Preparation of polyelectrolyte-coated pH-sensitive poly(styrene) microcapsules and their application to initiation-cessation control of an enzyme reaction

Poly(styrene) microcapsules, prepared by depositing the polymer around emulsified aqueous droplets, were coated with a synthesized polyelectrolyte; i.e., copolymer of maleic acid (MA) with methyl vinyl ether (MVE), co-poly(MA, MVE), or with styrene (St), copoly(Ma, St). The permeability of the capsule membrane was investigated under various pHs of the outer medium using n-propyl alcohol as a permeant. It became apparent that either copoly(MA, St)- or copoly(MA, MVE)-coated microcapsules function as a pH-sensitive capsule. In particular, the former showed a dramatic change of the permeability in response to small differences in pH (5-6). By reference to the viscometric and electrophoretic studies of both copolymers, these were interpreted as being due to a pH-induced alteration of the configuration of the copolymer coating on the surface of the capsule membrane. When sucrose was hydrolyzed in an aqueous suspension of the copoly(MA, St)-coated capsules into which invertase was loaded, the hydrolytic reaction was initiated at pH 5. 5 and stopped at pH 4. 5. Such initiation-cessation control was repeated reversibly without damaging the capsules.

Chemical waves in self-oscillating gels

The behaviors of a poly(N-isopropyl acrylamide) (PNIPA) gel coupled with the Belousov-Zhabotinsky (BZ) reaction has been investigated as a function of temperature and catalyst concentration. In this type of gel, the chemical oscillation in the BZ reaction induces periodic and autonomous swelling-shrinking volume changes of the gel, and conversely a volume change of the PNIPA gel affects the propagation of the chemical wave. Our attention was focused on the effects of mechanical changes on the chemical wave by utilizing the thermally driven volume phase transition of the gel. Both the velocity and the frequency of the chemical wave increased with increasing temperature, and abruptly decreased at the volume transition temperature of the gel, T(c). The diffusion of HBrO2, which is essential for wave propagation, was hindered with increasing temperature. The diffusion of HBrO2 through the gel network in the low temperature region was explained in the same way as a simple diffusion of inactive molecules through a restricted environment.

Light scattering, CD, and ligand binding studies of ferrihemoglobin-polyelectrolyte complexes

Quasi-elastic light scattering (QELS), electrophoretic light scattering (ELS), CD spectroscopy, and azide binding titrations were used to study the complexation at pH 6.8 between ferrihemoglobin and three polyelectrolytes that varied in charge density and sign. Both QELS and ELS show that the structure of the soluble complex formed between ferrihemoglobin and poly(diallyldimethylammonium chloride) [PDADMAC] varies with protein concentration. At fixed 1.0 mg/mL polyelectrolyte concentration, protein addition increases complex size and decreases complex mobility in a tightly correlated manner. At 1.0 mg/mL of greater protein concentration, a stable complex is formed between one polyelectrolyte chain and many protein molecules (i.e., an intrapolymer complex) with apparent diameter approximately 2.5 times that of the protein-free polyelectrolyte. Under conditions of excess polyelectrolyte, each of the three ferrihemoglobin-polyelectrolyte solutions exhibits a single diffusion mode in QELS, which indicates that all protein molecules are complexed. CD spectra suggest little or no structural disruption of ferrihemoglobin upon complexation. Azide binding to the ferrihemoglobin-poly(2-acrylamide-2-methylpropanesulfonate) [PAMPS] complex is substantially altered relative to the polyelectrolyte-free protein, but minimal change in induced by complexation with an AMPS-based copolymer of reduced linear charge density. The change in azide binding induced by PDADMAC is intermediate between that of PAMPS and its copolymer.

Biochemo-mechanical function of urease-loaded gels

A gel system is developed that undergoes a reversible volume phase transition in response to a small amount of urea. An N-isopropylacrylamide gel in which urease is immobilized by entrapping changes its equilibrium volume discontinuously when urea molecules are hydrolyzed by urease causing a change in pH that alters the osmotic balance of the gel triggering the phase transition. The system demonstrates a method of mechano-biochemical transformation where molecular recognition and biochemical reaction are achieved by an enzyme and the macroscopic amplification of the reaction is carried out by a gel capable of a volume phase transition. The work presented here is dedicated to Professor Allan S. Hoffman to honor his 60th birthday and his pioneering contribution to the science and technology of polymer gels, both as a scientist and as an educator.

Factors controlling the size of proteinoid microspheres

Proteinoid microspheres were prepared from aqueous solutions containing various metal halides under different pH values and ionic strengths. The effects of pH and ionic strength on the diameter of the microspheres and also the solubility of the proteinoid in hot solution (100 degrees C) were investigated by means of different physiochemical measurements. It is found that, under high ionic strength, the diameter of the microsphere is mainly affected by the salt concentration, while the pH of the system is the main factor when the ionic strength is low. Moreover, the change in the solubility with ionic strength and pH is found to show a striking resemblance to that in the diameter with both factors. On the basis of these results, the external and internal factors controlling the size of proteinoid microspheres are clarified, and a plausible mechanism of the proteinoid microsphere formation under prebiotic conditions is also discussed.

Potentiometric titration behavior of polyaspartic acid prepared by thermal polycondensation

The dissociation behavior of polyaspartic acid prepared by thermal polycondensation was studied by potentiometric titrations at various ionic strengths. From the analysis of the titration curves, the ratio of alpha- and beta-linkaged aspartyl residues was estimated at about 7:3 and the intrinsic dissociation constants of alpha- and beta-carboxyl groups are 3.25 and 4.35, respectively.