Acetylcholinesterase immobilization and characterization, and comparison of the activity of the porous silicon-immobilized enzyme with its free counterpart

Synthesis, Characterization, Optical Properties, Molecular Modeling and Urease Inhibition Analysis of Organic Ligands and Their Metal Complexes

Recently, screening of efficient urease inhibitors by employing organic small molecules metalloderivatives interests the scientific community due to their efficacy for treatment of urease triggered health complications. This study comprises the synthesis, urease inhibition activity, optical analysis and molecular modeling of hydrazinecarbothioamide and hydrazinecarboxamide metalloderivatives. Characterization of synthesized materials was done by UV-visible, fluorescence, NMR and FTIR spectroscopic analysis. Metalloderivatization of ligands induce increment in urease inhibition potential and effect was prominent for copper complexes with 10-fold enhancement, cobalt complex with 3.5 fold's enhancement and palladium with 2-fold increment in the inhibition efficacy toward urease when it was compared with reference urease inhibitor. Zinc and iron complexes cause declined urease inhibition activity of the bare ligand. The overall activity of hydrazinecarbothioamide slightly exceeds than that of hydrazinecarboxamide, possibly due to larger complexation ability of sulfur-based ligand in comparison to oxygenated derivatives i.e., hydrazinecarboxamide. The enzyme inhibition kinetics for the most active complexes represent the mixed type urease inhibition for 3a and competitive urease inhibition for 5a, as determined by Lineweaver-Burk plots. The docked scoring values for both the ligands were calculated to be 61.34, 64.72, 56.68, 62.94, 64.98 and 58.98. Three active hydrogen bonds were observed in docking complex upon computational analysis of most potent metallodrug 3a inside active region of targeted protein.

Conducting polymer-based electrochemical biosensor for the detection of acetylthiocholine and pesticide via acetylcholinesterase

A voltammetric biosensor for acetylthiocholine (ATCh) and paraoxon detection was successfully developed. To achieve this goal, polypyrrole (PPy) was synthesized onto the platinum (Pt) electrode surface in 0.30 M oxalic acid solution containing 25 mM pyrrole. PPy-coated Pt (Pt/PPy) electrode surface was covered with chitosan (Chi) (Pt/PPy/Chi). The acetylcholinesterase (AChE) enzyme was immobilized on the Pt/PPy/Chi electrode surface to build a voltammetric biosensor (Pt/PPy/Chi/AChE). The storage stability of the biosensor was determined to be 72% even after 60 days. The operational stability was determined to be 94% after 20 consecutive measurements. For the biosensor, the linear range was determined to be 30-50 µM for ATCh and 0.46-1.84 nM for paraoxon. The limit of detection (LOD) was determined to be 0.45 µM for ATCh and 0.17 nM for paraoxon.

Inhibition assays of free and immobilized urease for detecting hexavalent chromium in water samples

The present work describes the inhibition studies of free as well as immobilized urease by different heavy metals. Porous silicon (PS) films prepared by electrochemical etching were used for urease immobilization by physical adsorption. The enzyme was subjected to varying concentrations of Cr⁶⁺, Cr³⁺, Cu²⁺, Fe²⁺, Cd²⁺ and Ni²⁺ and analyzed for the variation in the activity. To study the effect of other heavy metals on the interaction of urease and Cr⁶⁺, free as well as immobilized urease was subjected to the combination of each metal ion with Cr⁶⁺. Results proved the sensitivity of free as well as immobilized urease towards heavy metals by observed reduction in activity. Immobilized urease showed less degree of inhibition compared to free urease when tested for inhibition by individual metal ions and in combination with Cr⁶⁺. IC₅₀ values were found higher for inhibition by the combination of metal ions with Cr⁶⁺. Interaction of heavy metal ions with functional groups in active site of urease and limitations of mass transfer are the two factors responsible for the variation in activity of urease. Relation between the variation of urease activity and amount of heavy metals can be applied in biosensor development for determining the concentration of Cr⁶⁺ present in the water samples.

MAPLE Assembled Acetylcholinesterase⁻Polyethylenimine Hybrid and Multilayered Interfaces for Toxic Gases Detection

Developing a controlled method for obtaining hybrid enzymatic-based interfaces for sensing application require the use of a multiuse, reusable sensor. By controlling the interface characteristics in terms of the surface chemistry, thickness, and roughness, a tailored response toward various toxic compounds can be obtained, regarding both materials used as active surfaces and fabrication methods. Herein, we report a preliminary study on using a laser-based method (i.e., matrix-assisted pulsed laser evaporation, or MAPLE) for obtaining active polymeric⁻enzymatic interfaces as hybrid or layered coatings for detecting toxic vapors. The MAPLE fabrication consisted of the simultaneous alternating evaporation of layers of polyethylenimine (PEI) and acetylcholinesterase (AchE) in order to obtain active surfaces as both hybrid PEI-AchE and a PEI/AchE layered coating, respectively. The deposition processes of the polymer and enzyme were carried out using a double-target system and a Nd:YAG pulsed laser, operating at 0.45 J/cm² fluences with a wavelength of 266 nm and a repetition rate of 10 Hz. Fourier transform infrared spectroscopy revealed no significant changes in the functional groups of both hybrid and layered coatings compared with the initial material. The thickness and roughness, as well as the morphologies of the coatings revealed by atomic force microscopy and scanning electron microscopy showed coatings thicker than two μm that had smooth surfaces and average roughness values below six nm. The sensors were tested with simulants for nerve gases and pesticides containing phosphonate ester groups, namely dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP), and a different sensitivity was shown to the selected chemical agents for each of the sensors. The best sensitivities for DMMP and DIMP obtained by using a PEI-AchE coated sensor are 65 kHz and 200 kHz, respectively, whereas the best sensitivity when using multilayered interfaces is 30 kHz and 10 KHz for DIMP and DMMP, respectively.

Biogenic porous silica and silicon sourced from Mexican Giant Horsetail (Equisetum myriochaetum) and their application as supports for enzyme immobilization

Porous silica-based materials are attractive for biomedical applications due to their biocompatibility and biodegradable character. In addition, inorganic supports such as porous silicon are being developed due to integrated circuit chip compatibility and tunable properties leading to a wide range of multidisciplinary applications. In this contribution, biosilica extracted from a rarely studied plant material (Equisetum Myriochaetum), its conversion to silicon and the potential for both materials to be used as supports for enzyme immobilization are investigated. E. myriochaetum was subject to conventional acid digestion to extract biogenic silica with a% yield remarkably higher (up to 3 times) than for other Equisetum sp. (i.e. E. Arvense). The surface area of the isolated silica was ∼400 m²/g, suitable for biotechnological applications. Biogenic silicon was obtained by magnesiothermic reduction. The materials were characterized by SEM-EDX, XRD, FT-IR, ICP-OES, TGA and BET analysis and did not contain significant levels of class 1 heavy elements (such as Pb, Cd, Hg and As). Two commercial peroxidases, horseradish peroxidase (HRP) and Coprinus cinereus peroxidase (CiP) were immobilized onto the biogenic materials using three different functionalization routes: (A) carbodiimide, (B) amine + glutaraldehyde and (C) amine + carbodiimide. Although both biogenic silica and porous silicon could be used as supports differences in behaviour were observed for the two enzymes. For HRP, loading onto biogenic silica via the glutaraldehyde immobilization technique (route B) was most effective. The loading of CiP showed a much higher peroxidase activity onto porous silicon than silica functionalized by the carbodiimide method (route A). From the properties of the extracted materials obtained from Equisetum Myriochaetum and the immobilization results observed, these materials appear to be promising for industrial and biomedical applications.

Covalent immobilization of acetylcholinesterase on a novel polyacrylic acid-based nanofiber membrane

In this study, polyacrylic acid-based nanofiber (NF) membrane was prepared via electrospinning method. Acetylcholinesterase (AChE) from Electrophorus electricus was covalently immobilized onto polyacrylic acid-based NF membrane by demonstrating efficient enzyme immobilization, and immobilization capacity of polymer membranes was found to be 0.4 mg/g. The novel NF membrane was synthesized via thermally activated surface reconstruction, and activation with carbonyldiimidazole upon electrospinning. The morphology of the polyacrylic acid-based membrane was investigated by scanning electron microscopy, Fourier Transform Infrared Spectroscopy, and thermogravimetric analysis. The effect of temperature and pH on enzyme activity was investigated and maxima activities for free and immobilized enzyme were observed at 30 and 35°C, and pH 7.4 and 8.0, respectively. The effect of 1 mM Mn²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Mg²⁺, Ca²⁺ ions on the stability of the immobilized AChE was also investigated. According to the Michaelis-Menten plot, AChE possessed a lower affinity to acetylthiocholine iodide after immobilization, and the Michaelis-Menten constant of immobilized and free AChE were found to be 0.5008 and 0.4733 mM, respectively. The immobilized AChE demonstrated satisfactory reusability, and even after 10 consecutive activity assay runs, AChE maintained ca. 87% of its initial activity. Free enzyme lost its activity completely within 60 days, while the immobilized enzyme retained approximately 70% of the initial activity under the same storage time. The favorable reusability of immobilized AChE enables the support to be employable to develop the AChE-based biosensors.