Double-Armed 18- and 21-Membered Macrocycles as Potential Chelators for Lead and Bismuth Radiopharmaceuticals.

With increasing clinical applications and interest in targeted alpha therapy, there is growing interest in developing alternative chelating agents for [212Pb]Pb2+ and [212/213Bi]Bi3+ that exhibit rapid radiolabeling kinetics and kinetic inertness. Herein we report the synthesis and detailed investigation of diacetate and dipicolinate 18- and 21-membered macrocyclic chelators BADA-18, BADA-21, BADPA-18, and BADPA-21 for the complexation of Pb2+ and Bi3+ ions with potential use in the preparation of radiopharmaceuticals. The formation of mononuclear complexes was established by using ESI-mass spectrometry, and their stability constants were determined by potentiometric titration. A thorough study of the structure of the metal complexes was carried out by using X-ray diffraction and NMR spectroscopy. It was shown how the stability of the complex is influenced by an increase in the size of the macrocycle, the replacement of acetate arms with picolinate ones, the rigidity of the ligand, as well as the type of conformation (syn- or anti-) of the metal complex. The new ligands were radiolabeled with [210Pb]Pb2+ and [207Bi]Bi3+, and the in vitro stability of the resulting complexes in a competitive environment of serum and biologically significant metal ions was assessed. Rapid complex formation in 1-2 min at room temperature, as well as the high kinetic inertness of the complexes Pb(BADPA-18) and Bi(BADPA-18) in biological media, demonstrate its potential for use in targeted radionuclide therapy.

BODIPY derivatives modified with carborane clusters: synthesis, characterization and DFT studies.

An efficient approach for the preparation of 3,5-dicarborane-substituted BODIPY conjugates was developed via the functionalization of 3,5-dibromo-8-pentafluorophenyl-BODIPY with neutral and anionic carborane S-nucleophiles. It was found that 3,5-dicarborane-substituted BODIPYs could be easily modified with a third carborane cluster using SNAr substitution reactions of the para-fluorine atom in the meso-pentafluorophenyl BODIPY substituent with the corresponding carborane S-nucleophile affording boron-enriched BODIPYs in good yields. The influence of bromine atom substitution with carborane moieties on the position of absorption and fluorescence bands and the fluorescence quantum yields of the prepared BODIPYs were analyzed. The crystal structures of BODIPYs 4 and 8 were investigated. Density functional theory methods (DFT wb97xd/6-31G* and wb97xd/lanl2dz) were performed to study the geometrical structures, electronic characteristics, the highest occupied and the lowest unoccupied molecular orbitals (HOMOs and LUMOs) and other chemical descriptors of the synthesized compounds.

Photoswitchable Photochromic Chelating Spironaphthoxazines: Synthesis, Photophysical Properties, Quantum-Chemical Calculations, and Complexation Ability.

The stable and efficient photochromic and photoswitchable molecular systems designed from spirooxazines are of increasing scientific and practical interest because of their present and future applications in advanced technologies. Among these compounds, chelating spironaphthoxazines have received widespread attention due to their efficient optical response after complexation with some metal ions being of biomedical interest and environmental importance, as well as their good cycle performance and high reliability, especially by metal ion sensing. In this mini-review, we summarize our results in the design of novel photoswitchable chelating spironaphthoxazines with specific substituents in their naphthoxazine or indoline ring systems in view of recent progress in the development of such molecular systems and their applications as metal ion sensors. The design, synthesis methods, and photoresponse of such spirooxazine derivatives relevant to their applications, as well as quantum-chemical calculations for these compounds, are presented. Examples of various design concepts are discussed, such as sulfobutyl, hydroxyl, benzothiazolyl, or ester and carboxylic acid as substituents in the chelating spironaphthoxazine molecules. Further developments and improvements of this interesting and promising kind of molecular photoswitches are outlined.

Synthesis of new acyclic chelators H4aPyta and H6aPyha and their complexes with Cu2+, Ga3+, Y3+, and Bi3.

In this article, we present the synthesis and characterization of new acyclic pyridine-containing polyaminocarboxylate ligands H4aPyta and H6aPyha, which differ in structural rigidity and the number of chelating groups. Their abilities to form complexes with Cu2+, Ga3+, Y3+, and Bi3+ cations, as well as the stability of the complexes, were evaluated by potentiometric titration method, radiolabeling with the corresponding radionuclides, in vitro studies, mass spectrometry, and HPLC. The structures of the resulting complexes were determined using NMR spectroscopy and DFT calculations. The results obtained made it possible to evaluate the influence of the structural features of the complexes on their stability. The developed chelators H4aPyta and H6aPyha were proved to be promising for further research in the field of radiopharmaceuticals.

Specific Fluorescent Probes for Imaging DNA in Cell-Free Solution and in Mitochondria in Living Cells.

New styryl dyes consisting of N-methylpyridine or N-methylquinoline scaffolds were synthesized, and their binding affinities for DNA in cell-free solution were studied. The replacement of heterocyclic residue from the pyridine to quinoline group as well as variation in the phenyl part strongly influenced their binding modes, binding affinities, and spectroscopic responses. Biological experiments showed the low toxicity of the obtained dyes and their applicability as selective dyes for mitochondria in living cells.

Tetrachromophoric Derivatives of Dibenzoylmethanatoboron Difluoride Based on Stereoregular Cyclotetrasiloxanes: Synthesis and Properties.

A series of new tetrachromophoric systems based on stereoregular tetracyclosiloxanes and dibenzoylmethanatoboron difluoride derivatives have been synthesized and characterized by a complex of physicochemical methods. The photophysical properties of the synthesized compounds are studied by electronic absorption, steady-state, and time-resolved fluorescence spectroscopy. In the synthesized compounds, four dibenzoylmethanatoboron difluoride (DBMBF2)-based fluorophores are in an all-cis arrangement with respect to a cyclotetrasiloxane scaffold. DFT calculations predict that they can form H-type dimers, trimers, or tetramers with an antiparallel orientation of their ground-state dipole moments. Under UV excitation, solutions of these compounds in polar and nonpolar solvents exhibit complex fluorescence consisting of monomer- and excimer-like emissions with different lifetimes. Global fitting analysis reveals the presence of at least four kinetically distinguishable species in the excited state. The studied compounds in solutions have CIE chromaticity coordinates very close to the white color point and are promising objects for the development of next-generation single-emission materials for white illumination.

Synthesis and Photophysical Properties of Novel Meta-Conjugated Organic Molecules with 1,3,5-Benzene Branching Units.

The synthesis and photophysical investigation of three novel meta-conjugated molecules based on 3,1,2-benzothiadiazole and thiophene-2,5-diyl derivatives linked through 1,3,5-benzene branching units are described. Each of them is a symmetrical molecule with two branching units, four identical lateral thiophene-containing fragments, and one central benzothiadiazole-containing fragment. To study the effect of the chemical structure on their photophysical properties, the molecules with different linearly conjugated lateral and central fragments due to incorporation of additional thiophene rings were synthesized and compared. It was shown that absorption spectra of the meta-conjugated molecules can be represented as a sum of absorption bands of model compounds for their peripheral and central fragments containing a common benzene ring being branched at the 1,3,5-benzene unit in the meta-conjugated molecules. Therefore, they cannot be considered simply as isolated π-conjugated systems of their peripheral and central fragments. Instead, DFT calculations showed that several transitions between the orbitals located in different regions of the meta-conjugated molecule are responsible for the formation of their absorption spectra, and they strongly depend on the degree of their overlapping. Theoretical absorption spectra reconstructed from the DFT data demonstrated a good agreement with the experimental results: the transitions with larger oscillator strength correspond to the bands with higher molar extinction coefficients and vice versa. It was shown that luminescence spectral maxima of the meta-conjugated molecules monotonically shift to the lower energy from 489 to 540 and 613 nm with increasing the number of thiophene rings in the peripheral and central fragments, respectively. However, luminescence quantum yield of the meta-conjugated molecules critically depends on the length of linearly conjugated fragments in its structure decreasing from 24% to 1.3% with increasing the number of thiophene rings in the lateral fragments but increasing to 90% in the molecule with more thiophene rings in both types of the fragments. The results obtained are well correlated to the ratio of radiative and nonradiative deactivation rate constants of the meta-conjugated molecules that indicates a high rate of internal conversion between the excited states corresponding to different fragments of the molecule. The CV measurements allowed estimating the HOMO, LUMO, and bandgap values of the target and model compounds, which confirm the presence of meta-conjugation within the molecules investigated. Thus, connection of linearly conjugated fragments through meta-positions (meta-conjugation) of a benzene ring leads to an intermediate option between fully conjugated and nonconjugated molecules due to partial delocalization of electron density through the 1,3,5-substituted benzene branching center.

Effect of Cp-Ligand Methylation on Rhodium(III)-Catalyzed Annulations of Aromatic Carboxylic Acids with Alkynes: Synthesis of Isocoumarins and PAHs for Organic Light-Emitting Devices.

An efficient protocol was developed for the synthesis of π-extended isocoumarins and polycyclic aromatic hydrocarbons based on the oxidative coupling of aromatic carboxylic acids with internal alkynes catalyzed by (cyclopentadienyl)rhodium complexes. The coupling chemoselectivity strongly depends on whether Cp or the methylated Cp* ligands are used. The pentamethyl derivative [Cp*RhCl2 ]2 predominantly gives isocoumarins, while the non-methylated complex [CpRhI2 ]n produces naphthalene derivatives. The polyaromatic carboxylic acids (such as 1-naphthoic acid, 1-pyrenecarboxylic acid, fluorene-1-carboxylic acid, and dibenzofuran-4-carboxylic acid) are suitable for this approach. A mixture of Cp*H/RhCl3 can be used as a catalyst instead of [Cp*RhCl2 ]2 . The structures of 3,4-diphenylindeno[1,2-h]isochromen-1(11H)-one and 7,10-dimethyl-8,9-diphenylbenzo[pqr]tetraphene were determined by X-ray diffraction. In addition, the optical properties of the prepared compounds were studied. 7,8-Diphenyl-10H-phenaleno[1,9-gh]isochromen-10-one was employed as an emissive layer for OLED manufacturing. The OLED emits yellow-green light with a maximum intensity 1740 cd ⋅ m-2 at 15 V.