Search results for "Cyclic compound"
showing 10 items of 819 documents
Imidazolate bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) complexes of a terpyridinophane azamacrocycle: a solution and solid state study.
2007
The dinuclear Cu2+ and Zn2+ as well as the mixed Cu2+-Zn2+ complexes of a 5,5''-pentaazaterpyridinophane ligand (L) are able to incorporate imidazolate (Im-) as a bridging ligand. The crystal structure of [Cu(2)L(Im)(Br)(H2O)](CF(3)SO(3))(2).3H2O (1) shows one copper coordinated by the three pyridine nitrogens of the terpyridine unit, one nitrogen of the imidazolate bridge (Im-) and one bromide anion occupying the axial position of a distorted square pyramid. The second copper atom is coordinated by the remaining imidazolate nitrogen, the three secondary nitrogens at the centre of the polyamine bridge and one water molecule that occupies the axial position. Magnetic measurements have been p…
Aryl-bis-(scorpiand)-aza receptors differentiate between nucleotide monophosphates by a combination of aromatic, hydrogen bond and electrostatic inte…
2014
Bis-polyaza pyridinophane scorpiands bind nucleotides in aqueous medium with 10–100 micromolar affinity, predominantly by electrostatic interactions between nucleotide phosphates and protonated aliphatic amines and assisted by aromatic stacking interactions. The pyridine-scorpiand receptor showed rare selectivity toward CMP with respect to other nucleotides, whereby two orders of magnitude affinity difference between CMP and UMP was the most appealing. The phenanthroline-scorpiand receptor revealed at pH 5 strong selectivity toward AMP with respect to other NMPs, based on the protonation of adenine heterocyclic N1. The results stress that the efficient recognition of small biomolecules with…
Cyclic [2]Pseudorotaxane Tetramers Consisting of Two Rigid Rods Threaded through Two Bis-Macrocycles: Copper(I)-Templated Synthesis and X-ray Structu…
2008
Variously substituted coordinating rigid rods have been synthesized which incorporate a central 4,7-phenanthroline nucleus attached to two 2-pyridyl groups via its 3 and 8 positions, so as to yield bis-bidentate chelates, the two-coordinating axes of the chelates being parallel to one another. Regardless of the nature of the substituents borne by the rods, the copper(I)-induced threading reaction of two such rods through the rings of two bis-macrocycles affords in a quantitative yield the 4-copper(I) threaded assembly. The [2]pseudorotaxane tetramers thus obtained have been fully characterized in solution and, for one of them, an X-ray structure could be obtained, confirming the threaded na…
A surprising switch in absolute configuration of anti-inflammatory macrolactones.
2016
Oxacyclododecindione-type macrolactones exhibit highly potent anti-inflammatory activities even at nanomolar concentration. After the determination of the relative configuration of the stereocenters at C14 and C15 by total synthesis of 4-dechloro-14-deoxyoxacyclododecindione and 14-deoxyoxacyclododecindione, the absolute configuration has now been assigned by X-ray crystallography. Surprisingly, the absolute configuration is (14S,15R) which differs for C15 from that of the well-known derivatives of (S)-curvularin. The biological activities of both enantiomers of 14-deoxyoxacyclododecindione, obtained by racemic synthesis and optical resolution, were investigated and the ring conformation of…
Remarkable Inertness of Copper(II) Chelates of Cyclen-Based Macrobicycles with Two trans-N-Acetate Arms
2013
Two cross-bridged cyclen-based macrocycles with two trans-N-acetic acid arms, one having a dibenzofuran (DBF) moiety as the bridge, H2L1, and the other a diphenyl ether (DPE) one, H2L2, were synthesized. Both compounds behave as "proton sponges." The thermodynamic stability constants for the Cu(2+), Zn(2+), Al(3+), and Ga(3+) complexes of both compounds were determined. They exhibit an excellent thermodynamic selectivity for copper(II), ensuring that metal ions largely present in the human body do not interfere with the copper(II) chelates. All complexes are very slow to form, and [CuL2] and [CuL1] are extremely inert to demetallate, especially [CuL2]. The acid-assisted dissociation of [CuL…
A self-assembled M8L6 cubic cage that selectively encapsulates large aromatic guests.
2011
Porphyrins cubed: A series of self-assembled M8L6 cubic cages that enclose a volume in excess of 1300 A3 were synthesized (see scheme). The porphyrinic walls of the cubes provide favorable sites for pnp interactions, leading to selectivity between large and chemically similar aromatic guests: three molecules of coronene are incorporated and the higher fullerenes C70nC84 are selectively bound in the presence of
Monoester copillar[5]arenes: synthesis, unusual self-inclusion behavior, and molecular recognition.
2012
The self-inclusion behavior of monoester copillar[5]arenes depends on the position of the ester group, which causes different guest selectivities. Monoester copillar[5]arenes bearing an acetate chain can form stable self-inclusion complexes in low- and high-concentration solution and exhibit high guest selectivity. However, a monoester copillar[5]arene bearing a butyrate chain can not form a self-inclusion complex and exhibits low guest selectivity. Thus, a new class of stable self-inclusion complexes of copillar[5]arenes was explored to improve the selectivity of molecular recognition.
Synthesis, characterisation and crystal structures of Schiff bases from the reaction of 4,6-O-ethylidene-β-D-glucopyranosylamine with substituted sal…
2001
Multiple chemical modifications were carried out on D-glucose to result in the corresponding Schiff bases. Such modifications performed on D-glucose not only helped in increasing the solubility of the products in nonaqueous solvents, but also restricted the anomerisation of the saccharide moiety in solution. NMR study of the products revealed the presence of the β-anomeric form of the saccharide moiety in Me2SO solution. All the compounds were characterised by analytical and spectral methods. The literature is devoid of any crystal structures of saccharide–Schiff base combinations of the type reported in this paper. The crystal structures of these molecules exhibited a tridentate, ONO bindi…
Amplification of Dissymmetry Factors in π-Extended [7]- and [9]Helicenes
2021
International audience; $\pi$-Extended helicenes constitute an important class of polycyclic aromatic hydrocarbons with intrinsic chirality. Herein, we report the syntheses of $\pi$extended [7]helicene $4$ and $\pi$-extended [9]helicene $6$ through regioselective cyclodehydrogenation in high yields, where a "prefusion" strategy plays a key role in preventing undesirable aryl rearrangements. The unique helical structures are unambiguously confirmed by X-ray crystal structure analysis. Compared to the parent pristine [7]helicene and [9]helicene, these novel $\pi$-extended helicenes display significantly improved photophysical properties, with a quantum yield of 0.41 for $6$. After optical res…
Easy preparation of Cp*-functionalized N-heterocyclic carbenes and their coordination to rhodium and iridium
2010
A simple high-yielding method for the preparation of a tetramethylcyclopentadienyl-NHC ligand is described. This ligand has been successfully coordinated to Rh and Ir. A related Cp*-NHC ligand with a -CH(2)CMePh- linker between the Cp* and the NHC is also described, together with its coordination to Rh and Ir. This latter ligand, affords the orthocyclometallation of the phenyl ring yielding a constrained structure in which the ligand is tridentate. All the complexes have been fully characterized and their crystal structures are described. Preliminary catalytic results on the beta-alkylation of secondary alcohols and N-alkylation of aniline with primary alcohols are also reported.