Schiff-base macrocycles: coordination chemistry and potential applications

In this thesis, a number of Schiff base compounds and their complexes have been synthesized and fully characterized. Moreover, some applications including their use in catalysis, specifically the ring opening polymerization of cyclic esters, is disclosed.Chapter 1. This chapter presents an introduction of the synthesis of macrocyclic Schiff bases together with their coordination chemistry. Applications of these Schiff base ligands and metal complexes are discussed. Topics include: photoluminescence studies; peroxidase-like mimetics; ring-opening polymerization of cyclic esters.Chapter 2. In this chapter, the catalytic behaviour of homo binuclear versus mixed-metal analogues is discussed. In particular, homo-dinuclear Co and Zn complexes derived from the macrocycle LH2, {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][CH2CH2(2-C6H4N)2]}2 (R = Me, tBu), revealed near inactivity for the ring opening polymerization (ROP) of the cyclic esters δ-valerolactone (δ-VL) and ε-caprolactone (ε-CL). By contrast, the hetero- bimetallic complexes [LCo(NCMe)(μ-Br)ZnBr]·nMeCN (n=3 or 3.25) were found to be efficient catalysts for the ROP of ε-CL and δ-VL.Chapter 3. This chapter looks at the emission properties of some of the macrocycles and their complexes. Specifically, the emission properties of a number of solvates of the [2+2] Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}2 (R = Me L1H2, tBu L2H2, Cl L3H2), formed by reacting 2,6-dicarboxy-4-R-phenol with 2,2′- oxydianiline (2-aminophenylether), (2-NH2C6H4)2O, have been investigated. The macrocycle L1-3H2 exhibited the different maximum emission wavelengths in different solvents, from max at 508 nm (in acetonitrile) to 585 nm (in dichloromethane). DFT studies on systems L1-3H2 involving solvents of different polarity (DMF versus n-hexane) indicated that the energy level gap increases with solvent polarity in line with the observed hypochromic shifts. Reaction of macrocycle L1H2 with three equivalents of ZnBr2, in the presence of Et3N, affords the complex [(ZnBr)(ZnNCMe)L1]2[ZnBr4]·2.5MeCN (9·2.5MeCN). In the case of L2H2, reaction with two equivalents of ZnBr2 affords [(ZnBr)L2H2][ZnBr3NCMe]·3MeCN (10·3MeCN), whilst in the presence of two equivalents of Et3N, work-up led to the isolation of the complex [(ZnBr)2L2]·4.5MeCN (11·4.5MeCN). The molecular structures of 9-11 are reported, together with their emission behaviour.Chapter 4. In this chapter, the coordination chemistry of the macrocycles is extended to iron, cobalt and copper. Reaction of the [2+2] Schiff-base macrocycles {[2-(OH)-5- (R)-C6H2-1,3-(CH)2][CH2CH2(2-C6H4N)2]}2 (R = Me, LMeH2; tBu, LtBuH2) with FeBr2 afforded the complexes [FeBr(L1/L2H2)][X] (X = 0.5(FeBr3)2O, LMe·2MeCN, 12·2MeCN; LtBu, 13·0.5MeCN, X = Br, LtBu 14·3MeCN), respectively. Reaction of LtBuH2 with [KFe(OtBu)3(THF)] (formed in-situ from FeBr2 and KOtBu), following work-up, led to the isolation of the complex [Fe(LtBu)(LtBuH)]·3MeCN (15·3MeCN), whilst with [CuBr2] afforded [CuBr(LtBuH2)][Br3]·2MeCN (16·2MeCN). Attempts to form mixed Co/Ti species by reaction of [CoBrL2][CoBr3(NCMe)] with [TiCl4] resulted in [L2H4][CoBr4]·2MeCN (17·2MeCN). Use of the related oxy-bridged Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}2 (R = Me, L1H2; tBu, L2H2) with CoBr2 led to the isolation of the complexes [(CoBr)2(L1)]·4C3H6O (18·4C3H6O), [Co(NCMe)2(L2H2)][CoBr4]·5MeCN (19·5MeCN), [Co(NCMe)6][CoBr3(MeCN)]2·2MeCN (20·2MeCN). For comparative structural/polymerization studies, the complexes {CoBr(NCMe)L4}2·2MeCN (21·2MeCN) and [Co(NCMe)2L4]2[CoBr3(NCMe)]2 (22), [FeBr(NCMe)L4]2·2MeCN (23·2MeCN) where L4H = 2,6-(CHO)2-4-tBu-C6H2OH, as well as the chelate-free salt [Fe(NCMe)6][FeBr3OFeBr3] (24) have been isolated and structurally characterized. The ability of these complexes to act as catalysts forthe ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and δ- valerolactone (δ-VL) has been investigated, as well as the co-polymerization of γ- CL with rac-lactide (γ-LA) and vice-versa.Chapter 5. This chapter discusses the formation of a large macrocycle and how its’ coordination chemistry with iron. The iron complex was evaluated for peroxidase- like catalytic activity. The [2+2] Schiff-base macrocycle {[2-(OH)-5-(CH3)-C6H2-1,3- (CH)2][O(2-C6H4N)2]}2 (L1H2) was reacted the with two equivalents of FeBr2 afforded either the salt complex [L1H2FeBr2]2[FeBr3OFeBr3]·7MeCN (25·7MeCN) or, in the presence of Et3N, [L1(FeBr)2]·3MeCN (26·3MeCN). The new larger [6+6] macrocycle {[2-(OH)-5-(CH3)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}6 (L5H6) reacts with four equivalents of FeBr2 to afford [Fe2(L2H2)][FeBr3OFeBr3]·4MeCN (27·4MeCN). For the first time, we have evaluated such iron Schiff-base complexes for peroxidase-like catalytic activity. The electron transfer and the formation of hydroxyl radical were investigated in order to probe the mechanism of the peroxidase-like activity. Moreover, these Fe complexes were utilized for the determination of H2O2 using the colorimetric method. The linear range of H2O2 detection was 0.5-5 mM and 6-10 mM with a detection limit (LOD) of 0.05 mM. The method has good selectivity against interferents including glucose, urea, uric acid and metal ions.Chapter 6 This chapter discuss the facile preparation, molecular structures and DFT studies of [2+2] [2+3] and [2+4] double layer macrocyclic Schiff-base compounds. The [2+3] compound has been used for the immobilization of Pd, and the morphology of the resulting composite was analyzed by PXRD and SEM. The Pd@Schiff base composite was employed as a peroxidase-like mimetic using 3,3′,5,5′-tetramethylbenzidine (TMB) as the substrate, and a colorimetric method for determining H2O2 was established.Chapter 7 This chapter presents the experimental procedures

Corrigendum to “Iron complexes of [2 + 2] and [6 + 6] Schiff-base macrocycles derived from 2,2′-oxydianiline and their applications” [Inorg. Chem. Commun. 139 (2022) 109376] (Inorganic Chemistry Communications (2022) 139, (S1387700322001848), (10.1016/j.inoche.2022.109376))

The correct formula of 3 is [Fe2(L2H4)][FeBr3OFeBr3]2‧8MeCN.The revised CIF has been deposited with the CSD An updated version of the supplementary information file is provided

Turning on ROP activity in a bimetallic Co/Zn complex supported by a [2+2] Schiff-base macrocycle

Homo-dinuclear Co and Zn complexes derived from the macrocycle LH2, {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][CH2CH2(2-C6H4N)2]}2 (R = Me, tBu), revealed near inactivity for the ring opening polymerization (ROP) of the cyclic esters δ-valerolactone (δ-VL) and ϵ-caprolactone (ϵ-CL). By contrast, the hetero-bimetallic complexes [LCo(NCMe)(μ-Br)ZnBr]·nMeCN (n = 3 or 3.25) were found to be efficient catalysts for the ROP of ϵ-CL and δ-VL

Iron complexes of [2+2] and [6+6] Schiff-base macrocycles derived from 2,2′-oxydianiline and their applications

Reaction of [2+2] and [6+6] Schiff-base macrocycles with FeBr2 are reported, together with preliminary studies of the applications of the iron-containing products. In particular, we have investigated peroxidase-like activity and determination of H2O2, as well as their ability to act as catalysts for ring opening polymerization of cyclic esters

Mono-oxo molybdenum(VI) and tungsten(VI) complexes bearing chelating aryloxides: synthesis, structure and ring opening polymerization of cyclic esters

The mono-oxo aryloxide complexes [M(O)(L1)2] (M = Mo (1·hexane), W(2·2MeCN)) have been prepared from [Mo(O)(Cl)4] or [W(O)(Ot-Bu)4] and two equivalents of the di-phenol 2,2/-ethylidenebis(4,6-di-tert-butylphenol) L1H2, respectively. Use of in-situ generated [Mo(O)(Ot-Bu)4] with two equivalents of L1H2 also led to the isolation of 1·2MeCN. In the presence of adventitious oxygen, attempts to generate in-situ [Mo(O)(Ot-Bu)4] and reaction with one equivalent of L1H2 afforded the bi-metallic complex [Mo(O)(L1)(-O)Li(THF)(MeCN)]2·2MeCN (3·2MeCN). Use of the tetra-phenol α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xyleneH4 (L2H4) with [Mo(O)(Oi-Pr)4] led to the isolation of {[Mo(O)]L2}2 (4), whilst the analogous tungsten complex {[W(O)]L2}2 (5) was isolated from the reaction of L2H4 with [W(O)(Ot-Bu)4]. Similar reaction of p-tert-butylcalix[4]areneH4 (L3H4) with [Mo(O)(Oi-Pr)4] afforded ([Mo(O)L3(NCMe)]·3MeCN (6·3MeCN). Modification of known routes were employed to access the complexes [W(Cl)2L3]·3.5MeCN (7·3.5MeCN) and ([W(O)L3(NCMe)] (8), whilst use of [WO(Ot-Bu)4] with L3H4 unexpectedly afforded [W(Ot-Bu)2L3]·MeCN (9·MeCN). The molecular crystal structures for 1 – 9 are reported, and the ability of these complexes to act as catalysts for the ring opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL), delta-valerolactone (delta-VL) and gamma-pentadecalactone (gamma-PDL) has been investigated. The molybdenum complexes 1 and 4 were the best performers for epsilon-Cl and delta-VL, but all complexes exhibited poor control and were also inactive toward the ROP of PDL

Silver Nanoparticle-Immobilized Schiff-Base Macrocycles as Nanozymes with Peroxidase Mimic Activity for Antibacterial Films

The development of nanozymes has emerged as a promising pathway for combating bacterial infections. In this work, Ag/Schiff base nanozymes are obtained through the in situ reduction method on [2 + 3] Schiff base macrocycles using eco-friendly reductant α-tocopherol. The silver prepared was found to be nanoscale by TEM, and Ag NPs grew and dispersed uniformly on the surface of the Schiff base macrocycle due to the abundance of the C═N double bonds. The peroxidase-like catalytic activity of the Ag/Schiff base was evaluated toward 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, and the Km values of 0.350 and 0.090 mM confirm the strong affinity of Ag/Schiff base for H2O2 and TMB. Moreover, the nanozyme exhibited good antibacterial properties against Streptococcus sanguinis, Pseudomonas aeruginosa, and Staphylococcus aureus, and in vivo tests confirmed that the Ag/Schiff base had negligible biotoxicity. Benefiting from the good antimicrobial and biosafety properties, the nanozymes were explored to prepare antibacterial films, and the bacterial inhibition zones demonstrated that the introduction of the Ag/Schiff base could prevent the growth of bacteria

Volcanic geology of Admiralty Bay, King George Island, Antarctica

At Admiralty Bay of central King George Island, Keller Peninsula, Ullman Spur and Point Hennequin are main Tertiary volcanic terranes. Field investigation and isotopic datings indicate that, there occurred three periods of eruptions (three volcanic cycles) and accompanying N-toward migration of the volcanic center on Keller Peninsula. After the second period of eruptions, the crater collapsed and a caldera was formed, then later eruptions were limited at the northern end of the peninsula and finally migrated to Ullman Spur. Thus Keller Peninsula is a revived caldera, and its volcanism migrated toward E with time. Point Hennequin volcanism happened more or less simultaneously with the above two areas, but has no clear relation in chemical evolution with them, frequently it belongs to another independent volcanic center

Luteolin Prevents H2O2-Induced Apoptosis in H9C2 Cells through Modulating Akt-P53/Mdm2 Signaling Pathway

Introduction. Luteolin, a falconoid compound in many Chinese herbs and formula, plays important roles in cardiovascular diseases. The underlying mechanism of luteolin remains to be further elaborated. Methods. A model of hydrogen peroxide- (H2O2-) induced H9C2 cells apoptosis was established. Cell viabilities were examined with an MTT assay. 2′,7′-Dichlorofluorescin diacetate (DCFH-DA) and flow cytometry were used to detect ROS level and apoptosis rate, respectively. The expressions of signaling proteins related to apoptosis were analyzed by western blot and mRNA levels were detected by real-time polymerase chain reaction (PCR). Quercetin was applied as positive drug. Results. Incubation with various concentrations of H2O2 (0, 50, 100, and 200 μM) for 1 h caused dose-dependent loss of cell viability and 100 μM H2O2 reduced the cell viability to approximately 50%. Treatments with luteolin and quercetin protected cells from H2O2-induced cytotoxicity and reduced cellular ROS level and apoptosis rate. Moreover, luteolin could downregulate the expressions of Bax, caspase-8, cleaved-caspase-3, and p53 in apoptotic signaling pathway. Further study showed that the expressions of Akt, Bcl-2, and Mdm2 were upregulated by luteolin. Conclusion. Luteolin protects H9C2 cells from H2O2-induced apoptosis. The protective and antiapoptotic effects of luteolin could be mediated by regulating the Akt-P53/Mdm2 apoptotic pathway

Pd-Immobilized Schiff Base Double-Layer Macrocycle: Synthesis, Structures, Peroxidase Mimic Activity, and Antibacterial Performance

Di-, tri-, and tetra-aldehydes have been employed to access new [2 + 2] [2 + 3] and [2 + 4] double-layer Schiff base macrocycles. The [2 + 3] compound has been used for the immobilization of Pd and the resulting composite has been employed as a peroxidase-like mimetic using 3,3′,5,5′-tetramethylbenzidine (TMB) as the substrate; the optimum conditions together with the catalytic kinetics of the enzyme-like activity is discussed. Based on the peroxidase-like catalytic activity, the Pd@Schiff base composite was found to exhibit excellent bactericidal activity against both Escherichia coli (Gram-negative bacterium) and Staphylococcus aureus (Gram-positive bacterium) in the presence of relatively low concentrations of H2O2. Furthermore, cytotoxicity measurements illustrate the biosafety of the Pd composite. The above-mentioned findings have the potential to guide the innovation of new Pd-based composites as enzyme mimetics and antibacterial materials