The green engine of life, revealed.
Imagine being able to unravel one of nature's most perfect processes—the magical ability of plants to capture sunlight and transform it into life-sustaining energy. This is exactly what Alexander Abramovich Krasnovsky, one of the greatest photobiochemists of the 20th century, dedicated his life to understanding.
His simple yet brilliant experiments illuminated the hidden chemical dance of photosynthesis, forever changing how science perceives the conversion of light into life 1 .
Alexander Abramovich Krasnovsky (1913–1993) was a pioneering intellectual whose curiosity about chlorophyll photochemistry placed him consistently ahead of his time 1 . Born in Odessa on August 26, 1913, his family moved to Moscow in 1921, where his scientific journey began 1 . He started working at a chemical factory in 1931 while pursuing his education, eventually graduating from the Moscow Institute of Chemical Technology in 1937 and earning his Ph.D. in 1940 1 .
From 1944 until his passing, Krasnovsky worked at the A.N. Bach Institute of Biochemistry of the USSR Academy of Sciences (now Russian Academy of Sciences), for a long time serving as the head of the Laboratory of Photobiochemistry 1 .
He was elected a corresponding member of the USSR Academy of Sciences in 1962 and later became a full member 1 . For 40 years, he also served as a professor at Moscow State University, where he attracted and nurtured talented young minds, creating what became known as the "Krasnovsky school" of photobiochemistry 1 .
Born in Odessa on August 26
Graduated from Moscow Institute of Chemical Technology
Obtained Ph.D. in Chemistry
Began work at Bach Institute of Biochemistry
Discovered the "Krasnovsky Reaction"
Elected corresponding member of USSR Academy of Sciences
Passed away on May 16
To appreciate Krasnovsky's contributions, we must first understand the fundamental mystery he sought to solve. Photosynthesis is the remarkable process where plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into carbohydrates and oxygen. For centuries, scientists knew that it happened, but the precise molecular mechanics—how chlorophyll actually managed to harness light energy—remained shrouded in mystery.
Before Krasnovsky's work, it was known that light energy triggered redox reactions in chlorophyll molecules, but the mechanism was completely unclear 1 . The scientific community lacked the experimental evidence to explain the primary steps of this vital process.
Krasnovsky was a primary initiator of photochemical studies of photosynthesis in Russia and one of the major pioneers of the idea that only by using physical and chemical methods could one truly elucidate the principles of light energy conversion in photosynthesis 1 .
Chlorophyll captures sunlight energy
Water molecules are split into oxygen, protons and electrons
Light energy converts to chemical energy (ATP, NADPH)
CO₂ is converted into carbohydrates
In 1948, Krasnovsky made the discovery that would cement his legacy in the annals of science—the phenomenon now universally known as the "Krasnovsky Reaction." 1
His groundbreaking experiment was elegant in its design and profound in its implications. He demonstrated that chlorophyll, when dissolved in a pyridine solution with ascorbic acid (vitamin C) as an electron donor, could be reversibly photoreduced 1 .
When he shone light onto the mixture, he observed the chlorophyll solution change color, with the formation of an intermediate product that absorbed light in the green region of the spectrum—what he descriptively called "pink chlorophyll" 1 .
Most remarkably, this reaction was reversible. In the dark, the reduced "pink" form would regenerate the original green chlorophyll 1 . This was the first experimental evidence showing that chlorophyll could participate in reversible photochemical redox reactions—exactly the type of behavior required for its role in the photosynthetic electron transport chain.
Procedure: Dissolved chlorophyll in pyridine solvent with ascorbic acid
Observation: Creation of a green solution
Significance: Established a controlled experimental system
Procedure: Exposed the solution to light
Observation: Color changed to pink ("pink chlorophyll")
Significance: Demonstrated photoreduction of chlorophyll
Procedure: Placed the pink solution in darkness
Observation: Color returned to green
Significance: Proved the reaction was reversible
Procedure: Repeated with related pigments (bacteriochlorophyll, pheophytin)
Observation: Similar reversible reactions observed
Significance: Showed phenomenon was fundamental to chlorophyll-type molecules
Krasnovsky's pioneering work relied on both conceptual brilliance and specific laboratory tools. The following "research reagents" were essential to his landmark discovery and continued investigations.
| Tool/Reagent | Function in Experiments |
|---|---|
| Chlorophyll & Analogues | The primary photosensitive pigment under study; its behavior in different states was the core research focus |
| Ascorbic Acid | Served as an electron donor in the classic reaction, facilitating the reduction of chlorophyll |
| Pyridine Solvent | Provided a suitable medium for dissolving chlorophyll and observing its photochemical behavior |
| Semiconductors (e.g., TiO₂) | Used in constructing models of photosynthetic reactions to understand light energy conversion principles |
| Bacterial Hydrogenase | Enzyme used in systems demonstrating light-induced production of molecular hydrogen |
| Low-Temperature Spectroscopy | Technique employed to study long-wavelength fluorescence and identify different chlorophyll forms |
Krasnovsky's methodology combined chemical analysis with physical measurement techniques:
Key Insight: By isolating chlorophyll from the complex cellular environment, Krasnovsky could study its fundamental photochemical properties without interference from other cellular components.
The impact of Krasnovsky's 1948 discovery rippled far beyond that initial observation. It formed the foundation for decades of subsequent research that would further decode the secrets of photosynthesis.
His work established that chlorophyll wasn't merely a passive light-harvesting antenna but an active participant in electron transport, serving as both donor and acceptor in photochemical reactions 1 .
This fundamental understanding helped pave the way for the monumental discoveries of the 1955-1965 period, which brought a revolution in photosynthetic thinking—including the Emerson Enhancement Effect, the concept of two light reactions, and the famous Z-scheme of photosynthesis 1 .
Krasnovsky and his colleagues made further crucial contributions by identifying the primary electron acceptors in different photosynthetic systems:
He also pioneered the idea that chlorophyll aggregation controls the formation of different chlorophyll forms in chloroplasts, helping explain the red shift and fluorescence quenching observed in living systems 1 .
Alexander Krasnovsky passed away on May 16, 1993, but his scientific legacy continues to illuminate the path for new generations of researchers 1 . He was remembered not only for his scientific brilliance but for his humanity—his love for painting, his knowledge of arts and literature, his humor, kindness, and patience 1 . Colleagues noted he had "a rare talent as a researcher, and lived his life mainly for science and in science" 1 .
In October 2013, the international scientific community gathered at the Russian Academy of Sciences for an conference titled "Photobiochemistry: Problems and Perspectives" to honor the 100th anniversary of his birth—a testament to his enduring influence 1 .
From that first observation of "pink chlorophyll" to our modern understanding of the photosynthetic reaction centers, Krasnovsky's work exemplifies how a simple, elegant experiment can transform our understanding of nature's most essential processes. He showed us that within the green leaves of plants lies not just the secret of life, but a sophisticated photochemical machinery that hums quietly under the sun, day after day.
Soviet Photobiochemist
Pioneer of chlorophyll photochemistry research
First demonstration of reversible photoreduction of chlorophyll in vitro, providing crucial evidence for understanding the primary steps of photosynthesis.