Subzero temperatures

Type J thermocouples (Table 11.58) are one of the most common types of industrial thermocouples because of the relatively high Seebeck coefficient and low cost. They are recommended for use in the temperature range from 0 to 760°C (but never above 760°C due to an abrupt magnetic transformation that can cause decalibration even when returned to lower temperatures). Use is permitted in vacuum and in oxidizing, reducing, or inert atmospheres, with the exception of sulfurous atmospheres above 500°C. For extended use above 500°C, heavy-gauge wires are recommended. They are not recommended for subzero temperatures. These thermocouples are subject to poor conformance characteristics because of impurities in the iron. 

Oils in Greases. Essentially the same type of oil is used in compounding a grease as would normally be selected for oil lubrication. Petroleum oils are used in about 99% of the grease produced and commonly are in the SAE 20—30 viscosity range with about 100 130 mm /s viscosity at 40°C. Such oils provide low volatiHty for long life at elevated temperatures (50) together with low torque down to subzero temperatures. 

Crystallization. Raw natural mbber may freeze or crystallize during transit or prolonged storage, particularly at subzero temperatures. The mbber then becomes hard, inelastic, and usually much paler in color. This phenomenon is reversible and must be differentiated from storage hardening. The rate of crystallization is temperature-dependent and is most rapid at —26° C. Once at this temperature, natural mbber attains its maximum crystallinity within hours, and this maximum is no more than 30% of the total mbber. 

Another development features a nonmetallic belt [Pla.st. Des. Process., 13 (July 1968)]. When rapid heat transfer is the objective, a glass-fiber, Teflon-coated construction in a thickness as httle as 0.08 mm (0.003 in) is selected for use. No performance data are available, but presumably the thin belt permits rapid heat transfer while taking advantage of the nonsticking property of Teflon. Another development [Food Process. Mark., 69 (March 1969)] is extending the capa-bihty of belt solidification by providing use of subzero temperatures. 

Compared with atactic polypropylene it has a lower softening point (less than 100°C compared with 154°C when assessed by ball and ring methods), has better resistance to subzero temperatures and is completely soluble in aliphatic hydrocarbons. The molecular mass of atactic polybut-l-ene is about twice that of an atactic polypropylene of similar melt viscosity. 

Freeze-drying, like all drying processes, is a method to separate liquid water from a wet solid product or from a solution or dispersion of given concentration. However, the main difference is that the liquid water is separated by solidification (i.e., the formation of ice crystals) and subsequent vacuum sublimation instead of evaporation. This allows a drying at subzero temperatures which can be advantageous in case of heat-sensitive products. There are two general applications... 

This has a very high resistance to impact damage, even at subzero temperatures. It has good creep strength in dry conditions up to 115°C but degrades by continuous exposures to water hotter than 65°C. It is resistant to aqueous solutions of acids, aliphatic hydrocarbons, paraffins, alcohols (except methanol), animal and vegetable fats and oils, but is attacked by alkalis, ammonia, aromatic and chlorinated hydrocarbons. 

Franks, F. The Properties of Aqueous Solutions at Subzero Temperatures, in Water — a Comprehensive Treatise, (ed. Franks, F.), Vol. 7, chapter 3, New York, Plenum Press 1982... 

The deprotonated flavin in the complex is readily attacked by molecular oxygen at C4a, giving 4a-hydroperoxide of the flavin-luciferase complex (intermediate A). This complex is an unusually stable intermediate, with a lifetime of tens of seconds at 20°C and hours at subzero temperatures, allowing its isolation and characterization (Hastings et al., 1973 Tu, 1979 Balny and Hastings, 1975 Vervoort et al., 1986 Kurfuerst et al., 1987 Lee et al., 1988). 

Figure 9. Molality of NaCI (mj in unfrozen portions of glycerol-NaCI-HjO solutions at various subzero temperatures. Curves apply to any glycerol-NaCI solution with stated R values, where R is %wt glycerol/%wt NaCI. (From Mazur et al., 1981.)...

Figure 11. A Survival of human red blood cells as a function of the molality of NaCi (m ) to which they are exposed after being frozen at 1.7 °C/min to various subzero temperatures while suspended in solutions of 0.5 ( ) or 1.0 (a) M glycerol in isotonic NaCI. Thawing was rapid. B Survival as a function of the fraction of water that remains unfrozen in the solutions. (From Mazur and Rigopoulos, 1983.)...

Leibo, S.P. (1976). Freezing damage of bovine erythrocytes Simulation using glycerol concentration changes at subzero temperatures. Cryobiol. 13,587-598. 

Mazur, P. (1963). Kinetics of water loss from cells at subzero temperatures and the likelihood of intracellular freezing. J. Gen. Physiol. 47, 347-369. 

Thom, F., Richter, E., Matthes, G. (1988). Reactions of erythrocyte membranes to forces at subzero temperatures. Cryobiol. 25,512 (abstract). 

Separation of amino acids, peptides, and proteins Amino acids are interesting molecules by themselves from an analytical point of view for two reasons. They are inherently enantiomeric and are the building blocks of peptides and proteins. The separation of amino acids is usually done through a derivatization process due to the fact that the absorbance in the UV is low. The most frequently used derivatization is done by fluorescent tagging. Sensitivity can reach the subfemtomole level.136 139 Temperature control can be used to separate conformers.140 Two conformers of Tyr-Pro-Phe-Asp-Val-Val-Gly-NH2 and four conformers of Tyr-Pro-Phe-Gly-Tyr-Pro-Ser-NH2 were separated at subzero temperatures by including glycerol as an antifreeze component of the buffer. 

Cryotherapy is a procedure used primarily for smaller, low-risk NMSCs with clearly defined margins. It involves delivering liquid nitrogen at subzero temperatures as a spray or with a supercooled metal probe to destroy the malignant tissue.5 It is contraindicated in metatypical or morpheaform BCC, in tumors that are invasive or recurrent, in hair-bearing skin that is susceptible to cryotherapy-induced alopecia, or in tumors with poorly defined borders. Cryotherapy is a cost-effective treatment that is easy for clinicians to deliver, but the recurrence rate is high with this procedure.5... 

Under subzero temperatures compounds were stable but upon being warmed they underwent ring opening to form one of the A-series agents. 

Champion, D., Blond, G., and Simatos, D. 1997. Reaction rates at subzero-temperature in frozen sucrose solutions A diffusion-controlled reaction. Cryo-Letters 18, 251-260. 

In Albany, NY, the state government started leasing Honda FCX hydrogen fuel cell cars on a cold November morning. Previous fuel cell vehicle demonstration programs have occurred in warmer areas to ensure that the fuel cell stacks would not freeze up. Subzero temperatures can change any liquid water present into expanding ice crystals that can puncture thin membranes or crack water lines. Honda has demonstrated that their fuel cell units can operate under winter conditions, this was an important achievement for practical fuel cell cars. 

Tsai, S. and Klinman, J.P. (2001). Probes of hydrogen tunneling with horse Uver alcohol dehydrogenase at subzero temperatures. Biochemistry 40, 2303-2311... 

At low temperatures, the behaviour can be acceptable down to -60°C or even less, down to -110°C according to grades and the mechanical constraints experienced. Figure 4.2 displays examples of stress at yield retention for polyethylenes at subzero temperatures. 

In another, similar study, Mukundan et al. [260] performed 100 freeze-thaw cycles (from -40 to 80°C) with different types of CFPs and CCs. After 100 cycles, no obvious degradation was observed in the carbon cloth DL in fact, the performance of the fuel cell slightly improved. On the other hand, after 45 cycles, the CFPs showed significant breakage of the carbon fibers at the edges between the flow channels and the landing widths (or ribs). Thus, it was concluded that this breakage could potentially become a serious failure mechanism in PEM fuel cells when the system was started at subzero temperatures. 

PROTEINS AT WORK STOP-ACTION PICTURES AT SUBZERO TEMPERATURES... 

III. X-Ray Studies at Subzero Temperatures Physical-Chemical Basis of Cryoprotection of Proteins in Solution and in the Crystalline... 

All these results are encouraging for investigators planning to use X-ray diffraction in mixed solvents at subzero temperatures and the rest of the present article will be devoted to a discussion of methods and preliminary results in this field. The methodology for cryoprotection of protein crystals, its physical-chemical basis, and the specific problems raised by the crystalline state, as well as the devices used to collect data at subzero temperatures, will be described. Limitations and perspectives of the procedure will be discussed critically. First attempts to determine the structure of productive enzyme-substrate intermediates through stop-action pictures will be described, as well as investigations showing that X-ray diffraction at selected normal and subzero temperatures can reveal protein structural dynamics. 

Work in solution is an absolute prerequisite for further studies of enzyme-substrate intermediates in the crystalline state. According to the Arrhenius relationship, k = A exp(—E IRT), which relates the rate constant k to the temperature, reactions normally occurring in the second to minute ranges might be sufficiently decreased in rate at subzero temperatures to permit intermediates to be stabilized, and occasionally purified by column chromatography if reactions are carried out in fluid solvent mixtures. Therefore, the first problem is to find a suitable cryoprotective solvent for the protein in question. 

An increasing number of enzyme-catalyzed reactions normally occurring in seconds to minutes have been successfully investigated in mixed solvents at subzero temperatures and have been resolved in time, step by step. Some examples are presented in the following sections. 

Investigating the same reaction in fluid mixed solvents in a range of subzero temperatures, Douzou and associates were able to obtain the temporal resolution of the reaction, step by step, by means of coolingheating cycles (Douzou et al., 1970). As an example, reactions carried out in a mixture of ethylene glycol and buffer, pH 6.5 (1 1 v/v), at -40°C gave the following result ... 

The various redox states of cytochrome P-450 (Fe ", Fe " " RH, Fe " " RH) as well as the metastable oxyferrous compound [(O2—Fe " ") RH] are obtained in ethylene glycol-water mixture their absorption spectra and formation rates are similar to those recorded in pure aqueous media. These identical spectra demonstrate that the intermediates obtained in the mixed solvent at normal and subzero temperatures are similar to those found in the productive enzyme pathway under normal conditions. This is an essential observation since the low-temperature procedure permits one to stabilize and accumulate intermediates and offers the opportunity of obtaining structural information about such intermediates—a result unattainable by classical fast-kinetic techniques. 

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