CO2 Hydration Reaction Research Articles

Activity-enhanced Cu@ZIF-8/Ag carbonic anhydrase mimic for CO2 hydration and conversion

Carbonic anhydrase (CA) is an enzyme with unrivaled catalytic activity for CO2 hydration reactions. However, its high cost and poor stability have severely limited its industrial application in CO2 uptake. Constructing CA mimics is a promising strategy to overcome these limitations. In this work, a novel ZIF-8-based CA mimic, Cu@ZIF-8/Ag, was fabricated for CO2 capture and storage. Esterase experiments confirmed that Cu@ZIF-8/Ag had higher CA-mimicking activity than ZIF-8 and Cu@ZIF-8, indicating that Cu-doping and in-situ growth of Ag nanoparticles significantly increased CA-like activity. Simulating the mineralization process in industrial applications, Cu@ZIF-8/Ag yielded the highest CaCO3 yields. Additionally, Cu@ZIF-8/Ag has good reusability, with catalytic activity over 10 % higher than ZIF-8 even after seven adsorption and regeneration cycles. This activity-enhanced Cu@ZIF-8/Ag carbonic anhydrase mimic shows great potential for future CO2 capture.

Water effect on CO2 absorption mechanism and phase change behavior in [N1111][Gly]/EtOH anhydrous biphasic absorbent: In density functional theory and molecular dynamics view

Ionic liquids-based anhydrous biphasic absorbents have the potential to lower the energy consumption for CO2 capture. Recent experimental studies have revealed that the presence of water in [N1111][Gly]/EtOH system leads to generation of a new CO2-product – bicarbonate and affects the phase change behavior. However, the reaction pathway for bicarbonate formation remains unclear. In this work, the reaction pathways were investigated in depth through quantum chemical calculations employing density functional theory, with reaction rate constants determined via transition state theory. Among the three possible reaction pathways, the base-catalyzed CO2 hydration reaction prevailed, i.e. a one-step reaction involving [Gly]-, H2O, and CO2. An H atom in H2O was transferred to [Gly]-’s amino group, forming protonated [Gly]-, and hydroxide combined with CO2 to generate bicarbonate. Additionally, molecular dynamics simulations were conducted to understand the phase change behaviors with varying water content. When water content exceeded 5 wt%, an increased water content led to reduced hydrogen bonding among products and enhanced hydrogen bonding of products-solvent with the solvent, diminishing product self-aggregation. No phase change behavior were observed at water contents up to 80 wt%. This study could well explain the experimental phenomena of water effect on CO2 absorption in [N1111][Gly]/EtOH, providing theoretical references for application of ILs-based anhydrous biphasic absorbent.

A novel PVI-PVA/PS composite membrane modified by metal ions for CO2 separation: Effect and mechanism

The membrane process is potentially more energy-efficient than conventional separation technologies in the separation of carbon dioxide (CO2) /nitrogen (N2) from flue gas. In this work, a series of PVI (Polyvinylimidazole)-PVA (Polyvinyl alcohol) /PS (Polysulfone) membranes were prepared by co-blending two polymers, PVI and PVA, as the separation layer of the fixed carrier composite membrane. The separation performance increased by the dual action of PVA and the imidazole group in the PVI. Furthermore, Mg2+-PVI-PVA/PS and Cu2+-PVI-PVA/PS composite membranes were developed by adding Mg2+ and Cu2+, and the separation performance was considerably improved by complexing metal ions with PVA and PVI. Especially, Mg2+-PVI-PVA/PS demonstrated superior separation performance, with a CO2 permeation rate of 12 GPU and a CO2/N2 separation factor of 183 at a pressure of 1 bar. What’s more, the mechanism study clarified that the prepared composite membrane mainly relies on the facilitated transfer mechanism to achieve the selective separation of CO2. The presence of water molecules significantly improved the CO2 permeability and separation selectivity, indicating that PVI-PVA and Mg2+ could promote the hydration reaction of CO2 and H2O, forming easily mobile HCO3- carriers.

Bimetallic zeolitic imidazolate frameworks Co/ZIF-8 crystals as carbonic anhydrase-mimicking nanozyme

Zeolitic imidazolate frameworks (ZIFs) materials are known for their excellent stability and their ability to provide an adjustable, controllable structure. The precise assembly of metal nodes and ligands in ZIFs enables them to possess active centers that closely resemble those found in natural enzymes. Building upon this, the objective of this study was to mimic the catalytic active center of natural carbonic anhydrase (CA) by employing defect coordination on the outer surface of bimetallic Co/ZIF-8 crystals. The synthesis process was meticulously controlled through the introduction of cobalt ions, resulting in the creation of a biomimetic CA with remarkable stability and catalytic prowess. The bimetallic Co/ZIF-8 nanozyme exhibited catalytic properties similar to those of natural enzymes. It efficiently facilitated the CO2 hydration reaction and demonstrated the ability to catalyze the reverse reaction. The esterase activity of all Co/ZIF-8 nanozymes was higher than that of the original ZIF-8 at room temperature. Notably, these nanozymes exhibited an impressive maximum esterase activity of 3.77 U/mg at 80 ℃, which surpassed the levels observed in natural CA. This enhancement can be attributed to the boosted catalytic activity of Co/ZIF-8, stemming from the introduction of metal ion doping, which increased the potential difference between bimetallic active centers and facilitated efficient charge transfer. Furthermore, thanks to the unique activation mechanism inherent in the structure of Co/ZIF-8, the esterase activity not only remained unaffected after 24 h of hydrothermal treatment, but also experienced a significant enhancement. This article represents a valuable breakthrough in the regulation and modification of ZIF-8, resulting in the fabrication of an efficient bimetallic Co/ZIF-8 nanozyme for CA-mimicking. These findings hold immense significance for further research and development in the realm of industrial CO2 capture catalysts.

Mechanism of a novel metal-free carbonic anhydrase.

The recently discovered metal-free carbonic anhydrase (CA) enzyme may significantly impact the global carbon dioxide (CO2) cycle, as it can irreversibly perform the CO2 hydration reaction. In this study, we investigated several key aspects of metal-free CA, including the identification of the catalytic site, the determination of the CO2 binding site, and the mechanism of catalysis. This is achieved through classical molecular dynamics (MD) simulations, quantum chemical density functional theory (DFT), and hybrid quantum mechanics/molecular mechanics (QM/MM) calculations. Our study indicates that the experimental structure based on X-ray crystallography, which shows the 'bicarbonate (HCO3-) product' trapped in the hydrophilic region of metal-free CA, might not accurately depict the actual enzyme-substrate interaction. Instead, the simulation reveals that CO2 prefers the hydrophobic zone, which serves as the primary catalytic site. It also highlights the strategic role of a gatekeeper residue (Phe504), which assists in regulating the transportation of CO2 by tilting its aromatic plane. Additionally, the hybrid QM/MM calculations establish that CO2 hydration is catalyzed within the hydrophobic zone by a deprotonated tyrosine with the help of an organized water chain.

A Carbonic Anhydrase, ZmCA4, Contributes to Photosynthetic Efficiency andModulates CO2 Signaling Gene Expression by Interacting with Aquaporin ZmPIP2;6 inMaize.

Carbonic anhydrase (CA) catalyzes the reversible CO2 hydration reaction that produces bicarbonate for phosphoenolpyruvate carboxylase (PEPC). This is the initial step for transmitting the CO2 signal in C4 photosynthesis. However, it remains unknown whether the maize (Zea mays L.) CA gene, ZmCA4, plays a role in the maize photosynthesis process. In our study, we found that ZmCA4 was relatively highly expressed in leaves and localized in the chloroplast and the plasma membrane of mesophyll protoplasts. Knock-out of ZmCA4 reduced CA activity, while overexpression of ZmCA4 increased rubisco activity, as well as the quantum yield and relative electron transport rate in photosystem II. Overexpression of ZmCA4 enhanced maize yield-related traits. Moreover, ZmCA4 interacted with aquaporin ZmPIP2;6 in bimolecular fluorescence complementation and co-immunoprecipitation experiments. The double-knock-out mutant for ZmPIP2;6 and ZmCA4 genes showed reductions in its growth, CA and PEPC activities, assimilation rate and photosystem activity. RNA-Seq analysis revealed that the expression of other ZmCAs, ZmPIPs, as well as CO2 signaling pathway homologous genes, and photosynthetic-related genes was all altered in the double-knock-out mutant compared with the wild type. Altogether, our study's findings point to a critical role of ZmCA4 in determining photosynthetic capacity and modulating CO2 signaling regulation via its interaction with ZmPIP2;6, thus providing insight into the potential genetic value of ZmCA4 for maize yield improvement.

CanB, a Druggable Cellular Target in Mycobacterium tuberculosis.

Treatment against tuberculosis can lead to the selection of drug-resistant Mycobacterium tuberculosis strains. To tackle this serious threat, new targets from M. tuberculosis are needed to develop novel effective drugs. In this work, we aimed to provide a possible workflow to validate new targets and inhibitors by combining genetic, in silico, and enzymological approaches. CanB is one of the three M. tuberculosis β-carbonic anhydrases that catalyze the reversible reaction of CO2 hydration to form HCO3- and H+. To this end, we precisely demonstrated that CanB is essential for the survival of the pathogen in vitro by constructing conditional mutants. In addition, to search for CanB inhibitors, conditional canB mutants were also constructed using the Pip-ON system. By molecular docking and minimum inhibitory concentration assays, we selected three molecules that inhibit the growth in vitro of M. tuberculosis wild-type strain and canB conditional mutants, thus implementing a target-to-drug approach. The lead compound also showed a bactericidal activity by the time-killing assay. We further studied the interactions of these molecules with CanB using enzymatic assays and differential scanning fluorimetry thermal shift analysis. In conclusion, the compounds identified by the in silico screening proved to have a high affinity as CanB ligands endowed with antitubercular activity.

Synthesis, Biological and In Silico Studies of Griseofulvin and Usnic Acid Sulfonamide Derivatives as Fungal, Bacterial and Human Carbonic Anhydrase Inhibitors.

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the essential reaction of CO2 hydration in all living organisms, being actively involved in the regulation of a plethora of patho-/physiological conditions. A series of griseofulvin and usnic acid sulfonamides were synthesized and tested as possible CA inhibitors. Since β- and γ- classes are expressed in microorganisms in addition to the α- class, showing substantial structural differences to the human isoforms they are also interesting as new antiinfective targets with a different mechanism of action for fighting the emerging problem of extensive drug resistance afflicting most countries worldwide. Griseofulvin and usnic acid sulfonamides were synthesized using methods of organic chemistry. Their inhibitory activity, assessed against the cytosolic human isoforms hCA I and hCA II, the transmembrane hCA IX as well as β- and γ-CAs from different bacterial and fungal strains, was evaluated by a stopped-flow CO2 hydrase assay. Several of the investigated derivatives showed interesting inhibition activity towards the cytosolic associate isoforms hCA I and hCA II, as well as the three γ-CAs and Malassezia globosa (MgCA) enzyme. Six compounds (1b-1d, 1h, 1i and 1j) were more potent than AAZ against hCA I while five (1d, 1h, 1i, 1j and 4a) showed better activity than AAZ against the hCA II isoform. Moreover, all compounds appeared to be very potent against MgCA with a Ki lower than that of the reference drug. Furthermore, computational procedures were used to investigate the binding mode of this class of compounds within the active site of human CAs.

Carbonic Anhydrase Inhibitors as Novel Antibacterials in the Era of Antibiotic Resistance: Where Are We Now?

Resistance to antibiotic treatment developed by bacteria in humans and animals occurs when the microorganisms resist treatment with clinically approved antibiotics. Actions must be implemented to stop the further development of antibiotic resistance and the subsequent emergence of superbugs. Medication repurposing/repositioning is one strategy that can help find new antibiotics, as it speeds up drug development phases. Among them, the Zn2+ ion binders, such as sulfonamides and their bioisosteres, are considered the most promising compounds to obtain novel antibacterials, thus avoiding antibiotic resistance. Sulfonamides and their bioisosteres have drug-like properties well-known for decades and are suitable lead compounds for developing new pharmacological agent families for inhibiting carbonic anhydrases (CAs). CAs are a superfamily of metalloenzymes catalyzing the reversible reaction of CO2 hydration to HCO3- and H+, being present in most bacteria in multiple genetic families (α-, β-, γ- and ι-classes). These enzymes, acting as CO2 transducers, are promising drug targets because their activity influences microbe proliferation, biosynthetic pathways, and pathogen persistence in the host. In their natural or slightly modified scaffolds, sulfonamides/sulfamates/sulamides inhibit CAs in vitro and in vivo, in mouse models infected with antibiotic-resistant strains, confirming thus their role in contrasting bacterial antibiotic resistance.

Biomimetic hydroxypropyl-β-cyclodextrin (Hβ-CD) / polyamide (PA) membranes for CO2 separation

Carbonic anhydrase (CA)-inspired membranes for CO2 separation were constructed by introducing hydroxypropyl-β-cyclodextrins (Hβ-CDs) into the polyamide networks, which were formed via interfacial polymerization reactions between trimesoyl chloride and tertiary amino-containing monomers. Hydrophobic inner cavities of Hβ-CDs with the hydrophilic exterior can be used to simulate the hydrophobic pockets of CA enzymes. Hydrophilic and hydrophobic regions were constructed via introducing Hβ-CDs into membranes, while the transport of nonpolar CO2 molecules and polar components (H2O and HCO3−) in CO2 hydration reactions could be enhanced. Meanwhile, tertiary amino groups in biomimetic membranes can act as the base catalysts for CO2 hydration reactions, which were deemed as carriers for facilitated transport membranes. Biomimetic membranes containing Hβ-CDs and tertiary amino groups exhibited outstanding CO2 permeance of 2792 GPU and CO2/N2 selectivity of 171 at 0.15 MPa, showing the potentials for low-pressure CO2 capture. Particularly, CO2 transport mechanisms were also analyzed for biomimetic facilitated-transport membranes, which can supply new visions for developing novel membrane materials for CO2 separation.

May Sulfonamide Inhibitors of Carbonic Anhydrases from Mammaliicoccus sciuri Prevent Antimicrobial Resistance Due to Gene Transfer to Other Harmful Staphylococci?

Mammaliicoccus sciuri, previously known as Staphylococcus sciuri, is a Gram-positive bacterium involved in gene transfer phenomena that confer resistance to multiple antibiotics. These plasmid-encoded genes can be easily transferred to other pathogenic staphylococci. Because antibiotic resistance is rising, inhibiting M. sciuri proliferation may be a credible strategy for restricting antimicrobial resistance gene transfer to other pathogenic bacteria. Recently, it has been shown that blocking bacterial carbonic anhydrases (CAs, EC 4.2.1.1), metalloenzymes sustaining bacterial metabolic activities, can reduce pathogen survival and fitness. Here, the recombinant M. sciuri γ-CA (MscCAγ) has been cloned and purified, utilizing the DNA recombinant technology. Its kinetic properties for the CO2 hydration reaction, as well as the sulfonamide inhibition profile, were investigated and compared with those reported earlier for MscCAβ (previously described as SauBCA) and the two off-target human CA isoforms (hCA I and hCA II). The recombinant MscCAγ showed significant hydratase activity. Moreover, the MscCAγ sulfonamide inhibitory profile was different from that of MscCAβ, implying that a varied amino acid set typifies the catalytic pocket of the two enzymes. These differences provide additional evidence for the possibility of developing novel CA class-specific inhibitors.

Harvesting, storing, and converting carbon from the ocean to create a new carbon economy: Challenges and opportunities

Ever-increasing anthropogenic CO2 emissions have required us to develop carbon capture, utilization, and storage (CCUS) technologies, and in order to address climate change, these options should be at scale. In addition to engineered systems of CO2 capture from power plants and chemical processes, there are emerging approaches that include the Earth (i.e., air, Earth, and ocean) within its system boundary. Since oceans constitute the largest natural sink of CO2, technologies that can enhance carbon storage in the ocean are highly desired. Here, we discuss alkalinity enhancement and biologically inspired CO2 hydration reactions that can shift the equilibrium of ocean water to pump more carbon into this natural sink. Further, we highlight recent work that can harvest and convert CO2 captured by the ocean into chemicals, fuels, and materials using renewable energy such as off-shore wind. Through these emerging and innovative technologies, organic and inorganic carbon from ocean-based solutions can replace fossil-derived carbon and create a new carbon economy. It is critical to develop these ocean-based CCUS technologies without unintended environmental or ecological consequences, which will create a new engineered carbon cycle that is in harmony with the Earth’s system.

Immobilization of carbonic anhydrase in a hydrophobic poly(ionic liquid): A new functional solid for CO2 capture

Poly(ionic liquid)s are interesting materials for CO2 separation due to their affinity towards CO2. Carbonic anhydrase, as an enzyme that catalyzes the hydration reaction of CO2, represents tremendous opportunities for enhanced CO2 capture in aqueous solutions. Yet, when used as a free enzyme solubilized in the liquid medium, it has limited practicality. Here, we report the study on carbonic anhydrase immobilization in poly(ionic liquid)s by entrapment. Due to limited enzyme solubility in the hydrophobic ionic liquid monomer solution, carbonic anhydrase was suspended instead of solubilized prior to bulk polymerization. The immobilization protocol was optimized to maximize the catalytic efficiency of the resulting solid by evaluating the effect of lyophilized suspension hydration and particle size. Immobilized carbonic anhydrase properties were investigated by measurement of kinetic parameters, reusability, thermal and storage stability. Using p-NPA hydrolysis as a model reaction, kinetic parameters were 0.22 s−1 mM−1 (kcat/Km) for free enzyme and 0.06 s−1 mM−1 for the immobilized biocatalyst, indicating a decrease of activity upon immobilization. Immobilized enzyme, however, presented better storage stability than free enzyme as after one month the activity did not change. In the case of dissolved carbonic anhydrase, it decreased by about 30%. The entrapped enzyme could be utilized in 5 consecutive cycles of CO2 hydration while keeping a relative activity superior to 60%.

The gram-negative bacterium Escherichia coli as a model for testing the effect of carbonic anhydrase inhibition on bacterial growth

Carbonic anhydrases, catalysing the reversible CO2 hydration reaction, contribute in all living organisms to the maintenance of stable metabolic functions depending on intracellular concentrations of carbon dioxide, bicarbonate, and protons. Recent studies have examined how CAs affect bacterial lifecycle, considering these enzymes druggable targets due to interference with their activities by using inhibitors or activators. Here, we propose Escherichia coli cells as a model for testing the effect of acetazolamide (AZA), a potent CA inhibitor, on bacterial survival by evaluating E. coli growth through its glucose consumption. AZA, at concentrations higher than 31.2 µg/mL, was able to impair E. coli growth and glucose uptake. AZA is a good inhibitor of the two recombinant E. coli CAs, the β-CA CynT2, and the γ-CA EcoCAγ, with KIs of 227 and 248 nM, respectively. This study provides a proof-of-concept, low-cost method for identifying effective CA inhibitors capable of impairing bacterial metabolism.

Pyrazolo[4,3-c]pyridine Sulfonamides as Carbonic Anhydrase Inhibitors: Synthesis, Biological and In Silico Studies.

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the essential reaction of CO2 hydration in all living organisms, being actively involved in the regulation of a plethora of patho-/physiological conditions. A series of chromene-based sulfonamides were synthesized and tested as possible CA inhibitors. On the other hand, in microorganisms, the β- and γ- classes are expressed in addition to the α- class, showing substantial structural differences to the human isoforms. In this scenario, not only human but also bacterial CAs are of particular interest as new antibacterial agents with an alternative mechanism of action for fighting the emerging problem of extensive drug resistance afflicting most countries worldwide. Pyrazolo[4,3-c]pyridine sulfonamides were synthesized using methods of organic chemistry. Their inhibitory activity, assessed against the cytosolic human isoforms hCA I and hCA II, the transmembrane hCA IX and XII, and β- and γ-CAs from three different bacterial strains, was evaluated by a stopped-flow CO2 hydrase assay. Several of the investigated derivatives showed interesting inhibition activity towards the cytosolic associate isoforms hCA I and hCA II, as well as the 3β- and 3γ-CAs. Furthermore, computational procedures were used to investigate the binding mode of this class of compounds within the active site of hCA IX. Four compounds (1f, 1g, 1h and 1k) were more potent than AAZ against hCA I. Furthermore, compound 1f also showed better activity than AAZ against the hCA II isoform. Moreover, ten compounds out of eleven appeared to be very potent against the γ-CA from E.coli, with a Ki much lower than that of the reference drug. Most of the compounds showed better activity than AAZ against hCA I as well as the γ-CA from E.coli and the β-CA from Burkholderia pseudomallei (BpsCAβ). Compounds 1f and 1k showed a good selectivity index against hCA I and hCA XII, while 1b was selective against all 3β-CA isoforms from E.coli, BpsCA, and VhCA and all 3γ-CA isoforms from E.coli, BpsCA and PgiCA.

Dual-function biomimetic carrier based facilitated transport mixed matrix membranes with high stability for efficient CO2/N2 separation

Realizing efficient carbon capture by high-performance CO2 separation membrane is significant to mitigate the increasing emissions of greenhouse gas CO2. Inspired by the extraordinary CO2 hydration ability of carbonic anhydrase (CA), a biomimetic MOF (CFA-1) which can mimic the CO2 hydration sites of CA but possesses better stability and the lower price was incorporated into Pebax to fabricated high-performance facilitated transport mixed matrix membranes. The optimal membrane has a CO2 permeability of 869 Barrer with a CO2/N2 ideal selectivity of 88.6 at 1 bar and 30 °C, which is 9.2 times and 2.8 times than the pristine Pebax membrane. Such superior CO2/N2 separation performance (far surpasses 2008 upper bound) is original from the dual-function of CFA-1: (1) provide extra pathways for gas diffusion and affinity sites for preferential CO2 adsorption; (2) facilitate CO2 transport in the membrane by efficiently catalyze CO2 hydration reaction. Furthermore, the Pebax/CFA-1 membranes fabricated can also exhibit excellent stability after being treated under high temperature and harsh pH, which is not available in the Pebax/CA membranes. Overall, such biomimetic dual-function MOFs may pave a new avenue to advance the high-performance CO2 facilitated transport membranes with excellent stability.

Carbonic Anhydrases II and IX in Non-ampullary Duodenal Adenomas and Adenocarcinoma.

Non-ampullary duodenal adenocarcinoma (DAC) is a rare malignancy. Little information is available concerning the histopathological prognostic factors associated with DAC. Carbonic anhydrases (CAs) are metalloenzymes catalyzing the universal reaction of CO2 hydration. Isozymes CAII, CAIX, and CAXII are associated with prognosis in various cancers. Our aim was to analyze the immunohistochemical expressions of CAII, CAIX, and CAXII in normal duodenal epithelium, duodenal adenomas, and adenocarcinoma and their associations with clinicopathological variables and survival. Our retrospective study included all 27 DACs treated in Oulu University Hospital during years 2000-2020. For comparison, samples of 42 non-ampullary adenomas were collected. CAII expression was low in duodenal adenomas and adenocarcinoma. CAIX expression in adenomas and adenocarcinoma was comparable with the high expression of normal duodenal crypts. Expression patterns in carcinomas were largely not related to clinicopathological features. However, low expression of CAII associated with poorer differentiation of the tumor (p=0.049) and low expression of CAIX showed a trend for association with nodal spread, although statistical significance was not reached (p=0.091). CAII and CAIX lost their epithelial polarization and staining intensity in adenomas. CAXII expression was not detected in the studied samples. CAs were not associated with survival. The prognostic value of CAII and CAIX downregulation should be further investigated. Both isozymes may serve as biomarkers of epithelial dysplasia in the duodenum.

Modeling and mutagenesis of amino acid residues critical for CO2 hydration by specialized NDH-1 complexes in cyanobacteria

The uptake of inorganic carbon in cyanobacteria is facilitated by an energetically intensive CO2-concentrating mechanism (CCM). This includes specialized Type-1 NDH complexes that function to couple photosynthetic redox energy to CO2 hydration forming the bicarbonate that accumulates to high cytoplasmic concentrations during the operation of the CCM, required for effective carbon fixation. Here we used a Synechococcus PCC7942 expression system to investigate the role of conserved histidine and cysteine residues in the CupB (also designated, ChpX) protein, which has been hypothesized to participate in a vectoral CO2 hydration reaction near the interface between CupB protein and the proton-pumping subunits of the NDH-1 complex. A homology model has been constructed and most of the targeted conserved residues are in the vicinity of a Zn ion modeled to form the catalytic site of deprotonation and CO2 hydration. Growth and CO2 uptake assays show that the most severe defects in activity among the targeted residues are due to a substitution of the predicted Zn ligand, CupB-His86. Mutations at other sites produced intermediate effects. Proteomic analysis revealed that some amino acid substitution mutations of CupB caused the induction of bicarbonate uptake proteins to a greater extent than complete deletion of CupB, despite growth under CO2-enriched conditions. The results are discussed in terms of hypotheses on the catalytic function of this unusual enzyme.

OH and O mediated interaction of CO2 with Ni(1 1 0) surface, and its implications on biomimetic CO2 hydration

Pre-coverage of a clean Ni(1 1 0) surface with OH and O plays an important role in activating CO2 molecules during a host of surface catalytic reactions involving CO2 and H2O. Appreciating this observation, the present work was designed to focus on providing detailed mechanistic insights into CO2 hydration reaction by Ni(1 1 0) surface, pre-covered by oxygenated surface species formed as a result of partial as well as complete dissociation of H2O. Density functional theory calculations were employed to investigate CO2 hydration with modified Ni(1 1 0) surfaces acting as biomimetic catalysts exhibiting carbonic anhydrase-like mechanism. Bader charge analysis was done to probe the charge distributions in different catalytic systems under study. Potential energy surfaces were developed for the formation of bicarbonate and carbonate. Our computational analysis conclusively demonstrates the feasibility of Ni(1 1 0) to act as biomimetic CO2 hydration catalyst, and the plausibility of carbonate formation to compete with biomimetic CO2 hydration.

Chromene-Containing Aromatic Sulfonamides with Carbonic Anhydrase Inhibitory Properties.

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the essential reaction of CO2 hydration in all living organisms, being actively involved in the regulation of a plethora of patho/physiological conditions. A series of chromene-based sulfonamides were synthesized and tested as possible CA inhibitors. Their inhibitory activity was assessed against the cytosolic human isoforms hCA I, hCA II and the transmembrane hCA IX and XII. Several of the investigated derivatives showed interesting inhibition activity towards the tumor associate isoforms hCA IX and hCA XII. Furthermore, computational procedures were used to investigate the binding mode of this class of compounds, within the active site of hCA IX.