20 research outputs found
Secondary structure of Ac-Ala-LysH polyalanine peptides (=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
Action spectroscopy of gas-phase carboxylate anions by multiple photon IR electron detachment/attachment
We report on a form of gas-phase anion action spectroscopy based on infrared
multiple photon electron detachment and subsequent capture of the free
electrons by a neutral electron scavenger in a Fourier Transform Ion Cyclotron
Resonance (FTICR) mass spectrometer. This method allows one to obtain
background-free spectra of strongly bound anions, for which no dissociation
channels are observed. The first gas-phase spectra of acetate and propionate
are presented using SF6 as electron scavenger and a free electron laser as
source of intense and tunable infrared radiation. To validate the method, we
compare infrared spectra obtained through multiple photon electron
detachment/attachment and multiple photon dissociation for the benzoate anion.
In addition, different electron acceptors are used, comparing both associative
and dissociative electron capture. The relative energies of dissociation (by
CO2 loss) and electron detachment are investigated for all three anions by DFT
and CCSD(T) methods. DFT calculations are also employed to predict vibrational
frequencies, which provide a good fit to the infrared spectra observed. The
frequencies of the symmetric and antisymmetric carboxylate stretching modes for
the aliphatic carboxylates are compared to those previously observed in
condensed-phase IR spectra and to those reported for gas-phase benzoate,
showing a strong influence of the solution environment and a slight substituent
effect on the antisymmetric stretch.Comment: Revised version, Submitted to J Phys Chem
Characterizing the Intramolecular H-bond and Secondary Structure in Methylated GlyGlyH+ with H2 Predissociation Spectroscopy
Konstruktion einer Elektrosprayquelle zur Erzeugung solvatisierter Biomoleküle - Nachweis von Sekundärstrukturen in der Gasphase
Infrared spectroscopic characterization of secondary structure elements of gas-phase biomolecules
IR spectroscopy of gas-phase C-60(-)
We present the IR spectrum of the gas-phase C-60(-) anion. The C-60(-) anions are mass-selected and trapped in an ion cyclotron mass spectrometer cell. The spectrum is obtained by recording the yield of electrons following infrared multiple photon absorption and subsequent electron detachment of the anions. Two bands are observed that correlate to two of the four IR-allowed transitions in neutral C-60. The results show that the higher frequency band is strongly shifted from its position in neutral C-60 and is a sensitive marker for the charge state. The band positions and intensities are compared to results obtained by theory as well as to known bands in solid samples and good agreement is found
Gas-phase IR spectra of intact alpha-helical coiled coil protein complexes
Electrospray ionization (ESI) is the softest ionization method that is currently available and it is widely accepted, that ESI generated ions of proteins and protein assemblies at certain conditions retain characteristic aspects of their solution-state conformation. ESI mass spectrometry (MS) therefore evolved as a useful tool to obtain information on composition, stoichiometry, and dynamics of non-covalently associated protein complexes. While tertiary structure information of proteins can be obtained from ion mobility spectrometry (IMS), only a few techniques yield direct information on the secondary structure of gas-phase peptides and proteins. We present here the mid-IR spectroscopic secondary structural analysis of three de novo designed alpha-helical coiled coil model peptides and their non-covalently associated complexes in the gas-phase. The conformational stability of such coiled coil peptides in solution is primarily driven by aggregation. Isolated monomers usually remain unfolded. Two of the investigated peptides were designed to assemble into stable alpha-helical complexes in acidic solution, while the third one remains monomeric and unfolded at these conditions. Monomer ions of all three peptides show comparable photodissociation IR spectra and therefore suggest an unfolded conformation in the gas phase. in contrast, considerable C=O stretch (amide-1) and N-H bend (amide-II) band shifts have been observed for the dieters which is consistent with an elevated H-bond content. These findings provide evidence that at least a fraction of the condensed phase a.-helical structure is retained in the gas-phase coiled coil complexes. (C) 2009 Elsevier B.V. All rights reserved
Exploring the conformational preferences of 20-residue peptides in isolation: Ac-Ala(19)-Lys + H+ vs. Ac-Lys-Ala(19) + H+ and the current reach of DFT
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Structure determination of anionic metal clusters via infrared resonance enhanced multiple photon electron detachment spectroscopy
Contains fulltext :
99024.pdf (publisher's version ) (Closed access