Given the following molar absorptivities of amino acids in #"0.1 M"# phosphate buffer at #"pH 7"#, find the ratio of the absorbance at #"260 nm"# over #"280 nm"#, the #A260:A280# ratio, for a mixture of #"2 mol"# of #"Trp"# and #"1 mol"# of #"Tyr"#?

Question

#epsilon_("Trp", 260) "3765 L/mol"cdot"cm"#
#epsilon_("Trp", 280) "5563 L/mol"cdot"cm"#

#epsilon_("Tyr", 260) "585 L/mol"cdot"cm"#
#epsilon_("Tyr", 280) "1185 L/mol"cdot"cm"#

Cameron Andrews · Accepted Answer

Considering the aforementioned amounts: #epsilon_("Trp", 260) ~~ "3765 L/mol"cdot"cm"#
#epsilon_("Trp", 280) ~~ "5563 L/mol"cdot"cm"# #epsilon_("Tyr", 260) ~~ "585 L/mol"cdot"cm"#
#epsilon_("Tyr", 280) ~~ "1185 L/mol"cdot"cm"# Beer's law informs us that #A = epsilonbc#, where #A# is absorbance, #b# is the path length of the cuvette, and #c# is the concentration of the substance... And so, #A_2//A_1 = epsilon_2//epsilon_1# for a fixed number of mols of the same substance. Note that #epsilon# is an intensive quantity, made extensive when multiplying by the mols of substance.  Therefore, we can formulate an equation for the #A260:A280# ratio, with #n_k# being the mols of the #k#th amino acid: #color(blue)(A_(260)/A_(280)) = (sum_i n_i epsilon_(260,i))/(sum_i n_i epsilon_(280,j))# #= ("2 mol Trp" cdot "3765 L/mol"cdot"cm" + "1 mol Tyr" cdot "585 L/mol"cdot"cm")/("2 mol Trp" cdot "5563 L/mol"cdot"cm" + "1 mol Tyr" cdot "1185 L/mol"cdot"cm")# #= color(blue)(0.659)# Look, the equation is the same in this article.

Luna Chen · Answer

undefined To find the A260:A280 ratio for the given mixture of amino acids, you can use the molar absorptivities provided for tryptophan (Trp) and tyrosine (Tyr) at 260 nm and 280 nm. Then, calculate the absorbance at each wavelength for the given concentrations of Trp and Tyr, and finally, find the ratio of the absorbance at 260 nm to the absorbance at 280 nm.

Given the following molar absorptivities of amino acids in #"0.1 M"# phosphate buffer at #"pH 7"#, find the ratio of the absorbance at #"260 nm"# over #"280 nm"#, the #A260:A280# ratio, for a mixture of #"2 mol"# of #"Trp"# and #"1 mol"# of #"Tyr"#?

#epsilon_("Trp", 260) ~~ "3765 L/mol"cdot"cm"# #epsilon_("Trp", 280) ~~ "5563 L/mol"cdot"cm"# #epsilon_("Tyr", 260) ~~ "585 L/mol"cdot"cm"# #epsilon_("Tyr", 280) ~~ "1185 L/mol"cdot"cm"#

#epsilon_("Trp", 260) "3765 L/mol"cdot"cm"#
#epsilon_("Trp", 280) "5563 L/mol"cdot"cm"#

#epsilon_("Tyr", 260) "585 L/mol"cdot"cm"#
#epsilon_("Tyr", 280) "1185 L/mol"cdot"cm"#