Enzymatic Alcohol Oxidation Research Articles

Aminoxyl Catalyzed Electrochemical Ethanol Detection: Development of a New Breathalyzer Using Molecular Catalysis

Blood alcohol concentration (BAC) is the indicator of alcohol intoxication, and its measurement has emerged as the most common analytical procedure requested by law enforcement. Due to its volatility, ethanol vapor can be detected in breath, and its vapor concentration is proportional to BAC. Currently available instrumentation used for breath alcohol content (BrAC) analysis include gas chromatography (GC) and GC coupled with mass spectrometry, infrared (IR) spectroscopy, and fuel cell based electrochemical sensors. GC and IR spectroscopy devices have some drawbacks such as size, initial cost, and operational expense. Electrochemical sensors are capable of miniaturization and are available as portable and handheld breathalyzers. However, the lack of a single use and disposable sensing element, resulting memory effect and the need for frequent recalibration is the main drawback of currently available electrochemical breathalyzers. There have been few attempts at designing a sensing element to improve the current methods of alcohol detection by electrochemical techniques, all relying on enzymatic alcohol oxidation.1 Herein, we report a proof-of-concept non-enzymatic breathalyzer, harnessing the unique catalytic activity of the aminoxyl radical/oxoammonium redox couple toward alcohol oxidation.2 The relatively low redox potentials of aminoxyls, the mild conditions required for use, and their selective interactions with ethanol are their advantages compared to currently available Pt based breathalyzers. Our functional sensing element consists of a screen-printed electrode in which the graphene oxide-based working electrode is modified with aminoxyl derivatives, of which 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl benzoate (TMB) was the most efficient derivative. Exposing this modified electrode to simulated breath that contains ethanol, while applying the required potential for oxidation of the aminoxyl radical, generates an electrocatalytic current proportional to the ethanol concentration in the breath. These simple, sensitive, durable, and inexpensive electrodes may contribute to the development of a single-use reliable ethanol sensor for personal or law enforcement applications. Heikenfeld, J.; Jajack, A.; Rogers, J.; Gutruf, P.; Tian, L.; Pan, T.; Li, R.; Khine, M.; Kim, J.; Wang, J.; Kim, J. Wearable Sensors: Modalities, Challenges, and Prospects. Lab Chip 2018, 18, 217.Nutting, J. E.; Rafiee, M.; Stahl, S. S. Tetramethylpiperidine N-Oxyl (TEMPO), Phthalimide N-Oxyl (PINO), and Related N-Oxyl Species: Electrochemical Properties and Their Use in Electrocatalytic Reactions. Chem. Rev. 2018, 118, 4834.

Lanthanide Chemistry: From Coordination in Chemical Complexes Shaping Our Technology to Coordination in Enzymes Shaping Bacterial Metabolism

Lanthanide chemistry has only been extensively studied for the last 2 decades, when it was recognized that these elements have unusual chemical characteristics including fluorescent and potent magnetic properties because of their unique 4f electrons.1,2 Chemists are rapidly and efficiently integrating lanthanides into numerous compounds and materials for sophisticated applications. In fact, lanthanides are often referred to as "the seeds of technology" because they are essential for many technological devices including smartphones, computers, solar cells, batteries, wind turbines, lasers, and optical glasses.3-6 However, the effect of lanthanides on biological systems has been understudied. Although displacement of Ca2+ by lanthanides in tissues and enzymes has long been observed,7 only a few recent studies suggest a biological role for lanthanides based on their stimulatory properties toward some plants and bacteria.8,9 Also, it was not until 2011 that the first biochemical evidence for lanthanides as inherent metals in bacterial enzymes was published.10 This forum provides an overview of the classical and current aspects of lanthanide coordination chemistry employed in the development of technology along with the biological role of lanthanides in alcohol oxidation. The construction of lanthanide-organic frameworks will be described. Examples of how the luminescence field is rapidly evolving as more information about lanthanide-metal emissions is obtained will be highlighted, including biological imaging and telecommunications.11 Recent breakthroughs and observations from different exciting areas linked to the coordination chemistry of lanthanides that will be mentioned in this forum include the synthesis of (i) macrocyclic ligands, (ii) antenna molecules, (iii) coordination polymers, particularly nanoparticles, (iv) hybrid materials, and (v) lanthanide fuel cells. Further, the role of lanthanides in bacterial metabolism will be discussed, highlighting the discovery that lanthanides are cofactors in biology, particularly in the enzymatic oxidation of alcohols. Finally, new and developing chemical and biological lanthanide mining and recycling extraction processes will be introduced.

A Critical Test of the “Tunneling and Coupled Motion” Concept in Enzymatic Alcohol Oxidation

The physical mechanism of C-H bond activation by enzymes is the subject of intense study, and we have tested the predictions of two competing models for C-H activation in the context of alcohol dehydrogenase. The kinetic isotope effects (KIEs) in this enzyme have previously suggested a model of quantum mechanical tunneling and coupled motion of primary (1°) and secondary (2°) hydrogens. Here we measure the 2° H/T KIEs with both H and D at the 1° position and find that the 2° KIE is significantly deflated with D-transfer, consistent with the predictions of recent Marcus-like models of H-transfer. The results suggest that the fast dynamics of H-tunneling result in a 1° isotope effect on the structure of the tunneling ready state: the trajectory of D-transfer goes through a shorter donor-acceptor distance than that of H-transfer.

Acetaldehyde emission from wood induced by the addition of ethanol

A mechanism of acetaldehyde emission from wood induced by the addition of ethanol was proposed. It is known that acetaldehyde generation is due to the oxidation of ethanol via a metabolic process involving alcohol dehydrogenase (ADH) in living bodies. However, it remains unclear whether the enzymatic alcohol oxidation is applicable to wood. We investigated possible factors of wood parts, conditioning, storage sites, and heating and sterilization treatments on acetaldehyde emission using the syringe method and HPLC analysis. We reconfirmed that acetaldehyde emission was observed only when ethanol was added to wood. Greater acetaldehyde emissions were obtained in heartwood compared to sapwood in both Japanese cedar (Cryptomeria japonica D. Don) and Japanese cypress (Chamaecyparis obtusa Endl.) specimens. In addition, an acetaldehyde conversion rate of 1–2 mol% was determined in green cedar heartwood samples, while, conversely, air-dried cedar heartwood samples showed 4–5 mol%. Ethylene oxide gas sterilization had the effect of decreasing acetaldehyde emission on air-dried wood, but not on green wood. Autoclave sterilization could completely prevent acetaldehyde emissions from both green and air-dried wood. These results suggested that an original ADH in wood and an attached ADH from the outside via microorganisms onto wood were assumed to be the primary causes of acetaldehyde emissions from wood induced by the addition of ethanol.