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The first selective functionalization of O-allyl-tyrosine genetically encoded in a Z-domain protein is described by using a photoactivated, nitrile imine mediated 1,3-dipolar cycloaddition reaction (photoclick chemistry) in Escherichia coli. Fluorescent cycloadducts are formed, which have enabled a facile monitoring of the reaction in vivo.

The reactivity and functionality of nanoparticles (NPs) are determined by the material- and size-dependent physicochemical properties at nanoscale. While single-type metallic NPs have been extensively studied for many potential applications, combination of multitype NPs and the interactions among them have received less attention. Here, an interesting synergistic effect between silver and palladium NPs is presented for using them together as lubricant additives. Dodecanethiol-modified Ag and Pd NPs were discovered to interact actively in a solution, changing their sizes, shapes, and electronic structures. A mixture of these two NPs was able to form a stable suspension in a lubricating oil and effectively improve tribological performance in the concentration range of 0.1-1 wt %. The Ag-Pd NP blend further reduced the friction and wear by >30% and >80%, respectively, compared with either NP alone at the same total NP concentration. The NPs and worn surfaces were characterized using a set of comprehensive analytical tools and the superior lubricating behavior was attributed to the formation of two types of protective tribofilms on the contact surfaces. [ABSTRACT FROM AUTHOR]

Low-dose corticosteroids may provide a favorable benefit/risk ratio for many therapeutic applications. However, the extremely low plasma drug concentrations achieved, in conjunction with the insufficient sensitivity/selectivity of current analytical methods, renders the evaluation of corticosteroid pharmacokinetics (PK) a significant challenge under such conditions. Furthermore, targeted therapeutic strategies involving administration by inhalation or intraocular injection could result in very low but sustained systemic corticosteroid concentrations, which must be quantified to determine potential side effects. Here we describe a robust method for the ultrasensitive quantification of corticosteroids in plasma samples. This was achieved by the combination of a selective solid-phase extraction (SPE) with a highly sensitive capillary LC (μLC)-MS/MS analysis. SPE washing and elution conditions were optimized so that target drugs are selectively extracted from plasma. By eliminating most undesirable compounds from the sample matrix, this selective SPE procedure enabled a high sample loading volume on the μLC column without compromising chromatographic performance and operational robusmess and helped to achieve ultralow detection limits for the corticosteroids in plasma. The effect of μLC separation on the signal-to-noise ratio of corticosteroid peaks in plasma samples was investigated. It was found that with sufficient μLC separation, sensitivity was improved because of a decrease in matrix effects and the removal of endogenous interferences. Detection limits of four clinically important corticosteroids (budesonide, dexamethasone, triamcinolone acetonide, and dexamethasone acetate) ranged from 0.2 to 1 pg/mL in plasma, and linearity was good for all drugs in the range of 5-5000 pg/mL. Accuracy was 88-107% and the variation (CV%) was 2.3-11.1%. A limit of quantification (LOQ) of 5 pg/mL was validated for all four compounds. We applied this method to quantify the low levels of triamcinolone acetonide (TACA) in porcine plasma following suprachoroidal administration, which is necessary to estimate systemic drug exposure resulting from this novel clinical approach for treating inflammatory diseases of the eye. TACA in plasma could be quantified at low pg/mL levels for up to 90 days posttreatment. To our knowledge, this is the first practical analytical approach that can monitor plasma corticosteroids after intraocular administration, given the ultralow plasma concentrations achieved. In summary, this strategy enables PK analysis of corticosteroids in treatment regimens that result in extremely low systemic concentrations, and the approach can be extended for the sensitive quantification of other drugs. [ABSTRACT FROM AUTHOR]

Gene expression changes underlie important biological and pharmacological responses. Although mRNA expression profiling is routine, quantification of low-abundance proteins, which typically represent key effectors of responses, remains challenging. A novel strategy was developed for sensitive and accurate quantification of low-abundance proteins in highly complex biological matrixes. First, the cysteine specificity of cleavable isotope-coded affinity tags (cICAT) was employed to reduce the complexity of the digested proteome of tissue homogenates and to improve the quantification of low-abundance proteins. Second, cICAT-treated tissue samples were analyzed on a capillary LC coupled to an ion trap MS to screen for the subset of cICAT-peptides, derived from target proteins of interest, that was successfully labeled and retrieved. Third, putatively identified peptides derived from target proteins were synthesized, cICAT-labeled, and used both to optimize multiple reactions monitoring (MRM) analysis and to confirm chromatographic retention time and fragmentation pattern. Finally, batch quantification of target peptides was performed using MRM on a LC/triple-quad MS/MS using 12C- (control) and 13C (experimental)- cICAT-labeled tissue mixtures. The utility of this method was demonstrated by elucidating the time-course of tyrosine aminotransferase induction in the liver of rats following treatment with the corticosteroid methylprednisolone (MPL). This approach significantly improved quantitative sensitivity, and the linear range was 10-fold greater than published previously. An additional advantage is that archived samples may be reinterrogated to investigate the regulation of additional targets that become of interest. Stored samples were sucessfully reinterrogated to monitor the induction of ornithine decarboxylase, which is also an MPL-induced protein. To our knowledge, this is the first report of an ICAT-based method that is capable of quantifying low-abundance proteins in highly complex samples, such as tissue homogenates. The approach enables simultaneous quantification of multiple effector proteins induced by biological or pharmacological stimuli, and the processed samples can be interrogated repeatedly as additional targets of interest arise. [ABSTRACT FROM AUTHOR]

A rapid, selective, and reliable strategy has been developed for the screening and identification of glycosides in biological samples: a crude extract was directly infused to a triple-quadrupole MS/MS and major glycosides were screened out with high confidence by an energy- gradient neutral loss scan (EGNLS) for the loss of sugar- (s); then these glycosides were further identified with LC/MS/MS. The proposed EGNLS method was established and optimized with 16 representative glycosides (including ginsenosides and the glycosides of flavones, anthraquinones, and terpenoids). The EGNLS method has two major advantages over the conventional fixed-energy neutral loss scan: (1) The latter is liable to "omit" some target compounds due to the usual mismatch between the preset collision energy and interested compounds' optimal collision energy (OCE), while EGNLS solves this problem by scanning over an energy range. (2) The EGNLS simultaneously measures the screened compounds' OCE, which not only are essential parameters for further LC/M S/MS analysis but also carry some structural information, as proved by this study. This strategy has been successfully demonstrated with the analysis of glycosides in Scutellaria viscidula Bge and transformed Panax hairy roots (the glycoside constitutions of both had not been studied before): without laborious separation processes; comprehensive glyco side information on those two plants was obtained by a rapid and simple procedure. This strategy is valuable for the study of glycosides in complex samples. [ABSTRACT FROM AUTHOR]

Examines the validated quantitation of underivatized amino acids in human blood samples. Development of volatile ion-pair reversed-phase liquid chromatography with isotope dilution tandem mass spectrometry; Dissociation spectra of amino acids; Analogous compounds of complex matrixes.