Tip enhanced laser ablation sample transfer for mass spectrometry

© 2015 Materials Research Society. Mass spectrometry is one of the primary analysis techniques for biological analysis but there are technological barriers in sampling scale that must be overcome for it to be used to its full potential on the size scale of single cells. Current mass spectrometry imaging methods are limited in spatial resolution when analyzing large biomolecules. The goal of this project is to use atomic force microscope (AFM) tip enhanced laser ablation to remove material from cells and tissue and capture it for subsequent mass spectrometry analysis. The laser ablation sample transfer system uses an AFM stage to hold the metal-coated tip at a distance of approximately 10 nm from a sample surface. The metal tip acts as an antenna for the electromagnetic radiation and enables the ablation of the sample with a spot size much smaller than a laser focused with a conventional lens system. A pulsed nanosecond UV or visible wavelength laser is focused onto the gold-coated silicon tip at an angle nearly parallel with the surface, which results in the removal of material from a spot between 500 nm and 1 um in diameter and 200 and 500 nm deep. This corresponds to a few picograms of ablated material, which can be captured on a metal surface for MALDI analysis. We have used this approach to transfer small peptides and proteins from a thin film for analysis by mass spectrometry as a first step toward high spatial resolution imaging

Synthesis and Asymmetric Resolution of α‑Azido-peroxides

An unprecedented synthesis of α-azido-peroxides has been developed using an FeCl₃-catalyst starting from carbonyl, TMS-azide, and hydroperoxide. Further, a base promoted decomposition of synthesized secondary α-azido-peroxides to provide the corresponding <i>tert</i>-butyl esters has been disclosed. Finally, an asymmetric kinetic resolution of such α-azido-peroxides has also been developed to provide chiral α-azido-peroxides in excellent enantiopurity

Trapping of Azidocarbenium Ion: A Unique Route for Azide Synthesis

For the first time, a sensitive azidocarbenium ion intermediate has been trapped with various nucleophiles to provide azides in excellent chemoselectivity. This provides a novel approach for the chemoselective synthesis of primary and secondary benzyl azides from aldehydes in a one-pot reaction. Enantioselective nucleophilic addition to the azidocarbenium ion has also been initiated

Trapping of Azidocarbenium Ion: A Unique Route for Azide Synthesis

For the first time, a sensitive azidocarbenium ion intermediate has been trapped with various nucleophiles to provide azides in excellent chemoselectivity. This provides a novel approach for the chemoselective synthesis of primary and secondary benzyl azides from aldehydes in a one-pot reaction. Enantioselective nucleophilic addition to the azidocarbenium ion has also been initiated

Synthesis and Asymmetric Resolution of α‑Azido-peroxides

An unprecedented synthesis of α-azido-peroxides has been developed using an FeCl₃-catalyst starting from carbonyl, TMS-azide, and hydroperoxide. Further, a base promoted decomposition of synthesized secondary α-azido-peroxides to provide the corresponding <i>tert</i>-butyl esters has been disclosed. Finally, an asymmetric kinetic resolution of such α-azido-peroxides has also been developed to provide chiral α-azido-peroxides in excellent enantiopurity

Tip-enhanced laser ablation sample transfer for biomolecule mass spectrometry

© 2014 American Society for Mass Spectrometry. Atomic force microscope (AFM) tip-enhanced laser ablation was used to transfer molecules from thin films to a suspended silver wire for off-line mass spectrometry using laser desorption ionization (LDI) and matrix-assisted laser desorption ionization (MALDI). An AFM with a 30 nm radius gold-coated silicon tip was used to image the sample and to hold the tip 15 nm from the surface for material removal using a 355 nm Nd:YAG laser. The ablated material was captured on a silver wire that was held 300 μm vertically and 100 μm horizontally from the tip. For the small molecules anthracene and rhodamine 6G, the wire was cut and affixed to a metal target using double-sided conductive tape and analyzed by LDI using a commercial laser desorption time-of-flight mass spectrometer. Approximately 100 fg of material was ablated from each of the 1 μm ablation spots and transferred with approximately 3% efficiency. For larger polypeptide molecules angiotensin II and bovine insulin, the captured material was dissolved in saturated matrix solution and deposited on a target for MALDI analysis

Primary Aminothiourea-Catalyzed Enantioselective Synthesis of Rauhut–Currier Adducts of 3‑Arylcyclohexenone with a Tethered Enone on the Aryl Moiety at the <i>Ortho</i>-Position

An enantioselective synthesis of Rauhut–Currier (RC) adducts from 3-aryl cyclohexenone with a tethered enone moiety at the <i>ortho</i>-position on the aryl group is accomplished. This method provides a wide range of valuable synthetic building blocks having a unique [6–5–6] all-carbon-fused tricyclic skeleton. A primary amine-containing thiourea, a bifunctional organocatalyst, was found to be an efficient catalyst for this transformation. The primary amine counterpart of the catalyst possibly activates the aliphatic enone via dienamine formation (HOMO activation), whereas the thiourea counterpart activates the tethered enone (LUMO activation). Considering the difficulty in achieving an RC reaction of β,β-disubstituted (alkyl and aryl) enones, this method would be significantly rewarding