Identifying the molecular basis of Laminin N-terminal domain Ca2+ binding using a hybrid approach.

Ca2+ is a highly abundant ion involved in numerous biological processes, particularly in multicellular eukaryotic organisms where it exerts many of these functions through interactions with Ca2+ binding proteins. The laminin N-terminal (LN) domain is found in members of the laminin and netrin protein families where it plays a critical role in the function of these proteins. The LN domain of laminins and netrins is a Ca2+ binding domain and in many cases requires Ca2+ to perform its biological function. Here, we conduct a detailed examination of the molecular basis of the LN domain Ca2+ interaction combining structural, computational, bioinformatics, and biophysical techniques. By combining computational and bioinformatic techniques with x-ray crystallography we explore the molecular basis of the LN domain Ca2+ interaction and identify a conserved sequence present in Ca2+ binding LN domains. These findings enable a sequence-based prediction of LN domain Ca2+ binding ability. We use thermal shift assays and isothermal titration calorimetry to explore the biophysical properties of the LN domain Ca2+ interaction. We show that the netrin-1 LN domain exhibits a high affinity and specificity for Ca2+, which structurally stabilizes the LN domain. This study elucidates the molecular foundation of the LN domain Ca2+ binding interaction and provides a detailed functional characterization of this essential interaction, advancing our understanding of protein-Ca2+ dynamics within the context of the LN domain.

Determination of subnanomolar levels of mercury (II) by using a graphite paste electrode modified with MWCNTs and Hg(II)-imprinted polymer nanoparticles.

Mercury ion-imprinted polymer nanoparticles (Hg-IP-NPs) were synthesized via precipitation polymerization by using itaconic acid as a functional monomer. A carbon paste electrode was impregnated with the synthesized Hg-IP-NPs and MWCNTs to obtain a highly sensitive and selective electrode for determination of Hg(II). Mercury ion is first accumulated on the electrode surface via an open circuit procedure. After reduction of Hg(II) ions to its metallic form at a negative pre-potential, square wave anodic stripping voltammetry was applied to generate the electrochemical signal. The high affinity of the Hg-IP-NPs for Hg(II) was substantiated by comparing of the signals of electrodes with imprinted and non-imprinted polymer. The beneficial effect of MWCNTs on the voltammetric signal is also demonstrated. Under the optimized conditions and at a typical working potential of +0.05 V (vs. Ag/AgCl), the electrode has a linear response in the 0.1-20 nmol L-1 Hg(II) concentration range and a 29 pM detection limit. The electrochemical sensitivity is as high as 1441 A·M-1·cm-2 which is among the best values known. The electrode was applied to the determination of Hg(II) in water samples. Graphical abstract Schematic representation of the sensor electrode modified with mercury-imprinted polymer nanoparticles, and the recognition and voltammetric determination steps.

A novel chloride selective potentiometric sensor based on graphitic carbon nitride/silver chloride (g-C3N4/AgCl) composite as the sensing element.

In this research, AgCl anchored graphitic carbon nitride (g-C3N4) was introduced as a novel potentiometric sensing element. A g-C3N4/AgCl-modified carbon paste electrode (CPE) was fabricated and used as an outstandingly selective potentiometric sensor to determine Cl- in water samples. The g-C3N4/AgCl nanocomposite was characterized with SEM, XRD and FT-IR techniques. It was demonstrated that, the incorporation of 5% of g-C3N4/AgCl, as a chloride ionophore in a CPE, results in a stable potential response of the electrode to chloride ion. The Nernstian slope of the electrode response was 55.4 (±0.3) mVdecade-1, over a wide linear concentration range of 1 × 10-6-1 × 10-1 mol L-1 and the detection limit of the electrode was estimated to be 4.0 × 10-7 mol L-1. The g-C3N4/AgCl-modified CPE electrode provided fast response time and long-term stability (more than 2 months) while the potential interfering ions such as I-, Br-, and CN- showed no significant effect on the potential response. Since these interfering ions affected the response of the CPE electrode, modified with AgCl, highlighting the interesting effect of g-C3N4 on the sensor performance. This innovative electrode was shown to be a sensitive and accurate sensor for chloride ion content estimation in water samples.

A new carbon paste electrode modified with MWCNTs and nano-structured molecularly imprinted polymer for ultratrace determination of trimipramine: The crucial effect of electrode components mixing on its performance.

A novel carbon nanocomposite paste electrode was prepared and used as a voltammetric sensor for ultratrace determination of trimipramine (TRI) which currently used for the treatment of psychiatric disorders. For this aim, nanoparticles of molecularly imprinted polymer (MIP), synthesized by precipitation polymerization method, and multi-walled carbon nanotubes (MWCNTs) were embedded in a nanocomposite paste electrode. The nanocomposite mixing style demonstrated a significant influence on the final electrode performance. The sensor exhibited linear response range of 1.0 × 10-10-2.5 × 10-8 mol L-1 and very high sensitivity of 2131 µA µâ€¯mol L-1. The lower detection limit of the sensor was calculated to be 4.5 × 10-11 mol L-1 (S/N = 3). This sensor was applied successfully for highly selective determination of TRI in pharmaceutical formulations, urine and serum samples without applying any sample pretreatment.

Trace level and highly selective determination of urea in various real samples based upon voltammetric analysis of diacetylmonoxime-urea reaction product on the carbon nanotube/carbon paste electrode.

In this study an innovative method was introduced for selective and precise determination of urea in various real samples including urine, blood serum, soil and water. The method was based on the square wave voltammetry determination of an electroactive product, generated during diacetylmonoxime reaction with urea. A carbon paste electrode, modified with multi-walled carbon nanotubes (MWCNTs) was found to be an appropriate electrochemical transducer for recording of the electrochemical signal. It was found that the chemical reaction conditions influenced the analytical signal directly. The calibration graph of the method was linear in the range of 1 × 10-7- 1 × 10-2 mol L-1. The detection limit was calculated to be 52 nmol L-1. Relative standard error of the method was also calculated to be 3.9% (n = 3). The developed determination procedure was applied for urea determination in various real samples including soil, urine, plasma and water samples.

Synthesis of nano-sized timolol-imprinted polymer via ultrasonication assisted suspension polymerization in silicon oil and its use for the fabrication of timolol voltammetric sensor.

A novel timolol voltammetric sensor based on the nano-sized molecularly imprinted polymer (nano-MIP)-modified carbon paste electrode was introduced. Timolol-imprinted polymers (MIP) were synthesized by the ultrasonic assisted suspension polymerization in silicon oil. The MIP nanoparticles were then embedded in a carbon paste (CP) electrode in order to prepare the nano-MIP-CP electrode. Timolol was extracted in the electrode for a definite time and then it was analyzed by square wave voltammetry, found to be an effective determination method. The electrode showed higher response to timolol, compared to the CP electrode, and CP electrode modified with non-imprinted polymer (nano-NIP-CP). Various factors, known to affect the response behavior of the nano-MIP-CP electrode, were investigated and optimized. The sensor exhibited distinct linear response ranges of 1.0×10-7-2.1×10-6M with the sensitivity of 71.523µAµM-1. The lower detection limit of the sensor was calculated to be 2.3×10-8M (S/N=3). The sensor was applied successfully for timolol determination in pharmaceutical formulations, blood serum and urine samples.