Chapter 1: Human Activity, Chemical Reactivity

Because atoms and molecules are invisible to the naked eye, chemists employ sophisticated analytical techniques such as spectroscopy, which examines how electromagnetic radiation interacts with matter to reveal molecular identity, and chromatography, which separates complex chemical mixtures into individual components. The chapter illustrates these methodologies through two landmark scientific investigations. David Dolphin's research team exploited the chemical properties of oxygen to develop photodynamic therapy, a medical treatment that leverages the high reactivity of singlet oxygen, an excited state of the oxygen molecule, to destroy diseased cells. By using porphyrin molecules as light-absorbing sensitizers, Dolphin's group converted ground-state oxygen into its toxic singlet form when activated by laser light, ultimately creating Visudyne, a pharmaceutical that has restored vision to over one million patients with age-related macular degeneration. The second investigation, conducted by chemist Gavin Flematti, identified karikinolide as the active compound in wood smoke that triggers seed germination after forest fires. Through repeated chromatographic separation and bioassay testing, Flematti isolated a previously unknown molecule and used mass spectrometry and nuclear magnetic resonance spectroscopy to determine its molecular structure, then synthesized it in the laboratory to confirm his findings. Remarkably, Flematti's subsequent research revealed that another smoke-derived compound, glyceronitrile, which decomposes to release cyanide ions, also promotes germination in certain plants, demonstrating that substances conventionally considered harmful can provide significant ecological benefits at minute concentrations. The chapter concludes by connecting laboratory chemistry to everyday observations, from atmospheric auroras to neon lighting, and challenges the misconception that natural substances are inherently safe while synthetic chemicals are inherently dangerous, emphasizing instead that informed chemical knowledge enables solutions to complex global challenges.