Manganese(IV) Complexes Derived from Polyfunctional Dihydrazone: Structural, Electrochemical and Antimicrobial Studies

Manganese(IV) complexes viz. [MnIV(nagh)(A)2]·2H2O and [MnIV(nagh)(NN)] have been synthesized from ligand bis(2-hydroxy-1-naphthaldehyde)glutaryldihydrazone (naghH4) and auxiliary ligands, A = H2O (1)/pyridine (2)/2-picoline (3)/3-picoline (4)/ 4-picoline (5) or NN = 2,2′-bipyridine (6)/1,10-phenanthroline (7). The elemental analysis, mass spectral and thermal studies supported the composition of all the manganese(IV) complexes. Structural aspects were determined from magnetic susceptibility, molar conductivity and spectral studies i.e. electronic, electron spin resonance and infrared. Their non-electrolytic nature were determined from molar conductances. Results from studies of magnetic moment, electronic and ESR suggested Mn(IV) ion in six-coordinate octahedral stereochemistry. The ligand coordinated to the metal in enolic form as a tetradentate in an anti-cis configuration as was correlated from IR data. Redox activities and antimicrobial potential against few Gram-positive and Gram-negative bacteria have been investigated for the dihydrazone and some manganese(IV) complexes.

Synthesis of 3-methyl-4H-benzo[b][1,4]thiazine-2-carboxylates using CAN as a catalyst and its conversion into guanidines.

Background: 1,4-benzothiazine carboxylates show wide application in the field of medicinal chemistry. Therefore, we have designed convenient and efficient method for the synthesis of 1,4-benzothiazine carboxylates. Objective: Synthesis of 1,4-benzothiazine carboxylates and its guanidines by simple and facile method using efficient catalyst. Method: Derivatives of 1,4-benzothiazine carboxylates were synthesized by cyclocondensing β-keto esters with 2- aminobenzenethiols using CAN as a catalyst at room temperature. 1,4-benzothiazine caboxylate,condensed with guanidine hydrochloride in the presence of sodium methoxide in DMF to obtained new 3-substituted-l-4Hbenzo[b][1,4]thiazine-2-carboxyguanidines (88-91%). Results: All the products were obtained with good to excellent yields within 40 min. Here, CAN oxidizes aminothiophenol into disulfide and then nucleophilic attack of enolic form of β-ketoesters on the disulphide and 1, 4-benzothiazine acetates, were obtained with good yields. Conclusion: We have designed convenient and efficient method for the synthesis of 1,4-benzothiazine carboxylates. Most remarkable features of this cyclocondensation such as use of efficient catalyst and non-volatile solvent under mild reaction condition to obtained excellent yield.

New Mono- and Diesters with Imidazoquinolinone Ring- Synthesis, Structure Characterization, and Molecular Modeling

The objective of the studies was to synthesize and characterize new mono- and diesters with an imidazoquinolin-2-one ring with the use of 2,3-dihydro-2-thioxo-1H-imidazo[4 ,5-c]-quinolin-4(5H)-ones and ethyl bromoacetate. The products were isolated at high yield and characterized by instrumental methods (IR, 1H-, 13C-, and 15N- NMR, MS-ESI, HR-MS, EA). In order to clarify the places of substitution and the structure of the derivatives obtained, molecular modeling of substrates and products was performed. Consideration of the possible tautomeric structures of the substrates confirmed the existence only the most stable keto form. Based on the free energy of monosubstituted ester derivatives, the most stable form were derivatives substituted at sulfur atom of enolic form the used imidazoquinolones. Enolic form referred only to nitrogen atom no 1. The modeling results were consistent with the experimental data. The HOMO electron densities at selected atoms of each substrate has shown that the most reactive atom is sulfur atom. It explained the formation of monoderivatives substituted at sulfur atom. The diester derivatives of the used imidazoquinolones had second substituent at nitrogen atom no. 3. The new diesters can be used as raw material for synthesis of thermally stable polymers, and they can also have biological activity.

Spectroscopic, Thermal and Antimicrobial Study of Some Transition Metal(II) Complexes of β-Diketones

A novel heterocyclic based β-diketone has been synthesized by the condensation of pyrazole-1-acetylchloride and sodium acetophenone. The product 1-phenyl-4-(pyrazole-1-yl)butane- 1,3-dione has been used for complexation with Mn(II), Fe(II) and Co(II) metal ions. The ligand β-diketone is found to exist in keto-enol tautomeric forms. The comparision of infrared spectra of complexes clearly indicates the coordination of the ligand from its enolic form. The magnetic moment and electronic spectra of all the metal complexes leads to the distorted octahedral symmetry around the metal ion. The ligand as well as its metal complexes has been screened for antimicrobial activity and antifungal activities. It is observed that the antimicrobial and antifungal activities get enhanced in complexes in respect to the free ligand.

Reversible Shifting of a Chemical Equilibrium by Light: The Case of Keto-Enol Tautomerism of a β-Ketoester

Manipulating the equilibrium between a ketone and an enol by exposure to light opens up ample opportunities in material chemistry and photopharmacology since it allows one to reversibly control the content of the enol tautomer, which acts as a hydrogen atom donor, with high spatio-temporal and energy resolution. Although tautomerization of β-ketoesters or their analogs was studied in numerous papers, their light-induced reversible tautomerization to give thermally stable enols (photoenolization) is an unexplored area. To shed light on this “blind spot”, we report an unprecedented property of diarylethene <b>2A</b> assembled from fragments of photoactive dithienylethene and a β-ketoester as part of the cyclohexenone bridge. In a pristine state, the tautomeric equilibrium of <b>2</b> is almost completely shifted towards the ketone. Photocyclization of the hexatriene system results in a new equilibrium system containing a significant fraction of the enol tautomer, both in polar and non-polar solvents. Due to the considerable spectral separation (35 nm), the keto-enol tautomerization process could be observed visually. The tendency of <b>2A </b>to undergo light-induced enolization was proved by isolating a related byproduct of photochemical 1,2-dyotropic rearrangement stabilized in the enolic form. Our results provide a novel tool for controlling the keto-enol tautomerism that might find use in the development of novel photocontrollable processes.

Reversible Shifting of a Chemical Equilibrium by Light: The Case of Keto-Enol Tautomerism of a β-Ketoester

Manipulating the equilibrium between a ketone and an enol by exposure to light opens up ample opportunities in material chemistry and photopharmacology since it allows one to reversibly control the content of the enol tautomer, which acts as a hydrogen atom donor, with high spatio-temporal and energy resolution. Although tautomerization of β-ketoesters or their analogs was studied in numerous papers, their light-induced reversible tautomerization to give thermally stable enols (photoenolization) is an unexplored area. To shed light on this “blind spot”, we report an unprecedented property of diarylethene <b>2A</b> assembled from fragments of photoactive dithienylethene and a β-ketoester as part of the cyclohexenone bridge. In a pristine state, the tautomeric equilibrium of <b>2</b> is almost completely shifted towards the ketone. Photocyclization of the hexatriene system results in a new equilibrium system containing a significant fraction of the enol tautomer, both in polar and non-polar solvents. Due to the considerable spectral separation (35 nm), the keto-enol tautomerization process could be observed visually. The tendency of <b>2A </b>to undergo light-induced enolization was proved by isolating a related byproduct of photochemical 1,2-dyotropic rearrangement stabilized in the enolic form. Our results provide a novel tool for controlling the keto-enol tautomerism that might find use in the development of novel photocontrollable processes.

Synthesis and Tautomerism of Curcumin Derivatives and Related Compounds

1,7-Bis(4′-hydroxy-3′-trifluoromethoxyphenyl)-1,6-heptadiene-3,5-dione (2a), related to curcumin, and thirteen 4-substituted derivatives were prepared and their keto/enol ratio in DMSO[D6] was determined by 19F NMR because the enolic form of these related curcumins had been shown to bind to amyloid plaques in the Alzheimer brain. The parent compound and the 4-ethoxycarbonyl derivative were almost 100 % in the enolic form that contains a conjugated hepta-1,4,6-trien-3-on-5-ol backbone. Enolisation decreased to varying amounts in the derivatives that had 4-substituted alkyl groups. Attempts to prepare the 4-hydroxypropyl derivative by hydrolysis of O-methoxymethyl 2m or O-tetrahydropyranyloxy 2n protected derivatives led to cyclised products. A related pyrimidine compound 6b that mimicked a fixed enol form was also prepared.

SYNTHESIS AND CHARACTERIZATION OF MALONIC ACID DIHYDRAZIDE AND ITS METAL COMPLEXES

A new series of complexes was synthesized by the reaction between malonyl dihydrazide (MAH) and manganese, copper, nickel, zinc, cadmium, cobalt and ferric salts in methanolic medium. The complexes were characterized by elemental analysis, molar conductance measurements, electronic, IR and 1H NMR spectral studies. Based on the results obtained, the stoichiometry of Fe(III)-MAH and Co(III)-MAH was proposed to be 1:3 and that for Cu(II)-MAH, Cd(II)-MAH, Zn(II)-MAH, Mn(II)-MAH, Ni(II)-MAH was proposed to be 1:2 (M:L). It was suggested that the nitrogen present in the azomethine (>C=N-) group of the enolic form present in the ligand was involved in the formation of complexes. A clear picturisation indicating the bonding sites were depicted for each complex. The metal complexes exhibit different geometries such as tetrahedral, square planar and octahedral arrangements.

Metal complexes of N'-(2-hydroxy-5-phenyldiazenyl) benzylideneisonicotinohydrazide: Synthesis, spectroscopic characterization and antimicrobial activity

A new series of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Hg(II) , VO(II), UO2(II) , Fe(III) and Ru(III) complexes of N'-(2-hydroxy-5- phenyldiazenyl)benzylideneisonicotinohydrazide(H2L) have been synthesized and characterized by elemental,1H-NMR, IR, UV-Vis., ESR, magnetic, thermogravimetric analyses(TG) and conductivity measurements. The spectral data show that, the ligand behaves as a neutral bidentate, (2), (4), (5), (6) and (14), monobasic bidentate, (3), (7), (8), (9) and (10), monobasic tridentate (11) and (16) or dibasic tridentate (12), (13) and (15) bonded to metal ions via the carbonyl oxygen atom in ketonic or enolic form, azomethine nitrogen atom and/or deprotonated phenolic hydroxyl oxygen. The ESR spectrum of solid vanadyl(II), complex (2) shows axially anisotropic spectrum with eight lines in the low field region and g?>g||, A||>>A?relationship, which is characteristics of distorted octahedral structure with dxy ground state. However, copper(II) complexes (4), (5) and (6) and manganese(II) complex (10) show an isotropic type while the copper(II) complexes (3) and (7)show an axial symmetry type with g||>g?>ge indicating a covalent bond character. The antibacterial and antifungal activities of the ligand and its metal complexes show mild activity compared with standard drugs (Tetracycline for bacteria and amphotricene B for fungi).

Synthesis, characterization and spectroscopic properties of some 2-substituted 1,3-indandiones and their metal complexes

New 2-acyl-1,3-indandione derivatives, compounds 1–4, were obtained by condensation of 2-acetyl-1,3-indandione with benzaldehyde, thiophene-2-aldehyde, thiophene-3-aldehyde and furane-2-aldehyde, respectively. The structures of the newly synthesized 2-substituted 1,3-indandiones were characterized by means of spectroscopic methods (FT-IR, 1H and 13C NMR, UV-Vis and MS). Based on the obtained results it is suggested that the compounds exist in the exocyclic enolic form. Mass spectral fragmentation paths are also proposed. In order to verify the possibility for tautomerization processes of the newly synthesized compounds their absorption spectra were recorded in various solvents. Furthermore, the complexation properties of the compounds with metal(II) ions were also studied. A series of non-charged complexes with Cu(II), Cd(II), Zn(II), Co(II) and Ni(II) was isolated and analyzed by elemental analyses and IR. The paramagnetic Cu(II) complexes were studied by EPR and distorted, flattened tetrahedral structures are predicted. The other metal complexes show the presence of water molecules, most probably coordinated to the metal ion, thus forming octahedral geometry. Ultimately, the studied properties of the newly synthesized compounds, 1–4, suggest that they may find application as extracting agents for metal ions, rather than as optical sensors.