Search

Various catalytic technologies are being developed to efficiently convert lignin into renewable chemicals. However, due to its complexity, catalytic lignin depolymerization often generates a wide and complex distribution of product compounds. Gas chromatography/mass spectrometry (GC-MS) is a common analytical technique to profile the compounds that comprise lignin depolymerization products. GC-MS is applied not only to determine the product composition, but also to develop an understanding of the catalytic reaction pathways and of the relationships among catalyst structure, reaction conditions, and the resulting compounds generated. Although a very useful tool, the analysis of lignin depolymerization products with GC-MS is limited by the quality and scope of the available mass spectral libraries and the ability to correlate changes in GC-MS chromatograms to changes in lignin structure, catalyst structure, and other reaction conditions. In this study, the GC-MS data of the depolymerization products generated from organosolv hybrid poplar lignin using a copper-doped porous metal oxide catalyst and a methanol/dimethyl carbonate co-solvent was analyzed by applying a factor analysis technique, positive matrix factorization (PMF). Several different solutions for the PMF model were explored. A 13-factor solution sufficiently explains the chemical changes occurring to lignin depolymerization products as a function of lignin, reaction time, catalyst, and solvent. Overall, seven factors were found to represent aromatic compounds, while one factor was defined by aliphatic compounds.

The photochemical delivery of bioactive small molecules to physiological targets provides the opportunity to control the location, timing, and dosage of such delivery. We will discuss recent developments of the synthesis and studies of various metal complexes designed for targeted release of the bioregulatory diatomics nitric oxide and carbon monoxide. Of considerable interest are those systems where the NO or CO precursor and/or the photochemical product is luminescent such that imaging techniques allow one to identify the release location.

Reaction of small increments of NO2 gas with sublimed amorphous layers of Mn(II)(TPP) (TPP = meso-tetra-phenylporphyrinato dianion) in a vacuum cryostat leads to formation of the 5-coordinate monodentate nitrato complex Mn(III)(TPP)(η(1)-ONO2) (II). This transformation proceeds through the two distinct steps with initial formation of the five coordinate O-nitrito complex Mn(III)(TPP)(η(1)-ONO) (I) as demonstrated by the electronic absorption spectra and by FTIR spectra using differently labeled nitrogen dioxide. A plausible mechanism for the second stage of reaction is offered based on the spectral changes observed upon subsequent interaction of (15)NO2 and NO2 with the layered Mn(TPP). Low-temperature interaction of I and II with the vapors of various ligands L (L = O-, S-, and N-donors) leads to formation of the 6-coordinate O-nitrito Mn(III)(TPP)(L)(η(1)-ONO) and monodentate nitrato Mn(III)(TPP)(L)(η(1)-ONO2) complexes, respectively. Formation of the 6-coordinate O-nitrito complex is accompanied by the shifts of the ν(N═O) band to lower frequency and of the ν(N-O) band to higher frequency. The frequency difference between these bands Δν = ν(N═O) - ν(N-O) is a function of L and is smaller for the stronger bases. Reaction of excess NH3 with I leads to formation of Mn(TPP)(NH3)(η(1)-ONO) and of the cation [Mn(TPP)(NH3)2](+) plus ionic nitrite. The nitrito complexes are relatively unstable, but several of the nitrato species can be observed in the solid state at room temperature. For example, the tetrahydrofuran complex Mn(TPP)(THF)(η(1)-ONO2) is stable in the presence of THF vapors (∼5 mm), but it loses this ligand upon high vacuum pumping at RT. When L = dimethylsulfide (DMS), the nitrato complex is stable only to ∼-30 °C. Reactions of II with the N-donor ligands NH3, pyridine, or 1-methylimidazole are more complex. With these ligands, the nitrato complexes Mn(III)(TPP)(L)(η(1)-ONO2) and the cationic complexes [Mn(TPP)(L)2](+) coexist in the layer at room temperature, the latter formed as a result of NO3(-) displacement when L is in excess.

Described are the synthesis and characterization of two, potentially tetradentate, N2S2 Schiff-base ligands, containing a disulfide bond, N,N′-bis(3-phenylprop-2-en-1-ylidene)-2,2′- disulfanediyldianiline (L1) and N,N′-bis(3,3-diphenylprop-2-en- 1-ylidene)-2,2′-disulfanediyldianiline (L2), and their reaction with Zn2+. Surprisingly, both L1 and L2 undergo reductive disulfide bond scission upon reaction with Zn2+ in alcoholic media to give, under alcohol oxidation, the respective Zn(NS) 2 complexes Zn(L3)2 (1) and Zn(L 4)2 (2), where the L3 and L4 are the respective bidentate thiolate-imine anions. The ligands L1 and L2 and the complexes 1 and 2 have been characterized spectroscopically, and the crystal and molecular structures of the two complexes have been determined by single crystal X-ray diffraction. The coordination geometry around Zn(II) centers in both complexes is a distorted tetrahedron. In addition, DFT calculations (B3LYP/LANL2DZ/6-311++G(d,p)) support the structure of 1. Cyclic voltammetric studies demonstrate that Zn(II) shifts the reduction potential of the disulfide ligands L1 and L2 to less negative values thus making them more susceptible to reductive cleavage of the disulfide bond. The results of semi-empirical PM6 calculations offer key insight into the nature of the transition state for this reaction. © 2014 Elsevier Ltd. All rights reserved.

Water-soluble iron(III) porphyrin and ferrihemoproteins (methemoglobin, metmyoglobin, oxidized cytochrome c, and catalase) associate with NO to yield the nitric oxide adducts. The equilibrium constants for association of ferrihemoproteins and NO are 1 order of magnitude larger than that of the water-soluble iron(III) porphyrin which is free from protein, suggesting that the proteins offset the forward and backward reaction rates in the equilibrium reactions. Nanosecond laser photolysis studies of the nitric oxide adducts of metmyoglobin, oxidized cytochrome c, and catalase, (NO)MbIII, (NO)CytIII, and (NO)CatIII, have been carried out. The transient detected after laser flash photolysis of (NO)CatIII is identified as CatIII. However, the transients observed for (NO)MbIII and (NO)CytIII at 50 ns after laser pulsing are ascribed to MbIIItr and CytIIItr, respectively, with the absorption spectra different from those of uncomplexed MbIII and CytIII. In particular, the absorption spectrum of CytIIItr markedly differs from that of the uncomplexed CytIII. The species MbIIItr and CytIIItr are found to change to MbIII and CytIII, respectively, within a few microseconds. The quantum yields for the photodissociation of NO from nitric oxide adducts of ferrihemoproteins are 1 order of magnitude less than that from the NO adduct of the water-soluble iron(III) porphyrin, probably due to fast geminate recombination reaction of NO and ferrihemoprotein in a heme pocket. The photochemistry of the nitric oxide adducts of hemoproteins and water-soluble iron(II) porphyrin is also described on the basis of laser phosolysis studies. © 1993, American Chemical Society. All rights reserved.

Reports on the kinetics of the autoxidation of aqueous nitric oxide are discussed. It is concluded that the correct rate law is -d[NO]/dt = 4kaq[NO]2[O2] with kaq = 2 x 10(6) M-2.s-1 at 25 degrees c and that a recent report of a rate law zero order in NO is incorrect.

The quenching of emission from the cluster-centered (ds/XMCT) excited state of the copper(I) cluster Cu4I4py4 (I, py = pyridine) by tris(β-dionato)chromium(III) complexes CrL3 and several organic substrates has been investigated in dichloromethane solution. The E00 energy of the excited state (I*) was estimated to be 1.66 µm−1 (2.06 V), and the reduction potential E1/2(I+/I*) was estimated as −1.78 V (vs the ferrocenium/ferrocene couple). Each of the CrL3 complexes (2Eg ∼ 1.3 µΜ−1) is capable of energy transfer quenching, and the rate of this process is shown to be about 107.9 M−1 s−1. Contributions to the quenching by an apparent electron-transfer mechanism were evident for those substrates with reduction potentials E1/2(Q/Q−) less than 1.4 V, i.e. reaction driving forces (−ΔGel°) greater than 0.4 V. The large driving force required can be attributed to a very slow I+/I* self-exchange rate and is indicative of large contributions from inner sphere terms to the total electron-transfer reorganization energy. Such contributions are a likely explanation of the substantially positive ΔHq‡ values (up to + 40 kJ mol−1) noted for organic quenchers with E1/2(Q/Q−) near 1.4 V. Pressure effect studies demonstrate that the activation volume (ΔVq‡) for energy-transfer quenching of the CrL3 species is ∼0 cm3 mol−1 while that of those quenchers which operate near the diffusion limit is ∼+7 cm3 mol−1, consistent with the expected effects on solvent viscosity. In contrast, for those systems with E1/2(Q/Q−) ∼ 1.4 V, substantially negative ΔVq‡ values were observed, a feature reflective of the solvent reorganization owing to charge creation upon electron transfer between I* and Q. © 1993, American Chemical Society. All rights reserved.

A number of the d10 and s2 metal clusters are brightly luminescent, some with strongly medium dependent and temperature dependent spectral profiles. Such emissions are often from excited states assigned as having a mixed d-s/XMCT character, the key feature being enhanced electronic population in metal-metal bonding orbitals in these states as evidenced by the large Stokes shifts between excitation and emission maxima. The observation of such emission bands is strongly favored by relatively short metal-metal distances in the clusters. This behavior parallels that of the d8-d8 dimers held by bridging ligands in cofacial configurations for which excitation leads to substantially increased bonding between metal centers. With π-unsaturated ligands L, emissions from XLCT excited states are often observed, and the luminescence thermochromism of such complexes is the result of different temperature and medium rigidity responses of these two types of excited states. The poor coupling between d-s/XMCT and XLCT states in clusters such as Cu4I4-(py)4 can be attributed to high barrier heights for curve crossing owing to different distortion trajectories once the molecule is prepared in one of the respective excited states. Ongoing studies in these laboratories continue to survey different luminative d10 and s2 cluster systems and to apply an arsenal of synthetic, theoretical, photophysical, and photochemical tools to extend our quantitative understanding of the relevant excited states. © 1993, American Chemical Society. All rights reserved.

The reaction kinetics of nitric oxide autoxidation in aerobic solutions were investigated by direct observation of the nitrite ion product and by trapping the strongly oxidizing and nitrosating intermediates formed in this reaction. The rate behavior observed for nitrite formation [rate = k3[O2][NO]2, k3 = (6 +/- 1.5) x 10(6) M-2 s-1 at 22 degrees C] was the same as found for oxidation of Fe(CN)6(4-) and of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and as for the nitrosation of sulfanilamide. There was a slight decrease in k3 to (3.5 +/- 0.7) x 10(6) M-2 s-1 at 37 degrees C. The second-order dependency for NO was observed at NO concentrations as low as 3 microM. The results of the competitive kinetics studies suggest that the key oxidizing intermediates, species which are both strong oxidants and nitrosating agents, are not one of those commonly proposed (NO2, N2O3, NO+, or O2NO-) but are one or more as yet uncharacterized NOx species.

Flash photolysis experiments have been carried out at ambient temperature to probe potential reaction intermediates in the carbonylation of the methylmanganese complex CH3Mn(CO)5 (M) togivetheacyl product CH3C(O)Mn(CO)5 (A). Photo-decarbonylation of A gives a long-lived transient C, whose time-resolved infrared spectrum shows but modest sensitivity to the coordinating ability of the solvent such as cyclohexane, perfluoromethylcyclohexane, tetrahydrofuran, and 2,5-dimethyl-THF. Notably, C has an unexpectedly long lifetime (exceeding milliseconds) in each of the solvents investigated. Kinetics studies in cyclohexane show the competing trapping by CO to re-form A and isomerization to M occurs with the respective rate constants kco = 3.8 × 103 M−1 s−1 and 10 s−1. The former value is 3 orders of magnitude less than expected for a solvento complex under these conditions. Thus, it is concluded that TRIR spectra and reactivity patterns of C reflect stabilization of this intermediate by η2-coordination of the acyl group. © 1993, American Chemical Society. All rights reserved.

Reported are the photophysical properties of the copper(I) halide clusters Cu4X4(dpmp)4 with the bulky organic base 2-(diphenylmethyl)pyridine (X = I, Br, Cl) which have been shown by previous crystal structure determinations to have “cubane”-like Cu4X4 cores with very similar Cu-Cu distances (2.87−3.01 Å). As solids at 77 K, these compounds each exhibit a strong, relatively long-lived emission band [λmaxem = 467, 487, and 505 nm; τ = 18.1, 10.0, and 10.0 µs (for X = I, Br, and Cl, respectively)], which is attributed to radiative decay from a halide to ligand charge transfer (XLCT) excited state. At higher temperatures, a weak shoulder appeared in the emission spectra for the Cu4I4(dpmp)4 and Cu4Br4(dpmp)4 solids (at ∼570 and ∼626 nm, respectively), and the relative intensities of these shoulders could be fit to the function A exp(-ΔE/RT), with ΔE = 990 ± 370 cm−1 for the appearance of this red emission in Cu4Br4(dpmp)4. The excited state (ES) lifetimes observed for these shoulders were identical to those observed for the still dominant higher energy bands. In analogy to earlier results with the copper(I) iodide cluster Cu4I4(py)4, this longer wavelength band was attributed to emission from a Cu4X4 core centered ES of mixed halide-to-copper charge transfer (XMCT) and metal centered “d-s” orbital parentage. The nature of such transitions in CU4X4L4 clusters is discussed with respect to the Cu−Cu distances in the ground state structures. © 1993, American Chemical Society. All rights reserved.

Photolysis of CpFe(CO)2(COCH3) (Cp = η5-C5H5) plus P(OCH3)3(L) in n-heptane solutions leads to the competitive decarbonylation to give CpFe(CO)2CH3 and ligand substitution to give CpFe(CO)L(COCH3). The application of hydrostatic pressure changes the relative quantum yields of the two processes, higher pressure strongly favoring the ligand photosubstitution pathway. These differences are interpreted in terms of the competitive reactions of the solvento intermediate CpFe(CO)(Sol)(COCH3) (S), shown previously (J. Am. Chem. Soc. 1991, 113, 9524–9528) to be formed by the initial photolysis step, i.e., the labilization of CO. The much more negative apparent activation volume for the ligand substitution pathway suggests that this proceeds via an associative mechanism of S, while the competing methyl migration to the metal may require simultaneous dissociation of the coordinated solvent molecule, Sol. © 1993, American Chemical Society. All rights reserved.

The quenching of emission from the metal to ligand charge-transfer (MLCT) state of the copper(I) complex Cu-(dpp)2+ (dpp = 2,9-diphenyl-l, 10-phenanthroline) by the uncharged chromium(III) complexes CrL3 (L =acetylacetonate, 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, l,l,l-trifluoro-2,4-pentanedionate) and several nitrobenzene derivatives has been investigated in dichloromethane, chloroform, and tetrahydrofuran solutions as a function of hydrostatic pressure (0.1−250 MPa). The patterns in all three solvents were similar. For those quenchers having reduction potentials E1/2(Q) < −1.6 V (vs the ferrocenium/ferrocene, Fc+/Fc, couple in dichloromethane), the principal bimolecular deactivation mode is energy transfer. In such cases, there is little effect of pressure on the quenching rate constant kq (Δq = ∼0 cm3 mol−1). In contrast, substantially more positive E1/2(Q) values lead to kq's approaching diffusion limits and significantly positive ΔV‡q values (up to +8 cm3 mol−1), reflecting the pressure-induced increases in solution viscosity. For E1/2(Q) ∼ −1.6 V, the dominant pressure-dependent term is electron transfer within the outer-sphere precursor complex, and the resulting charge creation in the transition state leads to substantially negative ΔV‡q values approaching −20 cm3 mol−1. © 1993, American Chemical Society. All rights reserved.

Kinetics studies of the reaction of the triruthenium cluster Ru3(CO)12 with the “highly dissociated” chloride salt [PPN]Cl to give the Ru3(CO)11Cl− anion in THF/CH2Cl2 solutions show a rate law first order in [Cl−] and in [Ru3(CO)12]. Rates are significantly higher in 90/10 than in 80/10 (v/v) THF/CH2Cl2 solutions, and the reactivity order is qualitatively the inverse of that of solvent acceptor properties. No intermediates were observed in the reactions. For Pco > 0.1 atm, the rates appeared nearly CO independent although systematic small rate increases were observed at lower PCO. It is suggested that the reaction with Cl− may involve competitive nucleophilic attack at both metal and carbonyl centers. © 1993, American Chemical Society. All rights reserved.

Ligand field excitation of hexaamminerhodium(III), Rh(NH3)63+, in aqueous solution results in the photoaquation of one coordinated NH3. The measured quantum yields at 23° are 0.075 mol/einstein for 313-nm excitation of the 1A1g → 1T1g transition and 0.07 for 254-nm excitation of the 1A1g → 1T2g transition, suggesting efficient interconversion of the higher energy state to a common reactive excited state. Under similar conditions, the quantum yield for the perdeuterated complex Rh(ND3)63+ is about twice as large (0.14 in H2O, 0.15 in D2O, 313-nm excitation). However, the temperature dependence of the photoaquation quantum yields is measurably greater for the perprotio complex than for the perdeuterio complex. To explain these results, it is proposed that temperature-independent weak coupling and temperature-dependent strong coupling mechanisms are competitive in the nonradiative deactivation of the reactive excited state of Rh(NH3)63+.

Efforts to find compounds selectively affecting cancer cells while sparing normal ones have continued to grow. Nitric oxide (NO) is critical in physiology and pathology, including cancer. It influences cellular processes like proliferation, apoptosis, and angiogenesis. The intricate interaction of NO with cancer cells offers innovative treatment possibilities, but its effects can vary by concentration and site. Ruthenium complexes capable of releasing NO upon stimulation show for this purpose. These versatile compounds can also enhance photodynamic therapy (PDT), a light-activated approach, which induces cellular damage. Ruthenium-based photosensitizers (PSs), delivering NO and producing reactive oxygen species (ROS), offer a novel strategy for improved cancer treatments. In this study, a nitro-ruthenium porphyrin conjugate: {TPyP[Ru(NO 2 )(bpy) 2 ] 4 }(PF 6 ) 4 , designated RuNO 2 TPyP, which releases NO upon irradiation, was investigated for its effects on lung cells (non-tumor MRC-5 and tumor A549) in 2D and 3D cell cultures. The findings suggest that this complex has potential for PDT treatment in lung cancer, as it exhibits photocytotoxicity at low concentrations without causing cytotoxicity to normal lung cells. Moreover, treatment of cells with RuNO 2 TPyP followed by light irradiation (4 J cm -2 ) can induce apoptosis, generate ROS, promote intracellular NO formation, and has anti-migratory effects. Additionally, the complex can modify tumor cell structures and induce photocytotoxicity and apoptosis in a 3D culture. These outcomes are attributed to the internalization of the complex and its subsequent activation upon light irradiation, resulting in NO release and singlet oxygen production.

Time-resolved radioluminescence (TRRL) properties of the Cu(I) cluster Cu 4 I 6 2- upon pulsed X-ray, β-ray or α-particle excitation are described. The longer (>2 μs) TRRL component displays exponential decay comparable to pulsed UV excitation; however, temporal behaviour at shorter times indicates that high local excited state density provides an alternative decay channel.

Isosorbide, a bicyclic C6 diol, has considerable value as a precursor for the production of bio-derived polymers. Current production of isosorbide from sorbitol utilizes homogeneous acid, commonly H 2 SO 4 , creating harmful waste and complicating separation. Thus, a heterogeneous acid catalyst capable of producing isosorbide from sorbitol in high yield under mild conditions would be desirable. Reported here is a quantitative investigation of the liquid-phase dehydration of neat sorbitol over sulfated zirconia (SZ) solid acid catalysts produced via sol-gel synthesis. The catalyst preparation allows for precise surface area control (morphology) and tunable catalytic activity. The S/Zr ratio (0.1-2.0) and calcination temperature (425-625 °C) were varied to evaluate their effects on morphology, acidity, and reaction kinetics and, as a result, to optimize the catalytic system for this transformation. With the optimal SZ catalyst, complete conversion of sorbitol occurred in <2 h under mild conditions to give isosorbide in 76% yield. Overall, the quantitative kinetics and structure-reactivity studies provided valuable insights into the parameters that govern product yields and SZ catalyst activity, central among these being the relative proportion of acid site types and Brønsted surface density., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

We show that annihilation dynamics between oppositely charged optical vortex pairs can be manipulated by the initial size of the vortex cores, consistent with hydrodynamics. When sufficiently close together, vortices with strongly overlapped cores annihilate more quickly than vortices with smaller cores that must wait for diffraction to cause meaningful core overlap. Numerical simulations and experimental measurements for vortices with hyperbolic tangent cores of various initial sizes show that hydrodynamics governs their motion, and reveal distinct phases of vortex recombination; decreasing the core size of an annihilating pair can prevent the annihilation event.

We show that a two-dimensional hydrodynamics model provides a physical explanation for the splitting of higher-charge optical vortices under elliptical deformations. The model is applicable to laser light and quantum fluids alike. The study delineates vortex breakups from vortex unions under different forms of asymmetry in the beam, and it is also applied to explain the motion of intact higher-charge vortices.

The dynamics of hydrogen peroxide reactions with metal carbonyls have received little attention. Given reports that therapeutic levels of carbon monoxide are released in hypoxic tumour cells upon manganese carbonyls reactions with endogenous H 2 O 2 , it is critical to assess the underlying CO release mechanism(s). In this context, a quantitative mechanistic investigation of the H 2 O 2 oxidation of the water-soluble model complex fac -[Mn(CO) 3 (Br)(bpCO 2 )] 2- , ( A , bpCO 2 2- = 2,2'-bipyridine-4,4'-dicarboxylate dianion) was undertaken under physiologically relevant conditions. Characterizing such pathways is essential to evaluating the viability of redox-mediated CO release as an anti-cancer strategy. The present experimental studies demonstrate that approximately 2.5 equivalents of CO are released upon H 2 O 2 oxidation of A via pH-dependent kinetics that are first-order both in [ A ] and in [H 2 O 2 ]. Density functional calculations were used to evaluate the key intermediates in the proposed reaction mechanisms. These pathways are discussed in terms of their relevance to physiological CO delivery by carbon monoxide releasing moieties., (© 2021 The Authors.)

Dinitrosyl iron complexes (DNICs) are spontaneously and rapidly generated in cells. Their assembly requires nitric oxide (NO), biothiols, and nonheme iron, either labile iron or iron-sulfur clusters. Despite ubiquitous detection by electron paramagnetic resonance in NO-producing cells, the DNIC's chemical biology remains only partially understood. In this Forum Article, we address the reaction mechanisms for endogenous DNIC formation, with a focus on a labile iron pool as the iron source. The capability of DNICs to promote S-nitrosation is discussed in terms of S -nitrosothiol generation associated with the formation and chemical reactivity of DNICs. We also highlight how elucidation of the chemical reactivity and the dynamics of DNICs combined with the development of detection/quantification methods can provide further information regarding their participation in physiological and pathological processes.

We describe here nitric oxide dioxygenation (NOD) by the dioxygen manganese porphyrin adducts Mn(Por)(η 2 -O 2 ) (Por 2- = the meso -tetra-phenyl or meso -tetra- p -tolylporphyrinato dianions, TPP 2- and TTP 2- ). The Mn(Por)(η 2 -O 2 ) was assembled by adding O 2 to sublimed layers of Mn II (Por). When NO was introduced and the temperature was slowly raised from 80 to 120 K, new IR bands with correlated intensities grew concomitant with depletion of the υ(O 2 ) band. Isotope labeling experiments with 18 O 2 , 15 NO, and N 18 O combined with DFT calculations provide the basis for identifying the initial intermediates as the six-coordinate peroxynitrito complexes (ON)Mn(Por)(η 1 -OONO). Further warming to room temperature led to formation of the nitrato complexes Mn(Por)(η 1 -ONO 2 ), thereby demonstrating the ability of these metal centers to promote NOD. However, comparable quantities of the nitrito complexes Mn(Por)(η 1 -ONO) are also formed. In contrast, when the analogous reactions were initiated with the weak σ-donor ligand tetrahydrofuran or dimethyl sulfide present in the layers, formation of Mn(Por)(η 1 -ONO 2 ) is strongly favored (∼90%). The latter are formed via a 6-coordinate intermediate (L)Mn(Por)(η 1 -ONO 2 ) (L = THF or DMS) that loses L upon warming. These reaction patterns are compared to those observed previously with analogous iron and cobalt porphyrin complexes.

In this article we discuss the fundamental chemical and physical properties of NO and related nitrogen oxides (NO 2 - , NO 2 , N 2 O 3 , etc.) under solution conditions relevant to mammalian biology., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The reaction of complex [Pt(Me)(DMSO)(pbz)], 1 , (pbz = 2-(2-pyridyl)benzimidazolate) with [PtMe(Cl)(DMSO) 2 ], B , followed by addition of bis(diphenylphosphino)acetylene (dppac), gave the novel tetranuclear platinum complex [Pt 4 Me 4 (μ-dppac) 2 (pbz) 2 Cl 2 ], 2 , bearing both the pbz and dppac ligands. In this structure, the pbz ligands are both chelating and bridging to stabilize the tetraplatinum framework. The tetranuclear Pt(II) complex was fully characterized by NMR spectroscopy, X-ray crystallography, and mass spectrometry, and its electronic structure was investigated and supported by DFT calculations.

Dinitrosyl iron complexes (DNICs) are ubiquitous in mammalian cells and tissues producing nitric oxide (NO) and have been argued to play key physiological and pathological roles. Nonetheless, the mechanism and dynamics of DNIC formation in aqueous media remain only partially understood. Here, we report a stopped-flow kinetics and density functional theory (DFT) investigation of the reaction of NO with ferrous ions and the low molecular weight thiols glutathione (GSH) and cysteine (CysSH) as well as the peptides WCGPC and WCGPY to produce DNICs in pH 7.4 aqueous media. With each thiol, a two-stage reaction pattern is observed. The first stage involves several rapidly established pre-equilibria leading to a ferrous intermediate concluded to have the composition Fe II (NO)(RS) 2 (H 2 O) x ( C ). In the second stage, C undergoes rate-limiting, unimolecular autoreduction to give thiyl radical (RS • ) plus the mononitrosyl Fe(I) complex Fe I (NO)(RS)(H2O) x following the reactivity order of CysSH > WCGPC > WCGPY > GSH. Time course simulations using the experimentally determined kinetics parameters demonstrate that, at a NO flux characteristic of inflammation, DNICs will be rapidly formed from intracellular levels of ferrous iron and thiols. Furthermore, the proposed mechanism offers a novel pathway for S-nitroso thiol (RSNO) formation in a biological environment.

Multiphoton excitation allows one to access high energy excited states and perform valuable tasks in biological systems using tissue penetrating near-infrared (NIR) light. Here, we describe new photoactive manganese tricarbonyl complexes incorporating the ligand 4'-p-N,N-bis(2-hydroxyethyl)amino-benzyl-2,2':6',2″-terpyridine (TPYOH), which can serve as an antenna for two photon NIR excitation. Solutions of Mn(CO) 3 (TPYOH)X (X = Br - or CF 3 SO 3 - ) complexes are very photoactive toward CO release under visible light excitation (405 nm, 451 nm). The same responses were also triggered by multiphoton excitation at 750 and 800 nm. In this context, we discuss the potential applications of these complexes as visible/NIR light photoactivated carbon monoxide releasing moieties (photoCORMs). We also report the isolation and crystal structures of the TPYOH complexes Mn(TPYOH)Cl 2 and [Mn(TPYOH) 2 ](CF 3 SO 3 ) 2 , to illustrate a possible photolysis product(s).

Thiyl radicals are detected by EPR as co-products of dinitrosyl iron complex (DNIC) formation. In demonstrating that DNIC formation generates RS˙ in a NO rich environment, these results provide a novel route for S-nitroso thiol formation.

Devices consisting of polymer disks (PDs) of optically clear or translucent, medical-grade silicone loaded with a new hydrophobic, oxygen-stable, photoactivated nitric oxide-releasing moiety (photoNORM) are described. The photoNORM is the new O -nitrito chromium(III) complex trans- [Cr(PetA)(ONO) 2 ](BF 4 ) (PetA = 5,14-dimethyl-7,12-diphenyl-1,4,8,11-tetraaza-cyclotetradecane), of which the synthesis, X-ray crystal structure, and solution-phase photochemistry are described. Several different commercially available silicone polymers were tested with this photoNORM, and nitric oxide photouncaging with 451 nm light from these systems is compared. In addition, PDs were loaded with the photoNORM and neodymium-sensitized upconverting nanoparticles (Nd-UCNPs). The Nd-UCNPs absorb NIR light at ∼800 nm and activate NO release from the trans- [Cr(PetA)(ONO) 2 ] + cation. The use of such ensembles as implants provides a potential strategy for the in vivo uncaging of NO at physiological targets triggered by tissue-transmitting NIR excitation. Also reported are the X-ray crystal structures of cis - and trans -{Cr(PetA)Cl 2 ]Cl., Competing Interests: The authors declare no competing financial interest.