Decarboxylation Of Acids Research Articles

Stability Increase of Phenolic Acid Decarboxylase by a Combination of Protein and Solvent Engineering Unlocks Applications at Elevated Temperatures.

Enzymatic decarboxylation of biobased hydroxycinnamic acids gives access to phenolic styrenes for adhesive production. Phenolic acid decarboxylases are proficient enzymes that have been applied in aqueous systems, organic solvents, biphasic systems, and deep eutectic solvents, which makes stability a key feature. Stabilization of the enzyme would increase the total turnover number and thus reduce the energy consumption and waste accumulation associated with biocatalyst production. In this study, we used ancestral sequence reconstruction to generate thermostable decarboxylases. Investigation of a set of 16 ancestors resulted in the identification of a variant with an unfolding temperature of 78.1 °C and a half-life time of 45 h at 60 °C. Crystal structures were determined for three selected ancestors. Structural attributes were calculated to fit different regression models for predicting the thermal stability of variants that have not yet been experimentally explored. The models rely on hydrophobic clusters, salt bridges, hydrogen bonds, and surface properties and can identify more stable proteins out of a pool of candidates. Further stabilization was achieved by the application of mixtures of natural deep eutectic solvents and buffers. Our approach is a straightforward option for enhancing the industrial application of the decarboxylation process.

Computational study of the solvation effect of supercritical water on o-phthalic acid decarboxylation by varying the solvent dielectric constant

This study investigates the solvation effect on the decarboxylation of o-phthalic acid using quantum calculations with a continuum solvation model with varying dielectric constants. Two mechanisms were considered: with and without a catalytic water molecule. The latter had a lower reaction barrier. Increasing the dielectric constant facilitates the hydrogen transfer but impedes C–C bond breaking in both mechanisms. The change in the free energies due to solvation of the transition state is generally greater than the reactant. The reaction barrier predominantly increased with the dielectric constant in both mechanisms. The Kirkwood slope estimated by plotting estimated rate constants against the Kirkwood polarity parameter, (ε−1)/(2ε+1), was close to the experimental value (only for the assisted mechanism). The simulations indicate that the solvation effect on the decarboxylation rate can be elucidated by considering the effect of dielectric constant of supercritical water.

Gypsum-derived CaO catalytic pyrolysis of palm oil in a continuously packed bed reactor

This study employed a Gypsum-derived CaO catalyst with 10 wt% MgCO3 to convert palm oil into biofuel via pyrolysis in a continuous packed-bed reactor at atmospheric pressure without purge gas. The reaction occurred within the 500–550 °C temperature range, with varying catalyst calcination temperatures. ASTM D86 distillation to separate the pyrolytic oil into biogasoline (75–150 °C), biokerosene (150–250 °C), and biodiesel (250–330 °C) was conducted. The physical and chemical properties of products and catalysts using various techniques were determined. Notably, calcination temperature changes minimally affected the final oxygen content in the product but significantly influenced the textural properties of the catalyst. At a reaction temperature of 525 °C, the 10% MgCO3 catalyst calcined at 850 °C yielded the highest volume of distilled product distilled from pyrolytic oil, accounting for 100% of pyrolytic oil (equivalent to 66.44 vol% of palm oil). It implies that 100% of pyrolytic oil could be converted to distilled oil completely by the distillation process. The primary constituents of the pyrolytic oil were aliphatic and olefinic compounds, with a notable presence of ketones, mainly in the C5 to C33 range. C17 ketones were prominent, constituting approximately 5 wt% of the pyrolytic oil (equivalent to 2.92 wt% of palm oil). These ketones likely resulted from the decarboxylation of carboxylic acids and aldol condensation reactions facilitated by CaO or MgO catalysts. CaO decarboxylation was confirmed by the presence of CaCO3 in the spent catalyst. Additionally, the pyrolytic oil exhibited an acidity of approximately 5.72 mg KOH/g, primarily attributed to phenolic compounds, confirmed through GCxGC-FID, GCxGC-TOFMS, and 1H NMR spectroscopy.

Oxidative decarboxylation of arylacetic acids and arylacetic esters with singlet molecular oxygen generated from trans-5-hydroperoxy-3,5-dimethyl-1,2-dioxolan-3-yl ethaneperoxate

Oxidative decarboxylation of arylacetic acids and arylacetic esters with singlet molecular oxygen generated from trans-5-hydroperoxy-3,5-dimethyl-1,2-dioxolan-3-yl ethaneperoxate

High-Concentration Alkane Output via In Situ Thermal-Assisted Photocatalytic Decarboxylation of Biomass-Derived Fatty Acid

High-Concentration Alkane Output via In Situ Thermal-Assisted Photocatalytic Decarboxylation of Biomass-Derived Fatty Acid

Photomediated Hydro(deutero)acylation of Olefins by Decarboxylative Addition of α-Oxocarboxylic Acids.

Acyl radicals have been generated from the decarboxylation of α-oxocarboxylic acids by using a readily accessible organic pyrimidopteridine photoredox catalyst under ultraviolet-A (UV-A) light irradiation. These reactive acyl radicals were smoothly added to olefins such as styrenes and diverse Michael acceptors, with the assistance of H2O/D2O as hydrogen donors, enabling easy access to a diverse range of ketones/β-deuterio ketones. A wide range of α-oxocarboxylic acids are compatible with this reaction, which shows a reliable, atom-economical, and eco-friendly protocol. Furthermore, postsynthetic diversifications and applications are presented.

Direct Photoreforming of Real-World Polylactic Acid Plastics into Highly Selective Value-Added Pyruvic Acid under Visible Light.

Although polylactic acid (PLA) represents a pivotal biodegradable polymer, its biodegradability has inadvertently overshadowed the development of effective recycling techniques, leading to the potential wastage of carbon resources. The photoreforming-recycling approach for PLA exhibits significant potential in terms of concepts and methods. However, the reaction faces enormous challenges due to the limited selectivity of organic oxidation products as well as the increased costs and challenging separation of organic products associated with alkali-solution-assisted prehydrolysis. Herein, we report an alkali-free direct-photoreforming pathway for real-world PLA plastics utilizing the Pd-CdS photocatalyst under visible-light illumination, obviating the need for chemical pretreatment of PLA. The devised pathway successfully produces H2 at a rate of 49.8 μmol gcat.-1 h-1, sustained over 100 h, and exhibits remarkable selectivity toward pyruvic acid (95.9% in liquid products). Additionally, experimental findings elucidate that Pd sites not only function as a typical cocatalyst for enhancing the photocatalytic evolution of H2 but also suppress competitive side reactions (e.g., lactic acid coupling or decarboxylation), consequently augmenting the yield and selectivity of pyruvic acid and H2. This investigation provides a straightforward and sustainable direct-photoreforming route capable of simultaneously mitigating and repurposing plastic waste into valuable chemicals, thus offering a promising solution to the current environmental challenges.

Probing Oxidation Mechanisms in Plasmonic Catalysis: Unraveling the Role of Reactive Oxygen Species.

Plasmon-induced oxidation has conventionally been attributed to the transfer of plasmonic hot holes. However, this theoretical framework encounters challenges in elucidating the latest experimental findings, such as enhanced catalytic efficiency under uncoupled irradiation conditions and superior oxidizability of silver nanoparticles. Herein, we employ liquid surface-enhanced Raman spectroscopy (SERS) as a real-time and in situ tool to explore the oxidation mechanisms in plasmonic catalysis, taking the decarboxylation of p-mercaptobenzoic acid (PMBA) as a case study. Our findings suggest that the plasmon-induced oxidation is driven by reactive oxygen species (ROS) rather than hot holes, holding true for both the Au and Ag nanoparticles. Subsequent investigations suggest that plasmon-induced ROS may arise from hot carriers or energy transfer mechanisms, exhibiting selectivity under different experimental conditions. The observations were substantiated by investigating the cleavage of the carbon-boron bonds. Furthermore, the underlying mechanisms were clarified by energy level theories, advancing our understanding of plasmonic catalysis.

Radical-Mediated Decarboxylative C-C and C-S Couplings of Carboxylic Acids via Iron Photocatalysis.

Despite the significant success of decarboxylative radical reactions, the catalytic systems vary considerably upon different radical acceptors, requiring renewed case-by-case reaction optimization. Herein, we developed an iron catalytic condition that enables the highly efficient decarboxylation of various carboxylic acids for a range of radical transformations. This operationally simple protocol was amenable to a wide array of radical acceptors, delivering structurally diverse oxime ethers, alkenylation, alkynylation, thiolation, and amidation products in useful to excellent yields (>40 examples, up to 95% yield).

Microbial contribution to 14 biogenic amines accumulation in refrigerated raw and deep-fried hairtails (Trichiurus lepturus)

Biogenic amines (BAs) produced by microbial decarboxylation of amino acids are crucial toxic nitrogenous compounds in fish. An optimized ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS) method with simple pretreatment was established to detect 14 BAs in both raw (control check, CK) and deep-fried (DF) hairtails. This method exhibited a good linear relationship with average recoveries of 73.3–120.0 % and relative standard deviations of 2.5–10.0 %, respectively. The total BAs in CK and DF hairtails decreased sharply to 338.2 and 25.3 mg/kg on the 9th day, respectively. Four BAs, including cadaverine (CAD), histamine (HIS), tyramine (TYR), and putrescine (PUT) accounted for 92.5–99.9 % of total BAs were selected as the dominant BAs. Bacterial analysis showed that the abundance of DF was relatively low. Further correlation analysis proved that Vibrio had a significant (p < 0.05) positive correlation with total BAs and could be the main BA-producing bacterium in DF hairtail. This work provides new evidence of the accumulation of BAs in refrigerated hairtail.

Inhibition of Food-Borne Pathogen Growth and Biogenic Amine Synthesis by Spice Extracts

Food-borne pathogens and their toxins cause significant health problems in humans. Formation of biogenic amines (BAs) produced by microbial decarboxylation of amino acids in food is undesirable because it can induce toxic effects in consumers. Therefore, it is crucial to investigate the effects of natural additives with high bioactivity like spice extracts to inhibit the growth of these bacteria and the formation of BAs in food. In the present study, the antibacterial effects of diethyl ether spice (sumac, cumin, black pepper, and red pepper) extracts at doses of 1% (w/v) on Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Klebsiella pneumoniae, Pseudomonas aeruginosa, Campylobacter jejuni, Aeromonas hydrophila, Salmonella Paratyphi A, and Yersinia enterocolitica) food-borne pathogen bacterial strains (FBP) were established. In addition, the accumulation of ammonia (AMN), trimethylamine (TMA), and biogenic amines (BAs) in tyrosine decarboxylase broth (TDB) was investigated by using high performance liquid chromatography (HPLC). Sumac extract exhibited the highest antibacterial potential against all FBPs, followed by cumin and peppers. AMN (570.71 mg/L) and TMA (53.66 mg/L) production were strongly inhibited by sumac extract in the levels of 55.10 mg/L for Y. enterocolitica and 2.76 mg/L for A. hydrophila, respectively. With the exception of S. aureus, black pepper dramatically reduced the synthesis of putrescine, serotonin, dopamine, and agmatine by FBP especially for Gram-negative ones. Furthermore, sumac extracts inhibited histamine and tyramine production by the majority of FBP. This research suggests the application of sumac extracts as natural preservatives for inhibiting the growth of FBPs and limiting the production of AMN, TMA, and BAs.

Orthovanadate intercalated CuFe-LDO catalyzed hydrothermal liquefaction of microalgae for low nitrogen bio-oil production

Hydrothermal liquefaction (HTL) of microalgae for bio-oil production is a promising strategy to avoid extensive fossil fuel utilization, while tandem amidation and Maillard reactions during hydrolysis of cellular compounds unavoidably result in formation of nitrogen containing (N-containing) compounds, reducing quality of bio-oil. Accordingly, VO43− intercalated Cu–Fe layered double oxides named as Cu2Fe-VO4-LDO is firstly synthesized to both catalyze hydrolysis of cellular compounds and block N-containing compounds formation. The results indicate Cu2Fe-VO4-LDO can improve bio-oil yield from 19.32 to 20.32 wt%, with decrease of N/C ratio from 0.70 of control to 0.67 of experimental group, and increase of H/C ratio from 0.129 to 0.132. The insert of VO43− provides more strong-acid sites, which are beneficial to hydrolysis of cellular compounds. Meanwhile, more strong-base sites of Cu2Fe-VO4-LDO promote decarboxylation of fatty acids and removing amino-group of amino acids, subsequently improve production of alkanes. Furthermore, the reversible oxidation of VO43− promotes oxidation of reducing sugars, blocking tandem amidation and Maillard reaction between intermedia of hydrolyzed lipids, carbohydrates, and proteins. This work reports a methodology for synthesis of Cu2Fe-VO4-LDO with strong acid-base sites and reversible oxidize interlayer sites, providing a strategy to simultaneously improve bio-oil yield and reduce its N/C ratio.

Functional production and biochemical investigation of an integral membrane enzyme for olefin biosynthesis.

Integral membrane enzymes play essential roles in a plethora of biochemical processes. The fatty acid desaturases (FADS)-like superfamily is an important group of integral membrane enzymes that catalyze a wide array of reactions, including hydroxylation, desaturation, and cyclization; however, due to the membrane-bound nature, the majority of these enzymes have remained poorly understood. UndB is a member of the FADS-like superfamily, which catalyzes fatty acid decarboxylation, a chemically challenging reaction at the membrane interface. UndB reaction produces terminal olefins that are prominent biofuel candidates and building blocks of polymers with widespread industrial applications. Despite the great importance of UndB for several biotechnological applications, the enzyme has eluded comprehensive investigation. Here, we report details of the expression, solubilization, and purification of several constructs of UndB to achieve the optimally functional enzyme. We gained important insights into the biochemical, biophysical, and catalytic properties of UndB, including the thermal stability and factors influencing the enzyme activity. Additionally, we established the ability and kinetics of UndB to produce dienes by performing di-decarboxylation of diacids. We found that the reaction proceeds by forming a mono-carboxylic acid intermediate. Our findings shed light on the unexplored biochemical properties of the UndB and extend opportunities for its rigorous mechanistic and structural characterization.

The prFMNH2-binding chaperone LpdD assists UbiD decarboxylase activation

The UbiD enzyme family of prenylated flavin (prFMN)-dependent reversible decarboxylases is near ubiquitously present in microbes. For some UbiD family members, enzyme activation through prFMNH2-binding and subsequent oxidative maturation of the cofactor readily occurs, both in vivo in a heterologous host and through in vitro reconstitution However, isolation of the active holo-enzyme has proven intractable for others, notably the canonical E. coli UbiD. We show E. coli heterologous expression of the small protein LpdD - associated with the UbiD-like gallate decarboxylase LpdC from Lactobacillus plantarum - unexpectedly leads to 3,4-dihydroxybenzoic acid decarboxylation whole cell activity. This activity was shown to be linked to endogenous E. coli ubiD expression levels. The crystal structure of the purified LpdD reveals a dimeric protein with structural similarity to the eukaryotic heterodimeric proteasome assembly chaperone Pba3/4. Solution studies demonstrate LpdD protein specifically binds to reduced prFMN species only. The addition of the LpdD:prFMNH2 complex supports reconstitution and activation of the purified E. coli apo-UbiD in vitro, leading to modest 3,4-dihydroxybenzoic acid decarboxylation. These observations suggest LpdD acts as a prFMNH2-binding chaperone, enabling apo-UbiD activation through enhanced prFMNH2 incorporation and subsequent oxidative maturation. Hence, while a single highly conserved flavin prenyltransferase UbiX is found associated with UbiD enzymes, our observations suggest considerable diversity in UbiD maturation, ranging from robust autocatalytic to chaperone-mediated processes. Unlocking the full (de)carboxylation scope of the UbiD-enzyme family will thus require more than UbiX co-expression.

Selective C–H acylation of quinolin-2(1H)-one with α-oxocarboxylic acids at the C3 position by sliver catalysis and its application in the synthesis of palbociclib

An efficient and selective method C3-H acylation of quinolin-2(1H)-one with at the C3 position has been developed. Active molecules containing acylquinolones were synthesized by silver-catalyzed decarboxylation of α-oxycarboxylic acids with quinolin-2(1H)-one in moderate to good yields. This reaction affords a broad substrate scope and good tolerance of functional groups. In addition, using this protocol, the marketed drug Palbociclib could be synthesized easily.

Synthesis of polyurethanes through the oxidative decarboxylation of oxamic acids: a new gateway toward self-blown foams.

Polyurethane (PU) thermoplastics and thermosets were prepared through the step-growth polymerization of in situ generated polyisocyanates through the decarboxylation of polyoxamic acids, in the presence of phenyliodine diacetate (PIDA), and polyols. The CO2 produced during the reaction allowed the access to self-blown polyurethane foams through an endogenous chemical blowing. The acetic acid released from ligand exchange at the iodine center was also shown to accelerate the polymerization reaction, avoiding the recourse to an additional catalyst. Changing simple parameters during the production process allowed us to access flexible PU foams with a wide range of properties.

Iodine-mediated decarboxylative coupling to synthesize β-sulfonyl-ene-amines/2,3-diarythio-pyrroles from α-amino acids and sodium sulfinates.

A novel process has been developed for the selective synthesis of β-sulfonyl-enamines and 2,3-diarylthiopyrroles. This process utilizes the decarboxylative coupling and β-C(sp3)-H functionalization of α-amino acids. In this reaction, iodine functions dually as a tandem catalyst to initiate the decarboxylation of α-amino acids and as an oxidant to facilitate the formation of organic sulfides. This innovative approach not only simplifies the synthesis but also enhances the yield and selectivity of the desired products.

Exploring Strategic Approaches for CvFAP Photodecarboxylation through Violet Light Irradiation

In this study, we describe a light-driven photocatalytic decarboxylation of palmitic acid and related fatty acids using Chlorella variabilis fatty acid photodecarboxylase (CvFAP). By utilizing violet light emitting diode (LED) light (50 W; 397 nm), we achieved a remarkable conversion efficiency of 99% within just 4 min, surpassing the previous 79% conversion achieved in 60 min using blue LED light (300 W; 439 nm). Importantly, the use of 50 W violet LED light also resulted in a lower enzyme photoinactivation rate when compared to 300 W blue LED. Comparing the whole-cell biocatalyst with the enzymatic extract, we found that the former demonstrated superior catalytic performance and reduced susceptibility to photoinactivation. Furthermore, whole-cell biocatalyst reuse was demonstrated after five sequential batches. Employing this approach, we successfully synthesized 26 mmol L-1 h-1 of pentadecane, showcasing a promising strategy to improve productivity. These findings represent a significant advancement in CvFAP photodecarboxylation processes compared to the literature, utilizing an alternative light source, with potential implications to the biofuel sector

Surveying the scope of aromatic decarboxylations catalyzed by prenylated-flavin dependent enzymes.

The prenylated-flavin mononucleotide-dependent decarboxylases (also known as UbiD-like enzymes) are the most recently discovered family of decarboxylases. The modified flavin facilitates the decarboxylation of unsaturated carboxylic acids through a novel mechanism involving 1,3-dipolar cyclo-addition chemistry. UbiD-like enzymes have attracted considerable interest for biocatalysis applications due to their ability to catalyse (de)carboxylation reactions on a broad range of aromatic substrates at otherwise unreactive carbon centres. There are now ∼35 000 protein sequences annotated as hypothetical UbiD-like enzymes. Sequence similarity network analyses of the UbiD protein family suggests that there are likely dozens of distinct decarboxylase enzymes represented within this family. Furthermore, many of the enzymes so far characterized can decarboxylate a broad range of substrates. Here we describe a strategy to identify potential substrates of UbiD-like enzymes based on detecting enzyme-catalysed solvent deuterium exchange into potential substrates. Using ferulic acid decarboxylase (FDC) as a model system, we tested a diverse range of aromatic and heterocyclic molecules for their ability to undergo enzyme-catalysed H/D exchange in deuterated buffer. We found that FDC catalyses H/D exchange, albeit at generally very low levels, into a wide range of small, aromatic molecules that have little resemblance to its physiological substrate. In contrast, the sub-set of aromatic carboxylic acids that are substrates for FDC-catalysed decarboxylation is much smaller. We discuss the implications of these findings for screening uncharacterized UbiD-like enzymes for novel (de)carboxylase activity.

Direct conversion of carboxylic acids to free thiols via radical relay acridine photocatalysis enabled by N-O bond cleavage.

Carboxylic acids and thiols are basic chemical compounds with diverse utility and widespread reactivity. However, the direct conversion of unprotected acids to thiols is hampered due to a fundamental problem - free thiols are incompatible with the alkyl radicals formed on decarboxylation of carboxylic acids. Herein, we describe a concept for the direct photocatalytic thiolation of unprotected acids allowing unprotected thiols and their derivatives to be obtained. The method is based on the application of a thionocarbonate reagent featuring the N-O bond. The reagent serves both for the rapid trapping of alkyl radicals and for the facile regeneration of the acridine-type photocatalyst.