Substrate temperature optimum

With the development of multichaimel spectroscopic ellipsometry, it is possible now to use real-time spectroscopic ellipsometers, for example, to establish the optimum substrate temperature in a film growth process [44, 42]. 

Luft and Tsuo have presented a qualitative summary of the effects of various plasma parameters on the properties of the deposited a-Si H [6]. These generalized trends are very useful in designing deposition systems. It should be borne in mind, however, that for each individual deposition system the optimum conditions for obtaining device quality material have to be determined by empirical fine tuning. The most important external controls that are available for tuning the deposition processs are the power (or power density), the total pressure, the gas flow(s), and the substrate temperature. In the following the effects of each parameter on material properties will be discussed. 

The i-poly(3HB) depolymerase of R. rubrum is the only i-poly(3HB) depolymerase that has been purified [174]. The enzyme consists of one polypeptide of 30-32 kDa and has a pH and temperature optimum of pH 9 and 55 °C, respectively. A specific activity of 4 mmol released 3-hydroxybutyrate/min x mg protein was determined (at 45 °C). The purified enzyme was inactive with denatured poly(3HB) and had no lipase-, protease-, or esterase activity with p-nitro-phenyl fatty acid esters (2-8 carbon atoms). Native poly(3HO) granules were not hydrolyzed by i-poly(3HB) depolymerase, indicating a high substrate specificity similar to extracellular poly(3HB) depolymerases. Recently, the DNA sequence of the i-poly(3HB) depolymerase of R. eutropha was published (AB07612). Surprisingly, the DNA-deduced amino acid sequence (47.3 kDa) did not contain a lipase box fingerprint. A more detailed investigation of the structure and function of bacterial i-poly(HA) depolymerases will be necessary in future. 

Kinetics of Bound and Free Enzyme. The kinetics of the IME were obtained with the recirculating differential reactor system as described above. The appropriate flow rate, the temperature optimum, and pH optimum as described above were used to most accurately establish the kinetic parameters for this IME emgmie. Substrate solutions from 3 to 150 mM cellobiose in 10 mM sodium acetate were appropriate for this portion of the study. Results were analyzed with the ENZFTT software package (Elsevier Publishers) that permits precise Lineweaver-Burk regressions. 

Figure 8.3 The effect of temperature of an enzyme reaction and the effect of the time-period of the activity measurements on the apparent temperature optimum (after Wiseman, 1975). The index numbers indicate the increase of temperature. It is important to note that in all cases the decrease of the rate of product formation is the consequence of partial inactivations only, i.e. the concentration of substrate must be enough to saturate the enzyme even at time...

The bioconversion of (4/ )-(-)-limonene to (4/ )-(-)-a-terpineol by immobilised fungal mycelia of Penicillium digitatum was described more recently [86]. The fungi were immobilised in Calcium alginate beads. These beads remained active for at least 14 days when they were stored at 4°C. a-Terpineol production by the fungus was 12.83 mg/g beads per day, producing a 45.81% bioconversion of substrate. The optimum conversion temperature was 28°C and the optimum pH was 4.5. The highest... 

This NAD-dependent enzyme was purified up to a specific activity of 1060 U/mg (diacetyl as substrate). The enzyme is stable at 57°C for 10 min, the temperature optimum is at 70°C. Besides diacetyl several other diketones were reduced. 

The brightly blue fluorescent nanofibers from MOP4 [117, 118, 123, 124] are aligned almost parallel with a mean width of several hundred nanometers and mean height of several tens nanometers, and a length of several hundred micrometers (Figure 8.4a). For the optimum substrate temperature of about Ts = 340 K,... 

All the substituted indolo[3,2-b]carbazoles (5) with long alkyl side-chains form highly crystalline thin films on vacuum deposition. The X-ray diffraction patterns of the thin films, deposited at respective optimum substrate temperatures, give sharp and intense crystalline diffraction peaks (Fig. 4.13). Table 4.2 summarizes the XRD data and extracted interlayer distances of molecular orders of indolo[3,2-h]carbazoles in crystalline thin films. Only 5e, which has no long alkyl chain, has broad XRD diffraction peaks indicative of its amorphous nature. These results... 

Figure 5.15 summarizes the analyses of the XRD measurements for the ZnO series deposited at different substrate temperature. The structural properties depend considerably on the substrate temperature and the reactive gas partial pressure. Films deposited at Ts = 200°C in transition mode reveal the optimum properties. 

In conclusion, for both AP-CVD and LP-CVD processes, only a narrow range of temperatures can be identified for optimum performance (a range that is typically 40°C-wide). Within this narrow temperature range highly oriented films are obtained that have electrical and optical properties suitable to act as transparent conductors in solar cells. The typical substrate temperature is around 400°C for the AP-CVD process, whereas it is around 160°C for the LP-CVD process. The two processes yield film orientations that are perpendicular to each other. 

Fructan fructan fructosyl transferase has a molecular weight of approximately 70 kDa and can be separated into five species with pH values between 4.5 and 5.0. The enzyme has a pH optimum for fructosyl transfer activity between 5.5 and 7.0 and a temperature optimum in the 25 to 35°C range. Like 1-SST, 1-FFT has a low Q10 (i.e., 1.14 between 25 and 5°C), indicative of its ability to function at relatively low temperatures (Koops and Jonker, 1994). The rate of transfer of fructosyl groups increases with substrate concentration up to 100 mol nr3. 

Urease has a molecular weight of590 000 30 000 and consists of six identical subunits. Each subunit contains two Ni ions of different valency which are involved in substrate binding and conversion. The isoelectric point of the protein is at pH 5 and the temperature optimum of the catalysis at 60°C. The kinetic constants for urea hydrolysis have been determined to be k+2 = 5870 s"1 and Km = 2.9 mmol/1. Other amides, such as formamide and semicarbazide, react much more slowly than urea. The pH optimum of urease depends on the nature of the buffer used and, with the exception of acetate buffer, equals the pJTs value of the buffer. The active center of urease contains an SH-group that is essential for the stability of the enzyme. Complexing agents, such as EDTA and reductants, are required for stabilization. 

A deoxyadenosylcobalamin-dependent ribonucleoside triphosphate reductase has been partially purified from cell free extracts of the extreme thermophile, Thermus X-l 14). The enzyme preparation catalyzed the reduction of GTP and CTP at comparable rates, while UTP and ATP were reduced at only one-tenth the rate of GTP reduction. Only the dithiols could serve as reducing substrates. The enzyme has a temperature optimum of 70°, and the allosteric regulation of the enzyme activity is also temperature-dependent. The reduction of ATP is specifically stimulated by dGTP only at a higher temperature. Maximum stimulation of ATP reduction is observed at approximately 75°, while no stimulation can be detected at 37°. The molecular weight determined by gel filtration was approximately 80,000 but no information about the subunit structure is yet available. 

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