Macrocyclic aromatic tetrasulfonamides with a stable cone conformation.
Aromatic tetrasulfonamide macrocycles carrying alkoxy side chains adopt a stable cone conformation in both the solid state and solution.
Crystallography, X-Ray↗
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Coordination chemistry of N-aminopropyl pendant arm derivatives of mixed N/S-, and N/S/O-donor macrocycles, and construction of selective fluorimetric chemosensors for heavy metal ions.
The coordination chemistry of the N-aminopropyl pendant arm derivatives (L1c-4c) of the mixed donor macrocyclic ligands [12]aneNS2O, [12]aneNS3, [12]aneN2SO, and [15]aneNS2O2(L1a-4a) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) in aqueous solution has been investigated. The protonation and stability constants with the aforementioned metal ions were determined potentiometrically and compared, where possible, with those of the unfunctionalised macrocycles. The measured values show that Hg(II) and Cu(II) in water have the highest affinity for all ligands considered, with the N-aminopropyl pendant arm weakly coordinating the metal centres. Crystals suitable for X-ray diffraction analysis were grown for the perchlorate salt (H2L1c)(ClO4)2.dmf, and for the 1 : 1 complexes [Cd(L3a)(NO3)2](1), [Cu(L4a)dmf](ClO4)2(2), [Zn(L1c)(ClO4)]ClO4(3), [Cd(L1c)(NO3)]NO3(4), and [Hg(L2c)](ClO4)2(5). Their structures show the macrocyclic ligands adopting a folded conformation, which for the 12-membered systems can be either [2424] or [3333] depending on the nature of the metal ion. L1c-4c were also functionalised at the primary amino pendant group with different fluorogenic subunits. In particular the N-dansylamidopropyl (Lnd, n= 1-4), and the N-(9-anthracenylmethyl)aminopropyl (Lne, n= 1, 2, 4, ) pendant arm derivatives of L1a-4a were synthesised and their optical responses to the above mentioned metal ions were investigated in MeCN/H2O (4 : 1 v/v) solutions.
Crystallography, X-Ray↗
Polyaza metacyclophanes as ditopic anion receptors.
Five macrocyclic polyaza metacyclophanes L1-L5 prepared by dipode coupling of the tosylated precursors have been studied. The basicity of the ligands has been measured potentiometrically and their ability to complex halides and perchlorate has been studied in the solid state by X-ray crystallography. The results reveal that the ligands generally act as ditopic halide receptors with even the largest, L5, being too small to envelop the anion. The ligand's basicity behaviour parallels that observed for related para-analogues. Despite the ready crystallisation of fluoride, HF2-, chloride, bromide, iodide and triiodide salts in the solid state, there appears to be little affinity for halides in aqueous solution in the pH range accessible via potentiometry. The results do give a detailed insight into the role of the aryl ring in restricting the conformational flexibility of the ligands and, hence, the ability to chelate perching anions.
Crystallography, X-Ray↗
Lanthanide luminescent switches: modulation of the luminescence of bis-macrocyclic based Tb(III) conjugates in water by H+, Na+ and K+.
The synthesis of four bis-macrocyclic conjugates made from the coupling of either diaza-15-crown-5 ethers (1 and 3) and diaza-18-crown-6 ethers (2 and 4) to either amide or carboxylate functionalized cyclen (1,4,7,10-tetraazacyclododecane), and their corresponding cationic Tb(III) complexes, Tb-1, Tb-2, and neutral complexes Tb-3 and Tb-4 are described. The effect on the ground, singlet excited states and the Tb(III) emission, was investigated either as a function of pH or the concentration of several Group I and II cations, upon excitation at 300 nm. The ground state and singlet excited states of the Tb(III) complexes were found to be modulated by ions such as H+, Na+ or K+, signifying the recognition of these ions by the crown ether receptors. In acidic media, below pH 4, the Tb(III) emission was highly pH sensitive, gradually increasing with large orders of magnitude of luminescence enhancements. For Tb-1 and Tb-2 complexes, the Tb(III) emission was also "switched on" in alkaline media above pH 8. At pH 7.4, the recognition of Na+ or K+ also gave rise to a significant change in the Tb(III) emission due to the modulation of the antenna-receptor moieties by these ions. For Tb-1 and Tb-3 the largest changes were seen for Na+, whereas for Tb-2 and Tb-4 the largest changes were seen for K+.
Hydrogen-Ion Concentration↗
Hydrogen bond directed synthesis of pyridazine and naphthyridine containing macrocycles.
This work describes a high-yielding, one-step synthesis of pyrizadine and naphthyridine containing macrocycles directed by intramolecular H-bonding.
Crystallography, X-Ray↗
The folded, tetrameric phosph(III)azane macrocycle [(P(mu-NtBu))2(1,4-(NH)2C6H4)]4.
The tetrameric macrocycle [(P(mu-NtBu))2(1,4-(NH)2C6H4)]4, obtained from the reaction of the phosphazane dimer [ClP(mu-NtBu)]2 with p-phenylenediamine, has an unusual folded conformation in the solid state and contains a roughly tetrahedral arrangement of endo N-H groups for the potential coordination of anions.
Aziridines↗
Kinetic and equilibrium studies on the polyazamacrocycle neotetren: metal-complex formation and DNA interaction.
The macrocyclic polyamine 2,5,8,11,14-pentaaza[15]-[15](2,9)[1,10]phenanthrolinophane (neotetren) is studied in its ability to coordinate Cu(ii) even at very low pH values and to interact, as a metal complex, with DNA. The kinetics and equilibria for 1 : 1 and 2 : 1 metal-ligand complexes formation are studied by the stopped-flow method and UV spectrophotometry. Differently protonated complexes are formed, with rate constants much lower than that of water exchange at copper(II) and other Cu(II)/amine systems, this behaviour being ascribed to ring effects and intra-molecular hydrogen bonds. Concerning the DNA/copper(II)-neotetren complexes interaction, analysis of data suggests an intercalative mode of binding. The kinetic results for both DNA/CuL and DNA/Cu(2)L systems agree with the sequence D + S <-->D,S <-->DS where the metal complexes (D) react with the DNA sites (S) leading to fast formation of an externally bound form (D,S) which is converted into an intercalated complex (DS). A very slow process is also detected and ascribed to a conformational change in the polynucleotide secondary structure where the metal centre plays a crucial role. Chromatographic experiments demonstrate that both the investigated Cu(II)/L complexes are able to cleave DNA, but only in the presence of hydrogen peroxide.
Binding Sites↗
Total synthesis of aspercyclide C.
The first total synthesis of (+)-aspercyclide C (1) is reported using a kinetically controlled RCM reaction to form the 11-membered, unsaturated lactone ring of this bioactive diaryl ether macrolide.
Lactones↗
Dimetallo[3.3]para- and metacyclophanes by self-assembly of pyridylmethyl armed-monoazatrithia- and monoazadithiaoxa-12-crown-4 ethers with Ag+ ions.
New pyridylmethyl armed-monoazadithiaoxa- and monoazatrithia-12-crown-4 have been prepared. The structures of the Ag+ complexes of the new ligands were investigated by X-ray crystallography, 1H NMR titrations, and FAB-MS measurements. In all cases, the Ag+ complexes form dimetallo[3.3]para- or metacyclophane structures depending on the position of the N atom of the pyridine rings.
Crown Ethers↗
Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(II) complexes.
Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN-R-NHSO2R1 = L) have been shown to be easily deprotonated to give neutral 2:1 complexes, [M(L - H)(2)], with Co(II), Ni(II), Cu(II) or Zn(II). The Ni(II) and Cu(II) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar N4(2-) donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail S=O...H-N((amine)) bonding between the two bidentate ligands. In the related tetrahedral Zn(II) complex the ends of the mutually perpendicular bidentate N2- units are too far apart to form a cyclic H-bonded system. X-Ray structure determinations on five free ligands provide evidence for extensive inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its N'-tert-butyl derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable inter-ligand H-bonding in the neutral 2:1 complexes, these ligands are relatively weak extractants, showing >50% loading of Cu(II) in "pH-swing" equilibria, 2L(org)+ M2+ = [M(L - H)2](org)+ 2 H+, only when the pH of the aqueous phase is raised above 4.
Crystallography, X-Ray↗
Total synthesis of floresolide B and Delta(6,7)-Z-floresolide B.
The total syntheses of the cytotoxin marine natural product floresolide B (1) and its Delta(6,7)-Z isomer (2) have been achieved through an olefin metathesis-based strategy.
Alkenes↗
Synthesis of chiral cyclic oligothiazolines: a novel structural motif for a macrocyclic molecule.
The synthesis of chiral cyclic oligo(4-beta-methyl)thiazolines is described; linear oligothiazolines were efficiently prepared by the iterative formation of a thiazoline ring and a two-directional block condensation, and construction of 24- to 36-membered cyclic oligothiazoline systems could be achieved by the head-to-tail cyclooligomerization of doubly deprotected linear fragments and subsequent thiazoline formation.
Macrocyclic Compounds↗
Highly diastereoselective amplification from a dynamic combinatorial library of macrocyclic oligoimines.
Cadmium promoted diastereoselective amplification of a single member from a dynamic combinatorial library of stereoisomeric oligoimines of different sizes allows the efficient preparation of a new macrocyclic polyamine.
Cadmium↗
[6 + 6] Schiff-base macrocycles with 12 imines: giant analogues of cyclohexane.
Hexagon-shaped [6 + 6] Schiff-base macrocycles with 12 imine bonds are reported. These giant macrocycles possess 6 N2O2 coordination environments and mass spectrometry evidence for hexametallation of one macrocycle is provided. Semi-empirical calculations reveal two stable conformations with boat and chair geometries for the macrocycles metallated with Ni(II), analogous to the conformations observed for cyclohexane.
Cyclohexanes↗
Synthesis of macrocyclic analogues of the neuroprotective agent glycyl-L-prolyl-L-glutamic acid (GPE).
The syntheses of seven macrocyclic analogues of the neuroprotective tripeptide glycyl-L-prolyl-L-glutamic acid (GPE) are described. Macrocycles 6 and 7 mimic the cis conformer of GPE whereas macrocycles 2-5, 8, and 9 mimic the trans conformer of GPE. The macrocyclic peptides of well-defined geometry were prepared via Grubbs ring closing metathesis of an appropriate diene precursor. In turn each of the diene precursors were prepared from the readily available allyl-substituted amino acid building blocks 12, 13, 14, 27, 36 and 51.
Macrocyclic Compounds↗
Reading the operation of an acid/base-controllable molecular switch by naked eye.
We report a pH-controllable molecular switch whose switching can be monitored by the naked eye; this system involves the formation of a complex between a [2]rotaxane--featuring dibenzylammonium and 4,4'-bipyridinium stations--and a TTF-side-walled molecular clip.
2,2'-Dipyridyl↗
Labelling monoclonal antibodies with macrocyclic radiometal complexes. A challenge for coordination chemists.
The technique consisting of labelling antibodies with radionuclides is a promising approach for the diagnosis and therapy of human cancers. In this paper the chemical aspects of radiolabelling with macrocyclic metal complexes are dealt with. The choice of the radioisotope, its coordination chemistry, the design of the bifunctional macrocyclic ligand, and its attachment to the monoclonal antibody are discussed. Finally several newer ideas for a better application are presented.
Antibodies, Monoclonal↗
Electrochemistry of copper complexes with macrocyclic polyamines containing pyrazole units.
The voltammetric behaviour of bi- and mono-nuclear complexes formed in solution by Cu(2+) with three polyazacyclophanes containing pyrazole units in aqueous solution is described. Cyclic and square wave voltammetric responses at glassy carbon electrodes indicate that the reduction of copper-macrocycle complexes in solution takes place in two successive one-electron per Cu transfer processes coupled with preorganization and protonation reactions that mimic the behaviour of superoxide dismutase. The electrochemistry of ternary Cu(2+)-receptor-dopamine complexes exhibits significant differences with respect to the protection of the neurotransmitter from post-electron transfer cyclization reactions.
Copper↗