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Koen Binnemans

Publications and source records attributed to Koen Binnemans.

15 recordsLinked to original sources
PubMed2006

Two-dimensional self-assembly and phase behavior of an alkoxylated sandwich-type bisphthalocyanine and its phthalocyanine analogues at the liquid-solid interface.

Lanthanide bisphthalocyanine complexes are interesting objects for the construction of two-dimensional (2D) ordered arrays with prospective applications in molecular electronics due to their unique semiconductor and electrochromic properties as well as their double-decker architecture. The 2D self-assembly of dodecyloxy-substituted (bisphthalocyaninato)erbium(III) has been studied at the solid (highly oriented pyrolytic graphite)-liquid interface by scanning tunneling microscopy. The results show that the bisphthalocyanine molecules form an ordered quadratic 2D lattice (a = b = 3.0 +/- 0.1 nm, gamma = 90 +/- 3 degrees), which is nearly identical to that formed by its (phthalocyaninato)cobalt(II) analogue bearing alkoxy chains of the same length. This clearly shows that sandwich molecules adsorb to the graphite surface by one of the phthalocyanine disks and its eight alkoxy groups. Despite the very similar mode of interaction with the surface, mixtures of alkoxylated (bisphthalocyaninato)erbium(III) with its (phthalocyaninato)cobalt(II) analogue show partial phase separation on the nanoscale: areas are enriched in one of the compounds. A much clearer phase separation between (bisphthalocyaninato)erbium(III) and (phthalocyaninato)cobalt(II) molecules was achieved by mixing molecules containing alkoxy groups of different length. The results provide insight for the development of well-ordered nanostructures of bisphthalocyanines in the presence of phthalocyanines, which could be of importance for future nanometer-scale functional materials.

Journal Article↗
PubMed2005

A propeller-like uranyl metallomesogen.

Uranyl triflate forms with three imidazo[4,5-f]-1,10-phenanthroline ligands a propeller-like complex that exhibits a hexagonal columnar phase. The ligand is not liquid-crystalline, but a mesophase is induced upon complex formation with the uranyl salt. The thermal behavior has been investigated by polarizing optical microscopy and by high-temperature X-ray diffraction. A model of the stacking of the molecules in the mesophase is proposed.

Journal Article↗
PubMed2005

Relaxometric study of copper [15]metallacrown-5 gadolinium complexes derived from alpha-aminohydroxamic acids.

Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from alpha-aminohydroxamic acids and with copper(II) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported.

Copper↗
PubMed2005

Paramagnetic liposomes containing amphiphilic bisamide derivatives of Gd-DTPA with aromatic side chain groups as possible contrast agents for magnetic resonance imaging.

Three amphiphilic DTPA bisamide derivatives containing long-chain phenylalanine esters (with 14, 16 and 18 carbon atoms in the alkyl chain) were synthesized and their corresponding gadolinium(III) complexes were prepared. The attempts to form paramagnetic micelles carrying the gadolinium(III) complexes yielded unstable or polydisperse micelles implying that the presence of the bulky aromatic side groups in the amphiphilic Gd-DTPA bisamide complexes results in an inefficient packing of the paramagnetic complex into micelles. All complexes were efficiently incorporated into liposomes consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), yielding stable and monodisperse paramagnetic liposomes. All liposomes had a comparable size, typically between 120 and 160 nm. As a result of the reduced mobility of the gadolinium(III) complexes, solutions of these supramolecular structures show a higher relaxivity than solutions of Gd-DTPA. However, the relaxivity gain is lower compared to compounds consisting of purely aliphatic chains of the same length, most likely due to the less efficient packing or increased local mobility of the gadolinium(III) complex. In the case of the Gd-DTPA bisamide complex with 18 carbon atoms, the immobilization inside the liposomal structure is less effective, probably because the aliphatic chains of the complex are longer than the alkyl chains of the DPPC host, resulting in a relatively high local mobility. The paramagnetic liposomes containing the Gd-DTPA bisamide complexes with 14 carbon atoms showed the highest relaxivity because the optimal length match between the hydrophobic chains of the DPPC and the ligand allowed very efficient packing of the paramagnetic complex into the liposome.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

Cyclam (1,4,8,11-tetraazacyclotetradecane) with one methylphosphonate pendant arm: a new ligand for selective copper(ii) binding.

The new ligand, [(1,4,8,11-tetraazacyclotetradecan-1-yl)methyl]phosphonic acid (H(2)te1P, H(2)L), was synthesized and its complexing properties towards selected metal ions were studied potentiometrically. The ligand forms a very stable complex with copper(ii)(logbeta(CuL)= 27.34), with a high selectivity over binding of other metal ions (i.e. logbeta(ZnL)= 21.03). The crystal structures of the free ligand (in its protonated form with bromide as counter-ion) and two copper(ii) complexes (obtained by crystallization at various pH) were determined. The free ligand adopts the common conformation for such macrocycles with the protonated nitrogen atoms in the corners of a virtual rectangle. In the trans-Br,O-[Cu(Br)(Hte1P)].H(2)O species, the central metal ion is surrounded by four in plane nitrogen atoms, one oxygen atom of the pendant moiety in the apical position and a bromide anion positioned trans to the oxygen atom, forming a distorted octahedral coordination sphere. In the compound [Cu(H(2)te1P)][Cu(Hte1P)]Br(3).6H(2)O, obtained from a highly acidic solution, the bromide anions are placed further away from the copper(ii) ion and the coordination environment (N(4)O) is thus square-pyramidal. In both structures, the protons are associated with non-coordinated phosphonate oxygen atoms.

Journal Article↗
PubMed2005

Synthesis, characterization, and pharmacokinetic evaluation of a potential MRI contrast agent containing two paramagnetic centers with albumin binding affinity.

A dinuclear gadolinium(III) complex of an amphiphilic chelating ligand, containing two diethylenetriamine-N,N,N',N'',N''-pentaacetate (DTPA) moieties bridged by a bisindole derivative with three methoxy groups, has been synthesized and evaluated as a potential magnetic resonance imaging (MRI) contrast agent. Nuclear magnetic relaxation dispersion (NMRD) measurements indicate that at 20 MHz and 37 degrees C the dinuclear gadolinium(III) complex has a much higher relaxivity than [Gd(DTPA)] (6.8 vs 3.9 s(-1) mmol(-1)). The higher relaxivity of the dinuclear gadolinium(III) complex can be related to its reduced motion and larger rotational correlation time relative to [Gd(DTPA)]. In the presence of human serum albumin (HSA) the relaxivity value of the noncovalently bound dinuclear complex increases to 15.2 s(-1) per mmol of Gd3+, due to its relatively strong interaction with this protein. The fitted value of the binding constant to HSA (Ka) was found to be 10(4) M(-1). Because of its interaction with HSA, the dinuclear complex exhibits a longer elimination half-life from the plasma, and a better confinement to the vascular space compared to the commercially available [Gd(DTPA)] contrast agent. Transmetalation of the dinuclear gadolinium(III) complex by zinc(II) has been investigated. Biodistribution studies suggest that the complex is excreted by the renal pathway, and possibly by the hepatobiliary route. In vivo studies indicated that half of the normal dose of the gadolinium(III) complex enhanced the contrast in hepatic tissues around 40 % more effectively than [Gd(DTPA)]. The dinuclear gadolinium(III) complex was tested as a potential necrosis avid contrast agent (NACA), but despite the binding to HSA, it did not exhibit necrosis avidity, implying that binding to albumin is not a key parameter for necrosis-targeting properties.

Animals↗
PubMed2005

Pentacopper(II) complexes of alpha-aminohydroxamic acids: uranyl-induced conversion of a 12-metallacrown-4 to a 15-metallacrown-5.

Effects of uranyl on the pentacopper(II) complexes of alpha-leucinehydroxamic acid and alpha-tyrosinehydroxamic acid were studied in water and methanol by means of electrospray ionisation mass spectrometry (ES-MS), absorption spectrophotometry, circular dichroism spectroscopy and proton NMR spectroscopy. All the measurements were consistent with the complete conversion of a 12-metallacrown-4 to a 15-metallacrown-5 upon addition of one equivalent of the uranyl ion. The uranyl ion is accommodated in the cavity formed by five copper(II) ions and five alpha-aminohydroxamate ligands. The 15-metallacrown-5 inclusion complexes have a high affinity for the uranyl ion. Competition studies showed that even in the presence of a large excess of calcium(II), the 15-metallacrown-5 remained stable, and no exchange reactions between calcium(II) and uranyl were observed. Extraction of uranyl from the 15-metallacrown-5 was also not detected in the presence of a large excess of 18-crown-6. Trivalent lanthanide ions can be partially sequestered by the 15-metallacrown-5, however, even these trivalent ions are displaced by uranyl.

Journal Article↗
PubMed2005

Spectroscopic properties of neodymium(III)-containing polyoxometalates in aqueous solution.

The spectroscopic properties of the neodymium(III)-containing polyoxometalates (POMs) [Nd(PW(11)O(39))(2)](11-), [Nd(PMo(2)W(9)O(39))(2)](11-), [Nd(PMo(4)W(7)O(39))(2)](11-), [Nd(PMo(6)W(5)O(39))(2)](11-), [Nd(SiMo(2)W(9)O(39))(2)](13-), [Nd(P(2)W(17)O(61))(2)](17-), [NdW(10)O(36)](9-), [NdP(5)W(30)O(110)](12-) and [NdAs(4)W(40)O(140)](25-) are described. Absorption spectra of aqueous solutions of the complexes have been recorded and the transition intensities are parameterised in terms of the Judd-Ofelt intensity parameters Omega(lambda) (lambda=2, 4, 6). Marked differences were found between the luminescence lifetimes of the complexes of the type Nd(POM) and those of the type Nd(POM)(2), due to a better shielding of the neodymium(III) ions from the bulk water molecules in the latter type of complexes.

Luminescent Measurements↗
PubMed2004

Rare-earth quinolinates: infrared-emitting molecular materials with a rich structural chemistry.

Near-infrared-emitting rare-earth chelates based on 8-hydroxyquinoline have appeared frequently in recent literature, because they are promising candidates for active components in near-infrared-luminescent optical devices, such as optical amplifiers, organic light-emitting diodes, .... Unfortunately, the absence of a full structural investigation of these rare-earth quinolinates is hampering the further development of rare-earth quinolinate based materials, because the luminescence output cannot be related to the structural properties. After an elaborate structural elucidation of the rare-earth quinolinate chemistry we can conclude that basically three types of structures can be formed, depending on the reaction conditions: tris complexes, corresponding to a 1:3 metal-to-ligand ratio, tetrakis complexes, corresponding to a 1:4 metal-to-ligand ratio, and trimeric complexes, with a 3:8 metal-to-ligand ratio. The intensity of the emitted near-infrared luminescence of the erbium(III) complexes is highest for the tetrakis complexes of the dihalogenated 8-hydroxyquinolinates.

Journal Article↗
PubMed2002

Mixed copper-lanthanide metallomesogens.

This paper describes the first examples of heteropolynuclear metallomesogens that contain both a transition metal ion and a trivalent lanthanide ion. Adducts were formed between a mesomorphic [Cu(salen)] complex (salen=2,2'-N,N'-bis(salicylidene)ethylenediamine) with six terminal tetradecyloxy chains and a lanthanide nitrate (Ln=La, Gd). Different stoichiometries were found, depending on the lanthanide ion: a trinuclear copper-lanthanum-copper complex [La(NO(3))(3)(Cu(salen))(2)] and a binuclear copper-gadolinium complex [Gd(NO(3))(3)Cu(salen)]. The compounds exhibit a hexagonal columnar mesophase (Col(H)) over a wide temperature-range with rather low melting temperatures. Although the clearing point could be observed for the parent [Cu(salen)] complex, the mixed f-d complexes decomposed in the high-temperature part of the mesomorphic domain before clearing. On the basis of X-ray diffraction measurements and molecular modelling, a structural model for the mesophase of the metal complexes is proposed.

Journal Article↗
PubMed2001

Coordinatively Unsaturated Metal Centers as Building Blocks for High Coordination Number Metallomesogens K.B. is a Postdoctoral Fellow of the Fund for Scientific Research, Flanders (Belgium). K.L. thanks the K.U. Leuven for financial support. Funding by the K.U. Leuven (GOA 98/3) and by the F.W.O.-Vlaanderen (G.0243.99) is gratefully acknowledged. The authors thank Prof. Görller-Walrand for providing laboratory facilities.

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Journal Article↗