Porphin-Template for Life One of our ancient progenitors, swimming around in the primordial soup, must have been attracted to the intricate, o i t h porphiu mt~.ecule,~~r perhaps it mas yet I,alanced,dt intrigued by 1111. numerous possibilities for substitutions and additiuns. \Vh.~ttverthe cause of the initial fascination. the porphin structure became a basic theme that recurred with elegant variations (called porphyrins) throughout the evolntionary process, as life differentiated into plants and animals and the numerous species of each. One set of variations coordinated with a maenesium atom and ~rodncedthe green-colored components of the photosynthetic process in nlants-the chloronhvlls. Another derivative chose instead to coordinate with &on to form the heme group, available for animal wrocesses such as resuiration-where it turns a hrilliant red upon reaction with oxygen. This common thread found in so manv life forms is also a common thread in three very different articles in this issue; although each treats a different topic, each also finds a porphyrin as a focal point. Senozan and Hunt (page 179) explore oxygen transport in animals in "Hemoglobin: Its Occurrence, Structure and Adaptation". They discuss the erratic use of the various hemoglobins throughout the animal kingdom, detail its structure in vertebrates, and show how i t functions. Another use of the heme group, this time in an enzyme which functions in the liver and elsewhere by reacting with impurities, is described in "Chemicals, Cancer, and Cytochrome P-450" by Alexander and Goff (page 179). The interesting (and ironic) feature of this particular porphyrin complex is that while performing its functions i t converts innocuous chemicals into Dotent carcinoeens-in fact most of the known carcinogens which are the center of so much controversy would be harmless were i t not for this bodily process. Turning to the plant kingdom, the porphyrin chlorophyll is one of "The Chemical Pigments of Plants"discussed by Alkema and Seager (page 183) in this month's Chem I Supolement. Thev discuss all of the tvpes of comuounds that produce color in plants and relate these to the s&sonal color changes that we observe in nature every year. Several laboratory experiments in this issue are also on biochemical topics and should be of interest to those who enjoyed the articles discussed above. They include: "A Simple Method for the Determination of Hemoglobin Oxygen Dissociation Curves" by Brittain (page 2531, "High Performance Liquid Chromatography of Vitamin A" by Bohman, Engdahl and Johnsson (page 2511, "Sulcatol: Synthesis of an Aggregation Pheromone" by Black and Slessor (page 2551, and "Com~arisonof Formation Constants for Nucleotide-PolvarninebandNncleotide-Magnesium Complexes" by Voige i d Elliott (page 257). u
Brownian Motion In his introduction to his paper "Simple Derivation of Phenomenological Brownian Motion Theory" Nordholm (page 187) states that he expects Brownian motion theory, 172
Journal of Chemical Education
long important to statistical physicists and certain engineers, to become a standard tool of chemists as well. He ooints out that, while data is collected on real systems in which many molecules interact. inter~retationsare usuallv in terms of isolated molecules and goes on to assert that "increasing attention will have to be given to the effect of the medium upon the properties of the molecules themselves." In an attempt to facilitate application of Brownian motion theory in new areas, he reexamines the derivation of the theory and presents a simple derivation that still allows a good . physical under. standkg of what is happening. In more specific applications of Brownian movement, Neumann (page 191) uses the concept to estahlish a simple theory of the melting transition for alkali halides and alkaline-earth oxides. and Matthews (uaee . - 246) presents a labomtory experiment ihr undergrduates rh 31 utilizei I4nmnian ~twtiont o yield a rcl~drleestimirte of Avuy,adro's nu~rher. ~
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Curriculum-Tailoring the Course to Changing Student Needs The past several drmdes Ii;~vc.seen significant changes in the char.wtzrijtiri
