99 research outputs found
2D NMR Methods for Structural Delineation of Copper(II) Complexes of Penicillin and Pilocarpine
A method was developed for delineating the structure of
paramagnetic metal complexes. The selective disappearance
of cross-peaks in proton-carbon shift correlated 2D NMR
maps was shown to uniquely depend upon the scalar and/or
dipolar interaction between ligand nuclei and the unpaired
electron(s), thus providing a means of identifying binding
sites. Copper(II) was shown to form metal complexes with
both Penicillin (PNC) and Pilocarpine (PLC) and the structure
of the two 1:2 complexes in water solution at physiological
pH were determined
Probing the role of metal ions on reversible peptideâprotein interactions by NMR
This work provides evidence that paramagnetic lanthanide ions constitute ideal probes suitable for investigations of metal effects upon peptideâreceptor interactions with the use of NMR methods. Cerium(III) is herein used for assessing metal effects upon the interaction between angiotensin II and a fragment from the AT1Areceptor. Angiotensin II forms a complex with cerium(III) in water while the fCT300â320receptor fragment is poorly affected by cerium(III). However, the addition of the fragment displaces cerium(III) from the complex, thus directly demonstrating the higher affinity of angiotensin II for the receptor and probing the peptide residues involved in receptor binding
Inferences on the Nature of a Cr(V) or Cr(IV) Species Formed by Reduction of Dichromate by a Bovine Liver Homogenate: NMR and Mass-Spectrometric Studies
A low-molecular weight chromium-containing fraction of the material resulting from dichromate
reduction by bovine liver homogenate was investigated by NMR and ES-MS. The ES-MS spectrum showed a
readily detectable peak at m/z = 786.1. The same molecular weight reasonably agreed with the relatively low
diffusion coefficient measured by NMR-DOSY experiments on the main species observed in the 1H NMR
spectrum. At least two downfield shifted and broad paramagnetic signals were apparent in the 1H NMR
spectrum. Temperature dependence of chemical shift was exploited in order to estimate the diamagnetic shift
of the signals in the diamagnetic region of the spectrum. 2D TOCSY, NOESY, COSY and 1H-3C HMQC
spectra revealed the presence of aromatic protons (which were assigned as His residues), Gly and some other
short chain amino-acids. Combinations of the molecular masses of such components together with acetate
(which is present in the solution) and chromium atoms allowed a tentative proposal of a model for the
compound
Characterization of Copper(II) Interactions with Sinefungin, a Nucleoside Antibiotic: Combined Potentiometric, Spectroscopic and DFT Studies
Interactions between sinefungin and copper(II) ions were investigated. Stoichiometry and stability constants of the
metal-free system and two mononuclear complexes present in solution were determined on the basis of potentiometric
data analysis. The results were compared to the Cu(II)-ornithine system due to structural similarities between both
molecules. Combined spectroscopic and theoretical studies allowed for determination of coordination pattern for
the Cu(II)-sinefungin complexes. At acidic pH, copper is bound in âglycine-likeâ coordination mode, identical with that
of ornithine. This involves α-amino group and the carboxyl oxygen. At higher pH, a âbis-complexâ is formed by two
sinefungin molecules. The second ligand binds in equatorial position displacing two water molecules, what results
in the stable {2N,2O} coordination. Both axial positions are supposed to be occupied by N1 nitrogen donors of adenine
moiety, what is confirmed by DFT calculations. They interact indirectly with copper(II) through water molecules as the
result of dominant syn conformation of purine
NMR Studies on Cu(II)-Peptide Complexes: Exchange Kinetics and Determination of Structures in Solution
The interaction of copper(II) with histidine containing peptides has recently acquired renewed interest following the established link between abnormal protein behaviour in neurodegenerative
processes and unpaired copper homeostasis. Five peptide sequences taken from the amyloid precursor protein and the prion protein were considered. Addition of paramagnetic Cu(II) ions to solutions of such peptides was not found to severely affect the appearance of NMR spectra, thus limiting the usual approach for structural determination. Exchange kinetics was shown to play a major role in determining the observed paramagnetic spin-lattice relaxation rates. Two
independent methods were suggested for evaluating the exchange rates of His-containing peptides from the copper-coordination sphere and to calculate copperâproton distances. In such a way
NMR was demonstrated to have the potential of providing detailed structures of the Cu(II)âpeptide complexes in solution
Structural features of the Zn(2+) complex with the single repeat region of "prion related protein" (PrP-rel-2) of zebrafish zPrP63-70 fragment
The interaction between Zn2+ and the single repeat of PrP-rel-
2 of zebrafish at physiological pH was investigated by NMR spectroscopy; the chemical shift mapping and the protonâproton distances were used to obtain the structural model of the Zn2+ complex
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