A tetrathiafulvalene-functionalized naphthalene diimide: synthesis, electrochemical and photophysical properties

A tetrathiafulvalene donor has been attached to the naphthalene diimide core via a rigid bridge affording a new planar molecular dyad. Its electronic properties have been studied experimentally by the combination of electrochemistry and UV-vis-NIR spectroscopy. Various electronic excited charge-transfer states are generated in different oxidation states, leading to almost full absorption in the visible to near-IR region with high extinction coefficients. The observed electronic properties are explained on the basis of density-functional-theory. In particular, the oxidized radical species show a strong tendency to undergo aggregation, in which the long-distance attractive interactions overcome the electrostatic repulsions.     

Biopesticide Encapsulation Using Supercritical CO2: A Comprehensive Review and Potential Applications

As an alternative to synthetic pesticides, natural chemistries from living organisms, are not harmful to nontarget organisms and the environment, can be used as biopesticides, nontarget. However, to reduce the reactivity of active ingredients, avoid undesired reactions, protect from physical stress, and control or lower the release rate, encapsulation processes can be applied to biopesticides. In this review, the advantages and disadvantages of the most common encapsulation processes for biopesticides are discussed. The use of supercritical fluid technology (SFT), mainly carbon dioxide (CO₂), to encapsulate biopesticides is highlighted, as they reduce the use of organic solvents, have simpler separation processes, and achieve high-purity particles. This review also presents challenges to be surpassed and the lack of application of SFT for biopesticides in the published literature is discussed to evaluate its potential and prospects.     

[Gd(AAZTA)]− Derivatives with n-Alkyl Acid Side Chains Show Improved Properties for Their Application as MRI Contrast Agents**

Herein, the synthesis and an extensive characterization of two novel Gd(AAZTA) (AAZTA=6-amino-6-methylperhydro-1,4-diazepine tetra acetic acid) derivatives functionalized with short (C₂ and C₄) n-alkyl acid functions are reported. The carboxylate functionality is the site for further conjugations for the design of more specific contrast agents (CAs). Interestingly, it has been found that the synthesized complexes display enhanced properties for use as MRI contrast agents on their own. The stability constants determined by using potentiometric titration and UV/Vis spectrophotometry were slightly higher than the one reported for the parent Gd(AAZTA) complex. This observation might be accounted for by the larger sigma-electron donation of the acyl substituents with respect to the one provided by the methyl group in the parent complex. As far as concerns the kinetic stability, transmetallation experiments with endogenous ions (e.g. Cu²⁺) implied that the Gd³⁺ ions present in these Gd(AAZTA) derivatives show somewhat smaller susceptibility to chemical exchange towards these ions at 25 °C, close to the physiological condition. The ¹H NMR spectra of the complexes with Eu^III and Yb^III displayed a set of signals consistent with half the number of methylene protons present on each ligand. The number of resonances was invariant over a large range of temperatures, suggesting the occurrence of a fast interconversion between structural isomers. The relaxivity values (298 K, 20 MHz) were consistent with q=2 being equal to 8.8 mm ⁻¹ s⁻¹ for the C₂ derivative and 9.4 mm ⁻¹ s⁻¹ for the C₄ one, that is, sensibly larger than the one reported for Gd(AAZTA) (7.1 mm ⁻¹ s⁻¹). Variable-temperature (VT)-T₂ ¹⁷O NMR measurements showed, for both complexes, the presence of two populations of coordinated water molecules, one in fast and one in slow exchange with the bulk water. As the high-resolution ¹H NMR spectra of the analogs with Eu^III and Yb^III did not show the occurrence of distinct isomers (as frequently observed in other macrocyclic lanthanide(III)-containing complexes), we surmised the presence of two fast-interconverting isomers in solution. The analysis of the ¹⁷O NMR VT-T₂ profiles versus temperature allowed their relative molar fraction to be established as 35 % for the isomer with the fast exchanging water and 65 % for the isomer with the water molecules in slower exchange. Finally, ¹H NMRD profiles over an extended range of applied magnetic field strengths have been satisfactory fitted on the basis of the occurrence of the two interconverting species.     

Intramolecular Charge-Transfer Dynamics in Benzodifuran-Based Triads

A facile and efficient approach for the synthesis of new conjugated donor-π-acceptor (D-π-A) chromophores has been developed, in which benzodifuran (BDF) and/or triphenyl amine (TPA) units are the donor moieties, linked by ethylenic bridges to electron-deficient anthraquinone (AQ) and 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) as the acceptor moieties. The resultant triads either with a symmetric A–D–A or an asymmetric D′–D–A structure show intense absorption bands in the visible spectral region due to efficient intramolecular charge transfer (ICT) from the HOMO localized on the BDF core to the LUMO localized on the AQ or the TCAQ unit. Electronic interactions between these redox-active components were studied by a combination of cyclic voltammetry, spectroelectrochemistry, UV-visible and ultrafast transient absorption spectroscopy. Analysis of the femtosecond excited-state dynamics reveal that all triads undergo a rapid charge recombination process which occurs within a few picoseconds, indicating that ethylenic linkers can facilitate electron delocalization among BDF and AQ/TCAQ units and thus impart effective electronic interactions between them.     

A Generalized Conditional Gradient Method for Dynamic Inverse Problems with Optimal Transport Regularization

We develop a dynamic generalized conditional gradient method (DGCG) for dynamic inverse problems with optimal transport regularization. We consider the framework introduced in Bredies and Fanzon (ESAIM: M2AN 54:2351–2382, 2020), where the objective functional is comprised of a fidelity term, penalizing the pointwise in time discrepancy between the observation and the unknown in time-varying Hilbert spaces, and a regularizer keeping track of the dynamics, given by the Benamou–Brenier energy constrained via the homogeneous continuity equation. Employing the characterization of the extremal points of the Benamou–Brenier energy (Bredies et al. in Bull Lond Math Soc 53(5):1436–1452, 2021), we define the atoms of the problem as measures concentrated on absolutely continuous curves in the domain. We propose a dynamic generalization of a conditional gradient method that consists of iteratively adding suitably chosen atoms to the current sparse iterate, and subsequently optimizing the coefficients in the resulting linear combination. We prove that the method converges with a sublinear rate to a minimizer of the objective functional. Additionally, we propose heuristic strategies and acceleration steps that allow to implement the algorithm efficiently. Finally, we provide numerical examples that demonstrate the effectiveness of our algorithm and model in reconstructing heavily undersampled dynamic data, together with the presence of noise.