Quantum Phenomena in Molecular and Biological Systems: A Decoherence-Based Decision Framework With Falsifiable Predictions and a Failure-Mode Taxonomy

Abstract

This review introduces a quantitative decision-making framework based on the Lindblad master equation and the formalism of open quantum systems. This framework facilitates the identification of phenomena within molecular and biological systems that require explicit quantum-mechanical analysis beyond classical approximations. It does not merely reiterate that quantum mechanics underpins all chemical processes; rather, this principle serves as a foundational premise rather than an original contribution. The significant contribution consists of a set of operational criteria derived from decoherence timescales, conditions for Markovian validity, boundaries of the computational domain, and requirements for experimental falsifiability. These criteria enable physicists or physical chemists to assess, for any molecular system and quantum hypothesis, whether the hypothesis is supported by evidence, remains speculative, or can be falsified through targeted experimentation. Three quantitative deliverables implement this framework. First, the τ_dec > τ_func condition is derived from the Lindblad formalism and applied numerically to each class of biological quantum phenomenon: enzyme hydrogen tunneling satisfies the condition by approximately one order of magnitude (τ_transit ≈ 0.1 femtoseconds vs. τ_dec ≈ 1 femtosecond in a hydrophobic active site); the radical pair mechanism satisfies it by one to fourteen times (τ_dec 1 to 10 microseconds vs. τ_func ≈ 710 nanoseconds at geomagnetic field strength); photosynthetic electronic coherence operates in the non-Markovian regime where the Lindblad equation fails and the τ_dec/τ_func ratio is marginal. Second, a failure-mode taxonomy is defined in Section 2 as the primary methodological tool: five criteria and a set of operationally testable red flags, applied as a running template to every phenomenon section throughout the review. Third, specific quantitative predictions are derived for each contested phenomenon, stating the observable, the predicted effect magnitude, and the control experiment distinguishing quantum from classical mechanisms. Quantum chemistry methods, including Density Functional Theory (DFT), Quantum Mechanics/Molecular Mechanics (QM/MM), and Fragment Molecular Orbital (FMO) techniques, are assessed within their rigorously validated accuracy domains. The approximately 1 kcal/mol accuracy of hybrid DFT applies to closed-shell main-group organic systems but does not extend to transition-metal complexes, open-shell species, or a broad range of pharmaceutical chemicals without explicit benchmarking. This limitation is consistently applied throughout the review and is not relaxed in discussions of applications. Kinetic isotope effects that surpass the zero-point-energy-corrected semiclassical limit of approximately 6.9 at 298 K exemplify nuclear tunneling phenomena in enzymatic catalysis. In drug design, deuterium isotope substitution exploits this effect through empirical substitution strategies rather than quantum tunneling calculations; these contributions are distinct and should not be conflated. Quantum computing satisfies the τ_dec > τ_func condition at the single-gate level but fails to meet the requirements at the circuit depth necessary for fault-tolerant molecular simulation without error correction.