Tea from the leaves of guayusa (Ilex guayusa) has a long history of consumption by Ecuadorian natives in regions where the plant is indigenous. The tea contains the methylxanthines caffeine and theobromine as well as chlorogenic acids, flavonoids, and sugars. Various studies were performed to evaluate the general and genetic toxicology of a standardized liquid concentrate of guayusa (GC). Guayusa concentrate was found to be negative in in vitro genotoxicity tests including the Ames test and a chromosome aberration study in human lymphocytes. The oral median lethal dose (LD50) of GC was >5,000 mg/kg for female rats. Guayusa concentrate was administered to male and female rats in a 90-day subchronic study at 1,200, 2,500, and 5,000 mg/kg/d of GC and a caffeine-positive control at 150 mg/kg/d corresponding to the amount of caffeine in the high-dose GC group. Effects observed in the GC-treated groups were comparable to those in the caffeine control group and included reductions in body weights, food efficiency, triglycerides values, and fat pad weights and increases in blood chemistry values for serum aspartate aminotransferase, serum alanine aminotransferase, and cholesterol and adaptive salivary gland hypertrophy. No signs of incremental toxicity due to any other components of guayusa were observed. The studies indicate no harmful effects of GC in these test systems.

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A bioinorganic chemistry study Research in bioinorganic chemistry has been remarkably successful in providing an increased understanding of biochemical processes at the molecular level.1 The literature in this interdisciplinary field is rapidly growing to accommodate the present level of activity (1), and several articles appearing in this Journal on bioinorganic topics attest to this dynamic state (2). Until very recently few experiments were available for undergraduates where actual biological systems were utilized to clearly illustrate the essential nature of metal ions in certain life processes (3). One system that has been studied successfully in our laboratory as part of a one semester undergraduate inorganic chemistry course consists of the hydrolytic metalloenzyme, carbonic anhydrase. The purpose of this article is to discuss selected bioinorganic aspects of carbonic anhydrase and to elaborate on experiments that will reinforce the students' understanding of not only the presence but also the essential role that metal ions have in some biological systems. The Native EnzymeCarbonic anhydrase (carbonate hydrolyase, EC 4.2.1,1) is a small enzyme with a molecular mass of about 30,000 which contains one divalent zinc ion per molecule. The physiological

Table I Electrolyte' (in propylene carbonate) t -0 18ec 10 aec 1 min 10 min 1 hr ----.-IBo (mA/am*) at time indiaated-0.257 m LiC104->12 10.2 7 . 8 5.4 2.8 1.6 <0.001 m HzO 0.02 m HzO 0.229 m LiC104->10 8 3.1 1.5 0.30 0.026 0.257 m LiC10,->5 -3 -1 -0.1 .. . .. . 0.54 m HzO time. Values previously r e p~r t e d~~~~~ are consistent with our measurements after 10 min to 1 hr. Our values at t = 0 were obtained by extrapolation on a tl'l scale. I n the dry (<0.001 m HzO) electrolyte, the doublelayer capacity (obtained from the initial portion of the potential-time trace) is approximately 45 pF/cm2, a reasonable value for a rough solid metal surface. In the presence of 0.54 m HzO, the capacity drops to as low as 0.3 pF/cm2, indicating the formation of a dielectric film (possibly LiOH) on the metallic surface. Itis not possible a t this time to distinguish between the effects of recrystallization of the cold-worked surface and the effect of trace water in dry electrolyte, but future experiments with ultradry electrolyte should make this distinction clear.* (7) Propylene carbonate was purified by distillation and analyzed by gas chromatography as described by R. Absorptivity of the OH Stretching VibrationSir: Several have reported the temperature dependence of the molar absorptivity for the fundamental OH stretching vibration of various monomeric molecules in dilute solution; corrections for this temperature dependence have been made by Hammaker, et al.,4 for solutions of methanol, t-butyl alcohol, and di-t-butyl carbinol in carbon tetrachloride. Finch and Lippincott6 have suggested that a true temperature dependence should exist for hydrogen-bonded complexes. Thus, if the solute should hydrogen bond to the solvent, a temperature dependence would be expected. However, Fletcher and Heller6 argue that the molar absorptivity should not change with temperature, and therefore consider any temperature adjust-100 90 80 70 >. h 60 8 9 5 0 5 40 E 30 6 20 1 0 O( e 35'C A 60'C I I I I I I I I I I 0. 1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 0 HEAD SPACE (mi) Figure 1. CH stretch of methanol in carbon tetrachloride at 35 and 60' as a function of the head space over the solution. concentration was 0.0048 M at 35".Change in the molar absorptivity for the OH andThe solution ment incorrect. Swenson,' in an attempt to determine the cause of this temperature dependence for methanol in carbon tetrachloride solution, has ascribed the decrease of the molar absorptivity with increasing temperature to reduced concentration of the methanol in solution due to evaporation of the methanol into the head space above the solution. Thus Swenson concludes that a true temperature dependence of the molar absorptivity does not exist. Because of the relative importance of the temperature dependence of the molar absorptivity to the interpretation of spectral data, it seemed that some of our preliminary results in this area should be reported. The change in the molar absorptivity as a function of increasing head space over a solution of methanol in carbon tetrach...

The authors describe and illustrate an apparatus for cleaning NMR tubes.