Combination of explainable machine learning and conceptual density functional theory: applications for the study of key solvation mechanisms.

We present explainable machine learning approaches for the accurate prediction and understanding of solvation free energies, enthalpies, and entropies for different salts in various protic and aprotic solvents. As key input features, we use fundamental contributions from the conceptual density functional theory (DFT) of solutions. The most accurate models with the highest prediction accuracy for the experimental validation data set are decision tree-based approaches such as extreme gradient boosting and extra trees, which highlight the non-linear influence of feature values on target predictions.

Parts per billion detection of uranium with a porphyrinoid-containing nanoparticle and in vivo photoacoustic imaging.

Chemical tools that can report radioactive isotopes would be of interest to the defense community. Here we report ∼250 nm polymeric nanoparticles containing porphyrinoid macrocycles with and without pre-complexed depleted uranium and demonstrate that the latter species may be detected easily and with high sensitivity via photoacoustic imaging. The porphyrinoid macrocycles used in the present study are non-aromatic in the absence of the uranyl cation, but aromatic after cation complexation.

Near-infrared-induced electron transfer of an uranyl macrocyclic complex without energy transfer to dioxygen.

Photoexcitation of dichloromethane solutions of an uranyl macrocyclic complex with cyclo[1]furan[1]pyridine[4]-pyrrole () at the near-infrared (NIR) band (1177 nm) in the presence of electron donors and acceptors resulted in NIR-induced electron transfer without producing singlet oxygen via energy transfer.

A hybrid macrocycle with a pyridine subunit displays aromatic character upon uranyl cation complexation.

Reported here is a new hybrid macrocycle, cyclo[1]furan[1]pyridine[4]pyrrole (1), that bears analogy to the previously reported mixed heterocycle system cyclo[2]pyridine[4]pyrrole (2) and cyclo[6]pyrrole 3, an all-pyrrole 22 π-electron aromatic expanded porphyrin. The oxidized, dianionic form of 1, [1 - 4H](2-), has been characterized as its uranyl complex. In contrast to 2 and 3 and in spite of the presence of a 2,6-disubstituted pyridine subunit, the uranyl complex of [1 - 4H](2-) displays solid-state structural and solution-phase spectroscopic features consistent with contributions to the overall electronic structure that involve a conjugated, (4n + 2) π-electron aromatic periphery.

The synthesis of rigid polycyclic structures for the study of diatropic or steric effects of a phenyl ring on CF bond.

Polycyclic compounds 1a-c were synthesized to study the diatropic effects of a flanking phenyl ring on nearby CH and CF bonds. (19)F NMR spectra of 1b and 1c were strongly deshielded compared with those of the ring-opened compounds 3b, 7b, and 7c. DMol3 calculations on 1a-c provided quantitative bond lengths and torsional angles to support the conclusion that the downfield shifts in the (19)F NMR spectra are mainly due to steric interactions between the CF bonds and the π clouds of the phenyl ring(s).

Design and synthesis of triazolyl coumarins as Hg2+ selective fluorescent chemosensors.

A series of triazolyl coumarin derivatives L1-L4, with and without spacer groups between the coumarin and the triazole groups, were synthesized as fluorescent sensors to study their binding ability and selectivity toward metal ions. Ligand L3, which contains an acetyl linker between the triazole and the coumarin, exhibited a high selectivity toward Hg(2+) in polar protic solvents MeOH-CHCl(3) (9 : 1, v/v) with fluorescent enhancement, furthermore, it was found to bind two Hg(2+) at a high concentration (>12.5 mM) of Hg(ClO(4))(2).

1,3-Alternate calix[4]arene as a homobinuclear ditopic fluorescent chemosensor for Ag+ ions.

A novel 1,3-alternate calix-[4]arene L, containing two different cationic binding sites of bis-triazoles and bis-enaminone groups, was synthesized and shown to be a homobinuclear ditopic fluorescent chemosensor for Ag(+) ions. The fluorescence intensity of L was selectively enhanced by binding with Ag(+) ions in methanol/chloroform (49:1, v/v) cosolvent. In the presence of most competing metal ions, L retains its selectivity toward Ag(+) ion.

Cooperative recognition of a copper cation and anion by a calix[4]arene substituted at the lower rim by a beta-amino-alpha,beta-unsaturated ketone.

We report herein a new ditopic calix[4]arene receptor 25,27-bis-{[4-amino-4-(1-naphthyl)-2-oxo-3-butenyl]oxy}-26,28-dihydroxycalix[4]arene (2) for the simultaneous complexation of anionic and cationic species. The host molecule 25,27-bis{[3-(1-naphthyl)-5-isoxazolyl]methoxy}-26,28-dihydroxycalix[4]arene (1) was synthesised first and was followed by a [Mo(CO)6]-mediated ring-opening reaction to give the target receptor 2. The binding properties of ligands 1 and 2 towards metal ions in CH3CN were investigated by UV/Vis and fluorescence spectroscopies.

Synthesis of upper-rim allyl- and p-methoxyphenylazocalix[4]arenes and their efficiencies in chromogenic sensing of Hg2+ ion.

A series of upper-rim p-allyl and p-methoxyphenylazocalix[4]arenes (6, 8, 9a,b, and 10a,b) were synthesized and shown to exhibit substantial color changes upon complexation with Hg2+ ion. Both the upper-rim p-allyl- and p-methoxyphenylazo groups on calix[4]arenes are proven to be key components in the recognition of Hg2+ ion. Job's plots revealed 1:1 binding stoichiometry for all these p-allyl- and p-arylazo-coupled calix[4]arenes with Hg2+ ions and Benesi-Hilderbrand plots were used for determination of their association constants.