席夫碱主要是指含有碳氮双键的亚胺或甲亚胺特性基团的一类有机化合物，早期的研究一般为缩胺类席夫碱。

Schiff base is the Types of organic compounds which contain C-N double bond of the imine or azomethine group characteristics. the early research focus on Amine Schiff base reduction.

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一旦具有该特性基团的化合物的相对含量发生变化，吸收系数必然相应变化，所以都存在“标准油”的选择问题。

Once the relative content of the compound with the characteristics of the group, changes, the absorption coefficient will surely change. Hence the problem of choice of standard oil has to be faced.

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R基团赋予氨基酸物理化学特性，例如极性（亲水性和疏水性）以及电荷（酸性或正电荷，碱性或负电荷）。

The R-groups give the amino acids their physical-chemical characteristics such as polarity (hydrophobic or hydrophilic) and charge (acidic or positive versus basic or negative).

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