共查询到20条相似文献,搜索用时 62 毫秒
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The Science of Nature - 相似文献
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对五种海洋微藻的脂类组成进行了测定,微藻在确定的条件下生长,分别于指数生长前期和稳定期收获,采用超声波萃取法提取脂肪酸,应用GC及GC-MS技术进行定量和定性分析。结果表明,在两个时期取得的同种藻体中,各主要脂类化合物的量存在明显变化。由此可以看出,实验藻体中多数脂肪酸都参与组成储能物质;多不饱和脂肪酸主要是以储能物质形式存在,在细胞膜中存在较少。 相似文献
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This study combines biology and mathematics, showing that a relatively simple question from molecular biology can lead to
complicated mathematics. The question is how to calculate the number of theoretically possible aliphatic amino acids as a
function of the number of carbon atoms in the side chain. The presented calculation is based on earlier results from theoretical
chemistry concerning alkyl compounds. Mathematical properties of this number series are highlighted. We discuss which of the
theoretically possible structures really occur in living organisms, such as leucine and isoleucine with a chain length of
four. This is done both for a strict definition of aliphatic amino acids only involving carbon and hydrogen atoms in their
side chain and for a less strict definition allowing sulphur, nitrogen and oxygen atoms. While the main focus is on proteinogenic
amino acids, we also give several examples of non-proteinogenic aliphatic amino acids, playing a role, for instance, in signalling.
The results are in agreement with a general phenomenon found in biology: Usually, only a small number of molecules are chosen
as building blocks to assemble an inconceivable number of different macromolecules as proteins. Thus, natural biological complexity
arises from the multifarious combination of building blocks. 相似文献
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采集了四川省内有代表性的26个土壤,对腐殖酸结合汞在土壤中的水平分布和在土壤剖面中的垂直分布进行了分析讨论.结果表明,腐殖酸结合汞及其两组分在土壤中的分布受到内在物源腐殖酸和外来汞源的决定性影响,以及土壤性质的影响.腐殖酸结合汞(HAs-Hg)和组分胡敏酸结合汞(HA-Hg)在不同土纲土壤中以淋溶土纲含量最高,其次是半水成土纲和初育土纲,最低是铁铝土纲;组分富里酸结合汞(FA-Hg)的含量以在半水成土纲中最低.在土壤剖面中,表现为土层越深,HAs-Hg与两组分含量、HA-Hg/FA-Hg比例越低. 相似文献
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随着对海洋中有机氮生物地球化学循环过程认识的逐步深入,氨基酸作为海洋有机氮库中最易被生物利用的组分之一愈加受到重视。关于海洋中氨基酸含量组成和生物可利用性的相关研究对认识海洋中有机氮的迁移和转化具有重要意义。本文详细阐述了海洋领域分光法和荧光法等溶解氨基酸测定方法及离子色谱和液相色谱等色谱分离方法的发展历程,并对应用最普遍的柱前衍生-反相液相色谱-荧光检测法等技术进行了更为详细的评述,列举了质谱技术、单体同位素分析技术和毛细管电泳等最新发展的技术方法,最后对其在海洋学中的应用进行展望。 相似文献
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Haloacetic acids, disinfection byproducts (DBPs) formed during drinking water chlorination process are carcinogens. The e cacy
of nanofiltration (NF) was examined for the removal of five regulated haloacetic acids (HAA5): chloro-, dichloro-, and trichloro-acetic
acid (CAA, DCAA, and TCAA); bromo-, and dibromo-acetic acid (BAA, and DBAA) in synthetic water. NF with the dense negatively
charged membrane (ES 10), is the most e cient in removing HAA5 than the loose negatively charged membrane (NTR 7410) and
neutral surface membrane (NTR 729HF), due to the greater electrostatic repulsion (Donan exclusion) and sieve e ect. Excellent HAA5
removal e ciency of 90%–100% could be obtained even at a low pressure of 1 105 Pa with ES 10. Changes in cross-flow velocity did
not e ect the performance of membranes with a small pore size such as ES 10 and NTR 729HF. The increase in HAA5 concentration
exhibited the adverse e ect on the performance of three membranes by strengthening the concentration polarization, which was the
driving force for the di usion of HAA anions across the membrane. 相似文献
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为了解稻草露天焚烧产生烟尘中正构脂肪酸的组成特征,在明火燃烧和闷烧条件下对6种稻草进行了模拟焚烧试验,采集了排放的烟尘,并用GC/MS进行测定.结果表明,稻草中的正构脂肪酸由C8~C34组成.明火烟尘中含有碳数为C8~C34的正构脂肪酸.其总含量的变化区间是8613.9~27225.0μg/g,平均值为15147.4μg/g.正构脂肪酸呈现以C16、C24为主、次碳峰的双峰式分布,并具有显著的偶碳数优势.其碳优势指数(CPI)的分布区间是3.08~6.41,平均值为4.31.平均碳链长度(ACL)为18.51~21.77,平均值是20.48.C24/C16值分布在0.11~0.41之间.闷烧烟尘中正构脂肪酸的碳数范围是C6~C34.其总含量的分布区间是59112.6~95214.3μg/g,平均值为76934.9 μg/g.呈与明火烟尘类似的双峰式分布,偶碳数优势显著.其CPI为3.88~5.24,平均值为4.38.ACL值分布在17.37~18.91之间,平均值为18.42.C24/C16比值为0.07~0.23.明火烟尘中C24/C16比值比稻草有所下降.闷烧烟尘中C24/C16比值均小于稻草和明火烟尘,正构脂肪酸的ACL也明显小于稻草和明火烟尘.烟尘中正构脂肪酸的组成相比原稻草已发生了明显的改变. 相似文献
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研究了乙酸、苯甲酸、酒石酸和柠檬酸对几种污染土中Cu的解吸及介质条件(如pH值、支持电解质)对其解吸的影响.结果表明,4种有机酸对污染土中Cu解吸的影响强弱为柠檬酸>酒石酸>乙酸≈苯甲酸;随着有机酸浓度升高,乙酸、苯甲酸、酒石酸对污染土中Cu的解吸率先降低后升高,柠檬酸对Cu的解吸率则一直升高;随着解吸液起始pH值由2升至8,柠檬酸对污染土中Cu的解吸率呈降低-升高-降低的变化,酒石酸对污染土中Cu的解吸率则一直降低;随着支持电解质浓度升高,酒石酸对污染土中Cu的解吸率趋于增大,且KCl为支持电解质时的解吸率略高于KNO3. 相似文献
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