How is it that simple particles like atoms and small molecules move randomly yet molecules that are more complex can move in coherent patterns? Wanting to get a group of students to think about this, I went to early published work on Brownian motion. Robert Brown's 1827 paper [1] was titled "A Brief Account of Microscopic Observations on the Particles Contained in the Pollen of Plants; and on the General Existence of Active Molecules in Organic and Inorganic Bodies". Brown observed pollen grains and "other particles, at least as numerous, of much smaller size, apparently spherical, and in rapid oscillatory motion" in water and became convinced that the motion "belonged to the particle itself." Vitalism, which held that organic matter was fundamentally different from inorganic matter, influenced Brown. In this view, the emergence of complex order from elementary "organic molecules" in embryogenesis is similar to crystal growth from elementary "inorganic molecules". He wrote that, initially, "I was disposed to believe that the minute spherical particles or Molecules . . . were in reality the supposed constituent or elementary Molecules of organic bodies". With admirable diligence, Brown looked for active molecules and found that "on examining various animal and vegetable tissues, whether living or dead, they were always found to exist". He then found that inorganic matter, "rocks of all ages, including those in which organic remains have never been found, yielded the molecules in abundance . . . a fragment of the Sphinx being one of the specimens examined." Brown even showed experimentally that a single "active molecule" in a water droplet within an emulsion of water and almond oil moved "with undiminished activity", and so "attractions and repulsions among the particles themselves" did not drive their random motion. Pollen grains and other Brownian particles are not self-propelled. Eighty-two years after Brown's paper, Einstein and Smoluchowski explained the origins of Brownian motion as interactions with solvent molecules.

Citation: Pack G (2012) Vital Molecules. J Thermodynam Cat 3:e107. doi: 10.4172/2157-7544.1000e107

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