phenylalanylalanine and alanylphenylalanine

In the search for new cytotoxic drugs, two copper complexes with isomeric dipeptides (Ala-Phe and Phe-Ala) were developed in order to determine the influence of their different structures in the modulation of the chemical, biochemical and biological properties. Spectroscopic, voltammetric and equilibrium studies were performed providing information about the chemical properties. The superoxide dismutase (SOD) activity was studied and showed differences of IC

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Cisplatin; Coordination Complexes; Copper; Dipeptides; DNA; Female; Humans; Inhibitory Concentration 50; Isomerism; MCF-7 Cells; Mice; Microscopy, Atomic Force; Molecular Docking Simulation; Plasmids; Structure-Activity Relationship; Superoxide Dismutase; Superoxides

Complexes of PheAla and AlaPhe with alkali metal ions Na(+) and K(+) are generated by electrospray ionization, isolated in the Fourier-transform ion cyclotron resonance (FT-ICR) ion trapping mass spectrometer, and investigated by infrared multiple-photon dissociation (IRMPD) using light from the FELIX free electron laser over the mid-infrared range from 500 to 1900 cm(-1). Insight into structural features of the complexes is gained by comparing the obtained spectra with predicted spectra and relative free energies obtained from DFT calculations for candidate conformers. Combining spectroscopic and energetic results establishes that the metal ion is always chelated by the amide carbonyl oxygen, whilst the C-terminal hydroxyl does not complex the metal ion and is in the endo conformation. It is also likely that the aromatic ring of Phe always chelates the metal ion in a cation-pi binding configuration. Along with the amide CO and ring chelation sites, a third Lewis-basic group almost certainly chelates the metal ion, giving a threefold chelation geometry. This third site may be either the C-terminal carbonyl oxygen, or the N-terminal amino nitrogen. From the spectroscopic and computational evidence, a slight preference is given to the carbonyl group, in an RO(a)O(t) chelation pattern, but coordination by the amino group is almost equally likely (particularly for K(+)PheAla) in an RO(a)N(t) chelation pattern, and either of these conformations, or a mixture of them, would be consistent with the present evidence. (R represents the pi ring site, O(a) the amide oxygen, O(t) the terminal carbonyl oxygen, and N(t) the terminal nitrogen.) The spectroscopic findings are in better agreement with the MPW1PW91 DFT functional calculations of the thermochemistry compared with the B3LYP functional, which seems to underestimate the importance of the cation-pi interaction.

Topics: Computer Simulation; Dipeptides; Metals, Alkali; Models, Chemical; Organometallic Compounds; Spectrophotometry, Infrared; Thermodynamics

The conformational preferences and infrared and ultraviolet spectral signatures of two model beta-peptides, Ac-beta3-hPhe-beta3-hAla-NHMe (1) and Ac-beta3-hAla-beta3-hPhe-NHMe (2), have been explored under jet-cooled, isolated-molecule conditions. The mass-resolved, resonant two-photon ionization spectra of the two molecules were recorded in the region of the S0-S1 origin of the phenyl substituents (37,200-37,800 cm(-1)). UV-UV hole-burning spectroscopy was used to determine the ultraviolet spectral signatures of five conformational isomers of both 1 and 2. Transitions due to two conformers (labeled A and B) dominate the R2PI spectra of each molecule, while the other three are minor conformers (C-E) with transitions a factor of 3-5 smaller. Resonant ion-dip infrared spectroscopy was used to obtain single-conformation infrared spectra in the 3300-3700 cm(-1) region. The infrared spectra showed patterns of NH stretch transitions characteristic of the number and type of intramolecular H-bonds present in the beta-peptide backbone. For comparison with experiment, full optimizations of low-lying minima of both molecules were carried out at DFT B3LYP/6-31+G*, followed by single point MP2/6-31+G* and selected MP2/aug-cc-pVDZ calculations at the DFT optimized geometries. Calculated harmonic vibrational frequencies and infrared intensities for the amide NH stretch vibrations were used to determine the beta-peptide backbone structures for nine of the ten observed conformers. Conformers 1B, 1D, and 2A were assigned to double ring structures containing two C6 H-bonded rings (C6a/C6a), conformers 1A and 2B are C10 single H-bonded rings, conformers 1C and 2D are double ring structures composed of two C8 H-bonded rings (C8/C8), and conformers 1E and 2E are double ring/double acceptor structures in which two NH groups H-bond to the same C=O group, thereby weakening both H-bonds. Both 1E and 2E are tentatively assigned to C6/C8 double ring/double acceptor structures, although C8/C12 structures cannot be ruled out unequivocally. Finally, no firm conformational assignment has been made for conformer 2C whose unusual infrared spectrum contains one very strong H-bond with NH stretch frequency at 3309 cm(-1), a second H-bonded NH stretch fundamental of more typical value (3399 cm(-1)), and a third fundamental at 3440 cm(-1), below that typical of a branched-chain free NH. The single conformation spectra provide characteristic wavenumber ranges for the amide NH stretch fundament

Topics: Alanine; Dipeptides; Models, Molecular; Peptides; Phenylalanine; Protein Conformation; Quantum Theory; Spectrophotometry, Infrared; Spectrophotometry, Ultraviolet