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Peter C Ford - One of the best experts on this subject based on the ideXlab platform.
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quantum dot fluorescence quenching pathways with cr iii complexes photosensitized no production from trans cr Cyclam ono 2
Journal of the American Chemical Society, 2008Co-Authors: Daniel Neuman, Alexis D Ostrowski, Alexander Mikhailovsky, Ryan O Absalonson, Geoffrey F Strouse, Peter C FordAbstract:Described is the photoluminescence (PL) of water-soluble CdSe/ZnS core/shell quantum dots (QDs) as perturbed by salts of the chromium(III) complexes trans-Cr(Cyclam)Cl2+ (1), trans-Cr(Cyclam)(ONO)2+ (2), and trans-Cr(Cyclam)(CN)2+ (3) (Cyclam = 1,4,8,11-tetraazacyclo-tetradecane). The purpose is to probe the characteristics of such QDs as antennae for photosensitized release of bioactive agents (in the present case, the bioregulatory molecule NO) from transition metal centers. Addition of 1 or 2 to a QD solution results in concentration-dependent quenching of the band edge emission, but 3 has a minimal effect. Added KCl strongly attenuates the quenching by 1, and this suggests that the Cr(III) cations and the QDs form electrostatic assemblies via ion pairing on the negatively charged QD surfaces. Quenching by 2, a known photochemical NO precursor, was accompanied by photosensitized NO release. All three, however, do quench the broad red emission (∼650−850 nm) attributed to radiative decay of surface trapp...
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synthesis and photophysical properties of new chromium iii complexes of n derivatized 1 4 8 11 tetraazacyclotetradecane ligands cis cr 1 8 r 2 Cyclam cl 2 cl where r is a pendant chromophore exclusive formation of the cis isomer
Inorganic Chemistry, 2003Co-Authors: Frank Derosa, Peter C FordAbstract:Several new chromium(III) complexes have been synthesized utilizing derivatives of the macrocyclic ligand Cyclam (1,4,8,11-tetraazacyclotetradecane) with various N-substituted chromophores in the 1 and 8 positions (1,8-R(2)Cyclam) where R = CH(3), CH(2)Ph, CH(2)Nph (Nph = naphthyl), and CH(2)Anth (Anth = anthracyl). X-ray crystal structures were determined for all four complexes, and these are formed exclusively in the cis configuration with the two tertiary amines in the "hinge" positions (i.e., along the folding axis) of the coordinated ligand. As a result, the cis isomers appear to be inert to isomerization under conditions dramatically more forcing than needed to effect the cis to trans isomerization of the unsubstituted Cr(Cyclam)Cl(2)(+) ion. Photophysical studies demonstrated that emission occurs solely from the metal-centered ligand field doublet excited states regardless of whether initial excitation is into the quartet ligand field bands or into the pi-pi bands of the pendant chromophore. Thus, excitation of the pendant chromophore results in efficient intramolecular energy transfer to the metal centered ligand field excited states.
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photoreactions of coordinated nitrite ion reversible nitric oxide labilization from the chromium iii complex trans cr Cyclam ono 2
ChemInform, 2001Co-Authors: Malcolm A Deleo, Peter C FordAbstract:Abstract An overview of the observed and likely photochemistry of transition metal nitrito compounds is presented with particular attention to the potential of using such nitrite ion complexes as the photochemical source for nitric oxide delivery to biological targets. In this context, recent studies at Santa Barbara regarding the photoreactions of the chromium(III) complex trans -Cr(Cyclam)(ONO) 2 + (Cyclam=1,4,8,11 tetraazacyclo-tetradecane) to give NO plus Cr(IV) (and subsequently Cr(V) complexes in the presence of dioxygen) are described.
Karl Wieghardt - One of the best experts on this subject based on the ideXlab platform.
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electronic structures of ru ii Cyclam et 2 dtc ru Cyclam tdt and ru Cyclam tdt 2 an x ray absorption spectroscopic and computational study tdt toluene 3 4 dithiolate et 2 dtc n n diethyldithiocarbamate 1
Inorganic Chemistry, 2009Co-Authors: Carsten Milsmann, Eckhard Bill, Thomas Weyhermuller, Serena Debeer George, Karl WieghardtAbstract:The reaction of [RuIII(Cyclam)Cl2]Cl with 2 equiv of sodium N,N-diethyldithiocarbamate in methanol afforded [RuII(Cyclam)(Et2dtc)](BPh4) (1(BPh4)). The same reaction with only 1 equiv of toluene-3,4-dithiol and a base yielded [Ru(Cyclam)(tdt)](PF6) (2(PF6)) which was oxidized by 1 equiv of ferrocenium hexafluorophosphate generating [Ru(Cyclam)(tdt)](PF6)2 (2ox(PF6)2). The crystal structures of 1 and 2 have been determined by X-ray crystallography at 100 K. The electronic structures of diamagnetic 1(BPh4), paramagnetic 2(PF6) (S = 1/2), and diamagnetic 2ox(PF6)2 have been studied by magnetochemistry, spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and 1H NMR spectroscopy. X-ray absorption spectroscopy on Ru K- and L-edges as well as S K-edges has been employed. Finally, the molecular and electronic structures of all three species have been calculated by using density functional theory (B3LYP). It is shown that 2ox comprises an electronic structure which is best described by three res...
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structural spectroscopic and computational study of an octahedral non heme fe no 6 8 series fe no Cyclam ac 2 0
Journal of the American Chemical Society, 2004Co-Authors: Ricardo Garcia Serres, Frank Neese, Eckhard Bill, Thomas Weyhermuller, Craig A Grapperhaus, Eberhard Bothe, Karl WieghardtAbstract:The reaction of low-spin [FeIICl(Cyclam-ac)] with NO in CH3CN yields the octahedral, non-heme (nitrosyl)iron complex [Fe(NO)(Cyclam-ac)](PF6) (2), S = 1/2, which can be one-electron oxidized with (tris(4-bromophenyl)ammoniumyl)hexachloroantimonate to the complex [Fe(NO)(Cyclam-ac)](PF6)2 (1'), S = 0, or complex [Fe(NO)(Cyclam-ac)]Cl(ClO4).H2O (1); (Cyclam-ac)- represents the pentadentate monoanion of 1,4,8,11-tetraazacyclotetradecane-1-acetic acid. Similarly, in CH3CN solution 2 can be electrochemically or chemically reduced by one-electron to the neutral complex [Fe(NO)(Cyclam-ac)]0 (3), S = 0. 1-3 represent members of the [FeNO]6-8 series, respectively. The electronic structure of these three species have been spectroscopically elucidated by EPR, UV-vis, Mossbauer, and IR spectroscopy. The crystal structures of 1 and 2 have been determined by X-ray crystallography. In addition, detailed density functional calculations have been performed for all three species taking into account the possibility that 3 is actually a protonated HNO or NOH species. For all complexes structures, energetics, IR parameters, and Mossbauer parameters as well as EPR parameters (g-values and hyperfine couplings) have been calculated using state-of-the art DFT methods which are compared to experiment. The results establish unequivocally that 3 is indeed the elusive [FeNO]8 species. Furthermore a detailed picture of the bonding in the low-spin non-heme iron nitrosyl series [FeNO]6, [FeNO]7, and [FeNO]8 has been developed. This allows a description of 1 as a low-spin ferrous complex containing an N-coordinated NO+, whereas 2 is a low-spin ferrous species with a NO* ligand and 3 is a low-spin ferrous complex with a coordinated NO-. On the basis of this description, all spectroscopic and geometric observables find a satisfactory interpretation.
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mononuclear nitrido iron v and oxo iron iv complexes via photolysis of Cyclam acetato feiii n3 and ozonolysis of Cyclam acetato feiii o3scf3 in water acetone mixtures
Inorganic Chemistry, 2000Co-Authors: Craig A Grapperhaus, Eckhard Bill, Bernd Mienert, Thomas Weyhermuller, Karl WieghardtAbstract:Reaction of the monoanionic, pentacoordinate ligand lithium 1,4,8,11-tetraazacyclotetradecane-1-acetate, Li(Cyclam-acetate), with FeCl3 yields, upon addition of KPF6, [(Cyclam-acetato)FeCl]PF6 (1) as a red microcrystalline solid. Addition of excess NaN3 prior to addition of KPF6 yields the azide derivative [(Cyclam-acetato)FeN3]PF6 (2a) as orange microcrystals. The X-ray crystal structure of the azide derivative has been determined as the tetraphenylborate salt (2b). Reaction of 1 with silver triflate yields [(Cyclam-acetato)Fe(O3SCF3)]PF6 (3), which partially dissociates triflate in nondried solvents to yield a mixture of triflate and aqua bound species. Each of the iron(III) derivatives is low-spin (d5, S = 1/2) as determined by variable-temperature magnetic susceptibility measurements, Mossbauer and EPR spectroscopy. The low-spin iron(II) (d6, S = 0) complexes 1red and 2ared have been prepared by electrochemical and chemical methods and have been characterized by Mossbauer spectroscopy. Photolysis of 2a at 419 nm in frozen acetonitrile yields a nearly colorless species in approximately 80% conversion with an isomer shift delta = -0.04 mm/s and a quadrupole splitting delta EQ = -1.67 mm/s. A spin-Hamiltonian analysis of the magnetic Mossbauer spectra is consistent with an FeV ion (d3, S = 3/2). The proposed [(Cyclam-acetato)FeV=N]+ results from the photooxidation of 2a via heterolytic N-N cleavage of coordinated azide. Photolysis of 2a in acetonitrile solution at -35 degrees C (300 nm) or 20 degrees C (Hg immersion lamp) results primarily in photoreduction via homolytic Fe-Nazide cleavage yielding FeII (d,6 S = 0) with an isomer shift delta = 0.56 mm/s and quadrupole splitting delta EQ = 0.54 mm/s. A minor product containing high-valent iron is suggested by Mossbauer spectroscopy and is proposed to originate from [((Cyclam-acetato)Fe)2(mu-N)]2+ with a mixed-valent (FeIV(mu-N)FeIII))4+S = 1/2 core. Exposure of 3 to a stream of oxygen/ozone at low temperatures (-80 degrees C) in acetone/water results in a single oxidized product with an isomer shift delta = 0.01 mm/s and quadrupole splitting delta EQ = 1.37 mm/s. A spin-Hamiltonian analysis of the magnetic Mossbauer yields parameters similar to those of compound II of horseradish peroxidase which are consistent with an FeIV=O monomeric complex (S = 1).
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photolysis of cis and trans feiii Cyclam n3 2 complexes spectroscopic characterization of a nitridoiron v species
Journal of the American Chemical Society, 1999Co-Authors: Karsten Meyer, Eckhard Bill, Bernd Mienert, And Thomas Weyhermuller, Karl WieghardtAbstract:Reaction of cis-[FeIII(Cyclam)Cl2]Cl in acidic H2O/CH3OH or CH3CN/H2O mixtures with NaN3 at 50 °C produced upon addition of NaClO4 or NaPF6 the complex trans-[FeIII(Cyclam)(N3)2]ClO4 (1a) or the hexafluorophosphate salt 1b, whereas at −18 °C the same reaction produced cis-[FeIII(Cyclam)(N3)2](ClO4) (2) (Cyclam = 1,4,8,11-tetraazacyclotetradecane). The crystal structures of 1b and 2 were determined by single-crystal X-ray crystallography. Complexes 1a, b, contain a low-spin (S = 1/2) and 2, a high-spin ferric ion (S = 5/2) as was established by variable-temperature magnetic susceptibility measurements and Mossbauer and X-band EPR spectroscopy. The low-spin trans-[(Cyclam)FeII(N3)2] and high-spin cis-[(Cyclam)FeII(N3)2] species were generated electrochemically in CH3CN solution and were characterized by Mossbauer spectroscopy. Photolysis of 1a in CH3CN at −35 °C and 20 °C with a Hg immersion lamp generated within 15 min a yellow solution. EPR and Mossbauer spectra show that a single high-valent species with...
Matthew H Todd - One of the best experts on this subject based on the ideXlab platform.
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copper ii complexes of n propargyl Cyclam ligands reveal a range of coordination modes and colours and unexpected reactivity
Dalton Transactions, 2021Co-Authors: Andrew J Counsell, Mengying Shi, Angus T Jones, James M Batten, Peter Turner, Matthew H Todd, Peter J RutledgeAbstract:The coordination chemistry of N-functionalised Cyclam ligands has a rich history, yet Cyclam derivatives with pendant alkynes are largely unexplored. This is despite the significant potential and burgeoning application of N-propargyl Cyclams and related compounds in the creation of diversely functionalised Cyclam derivatives via copper-catalysed azide–alkyne ‘click’ reactions. Herein we describe single crystal X-ray diffraction and spectroscopic investigations of the coordination chemistry of copper(II) complexes of Cyclam derivatives with between 1 and 4 pendant alkynes. The crystal structures of these copper complexes unexpectedly reveal a range of coordination modes, and the surprising occurrence of five unique complexes within a single recrystallisation of the tetra-N-propargyl Cyclam ligand. One of these species exhibits weak intramolecular copper-alkyne coordination, and another is formed by a surprising intramolecular copper-mediated hydroalkoxylation reaction with the solvent methanol, transforming one of the pendant alkynes to an enol ether. Multiple functionalisation of the tetra-N-propargyl ligand is demonstrated via a ‘tetra-click’ reaction with benzyl azide, and the copper-binding behaviour of the resulting tetra-triazole ligand is characterised spectroscopically.
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synthesis and evaluation of 1 8 disubstituted Cyclam naphthalimide conjugates as probes for metal ions
ChemistryOpen, 2016Co-Authors: Joseph K Wong, Andrew J Counsell, Peter Turner, Matthew H Todd, Sandra Ast, Roman Flehr, Patrick Crisologo, Peter J RutledgeAbstract:Fluorescent molecular probes for metal ions have a raft of potential applications in chemistry and biomedicine. We report the synthesis and photophysical characterisation of 1,8-disubstituted-Cyclam/naphthalimide conjugates and their zinc complexes. An efficient synthesis of 1,8-bis-(2-azidoethyl)Cyclam has been developed and used to prepare 1,8-disubstituted triazolyl-Cyclam systems, in which the pendant group is connected to triazole C4. UV/Vis and fluorescence emission spectra, zinc binding experiments, fluorescence quantum yield and lifetime measurements and pH titrations of the resultant bis-naphthalimide ligand elucidate a complex pattern of photophysical behaviour. Important differences arise from the inclusion of two fluorophores in the one probe and from the variation of triazole substitution pattern (dye at C4 vs. N1). Introducing a second fluorophore greatly extends fluorescence lifetimes, whereas the altered substitution pattern at the Cyclam amines exerts a major influence on fluorescence output and metal binding. Crystal structures of two key zinc complexes evidence variations in triazole coordination that mirror the solution-phase behaviour of these systems.
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incorporation of bulky and cationic Cyclam triazole moieties into marimastat can generate potent mmp inhibitory activity without inducing cytotoxicity
ChemistryOpen, 2013Co-Authors: Ngee Han Lim, Peter J Rutledge, Samantha Ellis, Hideaki Nagase, James A Triccas, Matthew H ToddAbstract:The synthesis and matrix metalloproteinase (MMP) inhibitory activity of a Cyclam-marimastat conjugate and its metal complexes are described. The conjugate, synthesized with a copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition ("click" reaction), contains two zinc-binding groups (ZBGs). The metal complexation behavior with copper(II) and zinc(II) was investigated using UV/Vis spectrophotometry and (1)H NMR spectroscopy, respectively, demonstrating that the first equivalent of the metal ion was chelated by the Cyclam-triazole moiety rather than the hydroxamic acid site. Thus, the corresponding mononuclear metal-Cyclam complexes were successfully prepared with one equivalent of the metal salt. Both the Cyclam-marimastat conjugate and its metal complexes exhibited slightly reduced potency against MMP-1, but essentially identical inhibitory activity against MMP-3. The conjugate and its metal complexes displayed little or no cytotoxicity, further supporting their potential suitability for imaging MMP localization and activity. To the best of our knowledge, this is the first report that describes the incorporation of metal complexes into an MMP inhibitor without influencing the preexisting ZBG, and the first report of the evaluation of structures containing more than one ZBG as MMP inhibitors.
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a synthetically simple click generated Cyclam based zinc ii sensor
Inorganic Chemistry, 2009Co-Authors: Emiliano Tamanini, Matthew H Todd, Arna Katewa, Lisa M Sedger, Michael WatkinsonAbstract:A Cyclam-based macrocyclic sensor has been prepared using synthetically simple “click” chemistry to link a fluorophore to the macrocyclic receptor. This sensor shows high selectivity for Zn(II) over a range of other metals, providing a significant enhancement of fluorescence intensity over a wide pH range. As such, this is the first Cyclam-based sensor demonstrated to be selective for Zn(II) and is the first example of a triazole being used as a coordinating ligand on an azamacrocycle. The sensor can access biologically available zinc in mammalian cells, sensing the Zn(II) flux that exists during apoptotic cell death.
Michael Watkinson - One of the best experts on this subject based on the ideXlab platform.
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a synthetically simple click generated Cyclam based zinc ii sensor
Inorganic Chemistry, 2009Co-Authors: Emiliano Tamanini, Matthew H Todd, Arna Katewa, Lisa M Sedger, Michael WatkinsonAbstract:A Cyclam-based macrocyclic sensor has been prepared using synthetically simple “click” chemistry to link a fluorophore to the macrocyclic receptor. This sensor shows high selectivity for Zn(II) over a range of other metals, providing a significant enhancement of fluorescence intensity over a wide pH range. As such, this is the first Cyclam-based sensor demonstrated to be selective for Zn(II) and is the first example of a triazole being used as a coordinating ligand on an azamacrocycle. The sensor can access biologically available zinc in mammalian cells, sensing the Zn(II) flux that exists during apoptotic cell death.
Thue W Schwartz - One of the best experts on this subject based on the ideXlab platform.
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molecular mechanism of action of monoCyclam versus biCyclam non peptide antagonists in the cxcr4 chemokine receptor
Journal of Biological Chemistry, 2007Co-Authors: Mette M. Rosenkilde, Lars Ole Gerlach, Renato T Skerlj, Dominique Schols, Sigrid Hatse, Gary Bridger, Thue W SchwartzAbstract:AMD3465 is a novel, nonpeptide CXCR4 antagonist and a potent inhibitor of HIV cell entry in that one of the four-nitrogen Cyclam rings of the symmetrical, prototype biCyclam antagonist AMD3100 has been replaced by a two-nitrogen N-pyridinylmethylene moiety. This substitution induced an 8-fold higher affinity as determined against (125)I-12G5 monoclonal CXCR4 antibody binding, and a 22-fold higher potency in inhibition of CXCL12-induced signaling through phosphatidylinositol accumulation. Mutational mapping of AMD3465 and a series of analogs of this in a library of 23 mutants covering the main ligand binding pocket of the CXCR4 receptor demonstrated that the single Cyclam ring of AMD3465 binds in the pocket around AspIV:20 (Asp(171)), in analogy with AMD3100, whereas the N-pyridinylmethylene moiety mimics the other Cyclam ring through interactions with the two acidic anchor-point residues in transmembrane (TM)-VI (AspVI:23/Asp(262)) and TM-VII (GluVII:06/Glu(288)). Importantly, AMD3465 has picked up novel interaction sites, for example, His(281) located at the interface of extracellular loop 3 and TM-VII and HisIII:05 (His(113)) in the middle of the binding pocket. It is concluded that the simple N-pyridinylmethylene moiety of AMD3465 substitutes for one of the complex Cyclam moieties of AMD3100 through an improved and in fact expanded interaction pattern mainly with residues located in the extracellular segments of TM-VI and -VII of the CXCR4 receptor. It is suggested that the remaining Cyclam ring of AMD3465, which ensures the efficacious blocking of the receptor, in a similar manner can be replaced by chemical moieties allowing for, for example, oral bioavailability.
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molecular interactions of Cyclam and biCyclam non peptide antagonists with the cxcr4 chemokine receptor
Journal of Biological Chemistry, 2001Co-Authors: Lars Ole Gerlach, Renato T Skerlj, Gary J Bridger, Thue W SchwartzAbstract:Abstract The non-peptide CXCR4 receptor antagonist AMD3100, which is a potent blocker of human immunodeficiency virus cell entry, is a symmetrical biCyclam composed of two identical 1,4,8,11-tetraazacyclotetradecane (Cyclam) moieties connected by a relatively rigid phenylenebismethylene linker. Based on the known strong propensity of the Cyclam moiety to bind carboxylic acid groups, receptor mutagenesis identified Asp171 and Asp262, located in transmembrane domain (TM) IV and TM-VI, respectively, at each end of the main ligand-binding crevice of the CXCR4 receptor, as being essential for the ability of AMD3100 to block the binding of the chemokine ligand stromal cell-derived factor (SDF)-1α as well as the binding of the receptor antibody 12G5. The free Cyclam moiety had no effect on 12G5 binding, but blocked SDF-1α binding with an affinity of 3 μm through interaction with Asp171. The effect on SDF-1α binding of a series of biCyclam analogs with variable chemical linkers was found to rely either only on Asp171, i.e. the biCyclams acted as the isolated Cyclam, or on both Asp171 and Asp262, i.e. they acted as AMD3100, depending on the length and the chemical nature of the linker between the two Cyclam moieties. A positive correlation was found between the dependence of these compounds on Asp262 for binding and their potency as anti-human immunodeficiency virus agents. It is concluded that AMD3100 acts on the CXCR4 receptor through binding to Asp171 in TM-IV and Asp262 in TM-VI with each of its Cyclam moieties, and it is suggested that part of its function is associated with a conformational constraint imposed upon the receptor by the connecting phenylenebismethylene linker.
