Passage Twenty-eight (Chemistry and Biology)

About a century ago, the Swedish physical scientist Arrhenius proposed a low of classical chemistry that relates chemical reaction rate to temperature. According to his equation, chemical reactions are increasingly unlikely to occur as temperature approaches absolute zero, and at absolute zero, reactions stop. However, recent experiment evidence reveals that although the Arrhenius equation is generally accurate in describing the kind of chemical reaction that occurs at relatively¹ high temperature, at temperatures closer to zero a quantum-mechanical effect known as tunneling comes into play; this effect accounts for chemical reactions that are forbidden by the principles of classical chemistry. Specifically, entire molecules³ can tunnel through the barriers of repulsive⁴ forces from other molecules and chemically react even though these molecules do not have sufficient energy, according to classical chemistry, to overcome the repulsive barrier.

The rate of any chemical reaction, regardless of the temperature at which it takes place, usually depends on a very important characteristic known as its activation⁵ energy. Any molecule² can be imagined to reside at the bottom of a so-called potential well of energy. S chemical reaction corresponds to the transition of a molecule from the bottom of one potential well to the bottom of another. In classical chemistry, such a transition can be accomplished⁶ only by going over the potential barrier between the well, the height of which remain constant and is called the activation energy of the reaction. In tunneling, the reacting molecules tunnel from the bottom of one to the bottom of another well without having to rise over the barrier between the two wells. Recently researchers have developed the concept of tunneling temperature: the temperature below which tunneling transitions greatly outnumber Arrhenius transitions, and classical mechanics gives way to its quantum counterpart.

This tunneling phenomenon at very low temperatures suggested my hypothesis about a cold prehistory of life: formation of rather complex organic molecules in the deep cold of outer space, where temperatures usually reach only a few degrees Kelvin. Cosmic rays might trigger the synthesis of simple molecules, such as interstellar formaldehyde, in dark clouds of interstellar dust. Afterward⁷ complex organic molecules would be formed, slowly but surely, by means of tunneling. After I offered my hupothesis, Hoyle and Wickramashinghe argued that molecules of interstellar formaldehyde have indeed evolved into stable polysaccharides such as cellulose and starch⁸. Their conclusions, although strongly disputed, have generated excitement among investigators⁹ such as myself who are proposing that the galactic clouds are the places where the prebiological evolution of compounds necessary to life occurred.

 

1.       The author is mainly concerned with

[A]. describing how the principles of classical chemistry were developed.

[B]. initiating¹⁰ a debate about the kinds of chemical reaction required for the development of life.

[C]. explaining how current research in chemistry may be related to broader biological concerns.

[D]. clarifying inherent ambiguities¹¹ in the laws of classical chemistry.

2.       In which of the following ways are the mentioned chemical reactions and tunneling reactions alike?

[A]. In both, reacting molecules have to rise over the barrier between the two wells.

[B]. In both types of reactions, a transition is made from the bottom of one potential well to the bottom of another.

[C]. In both types of reactions, reacting molecules are able to go through the barrier between the two wells.

[D]. In neither type of reaction does the rate of a chemical reaction depend on its activation energy.

3.       The author’s attitude toward the theory of a cold prehistory of life can best be described as

[A]. neutral.                   [B]. skeptical¹².

[C]. mildly positive.             [D]. very supportive.

4.       Which of the following best describes the hypothesis of Hoyle and Wickramasinghe?

[A]. Molecules of interstellar formaldehyde can evolve into complex organic molecules.

[B]. Interstellar formaldehyde can be synthesized by tunneling.

[C]. Cosmic rays can directly synthesize complex organic molecules.

[D]. The galactic clouds are the places where prebilogical evolution of compounds necessary to life occurred.

 

Vocabulary

1.       Arrhenius equation                 阿雷尼厄斯方程式

2.       Arrhennius (Svante August)          1859——1927 瑞典理化学家。1903年获诺贝尔化                                                            学奖

3.       quantum-mechanical effect           量子机械效应

4.       quantum mechanic                 量子力学

5.       tunnel                           挖隧道。这里指贯穿势垒

6.       tunnel through, onto                穿到……进到，贯穿

7.       repulsive                         排斥

8.       activation energy                  活化能量

9.       formaldehyde                     甲醛

10.   polysaccharide                    多糖醇，聚合酶

11.   cellulose                         纤维素

12.   starch                           淀粉

13.   galactic                          银河的，巨大的

14.   come into play                     开始活动/起作用

 

难句译注

1.         However, recent experiment evidence reveals that although the Arrhenius equation is generally accurate in describing the kind of chemical reaction that occurs at relatively high temperature, at temperatures closer to zero a quantum-mechanical effect known as tunneling comes into play; this effect accounts for chemical reactions that are forbidden by the principles of classical chemistry.

2.         Specifically, entire molecules can tunnel through the barriers of repulsive forces from other molecules and chemically react even though these molecules do not have sufficient energy, according to classical chemistry, to overcome the repulsive barrier.

3.         Recently researchers have developed the concept of tunneling temperature: the temperature below which tunneling transitions greatly outnumber Arrhenius transitions, and classical mechanics gives way to its quantum counterpart.

 

写作方法与文章大意

   文章论述了“贯穿势垒效应”，采用对比手法。先是经典化学定理和贯穿势垒效应之比较。说明两者使用的温度界限不同。低温时贯穿势垒效应作用取代经典力学。最后贯穿势垒现象和生活领域之关系。

 

答案祥解

1.        C. 说明现在化学研究如何能和更广泛的生物学领域有关。最后一段基本上都是谈与生化的关系。“极低温时的贯穿势垒现象证明我对寒冷的史前生命的假说：在外层空间极其寒冷处，温度一般只有K的几度光景，有相当复杂的有机分子形成。宇宙射线可能激发诸如星际甲醛单分子在星际尘埃的乌云中综合。以后，复杂的有机分子，慢慢的，但稳定的通过贯穿势垒的方式形成。”后又有两位化学家提出“星际甲醛分子确实进化为类似纤维素和淀粉等多糖酶。”他们的结论虽有争议，却实在令人振奋，特别是文章之作者，因为他正提出“巨大的云块这些地方，发生过生命所必须的前生物进化化合物。”

A. 描述经典化学定理如何发展。         B. 开展一场有关生命进化所需的那种化学反应的辩论。         C. 搞清楚经典化学定理所固有的模糊点。

2.        B. 两类反应中，都有一个从一个势阱底部到另一个势阱底部的跃迁。见第二段第三句起“化学反应跟分子从一个势阱的底部到另一个势阱的底部的跃迁相类似。在经典化学中，这种跃迁只有跨过两阱之间势垒才能完成。位垒之高度为常数（固定不变）。这种跃迁叫做能量活化。在贯穿势垒效应中作反应的分子从一个势阱的底部通到另一个势阱底部不需要上升跨越两阱之间的位垒。”

A. 两类反应中，反应中的分子都需跨越两阱间的栏栅。    C. 两类反应中，反应中的分子都能穿过两阱之间的位垒。        D. 两类反应中，没有一种化学反应的速率取决于能量活化。      这三项都不对， 见上文。

3.        C. 有点肯定。 见第1题答案注释译文。因为证实了作者之假设。

A. 中立。      B. 怀疑的。       D. 非常支持。

4.        A. 星际甲醛分子可以进化到复杂的有机分子。见第1题C答案注释译文。

B. 星际甲醛分子可以通过贯穿势垒方式加以综合。      C. 宇宙射线可以直接综合复杂的有机分子。        D. 大块云团是生命所需复合物前生物进化发生的地方。这三项也可从第1题C答案注译译文看出其错误点。

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