Reactions

Letters to the editor

Microdroplets

In a recently published interesting [article] (C&EN, Nov. 20, 2017, page 16), it was mentioned that the experimentally observed huge (up to 10³ times) intensification of chemical reactions in a dispersion of droplets in a continuous phase has not received any explanation. The goal of this letter is to provide one.

An intensified reaction can occur when the mass-transfer coefficient between the continuous phase and droplets becomes large enough. This can happen for nano-range droplets. Indeed, the mass-transfer coefficient is given by the well-known expression kR/D ~ (RU/v)^1/2(v/D)^1/3, where R is the radius of the droplet, U its velocity, v the kinematic viscosity, D the diffusion coefficient, and k the mass-transfer coefficient. Hence k ~ R^–1/2U^1/2v^–1/6D^2/3.

The above equation reveals that in the nano range (very small R), the mass transfer is increased in comparison to the non-nano range, and this can indeed increase the rate of the chemical reaction in droplets.
Eli Ruckenstein
Williamsville, N.Y.

Products perpetuating stereotypes

Sex-based discrimination is a common civil rights violation that takes many forms. How does it begin? How can we build more positive outcomes? The article “Confronting Sexual Harassment in Chemistry” from the Sept. 18, 2017, issue brought to light the different experiences between genders in chemistry. The idea that women use their sexuality to leverage career success is not unique to chemistry. It is a stereotype that undermines all types of valid discussions.

Last month a colleague and I were at Pittcon to plan our 2018–20 purchases. On day two of the expo, we were visiting a new vendor that sold a number of products that would increase our lab’s efficiency. The vendor shared a large booth with its sister company specializing in lab-themed gifts. There were a few plush “lab rat” toys displayed. One appeared to be female and wore a white lab coat with “Flirty” embroidered on it.

Here was a toy that perpetuated the gender bias stereotype. There was also a T-shirt with another female lab rat (named Testy) being told by a male lab rat that she was overreacting. It was a double entendre because Testy was holding a bubbling flask. Flirty was not an outlier; she was a trend. I reviewed the company’s website and found kid-sized T-shirts emblazoned with Flirty proclaiming, “Future Scientist” (or “Biologist” or “Physicist”). The male rats are Matt (founder’s son), Gym, and Slacker (I recommend renaming this one). Why not rename the female rats Testy, Flirty, and Petri as Marie, Shirley, and Rosalind?

Viewing these products made me think twice about doing any business with either company. The strongest power I have is as a consumer, and I will choose to forgo purchasing their products because of the latent sexism. I recognize the irony of me being labeled as “overreacting” about a toy by the same vocal minority that dismisses harassment claims. But I also see this as a clear example of the hidden sexism that is so ingrained in our profession that the joke has been monetized in an unironic manner. I struggle even to put my full name to this letter for fear of negative comments like “Just get over it” and “It’s just a joke.” However, I will take my inspiration from the Feb. 15 ACS webinar (“Sexual Harassment in the Sciences: Steps Forward”) that encouraged, “I’ll not be silent.”
Dorothy Colegrove
Anchorage

Aromas and chemistry

I found the article by Carrie Arnold in the Nov. 27, 2017, issue of C&EN (page 19) on the work of graduate student Bembibre and her supervisor Strlič in identifying the odors released by aging paper to be stimulating and possibly of importance in another area: possible odorous and nonodorous compounds emanating from vellum manuscripts. Even after paper was a common article of commerce, some important documents continued to be produced by scribes writing on the specially treated skins chiefly of calves, young goats, and lambs, called vellums, in general.

Perhaps their use of the combination of gas chromatography/mass spectrometry with injections made with solid-phase microextraction GC syringes could give bibliographic science a handle on (1) the animal source of the vellum; (2) the age of the vellum, both when first made and later after having been written on; and (3) possibly the methods used in the vellum preparation. Currently, ¹⁴C radiocarbon dating has been applied to determine vellum age (as the source was once living), but this involves some skin destruction to obtain a sufficient sample. And identifying the animal used for the vellum by microscopic analysis of skins to detect original hair follicles can sometimes pose problems in handling ancient manuscripts. The method of vellum preparation, such as treatment with alkali to remove residual hair (left in some cases) and soften the skins, is likely based mainly on the known practices used in their usual methods of preparation but is chiefly guesswork.

Wishing them continued success in further developing and employing their method, which I think could be of huge significance in handling old paper and, I am convinced, likely vellums.
Thomas F. Spande
Bethesda, Md.

Carrie Arnold credits the first aroma wheel to Ann Noble “in the 1980s” with flavor wheels for other products, like beer, coming later. The actual date of Noble’s aroma wheel seems to be 1984, five years after the publication of the beer flavor wheel by a subcommittee of the American Society of Brewing Chemists (J. Am. Soc. Brew. Chem. 1979, DOI: 10.1094/ASBCJ-37-0047). The wheel itself is on page 51.
Roger Barth
West Chester, Pa

From the web

Re: How science may help us smell the past

Readers commented on the intersection of smell and chemistry online.
cenm.ag/smellpast

Interesting work, but establishing a list of vocabulary words is only one piece of the puzzle. These metaphors or associations will differ from one person to another depending upon our individual experiences and associations. It is unlikely that we will be able to recreate the emotions associated with odors by historical figures because, as pointed out in the article, our odor experiences and associations will be very different.
Nick Sauer

As a retired lab rat from an environmental lab that included an odor panel to rate drinking water samples, I find the use of odor profiles through the human-instrument combination fascinating. At my home library I have a few books that date to the late 19th century and can detect and distinguish them by their distinctive odor, which I find mildly pleasant.
ken osborn

Here at the American Institute of the History of Pharmacy (UW Madison School of Pharmacy) we routinely open up one or two of our artifact cabinets so that visitors can experience “that old drugstore smell.” This experience is especially moving for pharmacists over the age of 70, who remember how pharmacies used to smell before modern manufacturing all but eliminated compounding from everyday pharmacy practice. The favorite aroma for most old-timers? Tincture of benzoin, of course!
Greg Higby

Corrections:

March 5, page 3: In the news story on the Chematica computer program, the description of how the program’s 50,000 synthetic rules were developed was incomplete. The rules were developed on the basis of reactions published in the chemical literature and insights from organic chemists on the team. Also, the story incorrectly stated that only one of the eight tested target molecules did not have a previously published synthetic route. In fact, two of the targets had not been synthesized before. The story also failed to point out that a contender to Chematica—ChemPlanner from John Wiley & Sons—will be integrated into SciFinderⁿ, which is a product from CAS, a division of the American Chemical Society. Finally, K. C. Nicolaou’s thoughts on how the program could improve lab productivity were described inaccurately. The sentence should have read: “ ‘These encouraging results should serve as a spark for another advancement in organic synthesis,’ says K. C. Nicolaou, a synthetic chemist at Rice University, adding that Chematica could increase speed and productivity in chemistry labs, especially if paired with automated synthesis machines.”