Letters

The stem of the issue

In his letter "Promising Too Much?" Dean C. Luehrs suggests that scientists should focus on adult rather than fetal stem cells and suggests that the "biomedical concerns" of President George W. Bush may not be "in conflict with good science" (C&EN, Sept. 6, page 6).

But clearly, to suggest that Bush's concerns are of "biomedical" origin is misleading. Bush's political base is in the religious right, and he is imposing stem cell restrictions based on the belief that a stem cell deserves equal status with a fetus or a baby--this has its basis in ideology, not science. Luehrs should note that first lady Laura Bush recently said that her husband's concern is an "ethical and moral issue" and that National Institutes of Health Director Elias A. Zerhouni wrote a letter on behalf of Bush in which he stated "The President's position is still predicated on his belief that taxpayer funds should not 'sanction or encourage further destruction of human embryos that have at least the potential for life' " (C&EN, May 24, page 11).

It may be that fetal stem cells eventually become a "cul-de-sac as far as useful medical applications is concerned," as Luehrs suggests. But it should be up to the individual scientist to decide when to give up the quest, not Luehrs, not the President, and certainly not the religious right.

David Marsh
Fort Worth

The chemistry behind SpaceShipOne

The crowning achievement of SpaceShipOne is not in succeeding in sending a person into space, but in doing so with equipment and techniques that are eminently practical and relatively inexpensive, something the National Aeronautics & Space Administration seems unable to do (C&EN Online Latest News, Oct. 5). Its success stems from the choice of propellants that power its rocket: rubber as the fuel and nitrous oxide, N₂O, as the oxidizer.

Rubber is cheap, available, easily moldable to most configurations, and very safe. Nitrous oxide, notorious as an anesthetic, is a liquid that can be stored in a low-pressure tank with none of the hazards or complexities associated with normal liquid oxidizers: oxygen, hydrogen peroxide, or exotic others. While very stable in storage, N₂O can be made to decompose to nitrogen and oxygen, producing temperatures in the range of 1,000 °F. At such conditions, oxygen spontaneously reacts with fuels such as rubber to produce the very high temperature gases needed to power a rocket.

When normal liquid propellants are used, pumps and their machinery and complex controls are often needed. By contrast, because nitrous oxide is stored at relatively high pressure, it can be injected via a controlled "faucet." Also, when the fuel is a normal solid propellant, it is premanufactured from a mixture of fuel and oxidizer materials under very controlled (and expensive) conditions to sizes and shapes carefully designed to control their subsequent burning rate. By contrast, the rubber used in SpaceShipOne need only be molded to an approximate shape within the tube in which combustion is to take place. Here it stays, until contacted by the very hot oxygen produced on decomposing a portion of the nitrous oxide, as previously mentioned. Then it reacts at a rate proportional to the flow of the latter to produce the needed high-temperature gases.

So when SpaceShipOne requires thrust, it is only necessary to open the valve connecting the nitrous oxide tank to the rubber container. Then, the nitrous oxide first encounters means to set off its decomposition (such as a hot electric heater), forming the hot oxygen-containing gases that react spontaneously with the surface of the rubber on contact to produce the necessary rocket temperature. To modulate thrust, nitrous oxide flow is controlled in much the same manner as an automobile gas pedal. After returning to Earth, the spent nitrous oxide and rubber are replaced. Overall, it is a clean, simple process.

The projected mission of SpaceShipOne includes achieving orbit, which will require further rocket power, and then returning safely to Earth, which will require countering reentry surface heating. I look forward to learning the novel means they will use to do so.

As an aside, four decades ago I studied a N₂O-carbon combustor under a small Navy project, and later novel means for reentry cooling with Air Force support. Both projects were successful, but neither was finalized. It would be fascinating if SpaceShipOne does both.

Leonard Greiner
Santa Ana, Calif.

Tempest in a teabag

I was surprised (to say the least) by the question posed on the cover of the Oct. 4 issue of C&EN--"Combichem: Saved By Diversity-Oriented Synthesis?" I am frankly more accustomed to seeing such supererogatory questions on the covers of publications on display near supermarket checkout counters. In this instance, C&EN does an unfortunate disservice to the many chemists engaged in this field--past, present, and future.

I am reminded that Mark Twain, upon reading his own obituary in the newspaper, said: "The rumors of my death have been greatly exaggerated." The vigor of research in combinatorial chemistry is reflected by the vigor of ACS's journal in this field. The Journal of Combinatorial Chemistry has rated in the top 10 multidisciplinary chemistry journals in the world, based on "impact factor," every year it has been evaluated by Thomson ISI. It continues to highlight both new organic synthesis methodology and total library synthesis, while at the same time increasing the publication of methods used in material, sensor, and catalyst discovery programs.

"Diversity-oriented synthesis" is a goal; combinatorial chemistry (that is, "matrix" synthesis) is a powerful means to that goal. Our journal is not the appropriate place for publication of syntheses in which the approach is to make x+y+z samples via x+y+z reactions. For all matrix synthesis approaches--work facilitating ways in which x+y+z reactions can yield x*y*z samples--JCC welcomes submissions regardless of the label used to describe the work.

Anthony W. Czarnik
Editor, Journal of Combinatorial Chemistry
Reno, Nev.