Abstract:Chemical derivatization of peptides allows efficient F2 laser single photon ionization (SPI) of Fmoc-derivatized peptides covalently bound to surfaces. Laser desorption photoionization mass spectrometry using 337-nm pulses for desorption and 157.6-nm pulses for threshold SPI forms large ions identified as common peptide fragments bound to either Fmoc or the surface linker. Electronic structure calculations indicate the Fmoc label is behaving as an ionization tag for the entire peptide, lowering the ionization … Show more
“…More recently, it has been suggested that the tagging of large biomolecules with light chromophores can facilitate their detection [25]. This idea has also been corroborated in our own studies on the photo-detection of large neutral amino acid and nucleotide clusters [26].…”
The volatilization and soft ionization of complex neutral macromolecules at low energies has remained an outstanding challenge for several decades [1]. Most volatilization techniques in mass spectrometry produce ions already in the source and most of them lead to particle velocities in excess of several hundred meters per second. For many macromolecules, post-ionization is inefficient since electronic or optical excitations can be followed by competing non-ionizing internal conversion, electron recapture, or fragmentation processes. Here, we explore the laser-assisted volatilization of neutral perfluoroalkyl-functionalized tetraphenylporphyrins as well as their single-photon ionization using vacuum ultraviolet (VUV) light at 157 nm. A systematic investigation of the ionization curves allows us to determine the molecular velocity distribution and ionization cross sections. We demonstrate the detection of single photon ionized intact organic molecules in excess of 10 kDa from a slow molecular beam.
“…More recently, it has been suggested that the tagging of large biomolecules with light chromophores can facilitate their detection [25]. This idea has also been corroborated in our own studies on the photo-detection of large neutral amino acid and nucleotide clusters [26].…”
The volatilization and soft ionization of complex neutral macromolecules at low energies has remained an outstanding challenge for several decades [1]. Most volatilization techniques in mass spectrometry produce ions already in the source and most of them lead to particle velocities in excess of several hundred meters per second. For many macromolecules, post-ionization is inefficient since electronic or optical excitations can be followed by competing non-ionizing internal conversion, electron recapture, or fragmentation processes. Here, we explore the laser-assisted volatilization of neutral perfluoroalkyl-functionalized tetraphenylporphyrins as well as their single-photon ionization using vacuum ultraviolet (VUV) light at 157 nm. A systematic investigation of the ionization curves allows us to determine the molecular velocity distribution and ionization cross sections. We demonstrate the detection of single photon ionized intact organic molecules in excess of 10 kDa from a slow molecular beam.
“…Even better, the use of 7.87-eV LDPI-MS with a low-IE tag (dimethyl amino benzene) coupled to the bisphenol A derivative led to strong signal enhancement (43). Tagging a covalently bound surface analyte with a low-IE species also permitted detection of small peptides covalently bound to an oxide via a siloxane linker (32). …”
Thanks to recent technological advances and singlephoton ionization's (SPI's) ability to detect all organics,Because the human eye does not detect IR radiation, we cannot see a warm object in the dark without an IR camera or other "transformation method". MS has the same problem: it cannot directly detect the objects of intereststhe analyte moleculessbut only their ionized counterparts. Therefore, the transformation methods that ionize the analyte molecules are of particular importance to MS. The invention of new ionization methods such as MALDI or ESI for MS detection of biomolecules has had an enormous influence on the development of MS and its applications in analytical chemistry.However, many ionization methods result in the formation not only of intact molecular ions but also of ion fragments. This is particularly true for electron impact (EI) ionization, the classical ionization method for smaller molecules ranging in mass up to ∼500 Da. EI uses electrons of 70-eV kinetic energy, near where maximal ionization efficiency occurs, 1 which makes it a "hard" ionization technique because the analytes are heavily fragmented upon ionization. The molecular peak is often barely visible in the mass spectra of labile compounds, although the fragment patterns do supply information about the presence of distinct functional groups in the investigated molecules. Furthermore, the fragment patterns of unknown substances can be used for a statistically based identification by comparison with EI-MS library data. The benefits of the latter feature made MS with EI the routine spectrometric detection method for GC. However, the frequent absence of information on the molecular weight of labile compounds is a severe disadvantage of EI, hampering the identification of unknowns. Furthermore, for complex mixtures of organic compounds, EI-MS requires a preseparation method such as GC; otherwise, the overlapping complex fragment patterns cannot be deconvoluted into mass spectra of individual compounds.These shortcomings of EI have led to a continuing demand for robust fragmentation-free or "soft" ionization methods for MS. Several soft ionization techniques have been developed, including methods based on chemical ionization (CI), field ionization (FI), and photoionization (PI). More recently, MALDI and ESI emerged and became the dominant soft ionization methods for polar
“…A home built laser desorption vacuum ultraviolet (VUV, 118 nm) postionization linear time‐of‐flight mass spectrometer (LDPI MS) is used for surface analysis of the model system. The advantage of VUV postionization in LDPI MS is that it enhances ionization yields with a minimum of fragmentation 14–16. LDPI MS is used to verify the preparation steps of the model dental composite by chemical analysis of the methacryloyl overlayer, Bis‐GMA‐methacryloyl overlayer, and several control surfaces.…”
Some dental composites consist of a polymerizable resin matrix bound to glass filler particles by silane coupling agents. The resin in these composites includes bisphenol A diglycidyl methacrylate (Bis-GMA) as well as other organic components. Silane coupling agents such as 3-(trimethoxysilyl) propyl methacrylate (MPS) have been used to improve the mechanical properties of the dental composites by forming a covalent bond between the glass filler particles and the resin. These resin-glass composites undergo material property changes during exposure to the oral environment, but degradation studies of the commercial composites are severely limited by their chemical complexity. A simplified model of the dental composite has been developed, which captures the essential chemical characteristics of the filler particle-silane-resin interface. This model system consists of the resin matrix compound Bis-GMA covalently bound via a methacryloyl overlayer to amorphous silicon oxide (SiO2) surface via a siloxane bond. Scanning electron microscopy shows the porous characteristic and elemental composition of the SiO2 film, which approximately mimics that of the glass filler particles used in dental composites. LDPI MS and XPS verify the chemistry and morphology of the Bis-GMA-methacryloyl overlayer. Preliminary results demonstrate that LDPI MS will be able to follow the chemical processes resulting from aging Bis-GMA-methacryloyl overlayers aged in water, artificial saliva, or other aging solutions.
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