Consider the curl of a pig's tail or the spiral on a seashell. Does it turn left or right? Many of us would not notice these natural manifestations of chirality. But stereochemists such as Christopher J. Welch, a process research fellow at Merck Research Laboratories, do. Stereochemists' eyes get trained in seeing shape and chirality, he says. And chirality "pops up all over the place."

	SPIRAL ACCESSORIES Petals twisted in left-handed helices adorn the flowers of this orchid, Trichopilia tortilis. PHOTO BY C. J. WELCH

Such as in Welch's home, where he grows orchids as a hobby. About 10 years ago, Welch noticed that some orchid species have flowers in which the usual bilateral symmetry is broken by the presence of twisted petals. The orchid literature contained little mention of asymmetric flowers, so he researched the topic himself.

Welch asked members of an Internet list of orchid enthusiasts to which he belongs to examine their collections for chiral flowers. These data, along with his observations at botanical gardens, orchid shows, commercial greenhouses, and private collections, turned up several species with chiral flowers [Malay. Orchid Rev., 32, 86 (1998)]. Interestingly, closely related species might bear petals twisted in the opposite direction. Welch has suggested that botanical descriptions should describe petal twist through the helix nomenclature used in stereochemistry.

When stereochemists exchange their favorite stories about chirality, Welch talks about orchids. He also mentions the Hindu god Vishnu when speculating about when humans became aware of the idea of chirality. Even in centuries-old statues, Vishnu is portrayed holding a left-handed chank shell. In nature, this form is exceedingly rare, probably fewer than one in a million, Welch says. "For many centuries, the left-handed chanks have been highly prized treasures," he says. "That Vishnu is always shown with the rare enantiomer is an unambiguous sign that the people who built those statues had an appreciation of chirality."

The exchange of favorite stories about handedness has inspired Welch to write a review on chirality at the organismic level in a new book, "Chirality in Natural and Applied Science" (W. J. Lough and I. Wainer, Eds., Blackwell Publishing, 2002). Here he surveys exterior asymmetry in microorganisms; plants; invertebrates; fish; birds; reptiles; amphibians; and mammals, including humans. Observing chirality in nature may be "a source of amusement for stereochemists," he writes, but there are also fundamental discoveries being made, such as those by developmental biologists about the role of chirality in the development of complex organisms.

Go to

CHIRAL ROUNDUP As pharmaceutical companies struggle, their suppliers diligently tend the fertile fields of chiral chemistry STEADY RISE Worldwide sales of single-enantiomer drugs approach $150 billion TAKING A MEASURE OF CHIRAL RICHES Researchers respond to high demand for ways to measure enantioenrichment quickly EARTHBOUND A Chemist's Eye For Chirality EXTRATERRESTRIAL How To Detect Enantioenrichment On Saturn's Moon Titan CALENDAR Events Highlight Chiral Chemistry

Chemical & Engineering News
Copyright © 2002 American Chemical Society