Chemistry · 9th Grade · Solutions and Acid-Base Chemistry · Weeks 28-36

Chemistry in Medicine: Drug Discovery

Students will investigate the role of chemistry in the discovery, design, and synthesis of pharmaceutical drugs.

• Common Core State Standards
• HS-LS1-6
• HS-PS1-2

About This Topic

Buffers and blood chemistry explore how certain systems can resist changes in pH when small amounts of acid or base are added. Students learn that a buffer is a mixture of a weak acid and its conjugate base, and they investigate how this 'chemical sponge' maintains stability. This topic is an essential application of HS-PS1-6 and HS-LS1-3, linking chemistry to human physiology and environmental health.

This unit is vital for understanding how our blood maintains a narrow pH range (around 7.4) to keep us alive. Students also explore the impact of ocean acidification, where the ocean's natural buffer system is being overwhelmed by excess CO2. This topic comes alive when students can test 'buffer capacity' in the lab or use simulations to see how buffers respond to 'acidic stress.'

Key Questions

1. Explain the chemical principles involved in drug-receptor interactions.
2. Analyze the stages of drug discovery and development from a chemical perspective.
3. Evaluate the ethical considerations in pharmaceutical research and development.

Learning Objectives

• Explain the chemical basis for drug-receptor binding using principles of intermolecular forces.
• Analyze the sequential steps in drug discovery, from target identification to preclinical testing.
• Evaluate the role of medicinal chemistry in modifying drug properties like solubility and bioavailability.
• Design a hypothetical synthesis pathway for a simple drug molecule, considering reaction conditions and reagents.
• Critique the ethical implications of clinical trials and drug pricing in pharmaceutical development.

Before You Start

Introduction to Organic Chemistry: Functional Groups

Why: Students need to recognize common organic functional groups to understand how they contribute to drug structure and reactivity.

Chemical Bonding and Intermolecular Forces

Why: Understanding the types of bonds and forces between molecules is crucial for explaining drug-receptor interactions.

Stoichiometry and Reaction Yields

Why: This knowledge is foundational for understanding the synthesis and purification of drug compounds.

Key Vocabulary

Pharmacophore	The specific arrangement of atoms and functional groups in a molecule that is responsible for its biological activity and interaction with a target.
Bioavailability	The fraction of an administered drug dose that reaches the systemic circulation unchanged, influencing its therapeutic effect.
Drug Target	A molecule, typically a protein or nucleic acid, that a drug binds to in order to produce its therapeutic effect or to block a harmful process.
Lead Compound	A molecule that shows promising activity against a drug target and serves as the starting point for further chemical modification and optimization.
Structure-Activity Relationship (SAR)	The relationship between the chemical structure of a molecule and its biological activity, used to guide the design of new drugs.

Watch Out for These Misconceptions

Common Misconception

Students often think that a buffer keeps the pH at exactly 7.

What to Teach Instead

Explain that a buffer can be designed to maintain *any* constant pH, whether it's acidic, basic, or neutral. Peer discussion about 'specialized buffers' for different parts of the body (like the stomach vs. blood) can help clarify this.

Common Misconception

Students may believe that a buffer can neutralize an infinite amount of acid.

What to Teach Instead

Clarify the concept of 'buffer capacity', once all the conjugate base is used up, the buffer fails. A 'stress test' lab where students add acid until the buffer 'breaks' helps them visualize this limit.

Active Learning Ideas

Inquiry Circle: The Buffer Challenge

Groups are given a beaker of plain water and a beaker of a buffer solution. They add drops of strong acid to both and record the pH change. They must work together to explain why the buffer's pH stayed stable while the water's pH crashed.

45 min·Small Groups

Think-Pair-Share: Blood pH and Breathing

Students are asked what happens to their blood pH when they hold their breath (increasing CO2). They discuss in pairs how the body's bicarbonate buffer system responds and why 'hyperventilating' has the opposite effect.

25 min·Pairs

Simulation Game: Ocean Acidification

Using a digital simulation, students increase the CO2 levels in a virtual ocean and observe the effect on pH and the health of coral reefs. They must identify the 'tipping point' where the ocean's natural buffers can no longer keep up.

40 min·Pairs

Real-World Connections

• Medicinal chemists at pharmaceutical companies like Pfizer and Merck use computational modeling and organic synthesis to design new antiviral medications, aiming to inhibit viral replication by targeting specific viral enzymes.
• Researchers at the National Institutes of Health (NIH) investigate novel drug delivery systems, such as nanoparticles, to improve the targeted delivery of cancer therapeutics, minimizing side effects for patients undergoing chemotherapy.
• The development of statins, like Lipitor, involved extensive medicinal chemistry to optimize compounds that inhibit HMG-CoA reductase, a key enzyme in cholesterol synthesis, significantly reducing cardiovascular disease risk.

Assessment Ideas

Discussion Prompt

Pose the question: 'Imagine you are a medicinal chemist tasked with designing a new pain reliever. What specific chemical properties would you aim to optimize in your lead compound, and why?' Encourage students to reference concepts like receptor binding and bioavailability.

Quick Check

Provide students with a diagram of a simple drug molecule and its receptor. Ask them to identify at least two types of intermolecular forces that could be involved in their binding and explain how modifying a specific functional group might affect this interaction.

Exit Ticket

Students write down the three main stages of drug discovery (e.g., discovery, preclinical, clinical) and provide one chemical challenge associated with each stage. For example, a challenge in discovery might be identifying a suitable drug target.

Frequently Asked Questions

What is a buffer and how does it work?

A buffer is a solution that resists changes in pH when small amounts of an acid or a base are added. It usually consists of a mixture of a weak acid and its conjugate base. The weak acid can neutralize added bases, while the conjugate base can neutralize added acids, keeping the overall pH stable.

Why is blood pH so important?

Human blood must stay within a very narrow pH range of 7.35 to 7.45. If the pH moves outside this range, even slightly, it can interfere with the shape and function of proteins and enzymes, leading to serious health problems or death. The body uses the bicarbonate buffer system to maintain this balance.

What is 'buffer capacity'?

Buffer capacity is the amount of acid or base that a buffer solution can neutralize before its pH begins to change significantly. It depends on the concentrations of the buffer components; a more concentrated buffer will have a higher capacity to resist pH changes than a dilute one.

How can active learning help students understand buffers?

Active learning, like 'The Buffer Challenge,' allows students to witness the 'magic' of pH stability. When they see a buffer 'absorb' acid without changing color or pH, it challenges their expectation that adding acid always makes things more acidic. This inquiry-based approach makes the complex chemistry of conjugate pairs feel like a necessary explanation for a remarkable physical event.