Unbuffered aqueous solutions

CAUTION All azides, particularly low molecular weight acyl and alkyl azides, are explosive, and great care should be taken while preparing and handling these materials. In addition, hydrazoic acid, which is liberated from unbuffered aqueous solutions of sodium azide, is highly toxic and all operations involving its use should be carried out in an efficient fume hood. 

The oxidation of adrenaline with excess potassium iodate in unbuffered aqueous solution gives a violet-brown solid this solid was first obtained by Richter and Blaschko in 1937 and considered to be 2-iodoadrenochrome (11).69 The iodine atom in the iodoamino-chromes (or the bromine atom in bromoadrenochrome) has recently been shown to occupy the 7-position in the aminochrome molecule,70 rather than the 2-position as originally believed. Consequently, the iodoadrenochrome referred to above should be formulated as a 7-iodo derivative (i.e., as 12). The iodoaminochromes presumably arise by iodination of the initially formed aminochromes (cf. ref. 3). 

This is a powerful reagent for reduction in alkaline solution. At a pH lower than 7, hydrosulfite decomposes with liberation of sulfur. If used in an unbuffered aqueous solution initially neutral, say for the reduction of an azo compound, the solution becomes progressively acidic because of the formation of sodium bisulfite. 

The Fenton reaction (1) was not used here to avoid any artefacts due to reactions of Fe with any organic acids formed. The reaction took place in an aqueous-phase simulation chamber, which consisted of a 450 mL Pyrex vessel. Unbuffered aqueous solutions were continuously stirred and maintained at 298 0.2 K. The light source was a 300 W xenon arc lamp (see Monod, et al. (2005) for further details on the apparatus). The initial concentrations of NMP and H2O2 were 5x10 and 1x10 mol L, respectively. During the reaction, aliquots of the solution were sampled at regular time intervals with an automatic sampler, and stored at 0 °C for further analysis. 

Decarboxylation. Most of the amino acids commonly found in proteins decompose by a slow, irreversible decarboxylation. The kinetics of decarboxylation of several amino acids have been studied by Abelson (45, 46), Conway and Libby (27), and Vallentyne (47, 48). The decarboxylation rates were determined by heating unbuffered aqueous solutions of the amino acids at elevated temperatures (between 100° and... 

A neutral unbuffered aqueous solution was stored in a polyethylene bottle. The pH reduced on storage to 4.3-4.5 but reverted to 6.5 when the solution was heated. The change was identified as carbon dioxide permeation with the formation of carbonic acid. Possible solutions include change of plastic, an overwrap or possibly a buffered formulation. 

In this section, we briefly provide preliminary results on the morphology of etch pits obtained on cleaved calcite crystals by dissolution in unbuffered aqueous solutions of maleic acid (3 mM) under both stationary conditions and through channel electrode experiments. Kinetic and morphological studies on the effect of maleic acid on the dissolution of calcium carbonate... 

Early studies identified hydroxylamine hydrochloride as an essential component for the success of the reaction. When added to an unbuffered aqueous solution, this additive results in dramatically enhanced catalytic activity, presumably through the binding of the oxygen atom to the remaining vacant coordination site of the bimetallic metallocarbene complex (species... 

Figure 2. The rates of uracil photolysis (uracil loss) in 10 M unbuffered aqueous solution at different partial pressures of oxygen...

The dc polarographic studies were carried out in buffered and in unbuffered aqueous solutions. Potentials were referenced against a Ag/AgCt saturated NaCt electrode. The electrochemical assignments and the apparatus used to collect the polarographic data have been previously described (14,15). 

Reduction of one of the four haem groups of human aquometHb A has been studied by pulse radiolysis. In unbuffered aqueous solution at 23 °C and pH 6.2 (7=0.1 mol I" ), the rate constant for the reaction with 4.2 x 10 1 mol s. Similar results were obtained for cyano- and azido-metHb and for deoxyHb (4.7, 4.4, and 4.3 x 10 1 mol s, respectively). From studies on the redox equilibria of fluoro- and azido-metHb it is concluded that the marked co-operativity and pH-dependence of E are not coupled to changes in the ferrihaem spin state. 

We have demonstrated a particularly clear and simple technique for evaluating the reactions of pyridinyl radicals in water through measurement of the pH changes resulting from radiolysis of pyridinium ions in unbuffered aqueous solutions containing isopropyl alcohol ( ). Radiolysis generates one proton for each pyridinyl radical, as set forth in Eq. 9. ( ). 

Fletcher, D., Sotiropoulos, S. Hydrogen adsorption-desorption and oxide formation-reduction on polycrystalline platinum in unbuffered aqueous solutions. 7. Chem. Soc. Faraday Trans. 1994, 90, 3663-3668. 

Interesting phenomena are observed in the reduction of nitroform (trinitromethane) at the dropping mercury electrode [29]. On polarograms in unbuffered aqueous solutions the first wave corresponds to one-step reduction of the undissociated (N02>3CH molecule, and the second and subsequent waves correspond to multistep reduction of its anion (N02)3C". Accordingly the polarograms for an unbuffered solution of the potassium salt of nitroform (nitroform is a strong acid with pK =0.15) only contain the multistep wave for the reduction of the anion (Curve 1, Fig. 3), and this remains practically... 

Eddowes M.J., Pedley D.G. and Webb B.C (1985) Response of an enzyme-modified pH-sensitive ion-selective device experimental study of a glucose oxidase-modified ISFET in buffer and unbuffer aqueous solution. Sensors Actuators, 7, 233-244. 

---