Electrochemical immunosensor designs for the determination of Staphylococcus aureus using 3,3-dithiodipropionic acid di(N-succinimidyl ester)-modified gold electrodes

The preparation of novel Staphylococcus aureus (S. aureus) amperometric immunosensing designs based on the covalent immobilization of RbIgG at gold electrodes using the heterobifunctional cross-linker 3,3-dithiodipropionic acid di(N-succinimidyl ester) (DTSP), are reported. Two different competitive immunosensing configurations have been tested and compared. In the first one, protein A-bearing S. aureus cells and HRP-labelled antiRbIgG compete for immobilized RbIgG binding sites, while in the second case HRP-labelled protein A was used. In both cases, the evaluation of the developed immunosensors performance was accomplished through the monitoring at 0.00 V (vs. Ag/AgCl) of the catalytic current originated after addition of hydrogen peroxide, using tetrathiafulvalene as redox mediator entrapped at the modified electrode surface by cross-linking with glutaraldehyde. Optimization of variables concerning the composition of the immunosensors as well as the detection conditions was carried out in 0.1 M NaAc/0.1 M NaCl buffer of pH 5.6. The configuration that employed antiRbIgG-HRP resulted in better analytical characteristics, with a detection limit of 1.4 × 10⁴ cells mL⁻¹ for S. aureus cells submitted to wall lyses by ultrasonic treatment. This immunosensor design was also evaluated using gold screen-printed electrodes in order to reduce the analysis time and cost. In this case, a limit of detection of 3.7 × 10² cells mL⁻¹ and a dynamic range from 1.3 × 10³ to 7.6 × 10⁴ cells mL⁻¹ was obtained. A RSD value of 10.5% was found for the responses to 9.6 × 10³S. aureus cells mL⁻¹ obtained with seven different Au/SPEs-immunosensors. These disposable immunosensors were applied to the quantification of S. aureus in milk spiked at two concentration levels, 1.2 × 10³ and 4.8 × 10³ cells mL⁻¹, with good recoveries.     

A New Sulfur‐containing Schiff‐Base Ligand and Binding to Copper(II) and Cobalt(II)

A new Schiff‐base ligand having a potentially coordinating thioether group (2‐quinoline‐N‐(2′‐methylthiophenyl)methyleneimine, qmtpm ) has been prepared. The synthesis, structure, UV‐Vis and EPR studies of one copper(II) and two cobalt(II) complexes from this ligand is reported. The X‐ray structures of the Cu^II and Co^II chlorido complexes 1 and 2 reveal the metal atoms in highly distorted square‐pyramidal environments constituted of one tridentate ligand and two anions. On the other hand, the thiocyanato Co^II compound 3 exhibits a distorted trigonal‐bipyramidal structure. These structural variations are apparently due to the different counter‐ions which leads to distinct lattice interactions. The spectroscopic data obtained by EPR and UV‐Vis investigations are in agreement with the solid‐state structures of the coordination compounds.     

The role of intermolecular interactions in the assemblies of Fe and Co tetrakis-isothiocyanatometalates with tris(1,10-phenanthroline)-Ru: Crystal structures of two dual-metal assemblies featuring octahedral cationic and tetrahedral anionic modules

Two new dual-metal assemblies: 2[Ru(phen)₃]²⁺·[Fe(SCN)₄]²⁻·2SCN⁻·4H₂O 1 and [Ru(phen)₃]²⁺·[Co(SCN)₄]²⁻2, (phen:1,10-phenanthroline), have been prepared and their structures were characterized by X-ray diffraction. In 1, the cationic octahedral enantiomers are arranged with a ΛΔΛΔΛ sequence supported by π-π stacking and the anionic inorganic tetrahedral units are oriented between these stacks by interacting with the nearby water molecules through strong O-H?O and O-H?S hydrogen bonds. In 2, homochiral double helices in the b-direction are revealed, with tetrakis-isothiocyanate Co^II anions arranged in the crystal to furnish one-dimensional (1D)-helical chains with S?S intermolecular interactions at 3.512(2) and 3.966(2) Å supporting [Ru(phen)₃]²⁺Λ- and Δ-helices with Ru?Ru shortest distance of 8.676(7) Å. In both 1 and 2, the supramolecular assembly is maintained by C-H?S hydrogen bonds extending between the phenanthroline aromatic carbons in the cationic nodes and the sulphur atoms of the isothiocyanates anions. Analysis of S?S interactions in isothiocyanate containing compounds using Cambridge structural database (CSD) showed an angle dependence categorizing these interactions into “type-I” and “type-II”.     

Evidence for Multiple Binding Modes in the Initial Contact Between SARS-CoV-2 Spike S1 Protein and Cell Surface Glycans**

Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required.     

Inside Cover: Acid-catalyzed Disulfide-mediated Reversible Polymerization for Recyclable Dynamic Covalent Materials (Angew. Chem. Int. Ed. 11/2023)

Poly(1,2-dithiolane)s are a family of intrinsically recyclable polymers due to their dynamic covalent disulfide linkages. Despite the common use of thiolate-initiated anionic ring-opening polymerization (ROP) under basic condition, cationic ROP is still not exploited. Here we report that disulfide bond can act as a proton acceptor, being protonated by acids to form sulfonium cations, which can efficiently initiate the ROP of 1,2-dithiolanes and result in high-molecular-weight (over 1000 kDa) poly(disulfide)s. The reaction can be triggered by adding catalytic amounts of acids and non-coordinating anion salts, and completed in few minutes at room temperature. The acidic conditions allow the applicability for acidic monomers. Importantly, the reaction condition can be under open air without inert protection, enabling the nearly quantitative chemical recycling from bulk materials to original monomers.     

面包酵母催化不对称还原2,5-己二酮

选用10种面包酵母,研究其对2,5-己二酮的不对称还原特性。筛选出一种酵母S.c No.6,对底物2,5-己二酮有较高的转化活性和对映体选择性。初始底物浓度20 mmol.L-1,经酵母转化48h,2,5-己二醇得率为84.0%,e.e.值94.8%。采用气相色谱-质谱联用技术确认酵母培养液中存在中间产物5-羟基-2-己酮,并推测酵母不对称还原2,5-己二酮的反应分两步进行,首先生成中间产物(S)-5-羟基-2-己酮,而后二次加氢生成(2S,5S)-2,5-己二醇。