•The most stable forms (DG, AFG) imply an interaction with the oxygen of the carbonyl of the carboxylic group. This differs from what was observed

with D-glucose(3). Interaction of the metal induces an important activation of the carbonyle (

CO frequency red-shifted by 139 cm-1). In the particular case

of the AFG coordination scheme, the tricoordination triggers a change in the pyranosic ring conformation.

• For D-glucose it has been demonstrated(3) _{that the elimination of C}

2H4O2 (60 Daltons) was due exclusively to a 0,2A cleavage according the Domon and

Costello convention.(4) _{Both experimental and theoretical results suggest a similar process D-glucuronic acid. On the one hand, the optimized structures}

show that the DG coordination strongly activates the C(1)-O(5) bond. On the other hand, the loss of 62 Daltons from m/z 341 may be attributed to simultaneous elimination of CO₂ and H₂O, suggesting that the m/z 341 ion includes the carboxylic group.

Mechanisms of fragmentation

• The following mechanism may be proposed for the

401 341  267 transition  DG, m/z 401 OH Pb O HO O O OH OH HO O O Pb OH m/z 341 HO HO O O Pb H m/z 267 OH O O H O 0,2_A

• Similar results are obtained with D-galactouronic. Consequently, the absolute configuration of the C(4) center has no influence upon the reactivity observed experimentally.

(3) Salpin et al., J. J. Phys. Chem. A 2003, 107, 2943. (1) Küchle et al.. Mol. Phys. 1991, 6, 1245.

(4) Domon and Costello. Glycoconjugate J. 1988, 5, 397. (2) Glendening et al. NBO program 3.1.