Biomedical subjects

S Zhou

Publications and source records attributed to S Zhou.

At least 55 records · Page 3Linked to original sources

PubMed2002

Extensive mosaic structure revealed by the complete genome sequence of uropathogenic Escherichia coli.

We present the complete genome sequence of uropathogenic Escherichia coli, strain CFT073. A three-way genome comparison of the CFT073, enterohemorrhagic E. coli EDL933, and laboratory strain MG1655 reveals that, amazingly, only 39.2% of their combined (nonredundant) set of proteins actually are common to all three strains. The pathogen genomes are as different from each other as each pathogen is from the benign strain. The difference in disease potential between O157:H7 and CFT073 is reflected in the absence of genes for type III secretion system or phage- and plasmid-encoded toxins found in some classes of diarrheagenic E. coli. The CFT073 genome is particularly rich in genes that encode potential fimbrial adhesins, autotransporters, iron-sequestration systems, and phase-switch recombinases. Striking differences exist between the large pathogenicity islands of CFT073 and two other well-studied uropathogenic E. coli strains, J96 and 536. Comparisons indicate that extraintestinal pathogenic E. coli arose independently from multiple clonal lineages. The different E. coli pathotypes have maintained a remarkable synteny of common, vertically evolved genes, whereas many islands interrupting this common backbone have been acquired by different horizontal transfer events in each strain.

Acute Disease↗

PubMed2002

Gas-liquid chromatography with a volatile "stationary" liquid phase.

A unique type of gas-liquid chromatography is described in which both mobile and "stationary" phases are composed of synthetic mixtures of helium and carbon dioxide. At temperatures below the critical point of the binary mixture and pressures above the vapor pressure of pure liquid carbon dioxide, helium and carbon dioxide can form two immiscible phases over extended composition ranges. A binary vapor phase enriched in helium can act as the mobile phase for chromatographic separations, whereas a CO2-rich liquid in equilibrium with the vapor phase, but condensed on the column wall, can act as a pseudostationary phase. Several examples of chromatographic separations obtained in "empty" capillary columns with no ordinary stationary liquid phase illustrate the range of conditions that produce such separations. In addition, several experiments are reported that confirm the proposed two-phase hypothesis. The possible consequences of the observed chromatographic phenomenon in the field of supercritical fluid chromatography with helium headspace carbon dioxide are discussed.

Journal Article↗

PubMed2002

A locust DNA-binding protein involved in gene regulation by juvenile hormone.

Although juvenile hormone (JH) has essential roles in insect development and reproduction, the molecular mechanisms of gene regulation by JH remain an enigma. In Locusta migratoria, the partially palindromic 15-nt sequence, GAGGTTCGAG(A)/(T)CCT(T)/(C), found upstream of a JH-induced gene, jhp21, was designated as a putative juvenile hormone response element (JHRE). When JH-deprived adult female locusts were treated with the active JH analog, methoprene, a fat body nuclear factor that bound specifically to JHRE appeared after 24 h. Binding exhibited a preference for an inverted repeat with GAGGTTC in the left half-site, a single nucleotide spacer, and a right half-site in which some variation is acceptable. Binding to JHRE was abolished by phosphorylation catalyzed by a C-type protein kinase present in the nuclear extracts. The DNA-binding protein is thus believed to be a transcription factor, which is brought to an active state through the action of JH and then participates in the regulation of certain JH-dependent genes.

Animals↗

PubMed2002

Sequences of elongation factors-1 alpha and -1 gamma and stimulation by juvenile hormone in Locusta migratoria.

Two cDNAs encoding the alpha and gamma subunits of translation elongation factor-1 (EF-1) have been cloned and sequenced from the African migratory locust, Locusta migratoria. Southern blotting and real-time PCR analyses indicated that these sequences represent single copy genes. Comparison with sequences from other species indicated greater conservation for EF-1 alpha than for EF-1 gamma. The developmental profiles for EF-1 alpha and -1 gamma mRNA expression in the fat body paralleled reported changes in the hemolymph juvenile hormone (JH) titer in the fifth instar and were elevated during early reproductive maturation in the female adult. In maturing adults, there was a greater accumulation of EF-1 alpha and -1 gamma transcripts in females than in males. The levels of both transcripts were greatly increased by an enriched diet, previously shown to elevate JH titers and accelerate vitellogenin production. Treating JH-deprived adult females with the JH analog, methoprene, resulted in more than doubling of transcript levels of both genes, supporting the hypothesis that JH could stimulate the accumulation of LmEF-1 alpha and -1 gamma transcripts. We suggest that production of elongation factors, increased by JH, may contribute to the massive protein synthesis required for egg production.

Amino Acid Sequence↗

PubMed2002

Remodelling of zero-stress state of small intestine in streptozotocin-induced diabetic rats. Effect of gliclazide.

BACKGROUND: Biomechanical properties in terms of residual strains in diabetic small intestine have not been studied. Furthermore, no data have been reported on affect of gliclazide on gastrointestinal complications of diabetes. AIMS: To determine remodelling of zero-stress state of small intestine in streptozotocin-induced diabetic rats and effect of gliclazide treatment. MATERIALS: Morphological properties and residual strains were studied in duodenum, jejunum and ileum obtained from diabetic rats, gliclazide-treated diabetic rats and normal rats (n = 8 each group). METHODS: Diabetes was induced by single intraperitoneal injection of 65 mg/kg streptozotocin. Gliclazide (10 mg kg(-1) day(-1) was injected directly into stomach lumen by intragastric gavage twice daily. Experimental period was 35 days. To approach no-load state; intestinal segments were surgically excised and cut transversely into short ring-shaped segments. Each ring was cut radially to obtain geometry of zero-stress state. Circumferential length, the wall thickness and opening angle were measured from digital images of each specimen and residual strains were computed. RESULTS: Blood glucose level of diabetic group (approximately 20 mmol/l) was consistently higher than that in normal group (approximately 4 mmol/l) after induction of diabetes (p < 0.001). Gliclazide lowered average blood glucose level to between 10 and 15 mmol/l (p < 0.001). Plasma insulin levels of both diabetic groups (average between 10 and 15 pmol/l) were significantly lower than those in normal group (average approximately 18 pmol/l, p < 0.05). Wet weight per unit length and wall thickness of duodenum, jejunum and ileum were significantly higher in Diabetes group than those in Normal group (p < 0.05). Opening angle and absolute value of residual strain were significantly smaller in duodenum and larger in jejunum and ileum in Diabetes group than in Normal group (p < 0.001). Gliclazide treatment partly restored these changes (p < 0.05). CONCLUSIONS: Diabetes induced morphometric and biomechanical remodelling in intestine. Gliclazide partly restored these changes.

Animals↗

PubMed2002

Ablation of bone, cartilage, and facet joint capsule using Ho:YAG laser.

OBJECTIVE: The objective of this study was to determine of the efficiency of holmium:YAG laser for bone ablation, compared to cartilage and soft tissue of the intervertebral foramen of the lumbosacral spine. BACKGROUND DATA: The holmium:YAG (Ho:YAG) laser has been used for ablation of bulging or prolapsed discs and also has the potential for decompression of the nerve root when there is narrowing of the foraminae (foraminoplasty). It is proposed that laser ablation of bone and ligament of the intervertebral foramen for nerve root decompression using the Ho:YAG laser is able to produce sufficient bone ablation without inducing significant thermal necrosis in surrounding tissues due to its short absorption length, which could result in significant clinical advantages. MATERIALS AND METHODS: Experiments were performed on samples of laminar bone, facet joint capsule, and cartilage for quantitative and qualitative determination of the effect of Ho:YAG ablation on tissue mass loss using a range of pulse energies from 0.5 to 1.5 J/P at 15 pulses/sec. RESULTS: The results showed a significant linear correlation between the mass loss and pulse energy, and between the mass loss and radiant exposure. Electron microscopy and histology showed that the Ho:YAG ablation resulted in a very sharp and clear border with little charring. Applying 0.01 k.J of total energy at two different settings (1.5 J/p, high power, and 0.5 J/p, low power) at 15 pulses/sec, the cross-sectional area/mm(2) of the ablated bone was measured, using light microscopy and the Scion Image analysis program. The ablated areas were 2.28 +/- 0.87 and 1.16 +/- 0.43 mm(2) at high and low power, respectively (p = 0.008).

Animals↗

PubMed2002

Genetic changes to optimize carbon partitioning between ethanol and biosynthesis in ethanologenic Escherichia coli.

The production of ethanol from xylose by ethanologenic Escherichia coli strain KO11 was improved by adding various medium supplements (acetate, pyruvate, and acetaldehyde) that prolonged the growth phase by increasing cell yield and volumetric productivity (approximately twofold). Although added pyruvate and acetaldehyde were rapidly metabolized, the benefit of these additives continued throughout fermentation. Both additives increased the levels of extracellular acetate through different mechanisms. Since acetate can be reversibly converted to acetyl coenzyme A (acetyl-CoA) by acetate kinase and phosphotransacetylase, the increase in cell yield caused by each of the three supplements is proposed to result from an increase in the pool of acetyl-CoA. A similar benefit was obtained by inactivation of acetate kinase (ackA), reducing the production of acetate (and ATP) and sparing acetyl-CoA for biosynthetic needs. Inactivation of native E. coli alcohol-aldehyde dehydrogenase (adhE), which uses acetyl-CoA as an electron acceptor, had no beneficial effect on growth, which was consistent with a minor role for this enzyme during ethanol production. Growth of KO11 on xylose appears to be limited by the partitioning of carbon skeletons into biosynthesis rather than the level of ATP. Changes in acetyl-CoA production and consumption provide a useful approach to modulate carbon partitioning. Together, these results demonstrate that xylose fermentation to ethanol can be improved in KO11 by redirecting small amounts of pyruvate away from fermentation products and into biosynthesis. Though negligible with respect to ethanol yield, these small changes in carbon partitioning reduced the time required to complete the fermentation of 9.1% xylose in 1% corn steep liquor medium from over 96 h to less than 72 h.

Acetic Acid↗

PubMed2001

Construction of a square-planar molecular box: self-assembly of palladium(II) complexes of 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2(11,14)]triacon-11,13,24,26(1),27,29-hexaene through hydrogen-bonding interactions.

Binuclear palladium(II) complexes of the macrocyclic polyamine 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2(11,14)]triacon-11,13,24,26(1),2 7,29-hexaene (L) are used to construct molecules having special shapes. In this study two binuclear palladium(II) complexes [Pd(2)LI(2)]I(2)and [Pd(2)LCl(2)](NO(3))(2).H(2)O are synthesized and structurally characterized. X-ray crystallography shows that both complexes exist as one-dimensional chains formed via intermolecular hydrogen-bonding N(3)-H(3C)---X in which X is I and Cl. Moreover, the ligands in both complexes adopt a boatlike conformation that may facilitate the formation of the tetranuclear complex. The cationic aqua complex [Pd(2)L(H(2)O)(m)(NO(3))(n)]((4-n)+, obtained by the treatment of [Pd(2)LI(2)]I(2)and [Pd(2)LCl(2)]Cl(2) with AgNO(3), is used as a building block for the construction of a tetranuclear palladium(II) complex [Pd(4)L(2)(C(2)O(4))(2)](NO(3))(4).6H(2)O. X-ray crystallography shows that the tetranuclear complex forms an open, hydrophobic box. These molecular boxes are connected via the hydrogen bond N(3)-H(3C)---O(4B) (symmetry code B: x, 1 + y, z) into a one-dimensional chain. A two-dimensional structure is formed via pi-pi stacking of the plane defined by C6 to C11 in the one chain and its symmetry-related plane (symmetry code C: -x, -1 - y, 2 - z) in another chain. This study exemplifies a new method for the assembly of molecular boxes using a macrocyclic ligand.

Journal Article↗

PubMed2001

Solution structures of two FHA1-phosphothreonine peptide complexes provide insight into the structural basis of the ligand specificity of FHA1 from yeast Rad53.

Rad53, a yeast checkpoint protein involved in regulating the repair of DNA damage, contains two forkhead-associated domains, FHA1 and FHA2. Previous combinatorial library screening has shown that FHA1 strongly selects peptides containing a pTXXD motif. Subsequent location of this motif within the sequence of Rad9, the target protein, coupled with spectroscopic analysis has led to identification of a tight binding sequence that is likely the binding site of FHA1: (188)SLEV(pT)EADATFVQ(200). We present solution structures of FHA1 in complex with this pT-peptide and with another Rad9-derived pT-peptide that has ca 30-fold lower affinity, (148)KKMTFQ(pT)PTDPLE(160). Both complexes showed intermolecular NOEs predominantly between three peptide residues (pT, +1, and +2 residues) and five FHA1 residues (S82, R83, S85, T106, and N107). Furthermore, the following interactions were implicated on the basis of chemical shift perturbations and structural analysis: the phosphate group of the pT residue with the side-chain amide group of N86 and the guanidino group of R70, and the carboxylate group of Asp (at the +3 position) with the guanidino group of R83. The generated structures revealed a similar binding mode adopted by these two peptides, suggesting that pT and the +3 residue Asp are the major contributors to binding affinity and specificity, while +1 and +2 residues could provide additional fine-tuning. It was also shown that FHA1 does not bind to the corresponding pS-peptides or a related pY-peptide. We suggest that differentiation between pT and pS-peptides by FHA1 can be attributed to hydrophobic interactions between the methyl group of the pT residue and the aliphatic protons of R83, S85, and T106 from FHA1.

Amino Acid Motifs↗

PubMed2001

Post-transcriptional modification in archaeal tRNAs: identities and phylogenetic relations of nucleotides from mesophilic and hyperthermophilic Methanococcales.

Post-transcriptional modifications in archaeal RNA are known to be phylogenetically distinct but relatively little is known of tRNA from the Methanococci, a lineage of methanogenic marine euryarchaea that grow over an unusually broad temperature range. Transfer RNAs from Methanococcus vannielii, Methanococcus maripaludis, the thermophile Methanococcus thermolithotrophicus, and hyperthermophiles Methanococcus jannaschii and Methanococcus igneus were studied to determine whether modification patterns reflect the close phylogenetic relationships inferred from small ribosomal subunit RNA sequences, and to examine modification differences associated with temperature of growth. Twenty-four modified nucleosides were characterized, including the complex tricyclic nucleoside wyosine characteristic of position 37 in tRNA(Phe) and known previously only in eukarya, plus two new wye family members of presently unknown structure. The hypermodified nucleoside 5-methylaminomethyl-2-thiouridine, reported previously only in bacterial tRNA at the first position of the anticodon, was identified by liquid chromatography-electrospray ionization mass spectrometry in four of the five organisms. The ribose-methylated nucleosides, 2'-O-methyladenosine, N(2),2'-O-dimethylguanosine and N(2),N(2),2'-O-trimethylguanosine, were found only in hyperthermophile tRNA, consistent with their proposed roles in thermal stabilization of tRNA.

Chromatography, High Pressure Liquid↗

PubMed2001

DNA array studies demonstrate convergent regulation of virulence factors by Cph1, Cph2, and Efg1 in Candida albicans.

Candida albicans, normally a human commensal, can cause fatal systemic infections under certain circumstances. Its unique ability to switch from yeast to hyphal growth in response to various environmental signals is inherent to its pathogenicity. Filamentation is regulated by multiple pathways including a Cph1-mediated mitogen-activated protein kinase pathway, an Efg1-mediated cAMP/PKA pathway, and a Cph2 pathway. To gain a general picture of how these various signaling pathways regulate differential gene expression during filamentation, we have constructed a partial C. albicans DNA array of 7,000 genes and used it to study the gene expression profiles using various mutants and growth conditions. By combining this novel technology with a new liquid medium in which cph1/cph1 is defective in filamentation, previously identified differentially expressed genes (ECE1, HWP1, HYR1, RBT1, SAPs5-6, and RBT4) are found to be regulated by all three pathways. In addition, two novel genes, DDR48 and YPL184, have been found to be differentially regulated during hyphal development and by all three pathways. This suggests that distinct filamentation signaling pathways converge to regulate a common set of differentially expressed genes. As one of the mechanisms for the observed convergence, we find that the transcription of a key regulator, TEC1, is regulated by Efg1 and Cph2. Importantly, most of the genes regulated by multiple filamentation pathways encode known virulence factors. Perhaps, C. albicans utilizes converging pathways to regulate its vital virulence factors to ensure its survival and pathogenicity in various host environments.

Basic Helix-Loop-Helix Proteins↗

PubMed2001

A potential role for human cohesin in mitotic spindle aster assembly.

The cohesin multiprotein complex containing SMC1, SMC3, Scc3 (SA), and Scc1 (Rad21) is required for sister chromatid cohesion in eukaryotes. Although metazoan cohesin associates with chromosomes and was shown to function in the establishment of sister chromatid cohesion during interphase, the majority of cohesin was found to be off chromosomes and reside in the cytoplasm in metaphase. Despite its dissociation from chromosomes, however, microinjection of an antibody against human SMC1 led to disorganization of the metaphase plate and cell cycle arrest, indicating that human cohesin still plays an important role in metaphase. To address the mitotic function of human cohesin, the subcellular localization of cohesin components was reexamined in human cells. Interestingly, we found that cohesin localizes to the spindle poles during mitosis and interacts with NuMA, a spindle pole-associated factor required for mitotic spindle organization. The interaction with NuMA persists during interphase. Similar to NuMA, a significant amount of cohesin was found to associate with the nuclear matrix. Furthermore, in the absence of cohesin, mitotic spindle asters failed to form in vitro. Our results raise the intriguing possibility that in addition to its well demonstrated function in sister chromatid cohesion, cohesin may be involved in spindle assembly during mitosis.

Animals↗

PubMed2001

Five unique compounds: xyloketals from mangrove fungus Xylaria sp. from the South China Sea coast.

Five unique metabolites, xyloketals A (1), B (2), C (3), D (4), and E (5), and the known 6 were isolated from mangrove fungus Xylaria sp. (no. 2508), obtained from the South China Sea. The structures of these compounds were elucidated by spectroscopic and X-ray diffraction experiments. Xyloketal A is a ketal compound with a C(3) symmetry and xyloketals B-E are its analogues. It was found that xytoketal C slowly rearranged to xytoketal B in DMSO-d(6)() solution at room temperature. Xyloketal A exhibited the activity of inhibiting acetylcholine esterase.

Acetylcholinesterase↗

PubMed2001

Metabotropic glutamate 1alpha receptors on peripheral primary afferent fibers: their role in nociception.

Several lines of evidence indicate that Group I metabotropic glutamate (mGlu) 1alpha receptors are involved in the processing of nociceptive information in the spinal cord. The goals of the present study are to document the role of mGlu1alpha receptors in peripheral nociception. To accomplish this we investigate the presence of mGlu1alpha receptors on peripheral primary afferent fibers and determine the behavioral effects of (S)-3,5-dihydroxyphenylglycine (S-DHPG), which is an mGlu1/5 receptor agonist and (RS)-1-aminoindan-1, 5-dicarboxylic acid (AIDA), a selective mGluR1alpha antagonist, on mechanical and thermal sensitivity and formalin-induced nociceptive behaviors. The anatomical studies at the electron microscopic level demonstrate that 32.4+/-2.9% of the unmyelinated axons and 21.6+/-4.7% of the myelinated axons are positively immunostained for mGlu1alpha receptors. Intraplantar injection of 0.1 or 1 mM S-DHPG results in a significant increase in mechanical sensitivity that persists for more than 60 min and this effect is blocked by co-injection of S-DHPG with 1 mM AIDA. Intraplantar injection of 40 microM AIDA+2% formalin significantly attenuates phase 2 lifting/licking and flinching behavior and this AIDA-induced effect is blocked with co-injection of 1 microM S-DHPG. In behavioral tests, intraplantar S-DHPG (0.1, 1.0, 10 mM) does not change tail flick latencies or paw withdrawal latencies to heat stimulation. These data indicate that mGlu1alpha receptors are present on peripheral cutaneous axons and activation of peripheral mGlu1alpha receptors contributes to mechanical allodynia and inflammatory pain but not thermal hyperalgesia.

Animals↗

PubMed2001

Interference with calcium-dependent mitochondrial bioenergetics in cardiac myocytes isolated from doxorubicin-treated rats.

In previous studies we showed that doxorubicin (DOX) interferes with mitochondrial calcium homeostasis and that cardiac mitochondria from DOX-treated rats express a dose-dependent, cumulative, and irreversible decrease in calcium-loading capacity. Associated with this is an increased sensitivity to calcium-induced cell killing of cardiac myocytes from DOX-treated rats. Because mitochondria play an important role in cytosolic calcium regulation, we questioned whether cardiac myocytes isolated from DOX-treated rats express an exaggerated response to interventions that increase cytosolic calcium. Adult male Sprague-Dawley rats received six weekly (sc) injections of either 2 mg/kg of doxorubicin or an equivalent volume of saline and were killed the following week. Cardiac myocytes were isolated and exposed in vitro to 25 microM of A23187, 20 mM of caffeine, or 500 microM of ouabain. A23187 and ouabain caused a dose-dependent increase in intracellular calcium, as measured fluorometrically with Fura-2AM. In the case of ouabain, the increase in cytosolic calcium was greater for myocytes from DOX-treated rats than for cells from control rats. With caffeine, however, the increase in intracellular calcium was not evident unless the mitochondria were depolarized. A23187 also caused depolarization of mitochondria, the extent of which was greater for cardiac myocytes from DOX-treated rats. All three agents caused depletion of cardiac myocyte ATP and cell killing, both of which were more profound in cells from DOX-treated rats than in controls. We suggest that by interfering with mitochondrial calcium regulation, long-term treatment with DOX renders myocytes susceptible to agents that increase cytosolic calcium, presumably by increasing the calcium-dependent disruption of mitochondrial function, leading to depletion of ATP and eventually cell death. This interference with mitochondrial calcium regulation may underlie the pathogenesis of DOX-induced cardiomyopathy.

Adenosine Triphosphate↗

PubMed2001

High-performance liquid chromatographic method for the estimation of the novel investigational anti-cancer agent SR271425 and its metabolites in mouse plasma.

A simple and reliable HPLC method was developed for the estimation of a new anti-cancer agent that belongs to the thioxanthone class, SR271425 in mouse plasma. SR271425, it's metabolites and internal standard (SR233377) were separated from plasma by liquid-liquid extraction using dichloromethane after quenching the plasma proteins with acetonitrile. Chromatography was performed on a reversed-phase C18 column using methanol-10 mM phosphate buffer, pH 3.5 (45:55) as mobile phase at a flow-rate of 0.8 ml/min for first 10 min and 1.4 ml/min for the next 15 min with UV-Vis detection at 264 nm and SR233377 as internal standard. The retention times of SR271425 and internal standard were 18.6 and 14.8 min, respectively. The limit of detection was 40 ng/ml and the limit of quantification was 78 ng/ml. This method was also able to detect the three metabolites of SR271425. The intra- and inter-day relative standard deviations were less than 13% at all concentrations. This analytical method was precise and reproducible for pharmacokinetics and metabolism studies of the drug in mice. SR271425 is proceeding to phase I clinical trials in 2001.

Animals↗

PubMed2001

Investigation on a novel core-coated microspheres protein delivery system.

Among the different approaches to achieve protein delivery, the use of polymers, specifically biodegraded, holds great promise. In this work, a new microsphere delivery system composed of alginate microcores surrounded by a biodegradable poly-DL-lactide-poly(ethylene glycol (PELA) was designed to improve the loading efficiency and stability of proteins. Alginate was solidified by calcium (MS-1), polylysine (MS-2) and chitosan (MS-3), respectively, to form different microcores. Human Serum Albumin (HSA), used as a model protein, was efficiently entrapped within the alginate microcores using a high-speed stirrer and then microencapsulated into PELA copolymer using a w/o/w solvent extraction method. DSC analysis of the microspheres revealed the efficient encapsulation of the alginate microcores, while the microcores were dispersed in the PELA matrix. SDS-PAGE results showed that HSA kept its structural integrity during encapsulation and release procedure. Microspheres were characterized in terms of morphology, size, loading efficiency, in vitro degradation and protein release. The degradation profiles were characterized by measuring the loss of microsphere mass, the decrease of polymer intrinsic viscosity and the reduction of PEG content of PELA coat. The release profiles were investigated from the measurement of protein presented in the release medium at various intervals. The results were that the degradation rate of these core-coated microspheres was MS-2>MS-1>MS-3. The extent of burst release from the core-coated microspheres in the initial protein release was lower than the 27% burst release from the conventional microspheres. In conclusion, the work presents a new approach for macromolecular drugs (such as protein, peptide drugs) delivery. The core-coated microspheres system may have potential use as a carrier for drugs that are poorly absorbed after oral administration.

Alginates↗

PubMed2001

Microscopic approach for the site distribution and thermodynamic properties of a single-component polymer subjected to an external field.

A microscopic statistical mechanics approach is proposed for a nonuniform single-component freely jointed tangential hard-sphere polymer in the framework of density-functional theory. The present approach avoids the use of single-chain simulation in the theory by treating bonding interaction on the basis of the properties of the Dirac delta function. The present excess free energy includes all terms of functional perturbative expansion around the uniform bulk fluid in the form of the Verlet-modified bridge function. The second-order direct correlation function of a uniform polymer melt as the input parameter is obtained by solving numerically the polymer-reference-interaction-site-model integral equation with the Percus-Yevick closure. Predictions of the present approach for such microscopic structural and thermodynamics properties as the site density distribution, the partition coefficient, and the adsorption isotherm near a hard wall or between two hard walls are compared with computer-simulation results and with those of previous theories. The comparison indicates that the present approach is more accurate than the previous integral equation theory and the most accurate Monte Carlo density-functional theories. The predicted oscillations of the medium-induced force between two hard walls immersed in polymer melts are consistent with the experimental results available in the literature. The relation of the present approach with self-consistent-field theory, as well as the differences between the two, are discussed.

Journal Article↗