A manganese porphyrin suppresses oxidative stress and extends the life span of streptozotocin-diabetic rats

Enhanced oxidative stress due to hyperglycemia has been implicated in diabetic complications and is considered a major cause of cell and tissue damage. The aim of the present study was to investigate whether synthetic manganese porphyrin, Mn(III) 5,10,15,20-tetrakis(N-methylpyridinium-2-yl)porphyrin (MnTM-2-PyP⁵⁺) can ameliorate diabetes-induced oxidative stress and affect life span of diabetic rats.

Diabetes was induced by a single (60 mg/kg) intraperitoneal injection of streptozotocin in male Wistar rats. Oxidative stress was monitored by measuring malondialdehyde levels (MDA) in blood plasma and erythrocytes using HPLC. The antioxidant status was assessed by measuring the total radical-trapping potential (TRAP) of blood plasma. Life span of the animals was used as an indication of the overall effect of MnTM-2-PyP⁵⁺. MnTM-2-PyP⁵⁺ was administered subcutaneously at 1 mg/kg for the duration of the experiment, five times/week followed by one week of rest.

Diabetes increased plasma and erythrocyte levels of MDA and decreased TRAP. MnTM-2-PyP⁵⁺ had no effect on blood glucose and glycosylated hemoglobin, but significantly increased TRAP and lowered MDA. This Mn porphyrin decreased mortality and markedly extended the life span of the diabetic animals.

MnTM-2-PyP⁵⁺ suppressed diabetes-induced oxidative stress, which presumably accounts for its beneficial effect on the life span of the diabetic rats. The results indicate that Mn(III) N-alkylpyridylporphyrins can be used as potent therapeutic agents in diabetes.     

Design and synthesis of N-benzylpiperidine-purine derivatives as new dual inhibitors of acetyl- and butyrylcholinesterase

The synthesis and biological evaluation of N-benzyl-(piperidin or pyrrolidin)-purines are described. Compounds derived from N-benzylpiperidine and N-substituted purines showed moderate acetylcholinesterase inhibition. Preliminary structure–activity relationships and a superimposition of the best compound with the active conformation of donepezil have revealed structural features that have been used in the design of more potent N-benzylpiperidine inhibitors bearing an 8-substituted caffeine fragment and a methoxymethyl linker. These new compounds are interesting dual inhibitors of acetylcholinesterase and butyrylcholinesterase and have been chosen for further optimisation.     

Non-heme manganese catalase--the 'other' catalase

Non-heme manganese catalases are widely distributed over microbial life and represent an environmentally important alternative to heme-containing catalases in antioxidant defense. Manganese catalases contain a binuclear manganese complex as their catalytic active site rather than a heme, and cycle between Mn(2)(II,II) and Mn(2)(III,III) states during turnover. X-ray crystallography has revealed the key structural elements of the binuclear manganese active site complex that can serve as the starting point for computational studies on the protein. Four manganese catalase enzymes have been isolated and characterized, and the enzyme appears to have a broad phylogenetic distribution including both bacteria and archae. More than 100 manganese catalase genes have been annotated in genomic databases, although the assignment of many of these putative manganese catalases needs to be experimentally verified. Iron limitation, exposure to low levels of peroxide stress, thermostability and cyanide resistance may provide the biological and environmental context for the occurrence of manganese catalases.     

N,N′-Ethylene-bis(3-methoxysalicylideneimine) mononuclear (4f) and heterodinuclear (3d–4f) metal complexes: Synthesis, crystal structure and luminescent properties

The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H₂L and Ln(NO₃)₃ · 6H₂O give rise to three mononuclear lanthanide complexes Ln(H₂L)(NO₃)₃ [H₂L = N,N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N,N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O₂O₂ set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac)₂ · H₂O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO₃)₃ · H₂O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N₂O₂ cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes.     

Short step enantioselective synthesis of (-)-swainsonine

Recent discovery of asymmetric desymmetrization of meso-heterocycles using (R,R)-(salen)manganese complex 2 as a catalyst allowed easy access to optically active 2,3,4-trisubstituted pyrrolidines. Taking advantage of this new reaction, we could achieve the short-step synthesis of (-)-swainsonine 1.     

Characteristic properties of N-Carboxybutyl chitosan

N-Carboxybutyl chitosans obtained from levulinic acid (4-oxo-pentanoic acid) and five crustacean chitosans (heteropolymers of N-acetylglucosamine and glucosamine) have been instrumentally characterized and found to have degree of N-carboxyalkylation 0·27. They dissolve in water and in water-ethanol mixtures without the need of any acid and give more viscous solutions than the corresponding chitosans. Their compatibility with other polymers and with salts has been surveyed, and the soluble chelates of Cr(III) and Pb(II) have been studied. The bacteriostatic activity of the N-carboxybutyl chitosans, together with other favorable properties, such as the viscosifying action, the enhanced film-forming ability, the moisturizing effect and the stabilization of emulsions, make these novel modified chitosans most suitable as functional cosmetic ingredients.     

Chemical and biological investigation of N-hydroxy-valdecoxib: An active metabolite of valdecoxib

The inhibition of cyclooxygenase enzymes plays an important role in the treatment of inflammatory diseases. N-Hydroxy-4-(5-methyl-3-phenylisoxazol-4-yl)benzenesulfonamide (3)—a primary metabolite of the highly selective COX-2 inhibitor valdecoxib—was synthesized and stabilized as its monohydrate (3a·H₂O). The anti-inflammatory properties of 3a·H₂O were investigated in carrageenan-induced edema and in acute and chronic pain models. Based on our biological investigation, we conclude that N-hydroxy-valdecoxib 3a is an active metabolite of valdecoxib.     

Decreased hepatic ischemia-reperfusion injury by manganese-porphyrin complexes

Reactive oxygen and nitrogen species have been implicated in ischemia-reperfusion (I/R) injury. Metalloporphyrins (MP) are stable catalytic antioxidants that can scavenge superoxide, hydrogen peroxide, peroxynitrite and lipid peroxyl radicals. Studies were conducted with three manganese-porphyrin (MnP) complexes with varying superoxide dimutase (SOD) and catalase catalytic activity to determine if the MnP attenuates I/R injury in isolated perfused rat livers. The release of the hepatocellular enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) was maximal at 1 min reperfusion, decreased rapidly and increased gradually by 90 min. Manganese tetrakis-(N-ethyl-2 pyridyl) porphyrin (MnTE-2-PyP) decreased ALT, AST, LDH at 1-90 min reperfusion, while manganese tetrakis-(N-methyl-2 pyridyl) porphyrin (MnTM-2-PyP) and manganese tetrakis-(ethoxycarbonyl) porphyrin (MnTECP) decreased ALT and LDH from 5 to 90 min reperfusion. The release of thiobarbituric acid-reacting substances (TBARS) was diminished by MnTE-2-PyP and MnTM-2-PyP at 90 min. The extent of protein nitration (nitrotyrosine, NT) was decreased in all three MnPs treated livers. These results demonstrate that MnP complexes can attenuate hepatic I/R injury and may have therapeutic implications in disease states involving oxidants.     

Synthesis of 2-(2-adamantyl)piperidines and structure anti-influenza virus A activity relationship study using a combination of NMR spectroscopy and molecular modeling

The 2-(2-adamantyl)piperidines 13 and 15a-c were synthesized and evaluated for anti-influenza virus A and B activity. The parent N-H compound 13 was 3–4 times more active than amantadine and rimantadine against H₂N₂ influenza A. N-alkylation of 13 resulted in derivatives 15a-c that were devoid of biological activity. This dramatic reduction in biological activity may be attributed to the different conformational properties between N-H and N-alkyl piperidines, as deduced from the combination of computational chemistry and NMR spectroscopy.     

Post functionalization of carboxymethylated starch and acrylonitrile based networks through amidoximation for use as ion sorbents

Carboxymethylation of starch provided carboxymethyl starch (CMS) and the modification was followed by grafting CMS with acrylonitrile (AN) using ammonium per sulphate-N,N,N,N-tetramethylethylene diamine as initiator–accelerator system. Crosslinked networks of CMS and AN were obtained using two crosslinkers, viz., N,N-methylenebisacrylamide and ethyleneglycoldimethacrylate. The networks were further reacted with hydroxylamine to generate metal ion active amidoxime groups. The synthesized hydrogels were characterized by FTIR, SEM, nitrogen analysis and swelling studies to evaluate water uptake and the candidate polymers were used as matrices for the sorption of Fe²⁺ ions, as a model metal ion, as a function of time, temperature, pH and ionic strength. An attempt was made to investigate the thermodynamics of its sorption behaviour.     

Characterization of novel alcohol dehydrogenase of Devosia riboflavina involved in stereoselective reduction of 3-pyrrolidinone derivatives

Optically active N-benzyl-3-pyrrolidinols are versatile chiral building blocks. Stereoselective reduction of N-benzyl-3-pyrrolidinone is an economical and environmentally friend means of synthesizing these compounds. Devosia riboflavina KNK10702 was discovered on screening as a source of a reducing enzyme giving the (R)-form N-benzyl-3-pyrrolidinol. An NADH-dependent alcohol dehydrogenase was purified to homogeneity through five steps from this microorganism. The relative molecular mass of the enzyme was estimated to be 58,000 on gel filtration and 28,000 on SDS-polyacrylamide gel electrophoresis. This enzyme reduced a broad range of carbonyl compounds in addition to N-substituted-3-pyrrolidinones. Some properties of the enzyme are reported herein.     

Electron paramagnetic resonance and spectrophotometric studies of the peroxide compounds of manganese-substituted horseradish peroxidase, cytochrome-c peroxidase and manganese-porphyrin model complexes

Peroxide compounds of manganese protoporphyrin IX and its complexes with apo-horseradish peroxidase and apocytochrome-c peroxidase were characterized by electronic absorption and electron paramagnetic resonance spectroscopies. An intermediate formed upon titration of Mn(III)-horseradish peroxidase with hydrogen peroxide exhibited a new electron paramagnetic resonance absorption at g = 5.23 with a definite six-lined 55Mn hyperfine (AMn = 8.2 mT). Neither a porphyrin pi-cation radical nor any other radical in the apoprotein moiety could be observed. The reduced form of Mn-horseradish peroxidase, Mn(II)-horseradish peroxidase, reacted with a stoichiometric amount of hydrogen peroxide to form a peroxide compound whose electronic absorption spectrum was identical with that formed from Mn(III)-horseradish peroxidase. The electronic state of the peroxide compound of manganese horseradish peroxidase was thus concluded to be Mn(IV), S = 3/2. Mn(III)-cytochrome-c peroxidase reacted with stoichiometry quantities of hydrogen peroxide to form a catalytically active intermediate. The electronic absorption spectrum was very similar to that of a higher oxidation state of manganese porphyrin, Mn(V). Since the peroxide compound of manganese cytochrome-c peroxidase retained two oxidizing equivalents per mol of the enzyme (Yonetani, T. and Asakura, T. (1969) J. Biol. Chem. 244, 4580-4588), this peroxide compound might contain an Mn(V) center.     

A series of heteroleptic complexes of the type fac-[MnL2] [H2L=derivatives of N-(2-hydroxybenzyl)glycine or N-(5-nitro-2-hydroxybenzyl)sarcosine] possessing unusual Mn(III) co-ordination spheres

The mononuclear manganese(III) complexes [C₅H₁₀NH₂][MnL₂] [L²⁻=a substituted N-(2-hydroxybenzyl)glycinate (hbg²⁻) viz. 3,5-dibromo- (3,5-Br-hbg²⁻), 3,5-dichloro- (3,5-Cl-hbg²⁻), 3-methyl-5-chloro- (3,5-Me,Cl-hbg²⁻), 5-bromo- (5-Br-hbg²⁻), 5-chloro- (5-Cl-hbg²⁻), 5-nitro- (5-NO₂-hbg²⁻) or N-(5-nitro-2-hydroxybenzyl)sarcosine (5-NO₂-hbs²⁻)] have been synthesised by reaction of the appropriate ligand with manganese(II) perchlorate under ambient conditions in a 2:1 molar ratio using piperidine as base. The structures of three of these complexes, [C₅H₁₀NH₂][Mn(3,5-Cl-hbg)₂] (2), [C₅H₁₀NH₂][Mn(5-NO₂-hbg)₂] (6) and [C₅H₁₀NH₂][Mn(5-NO₂-hbs)₂] (7) have been elucidated by single-crystal X-ray crystallography and each displays two similar, independent [MnL₂]⁻ ions in the asymmetric unit linked via piperidinium cations through hydrogen bonding. The ligands co-ordinate in a facial tridentate fashion with the three donor atoms being the phenolate and carboxylate oxygens and the amine nitrogen. The geometry at the Mn centres is compressed rhombic octahedral consistent with a pseudo-Jahn–Teller compression along the Mn–O(phenolate) axis. Mean bond lengths are in the ranges 1.886–1.889 Å for the Mn–O(phenolate), 2.062–2.125 Å for the Mn–O(carboxylate) and 2.091–2.184 Å for the Mn–N(amine) distances. The magnetic susceptibility and electronic and IR spectroscopic data are discussed with reference to the crystal structures.     

Oxidation and Mobility of Trivalent Chromium in Manganese-Enriched Clays during Electrokinetic Remediation

This article presents the results of an investigation that assessed the extent and effect of oxidation of Cr(III) in manganese-enriched clays on the electrokinetic remedial efficiency. Because chromium commonly exists along with nickel and cadmium at contaminated sites, the effects of changes in chromium redox chemistry on the migration of the coexisting nickel and cadmium was also studied. Bench-scale electrokinetic experiments were conducted using two different clays: kaolin, a typical low buffering soil, and glacial till, a high buffering soil. Tests were performed with 1000?mg/kg of Cr(III), 500?mg/kg of Ni(II), and 250?mg/kg of Cd(II), both with and without the presence of 1000?mg/kg of manganese. All of these experiments were conducted under a constant voltage gradient of 1.0?VDC/ cm. The experimental results showed that in the presence of manganese, percentages of oxidation of Cr(III) into Cr(VI) ranged from 67% in kaolin to 28% in glacial till even before the application of induced electric potential. The low extent of oxidation of Cr(III) in glacial till may be attributed to the initial precipitation of Cr(III) as Cr(OH)₃ resulting from high soil pH, reducing aqueous Cr(III) concentrations present within the soil. In kaolin, Cr(III), Ni(II), and Cd(II) under electric potential migrated toward cathode and precipitated near the cathode due to high soil pH. When manganese was present in kaolin, Cr(VI) that was formed due to the oxidation of Cr(III) migrated toward anode and adsorbed to the soil surfaces near the anode region due to low soil pH. However, remaining Cr(III) as well as Ni(II), and Cd(II) migrated towards and precipitated near the cathode due to high soil pH. In kaolin, the migration of Ni(II) and Cd(II) was retarded in the presence of manganese due to a larger soil zone of elevated pH near the cathode. In glacial till, the migration of Cr(III), Ni(II) and Cd(II) was insignificant due to precipitation resulting from high soil pH caused by the high buffering capacity of the soil. Cr(VI) that resulted from the partial oxidation of Cr(III) in the presence of manganese, however, migrated toward the anode. Overall, this study demonstrated that the effects of manganese on Cr(III) oxidation in low buffering soils can be significant, which can in turn affect the extent and direction of chromium migration under induced electric potential.     

15-MC-5 manganese metallacrowns hosting herbicide complexes. Structure and bioactivity

Interaction of manganese with salicylhydroxamic ligands leads to the formation of a series of 15-membered metallacrown Mn(II)(L)(2)[15-MC(Mn(III)N(shi))-5](py)(6) (L=alkanoato ligand). The crystal structure contains a neutral 15-membered metallacrown ring of the type [15-MC(Mn(III)N(shi))-5]. The metallacrown core consists of five Mn(III) and five shi(-3) ligands. The 15-membered metallacrown ring is formed by the succession of five structural moieties of the type [Mn(III)-N-O]. The diversity in the configuration (planar or propeller) for the ring Mn(III) ions gives to the metallacrown core flexibility and simultaneously allows the encapsulation of the sixth Mn(II). The encapsulated Mn(II) is seven-coordinate and is bound to the five hydroximate oxygen donors provided by the metallacrown core, and two oxygen atoms from the carboxylate herbicide ligands. Antibacterial screening data showed that among all the compounds tested, manganese metallacrowns are more active than the simple manganese herbicide or carboxylate complexes while an increase in the efficiency of [15-MC(Mn(III)N(shi))-5] towards the analogous [12-MC(Mn(III)N(shi))-4] can be observed.     

Towards an artificial model for Photosystem II: a manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative

In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P680+ in Photosystem II (PS II) in green plants, the supramolecular complex 4 has been synthesized. In this complex, a ruthenium(II) tris-bipyridine type photosensitizer has been linked to a manganese(II) dimer via a substituted L-tyrosine, which bridges the manganese ions. The trinuclear complex 4 was characterized by electron paramagnetic resonance (EPR) and electrospray ionization mass spectrometry (ESI-MS). The excited state lifetime of the ruthenium tris-bipyridine moiety in 4 was found to be about 110 ns in acetonitrile. Using flash photolysis in the presence of an electron acceptor (methylviologen), it was demonstrated that in the supramolecular complex 4 an electron was transferred from the excited state of the ruthenium tris-bipyridine moiety to methylviologen, forming a methylviologen radical and a ruthenium(III) tris-bipyridine moiety. Next, the Ru(III) species retrieved the electron from the manganese(II/II) dimer in an intramolecular electron transfer reaction with a rate constant kET > 1.0 x 10(7) s(-1), generating a manganese(II/III) oxidation state and regenerating the ruthenium(II) photosensitizer. This is the first example of intramolecular electron transfer in a supramolecular complex, in which a manganese dimer is covalently linked to a photosensitizer via a tyrosine unit, in a process which mimics the electron transfer on the donor side of PS II.     

Chiral discrimination in the energetics of formation of diastereomeric adducts involving polypeptides

Chiral discrimination in the energetics of formation of diastereomeric pairs between iron (III)-complex ions bound to poly(L -glutamate) or poly (D -glutamate) and L -catecholamines was measured by differential microcalorimetry at 25°C. When the association of substrates by Fe–polypeptide systems was virtually complete, diastereomeric discrimination energies of a few hundred calories per mol were observed, while diastereomeric discrimination entropies were found to be negligibly small. These results are consistent with the finding that the overall stereoselectivity in the electron transfer reaction between the optically active catecholamines and enantiomeric iron(III) materials—corresponding to Δ(ΔG^≠) values around 900 cal/mol—is largely controlled by transition state effects in the kinetics.     

Studies on the ferrochelatase activity of isolated rat liver mitochondria with special reference to the effect of oxidizable substrates and oxygen concentration

The mitochondrial ferrochelatase activity has been studied in coupled rat liver mitochondria using deuteroporphyrin IX (incorporated into liposomes of lecithin) and Fe(III) or Co(II) as the substrates.

1. 1. It was found that respiring mitochondria catalyze the insertion of Fe(II) and Co(II) into deuteroporphyrin. When Fe(III) was used as the metal donor, the reaction revealed an absolute requirement for a supply of reducing equivalents supported by the respiratory chain.

2. 2. A close correlation was found between the disappearance of porphyrin and the formation of heme which allows an accurate estimate of the extinction coefficient for the porphyrin to heme conversion. The value Δ (mM⁻¹ · cm⁻¹) = 3.5 for the wavelength pair 498 509 nm, is considerably lower than previously reported.

3. 3. The maximal rate of deuteroheme synthesis was found to be approx. 1 nM · min⁻¹ · mg⁻¹ of protein at 37 °C, pH 7.4 and optimal substrate concentrations, i.e. 75 μM Fe(III) and 50 μM deuteroporphyrin.

4. 4. Provided the mitochondria are supplemented with an oxidizable substrate, the presence of oxygen has no effect on the rate of deuteroheme synthesis.

The purification and characterization of a novel D(−)-specific carbamoylase enzyme from an Agrobacterium sp.

A carbamoylase enzyme was purified from a cell-free extract of Agrobacterium sp. with an overall yield of 81%. It was judged to be homogenous on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with a subunit molecular weight of 38,000 daltons. Further studies on the native enzyme suggested that the active enzyme was present as a dimer, with a pI of 5.5. It was able to cleave a variety of N-carbamoyl substrates, but was strictly D(−) specific. It was found to have a K_m of 0.82 m and a V_max of 31 U mg⁻¹ for D(−) N-carbamoyl hydroxyphenylglycine in the presence of 10 m dithiothreitol. It showed no metal ion requirements but was inhibited by iodoacetic acid and iodoacetamide, both thiol reagents. The N-terminal amino acid sequence of the enzyme was elucidated.     

Catalytic and electrochemical properties of new manganese(III) compounds of 2-(2′-hydroxyphenyl)-oxazoline (Hphox or HClphox). Molecular structures of [Mn(Clphox)2(MeOH)2](ClO4) and [Mn(phox)2(MeOH)2][Mn(phox)2(ClO4)2](H2O)2

New manganese(III) complexes of Hphox (2-(2′-hydroxyphenyl)-oxazoline) and HClphox (2-(5′-chloro-2′-hydroxyphenyl)-oxazoline) have been synthesised. The X-ray structures of [Mn(phox)₂(MeOH)₂][Mn(phox)₂(ClO₄)₂](H₂O)₂ and [Mn(Clphox)₂(MeOH)₂](ClO₄) show the manganese(III) ions to be octahedrally coordinated with methanol or perchlorate at the axial coordination sites. The cyclic voltammograms of the complexes, with the exception of [Mn(phox)₂(acac)] (Hacac=2,4-pentanedione), show an irreversible reduction wave of manganese(III) to manganese(II). After addition of an excess of 1-methylimidazole (1-Meim), the reduction process shifts towards lower potentials and becomes (quasi-) reversible, indicating that the presence of 1-Meim affects the catalytic efficiency of the complexes. The complexes catalyse the epoxidation of styrene by dihydrogen peroxide. The cumulative turnover numbers towards styrene oxide obtained after 15 min. vary from 16 for [Mn(Clphox)₂(MeOH)₂](ClO₄) to 26 for [Mn(phox)₂(acac)]. Ligand degradation appears to be the limiting factor for obtaining higher turnover numbers.