Oxygen-sensitive samples

Oxygen-sensitive samples such as enzymes from strictly anaerobic microorganisms which have been previously prepared anaerobically (e.g., in a glove box) can be transferred from their container (e.g., a capped septum bottle) to an empty EPR tube that has been made anaerobic on the manifold. The transfer can be done with an injection needle that has been made anaerobic in an empty septum bottle on the manifold. Note that after the transfer the connecting rubber has a hole, so any addition to this sample can only be made after it has been frozen and subsequently made anaerobic with a new, intact connecting rubber on the manifold. 

Both of these in situ devices use substantially less solution (volumes of solution samples for each kinetic run are usually of the order of a few cm3) than a typical piston-cylinder apparatus. The pill-box cell method has the advantage that the cell can be filled in an appropriate glove box for oxygen-sensitive samples or for nonaqueous solvent-based systems that are sensitive to moisture. Temperature control is exerted by fluid circulating through the metal block. 

The loading of moisture- or oxygen-sensitive samples into the Mettler thermobalance sample holder is conveniently carried out by use of the controlled atmosphere enclosure shown in Figure 3.9 (3). The sample is introduced, via an enclosed sample holder, into the enclosure and loaded into the furnace chamber after the controlled atmosphere has been introduced. After loading, the furnace chamber is closed and the enclosure is removed. 

DAS has rivb° 1.6156 and d25° 1.3992 the nuclear magnetic resonance spectrum has a singlet at 8.83 r and an A2B2 pattern at 2.62 r. Although DAS is very oxygen-sensitive, it is readily stored in sample bottles with serum caps. Complexes of many metals have been prepared exceptions include scandium, yttrium, lanthanum, and zinc. 

In order to reduce this effect, the samples should be protected from sunlight by wrapping the sample bottles in appropriate material. When dealing with oxygen sensitive compounds, the reactions should be performed under nitrogen or other inert gas atmosphere. 

Oxygen-sensitive membrane electrodes are commercially available. The electrode in such a system is covered with an oxygen-permeable plastic membrane, thus protecting it from impurities. The current is proportional to the activity of dissolved molecular oxygen, and at low concentration, to the amount of DO. Before the measurement of DO in the sample, calibrate the electrodes using standards of known DO concentrations (determined from iodometric titrations). 

Pressed pellets of BaTiC>3 were sintered in a platinum dish for six hours at 900°C in a controlled partial pressure of oxygen. The samples were quenched to room temperature, and the spectra recorded on a four-slit double-monochromator Raman spectrophotometer. An Ar+ laser with excitation at 514.5 nm was the source. The spectra were recorded at room temperature. Figure 4-30 shows the spectrum of BaTiC>3 whose Ba/Ti ratio is equal to 0.9999. The Raman spectrum is sensitive to the Ba/Ti ratio and theoxygen non-stoichiometry. The half-band width is variable as well as the intensity ratio of the 525 and 713 cm-1 bands. The ratio (I525/713) is at a minimum at the composition of 0.9999, and this can be observed in Fig. 4-31, which shows a plot of the intensity ratio (I525//713) vs. the Ba/Ti composition. 

The reactant powders were placed in a 45-mL steel container along with seven steel balls each with a diameter of 15 mm. Most impressively, the temperature of the sample was kept below 50°C. Because of the oxygen sensitivity of iron powder, the milling was done in a nitrogen atmosphere for just over 3 hours for complete conversion of a 5-gram sample. The use of steel milling balls in this... 

EDTA, DTT, Benzamidine-HCl and PMSF were used in the lysis buffer to inhibit proteases and minimise damage to the oxygen sensitive-enzyme. Keeping the sample on ice also reduced protease activity. 

A series of complex salts of [Ta(CO)6] and [Nb(CO)6] are synthesized by similar procedures described above. For the details, see [45]. The Nujol mull IR spectra in the v(CO) region exhibit a very broad asymmetric absorption band, while the spectra in polar solvents show one relatively sharp intense band. All the complexes are very oxygen sensitive in solution, while the solid samples can be handled in air for brief periods of time. 

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