Adjuvants Based on Hybrid Antibiotics Overcome Resistance in Pseudomonas aeruginosa and Enhance Fluoroquinolone Efficacy

The use of adjuvants that rescue antibiotics against multidrug‐resistant (MDR) pathogens is a promising combination strategy for overcoming bacterial resistance. While the combination of β‐lactam antibiotics and β‐lactamase inhibitors has been successful in restoring antibacterial efficacy in MDR bacteria, the use of adjuvants to restore fluoroquinolone efficacy in MDR Gram‐negative pathogens has been challenging. We describe tobramycin–ciprofloxacin hybrid adjuvants that rescue the activity of fluoroquinolone antibiotics against MDR and extremely drug‐resistant Pseudomonas aeruginosa isolates in vitro and enhance fluoroquinolone efficacy in vivo. Structure–activity studies reveal that the presence of both tobramycin and ciprofloxacin, which are separated by a C12 tether, is critical for the function of the adjuvant. Mechanistic studies indicate that the antibacterial modes of ciprofloxacin are retained while the role of tobramycin is limited to destabilization of the outer membrane in the hybrid.     

Exploring Helical Peptides and Foldamers for the Design of Metal Helix Frameworks: Current Trends and Future Perspectives

Flexible and biocompatible metal peptide frameworks ( MPFs) derived from short and ultra-short peptides have been explored for the storage of greenhouse gases, molecular recognition, and chiral transformations. In addition to short flexible peptides, peptides with specifically folded conformations have recently been utilized to fabricate a variety of metal helix frameworks ( MHFs ). The secondary structures of the peptides govern the structure-assembly relationship and thereby control the formation of three-dimensional (3D)- MHFs . Particularly, the hierarchical structural organization of peptide-based MHFs has not yet been discussed in detail. Here, we describe the recent progress of metal-driven folded peptide assembly to construct 3D porous structures for use in future energy storage, chiral recognition, and biomedical applications, which could be envisioned as an alternative to the conventional metal-organic frameworks (MOFs).     

Nanomechanical fingerprints of individual blocks of a diblock copolymer chain

Atomic force microscopy (AFM)-based single polymer chain pulling experiments have been used to study the structural transitions of individual homopolymer chains in water. Polystyrene (PS) showed a three-regime force-extension profile exhibiting a force plateau reminiscent of a first-order transition, as predicted theoretically, whereas poly(methyl methacrylate) (PMMA) showed a characteristic saw-tooth pattern reminiscent of multidomain disassembly behavior. The two distinct structural transtions provide fingerprints for the individual homopolymers, which can be used to identify individual blocks of symmetric and asymmetric PS- b-PMMA diblock copolymer chains.     

Langmuir-Blodgett thin films of quantum dots: synthesis, surface modification, and fluorescence resonance energy transfer (FRET) studies

We describe herein studies on as-prepared hydrophobic ZnS-CdSe quantum dots (QDs) at the air-water interface. Surface pressure-area (pi-A) isotherms have been used to study the monolayer behavior. Uniform, lamellar multilayer thin films of QDs were deposited by the Langmuir-Blodgett (LB) technique. The role of two different surfactant systems commonly employed in the synthesis of these QDs (trioctylphosphine oxide-octadecylamine (TOPO-ODA) system and trioctylphosphine oxide-tetradecylphosphonic acid (TOPO-TDPA) system) on the monolayer behavior and the quality of thin films produced has been investigated. The thin films were characterized by quartz crystal microgravimetry (QCM), contact angle measurements, fluorescence spectroscopy, and transmission electron microscopy (TEM). These QD films were further modified by an amphiphilic polymer, poly(maleic anhydride-alt-1-tetradecene) (PMA). The hydrophobic interaction between the polymers and the surfactants attached to the QDs drove the self-assembly process. The carboxylic acid functional groups in the polymer were also used to immobilize avidin. We have demonstrated a proof of concept for the biosensing strategy wherein the avidin-coated QD films attracted biotinylated gold nanoparticles, resulting in fluorescence resonance energy transfer (FRET) quenching of the thin films.     

Solvent dependent excited state spectral properties of 4-hydroxyacridine: Evidence for only water mediated excited state proton transfer process

The possibility of ground and excited state proton transfer reaction across the five member intramolecular hydrogen bonded ring in 4-hydroxyacridine (4-HA) has been investigated spectroscopically and the experimental results have been correlated with quantum chemical calculations. The difference in the emissive behaviour of 4-HA in different types of solvents is due to the presence of different species in the excited state. In non-polar solvents, the species present is non-fluorescing in nature, whereas 4-HA molecule shows normal emission from intramolecularly hydrogen bonded closed conformer in polar aprotic solvents. In polar protic solvents like MeOH, EtOH, etc. (except water), a single broad emission band is attributed to the hydrogen bonded solvated form of 4-HA. However, in case of water, fluorescence from the tautomeric form of 4-HA is observed apart from emission from the solvated form. Emission from the tautomeric form may arise due to double proton transfer via a single water molecule bonded to 4-HA. Evaluation of the potential energy surfaces by quantum chemical calculations using density functional theory (DFT) and time dependent density functional theory (TDDFT), however, points towards the possibility of proton transfer—both intrinsic intramolecular as well as water mediated in the first excited state of 4-HA.     

Magnetic field effect on photoinduced electron transfer between [Cu(phen)2]2+ and DNA

The magnetic field effect (MFE) on the photoinduced electron transfer (PET) reaction between the [Cu(phen)2]2+ complex and DNA has been studied in homogeneous buffer medium and in reverse micelles. The copper complex on photoexcitation can oxidize DNA in a deoxygenated environment. A prominent MFE is found even in a homogeneous aqueous medium for the triplet born radicals. The process of partial intercalation of [Cu(phen)2]2+ complex within DNA is responsible for such a rare observation. In reverse micelles, the MFE is not very much prominent because of the large separation distance between the component radicals of the geminate radical ion pairs generated through PET.     

Inactivation of human angiotensin converting enzyme by copper peptide complexes containing ATCUN motifs

The copper complex [KGHK-Cu]+ demonstrates catalytic inactivation of human angiotensin converting enzyme at sub-saturating concentrations, under oxidative conditions, with an observed rate constant k approximately 2.9 +/- 0.5 x 10(-2) min(-1).     

Carbonyl Displacement Reaction in Diiron Propane-Dithiolate Complex by Triphenylstibine: Crystal Structure of [Fe2(CO)6-n(SbPh3)n(μ-S2C3H6)] (n = 1 and 2)

Treatment of [Fe₂(CO)₆(μ-S₂C₃H₆)] (1) with triphenylstibine in a 1:1 molar ratio at room temperature in presence of Me₃NO resulted compound [Fe₂(CO)₅(SbPh₃)(μ-S₂C₃H₆)] (2) in 88% yield as red crystals. When the reaction was carried out under a 1:5 molar ratio in presence of Me₃NO, it resulted a monosubstituted compound [Fe₂(CO)₅(SbPh₃)(μ-S₂C₃H₆)] (2) in 63% yield along with a disubstituted compound [Fe₂(CO)₄(SbPh₃)₂(μ-S₂C₃H₆)] (3) in low yield (8%) as red crystals. Reaction of 2 with triphenylstibine in a 1:5 molar ratio under same condition resulted 3 in moderate yield (46%). Compounds 2 and 3 were characterized by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopic data. Crystal structures of the compounds were unambiguously determined by single crystal X-Ray diffraction studies. Compound 2 crystalized as monoclinic crystal system with the space group P2₁/c, a?=?9.464(4) Å, b?=?16.902(7) Å, c?=?17.081(7) Å, β?=?101.216(13)° and Z?=?4. Compound 3 was triclinic, space group P-1, a?=?9.552(3) Å, b?=?13.985(5) Å, c?=?16.487(6) Å, α?=?78.372(16)°, β?=?89.976(14)°, γ?=?71.638(11)° and Z?=?2.

Graphic Abstract

Two new diiron propane-1,3-dithiolate complexes, [Fe₂(CO)₅(SbPh₃)(μ-S₂C₃H₆)] (2) and [Fe₂(CO)₄(SbPh₃)₂(μ-S₂C₃H₆)] (3), were synthesized by the displacement of carbonyl groups from [Fe₂(CO)₆(μ-S2C₃H₆)] (1) with triphenylstibine, and the resulting complexes were structurally characterized.

Solid state molecular structure of compound 2 (left) and compound 3 (right)

     

Biocatalytic Approach for the Total Synthesis of (–)‐Malyngolide and Its C(5)‐Epimer

An enzymatic approach has been successfully utilized in the total synthesis of (–)‐malyngolide and its C(5)‐epimer. The required configuration was established by an enzymatic kinetic resolution and Sharpless asymmetric dihydroxylation.