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Biomedical subjects

R P Sijbesma

Publications and source records attributed to R P Sijbesma.

9 recordsLinked to original sources
PubMed2002

Hierarchical formation of helical supramolecular polymers via stacking of hydrogen-bonded pairs in water.

Bifunctional ureido-s-triazines provided with penta(ethylene oxide) side chains are able to self assemble in water, leading to helical columns via cooperative stacking of the hydrogen-bonded pairs (DADA array). Monofunctional ureido-s-triazines do not form such helical architectures. The presence of a linker, covalently connecting the two ureido-s-triazine units, is essential as it generates a high local concentration of aromatic units, favorable for stacking interactions. This hydrophobic stacking of the aromatic units occurs at concentrations as low as 5 x 10(-6) M and can be visualized by using fluorescence spectroscopy. The stacking generates a hydrophobic microenvironment that allows intermolecular hydrogen bonding to occur at higher concentrations because the hydrogen bonds are shielded from competitive hydrogen bonding with water. This hierarchical process results in the formation of a helical self-assembled polymer in water at concentrations above 10(-4) M. Chiral side chains attached to the ureido-s-triazine units bias the helicity of these columns as concluded from CD spectroscopy and "Sergeants and Soldiers" experiments.

Binding, Competitive↗
PubMed2001

A multiple hydrogen-bond scaffold based on dipyrimidin-2-ylamine.

A multiple hydrogen-bond array based on dipyrimidin-2-ylamine is presented, which is easily accessible. The influence of a preorganizing intramolecular hydrogen bond, tautomeric equilibria, and steric effects on the association behavior were investigated. X-ray diffraction shows that the molecules feature an ADA (acceptor-donor-acceptor) array of hydrogen-bonding sites in the solid state. The array persists in solution, and (1)H NMR titrations show that molecules with sterically nondemanding DAD arrays are selectively bound. [structure: see text]

Journal Article↗
PubMed2001

Inverse detection and heteronuclear editing in 1H-15N correlation and 1H-1H double-quantum NMR spectroscopy in the solid state under fast MAS.

Signal enhancement in heteronuclear correlation spectra as well as signal selection in 1H experiments can be achieved through inverse, i.e., 1H, detection in the solid state under fast MAS conditions. Using recoupled polarization transfer (REPT), a heteronuclear 1H-15N single-quantum correlation (HSQC) experiment is presented whose symmetrical design allows the frequency dimensions to be easily interchanged. By observing the 15N dimension indirectly and detecting on 1H, the sensitivity is experimentally found to be increased by factors between 5 and 10 relative to conventional 15N detection. In addition, the inverse 1H-15N REPT-HSQC scheme can be readily used as a filter for the 1H signal. As an example, we present the combination of such a heteronuclear filter with a subsequent 1H-1H DQ experiment, yielding two-dimensional 15N-edited 1H-1H DQ MAS spectra. In this way, specific selection or suppression of 1H resonances is possible in solid-state MAS experiments, by use of which the resolution can be improved and information can be unravelled in 1H spectra.

Journal Article↗
PubMed2000

Helical self-assembled polymers from cooperative stacking of hydrogen-bonded pairs.

The double helix of DNA epitomizes this molecule's ability to self-assemble in aqueous solutions into a complex chiral structure using hydrogen bonding and hydrophobic interactions. Non-covalently interacting molecules in organic solvents are used to design systems that similarly form controlled architectures. Peripheral chiral centres in assemblies and chiral side chains attached to a polymer backbone, have been shown to induce chirality at the supramolecular level, and highly ordered structures stable in water are also known. However, it remains difficult to rationally exploit non-covalent interactions for the formation of chiral assemblies that are stable in water, where solvent molecules can compete effectively for hydrogen bonds. Here we describe a general strategy for the design of functionalized monomer units and their association in either water or alkanes into non-covalently linked polymeric structures with controlled helicity and chain length. The monomers consist of bifunctionalized ureidotriazine units connected by a spacer and carrying solubilizing chains at the periphery. This design allows for dimerization through self-complementary quadruple hydrogen bonding between the units and solvophobically induced stacking of the dimers into columnar polymeric architectures, whose structure and helicity can be adjusted by tuning the nature of the solubilizing side chains.

Alkanes↗
PubMed1997

Reversible polymers formed from self-complementary monomers using quadruple hydrogen bonding.

Units of 2-ureido-4-pyrimidone that dimerize strongly in a self-complementary array of four cooperative hydrogen bonds were used as the associating end group in reversible self-assembling polymer systems. The unidirectional design of the binding sites prevents uncontrolled multidirectional association or gelation. Linear polymers and reversible networks were formed from monomers with two and three binding sites, respectively. The thermal and environmental control over lifetime and bond strength makes many properties, such as viscosity, chain length, and composition, tunable in a way not accessible to traditional polymers. Hence, polymer networks with thermodynamically controlled architectures can be formed, for use in, for example, coatings and hot melts, where a reversible, strongly temperature-dependent rheology is highly advantageous.

Dimerization↗
PubMed1987

Primary structure determination of seven novel N-linked carbohydrate chains derived from hemocyanin of Lymnaea stagnalis. 3-O-methyl-D-galactose and N-acetyl-D-galactosamine as constituents of xylose-containing N-linked oligosaccharides in an animal glycoprotein.

Hemocyanin from the freshwater snail Lymnaea stagnalis is a high-molecular-mass copper-containing glyco-protein which functions as oxygen carrier in the hemolymph. To release the carbohydrate chains, the protein was digested by pronase followed by hydrazinolysis and reduction. The oligosaccharide-alditols were purified by gel permeation chromatography on Bio-Gel P-4, followed by HPLC on a Lichrosorb-NH2 column. Using 500-MHz 1H-NMR spectroscopy, in conjunction with sugar, methylation and deamination analysis, the following seven novel primary oligosaccharide structures could be unravelled. (Formula: see text).

Acetylgalactosamine↗
PubMed1986

Primary structure of a low-molecular-mass N-linked oligosaccharide from hemocyanin of Lymnaea stagnalis. 3-O-methyl-D-mannose as a constituent of the xylose-containing core structure in an animal glycoprotein.

Hemocyanin from the freshwater snail Lymnaea stagnalis is a high-molecular-mass copper-containing oxygen-transport protein, which occurs freely dissolved in the hemolymph. It is a glycoprotein containing fucose, xylose, 3-O-methylmannose, 3-O-methylgalactose, mannose, galactose, N-acetylgalactosamine and N-acetylglucosamine residues as sugar constituents. The N-glycosidic carbohydrate chains of this glycoprotein were released by hydrazinolysis of a pronase digest and subsequently fractionated as oligosaccharide-alditols on Bio-Gel P-4 followed by Lichrosorb-NH2. Investigation with 500-MHz 1H-NMR spectroscopy, in conjunction with sugar and methylation analysis revealed the lowest-molecular-mass glycan chain to have the structure: (Formula: see text).

Animals↗