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At least 235 records · Page 13Linked to original sources
PubMed2001

Reentrant coil-to-globule-to-coil transition of a single linear homopolymer chain in a water/methanol mixture.

Both water and methanol are good solvents for poly( N-isopropylacrylamide) (PNIPAM) at room temperature, but strangely not a mixture of them. Using narrowly distributed linear PNIPAM chains (M(w) = 2.6x10(7) g/mol and M(w)/M(n)<1.1), we have, for the first time, observed a coil-to-globule-to-coil transition of a single PNIPAM chain when methanol was gradually added into water. This novel reentrant transition leads to insight into the complexation between methanol and water. We also found that the chain was crumpled in its globule state and the globule still contained approximately 80% of solvent in its hydrodynamic volume.

Journal Article↗
PubMed1998

Crystallization and preliminary X-ray diffraction analysis of antigen-binding fragments which are specific for antigenic conformations of sialic acid homopolymers.

Meningococcal meningitis is a severe childhood disease which often results in significant disability or death. Two major etiological agents of meningitis are the group B meningococci and capsular type K1 E. coli. The virulence of these organisms is attributable to structural mimicry between their common alpha(2-8)-polysialic acid capsular polysaccharide and human tissue antigens, which allows the bacteria to evade immune surveillance. There is currently no effective vaccine to protect against this infection. It has been demonstrated that the capsular polysaccharide of the bacteria can adopt a unique 'antigenic conformation'. This antigenic conformation has formed the basis for the development of an N-propionylated polysialic acid vaccine. Immunization trials in mice with this vaccine show the production of two groups of antibodies, of which only N-propionylated polysialic acid-specific were protective. Knowledge of the structure of the antigen-binding site which recognizes the protective epitope is essential to determining the antigenic conformation of the polysaccharides, and is a critical aspect in understanding and improving the action of potential vaccines. The antigen-binding fragments (Fab) of one protective (13D9) and one non-protective (6B9) monoclonal antibody specific for the capsular polysaccharides of group B meningococci have been crystallized and have undergone preliminary X-ray diffraction analysis. Both crystals are observed to scatter X-rays to approximately 1.7 A resolution at the A1 station at the Cornell High-Energy Synchrotron Source. 13D9 has an orthorhombic unit cell with a = 41.8, b = 102.3, c = 134.7 A, with space group P212121. Fab 6B9 has an orthorhombic unit cell with a = 89.6, b = 132.0 and c = 36.9 A, with space group P21212.

Animals↗
PubMed1990

Toxicity of, and histological lesions caused by, ribosome-inactivating proteins, their IgG-conjugates, and their homopolymers.

The toxicity of, and the lesions brought about by, several ribosome-inactivating proteins (bryodin, gelonin, momordin, pokeweed antiviral protein from seeds, saporin 6, trichokirin and momorcochin-S), either native, or conjugated to bovine IgG, or polymerized, were studied in the mouse. Severe necrotic liver damage was the main lesion present in animals receiving lethal doses of the proteins. The toxicity of ribosome-inactivating proteins increased after conjugation to IgG or homopolymerization. The toxicity of conjugates to mouse was not predictable from the inhibitory activity on cell-free protein synthesis.

Animals↗
PubMed2001

Cross-reactivity of Epstein-Barr virus-specific immunoglobulin M antibodies with cytomegalovirus antigens containing glycine homopolymers.

Timely and reliable detection of acute primary human cytomegalovirus (HCMV) infection is important in prenatal screening programs and for differential diagnosis of infectious mononucleosis-like disease. Enzyme-linked immunosorbent assays (ELISAs) based on HCMV proteins enable the sensitive detection of immunoglobulin M (IgM) antibodies during primary infection. However, concerns have been raised about possible cross-reactivities of the HCMV antigens used for the design of such ELISAs with IgM antibodies induced by Epstein-Barr Virus (EBV). In this study we investigated whether IgM antibodies generated during acute EBV infection reacted with recombinant HCMV antigens. Serum samples from patients with primary EBV infection frequently scored positive when tested in different HCMV IgM ELISAs, irrespective of whether conventional or recombinant antigens were used for the design of the HCMV IgM assays. Such cross-reactive IgM antibodies were found to be directed against short glycine-rich motifs contained within the nonstructural HCMV proteins pUL44 and pUL57. Further analyses revealed that these glycine-rich motifs were major antigenic domains for IgM antibodies induced during HCMV infection. Their deletion from recombinant proteins abrogated reactivity with IgM synthesized during HCMV infection. EBV-induced IgM antibodies that reacted with HCMV antigens showed similar kinetics of reactivity in HCMV- or EBV-specific assays in the course of primary EBV infection, indicating that the two populations of antibodies were highly overlapping. The results demonstrate that primary EBV infection leads to the induction of IgM antibodies that specifically bind to widely used diagnostic antigens of HCMV. This has to be considered in the interpretation of HCMV-specific IgM assays.

Amino Acid Motifs↗
PubMed2005

Block copolymer adsorption from a homopolymer melt to an amine-terminated surface.

Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiO(x), and SiO(x) functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiO(x).

Journal Article↗
PubMed1994

A new approach to determining homopolymer domain sizes in polycarbonate-polyether dialysis membranes by solid-state NMR.

The size of micro-separated domains of polyether (PEO), -[CH2CH2O]n-, and polycarbonate (PC), -[(C6H4)-C(CH3)2-(C6H4)-OCO2]m-, in the dialysis membrane 'Gambrane' have been determined using an advanced solid-state NMR technique which exploits differences in 1H spin diffusion. The characteristic diameter of a PEO domain is 4.8 +/- 1.4 nm and that of PC is 5.2 +/- 1.4 nm with a mixed phase region of 0.8 +/- 0.5 nm.

Dialysis↗
PubMed1988

Inhibition of human neutrophil elastase by polyguanylic acid and other synthetic RNA homopolymers.

Human neutrophils contain large amounts of a neutral serine protease, human neutrophil elastase (HNE), which has been implicated as a mediator of acute and chronic lung injury. We found that this enzyme is effectively inhibited, at physiological ionic strength, by several synthetic non-base-paired polyribonucleotides. Among the most active of these is polyguanylic acid (poly G). Inhibitory activity is greatest with high-molecular-weight poly G fractions, but poly G fractions even as low as 60K Mr (app) are effective. Both amidolysis of synthetic elastase substrates, such as succinyl-ala-ala-ala-p-nitroanilide, and proteolysis of elastin are blocked. Poly G inhibits elastin proteolysis even when subsequently added to mixtures of elastin and HNE that have first been preincubated together for 10 min. Under these conditions, polyribosylribitol phosphate, a polyanion derived from Haemophilus influenzae capsular polysaccharide, is not inhibitory. Complex formation between HNE and poly G is dependent on ionic rather than covalent interactions, since it is blocked by 0.6 M NaCl but not by inactivation of the enzyme's catalytic-site serine residue with diisopropylfluorophosphate. However, nonspecific ionic interactions alone cannot explain complex formation, since pancreatic elastase and cathepsin G, an even more basic serine protease from human neutrophils, do not form complexes with poly G, even at low ionic strength. Moreover, in the presence of the amphiphiles taurocholic acid and glycocholic acid, HNE is much less effectively blocked by poly G. Peptide chloromethyl ketone-inactivate HNE (which has its extended substrate-binding pocket occupied by the peptidyl inactivator) also fails to form complexes with poly G. These results indicate that HNE may utilize both hydrophobic and ionic binding sites to couple with poly G, and suggest that these sites may be close to or within the extended substrate-binding pocket of the enzyme.

Amino Acid Chloromethyl Ketones↗
PubMed1979

Characterization of homogeneous and pseudocomposite homopolymers and copolymers for articular cartilage replacement.

Semicrystalline swollen polymeric networks are prime candidates for biomedical applications. Purity, controlled structure, easy preparation, non-biodegradability and improved mechanical properties are some of their most important characteristics. New articular cartilage simulants in the form of hydrogels with surface hydroxyl groups have been developed and characterized. The mechanical properties and physical behavior of these materials are described by high elastic moduli, ultimate tensile strength and elongation at break, low tear propagation resistance and excellent friction properties. Crystallinities vary between 15% and 35% and the crystallites are stable within the range of practical applications. The hydrogels show no permeability to hyaluronic acid and can be grafted with cationic monomers or polymers to form boundary lubricant layers. Techniques have also been developed for the preparation of deformable pseudocomposites consisting of layers of swollen semicrystalline and amorphous polymer.

Biocompatible Materials↗