德国科学家发现贝壳能产生新型胶状物

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据每日科学网报道，全世界的化学家们也许可以从某些贝类获得新的知识。科学家近日发现，贝壳能产生一种能紧紧粘在金属和石头上的粘附剂，即使在水中也是如此，而且胶状物的粘度都非常强。这些贝类就像儿童玩具一样，产生的聚合物不仅不会造成自然界的二次污染，而且无毒，最有意思的是这种新型胶状物的产生过程也很有戏剧性。

据报道，这种新型胶状物是由德国马普聚合物研究院和德国美因茨大学的研究员共同发现。德国科学家表示，在不久的将来，人类也许可以利用贝类产生的90%的这种胶状聚合物，如此一来，就可以通过不使用任何其他化学粘合剂就能把物体粘到其他的金属和石头表面，就像儿童玩具一样可以“搭更多的积木”。

科学家发现，贝类生命力很强，最有意思的是这种新型胶状物的产生过程也很有戏剧性。当它们定居在海岸附近的海底时，海浪会来回地冲击它们。为了不被波浪冲走，这些贝类就使用特殊蛋白质来将自己紧紧地粘在其他物体上。在分泌的过程中，这些特殊的蛋白质就形成了这种新型胶状聚合物。它们的产生是伴随着贝壳的斗争。对于贝壳的这一点，即使是最优秀的工程师也很难达办到这一点——抵御水的冲击，形成水中的附着力。

与美因茨马普聚合物研究院主任汉斯-巴特和美因兹大学伍尔夫冈-崔梅尔教授共同研究的科学家们现在已经能够人工合成粘性贝类蛋白质聚合物。据介绍，这些聚合物包括分子长链和制造贝类蛋白质胶粘剂的化学剂。美因兹的研究员还发现，除非能携带粘合多巴的化学链中的键数量少于总数的10%，键数量与化学链的粘性完全没有关系。有了氨基酸二羟苯丙氨酸（别名：多巴），这些贝类就能紧紧地粘在水底的其他物体上。它的化学结构使其能与金属和矿物稳定地结合，并且它所包含的粘合蛋白质使它紧紧地粘在海底。

美因茨马普聚合物研究院主任汉斯-巴特说：“事实上，粘合作用在一定程度上与粘合剂的数量并没有多大的关系。”举例来说，化学家能制造一种聚合物来把它均匀地粘在各种物体上。多巴能与金属和矿物紧密的粘在一起。化学家能制造出其他带有该聚合体链的粘合剂来黏合木材，玻璃或骨骼。

现在科学家已经通过实验找出来一个方法。他们把一层该聚合物铺在钛表面。把这个钛尖端放到原子显微镜下，他们就能看到该聚合物的一条链，就像一个人能用手指把螺丝从桌子上捡起来。然后他们把钛尖端从边面分离，并且测量所需的力度。将钛表面和聚合物的多巴分离开所需的力度为67皮牛顿。这中聚合物本身就像一个松弹簧，在下一个连接点断开之前力度几乎保持不变。现在，这些研究员想要把这个实验的发现运用到生产粘合各种物质的聚合物。这样，我们的日常生活将会发生巨大的变化。


Shellfish Inspire New AdhesivesScienceDaily (Nov. 21, 2008) — Chemists can learn from some shellfish. Mussels, for example, produce an adhesive that sticks strongly to metal and stone, even under water. Chemists have reproduced the protein responsible for this in a synthetic material that contains the same adhesive elements. Irrespective of whether the adhesive is completely made up of these elements or whether they represent just a tenth of its make-up, adhesion is equally good.
These findings were made by researchers at the Max Planck Institute for Polymer Research and at the Johannes Gutenberg University in Mainz. It might be possible to use the 90% of the polymers that are not necessary to create a good bond for other functions by providing them with chemical adjuncts which will allow them to adhere to surfaces other than metal or stone.
Some shellfish have a hard life: when they settle at the bottom of the sea close to the coast, the constant surging to and fro of the surf pulls at them. So that they are not washed away by the waves, the shellfish use special proteins to attach themselves firmly to a foundation - an ability that engineers still find difficult to achieve: adhesion under water. The shellfish can do this thanks to the amino acid dihydroxyphenylalanine, also known as dopa. Its chemical structure allows it to form very stable bonds with metals and minerals and is contained in the adhesion proteins with which shellfish attach themselves to the sea bed.
Scientists working with Hans-Jürgen Butt, Director at the Max Planck Institute for Polymer Research in Mainz, and Professor Wolfgang Tremel from the University of Mainz, have now reproduced the adhesive shellfish proteins with artificial polymers. These consist of long chains of molecules and carry the same chemical adjuncts that make the shellfish proteins adhesive. As the researchers in Mainz have now discovered, the number of the links in the chain carrying the binding dopa adjuncts has no overall relevance for the chain’s adhesiveness, provided it is not less than 10% of the total.
The researchers measured the force which allowed them to detach different polymer chains from a surface. They tested polymers that consisted completely of links with the binding dopa adjunct and some where it was only present on a fifth or a tenth of the links. The force required to pull a single polymer from the surface was always the same: 67 piconewtons. This is equivalent to a millionth of the weight force of a flea. This force alone could not keep a shellfish on the bottom of the sea. However, the creatures attach themselves firmly with a dab containing innumerable polymer chains, which allows them to brave the movement of the waves.
"The fact that the adhesive effect is, to a certain extent, independent on the number of binding sites could be used to give the other links in the polymer other functions," says Hans-Jürgen Butt. For example, chemists could manufacture a polymer that adheres equally to different materials. Dopa bonds predominantly with metals and minerals. Chemists could provide other links in the polymer chain with adjuncts that adhere to wood, glass or bone. Adhesives which bond metal and bone would be interesting for securing artificial joints," says Wolfgang Tremel.
At first, the researchers in Mainz were puzzled as to why the adhesive strength of the polymer chains was largely independent of the number of adhesive links. "Normally, we imagine that an adhesive polymer is like a strip of scotch tape that adheres over the whole of its length," says Hans-Jürgen Butt. However, the more an adhesive strip bonds to a surface, the harder it is to pull it off. This model, which describes the adhesiveness of a polymer as a continuous force, does not apply to shellfish proteins and their artificial counterparts.
"We see our polymers as chains of single binding sites linked with very loose springs," says Wolfgang Tremel. When they peel them off, he and his team measure only the force with which a single binding site is anchored to the surface. How closely the adhesive links in the chain follow each other is then irrelevant.
The density of the binding sites would have an effect if a weight was pulling evenly across the whole length of the polymer and not from one end. "In practice, this only plays a part when the surface is completely level," explains Butt. "Most surfaces are very rough at nano level, so that a weight on one end always pulls more strongly there than on the other."
The scientists have designed their experiment to correspond to this detachment process. They apply a single layer of the polymer to a titanium surface. Using the titanium tip on an atomic force microscope, which only measures a few nanometers, they pick up a single chain of the polymer in the same way someone would pick up a thread from a table with their finger. Then they pull the tip away from the surface and measure the force required. They need 67 piconewtons to break the bond between the titanium surface and a dopa group on the polymer. As the polymer itself behaves like a loose spring, the force hardly falls before the next bond is broken, but remains almost constant.
The researchers now want to use the findings from this experiment to manufacture polymers with binding sites for different materials. The newly established Max Planck Graduate Center will be particularly suitable in future for pursuing this area of research as it will specialize in interdisciplinary projects of this nature.