Polymer microenvironment soluble polymers

The properties of the microenvironment of soluble synthetic polymers such as polymethacrylamide (PMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(2-vinylpyridine) (P-2VP), poly(4-vinylpyridine) (P-4VP), poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA), polystyrene (PS), poly(4[5]-vinylimidazole) (PVIm), and poly(N-2-hydroxypropyl methacrylamide) (PHPMA) and cross-lined polymers were studied by the shift and shape of the band in electronic spectra of a solvatochromic "reporter" molecule embedded in polymer chains. Preferential interaction of parts of the polymer molecule with a reporter and the shielding of interactions between solvent molecules and a reporter molecule of a polymer causes a shift and broadening of its solvatochromic band. This shift is mechanistically interpreted as a change in the polarity of the microenvironment of a polymer in solution in comparison with polarity of the solvent used. 4-(4-Hydroxystyryl)-N-alkylpyridinium-betaine, spiropyran-merocyanine, and l-dimethylamino-5-sulfonamidonaphthalene (Dansyl) reporters were used. In almost all cases the polarity of the polymer microenvironment was lower than that of the solvent. At the same time, the dependence of the nature of the environment on the distance of the reporters from the polymer chain was studied. 

The properties of the microenvironment of soluble and cross-linked synthetic polymers were studied using solvatochromic reporters bound to polymers. The polarity of the domain of polymer chains was estimated in one-component and binary solvents and compared with the polarity of solvents used. The polarity was expressed semiempirically by the absorption or emission band energy of a solvatochromic compound. The polarity of the microenvironment of soluble polymers and also the polarity in the vicinity of matrix of cross-linked polymers suspended in aqueous buffer was almost in all cases lower than that of the solvent. 

The activity of polymer-supported crown ethers depends on solvent. As shown in Fig. 11, rates for Br-I exchange reactions with catalysts 34 and 41 increased with a change in solvent from toluene to chlorobenzene. Since the reaction with catalyst 34 is limited substantially by intrinsic reactivity (Fig. 10), the rate increase must be due to an increase in intrinsic reactivity. The reaction with catalyst 41 is limited by both intrinsic reactivity and intraparticle diffusion (Fig. 10), and the rate increase from toluene to chlorobenzene corresponds with increases in both parameters. Solvent effects on rates with polymer-supported phase transfer catalysts differ from those with soluble phase transfer catalysts60. With the soluble catalysts rates increase (for a limited number of reactions) with decreased polarity of solvent60), while with the polymeric catalysts rates increase with increased polarity of solvent74). Solvents swell polymer-supported catalysts and influence the microenvironment of active sites as well as intraparticle diffusion. The microenvironment, especially hydration... 

Abstract Enantioselection in a stoichiometric or catalytic reaction is governed by small increments of free enthalpy of activation, and such transformations are thus in principle suited to assessing dendrimer effects which result from the immobilization of molecular catalysts. Chiral dendrimer catalysts, which possess a high level of structural regularity, molecular monodispersity and well-defined catalytic sites, have been generated either by attachment of achiral complexes to chiral dendrimer structures or by immobilization of chiral catalysts to non-chiral dendrimers. As monodispersed macromolecular supports they provide ideal model systems for less regularly structured but commercially more viable supports such as hyperbranched polymers, and have been successfully employed in continuous-flow membrane reactors. The combination of an efficient control over the environment of the active sites of multi-functional catalysts and their immobilization on an insoluble macromolecular support has resulted in the synthesis of catalytic dendronized polymers. In these, the catalysts are attached in a well-defined way to the dendritic sections, thus ensuring a well-defined microenvironment which is similar to that of the soluble molecular species or at least closely related to the dendrimer catalysts themselves. 

The sp values of most perfumery ingredients fall between ca. 16MPa1/2 (non-polar materials such as terpene hydrocarbons) and ca. 25 MPa1/2 (polar materials such as alcohols). In general, we expect that materials will have lower activity coefficients in microenvironments characterised by similar values of sp. For instance, limonene (sp value of 16.5) is expected to be compatible with plastics such as polyethylene and polypropylene (sp range typically 16-18), and to exhibit good solubility and retention in these polymers. We would anticipate that... 

The hydrophobic microenvironments created on the cross-linked polystyrene may raise the intrinsic peptide-hydrolyzing activity of the metal center, as noted above. The microdomains created on the synthetic polymer may facilitate complexation of the protein substrate with the catalytic center. Possible inactivation of the metal center by formation of hydroxo- or oxo-bridged dimers or oligomers can be prevented upon immobilization of the metal center to a sohd support. Higher pH values inaccessible by a soluble metal complex can be attained by the corresponding immobilized metal complex. The enhancement in the proteolytic activity of the Cu(II) complex of cyclen upon attachment to the polystyrene may be attributed to some of these effects. 

The many circumstances leading to the Henri equation for enzyme conversion of soluble substrates are first noted, followed by some kinetic forms for particulate and polymer hydrolysis. Effects common to immobilized enzyme systems are summarized. Illustrative applications discussed Include metabolic kinetics, lipid hydrolysis, enzymatic cell lysis, starch liquefaction, microenvironment influences, colloidal forces, and enzyme deactivation, all topics of interest to the larger themes of kinetics and thermodynamics of microbial systems. 

In the anhydrous microencapsulation, protein and excipients were suspended/dissolved in PLA/acetonitrile solution and then added to cottonseed oil to form an o/o emulsion with Span 85 as an emulsifier. Petroleum ether was then added to extract the acetonitrile and the microspheres were hardened. The microspheres were then recovered by filtration and dried under vacuum. As shown in Table 5 and Fig. 5, without the pore-forming PEG, only 36% BSA was released from PLA microspheres in 1-month of incubation with a total recovery (released-fall soluble and aggregated residue in polymer after release) of 76%. Blending in 30% of 35 kDa PEG with the PLA eliminated the BSA aggregation in polymer completely, with 82% of encapsulated BSA released in 1 month. The improved BSA stability in PLA/PEG microspheres could be attributed to a less acidic and more hydrophilic microenvironment in the polymer. As seen in Fig. 6, unlike PLGA 50/50, which caused a dramatic pH drop in the release medium after a 4-week incubation (41), a relatively neutral pH was retained in the release medium for both PLA and PLA/PEG microspheres. A slightly lower pH in the release medium incubated with PLA/PEG microspheres relative to that in PLA was also... 

From this observation one can predict that the absorption properties of a heterogeneous photosensitizer will be comparable to the absorption spectrum of its soluble equivalent. Thus if one knows the absorption properties of a monomeric model, takes into regard corrections for solvent and microenvironment, and measures the excitation fluorescence (or phosphorescence) spectrum of the polymer at low temperatures, these spectra should be essentially comparable. 

Treatment of the 8elenlum(IV) polymer with 30% H2O2 results In rapid loss of the color, presumably due to formation of the peracldi In a trlphase system at room temperature 1.5 mol X of the polymer and 1.5 - 1.8 equivalents of H2O2 were effective for oxidation of both olefins and ketones. Unlike the arsonated system, olefins opened readily to the trans dlols only In the case of tetramethylethylene could the epoxide be Isolated. Such a result may be due to partial oxidation to the selenonlc acid, a more powerful acid, or to a more aqueous microenvironment. The Baeyer-Vllllger reactions of ketones could be carried out In a similar fashion In a trlphase system some ester hydrolysis could be observed. Water soluble ketones and aromatic ketones were both unreactlve. The polymer can be recycled readily but becomes unstable If elevated temperatures are used In the reaction. Use of the catalyst under reaction conditions for 150h led to loss of less than 5% of the Initial selenium content. 

---