A BODIPY‐Based Molecular Rotor in Giant Unilamellar Vesicles: A Case Study by Polarization‐Resolved Time‐Resolved Emission and Transient Absorption Spectroscopy

Posted on 27 September 2023 by

The ellipsoidal geometry of the BODIPY-Ar-chol molecule results in a tri-exponential decay of anisotropy dynamics. The molecule‘s radius along the y-axis is 6.3 Å and fluid volume displaced by rotation along the y-axis is 11983.9 Å³. The largest fluid volume displacement along the y-axis induces the largest rotational relaxation time of 440 ps. Rotational relaxation time along the x and z axes follow accordingly.

Abstract

BODIPY and BODIPY-derived systems are widely applied as fluorophores and as probes for viscosity detection in solvents and biological media. Their orientational and rotational dynamics in biological media are thus of vital mechanistic importance and extensively investigated. In this contribution, polarization-resolved confocal microscopy is used to determine the orientation of an amphiphilic BODIPY-cholesterol derivative in homogeneous giant unilamellar vesicles (GUV) made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The BODIPY-moiety of the molecule is placed near the polar headgroups, and the cholesterol moiety is embedded in the membrane along the acyl chain of the lipids. The rotational relaxation of fluorophore is conventionally investigated by time-resolved emission anisotropy (TEA); and this method is also used here. However, TEA depends on the emission of the fluorophore and may not be useful to probe rotational dynamics of the non-emissive triplet states. Thus, we employ femtosecond transient absorption anisotropy (TAA), that relies on the absorption of the molecule to complement the studies of the amphiphilic BODIPY in DCM and GUV. The photoinduced anisotropy of the BODIPY molecule in DCM decays tri-exponentially, the decay components (sub-5 ps, 43 ps and 440 ps) of anisotropy are associated with the non-spherical shape of the BODIPY molecule. However, the anisotropy decay in homogenous GUVs follows a biexponential decay; which arises from the wobbling-in-a-cone motion of the non-spherical molecule in the high viscous lipid bilayer media. The observations for the BODIPY-chol molecule in the GUV environment by TAA will extend to the investigation of non-emissive molecules in cellular environment since GUV structure and size resembles the membrane of a biological cell.

Oxygen‐Mediated Surface Photoreactions: Exploring New Pathways for Sustainable Chemistry

Posted on 27 September 2023 by nIvano Alessandri, nIrene Vassalinin

Oxygen-mediated surface photoreactions are an extremely versatile tool for environmental remediation, recycling of critical raw materials and sustainable production of feedstocks. This Concept reviews recent works on this class of reaction, including examples of metal and polymer recovery and recycling from waste, metal-free oxidation of organic molecules and exploitation of persistent radicals for destroying pollutants and disinfection.

Abstract

This Concept analyses and reviews recent works that take advantage of oxygen-mediated surface photoreactions for addressing key issues in the fields of sustainable chemistry, circular production of feedstocks and environmental remediation. Examples of metal and polymer recovery and recycling from waste, metal-free oxidation of organic molecules and exploitation of persistent radicals for destroying pollutants and disinfection are discussed, highlighting common aspects, peculiarities, potential and limitations.

A Platinum(II) Boron‐dipyrromethene Complex for Cellular Imaging and Mitochondria‐targeted Photodynamic Therapy in Red Light

Posted on 27 September 2023 by

Acacplatin-RB, a cisplatin analog having acetylacetone-appended to boron-dipyrromethene (BODIPY) dye, exhibits mitochondrial localization and remarkable apoptotic red-light induced photodynamic therapy (PDT) forming singlet oxygen as reactive oxygen species. Moreover, this complex demonstrated decrease in mitochondrial membrane potential, disruption of microtubules under photoinduced conditions and anti-metastatic properties from wound-healing assay.

Abstract

Cisplatin-derived platinum(II) complexes [Pt(NH₃)₂(pacac)](NO₃) (1, DPP-Pt) and [Pt(NH₃)₂(Acac-RB)](NO₃) (2, Acacplatin-RB), where Hpacac is 1,3-diphenyl-1,3-propanedione and HAcac-RB is a red-light active distyryl-BODIPY-appended acetylacetone ligand, are prepared, characterized and their photodynamic therapy (PDT) activity studied (RB abbreviated for red-light BODIPY). Complex 2 displayed an intense absorption band at λ=652 nm (ϵ=7.3×10⁴ M⁻¹ cm⁻¹) and 601 nm (ϵ=3.1×10⁴ M⁻¹ cm⁻¹) in 1 : 1 DMSO-DPBS (Dulbecco's Phosphate Buffered Saline). Its emission profile includes a broad maximum at ~673 nm (λ_ex=630 nm). The fluorescence quantum yield (Φ_F) of HAcac-RB and 2 are 0.19 and 0.07, respectively. Dichlorodihydrofluorescein diacetate and 1,3-diphenylisobenzofuran assay of complex 2 indicated photogeneration of singlet oxygen (Φ_Δ: 0.36) as reactive oxygen species (ROS). Light irradiation caused only minor extent of ligand release forming chemo-active cisplatin analogue. The complex showed ~70–100 fold enhancement in cytotoxicity on light exposure in A549 lung cancer cells and MDA-MB-231 multidrug resistant breast cancer cells, giving half maximal inhibitory concentration (IC₅₀) of 0.9–1.8 μM. Confocal imaging showed its mitochondrial localization and complex 2 exhibited anti-metastasis properties. Immunostaining of β-tubulin and Annexin V-FITC/propidium iodide staining displayed complex 2 induced photo-selective microtubule rupture and cellular apoptosis, respectively.

Transmission Porosimetry Study on High‐quality Zr‐fum‐MOF Thin Films

Posted on 27 September 2023 by

Zr-fum-MOF thin films of high optical quality were synthesized using the solvothermal direct growth method. The optical properties of the thin films were investigated thoroughly in different gas atmospheres.

Abstract

Crystalline Zr-fum-MOF (MOF-801) thin films of high quality are prepared on glass and silicon substrates by direct growth under solvothermal conditions. The synthesis is described in detail and the influence of different synthesis parameters such as temperature, precursor concentration, and the substrate type on the quality of the coatings is illustrated. Zr-fum-MOF thin films are characterized in terms of crystallinity, porosity, and homogeneity. Dense films of optical quality are obtained. The sorption behavior of the thin films is studied with various adsorptives. It can be easily monitored by measuring the transmission of the films in gas flows of different compositions. This simple transmission measurement at only one wavelength allows a very fast evaluation of the adsorption properties of thin films as compared to traditional sorption methods. The sorption behavior of the thin films is compared with the sorption properties of Zr-fum-MOF powder samples.

Photophysical Properties of Boron‐Based Chromophores as Effective Moieties in TADF Devices: A Computational Study

Posted on 27 September 2023 by nPelin Ulukan, nAntonio Monari, nSaron Catakn

The relationship between molecular structure and photophysical properties of a range of boron-based TADF molecules were investigated to provide a clear approach to the structure-performance relation. Torsion angles, excited state energy alignments, singlet-triplet energy gaps, particle-hole orbital overlap extent and spin orbit coupling for reverse intersystem crossing processes were utilized.

Abstract

Thermally activated delayed fluorescence (TADF) materials have shown great potential in the design of organic metal-free optoelectronic devices and materials and, therefore, are the subject of intense investigations. This contribution presents the effects of various parameters on the photophysical properties of a series of boron-based TADF emitters. These include torsion angle, the changes in the electronic density, energy gap between the first excited singlet (S₁) and the first excited triplet states (T₁), oscillator strength (f) and spin-orbit coupling (SOC). Through a comprehensive structural analysis, we first show the most favorable conformation of the ground state of donor (D) and acceptor (A) moieties that are popular in TADF emitters. Further, the properties of the excited state manifolds are obtained with Tamm-Dancoff Approximation (TDA), thus rationalizing their optical and photophysical properties. Globally, our results settle the basis for the rationalization of the effects of different parameters on reverse intersystem crossing (RISC) probabilities, which is the rate-limiting step for TADF, thus favoring the rational design of novel highly efficient TADF materials with strong triplet exciton harvesting.

Good Practices and Practical Considerations for Research with Perfluoroalkyl Substances

Posted on 27 September 2023 by nChloe M. Taylor, nMichael C. Breadmore, nNathan L. Kilahn

Perfluoroalkyl substances (PFAS) are a class of molecules of increasing awareness and concern. Their unique properties, hazards, and complications are not always obvious, which can impede or convolute analyses, particularly at low concentrations. We have summarised “best practice” approaches for working with PFAS with the aim of enabling chemists to do so with increased confidence and safety.

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a class of hazardous pollutant that are ubiquitous in our modern world. Current research is driven by an increased awareness and concern regarding the safety of PFAS for the general population, while tightening regulations have prompted the need for detection and quantification techniques from a wide range of matrices. PFAS are a group of molecules offering unique behaviours, hazards, and complications that are not obvious or readily apparent from reading the literature. These peculiarities can impede or convolute analyses when not considered in experimental design. Drawing on the knowledge of a range of literature sources, this tutorial review looks to highlight and amalgamate the valuable suggestions and methodologies currently available to enable successful PFAS research in any laboratory.

Plastic Chip Electrode: An Emerging Multipurpose Electrode Platform

Posted on 27 September 2023 by nKinjal B. Patel, nSunil Luhar, nDivesh N. Srivastavan

Conventional electrodes are now falling behind in meeting the increasing technological demands. Innovative and tailored electrodes are believed to be the most promising solution to the problem. Polymer composite electrodes are an optimistic class of tailored electrodes. This review outlines a bird-eye account of the carbon polymer composites and discusses the state-of-the-art on the Plastic Chip Electrode (PCE) comprehensively. PCE is a bulk conducting, self-standing, composite electrode fabricated by a spontaneous solvent-based method. The application of PCE as a multipurpose electrode platform is discussed here.

Abstract

The properties of electrodes play a crucial role in the processes occurring on them. Therefore, a variety of materials have been tried as electrodes. Carbon composite materials are among the most admired ones. Use of composites as electrode material dates back to the mid of the last century when polymer-carbon composites were tried as general-purpose electrode platforms and epoxy impregnated graphite paste/ solid electrodes were tried in polarography. Later the composite electrodes have seen several phases of development. Plastic Chip Electrode (PCE) is a class of polymer composite electrode developed by our group. This monographic review gives a bird‘s eye account of polymer composite electrodes and appurtenant work, followed by elaborating on various aspects and state-of-the-art plastic chip electrodes.

Isolation of a Dodecanuclear Polyoxo Cluster {Nb12O21} Showing a Rare Case of Five‐fold Coordinated Niobium(V) Centers with a Square Pyramidal Geometry

Posted on 27 September 2023 by

Isolation of two large dodecameric {Nb₁₂O₂₁} clusters in the same lattice was achieved by combination of NbCl₄ ⋅ 2THF with anthracene-9-carboxylic acid. The clusters are constituted of octahedral niobium(V) centers associated with rarely seen square pyramidal niobium(V) cations.

Abstract

The reactivity of the complexing anthracene-9-carboxylate ligand has been investigated with a niobium(IV) tetrachloride precursor (NbCl₄ ⋅ 2THF) in isopropanol solvent. This resulted in the crystallization of a molecular assembly containing two distinct {Nb₁₂O₂₁} cores surrounded by multiple isopropanolate and anthracenoate ligands. The compound is formulated [Nb₁₂₍(μ₃-O)₃(μ-O)₁₈(C₁₅H₉O₂)₈(OⁱPr)₁₀] ⋅ [Nb₁₂(μ₃-O)₂(μ-O)₁₉(C₁₅H₉O₂)₈(OⁱPr)₁₀] illustrating the two different dodecameric oxo-clusters, for which the niobium(IV) precursor was oxidized in the niobium(V) state during the reactional process. The two distinct {Nb₁₂O₂₁} units mainly differs by the environment of the niobium centers, which exhibits unexpected five-fold coordination (square pyramid) for some of them, together with the classical six-fold coordination (octahedron) as usually found for niobium(V). In the crystallization process, the. IR spectroscopy was used to analyze the esterification reaction occurring between the anthracene acid an isopropanolate ligands responsible of the production of water used in the oxo-condensation of the niobium centers. ⁹³Nb Solid state NMR was tentatively used to assess the occurrence of the different niobium environments.

Protonation Behavior of a Tetrahydrido Molybdenum(IV) Complex with Organic and Inorganic Acids

Posted on 27 September 2023 by

Protonation of polyhydride complexes: conjugated base matters! The protonation of a neutral molybdenum(IV) tetrahydride complex was investigated using a range of proton sources. Whereas simple acid-base process was achieved in the case of a phosphonium, subsequent reactivity of the resulting cationic pentahydride species with conjugated base was typically observed.

Abstract

The reaction of [MoH₄(depe)₂] (1) (depe=1,2-bis(diethylphosphino)ethane) with different proton sources (HP^tBu₃ ⁺, C₆H₅COOH, C₆F₅COOH, H₂SO₄) was investigated. Whereas complete conversion of 1 into its protonated form is observed in the presence of the phosphonium salt, [MoH₅(depe)₂]⁺ only transiently forms upon treatment with the other acids. Further reactivity of the pentahydride complex is indeed noticed with the conjugated base, typically resulting in the formation of neutral (C₆F₅COOH, H₂SO₄) or cationic (PhCOOH) molybdenum dihydride complexes. The compounds were characterized by NMR spectroscopy and X-ray crystallographic studies were performed when suitable crystals were obtained.

Variation of Clasper Scent Gland Composition of Heliconius Butterflies from a Biodiversity Hotspot

Posted on 27 September 2023 by

Male Heliconius butterflies, which occur locally in three mimicry groups, show an extremely high diversity of compounds in their clasper scent glands. The more than 1,000 different compounds identified in 17 species are used for species-specific mixtures of volatile and non-volatile compounds, presumably used for chemical communication. (Photos: C. Jiggins)

Abstract

Male Heliconius butterflies possess two pheromone emitting structures, wing androconia and abdominal clasper scent glands. The composition of the clasper scent gland of males of 17 Heliconius and Eueides species from an overlapping area in Ecuador, comprising three mimicry groups, was investigated by GC/MS. The chemical signal serves as an anti-aphrodisiac signal that is transferred from males to females during mating, indicating the mating status of the female to prevent them from harassment by other males. In addition, the odour may also serve in predator defence. There is potential for convergence driven by mimicry, although, such convergence might be detrimental for species recognition of the butterflies within the mimicry ring, making mating more difficult. More than 500 compounds were detected, consisting of volatile, semi-volatile or non-volatile compounds, including terpenes, fatty acid esters or aromatic compounds. Several novel esters were identified by GC/MS and GC/IR data, microderivatisation and synthesis, including butyl (Z)-3-dodecenoate and other (Z)-3-alkenoates, 3-oxohexyl citronellate and 5-methylhexa-3,5-dienyl (E)-2,3-dihydrofarnesoate. The secretions were found to be species specific, potentially allowing for species differentiation. Statistical analysis of the compounds showed differentiation by phylogenetic clade and species, but not by mimicry group.