edlted by
WALTER A. WOLF Eisenhower College Seneca Falls. New York 13148
Protein Chemistry-Lecture
and Laboratory
J e f f r e y A. Hurlbut Metropolitan State Cdlepe Dmuer, CO 80204 Last year this chemistry department offered a new upper division course on protein chemistry. The course was a three-credit-hour, one-semester lecture and lahoratory class, and was quite successful both in attracting and in meeting the needs of many chemistry and biology majors. Since we could not find useful texts for either the lecture or the laboratory, we organized our own material. The lecture was organized into three sections: amino acids, proteins, and enzymes. Each section included lectures on structure, function, properties, nomenclature, synthesis, purification, quantitative analysis, and metabolism, as well as on numerous other selected topics. The lahoratory, on the other hand, gave the students some practical experience, and they selected five of the ten available experiments to perform. These experiments ranged from chromatographic separation of amino acids to the determination of the properties of the active site of a typical enzyme. Detailed copies of both the lecture outline and the laboratory experiments are available npon request.
Infinitely Variable Individualized Unknowns for Molecular Weight by Viscosity Don P a u l Miller Washhurn University Topeho, KS 66621 Individualized unknowns are relatively simple to prepare for experiments such as quantitative analysis, since the composition of samples may be varied infinitely. Abstract quantities such as the molecular weight are more difficult to individualize, especially when each unknown in the class is required to have similar behavior and use the identical experimental techniques as all other unknowns. A convenient method to generate many unique unknowns for the determination of molecular weight by viscosity is to mix homogeneous polymer powder with a low molecular weight compound in different amounts. The details for performing the viscosity experiment are found in most physical lahoratory textbooks, where the Mark-Houwink equation is used exclusively to determine the molecular weight. For pdydispersed polymers the method gives a result which lies between the number average and the weight average molecular weight, and depends on the weight distribution and the intermolecular interactions of a particular polymer. Since .
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distrihutiou of sainples by the addition of anhydrous glucose. However, the empirical constants in the Mark-Houwink equation are valid only for samples which have weight distributions close to the original distribution. This problem is overcome hv calibration of the method to find the relationship between the weight fraction of the polymer in the individualized sample and the experimental molecular weight. After 200 / Journal of Chemical Education
calibration, all students can use thesame conslanls, an11 n w d not be aware that the sample is a mixture. For unknowns made from mixtures of polyvinyl alcohol, MCB PX1295/7592, and anhydrous plucose, the results of the caiihration and four years of actuai student determinations fit the equation. M = 70000 f - 15000, where is the grams of polymer divided by grams of sample. The MarkHouwink equation used was [ q ]= 2.0 X lo-'' Mn.7%The students occasionallv guidance when extrapolating the . required . data through low concentration points to obtainthe valie of the intrinsic viscosity, because of nonlinearities a t concentrations less than 0.05 g of unknown per 100 ml of solution. In all other respects, the unknowns and data were well behaved, and the student results agreed well with the calibration.
An Analogy for Quantization of Energy Levels-Molecules as Books Stephen S. Washhurne a n d David R. Dalton Temple University Philadelphia, P A 19122 Early acceptance of the quantized nature of electromagnetic radiation (little bullets, packets of energy, etc.) and quantized atomic energy levels (Bohr atom, electron orbits, etc.) is -aenerallv found amone our beeinnine students. However. there still appears to be some resistance to the concept of molecular energy levels being quantized; and quantized not only electronically, but vibrationally and rotationally as well. As this concept is central to discussion of organic structure determination, photochemistry and molecular spectroscopy, it is essential that it be mastered early in a chemical curriculum. We use an analogy that students have found simple and intuitively reasonable. Consider molecules as books stores in a library. A library has several floors of stacks; each floor is an electronic energy level. Each floor has several shelves one above the other; each shelf is a vibrational level. Normally, of course, books are stored on shelves vertically, but if this (Molecular Energy) library stores its books horizontally, then each pile can be thought of as an ensemble of rotational levels, with a book (molecule) being at the bottom (closest to the shelf), in the middle, or on top of the pile. Now, each hook in a library muqt be in a discrete place, that is, it must he on the first or second level, not on the 11/2floor. Similarly, each book must be on a soecific shelf and in a soecific position (horizontallv) " . on that shelf; hence, particular vibrational and rotational levels. Clearly, too, electrnnic levels (fluors) are spaced further aoart than Gihrational levels (shelves), which, 'in turn, are furiher apart than rotational levels: The concepts of potential energy as height above the ground floor, electronic (ultraviolet) spectroscopy as transitions between flours, infrared spectroscopy as transitions between shelves, microwave spectroscopy as transitions between relative positions on a shelf, and the relative energies required for such transitions are thus easy to introduce. Finally, other concepts can he added, e.g., an adiacent (hillside) triplet librarv. uncertaintv. in position . (checked out or not) and momentum (intellectual curosity aroused), etc.. as thesubiect expands and as whimsvand time allow.
