Among Chemistry’s Hottest, There’s Water, Water, Everywhere

Among Chemistry’s Hottest, There’s Water, Water, Everywhere

by John Emsley

WHAT'S HOT IN CHEMISTRY
Rank	Paper	Cites This Period (Mar-Apr 06)	Rank Last Period (Jan-Feb 06)
1	P. Wernet, et al., "The structure of the first coordination shell in liquid water," Science, 304(5673): 995-9, 14 May 2004. [6 institutions worldwide] *820IV	20	5
2	K. Hata, et al., "Water-assisted highly efficient synthesis of impurity-free single-walled carbon nanotubes," Science, 306(5700): 1362-4, 19 November 2004. [AIST, Tsukuba, Japan] *873SP	18	†
3	S.D. Walker, et al., "A rationally designed universal catalyst for Suzuki-Miyaura coupling processes," Angew. Chem. Int. Ed., 43(14): 1871-6, 2004. [MIT, Cambridge, MA] *809TG	17	†
4	M. Mucha, et al., "Unified molecular picture of the surfaces of aqueous acid, base, and salt solutions," J. Phys. Chem. B, 109(16): 7617-23, 28 April 2005. [6 institutions worldwide] *919FM	16	†
5	*D.J. Milliron, et al., "Colloidal nanocrystal heterostructures with linear and branched topology,"* Nature, 430(6996): 190-5, 8 July 2004. [U. Calif., Berkeley; Lawrence Berkeley Natl. Lab., CA] *835GL	15	†
6	A. Dreuw, M. Head-Gordon, "Failure of time-dependent density functional theory for long-range charge-transfer excited states: The zincbacteriochlorin- bacteriochlorin and bateriochlorophyll- spheroidene complexes," J. Am. Chem. Soc., 126(12): 4007-16, 31 March 2004. [U. Frankfurt, Germany; U. Calif., Berkeley; Lawrence Berkeley Natl. Lab., CA] *806NK	15	†
7	E.A. Raymond, G.L. Richmond, "Probing the molecular structure and bonding of the surface of aqueous salt solutions," J. Phys. Chem. B, 108(16): 5051-8, 22 April 2004. [U. Oregon, Eugene] *813YR	15	†
8	S. Ghosal, et al., "Electron spectroscopy of aqueous solution interfaces reveals surface enhancement of halides," Science, 307(5709): 563-6, 28 January 2005. [U. Calif., Berkeley; Lawrence Berkeley Natl. Lab., CA; U. Nac. de la Plata, Argentina] *893BJ	15	†
9	J.L.C. Rowsell, et al., "Hydrogen sorption in functionalized metal-organic frameworks," J. Am. Chem. Soc., 126(18): 5666-7, 12 May 2004. [U. Michigan, Ann Arbor] *818TW	14	3
10	J. Wang, et al., "Development and testing of a general amber force field," J. Computat. Chem., 25(9): 1157-74, 15 July 2004. [Encysive Pharmaceut. Inc., Houston, TX; Novartis Inst. Biomed. Res., Basle, Switzlerland; Scripps Res. Inst., La Jolla, CA] *823PC	14	†
SOURCE: Thomson Scientific's Hot Papers Database. Read the Legend.

ondon buses are entertainingly unpredictable. You wait 20 minutes for one and then three turn up together. That was the feeling I got when I surveyed the current Hot Ten with its five papers dealing with water. What is making water such a hot topic? Part of the reason is undoubtedly our concern for the environment, in that we live on a planet covered mainly by a dilute solution of salts and whose chemistry we are still struggling to understand. Two of the papers mention this.

Papers currently at #1 and #2 were discussed in the January-February edition of Science Watch. Paper #1 is the work of Anders Nilsson and Lars Pettersson and deals specifically with liquid water itself. It reports work from the Stanford Synchrotron Radiation Laboratory, the Berliner Elektronenspeicherring-Gesellschaft für Synchrotron Strahlung (better known as BESSY), and the Universities of Stockholm, Linköping, and Utrecht. This paper is about the hydrogen bonding in liquid water and it overturned accepted theory by showing that it was not a random network of hydrogen bonds, with three per molecule on average, but that 80% of waters formed only two strong hydrogen bonds thereby creating chains and rings, and that these were embedded in a disordered cluster network connected by much weaker hydrogen bonds.

Paper #2 is mainly the work of Kenju Hata and Don Futaba at the National Institute of Advance Industrial Science and Technology, at Tsukuba, Japan. They found that traces of water were essential to the production of perfect carbon nanotubes.

Papers #4, #7, and #8 look at solutions of acids, bases, and salts. Paper #4 addresses a long-known but puzzling behavior of aqueous solutions: why do dissolved salts and bases increase the surface tension of water whereas acids decrease it? The answer comes from a collaboration of university researchers in five locales (the Czech Republic, Germany, and the U.S. states of Ohio, California, and Washington), headed by Pavel Jungwirth of the Academy of Sciences of the Czech Republic. The team used computational methods and VSF (vibrational sum frequency) spectroscopy to reveal that in aqueous salts and bases the metal cations are repelled from the surface but the anions are attracted to it although their positioning depends on their size and polarizabilty. In acids, on the other hand, the H₃O⁺ ions are attracted to the surface, where their hydrogen atoms form hydrogen bonds to surrounding water molecules, leaving the oxygen atom unbound and exposed. This explains why acids behave so differently in terms of surface tension.

Geraldine Richmond and Elizabeth Raymond of the University of Oregon have also used VSF spectroscopy to study the behavior of sodium halides in water and in mixtures of water and deuterated water (#7). Isotopic dilution showed that fluoride ions cause a tightening of the water structure by forming strong hydrogen bonds while chloride, bromide, and iodide ions cause a weakening of the hydrogen bonding and its partial collapse. They also found that the very top layer of water molecules suffers almost no disturbance from these dissolved salts.

Paper #8 is again a collaborative effort, from chemists at the University of California, Irvine (UCI), the Lawrence Berkeley National Laboratory, Berkeley, and the University of La Plata, Argentina; John Hemminger of UCI was the lead author. They used x-ray photoelectron spectroscopy to study the effect of dissolved potassium bromide and iodide on the surface phenomenon and found that in concentrated solutions there is particular enhancement of iodide concentration at the surface. They also found that their observations were in good agreement with computational simulations.

Chemists have always known that water was unique in many ways. It should be a gas at room temperature, but a network of hydrogen bonds makes it a liquid; ice should sink but even more hydrogen bonds form to keep it afloat; and it has a high surface tension due to its remarkable hydrogen bonding network. As long ago as 1910 it was observed that this last property was affected by dissolved salts, acids, and bases, although why this was, and why these behaved in different ways, could not be explained. Now it can.

Dr. John Emsley is based at the Department of Chemistry,
University of Cambridge, U.K.



	View the top 10 scientists and/or top 3 Hot Papers in Chemistry.

Science Watch^®, September/October 2006, Vol. 17, No. 5
Citing URL: http://www.sciencewatch.com/sept-oct2006/sw_sept-oct2006_page7.htm