NDLI: Dimeric Fe (II, III) complex of quinoneoxime as functional model of PAP enzyme: Mössbauer, magneto-structural and DNA cleavage studies

Content Provider	Springer Nature Link
Author	Salunke Gawali, Sunita Ahmed, Khursheed Varret, François Linares, Jorge Zaware, Santosh Date, Sadgopal Rane, Sandhya
Copyright Year	2008
Abstract	Purple acid phosphatase, (PAP), is known to contain dinuclear Fe2 + 2, + 3 site with characteristic Fe + 3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe2 + 2, + 3 (o-NQCH3ox) (o-NSQCH3ox)2 (CAT) H2O]. Fe-2: [Fe + 3(o-NQCH3ox) (p-NQCH3ox)2]2 a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. 57Fe Mössbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. 57Fe Mössbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe + 3]A and [Fe + 2]B sites. The hyperfine interaction parameters are δ A = 0.152, (ΔE Q)A = 0.598 mm/s with overlapping doublet at δ B = 0.410 and (ΔE Q)B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe + 3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQCH3ox ligand surrounding Fe + 3(h.s.) state generates small field gradient indicated by quadrupole split ΔE Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe2 + 2, + 3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g 1 = 4.17 and g 2 = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe + 3(h.s.) configuration. SQUID data of $\chi _m^{{\rm corr}} \mbox{.T}$ were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = −13.5 cm − 1 with an agreement factor of R = 1.89 × 10 − 5). The lower J value of antiferromagnetic exchange leads to Fe+3μ-(OH) Fe + 2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe + 3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = −12.4 cm − 1, g = 2.3 with R = 3.58 × 10 − 5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.
Starting Page	47
Ending Page	56
Page Count	10
File Format	PDF
ISSN	03043843
Journal	Hyperfine Interactions
Volume Number	185
Issue Number	1-3
e-ISSN	15729540
Language	English
Publisher	Springer Netherlands
Publisher Date	2008-10-11
Publisher Place	Dordrecht
Access Restriction	Subscribed
Subject Keyword	Acid phosphatase (APase) Valence tautomers Reconstituted acid phosphatase (RAPase) Mössbauer Magnetostructural studies Surfaces and Interfaces, Thin Films Condensed Matter Atoms, Molecules, Clusters and Plasmas Nuclear Physics, Heavy Ions, Hadrons
Content Type	Text
Resource Type	Article
Subject	Nuclear and High Energy Physics Atomic and Molecular Physics, and Optics Physical and Theoretical Chemistry Condensed Matter Physics

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