Low Molecular Weight Counterparts Research Articles

Thermomorphic Polyethylene-Supported Olefin Metathesis Catalysts

The preparation of polyethylene-oligomer (PE(olig))-supported N-heterocyclic carbene ligands (NHCs) and their Ru complexes is described. These complexes are structurally analogous to their low molecular weight counterparts and can serve as thermomorphic, recoverable/recyclable ring-closing metathesis (RCM) catalysts. Because of the insolubility of PE(olig)-supported species at 25 °C, such complexes can perform homogeneous RCM reactions at 65 °C and, upon cooling, precipitate as solids. This allows for their quantitative separation from solutions of products.

Poly(oligo-D-arginine) With Internal Disulfide Linkages as a Cytoplasm-sensitive Carrier for siRNA Delivery

Small interfering RNA (siRNA) has emerged as a therapeutic strategy for various diseases due to its target-specific gene silencing; however, its relatively high molecular weight, negative charge, and low stability hamper in vitro and in vivo applications. Approaches to overcome those drawbacks have relied on nonviral siRNA carriers based on cationic polymers or peptides. Nevertheless, cationic polymer-based siRNA carriers have yet to resolve intrinsic problems such as cytotoxicity and immunogenicity. An environment-sensitive carrier was recently proposed to enhance siRNA bioactivity and to reduce the carrier safety issues. Only a few studies, however, have shown cytoplasm-sensitive dissociation of the polyplex. In the present study, we clearly demonstrated decondensation of siRNA/poly(oligo-D-arginine) polyplex in the cytoplasm in response to intracellular glutathione (GSH) and the enhanced bioactivity of siRNA against VEGF (siVEGF) used as a model both in vitro and in an animal model. Reducible poly(oligo-D-arginine) (rPOA) rapidly dissociated in the cytoplasm, resulting in fast siRNA release to its target location while maintaining siRNA bioactivity both in vitro and in vivo.

Chelating oleyl-EDTA amphiphiles: self-assembly, colloidal particles, complexation with paramagnetic metal ions and promise as magnetic resonance imaging contrast agents

Chelating amphiphiles with N, N′-ethylene diamine tetraacetic acid (EDTA) conjugated via an ester bond to one or two oleyl chain/s (EDTA-MO and EDTA-BO) have been found to be capable of chelating a variety of metal ions including paramagnetic metal ions such as Manganese (Mn) and Gadolinium (Gd). Thermal behavior and stability were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). X-ray diffraction (XRD), polarizing optical microscopy (POM) and synchrotron small and wide angle X-ray scattering (SWAXS) were used to examine the neat and lyotropic liquid crystalline phases of these amphiphiles. Aqueous colloidal dispersions of EDTA-MO and EDTA-BO and their paramagnetic metal ion chelates were examined by synchrotron SAXS, cryogenic transmission electron microscopy (cryo-TEM) and light scattering. The complexed colloidal particles were evaluated as contrast enhancement agents (CEAs) for magnetic resonance imaging (MRI) using low field NMR. Neat EDTA-MO and EDTA-BO displayed lamellar crystalline structures at room temperature. EDTA-MO in excess water or sodium acetate solution exhibited a lamellar liquid crystalline phase (Lα) across a broad range of temperatures, whereas EDTA-BO displayed a very rich polymorphism from lamellar to inverse cubic and inverse hexagonal phases depending on the ionic strength of the aqueous solution and temperature employed. Dispersion of the bulk lyotropic liquid crystalline phases of both amphiphiles in aqueous Na-acetate solution yielded stable and predominantly liposomal particles at room temperature. Complexation of an EDTA-MO colloidal dispersion with Mn(II) or Gd(III) ions resulted in liposomal particles with significantly enhanced relaxivity values when compared with their low molecular weight counterparts Mn-EDTA and Gd-EDTA. In contrast, complexation of the EDTA-BO colloidal dispersion with Mn(II) altered the liposomal structure to highly ordered cylindrical multi-wall lipid nanotubes (MWLNTs). Again the relaxivity values were enhanced significantly in comparison with the Mn-EDTA analogue. In particular, the transverse relaxivity value of these complexed colloidal particles was enhanced significantly, which suggests that these MWLNTs have potential for use as both T1 and T2-weighted contrast agents.

Cyclin overexpression inhibits Smad 3 tumor suppression in breast cancer cells.

Abstract Abstract #5033 Introduction: The transcription factor Smad 3, a member of the TGFβ signaling cascade, contributes to G1 cell cycle arrest in breast cancer cell lines. Overexpression of the cell cycle regulatory protein cyclin E, and its low molecular weight (LMW) counterparts, has been associated with poor prognosis in breast cancer. Cyclin E has been shown to mediate phosphorylation within or near the linker region of Smad 3 by cyclin dependent kinase 2 (CDK 2), and to inhibit Smad 3 activity in normal mouse fibroblasts and epithelial cells. We hypothesize that overexpression of cyclin E may exert tumorigenic effects in breast cancer cell lines through the functional inhibition of Smad 3 mediated by CDK 2 phosphorylation.
 Methods: Endogenous levels of Smad 3 and phosphorylated Smad 3 in parental, vector only control, full length (FL), and two LMW forms of cyclin E overexpressing MCF-7 breast cancer cell lines were determined by western blotting. To elucidate the impact of cyclin E overexpression on Smad 3 function, constructs containing an empty vector, WT Smad 3, Smad 3 with a CDK phosphorylation site mutation within the linker region (Thr178), and outside the linker region (Thr8) were co-transfected with a Smad 3 reporter into the panel of MCF-7 cells. CDK2 or scrambled control siRNA was also transfected into the study panel of cells. Smad 3 function was then evaluated by luciferase reporter assays.
 Results: MCF-7 cells overexpressing FL or LMW cyclin E had a higher level of P- SMAD 3 as compared to the parental and vector only control cells. Total SMAD 3 levels were similar in all cells examined. Transfection of WT Smad 3 elicited an increase in reporter activity in parental and vector control cells, while both FL and LMW forms of cyclin E overexpressing cells were resistant to WT Smad 3 reporter induction. In parental and vector control MCF-7 cells, expression of the Smad 3 Thr178 mutation resulted in a three-fold induction in Smad 3 reporter activity as compared to the WT Smad 3 response. In FL and LMW cyclin E overexpressing cells, induction by the Thr178 mutation was more pronounced, as seen by a 5-fold and 8-fold induction of reporter activity in FL and LMW cyclin E cells, respectively. Transient transfection of the Thr8 mutation failed to evoke a reporter response in any of the panel of MCF-7 cells. MCF-7, FL, and LMW cyclin E cells demonstrated the greatest fold induction of Smad 3 reporter activity when transfected with CDK 2 siRNA.
 Conclusions: Overexpression of cyclin E may circumvent the growth inhibitory effects of Smad 3 signal transduction through the modulation of Smad 3 function. Specifically, this work indicates that cyclin E mediates Smad 3 inhibition in a CDK 2 dependent fashion in breast cancer cells. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5033.

Tensile and elastic properties of triblock copolymer based on aramide end‐segments and polyether mid‐segments

AbstractThe tensile and elastic behavior of triblock copolymers containing uniform aramide (TΦB) hard end‐segments (HS) and poly(tetramethylene oxide) (PTMO, Mn = 2900 g/mol) soft segments (SSs) was studied. The molecular weight of the copolymer was varied by changing the length of the soft mid‐segment; by extending the PTMO2900 with terephthalate units, the SS length was increased from 2900 g/mol to 21,000 g/mol and concurrently the aramide concentration decreased from 18 to 3 wt %. The mechanical properties were investigated by means of tensile testing, stress relaxation (SR) experiments, and cyclic tensile set (TS) tests. The E‐modulus was found to increase with increasing aramide content. The low molecular weight copolymers were brittle whereas the high molecular weight copolymers displayed large fracture strain values. The transition from brittle to ductile seemed to occur at a triblock copolymer molecular weight of 6600 g/mol. A strain‐induced crystallization was observed at strains above 250%, and both the fracture strain and stress were found to be highly dependant on the molecular weight of the copolymer. Cyclic tensile experiments showed that the materials had low TS values up to the strain hardening point. On the other hand, the SR data at 10% strain seemed to be little dependant on the molecular weight. The higher molecular weight copolymers did not display lower SR values than their low molecular weight counterparts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Monte Carlo Simulation of Interlamellar Isotactic Polypropylene

Monte Carlo molecular simulations are reported to investigate the amorphous region between crystalline lamellae of isotactic polypropylene ( iPP). It is the first such study in which consideration is given to the nature of pendant side groups on the polymer chain. The crystalline lamellae are modeled after the R2 crystal of iPP, while the interphase and amorphous domains are equilibrated with respect to both spatial and topological degrees of freedom. A united atom force field is used to describe the interactions between the methyl, methylene, and methyne moieties that constitute a polypropylene molecule. Mass density and bond orientational order profiles, distributions of chain populations, interphase thicknesses, interfacial energies, local conformations as characterized by torsional angle sequences, and chain reentry statistics are studied for three different temperatures. Our results match well with the available experimental data and provide a molecular level understanding of the interphase for isotactic polypropylene. A comparison with linear polyethylene (PE) reveals the effects of chemical architecture on the crystal -amorphous interphase in polymers. Semicrystalline polymers have found widespread use due to their excellent mechanical and barrier properties. The crystal- lization of polymers corresponds to a first-order phase transi- tion, 1 similar to other substances. However, a significant difference between long chain molecules and their low molecular weight counterparts lies in the kinetics of the crystallization process, because of which the complete incorporation of polymer molecules into the ordered crystalline state is rarely achieved. Thus, semicrystalline polymers are structurally nonhomoge- neous materials and invariably consist of an intimate mixture of crystalline and amorphous phases. These polymers exhibit properties that are a consequence of the combined attributes of ordered (crystalline) and disordered (amorphous) constituent regions, with the unique feature that both crystalline and noncrystalline elements are topologically connected by chains that meander their way from region to region. A comprehensive understanding of the behavior of polymers thus demands extensive knowledge not only of the individual phases but also the interplay between them. The existence and lamellar nature of polymers have been known for approximately half a century. 2-8 Various facets that describe the state of the system can be identified, including the gross morphological structure, degree

A novel polymeric chiral salen Mn(III) complex as solvent-regulated phase transfer catalyst in the asymmetric epoxidation of styrene

A novel solvent-regulated phase transfer catalyst of polymeric chiral salen Mn(III) complex with chiral diamine bridging was synthesized and its performance in the asymmetric epoxidation of styrene was investigated. In comparison with its low molecular weight counterpart of the homogeneous monomeric chiral salen Mn(III) complex, the polymeric chiral salen Mn(III) complex showed similar yield and enantioselectivity of the epoxide under the same reaction conditions. The effects of axial base, reaction temperature, and solvent on the catalytic performance of the polymeric chiral salen Mn(III) complex were investigated systematically. It was found that, under optimal reaction conditions, the yield of the epoxide and the enantioselectivity were as high as 98 and 47%, respectively. Furthermore, the polymeric chiral salen Mn(III) complex could be conveniently recovered for recycled use. Indeed the complex could be reused at least three times without significant losses of both activity and enantioselectivity.

Maize and radish sequester excess cadmium and zinc in different ways

The aims were to compare the reactions of radish and maize to excess cadmium (Cd), zinc (Zn) and Cd+Zn in terms of metal extractability and the amounts of metal in roots and shoots bound through phytochelatins (PCs). Seedlings were grown in hydroponics and exposed to 1 μM Cd, 50 μM Zn and their combination for 10 and 15 days. Tissues were extracted with buffer followed by acid. Buffer soluble metal was resolved by small-scale gel filtration. Six buffer extracts removed 87–95% of the Cd from roots of radish and maize, 43–57% of the Zn in their roots, yet 71–86% of the Cd and Zn in shoots. Acid removed most of the remaining metal. Buffer soluble Cd yielded three peaks including a prominent high molecular weight (HMW) PC-based complex and the low molecular weight (LMW) counterpart. In radish these complexes accounted for 69% of the Cd in the roots and 42% of the Cd in shoots, for maize 88% in the roots and 27% in the shoots. Most buffer soluble Zn (83–87%) from radish and maize roots and shoots eluted close to the total volume of the gel filtration column. A small Zn peak (4–7%) corresponding to the HMW Cd-binding complex was found in maize roots, not in radish. PCs were not prominent ligands for Zn in maize and not at all in radish. The ligands for most of the Zn remain unidentified.

Marine diatom uptake of iron bound with natural colloids of different origins

Natural colloids are abundant in seawater and are an intermediary in the fate, transport and bioavailability of many trace elements. Knowledge of the pathways and mechanisms of the biological uptake of colloidal Fe and other Fe species is of paramount importance in understanding Fe limitation on marine phytoplankton and thus carbon sequestration in the ocean. Whether the natural colloids serve as a source for the biological Fe requirements of marine phytoplankton, or just as a sink for particle-reactive metals in the oceans remains largely unknown. This study examined the bioavailability of Fe bound with colloids from different regions to a coastal diatom ( Thalassiosira pseudonana). Natural colloids were isolated by cross-flow ultrafiltration and radiolabeled with 59Fe before being exposed to phytoplankton. Control experiments were conducted to ensure that 59Fe radiolabeled onto the colloids remained mostly in the colloidal phase. Both the natural oceanic and coastal colloidal organic matter complexed Fe (1 nm–0.2 μm) can be biologically available to the marine diatom even though its uptake was lower than the low molecular weight counterparts. By comparing the measured Fe internalization fluxes and the calculated maximum diffusive uptake fluxes, it is evident that ligand exchange kinetics on the cell surface may control the internalization of macromolecular Fe. The calculated concentration factors under dark and light conditions were generally comparable. Colloidal Fe, as an important intermediary phase, can be actively involved in the planktonic food web transfer through biological uptake and regeneration processes. The bioavailable fraction of Fe may be substantially underestimated by only considering the truly dissolved Fe or overestimated when using the external fluxes, such as aerosol Fe, as the bioavailable fraction.

Effect of molecular weight and concentration of poly(acrylic acid) on the formation of a polymeric calcium phosphate cement.

Previous investigations have noted that the tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA) apatite forming calcium phosphate cement (CPC) possesses many favorable properties from a biomaterials standpoint. Despite these positive properties various shortcomings have limited clinical usage of these materials and fostered investigations into the effect of numerous additives. The present study concerns the effect of poly(acrylic acid) (PAA) addition and the influence of factors such as molecular weight and concentration of the additive on the properties of the set cement. One-way ANOVA was conducted using all results obtained, to firstly derive the influence of concentration within each molecular weight group, and secondly to derive the influence of molecular weight within each concentration group. All investigated mechanical properties were influenced by both molecular weight and concentration of the additive. Higher molecular weights tended to result in cements with shorter setting times and higher compressive, diametral and biaxial flexural strengths than their lower molecular weight counterparts. The effect of concentration on the properties of the set cement however was somewhat more complex, a negative correlation was observed between the initial setting time and PAA concentration. In regards to the final setting time, any correlation with concentration was difficult to derive as a consequence of the highly brittle nature of cements made with low concentrations. In regard to mechanical properties, intermediate concentrations tended to give higher strengths than both their higher and lower counterparts, however the exact pattern was largely specific to the mechanical strength test employed. We conclude that molecular weight and concentration of PAA influence the setting behavior and final mechanical properties of the TTCP/DCPA cement, and that selection of an appropriate PAA solution can lead to the production of cements with properties superior to those formed in the absence of the polymer.

Evaluation and optimization of two complementary cross-flow ultrafiltration systems toward isolation of coastal surface water colloids.

While colloidal phases in natural waters are important to the speciation and bioavailability of trace metals and organic compounds, accurate isolation of these submicron entities from their lower molecular-weight counterparts has proved challenging. Here, both laboratory and field experiments have been conducted to constrain integrity aspects of two different cross-flow filtration (CFF) systems. We tested both a commonly applied 5000 cm2 CFF system (Pellicon2, Millipore; manufacturer-specified 1 and 3 kDa cutoff) and a less studied mini-CFF system with a 50 cm2 membrane area (Pellicon Lab Scale XL, Millipore; with 5, 10, 100, and 1000 kDa cutoff). A natural water matrix amended with a series of fluorescently tagged colloidal probes was employed to demonstrate that a cross-flow ratio (CFR; retentate-to-permeate flux) > 15 was required for both of these systems to obtain high recoveries of colloids. Contrary to previous calibrations of CFF, also at colloid concentrations characteristic of natural waters, the established retention profiles for the colloid probes on these systems, when operated under CFR > 15, affirmed the manufacturer-specified cutoff values (in parentheses): 2.4 kDa (1 kDa), 3.3 kDa (3 kDa), 6.1 kDa (5 kDa) and 8.7 kD (10 kDa). A concentration factor (cf) > 10 was found necessary for the reliable determination of the colloidal pool of several elements in the surface waters of the open Baltic Sea. Application of CFR > 15 and cf > 10 returned recoveries around 100% for the studied organic carbon, Ca, Mo, Fe, Cu, and Ni on both systems. Furthermore, the trend of colloid association for the transition elements in the offshore Baltic surface waters followed expectations from their Irving-Williams series of coordination chemistry.

Screening Effects in Solutions of a Hyperbranched, Dendrimer-Like Polyester

We have previously shown that infrared spectroscopy can be used to “count” the number of contacts in hydrogen-bonded system. We use such information to determine appropriate self- and interassociation equilibrium constant values and at the same time take into account the intramolecular “screening” in polymer blends and solutions. The calculated values reported here for screening, and hence the accessibility of the functional groups in a hyperbranched polyester, are based on the interassociation equilibrium constants obtained from the low molecular weight counterparts of the hyperbranched repeat units and give a measure of the accessibility of functional groups in these highly branched systems.

Synthesis, characterization, biodegradation, and drug delivery application of biodegradable lactic/glycolic acid polymers. Part II: Biodegradation

A series of previously-synthesized lactic/glycolic acid polymers (PLGA) with various molar ratios of lactic to glycolic acid and various molecular weights were further studied with regard to their biodegradation behavior, and in particular, the factors affecting the biodegradation rate. The biodegradation of PLGA is affected by many factors including polymer composition, molecular weight, and nature of the incubating media. The biodegradation rate of PLGA containing higher content of lactic acid moiety is lower than those containing a lower content of lactic acid moiety. PLGAs with a higher molecular weight, degrade faster than those with a lower molecular weight, i.e. the molecular weight decreases more rapidly for higher molecular weight PLGAs than their lower molecular weight counterparts. Nature or properties of the hydrolysis/incubating media may have an effect on the biodegradation of PLGAs. A basic medium may slow down the biodegradation of PLGA in comparison with samples in an acidic medium. The rate of pH reduction for the incubating medium can be divided into three deferent phases, giving an inverted S-type pH profile for the non-buffered incubating media.

Structure and Rheological Behaviour of Arabinoxylans from Canadian Bread Wheat Flours

Water-soluble arabinoxylans from 10 flours of eight different varieties of the Canada western red spring (CWRS) wheat class (Neepawa, Katepwa, Roblin, Columbus, Benito, Lauro, Lancer, and Selkirk) were isolated and purified. Chemical analyses indicated only a small variation in the degree of branching among arabinoxylans; arabinose to xylose ratios ranged from 0.62 to 0.68. In contrast, substantial differences were found in the content of ferulic acid (0.93 to 1.52 mg/g), molecular size distribution, and in molecular weight (134,700-201,600) of the 10 arabinoxylan preparations. Oxidative gelation studies (using H202 peroxidase) revealed significant differences in the capacity of these polymers to form gels via intermolecular cross-linking. The values of elastic modulus, G', of arabinoxylan gels (10 g/L) varied from 5.8 Pa to 43.0 Pa. The high molecular weight arabinoxylans formed more rigid gels at low polymer concentration than did their low molecular weight counterparts. In addition to molecular weight, the ferulic acid content was an important determinant of gel network rigidity.

Structural and textural properties of calcium induced, hot-made alginate gels

The accepted mechanism of alginate gelation at ambient temperature is by formation of egg-box junctions between pairs of polyguluronate chain sequences and an included array of site-bound calcium ions. We now present evidence (circular dichroism and low-amplitude mechanical spectroscopy data) of similar regular interactions at high temperatures where all the active ingredients (alginate, salt and sequestrant) are hydrated in a hot medium. During controlled cooling, a second transition is obtained at low temperatures, which may be attributed to the lateral interaction of dimeric chains and thus the development of an extended, three-dimensional network. A subsequent temperature increase melts the second wave of structure formation, thus producing substantial thermal hysteresis, but preserves the ‘weak gel’ properties of the alginate-calcium reaction observed at elevated temperatures. At levels of salt higher than 40% calcium conversion aggregation can occur even at 90°C, leading to precipitation rather than a homogenous network. Prolonged refrigeration (72 h at 4–5°C) sustains a gradual molecular rearrangement to a self-supporting (visual evidence), firmer (frequency sweeps) network. Surprisingly, the strongest high guluronate alginate is not only more elastic than its low molecular weight counterpart (strain sweeps in dynamic oscillation) but it also exhibits higher yield strain on compression testing than the high molecular weight, high mannuronate sample. The distinct differences in the long-range properties of high guluronate and high mannuronate alginate samples with comparable molecular weights might serve as a guide for the development of reformed products with the desired characteristics.

The NH2-terminal extension of rat liver arginyl-tRNA synthetase is responsible for its hydrophobic properties

Rat liver arginyl-tRNA synthetase is found in extracts either as a component (Mr = 72,000) of the multienzyme aminoacyl-tRNA synthetase complex or as a low molecular weight (Mr = 60,000) free protein. The two forms are thought to be identical except for an extra peptide extension at the NH2-terminus of the larger form which is required for its association with the complex, but is unessential for catalytic activity. It has been suggested that interactions among synthetases in the multienzyme complex are mediated by hydrophobic domains on these peptide extensions of the individual proteins. To test this model we have purified to homogeneity the larger form of arginyl-tRNA synthetase and compared its hydrophobicity to that of its low molecular weight counterpart. We show that whereas the smaller protein displays no hydrophobic character, the larger protein demonstrates a high degree of hydrophobicity. No lipid modification was found on the high molecular weight protein indicating that the amino acid sequence itself is responsible for its hydrophobic properties. These findings support the proposed model for synthetase association within the multienzyme complex.

Lignosulfonate polymerization: Effect of cross‐linking agents

AbstractFactors affecting the thermosetting properties of spray‐ or freeze‐dried, ammonium‐based spent sulfite liquor, a material rich in lignosulfonates, were investigated. It was found that purified lignosulfonates did not thermoset readily, unless either monomeric wood sugars or formaldehyde were present. Under the conditions employed, the monosaccharides were more effective than formaldehyde as thermoset accelerators. This may be due to the greater functionality of the intermediate decomposition products of the carbohydrates, which would create more reactive sites for intermolecular bonding with lignin. In contrast to previous findings, it was found that lignosulfonates (of mol wt ≥ 10,000) underwent polymerization, and subsequent thermosetting, more rapidly than their lower molecular weight counterparts. This was established by HPLC size exclusion elution chromatography of each sample following thermal treatment. It was also observed that wood did not affect the rate of thermosetting.