Search results for "Hydrogen-ion concentration"

In Vitro Percutaneous Penetration of Acyclovir from Solvent Systems and Carbopol 971-P Hydrogels: Influence of Propylene Glycol

2005

The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER = 10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increase…

Effect of alkalosis on plasma epinephrine responses to high intensity cycle exercise in humans

2002

The purpose of this study was to determine the effects of alkalosis on epinephrine concentrations in response to a 90 s maximal exercise test. A group of ten healthy men ingested either a bicarbonate (BS) supplement (0.3 g x kg(-1) of body mass of sodium bicarbonate) or placebo mixture (P) prior to performing a 90 s maximal cycle ergometer test. An indwelling Teflon cannula was placed in the antecubital vein and blood samples were drawn at three times at rest separated by 10 min, immediately following the protocol, and at 2.5, 5, and 10 min post exercise to determine plasma epinephrine concentrations. Sodium bicarbonate ingestion significantly ( P0.05) induced alkalosis both at rest [mean (…

Slightly radiopaque uric acid calculi: impact upon therapeutic considerations?

1989

Ten patients with slightly radiopaque urinary calculi were treated by percutaneous litholapaxy or even open surgery. The stone analysis revealed uric acid as the main stone composite suggesting that these patients should have been treated by oral litholysis alone alkalinizing the urine and decreasing uric acid levels with allopurinol. CT density measurements proved that concrements with HE less than 600 can be successfully dissolved by oral medication alone. Twenty-four patients were subsequently treated by oral citrate alkalinizing the spontaneous urine to pH 6.8-7.2 dissolving even large staghorns within 6-8 weeks. CT density measurements have become a routine diagnostic procedure when po…

Effect of 3,4-dichloroaniline on the early life stages of the zebrafish (Brachydanio rerio): results of a comparative laboratory study.

1991

An early life-stage (ELS) test was conducted with the zebrafish and 3,4-dichloroaniline (3,4-DCA) in eight laboratories. Based on the results from all eight laboratories, an LOEC of 200 micrograms 3,4-dichloroaniline/liter applies for the early life stages of the zebrafish. Effects observed were reduction of the survival rate and malformations. If the 100 micrograms/liter concentration additionally tested by one laboratory is included in the assessment, an LOEC of 100 micrograms 3,4-DCA/liter is obtained for the survival rate and increase in length. The NOEC is 20 micrograms/liter. The present results of a comparative laboratory study with the zebrafish show that a 42-day ELS test can be co…

Phase selection of calcium carbonate through the chirality of adsorbed amino acids.

2007

New Insight to the Chemistry of Polyaza[n]paracyclophanes. A 15N NMR Study

2001

Preferential localization of Lactococcus lactis cells entrapped in a caseinate/alginate phase separated system.

2013

International audience; This study aimed to entrap bioprotective lactic acid bacteria in a sodium caseinate/sodium alginate aqueous two-phase system. Phase diagram at pH = 7 showed that sodium alginate and sodium caseinate were not miscible when their concentrations exceeded 1% (w/w) and 6% (w/w), respectively. The stability of the caseinate/alginate two-phase system was also checked at pH values of 6.0 and 5.5. Lactococcus lactis subsp. lactis LAB3 cells were added in a 4% (w/w) caseinate/1.5% (w/w) alginate two-phase system at pH = 7. Fluorescence microscopy allowed to observe that the caseinate-rich phase formed droplets dispersed in a continuous alginate-rich phase. The distribution of …

Determination of barbiturates in urine by micellar liquid chromatography and direct injection of sample.

2000

Abstract A liquid chromatographic procedure for the determination of six barbiturates (barbital, diallyl barbituric acid, phenobarbital, butabarbital, amobarbital and pentobarbital) in urine samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C 18 analytical column and a guard column of similar characteristics. The UV detector was set at 240 nm. A study to select adequate composition of the micellar mobile phase for the separation of these compounds in urine samples is performed. Maximum resolution was achieved with a 0.07 M sodium dodecylsulphate-0.3% propanol at pH 7.4 eluent. Limits of detection at 240 nm were ranged between 0.13 μg ml −1 for diallyl barbit…

Amyloid Fibrils Formation of Concanavalin A at Basic pH

2011

Mechanisms of partial unfolding and aggregation of proteins are of extreme interest in view of the fact that several human pathologies are characterized by the formation and deposition of protein-insoluble material, mainly composed of amyloid fibrils. Here we report on an experimental study on the heat-induced aggregation mechanisms, at basic pH, of concanavalin A (ConA), used as a model system. Thioflavin T (ThT) fluorescence and multiangle light scattering allowed us to detect different intertwined steps in the formation of ConA aggregates. In particular, the ThT fluorescence increase, observed in the first phase of aggregation, reveals the formation of intermolecular β-sheet structure wh…

Kinetics of different processes in human insulin amyloid formation.

2007

Human insulin has long been known to form amyloid fibrils under given conditions. The molecular basis of insulin aggregation is relevant for modeling the amyloidogenesis process, which is involved in many pathologies, as well as for improving delivery systems, used for diabetes treatments. Insulin aggregation displays a wide variety of morphologies, from small oligomeric filaments to huge floccules, and therefore different specific processes are likely to be intertwined in the overall aggregation. In the present work, we studied the aggregation kinetics of human insulin at low pH and different temperatures and concentrations. The structure and the morphogenesis of aggregates on a wide range…