Related Experiment Video
Updated: Nov 8, 2025
09:33
Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
3.6K
Prioritizing Direct Photolysis Products Predicted by the Chemical Transformation Simulator: Relative Reasoning and
Chenyi Yuan1, Caroline Tebes-Stevens2, Eric J Weber2
1Oak Ridge Institute for Science and Education (ORISE), hosted at United States Environmental Protection Agency, Athens, Georgia 30605, United States.
Environmental Science & Technology
|April 21, 2021
Summary
This study enhances the Chemical Transformation Simulator (CTS) by improving predictions of organic contaminant photolysis products in water. New algorithms reduce inaccurate predictions, increasing accuracy for environmental risk assessment.
Area of Science:
- Environmental Chemistry
- Photochemistry
- Computational Chemistry
Background:
- The US Environmental Protection Agency's Chemical Transformation Simulator (CTS) platform offers a reaction library for predicting direct photolysis products of organic contaminants in aquatic environments.
- The initial CTS library lacked differentiation in product formation likelihood, leading to an exponential increase in unobserved predicted products.
- Accurate prediction of photolysis products is crucial for environmental risk assessment and understanding contaminant fate.
Purpose of the Study:
- To improve the accuracy and precision of the CTS reaction library for predicting direct photolysis products of organic contaminants.
- To reduce the number of unobserved predicted products generated by the CTS platform.
- To identify dominant phototransformation pathways and guide future research.
Main Methods:
- Implemented relative reasoning algorithms to filter out unlikely photolysis products.
- Ranked reaction schemes based on transformation kinetics to remove slowly forming products.
- Evaluated the improved library using internal and external datasets, considering three generations of products.
Main Results:
- The enhanced library significantly improved prediction precision by 34% for the internal evaluation set and 53% for the external evaluation set.
- The refined approach effectively reduced the number of inaccurately predicted photolysis products.
- The improved library provided insights into dominant phototransformation pathways, suggesting new research directions.
Conclusions:
- The developed strategies successfully enhanced the predictive accuracy of the CTS platform for aquatic photolysis.
- This improvement is vital for more reliable environmental risk assessments of organic contaminants.
- The refined library facilitates a better understanding of contaminant fate and transformation in aquatic systems.
Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
2.0K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
2.0K
01:34The Z-Scheme of Electron Transport in Photosynthesis
11.6K
The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
11.6K
02:24Predicting Reaction Outcomes
9.1K
Kinetics describes the rate and path by which a reaction occurs. In contrast, thermodynamics deals with state functions and describes the properties, behavior, and components of a system. It is not concerned with the path taken by the process and cannot address the rate at which a reaction occurs. Although it does provide information about what can happen during a reaction process, it does not describe the detailed steps of what appears on an atomic or a molecular level. On the other hand,...
9.1K
02:13Energy Diagrams, Transition States, and Intermediates
18.5K
Free-energy diagrams, or reaction coordinate diagrams, are graphs showing the energy changes that occur during a chemical reaction. The reaction coordinate represented on the horizontal axis shows how far the reaction has progressed structurally. Positions along the x-axis close to the reactants have structures resembling the reactants, while positions close to the products resemble the products. Peaks on the energy diagram represent stable structures with measurable lifetimes, while...
18.5K
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
2.6K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.6K
01:11Radical Reactivity: Overview
2.3K
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
2.3K