Search results for "Carbonic acid"

Biocalcite and Carbonic Acid Activators

2017

Based on evolution of biomineralizing systems and energetic considerations, there is now compelling evidence that enzymes play a driving role in the formation of the inorganic skeletons from the simplest animals, the sponges, up to humans. Focusing on skeletons based on calcium minerals, the principle enzymes involved are the carbonic anhydrase (formation of the calcium carbonate-based skeletons of many invertebrates like the calcareous sponges, as well as deposition of the calcium carbonate bioseeds during human bone formation) and the alkaline phosphatase (providing the phosphate for bone calcium phosphate-hydroxyapatite formation). These two enzymes, both being involved in human bone for…

High-pressure flow-injection assembly. Indirect determination of glycine by atomic absorption spectrometry.

1991

A procedure for the determination of glycine is described. The method is based on the reaction of the analyte with finely powdered, solid copper(II) carbonate in a continuous-flow assembly. The optimum experimental conditions of pH, temperature, sample volume, flow-rate, column length and internal diameter, and the linear range of calibration, were studied. Interference from foreign substances that accompany this amino acid in pharmaceutical formulations was studied, and the method was applied to the determination of glycine.

Mass Transport Analysis of Bicarbonate Buffer: Effect of the CO2–H2CO3 Hydration–Dehydration Kinetics in the Fluid Boundary Layer and the Apparent Ef…

2019

The main buffering system influencing ionizable drug dissolution in the human intestinal fluid is bicarbonate-based; however, it is rarely used in routine pharmaceutical practice due to the volatility of dissolved CO2. The typical pharmaceutical buffers used fail to capture the unique aspects of the hydration-dehydration kinetics of the bicarbonate-CO2 system. In particular, CO2 is involved in a reversible interconversion with carbonic acid (H2CO3), which is the actual conjugate acid of the system, as follows CO2 + H2O ⇌ H2CO3. In contrast to ionization reactions, this interconversion does not equilibrate very rapidly compared to the diffusional processes through a typical fluid diffusion b…

New Tetrahydro-1,2,4,5-Tetrazinan-3-Ones and Oxoverdazyl Free Radicals

2006

A series of tetrahydro-1,2,4,5-tetrazinan-3-ones have been prepared by the reaction of carbonic acid bis (1-methylhydrazide) with aromatic aldehydes. These were oxidised to oxoverdazyl free radicals and used immediately for ESR spectroscopy studies that indicate that the unpaired electron is delocalised over the verdazyl ring. The ESR spectra can be very well simulated considering hyperfine couplings with the four nitrogen atoms of the verdazyl ring and the six hydrogen atoms of the two methyl groups bonded to it.

Modelling the transport of carbonic acid anions through anion-exchange membranes

2003

Electrodiffusion of carbonate and bicarbonate anions through anion-exchange membranes (AEM) is described on the basis of the Nernst � /Planck equations taking into account coupled hydrolysis reactions in the external diffusion boundary layers (DBLs) and internal pore solution. The model supposes local electroneutrality as well as chemical and thermodynamic equilibrium. The transport is considered in three layers being an anion exchange membrane and two adjoining diffusion layers. A mechanism of

Ester Hydrolases, ATPases and Carboanhydrases

1994

Many biomolecules are esterified with carbonic acid, phosphoric acid or sulphuric acid. The enzymes responsible for the hydrolytic cleavage of the esters are the carboxylester hydrolases, phosphoesterases and sulphatases. In addition to the phosphomonoesterases, we will also consider the phosphodiesterases and nucleases that are specific for cAMP and cGMP, as well as the ATPases that cleave phosphoric acid anhydride bonds. The ion-transporting ATPases will be discussed together with comparative biochemical data on ion channels. The chapter ends with a discussion of carboanhydrases.

Polymerization of diacetylene carbonic acid monolayers at the gas-water interface

1978

H2-Antihistaminika, 28. Mitt. Synthese und H2-antagonistische Wirkung 3-(3-piperidinomethyl-phenoxy)propyl-substituierter Kohlensäurederivate und Ana…

1986

Es wurden 3-(3-piperidinomethyl-phenoxy)propyl-substituierte Kohlensaurederivate wie Harnstoffe, Thioharnstoffe, Guanidine und Cyanoguanidine sowie analoge Nitroethendiamine dargestellt und am isolierten Meerschweinchenvorhof und zum Teil an der histaminstimulierten Sauresekretion der narkotisierten Ratte auf H2-antagonistische Wirkung untersucht. H2-Antihistaminics, XXVIII: Syntheses and H2-Antagonistic Activity of Derivatives of Carbonic Acid and Analogues Carrying a 3-[3-(Piperidinomethyl)phenoxy]propyl Substituent Derivatives of carbonic acid such as ureas, thioureas, guanidines, and cyanoguanidines as well as the analogous nitroethenediamines were prepared with a 3-[3-(piperidinomethyl…

Mechanistic analysis and experimental verification of bicarbonate-controlled enteric coat dissolution: Potential in vivo implications

2019

Enteric coatings have shown in vivo dissolution rates that are poorly predicted by traditional in vitro tests, with the in vivo dissolution being considerably slower than in vitro. To provide a more mechanistic understanding of this, the dependence of the release properties of various enteric-coated (EC) products on bulk pH and bicarbonate molarity was investigated. It was found that, at presumably in vivo-relevant values, the bicarbonate molarity is a more significant determinant of the dissolution profile than the bulk pH. The findings also indicate that this steep relationship between the dissolution of enteric coatings and bicarbonate molarity limits those coatings' performance in vivo.…

Organic carbonates as alternative solvents for asymmetric hydrogenation

2009

Organic carbonates like propylene carbonate (PC) or butylene carbonate (BC) belong to the class of aprotic, highly dipolar solvents (AHD). Interestingly, their potential as solvents for asymmetric catalysis has been overlooked for a long time. The aim of this work is to evaluate organic carbonates and other organic solvents like THF, CH2Cl2, and acetonitrile as well as members of the AHD-family (DMF, DMSO, etc.) as media for homogeneous asymmetric hydrogenation. For this reason cationic Rh-complexes based on chiral phosphine ligands were tested in the hydrogenation of typical benchmark substrates. In several trials, significant advantages of organic carbonates were found. In contrast to DMS…