title: Experimental and theoretical studies of sodium cation complexes of the deamidation and dehydration products of asparagine, glutamine, aspartic acid, and glutamic acid.
abstract: The deamidation and dehydration products of Na+(L), where L = asparagine (Asn), glutamine (Gln), aspartic acid (Asp), and glutamic acid (Glu), are examined in detail utilizing collision-induced dissociation (CID) with Xe in a guided ion beam tandem mass spectrometer (GIBMS). Results establish that the Na+(L) complexes decompose upon formation in our dc discharge/flow tube ion source to form a bis-ligand complex, Na+(L-HX)(HX), composed of a sodium cation, the (L-HX) decomposition product, and HX, where HX = NH3 for the amides and H2O for the acids. Analysis of the energy-dependent CID cross sections for the Na+(L-HX)(HX) complexes provides unambiguous identification of the (L-HX) fragmentation products as 3-amino succinic anhydride (a-SA) for Asx and oxo-proline (O-Pro) for Glx. Furthermore, these experiments establish the 0 K sodium cation affinities for these five-membered ring decomposition products and the H2O and NH3 binding affinities of the Na+(a-SA) and Na+(O-Pro) complexes after accounting for unimolecular decay rates, the internal energy of reactant ions, and multiple ion-molecule collisions. Quantum chemical calculations are determined for a number of geometric conformations of all reaction species as well as a number of candidate species for (L-HX) at the B3LYP/6-311+G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated examination of both the experimental work and quantum chemical calculations allows for a complete characterization of the products of deamidation and dehydration of Asx and Glx, as well as the details of Na+, H2O, and NH3 binding to the decomposition species.
authors: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
authors: A L
authors: AL
authors: Heaton
authors: S J
authors: SJ
authors: Ye
authors: P B
authors: PB
authors: Armentrout
mesh_terms: D000577:Amides / Q000737:chemistry*; D000596:Amino Acids / Q000737:chemistry*; D001216:Asparagine / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry; D018698:Glutamic Acid / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D012964:Sodium / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D000577:Amides; D000596:Amino Acids; D014867:Water; D005973:Glutamine; D001224:Aspartic Acid; D018698:Glutamic Acid; D001216:Asparagine; D012964:Sodium