Molar Mass Distribution and Chain Conformation of Polysaccharides from Fortunella margarita(Lour.) Swingle

In order to study the effects of different extraction methods on the molar mass distribution and chain conformation of Fortunella margarita （Lour.） Swingle polysaccharides （FP）, we used extraction by hot water （WFP）, ultrasonic-assisted treatment （UFP）, microwave-assisted treatment （MFP） and ultrasonic/microwave-assisted treatment （UMFP）, and then Fourier transform infrared （FT-IR） spectroscopy as well as 1H and 13C nuclear magnetic resonance （NMR） spectroscopy to characterize the structural properties of FP extracted. The molar weight （Mw）, polydispersity index （Mw/Mn）, root-mean-square （RMS） turning radius （Rg）, molar mass distribution and chain conformation of FP were studied systematically using size-exclusion chromatography （SEC）, multi-angle laser light-scattering （MALLS） and refractive index （RI）. WFP, UFP, MFP and UMFP are all typical carbohydrates according to 1H NMR, laC NMR and FT-IR measurements. The type of glycosidic linkage is mainly a fl-glycosidic bond with a small amount of a-glycosidic bond. The results obtained by the SEC-MALLS-RI system showed the molar masses of WFP and UMFP were distributed mainly in the range of 5.0x10^6-1.0x10^7 g-mo1-1 and they accounted for 57.80% and 56.84% of total FP, respectively. The molar masses of UFP and MFP were distributed mainly in the 1.0x10^6-5.0x10^6 g.mol-1 range, which accounted for 38.24% and 52.39% of FP, respectively. WFP and UMFP in water were uniform spherical polymers; UFP and MFP were typical highly branched polymers and the degree of branching for MFP was higher compared to UFP. These results indicated the ultrasonic- and microwave-assisted extraction methods caused a significant decrease of the molar mass of FP but the ultrasonic/microwave synergistic extraction method had no effect.

Chain Conformation and Local Rigidity of Soluble Polyimides(II):Isomerized Polyimides in THF

Two soluble isomerized polyimides（PIs） synthesized from 2,2＇-bis（3,4-dicarboxyphenyl）hexafluoropropane dianhydride（6FDA） with either 2,2＇-dimethylbenzidine（2,2＇-DMB） or 3,3＇-DMB were investigated by means of size-exclusion chromatography coupled with multi-angle laser light scattering,a viscometer and a refractive index detector in tetrahydrofuran（THF） with tetrabutylammonium bromide（TBAB） at 35 ℃.The corresponding parameters related to conformations α and ν,evaluated from the scaling relationships [η]=K η M α and R g =K g M ν,respectively,were 0.66±0.01 and 0.55±0.02 for poly（6FDA/3,3＇-DMB）,and 0.67±0.01 and 0.56±0.01 for poly（6FDA/2,2＇-DMB）,indicating a random coil conformation for both the samples in this mobile system.The persistence length l p and shift factor M L（relative molecular weight per unit contour length） were estimated from the relationship between intrinsic viscosity and molecular weight for the wormlike cylinder model proposed by Bohdanecky.Both l p and M L showed that the two PIs in THF are flexible chains and exhibit some local rigidity to some extent.

MODELING THE CHAIN CONFORMATION OF POLYMER MELTS IN CONTRACTION FLOW

A constitutive model of quasi-Newtonian fluid based on the type of flow is used in abrupt planar contraction now.The numerical results from finite element analysis are consistent with experimental data for stress patterns and velocityprofiles in the flow field. The chain conformations of polymer melts are then investigated in such a planar contraction byusing the phenomenological model with internal parameters proposed by the author. That is, the shape and orientation ofpolymer chain coils are predicted and discussed in different flow regions of the contraction flow field that possess simpleshear flow, extensional flow, vortical flow, and mixed flow respectively.

Temperature Dependence of Chain Conformation and Local Rigidity of Isomerized Polyimides in Dimethyl Formamide

Temperature dependence of chain conformation and local rigidity of two soluble isomerized polyimides （PIs）, poly（hexafluorodianhydride/3,3＇-dimethylbenzidine）[poly（6FDA/3,3＇-DMB）] and poly（hexafluorodianhy- dride/2,2＇-dimethylbenzidine）[poly（6FDA/2,2＇-DMB）] were investigated by dilute solution viscosity, size exclusion chromatography（SEC） coupled with multi-angle laser light scattering, viscometer, and refractive index detector in dimethylformamide（DMF） with either 0.1 mol/L LiBr or 3.1 mmol/L tetrabutylammonium bromide（TBAB） in the temperature range of 30 to 50 ~C. The scaling relationships of [t/]=K^M~ and Rg=KgMv obtained are employed to in- vestigate the temperature dependence of chain conformation for the two polyimides. The values of a and v are in the range of 0.66--0.69 and 0.53--0.56, respectively, for poly（6FDA/3,3＇-DMB）, meanwhile they are in the range of 0.64--0.68 and 0.53--0.56, respectively, for poly（6FDAJ2,2＇-DMB）. These results reveal that random coil conforma- tions for both Pls are not affected visibly with increasing temperature from 30 ~C to 50 ~C. However, values of more exact intrinsic viscosity from dilute solution measurement indicate there is only tiny coil extension or shrinkage for both PIs with temperature rising. Parameters related to chain flexibility of polymer, including persistence length lp, shift factor ME（relative molecular weight per unit contour length） and backbone diameter d are estimated from the relationship between intrinsic viscosity and molecular weight for the continuous wormlike cylinder model, which indicates that two samples are flexible chains, only the chain of poly（6FDA/3,3＇-DMB） is stiffer than that of poly（6FDA/2,2＇-DMB） slightly.

Temperature Effect on the Conformation Transition of Ultra-high Molecular Weight Polyethylene/Polypropylene Blends Undergoing Continuous Volume Extensional Flow:A Mesoscopic Simulation

Due to the multiformity and complexity of chain conformation under external flow and the challenge of systematically investigating the transient conformation and dynamic evolution process of polymer chains at the molecular level by means of present experimental techniques,a universal description of both chain conformation and dynamics with respect to continuous volume extensional flow(CVEF)is still absent.Taking into account the temperature effect,we performed dissipative particle dynamics(DPD)simulations with the particles corresponding to the repeat units of polymers over a wide temperature range and analyzed the correlation with the conformational properties of ultra-high molecular weight polyethylene/polypropylene(UHMWPE/PP)blend in response to the CVEF.With time evolution,the polymer chains become highly oriented parallel to the flow direction instead of the initial random coiling and self-aggregation.It is found that a high temperature is necessary for more substantial compactness to take place than low temperature.The low-k plateau and low-k peak in structure factor S(k)curves suggest a low degree of conformational diversity and a high degree of chain stretching.It is also concluded that the intra-molecular C-C bond interaction is the main driving force for the dynamics process of the chain conformations undergoing CVEF,where the motion of the alkyl chains is seriously restricted owing to the increase in bond interaction potential,resulting in a reduction of the difference in diffusion rates among alkyl chains.

Stimulus-responsive mechanism of salt-responsive polymer and its application in saturated saltwater drilling fluid

AM-AMPS-TAC polymers with different charge distribution are synthesized using acrylamide(AM),2-acrylamido-2-methylpropanesulfonate(AMPS)and 3-acrylamidopropyl trimethylammonium(TAC)at different feed ratios by polymerization in solution.The salt-responsive behavior,reasons leading to salt-responsiveness,and effects of polymers molecular structure on salt-responsiveness are studied by laboratory experiments to find out the adaptability of the polymers.Rheology test under stepwise shear mode shows that the AM-AMPS-TAC polymers have salt responsiveness,and the closer the feeds of AMPS and ATC,the more significant the salt responsiveness will be.Conformation change of polymers molecular chain under salt stimulus is studied by turbidity test and micro-morphology analysis,and the responsive mechanism is further investigated by intrinsic viscosity test and copolymer composition analysis.Results indicate that the salt-responsive behavior of AM-AMPS-TAC polymers derives from the"curled to expanded"transition of chain conformation under salt stimulus,and this transition is led by the screening effect of salt which weakens polymers intramolecular ionic bond.Application in saturated saltwater drilling fluid shows that the AM90-AMPS5-TAC5 polymer has the best salt-tolerance and temperature-tolerance when used together with fluid loss controller PAC-Lv.The drilling fluid saturated with NaCl can maintain stable viscosity,good dispersion and low fluid loss for long time under 150℃.

PREPARATION OF PERFLUOROOCTANOYL-MODIFIED POLY(VINYL-ALCOHOL)S AND THEIR ADSORPTION AT AN AIR-WATER INTERFACE

Perfluorooctanoyl modified poly(vinyl alcohol)s (FPVA) were prepared by means of substituting a small amount of hydroxyl groups on the backbone of poly(vinyl alcohol), for which the initial degree of polymerization is equal to 1750. The substitution extent, defined by the number of substituting units in a chain, for the four FPVA samples was in the range of 0.5-5 perfluorooctanoyl groups per chain. The FPVA samples with the highest substitution extent still had good solubility in water. It was shown by experimental measurement at 30.0 +/- 0.1 degreesC that the surface tension of the aqueous solution of the highest substituted FPVA decreased to 16.6 mN/m at a higher concentration, e.g. about 0.1 g/mL. Obviously, macromolecules of FPVA exhibit a very strong tendency to adsorb at the air-water interface, because the hydrophobic perfluorooctanoyl groups in FPVA have a very high surface activity as they are in small molecular fluorinated surfactants. The chain conformation of such a model polymer adsorbed on the air-water interface was also discussed.

Interleukin-10 promoter polymorphisms in patients with hepatitis B virus infection or hepatocellular carcinoma in Chinese Han ethnic population

BACKGROUND: Since single nucleotide polymorphisms (SNPs) can serve as gene markers, polymorphism profiles may help scientists to identify the full collection of genes that contribute to the development of complex diseases such as cancer. The distribution of interleukin-10 (IL-10) promoter polymorphisms in Chinese Han ethnic patients with hepatitis B virus (HBV) infection and hepatocellular carcinoma (HCC) was investigated in this study. METHODS: The polymorphisms of IL-10 promoter region were detected by pulymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and sequencing. Sixty-six health controls, 42 patients with HBV infection, 30 HCC patients, and cell line SMMC-7721 were examined this way. RESULTS: Polyrnorphisms of T/C or T/N on-872 site occurred frequently in Han ethnic population. Pulyrnorphisms were detected in HBV and HCC patients and cell line SMMC-7721. The hotspot among the pulymorphisms was inserting base A between-1058 and-1057. CONCLUSION: Polymorphisms of IL-10 promoter in HBV and HCC patients may be associated with HBV infection and HCC development.

Identification of CFTR Gene Mutations in Chinese Patients with Congenital Obstructive Azoospermia

ve To analyze the frequency and hot spot of CFTR gene mutations in Chinese patients with congenital obstructive azoospermia

Detecting drug resistant genetic mutation among pneumoconiosis patients complicated with tuberculosis in Mycobacterium tuberculosis L-forms application of PCR-SSCP technique in Huainan mining district

Objective： To study the relationship between drug resistant genetic mutation and drug resistance in Mycobacterium tuberculosis L-form, discuss the internal relationship between drug resistances and drug-resistant related genes and explore the value of PCR- SSCP to clinical application. Methods： A total of 52 clinically isolated strains of tuberculosis L-form were collected among 97 pneumoconiosis patients complicated with tuberculosis. The gene mutations of katG, rpoB and rpsL were detected by PCR-SSCP, and the results were compared with those analyzed by traditional antimicrobial susceptibility test（AST）. Results： The gene muta- tion rates of katG, rpoB and rpsL by PCR-SSCP were respectively 57.70% （30/52）, 65.38% （32/52） and 40.38% （21/52）. The rate of reversion was 78.85%（41/52） and the result of drag-resistant genes was invariable. The results of AST showed that there were 40 （76.92%） multi-drug resistant strains in 52 clinically isolated strains. The number for three-drug resistant strain was 21 （40.38%） and that of two-drug resistant was 19（36.54%）, but only 12（23.08%） strains were one drug resistant. The rate of total drug-resistance was 100%, but there were 15 strains of allied mutation of three genes, 16 of two mutations and 6 of only one by PCR-SSCP. The coincidences were respectively 71.43%, 84.12% and 50.00%. Then there was no significant difference between the allied mutations of multi-drug resistant gene and the mutations of only one drug resistant gene （P 〉 0.05）. Conclusion： PCR-SSCP technique has a higher sensibility and specificity to detect the genes of katG, rpoB and rpsL in tuberculosis L-form among pneumoconiosis complicated with tuberculosis,and the detecting rate of two drug resistant strains and three drug resistant strains was higher. The combined application of PCR-SSCP and AST has advantages at earlier diagnosis and guidance of clinical medications.

Theoretical Interpretation of Conformation Variations of Polydimethylsiloxane Induced by Nanoparticles

There has been controversy as to whether the addition of nanoparticles to a polymer melt causes perturbed chain structure of polymers. In this work, the chain conformations of polydimethylsiloxane（PDMS） with addition of polyhedral oligomeric silsesquioxane（POSS） nanoparticles have been studied using a classical density functional approach. Under the strong interactions of POSS-PDMS, the radius of gyration of PDMS in the nanocomposites can either increase or decline depending on particle loading. After adding nanoparticles with larger size or weaker interactions, both the increasing and the declining amplitudes can be largely suppressed. The results provide a deep understanding of chain conformation in polymer nanocomposites.

Prominently Promoting the Formation of Poly(butylene adipate) α-Form Crystals by Coalescing from Inclusion Complex

We successfully use a co-precipitation method to prepare inclusion complex between poly（butylene adipate） （PBA） chains （guest component） and urea molecules （host component）. The PBA/urea inclusion complex is confirmed to adopt a hexagonal crystal modification with lattice parameters ofa = 8.14 A and c = 10.92 A, and the interaction between PBA chains and urea is van der Waals force. The singly isolated PBA chains are suggested to take some gauche conformation, which is different from the all-trans conformation in r-form PBA. Furthermore, we employ the isolated PBA chains which are uniformly pre-established in a specific conformation in urea channels to regulate the crystal form of PBA for the first time. After removing the host urea molecules, the coalesced PBA chains are found to solely crystallize into a-form crystals at different coalescing temperatures. By comparing the FTIR spectra, it is found that PBA chains in inclusion complex plausibly contain some similar conformers as those in a-form crystal, which is suggested to be the intrinsic reason for the sole formation of a-form crystals. This research proves that inclusion complex can be used as a very effective method to regulate polymorphism of semi-crystalline polymers.

The Solvent Quality of Water for Poly(N-isopropylacrylamide) in the Collapsed State： Implications from Single-molecule Studies

Both of temperature（in water） and composition（in the water/methanol mixed solvent） can induce the coil-toglobule transition of poly（N-isopropylacrylamide）（PNIPAM）. The atomic force microscope（AFM） based single molecule force spectroscopy（SMFS） has been exploited to investigate the interactions between the polymer chain and solvent at the single-molecule level. It is found that the single-chain mechanics of PNIPAM show a remarkable dependence on the two external stimuli. A confusing experimental result is that all the force-extension（F-E） curves of unfolding an individual PNIPAM globule present a feature of elastic（monotonically increasing force） stretching but not plateau（constant force） stretching predicted by theory. In this article, we clarify that the presence of the interior solvent molecules in the single-chain globule is the origin of the discrepancy between the F-E curves obtained from theory and experiment. Although both of the external stimuli do tend to lower the solvent quality for PNIPAM, water and the water/methanol mixed solvent will never be the strongly poor solvent for PNIPAM, even at the worst condition.

Molecular Dynamics Simulations of Atomistic Hydration Structures of Poly(vinyl methyl ether)

Molecular dynamics simulations have been performed on the aqueous solutions of poly（vinyl methyl ether）（PVME） at various concentrations. Both radial and spatial distribution functions are used to investigate the detailed hydration structures. The structures of water are found to get increasingly concentrated when polymers are introduced and the water motions are severely hindered by the polymer matrix. At low concentrations, larger populations of tt conformers in meso dyads than those at higher concentrationsare found and this phenomenon is believed to be due to the increasing in bonding of water molecule to two ether oxygens in meso dyad. At higher concentrations, the size and conformations of polymers are quite similar to those in bulk. A transition of hydrogen bond fractions between PVME and water at around the concentration of 0.3 is observed and this value is perfectly in agreement with the results of conformational analysis and Raman spectra. Second neighbor hydrogen bond statistics revealed the domination of complicated hydrogen bond networks at low concentrations, but single hydrogen bonds as well as isolated clusters composed of 2-4 water molecules are usual around each polymer repeat unit.