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Significance Molecular imaging at the single-molecule level of large and flexible proteins such as monoclonal IgG antibodies is possible by low-energy electron holography after chemically selective sample preparation by native electrospray ion beam deposition (ES-IBD) from native solution conditions. The single-molecule nature of the measurement allows the mapping of the structural variability of the molecules that originates from their intrinsic flexibility and from different adsorption geometries. Additionally, we can distinguish gas-phase–related conformations and conformations induced by the landing of the molecules on the surface. Our results underpin the relation between the gas-phase structure of protein ions created by native electrospray ionization (ESI) and the native protein structure and are of relevance for structural biology applications in the gas phase., Imaging of proteins at the single-molecule level can reveal conformational variability, which is essential for the understanding of biomolecules. To this end, a biologically relevant state of the sample must be retained during both sample preparation and imaging. Native electrospray ionization (ESI) can transfer even the largest protein complexes into the gas phase while preserving their stoichiometry and overall shape. High-resolution imaging of protein structures following native ESI is thus of fundamental interest for establishing the relation between gas phase and solution structure. Taking advantage of low-energy electron holography’s (LEEH) unique capability of imaging individual proteins with subnanometer resolution, we investigate the conformational flexibility of Herceptin, a monoclonal IgG antibody, deposited by native electrospray mass-selected ion beam deposition (ES-IBD) on graphene. Images reconstructed from holograms reveal a large variety of conformers. Some of these conformations can be mapped to the crystallographic structure of IgG, while others suggest that a compact, gas-phase–related conformation, adopted by the molecules during ES-IBD, is retained. We can steer the ratio of those two types of conformations by changing the landing energy of the protein on the single-layer graphene surface. Overall, we show that LEEH can elucidate the conformational heterogeneity of inherently flexible proteins, exemplified here by IgG antibodies, and thereby distinguish gas-phase collapse from rearrangement on surfaces.

The aim of the present study was to examine neurocognitive function associated with chronic nicotine use. A total of 2163 healthy participants (1002 smokers, 1161 never-smoking controls) participated in a population-based case-control design. The main outcome measures were six cognitive domain factors derived from a neuropsychological test battery. In smokers, the battery was administered after controlled smoking of one cigarette. Analyses included age, sex and education as covariates. Results demonstrated small, but significant deficits in smokers for visual attention (P < 0.001) and cognitive impulsivity (P < 0.006), while verbal episodic memory, verbal fluency, verbal working memory, and Stroop-interference did not differ between groups. These attention/impulsivity deficits were also present in smokers with only a low amount of cigarette consumption. Lifetime nicotine use (pack-years) was not correlated with cognition in smokers. In conclusion, this study confirmed subtle and specific cognitive deficits in non-deprived smokers. The independence of these deficits from consumption intensity may argue for an a priori deficit of some cognitive abilities in smokers. These specific deficits may constitute intermediate phenotypes for genetic research on nicotine use.

The exploration and wide application of single walled carbon nanotubes (SWCNTs) require the development of new synthetic approaches enabling facile and fully rational CNT fabrication. In this communication the conversion of two precursors yielding the potential CNT seeds of (9, 0) zigzag and (6, 6) armchair nanotubes using surface-assisted cyclodehydrogenation on the Rh(111) single-crystal surface is reported. The conversion efficiency found is nearly 100% and the CNT-caps remain thermally stable on the Rh surface up to 820 K which is high enough for subsequent SWCNT growth. It is shown that Rh is a suitable catalyst for the controllable synthesis of SWCNTs by the surface assisted bottom-up strategy. (C) 2014 Elsevier Ltd. All rights reserved.

The coupling of atmospheric pressure ionization (API) sources like electrospray ionization (ESI) to vacuum based applications like mass spectrometry (MS) or ion beam deposition (IBD) is done by differential pumping, starting with a capillary or pinhole inlet. Because of its low ion transfer efficiency the inlet represents a major bottleneck for these applications. Here we present a nano-ESI vacuum interface optimized to exploit the hydrodynamic drag of the background gas for collimation and the reduction of space charge repulsion. Up to a space charge limit of 40 nA we observe 100% current transmission through a capillary with an inlet and show by MS and IBD experiments that the transmitted ion beams are well defined and free of additional contamination compared to a conventional interface. Based on computational fluid dynamics modelling and ion transport simulations, we show how the specific shape enhances the collimation of the ion cloud. Mass selected ion currents in the nanoampere range available further downstream in high vacuum open many perspectives for the efficient use of electrospray ion beam deposition (ES-IBD) as a surface coating method.

Electrospray-ion-beam deposition (ES-IBD) is a preparative mass spectrometry technique which produces highly purified samples of non-volatile molecules adsorbed on a surface. An ES-IBD mass spectrometer (MS) ionises the analyte, transfers it into the gas phase, removes contaminations with a mass filter in vacuum and deposits it with a controlled landing energy onto a substrate. ES-IBD coupled to microscopy can elucidate the structure of biomolecules and their assemblies. In conjunction with scanning tunnelling microscopy, glycan connectivity of oligosaccharides was revealed. For larger molecules, such as native protein complexes, efforts are underway to determine their structure and conformation by coupling ES-IBD to cryo-electron microscopy or low-energy electron holography. However, there are no instruments available dedicated to depositing large, native protein complexes controlled and efficiently. In this thesis, I have modified a commercial MS designed for the analysis of large, native protein complexes (Thermo ScientificTM Q ExactiveTM UHMR) for deposition. The modified instrument has adequate beam intensity and good landing energy control. In conjunction with electron microscopy, it was shown that the native shape of protein assemblies is retained after dehydration and deposition. I used an enzymatic assay to quantify the activity of the non-covalent protein complex alcohol dehydrogenase after deposition on a dry surface. Moreover, I developed another instrument for mass- and mobility-filtered deposition of both small and large molecules. Its atmosphere-pressure interface, the ion funnel, is optimised for high transmission and it has a continuous parallel flow ion mobility filter to enable conformation-selected deposition. Radio-frequency power switches with a flexible operation frequency permit to transmit any ion with a mass-to-charge range > 50 Th, in particular heavy ions. The basis for the development of the second MS was the detailed investigation of the transport processes within an ion funnel. I formulate a 4-step ion funnel transmission model underpinned by transmission measurements of a conventional ion funnel and ion trajectory simulations taking into account the gas flow field.