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PubMed2005

Dissipative particle dynamics study on the interfaces in incompatible A/B homopolymer blends and with their block copolymers.

Dissipative particle dynamics, a simulation technique appropriate at mesoscopic scales, has been applied to investigate the interfaces in immiscible binary A/B homopolymer blends and in the ternary systems with their block copolymers. For the binary blends, the interfacial tension increases and the interface thickness decreases with increasing Flory-Huggins interaction parameter chi while the homopolymer chain length is fixed. However, when the chi parameter and one of the homopolymer chain length is fixed, increasing another homopolymer chain length will induce only a small increase on interfacial tension and slight decrease on interface thickness. For the ternary blends, adding the A-b-B block copolymer will reduce the interfacial tension. When the mole number of the block copolymer is fixed, longer block chains have higher efficiency on reducing the interfacial tension than the shorter ones. But for the block copolymers with fixed volume fraction, shorter chains will be more efficient than the longer ones on reducing the interfacial tension. Increasing the block copolymer concentration reduces interfacial tension. This effect is more prominent for shorter block copolymer chains.

Journal Article↗
PubMed1996

The O polysaccharide chain of the lipopolysaccharide from Vibrio cholerae O76 is a homopolymer of N-[(S)-(+)-2-hydroxypropionyl]-alpha-L-perosamine.

Chemical and serological studies of LPS from Vibrio cholerae O76 (O76) were performed. The LPS of O76 contained D-glucose, D-galactose, L-glycero-D-manno-heptose, D-fructose, D-glucosamine, D-quinovosamine (2-amino-2,6-dideoxy-D-glucose) and L-perosamine (4-amino-4,6-dideoxy-L-mannopyranose). The sugar composition of the LPS from O76 was quite similar to that of LPS from V. cholerae O1 with the exception of the presence of a small amount of D-galactose in the LPS of O76. However, perosamine, a major sugar component of the LPS from O76, was in the L configuration in contrast to the D configuration of the perosamine in the LPS of V. cholerae O1. The L-perosamine was N-acylated with an (S)-(+)-2-hydroxypropionyl group in the LPS from O76. Structural analysis by NMR spectroscopy, as well as GC/MS, revealed that the O polysaccharide chain of the LPS from O76 was an alpha(1-->2)-linked homopolymer of N-[(S)-(+)-2-hydroxypropionyl]-L-perosamine. The serological cross-reactivity between the LPS of O76 and the LPS from other strains, such as V. cholerae O1 (Ogawa and Inaba O forms), Vibrio bio-serogroup 1875 (Original and Variant strains), V. cholerae O140 (Hakata) and Yersinia enterocolitica O9, was examined in passive haemolysis tests with sheep red blood cells that had been sensitized with LPS and antisera raised against whole cells of these bacteria. The latter six strains have in common the O antigen that includes Inaba antigen factor C, in addition to their own O-antigenic factors. Thus, they crossreact serologically. The O polysaccharide chains of the LPS of these six trains are known to consist exclusively of alpha(1-->2)-linked D-perosamine homopolymers and differences are found only among the N-acyl substituents. In passive haemolysis tests, the LPS of O76 did not cross-react serologically with any of the other LPS examined. Thus, the results obtained in this study support the hypothesis that Inaba antigen factor C, associated with the O antigens of these six strains, which include V. cholerae O1, is related substantially and exclusively to their alpha(1-->2)-linked homopolymers of N-acylated D-perosamine, and not to such homopolymers of N-acylated L-perosamine.

Acetylation↗
PubMed1996

Expression and loading of recombinant heavy and light chain homopolymers of rat liver ferritin.

The full-length genes for the heavy (H) and light (L) chains of ferritin isolated from a rat liver cDNA library were amplified using polymerase chain reaction. Each was inserted at the unique BglII site downstream of the p10 promoter of the baculovirus transfer vector pAcUW21. The genes were transferred separately to infectious Autographa californica nuclear polyhedrosis virus (AcNPV) expression vectors after in vivo homologous recombination. Ferritin homopolymers of either H or L chain were expressed up to approximately 1.5 mg per 100 ml of infected cultures (2.0 x 10(6) cells/ml) of Spodoptera frugiperda, Sf-21, 4 days postinfection. Both recombinant H chain ferritin (rH-Ft) and recombinant L chain ferritin (rL-Ft) assembled as multi-subunit complexes with predicted electrophoretic mobility. Neither rH-Ft nor rL-Ft homopolymers had ferroxidase activity in 50 mM NaCl, as we have reported previously for native ferritin [D. DeSilva, D. M. Miller, D.W. Reif, and S.D. Aust (1992) Arch. Biochem. Biophys. 293,409-415]. When ceruloplasmin, a copper-containing protein, was used as a ferroxidase, rH-Ft loaded iron at rates comparable those obtained with native rat liver apoferritin, but rL-Ft failed to load any iron. The initial rate of Fe(II) oxidation catalyzed by ceruloplasmin was increased in the presence of rH-Ft or rat liver ferritin but not in the presence of rL-Ft. A maximum of about 2500 atoms of iron were incorporated into both rH-Ft and rat liver ferritin. These results demonstrate that both rat liver rH-Ft and rL-Ft homopolymer can be properly produced by the baculovirus expression system and ceruloplasmin can only load iron into H chain ferritin. The physiological significance of these results is discussed.

Animals↗
PubMed2000

Radiolabeling, stability, and body distribution in rats, of low molecular weight polylactide homopolymer and polylactide-polyethyleneglycol copolymer.

In order to study its fate in vivo, a low molecular-weight polylactide homopolymer was derivatized with a p-methoxyphenyl moiety, so as to make it susceptible to radiolabeling with 125I. A low molecular weight polylactide-polyethyleneglycol copolymer capped with ap-methoxyphenyl residue was also synthesized. The derivatized polymers were successfully [125I]iodinated in organic medium. The radiolabeled products were freed from [125I]iodide by dialysis and shown to be stable for 24 h on incubation at 37 degrees C in buffered saline or in blood. On longer incubation at 37 degrees C in buffered saline the radiolabeled polylactide released [125I]iodide and [125I]iodinated 3-(p-methoxyphenyl)propionic acid. The radiolabeled copolymer was more stable on incubation at 37 degrees C in buffered saline, but some [125I]iodide was released. The tissue distribution of radioactivity was determined 5 min, 1, 5 and 24 h after injecting male rats with 125I-labeled homopolymer or copolymer. Intravenous, intraperitoneal and subcutaneous injection routes were employed. Further rats were injected with [125I]iodide, to aid interpretation of the data. After administration of labeled homopolymer, a high concentration of radioactivity was found in the liver tissue. The levels slowly decreased over 24 h, and the polymer was successively found in the small and large intestine and the faeces. This is probably indicative of excretion via the bile. Concurrently radioactivity was excreted in the urine. After administration of labeled copolymer, a high concentration of radioactivity was found in the liver and the residual soft tissue, the latter fraction containing two-thirds of the radioactivity one hour after injection. The precise tissue location that this result indicates was not identified. After 1 h radioactivity was excreted in the faeces, again probably via the bile, and in the urine. Tissue distributions after intraperitoneal or subcutaneous injections were concordant with the above results and interpretations, with the additional factor of slow clearance from the injection site.

Animals↗
PubMed1997

Evolutionary relationship among rfb gene clusters synthesizing mannose homopolymer as O-specific polysaccharides in Escherichia coli and Klebsiella.

In order to clarify the evolutionary relationship among rfb gene clusters synthesizing mannose homopolymer as O-specific polysaccharides in Escherichia coli and Klebsiella, we studied the DNA sequence of the boundary region between the rfb and his genes in a series of strains possessing mannose homopolymer as O-specific polysaccharide. All had a characteristic gene organization carrying no gene between the rfb and his genes. Further, the recombination event was suggested to occur at the same site of the hisI gene in those strains. It was suggested that there was a close evolutionary relationship among rfb gene clusters synthesizing mannose homopolymer as O-specific polysaccharide in E. coli and Klebsiella.

Bacterial Proteins↗
PubMed2005

Hydration of sulfonated polyimide membranes. II. Water uptake and hydration mechanisms of protonated homopolymer and block copolymers.

The hydration of sulfonated polyimide membranes in their protonated form is probed by infrared spectrometry using a recently described method. The membranes considered are the homopolymer, made of identical sulfonated repeat units, and two block copolymers composed of these units plus similar ones with no sulfonic groups in two different proportions. The experiments consist of registering series of spectra of these membranes at various hygrometries of the surrounding atmosphere. The quantitative analysis of the evolution of these spectra allows one to measure precisely the water uptake and to define in terms of chemical reactions the various hydration mechanisms that are active at a definite value of the hygrometry. It shows how the dried homopolymer significantly differs from the two dried block copolymers: in the homopolymer, a good proportion of SO(3)H groups that represent 83% of sulfonate groups, cannot establish H-bonds on C=O groups that are in a relatively small number. As a consequence, all coexisting SO(3)(-) groups are H-bonded to single H(3)O(+) cations with no extra H(2)O molecules. In both dried block copolymers, each SO(3)H group (60% of the sulfonate groups) establishes H-bonds on C=O groups that are in a sufficiently great number. These H-bonds stabilize these SO(3)H groups, and coexisting SO(3)(-) groups are H-bonded to cations that are found in the form of H(5)O(2)(+) or H(7)O(3)(+) that contain several H(2)O molecules. When the hygrometry increases, these differences get less marked but can be precisely defined.

Journal Article↗
PubMed2006

Comparison of ribonucleic acid homopolymer ionization energies and charge injection barriers.

Thin films of guanosine and uridine ribonucleic acid (RNA) homopolymers (poly rG, poly rU) were grown in high vacuum in several steps on highly oriented pyrolytic graphite (HOPG) using electrospray deposition. Between deposition steps, the sample surface was characterized with X-ray and ultraviolet photoemission spectroscopy (XPS, UPS). The resulting spectra series allowed the determination of the orbital alignment at the HOPG interface, as well as the ionization energies of the homopolymer thin films. Comparison with earlier results on cytidine and adenosine RNA homopolymers (poly rC, poly rA) indicates significant ionization energy and charge injection barrier differences between purines and pyrimidines.

Graphite↗
PubMedDate not supplied

Frictional properties of dilute block-copolymer solutions and homopolymer solutions. Application to molecular weight determination.

An equation for the translational diffusion coefficient of block copolymers in dilute solution has been obtained by modifying Zimm's equation for homopolymers to take into account the existence of dissimilar segments in block copolymers. Illustrative calculations for homopolymers and block copolymers have been made and the results for homopolymers have been compared with experiments and with the calculations of Yamakawa and Fujii. A procedure has been proposed to determine the molecular weight of a block copolymer from measurements of its limiting viscosity number and its sedimentation coefficient or translational diffusion coefficient.

Mathematics↗
PubMed1993

N-3-hydroxypropionyl-alpha-D-perosamine homopolymer constituting the O-chain of lipopolysaccharides from Vibrio bioserogroup 1875 possessing antigenic factor(s) in common with O1 Vibrio cholerae.

A structural study was performed by 13C-n.m.r. spectroscopy and methylation analysis of the O-chain of lipopolysaccharide (LPS) from Vibrio bioserogroup 1875 possessing antigenic factor(s) in common with O1 Vibrio cholerae. It was demonstrated to contain a linear homopolymer of (1-->2)-linked N-3-hydroxypropionyl-alpha-D-perosamine [4-(3-hydroxypropanamido)-4,6-dideoxy-alpha-D-mannopyranose], which is very similar to, but not identical with, both (1-->2)-linked linear N-3-deoxy-L-glycero-tetronyl(S-2,4-dihydroxybutyryl)-alpha-D - perosamine homopolymer and (1-->2)-linked linear N-acetyl-alpha-D-perosamine homopolymer which constitute the O-chains of O1 V. cholerae and non-O1 V. cholerae bioserogroup Hakata LPS respectively.

Acetylation↗
PubMed2006

Selection and slippage creating serine homopolymers.

Highly repetitive sequence within proteins is an abundant feature yet is considered by some to be the protein equivalent of "junk DNA." Homopolymer sequences, the most highly repetitive of this group, are typically encoded by trinucleotide repeats at the DNA level. It is thought that many of these sequences are produced by a replicative slippage mechanism. Recent studies suggest that these highly mutable regions within proteins may allow for rapid morphological evolution emerging from the increased variability afforded by such coding structures. However, in a homopolymer, it is difficult to determine if the repeated amino acid is due to slippage at the DNA level or due to selection at the protein level. Here we develop and test a model to detect cases for which the homopolymer tract has clearly been selected for, with no evidence of slippage at the DNA level. The polyserine tract within the phosphatidylserine receptor protein is used as an excellent example of one such case.

Amino Acid Sequence↗
PubMed2004

Wavelet treatment of the intrachain correlation functions of homopolymers in dilute solutions.

Discrete wavelets are applied to the parametrization of the intrachain two-point correlation functions of homopolymers in dilute solutions obtained from Monte Carlo simulations. Several orthogonal and biorthogonal basis sets have been investigated for use in the truncated wavelet approximation. The quality of the approximation has been assessed by calculation of the scaling exponents obtained from the des Cloizeaux ansatz for the correlation functions of homopolymers with different connectivities in a good solvent. The resulting exponents are in better agreement with those from recent renormalization group calculations as compared to the data without the wavelet denoising. We also discuss how the wavelet treatment improves the quality of data for correlation functions from simulations of homopolymers at varied solvent conditions and of heteropolymers.

Journal Article↗
PubMed2006

Topology of pseudoknotted homopolymers.

We consider the folding of a self-avoiding homopolymer on a lattice, with saturating hydrogen bond interactions. Our goal is to numerically evaluate the statistical distribution of the topological genus of pseudoknotted configurations. The genus has been recently proposed for classifying pseudoknots (and their topological complexity) in the context of RNA folding. We compare our results on the distribution of the genus of pseudoknots, with the theoretical predictions of an existing combinatorial model for an infinitely flexible and stretchable homopolymer. We thus obtain that steric and geometric constraints considerably limit the topological complexity of pseudoknotted configurations, as it occurs for instance in real RNA molecules. We also analyze the scaling properties at large homopolymer length, and the genus distributions above and below the critical temperature between the swollen phase and the compact-globule phase, both in two and three dimensions.

Binding Sites↗
PubMed2002

Tricontinuous cubic structures in ABC/A/C copolymer and homopolymer blends.

Using the Monte Carlo lattice-simulation technique, we present numerical evidence of the formation of gyroid and nongyroid tricontinuous cubic phases in high polymeric systems of ABC/A/C triblock copolymer and homopolymer blends. By increasing the volume fraction of homopolymer, a remarkable phase sequence G (gyroid) --> D (diamond) --> P (primitive) is observed, which is common to certain surfactant systems. Our results indicate that the ABC triblock copolymer system with blending homopolymers may be a zoo of cubic phases, suitable for comparative studies of these phases.

Lipid Bilayers↗
PubMed2006

Phase behavior of symmetric ternary block copolymer-homopolymer blends in thin films and on chemically patterned surfaces.

The phase diagram of symmetric ternary blends of diblock copolymers and homopolymers in thin films was determined as a function of increasing volume fraction of homopolymer (phi(H)) and was similar to that for these materials in the bulk. Blends with compositions in the lamellar region of the diagram (phi(H)< or =0.4) could be directed to assemble into ordered lamellar arrays on chemically striped surfaces if the characteristic blend dimension (L(B)) and the period of the stripes (L(S)) were commensurate such that L(S)=L(B)+/-0.10L(B). Blends with compositions in the microemulsion region of the diagram (phi(H) approximately 0.6) assembled into defect-free lamellar phases on patterned surfaces with L(S)> or =L(B), but formed coexisting lamellar (with period L(S)) and homopolymer-rich phases when L(S)<L(B).

Journal Article↗
PubMed1996

An N-[(R)-(-)-2-hydroxypropionyl]-alpha-L-perosamine homopolymer constitutes the O polysaccharide chain of the lipopolysaccharide from Vibrio cholerae O144 which has antigenic factor(s) in common with V. cholerae O76.

Chemical and serological studies were performed with the lipopolysaccharide (LPS) from Vibrio cholerae O144 (O144). The LPS of O144 contained D-glucose, D-galactose, L-glycero-D-manno-heptose, D-fructose, D-quinovosamine (2-amino-2,6-dideoxy-D-gluco-pyranose) and L-perosamine (4-amino-4,6-dideoxy-L-manno-pyranose). The perosamine, a major component sugar of the LPS from O144, was in an L-configuration, as is also the case in the LPS from V. cholerae O76 (O76), in contrast to the D-configuration of the perosamine in the LPS of V. cholerae O1. A structural analysis revealed that the O polysaccharide chain of the LPS from O144 is an alpha(1-->2)-linked homopolymer of (R)-(-)-2-hydroxypropionyl-L-perosamine. The serological cross-reactivity between O144 and O76 was clearly revealed by cross-agglutination and cross-agglutinin absorption tests with whole cells, as well as by passive hemolysis tests with sheep red-blood cells that had been sensitized with the LPS from O144 and O76. In contrast, in passive hemolysis tests, the LPS of O144 did not cross-react serologically with the LPSs from other strains such as V. cholerae O1 (Ogawa and Inaba), V. cholerae O140, Vibrio bio-serogroup 1875 (Original and Variant) and Yersinia enterocolitica O9. The LPSs from these strains consist of O polysaccharide chains composed of alpha(1-->2)-linked homopolymers of D-perosamine with various N-acyl groups, and they share the Inaba antigen factor C of V. cholerae O1 in common. The results obtained in this study demonstrate that the absolute configuration of the perosamine residue in homopolymers plays a very important role in the expression of the serological specificity of the Inaba antigen factor C of V. cholerae O1.

Agglutination Tests↗
PubMed1997

Homopolymer mutational hot spots mediate herpes simplex virus resistance to acyclovir.

In the majority of cases, the mechanism underlying the resistance to acyclovir (ACV) of herpes simplex viruses (HSVs) is thymidine kinase (TK) deficiency. Plaque isolates from eight ACV-resistant (ACVr) clinical isolates from AIDS patients, of which five reactivated, were sequenced to determine the genetic lesion within the tk gene conferring resistance and whether this may have correlated with reactivation potential. Mutations were clustered within two homopolymer nucleotide stretches. Three plaque isolates (1737-14, 90-150-3, and 89-650-5) had insertion mutations within a stretch of 7 guanosines, while two isolates (89-063-1 and 89-353-1) had frameshift mutations within a stretch of 6 cytosines (a deletion and an insertion, respectively). Mutations resulted in premature termination codons, and the predicted 28- and 32-kDa truncated TK products were detected by Western blot analysis of virus-infected cell extracts. The repair of one homopolymer frameshift mutation (in isolate 1737-14) restored TK activity, demonstrating that this mutation is the basis of TK deficiency. Of the five reactivated isolates, four were TK deficient and contained frameshift mutations while the fifth retained TK activity because of its altered-TK or Pol- phenotype. These data demonstrate that the majority of ACVr clinical isolates contain frameshift mutations within two long homopolymer nucleotide stretches which function as hot spots within the HSV tk gene and produce nonfunctional, truncated TK proteins.

Acyclovir↗
PubMedDate not supplied

A homopolymer stretch composed of variable numbers of cytidine residues in the terminal repeats of infectious laryngotracheitis virus.

A homopolymer stretch composed of variable numbers of cytidine residues was found within the inverted terminal repeats of infectious laryngotracheitis virus (ILTV). A polymerase chain reaction procedure was developed to amplify a 750-bp fragment containing this homopolymer stretch. This fragment was then sequenced directly to determine the number of repeated cytidine residues in this homopolymer stretch, which could be used for strain differentiation. By this procedure, vaccine strains of tissue culture origin could be differentiated into two types: type I contains eight repeated cytidine residues, whereas type II contains 10 such residues. Vaccine strains of chicken embryo origin could also be divided into two types: type I contains mainly 11 repeated cytidine residues, whereas type II contains 15-21 such repeats. In comparison, two of the five field isolates examined contain 12-13 repeats; the other three field isolates contain 15-19 repeats, which were similar to the type II chicken-embryo-origin vaccines. The number of repeated cytidine residues described here could serve as a marker for the strain differentiation and epidemiologic study of ILTV.

Animals↗
PubMed1992

Evaluation of polylactic acid homopolymers as carriers for bone morphogenetic protein.

Polylactic acid (PLA) homopolymers with molecular weights of 105,000; 21,000; 3300; 650; and 160d (PLA105000, PLA21000, PLA3300, PLA650, and PLA160, respectively) were prepared and evaluated as carriers for bone morphogenetic protein (BMP). Composites consisting of 4 mg of water-soluble, semipurified BMP and 100 mg of one of the PLA homopolymers were implanted into the dorsal muscles of mice. PLA105000/BMP, PLA21000/BMP, PLA3300/BMP, and PLA160/BMP composites failed to induce new bone formation; PLA105000, PLA21000, and PLA3300 elicited foreign-body reactions or chronic inflammation (or both), and PLA160 produced tissue necrosis. PLA650/BMP composites induced cartilage formation within one week and induced bone with hematopoietic marrow at three weeks postimplantation. PLA650/BMP composites were completely absorbed and replaced by new bone. The results suggest that within this group of PLA homopolymers, PLA650 may be the only type suitable for use as a BMP carrier.

Animals↗