Hydrogen—deuterium exchange at non-labile sites: A new reaction facet with broad implications for structural and dynamic determinations (original) (raw)
Related papers
2016
Derivatization of peptides as quaternary ammonium salts (QAS) is a known method for sensitive detection by electrospray ionization tandem mass spectrometry. Hydrogens at α-carbon atom in N,N,N-trialkylglycine residue can be easily exchanged by deuterons. The exchange reaction is base-catalyzed and is dramatically slow at lower pH. Introduced deuterons are stable in acidic aqueous solution and are not back-exchanged during LC-MS analysis. Increased ionization efficiency, provided by the fixed positive charge on QAS group, as well as the deuterium labeling, enables the analysis of trace amounts of peptides.
Gas-Phase Chemistry of Protonated Ethylamine: A Mass Spectrometric and Molecular Orbital Study
The Journal of Physical Chemistry, 1996
The unimolecular dissociation of protonated ethylamine, [CH 3 CH 2 NH 3 ] + , 1, has been examined by both mass spectrometric techniques and molecular orbital calculations. Metastable dissociations of various deuterated species demonstrate that the loss of ethene from 1 involves specifically a transfer of a hydrogen atom from the methyl to the NH 2 group. A very limited scrambling (4%) of the hydrogen atoms of the ethyl moiety is observed. Ab initio molecular orbital calculations have been performed at the MP4SDTQ/6-311G**//MP2/ 6-31G*+ZPE level of theory to examine the mechanism of the unimolecular dissociation of ions 1. It appears that 1 loses a molecule of ethene after a rate-determining isomerization into a proton-bound complex: [C 2 H 4 ‚‚‚-NH 4 ] + , 2. The marginal hydrogen scrambling is accounted for by 1,2-H shifts on the ethyl group inside a second, loosely bonded, complex involving an ethyl cation and a molecule of ammonia: [C 2 H 5 ‚‚‚NH 3 ] + , 3.
International Journal of Mass Spectrometry and Ion Processes, 1998
The effects of basic site proximity on gas-phase deprotonation and hydrogen/deuterium (H/D) exchange reactions were investigated for three model dodecapeptide ions in a Fourier transform ion cyclotron resonance mass spectrometer. Each peptide contained four high basicity lysine (K) residues and eight low basicity glycine (G) residues; however, the ordering of the residues differed. In the deprotonation studies, 'fully protonated' peptide ions, [M + 4H] 4+, where M = (KGG)4, (K2G4)2, and K4G8, were reacted with reference compounds of known basicities. Reaction efficiencies were in the order: [K4G8 + 4HI 4+ > [(K2G4)2 + 4H]a+~[(KGG)4 + 4H] 4+. The facile reaction of [K4G8 + 4HI 4+ is consistent with this ion having the highest Coulomb energy. For gas-phase H/D exchange reactions with d4-methanol, [K4G8 + 4H] 4÷ has the fastest exchange rate and undergoes the largest number of exchanges; 22 of the 26 labile hydrogens exchanged within the timescale studied. In contrast, [(KGG)4 + 4H] 4+ and [(K2G4)2 + 4HI *~ reacted more slowly, but at similar rates, with a maximum of 14 observed exchanges for both ions. Molecular dynamics calculations were conducted to gain insights into conformations. In the lowest energy structures for [(KGG)4 + 4H] '~ and [(K2G4) 2 + 4H] 4+, the lysine n-butylamino chains stretch out to minimize Coulomb energy; there is little or no intramolecular hydrogen bonding involving the protonated amino groups. In contrast, for [K4G8 + 4H] 4+, the proximity of the basicity residues makes minimization of the Coulomb energy difficult; instead, the structure becomes more compact with stabilization of the protonated amino groups by extensive intramolecular hydrogen bonding to heteroatoms in the peptide backbone. The calculated structures suggest that, in the H/D exchange reactions, the compact conformation of [KaG8 + 4H] 4+ allows stabilization of the methanolpeptide intermediate by hydrogen bonding, thus lowering the barrier to proton transfer within the complex. The diffuse conformations of [(KGG)4 + 4H] 4÷ and [(K2G4)2 + 4H] 4+ have lower Coulomb energies and fewer avenues for hydrogen bonding with methanol, which may limit their rate and extent of exchange.
The Hydrogen–Deuterium Exchange at α-Carbon Atom in N,N,N-Trialkylglycine Residue: ESI-MS Studies
Journal of The American Society for Mass Spectrometry, 2012
All solvents and reagents were used as supplied. Fmoc amino acid derivatives (Fmoc-Ala-OH, Fmoc-Asp(OBu t )-OH, Fmoc-Gln(Trt)-OH, Fmoc-Ile-OH, Fmoc-Lys(Mtt)-OH, Fmoc-Met-OH, Fmoc-Phe-OH, Fmoc-Pro-OH, Fmoc-Thr(Bu t )-OH, Fmoc-Val-OH, Fmoc-Tyr(Bu t )-OH) and the preloaded Wang resins (0.50-0.70 mmol/g) were purchased from Nova Biochem. 2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethylaminium tetrafluoroborate N-oxide (TBTU), the MBHA-Rink amide resin (0.69 mmol/g) and trifluoroacetic acid (TFA) were obtained from IrisBiotech. Betaine, triethylamine (Et 3 N), tripropylamine (Pr 3 N), tributylamine (Bu 3 N) and 1,4-diazabicyclo[2.2.2]octane (DABCO), used for QAS formation and solvents for peptide synthesis (N,N-dimethylformamide (DMF), dichloromethane (DCM), and (Nethyldiisopropylamine (DIEA) were obtained from Sigma Aldrich; iodoacetic acid from Merck; N,N'-diisopropylcarbodiimide (DIC) and triisopropylsilane (TIS) from Fluka. Deuterium oxide (D 2 O, 99.9% purity) was obtained from Cambridge Isotope Laboratories, Inc.
Hydrogen exchange and mass spectrometry: A historical perspective
Journal of the American Society for Mass Spectrometry, 2006
Protein molecules naturally emit streams of information-rich signals in the language of hydrogen exchange concerning the intimate details of their stability, dynamics, function, changes therein, and effects thereon, all resolved to the level of their individual amino acids. The effort to measure protein hydrogen exchange behavior, understand the underlying chemistry and structural physics of hydrogen exchange processes, and use this information to learn about protein properties and function has continued for 50 years. Recent work uses mass spectrometric analysis together with an earlier proteolytic fragmentation method to extend the hydrogen exchange capability to large biologically interesting proteins. This article briefly reviews the advances that have led us to this point and the understanding that has so far been achieved.
Hydrogen/deuterium exchange in mass spectrometry
Mass spectrometry reviews, 2018
The isotopic exchange approach is in use since the first observation of such reactions in 1933 by Lewis. This approach allows the investigation of the pathways of chemical and biochemical reactions, determination of structure, composition, and conformation of molecules. Mass spectrometry has now become one of the most important analytical tools for the monitoring of the isotopic exchange reactions. Investigation of conformational dynamics of proteins, quantitative measurements, obtaining chemical, and structural information about individual compounds of the complex natural mixtures are mainly based on the use of isotope exchange in combination with high resolution mass spectrometry. The most important reaction is the Hydrogen/Deuterium exchange, which is mainly performed in the solution. Recently we have developed the approach allowing performing of the Hydrogen/Deuterium reaction on-line directly in the ionization source under atmospheric pressure. Such approach simplifies the samp...
Site specificity in the H-D exchange reactions of gas-phase protonated amino acids with CH3OD
Organic Mass Spectrometry, 1993
H-D exchange reactions of methanol-d, with protonated amino acids were performed in an external-source Fourier transform mass spectrometer. Absolute rate constants were determined for the group which included glycine, alanine, valine, leucine, isoleucine and proline. By comparing reactivities with selected methyl esters, it was found that exchange on the carboxylic acid occurs 3-10 times faster than exchange on the amino group. No simple correlation is observed between the rates of H-D exchange on the acid group and the size of the alkyl group. However, the rates of exchange on the amine decrease with increasing gas-phase basicity. Glycine, the least basic amino acid, exchanges its amine hydrogens the fastest. These results are useful for determining the interaction of methanol with protonated amino acids and can provide insight into the H-D exchange reactions observed with polyprotonated proteins produced by electrospray ionization.
Hydrogen Isotope Exchange - The Foundation of C-H activation and Isotope Science in Drug Discovery
Angewandte Chemie (International ed. in English), 2017
The wide range of applications involving hydrogen isotopes in drug discovery and beyond dictates that their selective and efficient installation continues to present an important and continuing challenge to synthetic chemists. In this review advances in the field of hydrogen isotope exchange over the last ten years and related hydrogen isotope applications in a broad spectrum of disciplinary areas are brought together.
Use of H/D isotope effects to gather information about hydrogen bonding and hydrogen exchange rates
Journal of Magnetic Resonance, 2014
Polar side-chains in proteins play important roles in forming and maintaining three-dimensional structures, and thus participate in various biological functions. Until recently, most protein NMR studies have focused on the non-exchangeable protons of amino acid residues. The exchangeable protons attached to polar groups, such as hydroxyl (OH), sulfhydryl (SH), and amino (NH 2) groups, have mostly been ignored, because in many cases these hydrogen atoms exchange too quickly with water protons, making NMR observations impractical. However, in certain environments, such as deep within the hydrophobic interior of a protein, or in a strong hydrogen bond to other polar groups or interacting ligands, the protons attached to polar groups may exhibit slow hydrogen exchange rates and thus become NMR accessible. To explore the structural and biological implications of the interactions involving polar side-chains, we have developed versatile NMR methods to detect such cases by observing the line shapes of 13 C NMR signals near the polar groups, which are affected by deuterium-proton isotope shifts in a mixture of H 2 O and D 2 O. These methods allow the detection of polar side-chains with slow hydrogen-deuterium exchange rates, and therefore provide opportunities to retrieve information about the polar side-chains, which might otherwise be overlooked by conventional NMR experiments. Future prospects of applications using deuterium-proton isotope shifts to retrieve missing structural and dynamic information of proteins are discussed.
International Journal of Mass Spectrometry, 2010
Phenylalanine analogs were subjected to hydrogen/deuterium exchange (HDX) in both solution and the gas phase, and gas-phase infrared multiple photon dissociation spectra were obtained for each of the species. For sodium cation-attached N-acetylphenylalanine, gas-phase HDX took place at only one site. Comparison of spectra from both undeuterated and singly deuterated sodiated N-acetylphenylalanine showed band shifts for normal modes that involved mainly vibrations of the O-H group, indicating that gas-phase exchange occurs at the COOH hydrogen and not at the NH hydrogen. Conversely, HDX in solution did result in exchange of the NH hydrogen, even for the protected species O-methyl Nacetylphenylalanine and N-acetylphenylalanine O-methylglycine. Rate coefficients for gas-phase H/D exchange were measured for the single deuteration of sodiated N-acetylphenylalanine and all three deuterations of protonated N-acetylphenylalanine, and found to be in the range (1.5-3.6) × 10 −11 cm 3 /s. Density functional theory calculations predicted that the phenylalanine analogs, although of different size, have relatively similar structural features. These calculations showed that Na + interacts with the phenyl ring and all available carbonyl oxygens, thus essentially locking the structures into one basic conformation. This behavior is quite distinct from other amino acids which are more flexible, and where gas-phase exchange also occurs at the amine (NH) group.