Hypothesis

Restoration of damaged hair structure by replacing lost keratin is still of paramount interest. On account of the fact that native keratin is a highly cross-linked protein with numerous disulfide bonds but just a few nucleophilic thiol groups, binding affinity to hair is comparatively low. Hence, the design of reactive keratin derivatives bearing free sulfhydryl groups that are optionally S-protected and preactivated should enhance permanent binding to hair fibers.

Experiments

Keratin was extracted from human Caucasian hair and reduced with NaBH₄ to obtain free sulfhydryl groups (keratin-SH). These thiol groups were S-protected via disulfide linkage to 2-mercaptonicotinic acid (keratin-MNA). Hair fibers were either utilized in their natural form or chemically damaged by bleaching. Amount of keratin derivatives being bound to hair fibers was quantified by fluorescence detection of fluorescein isothiocyanate labeled keratins.

Findings

Both modifications induced higher affinity of keratin to hair fibers, resulting in up to 1.7-fold (keratin-MNA) improved binding to natural hair and up to 3.6-fold (keratin-MNA) improved binding to bleached hair. Confocal laser microscopy confirmed the accumulation of keratin derivatives in distinct regions of the cuticle layer. Thiol functionalization seems therefore to be a promising strategy for efficient durable binding of keratin to hair.

中文翻译：

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反应性角蛋白衍生物：与头发共价结合的有前途的策略

假设

通过替换丢失的角蛋白来恢复受损的头发结构仍然是最重要的问题。由于天然角蛋白是具有许多二硫键但仅有几个亲核硫醇基团的高度交联的蛋白质，因此与头发的结合亲和力相对较低。因此，带有游离巯基的反应性角蛋白衍生物的设计可以任选地经S-保护和预活化，应增强与头发纤维的永久结合。

实验

从人的白种人头发中提取角蛋白，并用NaBH ₄还原以获得游离的巯基（角蛋白-SH）。这些巯基通过二硫键与2-巯基烟酸（角蛋白-MNA）的二硫键被S-保护。毛发纤维要么以天然形式使用，要么因漂白而化学损坏。通过荧光检测异硫氰酸荧光素标记的角蛋白来定量结合到毛发上的角蛋白衍生物的量。

发现

两种修饰均导致角蛋白对头发纤维的亲和力更高，从而导致与天然头发的结合力提高了1.7倍（角蛋白MNA），而与漂白头发的结合力提高了3.6倍（角蛋白MNA）。共聚焦激光显微镜证实角质衍生物在表皮层的不同区域中的积累。因此，硫醇官能化似乎是使角蛋白与头发有效持久结合的一种有前途的策略。