Ancillary Groups Research Articles

Examining the Importance of Hydrogen Bonding and Proton Transfer in Iron Porphyrin-Mediated Carbon Dioxide Upconversion.

ConspectusThe title should give a sense of the "big picture" of this Account, but what is it really about? An unexpected change in research direction? A series of courageous and creative students? A team taking on challenging problems in chemistry? The answer is a definite "yes" to all of the above. More specifically, the problem in which we are interested is the upconversion or valorization of carbon dioxide. This problem has captured the attention of a great many chemists in earnest following the gas crisis of the 1970s and more recently galvanized due to climate concerns arising from the ongoing release of anthropogenic carbon. Addressing the problem of atmospheric carbon accumulation requires effort in two very broad areas: capture and conversion. Storage is an alternative to conversion, but this eliminates the opportunity to use what might be otherwise a waste product. Our group has investigated a series of modified versions of iron(III)-5,10,15,20-tetraphenylporphyrin (FeTPP) that can convert CO2 to carbon monoxide, which is a versatile and useful precursor for other syntheses. Following pioneering work from Savéant and his colleagues in the 1990s and thereafter, we started with a simple question: how many pendent ancillary groups that can donate H-bonds or protons are needed to support efficient CO2-to-CO conversion? Using a molecule with only one 2-hydroxylphenyl group, we demonstrated that the single prepositioned -OH group gave rise to efficient turnover, but only when experiments were carried out in a weakly H-bond-accepting solvent system. In other words, the ability of a solvent to accept H-bonds can impede CO2 reduction. We followed up with a deeper investigation of the influence of H-bonding interactions with external acids in FeTPP-mediated CO2 reduction. Savéant's framework mechanism appears to be independent of solvent, and rate differences can be approximated by considering H-bonding equilibria. Following that work, we sought to better understand the minimum catalyst design requirements with respect to internal H-bond/proton donors. To that end, we produced all possible isomers of tetraarylpoprhyrins with 2,6-dihydroxyphenyl + phenyl groups. All else being equal, the complexes with a formally trans orientation of the 2,6-dihydroxyphenyl groups performed the best. Most recently, we surveyed the roles of internal and external Brønsted acids with different pKa values. Surprisingly, the best-performing catalysts have more weakly acidic internal groups. Overall, our work has demonstrated that CO2 reduction mediated by porphyrin catalysts can be improved by considering solvent H-bonding, the orientation of internal H-bonding groups, and the balance of the pKa values of internal and external acids. The future for molecular electrocatalysts is promising as more ideas emerge about how to design molecules and conditions for CO2 reduction.

Understanding the Interplay of the Brønsted Acidity of Catalyst Ancillary Groups and the Solution Components in Iron-porphyrin-Mediated Carbon Dioxide Reduction.

The rapid and efficient conversion of carbon dioxide (CO2) to carbon monoxide (CO) is an ongoing challenge. Catalysts based on iron-porphyrin cores have emerged as excellent electrochemical mediators of the two proton + two electron reduction of CO2 to CO, and many of the design features that promote function are known. Of those design features, the incorporation of Brønsted acids in the second coordination sphere of the iron ion has a significant impact on catalyst turnover kinetics. The Brønsted acids are often in the form of hydroxyphenyl groups. Herein, we explore how the acidity of an ancillary 2-hydroxyphenyl group affects the performance of CO2 reduction electrocatalysts. A series of meso-5,10,15,20-tetraaryl porphyrins were prepared where only the functional group at the 5-meso position has an ionizable proton. A series of cyclic voltammetry (CV) experiments reveal that the complex with -OMe positioned para to the ionizable -OH shows the largest CO2 reduction rate constants in acetonitrile solvent. This is the least acidic -OH of the compounds surveyed. The turnover frequency of the -OMe derivative can be further improved with the addition of 4-trifluoromethylphenol to the solution. In contrast, the iron-porphyrin complex with -CF3 positioned opposite the ionizable -OH shows the smallest CO2 reduction rate constants, and its turnover frequency is less enhanced with the addition of phenols to the reaction solutions. The origin of this effect is rationalized based on kinetic isotope effect experiments and density functional calculations. We conclude that catalysts with weaker internal acids coupled with stronger external acid additives provide superior CO2 reduction kinetics.

Bis-tridentate Ir(III) Phosphors and Blue Hyperphosphorescence with Suppressed Efficiency Roll-Off at High Brightness.

Narrowband blue emitters are indispensable in achieving ultrahigh-definition OLED displays that satisfy the stringent BT 2020 standard. Hereby, a series of bis-tridentate Ir(III) complexes bearing electron-deficient imidazo[4,5-b]pyridin-2-ylidene carbene coordination fragments and 2,6-diaryloxy pyridine ancillary groups were designed and synthesized. They exhibited deep blue emission with quantum yields of up to 89% and a radiative lifetime of 0.71 μs in the DPEPO host matrix, indicating both the high efficiency and excellent energy transfer process from the host to dopant. The OLED based on Irtb1 showed an emission at 468 nm with a maximum external quantum efficiency (EQE) of 22.7%. Moreover, the hyper-OLED with Irtb1 as a sensitizer for transferring energy to terminal emitter v-DABNA exhibited a narrowband blue emission at 472 nm and full width at half-maximum (FWHM) of 24 nm, a maximum EQE of 23.5%, and EQEs of 19.7, 16.1, and 12.9% at a practical brightness of 100, 1000, and 5000 cd/m2, respectively.

Highly Efficient Luminescence from a Red Thermally Activated Delayed Fluorescence Emitter with Flexible Conformation of Ancillary Groups.

Robust scaffolds were typically applied in thermally activated delayed fluorescence (TADF) molecules to suppress the non-radiative decay, trigger the fast spin-flipping, and enhance the light out-coupling efficiency. Herein, we disclosed for the first time the positive effect of flexible conformation of ancillary groups on the photophysical properties of TADF emitter. The red TADF emitter Ph-TPA with flexible conformation demonstrated small excited-state structural distortion and low reorganization energy compared to the counterpart Mc-TPA with a rigid macrocycle. Consequently, Ph-TPA showed an excellent photoluminescent quantum yield (PLQY) of 92 % and a state-of-the-art external quantum efficiency (EQE) of 30.6 % at 630 nm. This work could deepen our understanding of structure-property relationships of organic luminophores and help us to rationalize the design of efficient TADF materials.

Pd(II) based anticancer drug candidates with 1,2-Aminoethyl piperidine scaffold and sulfur donor ancillary: Their in vitro bio-activity, molecular docking and DFT study

A series of Pd(II) complexes Pd-1 to Pd-6; out of these [Pd(PIEAM)(LC)]+; Pd-3, [Pd(PIEAM)(NALC)]; Pd-4, [Pd(PIEAM)(GSH)]; Pd-5 and [Pd(PIEAM)(DL-meth)]2+; Pd-6 have been synthesized from water soluble stable diaqua complex [Pd(PIEAM)(OH2)2](NO3)2; Pd-2. The Pd-2 complex was obtained from hydrolysis of [Pd(PIEAM)Cl2]; Pd-1 (where, PIEAM = 1,2-Aminoethyl piperidine, a bidentate carrier ligand and with ancillary groups like; LC = L-cysteine, NALC = N-acetyl-L-cysteine, GSH = Glutathione, DL-meth = DL-methionine). All these Pd-1-Pd-6 complexes were characterized by different spectroscopic studies, like; UV–Vis, FT-IR, 1H NMR, and ESI Mass analyses. The bioactivity and drug-likeness properties of the complexes were assessed by PASS and ADME prediction software. The bioactivity of the complexes was experimentally investigated on DNA binding properties by gel electrophoresis, electronic, fluorescence, and viscometric methods. The binding constant values of Pd-3 complex with CT DNA bining in both absorption (Kb = 7.50 × 104M−1)and fluorosence titration (KSV = 35.10 × 103 M−1) was found greater than other Pd-1, Pd-2, Pd-4-Pd-6 complexes (Kb = (4.25–0.64) × 104 M−1; KSV = (13.57–1.11) × 103 M−1). The comparison in BSA bining of Pd(II) complexes also suggested the higher binding constant of Pd-3 complex in both spectroscopic method (Kb = 32 × 103M−1; KSV = 2.32 × 104 M−1) than other Pd(II) complexes (Kb = 16–2.4 × 103M−1; KSV = 1.99–1.53 × 104 M−1). A theoretical investigation of the structural property and TD-DFT of the complexes was executed by DFT calculations. The detailed BSA binding activity of the complexes was performed by fluorescence quenching, synchronous, and 3D-fluorescence spectroscopic methods. Molecular docking of the complexes with DNA and BSA was under study for their binding mode and different weak forces. Their cytotoxic behaviors, like; anticancer activity by MTT assay and ROS (Reactive Oxygen Species) generation by NBT (Nitro Blue Tetrazolium) assay, were investigated. The cytotoxicity of the complexes was under investigation on human lung adenocarcinoma cell A549, colorectal carcinoma cell HCT 116, and normal human embryonic kidney cell HEK 293.

Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups

Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (η5-C5Me5)TiCl2(O-2,6-iPr2C6H3) (1), (η5-C5Me5)TiCl2(N=CtBu2) (2) and [Me2Si(η5-C5Me4)(NtBu)]TiCl2 (3), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex 1, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes 1 and 2, while both side insertion orientations are comparable for complex 3. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from 3. At the chain termination stage, β-H transfer was calculated to be a dominant chain termination route over β-H elimination, presumably owing to the thermodynamic perspective.

The Self-Aggregation of Porphyrins with Multiple Chiral Centers in Organic/Aqueous Media: The Case of Sugar- and Steroid-Porphyrin Conjugates.

An overview of the solvent-driven aggregation of a series of chiral porphyrin derivatives studied by optical methods (UV/Vis, fluorescence, CD and RLS spectroscopies) is herein reported. The investigated porphyrins are characterized by the presence in the meso-positions of glycol-, steroidal- and glucosteroidal moieties, conferring amphiphilicity and solubility in aqueous media to the primarily hydrophobic porphyrin platform. Aggregation of the macrocycles is driven by a change in bulk solvent composition, forming architectures with supramolecular chirality, steered by the stereogenic centers on the porphyrin peripheral positions. The aggregation behavior and chiroptical properties of the final aggregated species strongly depend on the number and stereogenicity of the ancillary groups that dictate the mutual spatial arrangement of the porphyrin chromophores and their further organization in larger structures, usually detectable by different microscopies, such as AFM and SEM. Kinetic studies are fundamental to understand the aggregation mechanism, which is frequently found to be dependent on the substrate concentration. Additionally, Molecular Mechanics calculations can give insights into the intimate nature of the driving forces governing the self-assembly process. The critical use of these combined methods can shed light on the overall self-assembly process of chirally-functionalized macrocycles, with important implications on the development of chiral porphyrin-based materials.

Observational Bias Within Hospital-Wide Hand Hygiene Program

Background: Hand hygiene (HH) is critical to prevent hospital-acquired infections. Running a successful HH program requires valid and accurate HH data to monitor the status and progress of HH improvement efforts. HH data are frequently subject to variable forms of bias, for which considerations must be made to enhance the validity of HH data. Objective: We assessed the extent to which observers may be prone to report more favorable HH rates when observing healthcare workers from the same professional group versus members of other job categories. Methods: We analyzed HH data from 48,543 electronically collected observations conducted by frontline healthcare workers in a 793-bed acute-care hospital from January 1, 2019, through July 31, 2019. All auditors received training on HH observations and proper use of the data collection application. Compliance data were sorted into peer versus nonpeer observations by profession. We compared HH compliance rates for members of each professional group when monitoring peers versus nonpeers. We further stratified results by ancillary professions (central transport, unit associates, food services, pharmacy, phlebotomy, rehabilitation services, and respiratory therapy) versus nonancillary professions (doctors, nurses, physician assistants, patient care assistants). Results: Of 12,488 ancillary observations, 7,184 (57.5%) were peer observations and 36,055 were nonancillary observations, of which 15,942 (44.2%) were peer observations. The percentage of peer-to-peer observations versus nonpeer observations varied by profession, ranging from 96% of central transport workers and 91% of environmental services observations to 21% of patient care assistants and 34% of physician’s assistants. Average compliance rates for peer versus nonpeer observations in ancillary groups were 98% (95% CI, 98.7%–99.2%) versus 83% (95% CI, 82.5%–84.5%). Average compliance rates nonancillary groups were 92% (95% CI, 92.0%–92.8%) for peers versus 88% (95% CI, 87.8%–88.7%) for nonpeers (Table 1). Conclusions: We documented a propensity for some categories of healthcare workers to record discrepant rates of HH compliance when observing members of the same peer group versus others. This effect was more pronounced amongst ancillary versus nonancillary services. This study adds to the literature of potential sources of bias in HH monitoring programs. Operational changes in HH program data collection may be warranted to try to mitigate these biases such as increasing the frequency of validation exercises conducted by nonaffiliated observers, weighting peer versus nonpeer observations differently, or switching to automated electronic monitoring systems.Funding: NoneDisclosures: None

Controlling the Oxygen Reduction Selectivity of Asymmetric Cobalt Porphyrins by Using Local Electrostatic Interactions.

The development and improvement of electrocatalysts for the 4H+/4e- reduction of O2 to H2O is an ongoing challenge. The addition of ancillary groups (e.g., hydrogen bonding, Brønsted acid/base) near the active site of metal-containing catalysts is an effective way to improve selectivity and kinetics of the oxygen reduction reaction (ORR). In this regard, iron porphyrins are among the most researched ORR catalysts. Closely related cobalt porphyrin ORR catalysts can function closer to the O2/H2O thermodynamic potential, but they tend to be less selective and follow a different mechanism than for the iron porphyrins. Herein, we explore strategies to extend the ideas about ancillary groups that have been developed for iron porphyrin ORR electrocatalysts to improve the performance of the corresponding cobalt complexes. We describe a series of porphyrin electrocatalysts that are modified versions of Co(5,10,15,20-tetraphenylporphyrin), where the 2-position of one of the phenyl groups contains -NH2, -N(CH3)2, and -N(CH3)3+. Investigations using cyclic voltammetry and hydrodynamic electrochemistry show that the presence of a cationic ancillary group gives rise to a catalyst that is selective for the conversion of O2 to H2O across a wide pH range. In contrast, the other catalysts are selective for reduction of O2 to H2O at pH 0, but produce H2O2 at higher pH. The ORR rate (∼106 M-1 s-1) and selectivity of the -N(CH3)3+-modified catalyst are invariant between pH 0 and 7. Quantum chemical calculations support the hypothesis that the enhancement of selectivity can be attributed to the distinct mechanism of O2 reduction by Co-porphyrins. Specifically, the mechanism relies on anionic, peroxide-bound intermediates. While protic ancillary groups are important in the performance of iron porphyrin ORR catalysts, we suggest that electrostatic stabilizers of O2-bound intermediates are more crucial for cobalt porphyrin ORR catalysts.

Development of Ruthenium Complex Based Sensitizers, Organic Based Sensitizers, and Co-sensitization System for Dye-sensitized Solar Cells

This paper reviews the recent development of ruthenium complex sensitizers, organic sensitizers, and co-sensitizers for dye-sensitized solar cell (DSSC) applications. The development of ruthenium sensitizers has progressed from thiocyanate (NCS) ligands containing bipyridyl, terpyridyl, quarterpyridyl, and cyclometalated ruthenium sensitizers to NCS-free analogs. The integration of organic moieties and ruthenium complex ancillary ligands into a single structure entity was also achieved in the DSSC industry. The development of organic sensitizers as an alternative to ruthenium-based sensitizers was also discussed according to their functional segment: donor, acceptor, and π-spacer. The modification of donor groups has been focused on introducing ancillary groups to increase the molar extinction coefficient and electron recombination resistance. Anchoring groups other than cyanoacrylic acids have been developed to improve the anchoring ability of organic sensitizers while maintaining their light-harvesting properties. A study was performed on π-spacers modified with different conjugation lengths and conjugated side chains in order to enhance the charge transfer within organic sensitizers. Co-sensitization systems, including metal-metal, metal-organic, and organic-organic systems with stepwise and “cocktail” co-sensitization methods will be discussed in this review.

Balancing Bulkiness in Gold(I) Phosphino-triazole Catalysis.

The syntheses of a series of 1‐phenyl‐5‐phosphino 1,2,3‐triazoles are disclosed, within which, the phosphorus atom (at the 5‐position of a triazole) is appended by one, two or three triazole motifs, and the valency of the phosphorus(III) atom is completed by two, one or zero ancillary (phenyl or cyclohexyl) groups respectively. This series of phosphines was compared with tricyclohexylphosphine and triphenylphosphine to study the effect of increasing the number of triazoles appended to the central phosphorus atom from zero to three triazoles. Gold(I) chloride complexes of the synthesised ligands were prepared and analysed by techniques including single‐crystal X‐ray diffraction structure determination. Gold(I) complexes were also prepared from 1‐(2,6‐dimethoxy)‐phenyl‐5‐dicyclohexyl‐phosphino 1,2,3‐triazole and 1‐(2,6‐dimethoxy)‐phenyl‐5‐diphenyl‐phosphino 1,2,3‐triazole ligands. The crystal structures thus obtained were examined using the SambVca (2.0) web tool and percentage buried volumes determined. The effectiveness of these gold(I) chloride complexes to serve as precatalysts for alkyne hydration were assessed. Furthermore, the regioselectivity of hydration of but‐1‐yne‐1,4‐diyldibenzene was probed.

Benzoimidazole‐Pyridylamido Zirconium and Hafnium Alkyl Complexes as Homogeneous Catalysts for Tandem Carbon Dioxide Hydrosilylation to Methane

AbstractNeutral ZrIV and HfIV alkyl/amido complexes stabilized by a tridentate N ligand that contains a “rolling” heterodentate benzoimidazole fragment have been prepared and characterized. The ultimate nature of the ligand denticity, the electronic properties of the ligand binding pocket and the metal coordination environment are controlled by the protection/deprotection of the benzoimidazole NH group. The metal precursor used [MIV(Bn)4 or MIV(NMe2)4] also has an influence on the final coordination sphere of the complex; indeed, a permanent central pyridine dearomatization occurs in the presence of dimethylamido ancillary groups. DFT calculations on the real system have been used to elucidate the mechanism. Selected alkyl species from this series have been scrutinized for the tandem hydrosilylation of CO2 to CH4 in combination with the strong Lewis acid B(C6F5)3 using a variety of hydrosilanes. A positive effect of the hardness modification of the ligand donor atom set is observed in the catalytic outcomes. Indeed, κ3{N−,N,N−}ZrIV(Bn)2 catalyzes the process to methane selectively with a turnover frequency as high as 272 h−1 (at 96 % substrate conversion) almost twice as much as that claimed for the benchmark κ3{O−,O,O−}ZrIV(Bn)2 complex under similar experimental conditions.

Probing the HIV-1 NCp7 Nucleocapsid Protein with Site-Specific Gold(I)-Phosphine Complexes.

In this work, we examined a series of thiophilic Au(I) compounds based on [Au(L)(PR3)] (L = Cl-, 4-dimethylaminopyridine (dmap); R= ethyl (Et), cyclohexyl (Cy)) for chemoselective auration of the C-terminal HIV nucleocapsid protein NCp7 F2 and the "full" HIV NCp7 (NC, zinc finger (ZnF)) as probes of nucleocapsid topography. The choice of phosphine allowed electronic and steric effects to be considered. The use of the heterocycle "leaving group" allowed us to study the effect of possible π-stacking with the essential tryptophan residue of NC on the reactivity and selectivity, mimicking the naturally occurring interaction between the zinc finger and nucleic acids. We also examined for comparison the "standard" gold-phosphine compound auranofin, which contains an S-bound glucose coordinated to the {Au(PEt3)} moiety. Both the nature of the phosphine and the nature of L affect the reactivity with the C-terminal NCp7 F2 and the "full" NC. 31P NMR spectroscopy showed the formation of long-lived {Au(PR3)}-ZnF species in all cases, but in the case of NCp7 F2, a selective interaction in the presence of the dmap ligand was observed. In the case of auranofin, an unusual Au-His (rather than Au-Cys) coordination was indicated on NC. The overall results suggest that it is useful to consider three aspects of zinc finger structure in considering the profile of chemical reactivity: (i) the zinc-bound cysteines as primary nucleophiles; (ii) the zinc-bound histidine as a "spectator" ligand; and (iii) ancillary groups not bound to Zn but essential for ZnF function such as the essential tryptophan in NCp7 F2 and NC. Modification of fully functional NC zinc finger by the Cy3P-containing species confirmed the inhibition of the NC-SL2 DNA interaction, as evaluated by fluorescence polarization.

(Amido)‐ and (Chlorido)titanium and ‐zirconium Complexes Coordinated by ansa‐Bis(amidinate) Ligands with a Rigid o‐Phenylene Linker

Bis(amido)–TiIV and –ZrIV complexes stabilized by the bis(amidinate) ligands {C6H4‐1,2‐[NC(tBu)N(2,6‐R2C6H3)]2}M(NMe2)2 [M = ZrIV, R = Me (3), R = iPr (4); M = TiIV, R = Me (5), R = iPr (6)] and {C6H4‐1,2‐[NC(tBu)N(2,6‐Me2C6H3)]2}Zr(NMe2)3H (3·HNMe2) were prepared in fairly good yields by treating a (bis)amidine ligand C6H4‐1,2‐[NC(tBu)N(2,6‐R2C6H3)H]2 [R = Me (1), iPr (2)] with an equimolar amount of the metal precursor M(NMe2)4 (M = ZrIV, TiIV). The salt metathesis reactions between equimolar amounts of the sodium amidinates C6H4‐1,2‐[NC(tBu)N(2,6‐R2C6H3)]2Na2 and ZrCl4(thf)2 were also scrutinized to synthesize the corresponding ZrIV bis(amidinate) dichlorides {C6H4‐1,2‐[NC(tBu)N(2,6‐R2C6H3)]2}ZrCl2 [R = Me (7), iPr (8)]. The coordination mode of the ligand to the MIV ions was strongly affected by the steric hindrance of the amidinate ligand (Me‐ vs. iPr‐substituted aniline moieties) as well as by the nature of the ancillary groups bound to the metal center (NMe2 vs. Cl). The bis(amido) ligand with the 2,6‐Me2C6H3 substituents at the amidinate nitrogen atoms coordinates to the zirconium ion in a tetradentate fashion both in solution and in the solid state (3 and 3·HNMe2). The compounds containing the bulkier 2,6‐iPr2C6H3 units prefer a tridentate coordination mode (4). With the smaller TiIV ion, the bis(amidinate) ligands from this series are tridentate in the solid state (5 and 6), whereas they reversibly switch their denticity from tridentate to tetradentate (κ3 vs. κ4) in solution depending on the temperature. The ZrIV complex 4, featuring the bulkier bis(amidinate) ligand 2, shows a behavior similar to that of its TiIV analogue, that is, a tridentate ligand coordination in the solid state and a temperature‐induced denticity change in solution. The standard thermodynamic parameters for the κ3/κ4 interconversions of the two model compounds 4 and 5 in [D8]toluene solution were determined from the respective linear van't Hoff plots. Finally, the ZrIV bis(chloride) complexes 7 and 8 invariably show a tetracoordinate mode for their bis(amidinate) ligands (1 and 2) in solution and in the solid state.

Adamantyl- and other polycyclic cage-based conjugates of desferrioxamine B (DFOB) for treating iron-mediated toxicity in cell models of Parkinson’s disease

The death of dopaminergic neurons is a major pathological hallmark of Parkinson’s disease (PD). Elevated iron within the substantia nigra of the PD brain is thought to catalyze this neuronal death through hydroxyl radical-derived oxidative damage. Removing this excess iron presents a potential therapeutic strategy for PD. Seventeen derivatives of the non-toxic iron chelator desferrioxamine B (DFOB) were prepared by the conjugation of adamantyl- (1–4, 8–12), deconstructed adamantyl units (5–7), norborna(e)ne- (13–16) or bicyclo[2.2.2]octane-based (17) ancillary fragments to the terminal amine group. The range of experimental logP values of 1–17 (logP=0.15–2.82) was greater than water soluble DFOB (logP −2.29), with the increased hydrophobicity designed to improve cell membrane carriage to facilitate intracellular iron sequestration. The first activity screen showed compounds with methyl-substituted adamantyl (1–3), noradamantyl (5), or 1-pentylbicyclo[2.2.2]octane (17) ancillary groups significantly rescued iron-mediated oxidative stress in confluent PD-relevant SK-N-BE2-M17 neuroblastoma cells (M17 cells) exposed to 1,1ʹ-dimethyl-4,4ʹ-bipyridinium (paraquat, PQ) or H2O2. The second dose-dependence screen ranked 1–3 and 17 as the top candidates (EC50 ∼10µM) in the rescue of PQ-treated M17 cells. The ancillary fragments of 1–3 and 17 clustered in a region defined by a close-to-zero dipole moment, logP values of 2–2.8 and a surface area:volume ratio of 0.60–0.61. Results of iron leaching studies indicate that the compounds may be operating via mechanisms beyond solely removing intracellular iron. The DFOB conjugates with methyl-substituted adamantyl ancillary groups (1–3) were the top and most consistent performers in this class of compound designed for PD.

ChemInform Abstract: A First Example of Cobalt‐Catalyzed Remote C—H Functionalization of 8‐Aminoquinolines Operating Through a Single Electron Transfer Mechanism.

AbstractA novel Co‐catalyzed remote nitration protocol for the preparation of 5‐ and 7‐nitro‐8‐aminoquinolines using installable and removable ancillary groups is described.

A theoretical investigation on the electronic structures and phosphorescent properties of three heteroleptic iridium(III) complexes with different substituted ancillary groups

ABSTRACTThree heteroleptic iridium(III) complexes 1, 2 and 3 bearing two cyclometalating 2′,6′-difluoro-2,3′-bipyridyl (dfpypy) chelates and one pyridyl pyrazolate ligand have been investigated by using the density functional theory/time-dependent density functional theory method to study the influence of the different substituent groups (―CF3 and ―N(CH3)2 moiety on the electronic structures, phosphorescent properties and the organic light-emitting diode performance. The lowest energy absorption wavelength calculated is in good agreement with the experimental value. The lowest energy emissions of complexes 1, 2 and 3 are localised at 454, 534 and 821 nm, respectively. Ionisation potential and electron affinity have been calculated to evaluate the injection abilities of holes and electrons into these complexes. The calculated results show that the different substitute groups affect the charge transfer rate and balance. Finally, we hope that this study can provide a good guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.

Harnessing Fluorescence versus Phosphorescence Ratio via Ancillary Ligand Fine-Tuned MLCT Contribution

A series of gold(I) alkynyl-diphosphine complexes (XC6H4C2Au)PPh2—spacer—PPh2(AuC2C6H4X); spacer = —C2(C6H4)nC2— (A1, n = 2, X = CF3; A2, n = 2, X = OMe; A3, n = 3, X = CF3; A4, n = 3, X = OMe), —(C6H4)n— (B5, n = 3, X = OMe; B6, n = 4, X = OMe) were prepared, and their photophysical properties were investigated. The luminescence behavior of the titled compounds is dominated by the diphosphine spacer, which serves as an emitting ππ* chromophore. The complexes exhibit dual emission, comprising low and high energy bands of triplet (phosphorescence) and singlet (fluorescence) origins, respectively. The electron-donating characteristics of ancillary groups X significantly affect the LLCT/MLCT contribution of both alkynyl ligand and the metal center into the lowest lying excited state. In turn, it substantially influences the rate of intersystem crossing kisc S1 → Tm (m ≥ 1) that allows for tuning the ratio fluorescence vs phosphorescence without alteration of the chromophore core. Quantum chemical analysis of...

Role of the Moiety Chirality in Determining the DNA Binding Characteristics of Threading Intercalators

Threading intercalators are small molecules that bind to DNA by threading their ancillary groups through the DNA bases to intercalate their middle planar section between the DNA base pairs. The high binding affinity and slow dissociation rates of threading intercalators have put them in the class of prospective anti-cancer drugs. In this study we explore the binding of a specific threading intercalator, the binuclear ruthenium complex ΛΛ-P (ΛΛ-[µ-bidppz(phen)4Ru2]4+) using optical tweezers. A single DNA molecule is held at a constant force and ΛΛ-P is introduced to the system in varying concentrations until equilibrium is achieved. Measurements of DNA extension at various concentrations of ΛΛ-P as a function of time provide the DNA equilibrium binding affinity and binding kinetics for this molecule. Preliminary data analysis at constant force suggests that ΛΛ-P exhibits significantly faster binding kinetics compared to the very similar ΔΔ-P [μ-bidppz(phen)4Ru2]4+. These complexes have the same chemical structure and only differ in their chirality, which suggests that the left handed (ΛΛ) threading moieties require less DNA structural distortion for threading compared with the right handed (ΔΔ) threading moieties.

In the Bottlebrush Garden: The Structural Aspects of Coordination Polymer Phases formed in Lanthanide Extraction with Alkyl Phosphoric Acids.

Coordination polymers (CPs) of metal ions are central to a large variety of applications, such as catalysis and separations. These polymers frequently occur as amorphous solids that segregate from solution. The structural aspects of this segregation remain elusive due to the dearth of the spectroscopic techniques and computational approaches suitable for probing such systems. Therefore, there is a lacking of understanding of how the molecular building blocks give rise to the mesoscale architectures that characterize CP materials. In this study we revisit a CP phase formed in the extraction of trivalent lanthanide ions by diesters of the phosphoric acid, such as the bis(2-ethylhexyl)phosphoric acid (HDEHP). This is a well-known system with practical importance in strategic metals refining and nuclear fuel reprocessing. A CP phase, referred to as a "third phase", has been known to form in these systems for half a century, yet the structure of the amorphous solid is still a point of contention, illustrating the difficulties faced in characterizing such materials. In this study, we follow a deductive approach to solving the molecular structure of amorphous CP phases, using semiempirical calculations to set up an array of physically plausible models and then deploying a suite of experimental techniques, including optical, magnetic resonance, and X-ray spectroscopies, to consecutively eliminate all but one model. We demonstrate that the "third phase" consists of hexagonally packed linear chains in which the lanthanide ions are connected by three O-P-O bridges, with the modifying groups protruding outward, as in a bottlebrush. The tendency to yield linear polynuclear oligomers that is apparent in this system may also be present in other systems yielding the "third phase", demonstrating how molecular geometry directs polymeric assembly in hybrid materials. We show that the packing of bridging molecules is central to directing the structure of CP phases and that by manipulating the steric requirements of ancillary groups one can control the structure of the assembly.