Enhancement of fast scan cyclic voltammetry detection of dopamine with tryptophanmodified electrodes

Fast scan cyclic voltammetry (FSCV) allows for real -time analysis of phasic neurotransmitter levels. Tryptophan (TRP) is an aromatic amino acid responsible for facilitating electron transfer kinetics in oxidoreductase enzymes. Previous work with TRP-modified electrodes showed increased sensitivity for cyclic voltammetry detection of dopamine (DA) when used with slower scan rates (0.05 V/s). Here, we outline an in vitro proof of concept for TRP-modified electrodes in FSCV detection of DA, and decreased sensitivity for ascorbic acid (AA). TRP-modified electrodes had a limit of detection (LOD) for DA of 2.480 ± 0.343 nM compared to 8.348 ± 0.405 nM for an uncoated electrode. Selectivity for DA/ascorbic acid (AA) was 1.107 ± 0.3643 for uncoated and 15.57 ± 4.184 for TRP-modified electrodes. Additionally, these TRP-modified electrodes demonstrated reproducibility when exposed to extended cycling. TRP-modified electrodes will provide an effective modification to increase sensitivity for DA

Phenylene Ethynylene and Phenylene Imine Macrocycles As Precursors for Organic Nanotubes

Single walled carbon nanotubes (SWCNTs) have unique physical, optical and electronic properties. Current production methods provide SWCNTs as a polydisperse mixture, with respect to helicity, diameter and length, and cannot be tuned to yield a discrete SWCNT isomer. A bottom up approach would yield a single SWCNT, which would allow for a better understanding of how chemical modification affects a carbon nanotube’s properties. Synthesis by this route has yet to be accomplished. Phenylene ethynylene macrocycles were synthesized by a stepwise linear fashion and cyclooligomerization. These macrocycles are Diels-Alder cycloaddition precursors for a rational synthesis of a (9,0) SWCNT segment. Additionally, these macrocycles are of interest due to their highly conjugated two dimensional networks, which gives rise to high quantum efficiency. Therefore, the optical properties of these macrocycles were studied in several of solvents. In addition, a novel reductive imination was examined and used to synthesize a series of phenylene imine macrocycles. These systems could be precursors towards organic N-doped SWCNTs by either a hetro-Diels-Alder cycloaddition or pyrrole ring formation

How Does BBr\u3csub\u3e3\u3c/sub\u3e Cyclize \u3ci\u3eo\u3c/i\u3e-Alkynylanisoles to Form Benzofurans?

Nature provides us with a wide array of chemicals that have beneficial uses. Cyclization reactions are important in the man-made creation of these chemicals. Past research by S3 scholar Samantha Ellis in Prof. Korich\u27s lab showed an unexpected cyclization reaction with o-alkynylanisoles in the presence of BBr3 instead of the expected ether cleavage reaction. We sought to understand this unusual reactivity using computational chemistry by comparing the energies of these competing pathways. However, we discovered that previously considered mechanisms for BBr3 assisted ether cleavage are incomplete. In this work we present an alternative mechanism for ether cleavage that has implications in a number of different reactions involving boron-containing reagents

Ether Cleavage Re-Investigated: Elucidating the Mechanism of BBr3- Facilitated Demethylation of Aryl Methyl Ethers

Boron tribromide is a versatile reagent utilized in diverse areas ranging from polymer chemistry to natural product synthesis.[1] Owing its high reactivity to the Lewis acidic boron center, BBr3 reactions include haloborylation,[2] boron–silicon exchange,[3] and rearrangement of 7,7-diphenylhydromorphone derivatives.[4] While there is no shortage in the diversity of BBr3-mediated reactions, many of the mechanisms for these transformations have not been fully elucidated. In this report we investigate the mechanism of ether cleavage by BBr3 [5–10] in anisole. Conceptually, demethylation of anisole is initiated by the formation of an ether adduct 1 followed by the loss of bromide. Free bromide nucleophilically attacks the methyl group of the cationic intermediate (2) cleaving the C–O bond and producing PhOBBr2, which undergoes hydrolysis upon aqueous work-up. While this pathway (Scheme 1) at first appears to be viable, we calculated that the formation of 2 and bromide in dichloromethane is thermodynamically inaccessible (ΔG = +38.9 kcal/mol). Recently, alternative mechanisms for ether cleavage were proposed by Sousa and Silva that involve unimolecular or bimolecular rate-determining steps that circumvent formation of bromide in solution (Scheme 2).[11] While a unimolecular process is kinetically favored for ethers containing one or more substituents (e.g. branched alkyl) that stabilize carbocation character in an SN1-like transition state, this barrier for demethylation of primary C atoms, like in the methyl group of anisole, lies too high on the potential energy surface to be accessible under reported reaction conditions. They found that a bimolecular process (Scheme 2, bottom) decreases the kinetic barrier for anisole demethylation significantly. During this reaction pathway, one of the bromides of the first ether adduct nucleophilically attacks the methyl group of the second ether adduct. This is analogous to an SN2 reaction with 180o attack of the methyl group by a bromide in the nucleophilic ether adduct. However, this bimolecular pathway produces two highly charged intermediates 2 and 3 that Sousa and Silva did not investigate. Their computational investigation stopped with the calculation of the initial kinetic barrier.[11] We speculate that these charged intermediates may undergo a similar bimolecular reaction to yield two equivalents of PhOBBr2 and MeBr. Moreover, if charged intermediates are formed then we believe an important set of mechanistic pathways may have been overlooked, namely, those where Lewis acidic BBr3 abstracts bromide from the ether complex to form BBr4 – in a mechanism related to the pathway introduced in Scheme 1

Prevalence of Cryptosporidium spp. and Giardia intestinalis in Swimming Pools, Atlanta, Georgia

Cryptosporidium spp. and Giardia intestinalis have been found in swimming pool filter backwash during outbreaks. To determine baseline prevalence, we sampled pools not associated with outbreaks and found that of 160 sampled pools, 13 (8.1%) were positive for 1 or both parasites; 10 (6.2%) for Giardia sp., 2 (1.2%) for Cryptosporidium spp., and 1 (0.6%) for both

Cryptosporidiosis Associated with Ozonated Apple Cider

We linked an outbreak of cryptosporidiosis to ozonated apple cider by using molecular and epidemiologic methods. Because ozonation was insufficient in preventing this outbreak, its use in rendering apple cider safe for drinking is questioned

Sporadic Cryptosporidiosis, North Cumbria, England, 1996–2000

Risk factors for sporadic cryptosporidiosis were determined in 152 patients and 466 unmatched controls who resided in two local government districts in North Cumbria, North West England, from March 1, 1996, to February 29, 2000. Risk was associated with the usual daily volume of cold unboiled tap water drunk (odds ratio [OR] 1.40, 95% confidence intervals [CI] 1.14 to 1.71 per pint consumed per day [p = 0.001]) and short visits to farms (OR 2.02, 95% CI 1.04 to 3.90, p = 0.04). Fifty-six (84%) of 67 fecal specimens from patients obtained from January 1, 1998, and February 29, 2000, were Cryptosporidium parvum genotype 2 (animal and human strain). Livestock fecal pollution of water sources appears to be the leading cause of human sporadic cryptosporidiosis in this population and shows the need for better protection of water catchments from livestock and improved drinking water treatment in this area of England