Light-Driven Hydrodefluorination of Electron-Rich Aryl Fluorides by an Anionic Rhodium-Gallium Photoredox Catalyst.

An anionic Rh-Ga complex catalyzed the hydrodefluorination of challenging C-F bonds in electron-rich aryl fluorides and trifluoromethylarenes when irradiated with violet light in the presence of H2 , a stoichiometric alkoxide base, and a crown-ether additive. Based on theoretical calculations, the lowest unoccupied molecular orbital (LUMO), which is delocalized across both the Rh and Ga atoms, becomes singly occupied upon excitation, thereby poising the Rh-Ga complex for photoinduced single-electron transfer (SET). Stoichiometric and control reactions support that the C-F activation is mediated by the excited anionic Rh-Ga complex. After SET, the proposed neutral Rh0 intermediate was detected by EPR spectroscopy, which matched the spectrum of an independently synthesized sample. Deuterium-labeling studies corroborate the generation of aryl radicals during catalysis and their subsequent hydrogen-atom abstraction from the THF solvent to generate the hydrodefluorinated arene products. Altogether, the combined experimental and theoretical data support an unconventional bimetallic excitation that achieves the activation of strong C-F bonds and uses H2 and base as the terminal reductant.

Two-photon uncaging of bioactive thiols in live cells at wavelengths above 800 nm.

Photoactivatable protecting groups (PPGs) are useful for a broad range of applications ranging from biology to materials science. In chemical biology, induction of biological processes via photoactivation is a powerful strategy for achieving spatiotemporal control. The importance of cysteine, glutathione, and other bioactive thiols in regulating protein structure/activity and cell redox homeostasis makes modulation of thiol activity particularly useful. One major objective for enhancing the utility of photoactivatable protecting groups (PPGs) in living systems is creating PPGs with longer wavelength absorption maxima and efficient two-photon (TP) absorption. Toward these objectives, we developed a carboxyl- and dimethylamine-functionalized nitrodibenzofuran PPG scaffold (cDMA-NDBF) for thiol photoactivation, which has a bathochromic shift in the one-photon absorption maximum from λmax = 315 nm with the unfunctionalized NDBF scaffold to λmax = 445 nm. While cDMA-NDBF-protected thiols are stable in the presence of UV irradiation, they undergo efficient broad-spectrum TP photolysis at wavelengths as long as 900 nm. To demonstrate the wavelength orthogonality of cDMA-NDBF and NDBF photolysis in a biological setting, caged farnesyltransferase enzyme inhibitors (FTI) were prepared and selectively photoactivated in live cells using 850-900 nm TP light for cDMA-NDBF-FTI and 300 nm UV light for NDBF-FTI. These experiments represent the first demonstration of thiol photoactivation at wavelengths above 800 nm. Consequently, cDMA-NDBF-caged thiols should have broad applicability in a wide range of experiments in chemical biology and materials science.

Methoxy-Substituted Nitrodibenzofuran-Based Protecting Group with an Improved Two-Photon Action Cross-Section for Thiol Protection in Solid Phase Peptide Synthesis.

Photoremovable caging groups are useful for biological applications because the deprotection process can be initiated by illumination with light without the necessity of adding additional reagents such as acids or bases that can perturb biological activity. In solid phase peptide synthesis (SPPS), the most common photoremovable group used for thiol protection is the o-nitrobenzyl group and related analogues. In earlier work, we explored the use of the nitrodibenzofuran (NDBF) group for thiol protection and found it to exhibit a faster rate toward UV photolysis relative to simple nitroveratryl-based protecting groups and a useful two-photon cross-section. Here, we describe the synthesis of a new NDBF-based protecting group bearing a methoxy substituent and use it to prepare a protected form of cysteine suitable for SPPS. This reagent was then used to assemble two biologically relevant peptides and characterize their photolysis kinetics in both UV- and two-photon-mediated reactions; a two-photon action cross-section of 0.71-1.4 GM for the new protecting group was particularly notable. Finally, uncaging of these protected peptides by either UV or two-photon activation was used to initiate their subsequent enzymatic processing by the enzyme farnesyltransferase. These experiments highlight the utility of this new protecting group for SPPS and biological experiments.

Synthesis, Characterization, and Electron-Transfer Properties of Ferrocene-BODIPY-Fullerene Near-Infrared-Absorbing Triads: Are Catecholopyrrolidine-Linked Fullerenes a Good Architecture to Facilitate Electron-Transfer?

A series of covalent ferrocene-BODIPY-fullerene triads with the ferrocene groups conjugated to the BODIPY π-system and the fullerene acceptor linked at the boron hub by a common catecholpyrrolidine bridge were prepared and characterized by 1D and 2D NMR, UV/Vis, steady-state fluorescence spectroscopy, high-resolution mass spectrometry, and, for one of the derivatives, X-ray crystallography. Redox processes of the new compounds were investigated by electrochemical (CV and DPV) methods and spectroelectrochemistry. DFT calculations indicate that the HOMO in all triads was delocalized between ferrocene and BODIPY π-system, the LUMO was always fullerene-centered, and the catechol-centered occupied orbital was close in energy to the HOMO. TDDFT calculations were indicative of the low-energy, low-intensity charge-transfer bands originated from the ferrocene-BODIPY core to fullerene excitation, which explained the similarity of the UV/Vis spectra of the ferrocene-BODIPY dyads and ferrocene-BODIPY-fullerene triads. Photophysical properties of the new triads as well as reference BODIPY-fullerene and ferrocene-BODIPY dyads were investigated by pump-probe spectroscopy in the UV/Vis and NIR spectral regions following selective excitation of the BODIPY-based antenna. Initial charge transfer from the ferrocene to the BODIPY core was shown to outcompete sub-100 fs deactivation of the excited state mediated by the catechol bridge. However, no subsequent electron transfer to the fullerene acceptor was observed. The initial charge separated state relaxes by recombination with a time constant of 150-380 ps.

Effect of extending conjugation via thiophene-based oligomers on the excited state electron transfer rates to ZnO nanocrystals.

Oligothiophene dyes with two to five thiophene units were anchored to oleate-capped, quantum-confined zinc oxide nanocrystals (ZnO NCs) through a cyanoacrylate functional group. While the fluorescence of the bithiophene derivative was too weak for meaningful quenching studies, the fluorescence of the dyes with three, four and five thiophene rings was quenched upon binding to the NCs. Ultrafast pump-probe spectroscopy was used to observe the singlet excited states of the free dyes dissolved in dichloromethane as well as attached to a ZnO NC dispersed in the same solvent. When the dyes were bound to ZnO NCs, ultrafast spectroscopic measurements revealed rapid disappearance of the singlet excited state and appearance of a new transient absorption at higher energy that was assigned to the oxidized dye based on the similar absorption observed upon oxidation of the dye using nitrosonium ion. The appearance lifetimes of the oxidized dyes were assigned to the excited state electron transfer and were 36 ± 2, 22.3 ± 3.9, 26.5 ± 1.5 and 19.4 ± 0.8 ps for bi-, ter-, quarter- and quinquethiophene dyes respectively. Two factors contributed to the similarity in the electron transfer lifetime. First the excited state energies of the dyes were similar, and second, the free energy for electron transfer reaction was sufficiently large to move the event into the energy-independent regime.

Evaluation of the Intramolecular Charge-Transfer Properties in Solvatochromic and Electrochromic Zinc Octa(carbazolyl)phthalocyanines.

2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato zinc(II) (3) and 2,3,9,10,16,17,23·24-octakis-(3,6-di-tert-butyl-9H-carbazole) phthalocyaninato zinc(II) (4) complexes were prepared and characterized by NMR and UV-vis spectroscopies, magnetic circular dichroism (MCD), matrix-assisted laser desorption ionization mass spectrometry, and X-ray crystallography. UV-vis and MCD data are indicative of the interligand charge-transfer nature of the broad band observed in 450-500 nm range for 3 and 4. The redox properties of 3 and 4 were probed by electrochemical and spectro-electrochemical methods, which are suggestive of phthalocyanine-centered first oxidation and reduction processes. Photophysics of 3 and 4 were investigated by steady-state fluorescence and time-resolved transient absorption spectroscopy demonstrating the influence of the carbazole substituents on deactivation from the first excited state in 3 and 4. Protonation of the meso-nitrogen atoms in 3 results in much faster deactivation kinetics from the first excited state. Spectroscopic data were correlated with density functional theory (DFT) and time-dependent DFT calculations on 3 and 4.

Effects of a phosphonate anchoring group on the excited state electron transfer rates from a terthiophene chromophore to a ZnO nanocrystal.

Terthiophene dyes were synthesized having a carboxylate or a phosphonate moiety at the 2-position which serves as an anchoring group to zinc oxide nanocrystals (ZnO NCs). Electronic absorption and fluorescence measurements, combined with reduction potentials, provided estimates of -1.81 and -1.86 V vs. NHE for the excited state reduction potential of the carboxylate and phosphonate, respectively. Static quenching was observed when the dyes were bound to the surface of acetate-capped ZnO NCs having a diameter of 2.8 nm. Stern-Volmer studies conducted at several dye concentrations established that a minor fraction of the adsorbed dye remained unquenched even at 1 : 1 dye to NC ratios. Adsorption isotherm measurements established that the phosphonate binds more strongly than the carboxylate and that saturation coverage was ∼1.2 dyes per nm2 for both dyes. Ultrafast transient absorption spectroscopic experiments were used to probe excited state dynamics. In the presence of ZnO NCs, disappearance of the singlet excited state of the dye corresponded to appearance of the spectroscopic signature of the oxidized dye with a time constant of 1.5 ± 0.1 and 6.1 ± 0.2 ps, respectively, for the carboxylate and phosphonate dye. The difference in the electron transfer rates was attributed to a larger electronic coupling for the dye having the carboxylate anchoring group.

Nitrodibenzofuran: A One- and Two-Photon Sensitive Protecting Group That Is Superior to Brominated Hydroxycoumarin for Thiol Caging in Peptides.

Photoremovable protecting groups are important for a wide range of applications in peptide chemistry. Using Fmoc-Cys(Bhc-MOM)-OH, peptides containing a Bhc-protected cysteine residue can be easily prepared. However, such protected thiols can undergo isomerization to a dead-end product (a 4-methylcoumarin-3-yl thioether) upon photolysis. To circumvent that photoisomerization problem, we explored the use of nitrodibenzofuran (NDBF) for thiol protection by preparing cysteine-containing peptides where the thiol is masked with an NDBF group. This was accomplished by synthesizing Fmoc-Cys(NDBF)-OH and incorporating that residue into peptides by standard solid-phase peptide synthesis procedures. Irradiation with 365 nm light or two-photon excitation with 800 nm light resulted in efficient deprotection. To probe biological utility, thiol group uncaging was carried out using a peptide derived from the protein K-Ras4B to yield a sequence that is a known substrate for protein farnesyltransferase; irradiation of the NDBF-caged peptide in the presence of the enzyme resulted in the formation of the farnesylated product. Additionally, incubation of human ovarian carcinoma (SKOV3) cells with an NDBF-caged version of a farnesylated peptide followed by UV irradiation resulted in migration of the peptide from the cytosol/Golgi to the plasma membrane due to enzymatic palmitoylation. Overall, the high cleavage efficiency devoid of side reactions and significant two-photon cross-section of NDBF render it superior to Bhc for thiol group caging. This protecting group should be useful for a plethora of applications ranging from the development of light-activatable cysteine-containing peptides to the development of light-sensitive biomaterials.

Tuning Up an Electronic Structure of the Subphthalocyanine Derivatives toward Electron-Transfer Process in Noncovalent Complexes with C60 and C70 Fullerenes: Experimental and Theoretical Studies.

Noncovalent π-π interactions between chloroboron subphthalocyanine (1), 2,3-subnaphthalocyanine (3), 1,4,8,11,15,18-(hexathiophenyl)subphthalocyanine (4), or 4-tert-butylphenoxyboron subphthalocyanine (2) with C60 and C70 fullerenes were studied by UV-vis and steady-state fluorescence spectroscopy, as well as mass (APCI, ESI, and CSI) spectrometry. Mass spectrometry experiments were suggestive of relatively weak interaction energies between compounds 1-4 and fullerenes. The formation of a new weak charge-transfer band in the NIR region was observed in solution only for subphthalocyanine 4 when titrated with C60 and C70 fullerenes. Molecular structures of the subphthalocyanines 2 and 4 as well as cocrystallite of 4 with C60 fullerene (4···C60) were studied using X-ray crystallography. One of the C60 fullerenes in the crystal structure of 4···C60 was found in the concave region between two subphthalocyanine cores, while the other three fullerenes are aligned above individual isoindole fragments of the aromatic subphthalocyanine. The excited-state dynamics in noncovalent assemblies were studied by transient absorption spectroscopy. The time-resolved photophysics data suggest that only electron-rich subphthalocyanine 4 can facilitate an electron-transfer to C60 or C70 fullerenes, while no electron-transfer from the photoexcited receptors 1-3 to fullerenes was observed in UV-vis and transient spectroscopy experiments. DFT calculations using the CAM-B3LYP exchange-correlation functional and the 6-31+G(d) basis set allowed an estimation of interaction energies for the noncovalent 1:1 and 1:2 (fullerene:subphthalocyanine) complexes. Theoretical data suggest that the weak (∼3.5-10.5 kcal/mol) van der Waals-type interaction energies tend to increase with an increase of the electron density at the subphthalocyanine core with compound 4 being the best platform for noncovalent interactions with fullerenes. DFT calculations also indicate that 1:2 (fullerene:subphthalocyanine) noncovalent complexes are more stable than the corresponding 1:1 assemblies.

6-Bromo-7-hydroxy-3-methylcoumarin (mBhc) is an efficient multi-photon labile protecting group for thiol caging and three-dimensional chemical patterning.

The photochemical release of chemical reagents and bioactive molecules provides a useful tool for spatio-temporal control of biological processes. However, achieving this goal requires the development of highly efficient one- and two-photon sensitive photo-cleavable protecting groups. Thiol-containing compounds play critical roles in biological systems and bioengineering applications. While potentially useful for sulfhydryl protection, the 6-bromo-7-hydroxy coumarin-4-ylmethyl (Bhc) group can undergo an undesired photoisomerization reaction upon irradiation that limits its uncaging efficiency. To address this issue, here we describe the development of 6-bromo-7-hydroxy-3-methylcoumarin-4-ylmethyl (mBhc) as an improved group for thiol-protection. One- and two-photon photolysis reactions demonstrate that a peptide containing a mBhc-caged thiol undergoes clean and efficient photo-cleavage upon irradiation without detectable photoisomer production. To test its utility for biological studies, a K-Ras-derived peptide containing an mBhc-protected thiol was prepared by solid phase peptide synthesis using Fmoc-Cys(mBhc)-OH for the introduction of the caged thiol. Irradiation of that peptide using either UV or near IR light in presence of protein farnesyltransferase (PFTase), resulted in generation of the free peptide which was then recognized by the enzyme and became farnesylated. To show the utility of this caging group in biomaterial applications, we covalently modified hydrogels with mBhc-protected cysteamine. Using multi-photon confocal microscopy, highly defined volumes of free thiols were generated inside the hydrogels and visualized via reaction with a sulfhydryl-reactive fluorophore. The simple synthesis of mBhc and its efficient removal by one- and two-photon processes make it an attractive protecting group for thiol caging in a variety of applications.

Femtosecond to nanosecond excited state dynamics of vapor deposited copper phthalocyanine thin films.

Vapor deposited thin films of copper phthalocyanine (CuPc) were investigated using transient absorption spectroscopy. Exciton-exciton annihilation dominated the kinetics at high exciton densities. When annihilation was minimized, the observed lifetime was measured to be 8.6 ± 0.6 ns, which is over an order of magnitude longer than previous reports. In comparison with metal free phthalocyanine (H2Pc), the data show evidence that the presence of copper induces an ultrafast relaxation process taking place on the ca. 500 fs timescale. By comparison to recent time-resolved photoemission studies, this is assigned as ultrafast intersystem crossing. As the intersystem crossing occurs ca. 10(4) times faster than lifetime decay, it is likely that triplets are the dominant excitons in vapor deposited CuPc films. The exciton lifetime of CuPc thin films is ca. 35 times longer than H2Pc thin films, while the diffusion lengths reported in the literature are typically quite similar for the two materials. These findings suggest that despite appearing to be similar materials at first glance, CuPc and H2Pc may transport energy in dramatically different ways. This has important implications on the design and mechanistic understanding of devices where phthalocyanines are used as an excitonic material.

Tuning Electronic Structure, Redox, and Photophysical Properties in Asymmetric NIR-Absorbing Organometallic BODIPYs.

Stepwise modification of the methyl groups at the α positions of BODIPY 1 was used for preparation of a series of mono- (2, 4, and 6) and diferrocene (3) substituted donor-acceptor dyads in which the organometallic substituents are fully conjugated with the BODIPY π system. All donor-acceptor complexes have strong absorption in the NIR region and quenched steady-state fluorescence, which can be partially restored upon oxidation of organometallic group(s). X-ray crystallography of complexes 2-4 and 6 confirms the nearly coplanar arrangement of the ferrocene groups and the BODIPY π system. Redox properties of the target systems were studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the first oxidation process in all dyads is ferrocene centered, while the separation between the first and the second ferrocene-centered oxidation potentials in diferrocenyl-containing dyad 3 is ∼150 mV. The density functional theory-polarized continuum model (DFT-PCM) and time-dependent (TD) DFT-PCM methods were used to investigate the electronic structure as well as explain the UV-vis and redox properties of organometallic compounds 2-4 and 6. TDDFT calculations allow for assignment of the charge-transfer and π → π* transitions in the target compounds. The excited state dynamics of the parent BODIPY 1 and dyads 2-4 and 6 were investigated using time-resolved transient spectroscopy. In all organometallic dyads 2-4 and 6 the initially excited state is rapidly quenched by electron transfer from the ferrocene ligand. The lifetime of the charge-separated state was found to be between 136 and 260 ps and demonstrates a systematic dependence on the electronic structure and geometry of BODIPYs 2-4 and 6.

Synthesis and charge-transfer dynamics in a ferrocene-containing organoboryl aza-BODIPY donor-acceptor triad with boron as the hub.

A N,N'-bis(ferroceneacetylene)boryl complex of 3,3'-diphenylazadiisoindolylmethene was synthesized by the reaction of an N,N'-difluoroboryl complex of 3,3'-diphenylazadiisoindolylmethene and ferroceneacetylene magnesium bromide. The novel diiron complex was characterized by a variety of spectroscopic techniques, electrochemistry, and ultrafast time-resolved methods. Spectroscopy and redox behavior was correlated with the density functional theory (DFT) and time-dependent DFT calculations. An unexpected degree of coupling between the two Fc ligands was observed. Despite a lack of conjugation between the donor and acceptor, the complex undergoes very rapid (τ = 1.7 ± 0.1 ps) photoinduced intramolecular charge separation followed by subpicosecond charge recombination to form a triplet state with a lifetime of 4.8 ± 0.1 µs.

Photodetachment, electron cooling, and recombination, in a series of neat aliphatic room temperature ionic liquids.

Transient absorption following photodetachment of a series of neat methyl-alkyl-pyrrolidinium bis(trifluoromethylsulfonyl)amides at 6.20 eV was measured with sub-picosecond time resolution in the visible and near-IR portions of the spectrum. This series spans the onset of structuring in the liquids in the form of polarity alternation. Excitation promotes the electron into a delocalized state with a very large reactive radius. Strong transient absorption is observed in the visible spectrum with a ∼700 fs lifetime, and much weaker, long-lived absorption is observed in the near-IR spectrum. Absorption in the visible is shown to be consistent with the hole, and absorption in the near-IR is assigned to the free solvated electron. Yield of free electrons is estimated at ∼4%, is insensitive to the size of the cation, and is determined in less than 1 ps. Solvation of free electrons depends strongly on the size of the cation and correlates well with the viscosity of the liquid. In addition to radiolytic stability of the aliphatic cations, ultrafast, efficient recombination of separated charge in NTf2 (-) based ionic liquids following photo-excitation near the band-gap may prevent subsequent reactive damage associated with anions.

Treatment for salivary gland hypofunction at both initial and advanced stages of Sjögren-like disease: a comparative study of bone marrow therapy versus spleen cell therapy with a 1-year monitoring period.

BACKGROUND AIMS: Non-obese diabetic mice (NOD) exhibit autoimmune Sjögren-like disease (SS-like). We reported previously that a combined-therapy consisting of immuno- and cell-based therapy rescued NOD from SS-like. However, therapies tested to date on NOD mice were aimed at the initial phase of SS-like. It is unknown whether therapies are effective in restoring salivary function when given at an advanced phase of SS-like. METHODS: The efficacy of two therapies (bone marrow versus spleen cells) was compared head-to-head for halting/reversing salivary hypofunction at two critical time points of SS-like (7-week-old NOD with normal saliva output and 20-week-old NOD with minimal saliva). NOD mice were divided into four groups: (i) control, (ii) complete Freund's adjuvant (CFA), (iii) bone marrow transplants with CFA or (iv) spleen cell transplants with CFA. Mice were monitored 8-12 months after therapy. RESULTS: Both cell therapies were effective during the initial phase of SS-like; salivary flow rates were maintained between 80-100% of pre-symptomatic levels. Spleen cell therapy was better than bone marrow when administered in the initial phase of SS-like. When cell therapies were given at an advanced phase of SS-like (20 weeks and older), salivary flow rates improved but were at best 50% of pre-symptomatic levels. Both cell therapies decreased tumor necrosis factor-α, transforming growth factor-ß1 levels and T and B cells while increasing epidermal growth factor and regulatory T cells. Elevated serum epidermal growth factor levels were measured in spleen-treated mice. CONCLUSIONS: A therapeutic effect in advanced phase disease, albeit in mice, holds promise for humans in which Sjögren syndrome is generally not diagnosed until a late stage.

Redox and photoinduced electron-transfer properties in short distance organoboryl ferrocene-subphthalocyanine dyads.

Reaction between ferrocene lithium or ethynylferrocene magnesium bromide and (chloro)boronsubphthalocyanine leads to formation of ferrocene- (2) and ethynylferrocene- (3) containing subphthalocyanine dyads with a direct organometallic B-C bond. New donor-acceptor dyads were characterized using UV-vis and magnetic circular dichroism (MCD) spectroscopies, NMR method, and X-ray crystallography. Redox potentials of the rigid donor-acceptor dyads 2 and 3 were studied using the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches and compared to the parent subphthalocyanine 1 and conformationally flexible subphthalocyanine ferrocenenylmethoxide (4) and ferrocenyl carboxylate (5) dyads reported earlier. It was found that the first oxidation process in dyads 2 and 3 is ferrocene-centered, while the first reduction as well as the second oxidation are centered at the subphthalocyanine ligand. Density functional theory-polarized continuum model (DFT-PCM) and time-dependent (TD) DFT-PCM methods were used to probe the electronic structures and explain the UV-vis and MCD spectra of complexes 1-5. DFT-PCM calculations suggest that the LUMO, LUMO+1, and HOMO-3 in new dyads 2 and 3 are centered at the subphthalocyanine ligand, while the HOMO to HOMO-2 in both dyads are predominantly ferrocene-centered. TDDFT-PCM calculations on compounds 1-5 are indicative of the π → π* transitions dominance in their UV-vis spectra, which is consistent with the experimental data. The excited state dynamics of the parent subphthalocyanine 1 and dyads 2-5 were investigated using time-resolved transient spectroscopy. In the dyads 2-5, the initially excited state is rapidly (<2 ps) quenched by electron transfer from the ferrocene ligand. The lifetime of the charge transfer state demonstrates a systematic dependence on the structure of the bridge between the subphthalocyanine and ferrocene.

Imprecision of high-sensitivity cardiac troponin assays at the female 99th-percentile.

BACKGROUND: An analytical benchmark for high-sensitivity cardiac troponin (hs-cTn) assays is to achieve a coefficient of variation (CV) of ≤ 10.0 % at the 99th percentile upper reference limit (URL) used for the diagnosis of myocardial infarction. Few prospective multicenter studies have evaluated assay imprecision and none have determined precision at the female URL which is lower than the male URL for all cardiac troponin assays. METHODS: Human serum and plasma matrix samples were constructed to yield hs-cTn concentrations near the female URLs for the Abbott, Beckman, Roche, and Siemens hs-cTn assays. These materials were sent (on dry ice) to 35 Canadian hospital laboratories (n = 64 instruments evaluated) participating in a larger clinical trial, with instructions for storage, handling, and monthly testing over one year. The mean concentration, standard deviation, and CV for each instrument type and an overall pooled CV for each manufacturer were calculated. RESULTS: The CVs for all individual instruments and overall were ≤ 10.0 % for two manufacturers (Abbott CVpooled = 6.3 % and Beckman CVpooled = 7.0 %). One of four Siemens Atellica instruments yielded a CV > 10.0 % (CVpooled = 7.7 %), whereas 15 of 41 Roche instruments yielded CVs > 10.0 % at the female URL of 9 ng/L used worldwide (6 cobas e411, 1 cobas e601, 4 cobas e602, and 4 cobas e801) (CVpooled = 11.7 %). Four Roche instruments also yielded CVs > 10.0 % near the female URL of 14 ng/L used in the United States (CVpooled = 8.5 %). CONCLUSIONS: The number of instruments achieving a CV ≤ 10.0 % at the female 99th-percentile URL varies by manufacturer and by instrument. Monitoring assay precision at the female URL is necessary for some assays to ensure optimal use of this threshold in clinical practice.

Communication: Trapping upconverted energy in neat platinum porphyrin films via an unexpected fusion mechanism.

Direct observation of an unexpected product from excited state fusion of two excited triplet states in platinum octaethylporphyrin is reported. Transient spectroscopy was used to identify the product as a metal centered (d, d) state that decays slowly compared with the rate of fusion. The reaction was demonstrated to be second order with a rate coefficient of k(TTF) = (5.4 ± 0.4) × 10(-10) cm(3) · s(-1). The results contrast with the common assumption that fusion proceeds directly to annihilation via rapid non-radiative deactivation of the products. Following visible photo-excitation, the fusion process results in energetic upconversion of the incident photons stored in the higher energy (d, d) state at irradiances below the threshold for multi-photon absorption.

Photochemical modulation of Ras-mediated signal transduction using caged farnesyltransferase inhibitors: activation by one- and two-photon excitation.

The creation of caged molecules involves the attachment of protecting groups to biologically active compounds such as ligands, substrates and drugs that can be removed under specific conditions. Photoremovable caging groups are the most common due to their ability to be removed with high spatial and temporal resolution. Here, the synthesis and photochemistry of a caged inhibitor of protein farnesyltransferase is described. The inhibitor, FTI, was caged by alkylation of a critical thiol group with a bromohydroxycoumarin (Bhc) moiety. While Bhc is well established as a protecting group for carboxylates and phosphates, it has not been extensively used to cage sulfhydryl groups. The resulting caged molecule, Bhc-FTI, can be photolyzed with UV light to release the inhibitor that prevents Ras farnesylation, Ras membrane localization and downstream signaling. Finally, it is shown that Bhc-FTI can be uncaged by two-photon excitation to produce FTI at levels sufficient to inhibit Ras localization and alter cell morphology. Given the widespread involvement of Ras proteins in signal transduction pathways, this caged inhibitor should be useful in a plethora of studies.

Photodetachment and electron reactivity in 1-methyl-1-butyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide.

The transient absorption spectrum in the range 500 nm-1000 nm was measured with ultrafast time resolution on a flowing neat, aliphatic, room-temperature ionic liquid following anion photodetachment. In this region the spectrum was shown to be a combination of absorption from the electron and the hole. Spectrally-resolved electron quenching determined a bimodal shape for the hole spectrum in agreement with recent computational predictions on a smaller aliphatic ionic liquid [Margulis et al., J. Am. Chem. Soc. 133, 20186 (2011)]. For time delays beyond 15 ps, spectral evolution qualitatively agrees with recent radiolysis experiments [Wishart et al., Faraday Discuss. 154, 353 (2012)]. However, the shape of the spectrum is different, reflecting the contrast in ionization energy between the two methods. Previously unobserved reactivity of the electron was found with a time constant of 300 fs. The results demonstrate solvent control of the rate coefficient for reaction between the electron and proton, with a rapid decline in the rate within the first picosecond.