![]() Visible absorption spectra of lutein and spinach Visible absorption spectra of beta-carotene and carrotįig ure 4. Example experimental spectra are given in Figures 3 and 4.įig ure 3. The instructor can, if desired, discuss the spectral peak for the chlorophyll in spinach which occurs above 600 nm. Using the spectrum of pure lutein as a guide, the appropriate wavelength of the lutein in spinach is determined. A couple of small pieces of fresh spinach are then dissolved in ethanol until a light color develops. The wavelength that corresponds to the lowest energy transition is then recorded. Next, a pure lutein gel capsule is punctured with a pin and a drop is dissolved in approximately 4 mL of ethanol until a light color develops. Using the spectrum of the pure beta-carotene as a guide, the appropriate wavelength of the beta-carotene is then determined. Light grinding with a stirring rod will aid dissolution. A few small pieces are shaved off the exterior of a carrot and likewise dissolved in ethanol until a light color develops. If their absorbance is too high, dilution is necessary. The students record the wavelength that corresponds to the lowest energy transition in the conjugated system (i.e. In our lab we use Spec-200 spectrophotometers as we have enough instruments for pairs of students to work with their own. After a light color develops, the absorption spectrum is obtained from 400 nm – 700 nm. Experimental To begin, a speck of beta-carotene is dissolved in approximately 4 mL of ethanol. The solutes proposed for this work are soluble enough in just a few minutes to make this experiment quick, safe, and even possible to do without a fume hood. Some of these compounds take a while to sufficiently dissolve in the solvent. When used in particle in a box experiments, polyenes and cyanine dyes are often dissolved in solvents such as cyclohexane. The chemical systems proposed in this work are beta-carotene and lutein, compounds found in common vegetables like carrots and spinach. Also of interest would be to use chemicals with which students may be more familiar and that they see in their daily life. ![]() Theoretically, other systems that have long, conjugated, nearly linear chains could also be used. All of these systems contain long conjugated systems that can be approximated at some level to being linear and therefore can be modelled using the quantum mechanical particle in a one dimensional box. More recently, polyenes, and polyynes have been used. Traditionally, chemicals like cyanine dyes have been used to model the one dimensional box system. Introduction Laboratory experiments concerning the particle in a one dimensional box have long been a staple in the undergraduate physical chemistry laboratory. ![]()
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