Short Linear Chains Research Articles

Pullulanase hydrolysis behaviors and hydrogel properties of debranched starches from different sources

In the present study, debranched starches (DBS) from different sources were prepared by treatment with pullulanase with an aim to investigate the differences in pullulanase hydrolysis and the hydrogel properties of the resulting DBS. The results indicated that all DBS were V-type starches with hollow, single-helical structures. Debranched maize starch (DBMS) and wheat starch (DBWS) performed similarly. Pullulanase treatment resulted in an obvious reduction in viscosity for all tested starches except debranched pea starch (DBPeS). The average molecular weight of small fragments of debranched potato starch (DBPoS) was higher than that of the other samples, and longer lateral chains tended to be cleaved by pullulanase for DBPoS. The results of the solubility and water-holding capacity analyses indicated the DBS starches were capable of capturing water to form hydrogels. DBPoS was more easily digested by gastrointestinal amylase, whereas its pea-source counterpart showed the opposite trend. The results confirmed that generation of short linear glucan chains by pullulanase hydrolysis effectively improved solubility and water-holding capacity, which contributed to their hydrogel-forming properties.

Waveguiding properties of short linear chains of nonspherical metal nanoparticles

We study numerically the discrete dispersion relations and waveguiding properties of relatively short linear chains of spherical and spheroidal silver nanoparticles. Simulations are based on the Drude model for the dielectric permittivity of metal and on the dipole approximation for the electromagnetic interaction of particles. We also simulate the dynamics of femtosecond optical pulse propagation along such chains. In the case that we consider (10 particles per chain), reflections from the chain terminals play a significant detrimental role. We show that dissipative traps can be used to reduce the effects of reflections. We also show that chains composed of oblate spheroids with sufficiently small aspect ratio (nanodisks) have better waveguiding properties when compared to chains made of particles with other spheroidal shapes. This includes a slower rate of decay, larger group velocity, and larger bandwidth.

Lubrication by physisorbed molecules in equilibrium with vapor at ambient condition: effects of molecular structure and substrate chemistry.

The effects of physisorbed organic vapor molecules on friction and wear were studied for various materials with different surface chemistries (metals, ceramics, glasses, carbons, polymers) and adsorbed species with distinct functional groups (short linear-chain, branched, and fluorinated alcohols with alkyl chain lengths up to five carbons as well as acetone and n-decane). Friction test results of stainless steel under equilibrium vapor adsorption conditions indicated that the longer chain length of the adsorbed alcohols results in lower friction and that n-pentanol gives the lowest friction and wear among the molecules investigated. The adsorption isotherm measurements revealed that the functional groups of the adsorbed molecules appear to play important roles in lubrication. Friction coefficients that ranged from 0.02 to 0.9 for the various materials in dry and humid environments converged to ∼0.15 for the inorganic solid materials tested in n-pentanol. These findings indicate that the molecular lubrication by the physisorbed species dominates the tribological behaviors of the inorganic solid materials, regardless of bulk mechanical properties. Tribotests using polymeric materials did not show the same lubricating effects for n-pentanol vapor. The failure of n-pentanol to lubricate polymeric materials may be due to vapor ingress into the polymer and the absence of an adsorbed surface layer.

Understanding Constraint Release in Star/Linear Polymer Blends

In this paper, we exploit the stochastic slip-spring model to quantitatively predict the stress relaxation dynamics of star/linear blends with well-separated longest relaxation times and we analyze the results to assess the validity limits of the two main models describing the corresponding relaxation mechanisms within the framework of the tube picture (Doi’s tube dilation and Viovy’s constraint release by Rouse motions of the tube). Our main objective is to understand and model the stress relaxation function of the star component in the blend. To this end, we divide its relaxation function into three zones, each of them corresponding to a different dominating relaxation mechanism. After the initial fast Rouse motions, relaxation of the star is dominated at intermediate times by the “skinny” tube (made by all topological constraints) followed by exploration of the “fat” tube (made by long-lived obstacles only). At longer times, the tube dilation picture provides the right shape for the relaxation of the stars. However, the effect of short linear chains results in time-shift factors that have never been described before. On the basis of the analysis of the different friction coefficients involved in the relaxation of the star chains, we propose an equation predicting these time-shift factors. This allows us to develop an analytical equation combining all relaxation zones, which is verified by comparison with simulation results.

Optical Response of Metallic Nanoparticle Heteroaggregates with Subnanometric Gaps

The optical response of metallic nanoparticle heteroaggregates with well‐defined, subnanometric interparticle gaps is studied both theoretically and experimentally for clusters formed by nanoparticles of different size and/or different material (Au and Ag). The optical spectra of the aggregates can be understood in terms of excitation of chain‐like plasmon modes, which are associated with short and long linear chains that constitute the cluster internally. The dependence of the optical properties of the aggregates on the size of the metallic nanoparticles, the interparticle gaps, and the dielectric environment is revealed in model electromagnetic calculations. A rigid molecular linker, cucurbit[5]uril, is used to experimentally form Au heteroaggregates of different sized particles, as well as heteroaggregates of silver and gold. It is shown that in both types of heteroaggregates, the ratio of the two different nanoparticles provides a versatile and easily controllable way to tailor the dominant long‐wavelength chain mode. Experimental tracing of the optical response of such heteroaggregates in time during aggregation supports the formation of long‐wavelength modes, which can be attributed to excitation of long chains inside the clusters.

Self-Assembly of Short Linear Chains to A- and B-Type Starch Spherulites and Their Enzymatic Digestibility

A novel process combining enzymatic debranching, melting, and crystallization was developed to produce spherulites from short linear α-1,4-linked glucans (short-chain amylose, SCA) with controlled enzyme digestibility. SCA was obtained by completely debranching waxy maize starch at 50 °C and 25% solids in 0.01 M sodium acetate buffer. The mixture was then heated to 180 °C followed by cooling and crystallization to form well-developed spherulites. Multiple analytical techniques including light microscopy, scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and synchrotron small-angle X-ray scattering (SAXS) covered over 5 orders of length scale and were applied to study the morphology and structure of the spherulites. Spherulites crystallized at low temperatures (4 and 25 °C) had a large size (5-10 μm), a B-type starch X-ray diffraction pattern, a lower melting temperature (70-110 °C), and a higher digestibility (Englyst method) compared to the spherulites crystallized at 50 °C, which had a small size (1-5 μm), an A-type diffraction pattern, a higher melting temperature (100-140 °C), and a lower digestibility. Intact spherulites along with small fragments were observed after digestion with a mixture of α-amyase and amyloglucosidase, indicating that digestion was not homogeneous and preferentially occurred in weak spherulites. A second exposure of the undigested residues to the amylases showed a similar digestive pattern as with the parent spherulites, suggesting that the spherulites were hydrolyzed by enzymes at essentially a constant digestion rate between 20 min and 3 h.

Activity Coefficients at Infinite Dilution for Organic Solutes Dissolved in Three 1-Alkyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquids Bearing Short Linear Alkyl Side Chains of Three to Five Carbons

In this work, we report the infinite dilution activity coefficients (γ1,2∞) of 39 to 43 diverse organic solutes dissolved in three 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids (IL) homologues bearing propyl, butyl, and pentyl n-alkyl side chains, respectively, as determined by inverse gas chromatography at temperatures from 323 K to 343 K. The organic solutes include various (cyclo)alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, thiophene, ethers, nitroalkanes, and ketones. The measured retention data were further transformed to gas-to-IL and water-to-IL partition coefficients using established thermodynamic approaches based upon the corresponding gas-to-water partition coefficients of the test solutes. Both sets of partition coefficients were interpreted with a modified form of the basic Abraham general solvation parameter model. The mathematical correlations obtained by regression analysis back-calculated the observed gas-to-IL and water-to-IL partition coeff...

Addition of α-O-GlcNAc to threonine residues define the post-translational modification of mucin-like molecules in Trypanosoma cruzi.

Trypanosoma cruzi, an intracellular protozoan etiologic agent of Chagas disease is covered by a dense coat of mucin-type glycoproteins, which is important to promote the parasite entry and persistence in the mammalian host cells. The O-glycosylation of T. cruzi mucins (Tc-mucins) is initiated by enzymatic addition of α-O-N-acetylglucosamine (GlcNAc) to threonine (Thr) by the UDP-GlcNAc:polypeptide α-N-acetylglucosaminyltransferase (pp-α-GlcNAcT) in the Golgi. The Tc-mucin is characterized by the presence of a high structural diversity of O-linked oligosaccharides found among different parasite strains, comprising two O-glycan Cores. In the Core 1, from strains principally associated with the domestic transmission cycle of Chagas disease, the GlcNAc O-4 is substituted with a β-galactopyranose (βGalp) unit, and in the most complex oligosaccharides the GlcNAc O-6 is further processed by the addition of β1 → 2-linked Galp residues creating a short linear Galp-containing chain. In the Core 2 structures, expressed by strains isolated from T. cruzi sylvatic hosts, the GlcNAc O-4 carries a β-galactofuranose (βGalf) unit and the GlcNAc O-6 can carry a branched Galpβ1 → 3[Galpβ1 → 2]Galpβ1 → 6 motif. The O-glycans carrying nonreducing terminal βGalp are available for sialylation by a surface T. cruzi trans-sialidase activity. Based on structural results, this review summarizes available data on the highly conserved process, which adds the GlcNAc unit in α-linkage to Thr residues the basis of the post-translational modification system in T. cruzi mucins. In addition, a mechanism unique employed by the parasite to transfer exogenous sialic acid residues to Tc-mucins is presented.

Bimodal architecture and rheological and foaming properties for gamma-irradiated long-chain branched polylactides

A series of long-chain branched polylactides (LCB-PLAs) were prepared from a linear PLA precursor by applying gamma radiation with addition of the trifunctional monomer, trimethylolpropane triacrylate (TMPTA) and their topological structures were investigated by size-exclusion chromatography coupled with a multiangle light scattering detector (SEC-MALLS) and rheology. SEC-MALLS measurements show that LCB-PLAs exhibit not only the increased weight-average molecular mass but also a bimodal architecture with a short linear chain fraction and a LCB fraction, as compared with LCB-PLA samples generated by electron-beam radiation, which only show the monomodal macromolecular structure. The introduction of LCB structure contributes to the enhancement of complex viscosity, shear-thinning and storage modulus, and the deviations of phase angle, δ from the “universal” curve of linear PLA in δ(|G*|) plots (van Gurp–Palmen plot). By the analysis of the thermorheological behaviors and determination of activation energies, the bimodal architecture is confirmed. Activation energies around 77 kJ mol−1 lead to an expectation that some linear macromolecules are still present in LCB-PLAs, while the higher activation energies at large phase angles are associated with the existence of the LCB ones. A conclusion with respect to the tree-like topography for LCB-PLAs is drawn from the molecular mass dependences of zero-shear viscosity (η0–Mw plot). An explanation to these findings is provided under the consideration of the radiation dose rate for the gamma radiation. The remarkable modification of PLA topological chain structure contributes to the improvement of the foaming properties of LCB-PLAs.

Natural Peptides with Potential Applications in Drug Development, Diagnosis, and/or Biotechnology

Natural Peptides with Potential Applications in Drug Development, Diagnosis, and/or Biotechnology

EXTENSIVE STUDY OF INTERACTION FORCE BETWEEN SPHERICAL COLLOIDS AND STAR POLYMERS

We consider a system consisting of very small colloidal particles clothed each by f end-grafted flexible polymer chains we regarded as star polymers, and hard spherical colloidal particles in a good solvent. Our main objective is to determine the expression of the interaction force between a spherical colloid and a star polymer as a function of distance between them. We limit ourselves to the case where the star polymer is smaller than the colloid. In the first part, the system is dissolved in a melt of short linear chains of polymerization degree P<N, where N denotes the polymerization degree of grafted chains. To compute the expected force, we consider two regimes: (1) high-grafting density [Formula: see text] and (2) small-grafting density (f < f*). For (f > f*), we show that the expression of the expected force coincides exactly with that of the case of a small molecular weight solvent. For (f < f*), we show that there is a change in behavior. In the second part, we assume that the lengths of the f grafted chains were randomly distributed and there is talk of a polydisperse star polymer. We show that the computation of the expected force depends on the relative values of the polymerization degree of longest grafted chain, N, when it is compared to the typical one Nc ~ f1/(α-1). Here α is the polydispersity exponent. We distinguish two regimes depending on whether N < Nc or N > Nc. For the regime with N < Nc, and comparing the expression of the force obtained for the monodisperse case, we can say that the polydispersity of grafted chains induce a drastic change of the force expression. For the regime with N > Nc, we found the existence of two distance-ranges. For small distances, the effective force expression is identical to that relative to the above case (N < Nc). But for high distances, the effective force expression is similar to the monodisperse case.

Study on melting and crystallization of short-linear chains from debranched waxy starches by in situ synchrotron wide-angle X-ray diffraction

In situ melting and crystallization of short-linear α-1,4-glucan (short-chain amylose, or SCA) from debranched waxy starches were investigated by synchrotron wide-angle X-ray diffraction. Amorphous SCA was prepared by dissolving completely debranched waxy starches in alkaline solution and neutralized by hydrochloric acid. When hydrated with 50% water at 25°C, all amorphous SCA crystallized immediately and gave a B-type structure. The SCA from debranched waxy potato starch had a longer average chain length and a higher melting temperature but relatively lower crystallinity upon hydration; it was not completely melted at 100°C and retained its original B-type structure during rapid cooling. In contrast, the SCA from debranched waxy wheat and waxy maize starches had a large portion of low molecular weight fractions, a higher crystallinity upon hydration, and a lower melting temperature. These differences suggest that amylopectin short chains crystallized more readily but their crystals were weaker than those of long chains. After the B-type crystals of hydrated SCA from waxy wheat and waxy maize starches melted, they reformed into the A-type polymorph upon rapid cooling. The thermal properties showed that the A-type polymorph of debranched waxy wheat and waxy maize starches had a higher melting temperature than their B-type structure.

Investigation on the spinnability of metallocene cyclic olefins copolymer melt

This work investigates the melt spinning process of the metallocene cyclic olefins copolymer (mCOC), which had never been successfully developed before. The shear-viscosity examination reveals that the mCOC has a mild shear thinning tendency due to the presence of cyclic olefins, but is very sensitive to the temperature variation. The optimal melt extrusion temperature for the mCOC is found between 320 and 330°C. The mCOC is known to have high Tg, which would cause early solidification, seriously broken filaments, and winding interruption during the melt spinning process. Accordingly, the traditional spinning process employing an air-quenching system at 18°C for polyolefins, such as polypropylene and polyethylene, is inappropriate for the mCOC. Experimental results reveal that in melt spinning of the mCOC, it is necessary to install a heating board of 1.4 meters length and heated up to 180°C to assisting with the spin draw ratio of the mCOC. The elongation rheology of the mCOC was found to be greatly affected by the presence of cyclic olefins. The optimal spinning speed is 1500 m/min. In such a speed, the spin draw ratio of the mCOC is 90, which is higher than the literature value of 10[11], but still far smaller than 200–400 for typical linear polymers. Experimental results suggest that hot drawing, with a drawing ratio of 1.15 and godet temperature of 200°C, can yield yarn with optimal tenacity of 1.4 g/den. Birefringence observations indicate that mCOC yarn, even via melt spinning and hot drawing, does not exhibit any bulk orientation. The result of X-ray diffraction implies that hot drawing can enhance the formation of nano-crystals with an average size of approximately 6.5 nm. This takes place on the short linear olefin chains among the cyclic segments. The degree of crystallization increases slightly as the godet temperature increases.

Developmental morphology of Sarcodia montagneana and S. grandifolia from New Zealand and a phylogeny of Sarcodia (Sarcodiaceae, Rhodophyta) based on rbcL sequence analysis

Despite its widespread distribution in the Indo-West Pacific Ocean, Sarcodia is one of the least understood genera among the red algae. Samples investigated from different parts of the Indo-West Pacific Ocean were well separated phylogenetically, based on rbcL base pair distances, and probably represent separate species. In this report we investigate the developmental morphology of two species from New Zealand: the type species, Sarcodia montagneana, and S. grandifolia (including S. ‘flabellata’). Molecular studies indicate that S. montagneana is restricted to the north-eastern part of the North Island and that S. grandifolia occurs from Wellington southwards as far as the Snares Islands. Thalli are multiaxial and consist of three primary layers: a surface layer of uninucleate cells, a cortex of five or six layers of polygonal multinucleate cells, and a medulla of multinucleate stellate cells. Secondary rhizoidal filaments are frequent to abundant in the medulla. Spermatangia occur in chains and release spermatia through a pore. The female reproductive system is procarpic and consists of a supporting cell that bears two side branches and a one-celled terminal carpogonium. The auxiliary cell is the basal cell of one of the side branches and is undifferentiated prior to fertilization. After presumed fertilization, the carpogonium separates into a terminal cell and a subterminal hypogynous cell that fuses with the auxiliary cell and deposits in it a single nucleus. The auxiliary cell cuts off a gonimoblast initial obliquely that first forms a short linear chain of gonimoblast cells. Cystocarp formation proceeds rapidly with the outward development of linear files derived from surface cells that differentiate into a terminal ostiole and inner and outer pericarp layers separated by a central cavity. The mature gonimoblasts consist of an inner gonimoblast reticulum of laterally fused cells that attach secondarily to outer cells of the inner pericarp and outer gonimoblast filaments that terminate in short chains of carposporangia. Tetrasporangia are zonately divided and are scattered over the thallus surface with new initials formed continuously. The morphological and molecular observations reported here contrast sharply with those of previous studies and are largely new to the Sarcodia literature.

Polyamine functionalized carbon nanotubes: synthesis, characterization, cytotoxicity and siRNA binding

In this work we have synthesized a new series of cationic carbon nanotubes (CNTs) for siRNA binding. Both single- and multi-walled CNTs have been modified by addition or amidation reaction with short linear polyamine chains including putrescine, spermidine and spermine. All the new conjugates have been characterized with several spectroscopic and microscopic techniques. Their cytotoxic effects have been assessed on human lung carcinoma cell line. Finally, we have analyzed their capacity to bind siRNA towards the development of new carriers for gene silencing applications. The dispersibility properties and the capacity to complex siRNA of the different conjugates were found to be strongly dependent on the position of the functional groups on CNTs (i.e. mainly at the tips following the amidation reaction or on the sidewalls by direct C–C addition).

Temperature-dependent structural behavior of self-avoiding walks on three-dimensional Sierpinski sponges

The statistics of self-avoiding random walks (SAWs), consisting of up to N=1280 steps, on deterministic fractal structures with infinite ramification, modeled by Sierpinski cubic lattices, in the presence of a finite temperature is investigated as a model for polymers absorbed on a disordered medium. Thereby, the three-dimensional Sierpinski sponge is defined by two types of sites with energy 0 and ϵ>0 , respectively, yielding a deterministic fractal energy landscape. The probability distribution function of the end-to-end distance of SAWs is obtained and its scaling behavior studied. In the limiting case of temperature T → ∞, the known behavior of SAWs on regular cubic lattices is recovered, while for T → 0 the resulting scaling exponents are confronted with previous calculations for much shorter linear chains based on the exact enumeration technique. For finite temperatures, the structural behavior of SAWs in three dimensions is compared to its two-dimensional counterpart and found to be intermediate between the two limiting cases (T → 0 and T → ∞, respectively), where the characteristic exponents, however, display a nontrivial dependence on temperature.

Proposal to Solve the Time−Stress Discrepancy of Tube Models

Recently, Liu et al. (Macromolecules 2006, 39, 3093) showed a systematic discrepancy of tube model predictions for describing the apparent plateau modulus of short (weakly entangled) linear chains while predicting very accurately their terminal relaxation times. In the present article, we investigate the origin of this problem, which We call time-stress discrepancy, by confronting our time-marching algorithm (TMA) with experimental viscoelastic data of nearly monodisperse linear polymers. We show that the contour length fluctuations of the outer molecular segments are overestimated, not taking into account the fact, that I chain needs a short but essential time to be considered in equilibrium ill its tube, Indeed, tube models consider that stress relaxation by reptation or contour length fluctuations starts at time t = 0 after an imposed small deformation, whereas in reality. there is a proceeding fast Rouse relaxation, which is especially important for shorter chains. Therefore, We propose to use a new segment coordinate system for describing the contour length fluctuations process, which restores the consistency with the tube definition and ensures that the necessary time for reaching an equilibrated system is equal to the relaxation time of an entanglement segment, tau(e). Results obtained with the so-corrected TMA model show I very good agreement with experimental data. In particular, the molecular-weight dependence of the apparent plateau modulus, the zero-shear viscosity, and the terminal relaxation time are now correctly predicted.

Impact of resistant starch on colonic crypt cytokinetics and cell cycle regulatory genes

Food is an immensely complex and endlessly varied matrix, rich in polymers of plant and animal origin, some of which resist hydrolysis by human digestive enzymes. The upper gastrointestinal tract...

Inhomogeneous electron liquids generated by Coulomb confinement of electrons with and without interparticle repulsions

The inhomogeneous electron liquid created through Coulomb confinement by a single-centre potential energy −Ze 2/r remains central to the fundamental 1/Z expansion: a pillar of analytic atomic theory. Therefore, some recent progress in this area of non-relativistic quantum mechanics is first discussed, the main focus being the Feynman propagator. The closely related Slater sum is also treated, differential equations being cited in both three and two dimensions. The effect of interparticle interactions on the density of the electron liquids will next be considered in two areas: (i) for models of He-like atomic ions with nuclear charge Ze where analytic ground state electron densities can be obtained, as well as the exact differential equations they satisfy, and (ii) fine-tuning of Hartree–Fock densities for four spherical atoms, Be, Ne, Mg and Ar. In (ii), a semi-empirical framework is now available in which the experimental ionisation potential replaces that of Koopmans. Densities having almost QMC quality are thereby available. Finally, the inhomogeneous electron liquids in short linear chains of H nuclei stabilised by one electron plus an intense magnetic field along the chain axis will be treated, fields considered being as found at the surfaces of some neutron stars.

PH-dependent swelling of hydrogels containing highly branched polyamine macromonomers

We examine the pH-dependent swelling of end-linked hydrogels containing high concentrations of amine-functional macromonomers. Gels are formed by end-linking of epoxide-terminated, linear poly(ethylene glycol) (PEG) to either amine-terminated poly(amidoamine) (PAMAM) dendrimers or highly branched poly(ethyleneimine) (PEI). After extraction in neutral water, the hydrogels are swollen in aqueous solutions of HCl or NH4OH to vary the external pH. Equilibrium volume swelling ratios (Qs) pass through a maximum value (Qmax) at an external pH denoted as pH∗ which is approximately 4–5 for the gels studied. The swelling behavior is modeled using Donnan equilibrium theory to describe the ion swelling pressure, with the Flory–Rehner phantom network expression representing the elastic and mixing contributions to the free energy. The model accurately predicts the maximum in swelling near pH=4–5, but overestimates Qmax for several of the gels due to neglecting the finite extensibility of the short linear PEG chains.