Carbon composite beads for immobilization of carbonic anhydrase

Boosted formic acid electro-oxidation on platinum nanoparticles and "mixed-valence" iron and nickel oxides

The modification of Pt nanoparticles (nano-Pt, assembled electrochemically onto a glassy carbon (GC) substrate) with hybrid multivalent nickel (nano-NiO_x) and iron (nano-FeO_x) oxide nanostructures was intended to steer the mechanism of the formic acid electro-oxidation (FAO) in the desirable dehydrogenation pathway. This binary modification with inexpensive oxides succeeded in mediating the reaction mechanism of FAO by boosting reaction kinetics "electron transfer" and amending the surface geometry of the catalyst against poisoning. The sequence of deposition was optimized where the a-FeO_x/NiO_x/Pt/GC catalyst (where "a" denotes a post-activation step for the catalyst at -0.5 V in 0.5 mol L^-1 NaOH) reserved the best hierarchy. Morphologically, while nano-Pt appeared to be spherical (ca. 100 nm in average diameter), nano-NiO_x appeared as flowered nanoaggregates (ca. 56 nm in average diameter) and nano-FeO_x (after activation) retained a plate-like nanostructure (ca. 38 nm in average diameter and 167 nm in average length). This a-FeO_x/NiO_x/Pt/GC catalyst demonstrated a remarkable catalytic efficiency (125 mA mg_Pt^-1) for FAO that was ca. 12.5 times that of the pristine Pt/GC catalyst with up to five times improvement in the catalytic tolerance against poisoning and up to -214 mV shift in the FAO's onset potential. Evidences for equipping the a-FeO_x/NiO_x/Pt/GC catalyst with the least charge transfer resistance and the highest stability among the whole investigated catalysts are provided and discussed.

Enzyme mediated transformation of CO2 into calcium carbonate using purified microbial carbonic anhydrase

In this study, a bacterial carbonic anhydrase (CA) was purified from Corynebacterium flavescens for the CO₂ conversion into CaCO₃. The synthesized CaCO₃ can be utilized in the papermaking industry as filler material, construction material and in steel industry. Herein, the CA was purified by using a Sephadex G-100 column chromatography having 29.00 kDa molecular mass in SDS-PAGE analysis. The purified CA showed an optimal temperature of 35 °C and pH 7.5. In addition, a kinetic study of CA using p-NPA as substrate showed V_max (166.66 μmoL/mL/min), K_m (5.12 mM), and K_cat (80.56 sec^-1) using Lineweaver Burk plot. The major inhibitors of CA activity were Na²⁺, K⁺, Mn²⁺, and Al³⁺, whereas Zn²⁺ and Fe²⁺ slightly enhanced it. The purified CA showed a good efficacy to convert the CO₂ into CaCO₃ with a total conversion rate of 65.05 mg CaCO₃/mg of protein. In silico analysis suggested that the purified CA has conserved Zn²⁺ coordinating residues such as His 111, His 113, and His 130 in the active site center. Further analysis of the CO₂ binding site showed conserved residues such as Val 132, Val 142, Leu 196, Thr 197, and Val 205. However, a substitution has been observed where Trp 208 of its closest structural homolog T. ammonificans CA is replaced with Arg 207 of C. flavescens. The presence of a hydrophilic mutation in the CO₂ binding hydrophobic region is a further subject of investigation.

Carbonic Anhydrase-Mimicking Supramolecular Nanoassemblies for Developing Carbon Capture Membranes

As a ubiquitous family of enzymes with high performance in converting carbon dioxide (CO₂) into bicarbonate, carbonic anhydrases (CAs) sparked enormous attention for carbon capture. Nevertheless, the high cost and operational instability of CAs hamper their practical relevance, and the utility of CAs is mainly limited to aqueous applications where CO₂-to-bicarbonate conversion is possible. Taking advantage of the chemical motif that endows CA-like active sites (metal-coordinated histidine), here we introduce a new line of high-performance gas separation membranes with CO₂-philic behavior. We first self-assembled a histidine-based bolaamphiphile (His-Bola) molecule in the aqueous phase and coordinated the resulting entities with divalent zinc. Optimizing the supramolecular synthesis conditions ensured that the resultant nanoparticles (His-NPs) exhibit high CO₂ affinity and catalytic activity. We then exploited the His-NPs as nanofillers to enhance the separation performance of Pebax MH 1657. The hydrogen-bonding interactions allowed the dispersion of His-NPs within the polymer matrix uniformly, as confirmed by microscopic, spectroscopic, and thermal analyses. The imidazole and amine functionalities of His-NPs enhanced the solubility of CO₂ molecules in the polymer matrix. The CA-mimic active sites of His-NPs nanozymes, on the other hand, catalyzed the reversible hydration of CO₂ molecules in humid conditions, facilitating their transport across the membranes. The resulting nanocomposite membranes displayed excellent CO₂ separation performance, with a high level of stability. At a filling ratio as low as 3 wt %, we achieved a CO₂ permeability of >145 Barrer and a CO₂/N₂ selectivity of >95 with retained performance under humid continuous gas feeds. The bio-inspired approach presented in this work offers a promising platform for designing durable and highly selective CO₂ capture membranes.

A new carbonic anhydrase identified in the Gram-negative bacterium (Chromohalobacter sp.) and the interaction of anions with the enzyme

In this study, the characterization and inhibition characteristic of α-class carbonic anhydrase from Chromohalobacter (ChCA) was documented for the first time. The carbonic anhydrase enzyme had 47.77% yield and 54.45-fold purity. The specific activity of the enzyme was determined as 318.52 U/mg proteins. Alternative substrate (4-nitrophenyl trifluoroacetate, 4-nitrophenyl phosphate, 4-nitrophenyl sulphate and 4-nitrophenyl acetate) were tested for the enzyme. K_M and V_max values for 4-nitrophenyl acetate were 4.57 mM and 4.29 EU/mL and for 4-nitrophenyl trifluoroacetate were 2.39 mM and 2.41 EU/mL. The anions, Cl^-, NO₂^-, NO₃^-, Br^-, ClO₃^-, ClO₄^-, I^-, CO₃^2- and SO₄^2-, inhibited the ChCA hydratase activity. Among nine anions, the strongest inhibitor activities were obtained with micro molar concentrations of NO₂^-, NO₃^-, Br^-, I^-, CO₃^2- (K_I values of 160-255 μM). Other four anions tested (Cl^-, ClO₃^-, ClO₄^- and SO₄^2-) showed moderate inhibitory activities (K_I values of 680-813.5 μM). The results obtained demonstrate that the anions we tested inhibit the Chromohalobacter CA (ChCA) enzyme as in other α-CAs in mammals; however, the susceptibility of ChCA resulted from anions differed significantly from that of other organism CAs.

Overview on immobilization of enzymes on synthetic polymeric nanofibers fabricated by electrospinning

The arrangement and type of support has a significant impact on the efficiency of immobilized enzymes. 1-dimensional fibrous materials can be one of the most desirable supports for enzyme immobilization. This is due to their high surface area to volume ratio, internal porosity, ease of handling, and high mechanical stability, all of which allow a higher enzyme loading, release and finally lead to better catalytic efficiency. Fortunately, the enzymes can reside inside individual nanofibers to remain encapsulated and retain their three-dimensional structure. These properties can protect the enzyme's tolerance against harsh conditions such as pH variations and high temperature, and this can probably enhance the enzyme's stability. This review article will discuss the immobilization of enzymes on synthetic polymers, which are fabricated into nanofibers by electrospinning. This technique is rapidly gaining popularity as one of the most practical ways to fibricate polymer, metal oxide, and composite micro or nanofibers. As a result, there is interest in using nanofibers to immobilize enzymes. Furthermore, present research on electrospun nanofibers for enzyme immobilization is primarily limited to the lab scale and industrial scale is still challanging. The primary future research objectives of this paper is to investigate the use of electrospun nanofibers for enzyme immobilization, which includes increasing yield to transfer biological products into commercial applications.

Utility of thermo-alkali-stable γ-CA from polyextremophilic bacterium Aeribacillus pallidus TSHB1 in biomimetic sequestration of CO2 and as a virtual peroxidase

Aeribacillus pallidus TSHB1 polyextremophilic bacterium produces a γ-carbonic anhydrase (ApCA), which is a homotrimeric biocatalyst with a subunit molecular mass of 32 ± 2 kDa. The enzyme is stable in the pH range between 8.0 and 11.0 and thus alkali-stable and moderately thermostable with T_1/2 values of 40 ± 1, 15 ± 1, and 8 ± 0.5 min at 60, 70, and 80 °C, respectively. Activation energy for irreversible inactivation "E _d " of carbonic anhydrase is 67.119 kJ mol^-1. The enzyme is stable in the presence of various flue gas contaminants such as SO₃^2-,SO₄^2-, and NO₃^- and cations Mg²⁺, Mn²⁺, Ca²⁺, and Ba²⁺. Fluorescence studies in the presence of N-bromosuccinimide and fluorescence quenching using KI and acrylamide revealed the importance of tryptophan residues in maintaining the structural integrity of the enzyme. ApCA is more efficient than the commercially available bovine carbonic anhydrase (BCA) in CO₂ sequestration. The enzyme was successfully used in biomineralization of CO₂ from flue gas. Replacement of active site Zn²⁺ with Mn²⁺ enabled ApCA to function as a peroxidase which exhibited alkali-stability and moderate thermostability like ApCA.

Immobilization and characterization of carbonic anhydrase purified from E. coli MO1 and its influence on CO₂ sequestration

The present investigation entails the immobilisation and characterisation of Escherichia coli MO1-derived carbonic anhydrase (CA) and its influence on the transformation of CO₂ to CaCO₃. CA was purified from MO1 using a combination of Sephadex G-75 and DEAE cellulose column chromatography, resulting in 4.64-fold purification. The purified CA was immobilised in chitosan-alginate polyelectrolyte complex (C-A PEC) with an immobilisation potential of 94.5 %. Both the immobilised and free forms of the enzyme were most active and stable at pH 8.2 and at 37 °C. The K(m) and V(max) of the immobilised enzyme were found to be 19.12 mM and 416.66 μmol min⁻¹ mg⁻¹, respectively; whereas, the K(m) and V(max) of free enzyme were 18.26 mM and 434.78 μmol min⁻¹ mg⁻¹, respectively. The presence of metal ions such as Cu²⁺, Fe²⁺, and Mg²⁺ stimulated the enzyme activity. Immobilised CA showed higher storage stability and maintained its catalytic efficiency after repeated operational cycles. Furthermore, both forms of the enzyme were tested for targeted application of the carbonation reaction to convert CO₂ to CaCO₃. The amounts of CaCO₃ precipitated over free and immobilised CA were 267 and 253 mg/mg of enzyme, respectively. The results of this study show that immobilised CA in chitosan-alginate beads can be useful for CO₂ sequestration by the biomimetic route.

Carbonic Anhydrase: An Efficient Enzyme with Possible Global Implications

As the global atmospheric emissions of carbon dioxide (CO2) and other greenhouse gases continue to grow to record-setting levels, so do the demands for an efficient and inexpensive carbon sequestration system. Concurrently, the first-world dependence on crude oil and natural gas provokes concerns for long-term availability and emphasizes the need for alternative fuel sources. At the forefront of both of these research areas are a family of enzymes known as the carbonic anhydrases (CAs), which reversibly catalyze the hydration of CO2into bicarbonate. CAs are among the fastest enzymes known, which have a maximum catalytic efficiency approaching the diffusion limit of 108 M−1s−1. As such, CAs are being utilized in various industrial and research settings to help lower CO2atmospheric emissions and promote biofuel production. This review will highlight some of the recent accomplishments in these areas along with a discussion on their current limitations.

Enzymatic Carbon Dioxide Capture

In the past decade, the capture of anthropic carbonic dioxide and its storage or transformation have emerged as major tasks to achieve, in order to control the increasing atmospheric temperature of our planet. One possibility rests on the use of carbonic anhydrase enzymes, which have been long known to accelerate the hydration of neutral aqueous CO2 molecules to ionic bicarbonate species. In this paper, the principle underlying the use of these enzymes is summarized. Their main characteristics, including their structure and catalysis kinetics, are presented. A special section is next devoted to the main types of CO2 capture reactors under development, to possibly use these enzymes industrially. Finally, the possible application of carbonic anhydrases to directly store the captured CO2 as inert solid carbonates deserves a review presented in a final section.