Alaganandan Nanthakumar's research while affiliated with Johns Hopkins University and other places

... For instance, Masuda and co-workers synthesized various TMPA-based ligands (including NH 2 TMPA, the system of interest in this current study) and demonstrated their H-bonding capabilities, which help stabilize dicopper(II) trans-peroxide complexes. 107,108 Similarly, F 8 has also long been utilized in heme models 10,101,109,110 due to its ease in synthesis and therefore provides a direct comparison with analogues in the literature. Following previously established methods, dioxygen was bubbled through an equimolar mixture of the reduced metal-ligand complexes 111 at −90 °C in 2-methyltetrahydrofuran (MeTHF) as solvent to generate HS heme-peroxo-copper complexes (Scheme 1) and subsequent addition of 1 equiv of an exogenous base has been shown to form LS heme-peroxo-copper analogues (Scheme 1, Pathway 1). ...

... For this purpose, initially Cu-TMPA (TMPA = tris(2-pyridylmethyl)amine) and FeTPP (TPP = tetrakis(phenyl)porphyrin) complexes were used. 36,37 In fact, on reaction of O 2 with an equimolar mixture of [(TMPA)Cu I (RCN)] + (1a) and (F 8 TPP)Fe II (F 8 TPP = tetrakis(2,6-difluorophenyl)porphyrin) (2a) an oxo-bridged heme-Cu complex [(F 8 TPP)Fe III O Cu II (TMPA)] + (3b) was detected at room temperature. However, low temperature (in the range of − 94°C to − 75°C) stopped-flow UV-Vis spectroscopy showed the formation of (S)-(F 8 TPP)Fe III (O 2− ) i.e., a heme-superoxide intermediate (where S is solvent, acetone in this case, λ max = 537 nm) initially within the mixing time (~1 ms) which then reacted with the reduced Cu complex yielding a heteronuclear peroxo intermediate [(F 8 TPP)Fe III (O 2− ) Cu II (TMPA)] (3a) (λ max = 556 nm) in preference to homonuclear (μ-peroxo heme-only or copper-only) ones (Fig. 2). ...

... To unambiguously characterize this, we synthesized the iron complexes IITK4003 and IITK4004 and characterized them by various spectroscopic techniques and X-ray crystallography studies (Figure 3, S1-S5, scheme S1, S2, Table S1). [33][34][35] Iron complexes IITK4003 and IITK4004 were found to show comparable growth inhibition activity against both Huh-7 and U2OS cells as in the ligands treatment alone ( Figure 3A, B). Remarkably, IITK4003 exhibited an exceptional antiproliferative activity with an EC 50 of 340 nM against Huh-7 cells, a 3-fold better than the parent ligand IITK4001 ( Figure 3A). ...

... The bridging oxo moiety can be reversibly protonated to give the corresponding m-hydroxo complex, [(P)Fe III -(OH)-Cu II (L)] + , and with protonation, bending of the Fe-O(H)-Cu moiety and lengthening of the Fe III −O(H) and Cu II −O(H) bonds occurs, which conse quently lowers the degree to which the iron atom is pulled out of the porphyrin plane [108,116,117]. Holm and coworkers reported the only crystal structure of a mhydroxo heme/Cu complex utilizing the OEP framework (i.e., [(OEP)Fe III -(OH)-Cu II (Me 5 dien)(OClO 3 )] + ) [118]. ...

... The reaction yield was improved to >90% in a later report by Hickman et al. which used an analogous Fe-TPP catalyst (TPP ¼ meso-tetraphenylporphyrin). 96 Watersoluble Fe-porphyrin catalysts reported by Su and co-workers were found to promote allylic hydrogen abstraction in aqueous media at room temperature while epoxidation only occurred at potentials above which the catalyst was no longer stable. 97,98 Chemoselective catalytic systems with high faradaic efficiencies and long-term stabilities are yet to be discovered for the future commercial application of electrochemical oxygenation of olens. ...

... Note, however, that the cupric ligations in these complexes are significantly different from one another. A similar degree of bending was reported for the protonation of [(F 8 TPP)Fe III -O-Cu II (TMPA)] + , wherein the Fe-O-Cu moiety approaches linearity (i.e., 178°) [119] and the Fe-(OH)-Cu moiety is significantly more bent (i.e., 157°) as confirmed by EXAFS [116]. ...

... Such complexes are broadly embraced as synthetic models for the active site of cytochrome c oxi dase in which heme-a 3 and Cu B are adjacent to one another. As a crucial component of the electron transport chain, CcO catalyzes the four electron, four proton reduction of dioxygen to water and simultaneously generates the electrochemical gradient across the membrane, necessary for ATP production [108][109][110]. Karlin and coworkers have done significant work on synthetic heme/Cu models over the years and demonstrated that the related m-oxo heme/Cu complexes can be prepared by dioxygen or acid−base chemistry [111][112][113]. ...

... Yields and characterization data for specific porphyrinate ligands appear below. Spectroscopic data (UV-vis, IR, and EPR) matched those available in the literature [24,25,28,38,53,54]. All fluoro complexes were found to retain variable amounts of water, which could be observed as a broad singlet near 0 ppm in the 1 H NMR spectrum. ...

... Fluoro-iron(III) porphyri nates have been structurally characterized for a series of different porphyrin ligands and various aspects of their spectroscopy have been examined in detail [24][25][26][27][28][29][30][31][32]. Particular attention has been paid to the effects of fluoride ligation in modulating the reactivity of high valent oxo-iron porphyrinates and in determining the electronic structure of porphyrin p-cation radicals [33][34][35][36][37][38][39][40][41][42][43][44]. In addition, fluoro-iron(III) porphyrinates are also of interest as models for fluoride interaction with heme proteins [45][46][47][48]. ...