Carbon nanotube-modified microelectrodes for simultaneous detection of dopamine and serotonin in vivo

Dopamine and serotonin are important neurotransmitters that interact in the brain. While dopamine is easily detected with electrochemical sensors, the detection of serotonin is more difficult because reactive species formed after oxidation can adsorb to the electrode, reducing sensitivity. Carbon nanotube treatments of electrodes have been used to increase the sensitivity, promote electron transfer, and reduce fouling. Most methods have focused on nanotube coatings of large electrodes and slower electrochemical techniques that are not conducive to measurements in vivo. In this study, we investigated carbon-fiber microelectrodes modified with single-walled carbon nanotubes for the co-detection of dopamine and serotonin in vivo. Using fast-scan cyclic voltammetry, S/N ratios for the neurotransmitters increased after nanotube coating. Electrocatalytic effects of nanotubes were not apparent at fast scan rates but faster kinetics were observed with slower scanning. Nanotube-modified microelectrodes showed significantly less fouling after exposure to serotonin than bare electrodes. The nanotube-modified electrodes were used to monitor stimulated dopamine and serotonin changes simultaneously in the striatum of anesthetized rat after administration of a serotonin synthetic precursor. These studies show that nanotube-coated microelectrodes can be used with fast scanning techniques and are advantageous for in vivo measurements of neurotransmitters because of their greater sensitivity and resistance to fouling.     

An electrochemiluminescence-based competitive displacement immunoassay for the type-2 brevetoxins in oyster extracts

A new competitive electrochemiluminescence-based immunoassay for the type-2 brevetoxins in oyster extracts was developed. The assay was verified by spiking known amounts of PbTx-3 into 80% methanol extracts of Gulf Coast oysters. We also provide preliminary data demonstrating that 100% acetone extracts, aqueous homogenates, and the clinical matrixes urine and serum can also be analyzed without significant matrix interferences. The assay offers the advantages of speed ( 2 h analysis time); simplicity (only 2 additions, one incubation period, and no wash steps before analysis); low limit of quantitation (conservatively, 50 pg/mL = 1 ng/g tissue equivalents); and a stable, nonradioactive label. Due to the variety of brevetoxin metabolites present and the lack of certified reference standards for liquid chromatography-mass spectrometry confirmation, a true validation of brevetoxins in shellfish extracts is not possible at this time. However, our assay correlated well with another brevetoxin immunoassay currently in use in the United States. We believe this assay could be useful as a regulatory screening tool and could support pharmacokinetic studies in animals and clinical evaluation of neurotoxic shellfish poisoning victims.     

Rapid and simultaneous determination of capecitabine and its metabolites in mouse plasma, mouse serum, and in rabbit bile by high-performance liquid chromatography

A rapid high-performance liquid chromatography method has been developed for simultaneous determination of capecitabine and its metabolites: 5'-deoxy-5-fluorocytidine (5'-DFCR), 5'-deoxy-5-fluorouridine (5'-DFUR) and 5-fluorouracil (5-FU). 5'-DFCR was synthesized by hydrolyzing capecitabine using commercially available carboxyl esterase (CES) and characterized by NMR, mass spectrometry and elemental analysis. Base-line separations between capecitabine, 5'-DFCR, 5'-DFUR and 5-FU were found with symmetrical peak shapes on a Discovery RP-amide C16 column using 10 mM ammonium acetate at pH 4.0 and methanol as the mobile phase. The retention times of capecitabine, 5'-DFCR, 5'-DFUR and 5-FU were 8.9, 5.0, 5.3 and 3.0 min, respectively. Linear calibration curves were obtained for each compound across a range from 1 to 500 microg ml(-1). The intra- and inter-day relative standard deviations (%RSD) were <5%. A single-step protein precipitation method was employed for separation of the analytes from bio-matrices. Greater than 85% recoveries were obtained for capecitabine, 5'-DFCR, 5'-DFUR and 5-FU from bio-fluids including mouse plasma, mouse serum and rabbit bile.     

Chemistry of 4-alkylaryloxenium ion "precursors": sound and fury signifying something?

Quinol esters 2b, 2c, and 3b and sulfonamide 4c were investigated as possible precursors to 4-alkylaryloxenium ions, reactive intermediates that have not been previously detected. These compounds exhibit a variety of interesting reactions, but with one possible exception, they do not generate oxenium ions. The 4-isopropyl ester 2b predominantly undergoes ordinary acid- and base-catalyzed ester hydrolysis. The 4-tert-butyl ester 2c decomposes under both acidic and neutral conditions to generate tert-butanol and 1-acetyl-1,4-hydroquinone, 8, apparently by an SN1 mechanism. This is also a minor decomposition pathway for 2b, but the mechanism in that case is not likely to be SN1. Decomposition of 2c in the presence of N3- leads to formation of the explosive 2,3,5,6-tetraazido-1,4-benzoquinone, 14, produced by N3--induced hydrolysis of 8, followed by a series of oxidations and nucleophilic additions by N3-. No products suggestive of N3--trapping of an oxenium ion were detected. The 4-isopropyl dichloroacetic acid ester 3b reacts with N3- to generate the two adducts 2-azido-4-isopropylphenol, 5b, and 3-azido-4-isopropylphenol, 11b. Although 5b is the expected product of N3- trapping of the oxenium ion, kinetic analysis shows that it is produced by a kinetically bimolecular reaction of N3- with 3b. No oxenium ion is involved. The sulfonamide 4c predominantly undergoes a rearrangement reaction under acidic and neutral conditions, but a minor component of the reaction yields 4-tert-butylcresol, 17, and 2-azido-4-tert-butylphenol, 5c, in the presence of N3-. These products may indicate that 4c generates the oxenium ion 1c, but they are generated in very low yields (ca. 10%) so it is not possible to definitively conclude that 1c has been produced. If 1c has been generated, the N3--trapping data indicate that it is a very short-lived and reactive species in H2O. Comparisons with similarly reactive nitrenium ions indicate that the lifetime of 1c is ca. 20-200 ps if it is generated, so it must react by a preassociation process. Density functional theory calculations at the B3LYP/6-31G*//HF/6-31G* level coupled with kinetic correlations also indicate that the aqueous solution lifetimes of 1a-c are in the picosecond range.     

Highly Selective Targeting of Ovarian Cancer with the Photosensitizer PEG-m-THPC in a Rat Model

Photodynamic therapy (PDT) uses light to activate a photosensitizer that has been absorbed or retained preferentially by cancer cells after systemic administration. The first pegylated photosensitizer, tetrakis-(m-methoxypolyethylene glycol) derivative of 7,8-dihydro-5,10,15,20-tetrakis(3-hydroxyphenyl)-21,23-[H]-porphyrin (PEG-m-THPC), was evaluated to target selectively unresectable pelvic ovarian cancer bulks. Our goals were two-fold: (1) to establish an ovarian cancer model suitable for the development of debulking techniques and (2) to characterize the pharmacokinetics and tumor selectivity of PEG-m-THPC by fluorescence microscopy. NuTu-19 ovarian cancer cells were injected into the caudal part of the right psoas muscle of Fisher rats. Five weeks later, 30 mg/kg body weight of PEG-m-THPC was injected intravenously. Necropsy was performed between 4 and 10 days following drug application, and fluorescence of the tumor and various abdominal organs was measured. All rats developed bulky pelvic tumors with an average diameter of 2.6 cm (+/- 0.6 SD). Tumor masses were encompassing and infiltrating pelvic organs in a similar manner to ovarian cancers in humans. Fluorescence of cancer tissue was maximal 8-10 days following drug application. At 8 days, the tumor-to-tissue ratio was 40:1 (+/- 12 SE) for most abdominal organs. We conclude that this tumor model may be used for the study of new pelvic debulking techniques, and that the tumor selectivity of PEG-m-THPC is exceptionally high 8 days after drug application. Based on these data, we are currently developing a PDT-based minimally invasive debulking technique for advanced ovarian cancer.     

Bond dissociations in hypervalent ammonium radicals prepared by collisional neutralization of protonated six-membered nitrogen heterocycles

Hypervalent organic ammonium radicals were generated by collisional neutralization with dimethyl disulfide of protonated 1,4-diazabicyclo[2.2.2]octane (1H⁺), N,N′-dimethylpiperazine (2H⁺) and N-methylpiperazine (3H⁺). The radicals dissociated completely on the 5.1 μs time-scale. Radical 1H^• underwent competitive N−H and N−C bond dissociations producing 1,4-diazabicyclo[2.2.2]octane and small ring fragments. Dissociations of radical 2H^• proceeded by N−H bond dissociation and ring cleavage, whereas N−CH₃ bond cleavage was less frequent. Radical 3H^• underwent N−H, N−CH₃ and N−C_ring bond cleavages followed by post-reionization dissociations of the formed cations. The pattern of bond dissociations in the hypervalent ammonium radicals derived from six-membered nitrogen heterocycles is similar to those of aliphatic ammonium radicals. © 1997 John Wiley & Sons, Ltd.     

Lamb wave detection of limpet mines on ship hulls

This paper describes the use of ultrasonic guided waves for identifying the mass loading due to underwater limpet mines on ship hulls. The Dynamic Wavelet Fingerprint Technique (DFWT) is used to render the guided wave mode information in two-dimensional binary images because the waveform features of interest are too subtle to identify in time domain. The use of wavelets allows both time and scale features from the original signals to be retained, and image processing can be used to automatically extract features that correspond to the arrival times of the guided wave modes. For further understanding of how the guided wave modes propagate through the real structures, a parallel processing, 3D elastic wave simulation is developed using the finite integration technique (EFIT). This full field, technique models situations that are too complex for analytical solutions, such as built up 3D structures. The simulations have produced informative visualizations of the guided wave modes in the structures as well as mimicking directly the output from sensors placed in the simulation space for direct comparison to experiments. Results from both drydock and in-water experiments with dummy mines are also shown.     

Low-pressure pyrolysis of tBu2SO: synthesis and IR spectroscopic detection of HSOH

Sulfenic acid (HSOH, 1 ) has been synthesized in the gas‐phase by low‐pressure high‐temperature (1150 °C) pyrolysis of di‐tert‐butyl sulfoxide (tBu₂SO, 2 ) and characterized by means of matrix isolation and gas‐phase IR spectroscopy. High‐level coupled‐cluster (CC) calculations (CCSD(T)/cc‐pVTZ and CCSD(T)/cc‐pVQZ) support the first identification of the gas‐phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix‐isolated 1 have been assigned, and its rotational‐resolved gas‐phase IR spectrum provides additional information on the O–H and S–H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gas‐phase FT‐IR spectroscopy reveal that, up to 500 °C, 2 decomposes selectively into tert‐butylsulfenic acid, (tBuSOH, 3 ), and 2‐methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3 a ) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas‐phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6‐311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3 , monitored by matrix IR spectroscopy, yields short‐lived 1 along with 2‐methylpropene, but also H₂O, and most probably sulfur atoms. In addition, HSSOH ( 6 ), H₂, and S₂O are found among the final pyrolysis products observed at 1150 °C in the gas phase owing to competing intra‐ and intermolecular decomposition routes of 3 . The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6‐311G* and second‐order Møller–Plesset (MP2/6‐311G* and RI‐MP2/QZVPP) levels of theory.     

Separation of tricomponent protein mixtures with triblock nanorods

Two-component triblock magnetic nanorods with gold end blocks and nickel interior blocks have been synthesized and used as affinity templates for the simultaneous and efficient separation of a three-component protein mixture. The gold blocks were selectively functionalized with 11-amino-1-undecanethiol, and then glutaraldehyde was used to covalently attach nitrostreptavidin to them. His-tagged proteins bind to the nickel block and biotin-tagged proteins bind to the functionalized gold ends, allowing one to separate a mixture of three proteins with a single material. Each surface-bound protein can be released selectively using imidazole for the His-tagged protein and biotin for the biotinylated protein.     

Decarboxylation of 2,2'-bipyridinyl-4,4'-dicarboxylic acid diethyl ester during microwave synthesis of the corresponding trichelated ruthenium complex

Microwave reaction of RuCl3 with 2,2'-bipyridinyl-4,4'-dicarboxylic acid diethyl ester (debpy) in ethylene glycol generated Ru(bpy)3(2+) instead of the expected Ru(debpy)3(2+). Gas chromatography-mass spectrometry analysis of the headspace revealed CO2, and Ru(bpy)3(2+) was recovered from the filtrate. Further experiments suggest that RuCl3 decarboxylates debpy during microwave synthesis.