PHOSPHOTUNGSTATE: A "UNIVERSAL" (NONSPECIFIC) PRECIPITANT FOR POLAR POLYMERS IN ACID SOLUTION
PHOSPHOTUNGSTATE: A "UNIVERSAL" (NONSPECIFIC) PRECIPITANT FOR POLAR POLYMERS IN ACID SOLUTION
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磷钨酸盐：酸性溶液中极性聚合物的“通用”（非特异性）沉淀剂
DOI：
10.1177/19.11.689
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发表时间：
1971
影响因子：
3.2
通讯作者：
J. Scott
中科院分区：
文献类型：
--
作者：
J. Scott
磷钨酸（PTA）在低pH值下是多糖特异性染色剂（3）的说法最近受到质疑（2）。相反，有人提出，任何羟基聚合物（不一定是多糖）都可以通过在低pH值下羟基的质子化形成能够在salthike络合物中沉淀PTA的聚阳离子（5）。下面简要地提到了两个推论：（a）预期其他聚阳离子（特别是蛋白质）将以相同的方式反应;（B）PTA必须在非常低的pH值下解离（阴离子）（例如，内10 NH，SO 4）;即，那一定是很强的酸对这些问题的审议产生了进一步的结果，这些结果附在后面。1.有许多聚合物，在中性pH下未电离，含有极性基团，其可以在强酸中质子化，通过多羟基化合物设想的过程产生聚阳离子。两个这样的基团是醚（R-O-R '）和酰胺（R-CO-NR' R”）。如前所述，在添加和不添加强酸（HCl或H2SO 4）的情况下，测试了几种聚醚和聚酰胺沉淀PTA的能力（5）。发现这两类聚合物在比先前测试的多羟基聚合物高得多的pH下通过PTA沉淀（表I）。这些结果与所提出的机制是一致的，因为两组都是更碱性的（即，更容易质子化）（参见，例如，参考文献1）。特别地，与未醚化的多糖相比，即使在不存在添加的无机酸的情况下，多糖的烷基醚也可通过PTA沉淀。这些结果和先前发表的结果可以概括;任何溶解在酸水溶液中的聚合物在pH值高于-1时产生聚阳离子，将与PTA发生静电相互作用，并可能沉淀（图1）。甚至聚阴离子也可以沉淀（5），但它们的负电荷必须在它们变成阳离子之前被抑制，在聚酯硫酸盐的情况下，这需要非常高浓度的添加强酸。与羟基相比，醚基的碱性更大，这表明具有许多分支点的多糖应在比直链多糖更高的pH下沉淀，直链多糖中糖苷（醚）键的数目不成比例地少（参见糖原（5））。类似地，具有最基本的碱性羟基的那些聚合物应该比其中羟基经受诱导效应等的那些聚合物更容易沉淀。通过使它们更酸性的相邻基团（ef.聚乙烯醇（5））。
The claim that phosphotungstic acid (PTA) at low pH is a polysaccharide-specific stain (3) was recently challenged (2). Instead, it was proposed that any hydroxylic polymer (not necessarily polysaccharide) could, by protonation of hydroxyl groups at low pH, form polycations capable of precipitating PTA in a salthike complex (5). Two corollaries follow, which were touched on briefly: (a) other polycations (particularly proteins) would be expected to react in the same way; (b) PTA must be dissociated (anionic) at very low pH (e.g., inn 10 N H,S04); i.e., it must be a very strong acid. Consideration of these points produced further results, which are appended. 1. There are many polymers, un-ionized at neutral pH, containing polar groups which could protonate in strong acid, producing polycations by the process envisaged for polyhydroxyhic compounds. Two such groups are ether (R-O-R’) and amide (R-CO-NR’R”). Several polyethers and polyamides were tested for their ability to precipitate PTA, with and without added strong acid (HC1 or H2SO4), as described previously (5). It was found that both classes of polymers were precipitated by PTA at considerably higher pH than the polyhydroxyhic polymers tested previously (Table I). These results are compatible with the suggested mechanism, in that both groups are more basic (i.e., more easily protonated) than the hydroxyl group (see, for example, Reference 1). In particular, the alkyl ethers of polysaccharides are precipitable by PTA even in the absence of added mineral acid, in contrast to unetherified polysaccharides. These results, and those previously published, can be generalized; any polymer which dissolves in aqueous acid to produce a polycation at pH’s above -1 will interact electrostatically with PTA and will probably be precipitated (Fig. 1). Even polyanions can be precipitated (5), but their negative charge must be suppressed before they can become cationic, which in the case of polyestersulfates requires a very high concentration of added strong acid. The greater basicity of the ether group as compared with hydroxyl suggests that polysaccharides with many branch points should be precipitated at higher pH than linear polysaccharides in which the number of glycosidic (ether) links is proportionately less (cf. glycogen (5)). Similarly, those polymers with the niost basic hydroxyl groups should be more easily precipitated than those in which the hydroxyl groups are subject to inductive effects, etc., by neighboring groups which render them more acidic (ef. polyvinyl alcohol (5)).