Correlating Sensory Assessment of Smoke-Tainted Wines with Inter-Laboratory Study Consensus Values for Volatile Phenols.

Vineyard exposure to wildfire smoke can taint grapes and wine. To understand the impact of this taint, it is imperative that the analytical methods used are accurate and precise. This study compared the variance across nine commercial and research laboratories following quantitative analysis of the same set of smoke-tainted wines. In parallel, correlations between the interlaboratory consensus values for smoke-taint markers and sensory analyses of the same smoke-tainted wines were evaluated. For free guaiacol, the mean accuracy was 94 ± 11% in model wine, while the free cresols and 4-methylguaiacol showed a negative bias and/or decreased precision relative to guaiacol. Similar trends were observed in smoke-tainted wines, with the cresols and glycosidically bound markers demonstrating high variance. Collectively, the interlaboratory results show that data from a single laboratory can be used quantitatively to understand smoke-taint. Results from different laboratories, however, should not be directly compared due to the high variance between study participants. Correlations between consensus compositional data and sensory evaluations suggest the risk of perceivable smoke-taint can be predicted from free cresol concentrations, overcoming limitations associated with the occurrence of some volatile phenols, guaiacol in particular, as natural constituents of some grape cultivars and of the oak used for barrel maturation.

Development and Interlaboratory Evaluation of an LC-MS/MS Method for the Quantification of Lysozyme in Wine Across Independent Instrument Platforms.

BACKGROUND: Various processing aids and fining agents are used in winemaking to help improve sensory characteristics. Some of these materials may contain or be derived from allergenic foods, such as eggs. In order to ensure food safety and that products meet regulatory compliance, it is essential to have robust and effective analytical methods to verify the removal of allergenic proteins following their use. Current methods include ELISA and MS methods, which can target either whole foods or individual proteins, and provide either quantitative data or qualitative confirmation of proteins. MS methods offer the potential to test for multiple proteins within a single assay to improve cost and efficiency, whereas ELISA methods typically analyze for a single protein per assay. OBJECTIVE: This study focuses on the development of a LC-tandem MS (MS/MS) quantitative method for lysozyme in white wine and compares performance across two laboratories utilizing two different instrument platforms. METHODS: Lysozyme target peptides were selected by conducting bottom-up discovery proteomics. Candidate targets were evaluated using parallel reaction monitoring (PRM) or selected reaction monitoring (SRM) LC-MS/MS, depending on the instrument in each laboratory. Quantification of lysozyme was conducted using internal, stable isotope-labeled synthetic peptide standards. RESULTS: Three of eight candidate target peptides showed performance suitable for the final quantitative method. White wine spiked with 0.1 and 0.5 ppm lysozyme demonstrated quantitative recovery of 70-120%. While the PRM method delivered better repeatability, the SRM method gave higher quantitative recovery values. CONCLUSION: A targeted LC-MS/MS method for quantification of lysozyme in white wine has been developed and deployed on two different MS instrument platforms in two laboratories. HIGHLIGHTS: Both SRM and PRM targeted LC-MS/MS methodologies can be used for quantification of lysozyme in white wine. This study is among the first to evaluate an MS method for food allergen quantification in multiple laboratories.

Coupling carbon dioxide reduction with water oxidation in nanoscale photocatalytic assemblies.

The reduction of carbon dioxide by water with sunlight in an artificial system offers an opportunity for utilizing non-arable land for generating renewable transportation fuels to replace fossil resources. Because of the very large scale required for the impact on fuel consumption, the scalability of artificial photosystems is of key importance. Closing the photosynthetic cycle of carbon dioxide reduction and water oxidation on the nanoscale addresses major barriers for scalability as well as high efficiency, such as resistance losses inherent to ion transport over macroscale distances, loss of charge and other efficiency degrading processes, or excessive need for the balance of system components, to mention a few. For the conversion of carbon dioxide to six-electron or even more highly reduced liquid fuel products, introduction of a proton conducting, gas impermeable separation membrane is critical. This article reviews recent progress in the development of light absorber-catalyst assemblies for the reduction and oxidation half reactions with focus on well defined polynuclear structures, and on novel approaches for optimizing electron transfer among the molecular or nanoparticulate components. Studies by time-resolved optical and infrared spectroscopy for the understanding of charge transfer processes between the chromophore and the catalyst, and of the mechanism of water oxidation at metal oxide nanocatalysts through direct observation of surface reaction intermediates are discussed. All-inorganic polynuclear units for reducing carbon dioxide by water at the nanoscale are introduced, and progress towards core-shell nanotube assemblies for completing the photosynthetic cycle under membrane separation is described.

Investigating the effects of solvent on the ultrafast dynamics of a photoreversible ruthenium sulfoxide complex.

The photochromic complex [Ru(bpy)2(pySO)](2+) [pySO is 2-(isopropylsulfinylmethyl)pyridine] undergoes wavelength specific, photoreversible S → O and O → S linkage isomerizations. Irradiation of the ground state S-bonded complex with blue light produces the O-bonded isomer, while irradiation of the O-bonded isomer with green light produces the S-bonded isomer. Furthermore, isomerization time constants are solvent-dependent. Ultrafast transient absorption spectroscopy has been employed to investigate the relaxation processes that lead to S → O isomerization in 1,2-dichloroethane, propylene carbonate, and ethylene glycol. The isomerization is most rapid in 1,2-dichloroethane and slowest in ethylene glycol. Photochemical reversion of the O-bonded isomer in propylene carbonate has further been investigated and indicates similar relaxation or isomerization kinetics, though the excited states that lead to isomerization are distinct between the S- and O-bonded isomers.

Light induced carbon dioxide reduction by water at binuclear ZrOCo(II) unit coupled to Ir oxide nanocluster catalyst.

An all-inorganic polynuclear unit consisting of an oxo-bridged binuclear ZrOCo(II) group coupled to an iridium oxide nanocluster (IrO(x)) was assembled on an SBA-15 silica mesopore surface. A photodeposition method was developed that affords coupling of the IrO(x) water oxidation catalyst with the Co donor center. The approach consists of excitation of the ZrOCo(II) metal-to-metal charge-transfer (MMCT) chromophore with visible light in the presence of [Ir(acac)3] (acac: acetylacetonate) precursor followed by calcination under mild conditions, with each step monitored by optical and infrared spectroscopy. Illumination of the MMCT chromophore of the resulting ZrOCo(II)-IrO(x) units in the SBA-15 pores loaded with a mixture of (13)CO2 and H2O vapor resulted in the formation of (13)CO and O2 monitored by FT-IR and mass spectroscopy, respectively. Use of (18)O labeled water resulted in the formation of (18)O2 product. This is the first example of a closed photosynthetic cycle of carbon dioxide reduction by water using an all-inorganic polynuclear cluster featuring a molecularly defined light absorber. The observed activity implies successful competition of electron transfer between the IrO(x) catalyst cluster and the transient oxidized Co donor center with back electron transfer of the ZrOCo light absorber, and is further aided by the instant desorption of the CO and O2 product from the silica pores.

Ultrafast spectroscopy of a photochromic ruthenium sulfoxide complex.

Photochromic [Ru(bpy)(2)(OSO)](PF(6)), where bpy is 2,2'-bipyridine and OSO is 2-methylsulfinylbenzoate, was investigated by femtosecond transient absorption spectroscopy. The results show that for both S- and O-bonded isomers, a (3)MLCT state is formed on a femtosecond time scale. Also observed is the formation of multiple metal-to-ligand charge-transfer (MLCT) states, representing different conformers, prior to isomerization on the picosecond time scale. These results and others are compiled in an energy diagram depicting these results.

Solvent effects on isomerization in a ruthenium sulfoxide complex.

We report the structure, electrochemistry, and isomerization kinetics for [Ru(bpy)(biq)(OSO)](PF(6)), where bpy is 2,2'-bipyridine, biq is 2,2'-biquinoline, and OSO is 2-methylsulfinylbenzoate. UV-visible and infrared data are suggestive of intramolecular S-->O and O-->S isomerization of the sulfoxide. Cyclic voltammetry reveals evidence for isomerization triggered by oxidation and reduction. Of particular note is the variation of the S-->O isomerization rate constant in different solvents. The rates were found to be 3.2 (+/-0.4) s(-1) in propylene carbonate, 0.80 (+/-0.03) s(-1) in acetonitrile, and 0.26 (+/-0.01) s(-1) in dichloromethane.

Excited state distortion in photochromic ruthenium sulfoxide complexes.

A series of photochromic ruthenium sulfoxide complexes of the form [Ru(bpy)(2)(OSOR)](+), where bpy is 2,2'-bipyridine and OSOR is 2-(benzylsulfinyl)benzoate (OSOBn), 2-(napthalen-2-yl-methylsulfinyl)-benzoate (OSONap), or 2-(pentafluorophenylmethanesulfinyl)benzoate (OSOBnF(5)), have been synthesized and characterized. In aggregate, the data are consistent with phototriggered isomerization of the sulfoxide from S-bonded to O-bonded. The S-bonded complexes feature (3)MLCT absorption maxima at 388 nm (R = BnF(5)), 396 nm (R = Bn), and 400 nm (R = Nap). Upon charge transfer excitation the S-bonded peak diminishes concomitant with new peaks growing in at approximately 350 and approximately 495 nm. Spectroscopic and electrochemical data suggest that the electronic character of the substituent on the sulfur affects the properties of the S-bonded complexes, but not the O-bonded complexes. The isomerization is reversible in methanol solutions and, in the absence of light, thermally reverts to the S-bonded isomer with biexponential kinetics. The quantum yields of isomerization (Phi(s-->o)) were found to be 0.32, 0.22, and 0.16 for the R = BnF(5), Bn, and Nap complexes, respectively. Kinetic analyses of femtosecond transient absorption data were consistent with a nonadiabatic mechanism in which isomerization occurs from a thermally relaxed (3)MLCT state of S-bonded (or eta(2)-sulfoxide) character directly to the singlet O-bonded ground state. The time constants of isomerization (tau(s-->o)) were found to be 84, 291, and 427 ps for the R = BnF(5), Bn, and Nap complexes, respectively. Analysis of room temperature absorption and 77 K emission spectra reveal significant distortion between the S-bonded ground state ((1)GS(S)) and singlet metal-to-ligand charge transfer state ((1)MLCT(S)) and thermally relaxed (3)MLCT, respectively. The distortion is primarily attributed to low frequency metal-ligand and S horizontal lineO vibrational modes, which are intrinsically involved in the isomerization pathway.

Photochromic ruthenium sulfoxide complexes: evidence for isomerization through a conical intersection.

The complexes [Ru(bpy)(2)(OS)](PF(6)) and [Ru(bpy)(2)(OSO)](PF(6)), where bpy is 2,2'-bipyridine, OS is 2-methylthiobenzoate, and OSO is 2-methylsulfinylbenzoate, have been studied. The electrochemical and photochemical reactivity of [Ru(bpy)(2)(OSO)](+) is consistent with an isomerization of the bound sulfoxide from S-bonded (S-) to O-bonded (O-) following irradiation or electrochemical oxidation. Charge transfer excitation of [Ru(bpy)(2)(OSO)](+) in MeOH results in the appearance of two new metal-to-ligand charge transfer (MLCT) maxima at 355 and 496 nm, while the peak at 396 nm diminishes in intensity. The isomerization is reversible at room temperature in alcohol or propylene carbonate solution. In the absence of light, solutions of O-[Ru(bpy)(2)(OSO)](+) revert to S-[Ru(bpy)(2)(OSO)](+). Kinetic analysis reveals a biexponential decay with rate constants of 5.66(3) x 10(-4) s(-1) and 3.1(1) x 10(-5) s(-1). Cyclic voltammograms of S-[Ru(bpy)(2)(OSO)](+) are consistent with electron-transfer-triggered isomerization of the sulfoxide. Analysis of these voltammograms reveal E(S)(o)' = 0.86 V and E(O)(o)' = 0.49 V versus Ag/Ag(+) for the S- and O-bonded Ru(3+/2+) couples, respectively, in propylene carbonate. We found k(S-->O) = 0.090(15) s(-1) in propylene carbonate and k(S-->O) = 0.11(3) s(-1) in acetonitrile on Ru(III), which is considerably slower than has been reported for other sulfoxide isomerizations on ruthenium polypyridyl complexes following oxidation. The photoisomerization quantum yield (Phi(S-->O) = 0.45, methanol) is quite large, indicating a rapid excited state isomerization rate constant. The kinetic trace at 500 nm is monoexponential with tau = 150 ps, which is assigned to the excited S-->O isomerization rate. There is no spectroscopic or kinetic evidence for an O-bonded (3)MLCT excited state in the spectral evolution of S-[Ru(bpy)(2)(OSO)](+) to O-[Ru(bpy)(2)(OSO)](+). Thus, isomerization occurs nonadiabatically from an S-bonded (or eta(2)-sulfoxide) (3)MLCT excited state to an O-bonded ground state. Density functional theory calculations support the assigned spectroscopy and provide insight into ruthenium ligand bonding.

Quenching mechanism of Zn(salicylaldimine) by nitroaromatics.

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL(R) was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL(R) ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL(R) with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL(R) with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 --> ZnL(+) + ArNO2(-). A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (lambda = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL(+) (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL --> ZnL(+) oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL(R) as sensors, as well as for potential photoinduced charge transfer chemistry.