Chemists Aglow Over Luminescence in Gold Compounds

Chemists Aglow Over Luminescence in Gold Compounds

by Dr. John Emsley

WHAT'S HOT IN CHEMISTRY...

Rank	Paper	Citations This Period Jul- Aug 97	Rank Last Period May- Jun 97
1	M. Wilm, M. Mann, "Analytical properties of the nanoelectrospray ion source," Analyt. Chem., 68(1):1-8, 1 January 1996. [European Molec. Bio. Lab., Heidelberg, Germany] *TN244	18	†
2	D.E. Woon, T.H. Dunning, "Gaussian basis sets for use in correlated molecular calculations. V. Core-valence basis sets for boron through neon," J. Chem. Phys., 103(11):4572-85, 15 September 1995. [Battelle Mem. Inst., Richland, WA] *RU110	16	†
3	R. Koradi, M. Billeter, K. Wüthrich, "MOLMOL: a program for display and analysis of macromolecular structures,"J. Molec. Graphics, 14(1):51-5, February 1996. [ETH-Hönggerberg, Zurich, Switzerland] *UH515	12	†
4	P. Schwab, R.H. Grubbs, J.W. Ziller, "Synthesis and applications of RuCl₂(=CHR')(PR₃)₂: the influence of the alkylidene moiety on metathesis activity," J. Amer. Chem. Soc., 118(1):100-10, 10 January 1996. [Caltech, Pasadena; U. Calif., Irvine] *TQ161	9	†
5	A.P. Scott, L. Radom, "Harmonic vibrational frequencies: an evaluation of Hartree-Fock, Møller-Plesset, quadratic configuration interaction, density functional theory, and semiempirical scale factors," J. Phys. Chem., 100(41):16502-13, 10 October 1996. [Australian. Natl. U., Canberra] *VL579	9	6
6	J.M. Forward, et al., "Luminescence studies of gold(I) thiolate complexes," Inorg. Chem., 34(25):6330-6, 6 December 1995. [Texas A&M U., College Station] *TJ250	8	†
7	M.T. Cicerone, M.D. Ediger, "Enhanced translation of probe molecules in supercooled o-terphenyl: Signature of spatially heterogeneous dynamics?" J. Chem. Phys., 104(18):7210-8, 8 May 1996. [U. Wisconsin, Madison] *UJ114	8	†
8	M.W. Feyereisen, D. Feller, D.A. Dixon, "Hydrogen bond energy of the water dimer," J. Phys. Chem., 100(8):2993-7, 22 February 1996. [Cray Res., Eagan, MN; Battelle Mem. Inst., Richland, WA; Du Pont Co. Inc., Wilmington, DE] *TX257	8	†
9	T. Lenzer, et al., "Trajectory simulations of collisional energy transfer in highly excited benzene and hexafluorobenzene," J. Chem. Phys., 103(2):626-41, 8 July 1995. [U. Göttingen, Germany; U. Sydney, Australia; U. Melbourne, Australia] *RH105	7	8
10	G. Knühl, P. Sennhenn, G. Helmchen, "New Chiral ß-phosphinocarboxylic acids and their application in palladium-catalysed asymmetric allylic alkylations," J. Chem. Soc.-Chem. Comm., (18):1845-6, 21 September 1995. [U. Heidelberg, Germany] *RW899	7	†

SOURCE: ISI's Hot Papers Database. Read the full legend.

It was reported in August of this year that a finger that wears a gold ring suffers less arthritis in old age than other fingers on the same hand. It hardly seems credible that the metal itself could be responsible for preventing this debilitating disease. Or could it? There are some gold-based anti-arthritic drugs, such as Auranofin (a.k.a. Ridaura), in which there is an atom of this metal at the molecule's center, and to which are attached a phosphine on one side and a thiolate on the other. Hot Paper #6, from the group headed by John P. Fackler, Jr., at Texas A&M University, reports on such compounds, describing their strange ability to luminesce. The paper tells of 10 new gold compounds with a variety of phosphines and thiolates attached, and with the thiolates modified by chlorine atoms or methoxy groups so that they alter the electron density around the central gold atom.

All the compounds exhibited luminescence at liquid nitrogen temperature -196°C, and three at room temperature. The emitted light ranges from red to blue. Triphenylphosphine compounds show two luminescent lifetimes, one lasting micro- seconds (due to a sulfur-to-gold electron transition) and the other lasting only nanoseconds (due to transitions within the phosphines). Non-aromatic phosphines showed only the long lifetime emission. The luminescence did not vary in a predictable manner, and Fackler thinks this is due to gold-to-gold interactions between neighboring molecules, and substituent effects on the thiolates. Richard Staples, now at Harvard University, analyzed four of the new compounds by X-ray crystallography but found that only two had short gold-to-gold distances. Fackler concludes that the color of the emitted light is not diagnostic of such short distances, rather that they cause a shift towards the red end of the spectrum.Electron-withdrawing chlorine atoms were a major influence on the emission maxima, and when there were two of these the luminescence was at lower wavelengths (485 nm) than when there was only one (702 nm) or none at all (596 nm).

Contacted by Science Watch, Fackler expressed surprise that #6 is currently the most cited of his recent papers, since it was not his first to describe luminescence in gold compounds. Nevertheless, he can explain the interest in his work: "Gold thiols are involved in the drugs used to treat rheumatoid arthritis," he says, "possibly because they quench singlet oxygen, which is thought to form in the cells of arthritic patients." Fackler has published on this in Metal Based Drugs (1:459, 1995), and his recent work has demonstrated that the luminescence in many gold compounds is quenched by molecules such as oxygen, sulfur dioxide, and nitric oxide (NO).

"Another reason is the interest in using gold compounds as chemical sensors because of their luminescence, rather than their drug application," Fackler continues. "The rare-metals suppliers Johnson Matthey now advertise luminescent gold compounds for this purpose." Fackler first reported the luminescence of gold thiolates in Inorganic Chemistry (33[13]:2790-8, 1994), and with Zerihun Assefa and Jennifer Forward he has written a major review on the subject, which should appear later this year in Plenum's Modern Inorganic Chemistry series. Assefa now works at Oak Ridge National Laboratory in Tennessee, and Forward is with Procter and Gamble in the U.K.

This year the Texas A&M team has published papers on 3-coordinate mono-nuclear gold compounds that luminesce (Acta Cryst. C, 53:195-7, 1997), and on the oxidative addition reaction of dinuclear gold compounds in their excited state (Polyhedron, 16[1]:1-17, 1997). Despite the interest in Fackler's work, his recent grant applications to the NSF were unsuccessful, but work goes on thanks to continuing support from The Welch Foundation.

Readers seeking information about gold drugs via the Internet should consult http://www.orthop.washington.edu.