Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridineN-oxide. I. The 4-methyl derivative

Summary TheN-methyl-2-[1-(2-pyridinyl-1-oxide)ethylidene]hydrazinecarbothioamide, HLO4M, has been used to prepare a series of Co^III, Ni^II and Cu^II complexes. Species with two deprotonated LO4M ligands, one LO4M and one HLO4M ligand, two HLO4M ligands and one HLO4M ligand with two small anionic ligands have been isolated. The deprotonated LO4M bonds as a tridentate ligandvia theN-oxide oxygen, the imine nitrogen (N¹ and the sulphur while the HLO4M ligand coordinates primarily as a bidentate ligandvia only the first two atoms listed above. I.r., electronic, mass and e.s.r. spectra have been used to determine the nature of these complexes. One of the more striking differences between these compounds and those prepared with other thiosemicarbazones of 2-acetylpyridine and 2-acetylpyridineN-oxide is that tetrahedral yellow [Ni(HL)X₂] rather than planar brown [NiLX] (X=Cl or Br) solids have been isolated with this ligand. Other differences in the nature of the coordination spheres of the various metal ions occur with this particular ligand when compared to previously studied thiosemicarbazone complexes.NATO Fellow, on leave from Medical Faculty, Istanbul University.     

Nickel(II) complexes of a thiosemicarbazone prepared from 2-Acetylpyridine

Summary The ligand 3-azabicyclo[3.2.2]nonane-3-thiocarboxylic acid 2-[1-(2-pyridinyl)ethylidene]hydrazide (HL), which is observed in an unusual tautomeric form in the solid state, and its selenium analogue (HLSe) have been used to prepare a series of nickel(II) complexes. Compounds of the general formula [NiLX] (X=Cl, Br, NCS, N₃, NO₂ or NCSe) as well as [Ni(LSe)Cl] have been found to be diamagnetic, planar complexes. A single crystal study of [NiL(NCS)] shows the deprotonated ligand bound in a tridentate mannervia its pyridyl nitrogen, imine nitrogen and the thione sulphur atom with the nitrogen atom of the thiocyanato-ligand occupying the fourth coordination position. The solids prepared from the nickel(II) salts having tetrafluoroborate, nitrate and iodide ions approximate to octahedral symmetry and have neutral HL ligands coordinated in a bidentate fashionvia the pyridine and imine nitrogens with the remaining coordination sites being occupied by the anions or water molecules. The [NiL₂] solid is also octahedral with the two deprotonated ligands bonding as tridentate groupsvia the same atoms as in the [NiLX] complexes.     

Plasma desorption mass spectrometry of transition metal complexes of thio- and selenosemicarbazones of 2-acetylpyridines

Summary Californium-252 plasma desorption mass spectra were recorded for complexes of the anions of various thio-and seleno-semicarbazones of 3-acetylpyridines(1–4) with the transition metal ions iron(III) and cobalt(II). Positive ion spectra gave clear evidence of the cation present and fragmentation with loss of ligands or parts of ligands was straightforward. Negative ion spectra likewise provided evidence of the intact anion except with tetracoordinate metal halide systems [MX₄]^– which lost one or more halide atoms. Evidence of fragmentation of the ligand and recombination of the fragments with the metal ion was also observed in the negative ion mode. Spectra were used to revise the structure of a complex previously reported as [FeLCl₂]⁽¹⁾ to [FeL₂]⁺[FeCl₄]^–.     

Transition metal ion complexes of a thiosemicarbazone derived from 6-methyl-2-acetylpyridine

Summary A series of metal ion complexes of the thiosemicarbazone, 3-azabicyclo[3.2.2]nonane-3-thiocarboxylic acid 2-[1-(6-methyl-2-pyridinyl)ethylidene]hydrazide (6 MLH) have been prepared and spectrally characterized. The ligand undergoes deprotonation to coordinatevia the thione sulphur, the imine nitrogen and the pyridyl nitrogen. A single anionic ligand such as Cl^–, Br^– and NO₃ ^– completes the bonding to the Cu^II and Ni^II centre. The compound derived from CoCl₂ contains two 6 MLH ligands bound to a Co^II centre and a CoCl ₄ ^2– counter ion. Complexes derived from perchlorate salts may feature 6 MLH, 6 ML, or both with the Co^II being oxidized to Co^III. The solids were characterized by i.r., electronic and e.s.r. spectroscopy. In addition, electronic and e.s.r. spectra of their chloroform solutions were recorded.NATO Fellow, on leave from Istanbul Medical Faculty, Istanbul University.     

Copper(II) complexes of thiosemicarbazones derived from 2-acetylpyridine and its n-oxide

A series of Cu(II) complexes of the thiosemicarbazone, 3-azabicyclo[3.2.2]-nonene-3-thiocarboxylic acid 2-[1-(2-pyridinyl)ethylidene]hydrazide(HL) and the corresponding N-oxide (HLO) have been prepared and characterized. Both ligands undergo deprotonation and appear to coordinate via the thione sulfur, the imine nitrogen and the pyridyl nitrogen (or N-oxide oxygen). A single anionic ligand such as Cl^?, Br^?, NCS^? and N^?₃ completes the bonding to the Cu(II) center of these 4-coordinate complexes. When the complexes are prepared using Cu(II) perchlorate, the solids isolated contain a neutral thiosemicarbazone ligand as well as the deprotonated ligand. The solids are primarily characterized by IR, electronic and electron spin resonance spectroscopy. In addition, electronic and ESR spectra of their chloroform solutions were recorded. Most of the solids (except the nitrates) were unaltered upon dissolution. Simulation of the solution ESR spectra was used to estimate the coupling constants of the various coordinated nuclei.     

Synthesis of bridgehead nitrogen heterocycles

Reductive cyclizations of N-[2-(2-pyridyl)ethyl]imides were accomplished by employing a palladium on carbon catalyst in ethanolic acetic acid as the hydrogenation medium. Reduction of the corresponding N-[2-(2-quinolyl)ethyl]imides ceased at the 1,2,3,4-tetrahydroquinolyl stage. Controlled reduction of the tetrahydroquinolyl imides with sodium borohydride gave amido alcohols which afforded bridgehead nitrogen heterocycles upon cyclodehydration.     

The chemical and antifungal properties of the copper(II) complexes of 2-acetylpyrazine4 N-methyl-,4 N-dimethyl-, and 3-hexamethyleneiminylthiosemicarbazone

Summary Copper(II) complexes of 2-acetylpyrazine² N-methyl-,⁴ N-dimethyl- and 3-hexamethyleneiminylthiosemicarbazone have been prepared and characterized. Inhibition of the growth ofAspergillus niger andPaecilomyces bariotii by both the thiosemicarbazones and their copper(II) complexes is included.     

Intermediate spin iron(III) complexes of N4,N4-disubtituted 2-acetylpyridine thiosemicarbazone

Summary Magnetic susceptibility and Mössbauer spectroscopy measurements have been carried out on [Fe^III(SAm)Cl₂], and indicate an intermediate spin state for the ferric ion. The temperature-independent magnetic moment of (4.17±0.05) _B, the quadrupole splitting=4.09 mm s^–1 and isomer shift=0.133 mm s^–1 are in agreement with such formulation. These studies, together with infrared data, are used to suggest a possible structure of the complex.     

Simulation analysis of formycin 5′-monophosphate analog substrates in the ricin A-chain active site

Summary Ricin is an RNA N-glycosidase that hydrolyzes a single adenine base from a conserved loop of 28S ribosomal RNA, thus inactivating protein synthesis. Molecular-dynamics simulation methods are used to analyze the structural interactions and thermodynamics that govern the binding of formycin 5-monophosphate (FMP) and several of its analogs to the active site of ricin A-chain. Simulations are carried out initiated from the X-ray crystal structure of the ricin-FMP complex with the ligand modeled as a dianion, monoanion and zwitterion. Relative changes in binding free energies are estimated for FMP analogs constructed from amino substitutions at the 2- and 2-positions, and from hydroxyl substitution at the 2-position.