n e w s of t h e w e e k
Fluorescent molecule measures temperature A newly developed fluorescent molecular thermometer could open the way to the design of molecular probes for temperature imaging in biological fluids. The fluorescent molecule, a nickel (II) complex of a tetraaza macrocycle covalently linked to a naphthalene fluorophore, was synthesized by chemistry professor Luigi Fabbrizzi and coworkers at the University of Pavia, Italy [Chem. Commun., 1999,1191]. "The light intensity of this new fluorescent molecule increases with increasing temperature," Fabbrizzi tells C&EN. As the team showed, the fluorescence emission intensity of a solution of the complex increased steadily over the temperature range of 27 to 65 °C. Fabbrizzi notes that a number of luminescent molecular sensors have been developed for determining analytes such as metal ions and anions. These rely on electron transfer between a luminophore and a receptor for the analyte. "We followed the same modular approach to design a fluorescent sensor of a physical quantity—that is, temperature— rather than a chemical quantity," Fabbrizzi explains. "We linked a classical organic fluorophore, naphthalene, to a molecular fragment whose electronic properties are strongly affected by temperature." The nickel (II) complex of the synthetic macrocycle exists in two different electronic states. One state, in which all the electrons of the metal ion are paired, does not affect the light emission of the nearby naphthalene subunit. The other state, in which two electrons are unpaired, quenches the emission of the fluorophore. Both states coexist in solution at equilibrium, but the interconversion between the two states is temperature dependent. Molecular probes based on such complexes could be used for intracellular temperature imaging with both spatial and temporal resolution, Fabbrizzi suggests. "Conspicuous heat production and consequent temperature increase in subcellular regions may be indicative of pathogenesis," he points out. "Moreover, the occurrence of metabolic activities can be monitored through heat release and temperature change. Due to the high sensitivity of fluorometric techniques, molecular probes of this type can be used at very low, noninvasive concentration levels." 6
JULY 12,1999 C&EN
There have been several reports of fluorescent sensors for temperature and other physical properties, A. Prasanna de Silva, chemistry professor at Queen's University, Belfast, Northern Ireland, points out. But, he says, "Fabbrizzi's paper is distinguished by the use of metal complexes for this purpose." Plus, he adds, "the modular construction is attractive owing to its flexibility." The Italian team currently is considering the design of other two-component fluorescent temperature sensors. "We are, for example, looking at replacing the naphthalene fluorophore with different luminescent fragments displaying especially high emission and
Macrocycle is linked to naphthalene fluorophore
providing full solubility in aqueous media, while keeping the same Ni(II)based temperature-sensitive subunit," Fabbrizzi notes. Michael Freemantle
Monsanto offers up sweeteners and gums Monsanto has put two more businesses on the block in its quest to raise money to pay down the debts it accrued buying seed companies to build up its favored life sciences business. In addition to earlier plans to sell its algins food ingredients, the company now is seeking buyers for its artificial sweetener and biogums businesses. Combined sales of these businesses were $1 billion in 1998. This latest sale is another piece of a restructuring plan announced in November 1998 to raise about $5 billion and cut about 2,500 jobs (C&EN, Nov. 16,1998, page 12). In January, Monsanto sold its Ortho lawn-and-garden business to Scotts for $300 million. Then, in May, it sold NSC Technologies, a pharmaceutical intermediates and bulk active chemicals producer, to Great Lakes Chemical for $125 million. It has been advertising its Stoneville Pedigreed Seed business all year. Monsanto's nutrition and consumer products division—which included the sweeteners, algins, biogums, and Ortho businesses—had 1998 sales of $1.53 billion. The division contributed about 18% of the company's total sales and about 23% of %its operating earnings. The sweeteners business, which Monsanto aggressively built up in the 1980s, includes a number of familiar consumer products such as the artificial sweeteners NutraSweet and Equal. A Searle scientist, working with amino acids to develop an ulcer treatment, discovered aspartame in 1965
It was launched in 1981 as NutraSweet and went off patent in late 1992. Included in the business is a new patented sweetener, neotame, for which Monsanto is now seeking marketing approval from the Food & Drug Administration. The gums business has a shorter company history. In February 1995, Monsanto paid $1.08 billion to acquire Merck's food gums business. Alginates are extracted from seaweeds and are used in foods, drugs, and industrial products for stabilizing, suspending, and gelling. Biogums include xanthan and gellan gums and blends. Monsanto says the divestiture process will "begin immediately and be completed as quickly as possible." Assets worth an estimated $1.5 billion to $2 billion are up for sale. These include sweetener manufacturing sites in Augusta, Ga.; Mount - Prospect, HI.; and Gravelines, France, and gum manufacturing sites in San Diego; Okmulgee, Okla.; and Knowsley, England. About 2,100 manufacturing, sales, and administrative employees are connected with ^ the businesses. Monsanto is now targeting what it calls "science-based nutrition," working to alter the nutritional composition of major crops and creating food ingredients
