Industrial Chemistry
Introduction
to Special Issue
Fuels, pharmaceuticals, plastics, paints, and countless other
components of modern life are prepared through chemical synthesis at
the industrial scale. At the molecular level, chemical processes take
place in much the same way whether the bulk material is being collected
in fractions of a milligram or hundreds of kilograms. At the industrial
scale, however, cost can be a concern, and factors such as waste
disposal and reaction efficiencies require special consideration. A
special section of the 7 Aug 2009 Science elaborated on the
challenges and opportunities in industrial chemistry as the field
embarks on its second century of development. Four Perspectives
discussed the design of chemical reactors, the future of pharmaceutical
process chemistry, reinventing the world's most common synthetic
polymers, and efforts to replace petroleum with biofuels. News stories,
meanwhile, explored efforts to reform the U.S. Toxic Substances Control
Act, and the quest for faster, more effective toxicology tests (listen
to the related podcast
interview). In a Science Careers feature, young chemists
offered impressions and advice to others planning to make the leap from
academia to industry.
Stemming the Flu
The distribution of vaccines for infectious diseases like influenza is
a complex issue lying at the intersection of public health, economics,
and ethics. Mathematical modeling of disease transmission can be a
valuable tool for guiding policy, and in a Report published online,
ahead of print, in Science Express on 20 Aug 2009, Medlock
and Galvani presented an analysis of how to distribute influenza
vaccine among different age groups in a way that will minimize spread
of the virus. The team used survey-based data and mortality data from
historical influenza pandemics to determine optimal vaccine allocation
based on five different measures: deaths, infections, years of life
lost, contingent valuation, and economic costs. They found that optimal
vaccination is achieved by prioritization of schoolchildren (ages 5 to
19) and adults aged 30 to 39 years. This is because schoolchildren are
most responsible for transmission, and their parents serve as bridges
to the rest of the population. The results suggest that the current
recommendations for vaccine distribution from the U.S. Centers for
Disease Control and Prevention, for both seasonal influenza and the
more recent swine-origin HINI influenza, probably need to be revised to
account for age-related patterns of transmission. Lead author Jan
Medlock discussed the work in a related podcast
interview.
The Gamma-Ray Sky
Pulsars are fast-spinning neutron stars that emit radiation across the
electromagnetic spectrum. Although there are more than 1800 known radio
pulsars, until recently, only seven were observed to pulse in gamma
rays, and they were all discovered at other wavelengths. Results from
the Fermi Gamma-ray Space Telescope, launched in 2008, are now helping
to illuminate the gamma-ray sky (see the Perspective
by J. P. Halpern). In a Research Article in the 14 Aug 2009 Science
(published online 2 Jul), Abdo et
al. reported the detection of 16 gamma-ray pulsars using the
Large Area Telescope, the main instrument on Fermi. Thirteen of these
pulsars coincide with previously unidentified gamma-ray sources, and
many are associated with supernova remnants. With time, pulsars slow
down and cease to radiate -- but they can live a second life in binary
systems where they can acquire mass and spin momentum from their
companions and radiate anew as millisecond pulsars. In a Report in the
same issue, Abdo et
al. reported the detection of pulsed gamma rays from eight
millisecond pulsars rotating faster than 200 times per second. The
gamma-ray pulse profiles and spectral properties resemble those of
young gamma-ray pulsars, suggesting that they share the same basic
emission mechanism in which the gamma rays are produced in the outer
magnetosphere of the neutron star. Finally, in another study, Abdo et
al. reported detection of gamma-ray emissions from the
globular cluster 47 Tucanae. The data indicate that the emissions
derive from as many as 60 millisecond pulsars within the cluster --
twice as many as predicted by radio observations.
Designer DNA Curves
DNA nanotechnology aims to use DNA as a molecular engineering material
to create nanostructures with controlled geometries, topologies, and
periodicities and to organize matter with nanometer precision. Now, in
a Report in the 7 Aug 2009 Science, Dietz
et al. describe an important step toward building
sophisticated molecular machines: engineering complex DNA shapes that
can twist and curve at the nanoscale. The principal building blocks of
the novel structures are DNA bundles, arranged in honeycomb lattices.
Targeted insertions and deletions of base pairs in some DNA helices but
not others, creates stress in the DNA bundles and causes them to twist
or bend in controllable ways. The researchers were able to produce
curvatures as tight as 6 nanometers and combine multiple curved
elements to build intricate nanostructures including a wireframe beach
ball and square-toothed gears (listen to a related podcast
interview with senior author William Shi). An accompanying Perspective
by Y. Liu and H. Yan explained that although other groups have created
DNA nanostructures with curved features, the new study is different in
that the curvatures continuously connect different DNA nanostructure
domains and can be quantitatively controlled.
Mapping Maize
Corn, or maize, is a staple food crop in much of the world, as well as
a source of cooking oil, grain alcohol, livestock feed, and biofuel.
Maize strains display tremendous variation in traits of agronomic
importance -- such as yield and pest resistance -- due to genetic
variation in multiple regions of DNA referred to as quantitative trait
loci (QTL). In the 7 Aug 2009 Science,
Buckler et al. and
McMullen et al. described the genetic properties of a new
resource for mapping quantitative traits in maize and used the resource
to study the genetic architecture of flowering time. The researchers
crossed a common reference strain to 25 diverse maize lines.
Individuals resulting from each of the 25 crosses (families) were
self-fertilized for four further generations to create a population of
5000 inbred lines, capturing ~136,000 recombination events. Variation
in recombination was not attributable to QTLs with general effects on
recombination, but rather to numerous and localized regions of
variation in recombination specific to each family. Nearly a million
plants were used to dissect variation in maize flowering time.
Consistent with results from mice, flies, and humans for many different
quantitative traits, the researchers found that differences in
flowering time were not caused by a few genes with large effects, but
by numerous QTL with small effects. An accompanying
Perspective by T. F. C. Mackay highlighted the studies.
Friendly Fire
The controlled use of fire was a breakthrough development in human
evolution, allowing for the production of warmth and light, cooking,
and protection from predators. In the 14 Aug 2009 Science, Brown
et al. offered evidence that early modern humans were
using fire to improve the processing of raw materials about 72,000
years ago and possibly as early as 164,000 years ago in coastal South
Africa. The find adds to the evidence that a wide range of
sophisticated behaviors -- including jewelry making and symbolism --
were flourishing around the same time (see the ScienceNOW
story by A. Curry). Experiments of heat-treating and analysis of
artifacts from multiple archaeological sites indicate that stone
materials, including tools crafted from silica-rich silcrete, were
systematically manipulated with fire to improve their flaking
properties. In an accompanying Perspective,
J. Webb and M. Domanski explained how heat treatment can improve tool
production, noting that "[b]y enabling the manufacture of more
efficient tools, heat treatment may have played a key role in allowing
early modern humans to spread rapidly from the relatively benign
environments of southern Africa into the colder, more hostile
environments of Europe."
Imitation and Affiliation
Imitation may be the sincerest form of flattery, but it's also a good
way to make friends. When others mimic us -- often unconsciously and
unintentionally -- we like them more, empathize with them more, and are
more helpful and generous toward them. Some researchers suggest that
imitation has played an important role in human evolution by helping to
maintain harmonious relationships. According to a new Report in the 14
Aug 2009 Science, the social consequences of mimicry may have
deeper evolutionary roots than previously thought. Paukner
et al. showed that capuchin monkeys, a highly social
primate species, prefer human imitators over non-imitators in a variety
of ways: The monkeys look longer at imitators, spend more time in
proximity to imitators, and choose to interact more frequently with
them in a token exchange task (see the related ScienceNOW
story by E. Pennisi). An accompanying
Perspective by J. Call and M. Carpenter highlighted the study and
commented that "[f]uture studies will be needed to ascertain precisely
what type of social information nonhuman animals extract from social
mimicry."
Chemosensory Cilia
Epithelial cells that line the human airway are constantly bombarded by
environmental hazards, including toxins, viruses, and bacteria. The
airway rids itself of these irritants by secreting mucus to "capture"
harmful substances and by increasing the beat frequency of motile cilia
on epithelia cells to sweep the mucus out of the system. It has been
assumed that motile cilia serve a purely motor function, but in a
Report in the 28 Aug 2009 Science (published online 23 Jul), Shah
et al. show that these organelles are also
chemosensory, expressing bitter taste receptors and their associated
signaling machinery. The researchers found that when stimulated with
bitter compounds, cultured human airway epithelial cells respond with
an increase in intracellular calcium ion concentration and a
concomitant increase in ciliary beat frequency. Thus, airway epithelia
contain a cell-autonomous system in which motile cilia both sense
noxious substances entering airways and initiate a defensive mechanical
mechanism to help eliminate the offending compound. An accompanying Perspective
by S.C. Kinnamon and S.D. Reynolds highlighted the study.
Early Solar System Chronometer
Models of the evolution of the early solar system rely on knowledge of
the precise time scales for the physical and chemical processes that
occurred in the early accretion disk. The short-lived radioactive
aluminum isotope 26-Al has long been used as a relative chronometer of
these early solar system processes, but its accuracy rests on the
assumption that it was uniformly distributed in the initial solar
accretion disk. In a Report in the 21 Aug 2009 Science, Villeneuve
et al. validated this assumption on the basis of
high-precision isotopic analyses of materials from primitive
meteorites. The researchers used secondary ion mass spectrometry to
measure magnesium isotopic compositions (26-Al decays to 26-Mg) and
Mg/Al ratios in chondrules, the basic building blocks of primitive
meteorites, and then calculated the 26-Al/27-Al ratio at the time of
crystallization of each chondrule. Their results confirm that 26-Al was
indeed uniform in the early solar system to about the 10% level and
also show that chondrules formed in discrete events over a time period
of more than 1 million years. An accompanying
Perspective by A.M. Davis discussed the findings and the new
questions they raise about early solar system processes.
Major Ozone Threat
Stratospheric ozone is depleted by many different chemicals, the most
recognized being the chlorofluorocarbons (CFCs) responsible for causing
the Antarctic ozone hole. Now, in a Report published online, ahead of
print, in Science Express, Ravishankara
et al. report that another chemical, nitrous oxide, is
the single greatest ozone-depleting substance in the atmosphere today
-- and is expected to remain the dominant ozone-depleting chemical
throughout the 21st century, if emissions are not controlled. Global
anthropogenic emission of nitrous oxide now -- produced mainly as a
byproduct of fertilization, fossil fuel combustion and industrial
processes, and biomass and biofuel burning -- is roughly 10 million
tonnes per year compared to slightly more than a million tonnes from
all CFCs at the peak of their emissions. Unlike CFCs, nitrous oxide has
both natural and human-made sources. Moreover, its use and emissions
are not regulated by the Montreal Protocol, an international treaty
that has been successful in helping to stem emissions of
ozone-depleting substances and in reversing the growth rate of the
ozone hole. The researchers note that limiting future nitrous oxide
emissions would enhance the recovery of the ozone layer from its
depleted state, and -- because nitrous oxide is also a potent
greenhouse gas -- would also reduce the anthropogenic forcing of the
climate system. Lead author A. R. Ravishankara discussed the work in a
related podcast
interview.
Clues to Coat Variation
Two studies reported in Science this month investigated the
molecular mechanisms that underlie variation in coat color and type in
mice and dogs.
-- Linnen
et al. (28 Aug 2009) investigated the molecular
mechanisms underlying color variation in deer mice living on the
Nebraska Sand Hills. The mice that live on the sand are much lighter in
color than mice living nearby on darker soils. The researchers found
that the paler color is due to changes at the Agouti coat color locus
that arose de novo after the formation of the Sand Hills. Their
findings demonstrate that rapid adaptive change does not always rely on
preexisting genetic variation.
-- Cadieu
et al. (published online 27 Aug 2009) examined the genetic
basis of coat growth pattern, length, and curl in domestic dog breeds.
The team performed genome-wide association studies of more than 1000
dogs from 80 domestic breeds and found that distinct mutations in just
three genes together account for the majority of coat phenotypes in
purebred dogs in the United States.
In Science Signaling
How Worms Learn with PKD
UUpon activation by various hormones and neurotransmitters,
phospholipase C (PLC) catalyzes the production of the
membrane-associated second messenger diacylglycerol (DAG), which is
known for its role in recruiting and activating various isoforms of
protein kinase C (PKC). DAG also recruits and, along with PKC,
activates protein kinase D (PKD). PKD phosphorylates substrates
distinct from those targeted by PKC, and studies in cultured cells have
suggested that PKD may regulate numerous cellular processes, but its
specific in vivo functions have remained unclear. In a Research Article
in the 11 Aug 2009 issue, Fu et
al. reported that two isoforms of PKD are found in the nematode
Caenorhabditis elegans -- one in the intestine and the
other in the nervous system. C. elegans learns to avoid sodium
ions, normally a strong attractant, after being exposed to
sodium-containing solutions in the absence of food. Experiments with
various mutant and transgenic animals revealed that activation of
neuronal and intestinal PKDs through the PLC-DAG-PKC signaling pathway
was critical to this salt taste–induced learning.
Also in Science Signaling
this month:
--
Bader highlighted computational and experimental techniques for
analyzing signaling networks (4 Aug 2009)
--
Yasukawa et al. demonstrated that a protein that mediates
mitochondrial fusion also suppresses innate immune responses to viral
infection (18 Aug 2009)
--
Grillet et al. presented a slideshow on mechanotransduction
in the mammalian inner ear (25 Aug 2009)
Image credits (in order of appearance): I. W. Davies and C. J. Welch;
Hendrik Dietz; Wei Ming/La Trobe University; Tom Moninger (epithelia
generated by Phil Karp); Emily Kay.
