PubMed · 4652668
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O E Araujo. 1972. Thixotropy measured using a weight-actuated viscometer.. https://doi.org/10.1002/jps.2600611141
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A new approach to construct a second-generation amperometric biosensor is described. The classical dye methylene green as a probing-needle mediator and horseradish peroxidase as a base enzyme were coimmobilized in the same montmorillonite-modified bovine serum albumin (BSA)-glutaraldehyde matrix to construct a H2O2 sensor. The immobilization matrix was formed from the pretreated sodium montmorillonite colloid in which the enzyme and the cross-linker were dissolved. Immobilization of methylene green from the dye mother solution was attributed to the adsorption function of the montmorillonite, whereas immobilization of horseradish peroxidase was attributed to the cross-linking function of the BSA-glutaraldehyde as usual. Cyclic voltammetry and potentiostatic measurements indicated that methylene green efficiently mediated electrons from the base electrode to the enzyme in the matrix. The sensor responded rapidly to low H2O2 concentration and achieved 95% of the steady-state current in less than 20 s, with a detection limit of 4.0 x 10(-7) M H2O2.
The changes in the distribution of the ionic species of a drug due to interactions with a clay surface may have important consequences in drug therapy. The binding of chlordiazepoxide (CDO) into montmorillonite clay, veegum: HV (V), surface was studied under several pH conditions. In vitro drug release behaviour from CDO-V products was investigated. Changes in the partial molar free energy of the ionic species of CDO, delta Gi (i = CDO, CDOH+) as a result of interaction with V were determined by using differential absorbance spectroscopic techniques at 260 and 310 nm. The stronger interaction between the negatively charged clay surface and the protonated species (CDOH+) relative to the parent compound is responsible for the apparent displacement of its pKa value in V suspensions from 4.64 to 5.67. In vitro drug release behaviour from CDO-V product to the simulated gastrointestinal fluids showed a controlled pattern. The in vivo results indicated a prolonged drug effect after the oral administration of drug-clay preparation.
Polymerization shrinkage is a major limitation of dental composites. It generates internal stresses within bonded restorations and leads to marginal leakage, sensitivity and recurrent decay in the absence of adequate bonding. A method is presented for formulating composites that cure at constant volume by adding to the resin system small amounts of the hydrated mineral montmorillonite (MMT), which has been modified by replacing part of its hydration water with ammonia (NH3). The polymerization exotherm of composites containing ammonia-modified montmorillonite (NH3/MMT), cured at ambient temperatures, raises their temperature to between 60 and 80 degrees C, which causes the NH3/MMT particles to swell and counteract polymerization shrinkage. The polymerization shrinkage was measured for the BIS-GMA resin system, without filler, to which had been added NH3/MMT. The addition of 4 to 5 weight percent NH3/MMT resulted in zero polymerization shrinkage. An experimental composite was formulated using the BIS-GMA resin system, hydroxyapatite filler and 4 weight percent NH3/MMT. Cured samples developed compressive strength and hardness comparable to reported values for dental composite resins. Porosity was not detected by scanning electron microscopy. The use of NH3/MMT for formulating polymeric systems that cure at constant volume should be explored for application in direct dental composites.