共查询到20条相似文献,搜索用时 671 毫秒
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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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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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The Science of Nature - 相似文献
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L. Martos 《Die Naturwissenschaften》1956,43(17):399-400
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The biodegradability of 30 substituted phenols and benzoic acids was determined by BOD technique.The molecular weight (MW), heat of formation(Hf)and the energy of the highest occupied molecular orbital(EHOMO)of the studied compounds were calculated by the quantum chemical method MOPAC6.0-AM1.The quantitative structure-biodegradability relationshiops(QSBRs)were developed by the linear regression method and neural network approach,respectively.It has been shown that the neural network method is able to provide a superior fit to the training set data and test set data and produce a lower prediction error than the linear regression method. 相似文献
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Schobert R 《Die Naturwissenschaften》2007,94(1):1-11
Natural products containing tetronic acid or tetramic acid moieties continue to attract the interest of chemists, biologists,
and physicians due to their challenging structures and to the wide range of biological activities they display. This review
portrays the structural varieties of tetronic and tetramic acids and the spectrum of possible therapeutically relevant effects
in man for exemplary derivatives. Their biosynthetic origin from α-amino and α-hydroxy acids is briefly discussed as is the
relationship between their structures and their modes of interaction with biochemical effectors such as metal cations or enzymes.
A short overview of laboratory syntheses of the heterocyclic core structures of tetramic and tetronic acids is provided with
an emphasis on those emulating the biosynthesis. A synthesis from the α-amino or α-hydroxy esters and the cumulated phosphorus
ylide Ph3PCCO based upon a domino addition–intra-Wittig alkenation sequence is presented with applications to the preparation of the
antibiotics reutericyclin and tenuazonic acid, the cytotoxic melophlin B, and the enzyme inhibitor RK-682. Procedural advantages
of immobilizing either starting component by attaching it to a resin and its exploitation in the parallel synthesis of libraries
of potential drug candidates are described. The basic domino reaction can even be extended by further C–C bond forming steps
when starting from suitable α-hydroxy or α-amino allyl esters. Depending on the chosen reaction conditions, bioactive intermediates
of formally three to seven step long cascades can be obtained. Among them, herbicidal 3-alkyltetronic acids and lactone endoperoxides
with antiplasmodial activity exceeding that of the natural antimalarial lead artemisinin. Hence, this domino reaction gives
access to diversely functionalized derivatives of tetronic and tetramic acids. As it can also be ported to solid phase, it
is ideally suited for parallel and combinatorial processing. Future developments might include running such domino sequences
in continuous mode in arrays of “labs on microchips”. 相似文献
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