Scaling the Process Chemistry of a COVID-19 Antiviral Pharmaceutical Down for a Multistep Synthesis Experiment in the Undergraduate Teaching Laboratory

Molnupiravir is an orally bioavailable direct acting antiviral agent that received emergency use authorization in late 2021 from the FDA for the treatment of patients with mild, moderate, or severe COVID-19. This prodrug is metabolized into a ribonucleoside that is incorporated into the viral RNA during replication. Its tautomerization between cytidine- and uridine-like forms ultimately causes multiple irreversible errors in the genetic code of the virus, which prevents successful viral replication. There are multiple process chemistry routes for molnupiravir synthesis published in the literature that attempt to maximize synthetic yield while minimizing cost and waste, which are goals similar to those of an implementable educational laboratory experiment for the teaching laboratory. We have developed a multiweek laboratory module for undergraduate students in which students conduct a multistep synthesis of molnupiravir. Specifically, our Organic Chemistry II Laboratory students performed the final two steps of molnupiravir synthesis using procedures derived directly from the published process chemistry literature. We utilized this opportunity to introduce students to reading and interpreting these primary experimental sources. Students obtained authentic characterization data via high pressure liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy to assess the conversion and purity of their products at each synthetic step. We report our in-lab activities and student generated data as well as suggestions for how this laboratory experiment could be tailored to meet similar learning objectives in other courses, such as medicinal chemistry or capstone laboratory courses, and as a function of available instrumentation.

Exploring the Chemistry of the Mechanical Bond: Synthesis of a [2]Rotaxane through Multicomponent Reactions

The synthesis of a [2]rotaxane through three- or five-component coupling reactions has been adapted to an organic chemistry experiment for upper-division students. The experimental procedure addresses the search for the most favorable reaction conditions for the synthesis of the interlocked compound, which is obtained in a yield of up to 71%. Moreover, the interlocked nature of the rotaxane is proven by NMR spectroscopy. The content of the sessions has been designed on the basis of a proactive methodology whereby upper-division undergraduate students have a dynamic role. The laboratory experience not only introduces students to the chemistry of the mechanical bond but also reinforces their previous knowledge of basic organic laboratory procedures and their skills with structural elucidation techniques such as NMR and FT-IR spectroscopies. The experiment has been designed in such a customizable way that both experimental procedures and laboratory material can be adapted to a wide range of undergraduate course curricula.

A Cost-Effective Microfluidic Device to Teach the Principles of Electrophoresis and Electroosmosis

Electrophoresis is integral to analytical and biochemistry experiences in undergraduate education; however, fundamental principles of the method are often taught in upper-level laboratories through hands-on experiences. A laboratory activity is reported that teaches the concepts of electrophoretic mobility and electroosmotic flow. A single reuseable instrument, called a mini-E, costs 37 USD and consists of a DC power supply, a voltmeter, platinum electrodes, and a chip cast in polydimethylsiloxane. This activity uses common reagents costing only 0.02 USD per student. Experiments are devised that allow students to investigate the properties of electrophoretic flow and electroosmotic flow by separating the two commonly used food dyeing agents Brilliant Blue FCF and Allura Red AC in vinegar and in a solution of ammonium hydroxide. A dark-purple mixture of these dyes is separated into red and blue bands that are easily visualized. The migration order of the dyes differs when the separation is performed under conditions of reversed polarity and suppressed electroosmotic flow (vinegar) compared to conditions of normal polarity and active electroosmotic flow (ammonium hydroxide). When delivered to chemistry majors, students had a significant gain in their ability to apply the concepts of electroosmosis and electrophoresis to predict analyte migration. Although this activity targets upper-level chemistry content, it can also be adapted for other laboratory experiences.

Hybrid Model Teaching in the Postepidemic Period: From Nucleic Acid to Antigen for the Fluorescence Analysis of SARS-CoV-2

Owing to the global spread of the coronavirus disease 2019 (COVID-19), education has shifted to distance online learning, whereas some face-to-face courses have been resumed with the improvement of the outbreak prevention and management situation, including a laboratory course for senior undergraduate students in chemical biology. Here, we present an innovative chemical biology experiment covering COVID-19 topics, which was created for third-year undergraduates. The basic principles of two nucleic-acid- and antigen-based diagnostic techniques for SARS-CoV-2 are demonstrated in detail. These experiments are designed to provide students with comprehensive knowledge of COVID-19 and related diagnoses in daily life. Crucially, the biosafety of this experimental manipulation was ensured by using artificial nucleic acids and recombinant protein. Furthermore, an interactive hybrid online-facing teaching model was designed to cover the key mechanism regarding PCR and serological tests of COVID-19. Finally, a satisfactory evaluation was obtained through a questionnaire, and simultaneously, reasonable improvements to the course design were suggested. The proposed curriculum provides all the necessary information for other instructors to create new courses supported by research.

Introduction to Pharmaceutical Co-amorphous Systems Using a Green Co-milling Technique

The concept of co-amorphous systems is introduced in an integrated laboratory experiment, designed for advanced chemistry students, using solvent-free, environmentally friendly mechanochemistry. The dual-drug naproxen-cimetidine co-amorphous system (NPX-CIM) is investigated as an example of the emergent field of medicinal mechanochemistry. Students are trained in solid-state characterization techniques including X-ray powder diffraction, Fourier-transform infrared spectroscopy, and thermal analysis by differential scanning calorimetry. This lab experiment also provides an opportunity to discuss the relevance of different solid forms of pharmaceutics, emphasizing particular properties of disordered materials. This experiment can easily fit the curriculum of any Chemistry or Pharmacy master level degree in courses dealing with instrumental analysis, solid state chemistry, or green chemistry, for classes of 6 to 18 students, in a 5-h lab session. Suggestions to adapt it to the use of a single characterization technique are provided.

Integrated Science Teaching in Atmospheric Ice Nucleation Research: Immersion Freezing Experiments

This paper introduces hands-on curricular modules integrated with research in atmospheric ice nucleation, which is an important phenomenon potentially influencing global climate change. The primary goal of this work is to promote meaningful laboratory exercises to enhance the competence of students in the fields of science, technology, engineering, and math (STEM) by applying an appropriate methodology to laboratory ice nucleation measurements. To achieve this goal, three laboratory modules were developed with 18 STEM interns and tested by 28 students in a classroom setting. Students were trained to experimentally simulate atmospheric ice nucleation and cloud droplet freezing. For practical training, this work utilized a simple freezing assay device called the West Texas Cryogenic Refrigerator Applied to Freezing Test (WT-CRAFT) system. More specifically, students were provided with hands-on lessons to calibrate WT-CRAFT with deionized water and apply analytical techniques to understand the physicochemical properties of bulk water and droplet freezing. All procedures to implement the developed modules were typewritten during this process, and shareable read-ahead exploration materials were developed and compiled as a curricular product. Additionally, students conducted complementary analyses to identify possible catalysts of heterogeneous freezing in the water. The water analyses included: pH, conductivity, surface tension, and electron microscopy-energy-dispersive X-ray spectroscopy. During the data and image analysis process, students learned how to analyze droplet freezing spectra as a function of temperature, screen and interpret the data, perform uncertainty analyses, and estimate ice nucleation efficiency using computer programs. Based on the formal program assessment of learning outcomes and direct (yet deidentified) student feedback, we broadly achieved our goals to (1) improve their problem-solving skills by combining multidisciplinary science and math skills and (2) disseminate data and results with variability and uncertainty. The developed modules can be applied at any institute to advance undergraduate and graduate curricula in environmental science.

A Day in the Life: Characterization of Doctoral Bench Research in Synthetic Chemistry Using Phenomenological Case Studies

Despite decades of reform efforts, STEM education continues to face calls for improvement, especially regarding the teaching laboratory. Establishing an empirical understanding of the types of hands-on, psychomotor skills that students need to learn to succeed in downstream careers could help ensure laboratory courses are promoting authentic learning. Therefore, this paper reports phenomenological grounded theory case studies characterizing the nature of benchwork in synthetic organic chemistry graduate research. Through first-person video data and retrospective interviews, the results illustrate how organic chemistry students use psychomotor skills to conduct doctoral research and where they acquired those skills. By understanding the role that psychomotor skills play in authentic benchwork and the role that teaching laboratories play in the development of those skills, chemical educators could revolutionize undergraduate laboratory experiences by enabling evidence-based incorporation of the psychomotor component into laboratory learning objectives.

A Low-Cost and Simple Demonstration of Freezing Point Depression and Colligative Properties with Common Salts and Ice Cream

A laboratory activity was developed to teach freezing point depression and colligative properties to introductory-level chemistry students. The laboratory uses food-grade reagents and is delivered in two units that can be taught in a single 2 hour session or two separate sessions. The total cost of the consumables is 1 USD. In the first part of this two-part activity, students perform measurements on the properties of five salt solutions to better know and understand freezing point depression. In the second part of the activity, students apply their knowledge and understanding of freezing point depression to make ice cream. The ice-cream-making experiment is delivered as a group activity to encourage reflection. Centering this experiment on ice cream allows students to connect properties described in chemistry to everyday life. The solutions used in the experiment are reusable and nonhazardous. The experiment can be implemented in a classroom, in a teaching laboratory, or at home.

Necessity is the Mother of Invention: A Remote Molecular Bioinformatics Practical Course in the COVID-19 Era

The COVID-19 pandemic has brought many challenges to human beings, related to not only health and way of life but also teaching because of the interruption of the standard training at universities imposed by lockdowns. Concerning the latter, the academic community had to reinvent itself, in many ways, to carry on with prepandemic education. This article focuses on the use of modern technology and software to create a virtual, highly interactive classroom where a remote but still hands-on course on molecular bioinformatics can be taught, motivating the university students and helping them learn the course contents without significant compromises imposed by successive lockdowns. We implemented such a virtual hands-on molecular bioinformatics course in the second semester of the 2020/2021 academic year. Furthermore, we compared the learning outcomes with those for the earlier editions of the same course in the pre-COVID-19 era, in which the more traditional teaching method was used where all teaching was delivered with physically present lecturers. The virtual classroom proposed here allowed the students to develop skills close to, although slightly below, those obtained with physically present learning.

Human Salivary α-Amylase and Starch Digestion: A Simple and Inexpensive At-Home Laboratory Experience in Times of the COVID-19 Pandemic

The first case of coronavirus disease 2019 in Colombia was detected on March 6, 2020. Subsequently, schools, colleges, and universities were closed on March 26, which forced a massive migration to virtual education and impacted laboratory-based teaching courses. The teaching of biochemistry requires an experimental component that virtual laboratories cannot emulate. To address this concern, the article describes an at-home biochemistry laboratory experience that explores the hydrolysis of starch by α-amylase as a function of enzyme concentration, reaction time, and pH. The general success of the experience was assessed through the quality of information submitted through laboratory reports and feedback from students. A total of 19 laboratory reports were reviewed, and 50 students were surveyed. The analysis indicated that approximately 90% of students expressed favorable opinions about the experience. They understood the objective of the practice, identified the function of each material, and explained the relationship between the obtained results and concepts of enzyme activity presented in theoretical classes. Finally, the study concluded that the at-home laboratory experience is inexpensive and easy to perform outside the traditional laboratory. Furthermore, it enables a genuine practical experience with observations, data collection, analysis, and discussion of results, which meets the expectations for pharmaceutical chemistry students at the Universidad El Bosque in Bogotá, Colombia.

As Similar As Possible, As Different As Necessary - On-Site Laboratory Teaching during the COVID-19 Pandemic

Most of the available information on studying under the challenging conditions brought about by the COVID-19 pandemic emphasizes a variety of aspects on how to digitalize the whole teaching process. Thus, several useful and potentially game-changing strategies have been reported recently. In contrast to the digitalization of teaching, in this article, we focus on the reverse process: transitioning back to offline teaching, which is unavoidable especially for the acquisition of practical skills during chemistry studies. In this work, we describe our own experience acquired during the Organic Chemistry practical course at the University of Vienna, which was held in June 2020 and onwards. The article contains descriptions of precautions and measures that were taken, additional materials, and necessary changes made in order to safely continue on-site course teaching. We anticipate that this set of precautions can be used in an adapted fashion for any type of laboratory course. Further, we offer a critical analysis of students' and instructors' opinions concerning the changes and well-being during the course. Those opinions were collected via a detailed survey. From our experience, with careful planning and responsible behavior, a return to on-site education is possible and warmly welcomed by all involved participants. The detailed description of our course may also be useful for those who need to start a new organic laboratory course or want to improve an existing one.

LAB Theory, HLAB Pedagogy, and Review of Laboratory Learning in Chemistry during the COVID-19 Pandemic

The role and efficacy of the laboratory in chemical education have recently been a subject of renewed discussion as researchers are called upon to address the question of whether laboratory education lives up to expectations. The COVID-19 pandemic, which forced most of the global student population to temporarily adopt remote learning, offers an unparalleled case study to investigate types of outcomes resulting from a variety of adjustments made to laboratory education. This scoping review article focuses on the reports of laboratory learning in chemistry and closely related disciplines during COVID-19 to analyze the types of adjustments made to laboratory curricula and the immediate effect of these adjustments on students. The aggregated findings suggest that a lack of hands-on laboratory experience was detrimental to certain types of learning and engagement but that other types of learning were successfully achieved remotely. For researchers, departments, and university administrators, the differentiation in these findings could help inform the ongoing discussion about the future of laboratory education. For instructors and student support staff, the findings indicate potential areas of deficiency and strength for the COVID-19 student cohort going forward. Finally, a laboratory learning theory and pedagogy are proposed to guide the use of the laboratory in chemical education and potentially in other laboratory-based sciences as well.

Anaerobic digestion as a laboratory experiment for undergraduate biochemistry courses

Compared to aerobic catabolism, the theories and experiments of anaerobic catabolism are not covered in depth in biochemistry education curricula. Anaerobic digestion (AD) is a feasible method for converting common organic compounds to renewable energy-methane that has drawn a great deal of attention in practical applications. In this study, we designed an AD laboratory experiment for use in undergraduate biochemistry courses to supplement the knowledge of metabolic networks in biochemistry and extend the information presented in biochemistry textbooks. In this laboratory experiment, students explored the methane production performance of wheat straw (WS; a representative and commonly available agricultural waste) and mastered a reasonable method for utilizing this new biochemical reaction to convert organic wastes from renewable resources to methane. Basic experimental procedures, such as a biochemical methane potential (BMP) assay, data analysis, and graphic presentations were organized to provide students with abundant hands-on experience. Furthermore, calculations of significant parameters, such as total solids (TS), volatile solids (VS), experimental methane yield (EMY), maximum theoretical methane production (MMP), and biodegradability (B_D ), were also performed. From this AD experiment, students learned not only a new series of biochemical reactions but also a novel strategy to achieve cleaner methane production from organic wastes, exhibiting a positive impact for students' learning in biochemistry course.

Colorimetric Hydrogel from Natural Indicators: A Tool for Electrochemistry Education

The electrolysis of water is popular both as lab work and as a demonstration. In this activity, the electrolysis of water in the presence of a pH indicator is used to produce text and symbols. This report describes the design of an environmentally friendly setup of a writing board utilizing the electrolysis of water in a hydrogel environment. The activity can be performed by only using chemicals and materials that are easily accessible to everyone, with no special permit needed. The writing board has been developed mainly as an outreach activity for our faculty and has been assessed during visits from upper secondary school students.

The Building Blocks of Battery Technology: Using Modified Tower Block Game Sets to Explain and Aid the Understanding of Rechargeable Li-Ion Batteries

While Li-ion batteries are abundant in everyday life from smart phones to electric vehicles, there are a lack of educational resources that can explain their operation, particularly their rechargeable nature. It is also important that any such resource can be understood by a wide range of age groups and backgrounds. To this end, we describe how modified tower block games sets, such as Jenga, can be used to explain the operation of Li-ion batteries. The sets can also be utilized to explain more advanced topics such as battery degradation and challenges with charging these batteries at high rates. In order to make the resource more inclusive, we also illustrate modifications to prepare tactile tower block sets, so that the activity is also suitable for blind and partially sighted students. Feedback from a range of groups supports the conclusion that the tower block sets are a useful tool to explain Li-ion battery concepts.

Demonstrating Basic Properties and Application of Polarimetry Using a Self-Constructed Polarimeter

An easily constructed and inexpensive polarimeter with an optical rotation angle resolution of about 0.5° is presented. It is made from small pieces of polarizing film, 2 LEDs, a protractor, and a few wires, all held in place with plastic interlocking toy bricks, such as Lego bricks. The instrument was used to demonstrate the optical rotation of plane polarized light as a function of concentration, path length, temperature, and wavelength, and to determine enantiomeric excess in solutions of arabinose, the amount of limonene in citrus ski wax remover, and optical rotations of various types of honeys and essential oils. Results were comparable to values obtained on a commercial scientific instrument, and with literature values.

Plane and Frieze Symmetry Group Determination for Educational Purposes

Three-dimensional symmetry plays a crucial role in crystallography education. The educational process can be facilitated by introducing the analysis of friezes and plane patterns such as parquets before presenting more sophisticated crystal structures. Analysis of the symmetry of parquets can serve as an opportunity to follow the full routine of finding symmetry group symbols through incorporation of a two-step procedure involving the determination of Bravais lattice type. The aim of this paper is to provide a simple description of the analysis of Bravais lattices and pattern symmetry that can be used by students as well as crystallography educators. The procedure is also summarized in the form of comprehensive tree charts. This form is easy to use and popular with students. It may also aid in the retention of certain facts concerning crystallographic methodology. Examples of patterns in frieze and parquet forms were taken from the interiors of Kórnik Castle (Poland), which exhibit Moorish-style ornamentation including dichroic patterns and constitute an important locus of cultural heritage capable of strengthening students' motivation.

Experimenting with At-Home General Chemistry Laboratories During the COVID-19 Pandemic

During the COVID-19 pandemic, an at-home laboratory program was created and implemented for a section of the general chemistry course at the University of Southern California. The experiments were designed to only utilize safe household items and no special equipment. These laboratory activities, spanning over 4 weeks, focused on concepts usually covered in the final one-third of our second-semester chemistry laboratory, including pH, acid-base titrations, buffers, solubility, phase equilibria, and thermodynamics. In this article, we describe the design of the laboratories and our experience with this experiment, while also providing an assessment on how similar activities could be integrated profitably into a regular general chemistry course.

Valorization of Sour Milk to Form Bioplastics: Friend or Foe?

A demonstration was developed to introduce students to waste valorization in order to form bioplastics. Waste valorization is the process of reusing, recycling, or composting, from waste, useful products or sources of energy. In this demonstration, waste valorization is introduced by converting sour milk into a bioplastic via the addition of lemon juice upon heating. Utilizing lemon juice to perform the acidification offers a greener procedure than the traditional formaldehyde (used commercially to make galalith) and enhances the transferability in remote locations such as the Amazon Rainforest in comparison to vinegar. Students can establish connections to relevant United Nations Sustainable Development Goals (UN SDGs) by adopting a systems thinking approach. However, through this, it is noteworthy that this process is also used (particularly in the Indian subcontinent) to make paneer, a farmer cheese. While this also enables students to make a link to additional UN SDGs pertaining to "zero hunger", there is an ethical discussion to be had as to whether such a process that is utilized to feed malnourished citizens should be used to make a decorative bioplastic. As such, despite this demonstration being transferrable, instructors may consider carefully whether to utilize this resource, and, if so, to use this as an opportunity to teach the importance of ethics in science.

Lab-on-a-Chip: Frontier Science in the Classroom

Lab-on-a-chip technology is brought into the classroom through development of a lesson series with hands-on practicals. Students can discover the principles of microfluidics with different practicals covering laminar flow, micromixing, and droplet generation, as well as trapping and counting beads. A quite affordable novel production technique using scissor-cut and laser-cut lamination sheets is presented, which provides good insight into how scientific lab-on-a-chip devices are produced. In this way high school students can now produce lab-on-a-chip devices using lamination sheets and their own lab-on-a-chip design. We begin with a review of previous reports on the use of lab-on-a-chip technology in classrooms, followed by an overview of the practicals and projects we have developed with student safety in mind. We conclude with an educational scenario and some initial promising results for student learning outcomes.

Show Yourself, Asparaginase: An Enzymatic Reaction Explained through a Hands-On Interactive Activity

Determining the catalytic activity of an enzyme can be the perfect method for its identification, for example during purification procedures or for isolation purposes. Herein, we used a pharmaceutically relevant protein to bring the concept of enzymatic activity to the classroom. We designed a hands-on interactive activity in which a medically relevant enzyme, asparaginase, was distinguished from a nonenzymatic protein based on its specific enzymatic activity. The experiment was carried out in the classroom, designed to impact different educational levels from elementary to high school. Our main purposes were to promote the emerging field of protein-based drugs as a source of scientific careers in bionanotechnology and to show the students an image of a "scientist" as that of a common and educated person working in an exciting profession. In addition of being inexpensive, this activity proved to be adaptable for various educational levels and can be easily implemented in different scenarios, for example, scientific fairs, some schools, and so forth.

Adenine Synthesis in a Model Prebiotic Reaction: Connecting Origin of Life Chemistry with Biology

Many high school laboratory experiments demonstrate concepts related to biological evolution, but few exist that allow students to investigate life's chemical origins. This series of laboratory experiments has been developed to allow students to explore and appreciate the deep connection that exists between prebiotic chemistry, chemical evolution, and contemporary biological systems. In the first experiment of the series, students synthesize adenine, one of the purine nucleobases of DNA and RNA, from plausibly prebiotic precursor molecules. Students compare their product to authentic standards using thin-layer chromatography. The second and third experiments of the series allow students to extract DNA from a familiar organism, the strawberry, and hydrolyze it, releasing adenine, which they can then compare to the previously chemically-synthesized adenine. A fourth, optional experiment is included where the technique of thin-layer chromatography is introduced and chromatographic skills are developed for use in the other three experiments that comprise this series. Concepts relating to organic and analytical chemistry, as well as biochemistry and DNA structure, are incorporated throughout, allowing this series of laboratory experiments to be easily inserted into existing laboratory courses and to reinforce concepts already included in any high school chemistry or biology curriculum.

Enzymatic Resolution of 1-Phenylethanol and Formation of a Diastereomer: An Undergraduate H NMR Experiment To Introduce Chiral Chemistry

This organic laboratory experiment introduces students to stereoselective enzyme reactions, resolution of enantiomers, and NMR analysis of diastereomers. The reaction between racemic 1-phenylethanol and vinyl acetate in hexane to form an ester is catalyzed by acylase I. The unreacted alcohol is then treated with a chiral acid and the resulting ester diastereomer is analyzed by NMR. This experiment is suitable for group work in the laboratory as several diastereomers are synthesized and compared to determine which enantiomer of 1-phenylethanol reacts with the enzyme.

Visualizing Fluorescence: Using a Homemade Fluorescence "Microscope" to View Latent Fingerprints on Paper

We describe an inexpensive handheld fluorescence imager (low-magnification microscope), constructed from poly(vinyl chloride) pipe and other inexpensive components for use as a teaching tool to understand the principles of fluorescence detection. Optical filters are used to select the excitation and emission wavelengths and can be easily interchanged to accommodate different fluorescent samples. As a demonstration, we used the fluorescence imager to view lawsone-dyed fingerprints on paper, which fluoresce red when illuminated with green light. This emission can be seen by viewing the sample through the instrument by eye, or the fluorescence can be captured by a camera. The entire imager can be built for less than $300.

Surface Plasmon Resonance: An Introduction to a Surface Spectroscopy Technique

Surface plasmon resonance (SPR) has become an important optical biosensing technology in the areas of biochemistry, biology, and medical sciences because of its real-time, label-free, and noninvasive nature. The high cost of commercial devices and consumables has prevented SPR from being introduced in the undergraduate laboratory. Here we present an affordable homemade SPR device with all of its components accessible to visualization. This design allows ease of integration with electrochemistry and makes the device suitable for education. We describe a laboratory experiment in which students examine the relationship between the SPR angle and the solution refractive index at the interface and perform a coupled SPR-electrochemistry experiment. Students also study the antibody-antigen binding activity. Most of the experimental work was done as a project by a grade 12 high-school student under proper supervision. We believe that the SPR device and the SPR laboratory will enhance undergraduate chemical education by introducing students to this important modern instrumentation and will help students to learn and understand the molecular interactions occurring at interfaces.

Photoacoustic Experimental System To Confirm Infrared Absorption Due to Greenhouse Gases

An experimental system for detecting infrared absorption using the photoacoustic (PA) effect is described. It is aimed for use at high-school level to illustrate the difference in infrared (IR) absorption among the gases contained in the atmosphere in connection with the greenhouse effect. The experimental system can be built with readily available components and is suitable for small-group experiments. The PA signal from a greenhouse gas (GHG), such as CO(2), H(2)O, and CH(4), can be detected down to a concentration of 0.1%. Since the basic theory of the PA effect in gases due to IR absorption is straightforward, the experiments with this PA system are accessible to students. It can be shown that there is a significant difference in IR absorption between GHGs and the major components of the atmosphere, N(2), O(2), and Ar, which helps students understand that the minor components, that is, the GHGs, determine the IR absorptivity of the atmosphere.