Soft-landing electrospray ion beam deposition of sensitive oligoynes on surfaces in vacuum

AbstractAdvances in synthetic chemistry permit the synthesis of large, highly functional, organic molecules. Characterizing the complex structure of such molecules with highly resolving, vacuum-based methods like scanning probe microscopy requires their transfer into the gas phase and further onto an atomically clean surface in ultrahigh vacuum without causing additional contamination. Conventionally this is done via sublimation in vacuum. However, similar to biological molecules, large synthetic compounds can be non-volatile and decompose upon heating. Soft-landing ion beam deposition using soft ionization methods represents an alternative approach to vacuum deposition. Using different oligoyne derivatives of the form of R1(CC)nR2, here we demonstrate that even sensitive molecules can be handled by soft-landing electrospray ion beam deposition. We generate intact molecular ions as well as fragment ions with intact hexayne parts and deposit them on clean metal surfaces. Scanning tunneling microscopy shows that the reactive hexayne segments of the molecules of six conjugated triple bonds are intact. The molecules agglomerate into ribbon-like islands, whose internal structure can be steered by the choice of the substituents. Our results suggest the use of ion beam deposition to arrange reactive precursors for subsequent polymerization reactions

Fast Molecular Compression by a Hyperthermal Collision Gives Bond-Selective Mechanochemistry

Using electrospray ion beam deposition, we collide the complex molecule Reichardt’s Dye (C41H30NO+) at low, hyperthermal translational energy (2 - 50 eV) with a Cu(100) surface and image the outcome at single-molecule level by scanning tunneling microscopy. We observe bond-selective reaction induced by the translational kinetic energy. The collision impulse compresses the molecule and bends specific bonds, prompting them to react selectively. This dynamics drives the system to seek thermally inaccessible reactive pathways, since the compression timescale (sub-ps) is much shorter than the thermalization timescale (ns), thereby yielding reaction products that are unobtainable thermally

Electrospray Ion Beam Deposition of Complex Non-Volatile Molecules

The rational synthesis of novel materials requires the control over the arrangement of matter in order to meet the desired properties for applications and devices. Ultimately, control means to define the place of each atom and determine its chemical state, as well as being able to confirm the result in a measurement. Control at the atomic level can be achieved with scanning tunneling microscopy (STM), both in imaging and atomic manipulation. The latter, however, can never be used in meso- or even macroscopic material synthesis. Self-ordering phenomena determines atomic control in material synthesis as well, observed for instance in protein folding or in molecular beam epitaxy (MBE) technology. In both cases the atomically determined arrangement of the atoms in the structure is controlled only by environmental parameters that steer the self-ordering phenomena. In this thesis I show that electrospray ion beam deposition (ES-IBD) or ion soft-landing is a material processing technique, which combines and even extends the level of control offered by MBE. It is demonstrated that a vast range of complex organic materials including peptides and proteins is now available to ultrapure vacuum processing and moreover completely novel schemes of controlling self-ordering processes are provided. In-situ STM is applied to investigate the structure formation of complex molecules deposited by ES-IBD on well-defined, clean, and atomically flat surfaces in ultrahigh vacuum at the greatest detail. This allows us to explore the novel control features that are intrinsic to the ES-IBD deposition process like online coverage monitoring, deposition energy control, and mass-selection to select charge states or reactive species. The molecules studied here include organic molecular salts, dye molecules, reactive polymer building blocks, and finally peptides and proteins. Crystalline layer-by-layer as well as island growth was observed and revealed the equivalence to conventional MBE growth. On the basis of these deposition experiments the crucial influence of clusters in the ion beam for high material flux was discovered. Furthermore, it was found that the chemical state of the molecule is a key factor for the deposition result as chemical reactions can be induced or the self-assembly behavior can be altered. Alongside the capability to handle also extremely reactive molecules, the feasibility to control chemical reactions occurring as a result of an external stimulus to a specifically selected reactive species is demonstrated. Employing the control parameters that are specific to ES-IBD like charge state selection and deposition energy to complex biomolecules opens up new perspectives for vacuum deposition. In addition to the self-assembly governed by the molecule-substrate and molecule-molecule interaction, it was possible to actively steer the structure formation of proteins by influencing their stiffness and their reactivity through their charge state as well as by the deposition energy, parameters intrinsic to the ES-IBD method. Hence, electrospray ion beam deposition is indeed a tool to prepare well defined surface coatings at highest level of control and complexity. To be relevant for industrial applications, the performance of the system has to be further improved, most importantly in terms of deposition rate. In general, ES-IBD enables new approaches for the growth of functional coatings but also serving as perfect sample preparation tool for the characterization of complex molecules on the atomic scale by scanning probe or more general surface science methods

Material and charge transport of large organic salt clusters and nanoparticles in electrospray ion beam deposition

Electrospray ion beam deposition (ES-IBD) or ion soft landing has been demonstrated as a technique suitable for processing nonvolatile molecules in vacuum under perfectly controlled conditions, an approach also desirable for the deposition of nanoparticles. Here, we present results from several approaches to generate, characterize, and deposit nanoparticle ion beams in vacuum for deposition. We focus on cluster ion beams generated by ESI of organic salt solutions. Small cluster ions of the salts appear in the mass spectra as defined peaks. In addition, we find nanoparticle-sized aggregates, appearing as a low intensity background at high m/z-ratio, and show by IBD experiments that these clusters carry the major amount of material in the ion beam. This transition from clusters to nanoparticles, and their successful deposition, shows that ES-IBD can in principle handle ion beams of very heavy and highly charged nanoparticles. In related experiments, however, we found the deposition of nanoparticles from dispersions to be of low reproducibility, due to the lack of control by mass spectrometry

Two-Dimensional Folding Of Polypeptides Into Molecular Nanostructures At Surfaces

Herein we report the fabrication of molecular nanostructures on surfaces via two-dimensional (2D) folding of the nine amino acid peptide bradykinin. Soft-landing electrospray ion beam deposition in conjunction with high-resolution imaging by scanning tunneling microscopy is used to fabricate and investigate the molecular nanostructures. Subnanometer resolved images evidence the large conformational freedom of the molecules if thermal motion is inhibited and the formation of stable uniform dimers of only one specific conformation when diffusion can take place. Molecular dynamics modeling supported by density functional theory calculations give atomically precise insight into the induced-fit binding scheme when the folded dimer is formed. In the absence of solvent, we find a hierarchy of binding strength from polar to nonpolar, manifested in an inverted polar-nonpolar segregation which suppresses unspecific interactions at the rim of the nanostructure. The demonstrated 2D-folding scheme resembles many key properties of its native 3D counterpart and shows that functional, molecular nanostructures on surfaces fabricated by folding could be just as versatile and specific

Active Conformation Control of Unfolded Proteins by Hyperthermal Collision with a Metal Surface

The physical and chemical properties of macromolecules like proteins are strongly dependent on their conformation. The degrees of freedom of their chemical bonds generate a huge conformational space, of which, however, only a small fraction is accessible in thermal equilibrium. Here we show that soft-landing electrospray ion beam deposition (ES-IBD) of unfolded proteins allows to control their conformation. The dynamics and result of the deposition process can be actively steered by selecting the molecular ion beam's charge state or tuning the incident energy. Using these parameters, protein conformations ranging from fully extended to completely compact can be prepared selectively on a surface, as evidenced on the subnanometer/amino acid resolution level by scanning tunneling microscopy (STM). Supported by molecular dynamics (MD) simulations, our results demonstrate that the final conformation on the surface is reached through a mechanical deformation during the hyperthermal ion surface collision. Our experimental results independently confirm the findings of ion mobility spectrometry (IMS) studies of protein gas phase conformations. Moreover, we establish a new route for the processing of macromolecular materials, with the potential to reach conformations that would be inaccessible otherwise

Chemical modification of graphene via hyperthermal molecular reaction

Chemical functionalization of graphene is achieved by hyperthermal reaction with azopyridine molecular ions. The one-step, room temperature process takes place in high vacuum (10–7 mbar) using an electrospray ion beam deposition (ES-IBD) setup. For ion surface collisions exceeding a threshold kinetic energy of 165 eV, molecular cation beams of 4,4′-azobis(pyridine) covalently attach to chemical vapor deposited (CVD) graphene. A covalent functionalization degree of 3% of the carbon atoms of graphene is reached after 3–5 h of ion exposure of 2 × 1014 azopyridinium/cm2 of which 50% bind covalently. This facile approach for the controlled modification of graphene extends the scope of candidate species that would not otherwise react via existing conventional methods.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Electroquímica y Energía Química (CELEQ

Readiness of Ghanaian health facilities to deploy a health insurance claims management software (CLAIM-it)

INTRODUCTION: Inadequate, inefficient and slow processing of claims are major contributors to the cost of health insurance schemes, and therefore undermining their sustainability. This study uses the Technology, Organisation and Environment (TOE) framework to examine the preparedness of health facilities of the Christian Health Association of Ghana (CHAG) to implement a digital mobile health insurance claims processing software (CLAIM-it), which aims to increase efficiency. METHODS: The study used a cross-sectional mixed method design to collect data (technology and human capital capacity and baseline operational performance of claims management) from a sample of 20 CHAG health facilities across Ghana. While quantitative data was analysed using simple descriptive statistics statistics (frequencies, mean, minimum and maximum values), qualitative interviews were recorded, transcribed and abstracted into two major themes that were reported to re-enforce the quantitative findings. RESULTS: The quantitative results revealed challenges including inadequate computers and accessories, adequate numbers and skills for claims processing, poor intranets and internet access, absence of a robust post-implementation support system and inadequate standard operating procedures (SOPs) for seamless automation of claims processing. In addition to the above, the qualitative results emphasised the need to make CLAIM-it more flexible and capable of being integrated into third-party softwares. Notwithstanding the challenges, decision-makers in CHAG health facilities see the CLAIM-it software as having better functionality and superior capabilities compared to existing claims processing systems in Ghana. CONCLUSION: Notwithstanding the challenges, the CLAIM-it software is more likely to be adopted by decision-makers, given the positive perception in terms of superior functionality. It is important that key actors in claims management at the National Health Insurance collaborate with relevant stakeholders to adopt the CLAIM-it software for claims processing and management in Ghana