Mn Centers Research Articles

Controlled exchange bias behavior of manganese nanoparticles

Mn(0) colloids were synthesized by solvated metal atom dispersion approach utilizing hexadecylamine, toluene, and THF as coordinating ligands. Mn-toluene and Mn-THF nanoparticles were found to be highly pyrophoric in nature and demand careful handling whereas, Mn-HDA nanoparticles undergo slow oxidation. TEM micrographs revealed formation of nanoparticles between 3 and 6 nm. Magnetic studies of these three samples displayed shift in the field-cooled M−H hysteresis loop which has been attributed to exchange bias behavior. The exchange bias field, HE measured at 5 K varies with change in coordinating ligands around the Mn center which are 1217 Oe, 4408 Oe and, 6350 Oe for Mn-HDA, Mn-toluene and Mn-THF nanoparticles, respectively. The large exchange bias field has been attributed to the presence of uncompensated antiferromagnetic surface spins and the exchange interactions at the nanoparticle surface due to surface oxidation.

Bifunctional ligand enabled selective alkoxycarbonylation of aliphatic alkenes

Carbazole derived phosphine ligands containing pyridine moiety were designed and prepared. It allows the challenging Pd-catalyzed Markovnikov-selective alkoxycarbonylation of aliphatic alkenes to give the branched ester products (28 examples; 51–97% branch selectivity). Preliminary mechanistic studies support that the bridging bromide between Pd and Mn centers is crucial for the enhancement of regioselectivity.

Two transition complexes based on 1H-benzimidazole-5,6-dicarboxylic acid: Synthesis, structure and photocatalytic degradation of dyes

Metal-organic frameworks [Co(Hbidc)(H2O)2] (1) and [Mn(Hbidc)(H2O)] (2), with multidentate 1H-benzimidazole-5,6-dicarboxylic acid (H3bidc) ligand, have been synthesized under hydro/solvothermal conditions and structurally characterized by elemental analysis, IR spectrum, and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that the center Co atom of complex 1 is six-coordinated with three-dimensional supramolecular structure and center Mn of complex 2 is five-coordinated with exhibiting a 2D layered network. The photodegradation of Crystal violet dye and Methylene blue dye were studied firstly by complexes 1 and 2 as photocatalysts. Research result indicates that the degradation rate for complex 1 can reach 89.85% , 90.6% and that for complex 2 can reach 88.28% , 79.48%. At the same time, corresponding to photocatalytic kinetics was performed.

Hollow Meso-crystalline Mn-doped Fe3O4 Fenton-like catalysis for ciprofloxacin degradation: Applications in water purification on wide pH range

Herein, an unprecedented heterogeneous Fenton-like catalyst with a hollow meso-crystalline Fe3O4 catalyst doped with Mn was prepared for the first time through a one-pot method, which can effectively activate H2O2 in a wide pH range and has good stability. The results show the catalyst can achieve rapid degradation of ciprofloxacin (CIP) under the conditions of pH = 4.5 to pH = 9.5, which greatly expands the application conditions of Fenton. Sufficient experimental exploration clearly demonstrated that the uniform doping of Mn in Fe3O4 crystal lattice, and the formation process of Mn-doped Fe3O4 hollow meso-crystalline microspheres was reasonably analyzed based on Ostwald curing theory and bubble theory. The dual reaction center theory reasonably explains the reaction mechanism of the catalyst. The H2O2 adsorbed on the electron-rich Fe center is reduced to •OH, while the H2O2 adsorbed on the electron-deficient Mn center is oxidized to •O2–/HO2•, •OH and •O2–/HO2• are further converted to 1O2, which participates in involved in the degradation process of CIP. This research provides new ideas for the rational design of catalysts that can apply the heterogeneous Fenton reaction to actual water purification in a wide pH range.

Instigating the In Vitro Anticancer Activity of New Pyridine-Thiazole-Based Co(III), Mn(II), and Ni(II) Complexes: Synthesis, Structure, DFT, Docking, and MD Simulation Studies.

The perchlorate salt of (4-(4-methoxy phenyl)-2-(2-(1-pyridine-2-yl)ethylidene)hydrazinyl)thiazole (PytH·ClO4) and its metal perchlorate derivatives, namely, [Co(Pyt)2]ClO4 (1), [Mn(PytH)2](ClO4)2 (2), and [Ni(PytH)2](ClO4)2 (3), have been synthesized and characterized through single X-ray crystallography and spectroscopic methods. The ligand crystallizes in a space group P21/n in a nearly planar structure. The overall geometry of the complex salts is described as a distorted octahedron with a MN6 chromophore. The ligand (PytH·ClO4) behaves as a neutral N,N,N-tridentate donor toward the "soft" Mn(II) and Ni(II) centers, whereas the deprotonated ligand stabilizes the "hard" Co(III) center. The DNA binding constant (Kb) values of PytH·ClO4, 1, 2, and 3 are determined using the UV-vis spectroscopic method, and the Kb values are 9.29 × 105, 7.11 × 105, 8.71 × 105, and 7.82 × 105 mol-1, respectively, indicating the intercalative mode of interactions with CT-DNA. All the derivatives show effective antiproliferative activity against U-937 human monocytic tumor cells with IC50 values 4.374 ± 0.02, 5.583 ± 0.12, 0.3976 ± 0.05, and 11.63 ± 0.01 μM for PytH·ClO4, 1, 2, and 3, respectively. The best apoptosis mode of cell death is shown by 2 followed by PytH·ClO4 and 1 at an equivalent concentration of IC50 values. The combined molecular docking and dynamics simulation study evaluates the binding energies of anticancer agents, providing groove binding property with DNA. The 20 ns molecular dynamics simulation study reveals the maximum DNA binding stability of 2 corroborating the experimental results. The new class of metal derivatives of pyridine-thiazole can be used for advanced cancer therapeutics.

X-ray-Triggered CO Release Based on GdW10/MnBr(CO)5 Nanomicelles for Synergistic Radiotherapy and Gas Therapy.

Carbon monoxide (CO) therapy has become a hot topic in the field of gas therapy because of its application prospect in the treatment of various diseases. Due to the high affinity for human hemoglobin, the main challenge of CO-loaded nanomedicine is the lack of selectivity and toxicity in the delivery process. Although many commercial CO-releasing molecules (CORMs) have been widely developed because of their ability to deliver CO, CORMs still have some disadvantages, including difficult on-demand controlled CO release, poor solubility, and potential toxicity, which are limiting their further application. Herein, an X-ray-triggered CO-releasing nanomicelle system (GW/MnCO@PLGA) based on GdW10 nanoparticles (NPs) (GW) and MnBr(CO)5 (MnCO) encapsulating in the poly(lactic-co-glycolic acid) (PLGA) polymer was constructed for synergistic CO radiotherapy (RT). The production of strongly oxidative superoxide anion (O2-•) active species can lead to cell apoptosis under the X-ray sensitization of GW. Moreover, strongly oxidative O2-• radicals further oxidize and compete with the Mn center, resulting in the on-demand release of CO. The radio/gas therapy synergy to enhance the efficient tumor inhibition of the nanomicelles was investigated in vivo and in vitro. Therefore, the establishment of an X-ray-triggered controlled CO release system has great application potential for further synergistic RT CO therapy in deep tumor sites.

Dissociation of a tripodal pyridyl-pyrazole ligand and assortment of metal complex: Synthesis, structure, DFT, thermal stability, cytotoxicity, DNA cleavage, and molecular docking studies

A tripodal pyridyl-pyrazole based N,N,O donor ligand (L) has been designed, and it's copper(II) complex, [Cu(L1)Cl2]2.(dmpzH)2 (1) where dmpzH refers protonated dimethylpyrazole, and manganese(II) complex, [Mn(L)(Cl)2] (2)] have been synthesized and characterized by a combination of various spectroscopy, X-ray crystallography, electrochemical, thermogravimetric and density functional theory. The X-ray structure of 1 showed the copper(II) coordinated by the two sets of NO donors which had been assorted from the ligand (L) along with two bridging and one terminal chloride atoms. The distorted square-planar centrosymmetric structure of 1 is further stabilized by the hydrogen bonding with exogenous protonated pyrazole units that had been extracted from L. The title ligand retained its original structure when bound with Mn(II) giving a pseudo-octahedral geometry. The central Mn(II) was coordinated by two pyrazolyl nitrogen (N1, N7), one tertiary amine nitrogen (N3), one carbohydrazide oxygen atom O1, and two exogenous chloride ions in a cis disposition. Cytotoxicity experiments carried out in a series of human cell lines (IMR-32, HepG2 and HeLa) to confirm the apoptotic mechanism of cell death, predominantly in IMR-32. The DNA cleavage studies were then performed in the presence of the synthesized compounds to verify the influence of ligand structural features in their nuclease activity. Complex 2 was able to cause double-strand DNA scissions both in an oxidizing and reducing environment, whereas complex 1 broke the single-strand DNA in a reducing environment only, suggesting its potential anticancer therapeutics. To shed a better understanding of DNA-substrate interaction, a molecular docking study was performed.

Intense green luminescence in Mn-doped gallogermanate nanostructured glass

Mn-activated optical materials have been demonstrated to be promising for various applications such as light-emitting device, tunable lasers and smart sensors. Most of the candidates belong to the single crystals and crystalline powders, and few reports involve about the glass-derived materials. This letter reports the fabrication of active Mn-doped nanostructured glass sample via control of the crystallization of a typical gallogermanate glass. LiGa5O8 and LiGaGeO4 can precipitate after heat-treatment, and Mn centers selectively incorporate into the crystalline phase. Importantly, the luminescence can be switched from red to green colour and the intensity can be enhanced simultaneously. Furthermore, the luminescence properties can be tuned via control of the phase of the nanostructured glass.

Incorporation of a boryl pendant as the trigger in a methacrylate polymer for backbone degradation.

Alkenylboronate units were incorporated into poly(methyl methacrylate) as trigger sites for backbone degradation. The complexation of a fluoride anion to the boron pendant and subsequent activation by a manganese salt triggered the degradation through the generation of a main-chain carbon radical and β-scission in an adjacent methacrylate unit. The addition of catechol was required, and presumably the chelate coordination to the Mn center was crucial for the degradation.

Binuclear Alkyne Manganese Carbonyls: Their Rearrangements to Allene, Allyl, and Vinylcarbene Derivatives by Hydrogen Migration from Methyl Substituents

AbstractBinuclear alkyne manganese carbonyls of the type (RC≡CR')Mn2(CO)n (R and R'=methyl or dimethylamino; n=8, 7, 6) and their isomers related to the experimentally known (MeC2NEt2)Mn2(CO)n (n=8, 7) structures have been investigated by density functional theory. The alkyne ligand remains intact in the only low energy (Me2N)2C2Mn2(CO)8 isomer, which has a central Mn2C2 tetrahedrane unit and is otherwise analogous to the well‐known (alkyne)Co2(CO)6 derivatives except for one more CO group per metal atom. The low‐energy structures of the unsaturated (Me2N)2C2Mn2(CO)n (n=7, 6) systems include isomers in which the nitrogen atom of one of the dimethylamino groups as well as the C≡C triple bond of the alkyne is coordinated to the central Mn2 unit. In other low‐energy (Me2N)2C2Mn2(CO)n (n=7, 6) isomers the alkyne C≡C triple bond has broken completely to form two separate bridging dimethylaminocarbyne Me2NC ligands analogous to the experimentally known iron carbonyl complex (Et2NC)2Fe2(CO)6. The (alkyne)Mn2(CO)n (n=8, 7, 6) systems of the alkynes MeC≡CMe and Me2NC≡CMe with methyl substituents have significantly more complicated potential surfaces. In these systems the lowest energy isomers have bridging ligands derived from the alkyne in which one or two hydrogen atoms have migrated from a methyl group to one or both of the alkyne carbon atoms. These bridging ligands include allene, manganallyl, and vinylcarbene ligands, the first two of which have been realized experimentally in research by Adams and coworkers. Theoretical studies suggest that the mechanism for the conversion of the simple alkyne octacarbonyl (MeC2NMe2)Mn2(CO)8 to the dimethylaminomanganaallyl complex Mn2(CO)7[μ‐η4‐C3H3Me2] involves decarbonylation to the heptacarbonyl and the hexacarbonyl complexes. Subsequent hydrogen migrations then occur through intermediates with C−H−Mn agostic interactions to give the final product. Eight transition states for this mechanistic sequence have been identified with activation energies of ∼20 kcal/mol for the first hydrogen migration and ∼14 kcal/mol for the second hydrogen migration.

Hydrosilylation of Aldehydes and Ketones Catalyzed by a 2-Iminopyrrolyl Alkyl-Manganese(II) Complex.

A well-defined and very active single-component manganese(II) catalyst system for the hydrosilylation of aldehydes and ketones is presented. First, the reaction of 5-(2,4,6-iPr3C6H2)-2-[N-(2,6-iPr2C6H3)formimino]pyrrolyl potassium (KL) and [MnCl2(Py)2] afforded the binuclear 2-iminopyrrolyl manganese(II) pyridine chloride complex [Mn2{κ2N,N'-5-(2,4,6-iPr3C6H2)-NC4H2-2-C(H)═N(2,6-iPr2C6H3)}2(Py)2(μ-Cl)2] 1. Subsequently, the alkylation reaction of complex 1 with LiCH2SiMe3 afforded the respective (trimethylsilyl)methyl-Mn(II) complex [Mn{κ2N,N'-5-(2,4,6-iPr3C6H2)-NC4H2-2-C(H)═N(2,6-iPr2C6H3)}(Py)CH2SiMe3] 2 in a good yield. Complexes 1 and 2 were characterized by elemental analysis, 1H NMR spectroscopy, Evans' method, FTIR spectroscopy, and single-crystal X-ray diffraction. While the crystal structure of complex 1 has been identified as a binuclear entity, in which the Mn(II) centers present pentacoordinate coordination spheres, that of complex 2 corresponds to a monomer with a distorted tetrahedral coordination geometry. Complex 2 proved to be a very active precatalyst for the atom-economic hydrosilylation of several aldehydes and ketones under very mild conditions, with a maximum turnover frequency of 95 min-1, via a silyl-Mn(II) mechanistic route, as asserted by a combination of experimental and theoretical efforts, the respective silanes were cleanly converted to the respective alcoholic products in high yields.

Regulating the Interfacial Electron Density of La0.8Sr0.2Mn0.5Co0.5O3/RuOx for Efficient and Low-Cost Bifunctional Oxygen Electrocatalysts and Rechargeable Zn-Air Batteries.

La0.8Sr0.2Mn0.5Co0.5O3 (LSMC) perovskite anchored with RuOx (LSMC-Ru) is fabricated as a new bifunctional electrocatalyst, with low dosage (2.43 wt %) and high utilization of noble metal Ru. The LSMC-Ru exhibits outstanding bifunctional activity with a low potential gap of 0.72 V between the oxygen evolution reaction (OER) potential at 10 mA cm-2 and the oxygen reduction reaction (ORR) half-wave potential. The strong electronic interaction between RuOx and LSMC is confirmed by both experiments and theoretical calculations. Consequently, the electron-rich Mn centers promote ORR, while the electron-deficient Ru centers facilitate OER. A Zn-air battery using the LSMC-Ru air electrode delivers a peak power density of 159 mW cm-2 and a low charge-discharge potential gap of 0.58 V at 2 mA cm-2. The high round-trip energy efficiency of 60.6% is retained after 300 cycles. This strategy of anchoring a low dosage noble metal catalyst to perovskite can be extended to other systems of noble metal-non-noble metal composite electrocatalysts to achieve both competitive performance and low cost.

A Long‐Life Manganese Oxide Cathode Material for Aqueous Zinc Batteries with a Negatively Charged Porous Host to Promote the Back‐Deposition of Dissolved Mn2+

AbstractManganese oxide is a promising cathode material for rechargeable aqueous zinc batteries. However, the cycling stability is seriously limited by Mn dissolution. Herein, a negatively charged porous carbon host is proposed for manganese oxide to ensure stable cycling. It is derived from a metal–organic framework with Zn and Mn centers. The organic ligands transform into porous carbon upon calcination, and Zn vaporizes to generate a negatively charged surface. It provides abundant reaction sites, electron transport network, and most importantly, strong attractions towards Mn2+ cations by electrostatic interactions. The Mn2+ dissolved from manganese oxide reversibly deposits back to the cathode as demonstrated by mechanism studies, and active species is preserved for energy storage. In the electrolyte of 3 m ZnSO4 without Mn2+ additives, the composite cathode achieves an ultra‐long life over 11 000 cycles at 2 A g−1. It also delivers 275 mAh g−1 capacity (based on the total mass of the composite) at 0.1 A g−1. This work proposes an effective strategy to realize the stable cycling of manganese oxide cathode materials in aqueous zinc batteries.

Multiple-Site Concerted Proton-Electron Transfer in a Manganese-Based Complete Functional Model for [FeFe]-Hydrogenase.

The active site of [FeFe]-hydrogenase (H2 ase) is preorganized with an amine (azadithiolate) as a proton relay and a [4Fe4S] subunit as an electron reservoir, which together lower the overpotential for proton reduction and hydrogen oxidation by multiple-site concerted proton-electron transfer (MS-CPET). Herein, we report a mononuclear manganese complex, fac-[Mn(CO)3 (6-(2-hydroxyphenol)-2-pyridine-2-quinoline) Br] (1), as a rare model to fully mimic the functions of the H2 ase. In 1, a redox-active bidentate ligand with a pendent phenol replicates the roles of the electron reservoir and the proton relay in the enzyme. Experimental and theoretical studies revealed two consecutive MS-CPET processes in the catalytic cycle, in each of which an electron stored in the reductive ligand and a proton at the proximal phenol moiety are transferred to the Mn center in a concerted way. By virtue of this mechanism, complex 1 exhibited a low overpotential comparable to that of natural enzyme in electrochemical hydrogen production using phenol as a proton source.

Multiple‐Site Concerted Proton–Electron Transfer in a Manganese‐Based Complete Functional Model for [FeFe]‐Hydrogenase

AbstractThe active site of [FeFe]‐hydrogenase (H2ase) is preorganized with an amine (azadithiolate) as a proton relay and a [4Fe4S] subunit as an electron reservoir, which together lower the overpotential for proton reduction and hydrogen oxidation by multiple‐site concerted proton–electron transfer (MS‐CPET). Herein, we report a mononuclear manganese complex, fac‐[Mn(CO)3(6‐(2‐hydroxyphenol)‐2‐pyridine‐2‐quinoline) Br] (1), as a rare model to fully mimic the functions of the H2ase. In 1, a redox‐active bidentate ligand with a pendent phenol replicates the roles of the electron reservoir and the proton relay in the enzyme. Experimental and theoretical studies revealed two consecutive MS‐CPET processes in the catalytic cycle, in each of which an electron stored in the reductive ligand and a proton at the proximal phenol moiety are transferred to the Mn center in a concerted way. By virtue of this mechanism, complex 1 exhibited a low overpotential comparable to that of natural enzyme in electrochemical hydrogen production using phenol as a proton source.

Sulfur cathodes based on dual-functional GMs-MnOOH for high performance lithium sulfur batteries

Lithium-sulfur batteries (LSBs) have been regarded as a next generation energy storage systems candidate due to its high theoretical energy density. However, the polysulfide dissolution and the sluggish redox reaction kinetics still hinder its practical applications. Herein, a 2D layered graphene micro-sheets, loaded with mesoporous MnOOH (GMs-MnOOH) as an energetic sulfur host for LSBs is reported. This sulfur host material works in two ways: anchoring sulfur and lithium polysulfides by nonpolar GMs and Lewis acidic Mn (III) center of porous structure MnOOH. As a result, with a sulfur content of 56 wt%, GMs-MnOOH/S cathodes present significantly improved rate performance and cycling stability. The GMs-MnOOH/S electrode delivered a specific capacity of 952mAhg−1 and 807mAhg−1 at 1C and 2C, respectively. This work provides a promising guidance to realize highly efficient hosts for Li-S batteries with high sulfur loading.

Solvent driven structural topologies involving unconventional O[sbnd]H(methanol)⋯π contact and anti-cooperative HB⋯anion-π⋯HB assemblies with unusual enclathration of dual guest (H2O)4 cores in Mn(II) and Ni(II) coordination compounds: Antiproliferative evaluation and theoretical studies

Two Mn(II) and Ni(II) coordination complexes viz. [Mn(phen)2(2,6-PDC)]·2CH3OH (1) and [Ni(2,6-PDC)2][Ni(H2O)4(en)]·6H2O (2) (phen = 1,10-phenanthroline, 2,6-PDC = 2,6-pyridinedicarboxylate and en = ethylenediamine) have been isolated at ambient conditions and characterized by elemental analysis, FT-IR, electronic spectroscopy, TGA and single crystal X-ray diffraction. Switching the solvent from methanol to water has changed the structural topologies of the compounds. Compound 1 is composed of a hepta-coordinated Mn(II) centre with two bidentate phen and one tridentate 2,6-PDC; whereas compound 2 is composed of cationic [Ni(H2O)4(en)]2+ and anionic [Ni(2,6-PDC)2]2– moieties with hexa-coordinated Ni(II) centers. Crystal structure analysis of compound 1 unfolds the presence of unorthodox OH(methanol)⋯π interactions involving the uncoordinated methanol molecules. The unusual enclathration of dual H-bonded guest (H2O)4 cores in the hexameric Ni(II) hosts in compound 2 provides rigidity to the crystal structure. The antiparallel π-stacked dimers and anti-cooperative HB···anion-π···HB assemblies observed in the solid-state structures of 1 and 2 respectively have been studied theoretically using DFT calculations and NCI plot index computational tools. In vitro anticancer evaluation of the compounds considering cell cytotoxicity and apoptosis assay showed significant concentration dependent cytotoxicity in Dalton’s lymphoma (DL) cancer cells with nominal effects in normal PBMC cells. To elucidate the possible mode of action of the cytotoxic behavior of the compounds, in silico docking studies have been carried out which revealed the efficient interaction of the compounds with the active sites of antiapototic cancer target proteins. The inhibitions of the activities of antiapoptotic target proteins have been further investigated using western blot analysis.

A new manganese(II) coordination polymer constructed with 5.5′-(benzene)-1,4-diyl)-bis(oxy) diterphthalic acid: synthesis, structure analysis and magnetic properties

A new 2D manganese(II) coordination polymer, namely [Mn(L)0.5(2,2′-bipy)]n·nH2O (1), has been constructed hydrothermally based on manganese acetate and the mixed ligands including the 5.5′-(benzene)-1,4-diyl)-bis(oxy) diterphthalic acid (H4L) and auxiliary 2,2′-bipyridine (2,2′-bipy). The compound was characterized by elemental analyses, was characterized by elemental analysis, infrared spectrum and single-crystal and powder X-ray diffractions, and thermal analyses. Single-crystal X-ray diffraction analyses revealed that compound 1 crystallize in the triclinic system, space group P-1. The adjacent Mn(II) ions are bridged by µ6-L4− ligands, producing a 2D layer. Magnetic studies for compound 1 demonstrate an antiferromagnetic coupling between the adjacent Mn(II) centers.

Ultrafine-Mn2O3@N-doped porous carbon hybrids derived from Mn-MOFs: Dual-reaction centre catalyst with singlet oxygen-dominant oxidation process

Ultrafine-Mn2O3@N-doped porous carbon hybrids [Mn2O3@NC] derived from Mn-MOFs was constructed with 1O2 and O2−• as main Reactive oxygen species (ROS). Cation-π bonds and N-Mn complexation induced the formation of electron-rich Mn centre which provided electron for peroxymonosulfate activation to produce radicals, accompanying with generation of 1O2 via chain reaction. Notably, the porous structure of N-doped carbon shell could not only facilitate free radical recombination for generation of 1O2 but also provide adsorption sites for organics. On the other hand, as electron-poor centre, N-doped carbon shell could improve the electrons transfer from organic intermediate radicals to electron-rich Mn centre via π -π reaction, C-O-Mn and C-N-Mn bonds, which promote the redox of Mn to avoid peroxymonosulfate invalid decomposition. Being attributed to synergistic effects of dual-reaction centres and strong oxidation ability of 1O2, Mn2O3@NC achieved high mineralization of BPA at low-dose peroxymonosulfate (0.033 g/L).

Controlling the Reactivity of a Metal-Hydroxo Adduct with a Hydrogen Bond.

The enzymes manganese lipoxygenase (MnLOX) and manganese superoxide dismutase (MnSOD) utilize mononuclear Mn centers to effect their catalytic reactions. In the oxidized MnIII state, the active site of each enzyme contains a hydroxo ligand, and X-ray crystal structures imply a hydrogen bond between this hydroxo ligand and a cis carboxylate ligand. While hydrogen bonding is a common feature of enzyme active sites, the importance of this particular hydroxo-carboxylate interaction is relatively unexplored. In this present study, we examined a pair of MnIII-hydroxo complexes that differ by a single functional group. One of these complexes, [MnIII(OH)(PaPy2N)]+, contains a naphthyridinyl moiety capable of forming an intramolecular hydrogen bond with the hydroxo ligand. The second complex, [MnIII(OH)(PaPy2Q)]+, contains a quinolinyl moiety that does not permit any intramolecular hydrogen bonding. Spectroscopic characterization of these complexes supports a common structure, but with perturbations to [MnIII(OH)(PaPy2N)]+, consistent with a hydrogen bond. Kinetic studies using a variety of substrates with activated O-H bonds, revealed that [MnIII(OH)(PaPy2N)]+ is far more reactive than [MnIII(OH)(PaPy2Q)]+, with rate enhancements of 15-100-fold. A detailed analysis of the thermodynamic contributions to these reactions using DFT computations reveals that the former complex is significantly more basic. This increased basicity counteracts the more negative reduction potential of this complex, leading to a stronger O-H BDFE in the [MnII(OH2)(PaPy2N)]+ product. Thus, the differences in reactivity between [MnIII(OH)(PaPy2Q)]+ and [MnIII(OH)(PaPy2N)]+ can be understood on the basis of thermodynamic considerations, which are strongly influenced by the ability of the latter complex to form an intramolecular hydrogen bond.