Metal cation binding to gas-phase pentaalanine: divalent ions restructure the complex.
Robert C Dunbar1, Jeffrey D Steill, Nicolas C Polfer
1Chemistry Department, Case Western Reserve University, Cleveland, Ohio 44106, USA. rcd@po.cwru.edu
The Journal of Physical Chemistry. A
|August 30, 2012
Summary
Metal ions influence pentaalalanine structure. Doubly charged ions create rigid shells, while singly charged ions favor hydrogen bonds, impacting metal ion chelation.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Spectroscopy
Background:
- Peptides are crucial biomolecules with diverse structures and functions.
- Understanding how metal ions interact with peptides is essential for biological and chemical applications.
- Pentaalalanine serves as a model system to study peptide-metal ion interactions.
Purpose of the Study:
- To investigate the structural consequences of metal ion complexation in pentaalalanine.
- To elucidate the role of metal ion charge and binding strength in determining peptide conformation.
- To differentiate between coordination and hydrogen bonding interactions in peptide-metal ion complexes.
Main Methods:
- Conformational analysis using infrared multiple photon dissociation (IRMPD) spectroscopy.
- Density functional theory (DFT) computations to model and predict complex structures.
- Analysis of vibrational frequencies, particularly the C═O stretching mode, for structural insights.
Main Results:
- Doubly charged alkaline earth metal ions (Ca(2+), Ba(2+)) induce highly structured chelation shells with six binding sites and no hydroxyl hydrogen bonding.
- Singly charged alkali metal ions (Na(+), K(+), Cs(+)) favor structures with intramolecular hydrogen bonds, leading to less chelation.
- The favored coordination mode depends on ionic charge and binding strength, not ionic radius.
Conclusions:
- Metal ion charge and binding strength are key determinants of pentaalalanine conformation.
- IRMPD spectroscopy and DFT computations effectively distinguish between different coordination and hydrogen bonding patterns.
- These findings provide insights into the fundamental principles governing peptide-metal ion interactions.
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