Search results for "Macromolecule"

Adsorption of triblock copolymers and their homopolymers at laponite clay/solution interface. Role played by the copolymer nature

2009

The adsorption thermodynamics of copolymers, based on ethylene oxide (EO) and propylene oxide ( PO) units, at the laponite (RD) clay/liquid interface was determined at 298 K. The copolymer nature was tuned at molecular level by changing the hydrophilicity, the architecture and the molecular weight (Mw) keeping constant the EO/PO ratio. Polyethylene (PEGs) and polypropylene (PPGs) glycols with varying Mw and their mixture were also investigated to discriminate the role of the EO and the PO segments in the adsorption process. Enthalpies of transfer of RD, at fixed concentration, from water to the aqueous macromolecule solutions as functions of the macromolecule molality were determined. They …

Thermal diffusion of dextran in aqueous solutions in the absence and the presence of urea.

2006

The Ludwig-Soret effect was studied for aqueous solutions of dextran in the temperature range 15T55 degrees C taking into account the effect of the addition of urea. In the absence of urea, the Soret coefficient S(T) changes sign; it is positive for T45.0 degrees C but negative for T45.0 degrees C. The positive sign of S(T) means that the dextran molecules migrate toward the cold side of the fluid; this behavior is typical for polymer solutions, whereas a negative sign indicates the macromolecules move toward the hot side. The addition of urea to the aqueous solution of dextran rises S(T) and reduces the inversion temperature. For 2 M urea the change in the sign of S(T) is observed at T = 2…

Interactions of quinine with polyacrylic and poly-L-glutamic acids in aqueous solutions

2004

Abstract Drug-loaded polymers provide an attractive form for controlled drug delivery systems. A proper knowledge of polymer–drug interactions can aid in the designing of polymers for various drug-delivery applications. In this paper we have investigated the interaction of a drug such as quinine, with synthetic macromolecules such as poly(acrylic acid), PAA, and poly(L-glutamic acid), PGA, at pH 7 and 37 °C by fluorescence spectroscopy and viscometry. The analysis of the binding isotherms revealed that the association process is positive cooperative up to a threshold concentration and then it is negative. In addition, the thermodynamic parameters vary along the isotherm. Results also sugges…

1983

Poly(ethylene glycol)s grated onto suitably functionalized, crosslinked polystyrenes were introduced as a new class of multidetachably immobilized hydrophilic macromolecular supports for the synthesis of peptides. This new polymeric carrier system facilitates both the homogeneous solvation of the reaction site and the insolubilization of the substrate, which are prerequisites for an efficient multistep synthesis using polymeric supports. In these support systems, a strongly solvated hydrophilic linear chain molecule, poly(ethylene glycol) (PEG)1 , is attached to an insoluble, crosslinked polystyrene through suitable anchoring linkages. At the free chain end of this supported PEG, amino acid…

Precision Anisotropic Brush Polymers by Sequence Controlled Chemistry

2020

The programming of nanomaterials at molecular length-scales to control architecture and function represents a pinnacle in soft materials synthesis. Although elusive in synthetic materials, Nature has evolutionarily refined macromolecular synthesis with perfect atomic resolution across three-dimensional space that serves specific functions. We show that biomolecules, specifically proteins, provide an intrinsic macromolecular backbone for the construction of anisotropic brush polymers with monodisperse lengths via grafting-from strategy. Using human serum albumin as a model, its sequence was exploited to chemically transform a single cysteine, such that the expression of said functionality is…

Recycling of dry and wet polyamide 6

2002

Recycling of polycondensation polymers can give rise to secondary materials with good mechanical properties only if a careful drying is carried out before the melt reprocessing operations. The presence of humidity provokes the hydrolytic chain scission of the macromolecules and the consequent decrease of molecular weight and properties. In this work, the drying step was substituted by the addition of an antioxidant that is able to protect the macromolecules because it is the autioxidant is more prone to hydrolysis, thus removing the water from the melt. The mechanical properties of polyamide 6 reprocessed more times in wet conditions and in the presence of this stabilizer are even better th…

Significance of various enzymes in the control of reactive metabolites

1987

Most chemical carcinogens are relatively inert and need metabolic activation to the ultimately carcinogenic species. The concentration of such species is controlled by several different enzymes. Especially well studied is the important group of enzymes responsible for the control of reactive epoxides. Many natural, as well as man-made foreign compounds, including pharmaceuticals, possess olefinic or aromatic double bonds. Such compounds can be transformed to epoxides by microsomal monooxygenases present in many mammalian organs. By virtue of their electrophilic reactivity, such epoxides may spontaneously react with nucleophilic centres in the cell and thus covalently bind to DNA, RNA and pr…

Chemical conjugation of dexamethasone to a polyaspartamide and in vitro evaluation studies

2004

Two macromolecular conjugates of dexamethasone containing different drug amounts were synthesized using PHEA as the polymeric carrier and a succinic group as spacer. The content of linked drug was equal to 25.3% w/w (conjugate A) and 12.7% w/w (conjugate B). Both polymeric conjugates, unlike the free drug, were water-soluble and the amount of unlinked drug was evaluated to be approximately about 0.01% w/w. Both conjugates were relatively stable in vitro at pH 7.4 whereas in the presence of esterase only the conjugate B was able to release drug under the used experimental conditions. This dissimilar behavior has been attributed to the distinct macromolecular conformations assumed in aqueous …

Fullerene-Containing Polymers: An Overview

2009

Self-assembly properties of the proteinaceous coat secreted by the ?slime? variant of Neurospora crassa

1989

The proteinaceous extracellular material (PEM) synthesized by the cells of the ‘slime” strain of Neurospora crassa (see Martinez et al. 1989) was solubilized by treatment with urea or guanidine. Removal of these chemicals by dialysis, caused reassembly of the solubilized proteins into material with the same microscopic appearance as the original PEM. Polypeptide patterns from both native and reassembled structures were identical. Dialysis-mediated reassembly of the solubilized proteins appeared to be dependent on both concentration of the soluble macromolecules and time. Gel chromatography of PEM solubilized with different agents revealed two discrete populations of complexes with molecular…