变压发泡工艺对聚氨酯泡沫泡孔结构控制的研究

利用变压发泡可实现对聚氨酯泡沫泡孔结构的控制,得到气孔细密均匀的泡沫体。主要探讨了变压发泡工艺下,恒压时间、压力大小对泡沫泡孔结构的影响     

Responses to major categories of food chemicals by the lizard Podarcis lilfordi

Many lizards are capable of identifying food using only chemical cues from food surfaces, but almost nothing is known about the types of compounds that are effective stimuli. We experimentally studied lingual and biting responses by a lacertid lizard, Podarcis lilfordi, to single representatives of three major categories of food chemicals, sucrose as a carbohydrate, pure pork fat as a mixture of lipids, and bovine gamma globulin as a protein. In 60-sec trials in which stimuli were presented on cotton swabs, the lizards detected all three stimuli, exhibiting more tongue-flicks, licks, or bites, or a greater tongue-flick attack score (TFAS; overall measure of response strength to prey stimuli) than to deionized water. The initial response to all stimuli was tongue-flicking, but the lizards discriminated among the types of chemical stimuli. After preliminary tongue-flicks, the lizards responded to sucrose solutions by licking at high rates, to pure pork fat by biting, and to protein by a combination of additional tongue-flicks and biting. Biting is a feeding response to prey or solid plant material. Licking is a feeding response to sugars in nectar or ripe fruit. Its frequency increased with sucrose concentration. Our data suggest that lizards can identify several types of chemicals associated with food and direct feeding attempts to sources of such chemicals in the absence of visual cues.     

Enhanced biosurfactant production by <Emphasis Type="Italic">Corynebacterium alkanolyticum</Emphasis> ATCC 21511 using self-cycling fermentation

Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 was accomplished in a self-cycling fermenter (SCF) on a hexadecane substrate. The phospholipid biosurfactant produced during each cycle could be monitored rapidly using fluorescence spectroscopy. By optimizing the cycling pattern of the SCF, significantly better yields of biosurfactant were obtained than previously reported for this microorganism. It was also possible to virtually eliminate the hydrocarbon residue in the product. Harvest concentrations of 1.9 g L⁻¹ were obtained by using a two-stage fermentation. The first step was the growth of C. alkanolyticum in an SCF to yield a harvest of synchronous cells. These cells were transferred to a second vessel for the production stage. The concentration of biosurfactant could be further increased to 2.7 g L⁻¹ by the addition of more hexadecane at the beginning of the second stage.     

Inhibition of cholesterol synthesis by cyclopropylamine derivatives of squalene in human hepatoblastoma cells in culture

Two squalene derivatives, trisnorsqualene cyclopropylamine and trisnorsqualeneN-methylcyclopropylamine, were synthesized and tested for inhibition of lanosterol and squalene epoxide formation from squalene in rat hepatic microsomes, and for the inhibition of cholesterol syntheses in human cultured hepatoblastoma (HepG2) cells. Trisnorsqualene cyclopropylamine inhibited [³H]-squalene conversion to [³H]squalene epoxide in microsomes (IC₅₀=5.0 μM), indicating that this derivative inhibited squalene mono-oxygenase. Trisnorsqualenen-methylcyclopropylamine inhibited [³H]squalene conversion to [³H]lanosterol (IC₅₀=12.0 μM) and caused [³H]-squalene epoxide to accumulate in microsomes, indicating that this derivative inhibited 2,3-oxidosqualene cyclase. Cholesterol biosynthesis from [¹⁴C]acetate in HepG2 cells was inhibited by both derivatives (IC₅₀=1.0 μM for trisnorsqualene cyclopropylamine; IC₅₀=0.5 μM for trisnorsqualeneN-methylcyclopropylamine). Cells incubated with trisnorsqualene cyclopropylamine accumulated [¹⁴C]squalene, while cells incubated with trisnorsqualeneN-methylcyclopropylamine accumulated [¹⁴C]squalene epoxide and [¹⁴C]squalene diepoxide. The concentration range of inhibitor which caused these intermediates to accumulate coincided with that which inhibited cholesterol synthesis. The results indicate that cyclopropylamine derivatives of squalene are effective inhibitors of cholesterol synthesis, and that substitutions at the nitrogen affect enzyme selectivity and thus the mechanism of action of the compounds.     

Lipase G-Catalyzed synthesis of monoglycerides in organic solvent and analysis by HPLC

Monoglycerides were synthesized with Lipase G fromPenicillium sp. as biocatalyst. This enzyme successfully catalyzed the esterification of glycerol with oleic acid (18:1 n-9) or eicosapentaenoic acid, EPA (20:5 n-3) in hexane. Esterification at 40°C for 24 hr resulted in 86.3 mol% and 64.3 mol% incorporation of 18:1 n-9 and 20:5 n-3, respectively. Lipase GC fromGeotrichum candidum was not effective in esterifying the fatty acids under the present experimental conditions. Lipase G was able to incorporate 98.5 mol% and 98.1 mol% of 18:1 n-9 onto glycerol in 24 hr or less at 25°C and 37°C, respectively, in the absence of molecular sieve 4A. The product formed was analyzed by high performance liquid chromatography (HPLC) with a combined evaporative light scattering mass detector (ELSD) and ultraviolet detection at 206 nm. The result of this study demonstrates that Lipase G is capable of incorporating long-chain fatty acids of potential health benefit onto glycerol.     

Circulating Organ-Specific MicroRNAs Serve as Biomarkers in Organ-Specific Diseases: Implications for Organ Allo- and Xeno-Transplantation

Different cell types possess different miRNA expression profiles, and cell/tissue/organ-specific miRNAs (or profiles) indicate different diseases. Circulating miRNA is either actively secreted by living cells or passively released during cell death. Circulating cell/tissue/organ-specific miRNA may serve as a non-invasive biomarker for allo- or xeno-transplantation to monitor organ survival and immune rejection. In this review, we summarize the proof of concept that circulating organ-specific miRNAs serve as non-invasive biomarkers for a wide spectrum of clinical organ-specific manifestations such as liver-related disease, heart-related disease, kidney-related disease, and lung-related disease. Furthermore, we summarize how circulating organ-specific miRNAs may have advantages over conventional methods for monitoring immune rejection in organ transplantation. Finally, we discuss the implications and challenges of applying miRNA to monitor organ survival and immune rejection in allo- or xeno-transplantation.     

Comparison of the bligh and dyer and folch methods for total lipid determination in a broad range of marine tissue

For many studies, it is important to measure the total lipid content of biological samples accurately. The Bligh and Dyer method of extraction was developed as a rapid but effective method for determining total lipid content in fish muscle. However, it is also widely used in studies measuring total lipid content of whole fish and other tissues. Although some investigators may have used modified Bligh and Dyer procedures, rarely have modifications been specified nor has their effectiveness been quantitatively evaluated. Thus, we compared this method with that of the classic Folch extraction in determining total lipid content of fish samples ranging from 0.5 to 26.6% lipid. We performed both methods as originally specified, i.e., using the chloroform/methanol/water ratios of 1:2:0.8 and 2:2:1.8 (before and after dilution, respectively) for Bligh and Dyer and of 8:4:3 for Folch, and with the initial solvent/sample ratios of (3+1):1 (Bligh and Dyer) and 20:1 (Folch). We also compared these with several other solvent/sample ratios. In samples containing <2% lipid, the results of the two methods did not differ. However, for samples containing >2% lipid, the Bligh and Dyer method produced significantly lower estimates of lipid content, and this underestimation increased significantly with increasing lipid content of the sample. In the highest lipid samples, lipid content was underestimated by up to 50% using the Bligh and Dyer method. However, we found a highly significant linear relationship between the two methods, which will permit the correction of reported lipid levels in samples previously analyzed using an unmodified Bligh and Dyer extraction. In the future, modifications to procedures and solvent/sample ratios should be described.     

In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid‐acid‐catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature‐dependent volatile‐product‐slate changes when the polymer was cracked with HZSM‐5 and HY zeolites and the protonated form of MCM‐41. Volatile‐product distributions depended on the catalyst acidity and pore size. With HZSM‐5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30–40°C higher than those required for olefin production. Small olefins (C₃–C₅) were the most abundant products when HZSM‐5 and MCM‐41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C₄–C₈). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM‐5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile‐product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3118–3125, 2001     

Tert-butyl acetate: Non-HAP solvent for high-solids epoxy formulations

Xylene is the traditional diluent solvent for formulating epoxy/amine paints used in protective coatings and linings. Currently, it is under regulatory pressure because it is on the hazardous air pollutant (HAP) list and it is also a volatile organic compound (VOC). Ketones and acetate esters are powerful solvents, but their use is limited by their reaction with the amine curatives before paint application. Tert-butyl acetate (t-BAc) proposed as a VOC-exempt solvent, is a nonreactive, non-HAP solvent suitable for both the epoxy resin and amine curative sides of a two-component epoxy system. Molecular modeling predicts very low reactivity of the t-BAc ester functionality with amine nucleophiles as a result of steric hindrance. Long-term aging studies with amine curatives in t-BAc solutions confirm these theoretical results. Kinetics of the reaction of amines with t-BAc and its n-butyl acetate isomer support the view that steric hindrance plays a major role in amine solution stability. Presented at the International Waterborne, High-Solids, and Powder Coatings Symposium, February 21–23, 2001, New Orleans, LA. 3801 West Chester Pike, Newtown Square, PA 19073.     

Pheromonal Discrimination of Sex by Male and Female Leopard Geckos (Eublepharis macularius)

The ability of male and female Eublepharis macularius to discriminate among pheromones of males and females and a blank control was investigated. Stimuli were presented on ceramic tiles in the animal's home cages. Males tongue-flicked at significantly lower rates in response to male stimuli than to female and control stimuli. Males also performed aggressive behaviors toward male, but not female or control, stimuli, and tail vibrations toward female, but not male or control, stimuli. Mean tongue-flick rates by females did not differ significantly among conditions. Discrimination of male pheromones by females was demonstrated by greater performance of labial-licking and chin-rubbing in response to male stimuli than to either female or control stimuli.