Secondary structure of Ac-Alan_n-LysH+^+ polyalanine peptides (nn=5,10,15) in vacuo: Helical or not?

The polyalanine-based peptide series Ac-Ala_n-LysH+ (n=5-20) is a prime example that a secondary structure motif which is well-known from the solution phase (here: helices) can be formed in vacuo. We here revisit this conclusion for n=5,10,15, using density-functional theory (van der Waals corrected generalized gradient approximation), and gas-phase infrared vibrational spectroscopy. For the longer molecules (n=10,15) \alpha-helical models provide good qualitative agreement (theory vs. experiment) already in the harmonic approximation. For n=5, the lowest energy conformer is not a simple helix, but competes closely with \alpha-helical motifs at 300K. Close agreement between infrared spectra from experiment and ab initio molecular dynamics (including anharmonic effects) supports our findings.Comment: 4 pages, 4 figures, Submitted to JPC Letter

Einfangen biomolekularer Ionen in suprafluiden Helium-Tröpfchen

The He droplet technique is a versatile method for investigating molecules in a broad range of species at sub-Kelvin temperatures. In the framework of this thesis, an experiment has been setup which allows for studying intrinsic properties of large biomolecules such as peptides and proteins under well- defined conditions. The He droplet technique is combined with an electrospray ion source, a quadrupole mass filter, and a linear hexapod ion trap in which mass-to-charge selected gas-phase biomolecular ions are accumulated. The trap then serves as a pickup cell for He droplets that pass through the trap and pick up the species of interest, cool them down to their equilibrium temperature of approximately 0.37 K, transport them out of the trap, and such make them accessible for further investigation with the experimental method of choice, for example laser spectroscopy. Obtained spectra can reveal a high resolution comparable to those of isolated gas-phase molecules with little perturbances by the helium environment. Helium droplets are generated in a pulsed supersonic nozzle beam expansion. Two different He droplet sources have been installed and characterized. The sizes and size distributions of the droplets have been measured and it turns out that the most probable droplet sizes depend on the embedded particle, the respective source installed, and on the source conditions applied such as the expansion temperature and pressure which provides for manipulation of the droplet size as required.Die Helium-Tröpfchentechnik ist eine experimentelle Methode zur Untersuchung von Molekülen, die vielseitig anwendbar ist auf viele unterschiedliche Arten von Molekülen, von atomaren Ionen bis hin zu großen Proteinen. Im Rahmen dieser Doktorarbeit wurde ein Experiment aufgebaut, welches über eine Kombination der He-Tröpfchentechnik mit einer Elektrospray-Ionenquelle, eines Quadrupol-Massenfilters sowie einer linearen Hexapol-Ionenfalle einen neuartigen Ansatz zur Erforschung großer Biomoleküle unter wohldefinierten Bedingungen bietet. Peptide oder Proteine werden in der Falle akkumuliert, die gleichzeitig als Pickup-Zelle dient: Dort gespeicherte Ionen können von hindurchfliegenden He-Tröpfchen eingefangen werden, intern auf die Tröpfchentemperatur von etwa 0.37 K abgekühlt und aus der Falle transportiert werden und werden somit zugänglich gemacht für weiterführende Untersuchungen mit der experimentellen Methode der Wahl, z.B. Laser-Spektropskopie. Dabei gewonnene Spektren weisen eine hohe Auflüsung auf, die vergleichbar ist mit der von Spektren isolierter Moleküle in der Gasphase, und zeigen lediglich geringe Einflüsse durch die Helium-Matrix. Es wurden zwei verschiedene He- Tröpfchenquellen eingesetzt und charakterisiert. Die Größen und Größenverteilungen der Tröpfchen wurden bestimmt, und es zeigt sich, dass die häufigste Größe in der Verteilung von sowohl dem eingelagerten Molekül, als auch von der verwendeten Quelle sowie von den angelegten Expansionsparametern abhängt. Dies bietet gewissermaßen die Möglichkeit zur Einstellung der gewünschten Tröpfchengröße z.B. über Druck und Temperatur in der Expansion

Catching proteins in liquid helium droplets

Contains fulltext : 99068.pdf (preprint version ) (Open Access

Global Opportunities for Small/Medium Enterprises in emobility (GO4SEM)

Europe has successfully extended its competencies in key enabling technologies for electric mobility in recent years, especially in the field of information and communication technologies, components and systems (ICT). Small and medium size companies (SMEs) have played a crucial role as sources of creativity at all stages of the supply chain. Given the new supply chains for e-mobility being established worldwide, many potential target markets are located outside of Europe, e.g. in highly innovative regions such as the United States, Japan and South Korea or in emerging markets like China and India. In light of this situation, “Global Opportunities for Small and Medium Size Companies in Electric Mobility” (GO4SEM), coordinated by the Vrije Universiteit Brussel (VUB) and the European Association of Automotive Suppliers (CLEPA), is aimed at giving policy advice to sustain and enhance the successful access of European SME’s in supply chains in the abovementioned global markets. For this purpose the GO4SEM consortium (consisting of SMEs and regional clusters, Tier-1 automotive suppliers, and research institutions from all around Europe) intends to spread awareness of international market developments and technological trends in the electric mobility context, triggering an engagement of European SMEs in global FEV value chains by indicating potential and to show opportunities for bringing in expert knowledge. Furthermore, recommendations on standardization, education, and research matters are formulated. In a broader sense, the project will support to strengthen the global competitiveness of the European industry being active in the domain of electric mobility by linking the relevant stakeholders, preparing them for and increasing the awareness of the opportunities and challenges of worldwide developments. This contribution will present the output of the first term of the project. Firstly, in terms of mapping the global e-mobility supply chains and identifying possible entry points considering the above-mentioned target markets

Secondary Structure of Ac-Ala_<i>n</i>-LysH⁺ Polyalanine Peptides (<i>n</i> = 5,10,15) in Vacuo: Helical or Not?

The polyalanine-based peptide series Ac-Ala_<i>n</i>-LysH⁺ (<i>n</i> = 5−20) is a prime example that a secondary structure motif that is well-known from the solution phase (here: helices) can be formed in vacuo. Here we revisit the series members <i>n</i> = 5,10,15, using density functional theory (van der Waals corrected generalized gradient approximation) for structure predictions, which are then corroborated by room temperature gas-phase infrared vibrational spectroscopy. We employ a <i>quantitative</i> comparison based on Pendry’s reliability factor (popular in surface crystallography). In particular, including <i>anharmonic</i> effects into calculated spectra by way of ab initio molecular dynamics produces remarkably good experiment−theory agreement. We find the longer molecules (<i>n</i> = 10,15) to be firmly α-helical in character. For <i>n</i> = 5, calculated free-energy differences show different H-bond networks to still compete closely. Vibrational spectroscopy indicates a predominance of α-helical motifs at 300 K, but the lowest-energy conformer is not a simple helix