Linear and cyclic aliphatic carboxamides of the Murchison meteorite: hydrolyzable derivatives of amino acids and other carboxylic acids     

Cooper GW  Cronin JR 《Geochimica et cosmochimica acta》1995,59(5):1003-1015

Analyses of fractionated aqueous extracts of the Murchison meteorite by gas chromatography-mass spectrometry after silylation with N-methyl-N (tert-butyldimethylsilyl) trifluoroacetamide have revealed an extensive series of linear and cyclic aliphatic amides. These include monocarboxylic acid amides, dicarboxylic acid monoamides, hydroxy acid amides, lactams, carboxy lactams, lactims, N-acetyl amino acids, and substituted hydantoins. Numerous isomers and homologues through at least C8 were observed in all cases, except for the N-acetyl amino acids and hydantoins. Carboxy lactams, lactams, hydantoins, and N-acetyl amino acids are converted to amino acids by acid hydrolysis, thus, these compounds qualitatively account for the earlier observation of acid-labile amino acid precursors in meteoritic extracts. Laboratory studies of the spontaneous decomposition of N-carbamyl-alpha-amino acids and their dehydration products, the 5-substituted hydantoins, have led to the recognition of a series of aqueous phase reactions by which amino acids and cyanic acid/cyanate ion in the primitive parent body might have given rise to several of the observed classes of amides, as well as to monocarboxylic acids, dicarboxylic acids, and hydroxy acids. A previously undescribed reaction of 5-substituted hydantoins with cyanic acid/cyanate ion to give carboxamides of the 5-substituent groups was observed in the course of these studies. The presence of an extensive suite of amides in a CM chondrite appears to be consistent with the interstellar-parent body formation hypothesis for the organic compounds of these meteorites. The presence of carboxy lactams and lactams along with free amino acids suggests the possibility of further chemical evolution of meteorite amino acids by thermal polymerization. The cyclic amides, given their potential for hydrogen-bonded pair formation, might be considered candidate bases for a primitive sequence coding system.  相似文献   

Survival of microorganisms in smectite clays: implications for Martian exobiology     

Moll DM  Vestal JR 《Icarus》1992,98(2):233-239

Manned exploration of Mars may result in the contamination of that planet with terrestrial microbes, a situation requiring assessment of the survival potential of possible contaminating organisms. In this study, the survival of Bacillius subtilis, Azotobacter chroococcum, and the enteric bacteriophage MS2 was examined in clays representing terrestrial (Wyoming type montmorillonite) or Martian (Fe(3+)-montmorillonite) soils exposed to terrestrial and Martian environmental conditions of temperature and atmospheric pressure and composition, but not to UV flux or oxidizing conditions. Survival of bacteria was determined by standard plate counts and biochemical and physiological measurements over 112 days. Extractable lipid phosphate was used to measure microbial biomass, and the rate of 14C-acetate incorporation into microbial lipids was used to determine physiological activity. MS2 survival was assayed by plaque counts. Both bacterial types survived terrestrial or Martian conditions in Wyoming montmorillonite better than Martian conditions in Fe(3+)-montmorillonite. Decreased survival may have been caused by the lower pH of the Fe(3+)-montmorillonite compared to Wyoming montmorillonite. MS2 survived simulated Mars conditions better than the terrestrial environment, likely due to stabilization of the virus caused by the cold and dry conditions of the simulated Martian environment. The survival of MS2 in the simulated Martian environment is the first published indication that viruses may be able to survive in Martian type soils. This work may have implications for planetary protection for future Mars missions.  相似文献   

Patterns of American rice consumption in 1955 and 1980     

Shortridge JR  Shortridge BG 《Geographical review》1983,73(4):417-429

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Porphyrin and chlorin distributions in a Late Pliocene lacustrine sediment     

Keely BJ  Harris PG  Popp BN  Hayes JM  Meischner D  Maxwell JR 《Geochimica et cosmochimica acta》1994,58(17):3691-3701

The tetrapyrroles in a highly immature Late Pliocene lacustrine sediment (Willershausen, Germany) show a simple distribution of both chlorin and porphyrin components as the free bases. The major components are C32 desoxophylloerythroaetioporphyrin (DPEP), a C33 bicycloalkano porphyrin, the chlorin analogue of the latter, and desoxophylloerythrin and its chlorin counterpart. The structure of the novel bicycloalkano chlorin was determined using a combination of two-dimensional phase-sensitive COSY NMR and nOe studies. Measurements of delta 13C and other data indicate that DPEP and the bicycloalkano porphyrin were derived from the chlorophyll(s) of photosynthetic organisms utilising a common source of CO2, probably diatoms. The occurrence of DPEP and other minor alkyl porphyrins indicates that the chlorophyll defunctionalisation pathway leading to these components can occur at low temperature and was probably biologically mediated, as was the condensation leading to the fused ring components.  相似文献   

北部湾盆地全油基钻井液技术研究与应用          下载免费PDF全文

陈浩东  李龙  郑浩鹏  徐一龙  邓诚  余定泽 《探矿工程》2018,45(12):1-4

南海西部北部湾海域地质构造复杂,一直以来是钻完井事故的多发区。面对边际油田开发难度的不断增加,针对该海域涠洲组易垮塌、断层多、易井漏、易发生卡钻和储保难度大等特征,通过室内配伍实验,分析各材料加量比例,确定配方,形成了一套新型全油基钻井液体系。通过现场应用表明,与常规油基钻井液对比,全油基钻井液具有更强的封堵能力和抑制性,润滑性能好,抗污染能力强,井眼清洁好,储层保护效果好,有效提高机械钻速,解决了传统强封堵油基钻井液体系出现的诸多问题,达到了综合提速的效果。  相似文献   

Migration and the transformation of employment and household structures     

Heaton TB  Hawley AH  Udry JR  Boonlert-leoprapai 《Singapore journal of tropical geography》1982,3(1):34-43

Data collected in Colombia and Thailand in 1977 are used to "compare the employment and household characteristics of migrants before and after the move in order to assess the degree of change which accompanies migration. Moreover, these comparisons [are] made for migration streams between places at different levels in the urban hierarchy with the intention of determining within which streams the greatest transformations occur."  相似文献   

Population trends and the status of population policy in Africa     

Rogge JR 《The Journal of geography》1982,81(5):164-174

There is every indication that Africa's population growth will remain well above the world average for the remainder of this decade and probably for the rest of this century. With the exception of the island states and parts of North Africa, fertility levels show little indication of change. This is in part a reflection of little desire for small families, as well as a consequence of limited or even restricted family planning services. Great diversity in attitudes regarding population policy prevails among African governments, ranging from extreme pronatal to committed antinatal. Even with antinatal policies, however, many African states have yet to attain any significant success in depressing their rates of growth. To date, Mauritius can be cited as the only state to have almost achieved the transition from high to low fertility. The consequence of these continuing trends is that Africa will see further increases in its youth dependency ratio. Pressures on infrastructural services will therefore increase, and the problems of generating employment will intensify. While demographic factors are by no means the only ones creating economic stress on the continent, they clearly are contributory. Unlike Asia or parts of Latin America, Africa's problem is less a matter of too many people but rather 1 of excessive growth in too short a time frame. A realistic and effective long-term population policy, therefore, is an immediate need. Several countries including Nigeria (with a pouplation of over 80 million) are experiencing a crude birth rate of 50 or more/1,000. At least 4 countries, including Kenya, are currently doubling their population in 20 years or less. With these current population trends, a demographic transition to low vital rates must assume passage through an even higher growth phase than is currently being experienced because the fall in birth rates tends to occur much later than the fall in death rates. Government population policies and the status of family planning activities are illustrated according to natal sentiments and attitudes. Trends in national vital rates and of population structures in Africa are illustrated.  相似文献   

Molecular and isotopic analyses of the hydroxy acids, dicarboxylic acids, and hydroxicarboxylic acids of the Murchison meteorite     

Cronin JR  Pizzarello S  Epstein S  Krishnamurthy RV 《Geochimica et cosmochimica acta》1993,57(19):4745-4752

The hydroxymonocarboxylic acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison meteorite were analyzed as their tert-butyldimethylsilyl derivatives using combined gas chromatography-mass spectrometry. The hydroxydicarboxylic acids have not been found previously in meteorites. Each class of compounds is numerous with carbon chains up to C8 or C9 and many, if not all, chain and substitution position isomers represented at each carbon number. The alpha-hydroxycarboxylic acids and alpha-hydroxydicarboxylic acids correspond structurally to many of the known meteoritic alpha-aminocarboxylic acids and alpha-aminodicarboxylic acids, a fact that supports the proposal that a Strecker synthesis was involved in the formation of both classes of compounds. Isotopic analyses show these acids to be D-rich relative to terrestrial organic compounds as expected; however, the hydroxy acids appear to be isotopically lighter than the amino acids with respect to both carbon and hydrogen. The latter finding would not be expected if both classes of compounds came exclusively from common precursors as would have been the case for a Strecker synthesis.  相似文献   

月球地质结构及其岩石学特征   总被引：1，自引：0，他引：1  

郭迪江 Graig  JR 《地质科技情报》1995,14(4):29-32

简要介绍了美国ＮＡＳＡ阿波罗计划所获得的有关月球地质结构的一些新资料，结合笔者对月球岩石光片，薄片的镜下观察，简要介绍了月球岩石的岩石学特征，并讨论了有关月球的演化起源问题。  相似文献   

碳酸钙填料市场趋势与发展     

Vidal  JR 《江苏地质科技情报》1995,(2):23-24

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