A commercial quadrupole/time-of-flight (QqTOF) tandem mass spectrometer has been adapted for ion/ion reaction studies. To enable mutual storage of oppositely charged ions in a linear ion trap, the oscillating quadrupole field of the second quadrupole of the system (Q2) serves to store ions in the radial dimension while auxiliary RF is superposed on the end lenses of Q2 during the reaction period to create barriers in the axial dimension. A pulsed dual electrospray (ESI) source is directly coupled to the instrument interface for the purpose of proton transfer reactions. Singly and doubly charged protein ions as high in mass as 66 kDa are readily formed and observed after proton transfer reactions. For the modified instrument, the mass resolving power is about 8000 for a wide m/z range and the mass accuracy is ~20 ppm for external calibration and ~5 ppm for internal calibration after ion/ion reactions. Parallel ion parking is demonstrated with a six-component protein mixture, which shows the potential application of reducing spectral complexity and concentrating certain charge states. The current system has high flexibility with respect to defining MS n experiments involving collisioninduced dissociation (CID) and ion/ion reactions. Protein precursor and CID product masses can be determined with good accuracy, providing an attractive platform for top-down proteomics. Electron transfer dissociation (ETD) ion/ion reactions are implemented by using a pulsed nano-ESI/ atmospheric pressure chemical ionization (APCI) dual source for ionization. The reaction between protonated peptide ions and radical anions of 1,3-dinitrobenzene formed exclusively c-and z-type fragment ions.
Inhibition of the bromodomain of the transcriptional regulator CBP/P300 is an especially interesting new therapeutic approach in oncology. We recently disclosed in vivo chemical tool 1 (GNE-272) for the bromodomain of CBP that was moderately potent and selective over BRD4(1). In pursuit of a more potent and selective CBP inhibitor, we used structure-based design. Constraining the aniline of 1 into a tetrahydroquinoline motif maintained potency and increased selectivity 2-fold. Structure-activity relationship studies coupled with further structure-based design targeting the LPF shelf, BC loop, and KAc regions allowed us to significantly increase potency and selectivity, resulting in the identification of non-CNS penetrant 19 (GNE-781, TR-FRET IC = 0.94 nM, BRET IC = 6.2 nM; BRD4(1) IC = 5100 nΜ) that maintained good in vivo PK properties in multiple species. Compound 19 displays antitumor activity in an AML tumor model and was also shown to decrease Foxp3 transcript levels in a dose dependent manner.
The alternate operation of nanoelectrospray ionization and atmospheric pressure chemical ionization, using a common atmosphere/vacuum interface and ion path, has been implemented to facilitate ion/ion reaction experiments in a linear ion trap-based tandem mass spectrometer. The ion sources are operated in opposite polarity modes whereby one of the ion sources is used to form analyte ions while the other is used to form reagent ions of opposite polarity. This combination of ion sources is well-suited to implementation of experiments involving multiply charged ions in reaction with singly charged ions of opposite polarity. Three analytically useful ion/ion reaction types are illustrated: the partial deprotonation of a multiply protonated protein, the partial protonation of a multiply deprotonated oligonucleotide, and electron transfer to a multiply protonated peptide. The approach described herein is attractive in that it enables both single proton-transfer and single electron-transfer ion/ion reaction experiments to be implemented without requiring major modifications to the tandem mass spectrometer hardware. Furthermore, a wide range of reactant ions can be formed with these ionization methods and the pulsed nature of operation appears to lead to no significant compromise in the performance of either ion source.
A pulsed dual electrospray ionization source has been developed to generate positive and negative ions for subsequent ion/ion reaction experiments. The two sprayers, typically a nano-electrospray emitter for analytes and an electrospray emitter for reagents, are positioned in a parallel fashion close to the sampling orifice of a triple quadrupole/linear ion trap tandem mass spectrometer (Sciex Q TRAP). The potentials applied to each sprayer are alternately pulsed so that ions of opposite polarity are generated separately in time. Ion/ion reactions take place after ions of each polarity are sequentially injected into a high-pressure linear ion trap, where axial trapping is effected by applying an auxiliary radio frequency voltage to the end lenses. The pulsed dual electrospray source allows optimization of each sprayer and can be readily coupled to any spray interface with no need for instrument modifications, provided the potentials required to transmit the ion polarity of interest can be alternated in synchrony with the emitter potentials. Ion/ion reaction examples such as charge reduction of multiply charged protein ions, charge inversion of peptides ions, and protein-protein complex formation are given to illustrate capabilities of the pulsed dual electrospray source in the study of gas-phase ion/ion chemistry. T he advent of electrospray ionization (ESI) mass spectrometry has revolutionized the analysis of many biologically important macromolecules [1,2]. Both the polarity and the magnitude of the charge associated with an ionized biomolecule play important roles in the use of tandem mass spectrometry for the identification and structural characterization of the biomolecule from which the ions were derived. Ion/ion reactions provide efficient means for manipulating the identities of gas-phase ions after their initial formation [3,4], including altering ion polarity and absolute charge. Applications of charge manipulation via ion/ ion reactions include: mixture analysis [5][6][7][8], especially with the application of the "ion parking" technique for gas-phase concentration and charge state purification [9], the formation of ions that cannot be directly produced by ESI for subsequent tandem mass spectrometry studies [10], and the reduction of the product ion charge states to singly and doubly charged so as to simplify the interpretation of product ion spectra [11][12][13][14][15][16]. Electron-transfer ion/ion reactions have recently been described as a means of inducing structurally informative dissociation, giving rise to cleavages analogous to those noted in electron capture dissociation [17][18][19][20][21]. In this regard, ion/ion reactions play a role as a probe of primary structure.Electrodynamic ion traps, either a quadrupole ion trap or a linear ion trap (LIT), are particularly useful reaction vessels for ion/ion reactions because of their ability to store oppositely-charged ions simultaneously [22] as well as their ion isolation and MS n functionalities [23]. Most ion/ion reaction studies involving m...
Stable aqueous colloids of 2-3 nm In 2 S 3 nanocrystals have been prepared by using the classical method of nanoparticle stabilization by low molecular weight thiols. TEM crystal lattice spacing, X-ray diffraction, EDAX data, and electron diffraction indicate that the nanoparticles are predominantly in -In 2 S 3 form. They exhibit relatively strong excitonic emission at 360-380 nm with a quantum yield of 1.5%. The excitonic radiative lifetime is 350 ns, which indicates that a direct allowed electronic transition is responsible for this emission. The NMR lines of the stabilizer are strongly broadened and shifted as a result of deshielding induced by electron withdrawing by positively charged metal ions. This effect quickly wears off as the carbon chain becomes longer and the separation between the hydrogen atoms of the stabilizer and the semiconductor surface increases. The broadening is attributed to the reduced mobility of the stabilizer in the nanoparticle shell. For CdS nanoparticles of the same size, this effect was found to be substantially stronger than for In 2 S 3 . The lower density of metal centers in In 2 S 3 than in CdS, which serve as anchor points for the stabilizer, promotes greater mobility of the stabilizer moieties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.