 Temple of Light Provides Answers to a Chemist’s Prayer |
by John
Emsley |
|
| WHAT'S
HOT IN CHEMISTRY |
| Rank |
Paper |
Citations
This Period (Nov-Dec 02) |
Rank
Last Period (Sep-Oct 02) |
| 1 |
Z.W. Pan, Z.R.
Dai, Z.L. Wang, "Nanobelts of
semiconducting oxides," Science,
291(5510): 1947-9,
9 March 2001
. [Georgia Inst. Tech.,
Atlanta
] *409TK |
24 |
1 |
| 2 |
V.F. Puntes,
K.M. Krishnan, A.P. Alivisatos, "Colloidal
nanocrystal shape and size control: The case of cobalt,"
Science, 291(5511):
2115-7,
16 March 2001
. [U.
Calif.
, Berkeley;
Lawrence
Berkeley
Lab., CA] *412PP
21 |
21 |
† |
| 3 |
R.J. Chen, et
al., "Noncovalent sidewall functionalization of single-walled carbon
nanotubes for protein immobilization,"
J. Amer. Chem. Soc.,
123(16): 3838-9,
25 April 2001
. [
Stanford U.
,
CA
] *428CA |
18 |
† |
| 4 |
Y. Cui, et
al., "Nanowire nanosensors for highly sensitive and selective detection
of biological and chemical species,"
Science, 293(5533):
1289-92,
17 August 2001
. [
Harvard
U.
,
Cambridge
,
MA
] *463TD |
15 |
9 |
| 5 |
J.L. Bahr, et
al. "Functionalization of carbon nanotubes by electrochemical reduction
of aryl diazonium salts: a bucky paper electrode,"
J. Amer. Chem. Soc.,
123(27): 6536-42,
11 July 2001
. [
Rice
U.
,
Houston
,
TX
] *452AQ |
14 |
† |
| 6 |
O.J. Plante,
E.R. Palmacci, P.H. Seeberger, "Automated
solid-phase synthesis of oligosaccharides,"
Science,
291(5508):1523-7,
23 February 2001
. [MIT,
Cambridge
,
MA
] *405HF |
13 |
† |
| 7 |
R.C. Jin, et
al., "Photoinduced conversion of silver nanospheres to nanoprisms,"
Science, 294(5548):
1901-3,
30 November 2001
. [Northwestern U.,
Evanston
,
IL
] 497PQ |
13 |
† |
| 8 |
L. Manna, E.C.
Scher, A.P. Alivisatos, "Synthesis
of soluble and processable rod-, arrow-, and teardrop-shaped CdSe
nanocrystals," J.
Amer. Chem. Soc., 122(51): 12700-6,
27 December 2000
. [U.
Calif.
, Berkeley; L. Berkeley Natl. Lab., CA]
*386DN |
12 |
† |
| 9 |
R.J. Levis,
G.M. Menkir, H. Rabitz, "Selective
bond dissociation and rearrangement with optimally tailored, strong-field
laser pulses," Science, 292(5517): 709-13,
27 April 2001
. [Wayne St. U.,
Detroit
, MI;
Princeton U.
,
NJ
]
*428TX |
11 |
† |
| 10 |
J.T.
Hu, et al., "Linearly polarized emission from colloidal semiconductor quantum
rods," Science, 292(5524): 2060-3,
15 June 2001
. [U.
Calif.
, Berkeley; L. Berkeley Natl. Lab., CA]
*442KP |
11 |
† |
SOURCE:
ISI’s Hot
Papers Database. 
the Legend. |
 hen
a molecule is supplied with sufficient energy to break it apart, the
result is generally a scrap heap of useless fragments. Even when the
amount of energy is carefully controlled, so as to break the molecule
into useful components, these will invariably be the products that come
from the breaking of the weakest bond in the molecule. The laws of
thermodynamics rule that it could not be otherwise—but laws, like
chemical bonds, are there to be broken, or at least circumvented.
If
you knew exactly all the vibrational and electronic frequencies of a
molecule then you could launch a pulse of energy targeted to transform
the molecule into something more desirable. While chemists of a few
years ago might have prayed that such a reaction would be possible,
there was no way in which it could be achieved. Today we know it can be
done, thanks in no small measure to the research reported in paper #9.
This reveals how the bonds in three very different ketones can be
selectively broken, and is the work of Robert Levis, now at
Temple
University
,
Philadelphia
,
and Herschel Rabitz of
Princeton
University
.
(
Levis
was based at
Wayne
State University
,
Michigan
,
when #9 was published.)
In
the May/June 2000 issue of Science
Watch (11[3]: 7), I
reported on the groundbreaking work of a group of German chemists at the
University of Wurzburg headed by Gustav Gerber, who had shown that the
individual bonds of an organometallic complex (dicarbonylchloro
cyclopentadienyl iron) could be broken at will using a femtosecond laser
pulse generator. Later work from that group extended the technique to
weakly bound clusters, but the
Levis
group has gone one step further and ambitiously tackled ordinary organic
molecules. The results are quite remarkable.
Levis
and colleagues used strong-field near-infrared laser pulses (centered
around 800 nanometers) to zap acetone, trifluoroacetone, and
acetophenone with ultra-intense and ultra-fast radiation to make a
specific product, such as toluene from acetophenone. What is even more
remarkable is that the yields of product could be optimized by letting
the apparatus work out the right phases and amplitudes for the laser
frequencies needed to achieve the desired result. The target molecules
are first engulfed with 40 distinct laser pulses, each of which will
interact with, and break up, the molecule in different ways. The
resulting fragments are analyzed by time-of-flight mass spectrometry to
detect the desired product. The laser is then automatically adjusted so
as to increase the output of this, until the optimal laser pulse is
found that will form only the desired product.
The
process is not just one of breaking bonds, as the formation of toluene
from acetophenone shows. Normal mass spectrometry of acetophenone, in
which all variety of bonds are broken, shows no recombination of
molecular fragments to form toluene, nor would this be expected. And nor
was the formation of toluene anticipated either in the current work,
because the phenyl group and the methyl group that come together to form
it are bound in the acetophenone with very different bond energies—100
and 85 kcals per mole respectively—which in theory respond to very
different laser pulses. The formation of toluene was not merely a trace
by-product, and tailoring the laser optimized its yield as well. This
discovery shows an unexpected potential of the new technique, and
according to
Levis
,
it might well find wide applicability.
"Closed-loop
strong-field laser control promises great things for the future,
especially in high technology applications, photodynamic therapy, and
even in the detection of chemical and biological agents. The strong
laser field hijacks the molecule’s personality to produce the desired
reaction," is how he describes it to Science
Watch, adding, "we have just recently inaugurated the first
center for adaptive photonics at
Temple
University
,
focusing on research and development in this area." If you’d like
to know more about Levis’s area of expertise then read his review in Journal
of Physical Chemistry A (R.J. Levis and H.A. Rabitz, 106[27]:
6427-44, 2002).
Dr.
John Emsley is based at the Department of Chemistry, Cambridge
University, U.K.
Science
Watch®, MAY/JUNE 2003, Vol. 14, No. 3
Citing URL:
http://www.sciencewatch.com/may-june2003/sw_may-june2003_page5.htm |
|
.
