Well-defined higher-molecular-weight polyacrylonitrile via RAFT technique in the presence of disulfide compounds as a source of chain transfer agent

Well-defined polyacrylonitrile with a higher number-average molecular weight (R.) up to 200,000 and a lower polydispersity index (PDI, 1.7-2.0) was firstly obtained via reversible addition-fragmentation chain transfer (RAFT) process. This was achieved by selecting a stable, easy way to prepare disulfide compound intermediates including bis(thiobenzoyl) disulfide (BTBDS) and bis(thiophenylacetoyl) disulfide (BTPADS) to react with azobis(isobutyronitrile) to directly synthesize RAFT agents in situ.

Phosphine-Free Synthesis of High-Quality CdSe Nanocrystals in Noncoordination Solvents: "Activating Agent" and "Nucleating Agent" Controlled Nucleation and Growth

CdSe nanocrystals (NCs) are prepared in noncoordination solvents (1-octadecene (ODE) and paraffin liquid) with Ion g-chain primary alkylamine as the sole ligand, ODE-Se, and cadmium fatty acid salt as precursors. The obtained NCs meet the four fundamental parameters for high-quality NCs: high crystallinity, narrow size distribution, moderate photoluminescence quantum yield, and broad range size tunableness. Further, by simply regulating the relative molar ratio of alkylamine to cadmium precursor, the regular sized "nuclei" and final obtained NCs can be produced predictably within a certain size range.

Multiplex binding modes of toluidine blue with calf thymus DNA and conformational transition of DNA revealed by spectroscopic studies

It is noteworthy to understand the details of interactions between antitumor drugs and DNA because the binding modes and affinities affect their antitumor activities. Here, The interaction of toluidine blue (TB), a potential antitumor drug for photodynamic therapy of tumor, with calf thymus DNA (ctDNA) was explored by UV-vis, fluorescence, circular dichroism (CD) spectroscopy, UV-rnelting method and surface-enhance Raman spectroscopy (SERS). The experimental results suggest that TB could bind to ctDNA via both electrostatic interaction and partial intercalation.

Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with beta-Phase Nucleating Agent

The microstructure and mechanical properties of beta-nucleated iPP before and after being annealed at different temperatures (90-160 degrees C) have been analyzed, Annealing induced different degrees of variation in fracture toughness of beta-nucleated iPP samples. namely, slight enhancement at relatively low annealing temperatures (< 110 degrees C) and great improvement at moderate temperatures (120-130 degrees C), whereas dramatic deterioration at relatively high temperatures ( > 140 degrees C) has been observed. The variation of fracture toughness of beta-nucleated iPP is observed to be dependent on the content of beta-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the beta-nucleated iPP after being annealed.

Poly(ethylene glycol-co-propylene glycol) as a Macromolecular Plasticizing Agent for Polylactide: Thermomechanical Properties and Aging

Finding a Suitable plasticizer for polylactide (PLA) is necessary to overcome its brittleness and enlarge its range of applications. In this study, commercial PLA was melt-blended with a new plasticizer, an ethylene glycol/propylene glycol random copolymer [poly(ethylene glycol-co-propylene glycol) (PEPG)] with a typical number-average molecular weight of 1.2 kDa and an ethylene glycol content of 78.7 mol %. The thermal properties, crystallization behavior, and mechanical properties of the quenched blends and the properties of the blends after storage for 2 months under the ambient conditions were investigated in detail. The advantage of using PEPG is that it does not crystallize at room temperature and has good compatibility with PLA. The quenched PLA/PEPG blends were homogeneous and amorphous systems. With an increase in the PEPG content (5-20%), the glass-transition temperature, tensile strength, and modulus of the blends decreased, whereas the elongation at break and crystallizability increased dramatically. The cold crystallization of PLA resulted in phase separation of the PLA/PEPG blends by annealing of the blends at the crystallization temperature.

Biodegradable amphiphilic polymer-drug conjugate micelles

The coupling of drugs to macromolecular carriers received an important impetus from Ringsdorf's notion of polymer-drug conjugates. Several water-soluble polymers, poly(ethylene glycol), poly[N-(2-hydroxypropyl) methacrylamidel, poly(L-glutamic acid) and dextran, are studied intensively and have been utilized successfully in clinical research. The promising results arising from clinical trials with polymer-drug conjugates (e.g., paclitaxel, doxorubicin, camptothecins) have provided a firm foundation for other synthetic polymers, especially biodegradable polymers, used as drug delivery vehicles. This review discusses biodegradable polymeric micelles as an alternative drug-conjugate system. Particular focus is on A-B or B-A-B type biodegradable amphiphilic block copolymer such as polylactide, morpholine-2,5-dione derivatives and cyclic carbonates, which can form a core-shell micellar structure, with the hydrophobic drug-binding segment forming the hydrophobic core and the hydrophilic segment as a hydrated outer shell. Polymeric micelles can be designed to avoid uptake by cells of reticuloendothelial system and thus enhance their blood lifetime via the enhanced permeability and retention effect.

Suppression of phase separation in PC/PMMA blend film by thermoset oligomer

Phase separation of bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) thin blend film is suppressed by addition of solid epoxy oligomer. Epoxy has strong intermolecular interactions with both PC and PMMA, while PC and PMMA are quite incompatible with each other. Consequently, phase separation in the PC/PMMA blend film pushes epoxy to the interface; at the same time, PC and epoxy react readily at the interface to form a cross-linking structure, binding PMMA chains together. Therefore, the interface between PC and PMMA is effectively reinforced, and the PC/PMMA thin blend film is stabilized against phase separation. On the other hand, only an optimal content of epoxy (i.e., 10 wt %) can serve as an efficient interfacial agent. In contrast to the traditional reactive compatibilization, here we observed that the cross-linking structure along the interface is much more stable than block or graft copolymers. Atomic force microscopy (AFM) is used to characterize the morphological changes of the blend films as a function of annealing time. Two-dimensional fast Fourier transform (2D-FFT) of AFM data allows quantitative investigation of the scaling behavior of phase separation kinetics.

Single-walled carbon nanotubes binding to human telomeric i-motif DNA: significant acceleration of S1 nuclease cleavage rate

Single-walled carbon nanotubes (SWNTs) binding to human telomeric i-motif DNA can significantly accelerate S1 nuclease cleavage rate by increasing the enzyme turnover number.

Daunomycin binding to detergent micelles: A model system for evaluating the hydrophobic contribution to drug-DNA interactions

The interaction of daunomycin with sodium dodecyl sulfate and Triton X-100 micelles was investigated as a model for the hydrophobic contribution to the free energy of DNA intercalation reactions. Measurements of visible absorbance, fluorescence lifetime, steady-state fluorescence emission intensity, and fluorescence anisotropy indicate that the anthraquinone ring partitions into the hydrophobic micelle interior. Fluorescence quenching experiments using both steady-state and lifetime measurements demonstrate reduced accessibility of daunomycin in sodium dodecyl sulfate micelles to the anionic quencher iodide and to the neutral quencher acrylamide. Quenching of daunomycin fluorescence by iodide in Triton X-100 micelles was similar to that seen with free daunomycin. Studies of the energetics of the interaction of daunomycin with micelles by fluorescence and absorbance titration methods and by isothermal titration calorimetry in the presence of excess micelles revealed that association with sodium dodecyl sulfate and Triton X-100 micelles is driven by a large negative enthalpy. Association of the drug with both types of micelles also has a favorable entropic contribution, which is larger in magnitude for Triton X-100 micelles than for sodium dodecyl sulfate micelles.

Downhill kinetics of biomolecular interface binding: Globally connected scenario

We study the kinetics of the biomolecular binding process at the interface using energy landscape theory. The global kinetic connectivity case is considered for a downhill funneled energy landscape. By solving the kinetic master equation, the kinetic time for binding is obtained and shown to have a U-shape curve-dependence on the temperature. The kinetic minimum of the binding time monotonically decreases when the ratio of the underlying energy gap between native state and average non-native states versus the roughness or the fluctuations of the landscape increases. At intermediate temperatures,fluctuations measured by the higher moments of the binding time lead to non-Poissonian, non-exponential kinetics. At both high and very low temperatures, the kinetics is nearly Poissonian and exponential.

Drug-human serum albumin binding studied by capillary electrophoresis with electrochemiluminescence detection

A new technique for investigating drug-protein binding was developed employing capillary electrophoresis (CE) coupled with tris(2,2'-bipyridyl) ruthenium(II) [Ru(bPY)(3)(2+)] electrochemiluminescence (ECL) (CE-ECL) detection after equilibrium dialysis. Three basic drugs, namely pridinol, procyclidine and its analogue trihexyphenidyl, were successfully separated by capillary zone electrophoresis with end-column Ru(bPY)(3)(2+) ECL detection. The relative drug binding to human serum albumin (HSA) for each single drug as well'as for the three drugs binding simultaneously was calculated. It was found that the three antiparkinsonian drugs compete for the same binding site on HSA. This work demonstrated that Ru(bPY)(3)(2+) CE-ECL can be a suitable technique for studying drug-protein binding.

Influence of shear on crystallization behavior of the beta phase in isotactic polypropylene with beta-nucleating agent

Wide-angle X-ray diffraction (WAXD) was used to investigate the effects of shear on the crystallization behavior of polypropylene (PP) with beta-nucleating agent. The melt was subjected to shear at the shear rate from 0.5 to 60 s(-1) for 5 s with a CSS450 shear stage. For the PP with low content of the additive, the formation mechanism of the beta crystals is almost the same as that of pure isotactic polypropylene (iPP), viz., shear induces. Otherwise, for the samples with high content of the additive, the formation mechanism of the beta form are nucleating agent induces. The results clearly show that shear restrains the formation of high beta phase for the melt with additive.

Gadolinium heteropoly complex K-17[Gd(P2W17O61)(2)] as a potential MRI contrast agent

Gadolinium heteropoly complex K-17[Gd(P2W17O61)(2)] has been evaluated by in vitro and in vivo experiments as a potential contrast agent for magnetic resonance imaging (MRI). The thermal analysis and conductivity study indicate that this complex has good thermal stability and wide pH stability range. The T-1 relaxivity is 7.59 mM(-1) s(-1) in aqueous solution and 7.97 mM(-1) s(-1) in 0.725 mmol l(-1) bovine serum albumin (BSA) solution at 25degreesC and 9.39 T, respectively. MR imaging of three male Sprague-Dawley rats showed remarkable enhancement in rat liver after intravenous injection, which persisted longer than with Gd-DTPA. The signal intensity increased by 57.1 +/- 16.9% during the whole imaging period at 0.082 mmol kg(-1) dose. Our preliminary in vitro and in vivo studies indicate that K-17[Gd(P2W17O61)(2)] is a potential liver-specific MRI contrast agent.

Enthalpy/entropy compensation: Influence of DNA flanking sequence on the binding of 7-amino actinomycin D to its primary binding site in short DNA duplexes

The effect of the context of the flanking sequence on ligand binding to DNA oligonucleotides that contain consensus binding sites was investigated for the binding of the intercalator 7-amino actinomycin D. Seven self-complementary DNA oligomers each containing a centrally located primary binding site, 5'-A-G-C-T-3', flanked on either side by the sequences (AT)(n) or (AA)(n) (with n = 2, 3, 4) and AA(AT)(2), were studied. For different flanking sequences, (AA)(n)-series or (AT)(n)-series, differential fluorescence enhancements of the ligand due to binding were observed. Thermodynamic studies indicated that the flanking sequences not only affected DNA stability and secondary structure but also modulated ligand binding to the primary binding site. The magnitude of the ligand binding affinity to the primary site was inversely related to the sequence dependent stability. The enthalpy of ligand binding was directly measured by isothermal titration calorimetry, and this made it possible to parse the binding free energy into its energetic and entropic terms.

Separation of yttrium from heavy lanthanide by CA-100 using the complexing agent

The selective extraction of yttrium front heavy lanthanide by liquid-liquid extraction using CA-100 in the presence of the complexing agent, such as EDTA, DTPA, and HEDTA was investigated. The extraction of heavy lanthanide in the present of the complexing agent was Suppressed when compared to that of Y because of the masking effect, but the selective extraction of Y was enhanced. All complexing agents formed 1: 1 complex with rare earth elements (RE), and only free rare earth ions could take part in the extraction. The condition for separation was obtained by exploring the effects of the complexing agent concentration, the extractant concentration, pH and the equilibration time on the extraction of the heavy rare earth elements.