Ligand‐Flexibility Controlled and Solvent‐Induced Nuclearity Conversion in Cu^II‐Based Catecholase Models: A Deep Insight Through Combined Experimental and Theoretical Investigations

Abstract

A Schiff-base ligand, 4-bromo-2-[(2-hydroxy-1,1-dimethylethylimino)methyl]phenol (HL1), and its reduced analogue 4-bromo-2-[(2-hydroxy-1,1-dimethylethylamino)methyl]phenol (HL2) have been synthesized. Treatment of HL1 and HL2 with Cu(ClO4)2·6 H2O in the presence of sodium dicyanamide in MeOH and MeCN has been investigated. HL1 generates [Cu(L1)(MeOH)(dca)] (1) in MeOH (dca = dicyanamide) but [Cu2(L1)2(dca)2] (2) in MeCN. HL2 in MeOH produces [Cu4(L2)4(MeOH)2(ClO4)2] (3). On the other hand, in MeCN an interesting redox reaction is observed. CuII undergoes reduction, and [CuI(MeCN)4](ClO4) (4) is formed with concomitant oxidation of HL2 to HL1. The solvent-dependent nuclearity change (i.e, conversion of mononuclear species 1 into dinuclear species 2) has been investigated by ESI-MS, through the addition of MeCN to a methanolic solution of 1, and the origin of the conversion has been explained by means of DFT calculations. The catecholase activity of 1, 2 and 3 in MeCN and DMF has been investigated with the model substrates 3,5-di-tert-butylcatechol (3,5-DTBC), tetrachlorocatechol (TCC) and pyrocatechol (PRC). Compound 1 is inactive with all substrates, whereas 2 is active only with 3,5-DTBC in DMF. In contrast, 3 – which exists as a dinuclear species in solution, as is evident from ESI-MS – is highly active with all three substrates, especially in MeCN. The exceptionally high catalytic activity of 3 over 2 is likely to be due to the higher flexibility of the reduced Schiff-base ligand in comparison with its Schiff base analogue

Cu(ii) complexes of a tridentate N,N,O-donor Schiff base of pyridoxal: synthesis, X-ray structures, DNA-binding properties and catecholase activity

“…1,4,10,11 Model complexes have played an important role in understanding the structural, spectroscopic and catalytic properties of the copper sites in protiens. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Various workers have tried to rationalize the catalytic efficiency of the catechol oxidation reaction with variety of parameters like redox potentials, solvent effect, pH of the medium, number and nature of bridging ligands, effect of secondary coordination sphere etc., however our knowledge in this direction is still sketchy and incomplete. 12,13,[17][18][19][20][21][22][23][24][25][26] Therefore, there is need for study of new model complexes showing catecholase activity and exploration of relationship between their structural, spectroscopic and catalytic properties.…”

Unprecedented pseudo-zeroth-order kinetics of the catecholase-like activity of mixed-valence MnIIMn2III complexes

“…For complexes 1 and 2 , the initial rate constant values of 413.4 and 414 h −1 , respectively, are almost three times higher than the previously reported highly active tetranuclear copper( ii ) complex in acetonitrile, where the catalyst-to-substrate ratio was 1 : 100. 53…”

“…For complexes 1 and 2, the initial rate constant values of 413.4 and 414 h À1 , respectively, are almost three times higher than the previously reported highly active tetranuclear copper(II) complex in acetonitrile, where the catalyst-to-substrate ratio was 1 : 100. 53 The average rate constant values were obtained by dividing the difference between final and initial absorbance by the time required for complete conversion. The final absorbance was considered after 150 min of the reaction.…”

Mononuclear iron(III) complexes derived from tridentate ligands containing non‐innocent phenolato donors: Self‐activated nuclease, protease, and phenoxazinone synthase activity studies

“…New peak observed at 0.70 eV was due to oxidation of 2‐aminophenol to o ‐benzoquinone monoamine and is shown in Figure S29. [ 83 ]…”