Osmium Complexes Research Articles

Vicinal Diol-Tethered Nucleobases as Targets for DNA Redox Labeling with Osmate Complexes.

Six-valent osmium (osmate) complexes with nitrogenous ligands have previously been used for the modification and redox labeling of biomolecules involving vicinal diol moieties (typically, saccharides or RNA). In this work, aliphatic (3,4-dihydroxybutyl and 3,4-dihydroxybut-1-ynyl) or cyclic (6-oxo-6-(cis-3,4-dihydroxypyrrolidin-1-yl)hex-2-yn-1-yl, PDI) vicinal diols are attached to nucleobases to functionalize DNA for subsequent redox labeling with osmium(VI) complexes. The diol-linked 2'-deoxyribonucleoside triphosphates were used for the polymerase synthesis of diol-linked DNA, which, upon treatment with K2 OsO3 and bidentate nitrogen ligands, gave the desired Os-labeled DNA, which were characterized by means of the gel-shift assay and ESI-MS. Through ex situ square-wave voltammetry at a basal plane pyrolytic graphite electrode, the efficiency of modification/labeling of individual diols was evaluated. The results show that the cyclic cis-diol (PDI) was a better target for osmylation than that of the flexible aliphatic ones (alkyl- or alkynyl-linked). The osmate adduct-specific voltammetric signal obtained for OsVI -treated DNA decorated with PDI showed good proportionality to the number of PDI per DNA molecule. The OsVI reagents (unlike OsO4 ) do not attack nucleobases; thus offering specificity of modification on the introduced glycol targets.

Determination of Glycoproteins by Microchip Electrophoresis Using Os(VI)-Based Selective Electrochemical Tag

Glycoproteins are excellent biomarkers for diagnosis and prognosis of several illnesses. α-1-Acid glycoprotein (AGP) and transferrin (Tf) are the main glycoproteins present in the serum, whose levels are increased during disease or injury. In this work, a selective detection of these glycoproteins using a microchip electrophoresis-electrochemical detection (ME-ED) platform is proposed for the first time. Because of the reduced sensitivity of glycoproteins, they were labeled with an electrochemical tag (osmium(VI) complex), which binds only to glycans, increasing the amperometric signal. Interestingly, oxidation potential of glycoprotein-Os(VI) adducts started at +0.50 V (vs Ag/AgCl) while nontagged glycoproteins started at +0.60 V. So, when the detection potential is set at +0.50 V, only glycoproteins tagged with Os(VI) complex are detected, avoiding the interference of the rest of the proteins. Determination of AGP and Tf was successfully demonstrated in the analysis of a certified human serum reference material yielding excellent accuracy (Er ≤ 4%) in just 400 s. This work offers new possibilities for ED for glycoprotein analysis in microfluidic systems, which has been dominated by fluorescence and MS detection until now. It is worth mentioning that ED has two interesting advantages with respect to others in the point-of-care testing field: easy miniaturization (bedside devices) and low cost.

Oxido‐Hydroxido‐ and Oxido‐Aminato‐Osmium(V) Complexes with a Cyclohexanediamine‐Based Tetradentate Ligand as Active Oxidants for Dihydroxylation and Aminohydroxylation of Alkenes

Six‐coordinate osmium(III) complexes coordinated by a cyclohexanediamine‐based tetradentate ligand [trans‐N,N′‐dimethyl‐N,N′‐bis(2‐pyridylmethyl)‐1,2‐cyclohexanediamine: BPMCN] are synthesized. The remaining two coordination sites are occupied by chloride (Cl–), triflate (OTf–), or hydroxide/water (OH–/H2O) to complete the octahedral osmium(III) centers; [OsIIIX2(BPMCN)]+ (X = Cl– or OTf–) and [OsIII(OH)(H2O)(BPMCN)]2+. The OsIII(OH)(H2O) complex catalyzes cis‐dihydroxylation and cis‐aminohydroxylation of styrene with hydrogen peroxide (H2O2) and chloramine‐T (TsNClNa) to yield the corresponding diol and aminoalcohol, respectively. The oxido‐hydroxido‐osmium(V) complex {[OsV(O)(OH)(BPMCN)]2+} is isolated as the active oxidant of the dihydroxylation. The oxidation of the OsIII(OH)(H2O) complex with chloramine‐T yields oxido‐aminato‐osmium(V) complex, [OsV(O)(NHTs)(BPMCN)]2+. Comparison of the crystal structure with those of the oxido‐hydroxido‐osmium(V) complex and related imido‐ and amino‐osmium complexes indicates that the –NHTs group works as a monoanionic aminate ligand and the osmium(V)–NHTs bond has a single bond character [Os–N; 2.058(4) Å]. The oxido‐aminato‐osmium(V) complex is revealed as the active oxidant for the aminohydroxylation by the direct reaction of the complex with styrene. The characterization of the complex allows us to propose the catalytic mechanism of the aminohydroxylation of alkenes.

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes.

In a systematic survey of luminescent bis(terdentate) osmium(II) complexes, a tipping point involving a reversal in photophysical tuning is observed whereby increasing stabilization of the ligand-based lowest unoccupied molecular orbital (LUMO) results in a blue shift in the optical absorption and emission bands. The complexes [Os(N^N'^N″)2]2+ [N^N'^N″ = 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine (Os1), 2,6-bis(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os2), 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyridyl (Os3), 2-(pyrid-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os4), 2-(pyrazin-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyridine (Os5), and 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyrazinyl (Os6)] have been prepared and characterized, and all complexes display phosphorescence ranging from the orange to near-IR regions of the spectrum. Replacement of the central pyridine in the ligands of Os1 by the more π-accepting pyrazine in Os2 results in a 55 nm red shift in the triplet metal-to-ligand charge-transfer-based emission band, while a larger red shift of 107 nm is observed for the replacement of one of the triazole donors in the ligands of Os1 by a second pyridine ring in Os3 (λemmax = 702 nm). Interestingly, replacement of the central pyridine ring in the ligands of Os3 by pyrazine (Os4,λemmax = 702 nm) fails to result in a further red shift in the emission band. Reversal of the relative positions of the pyridine and pyrazine donors in Os5 (λemmax = 733 nm) compared to Os4 does indeed result in the expected red shift in the emission with respect to that for Os3 based on the increased π-acceptor character of the ligands present. However, an inversion in emission tuning is observed for Os6, in which the incorporation of a second pyrazine donor in the ligand architecture results in a blue shift in the optical absorption and emission maxima (λemmax = 710 nm). Electrochemical studies reveal that while incorporating pyrazine in the ligands indeed results in an expected anodic shift in the first reduction potential through stabilization of the ligand-based LUMO, there is also a concomitant anodic shift in the OsII/OsIII-based oxidation potential. This stabilization of the metal-based highest occupied molecular orbital (HOMO) thus nullifies the effect of stabilization of the LUMO in Os4 compared to Os3, resulting in these complexes having coincident emission maxima. For Os6, stabilization of the HOMO through the incorporation of two pyrazine donors in the ligand structure now exceeds stabilization of the LUMO, resulting in a larger HOMO-LUMO gap and a counterintuitive blue shift in the optical properties in comparison with those of Os5. While it is known that the replacement of ligands (e.g., replacing bipyridyl with bipyrazinyl) can result in a larger HOMO-LUMO energy gap through greater stabilization of the HOMO, these results importantly allow us to capture the tipping point at which this inversion in photophysical tuning occurs. This therefore enables us to explore the limits available in emission tuning with a relatively simple and minimalist ligand structure.

Effect of Metal on the Properties of the Azopyridine Complexes of Iron, Ruthenium and Osmium

The theoretical study of α-, β-, γ-, δ-, ε- MCl2(Azpy)2 isomers with (M = Fe, Os and Ru) complexes is carried out using Density Functional Theory (DFT) at the B3LYP / LANL2DZ level. This study is focused not only on the effect of metals over geometric, electronic and reactivity parameters, but also on their anti-cancer effect. Its results that the geometric parameters undergo small modifications. These modifications evolve from iron to osmium through ruthenium complexes. Thus, the lengths of the bonds M-X (with X = Cl, N2, Npy) follow the following order Fe-X <Ru-X <Os-X. However, regarding their angular variation that undergoes deformation through the octahedron shape, it could be related to Jahn Teller effect. Also, the substitution of Ru by Os would increase the reactivity of these complexes. Among the isomers studied, the ε-Fe, δ-Ru and δ-Os complexes are likely to bind easily to the DNA. The values of the dipole moments are arranged in the following order: μ (ε-M)> μ (β-M)> μ (α-M)> μ (γ-M)> μ (δ-M) within these azopyridine complexes. Finally, we notice that the substitution of Ru by Os improves the cytotoxicity and the fluorescence of these complexes. The δ-Os isomer has the best cytotoxic and photosensitive characteristics of these azopyridine complexes and would be the ideal isomer for the diagnosis and treatment of cancers.

Distinguishing the glycan isomers 2,3-sialyllactose and 2,6-sialyllactose by voltammetry after modification with osmium(VI) complexes

Altered glycosylation is a universal feature of cancer cells and certain glycans are well-known markers of tumor progression. In this work we studied two glycan isomers, 2,3-sialyllactose (3-SL) and 2,6-sialyllactose (6-SL), frequently appearing in glycoproteins connected with cancer. A combination of square wave voltammetry and glycan modification with osmium(VI) N,N,N′,N′-tetramethylethylenediamine (Os(VI)tem) allowed to distinguish between these regioisomers, since the 6-SL molecule can bind three Os(VI), while the 3-SL only two Os(VI) moieties, as experiments using capillary electrophoresis, inductively coupled plasma mass spectrometry and thin layer chromatography showed. A similar pattern of Os(VI)-modification was found for isomers of sialyl-N-acetyllactosamine and sialylgalactose. Covalent adducts of Os(VI)tem with glycans yielded three reduction voltammetric peaks. The ratio of peak I/peak II heights depends on the content of individual regioisomer in the sample. Our proposed approach allows the determination of isomer percentage representation in the mixture after one voltammogram recording. These results show a new appropriate method for the discrimination of glycan isomers containing terminal sialic acid important for distinguishing between cancerous and non-cancerous origin of biomarkers.

Specific and Rapid Glucose Detection Using NAD‐dependent Glucose Dehydrogenase, Diaphorase, and Osmium Complex

AbstractSelective glucose measurement in serum and blood and rapid glucose measurement using nicotinamide adenine dinucleotide (NAD)‐dependent glucose dehydrogenase (NAD‐GDH) are still very challenging. Here, we report a selective and rapid glucose sensor, based on electrochemical‐enzymatic‐enzymatic (ENN) redox cycling involving bis(2,2‐bipyridyl)dichloroosmium(II) [Os(bpy)2Cl2], diaphorase (DI), NAD+, NAD‐GDH, and glucose. DI and Os(bpy)2Cl2 are used to obtain fast mediated oxidation of NADH that is generated as a result of glucose oxidation by NAD‐GDH. DI and NAD‐GDH are co‐immobilized via affinity binding on an avidin‐modified indium tin oxide electrode to obtain fast and stable ENN redox cycling. Two enzymes (DI and NAD‐GDH) and two electron mediators [Os(bpy)2Cl2 and NAD+] are insensitive to oxygen. The applied potential (0.0 V vs Ag/AgCl) is low enough to minimize interfering electrochemical reactions, and the redox reactions of Os(bpy)2Cl2 with interfering species are slow. NAD‐GDH is much less reactive to problematic monosaccharides such as xylose, fructose, galactose, and mannose than glucose. Artificial serum containing 5 % (w/v) human serum albumin shows a similar electrochemical background level in serum. All results enable us to obtain selective and reproducible glucose detection. The fast ENN redox cycling allows sensitive glucose detection with a wide range of concentrations in artificial serum with a short measuring time (5 s) without an incubation period.

Cycloosmathioborane Compounds: Other Manifestations of the Hückel Aromaticity.

The discovery of cycloosmathioborane compounds is reported. These species, which are prepared by the simultaneous dehydrogenation of a trihydride hydrogensulfide osmium(IV) complex and a BH3NHR2 amine-borane, bear an Os-S-B three-membered ring, being a manifestation of the 4 n + 2 Hückel aromaticity in which n = 0 and where the two π electrons of the ring are provided by the S atom.

Capturing the interplay between spin–orbit coupling and non-Condon effects on the photoabsorption spectra of Ru and Os dyes

A theoretical protocol developed to study the low-energy tail of the absorption spectrum of homoleptic biscyclometalated ruthenium and osmium complexes.

Synthesis and reactivity of an osmium(iii) aminoguanidine complex.

The biological activities of aminoguanidine (GNH2) and its derivatives have been extensively studied due to their properties as radical scavengers and antioxidants. Some of their biological activities may result from their binding to various metals present in biological systems. However, the reactivity of coordinated aminoguanidines has not been investigated. We report herein the synthesis, structure and reactivity of a novel osmium(iii) complex bearing the parent aminoguanidine, mer-[Os{NHC(NH2)(NHNH2)}(L)(CN)3]- (OsGNH2, HL = 2-(2-hydroxyphenyl)benzoxazole). The antioxidant properties of OsGNH2 have been investigated by reactions with various oxidants, including O2, H2O2, m-chloroperbenzoic acid (m-CPBA) and Ce(iv). Various osmium products are produced, which depend on the type of oxidant used. OsGNH2 is readily oxidized by O2 or H2O2 under ambient conditions to afford an osmium(iii) formamidine complex, [OsIII(NH2C[double bond, length as m-dash]NH)(L)(CN)3]- (OsFA, FA = formamidine). With m-CPBA, the nitrosyl complex, mer-[Os(NO)(L)(CN)3]- (OsNO), is formed instead. On the other hand, the nitrido complex mer-[Os(N)(L)(CN)3]- (OsN) is produced when the one-electron oxidant (NH4)2[CeIV(NO3)6] (Ce(iv)) is employed. The molecular structures of OsGNH2 and OsFA have been determined by X-ray crystallography. The oxidation of OsGNH2 to OsFA by O2 or H2O2 is proposed to go through initial dehydrogenation to give a diazoamidine intermediate. In the oxidation by m-CPBA and Ce(iv), it is proposed that the initially formed OsFA is further oxidized to OsNO and OsN, respectively, via osmium(iii) hydrogen cyanamido and osmium(iv) cyanoimido intermediates.

Heteroleptic [Os(Cl)(CO)(P^P)(pbi)] complexes bearing bidentate phosphine and 2-(2-pyridyl)benzimidazolate ligands: impact of isomerism on their luminescence properties.

A series of six [Os(Cl)(CO)(P^P)(pbi)] complexes have been synthesized and characterized using FT-IR, 1H NMR, and 31P NMR spectroscopy. Their molecular structures have been confirmed by means of X-ray diffraction studies. For each of the studied bidentate phosphines (P^P = cis-1,2-bis(diphenylphosphino)ethene - dppv, 1,2-bis(diphenylphosphino)ethane - dppe, 1,2-bis(diphenylphosphino)benzene - dppb) the applied synthesis procedure has afforded preparation of two isomers with pseudo-octahedral coordination of the osmium(ii) ion. According to X-ray data, the obtained isomers, green emissive [OC-6-24] and yellow emissive [OC-6-23] species, differ mainly in the arrangement of the 2-(2-pyridyl)benzimidazolate (pbi) anion in their structures. In the [OC-6-24] isomers the benzoimidazole fragment of the pbi ligand is located trans to the coordinated CO molecule, whereas the cis conformation is characteristic of the [OC-6-23] isomers. Each of trans-[Os(Cl)(CO)(P^P)(pbi)] shows intense green emission attributable to the excited triplet state of the pbi ligand, whereas the yellow emission from the excited cis-[Os(Cl)(CO)(P^P)(pbi)] indicates slight metal-to-ligand charge transfer character (from the Os(Cl)(CO)(P^P)+ fragment to the pbi ligand). The investigated complexes are generally well emissive with emission quantum yields up to 0.49 and emission lifetimes in the range of 10-150 μs. Only the yellow emissive cis-[Os(Cl)(CO)(dppv)(pbi)] complex exhibits remarkably different photophysical behaviour despite the fact that all three cis-[Os(Cl)(CO)(P^P)(pbi)] isomers emit in the same spectral region. In the view of DFT/TD-DFT results this has been explained by the presence of an additional excited dark state possessing distinct charge transfer character (from the Os(Cl)(CO)(pbi) fragment to the dppv ligand).

Pentamethylcyclopentadienyl osmium complexes that contain diazoalkane, dioxygen and allenylidene ligands: preparation and reactivity.

Diazoalkane complexes [Os(η5-C5Me5)(N2CAr1Ar2)(PPh3){P(OR)3}]BPh4 (1, 2) [R = Me (1), Et (2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b); Ar1Ar2 = C12H8 (fluorenyl) (c)] were prepared by reacting bromo-compounds OsBr(η5-C5Me5)(PPh3){P(OR)3} with an excess of diazoalkane in ethanol. The treatment of diazoalkane complexes 1 and 2 with acetylene under mild conditions (1 atm, RT) led to dipolar (3 + 2) cycloaddition affording 3H-pyrazole derivatives [Os(η5-C5Me5)(η1-[upper bond 1 start]N[double bond, length as m-dash]NC(C12H8)CH[double bond, length as m-dash]C[upper bond 1 end]H)(PPh3){P(OR)3}]BPh4 (6, 7) [R = Me (6), Et (7)] whereas reactions with terminal alkynes R1C[triple bond, length as m-dash]CH (R1 = Ph, p-tolyl, COOMe) gave vinylidene derivatives [Os(η5-C5Me5){[double bond, length as m-dash]C[double bond, length as m-dash]C(H)R1}(PPh3){P(OR)3}]BPh4 (8b-d, 9b-d) [R = Me (8), Et (9); R1 = Ph (b), p-tolyl (c), COOMe (d)]. Exposure to air of dichloromethane solutions of complexes 1 and 2 produced dioxygen derivatives [Os(η5-C5Me5)(η2-O2)(PPh3){P(OR)3}]BPh4 (10, 11) [R = Me (10), Et (11)]. Allenylidene [Os][double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CR1R2 (12-14) [R1 = R2 = Ph (12, 13); R1 = Ph, R2 = Me (14)], vinylvinylidene [Os][double bond, length as m-dash]C[double bond, length as m-dash]C(H)C(Ph)[double bond, length as m-dash]CH2 (15) and 3-hydroxyvinylidene [Os][double bond, length as m-dash]C[double bond, length as m-dash]C(H)C(H)R2(OH) (16, 17) [R2 = Ph (16), H (17)] derivatives were also prepared. The vinylidene complex [Os(η5-C5Me5)([double bond, length as m-dash]C[double bond, length as m-dash]CH2)(PPh3){P(OMe)3}]BPh4 (8a) reacted with PPh3 to afford the alkenylphosphonium derivative [Os(η5-C5Me5){η1-C(H)[double bond, length as m-dash]C(H)PPh3}(PPh3){P(OMe)3}]BPh4 (18) whereas vinylidene complexes 8 and 9 reacted with water leading to the hydrolysis of the alkyne and the formation of carbonyl complexes [Os(η5-C5Me5)(CO)(PPh3){P(OR)3}]BPh4 (19, 20). The complexes were characterised by spectroscopic data (IR and NMR) and by X-ray crystal structure determination of [Os(η5-C5Me5){[double bond, length as m-dash]C[double bond, length as m-dash]C(H)p-tolyl}(PPh3){P(OEt)3}]BPh4 (9c), [Os(η5-C5Me5)(η2-O2)(PPh3){P(OMe)3}]BPh4 (10) and [Os(η5-C5Me5)(CO)(PPh3){P(OMe)3}]BPh4 (19).

Mechanistic insights into asymmetric transfer hydrogenation of pyruvic acid catalysed by chiral osmium complexes with formic acid assisted proton transfer.

A density functional theory study of the asymmetric transfer hydrogenation of pyruvic acid to ł- and d-lactic acids catalysed by a chiral osmium complex OsH[(R,R)TsNCH(Ph)CH(Ph)NH2](η6-p-cymene) reveals a formic acid assisted enantio-determining proton-coupled hydride transfer mechanism. Activation strain model analysis indicates that the C-H/π interaction between η6-arene and carboxyl ligands has a significant influence on the enantioselectivity. The replacement of p-cymene by 4-isopropyl biphenyl or phenyl is highly likely to improve the catalytic performance of the complex.

Comprehensive Study of Mononuclear Osmium Complexes with Various Pyrene Ligands

New mononuclear osmium complexes M1–M4 with various NCN‐cyclometalating pyrene ligands were synthesized and thoroughly characterized with particular emphasis on the nature of NCN‐cyclometalating pyrene ligands on the properties of target compounds. Structural properties were achieved by using the theoretical studies (DFT). Moreover, spectroscopic and theoretical studies (TD‐DFT) show the character of transitions and allow to understand the behavior of molecules during the stepwise oxidative titrations by using the cerium ammonium nitrate (CAN) solutions what resulted in M1+–M4+. The obtained experimental and theoretical data show the significant differences between the mononuclear osmium complexes M1–M4 in reference to used pyrene ligands.

Orthometalated N-(Benzophenoxazine)-o-aminophenol: Phenolato versus Phenoxyl States.

The molecular and electronic structures of the orthometalated ruthenium(III) and osmium(III) complexes of N-(benzophenoxazine)-o-aminophenol (OXLH2) that exhibits versatile redox activities are reported. The redox chemistry of OXLH2 is remarkably different from that of N-(aryl)-o-aminophenol (APLH2). The study established that OXLH2 is redox noninnocent and is a precursor of a phenoxyl radical. One of the C–H bonds of OXLH2 is activated by ions, and OXLH2 reveals three different redox states as dianionic phenolato (OXL2–), monoanionic phenoxyl radical (OXL•–), and zwitterionic phenoxium cation (OXL±) states. The reaction of OXLH2 with [RuII(PPh3)3Cl2] in boiling toluene in air affords an orthometalated OXL2– complex of ruthenium(III), trans-[(OXL2–)RuIII(PPh3)2(Cl)] (1), whereas the similar reaction with [OsII(PPh3)3Br2] yields an orthometalated OXL•– complex, cis-[(OXL•–)OsIII(PPh3)Br2] (2). 1 and 2 exhibit ligand-based reversible redox waves due to OXL•–/OXL2–, OXL±/OXL•–, and MIII/MII couples. The 1+ ion is a OXL•– complex of ruthenium(III). 2– exhibits temperature-dependent valence tautomerism due to [OsII(OXL•–) ↔ OsIII(OXL2–)] equilibrium. 22– is a OXL2– complex of osmium(II), while 12+ and 2+ are OXL± complexes of metal(III). 2 is an oxidant and effective catalyst for oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone, and the turnover number is 119.7 h–1. The UV–vis–NIR absorption spectrum of 1 displays an NIR band at 800 nm due to an intra-ligand-charge-transfer transition, which is absent in 2 incorporating a OXL•– radical. The molecular and electronic structures of 1 and 2 and their oxidized and reduced analogues were confirmed by single-crystal X-ray crystallography, variable-temperature electron paramagnetic resonance spectroscopy, spectroelectrochemical measurements, and density functional theory calculations.

Photophysical and Cellular Imaging Studies of Brightly Luminescent Osmium(II) Pyridyltriazole Complexes.

The series of complexes [Os(bpy)3- n(pytz) n][PF6]2 (bpy = 2,2'-bipyridyl, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, 1 n = 0, 2 n = 1, 3 n = 2, 4 n = 3) were prepared and characterized and are rare examples of luminescent 1,2,3-triazole-based osmium(II) complexes. For 3 we present an attractive and particularly mild preparative route via an osmium(II) η6-arene precursor circumventing the harsh conditions that are usually required. Because of the high spin-orbit coupling constant associated with the Os(II) center the absorption spectra of the complexes all display absorption bands of appreciable intensity in the range of 500-700 nm corresponding to spin-forbidden ground-state-to-3MLCT transitions (MLCT = metal-to-ligand charge transfer), which occur at significantly lower energies than the corresponding spin-allowed 1MLCT transitions. The homoleptic complex 4 is a bright emitter (λmaxem = 614 nm) with a relatively high quantum yield of emission of ∼40% in deoxygenated acetonitrile solutions at room temperature. Water-soluble chloride salts of 1-4 were also prepared, all of which remain emissive in aerated aqueous solutions at room temperature. The complexes were investigated for their potential as phosphorescent cellular imaging agents, whereby efficient excitation into the 3MLCT absorption bands at the red side of the visible range circumvents autofluorescence from biological specimens, which do not absorb in this region of the spectrum. Confocal microscopy reveals 4 to be readily taken up by cancer cell lines (HeLa and EJ) with apparent lysosomal and endosomal localization, while toxicity assays reveal that the compounds have low dark and light toxicity. These complexes therefore provide an excellent platform for the development of efficient luminescent cellular imaging agents with advantageous photophysical properties that enable excitation and emission in the biologically transparent region of the optical spectrum.

Disposable carbon nanotube scaffold films for fast and reliable assessment of total α1-acid glycoprotein in human serum using adsorptive transfer stripping square wave voltammetry.

Alpha-1-acid glycoprotein (AGP) is a serum glycoprotein whose levels are increased two or three times during disease or injury. This makes it a potential biomarker for inflammatory bowel diseases and sepsis. Consequently, fast, simple, and cheap analytical methods for prognosis, diagnosis, and follow-up of these diseases are demanded. In this work, we propose a simple electrochemical approach based on carbon nanotubes scaffold films (CNSFs) for total AGP determination in serum samples. Firstly, AGP is labeled with an electrochemical tag (osmium(VI) complex), and then the total amount of AGP is quantified by adsorptive transfer stripping square wave voltammetry (AdTSWV). Multi-walled carbon nanotubes scaffold films (MWSFs) yielded the best analytical performance in terms of sensitivity with a good limit of detection of 0.6mgL-1 for AGP determination in serum samples, in less than 20min. A simplified AGP calibration and its sequential serum sample analysis strategy with good accuracy (81%) and excellent reproducibility (RSD < 1%) was additionally proposed to meet the point-of-care/needs requirements. Graphical abstract Multi-walled carbon nanotubes scaffold films for total AGP determination on disposable platforms integrating single-point calibration and sequential sample analysis.

Near-Infrared Luminescent Osmium(II) Complexes with an Intrinsic RNA-Targeting Capability for Nucleolus Imaging in Living Cells.

Os(II) polypyridyl complexes usually display an excellent NIR (near-infrared) emission, which conforms to the optical window in a biological system. At the moment, there is only one commercial RNA dye, SYTO RNA-Select, which emits green fluorescence and only stains RNA in the fixed cells. Therefore, it is necessary to study NIR-emitting RNA probes in the live cells. Here, we study two novel osmium complexes with NIR luminescence for cell imaging and find the specific binding ability of these two osmium complexes with RNA. The osmium(II) complexes can selectively light up RNA and enable NIR luminescent imaging of RNA of the nucleus of the live cells. It is the first example of osmium complexes in application of RNA-specific luminescence imaging. This work suggests that RNA might be a novel target of osmium complexes.

A balance of redox and ligand-exchange processes in the reaction of H2[OsCl6] with thiourea: Isolation and characterization of a novel osmium complex [(NH2)2CSSC(NH2)2]2[OsIVCl6]Cl2·3H2O

A novel complex with the stoichiometry [(NH2)2CSSC(NH2)2]2[OsIVCl6]Cl2·3H2O (1) is isolated as a product of the reaction of H2[OsCl6] with thiourea in concentrated HCl under deliberately optimized conditions favoring a partial thiourea oxidation to α,α′-dithiobisformamidinium dication but preserving hexachloroosmate [OsCl6]2- anions. A bromide analogue [(NH2)2CSSC(NH2)2]2[OsIVBr6]Br2·3H2O 2 is afforded by a similar reaction. A counter synthesis of 1 is accomplished via the direct ion-exchange reaction between H2[OsCl6] and [S2C2(NH2)4]Cl2. Crystal structures of 1 and 2 are unambiguously established by synchrotron radiation-based single-crystal X-ray diffraction at 100 K. The two compounds are isostructural and are crystallized in the orthorhombic space group Cmcm, Z = 4. Unit cell parameters are for 1:a = 11.279(2) Å, b = 13.611(3) Å, c = 16.731(3) Å; for 2: a = 11.695(2) Å, b = 14.005(3) Å, c = 17.015(3) Å. The osmium atoms in [OsX6]2− (X = Cl or Br) anions adopt slightly distorted octahedral coordination. The α,α′-dithiobisformamidinium cations are paired into rings via the NH…Cl− hydrogen bonds. The rings are further linked into a spatial network by H-bonds with water molecules and S…Cl nonvalence interactions.

In Vivo Selectivity and Localization of Reactive Oxygen Species (ROS) Induction by Osmium Anticancer Complexes That Circumvent Platinum Resistance.

Platinum drugs are widely used for cancer treatment. Other precious metals are promising, but their clinical progress depends on achieving different mechanisms of action to overcome Pt-resistance. Here, we evaluate 13 organo-Os complexes: 16-electron sulfonyl-diamine catalysts [(η6-arene)Os(N,N′)], and 18-electron phenylazopyridine complexes [(η6-arene)Os(N,N’)Cl/I]+ (arene = p-cymene, biphenyl, or terphenyl). Their antiproliferative activity does not depend on p21 or p53 status, unlike cisplatin, and their selective potency toward cancer cells involves the generation of reactive oxygen species. Evidence of such a mechanism of action has been found both in vitro and in vivo. This work appears to provide the first study of osmium complexes in the zebrafish model, which has been shown to closely model toxicity in humans. A fluorescent osmium complex, derived from a lead compound, was employed to confirm internalization of the complex, visualize in vivo distribution, and confirm colocalization with reactive oxygen species generated in zebrafish.