Gilles Frison | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)
Papers by Gilles Frison
European Journal of Inorganic Chemistry, Jul 19, 2013
Chemistry - A European Journal, Aug 16, 2013
Chemical communications (Cambridge, England), Jan 21, 2015
Unexpected and unprecedented directed remote lateral lithiation at one CH(CH3)2 of the 3-(2,6-di-... more Unexpected and unprecedented directed remote lateral lithiation at one CH(CH3)2 of the 3-(2,6-di-isopropylphenyl) wingtip took place upon the reaction of functionalised N-heterocyclic carbene-type molecules with excess of LiCH2SiMe3, leading to dilithiated dianionic 4-amido-N-heterocyclic carbenes. DFT calculations show that the nature of the isolated species are under thermodynamic control.
Journal of The American Society for Mass Spectrometry, 2011
Electron capture dissociation (ECD) of a series of five residue peptides led to the observation t... more Electron capture dissociation (ECD) of a series of five residue peptides led to the observation that these small peptides did not lead to the formation of the usual c/z ECD fragments, but to a, b, y, and w fragments. In order to determine how general this behavior is for small sized peptides, the effect of peptide size on ECD fragments using a complete set of ECD spectra from the SwedECD spectra database was examined. Analysis of the database shows that b and w fragments are favored for small peptide sizes and that average fragment size shows a linear relationship to parent peptide size for most fragment types. From these data, it appears that most of the w fragments are not secondary fragments of the major z ions, in sharp contrast with the proposed mechanism leading to these ions. These data also show that c fragment distributions depend strongly on the nature of C-terminal residue basic site: arginine leads to loss of short neutral fragments, whereas lysine leads to loss of longer neutral fragments. It also appears that b ions might be produced by two different mechanisms depending on the parent peptide size. A model for the fragmentation pathways in competition is proposed. These relationships between average fragment size and parent peptide size could be further exploited also for CID fragment spectra and could be included in fragmentation prediction algorithms.
Journal of the American Society for Mass Spectrometry, 2007
Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagg... more Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)(2+) ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)(2+) dications by electrospray. ECD of (TMPP-ac-peptide + H)(2+) resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)(+) ions were detected. The dissociations involved loss of H, formation of (TMPP + H)(+), and N-C(alpha) bond cleavages giving TMPP-CH(2)CONH(2)(+) (c(0)) and c(1) fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)(2+) resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph(3)P-ac-GK + H)(2+) and (H(3)P-ac-GK + H)(2+) analogs indicated that the doubly charged ions contained the lysine side-chain NH(3)(+) group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 A in the most stable dication conformers. The intrinsic recombination energies of the TMPP(+)-ac and (GK + H)(+) moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)(+*) ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)(+*) ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N-C(alpha) bonds to give rise to the c(1) fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c(0) fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD.
Physical Chemistry Chemical Physics, 2011
Acid-base thermochemistry of isolated amino acids containing oxygen or sulfur in their side chain... more Acid-base thermochemistry of isolated amino acids containing oxygen or sulfur in their side chain (serine, threonine, cysteine and methionine) have been examined by quantum chemical computations. Density functional theory (DFT) was used, with B3LYP, B97-D and M06-2X functionals using the 6-31+G(d,p) basis set for geometry optimizations and the larger 6-311++G(3df,2p) basis set for energy computations. Composite methods CBS-QB3, G3B3, G4MP2 and G4 were applied to large sets of neutral, protonated and deprotonated conformers. Conformational analysis of these species, based on chemical approach and AMOEBA force field calculations, has been used to identify the lowest energy conformers and to estimate the population of conformers expected to be present at thermal equilibrium at 298 K. It is observed that G4, G4MP2, G3B3, CBS-QB3 composite methods and M06-2X DFT lead to similar conformer energies. Thermochemical parameters have been computed using either the most stable conformers or equilibrium populations of conformers. Comparison of experimental and theoretical proton affinities and Δ(acid)H shows that the G4 method provides the better agreement with deviations of less than 1.5 kJ mol(-1). From this point of view, a set of evaluated thermochemical quantities for serine, threonine, cysteine and methionine may be proposed: PA = 912, 919, 903, 938; GB = 878, 886, 870, 899; Δ(acid)H = 1393, 1391, 1396, 1411; Δ(acid)G = 1363, 1362, 1367, 1382 kJ mol(-1). This study also confirms that a non-negligible ΔpS° is associated with protonation of methionine and that the most acidic hydrogen of cysteine in the gas phase is that of the SH group. In several instances new conformers were identified thus suggesting a re-examination of several IRMPD spectra.
Science, 2005
Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic... more Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic oxidations. We report that transition metal coordination also supports an aminyl radical, resulting in a stable crystalline complex: [Rh(I)(trop2N.)(bipy)]+OTf- (where trop is 5-H-dibenzo[a,d]cycloheptene-5-yl, bipy is 2,2'-bipyridyl, OTf- is trifluorosulfonate). It is accessible under mild conditions by one-electron oxidation of the amide complex [Rh(I)(trop2N)(bipy)], at a potential of -0.55 volt versus ferrocene/ferrocenium. Both electron paramagnetic resonance spectroscopy and density functional theory support 57% localization of the unpaired spin at N. In reactions with H-atom donors, the Rh-coordinated aminyl behaves as a nucleophilic radical.
![Research paper thumbnail of Binding of Specialty Phosphines to Metals: Synthesis, Structure, and Solution Calorimetry of the Phosphirane Complex [PtMe 2 ( i Pr BABAR-Phos) 2 ]](https://attachments.academia-assets.com/44004079/thumbnails/1.jpg)
](Organometallics, 2003
The complex [PtMe 2 ( iPr BABAR-Phos) 2 ] (3) was prepared in a clean and quantitative ligand sub... more The complex [PtMe 2 ( iPr BABAR-Phos) 2 ] (3) was prepared in a clean and quantitative ligand substitution reaction from [PtMe 2 (cod)] (1; cod ) η 4 -1,5-cyclooctadiene) and the phosphirane iPr BABAR-Phos (2). The structure of 3 was determined by X-ray diffraction. The Pt-P bonds (∼2.26 Å) lie in the shorter range of Pt II -P bonds, although the 1 J( 195 Pt 31 P) coupling (1840 Hz) is quite small. The enthalpy for this ligand substitution reaction was measured by solution calorimetry and found to be exothermic by 11.8 kcal/mol, a relatively low exothermicity for a reaction involving a tertiary phosphine in this Pt system. Calculations using density functional theory (DFT) on the B3LYP level were applied using the simplified model reaction [PtH 2 (cod)] + 2(H 2 N)PC 2 H 4 f [PtH 2 {(H 2 N)PC 2 H 4 } 2 )] + cod, and these also gave a rather low substitution enthalpy (-17 kcal/mol). A charge decomposition analysis (CDA) was performed for Pt(II) and Pt(0) complexes with the simple P-amino phosphirane (H 2 N)PC 2 H 4 and PH 3 as ligands. Contrary to expectations, it is found that the phosphirane acts as a relatively good electron donor, while its electron-acceptor properties are not significantly different from those of other phosphines. The particularly low reaction enthalpy may thus be due to a low directionality of the donor orbitals toward the metal center.
Journal of The American Society for Mass Spectrometry, 2011
Electron capture dissociation (ECD) of a series of five residue peptides led to the observation t... more Electron capture dissociation (ECD) of a series of five residue peptides led to the observation that these small peptides did not lead to the formation of the usual c/z ECD fragments, but to a, b, y, and w fragments. In order to determine how general this behavior is for small sized peptides, the effect of peptide size on ECD fragments using a complete set of ECD spectra from the SwedECD spectra database was examined. Analysis of the database shows that b and w fragments are favored for small peptide sizes and that average fragment size shows a linear relationship to parent peptide size for most fragment types. From these data, it appears that most of the w fragments are not secondary fragments of the major z ions, in sharp contrast with the proposed mechanism leading to these ions. These data also show that c fragment distributions depend strongly on the nature of C-terminal residue basic site: arginine leads to loss of short neutral fragments, whereas lysine leads to loss of longer neutral fragments. It also appears that b ions might be produced by two different mechanisms depending on the parent peptide size. A model for the fragmentation pathways in competition is proposed. These relationships between average fragment size and parent peptide size could be further exploited also for CID fragment spectra and could be included in fragmentation prediction algorithms.
Journal of the American Society for Mass Spectrometry, 2007
Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagg... more Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)(2+) ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)(2+) dications by electrospray. ECD of (TMPP-ac-peptide + H)(2+) resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)(+) ions were detected. The dissociations involved loss of H, formation of (TMPP + H)(+), and N-C(alpha) bond cleavages giving TMPP-CH(2)CONH(2)(+) (c(0)) and c(1) fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)(2+) resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph(3)P-ac-GK + H)(2+) and (H(3)P-ac-GK + H)(2+) analogs indicated that the doubly charged ions contained the lysine side-chain NH(3)(+) group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 A in the most stable dication conformers. The intrinsic recombination energies of the TMPP(+)-ac and (GK + H)(+) moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)(+*) ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)(+*) ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N-C(alpha) bonds to give rise to the c(1) fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c(0) fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD.
The Journal of Physical Chemistry Letters, 2011
Electron capture and electron transfer dissociations are bioanalytical methods for fragmenting ca... more Electron capture and electron transfer dissociations are bioanalytical methods for fragmenting cations after reduction by an electron. Previous computational studies based on conventional DFT schemes have concluded that the first step of these processes, the attachment of the electron, leads to extensive delocalization of the spin density in the intermediate radical cation. Here we show that most DFT methods produce unphysical results when studying single electron reduction of a dicationic peptide. This is not the case for post-HF methods and long-range corrected functionals that show satisfying electron affinities, intermolecular interaction energies, and spin density trends. Our results suggest that the charged group with the highest electron affinity on the precursor cation is also the site of spin density in the electronic ground state after electron attachment. These findings have important implications for the interpretation of experimental data from electron-based processes in biomolecules and may guide the development of new functionals.
Journal of Organometallic Chemistry, 1998
A comparative theoretical study of the terminal phosphinidene complexes HPCr(CO) 5 , HPTi(Cp 2 ) ... more A comparative theoretical study of the terminal phosphinidene complexes HPCr(CO) 5 , HPTi(Cp 2 ) and HPTiCl 2 , at the MP2 and DFT levels, has been carried out. The calculated results have then been used for determining the electron localization function (ELF) in these moieties. Both techniques show that in the singlet ground state of HPCr(CO) 5 , one gets a weak double P -Cr bond, with an electrophilic character on P (i.e. electron-deficient center). Conversely, in the singlet ground state of Ti complexes, the P-Ti bond shows a greater double bond character than in the P -Cr linkage, associated with an overall nucleophilic character of P. These results are in good agreement with all available experimental data.
The Journal of Organic Chemistry, 2002
Quantum-chemical DFT calculations using the B3LYP functionals have been carried out for 1-R-subst... more Quantum-chemical DFT calculations using the B3LYP functionals have been carried out for 1-R-substitued phospholes and some 1-R-substitued 3,4-dimethylphospholes where R = H, Me, Ph, CN, OH, OMe, F, Cl, and Br. The aromaticity of the phospholyl rings is interpreted as a function of geometric, magnetic, and energetic indexes. It is shown, in agreement with previous experimental results, that phosphole aromaticity does not correlate with pyramidality at phosphorus. Variation of hyperconjugative and, to a lesser extent, conjugative effects is responsible for the change in cyclic delocalization for the phospholes studied here.
The Journal of Organic Chemistry, 1999
Geometries, aromatic character, Mulliken charge distribution, and MO diagrams of 1,2-aza-, 1,3,2d... more Geometries, aromatic character, Mulliken charge distribution, and MO diagrams of 1,2-aza-, 1,3,2diaza-, 1,3-aza-, and 1,3,5-diazaphosphinines have been calculated and compared to those of phosphinine and pyridine. This study reveals that the introduction of nitrogen atoms at the position adjacent to phosphorus significantly reduces the aromatic delocalization and induces a [1,4] dipolar character through an increase of the positive charge on the P atom. This phenomenon does not occur in 1,3-aza-and 1,3,5-diazaphosphinines, which exhibit a poor dipolar character. This comparison confirms the high reactivity of 1,3,2-diazaphosphinines toward alkynes. A [4 + 2] cycloaddition reaction between these two types of diazaphosphinines and acetylene has been modelized. Calculated geometries of the resultant [4 + 2] diazabarrelene cycloadducts and that of their respective transition states reveal that, especially with 1,3,2-diaza isomers, the cycloaddition proceeds via a disymmetrical pathway that involves the preliminary formation of the P-C bond.
Comptes Rendus Chimie, 2002
At 170°C, 1,1'-bis(3,4-dimethylphospholyl)ferrocene (7) isomerises through the corresponding 2H-p... more At 170°C, 1,1'-bis(3,4-dimethylphospholyl)ferrocene (7) isomerises through the corresponding 2H-phospholes that are trapped by diphenylacetylene to give the 1,1'-ferrocenylene-bridged bis-1-phosphanorbornadiene (6). After resolution with an optically pure palladium complex, (R,R)-and (S,S)-(6) are tested in the asymmetric hydrogenation of a dehydroaminoacid, hydroformylation of styrene, and allylation of sodium malonate. To cite this article: G. Frison et al., C. R. Chimie 5 (2002) 245-249 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS phosphole / phosphanorbornadiene / ferrocene / asymmetric catalysis Résumé -A 170°C, le 1,1'-bis(3,4-diméthylphospholyl)ferrocene (7) s'isomérise pour donner les 2H-phospholes correspondants que l'on peut piéger par le diphénylacétylene. Après purification du racémique, l'adduit [4+2] qui en résulte, rac-(6), peut être dédoublé en ses deux énantiomères à l'aide d'un complexe énantiopur de palladium. Les énantiomères (R,R)-et (S,S)-(6) ont été testés dans l'hydrogénation asymétrique d'un déhydroaminoacide, dans l'hydroformylation asymétrique du styrène et dans l'allylation asymétrique du malonate de sodium, avec des résultats moyens. Pour citer cet article : G. Frison et al., C. R. Chimie 5 (2002) 245-249 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS phosphole / phosphanorbornadiène / ferrocène / catalyse asymétrique * Correspondence and reprints. 9 (d, J = 7.0 Hz); 8b (0.94 g, 35%): 31 P NMR (CDCl 3 ) δ 55.7; 1 H NMR (CDCl 3 ) δ 1.44 (s, 6H),1.70 (d, J = 5.7 Hz, 6H), 2.54 (s, 6H), 2.70 (d, J + 10.0 Hz, 2H), 2.83 (s, 6H), 3.78 (m, 2H), 2.89 (s, 6H), 3.0 (d, J = 10 Hz, 2H), 3.75 (s, 4H), 3.87 (s, 2H), 4.36 (s, 2H), 4.79 (s, 2H), 5.69 (t, J = 7.0 Hz, 2H), 5.82 (t, J = 7.0 Hz, 2H), 6.51 (t, J = 7.3 Hz, 2H), 6.70-7.30 (m, 22H); 13 C NMR (CDCl 3 ) δ 16.9 (d,
![Research paper thumbnail of TROPDAD: A New Ligand for the Synthesis of Water-Stable Paramagnetic[16+1]-Electron Rhodium and Iridium Complexes](https://attachments.academia-assets.com/44004808/thumbnails/1.jpg)
](Chemistry - A European Journal, 2003
The new tetradentate ligand 1,4-bis(5 H-dibenzo[a,d]cyclohepten-5yl)-1,4-diazabuta-1,3-diene ( H ... more The new tetradentate ligand 1,4-bis(5 H-dibenzo[a,d]cyclohepten-5yl)-1,4-diazabuta-1,3-diene ( H tropdad) allows the syntheses of the 16-electron cationic rhodium complexes [M( H tropdad)](O 3 SCF 3 ) (M Rh, Ir). The structure of the rhodium complex was determined by X-ray analysis and points to a description of these as [M 1 ( H tropdad) 0 ] with short CN bonds (av 1.285 ä) and a long CÀC bond (1.46 ä) in the diazabutadiene (dad) moiety, that is the M 3 dad charge-transfer is negligible. Both [Rh( H tropdad)] and [Ir( H tropdad)] are reduced at very low potentials (E 1 1/2 À 0.56 V and E 1 1/2 À 0.35 V, respec-tively) which allowed the quantitative synthesis of the neutral paramagnetic complexes [M( H tropdad)] 0 (M Rh, Ir) by reacting the cationic precursor complexes simply with zinc powder. The [M( H tropdad)] 0 complexes are stable against protic reagents in organic solvents. Continuous wave and pulse EPR spectroscopy was used to characterize the paramagnetic species and the hyperfine coupling constants were deter-mined: [Rh( H tropdad)] 0 : A iso ( 14 N) 11.9 MHz, A iso ( 1 H) 14.3 MHz, A iso ( 103 Rh) À 5.3 MHz; [Ir( H tropdad)] 0 : A iso ( 14 N) 11.9 MHz, A iso ( 1 H) 14.3 MHz. In combination with DFT calculations, the experimentally determined g and hyperfine matrices could be orientated within the molecular frame and the dominant spin density contributions were determined. These results clearly show that the complexes [M( H tropdad)] 0 are best described as [M 1 ( H tropdad) .À ] with a [16 1] electron configuration.
Chemical Communications, 2012
A double ring-expansion methodology allows the stepwise synthesis of tri- and tetra-phosphaporhyr... more A double ring-expansion methodology allows the stepwise synthesis of tri- and tetra-phosphaporhyrinogens. Structural and calculational methods reveal extended delocalisation about their phospholide centres.
Journal of the American Chemical Society, 2008
In this study, we propose the first spectroscopic structural characterization of c-type ions prod... more In this study, we propose the first spectroscopic structural characterization of c-type ions produced by ECD of a peptide. The structure of c-type ions formed by electron capture dissociation and the overall mechanism leading to their formation are still a question of debate. Depending on the mechanism, c-type ions have been proposed to have either an enol-imine structure (-C(OH)NH) or an amide one (-C(O)-NH2). Since these ions are isomeric, mass spectrometry only cannot discriminate between them, but infrared spectroscopy can bring experimental evidence and help determine which scheme is operative. Using the coupling between a tunable free electron laser and a FT-ICR mass spectrometer, we show that c-type ions have an amide structure, characterized by an IR signature of the C=O stretch at 1731 cm(-1). This result is particularly interesting from the perspective of the elucidation of the ECD mechanism.
European Journal of Inorganic Chemistry, Jul 19, 2013
Chemistry - A European Journal, Aug 16, 2013
Chemical communications (Cambridge, England), Jan 21, 2015
Unexpected and unprecedented directed remote lateral lithiation at one CH(CH3)2 of the 3-(2,6-di-... more Unexpected and unprecedented directed remote lateral lithiation at one CH(CH3)2 of the 3-(2,6-di-isopropylphenyl) wingtip took place upon the reaction of functionalised N-heterocyclic carbene-type molecules with excess of LiCH2SiMe3, leading to dilithiated dianionic 4-amido-N-heterocyclic carbenes. DFT calculations show that the nature of the isolated species are under thermodynamic control.
Journal of The American Society for Mass Spectrometry, 2011
Electron capture dissociation (ECD) of a series of five residue peptides led to the observation t... more Electron capture dissociation (ECD) of a series of five residue peptides led to the observation that these small peptides did not lead to the formation of the usual c/z ECD fragments, but to a, b, y, and w fragments. In order to determine how general this behavior is for small sized peptides, the effect of peptide size on ECD fragments using a complete set of ECD spectra from the SwedECD spectra database was examined. Analysis of the database shows that b and w fragments are favored for small peptide sizes and that average fragment size shows a linear relationship to parent peptide size for most fragment types. From these data, it appears that most of the w fragments are not secondary fragments of the major z ions, in sharp contrast with the proposed mechanism leading to these ions. These data also show that c fragment distributions depend strongly on the nature of C-terminal residue basic site: arginine leads to loss of short neutral fragments, whereas lysine leads to loss of longer neutral fragments. It also appears that b ions might be produced by two different mechanisms depending on the parent peptide size. A model for the fragmentation pathways in competition is proposed. These relationships between average fragment size and parent peptide size could be further exploited also for CID fragment spectra and could be included in fragmentation prediction algorithms.
Journal of the American Society for Mass Spectrometry, 2007
Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagg... more Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)(2+) ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)(2+) dications by electrospray. ECD of (TMPP-ac-peptide + H)(2+) resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)(+) ions were detected. The dissociations involved loss of H, formation of (TMPP + H)(+), and N-C(alpha) bond cleavages giving TMPP-CH(2)CONH(2)(+) (c(0)) and c(1) fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)(2+) resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph(3)P-ac-GK + H)(2+) and (H(3)P-ac-GK + H)(2+) analogs indicated that the doubly charged ions contained the lysine side-chain NH(3)(+) group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 A in the most stable dication conformers. The intrinsic recombination energies of the TMPP(+)-ac and (GK + H)(+) moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)(+*) ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)(+*) ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N-C(alpha) bonds to give rise to the c(1) fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c(0) fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD.
Physical Chemistry Chemical Physics, 2011
Acid-base thermochemistry of isolated amino acids containing oxygen or sulfur in their side chain... more Acid-base thermochemistry of isolated amino acids containing oxygen or sulfur in their side chain (serine, threonine, cysteine and methionine) have been examined by quantum chemical computations. Density functional theory (DFT) was used, with B3LYP, B97-D and M06-2X functionals using the 6-31+G(d,p) basis set for geometry optimizations and the larger 6-311++G(3df,2p) basis set for energy computations. Composite methods CBS-QB3, G3B3, G4MP2 and G4 were applied to large sets of neutral, protonated and deprotonated conformers. Conformational analysis of these species, based on chemical approach and AMOEBA force field calculations, has been used to identify the lowest energy conformers and to estimate the population of conformers expected to be present at thermal equilibrium at 298 K. It is observed that G4, G4MP2, G3B3, CBS-QB3 composite methods and M06-2X DFT lead to similar conformer energies. Thermochemical parameters have been computed using either the most stable conformers or equilibrium populations of conformers. Comparison of experimental and theoretical proton affinities and Δ(acid)H shows that the G4 method provides the better agreement with deviations of less than 1.5 kJ mol(-1). From this point of view, a set of evaluated thermochemical quantities for serine, threonine, cysteine and methionine may be proposed: PA = 912, 919, 903, 938; GB = 878, 886, 870, 899; Δ(acid)H = 1393, 1391, 1396, 1411; Δ(acid)G = 1363, 1362, 1367, 1382 kJ mol(-1). This study also confirms that a non-negligible ΔpS° is associated with protonation of methionine and that the most acidic hydrogen of cysteine in the gas phase is that of the SH group. In several instances new conformers were identified thus suggesting a re-examination of several IRMPD spectra.
Science, 2005
Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic... more Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic oxidations. We report that transition metal coordination also supports an aminyl radical, resulting in a stable crystalline complex: [Rh(I)(trop2N.)(bipy)]+OTf- (where trop is 5-H-dibenzo[a,d]cycloheptene-5-yl, bipy is 2,2'-bipyridyl, OTf- is trifluorosulfonate). It is accessible under mild conditions by one-electron oxidation of the amide complex [Rh(I)(trop2N)(bipy)], at a potential of -0.55 volt versus ferrocene/ferrocenium. Both electron paramagnetic resonance spectroscopy and density functional theory support 57% localization of the unpaired spin at N. In reactions with H-atom donors, the Rh-coordinated aminyl behaves as a nucleophilic radical.
Organometallics, 2003
The complex [PtMe 2 ( iPr BABAR-Phos) 2 ] (3) was prepared in a clean and quantitative ligand sub... more The complex [PtMe 2 ( iPr BABAR-Phos) 2 ] (3) was prepared in a clean and quantitative ligand substitution reaction from [PtMe 2 (cod)] (1; cod ) η 4 -1,5-cyclooctadiene) and the phosphirane iPr BABAR-Phos (2). The structure of 3 was determined by X-ray diffraction. The Pt-P bonds (∼2.26 Å) lie in the shorter range of Pt II -P bonds, although the 1 J( 195 Pt 31 P) coupling (1840 Hz) is quite small. The enthalpy for this ligand substitution reaction was measured by solution calorimetry and found to be exothermic by 11.8 kcal/mol, a relatively low exothermicity for a reaction involving a tertiary phosphine in this Pt system. Calculations using density functional theory (DFT) on the B3LYP level were applied using the simplified model reaction [PtH 2 (cod)] + 2(H 2 N)PC 2 H 4 f [PtH 2 {(H 2 N)PC 2 H 4 } 2 )] + cod, and these also gave a rather low substitution enthalpy (-17 kcal/mol). A charge decomposition analysis (CDA) was performed for Pt(II) and Pt(0) complexes with the simple P-amino phosphirane (H 2 N)PC 2 H 4 and PH 3 as ligands. Contrary to expectations, it is found that the phosphirane acts as a relatively good electron donor, while its electron-acceptor properties are not significantly different from those of other phosphines. The particularly low reaction enthalpy may thus be due to a low directionality of the donor orbitals toward the metal center.
Journal of The American Society for Mass Spectrometry, 2011
Electron capture dissociation (ECD) of a series of five residue peptides led to the observation t... more Electron capture dissociation (ECD) of a series of five residue peptides led to the observation that these small peptides did not lead to the formation of the usual c/z ECD fragments, but to a, b, y, and w fragments. In order to determine how general this behavior is for small sized peptides, the effect of peptide size on ECD fragments using a complete set of ECD spectra from the SwedECD spectra database was examined. Analysis of the database shows that b and w fragments are favored for small peptide sizes and that average fragment size shows a linear relationship to parent peptide size for most fragment types. From these data, it appears that most of the w fragments are not secondary fragments of the major z ions, in sharp contrast with the proposed mechanism leading to these ions. These data also show that c fragment distributions depend strongly on the nature of C-terminal residue basic site: arginine leads to loss of short neutral fragments, whereas lysine leads to loss of longer neutral fragments. It also appears that b ions might be produced by two different mechanisms depending on the parent peptide size. A model for the fragmentation pathways in competition is proposed. These relationships between average fragment size and parent peptide size could be further exploited also for CID fragment spectra and could be included in fragmentation prediction algorithms.
Journal of the American Society for Mass Spectrometry, 2007
Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagg... more Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)(2+) ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)(2+) dications by electrospray. ECD of (TMPP-ac-peptide + H)(2+) resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)(+) ions were detected. The dissociations involved loss of H, formation of (TMPP + H)(+), and N-C(alpha) bond cleavages giving TMPP-CH(2)CONH(2)(+) (c(0)) and c(1) fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)(2+) resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph(3)P-ac-GK + H)(2+) and (H(3)P-ac-GK + H)(2+) analogs indicated that the doubly charged ions contained the lysine side-chain NH(3)(+) group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 A in the most stable dication conformers. The intrinsic recombination energies of the TMPP(+)-ac and (GK + H)(+) moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)(+*) ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)(+*) ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N-C(alpha) bonds to give rise to the c(1) fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c(0) fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD.
The Journal of Physical Chemistry Letters, 2011
Electron capture and electron transfer dissociations are bioanalytical methods for fragmenting ca... more Electron capture and electron transfer dissociations are bioanalytical methods for fragmenting cations after reduction by an electron. Previous computational studies based on conventional DFT schemes have concluded that the first step of these processes, the attachment of the electron, leads to extensive delocalization of the spin density in the intermediate radical cation. Here we show that most DFT methods produce unphysical results when studying single electron reduction of a dicationic peptide. This is not the case for post-HF methods and long-range corrected functionals that show satisfying electron affinities, intermolecular interaction energies, and spin density trends. Our results suggest that the charged group with the highest electron affinity on the precursor cation is also the site of spin density in the electronic ground state after electron attachment. These findings have important implications for the interpretation of experimental data from electron-based processes in biomolecules and may guide the development of new functionals.
Journal of Organometallic Chemistry, 1998
A comparative theoretical study of the terminal phosphinidene complexes HPCr(CO) 5 , HPTi(Cp 2 ) ... more A comparative theoretical study of the terminal phosphinidene complexes HPCr(CO) 5 , HPTi(Cp 2 ) and HPTiCl 2 , at the MP2 and DFT levels, has been carried out. The calculated results have then been used for determining the electron localization function (ELF) in these moieties. Both techniques show that in the singlet ground state of HPCr(CO) 5 , one gets a weak double P -Cr bond, with an electrophilic character on P (i.e. electron-deficient center). Conversely, in the singlet ground state of Ti complexes, the P-Ti bond shows a greater double bond character than in the P -Cr linkage, associated with an overall nucleophilic character of P. These results are in good agreement with all available experimental data.
The Journal of Organic Chemistry, 2002
Quantum-chemical DFT calculations using the B3LYP functionals have been carried out for 1-R-subst... more Quantum-chemical DFT calculations using the B3LYP functionals have been carried out for 1-R-substitued phospholes and some 1-R-substitued 3,4-dimethylphospholes where R = H, Me, Ph, CN, OH, OMe, F, Cl, and Br. The aromaticity of the phospholyl rings is interpreted as a function of geometric, magnetic, and energetic indexes. It is shown, in agreement with previous experimental results, that phosphole aromaticity does not correlate with pyramidality at phosphorus. Variation of hyperconjugative and, to a lesser extent, conjugative effects is responsible for the change in cyclic delocalization for the phospholes studied here.
The Journal of Organic Chemistry, 1999
Geometries, aromatic character, Mulliken charge distribution, and MO diagrams of 1,2-aza-, 1,3,2d... more Geometries, aromatic character, Mulliken charge distribution, and MO diagrams of 1,2-aza-, 1,3,2diaza-, 1,3-aza-, and 1,3,5-diazaphosphinines have been calculated and compared to those of phosphinine and pyridine. This study reveals that the introduction of nitrogen atoms at the position adjacent to phosphorus significantly reduces the aromatic delocalization and induces a [1,4] dipolar character through an increase of the positive charge on the P atom. This phenomenon does not occur in 1,3-aza-and 1,3,5-diazaphosphinines, which exhibit a poor dipolar character. This comparison confirms the high reactivity of 1,3,2-diazaphosphinines toward alkynes. A [4 + 2] cycloaddition reaction between these two types of diazaphosphinines and acetylene has been modelized. Calculated geometries of the resultant [4 + 2] diazabarrelene cycloadducts and that of their respective transition states reveal that, especially with 1,3,2-diaza isomers, the cycloaddition proceeds via a disymmetrical pathway that involves the preliminary formation of the P-C bond.
Comptes Rendus Chimie, 2002
At 170°C, 1,1'-bis(3,4-dimethylphospholyl)ferrocene (7) isomerises through the corresponding 2H-p... more At 170°C, 1,1'-bis(3,4-dimethylphospholyl)ferrocene (7) isomerises through the corresponding 2H-phospholes that are trapped by diphenylacetylene to give the 1,1'-ferrocenylene-bridged bis-1-phosphanorbornadiene (6). After resolution with an optically pure palladium complex, (R,R)-and (S,S)-(6) are tested in the asymmetric hydrogenation of a dehydroaminoacid, hydroformylation of styrene, and allylation of sodium malonate. To cite this article: G. Frison et al., C. R. Chimie 5 (2002) 245-249 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS phosphole / phosphanorbornadiene / ferrocene / asymmetric catalysis Résumé -A 170°C, le 1,1'-bis(3,4-diméthylphospholyl)ferrocene (7) s'isomérise pour donner les 2H-phospholes correspondants que l'on peut piéger par le diphénylacétylene. Après purification du racémique, l'adduit [4+2] qui en résulte, rac-(6), peut être dédoublé en ses deux énantiomères à l'aide d'un complexe énantiopur de palladium. Les énantiomères (R,R)-et (S,S)-(6) ont été testés dans l'hydrogénation asymétrique d'un déhydroaminoacide, dans l'hydroformylation asymétrique du styrène et dans l'allylation asymétrique du malonate de sodium, avec des résultats moyens. Pour citer cet article : G. Frison et al., C. R. Chimie 5 (2002) 245-249 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS phosphole / phosphanorbornadiène / ferrocène / catalyse asymétrique * Correspondence and reprints. 9 (d, J = 7.0 Hz); 8b (0.94 g, 35%): 31 P NMR (CDCl 3 ) δ 55.7; 1 H NMR (CDCl 3 ) δ 1.44 (s, 6H),1.70 (d, J = 5.7 Hz, 6H), 2.54 (s, 6H), 2.70 (d, J + 10.0 Hz, 2H), 2.83 (s, 6H), 3.78 (m, 2H), 2.89 (s, 6H), 3.0 (d, J = 10 Hz, 2H), 3.75 (s, 4H), 3.87 (s, 2H), 4.36 (s, 2H), 4.79 (s, 2H), 5.69 (t, J = 7.0 Hz, 2H), 5.82 (t, J = 7.0 Hz, 2H), 6.51 (t, J = 7.3 Hz, 2H), 6.70-7.30 (m, 22H); 13 C NMR (CDCl 3 ) δ 16.9 (d,
Chemistry - A European Journal, 2003
The new tetradentate ligand 1,4-bis(5 H-dibenzo[a,d]cyclohepten-5yl)-1,4-diazabuta-1,3-diene ( H ... more The new tetradentate ligand 1,4-bis(5 H-dibenzo[a,d]cyclohepten-5yl)-1,4-diazabuta-1,3-diene ( H tropdad) allows the syntheses of the 16-electron cationic rhodium complexes [M( H tropdad)](O 3 SCF 3 ) (M Rh, Ir). The structure of the rhodium complex was determined by X-ray analysis and points to a description of these as [M 1 ( H tropdad) 0 ] with short CN bonds (av 1.285 ä) and a long CÀC bond (1.46 ä) in the diazabutadiene (dad) moiety, that is the M 3 dad charge-transfer is negligible. Both [Rh( H tropdad)] and [Ir( H tropdad)] are reduced at very low potentials (E 1 1/2 À 0.56 V and E 1 1/2 À 0.35 V, respec-tively) which allowed the quantitative synthesis of the neutral paramagnetic complexes [M( H tropdad)] 0 (M Rh, Ir) by reacting the cationic precursor complexes simply with zinc powder. The [M( H tropdad)] 0 complexes are stable against protic reagents in organic solvents. Continuous wave and pulse EPR spectroscopy was used to characterize the paramagnetic species and the hyperfine coupling constants were deter-mined: [Rh( H tropdad)] 0 : A iso ( 14 N) 11.9 MHz, A iso ( 1 H) 14.3 MHz, A iso ( 103 Rh) À 5.3 MHz; [Ir( H tropdad)] 0 : A iso ( 14 N) 11.9 MHz, A iso ( 1 H) 14.3 MHz. In combination with DFT calculations, the experimentally determined g and hyperfine matrices could be orientated within the molecular frame and the dominant spin density contributions were determined. These results clearly show that the complexes [M( H tropdad)] 0 are best described as [M 1 ( H tropdad) .À ] with a [16 1] electron configuration.
Chemical Communications, 2012
A double ring-expansion methodology allows the stepwise synthesis of tri- and tetra-phosphaporhyr... more A double ring-expansion methodology allows the stepwise synthesis of tri- and tetra-phosphaporhyrinogens. Structural and calculational methods reveal extended delocalisation about their phospholide centres.
Journal of the American Chemical Society, 2008
In this study, we propose the first spectroscopic structural characterization of c-type ions prod... more In this study, we propose the first spectroscopic structural characterization of c-type ions produced by ECD of a peptide. The structure of c-type ions formed by electron capture dissociation and the overall mechanism leading to their formation are still a question of debate. Depending on the mechanism, c-type ions have been proposed to have either an enol-imine structure (-C(OH)NH) or an amide one (-C(O)-NH2). Since these ions are isomeric, mass spectrometry only cannot discriminate between them, but infrared spectroscopy can bring experimental evidence and help determine which scheme is operative. Using the coupling between a tunable free electron laser and a FT-ICR mass spectrometer, we show that c-type ions have an amide structure, characterized by an IR signature of the C=O stretch at 1731 cm(-1). This result is particularly interesting from the perspective of the elucidation of the ECD mechanism.