MS(n) experiments involving low energy collisionally activated dissociation (CAD) in a quadrupole ion trap were used to characterize the fragmentation of alkali, alkaline earth and transition metal complexes of five cyclic peptides, and the results were compared with those obtained for protonated cyclic peptides. Complexes with metal ions produced enhanced abundances of the most diagnostic fragments for elucidating the primary structures. For cyclosporin A, nickel and lithium complexes gave additional sequence information compared with the protonated peptide. For depsipeptides, sodium and lead complexes were superior to the protonated peptide or other metal complexes for sequencing residues, and CAD of the lead complexes led to preferential cleavage of two residues at a time. For cyclic lipopeptides, complexes with silver, nickel and strontium ions provided enhanced abundances of key fragment ions.

In the present study, electrospray ionization mass spectrometry is used to evaluate the metal-binding selectivities of an array of novel caged macrocycles for mercury(II), lead(II), cadmium(II), and zinc(II) ions. In homogeneous methanol/chloroform solutions as well as extractions of metals from aqueous solution by macrocycles in chloroform, it is found that the type of heteroatom (S, O, N), cavity size, and presence of other substituents influence the metal selectivities. Several of the macrocycles in this study bind mercury ion very selectively and efficiently in the presence of many other metal ions and have an avidity toward mercury that was tunable by the size and combination of heteroatoms in the macrocycle ring and the number of cage groups attached. The extraction mechanism was further investigated by determining the variation in extraction selectivity as a function of the counterions of the mercury salts.

No abstract

Resolution improvements in dipolar resonant excitation have been examined in a round-rod quadrupolar collision cell for values of the Mathieu characteristic exponent ␤ equal to n/p, where n and m are small integers (prime ␤ values) versus other ␤ values where n and p are not small (ordinary␤ values). The trajectories of ions moving in the time-varying electric fields of a quadrupole with and without buffer-gas molecules were calculated to determine the relationship of prime and ordinary ␤ values to frequency resolution for resonant ion excitation and ejection. For prime ␤ values, the ion trajectory in the hyperbolic quadrupole field will be exactly periodic with a period of at most 4 p/⍀, where ⍀ is the angular frequency of the main drive radio-frequency ( . By scanning the RF voltage, trapped ions may be ejected one m/z ratio at a time out of the confining electric field for detection. While the ions are confined, ion-molecule reactions may be carried out. Additionally, the kinetic energy of the trapped ions can be increased by applying a dipolar AC potential that is resonant with the secular frequency of the motion of ions ( 0 ) of one or more m/z values. This increased kinetic energy can be used to selectively eject the ions from the trapping field, or to add internal energy to the confined ions through collisions with a neutral gas added to the trap. This dipolar resonant excitation has been a common method for performing mass-selective ejection and fragmentation of ions confined in Paul traps and, more recently, in linear ion traps [2][3][4]. The theory of instability space, as it relates to auxiliary AC excitation in a linear and 3D quadrupole trap for quadrupolar resonant excitation, has been addressed [5][6][7]. The trajectories of ions in a linear ion trap with dipolar auxiliary excitation have been examined by Franzen [8]; those for hyperbolic and circular quadrupole rods with and without collision gas by Collings et al. [2].In tandem mass spectrometry (MS/MS), resolution of the product ions is sometimes crucial as many fragments have similar m/z values [9 -15]. Unambiguous product-ion assignment often requires better than unit-mass resolution to resolve "isobaric" interferences, which are particularly acute when the analyte is the minor component. Two factors that degrade m/z resolution after dipolar resonance excitation are increasing collisions with buffer-gas molecules [2] and increasing dipolar voltage amplitude [16]. One method to increase resolution is to excite the ions in such a way to reduce the frequency composition and the periodicity of the ions' motion in the electric field. In the present study, we used simulation software to determine the trajectories of ions [17] moving in a time-varying electric field and colliding with buffer-gas molecules in a linear quadrupole reaction cell with the instrumentally common and practical round-rod geometry.It is a common misconception that an ion trajectory within the quadrupolar field is necessarily aperiodic. As we will show below, provided that the...

Electrospray ionization mass spectrometry (ESI-MS) is used to evaluate the metal binding selectivities of an array of novel caged macrocycles for silver, gold, copper, nickel, zinc, iron, lead, manganese and alkali metal ions. It is found that five of the new compounds display silver selectivity, and their relative affinities for various metals depend on the type, number, and arrangement of heteroatoms (N, O), the cavity size, and the presence of aromatic substituents. Alkali metal cation binding studies are used to evaluate the size-selectivities of the cavities of the macrocycles. Electronic structure calculation by B3LYP density function theory methods were used to model the metal complexes. The presence of nitrogen atoms in the macrocyclic ring is essential for silver selectivity over other transition metals and alkali metal ions, and the presence of aromatic groups also enhances silver avidity. Macrocycle 3, a triaza-18-crown-6 analog modified with two phenyl groups and a cage group, is capable of selective extraction of Ag+ from aqueous solutions in the presence of other transition metal ions and the most common alkali and alkaline earth metal ions.