Circle cell

Figure 5.5 Detail of HP IR spectra from measurement of migratory insertion of [lrMe(CO)2l3r iti Circle cell showing Ir species in PhCI at 93 °C and 5.5 bar.

This paper contains results of the investigation of the dynamics of the hydrolysis of several alkoxysilane compounds and the condensation of the silanols resulting from that hydrolysis. FTIR spectroscopy used in conjunction with the CIRCLE cell has proved to be well suited for these investigations. 

The combination of FTIR spectroscopy and the CIRCLE cell sampling technique proved useful in the investigation of the hydrolysis and condensation... 

Proteins readily adsorb to surfaces, including the IRE of the CIRcle cell. After every experiment, the IRE and cell body needed to be thoroughly cleaned. All contaminated parts were scrubbed with a... 

In order to test whether our CIRcle cell spectra were dominated by adsorbed protein or protein in solution, we ran spectra of a series of lysozyme solutions ranging in concentration from 0.12 to 102. The IR response of the amide I and II bands at 1653 and 1543 cm-1 is nearly linear with concentration between 5 and 102 lysozyme. However, the IR intensities change very little between 0.1 and 12, strongly suggesting that most of the signal we observe at 0.12 concentration is due to adsorbed lysozyme. Since our study of subtilisin BPN was done at 0.012, we are almost certainly observing only adsorbed species in our ATR spectra. 

From the adsorption-isotherm experiments, it is shown that BPN adsorbs about twenty-times more on hydrophobic quartz than on hydrophilic quartz at 100 ppm. It is also known that BPN autolyzes readily, especially on hydrophobic surfaces (Brode, III, P. F. and Rauch, D. S., The Procter Gamble Company, unpublished results). For the first BPN experiments, the Ge IRE was used directly after cleaning. "Clean" Ge has a water contact angle of about 45°, somewhere between hydrophobic and hydrophilic. To avoid spectral interferences from the Tris buffer bands, the buffer was eliminated from the BPN solutions used for the CIRcle cell experiments. Only CaCl2 (10 mM final concentration) was used to stabilize the BPN against autolysis, and the solution was adjusted to a pH of 8.6 using... 

Figure 3. A series of spectra of 100 ppm subtilisin BPN from 6 to 180 minutes after injection into the CIRcle cell. The solvent spectrum has been subtracted.

Using a cylindrical internal reflectance (CIRcle) cell and GC-IR data collection software, it was determined for both lysozyme and BPN, that most of the enzyme adsorption occurred within ten seconds after injection. Nearly an order-of-magnitude more BPN adsorbed on the hydrophobic surface than the hydrophilic one, while lysozyme adsorbed somewhat more strongly to the hydrophilic Ge surface. Over time periods of about one day, the lysozyme layer continued to increase somewhat in thickness, while BPN maintained its initial coverage. 

E.H. Braue, Ir. and M.G. Pannella, CIRCLE CELL FT-IR analysis of chemical warfare agents in aqueous solutions, Appl. Spedrosc., 44, 1513-1520 (1990). 

Fig. 5.2.3. Absorption spectra of water recorded in the transmission mode (TR, 0.0025 mm path length) and in CIRCLE cell (CATR, ZnSe macro rod crystals). Resolution 4cm-1, 32 scans...

Fig. 5.2.4. Absorption spectra of alkaline solutions in a CIRCLE cell (resolution 4cm, 32 scans). The spectra are measured against water...

Of the large number of possible IRE shapes (Harrick, 1979) only few are usually used for the membrane method. Their shapes are like a trapezoid or parallelepiped. Cylindrical IRE with conical ends (Tunnel Cell, Circle Cell (Doyle, 1990)) and even optical fibers are also possible. 

E. El. J. Braue and M. G. Pannella, Circle Cell FT-IR Analysis of Chemical Warfare Agents in Aqueous Solutions,, 4pp/. Spectrosc. 44, 1513 (1990). 

Figure 4. The effect of analog substrate (biphenyl) addition and introduction of Acinetobacter P6 on the degradation of PCB Arochlor 1242 (100 mg/kg) in soil. Addition of biphenyl with P6 at I09 (triangles) or 10 (closed circles) cells/mL inoculum reduced the adaptation period compared to noninoculated soil (squares). Acinetobacter P6 added to soil without biphenyl had no effect on degradation (open circles). (Reproduced with permission from Ref. 52. Copyright 1985 American Society of Agronomy.)...

Figure 4.16 Diffusion coefficients for molecules in the tissue interstitial space. The diffusion coefficients were measured by quantitative autoradiography and quantitative fluorescence methods, iontophoresis, and FPR. The measurements were made in brain slices (circles), cell cultures (cross), brain of animals (triangles), tissues in animals (squares), and tumors in animals (inverted triangles). Data for the diffusion of size fractionated dextrans, BSA, and IgG in granulation tissue and tumor tissue within a chamber in the rabbit ear [20, 21]. Symbol size indicates species in order of increasing size rats, rabbits, turtle, skate, dog, monkey. A previous versions of this plot has appeared [52]. The solid line represents the best-fit diffusion coefficient vs (see Figure 4.4).

A CIRCLE cell can be used in studies of ultrathin films on fibers (Fig. 4.14) [180]. Comparing spectra recorded for the fibers that are (a) aligned along and (b) coiled around a cylindrical IRE provides information abont orientation of surface species with respect to the fiber axis. This is because fibers are highly crystalline, and as IR radiation passes through them, it becomes polarized in parallel and perpendicular directions. As a result, the absorption bands due to the modes with different TDMs with respect to the fiber surface have different intensities for the two positions of the fibers with respect to the IRE. 

Figure 17. (Top) The absorbance spectrum of a levitated bubble of LGP1845. (Bottom) The Circle Cell spectrum of LGP1845. Because of the longer pathlength, the bubble spectrum is more intense, but the spectral features match well between the two.

Fig. 2.2 Details of the amorphous silica model used in [38, 39] with an oxygen vacancy present as an Si-Si bond enclosed by a circle. Cell dimensions are 10.08 x 10.08 x 14.26 A. The model contains 95 atoms with periodic boundary conditions. The small dark spheres are O atoms and the large light-gray spheres are Si atoms...

ATR accessories for the measurement of liquids are not restricted to IREs with a trapezoidal or parallelpiped geometry. Alternatively, liquids can be measured with cylindrical IREs. A cylindrical internal reflection element is a rod that has a cone at each end, as shown in Figure 15.10. The cone typically has a 45° half-angle at the apex. The IRE is sealed into a liquid cell that exposes most of the rod to the liquid, and only the ends of the cell extend beyond the cell. Two geometries for cylindrical IREs are shown in Figure 15.11. The first (Figme 15.11a) is the CIRCLE cell (Thermo Spectroscopy Division, Madison, Wisconsin), where CIRCLE is an... 

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