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1. C–H⋯S hydrogen bonding interactions

   https://doi.org/10.1039/D1CS00838B  

   Fargher, Hazel A.; Sherbow, Tobias J.; Haley, Michael M.; Johnson, Darren W.; Pluth, Michael D. (February 2022, Chemical Society Reviews)

   The short C–H⋯S contacts found in available structural data for both small molecules and larger biomolecular systems suggest that such contacts are an often overlooked yet important stabilizing interaction. Moreover, many of these short C–H⋯S contacts meet the definition of a hydrogen bonding interaction. Using available structural data from the Cambridge Structural Database (CSD), as well as selected examples from the literature in which important C–H⋯S contacts may have been overlooked, we highlight the generality of C–H⋯S hydrogen bonding as an important stabilizing interaction. To uncover and establish the generality of these interactions, we compare C–H⋯S contacts with other traditional hydrogen bond donors and acceptors as well as investigate how coordination number and metal bonding affect the preferred geometry of interactions in the solid state. This work establishes that the C–H⋯S bond meets the definition of a hydrogen bond and serves as a guide to identify C–H⋯S hydrogen bonds in diverse systems. 

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2. Investigation of physicochemical drivers directing ionic liquid assembly on polymeric nanoparticles

   https://doi.org/10.1002/elsa.202300013  

   Edgecomb, Sara_X; Hamadani, Christine_M; Roberts, Angela; Taylor, George; Merrell, Anya; Suh, Ember; Yaddehige, Mahesh_Loku; Chandrasiri, Indika; Watkins, Davita_L; Tanner, Eden_E_L (October 2023, Electrochemical Science Advances)

   Abstract Ionic liquids (ILs) have emerged as promising biomaterials for enhancing drug delivery by functionalizing polymeric nanoparticles (NPs). Despite the biocompatibility and biofunctionalization they confer upon the NPs, little is understood regarding the degree in which non‐covalent interactions, particularly hydrogen bonding and electrostatic interactions, govern IL‐NP supramolecular assembly. Herein, we use salt (0‐1 M sodium sulfate) and acid (0.25 M hydrochloric acid at pH 4.8) titrations to disrupt IL‐functionalized nanoassembly for four different polymeric platforms during synthesis. Through quantitative¹H‐nuclear magnetic resonance spectroscopy and dynamic light scattering, we demonstrate that the driving force of choline trans‐2‐hexenoate (CA2HA 1:1) IL assembly varies with either hydrogen bonding or electrostatics dominating, depending on the structure of the polymeric platform. In particular, the covalently bound or branched 50:50 block co‐polymer systems (diblock PEG‐PLGA [DPP] and polycaprolactone [PCl]‐poly[amidoamine] amine‐based linear‐dendritic block co‐polymer) are predominantly affected by hydrogen bonding disruption. In contrast, a purely linear block co‐polymer system (carboxylic acid terminated poly[lactic‐co‐glycolic acid]) necessitates both electrostatics and hydrogen bonding to assemble with IL and a two‐component electrostatically bound system (electrostatic PEG‐PLGA [EPP]) favors hydrogen‐bonding with electrostatics serving as a secondary role. 

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3. Diverse Coordination Geometries Derived from Trisaminocyclohexane Ligands with Appended Outer‐Sphere Hydrogen Bond Donors

   https://doi.org/10.1002/ejic.202300434  

   Ekanayake, Danushka_M; Sheridan, Patrick_E; Lindeman, Sergey_V; Fiedler, Adam_T (September 2023, European Journal of Inorganic Chemistry)

   Abstract With the aim of constructing hydrogen‐bonding networks in synthetic complexes, two new ligands derived fromcis,cis‐1,3,5‐triaminocyclohexane (TACH) have been prepared that feature pendant pyrrole or indole rings as outer‐sphere H‐bond donors. The TACH framework offers a facial arrangement of threeN‐donors, thereby mimicking common coordination motifs in the active sites of nonheme Fe and Cu enzymes. X‐ray structural characterization of a series of Cu^I‐X complexes (X=F, Cl, Br, NCS) revealed that these neutral ligands (H₃L^R, R=pyrrole or indole) coordinate in the intended facialN₃manner, yielding four‐coordinate complexes with idealizedC₃symmetry. The N−H units of the outer‐sphere heterocycles form a hydrogen‐bonding cavity around the axial (pseudo)halide ligand, as verified by crystallographic, spectroscopic, and computational analyses. Treatment of H₃L^pyrroleand H₃L^indolewith divalent transition metal chlorides (M^IICl₂, M=Fe, Cu, Zn) causes one heterocycle to deprotonate and coordinate to the M(II) center, giving rise to tetradentate ligands with two remaining outer‐sphere H‐bond donors. Further ligand deprotonation is observed upon reaction with Ni(II) and Cu(II) salts with weakly coordinating counteranions. The reported complexes highlight the versatility of TACH‐based ligands with pendant H‐bond donors, as the resulting scaffolds can support multiple protonation states, coordination geometries, and H‐bonding interactions. 

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4. Cage Match: Comparing the Anion Binding Ability of Isostructural Versus Isofunctional Pairs of Metal‐Organic Nanocages

   https://doi.org/10.1002/chem.202303013  

   Dutton, Kaitlyn_G; Jones, Taro_J; Emge, Thomas_J; Lipke, Mark_C (November 2023, Chemistry – A European Journal)

   Abstract Affinities of six anions (mesylate, acetate, trifluoroacetate,p‐toluenecarboxylate,p‐toluenesulfonate, and perfluorooctanoate) for three related Pt²⁺‐linked porphyrin nanocages were measured to probe the influence of different noncovalent recognition motifs (e. g., hydrogen bonding, electrostatics, π bonding) on anion binding. Two new hosts of M₆L₃¹²⁺(1b) and M₄L₂⁸⁺(2) composition (M=(en)Pt²⁺, L=(3‐py)₄porphyrin) were prepared in a one‐pot synthesis and allowed comparison of hosts that differ in structure while maintaining similar N−H hydrogen‐bond donor ability. Comparisons of isostructural hosts that differ in hydrogen‐bonding ability were made between1band a related M₆L₃¹²⁺nanoprism (1a, M=(tmeda)Pt²⁺) that lacks N−H groups. Considerable variation in association constants (K₁=1.6×10³ M⁻¹to 1.3×10⁸ M⁻¹) and binding mode (exovs.endo) were found for different host–guest combinations. Strongest binding was seen betweenp‐toluenecarboxylate and1b, but surprisingly, association of this guest with1awas only slightly weaker despite the absence of NH⋅⋅⋅O interactions. The high affinity betweenp‐toluenecarboxylate and1acould be turned off by protonation, and this behavior was used to toggle between the binding of this guest and the environmental pollutant perfluorooctanoate, which otherwise has a lower affinity for the host. 

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5. Synthesis, Reductive Reactivity and Anticancer Activity of Cobalt(III)– and Manganese(III)–Salen Complexes

   https://doi.org/10.3390/chemistry7030085  

   Kanina, Amy; Mei, Haiyu; Palma, Cheska; Neary, Michelle C; Cheng, Shu-Yuan; Zhang, Guoqi (June 2025, Chemistry)

   Mn(III)– and Co(III)–salen complexes (Mn-1 and Co-2) have been synthesized by a simple one-pot procedure through oxidation of Mn(II) and Co(II) precursors in air. X-ray structural analysis reveals that both complexes adopt similar coordination modes, including a typical square planar metal/salen coordination sphere, which is further occupied by two axial ligands, i.e., an acetate anion and a water molecule. Despite their structural similarity, they are not isomorphous given their distinct cell parameters. In the solid-state structures, both complexes exist as hydrogen-bonded dimers through hydrogen bonding interactions between the axially coordinating water molecules and outer O4 cavity from another molecule of the complex. The reductive activity of both complexes has been explored. While the reaction of Mn-1 with potassium triethylborohydride was unsuccessful, leading to a complicated mixture, the use of Co-2 furnished the formation of a novel product (CoK-3) that was isolated as red crystals in reasonable yield. CoK-3 was characterized as a heterometallic dimer involving the coordination of a K+ ion within the O4 cavity of a semi-hydrogenated salen/cobalt complex while the cobalt center has been reduced from Co(III) to Co(II). In addition, an attempt at reducing Co-2 with pinacolborane resulted in the isolation of crystals of Co-4, whose structure was determined as a simple square planar CoII–salen complex. Finally, three complexes (Mn-1, Co-2 and CoK-3) have been investigated for their cytotoxic activities against two human breast cancer cell lines (MCF-7 and MDA-MB 468) and a normal breast epitheliel cell line (MCF-10A), with cisplatin used as a reference in order to discover potential drug candidates that may compete with cisplatin. The results reveal that Co-2 can be a promising drug candidate, specifically for the MCF-7 cancer cells, with minimal damage to healthy cells. 

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