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1. Co II Complexes as Liposomal CEST Agents

   https://doi.org/10.1002/anie.202003479  

   Abozeid, Samira M. ; Asik, Didar ; Sokolow, Gregory E. ; Lovell, Jonathan F. ; Nazarenko, Alexander Y. ; Morrow, Janet R. ( May 2020 , Angewandte Chemie International Edition)

   Three paramagnetic Co^IImacrocyclic complexes containing 2‐hydroxypropyl pendant groups, 1,1′,1′′,1′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetrakis‐ (propan‐2‐ol) ([Co(L1)]²⁺, 1,1′‐(4,11‐dibenzyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐diyl)bis(propan‐2‐ol) ([Co(L2)]²⁺), and 1,1′‐(4,11‐dibenzyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐diyl)bis(octadecan‐2‐ol) ([Co(L3)]²⁺) were synthesized to prepare transition metal liposomal chemical exchange saturation transfer (lipoCEST) agents. In solution, ([Co(L1)]²⁺) forms two isomers as shown by¹H NMR spectroscopy. X‐ray crystallographic studies show one isomer with 1,8‐pendants incis‐configuration and a second isomer with 1,4‐pendants intrans‐configuration. The [Co(L2)]²⁺complex has 1,8‐pendants in acis‐configuration. Remarkably, the paramagnetic‐induced shift of water¹H NMR resonances in the presence of the [Co(L1)]²⁺complex is as large as that observed for one of the most effective Ln^IIIwater proton shift agents. Incorporation of [Co(L1)]²⁺into the liposome aqueous core, followed by dialysis against a solution of 300 mOsm L⁻¹produces a CEST peak at 3.5 ppm. Incorporation of the amphiphilic [Co(L3)]²⁺complex into the liposome bilayer produces a more highly shifted CEST peak at −13 ppm. Taken together, these data demonstrate the feasibility of preparing Co^IIlipoCEST agents.

    

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2. Co( ii ) complexes of tetraazamacrocycles appended with amide or hydroxypropyl groups as paraCEST agents

   https://doi.org/10.1039/d3dt01572f  

   Raymond, Jaclyn J. ; Abozeid, Samira M. ; Sokolow, Gregory E. ; Bond, Christopher J. ; Yap, Constance E. ; Nazarenko, Alexander Y. ; Morrow, Janet R. ( July 2023 , Dalton Transactions)

   Co( ii ) complexes of 1,4,7,10-tetraazacyclododecane (CYCLEN) or 1,4,8,11-tetraazacyclotetradecane (CYCLAM) with 2-hydroxypropyl or carbamoylmethyl (amide) pendants are studied with the goal of developing paramagnetic chemical exchange saturation transfer (paraCEST) agents. Single-crystal X-ray diffraction studies show that two of the coordination cations with hexadentate ligands, [Co(DHP)] 2+ and [Co(BABC)] 2+ , form six-coordinate complexes; whereas two CYCLEN-based complexes with potentially octadentate ligands, [Co(THP)] 2+ and [Co(HPAC)] 2+ , are seven-coordinate with only three of the four pendant groups bound to the metal center. 1 H NMR spectra of these complexes suggest that the six-coordinate complexes are present as a single isomer in aqueous solution. For the complexes which are seven-coordinate in the solid state, one is highly fluxional in aqueous solution on the NMR time scale ([Co(HPAC)] 2+ ), whereas the NMR spectrum of [Co(THP)] 2+ is consistent with an eight-coordinate complex with all pendants bound. Co( ii ) complexes of CYCLEN derivatives show CEST effects of low intensity that are assigned to NH or OH groups of the pendants. One complex, [Co(DHP)] 2+ , shows a highly-shifted CEST peak at 113 ppm versus bulk water, attributed to OH protons. However, the CEST effect is largest for two Co( ii ) CYCLAM-based complexes with coordinated amide groups that undergo NH proton exchange. All five complexes are inert towards dissociation in buffered solutions containing carbonate and phosphate and towards trans-metalation by excess Zn( ii ). These data give insight into the production of an intense CEST effect for tetraazamacrocyclic complexes with pendant groups containing NH or OH exchangeable protons. The intense and highly shifted CEST peak(s) of the CYCLAM-based complexes suggest that they are promising for further development as paraCEST agents. 

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3. Further Studies of Co III (TIM) Mono‐Alkynyl and Bis‐Alkynyl Complexes

   https://doi.org/10.1002/ejic.202200641  

   Rodriguez Segura, Leobardo ; Cox, Kenneth E. ; Samayoa‐Oviedo, Hugo Y. ; Ren, Tong ( December 2022 , European Journal of Inorganic Chemistry)

   A new series of mono‐ and bis‐alkynyl Co^III(TIM) complexes (TIM=2,3,9,10‐tetramethyl‐1,4,8,11‐tetraazacyclotetradeca‐1,3,8,10‐tetraene) is reported herein. Thetrans‐[Co(TIM)(C₂R)Cl]⁺complexes were prepared from the reaction betweentrans‐[Co(TIM)Cl₂]PF₆and HC₂R (R=tri(isopropyl)silyl or TIPS (1), ‐C₆H₄‐4‐^tBu (2), ‐C₆H₄‐4‐NO₂(3 a), andN‐mesityl‐1,8‐naphthalimide or NAP^Mes(4 a)) in the presence of Et₃N. The intermediate complexes of the typetrans‐[Co(TIM)(C₂R)(NCMe)](PF₆)(OTf),3 band4 b, were obtained by treating3 aand4 a, respectively, with AgOTf in CH₃CN. Furthermore, bis‐alkynyltrans‐[Co(TIM)(C₂R)₂]PF₆complexes,3 cand4 c, were generated following a second dehydrohalogenation reaction between3 band4 b, respectively, and the appropriate HC₂R in the presence of Et₃N. These new complexes have been characterized using X‐ray diffraction (2,3 a,4 a, and4 c), IR,¹H NMR, UV/Vis spectroscopy, fluorescent spectroscopy (4 c), and cyclic voltammetry.

    

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4. Crystal structures of two (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) complexes

   https://doi.org/10.1107/S2053229619013925  

   Clendening, Reese A. ; Zeller, Matthias ; Ren, Tong ( November 2019 , Acta Crystallographica Section C Structural Chemistry)

   Reported in this contribution are the synthesis and crystal structures of two new Fe III complexes of 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (HMC), namely, dichlorido(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) chloride, [FeCl 2 (C 16 H 36 N 4 )]Cl or cis -[FeCl 2 ( rac -HMC)]Cl ( 1 ), and dichlorido(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) tetrachloridoferrate, [FeCl 2 (C 16 H 36 N 4 )][FeCl 4 ] or trans -[FeCl 2 ( meso -HMC)][FeCl 4 ] ( 2 ). Single-crystal X-ray diffraction studies revealed that both 1 and 2 adopt a pseudo-octahedral geometry, where the macrocycles adopt folded and planar geometries, respectively. The chloride ligands in 1 are cis to each other, while those in 2 have a trans configuration. The relevant bond angles in 1 deviate substantially from an ideal octahedral coordination geometry, with the angles between the cis substituents varying from 81.55 (5) to 107.56 (4)°, and those between the trans -ligating atoms varying from 157.76 (8) to 170.88 (3)°. In contrast, 2 adopts a less strained configuration, in which the N—Fe—N angles vary from 84.61 (8) to 95.39 (8)° and the N—Fe—Cl angles vary from 86.02 (5) to 93.98 (5)°. 

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5. Electron transport in a sequentially doped naphthalene diimide polymer

   https://doi.org/10.1039/d0ma00406e  

   Al Kurdi, Khaled ; Gregory, Shawn A. ; Jhulki, Samik ; Conte, Maxwell ; Barlow, Stephen ; Yee, Shannon K. ; Marder, Seth R. ( September 2020 , Materials Advances)

   null (Ed.)

   The effects of sequential n-doping on a high-electron-mobility naphthalene-diimide-based copolymer poly[( N , N ′-bis(2-decyltetradecyl)-naphthalene-1,8:4,5-bis(dicarboximide)-2,6-diyl)-(selenophene-2,5-diyl)-(benzo[ c ][1,2,5]thiadiazole-4,7-diyl)-(selenophene-2,5-diyl)], PNBS, are reported. Grazing-incidence XRD measurements show that PNBS doped with 2,2′-bis(4-(dimethylamino)phenyl)-1,1′,3,3′-tetramethyl-2,2′,3,3′-tetrahydro-1 H ,1′ H -2,2′-bibenzo[ d ]imidazole, (N-DMBI) 2 , has increased order relative to both the pristine polymer and a film doped with ruthenium pentamethylcyclopentadienyl mesitylene dimer. Films of PNBS optimally doped with (N-DMBI) 2 show electrical conductivities approaching 2 mS cm −1 in air. Temperature-dependent electrical measurements suggest that the polaronic charge carriers are highly localized, which is consistent with the moderate conductivity values obtained. 

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