Redox chemistry

Selective oxidation of galacturonic residues of oligo and polyuronic acids by Cr VI affords CO 2 /HCO 2 H, oxidized uronic acid, and Cr III as final redox products. Kinetic studies show that the redox reaction proceeds through a mechanism combining Cr VI ? Cr IV ? Cr II and Cr VI ? Cr IV ? Cr III pathways. The mechanism is supported by the observation of free radicals, CrO 2 2+ and Cr V as reaction intermediates. The EPR spectra show that five-and six coordinated oxo-Cr V intermediates are formed. Penta-coordinated oxo-Cr V species are present at any [H + ], whereas hexa-coordinated ones are only observed at pH <1. At low pH Cr V predominating species are coordinated by carboxylate groups and O ring (g iso = 1.9783/5). At pH 7.5, the predominating ones are those coordinated by alcoholate groups of the ligand (g iso = 1.9800). Polygal can reduce Cr VI and efficiently trap Cr III . This behaviour represents an interesting model for the study of biomaterials, which possess a high proportion of polygal, in order to remove chromium from polluted waters.

In‐source oxidation: In‐source photocatalytic redox reactions for inducing peptide fragmentation are achieved on a TiO2‐derived target plate during laser desorption ionization mass spectrometry in the presence of samples and glucose acting as both an electron donor and a hole conductor (see scheme).magnified imageIn‐source photocatalytic redox reactions based on a photosensitive target plate have been developed to realize peptide fragmentation during laser desorption ionization. Sample peptides and glucose are simply deposited on a spot of sintered TiO2 nanoparticles. With the irradiation of UV laser on TiO2, electrons are excited from the valence to the conduction band, leaving oxidative holes and reductive electrons to drive various in‐source redox reactions. Glucose, working here as a hole scavenger and conductor, can favor both on‐surface reduction and long distance in‐plume oxidation, therefore inducing peptide fragmentation. CαC backbone cleavage was observed to generate a,x ...

The first artificially made set of electron acceptors is presented that are derived from a unique platform Cs[3,3′‐Co(C2B9H11)2], for which the redox potential of each differs from its predecessor by a fixed amount. The sequence of electron acceptors is made by substituting one, two, or more hydrogen atoms by chlorine atoms, yielding Cs[3,3′‐Co(C2B9H11−yCly)(C2B9H11−zClz)]. The higher the number of chlorine substituents, the more prone the platform is to be reduced. The effect is completely additive, so if a single substitution implies a reduction of 0.1 V of the redox potential of the parent complex, then ten substitutions imply a reduction of 1 V.

Visible‐light photoredox catalysis has recently emerged as a viable alternative for radical reactions otherwise carried out with tin and boron reagents. It has been recognized that by merging photoredox catalysis with flow chemistry, slow reaction times, lower yields, and safety concerns may be obviated. While flow reactors have been successfully applied to reactions carried out with UV light, only recent developments have demonstrated the same potential of flow reactors for the improvement of visible‐light‐mediated reactions. This review examines the initial and continuing development of visible‐light‐mediated photoredox flow chemistry by exemplifying the benefits of flow chemistry compared with conventional batch techniques.

Introduced in the late sixties, non‐innocent (or redox) ligands have been extensively studied for their unusual and intriguing chemical behavior. Their ability to delocalize and/or provide electrons to the metal center of organometallic complexes confers them undisputable chemical interest and has proved valuable in the development of novel synthetic methodologies. This review will focus on the chemistry and applications of low‐valent iron complexes bearing potentially non‐innocent ligands. Because of the elusive nature of these ligands, and whenever possible, theoretical calculations and analysis of spectroscopic data will be presented in an effort to provide insights into the catalytic activity of the complexes.

Multistage organic redox systems, [1] in particular, electrochemically highly amphoteric compounds with a small HOMO/LUMO gap (HLG, for example, E ox ÀE red < 0.5 eV), are of current interest due to their potential applications in molecular electronics and optoelectronics. [2] Consequently, research efforts have been directed toward the design and synthesis of molecular systems composed of powerful electron donor (D) and acceptor (A) units. However, any strong electronic interaction in such molecules renders them neither strong electron donors nor acceptors. In practice, therefore, D and A components are often covalently linked by saturated flexible or rigid s spacers (D-s-A). Thereby, the structural D and A moieties on which the HOMO and LUMO are localized, respectively, are kept apart from each other. This hinders their strong coupling in the electronic ground state, so as to keep the HLG small. [3] Conjugated bridges of D-p-A assemblies, although providing easier steric control, generally favor stronger electronic coupling. Besides the amphoteric ground-state properties, photoinduced intramolecular charge-transfer (CT) processes may result in interesting photophysical phenomena such as longlived, charge-separated states. From a preparative point of view, the linkage of a strong donor (e.g., tetrathiafulvalene (TTF)) to a strong acceptor (e.g., 7,7',8,8'-tetracyano-p-quinodimethane (TCNQ)) in a D-p-A system is a synthetic challenge. [3] In response, we recently introduced a concept for the annulation of TTF derivatives to acceptor moieties and reported synthetic routes to various fused D-p-A assemblies. [4] All of them are tailored into rigid and planar configurations exhibiting defined symmetries, thus providing full geometric control over the relative positions and orientations of the subunits. As the focal point of the work presented herein, we explore the synthesis of a new system, in which both strong electron-donor and strong electron-acceptor properties are organized into an annulated molecular D-p-A triad for probing the resulting HLG. More specifically, the first example of the annulated assembly (1), incorporating TTF and TCNQ-type bithienoquinoxaline, is presented. As will be demonstrated, a pronounced electrochemical amphotericity can be achieved in a way that precludes strong electronic coupling of the energetically close-lying HOMO and LUMO within the fused D-p-A system. Essentially, this is due to the strict symmetry control of the planar conjugate. Additionally, the remarkable redox properties are combined with strong photoinduced intramolecular CT transitions. A direct condensation reaction of 5,6-diamino-2-(4,5-bis- ), [4c] with a TCNQ-type bithienoquinoid (P3) afforded 1 in 86 % yield. Similarly, the reference compound 2 was obtained in good yield (Scheme S1 in the Supporting Information). It is noteworthy that the annulation of a quinoxaline group to the TTF core could lead to a considerable increase in stability and charge mobility of the resulting D-A molecules. [a] X.

The cytotoxicity of ceria ultimately lies in its electronic structure, which is defined by the crystal structure, composition, and size. Despite previous studies focused on ceria uptake, distribution, biopersistance, and cellular effects, little is known about its chemical and structural stability and solubility once sequestered inside the liver. Mechanisms will be presented that elucidate the in vivo transformation in the liver. In vivo processed ceria reveals a particle‐size effect towards the formation of ultrafines, which represent a second generation of ceria. A measurable change in the valence reduction of the second‐generation ceria can be linked to an increased free‐radical scavenging potential. The in vivo processing of the ceria nanoparticles in the liver occurs in temporal relation to the brain cellular and protein clearance responses that stem from the ceria uptake. This information is critical to establish a possible link between cellular processes and the observed in v...

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Biomolecular condensates (BCs) are membraneless hubs enriched with proteins and nucleic acids that have emerged as important players in many cellular functions. Uncovering the sequence determinants of proteins for phase separation is essential in understanding the biophysical and biochemical properties of BCs. Despite significant discoveries in the past decade, the role of cysteine residues in BC formation and dissolution has remained unknown. Here, to uncover the involvement of disulfide cross-links and their redox sensitivity in BCs, we designed a “stickers and spacers” model of phase-separating peptides interspersed with cysteines. Through biophysical investigations, we learned that cysteines promote liquid–liquid phase separation in oxidizing conditions and perpetuate liquid condensates through disulfide cross-links, which can be reversibly tuned with redox chemistry. By varying the composition of cysteines, subtle but distinct changes in the viscoelastic behavior of the condensates were observed. Empirically, we conclude that cysteines function neither as stickers nor spacers but as covalent nodes to lower the effective concentrations for sticker interactions and inhibit system-spanning percolation networks. Together, we unmask the possible role of cysteines in the formation of biomolecular condensates and their potential use as tunable covalent cross-linkers in developing redox-sensitive viscoelastic materials.

The reaction of NO with [(tBu 2 PCH 2 SiMe 2)NSiMe 2-CH 2 PtBu(CMe 2 CH 2)]RhH, a functional equivalent of "(PNP)-Rh," rapidly forms (PNP)Rh(N 2) and (PNP)Rh(NO)(NO 2). Detected intermediates include (PNP)Rh(NO), characterized by its NMR, EPR and IR spectra as well as by DFT calculation, as having the neutral NO-centered radical Lewis base donating to Rh I. One other intermediate is detected, using a combi-[a

The homoleptic complexes of cerium with the tris(piperidinyl)imidophosphorane ligand, [NP(pip) 3 ] − , present the most negative Ce 3+/4+ redox couple known (<−2.64 V vs Fc/Fc +). This dramatic stabilization of the cerium tetravalent oxidation state [>4.0 V shift from the Ce 3+/4+ couple in 1 M HClO 4 (aq)] is established through reactivity studies. Spectroscopic studies (UV−vis, electron paramagnetic resonance, and Ce L 3-edge X-ray absorption spectroscopy), in conjunction with density functional theory studies, reveal the dominant covalent metal−ligand interactions underlying the observed redox chemistry and the dependence of the redox potential on the binding of potassium in the inner coordination sphere.

The kinetics of reduction of the mer‐[RuIII(pic)3] complex (pic– = picolinato) by ascorbic acid (AscH2) leading to formation of a red ruthenium(II) species have been studied spectrophotometrically by using both conventional mixing and stopped‐flow methods. The reaction was followed as a function of the reductant concentration over a wide pH range (1.0–7.4). Electron transfer proceeds by an outer‐sphere mechanism involving three protolytic forms of ascorbic acid, AscH2, AscH– and Asc2–, for which specific rate constants have been determined. The Gibbs&#39; energy of activation was found to correlate linearly with the HOMO energies of the protolytic forms of the reductant. The mer‐[RuIII(pic)3] complex is too sparingly soluble in water to inhibit the growth of the Escherichia coli (ATCC 8739) strain. Its cytotoxicity against non‐tumorigenic cells precludes its potential use as an anticancer agent.

Pristine water bodies in the Negro River basin, Brazilian Amazon, show relatively high concentrations of mercury. These waters are characterized by acidic pH, low concentrations of suspended solids, and high amounts of dissolved organic matter and are exposed to intense solar radiation throughout the year. This unique environment creates a very dynamic redox chemistry affecting the mobility of mercury due to the formation of the dissolved elemental species (Hg 0). It has been shown that in this so-called black water, labile organic matter from flooded forest is the major scavenger of photogenerated H 2 O 2. In the absence of hydrogen peroxide, these black waters lose their ability to oxidize Hg 0 to Hg 2? , thus increasing Hg 0 evasion across the water/atmosphere interface, with average night time values of 3.80 pmol m-2 h-1. When the dry period starts, labile organic matter inputs gradually diminish, allowing the increasing concentration of H 2 O 2 to re-establish oxidative water conditions, inhibiting the metal flux across the water/atmosphere interface and contributing to mercury accumulation in the water column.

Polyoxovanadate Na6V10O28 is investigated for the first time as electrode material for supercapacitors (SCs). The electrochemical properties of Na6V10O28 electrodes are studied in Li+‐containing organic electrolyte (1 M LiClO4 in propylene carbonate) by galvanostatic charge/discharge and cyclic voltammetry in a three‐electrode configuration. Na6V10O28 electrodes exhibit high specific capacitances of up to 354 F g−1. An asymmetric SC with activated carbon as positive electrode and Na6V10O28 as negative electrode is fabricated and exhibits a high energy density of 73 Wh kg−1 with a power density of 312 W kg−1, which successfully demonstrates that Na6V10O28 is a promising electrode material for high‐energy SC applications.

Vinyl-Transfer Reaction [a] Unless otherwise mentioned, 0.5 mmol of 1 a and 0.5 mmol of 2 were reacted in a sealed vial. [b] Yields after acid-base workup. Scheme 2. Evidence for the formation of intermediate 5. Scheme 3. BF 3 •OEt 2-mediated synthesis of 7.

One-electron redox changes of bound nitrosyl species [1] are at the heart of the enzymatic processes involving reversible conversions of NO 2 À into NH 3 , which occur either in bacterial processes in soils [2] or in the biosynthesis/degradation events of nitrogen monoxide (NO) in the biological fluids of mammals. [3] This explains the interest in the coordination chemistry of NO and the very reactive redox-active partners, the nitrosonium cation (NO +) and the nitroxyl anion (NO À). [4] The three diatomic entities have been identified when bound to transition metals. Although a fragment model considering covalent interactions between the metal and nitrosyl is currently employed, [5] detailed spectroscopic measurements and/or theoretical calculations frequently allow the use of a limiting description comprising NO + , NOC, and NO À ligands bound to metals with the corresponding formal charges. [4, 5] The chemistry of NO + and NOC complexes is reasonably well understood. [1, 4] Structural, spectroscopic, and/or kinetic studies have been reported for NO À complexes, mainly with five-and six-coordinated Co III , [6, 7a-e] Cr III , [7f-h] , Fe III , [7i,j] and Pt IV compounds. [7k] Recently, NO À has been characterized in an iron(II) cyclam derivative, as a product of the successive (reversible) reductions of the corresponding NO + complex in CH 3 CN. [1b] Complexes containing HNO, the acid conjugate of NO À , have been obtained with low-spin d 6 metals of the second-and third-row transition series (Ru II , Os II , Ir III , Re I), and are reported to be short-lived in solution. [8] X-ray structures of derivatives of the first three metals have been reported after isolation from non-aqueous media. [9] The insolubility in aqueous solutions limits their bioinorganic [*] A

Four new RuIICl and RuIIH2O complexes containing the meridional 2,2’:6’,2”‐terpyridine (trpy) ligand and the chelating 2‐(5‐phenyl‐1H‐pyrazol‐3‐yl)pyridine (H3p) ligand of general formula in‐ and out‐[RuII(trpy)(H3p)(X)]n+ (X=Cl, n=1; X=H2O, n=2) have been prepared, isolated and thoroughly characterized both in solution and in the solid state. In solution, all the complexes are characterized spectroscopically by UV/Vis and NMR, and their redox properties investigated by means of cyclic voltammetry, square wave voltammetry, and coulometry. In the solid state, monocrystal X‐ray diffraction analysis was carried out for the in and out RuCl complexes. The capacity of the Ru‐aqua complexes to act as water oxidation catalysts (WOCs) was also investigated chemically, electrochemically, and photochemically. The performance of these complexes has also been compared to two previously described complexes of general formula in‐ and out‐[RuII(trpy)(Hbpp)(H2O)]2+ (Hbpp is 2,2′‐(1H‐pyrazole‐3,5‐...

Selective oxidation of galacturonic residues of oligo and polyuronic acids by Cr VI affords CO 2 /HCO 2 H, oxidized uronic acid, and Cr III as final redox products. Kinetic studies show that the redox reaction proceeds through a mechanism combining Cr VI ? Cr IV ? Cr II and Cr VI ? Cr IV ? Cr III pathways. The mechanism is supported by the observation of free radicals, CrO 2 2+ and Cr V as reaction intermediates. The EPR spectra show that five-and six coordinated oxo-Cr V intermediates are formed. Penta-coordinated oxo-Cr V species are present at any [H + ], whereas hexa-coordinated ones are only observed at pH <1. At low pH Cr V predominating species are coordinated by carboxylate groups and O ring (g iso = 1.9783/5). At pH 7.5, the predominating ones are those coordinated by alcoholate groups of the ligand (g iso = 1.9800). Polygal can reduce Cr VI and efficiently trap Cr III. This behaviour represents an interesting model for the study of biomaterials, which possess a high proportion of polygal, in order to remove chromium from polluted waters.

Selective oxidation of galacturonic acid residues of apple pectin by Cr VI affords CO 2 /HCO 2 H, oxidized pectin, and Cr III as final redox products. The reaction shows first-order kinetics in [pectin], [Cr VI ], and [H R ], at fixed ionic strength and temperature. Kinetic studies show that the redox reaction proceeds through a mechanism combining Cr VI ! Cr IV ! Cr II and Cr VI ! Cr IV ! Cr III pathways. The mechanism is supported by the observation of free radicals, CrO 2 2 R (the formation of which implies involvement of Cr II and Cr IV) and Cr V (formed in monoelectronic redox processes) as reaction intermediates. The reduction of Cr IV and Cr V by pectin was independently studied and found to occur more than 10 3 times faster than pectin R Cr VI reaction, in acid medium. At pH 3-5, apple pectin R Cr VI redox reaction is slow, oxo-chromate(V)-pectin species stabilize and remain in solution during several hours. The present results show that these abundant and ubiquitous components of the cell walls of all land plants are able to reduce Cr IV-VI or stabilize high-valent chromium depending on pH.

Active colloidal catalysts inspired by glutathione peroxidase (GPx) were synthesized by integration of catalytically active selenium (Se) moieties into aqueous microgels. A diselenide crosslinker (Se X‐linker) was successfully synthesized and incorporated into microgels through precipitation polymerization, along with the conventional crosslinker N,N′‐methylenebis(acrylamide) (BIS). Diselenide bonds within the microgels were cleaved through oxidation by H2O2 and converted to seleninic acid whilst maintaining the intact microgel microstructure. Through this approach catalytically active microgels with variable amounts of seleninic acid were synthesized. Remarkably, the microgels exhibited higher catalytic activity and selectivity at low reaction temperatures than the molecular Se catalyst in a model oxidation reaction of acrolein to acrylic acid and methyl acrylate.

Polymeric nanoparticles were synthesized using both a photoinduced and base-catalyzed free radical polymerization method. These mild room temperature approaches allow sensitive molecules, such as dyes, to be encapsulated. Using this method, near infrared dye loaded nanoparticles for lymphatic migration and lymph nodes localization were synthesized. After injection into a large animal, we observed migration of the nanoparticles over 20 cm to the sentinel lymph. Nanoparticle migration was observed for nanoparticles of 50 nm but not 100 nm in diameter. These investigations further support the development of new materials and clinical approaches to treat cancer including identification of nodal disease, characterization of the extent of disease, and establishment of treatment regimes. Keywords nanoparticles; polymerization; redox chemistry; imaging agents; drug delivery Nanoparticles are finding ever increasing uses in a wide range of fields including photonics, catalysis and medicine, and identification of new compositions and synthetic methods is key

Mono‐ and bis(acyl)phosphane oxides are usually utilized as photoinitiators for radical polymerizations. This manuscript reveals the electrochemically reversible reductions of these molecules, leading to the corresponding radical anions. The radical anions, which have been characterized by EPR and ENDOR spectroscopy, display remarkable delocalization and ion‐pairing behavior that can be rationalized by theoretical calculations.

The iron(III) chelating ability of some glycosyl derivatives of curcuminoids is tested by means of UV, potentiometric and NMR studies. The pKa of the ligands and the stability constants of their Fe3+ and Ga3+ complexes are evaluated by UV spectroscopy. The only metal binding site of the ligand is the β‐dioxo moiety; the glycosyl moiety does not interact with the metal ion at acidic pH values but it helps to stabilise metal/ligand (1:2) complexes by means of hydrophilic interactions. By comparing the pFe3+ of our ligands with those reported for other chelating agents we suggest using these molecules as pro‐drugs in iron overload treatment. Some of the more water‐soluble derivatives are also tested for their antioxidant properties “in vitro” in biological systems and proved to act as free‐radical scavengers inhibiting the iron redox cycle. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The reactivity of a stable copper(II) complex bearing fully oxidized iminobenzoquinone redox ligands towards nucleophiles is described. In sharp contrast with its genuine low-valent counterpart bearing reduced ligands, this complex performs high-yielding C-N bond formations. Mechanistic studies suggest that this behavior could stem from a mechanism akin to reductive elimination occurring at the metal center but facilitated by the ligand: it is proposed that a masked high oxidation state of the metal can be stabilized as a lower copper(II) oxidation state by the redox ligands without forfeiting its ability to behave as a high-valent copper(III) center. These observations are substantiated by a combination of advanced EPR spectroscopy techniques with DFT studies. This work sheds light on the potential of redox ligands as promoters of unusual reactivities at metal centers and illustrates the concept of masked high-valent metallic species.

Supporting Information Experimental Section Fenton Chemistry: A series of solutions were prepared with Na 2 HPO 3 or NaH 2 PO 2 in concentrations between 0.001 M to 0.1 M, iron (as FeCl 2 × 4H 2 O or as FeSO 4) concentrations between 0.001 M to 0.1 M, and H 2 O 2 concentrations between 0.002 M to 0.5 M (Table S1), each with a starting pH of 7±1, unless otherwise noted. Peroxide was added last to promote the reactions. One experiment was performed with a formaldehyde concentration of 1.2 M to act as a reductant. The solutions were stirred for 1-20 days, a 2 mL aliquot of each solution was extracted and placed in 2 mL of a 1:1 mixture of 10 M NaOH solution and D 2 O to quench the reaction, precipitate Fe III and prepare the sample for analysis by NMR. Decanted samples were analyzed using 31 P NMR on a Varian 300 four-nucleus probe FT-NMR spectrometer at 121.43 MHz and 24.5 ºC for 256 to 6000 scans following prior work [6a,c] , or on a Bruker Avance 500 four-nucleus FT-NMR system operating at 25°C and 202.46 MHz for phosphorus with 400-9000 scans. Spectra were acquired in both 1 H-decoupled and coupled modes. The peaks were identified based on comparison to known standards and previous work, with abundances determined from peak areas. [6,15] From these data, we determine that approximately 34.5% of reduced P becomes oxidized to condensed P (Fig. S1, vide infra). Some solutions were prepared with a starting solution pH of 13. In these experiments, the Fe II precipitated to green rust and did not promote any Fenton chemistry. These solutions also showed no oxidation of reduced compounds. From these experiments, we determined that the reactions were quenched by addition of base to the solution, hence the addition of NaOH does not promote further reaction of phosphorus species.

A series of the octahedral hexarhenium(iii) complexes containing a variable number of diphosphine (diphos) or diphosphine ± monoxide (di-phosO) ligands have been prepared by the substitution of the diphosphine Ph 2 P(CH 2) n PPh 2 (n 1 to 5) for the iodide ions in the parent octahedral hexarhenium cluster compound [Re 6 Se 8 I 6 ] 3À. The diphosphine Ph 2 P-(CH 2) n PPh 2 ligands adopt an h 1-bonding mode with the Re 6 (m 3-Se) 8 core, and the P donor atom in the pendant arm is noncoordinated and oxygenated in most cases. The series of new hexarhenium(iii) complexes have been well-defined by 1 H, 13 C, and 31 P NMR spectroscopic and FAB-MS data. Four compounds among the series were characterized by X-ray structural determination. Geometrical isomers were identified by NMR spectroscopy as well as by the structural determinations. The apical ligand substitution induces significant change in the redox potentials and the photophys-ical properties of the Re 6 (m 3-Se) 8 core. The E 1/2 value of the reversible process Re III 6 /Re III 5 Re IV becomes more positive with the increasing number of the coordinated P donors. The phosphine-substituted hexarhenium(iii) derivatives are highly luminescent, with microsecond scale emissive lifetime at ambient temperature, and the fully substituted derivatives with the formula [Re 6 Se 8-(h 1-diphosO) 6 ] 2 display the strongest luminescence with the longest emission lifetimes.

Additional experimental details for the preparation of actinyl solutions, complexes and crystals. 1. Experimental Section 1.1. Warning! 237 Np and 239 Pu are high specific activity radionuclides and, along with their daughter products, pose considerable safety hazards from alpha, beta and gamma radiation This work was performed in radiological facilities appropriate for the activity levels used. Radionuclides were obtained from internal laboratory stocks. Multiple containment techniques were employed as, and when, necessary. 1.2. General Instrument Procedures. The 1 H NMR was recorded on Bruker spectrometers operated at 400 MHz with CD 2 Cl 2 and CD 3 CN as solvents. The samples of (NpO 2)(t-butyl Salen)(CH 3 CN) and NpO 2)(t-butyl Salen)(CH 3 CN) were dissolved in CD 3 CN and CD 2 Cl 2 respectively and doubly contained within a PTFE insert to a standard glass NMR tube prior to analysis. IR data were recorded on a Fourier transform infrared (FTIR) spectrophotometer in the range 400-4000 cm-1 with the samples prepared as KBR pellets. Electrospray ionization mass spectrometry was performed on ESI LC-TOF Micromass LCT 3, positive mode, m/z range 100-300 and 200-1000. UV-Vis-nIR data was collected using a Cary 6000i UV-vis-nIR spectrophotometer with a xenon lamp in the range of 200-1300 nm. 1.3. X-ray Crystallography. Crystals of compounds formed between t-butyl Salen and UO 2 2+ , NpO 2 2+ and PuO 2 2+ were obtained in good yield from CH 3 CN solutions stored in a freezer set at-15˚ C (details of the procedure are given in section 1.6.

Materials Archaeoglobus fulgidus organism was obtained from the American Tissue Culture Center. TOPO and TOPO Zero Blunt PCR cloning kits were obtained from Invitrogen (Carlsbad, CA). NovaBlue competent cells, Rosetta™ (DE3)pLysS competent cells, and plasmid pET-28a were purchased from Novagen (Madison, WI, USA). pfuTurbo polymerase and PCR Optimization Kit were obtained from Strategene (Cedar Creek, TX, USA). Primers were obtained from Integrated DNA Technologies (Coralville, IA, USA). Nickel nitrilotriacetic (Ni-NTA) acid-agarose gel was purchased from Qiagen (Valencia, CA, USA). Restriction enzymes were purchased from New England BioLabs (Ipswich, MA, USA). Kanamycin, chloroamphenicol, N-2-hydroxyethyl-piperazine-N`-2-ethanesulfonic acid (HEPES), tris(hydroxymethyl)-aminomethane (TRIS-HCl), (ethylenediamine)tetra acetic acid (EDTA), 1,4-dithio-DL-threitol (DTT), and phenyl-methyl-sulfonyl fluoride (PMSF) were obtained from Sigma-Aldrich (St. Louis, MA, USA).

Mono-and bisacylphosphaneoxides are usually utilized as photoinitiators for radical polymerizations. This manuscript reveals the electrochemically reversible reductions of these molecules, leading to the corresponding radical anions. The radical anions are characterized by EPR and ENDOR spectroscopies. They display remarkable delocalization and ionpairing phenomena, which can be rationalized by theoretical calculations.

One way to improve the synthetic efficiency of the redox reaction is to couple the reduction/oxidation steps with the desired skeletal bond formations. [1] This strategy removes the need for extra steps for the generation or protection of reactive functional groups, or for oxidation state adjustment. However, this requires that the redox precursors are more readily available than, and able to be catalytically transformed in situ into, their functional group counterparts that undergo the desired transformation. [2] Recently, a number of gold-catalyzed redox-exchange procedures via oxygen transfer have been reported. For example, Toste and co-workers and Zhang and co-workers reported sulfoxide-mediated or amine-N-oxide-mediated redox reactions to generate carbene equivalents for sp 2 or sp 3 C À H functionalization or 1,2-pinacol shifts. [3-5] Furthermore, we have reported the waste-free generation of azomethine ylide from an intramolecular redox reaction between a nitrone and an alkyne. [6] The unique advantage of using nitrones as oxidants is that they are derived from readily available hydroxylamines and therefore do not require stoichiometric oxidants such as mCPBA (metachloroperbenzoicacid) or H 2 O 2 for the substrate preparation. [4] Furthermore, two highly versatile intermediates, namely an imine or a metal carbenoid, could be generated in situ, which can be advantageously utilized in the rapid assembly of pharmaceutically important N heterocycles through cascade reactions. We focused on the 1-aminoindane framework, which is a common core of medicinal agents with various activities, such as CB2 agonists, NMDA receptor agonists, and inhibition of neuronal monoamine re-uptake. [7] The 5,6-fused piperidine [*] H.

The magnetic and optical properties of the divalent state of europium make this ion extremely attractive for use in materials, [1] catalysis, [2] luminescence, [3] magnetic, [4] and diagnostic-medical [5] applications. A major hindrance to the use of Eu II in many of these applications is the extreme propensity of the ion to oxidize to Eu III , especially in aqueous solution. Research efforts aimed at increasing the stability of aqueous Eu II have yielded little success: [6, 7] even the most stable aqueous Eu II complex reported (4,7,13,16,21,24hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane europium(II), 1-Eu) is not stable enough in aqueous solution for practical use. [8, 9] Our research group has generated Eu II complexes in aqueous solution, and here we report the most oxidatively-stable aqueous Eu II complexes known. Our strategy for favoring Eu II over Eu III in aqueous solution involves the synthesis and use of ligands that would preferentially coordinate to large, soft, electron-rich metals like Eu II. The template for our ligand design was cryptand 1 because 1-Eu is the most oxidatively-stable, aqueous Eu II complex previously reported. [8] The stability of 1-Eu is partially due to the better size match of the cavity of cryptand 1 (1.4) to the Eu II ion (1.25) relative to the Eu III ion (1.07). [10] We hypothesized that further oxidative stabilization could be achieved by modifying the structure of cryptand 1 using four principles of coordination chemistry to stabilize electron-rich metals. [6, 11] Specifically, our goals were 1) to increase the steric bulk surrounding cryptand 1 to minimize interactions between Eu II and its environment; 2) to reduce the Lewis basicity of cryptand 1 to favor the electronrich Eu II over Eu III ; 3) to change the cavity size of the cryptand to match the size of the Eu II ion preferentially; and 4) to modify the hard-soft, acid-base (HSAB) properties of cryptand 1 to coordinate Eu II over Eu III. To implement these strategies, we studied cryptands 1-6 (Scheme 1).

The isomeric bis(tridentate) hydrazone ligand strands 1 a–c react with [Ru(terpy)Cl3] (terpy=2,2′:6′,2′′‐terpyridine) to give dinuclear rack‐type compounds 2 a–c, which were characterised by several techniques, including X‐ray crystallography and NMR methods. The absorption spectra, redox behaviour and luminescence properties (both in fluid solution at room temperature and in rigid matrix at 77 K) of the ligand strands 1 a–c and of the metal complexes 2 a–c have been studied. Compounds 1 a–c exhibit absorption spectra dominated by intense π–π* bands, which, in the case of 1 b and 1 c, extend within the visible region, while the absorption spectra of the rack‐type complexes 2 a–c show intense bands both the in the UV region, due to spin‐allowed ligand‐centred (LC) transitions, and in the visible, due to spin‐allowed metal‐to‐ligand charge‐transfer (MLCT) transitions. The energy position of these bands strongly depends on the ligand strand: in the case of 2 a, the lowest energy MLCT b...

The direct intercalation of a pyrazolate-bridged platinum(II) bipyridyl dimer ([{Pt(dmbpy)(μ-pz)} 2 ] 2+ ; dmbpy = 4,4′-dimethyl-2,2′-bipyridine, pz − = pyrazolate) within a zirconium phosphate (ZrP) framework has been accomplished. The physical and spectroscopic properties of [{Pt(dmbpy)(μ-pz)} 2 ] 2+ intercalated in ZrP were investigated by X-ray powder diffraction and X-ray photoelectron, infrared, absorption, and luminescence spectroscopies. Zirconium phosphate layers have a special microenvironment that is capable of supporting a variety of platinum oxidation states. Diffuse reflectance spectra from powders of the blue-gray intercalated materials show the formation of a low-energy band at 600 nm that is not present in the platinum dimer salt. The nonintercalated complex is nonemissive in room-temperature fluid solution, but gives rise to intense blue-green emission in a 4:1 ethanol/methanol 77 K frozen glassy solution. Powders and colloidal suspensions of [{Pt(dmbpy)(μ-pz)} 2 ] 2+-exchanged ZrP materials exhibit intense emissions at room-temperature.

The use of organic materials with reversible redox activity holds enormous potential for next‐generation Li‐ion energy storage devices. Yet, most candidates are not truly sustainable, i.e., not derived from renewable feedstock or made in benign reactions. Here an attempt is reported to resolve this issue by synthesizing an organic cathode material from tannic acid and microporous carbon derived from biomass. All constituents, including the redox‐active material and conductive carbon additive, are made from renewable resources. Using a simple, sustainable fabrication method, a hybrid material is formed. The low cost and ecofriendly material shows outstanding performance with a capacity of 108 mAh g−1 at 0.1 A g−1 and low capacity fading, retaining approximately 80% of the maximum capacity after 90 cycles. With approximately 3.4 V versus Li+/Li, the cells also feature one of the highest reversible redox potentials reported for biomolecular cathodes. Finally, the quinone‐catecholate re...

The use of organic materials with reversible redox activity holds enormous potential for next‐generation Li‐ion energy storage devices. Yet, most candidates are not truly sustainable, i.e., not derived from renewable feedstock or made in benign reactions. Here an attempt is reported to resolve this issue by synthesizing an organic cathode material from tannic acid and microporous carbon derived from biomass. All constituents, including the redox‐active material and conductive carbon additive, are made from renewable resources. Using a simple, sustainable fabrication method, a hybrid material is formed. The low cost and ecofriendly material shows outstanding performance with a capacity of 108 mAh g−1 at 0.1 A g−1 and low capacity fading, retaining approximately 80% of the maximum capacity after 90 cycles. With approximately 3.4 V versus Li+/Li, the cells also feature one of the highest reversible redox potentials reported for biomolecular cathodes. Finally, the quinone‐catecholate re...

Siamese-twin porphyrin is a pyrazole-containing expanded porphyrin incorporating two porphyrin-like binding pockets. The macrocycle, however, does not possess an aromatic π system but rather two separated conjugation pathways that are isolated by the pyrazole junctions. Mono-and bimetallic complexes of the Siamese-twin porphyrin are known. This work addresses in detail the electronic consequences that monometalation (with Pd II) has on the electronic properties of the nonmetalated binding pocket by studying the solid-state structure, acid/base, and electrochemical properties of the monopalladium twin-porphyrin complex. Specifically, metalation leads to a switch of the protonation sites of the free-base pocket. The unusual location of the protons at adjacent pyrrolic nitrogen atoms was revealed using X-ray diffraction and 1D/2D NMR spectroscopy. The oneelectron oxidation and reduction events are both ligand-centered, as derived by spectroelectrochemical and electron paramagnetic resonance measurements, but are located on different halves of the molecule. Single-electron oxidation (−0.32 V vs Fc/Fc +) generated an organic radical centered on the metal-coordinating side of the ligand, while single-electron reduction (−1.59 V vs Fc/Fc +) led to the formation of an organic radical on the free-base side of the macrocycle. Density functional theory calculations corroborated the redox chemistry observed. The possibility of selectively preparing the monometallic complexes carrying two distinct redox sitesa metal-containing oxidation site and a metal-free reduction sitefurther expands the potential of Siamese-twin porphyrins to serve as an adjustable platform for multielectron redox processes in chemical catalysis or molecular electronics applications.

We discuss here the chemical oxidation of a high-spin iron(II) complex containing the 1,3-bis(2′benzimidazolylimino)isoindoline ligand (HL 1) using tris(4-bromophenyl)aminium hexachloroantimonate (Magic Blue). The product was X-ray structurally, spectroscopically (Mössbauer, FT-IR, UV-vis) and electrochemically characterized and can be formulated as [Fe III (L 1) 2 ][Fe III (L 1 H −2)(L 1)] (1), a low-spin iron(III) 1D coordination polymer with strong H-bonds between ligands and N,N-dimethylformamide (DMF) solvent molecules in the solid phase. The redox potential of the [Fe II (L 1) 2 ] complex at − 407 mV vs. ferrocene in DMF is shifted to the anodic direction only by 12 mV in the case of 1 against the expected cathodic shift upon proton loss from the ligand. The difference in the spin state of [Fe II (L 1) 2 ] and 1, and the impact of H-bonds (detected in the crystal structure) that are able to facilitate proton-coupled electron transfer have been considered as plausible explanations.

The reaction of 1,5-PhP2N& with 2 molar equiv of M[BEt3H] in THF produces {M2[Ph4P2N4S2]}fl (4a, M = Li; 4b, M = Na; 4c, M = K) in quantitative yields with the concomitant evolution of H2 gas. The lithium and sodium derivatives are obtained as insoluble, yellow powders, whereas (K2[Ph4P2N4&]},, (6(31P) = 33.5 ppm) is soluble in THF when formed initially. The reaction of (Na2[Ph4P2N4&]}, with CH212 in THF yields Ph4P2N4S2-CH2 (Sa) in excellent yields. The methylene-bridged compound Sa is readily deprotonated by LiN(SiMe3)z in THF, and the subsequent addition of Me1 produces Ph4P2N4S2CHMe (a). In a similar way, Sb can be deprotonated and methylated to give Ph4P2N4S2CMe2. The reaction of { N~Z [ P~P~N~S~]) , , with (Cp*RhC12)2 in THF affords Cp*Rh(Ph&N4S2) (6), which can also be produced by the oxidative addition of 1,5-Ph&N& to Cp*Rh(C2H&. The X-ray structure of 6 reveals that the heterocyclic P2N& ligand is bonded to Rh in a tridentate (v3-N,S,S') fashion with d(Rh-N) = 2.135(5) A. Crystals of 6 are triclinic, space group

Complexes of 2,2&#39;-biimidazole with bivalent iron, cobalt, nickel and copper, and trivalent iron are described. The ligand produces a relatively weak field and all complexes are high-spin and markedly less stable than corresponding complexes of 2,2&#39;-bipyridine or 2-(2-pyridyl)imidazole. Inner complexes, M(L-H)2, derived from the monoanion of biimidazole are also described. The complexes are characterized by magnetic and spectral data.

One monometallic and three bimetallic ruthenium nitrosyl (RuNO) complexes are presented and fully characterized in reference to a parent monometallic complex of formula [FTRu(bpy)(NO)]3+, where FT is a fluorenyl‐substituted terpyridine ligand, and bpy the 2,2’‐bipyridine. These new complexes are built with the new ligands FFT, TFT, TFFT, and TF‐CC‐TF (where an alkyne C≡C group is inserted between two fluorenes). The crystal structures of the bis‐RuNO2 and bis‐RuNO complexes built from the TFT ligand are presented. The evolution of the spectroscopic features (intensities and energies) along the series, at one‐photon absorption (OPA) correlates well with the TD‐DFT computations. A spectacular effect is observed at two‐photon absorption (TPA) with a large enhancement of the molecular cross‐section (σTPA), in the bimetallic species. In the best case, σTPA is equal to 1523±98 GM at 700 nm, in the therapeutic window of transparency of biological tissues. All compounds are capable of relea...

for helpful discussions, and M. Kayas, S. Schneider, and P. Smie for the technical assistance during the preparation of the manuscript. Supporting information for this article, including experimental details, quantum chemical calculations, thermodynamic investigations, and crystallographic details, is available on the WWW under

This research studies the characteristics of aluminum 2024, 304 stainless steel, and 1018 steel during lapping with three different types of abrasives, namely, garnet, silicon carbide, and white aluminum oxide, through detailed experimental analysis. Specifically, the effects of different abrasives on material removal rate and surface finish were evaluated. It was found that silicon carbide and white aluminum oxide abrasives removed more material per minute than garnet. A higher mean frictional force and mean coefficient of friction were obtained in aluminum lapped with SiC and white Al 2 O 3 abrasives, and a lower mean frictional force was obtained in 304 stainless steel lapped with SiC. From geometric and energy-dispersive spectroscopy analysis obtained using scanning electron microscopy, it was confirmed that some abrasives became embedded into the lapped metal substrates. No burn was observed on the lapped samples, and scratches and unfinished lapped parts were observed mainly in 304 stainless steel. In order to determine the quantitative influence of each variable, an analysis of variance was performed. It was found that the main effects of abrasive types, size of abrasives, and type of work material had statistically significant influence on material rate and surface finish. In addition, there was a highly significant two-way interaction between abrasives and workpiece.

Pairing lithium and oxygen in aprotic solvents can theoretically lead to one of the most promising electrochemical cells available. If successful, this system could compete with technologies such as the internal combustion engine and provide an energy density that can accommodate electric vehicle demands. However, there are many problems that have inhibited this technology from becoming realistic. One of the main reasons is capacity fading after only a few cycles, which is caused by the instability of electrolyte solutions in the presence of reduced oxygen species like O 2 C À and O 2 2À. In recent years, using various analytical tools, researchers have been able to isolate the breakdown products arising from the reactions occurring between the aprotic solvent and the reduced oxygen species. Nevertheless, no solvents have yet been found that are fully stable throughout the reduction and oxidation processes. However, an understanding of these decomposition mechanisms can help us in designing new systems that are more stable toward the aggressive conditions taking place in LiÀO 2 cell operation. This review will include analytical studies on the most widely used solvents in current LiÀO 2 research.

Supporting Information Experimental Section Fenton Chemistry: A series of solutions were prepared with Na 2 HPO 3 or NaH 2 PO 2 in concentrations between 0.001 M to 0.1 M, iron (as FeCl 2 × 4H 2 O or as FeSO 4) concentrations between 0.001 M to 0.1 M, and H 2 O 2 concentrations between 0.002 M to 0.5 M (Table S1), each with a starting pH of 7±1, unless otherwise noted. Peroxide was added last to promote the reactions. One experiment was performed with a formaldehyde concentration of 1.2 M to act as a reductant. The solutions were stirred for 1-20 days, a 2 mL aliquot of each solution was extracted and placed in 2 mL of a 1:1 mixture of 10 M NaOH solution and D 2 O to quench the reaction, precipitate Fe III and prepare the sample for analysis by NMR. Decanted samples were analyzed using 31 P NMR on a Varian 300 four-nucleus probe FT-NMR spectrometer at 121.43 MHz and 24.5 ºC for 256 to 6000 scans following prior work [6a,c] , or on a Bruker Avance 500 four-nucleus FT-NMR system operating at 25°C and 202.46 MHz for phosphorus with 400-9000 scans. Spectra were acquired in both 1 H-decoupled and coupled modes. The peaks were identified based on comparison to known standards and previous work, with abundances determined from peak areas. [6,15] From these data, we determine that approximately 34.5% of reduced P becomes oxidized to condensed P (Fig. S1, vide infra). Some solutions were prepared with a starting solution pH of 13. In these experiments, the Fe II precipitated to green rust and did not promote any Fenton chemistry. These solutions also showed no oxidation of reduced compounds. From these experiments, we determined that the reactions were quenched by addition of base to the solution, hence the addition of NaOH does not promote further reaction of phosphorus species.

The oxidation of D-myo-inositol (Myo) by Cr VI yields the inosose and Cr 3+ as final products when an excess of cyclitol over Cr VI is used. The redox reaction takes place through the combination of Cr VI ! Cr IV ! Cr II and Cr VI ! Cr IV ! Cr III pathways. Intermediacy of Cr IV was evidenced by the detection of CrO 2 2þ , formed by reaction of Cr II with O 2. The EPR spectra show that five-and sixcoordinated oxo-Cr V intermediates are formed, with the cyclitol acting as bidentate ligand. Penta-coordinated oxo-Cr V species are present at any [H + ], whereas hexa-coordinated ones are only observed at pH < 1, where rapidly decompose to the redox products. At higher pH, where hexa-coordinated oxo-Cr V species are not observed, oxo-Cr V bischelates are stable enough to remain long time in solution.