Carbazole-Dendronized Luminescent Radicals

A series of carbazole-dendronized tris(2,4,6-trichlorophenyl)methyl (TTM) radicals have been synthesized. The photophysical properties of dendronized radicals up to the fourth generation were compared systematically to understand how structure–property relationships evolve with generation. The photoluminescence quantum yield (PLQY) was found to increase with the increasing generation, and the fourth generation (G4TTM) in cyclohexane solution showed a PLQY as high as 63 % at a wavelength of 627 nm (in the deep-red region) from the doublet state. The dendron modification strategy also showed a blue-shift of the emission on increasing the generation number, and the photostability was also increased compared to the bare TTM radical.     

Dual Nickel(II)/Mechanoredox Catalysis: Mechanical-Force-Driven Aryl-Amination Reactions Using Ball Milling and Piezoelectric Materials

The combination of a nickel(II) catalyst and a mechanoredox catalyst under ball-milling conditions promotes mechanical-force-driven C−N cross-coupling reactions. In this nickel(II)/mechanoredox cocatalyst system, the modulation of the oxidation state of the nickel center, induced by piezoelectricity, is used to facilitate a highly efficient aryl-amination reaction, which is characterized by a broad substrate scope, an inexpensive combination of catalysts (NiBr₂ and BaTiO₃), short reaction times, and an almost negligible quantity of solvents. Moreover, this reaction can be readily up-scaled to the multi-gram scale, and all synthetic operations can be carried out under atmospheric conditions without the need for complicated reaction setups. Furthermore, this force-induced system is suitable for excitation-energy-accepting molecules and poorly soluble polyaromatic substrates that are incompatible with solution-based nickel(II)/photoredox cocatalysts.     

Low-Frequency Sub-Terahertz Absorption in HgII−XCN−FeII (X=S,Se) Coordination Polymers

Self-assembly Fe^II complexes of phenazine (Phen), quinoxaline (Qxn), and 4,4′-trimethylenedipyridine (Tmp) with tetrahedral building blocks of [Hg^II(XCN)₄]²⁻ (X=S or Se) formed six new high-dimensional frameworks with the general formula of [Fe(L)_m][Hg(XCN)₄]⋅solvents (L=Phen, m/X=2/S, 1 ; L=Qxn, m/X=2/S, 2 ; L=Qxn, m/X=1/S, 3 ; L=Qxn, m/X=1/Se, 3-Se ; L=Tmp, m/X=1/S, 4 ; and L=Tmp, m/X=1/Se, 4-Se ). 1 , 3 , and 3-Se show an intense sub-terahertz (sub-THz) absorbance of around 0.60 THz due to vibrations of the solvent molecules coordinated to the Fe^II ions and crystallization organic molecules. In addition, crystals of 1 , 4 , and 4-Se display low-frequency Raman scattering with exceptionally low values of 0.44, 0.51, and 0.53 THz, respectively. These results indicate that heavy metal Fe^II−Hg^II systems are promising platforms to construct sub-THz absorbers.     

Front Cover: Water-Solvation-Dependent Spin Transitions in Cobalt(II)-Octacyanidometallate Complexes (Eur. J. Inorg. Chem. 30/2023)

The spin-crossover (SCO) and charge-transfer (CT) phenomena, the switching processes between two distinguishable magnetic states, are promising for developing materials capable of sophisticated memory and sensing functionalities. The majority of SCO systems are based on iron(II) complexes. However, cobalt(II)-2,2′:6′,2′′-terpyridine (terpy) systems emerge as a promising alternative. In this work, new complex salts [Co^II(terpy)₂]₂[Mo^IV(CN)₈] ⋅ 15H₂O, Co₂Mo (H₂O), and [Co^II(terpy)₂]₃[W^V(CN)₈]₂ ⋅ 12H₂O, Co₃W₂ (H₂O) were synthesized and physiochemically characterized. Structural studies for both compounds revealed [Co(terpy)₂]²⁺ layers pillared by octacyanidometallate anions and completed with water molecules between them. Magnetic studies confirmed that the (de)solvated phases of both complexes exhibit partial SCO on the cobalt(II) centers: Co^II−LS (S_Co(II)-LS=¹/₂)↔Co^II−HS (S_Co(II)-HS=³/₂). Moreover, handling dehydrated samples in a high-humidity environment leads to partial recovery of previous magnetic properties via humidity-induced SCO for Co₂Mo : Co^II−HS→Co^II−LS, and the new phenomenon of isothermal humidity-activated charge-transfer-induced spin transition, which we define here as HACTIST, for Co₃W₂ : Co^II−HS⋅⋅⋅W^V (S_Co(II)-HS=³/₂ and S_W(V)=¹/₂)→Co^III−LS⋅⋅⋅W^IV (S_W(IV)=0 and S_Co(III)-LS=0). These comprehensive studies shed light on the water-solvation-dependent spin transitions in Co(II)-octacyanidometallate(IV/V) complexes.     

Spectroscopic investigation of Ginkgo biloba terpene trilactones and their interaction with amyloid peptide Abeta(25-35)

The beneficial effects of Ginkgo biloba extract in the "treatment" of dementia are attributed to its terpene trilactone (TTL) constituents. The interactions between TTLs and amyloid peptide are believed to be responsible in preventing the aggregation of peptide. These interactions have been investigated using infrared vibrational absorption (VA) and circular dichroism (VCD) spectra. Four TTLs, namely ginkgolide A (GA), ginkgolide B (GB), ginkgolide C (GC) and bilobalide (BB) and amyloid Abeta(25-35) peptide, as a model for the full length peptide, are used in this study. GA-monoether and GA-diether have also been synthesized and investigated to help understand the role of individual carbonyl groups in these interactions. The precipitation and solubility issues encountered with the mixture of ginkgolide+Abeta peptide for VA and VCD studies were overcome using binary ethanol-D(2)O solvent mixture. The experimental VA and VCD spectra of GA, GB, GC and BB, GA-monoether and GA-diether have been analyzed using the corresponding spectra predicted with density functional theory. The time-dependent experimental VA and VCD spectra of Abeta(25-35) peptide and the corresponding experimental spectra in the presence of TTLs indicated that the effect of the TTLs in modulating the aggregation of Abeta(25-35) peptide is relatively small. Such small effects might indicate the absence of a specific interaction between the TTLs and Abeta(25-35) peptide as a major force leading to the reduced aggregation of amyloid peptides. It is possible that the therapeutic effect of G. biloba extract does not originate from direct interactions between TTLs and the Abeta(25-35) peptide and is more complex.     

pH-Dependent isotope exchange and hydrogenation catalysed by water-soluble NiRu complexes as functional models for [NiFe]hydrogenases

The pH-dependent hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes and hydrogenation of the carbonyl compounds have been investigated with water-soluble bis(mu-thiolate)(mu-hydride)NiRu complexes, Ni(II)(mu-SR)(2)(mu-H)Ru(II) {(mu-SR)(2) = N,N'-dimethyl-N,N'-bis(2-mercaptoethyl)-1,3-propanediamine}, as functional models for [NiFe]hydrogenases. In acidic media (at pH 4-6), the mu-H ligand of the Ni(II)(mu-SR)(2)(mu-H)Ru(II) complexes has H(+) properties, and the complexes catalyse the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes. A mechanism of the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes through a low-valent Ni(I)(mu-SR)(2)Ru(I) complex is proposed. In contrast, in neutral-basic media (at pH 7-10), the mu-H ligand of the Ni(II)(mu-SR)(2)(mu-H)Ru(II) complexes acts as H(-), and the complexes catalyse the hydrogenation of carbonyl compounds.     

Ligand-to-metal charge-transfer dynamics in a blue copper protein plastocyanin: a molecular dynamics study

Equilibrium and nonequilibrium dynamics of a blue copper protein plastocyanin in an oxidized state are studied by molecular dynamics (MD) simulation. Potential energy functions of the lowest seven electronic states, including ligand-to-metal charge-transfer (LMCT) and copper d --> d excited states, were taken from our previous work (Ando, K. J. Phys. Chem. B 2004, 108, 3940), which employed ab initio molecular orbital and density functional calculations on the active-site model. The equilibrium MD simulations in the ground state indicate that ligand motions coupled to transition from the ground state to the LMCT state are mostly represented by stretching and bending vibrations of the Cu-S(Cys) distance, Ndelta(His)-Cu-Ndelta(His) angle, and S(Cys)-Cu-[Ndelta(His)]2 trigonal pyramid structure. The nonequilibrium dynamics on the LMCT potential exhibit rapid decays in which surface crossings to the d --> d and the first excited states occur in 70-80 fs. The crossing dynamics mostly correlate with cleavage of the Cu-S(Cys) bond and the associated response in the Ndelta(His)-Cu-Ndelta(His) moiety. The average dynamics of the vertical energy gap coordinates exhibit an overdamped decay with a recurrence oscillation in 500 fs, which shows clear coherence surviving after the ensemble averaging. This oscillation stems mostly from the recoiling motion of the Ndelta(His)-Cu-Ndelta(His) part. The dynamics of the energy gaps after this coherent oscillation are randomized such that the ensemble average yields flat profiles along time, although each single trajectory exhibits fluctuations with amplitudes large enough to reach surface crossings. These indicate that the relaxation from the LMCT state first occurs via ballistic and coherent potential crossings in 70-80 and 500 fs, followed by thermally activated random transitions.     

Nickel-catalyzed carboxylation of organozinc reagents with CO2

An efficient nickel catalyst system for the carboxylation of organozinc reagents with CO(2) under very mild conditions has been developed. The catalyst system complements the conventional methods and enables the direct synthesis of various saturated carboxylic acid derivatives from the corresponding alkylzinc reagents and CO(2).