Nickel-cysteine binding supported by phosphine chelates.

Area of Science:

• Coordination Chemistry
• Bioinorganic Chemistry
• Organometallic Chemistry

Background:

• Nickel-cysteine interactions are crucial in biological systems and catalysis.
• Understanding the structural and stability factors of nickel-cysteine complexes is essential.
• Chelating phosphines are widely used ligands in coordination chemistry.

Purpose of the Study:

• To investigate the effect of chelating phosphines (dppe and triphos) on the structure and pH-dependent stability of nickel-cysteine complexes.
• To elucidate the coordination sphere and bonding interactions within these complexes.
• To assess the selectivity of nickel centers for different amino acids, particularly N-terminus cysteine.

Main Methods:

• Synthesis of nickel complexes with L-cysteine, L-cysteine ethyl ester, and cystamine using 1,2-Bis(diphenylphosphino)ethane (dppe) and 1,1,1-tris[(diphenylphosphino)methyl]ethane (triphos).
• Characterization using 31P {1H} NMR spectroscopy and single-crystal X-ray diffraction.
• pH-dependent stability studies in aqueous media and investigation of heterogeneous systems with cysteine-anchored beads.

Main Results:

• Square-planar P2NiSN coordination spheres were confirmed for dppe complexes.
• Triphos complexes exhibited fluxional behavior at room temperature, attributed to a trans P-Ni-S pi interaction.
• Nickel centers demonstrated high selectivity for N-terminus cysteine over methionine and serine in heterogeneous systems.

Conclusions:

• Chelating phosphines play a significant role in dictating the structure and stability of nickel-cysteine complexes.
• The Ni-S pi interaction influences the coordination dynamics and electron density distribution.
• The findings highlight the specific binding preference of nickel for N-terminus cysteine, relevant for understanding biological roles and designing new catalysts.