CD Measurements Research Articles

Cadmium Effects on Hyssop (Hyssopus officinalis L.) Morphology and Cd Uptake in Relation to Substrate Acidity/Alkalinity

Hyssop (Hyssopus officinalis), is a herb with a wide range of use in food preparation and herbal medicine. It is a perennial shrub through which pollutants such as Cd may enter the human food chain Therefore, the aim of this research was to examine the extent to which Cd added to the growth substrate is accumulated by hyssop plants and whether Cd affects the plant’s morphology. Hyssop plants were grown in pots containing a uniform mixture of either moderately acidic or slightly alkaline substrate consisting of peat and perlite (1:1 v/v) to which Cd (CdSO4*8/3H2O) was added (0-control, 1, 2 and 5 mg Cd L-1) during the course of growth. No symptoms of toxicity or nutrient deficiency as well as no differences in plant height were attributed to Cd application irrespective of the growth stage or substrate. Cadmium uptake by aerial organs (shoots) and underground organs (roots) of hyssop increased with Cd application and was higher in the moderately acidic than in the slightly alkaline soil environment. Hyssop is a Cd accumulator and accumulation occurred mainly in the roots in the acidic substrate. Measurement of extractable Cd by diethylene triamine penta acetic acid – triethanol amine (DTPA-TEA) could be used to predict Cd uptake by hyssop plants.

Strong seasonality in the cadmium and phosphate cycling at the subtropical convergence, south-eastern New Zealand

The global distribution of dissolved cadmium (Cd) in the world’s oceans is generally well understood. However, information on seasonal variability of this and other trace metals in the open ocean is difficult to obtain and, therefore, our understanding is limited. Here, we present a 3-year time series of field measurements of dissolved and particulate Cd and phosphate (PO4) from a transect across the subtropical convergence, south-eastern New Zealand. In the final year of study, the bioactive trace metals (iron, Fe; zinc, Zn; cobalt, Co) and nutrients (nitrate, NO3; silicate, Si(OH)4) were also measured to identify their influence on Cd cycling in the region. Cadmium varied seasonally from 0.009 to 0.137nM in the sub-Antarctic surface waters (SASW). Zinc in SASW varied between 0.03 and 0.011nM, which is low enough to suggest Zn limitation year-round. The seasonal input of dissolved Fe may stimulate phytoplankton growth in summer where microplankton (especially diatoms) dominate the phytoplankton distribution. The Cd:PO4 ratio also varied strongly with season (0.015×10–3 to 0.05×10–3). This seasonal variation in the Cd:PO4 ratio is productivity driven as revealed in the characteristic trend in the Cd:PO4 ratio, particulate Cd and chlorophyll-a measurements. The high seasonal variability between Cd and PO4 complicates the application of the Cd proxy for the reconstruction of historical PO4 concentrations in SASW.

High sensitivity fiber sensor for measurement of Cd2+ concentration in aqueous solution based on reflective Mach-Zehnder interference with temperature calibration.

We propose a novel fiber chemical sensing system based on reflective Mach-Zehnder interference with temperature calibration for the measurement of Cd2+ in aqueous solution. The sensing system has high measurement sensitivity of Cd2+ with an estimated minimum detection limit of 4×10-7 mol/L at a spectral resolution of 0.02 nm and with long-term stability. The fiber sensing head is prepared by coating a sensing membrane on a fused tapering single-mode fiber. The thiourea group of the sensing membrane has an effective combination effect on Cd2+. Disturbance from ambient temperature fluctuation on the measurement of Cd2+ concentration can be eliminated with the fiber Bragg grating.

The gelatinase biosynthesis-activating pheromone binds and stabilises the FsrB membrane protein in Enterococcusfaecalis quorum sensing.

Quorum‐sensing mechanisms regulate gene expression in response to changing cell‐population density detected through pheromones. In Enterococcus faecalis, Fsr quorum sensing produces and responds to the gelatinase biosynthesis‐activating pheromone (GBAP). Here we establish that the enterococcal FsrB membrane protein has a direct role connected with GBAP by showing that GBAP binds to purified FsrB. Far‐UV CD measurements demonstrated a predominantly α‐helical protein exhibiting a small level of conformational flexibility. Fivefold (400 μm) GBAP stabilised FsrB (80 μm) secondary structure. FsrB thermal denaturation in the presence and absence of GBAP revealed melting temperatures of 70.1 and 60.8 °C, respectively, demonstrating GBAP interactions and increased thermal stability conferred by GBAP. Addition of GBAP also resulted in tertiary structural changes, confirming GBAP binding.

The Effects of Gene-Environment Interactions Between Cadmium Exposure and Apolipoprotein E4 on Memory in a Mouse Model of Alzheimer's Disease.

Cadmium (Cd) is a heavy metal of great public health concern. Recent studies suggested a link between Cd exposure and cognitive decline in humans. The ε4 allele, compared with the common ε3 allele, of the human apolipoprotein E gene (ApoE) is associated with accelerated cognitive decline and increased risks for Alzheimer's disease (AD). To investigate the gene-environment interactions (GxE) between ApoE-ε4 and Cd exposure on cognition, we used a mouse model of AD that expresses human ApoE-ε3 (ApoE3-KI [knock-in]) or ApoE-ε4 (ApoE4-KI). Mice were exposed to 0.6 mg/l CdCl2 through drinking water for 14 weeks and assessed for hippocampus-dependent memory. A separate cohort was sacrificed immediately after exposure and used for Cd measurements and immunostaining. The peak blood Cd was 0.3-0.4 µg/l, within levels found in the U.S. general population. All Cd-treated animals exhibited spatial working memory deficits in the novel object location test. This deficit manifested earlier in ApoE4-KI mice than in ApoE3-KI within the same sex and earlier in males than females within the same genotype. ApoE4-KI but not ApoE3-KI mice exhibited reduced spontaneous alternation later in life in the T-maze test. Finally, Cd exposure impaired neuronal differentiation of adult-born neurons in the hippocampus of male ApoE4-KI mice. These data suggest that a GxE between ApoE4 and Cd exposure leads to accelerated cognitive impairment and that impaired adult hippocampal neurogenesis may be one of the underlying mechanisms. Furthermore, male mice were more susceptible than female mice to this GxE effect when animals were young.

Assessment on the binding characteristics of dasatinib, a tyrosine kinase inhibitor to calf thymus DNA: insights from multi-spectroscopic methodologies and molecular docking as well as DFT calculation

The binding characteristics of calf thymus DNA (ct-DNA) with dasatinib (DSTN), a tyrosine kinase inhibitor was assessed through multi-spectroscopic methodologies and viscosity measurement combined with molecular docking as well as DFT calculation to understand the binding mechanism, affinity of DSTN onto ct-DNA, effect of DSTN on ct-DNA conformation, and among others. The results confirmed DSTN bound onto ct-DNA, leading to forming the DSTN–ct-DNA complex with the binding constant of 4.82 × 103 M−1 at 310 K. DSTN preferentially inserted to the minor groove of ct-DNA with rich A-T region, that was the binding mode of DSTN onto ct-DNA was groove binding. The enthalpic change (ΔH0) and entropic change (ΔS0) during the binding process of DSTN with ct-DNA were 128.9 kJ mol−1 and 489.2 J mol−1 K−1, respectively, confirming clearly that the association of DSTN with ct-DNA was an endothermic process and the dominative driven-force was hydrophobic interaction. Meanwhile, the results also indicated that there was a certain extent of electrostatic force and hydrogen bonding, but they maybe play an auxiliary role. The CD measurement results confirmed the alteration in the helical configuration of ct-DNA but almost no change in the base stacking after binding DSTN. The results revealed that there was the obvious change in the conformation, the dipole moment, and the atomic charge distribution of DSTN in the B-DNA complexes, compared with free DSTN, to satisfy the conformational adaptation. From the obtained fronitier molecular orbitals of DSTN, it can be inferred that the nature of DSTN alters with the change of the environment around DSTN. Communicated by Ramaswamy H. Sarma

Variability of Seminal Plasma Cadmium Concentrations and Its Associations with Semen Quality among Healthy Chinese Men Screened as Potential Sperm Donors

TPS 631: Metals and health 1, Johan Friso Foyer, Floor 1, August 27, 2019, 3:00 PM - 4:30 PM Background: Cadmium (Cd) is a well-documented toxic metal, which has demonstrated adverse effects on male semen quality in animal studies. However, the results from human studies are inconsistent, probably due to the high within-subject variability in measurements of Cd in biological specimens and semen quality parameters. Objectives: To characterize the variability of Cd concentrations in seminal plasma and assessed its associations with repeated measurements of semen quality among healthy men who came to the Hubei Province Human Sperm Bank for donations screening. Methods: The reproducibility of Cd concentrations in 232 seminal plasma samples collected from 93 men was assessed using the intraclass correlation coefficient (ICC). The associations of Cd in within-subject pooled seminal plasma (n=1156) with repeated measurements of semen quality parameters (n = 5619) were assessed using linear mixed models with an individual-specific random intercept. Semen analyses were conducted by qualified laboratory technologists following the guidelines of the World Health Organization, and Cd concentration was determined by inductively coupled plasma-mass spectrometry. Results: Cd was detected in > 85% of the seminal plasma specimens. Fair to good reproducibility (ICC = 0.71) was achieved for serial measurements of Cd. Compared with men in the lowest Cd quartile, men in the highest quartile of Cd had a reduced semen volume and total motility of 3.25% (95% CI: -6.29%, -0.20%; p for trend = 0.027) and -1.88% (95% CI: -3.82%, 0.10%; p for trend = 0.083), respectively. Similar results were achieved when modeling Cd concentration (log-transformed) as a continuous variable in cubic spline models. Conclusion: Cd in seminal plasma were relatively stable. Exposure to high Cd may adversely affect semen volume and motility. Future studies in a larger and general population are needed to verify our findings.

Temperature-controlled assembly of homochiral metal-organic frameworks from 2D helical layers to 3D frameworks

Two pairs of homochiral metal-organic frameworks (HOMFs), {[Zn((R)-CBA) (1.3- DIB)]·H2O}n(1-D), {[Zn((S)-CBA) (1.3-DIB)]·H2O}n(1-L), [Zn2((R)-CBA)2 (1.3-DIB)2]n (2-D) and [Zn2((S)-CBA)2(1.3-DIB)2]n (2-L), have been synthesized by using lactate derivatives (R)/(S)-H2CBA and N-donor ancillary 1,3-DIB ligands at different reaction temperatures (H2CBA = 4-(1-carboxyethoxy)benzoic acid, 1,3-DIB = 1,3-di(1H-imidazole-1-yl) benzene). Complexes 1-D and 1-L are two-dimensional (2D) layers based on three kinds of chiral helical chains, while complexes 2-D and 2-L are four-connected three-dimensional (3D) frameworks with cds nets. The resulting homochiral complexes have been characterized by PXRD, TGA, IR and CD measurements. Additionally, complexes 1-D and 2-D exhibit different photoluminescence behaviors in solid sate compared to ligand (R)-H2CBA. The work has shown that the dimensionality of HMOFs can be regulated by the reaction temperature.

Central (S) to Central (M=Ir, Rh) to Planar (Metallocene, M=Fe, Ru) Chirality Transfer Using Sulfoxide‐Substituted Mesoionic Carbene Ligands: Synthesis of Bimetallic Planar Chiral Metallocenes

Enantiopure bimetallic systems containing three different elements of chirality, namely a main-group-based chiral center (sulfur), a transition-metal chiral center (rhodium or iridium), and a planar chiral element (ferrocene or ruthenocene), have been prepared by a sequence of diastereoselective reactions. The chirality of the chiral sulfur center attached to C-5 of a 1,2,3-triazolylidene mesoionic carbene (MIC) ligand coordinated to a metal (Ir, Rh) was transferred through the formation of bimetallic complexes having a chiral-at-metal center and a planar chiral metallocene by C-H activation of the sandwich moiety (M=Fe, Ru). The sense of the planar chirality formed in this sequence of reactions depended on the nature of the ligands at the metal center of the starting complex. The configurations of these species were assigned on the basis of a combination of X-ray diffraction and CD measurements. An electrochemical study of these bimetallic complexes in coordinating solvents showed an equilibrium between the cationic complexes and the neutral species. The effect of the half-sandwich moiety on the oxidation potentials of the system is remarkable, producing notable cathodic displacements. DFT calculations support these findings.

Natural compound safranal driven inhibition and dis-aggregation of α-synuclein fibrils

Self-assembly of α-synuclein (α-Syn) is linked with a variety of neurodegenerative diseases collectively called as α-synucleiopathies. Therefore, discovering suitable inhibitors for this self-association process of α-Syn is a subject of intense research. In this background, we have demonstrated here that the natural compound, Safranal, delays/inhibits α-Syn fibrillation/aggregation, and we have also characterized its mode of action. The α-Syn fibrillation/aggregation kinetics studies in combination with TEM studies demonstrated that Safranal effectively inhibits α-Syn fibrillation/aggregation. NMR studies revealed that Safranal binds with α-Syn and stabilizes the monomeric protein. ANS fluorescence and CD measurements indicated that Safranal binds to the hydrophobic residues of the protein and causes delay in the formation of β-sheet rich structures which are crucial for the fibrillation to occur. The results obtained from fluorescence quenching, NMR and ANS binding assays, when analysed taking into consideration the molecular structure of Safranal provide valuable insights into the mechanism of inhibition of α-Syn fibrillation/aggregation. We infer that inhibition of α-Syn fibrillation/aggregation is primarily driven by hydrophobic interactions between Safranal and the protein. Further, Safranal is also seen to dis-aggregates pre-formed α-Syn fibrils. These findings implicate that Safranal could become a potent therapeutic intervention in Parkinson's disease and other protein aggregation related disorders.

Mechanisms of aggregation and fibril formation of the amyloidogenic N-terminal fragment of apolipoprotein A-I

The N-terminal (1-83) fragment of the major constituent of plasma high-density lipoprotein, apolipoprotein A-I (apoA-I), strongly tends to form amyloid fibrils, leading to systemic amyloidosis. Here, using a series of deletion variants, we examined the roles of two major amyloidogenic segments (residues 14-22 and 50-58) in the aggregation and fibril formation of an amyloidogenic G26R variant of the apoA-I 1-83 fragment (apoA-I 1-83/G26R). Thioflavin T fluorescence assays and atomic force microscopy revealed that elimination of residues 14-22 completely inhibits fibril formation of apoA-I 1-83/G26R, whereas Δ32-40 and Δ50-58 variants formed fibrils with markedly reduced nucleation and fibril growth rates. CD measurements revealed structural transitions from random coil to β-sheet structures in all deletion variants except for the Δ14-22 variant, indicating that residues 14-22 are critical for the β-transition and fibril formation. Thermodynamic analysis of the kinetics of fibril formation by apoA-I 1-83/G26R indicated that both nucleation and fibril growth are enthalpically unfavorable, whereas entropically, nucleation is favorable, but fibril growth is unfavorable. Interestingly, the nucleation of the Δ50-58 variant was entropically unfavorable, indicating that residues 50-58 entropically promote the nucleation step in fibril formation of apoA-I 1-83/G26R. Moreover, a residue-level structural investigation of apoA-I 1-83/G26R fibrils with site-specific pyrene labeling indicated that the two amyloidogenic segments are in close proximity to form an amyloid core structure, whereas the N- and C-terminal tail regions are excluded from the amyloid core. These results provide critical insights into the aggregation mechanism and fibril structure of the amyloidogenic N-terminal fragment of apoA-I.

Polyethylene glycols affect electron transfer rate in phenosafranin-DNA complex.

Long distance electron transfer (ET) between small ligands and DNA is a much studied phenomenon and is principally believed to occur through electron (or hole) hopping. Several studies have been carried out in aqueous environments while in real biological milieu the DNA molecules experience a more dense and heterogeneous environment containing otherwise indifferent molecular crowders. It is therefore expected that the ET could get modified in the presence of crowding agent and to investigate that we have made elaborate studies on steady state and time-resolved (picosecond (ps) and femtosecond (fs)-resolved) emission properties of a phenosafranine (PSF) intercalated to calf thymus (CT) DNA in the presence of ethylene glycol (EG) and polyethylene glycols (PEG) of different chain lengths (PEG 200, 400 and 1000). The emission of PSF gets considerably quenched when intercalated to DNA; the quenching is released when PEGs are added into it. The structural integrity of the CT DNA has been established using circular dichroism spectroscopy. CD measurements have evidenced only marginal changes in the DNA structure upon the addition of PEGs. ps-Resolved fluorescence measurements show significant decrease in the contribution of the DNA induced quenched time-constant of PSF upon the addition of PEGs, however, fs-resolved measurements show less noticeable changes in the time constants. Our study shows that the electron hopping rate through the guanine base in DNA core remains unaffected whereas the 'through space' electron transfer process does get affected in the presence of molecular crowders.

Aspartic protease from Aspergillus niger: Molecular characterization and interaction with pepstatin A

In the pursuit of industrial aspartic proteases, aspergillopepsin A-like endopeptidase from the fungi Aspergillus niger, was identified and cultured by solid state fermentation. Conventional chromatographic techniques were employed to purify the extracellular aspartic protease to apparent homogeneity. The enzyme was found to have single polypeptide chain with a molecular mass of 50 ± 0.5 kDa. The optimum pH and temperature for the purified aspartic protease was found to be 3.5 and 60 °C respectively. The enzyme was stable for 60 min at 50 °C. The purified enzyme had specific activity of 40,000 ± 1800 U/mg. The enzyme had 85% homology with the reported aspergillopepsin A-like aspartic endopeptidase from Aspergillus niger CBS 513.88, based on tryptic digestion and peptide analysis. Pepstatin A reversibly inhibited the enzyme with a Ki value of 0.045 μM. Based on homology modeling and predicted secondary structure, it was inferred that the aspartic protease is rich in β-structures, which was also confirmed by CD measurements. Interaction of pepstatin A with the enzyme did not affect the conformation of the enzyme as evidenced by CD and fluorescence measurements. Degree of hydrolysis of commercial substrates indicated the order of cleaving ability of the enzyme to be hemoglobin > defatted soya flour > gluten > gelatin > skim milk powder. The enzyme also improved the functional characteristics of defatted soya flour. This aspartic protease was found to be an excellent candidate for genetic manipulation for biotechnological application in food and feed industries, due to its high catalytic turn over number and thermostability.

Macroalgae as spatial and temporal bioindicators of coastal metal pollution following remediation and diversion of acid mine drainage

Acid mine drainage (AMD) is a significant contributor of metal pollution leading to ecosystem damage. Bioindicator organisms such as intertidal brown macroalgae have an important role in quantifying the risks of metal bioaccumulation in coastal locations exposed to AMD contamination. Measurement of As, Cd, Cu, Fe, Pb, and Zn accumulation was performed in Fucus serratus, Fucus vesiculosus and Ascophyllum nodosum sampled from two marine locations near to an abandoned Cu mine in Anglesey, Wales, UK. Transect samples were taken from a coastal location (Amlwch) that has seen a substantial increase in AMD contamination over 15 years, in comparison to a nearby estuarine location (Dulas Estuary leading to Dulas Bay) with a historic legacy of pollution. These were compared with samples from the same sites taken 30 years earlier. Some of the Dulas macroalgae samples had Cd, Cu and Zn concentrations that were above background but in general indicated a non-polluted estuary in comparison to substantial pollution over previous decades. In contrast, Fucus samples collected from directly below an AMD outflow at Amlwch showed extremely elevated metal bioaccumulation (>250 mg Fe g−1, >6 mg Cu g−1, >2 mg Zn g−1, >190 μg As g−1) and evidence of macroalgae toxicity, indicating severe pollution at this site. However, the pollution dispersed within 200 m of the outflow source. This study has demonstrated the efficiency of three brown macroalgae species as indicators for metal bioavailability at high spatial resolution and over time.

Residual biomass of coffee as a binding agent in diffusive gradients in thin-films technique for Cd, Cu, Ni, Pb and Zn measurement in waters

Spent coffee grounds (SCG) immobilized in agarose gel are proposed as a novel binding agent for application in the Diffusive Gradients in Thin films (DGT) technique for the determination of Cd, Cu, Ni, Pb and Zn in waters. The SCG-agarose gel was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectrometry and Porosimetry by nitrogen adsorption. Elution of analytes from the binding agent was effectively performed with 2 mol L−1 HCl. The effects of key DGT parameters (e.g. immersion time, ionic strength and pH) were evaluated with a deployment of DGT devices (DGT-SCG) in synthetic solutions with ionic strengths between 0.005 mol L−1 and 0.1 mol L−1 and within a pH range of 3.5–8.0. The results were in excellent agreement with the predicted theoretical curve for mass uptake. Consistent results were found for solutions with ionic strengths between 0.005 mol L−1 and 0.1 mol L−1 and within a pH range of 3.5–8.0. The DGT-SCG performance was also evaluated in two spiked river water samples (Corumbataí and Piracicaba river) with satisfactory uptake values (CDGT-SCG/Csol) between 0.74 and 1.53. The proposed DGT-SCG opens opportunities for using residual biomass as binding phase in the DGT technique, showing low costs in production and complying with “green” technology approaches.

Proximity of the maxillary artery to the neck of the mandibular condyle: anatomical study.

The objective of this study was to evaluate the anatomical distance of the maxillary artery, the most superior portion of the condyle and subcondyle in standardized coronal sections, acquired from 16 hemifaces in 8 cadavers. Measurements were taken to evaluate the distance between the uppermost portion of the mandibular condyle and the height of the maxillary artery (AB) and between the lateral (CD) and medial (EF) sides of the condylar neck to the artery. The mean for AB was 21.1mm hemiface right and 22.9mm left on the anterior face, 22.5mm and 20.7mm, respectively, on the rear face. The CD measurement presented 6.7mm right side in the anterior face and 6.3mm left, and the posterior face was 6.3mm right side and 5.4mm left; EF presented a mean of 2.2mm right and 1.5mm left on the anterior face and 1.6mm for both sides on the posterior face. There was no statistically significant difference between hemifaces. The proximity of the maxillary artery to the medial face of the neck of the mandibular condyle is millimetric and presents risks of severe hemorrhage for interventions in the infratemporal fossa.

New cytotoxic biflavones from Selaginella doederleinii

Three new biflavones, apigenin-(3′,8″)-chrysin (1), (2S)-2,3-Dihydroametoflavone 5,4′-dimethyl ether (2), and (2S)-5″,7″-Dihydroxy-2″-phenoxychromonyl-(4′″,3′)-naringenin (3), together with seven known biflavones (4–10) were isolated from the 75% EtOH extract of Selaginella doederleinii. The structures of new compounds were established by application of spectroscopic methods, including 1D and 2D NMR, HRMS, and CD measurements. In addition, all new compounds were evaluated for their cytotoxic potential against three human cancer cell lines A549, MCF-7, and SMMC-7721 in vitro. Compound 2 exhibited potent cytotoxic activity with IC50 values ranging from 6.35 to 10.18 μM.

Interaction of Mitoxantrone-Loaded Cholesterol Modified Pullulan Nanoparticles with Human Serum Albumin and Effect on Drug Release

To clarify nanoparticle-protein interaction and their action characteristics, the interactions between MTO-CHP NPs and human serum albumin (HSA) were studied by isothermal titration calorimetry (ITC), fluorescence spectroscopy, dynamic light scattering (DLS), and circular dichroism spectroscopy (CD). Hydrophobically modified pullulan (CHP) nanoparticles (NPs) loaded with mitoxantrone (MTO) were prepared (MTO-CHP NPs) with size 166.9 nm. The spherical shape was verified by transmission electron microscopy (TEM). The ITC results demonstrated an interaction between MTO-CHP NPs mainly by hydrophobic interaction force, electrostatic force, and hydrogen bonding. The mean binding constant KA was 0.832×104 M−1 and mean HSA coverage 0.939±0.302. MTO-CHP NPs could quench the fluorescence intensity of HSA, which gradually decreased to be balanced in 9 h and indicated the completion of the complexation. The size and zeta potential changes of the combined particle were dynamically detected with DLS at 0, 3, 6, 9, 12, 15, and 18 h. When the reaction was completed at 9 h, the particle size and potential remained stable, accompanied by a size change from 89.91 to about 145 nm and potential change from -15 to -3 mV, respectively. The results of CD measurement showed that the change in ellipticity of HSA at 208 nm was similar to the fluorescence spectra and DLS measurements with MTO-CHP NPs combined with HSA. At the beginning of the reaction, the proportion of α-helix was 52.3% to 43.7%, which decreased by 39.1% at compound stabilization. The release of MTO from MTO-CHP NPs at pH=5.6 was significantly accelerated, whereas that of MTO from HSA-MTO-CHP NPs was significantly reduced, and the drug release was significantly slowed down even under acidic conditions, which indicates the beneficial effect of HSA on the persistence and stability of the HSA-MTO-CHP NP compound.

A novel bismuth imidazolate-based sensor for detection of trace lead(II)

A new type of bismuth electrode (BiImE) for anodic stripping voltammetric detection of trace Pb(II), which is based on a bismuth imidazolate (BiIm) sensing coating, is presented. A simple preparation protocol was adopted via drop-casting a rapidly drying methanol suspension of amorphous BiIm, serving as a source of bismuth ions, onto a supporting glassy carbon electrode. The BiIm sensing material was characterized and several key parameters influencing the preparation and performance of BiImE were investigated. The BiImE revealed good linear response in the two examined concentration ranges of 10–100 μg L−1 and 1–10 μg L−1 with r2 of 0.998 and 0.995, respectively, a low limit of detection (3σ) of 0.1 μg L−1 Pb(II) associated with 240 s accumulation, and a favorable repeatability with RSD of 3.8%. Even after scanning the potential toward more positive values than the re-oxidation potential of bismuth, the BiImE could be reused several times without any significant loss of performance, hence making it superior compared to its ex situ prepared counterparts while exhibiting advantages of the in situ prepared analogues. The applicability of BiImE was demonstrated through measuring Pb(II) in a real tap water sample. Preliminary experiments also proved its suitability for simultaneous measurement of trace Pb(II) and Cd(II).

Investigation of the role of central metal ion of Cyathus bulleri laccase 1 using guanidinium chloride-induced denaturation.

The structure and folding/unfolding kinetics of Cyathus bulleri laccase 1 (Lcc1), expressed in Pichia pastoris, were analyzed by spectroscopic methods to understand the role of central metal ion. Far UV CD structure analysis revealed major β-sheet and minor α helical segments present in the Lcc1. A significant change in the spectrum of Lcc1, indicative of unfolding of secondary structures, was observed with increasing concentrations of guanidinium chloride (GdnHCl) during Trp fluorescence, absorption and CD measurements. A similar trend was also noticed for enzyme activity with respect to GdnHCl concentrations. To establish the role of copper ion in the catalytic activity of laccase, a complete removal of copper was carried out and addition of copper was found to restore the structure and activity during the refolding process. The apo form was also reconstituted by addition of zinc ion which restored nearly 84% of enzyme activity, indicating non-essential role of copper in maintaining conformation and activity. Structural studies and inductively coupled plasma mass spectrometry data supported these observations.