Passage
In polluted urban environments, airborne proteins can undergo nitration reactions that increase their allergenic potential toward the human respiratory system. For example, upon exposure to ozone (O₃) and nitrogen dioxide (NO₂) under atmospheric conditions, the amino acid tyrosine is known to undergo a two-step irreversible reaction leading to the formation of nitrotyrosine. The first step involves the formation of a reactive oxygen intermediate (ROI) tyrosyl radical through oxidation of the phenolic site of tyrosine. Nitrotyrosine is then formed in the second step through addition of NO₂ by a radical-radical termination reaction. The elementary steps for this reaction are shown in Scheme 1.
Scheme 1 Elementary steps of nitration of tyrosineAirborne protein particles can exist in a variety of environments including the aqueous phase, gaseous phase, or as conglomerates with other biomolecules such as lipids. Because the thermodynamic properties and kinetics of the nitration reaction vary based on the chemical environment in which it occurs, recent studies have focused on understanding the reaction under different conditions.Density functional theory is a powerful computational quantum-mechanical modeling method that can determine the properties of many-electron systems by producing approximate solutions to the Schrödinger equation. Researchers used density functional theory to model the geometries and potential energy surfaces of the reactants, intermediates, and products of the nitration reaction in gaseous, aqueous, and lipid-rich environments. From this modeling, the thermodynamic and kinetic properties were calculated. Figure 1 shows the calculated activation energies E_a in kJ/mol, and Table 1 lists the associated thermochemical properties for both steps of the reaction in all three environments.
Figure 1 Calculated activation energies for each step of the studied reactions in three environmentsTable 1 Calculated Thermochemical Properties of the Studied Reactions (298.15 K)
Adapted from Sandhiya L, Kolandaivel P, Senthilkumar K. Oxidation and nitration of tyrosine by ozone and nitrogen dioxide: reaction mechanisms and biological and atmospheric implications. J Phys Chem B. 2014;118(13) :3479-90.
-Which of the following are true concerning the overall reaction in an aqueous environment?The rate constant increases exponentially with increasing temperature.The rate constant increases exponentially with decreasing activation energy.The reaction rate decreases exponentially with increasing activation energy.The rate constant of the catalyzed reaction will be smaller than the rate constant of the uncatalyzed reaction.

Question

Passage
In polluted urban environments, airborne proteins can undergo nitration reactions that increase their allergenic potential toward the human respiratory system. For example, upon exposure to ozone (O₃) and nitrogen dioxide (NO₂) under atmospheric conditions, the amino acid tyrosine is known to undergo a two-step irreversible reaction leading to the formation of nitrotyrosine. The first step involves the formation of a reactive oxygen intermediate (ROI) tyrosyl radical through oxidation of the phenolic site of tyrosine. Nitrotyrosine is then formed in the second step through addition of NO₂ by a radical-radical termination reaction. The elementary steps for this reaction are shown in Scheme 1.

Scheme 1 Elementary steps of nitration of tyrosineAirborne protein particles can exist in a variety of environments including the aqueous phase, gaseous phase, or as conglomerates with other biomolecules such as lipids. Because the thermodynamic properties and kinetics of the nitration reaction vary based on the chemical environment in which it occurs, recent studies have focused on understanding the reaction under different conditions.Density functional theory is a powerful computational quantum-mechanical modeling method that can determine the properties of many-electron systems by producing approximate solutions to the Schrödinger equation. Researchers used density functional theory to model the geometries and potential energy surfaces of the reactants, intermediates, and products of the nitration reaction in gaseous, aqueous, and lipid-rich environments. From this modeling, the thermodynamic and kinetic properties were calculated. Figure 1 shows the calculated activation energies E_a in kJ/mol, and Table 1 lists the associated thermochemical properties for both steps of the reaction in all three environments.

Figure 1 Calculated activation energies for each step of the studied reactions in three environmentsTable 1 Calculated Thermochemical Properties of the Studied Reactions (298.15 K)

Adapted from Sandhiya L, Kolandaivel P, Senthilkumar K. Oxidation and nitration of tyrosine by ozone and nitrogen dioxide: reaction mechanisms and biological and atmospheric implications. J Phys Chem B. 2014;118(13) :3479-90.
-Which of the following are true concerning the overall reaction in an aqueous environment?The rate constant increases exponentially with increasing temperature.The rate constant increases exponentially with decreasing activation energy.The reaction rate decreases exponentially with increasing activation energy.The rate constant of the catalyzed reaction will be smaller than the rate constant of the uncatalyzed reaction.

Quizplus · Accepted Answer

11ecba2d_119c_66cd_a3bf_e91e1c6e15fc_MD0008_00 The Arrhenius equation 11ecba2d_119c_66ce_a3bf_abb13ab9edea_MD0008_00 relates the rate constant k of a reaction with its activation energy and temperature. The negative exponent in the equation can be rewritten with the exponential term 11ecba2d_119c_8ddf_a3bf_1ff19694d859_MD0008_00 in the denominator as 11ecba2d_119c_8de0_a3bf_77dd69415a1e_MD0008_00 . Increasing the temperature of a reaction gives a smaller value of the exponential term. Because it is in the denominator, a smaller exponential term gives an increased value for k (Number I). Decreasing the activation energy E_a also gives a smaller exponential term, and therefore k increases exponentially with decreasing E_a (Number II). Conversely, k decreases exponentially with increasing E_a. According to the rate law equation, the rate of a given reaction is directly proportional to the rate constant. Therefore, the reaction rate also decreases exponentially with increasing E_a (Number III). (Number IV) Catalysts lower the value of E_a of reactions, and therefore an uncatalyzed reaction has a higher E_a than the catalyzed reaction. Because uncatalyzed reactions have a higher E_a, the reaction has a decreased rate constant with respect to the rate constant of the catalyzed reaction. Educational objective: The Arrhenius equation describes the relationship between the rate constant and the temperature and activation energy of a reaction. Both the rate constant and the rate of reaction decay exponentially with increasing activation energy and increase exponentially with increasing temperature. Because catalysts lower the activation energy of a reaction, the rate constant is greater for a catalyzed reaction than for an uncatalyzed reaction.

Passage In Polluted Urban Environments, Airborne Proteins Can Undergo Nitration Reactions