Divalent metal ion modulation of a simple peptide-based hydrogel: self-assembly and viscoelastic properties.

Peptide self-assembly has been highly studied to understand the pathways in forming higher order structures along with the development and application of resulting hydrogel materials. Driven by noncovalent interactions, peptide hydrogels are stimuli-responsive to any addition to its gelling conditions. Here, a Phe-His based peptide, C14-FH(Trt)-OH, was synthesized and characterized with 1H NMR, FT-IR, MS, UV-vis spectroscopies and elemental analysis. Based on SEM imaging, the dipeptide conjugate was capable of forming a nanofibrous, interconnected network encapsulating buffer to produce a supramolecular hydrogel. Through the addition of Zn2+ and Cu2+, there is a clear change in the self-assembled nanostructures characterized through SEM. With this effect on self-assembly follows a change in the viscoelastic properties of the material, as determined through rheological frequency sweeps, with 2 and 3 orders of magnitude decreases in the elastic modulus G' in the presence of Zn2+ and Cu2+ respectively. This highlights the tunability of soft material properties with peptide design and self-assembly, through metal ions and Nδ-directed coordination.

Development of a Bacterial Enzyme-Based Biosensor for the Detection and Quantification of Selenate.

An enzymatic biosensor has been developed for the determination of selenate (SeO4 2- ), in which selenate reductase (SeR) is chemically attached to a gold disk electrode by lipoic acid N-hydroxysuccinimide ester as linker, allowing the catalytic reduction of the SeO4 2- to SeO3 2- . Modification of the gold electrode was characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and electrochemistry. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were performed in different buffers for selenate determination. Under optimum conditions, the calibration curve was linear over the range 7.0-3900.0 µg L-1 with limits of detection and quantification of 4.97 and 15.56 µg L-1 , respectively. The possible interference of the relevant oxyanions SO4 2- , NO3 - , NO2 - , PO4 3- and AsO4 3- in the determination of SeO4 2- was studied. Finally, the proposed biosensor was used to determine SeO4 2- with recovery between 95.2 and 102.4 % in different real water samples.

Facile bimetallic co-amplified electrochemical sensor for folic acid sensing based on CoNPs and CuNPs.

Folic acid (FA) is essential for human health, particularly for pregnant women and infants. In this work, a glassy carbon electrode (GCE) was modified by a bimetallic layer of Cu/Co nanoparticles (CuNPs/CoNPs) as a synergistic amplification element by simple step-by-step electrodeposition, and was used for sensitive detection of FA. The proposed CuNPs/CoNPs/GCE sensor was characterized by differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and field emission scanning electron microscopy (FESEM). Then, under optimal conditions, a linear relationship was obtained in the wide range of 110.00-1750.00 µM for the detection of FA with a limit of detection (LOD) of 34.79 µM (S/N = 3). The sensitivity was calculated as 0.096 µA µM-1 cm-2. Some interfering compounds including glucose (Glc), biotin, dopamine (DA), and glutamic acid (Glu) showed little effect on the detection of FA by amperometry (i-t). Finally, the average recovery obtained was in a range of 91.77-110.06%, with a relative standard deviation (RSD) less than 8.00% in FA tablets, indicating that the proposed sensor can accurately and effectively detect the FA content in FA tablets.

Metal-dependent electrochemical discrimination of DNA quadruplex sequences.

Films of four different DNA quadruplex-forming (G4) sequences (c-KIT, c-MYC, HTelo, and BCL2) on gold surfaces were investigated by electrochemical impedance spectroscopy (EIS) to evaluate whether they evoke unique electrochemical responses that can be used for their identification. This could render EIS an alternative means for the determination of G4 sequences of unknown structure. Towards, this end, cation-dependent topology changes in the presence of either K+, K+ in combination with Li+, or Pb2+ in the presence of Li+ were first evaluated by circular dichroism (CD) spectroscopy, and electrochemical studies were performed subsequently. As a result, G4-sequence specific charge transfer resistance (RCT) patterns were in fact observed for each G4 sequence, allowing their discrimination by EIS.

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine.

Electrocatalytic reduction of CO2 into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO2 in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO2 reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO2 reduction than their smooth polycrystalline electrode counterparts, indicating improved CO2 reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO2 reduction.

Synthesis and Biochemical Evaluation of Nicotinamide Derivatives as NADH Analogue Coenzymes in Ene Reductase.

Nicotinamide and pyridine-containing conjugates have attracted a lot of attention in research as they have found use in a wide range of applications including as redox flow batteries and calcium channel blockers, in biocatalysis, and in metabolism. The interesting redox character of the compounds' pyridine/dihydropyridine system allows them to possess very similar characteristics to the natural chiral redox agents NAD+ /NADH, even mimicking their functions. There has been considerable interest in designing and synthesizing NAD+ /NADH mimetics with similar redox properties. In this research, three nicotinamide conjugates were designed, synthesized, and characterized. Molecular structures obtained through X-ray crystallography were obtained for two of the conjugates, thereby providing more detail on the bonding and structure of the compounds. The compounds were then further evaluated for biochemical properties, and it was found that one of the conjugates possessed similar functions and characteristics to the natural NADH. This compound was evaluated in the active enzyme, enoate reductase; like NADH, it was shown to help reduce the C=C double bond of three substrates and even outperformed the natural coenzyme. Kinetic data are reported.

Electrochemical studies of human nAChR a7 subunit phosphorylation by kinases PKA, PKC and Src.

Nicotinic acetylcholine receptors (nAChR) are ion channels which regulate a numerous of neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin and glutamate. These receptors are important targets for the study of a plethora of diseases such as Alzheimer's disease, schizophrenia, Parkinson's Disease, cancer, inflammation, etc. The α7 subunits are especially interesting in that they are commonly occurring and are critical sites of regulation. Herein we report the phosphorylation of the human nAChR α7 subunits, by the kinases PKA, PKC and Src, by both biochemical and electrochemical techniques along with the kinetics of each phosphorylation reaction. Phosphorylation was investigated through changes in current density as well as impedance and X-ray photo electron spectroscopy (XPS) and the kinetics were determined electrochemically using the surface Michaelis-Menten model. Our results clearly demonstrate the phosphorylation of the nAChR α7 and the invaluable strength of surface electrochemical techniques in the investigation of protein phosphorylation.

Enzyme Entrapment in Amphiphilic Myristyl-Phenylalanine Hydrogels.

Supramolecular amino acid and peptide hydrogels are functional materials with a wide range of applications, however, their ability to serve as matrices for enzyme entrapment have been rarely explored. Two amino acid conjugates were synthesized and explored for hydrogel formation. These hydrogels were characterized in terms of strength and morphology, and their ability to entrap enzymes while keeping them active and reusable was explored. It was found that the hydrogels were able to successfully entrap two common and significant enzymes-horseradish peroxidase and -amylase-thus keeping them active and stable, along with inducing recycling capabilities, which has potential to further advance the industrial biotransformation field.

Supramolecular Assembly of Peptide and Metallopeptide Gelators and Their Stimuli-Responsive Properties in Biomedical Applications.

Supramolecular gels are a fascinating class of soft materials that have attracted significant attention in recent years. They are composed of small molecule gelators that assemble into supramolecular network structures. The resulting space is filled with solvent. Some gel materials are able to respond to various stimuli making them attractive drug delivery vehicles and as matrices for tissue regeneration. Peptide-based gel materials are particularly attractive as they possess numerous advantages including biocompatibility and biodegradability. Stimuli-responsive peptides that alter properties as a function of pH, redox, temperature, and enzymes offer the potential to create materials with tunable characteristics. In addition, the ability of metal ions to improve the strength of gelation or act as a scaffold has become an interesting approach to develop dynamic peptide gel materials. In this review, the stimuli-responsive properties (pH, redox, temperature, and enzyme responsive properties), as well as the biocompatible/-degradable nature of the peptide gelators are highlighted. In addition, metal ions are discussed as a stimulus to enhance peptide gelation and a number of potential applications of these peptide gelators are provided with an outlook on future directions.

AgI -Induced Switching of DNA Binding Modes via Formation of a Supramolecular Metallacycle.

The histidine derivative L1 of the DNA intercalator naphthalenediimide (NDI) forms a triangular AgI complex (C2). The interactions of L1 and of C2 with DNA were studied by circular dichroism (CD) and UV/Vis spectroscopy and by viscosity studies. Different binding modes were observed for L1 and for C2, as the AgI complex C2 is too large in size to act as an intercalator. If AgI is added to the NDI molecule that is already intercalated into a duplex, higher order complexes are formed within the DNA duplex and cause disruptions in the helical duplex structure, which leads to a significant decrease in the characteristic CD features of B-DNA. Thus, via addition of a metal we show how a classic and well-known organic intercalator unit can be turned into a partial metallo insertor. We also show how electrochemical impedance spectroscopy (EIS) can be used to probe DNA binding modes on DNA films that are immobilized on gold surfaces.

Electron Transfer in Spacer-Free DNA Duplexes Tethered to Gold via dA10 Tags.

Electrical properties of DNA critically depend on the way DNA molecules are integrated within the electronics, particularly on DNA-electrode immobilization strategies. Here, we show that the rate of electron transport in DNA duplexes spacer-free tethered to gold via the adenosine terminal region (a dA10 tag) is enhanced compared to the hitherto reported DNA-metal electrode tethering chemistries. The rate of DNA-mediated electron transfer (ET) between the electrode and methylene blue intercalated into the dA10-tagged DNA duplex approached 361 s-1 at a ca. half-monolayer DNA surface coverage ΓDNA (with a linear regression limit of 670 s-1 at ΓDNA → 0), being 2.7-fold enhanced compared to phosphorothioated dA5* tethering (6-fold for the C6-alkanethiol linker representing an additional ET barrier). X-ray photoelectron spectroscopy evidenced dA10 binding to the Au surface via the purine N, whereas dA5* predominantly coordinated to the surface via sulfur atoms of phosphothioates. The latter apparently induces the DNA strand twist in the point of surface attachment affecting the local DNA conformation and, as a result, decreasing the ET rates through the duplex. Thus, a spacer-free DNA coupling to electrodes via dA10 tags thus allows a perspective design of DNA electronic circuits and sensors with advanced electronic properties and no implication from more expensive, synthetic linkers.

Hg(ii) interactions with T-rich regions in oligonucleotides: effects of positional variations on the electrochemical properties.

Hg(ii) binding to thymine-rich oligonucleotides (ODNs) is investigated electrochemically. The focus of this study is to probe the effects of position on the electrochemical response. For this purpose, three oligonucleotides were investigated in which the position of a hexa-thymine repeat is varied within a surface-supported oligonucleotide. The hexa repeats were placed in the top, middle, and bottom positions within the strand with respect to the gold surface. The effects were monitored by electrochemical impedance spectroscopy and scanning electrochemical microscopy. Using charge transfer resistance (RCT) and tip current (I) as a measure, it was possible to monitor the effects of Hg(ii) binding to the ds-oligonucleotide. The extent of film resistance reduces as the T-rich region moves from the bottom to top position within the film. The T-rich region closer to the gold surface probably builds less flexible and more rigid T-Hg(ii)-T basepairs compared to the other two positions and is expected to stay in the upright orientation on the surface. This in turn results in significant differences in the electrochemical readout, demonstrating that the position of T-rich sequences within an oligonucleotide strand matters.

Detection of the Lipopeptide Pam3CSK4 Using a Hybridized Toll-like Receptor Electrochemical Sensor.

Electrochemical detection of Pam3CSK4, a synthetic triacylated lipopeptide that mimics the structural moieties of its natural Gram negative bacterial pathogen-associated molecular pattern (PAMP) counterpart, has been achieved using hybridized toll-like receptors (TLR) combining TLR1 and TLR2 onto a single sensor surface. These sensors represent the first hybridized TLR sensors. The limit of detection for Pam3CSK4 attained was 7.5 µg/mL, which is within the same order of magnitude for that of the more labor-intensive and time-consuming cell-assay technique, 2.0 µg/mL. The results gathered in these electrochemical experiments show that sensors fabricated by immobilizing a mixture of cooperative TLR1 and -2 generate higher responses when exposed to the analyte in comparison to the control sensors fabricated using pure TLR1 or -2 standalone. A PAMP selectivity test was carried out in line with our inspiration from the mammalian innate immune response. TLRs1-5 as standalone biorecognition elements and the hybridized "TLR1 and 2" sensor surface were investigated, understanding the known TLR-PAMP interactions, through the exploitation of this electrochemical sensor fabrication technique. The experimental result is consistent with observations from previously published in vivo and in vitro studies, and it is the first demonstration of the simultaneous evaluation of electrochemical responses from multiple, unique fabricated TLR sensor surfaces against the same analyte.

A Bioorganometallic Approach to Study Histidine Kinase Autophosphorylations.

Auto-phosphorylation of bacterial histidine kinases PhoR, PhoQ, and EnvZ has been investigated using adenosine-5'-[γ-ferrocene] triphosphate (Fc-ATP) as a cosubstrate for the first time. The study has been carried out in solution and on surface. Results from biochemical multiplex assay and surface electrochemical/optical methods are consistent, which successfully demonstrates that Fc-ATP is an efficient cosubstrate for histidine kinase auto-phosphorylations. The study also has discovered that the concentration of Fc-ATP influences the autophosphorylation efficiency. This developed methodology will provide a powerful tool in studying such biological processes towards further understanding of the involved mechanism.

Helically Chiral Peptides That Contain Ferrocene-1,1'-diamine Scaffolds as a Turn Inducer.

A series of peptides that contain homo- and heterochiral Ala-Pro sequences attached to the turn-inducing ferrocene-1,1'-diamine scaffold were synthesized. The effects of the backbone chirality and the N-terminal group (Boc/Ac) on the conformational properties of the novel peptidomimetics were thoroughly explored by IR, NMR, and CD spectroscopy and the experimental observations were corroborated by DFT studies in solution. The most stable conformers of the homochiral peptides adopted the interstrand hydrogen-bond patterns, realized through ten- and thirteen-membered rings. The common feature of the most stable conformers of the heterochiral peptides was the adoption of the turn-like structures that feature the simultaneous intra- (seven-membered) and interstrand (sixteen-membered) hydrogen-bonded rings. An exchange of two N-terminal groups had a somewhat larger influence on the distribution of the hydrogen-bond patterns in homochiral than in heterochiral derivatives. The homochiral peptides that contain pyridine moieties as metal coordination sites formed 1:1 complexes with divalent metal ions, which included Zn2+ , Cd2+ , Cu2+ and Fe2+ .

Interactions of Hg(ii) with oligonucleotides having thymine-thymine mispairs. Optimization of an impedimetric Hg(ii) sensor.

The present work describes the effect of the number of thymine-thymine mispairs in single strand DNA probes on Hg(ii) interactions and further to develop a highly sensitive DNA based impedimetric sensor for Hg(ii) detection. To achieve this goal, the influence of the number of T-T mispairs on the signal response prompted by DNA-Hg(ii) binding interactions was examined on three designed DNA probes: 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCACACGTTCCTTACGC-3', 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCACATTTTCCTTTTGC-3', 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCATTTTTTCCTTTTTT-3' having 2T-T, 4T-T and 6T-T mispairs with identical length, respectively. This study revealed that the number of T-T mispairs plays a critical role in maximizing the signal intensity of DNA-Hg(ii) binding interactions. Based on these results, DNA comprising maximum number of T-T mispairs was further utilized for construction of the Hg(ii) sensor, which exhibited a linear correlation between the change in charge transfer resistance (ΔRCT) and the concentration of Hg(ii) over the range of 1.0 × 10-5 M to 1.0 × 10-10 M with a lower detection limit of 3.2 × 10-11 M. The selectivity was tested against 12 different metal ions including Hg(ii). The ΔRCT response from Hg(ii) is 3 times higher than the nearest competitor Pb(ii) and approximately 10 times than other ions. The potential application of such a robust and label-free DNA sensor was demonstrated by analyzing environmental samples collected from Lake Ontario.

On the Role of Chirality in Guiding the Self-Assembly of Peptides.

Homochirality in peptides is crucial in sustaining "like-like" intermolecular interactions that allow the formation of assemblies and aggregates and is ultimately responsible for the resulting material properties. With the help of a series of stereoisomers of the tripeptide F-F-L, we demonstrate the critical role that peptide stereochemistry plays in the self-assembly of peptides, guided by molecular recognition, and for self-sorting. Homochiral self-assemblies are thermally and mechanically more robust compared to heterochiral self-assemblies. Morphological studies of the multicomponent peptide systems showed that aggregates formed from homochiral peptides possessed a uniform nano-fibrous structure, whereas heterochiral systems resulted in self-sorted systems with a heterogeneous morphology. In essence, homochiral peptides form the stronger aggregates, which may be one of reasons why homochirality is preferred in living systems.

DNA Films Containing the Artificial Nucleobase Imidazole Mediate Charge Transfer in a Silver(I)-Responsive Way.

The first sequence-dependent study of DNA films containing metal-mediated base pairs was performed to investigate the charge transfer resistance (RCT ) of metal-modified DNA. The imidazole (Im) deoxyribonucleoside was chosen as a highly AgI -specific ligandoside for the formation of Im-AgI -Im complexes within the duplexes. This new class of site-specifically metal-modified DNA films was characterized by UV, circular dichroism (CD), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of these systems were investigated by means of electron impedance spectroscopy and scanning electrochemical microscopy. Taken together, these experiments indicated that the incorporation of AgI ions into the DNA films leads to reduced electron transfer through the DNA films. A simple device was proposed that can be switched reversibly between two distinct states with different charge transfer resistance.

Ferrocene-Modified Phospholipid: An Innovative Precursor for Redox-Triggered Drug Delivery Vesicles Selective to Cancer Cells.

Controlled payload release is one of the key elements in the creation of a reliable drug delivery system. We report the discovery of a drug delivery vessel able to transport chemotherapeutic agents to target cancer cells and selectively trigger their release using the electrochemical activity of a ferrocene-modified phospholipid. Supported by in vitro assays, the competitive advantages of this discovery are (i) the simple one step scalability of the synthetic process, (ii) the stable encapsulation of toxic drugs (doxorubicin) during transport, and (iii) the selective redox triggering of the liposomes to harness their cytotoxic payload at the cancer site. Specifically, the redox-modified giant unilamellar vesicle and liposomes were characterized using advanced methods such as scanning electrochemical microscopy (SECM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and fluorescent imaging.

Effects of bipyramidal gold nanoparticles and gold nanorods on the detection of immunoglobulins.

Two types of gold nanoparticles are compared for their use in a sensor for immunoglobulin detection - bipyramidal gold nanoparticles (GBPs) and gold nanorods (GNRs). Using surface plasmon resonance spectroscopy and square wave voltammetry allowed us to evaluate the utilities of these two types of gold nanoparticles in a label-free detection of the analyte IgG. However both systems showed a significant enhancement in sensitivity over a nanoparticle free system, showing a 64-fold enhancement for the GBP-containing sensor and a 16-fold enhancement for the GNR-containing sensor systems.