Temperature-dependent separation of bryostatin 18 and 10 by high performance liquid chromatography

Summary The temperature-dependent separation of bryostatins by HPLC was examined on an octadecyl bonded stationary phase, using column temperatures between 0 and 40°C and mobile phase temperatures from 0 to 25°C. The retention time and resolution of bryostatins changed drastically and separation improved with decreasing temperature. A column temperature of less than 5°C and a mobile phase temperature of less than 15°C is recommended for a good resolution of bryostatins for routine work.     

Molecular distillation

Molecular distillation was studied for the separation of tocopherols from soya sludge, both experimentally and by simulation, under different operating conditions, with good agreement. Evaporator temperatures varied from 100°C to 160°C and feed flow rates ranged from 0.1 to 0.8 kg/h. The process pressure was maintained at 10⁻⁶ bar, the feed temperature at 50°C, the condenser temperature at 60°C, and the stirring at 350 rpm. For each process condition, samples of both streams (distillate and residue) were collected and stored at −18°C before tocopherols analyses. Owing to the differences between molecular weights and vapor pressures of free fatty acids and tocopherols, tocopherols preferentially remained in the residue at evaporator temperatures of 100°C and 120°C, whereas for higher temperatures (140°C and 160°C) and lower feed flow rate, tocopherols tended to migrate to the distillate stream.     

Kinetic migration studies using Porapak as solid-food simulant to assess the safety of paper and board as food-packaging materials

Porapak has been studied as a solid-food simulant in experiments on paper and board packaging. Three samples of paper with different recycled pulp content and surface treatment, and of different grammage and thickness, were used for the studies. Kinetic behaviour from 25 °C to 100 °C and different contact times ranging from 5 min at 100 °C to 10 days at 25 °C were studied using Porapak or, occasionally, Tenax or milk powder. Similar results were obtained with Porapak and Tenax but those from Porapak were more stable with temperature. Porapak behaves as good solid-food simulant even at high temperature.     

Temperature-dependent ratcheting of PTFE gaskets under cyclic compressive loads with small stress amplitude

Uniaxial stress-controlled ratcheting experiments on PTFE gaskets under cyclic compressive loads with small stress amplitude were performed. The effect of temperature on the deformation behavior was considered. Results showed that the compressive modulus decreases rapidly when the temperature increases from 100 °C to 200 °C. Compressive ratcheting deformation with cycles increase significantly with the increases of temperature. The ratcheting deformations at 100 °C, 150 °C and 200 °C are nearly two, three and five times that at room temperature, respectively. Most of ratcheting deformation mainly occurs during the first 20 cycles because the subsequent ratcheting rate and strain range are small and much less than those in the previous cycles. The accumulated deformation under cyclic loads with small stress amplitude is relatively approach to the static compressive creep with the same peak stress. Therefore, the accumulated deformation with time of PTFE gaskets obtained by cyclic compression with small stress amplitude can be estimated by the corresponding static creep deformation with good accuracy under the approximate stress rate and the same temperature, especially at room temperature.     

Temperature calibration of a mass spectrographic evolved gas analysis system

Because of the vacuum used in mass spectrographic evolved gas analysis, the usual effects of temperature lag between actual and apparent sample temperatures are exaggerated. Factors contributing to this temperature difference are discussed. The melting point of various metals in the range 110–1100°C are used to obtain insights and estimates regarding these temperature discrepancies at different heating rates, utilizing a variety of sample holders. In general, if the sample is in good contact with the heated supporting surface, the agreement between the observed and reported equilibrium melting temperatures is good at heating rates of ? ～ 20°C min. At higher heating rates the differences become larger (?10°C) and the effect increases with increasing temperature of melting. For sample holders which are not in good contact with the sample, hot spots can develop at high temperatures due to unequal thermal radiation. Under these circumstances the apparent melting point can be considerably lower than the actual equilibrium temperature and less dependent upon heating rate.     

Effects of trapping temperature and film thickness in purge and trap with whole column cryotrapping on fused silica columns

The effects of trapping temperature and column film thickness were investigated with respect to their ability to promote effective cryofocusing on fused silica capillary columns. The study was a further development of the purge and trap with whole column cryotrapping (P&T/WCC) method. The rates at which compounds could be thermally desorbed from a P&T unit and transferred to a column (with zero split) were first examined. A near quantitative transfer of the desorbable analytes was obtained with a 4 min, 180°C, 20 mL/min desorption. The compounds tested included naphthalene. Columns with film thicknesses from 0.12 to 3.0 μm were then investigated in P&T/WCC analyses with WCC temperatures ranging from ?80 to 0°C. The trapping took place from a transfer line gas stream initially at 175°C. The volatilities of the compounds examined varied from that of 1,1-dichloroethene to 1,1,2,2-tetrachloroethane. A higher film thickness was found to ease the WCC temperature requirements. Within each column type, the warmest WCC temperatures which allowed good cryotrapping with no significant increases in peak width were: 0.25 μm, ?70°C; 1.0 μm, ?50°C; 3.0 μm, ?20°C. In addition to being quantitative, the trapping provided good chromatography.     

Characteristics of Ag/Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>/p-Si heterostructure prepared by sol-gel processing

The metal-ferroelectric-semiconductor (MFS) heterostructure has been fabricated using Bi_3.25La_0.75Ti₃O₁₂ (BLT) as a ferroelectric layer by sol-gel processing. The effect of annealing temperature on phase formation and electrical characteristics of Ag/BLT/p-Si heterostructure were investigated. The BLT thin films annealed at from 500°C to 650°C are polycrystalline, with no pyrochlore or other second phases. The C-V curves of Ag/BLT/p-Si heterostructure annealed at 600°C show a clockwise C-V ferroelectric hysteresis loops and obtain good electrical properties with low current density of below 2×10⁻⁸ A/cm² within ±4 V, a memory window of over 0.7 V for a thickness of 400 nm BLT films. The memory window enlarges and the current density reduces with the increase of annealing temperature, but a annealing temperature over 600°C is disadvantageous for good electrical properties.     

Effect of subambient temperature on RP-HPLC of β-carotene isomers

Summary (E)-β-carotene and three mono-(Z)-isomers (9(Z)-, 13(Z)-, 15(Z)-) were eluted isocratically on a VYDAC 201TP54 column, using column temperatures between +30°C and −7°C. In this temperature range, their elution order changed dramatically with decreasing temperature. Nearly baseline separation of the four isomers within one hour was achieved at −7°C. For laboratory routine, temperatures of 9±2°C can be recommended. Thus, a good resolution of β-carotene- and lycopene-isomers (e.g. in tomato products) within 30 minutes is possible.     

Crosslinking of polyimides via spirodilactone unit in polymer backbone

A new approach for the crosslinking of polyimides via the lactamization of spirodilactone unit in polyimide backbone was studied by two means: model reaction and the comparison of the properties of the polyimide precursors to those of the crosslinking polymers. Polyimides 4 and 5 were soluble in N,N′dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N′-methylpyrrolidone (NMP), and other common organic solvents, whereas their corresponding crosslinking polymers were insoluble in these solvents. The glass transition temperatures for polyimide 5 and its crosslinking polymer were 262°C and 291°C, whereas those for polyimide 4 and its crosslinking polymer were 265°C and 360°C. The weight-loss rate of the crosslinking polymers was apparently slower than that of the precursors when the temperature was > 400°C. The 10% weight-loss temperature for the polyimides 4 and 5 was < 500°C, whereas that for the crosslinking polymers was close to or above 600°C. The results indicate that this type of crosslinking polymer has good thermal properties. The temperature for the formation of lactam was above 180°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3680–3686, 1999     

Design and synthesis of a tribranched phenylethynyl‐terminated aryl ether compound and its use as a reactive diluent for PETI‐5

In this study, a tribranched, phenylethynyl‐terminated aryl ether compound (Tri‐PE‐PAEK) was synthesized. This novel star‐shaped compound exhibits a good combination of properties, such as a low melting temperature (252 °C) and good solubility in aprotic solvents, as well as a low melt viscosity (0.1 P at 280 °C). All these advantages make it a good candidate material for modern processing techniques such as resin infusion and resin transfer molding, which are the most favorable methodologies for current economical manufacturing of polymer matrix/carbon fiber composites. Furthermore, after undergoing thermal curing to yield a network at 370 °C for 1 h, a cured sample exhibited an unexpectedly higher glass transition temperature (370 °C), storage modulus retention above the glass transition temperature, and good thermal stability. In addition, this compound can be used as a reactive diluent for phenylethynyl‐terminated imide oligomer, which has the molecular weight of 5000 g/mol (PETI‐5) to reduce its viscosity and lower the minimum temperature of the minimum viscosity. Meanwhile, the toughness of a cured blended resin can be greatly increased with the addition of just 10% Tri‐PE‐PAEK to PETI‐5. Further loading levels of Tri‐PE‐PAEK in the blending would lead to a higher storage modulus and a higher mechanical strength without compromising the thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4844–4854, 2007     

Evaluation of thermally pretreated silica stationary phases under hydrophilic interaction chromatography conditions

Three novel hydrophilic interaction chromatography columns packed with bare silica 2.6 μm superficially porous particles were evaluated. These stationary phases undergo a different pretreatment temperature (400, 525, and 900°C) that might influence their kinetic performance and thermodynamic properties. In the first instance, we demonstrated that the performance of these columns was inferior to the commercial ones in the low plate count range (10 000 plates), but was more favorable for N values beyond 40 000 plates. Thanks to its high permeability and reasonable flow resistance (φ = 695), together with a minimum reduced heights equivalent to a theoretical plate value of only 2.4, the stationary phase pretreated at 400°C was particularly attractive for N > 70 000 plates with a remarkably low impedance value (E = 2488). In a second step, the impact of pretreatment temperature was evaluated using two mixtures of polar substances, namely nucleobases and derivatives, as well as nicotine and derivatives. Retentions and selectivities achieved on the tested stationary phases were appropriate, but selectivity differences were minor when modifying pretreatment temperature from 400 to 525°C. When we increased the pretreatment temperature up to 900°C, the surface chemistry was more seriously modified. Finally, the columns presented a good stability even at high temperature (70°C), especially for the phases pretreated at 400 and 525°C.     

Novel processable aromatic thermoplastic polyimides: Films,adhesives, moldings,and graphite composites

Novel hot-melt type flexible, tough, thermally stable, processable, thermoplastic, aromatic polyimides have been synthesized involving reaction of a keto-ether containing diamine with hinged aromatic dianhydrides followed by thermal and chemical cyclodehydration. Inherent viscosity in DMAC at 35°C of the synthesized polymers ranged 1.02 to 1.4 dl/g (0.5% solution). The polymers showed a glass transition temperature (T_g) of 250°C to 180°C as determined by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Thermogravimetric analysis showed polymer stability up to 510°C, in both air and nitrogen atmospheres. All the polymers have shown good melt-flow. Films of 1.5–2.8 ml thickness were made and tested for mechanical properties at room temperature, 177°C and 210°C. The developed films are suitable for adhesion of Ti/Ti specimens and showed a lap shear strength of 5575 psi. Melt-fusion of the polymers gave tough moldings. Graphite cloth composites have been made and tested for mechanical properties.     

Light-scattering study on cellulose diacetate in 2-butanone

Light-scattering measurements were carried out on three well-fractionated samples of cellulose diacetate (degree of substitution = 2.46) in acetone at 25°C and in 2-butanone at 30–60°C. For the system cellulose diacetate-2-butanone, the theta temperature, Θ, has been quoted as 37°C from cloud-point measurements; it was intended to examine further 2-butanone as a theta solvent. The value of Θ, defined as the temperature at which the second virial coefficient vanishes, was found to be 50°C. This difference in Θ was attributed to association of the dissolved polymer molecules. On the other hand, the weight-average molecular weights obtained in 2-butanone at 50°C were in accord with those determined in a good solvent, acetone. It was established that 2-butanone was a theta solvent for cellulose diacetate with Θ = 50°C. The molecular dimensions observed in 2-butanone were however unreasonably large. Therefore, determinations of the unperturbed dimensions and other conformational parameters in this solvent are withheld. Solution stability and association were examined by light scattering. It was deduced that the difficulty in dissolving the polymer in 2-butanone arose from the copolymeric nature of cellulose diacetate.     

Thermoelectric‐based temperature‐controlling system for in‐tube solid‐phase microextraction

A temperature‐controlling device for in‐tube solid‐phase microextraction was developed based on thermoelectric cooling and heating. This device can control the temperature of the capillary column from 0 to 100°C by applying a voltage to a Peltier cooler or stainless steel tube. The extraction temperatures for angiotensin I, propranolol, and ranitidine were optimized. In all cases, setting the temperature to 10°C for extraction achieved the best extraction efficiency. Desorption showed minimum peak broadening at 70°C, contributing to better chromatographic performance. Propranolol was selected as a model compound to compare the performance of temperature‐controlled in‐tube solid‐phase microextraction at optimized conditions. Calibration curves exhibited good linearity (R² > 0.999) over the studied range, and the limit of detection and limit of quantification were about three times lower than those obtained at standard conditions (30°C extraction and desorption).     

Effect of temperature on sulfate transport in two Penicillia

We studied the effects of temperature on the sulfate permease of Penicillium chrysogenum (PC) (a mesophile with a growth temperature range of 4-35°C) and Penicillium duponti (PD) (a thermophile with a growth temperature range of 27-58°C). Arrhenius plots of sulfate permease activity from mycelia grown at 50°C (PD), 30°C (PD and PC) or 8°C (PC) indicate that at temperatures below the transition point there is little difference in the activation energy of sulfate permease in mycelia from PD grown at 50°C or 30°C or PC grown at 30°C or 8°C; however, the temperature of the transition point for the permease from each set of mycelia assayed reflects the optimum growth temperature of the fungal source. Transitions occur at 15 °C for mycelia from PC and 35 ° C for PD mycelia. Kinetic measurements indicate that the K_m of sulfate permease in PC cells grown at a variety of temperatures is essentially the same at various temperatures. As an example, the K_m of 8°C or 30°C grown PC is about 55 μM at 25°C and 45 μM at 8°C. V_max measurements reflect growth conditions such as temperature and growth stage. p]Lipid composition of the mycelia dramatically reflect growth temperatures. Double bond index values vary from 1.94 for PC grown at 8°C to 0.81 for PD grown at 50°C. The percentage of total fatty acid represented by linolenic acid varies from 45% in 8°C grown PC to 4.2% or less in 30°C grown PC. No linolenic is found in mycelia from PD.     

Use of two different coating temperatures for a cold fiber headspace solid‐phase microextraction system to determine the volatile profile of Brazilian medicinal herbs

In this study, the experimental extraction conditions on applying headspace solid‐phase microextraction and cold fiber headspace solid‐phase microextraction (CF‐HS‐SPME) procedures to samples of six medicinal herbs commonly found in southern Brazil were optimized. The optimized conditions for headspace solid‐phase microextraction were found to be an extraction temperature of 60°C and extraction time of 40 min. For CF‐HS‐SPME, the corresponding values were 60°C and 15 min. In the case of the coating temperature for the CF‐HS‐SPME system, two approaches were investigated: (i) Temperature of 5°C applied during the whole extraction procedure; and (ii) the use of two fiber temperatures in the same extraction procedure with the aim of extracting the volatile and semivolatile compounds, the ideal condition being 60°C for the first 7.5 min and 5°C for the final 7.5 min. The three extraction procedures were compared. The CF‐HS‐SPME procedure had good performance only for the more volatile compounds whereas the strategy using two coating temperatures in the same procedure showed good performance for all compounds studied. It was also possible to determine the profile for the volatile fraction of each herb studied applying this technique followed by GC‐MS.     

Studies on alkaline protease produced by Bacillus sp. NG312

An alkalophilic hyperproducer of alkaline protease, Bacillus sp. NG312, was isolated, and the enzyme showed maximum activity at pH 11.0 and 60°C. The temperature optimum was increased by 10°C in presence of Ca²⁺. The crudeenzyme was found to have half-life of 11 d at 37°C and maximum stability at pH 9.0–10.0. It also exhibited very good stability in presence of detergent components and some locally available commericial detergent powders.     

Exploration of the Oxazolidinthione Protecting System for the Synthesis of Sialic Acid Glycosides

An N-acetyl oxazolidinthione-protected sialyl thioglycoside was synthesized and its use as a sialyl donor studied. The strongly electron-withdrawing nature of the oxazolidinthione moiety is such that activation could not be achieved at ?78°C. Couplings were therefore conducted at the lowest convenient temperature (?50°C). Glycosides were formed in good yield but in two out of three cases studied selectivities were lower than those seen with the corresponding N-acetyl oxazolidinone-protected donor. The resulting N-acetyl oxazolidinthione-protected disaccharides were converted to the corresponding N-acetyl oxazolidinones by treatment with N-iodosuccinimide and triflic acid in the presence of water at 0°C.     

WATER-SOLUBLE CHITIN OF LOW DEGREE OF DEACETYLATION

It was found that regenerated chitin obtained by a concentrated alkali treatment at a low temperature is water soluble. Chitin with 38% deacetylation, obtained by treatment with 15 wt.% NaOH at 10°C for four days, showed very good solubility in water at room temperature; whereas, eight days at 3°C were needed to prepare soluble chitin with 25% deacetylation. For this low-temperature deacetylation, two conditions were necessary to make α-chitin water soluble; first, an extended alkali treatment (e.g., at least four days in 15% alkali solution at 3°C) was required; and second, the degree of deacetylation required was more than 25%. The structural difference in regenerated chitin samples prepared at 3 and 25°C with the same degree of deacetylation (30%) were examined by X-ray diffraction and deamination analyses suggesting that the distribution of N-acetyl groups in the former chitin molecule was more random than those in the latter. This conclusion was supported by enzymatic analyses with chitinase or lysozyme.     

Internal acetylene unit linked para to the aromatic ring as a crosslink site for polyimide

Crosslinking behavior of internal acetylene units linked para to the aromatic rings was investigated by preparing polyimide from 4,4′-diaminodiphenylacetylene (p-intA) and 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA). Polyimide was also prepared from 1,4-phenylenediamine (PDA) and 6FDA for comparison. The polymers were moderately to highly viscous at the stage of polyamide acid. Thermal imidization gave polyimide having acetylene units that are linked para to the aromatic connecting units. Differential scanning calorimetry (DSC) measurement of the polymer revealed that exotherm due to the crosslinking of the acetylene unit appeared at ca. 330°C. After thermal treatment at high temperature such as 350 and 400°C, onset of the exotherm shifted to higher temperature and the amount of the exotherm became smaller. The dynamic mechanical properties of the uncrosslinked polyimide film treated at 250°C had a glass transition temperature (T_g) at 330°C with a considerable drop in the storage modulus at this temperature. After the film was exposed to a higher temperature to induce crosslinking, the T_g was observed to increase to above 400°C and the storage modulus was maintained to higher temperatures. Tensile properties of the polyimide showed that the films had good mechanical properties. © 1996 John Wiley & Sons, Inc.