Biomedical subjects
Roeland J. M. Nolte
Publications and source records attributed to Roeland J. M. Nolte.
Protein-Polymer Hybrid Amphiphiles This research was supported by the Netherlands Foundation for Chemical Research (CW-NWO), the EC TMR Sisitomas and ESF Smarton programs, and the Ministerio de Educación y Cultura (Spain). The authors thank H. P. M. Geurts, P. J. H. M. Adams, and J. L. J. van Dongen for experimental assistance.
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Self-Assembly and Manipulation of Crown Ether Phthalocyanines at the Gel-Graphite Interface This work was supported by the EU-TMR project SISITOMAS (project reference FMRX970099), the European Science Foundation through SMARTON, and the Volkswagen-Stiftung.
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X-ray Absorption Spectroscopic Studies of the Copper(I) Complexes of Crown Ether Appended Bis{(2-pyridyl)ethyl}amines and Their Dioxygen Adducts.
An X-ray absorption spectroscopic study of the Cu complexes of the bis{(2-pyridyl)ethyl}-appended monoaza crown ether 1, diaza crown ether 2, and diphenylglycoluril diaza basket 3 is reported. Following detailed analysis of the spectra of the crystallographically characterized model compound tetrapyridyl Cu(II) bis(nitrato pyridine) (4), the contributions of the ring atoms of the coordinating pyridine to the EXAFS were simulated using a multiple-scattering approach and the final parameters obtained by restrained refinement. Oxygenation of the Cu(I) complexes resulted in a large increase of the intensity of the major peak in the phase-corrected Fourier transform. This was interpreted as evidence for a &mgr;-eta(2):eta(2)-peroxo coordination mode of the oxygen between the copper ions, which had changed valence from Cu(I) to Cu(II) as judged from the edge position. This oxygen binding mode is reminiscent of that of hemocyanin, but the Cu-Cu distances are significantly shorter in the model than in the enzyme and vary with solvent. The EXAFS of the oxygenated complexes was simulated in a new approach in which, besides the parameters of the pyridine unit, those of an additional multiple scattering unit describing the geometry of the Cu-O(2)-Cu moiety were also refined.
Synthesis and Photophysical Properties of Porphyrin-Functionalized Molecular Clips.
Different clip-shaped receptor molecules functionalized at one side-wall with a porphyrin unit have been synthesized by a condensation involving a diamino glucoluril derivative and a porphyrin dione. A similar condensation reaction with a porphyrin tetraone resulted in porphyrin molecule with two receptor sites. The binding and photophysical properties of some of these porphyrin-receptor molecules are described.
Synthesis, Conformational Analysis, and Binding Properties of Molecular Clips with Two Different Side Walls.
A new general route toward the synthesis of diphenylglycoluril clips with two different side walls starting from the new precursor 6b and the known compound 2b is described. A variety of clips are accessible in this way, some of them containing metal binding ligand systems, viz. phenanthroline, pyridine, salophen, and porphyrin for future applications as supramolecular catalysts. The physical and binding properties of the new clips are presented and discussed.
Synthesis and Conformational Behavior of Rhodium(I) Metallohosts Derived from Diphenylglycoluril.
The design and synthesis of molecules containing both a substrate-binding cavity and a nearby catalytically active metal center is a useful approach to the development of synthetic systems that function according to the principles of enzymes. To this end the receptor molecule 2a, derived from diphenylglycoluril, was functionalized with triaryl phosphite ligands to give the receptor ligand 2d. Exchange reactions of 2d with (diketonate)Rh(CO)(2), (diketone = acetylacetone, dibenzoylmethane, or dipivaloylmethane) led to the formation of the metallohosts 3a-c, respectively. The properties and conformational behavior of these metal complexes were studied by NMR techniques. Reaction of compounds 3 with H(2) in the presence of a small excess of additional triphenyl phosphite yields the rhodium(I) hydride complex 5. The metallohosts are capable of binding dihydroxybenzene guests in their cavities by hydrogen bonding and pi-pi stacking interactions. On binding a substrate the conformational behavior of hosts 3a-c was affected considerably.
Dithiacrown Ether Substituted Porphyrazines: Synthesis, Single-Crystal Structure, and Control of Aggregation in Solution by Complexation of Transition-Metal Ions.
The synthesis of novel magnesium, copper, and metal-free porphyrazines, peripherally substituted with dithia-7-crown-2 (MPz(7)), dithia-15-crown-5 (MPz(15)), and dithia-18-crown-6 (MPz(18)) macrocycles is reported. These compounds are prepared starting from dicyanoethylene containing crown ethers 3, 2(1), and 2(2), respectively, which contain sulfur as well as oxygen heteroatoms. The "crowned" porphyrazines bind silver(I) and mercury(II) perchlorates. UV/vis spectroscopy and electron paramagnetic resonance measurements reveal that addition of the transition-metal ions leads to dimerization of the porphyrazine complexes. In the case of the dithia-18-crown-6-substituted porphyrazines, the dimers break up to form monomeric 6:1 guest-host complexes when more than 2 equiv of the metal ion is added. The single-crystal structures of the crown ether 2(2) and the porphyrazine MgPz(18) are presented. Compound C(14)H(20)N(2)O(4)S(2) (2(2)) crystallizes in the monoclinic space group P2(1)/c with a = 10.9310(13) Å, b = 19.383(3) Å, c = 8.6976(14) Å, beta = 108.898(11) degrees, V = 1743.5(5) Å(3), and Z = 4. The structure refinement converged to R = 0.0366 and R(w) = 0.0504. Compound C(56)H(82)MgN(8)O(17)S(8) (MgPz(18)) crystallizes in the triclinic space group P&onemacr; with a = 9.584(3) Å, b = 17.672(2) Å, c = 19.620(4) Å, alpha = 84.904(14) degrees, beta = 85.21(2) degrees, gamma = 89.29(2) degrees, V = 3298.4(13) Å(3), and Z = 2. The structure refinement converged to R1 = 0.0839 and wR2 = 0.2196. The electrical properties of H(2)Pz(18) have been studied by complex impedance spectroscopy. The bulk electrical conductivity of this compound is approximately 1 order of magnitude higher than that of the corresponding 18-crown-6 phthalocyanine.