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喜欢科学,偏爱自然科学。也喜欢技术,儿时喜围观打锡壶的和锔盆锔锅的。当过工人,当过兵,第二故乡是湖南、广西和广东。

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贻贝的秘密  

2015-06-08 16:28:19|  分类: 科学与技术 |  标签: |举报 |字号 订阅

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贻贝类的生活,总体来说,不怎么太让人兴奋。其海生品种的主要成员,生长着一对硬壳的软体动物,用大部分时间粘附在岩石上,依靠过滤它们周围的海水获取食物。不过还是有科学家花费了多年时间来研究这种简单的生物,仔细审视它们静止的生活方式,寻求破解它们最大的秘密:贻贝是如何粘在某个地方的?即使在不断地波浪冲刷中贻贝也能牢固地把它们自己粘在又湿又滑的岩石上。

第一个着手解决这个贻贝秘密的人是赫伯特-韦特(Herbert Waite)。在上个世纪70年代他作为哈佛大学的一名研究生,开始在康涅狄格州的海边上收集贻贝并把它们带回实验室。他开始分析这种粘性“线”的化学构成,这些“线”被称为足丝,贻贝就是用它们把自己粘到岩石上的。

贻贝用一种类似于“模型注塑”的过程来产生像毛发一样的足丝:在它们强健的足部形成一个凹槽,再把一种液体的蛋白质挤进去,这液体只用几秒钟就变成固体的线,在每根线的终端是一个粘性的“垫子”,它们牢牢地粘在岩石或者其他任何贻贝所贴附的坚硬表面上。

韦特分解了在贻贝足丝中、粘性终端垫中和分泌这些液体蛋白质的腺体中的蛋白质。在所有这些结构中他都发现了同一种不常见的称为左旋多巴(L-dopa)的氨基酸。这种分子已知在植物和人体中都有产生,在人体中它是作为神经递质多巴胺的前期材料,这也是为什么它被用于治疗帕金森病的原因(注:严格地说它只能减轻症状,并不能治疗帕金森病,甚至不能延缓这种疾病的进展)。

原来左旋多巴是贻贝粘贴能力之所在。

这种分子的关键部分是邻苯二酚的侧链,它由带两个羟基的苯环构成。这些羟基构成与岩石、船体以及任何贻贝要把自己粘上去的物体的结合。

自从韦特的发现以来又有许多不同种类的贻贝胶被发现,全部都包含左旋多巴,现在它们有一个集合名词:贻贝粘性蛋白(MAP – mussel adhesive protein)。

MAP研究中最令人振奋的部分,同时也是大部分对贻贝研究的背后推动力,是这种分子在人类社会的应用。富含左旋多巴或者其他包含邻苯二酚化合物的合成胶,正在被研发作为外科手术工具和用于治疗疾病。一个很有希望的领域是新生儿手术,这是个很大的挑战因为他们的粘膜非常娇嫩,难以缝合。使用模仿贻贝的胶将会容易得多,它在湿润条件下也能粘合并且不会引发麻烦的免疫反应。

能抗水的胶还能帮助治疗动脉中有斑块生成的病人。在这类病人的球囊血管成形术中,支架被置入以扩张病人狭窄的血管,在此支架上涂有一层抗炎药以降低斑块的生成,可是现在至少95%的药物在血流中被冲刷掉了。使用生物胶把药物粘在支架上可以显著地减少这种损失,延长支架的寿命。

赫伯特-韦特的实验室如今隶属于加利福尼亚大学圣芭芭拉分校,其研究者们在仿贻贝胶以外还研发了一种富含邻苯二酚的能够自愈的合成高分子材料。可能的应用包括制造几乎不需要手术维护的人工膝关节和髋关节。

仿贻贝胶还有一项可能的应用与我们的直觉相违背。海运业的一个大问题是粘附到船体上“搭便车”的生物的积聚,这包括贻贝、海藻、海生介(藤壶)以及其他结壳生物。这种人们所谓的生物积垢会增加阻力,提高燃料消耗。过去,有毒的化合物TBT(三丁基锡)被用作防污涂料。不过当它析出到环境中时就会造成很大的生态问题,已经被世界各国禁用。一个替代的方法将是用生物胶把其他不那么有害的防污垢成分牢固地粘到船底,从而避免对环境的进一步破坏。于是,在贻贝的粘合秘密被发现的今天,它的能防水的胶可以被反过来用于帮助防止贻贝自身的粘贴。

——《元素中的化学》,(英国)皇家化学学会 2015.5.6

(这个节目的更新很规律,podcast订阅地址:http://www.rsc.org/chemistryworld/podcasts/elements_podcast.xml)

For the most part, life as a mussel is not exactly exciting. These twin-shelled mollusks, the key ingredient in moules marinière - spend most of their time stuck to rocks sifting the water around them for food. But there are scientists who have spent years studying the simple creatures, scrutinizing their sedentary lifestyle and puzzling over their big secret: how do mussels stay stuck in place? Even with the constant ponding of waves, mussels are able to firmly fix themselves to wet, slippery rocks.

The first person to begin solving this mussel mystery was Herbert Waite. As a graduate student at Harvard in the nineteen seventies he began gathering mussels from along the Connecticut shoreline and bringing them back to the lab. He set about analyzing the chemical makeup of this sticky threads - known as byssus - which mussels use to attach themselves to rocks.

Mussels produce hair-like byssus threads in a process similar to injection-moulded plastics: a groove forms in their muscly foot into which they squeeze liquid protein, which takes seconds to set into a solid strand. A sticky pad at the end of each thread sticks firmly to the rock, or any other hard surface the mussel presses it against.

Waite broke down the proteins in byssus threads, in their sticky ends and in the glands that produce them. In all these structures he kept finding the same, rare amino acid called L-dopa (or 3, 4-dihydoxy-L-phenylalanine). This molecule is known to occur in plants and it’s made in humans as a precursor to the neurotransmitter dopamine, which is why it is used as a treatment for Parkinson’s disease.

It turns out that L-dopa is also responsible for the mussel’s ability to stick.

The key part of the molecule is the catechol side-chain, made up of the benzene ring with two hydroxyl groups attached. These hydroxyl groups form bonds with the rock, boat hull, or whatever else the mussel is trying to fix itself to.

Since Waite’s discovery, many different mussel glues are discovered, all of them containing L-dopa, and are now known collectively as mussel adhesive protein, or MAPs.

The most exciting part of MAP research - and the driving force behind much of the mussel-oriented research - is the use of these molecules in the human world.

Synthetic glues, rich in L-dopa or other catechol-containing compounds, are being developed as surgical tools and to treat disease. A promising area is operating on newborn babies, which is a great challenge because foetal membranes are extremely delicate and difficult to suture. This could become much easier with mussel-inspired glues that work when wet and don’t trigger problematic immune responses.

A squirt of waterproof glue could also help treat people suffering from a buildup of plaque in their arteries. Balloon angioplasties and stents are inserted to widen blood vessels and covered in anti-inflammatory drugs, but at the moment at least ninety-five per cent of this gets flushed away in the bloodstream. Using bio-glue to stick the drugs in place could drastically reduce this wastage and prolong the stents’ lifespan.

As well as mussel-inspired glues, researchers at Herbert Waite’s lab, now at the University of California Santa Barbara, have developed a catechol-rich synthetic polymer that can heal itself. Potential applications include the manufacture of artificial knee and hip joints that would require very little surgery to maintain.

And there is one more potential use of mussel-inspired glues that’s rather counterintuitive.

A major problem for the maritime industry is the accumulation on vessel hulls of unwanted hitchhikers, including mussels, seaweeds, barnacles and other encrusting organisms. Known as Bio-fouling, this increases drag and pushes up fuel bills. In the past, the toxic compound TBT (tributyl tin) was used as an antifoulant. But it caused major ecological problems when it leached into the environment and has now been banned worldwide.

An alternative would be to use bio-glues to fix other, less harmful antifouling agents firmly to boat bottoms, thus avoiding any more environmental damage. So now that their secrets of sticking have been unlocked, waterproof glues could be used to help stop the mussels themselves from getting stuck.

-- Chemistry in its element, Royal Society of Chemistry, UK 2015.5.6

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