Further mechanistic information on the reaction between FeIII(edta) and hydrogen peroxide: observation of a second reaction step and importance of pH

A detailed study of the effect of buffer, temperature, and pressure on the reaction of hydrogen peroxide with [Fe(III)(edta)H(2)O](-) was performed using stopped-flow techniques. The reaction was found to consist of two steps and resulted in the formation of the already characterized high-spin Fe(III) side-on bound peroxo complex. The second step of the reaction was found to be independent of the hydrogen peroxide concentration. Formation of the purple peroxo complex is only observable above pH 7.5. Both reaction steps are affected by specific and general acid-catalysis. Five different buffer systems were used to clarify the role of general acid-catalysis in these reactions. Both reaction steps reveal an element of reversibility, which disappears on decreasing the acid concentration. The positive volumes of activation for both the forward and reverse reactions of the first step suggest a dissociative interchange substitution process for the reversible end-on binding of hydrogen peroxide to [Fe(III)(edta)H(2)O](-). The small negative volume of activation for the second reaction step suggests an associative interchange mechanism for the formation of the side-on bound peroxo complex that is accompanied by dissociation of one of the four carboxylates of edta. A detailed mechanism in agreement with all the reported kinetic data is presented.     

Simple spectrophotocolorimetric method for quantitative determination of gold in nanoparticles

A simple spectrophotocolorimetric method devoted to the measurement of gold content in nanoparticles (NPs) was developed. It includes two steps: (i) metal gold NPs (Au NPs) are oxidized into the AuCl₄⁻ anion using a 5 × 10⁻² M HCl-1.5 × 10⁻² M NaCl-7 × 10⁻⁴ M Br₂ solution, next (ii) AuCl₄⁻ concentration is measured using a spectrophotometric assay based on the reaction of AuCl₄⁻ with the cationic form of Rhodamine B to give a violet ion pair complex. This latter is extracted with diisopropyl ether and the absorbance of the organic complex is measured at 565 nm. The method is linear in the range 6-29 μM of AuCl₄⁻ with a limit of detection of 4.5 μM.The analytical method was optimized with respect of bromine excess to obtain complete Au NPs oxidation. The method was applied to two types of Au NPs currently under investigation: citrate-stabilized Au NPs and Au NPs capped with dihydrolipoic acid (Au@DHLA). Both the gold content of Au NPs and the concentration of NPs (using NP diameter measured by transmission electron microscopy) have been calculated.     

A simple method to identify ether lipids in spermatozoa samples by MALDI-TOF mass spectrometry

Plasmalogens (alkenylacyl glycerophospholipids) are important lipid constituents of many tissues and cells (e.g., selected spermatozoa). Since the molecular weights of plasmalogens overlap with that of diacyl- or alkyl acyl lipids, sophisticated mass spectrometry (MS; including MS/MS) analysis is normally used for the unequivocal identification of plasmalogens. We will show here that a simple matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (without MS/MS capability) in combination with acidic hydrolysis and subsequent derivatization with 2,4-dinitrophenylhydrazine (DNPH) and/or digestion with phospholipase A₂ (PLA₂) is sufficient to determine the contributions of ether lipids in spermatozoa extracts. As neither diacyl nor alkylacyl lipids are sensitive to acids and do not react with DNPH, the comparison of the mass spectra before and after treatment with acids and/or DNPH addition readily provides unequivocal information about the plasmalogen content. Additionally, the released aldehydes are readily converted into the 2,4-dinitrophenylhydrazones and can be easily identified in the corresponding negative ion mass spectra. Finally, PLA₂ digestion is very useful in confirming the presence of plasmalogens. The suggested method was validated by analyzing roe deer, bovine, boar, and domestic cat spermatozoa extracts and comparing the results with isolated phospholipids.

Injection locking of mid‐infrared quantum cascade laser at 14 GHz,by direct microwave modulation

Compact laser sources operating in mid infrared spectral region with stable emission are important for applications in spectroscopy and wireless communication. Quantum cascade lasers (QCL) are unique semiconductor sources covering mid infrared frequency range. Based on intersubband transitions, the carrier lifetime of these sources is in the ps range. For this reason their frequency response to direct modulation is expected to overcome the limits of standard semiconductor lasers. In this work injection locking of the roundtrip frequency of a QCL emitting at 9 μm is reported. Inter modes laser frequency separation is stabilized and controlled by an external microwave source. Designing an optical waveguide embedded in a microstrip line a flat frequency response to direct modulation up to 14 GHz is presented. Injection locking over MHz frequency range at 13.7 GHz is demonstrated. Numerical solutions of injection locking theory are discussed and presented as tool to describe experimental results.     

Crosslinked Redox‐Responsive Micelles Based on Lipoic Acid‐Derived Amphiphiles for Enhanced siRNA Delivery

Successful application of gene silencing approaches critically depends on systems that are able to safely and efficiently deliver genetic material such as small interfering RNA (siRNA). Due to their beneficial well‐defined dendritic nanostructure, self‐assembling dendrimers are emerging as promising nanovectors for siRNA delivery. However, these kinds of vectors are plagued with stability issues, especially when considered for in vivo applications. Therefore, in the present study, disulfide‐based temporarily fixed micelles are developed that can degrade upon reductive conditions, and thus lead to efficient cargo release. In detail, lipoic acid‐derived crosslinked micelles are synthesized based on small polymerizable dendritic amphiphiles. Particularly, one candidate out of this series is able to efficiently release siRNA due to its redox‐responsive biodegradable profile when exposed to simulated intracellular environments. As a result, the reduction‐triggered disassembly leads to potent gene silencing. In contrast, noncrosslinkable, structurally related constructs fails under the tested assay conditions, thereby confirming the applied rational design approach and demonstrating its large potential for future in vivo applications.

     

ortho-Lithium/magnesium carboxylate-driven aromatic nucleophilic substitution reactions on unprotected naphthoic acids

Substitution of an ortho-fluoro or methoxy group in 1- and 2-naphthoic acids furnishing substituted naphthoic acids occurs in good to excellent yields upon reaction with alkyl/vinyl/aryl organolithium and Grignard reagents, in the absence of a metal catalyst without the need to protect the carboxyl (CO(2)H) group. This novel nucleophilic aromatic substitution is presumed to proceed via a precoordination of the organometallic with the substrate, followed by an addition/elimination.     

Ru(TAP)3]2+-photosensitized DNA cleavage studied by atomic force microscopy and gel electrophoresis: a comparative study

Topological modifications of plasmid DNA adsorbed on a variety of surfaces were investigated by using atomic force microscopy (AFM). On mica modified with 3-aminopropyltriethoxysilane (APS) or poly-L-lysine, the interaction between the plasmid DNA and the surface "freezes" the plasmid DNA conformation deposited from solution, and the AFM images resemble the projection of the three-dimensional conformation of the plasmid DNA in solution. Modified mica with low concentrations of Mg(2+) leads to a decrease in the interaction strength between plasmid DNA and the substrate, and the AFM images reflect the relaxed or equilibrium conformation of the adsorbed plasmid DNA. Under these optimized deposition conditions, topological modifications of plasmid DNA were produced under irradiation in the presence of [Ru(TAP)(3)](2+) (TAP = 1,4,5,8-tetraazaphenanthrene), which is a non-intercalating complex, and were followed as a function of illumination time. The observed structural changes correlate well with the conversion of the supercoiled covalently closed circular form (ccc form) into the open circular form (oc form), induced by a single-strand photocleavage. The AFM results obtained after fine-tuning of the plasmid DNA-substrate interaction compare well with those observed from gel electrophoresis, indicating that under the appropriate deposition conditions, AFM is a reliable technique to investigate irradiation-induced topological changes in plasmid DNA.     

LC-MS/MS analysis of Δ9-tetrahydrocannabinolic acid A in serum after protein precipitation using an in-house synthesized deuterated internal standard

An assay based on liquid chromatography/tandem mass spectrometry is presented for the fast, precise and sensitive quantitation of Δ9-tetrahydrocannabinolic acid A (THCA) in serum. THCA is the biogenetic precursor of Δ9-tetrahydrocannabinol in cannabis and has aroused interest in the pharmacological and forensic field especially as a potential marker for recent cannabis use. After addition of deuterated THCA, synthesized from D(3)-THC as starting material, and protein precipitation, the analytes were separated using gradient elution on a Luna C18 column (150 × 2.0 mm × 5 μm) with 0.1% formic acid and acetonitrile/0.1% formic acid. Data acquisition was performed on a triple quadrupole linear ion trap mass spectrometer in multiple reaction monitoring mode with negative electrospray ionization. After optimization, the following sample preparation procedure was used: 200 μL serum was spiked with internal standard solution and methanol and then precipitated 'in fractions' with 500 μL ice-cold acetonitrile. After storage and centrifugation, the supernatant was evaporated and the residue redissolved in mobile phase. The assay was fully validated according to international guidelines including, for the first time, the assessment of matrix effects and stability experiments. Limit of detection was 0.1 ng/mL, and limit of quantification was 1.0 ng/mL. The method was found to be selective and proved to be linear over a range of 1.0 to 100 ng/mL using a 1/x weighted calibration model with regression coefficients >0.9996. Accuracy and precision data were within the required limits (RSD ≤ 8.6%, bias: 2.4 to 11.4%), extractive yield was greater than 84%. The analytes were stable in serum samples after three freeze/thaw cycles and storage at -20 °C for one month.