主题：【分享】USP30-NF25比旋度《781》翻译

781  OPTICAL ROTATION 旋光

Many pharmaceutical substances are optically active in the sense that they rotate an incident plane of polarized light so that the transmitted light emerges at a measurable angle to the plane of the incident light. This property is characteristic of some crystals and of many pharmaceutical liquids or solutions of solids. Where the property is possessed by a liquid or by a solute in solution, it is generally the result of the presence of one or more asymmetric centers, usually a carbon atom with four different substituents. The number of optical isomers is 2n, where n is the number of asymmetric centers. Polarimetry, the measurement of optical rotation, of a pharmaceutical article may be the only convenient means for distinguishing optically active isomers from each other and thus is an important criterion of identity and purity.
很多药用物质具有光学活性，他们能够使入射的平面偏振光旋转，这样射出的光线与入射光线的角度形成可测量的角度。这个性质是一些结晶状物体或者药用液体或固体的溶液所具有的特性。在某种液体或者溶液中的溶质具有该性质的情况下，这通常是存在着一个或者多个不对称中心的结果，经常是一个碳原子与四个不同的取代基。光学异构体的数量是2 n，在此n是不对称中心的数量。药用物质的旋光测定法，即测定光学旋转的方法，也许是用于区分具有光学活性的异构体的方法中唯一简便的方法。因此，该方法是鉴别和纯度的一个重要标准。

Substances that may show optical rotatory power are chiral. Those that rotate light in a clockwise direction as viewed towards the light source are dextrorotatory, or (+) optical isomers. Those that rotate light in the opposite direction are called levorotatory or (–) optical isomers. (The symbols d- and l-, formerly used to indicate dextro- and levorotatory isomers, are no longer sanctioned owing to confusion with D- and L-, which refer to configuration relative to D-glyceraldehyde. The symbols R and S and  and  are also used to indicate configuration, the arrangement of atoms or groups of atoms in space.)
能够表现出旋光能力的物质是手性的。那些朝向光源观察时按顺时针方向旋转光线的物质是右旋性的或者(+)光学异构体。（其符号d- 和 l-，原先是用来表示右旋的和左旋的异构体，现在由于容易与D-和L-混淆而不再使用，这两个符号涉及与D-甘油醛相关的结构）。符号R和S以及 和 也都是用于表示结构、原子或原子组在空间中的排列。

The physicochemical properties of nonsuperimposable chiral substances rotating plane polarized light in opposite directions to the same extent, enantiomers, are identical, except for this property and in their reactions with other chiral substances. Enantiomers often exhibit profound differences in pharmacology and toxicology, owing to the fact that biological receptors and enzymes themselves are chiral. Many articles from natural sources, such as amino acids, proteins, alkaloids, antibiotics, glycosides, and sugars, exist as chiral compounds. Synthesis of such compounds from nonchiral materials results in equal numbers of the enantiomers, racemates. Racemates have a net null optical rotation, and their physical properties may differ from those of the component enantiomers. Use of stereoselective or stereospecific synthetic methods or separation of racemic mixtures can be used to obtain individual optical isomers.
具有在相反方向旋转平面偏振光到同样程度的理化特性的不可重叠手性物质，即对映结构体，除了上述特性以及与其他手性物质进行的反应的区别之外，是完全相同的。由于生物受体和酶自身均是手性的，对映异构体经常在药理与毒理方面展现出深刻的差异。许多天然来源的物品，例如氨基酸、蛋白质、生物碱、抗生素、糖苷、蔗糖等，以手性化合物的形式存在。使用非手性物料合成此类化合物导致等量的对映异构体和外消旋物。外消旋物有净无效旋光（net null optical rotation），并且他们的物理特性可能与那些组成部分中的对应结构体不同。可以使用立体选择或立体专一的合成方法，或者外消旋混合物的分离，来获得单独的光学异构体。

Measurement of optical rotation is performed using a polarimeter.* The general equation used in polarimetry is:
旋光的测量使用一个旋光计来完成。旋光测定法中通用的公式为：

where [ ] is the specific rotation at wavelength  , t is the temperature, a is the observed rotation in degrees ( ), l is the pathlength in decimeters, and c is the concentration of the analyte in g per 100 mL. Thus, [ ] is 100 times the measured value, in degrees ( ), for a solution containing 1 g in 100 mL, measured in a cell having a pathlength of 1.0 decimeter under defined conditions of incident wavelength of light and temperature. For some Pharmacopeial articles, especially liquids such as essential oils, the optical rotation requirement is expressed in terms of the observed rotation, a, measured under conditions defined in the monograph.
其中，[ ]是在波长 条件下的比旋度，t是温度，a是观测到的以度( )为单位的旋转，l是以分米为单位的通道长度，c是以克/100mL为单位被分析物的浓度。因此，当100mL中含有1克的溶液，在通道长度为1.0分米的单位中，并使用规定的入射光波长和温度的情况下，[ ]是测量值的100倍。对于某些药典物质来说，尤其是香精油之类的液体，旋光的规定表达为在该各论中所规定的条件下进行测定，所观察到的旋转，a。

Historically, polarimetry was performed using an instrument where the extent of optical rotation is estimated by visual matching of the intensity of split fields. For this reason, the D-line of the sodium lamp at the visible wavelength of 589 nm was most often employed. Specific rotation determined at the D-line is expressed by the symbol:
历史上，旋光测定法检测所使用的仪器中，旋光的程度是通过肉眼观察分离区域的亮度。由于这个原因，可见波长589nm的纳灯的D-线是最经常使用的。用D-线检测的比旋度的表示方法为：

and much of the data available are expressed in this form. Use of lower wavelengths, such as those available with the mercury lamp lines isolated by means of filters of maximum transmittance at approximately 578, 546, 436, 405, and 365 nm in a photoelectric polarimeter, has been found to provide advantages in sensitivity with a consequent reduction in the concentration of the test compound. In general, the observed optical rotation at 436 nm is about double and at 365 nm about three times that at 589 nm. Reduction in the concentration of the solute required for measurement may sometimes be accomplished by conversion of the substance under test to one that has a significantly higher optical rotation. Optical rotation is also affected by the solvent used for the measurement, and this is always specified.
并且，很多得到的数据用次形式表示。使用较低的波长，例如那些利用光电旋光计过滤掉汞灯线在578、546、436、405、365nm的最大能见度所产生的，已经被发现有利于增加检验敏感性，并最终导致供试品浓度的降低。通常情况下，观察到的旋光在436nm条件下大约是两倍于589nm，而在365nm条件下是三倍。检验必须的溶质浓度的减少有时候可以通过将供试品转换为具有显著高旋光性的物质来实现。旋光还受检验所用溶剂的影响，而此溶剂总是作出明确规定的。


USP30-NF25比旋度《781》