Chemical reactivities of tetrapyrrole pigments: a comparison of experimental behaviour with the results of s.c.f.-π-m.o. calculations

1976 ◽  
Vol 273 (924) ◽  
pp. 335-352 ◽  
Keyword(s):  
Metal Ions ◽  
Metal Complexes ◽  
Experimental Work ◽  
Oxidation Potential ◽  
Central Metal ◽  
Reversible Reactions ◽  
Specific Reactivity ◽  
Cleavage Reactions ◽  
Recent Experimental Work ◽  
Experimental Behaviour

Porphyrins are highly σ-electron donating bases and very weak π-acids. Hence they increase the electron density on central metal ions, e.g. iron, which leads to the specific reactivity of haem cytochromes, haemoglobin and oxidizing enzymes. The macrocyclic chlorin ligand behaves similarly but to a lesser degree which explains the comparably low oxidation potential of chlorophyll. Phlorins, oxophlorins, oxa- and aza-porphyrins, tetradehydrocorrins, corrins and biliverdins all produce metal complexes which have a similar geometry to that of metalloporphyrins, but their reactivity patterns are different. In contrast to themetalloporphyrins which undergo many fully reversible reactions, these compounds tend to irreversible addition and cleavage reactions. These tetrapyrrole ligands are stronger π-acids than porphyrins. Results of some recent experimental work and π-electron s.c.f. calculations are presented in support of these generalizations.

Molecular assemblies based on strong axial coordination in metal complexes of saddle-distorted dodecaphenylporphyrins

2015 ◽  
Vol 19 (01-03) ◽  
pp. 32-44 ◽  
Author(s):  
Tomoya Ishizuka ◽  
Shunichi Fukuzumi ◽  
Takahiko Kojima
Keyword(s):  
Electron Transfer ◽  
Metal Ions ◽  
Metal Complexes ◽  
Photoinduced Electron Transfer ◽  
Oxidation Potential ◽  
Metal Center ◽  
Lewis Acidity ◽  
Central Metal ◽  
Axial Coordination ◽  
Keggin Type

In this mini-review, we have highlighted our works on metal complexes having saddle-distorted dodecaphenylporphyrin (DPP) and its derivative as ligands in the light of enhancement of the Lewis acidity of a metal center coordinated by the porphyrin. The important point through this mini-review is ill-overlap of the out-of-plane lone pairs of pyrrole nitrogen atoms with σ-orbitals of the metal center bound to the saddle-distorted porphyrin core. The enhanced Lewis acidity of the central metal ions enabled us to construct stable molecular complexes through axial coordination using metal–DPP (M(DPP)) moieties ( M = Mo V or Sn IV ) and molecular or ionic entities with Lewis-basic coordination sites, including Keggin-type polyoxometallates (POM), which are known to have weak Lewis basicity and thus hard to coordinate to metal ions. A discrete 1:2 complex with a Ru -substituted POM performs catalytic substrate oxidation reactions in organic solvents. A 1:1 complex between Sn IV ( DPP ) and a Keggin-type POM exhibited photoinduced electron transfer, in which the Sn IV ( DPP ) moiety acts as an electron donor and the POM as an electron acceptor. Besides POM, other electron acceptors, including μ3-oxo trinuclear Ru III clusters and anthraquinone, having carboxyl groups as a linker unit also formed stable complexes with DPP-metal complexes as axial ligands to perform photoinduced electron transfer. Successful photoreactions of the M(DPP)-acceptor complexes are mainly enabled by the enhanced Lewis acidity of the DPP-metal complexes for the stabilization of the assemblies and also by lowering the oxidation potential of the porphyrin ligand to gain larger driving force of electron transfer to form an electron-transfer state with avoiding intersystem crossing. The stability and photochemical behavior are in sharp contrast to those for metal complexes with planar porphyrins as ligands.

Hairpin and hammerhead ribozymes: how different are they?

2002 ◽  
Vol 30 (6) ◽  
pp. 1116-1119 ◽  
Author(s):  
J. M. Burke
Keyword(s):  
Metal Ions ◽  
Conformational Changes ◽  
Experimental Work ◽  
Hammerhead Ribozyme ◽  
Active Conformation ◽  
Hairpin Ribozyme ◽  
Hammerhead Ribozymes ◽  
Active Structure ◽  
Catalytic Function ◽  
Recent Experimental Work

Recent experimental work on the hairpin and hammerhead ribozymes suggests that they have more similarities than previously suspected. Notably, each is now known to function as a true RNA catalyst, not requiring metal ions for folding or catalytic function. The active conformation of the hairpin ribozyme has been established by crystallography, and is well supported by biochemical and biophysical evidence that has identified conformational changes and key nucleotides required for catalysis. Analogous work is under way to establish the active structure of the hammerhead ribozyme.

Collision-Induced Dissociation Studies of Alkali Metal Adducts of Tetracyclines and Anti-Viral Agents by Electrospray Ionization, Hydrogen/Deuterium Exchange and Multiple Stage Mass Spectrometry

2008 ◽  
Vol 14 (5) ◽  
pp. 281-297 ◽  
Author(s):  
Amin Kamel ◽  
Burnaby Munson
Keyword(s):  
Metal Ions ◽  
Metal Complexes ◽  
Metal Ion ◽  
Mass Spectra ◽  
Collision Induced Dissociation ◽  
Guanine Derivatives ◽  
Product Ions ◽  
Hydrogen Deuterium ◽  
Cleavage Reactions ◽  
Metal Adducts

The collision-induced dissociation (CID) mass spectra were obtained for the X+-adducts (X = Na+ or Li+) of five tetracyclines, four pyrimidine and three purine derivatives and their fully D-exchanged species in which the labile hydrogens were replaced by deuterium by either gas- or liquid-phase exchange. The CID spectra were obtained for [M + Na]+ and [M + Li]+ and the exchanged analogs, [M(D) + Na]+ and [M(D) + Li]+, and compositions of product ions and mechanisms of decomposition were determined by comparison of the MS n spectra of the undeuterated and deuterated species. Metal ions are bound to the base of purine and pyrimidine anti-viral agents and dissociate primarily to give the metal complexes of the base [B + X]+. For vidarabine monophosphate, however, the metal ions are bound to the phosphate group, resulting in unique and characteristic cleavage reactions not observed in the uncomplexed system and dissociate through the loss of phosphate and/or a phosphate metal ion complex. The [B + X]+ of these anti-viral agents are relatively stable and show little or no fragmentation compared to [B + H]+. The CID of [B + X]+ of guanine derivatives occurs mainly through elimination of NH3 and that of trifluoromethyl uracil dissociates primarily through the loss of HF. For tetracyclines, metal ions are bound to ring A at the tricarbonylmethyl group and dissociate initially by the loss of NH3/ND3 from [MH + X]+ and [MD – X]+. The CID spectra of [M + X]+ of tetracyclines are somewhat similar to those of [M + H]+. The dominant fragments from the metal complexes of these compounds are charge remote decompositions involving molecular rearrangements and the loss of small stable molecules. Additionally, tetracyclines and the anti-viral agents show more selectivity towards the Li+ ion than the corresponding complexes with Na+ or K+.

Discotic liquid crystals of transition metal complexes 41: influence of rare-earth metal ions on clearing points of sandwich-type bis[octakis(3,4-didodecyloxyphenoxy)phthalocyaninato]lanthanoid(III) complexes

2009 ◽  
Vol 13 (08n09) ◽  
pp. 927-932 ◽  
Author(s):  
Hidetomo Mukai ◽  
Kazuaki Hatsusaka ◽  
Kazuchika Ohta
Keyword(s):  
Phase Transition ◽  
Rare Earth ◽  
Metal Ions ◽  
Metal Complexes ◽  
Rare Earth Metal ◽  
Earth Metal ◽  
Central Metal ◽  
Phase Transition Behavior ◽  
Transition Behavior ◽  
Sandwich Type

It has long been believed that the phase transition behavior and clearing points (c.p.s.) of phthalocyanine-based metallomesogens scarcely change regardless of the kind of central metal. In this work, we have synthesized a series of novel sandwich-type phthalocyanine-based lanthanoid complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-didodecyloxyphenoxy)phthalocyaninato]lanthanoid(III) (abbreviated as {[(C12O)2PhO]8Pc}2M, M = La, Ce, Eu, Gd, Tb, Yb and Lu : 1–7). Their mesomorphic properties were investigated by polarization microscope, DSC and temperature-dependent X-ray diffraction techniques to compare with the phase transition behavior and c.p.s. of the complexes. Very interestingly, the c.p.s. of these seven rare-earth metal complexes increased in an order of La (1) → Ce (2) → Eu (3), reached to a maximum for Gd (4), and decreased in an order of Tb (5) → Yb (6) → Lu (7). We have noticed that their rise and fall of c.p.s. correspond to the values of total spin quantum number (S) of the central rare-earth metal ions. Thus, it was found, for the first time in metallomesogens, that the S values of central rare-earth metal ions strongly influence their c.p.s.

scholarly journals Changes in the absorption spectra and colour of tetraphenylporphyrins after redox reactions

2020 ◽  
Vol 44 (9-10) ◽  
pp. 613-617
Author(s):  
Kazuya Ogawa ◽  
Yuria Umetsu ◽  
Kenji Kamimura
Keyword(s):  
Metal Complexes ◽  
Absorption Spectra ◽  
Redox Reactions ◽  
Reduction Potential ◽  
Oxidation Potential ◽  
Sample Solution ◽  
Central Metal ◽  
Reduction Reactions ◽  
Electrochromic Properties ◽  
Cv Measurements

In this study, we have investigated the electrochromic properties including the change in absorption spectra and colour after oxidation and reduction reactions of tetraphenylporphyrin and its metal complexes in dichloromethane. The first oxidation potential is determined from CV measurements, and the reduction potential is estimated from comparison with literature values. Electrolytic reactions are carried out by applying the oxidation potential and reduction potential to each sample solution. The metals used are Ag(II), Cu(II), Fe(III), Mg(II), Mn(III), Ni(II) and Zn(II). Various colours can be expressed after the redox reactions by changing the central metal.

Synthesis, Characterization and in vitro Biological Evaluation of a New Schiff Base Derived from Drug and its Complexes with Transition Metal Ions

2018 ◽  
Vol 69 (7) ◽  
pp. 1678-1681
Author(s):  
Amina Mumtaz ◽  
Tariq Mahmud ◽  
M. R. J. Elsegood ◽  
G. W. Weaver
Keyword(s):  
Schiff Base ◽  
Transition Metal ◽  
Metal Ions ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Free Ligand ◽  
Transition Metal Ions ◽  
Biological Evaluation ◽  
Pyridoxal Hydrochloride

New series of copper (II), cobalt (II), zinc (II), nickel (II), manganese (II), iron (II) complexes of a novel Schiff base were prepared by the condensation of sulphadizine and pyridoxal hydrochloride. The ligand and metal complexes were characterized by utilizing different instrumental procedures like microanalysis, thermogravimetric examination and spectroscopy. The integrated ligand and transition metal complexes were screened against various bacteria and fungus. The studies demonstrated the enhanced activity of metal complexes against reported microbes when compared with free ligand.

scholarly journals Steady state charge conduction through solution processed liquid crystalline lanthanide bisphthalocyanine films

2019 ◽  
Vol 23 (11n12) ◽  
pp. 1603-1615
Author(s):  
Chandana Pal ◽  
Isabelle Chambrier ◽  
Andrew N. Cammidge ◽  
A. K. Sharma ◽  
Asim K. Ray
Keyword(s):  
Metal Ions ◽  
Liquid Crystalline ◽  
Microscopy Study ◽  
Individual Characteristics ◽  
Central Metal ◽  
Force Microscopy ◽  
Atomic Force ◽  
Double Decker ◽  
Order Of Magnitude ◽  
Chain Lengths

In-plane electrical characteristics of non-peripherally octyl(C[Formula: see text]H[Formula: see text]- and hexyl(C[Formula: see text]H[Formula: see text]-substituted liquid crystalline (LC) double decker lanthanide bisphthalocyanine (LnPc[Formula: see text] complexes with central metal ions lutetium (Lu), and gadolinium (Gd) have been measured in thin film formulations on interdigitated gold (Au) electrodes for the applied voltage ([Formula: see text] range of [Formula: see text]. The conduction mechanism is found to be Ohmic within the bias of [Formula: see text] while the bulk limited Poole–Frenkel mechanism is responsible for the higher bias. The compounds show individual characteristics depending on the central metal ions, substituent chain lengths and their mesophases. Values of 67.55 [Formula: see text]cm[Formula: see text] and 42.31 [Formula: see text]cm[Formula: see text] have been obtained for room temperature in-plane Ohmic conductivity of as-deposited octyl lutetium (C[Formula: see text]LuPc[Formula: see text] and hexyl gadolinium (C[Formula: see text]GdPc[Formula: see text] films, respectively while C[Formula: see text]GdPc[Formula: see text] films exhibit nearly two orders of magnitude smaller conductivity. On annealing at 80[Formula: see text]C, Ohmic conductivities of C[Formula: see text]LuPc[Formula: see text] and C[Formula: see text]GdPc[Formula: see text] are found to have increased but the conductivity of C[Formula: see text]GdPc[Formula: see text] decreased by more than one order of magnitude to 1.5 [Formula: see text]cm[Formula: see text]. For physical interpretation of the charge transport behavior of these three molecules, their UV-vis optical absorption spectra in the solution and in as-deposited and annealed solid phases and atomic force microscopy study have been performed. It is believed that both orientation and positional reorganizations are responsible, depending upon the size of the central ion and side chain length.

scholarly journals Utilization and simulation of innovative new binuclear Co(ii), Ni(ii), Cu(ii), and Zn(ii) diimine Schiff base complexes in sterilization and coronavirus resistance (Covid-19)

2021 ◽  
Vol 19 (1) ◽  
pp. 772-784
Author(s):  
Moamen S. Refat ◽  
Ahmed Gaber ◽  
Walaa F. Alsanie ◽  
Mohamed I. Kobeasy ◽  
Rozan Zakaria ◽  
...  
Keyword(s):  
Schiff Base ◽  
Molecular Docking ◽  
Metal Ions ◽  
Free Ligand ◽  
Schiff Base Complexes ◽  
Hydroxyl Groups ◽  
Binuclear Complexes ◽  
Central Metal ◽  
H Nmr ◽  
Biological Studies

Abstract This article aimed at the synthesis and molecular docking assessment of new diimine Schiff base ligand, namely 2-((E)-(2-((Z)-2-(4-chlorophenyl)-2-hydroxyvinyl)hydrazono) methyl)-6-methoxyphenol (methoxy-diim), via the condensation of 1-(4-chloro-phenyl)-2-hydrazino-ethenol compound with 2-((E)-(2-((Z)-2-(4-chlorophenyl)-2-hydroxy vinyl) hydrazono)methyl)-6-methoxyphenol in acetic acid as well as the preparation of new binuclear complexes of Co(ii), Ni(ii), Cu(ii), and Zn(ii). The following synthesized complexes were prepared in a ratio of 2:1 (metal/ligand). The 1H-NMR, UV-Vis, and FTIR spectroscopic data; molar conductivity measurements; and microanalytical, XRD, TGA/DTG, and biological studies were carried out to determine the molecular structure of these complexes. According to the spectroscopic analysis, the two central metal ions were coordinated with the diamine ligand via the nitrogen of the hydrazine and oxygen of the hydroxyl groups for the first metal ions and via the nitrogen of the hydrazine and oxygen of the phenol group for the second metal ions. Molecular docking for the free ligand was carried out against the breast cancer 3hb5-oxidoreductase and the 4o1v-protein binding kidney cancer and COVID-19 protease, and good results were obtained.

scholarly journals Carbonic Anhydrase Inhibitors Part 721 Synthesis and Antiglaucoma Properties of Metal Complexes of p-Fluorobenzolamide

1999 ◽  
Vol 6 (2) ◽  
pp. 67-73 ◽  
Author(s):  
Claudiu T. Supuran ◽  
Andrea Scozzafava ◽  
Luca Menabuoni ◽  
Francesco Mincione ◽  
Fabrizio Briganti ◽  
...  
Keyword(s):  
Intraocular Pressure ◽  
Carbonic Anhydrase ◽  
Metal Ions ◽  
Metal Complexes ◽  
Carbonic Anhydrase Inhibitors ◽  
Physico Chemical ◽  
New Compounds

Metal complexes of a heterocyclic sulfonamides possessing very strong carbonic anhydrase (CA) inhibitory properties, i.e., 5-(p-fluorobenzenesulfonylamido)-1,3,4-thiadiazole-2-sulfonamide (p-fluorobenzolamide) were prepared. The new complexes contained metal ions such as Zn(II), Cu(II), Co(II), Ni(II), Cd(II) and Mn(II). The new compounds were characterized by standard physico-chemical procedures, and assayed as inhibitors of three CA isozymes, CA I, II and IV. Very good inhibition has been evidenced both for the parent sulfonamides as well as for the prepared complexes, against all three investigated isozymes. Some of these new complexes as well as the parent sulfonamide, strongly lowered intraocular pressure (IOP) in normotensive rabbits when administered as a 2% solution into the eye.

Radioactive Tracer Study Performed in a Dipole Geometry in a Highly Conductive Fracture Zone

1990 ◽  
Vol 212 ◽  
Author(s):  
Johan Byegård ◽  
Gunnar Skarnemark ◽  
Mats Skålberg
Keyword(s):  
Metal Ions ◽  
Metal Complexes ◽  
Fracture Zone ◽  
Radioactive Tracer ◽  
Tracer Experiment ◽  
Tracer Study ◽  
Redox Potentials ◽  
Chemical Analogue

ABSTRACTA radioactive tracer experiment has been performed in a highly conductive fracture zone, using a dipole geometry. Anions (131I− and 82Br−) and complexed metal ions (51Cr-EDTA, 58Co-EDTA, 111In-EDTA, 140La-DOTA, 160Tb-EDTA, 169Yb-EDTA and 177Lu-DOTA) have been injected and their properties as non-sorbing tracers were evaluated. Besides, studies of slightlysorbing cations (24Na+, 58Co2+, 86Rb+ and 201T1+) were performed. 99mTcO4 and its chemical analogue 186ReO4 were also injected to study the behaviour of Tc at low redox-potentials. Breakthrough was obtained for Re and for all metal complexes and anions. Some differences in the recovery yields could be seen. No transport of cations, except for Na, could be measured. No breakthrough of Tc could be observed. This indicates that TcO4− was reduced and sorbed.

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