Intramolecular interactions and the neutral loss of ammonia from collisionally activated, protonated ω-aminoalkyl-3-hydroxyfurazans

Gas phase fragmentation reactions of monoprotonated 4-(3-aminopropyl)- and 4-(4-aminobutyl)-3-hydroxyfurazan were investigated to examine potential interactions between functional groups. The two heterocyclic alkyl amines were ionized by electrospray ionization (ESI, positive mode) and fragmented using tandem mass spectrometry (MS/MS). The fragmentation pathways were characterized using pseudo MS3 experiments, precursor-ion scans, and density functional computations. For both heterocyclic ions, loss of ammonia was the only fragmentation process observed at low collision energies. Computational analysis indicated that the most feasible mechanism was intramolecular nucleophilic displacement of ammonia from the protonated ω-aminoalkyl side chain by N5 of the furazan ring. The alkylated nitrogen in the resulting bicyclic product ion facilitated N-O bond cleavage; subsequent neutral losses of nitric oxide (NO) and carbon monoxide (CO) occurred by homolytic bond cleavages. Next in the multistep sequence, neutral loss of ethylene from a radical cation was observed. A less favorable, competing fragmentation pathway of protonated 4-(3-aminopropyl)-3-hydroxyfurazan was consistent with cleavage of the 3-hydroxyfurazan ring and losses of NO and CO. Overall, the similar fragmentation behavior found for protonated 4-(3-aminopropyl)- and 4-(4-aminobutyl)-3-hydroxyfurazan differed from that previously characterized for furazan analogs with shorter alkyl chains. These observations demonstrate that a small change in the structure of multifunctional, heterocyclic alkyl amines may significantly influence interactions between distinct functional groups and the nature of the fragmentation process.

Dopamine Modulates Effective Connectivity in Frontal Cortex

There is increasing evidence that the left lateral frontal cortex is hierarchically organized such that higher-order regions have an asymmetric top-down influence over lower order regions. However, questions remain about the underlying neuroarchitecture of this hierarchical control organization. Within the frontal cortex, dopamine plays an important role in cognitive control functions, and we hypothesized that dopamine may preferentially influence top-down connections within the lateral frontal hierarchy. Using a randomized, double-blind, within-subject design, we analyzed resting-state fMRI data of 66 healthy young participants who were scanned once each after administration of bromocriptine (a dopamine agonist with preferential affinity for D2 receptor), tolcapone (an inhibitor of catechol-O-methyltransferase), and placebo, to determine whether dopaminergic stimulation modulated effective functional connectivity between hierarchically organized frontal regions in the left hemisphere. We found that dopaminergic drugs modulated connections from the caudal middle frontal gyrus and the inferior frontal sulcus to both rostral and caudal frontal areas. In dorsal frontal regions, effectivity connectivity strength was increased, whereas in ventral frontal regions, effective connectivity strength was decreased. These findings suggest that connections within frontal cortex are differentially modulated by dopamine, which may bias the influence that frontal regions exert over each other.

Precise temperature control and rapid heating/cooling of infrared spectroscopy samples with a two-stage thermoelectric device

The design and performance of an apparatus for heating and cooling samples during variable temperature infrared spectroscopy studies are described. The apparatus incorporates two thermoelectric device modules in a stacked configuration. The cascaded devices are powered in parallel and contained within a metal enclosure that maintains their alignment and applies clamping pressure between them to maximize thermal conductivity. By using this apparatus, sample temperatures can be increased or decreased at 2 °C s-1 rates and isothermal temperatures can be maintained precisely (±0.1 °C). The rapid heating and cooling capabilities of the apparatus facilitate programmed temperature step heating/cooling profiles with isothermal infrared spectrum measurements at pre-selected temperatures. Using linear heating and cooling temperature ramps, subtle temperature-dependent poly(styrene) infrared spectrum changes are elucidated and correlated with sample temperature. Results obtained by using a temperature step sample heating profile are compared with those obtained by using linear temperature ramp heating and cooling to characterize silica gel dehydration and re-hydration processes. By comparing infrared spectra acquired at different temperatures while heating and cooling the sample, silica gel spectrum changes associated with water desorption/adsorption and the thermal expansion/contraction of the Si-O-Si network are differentiated.

Neuroinflammation and white matter alterations in occupational manganese exposure assessed by diffusion basis spectrum imaging

OBJECTIVE

To evaluate in-vivo neuroinflammation and white matter (WM) microstructural integrity in occupational manganese (Mn) exposure.

METHODS

We assessed brain inflammation using Diffusion Basis Spectrum Imaging (DBSI) in 26 Mn-exposed welders, 17 Mn-exposed workers, and 26 non-exposed participants. Cumulative Mn exposure was estimated from work histories and the Unified Parkinson's Disease Rating Scale motor subsection 3 (UPDRS3) scores were completed by a movement specialist. Tract-based Spatial Statistics allowed for whole-brain voxel-wise WM analyses to compare WM DBSI-derived measures between the Mn-exposed and non-exposed groups. Exploratory grey matter region of interest (ROI) analyses examined the presence of similar alterations in the basal ganglia. We used voxelwise general linear modeling and linear regression to evaluate the association between cumulative Mn exposure, WM or basal ganglia DBSI metrics, and UPDRS3 scores, while adjusting for age.

RESULTS

Mn-exposed welders had higher DBSI-derived restricted fraction (DBSI-RF), higher DBSI-derived nonrestricted fraction (DBSI-NRF), and lower DBSI-derived fiber fraction (DBSI-FF) in multiple WM tracts (all p < 0.05) in comparison to less-exposed workers and non-exposed participants. Basal ganglia ROI analyses revealed higher average caudate DBSI-NRF and DBSI-derived radial diffusion (DBSI-RD) values in Mn-exposed welders relative to non-exposed participants (p < 0.05). Caudate DBSI-NRF was also associated with greater cumulative Mn exposure and higher UPRDS3 scores.

CONCLUSIONS

Mn-exposed welders demonstrate greater DBSI-derived indicators of neuroinflammation-related cellularity (DBSI-RF), greater extracellular edema (DBSI-NRF), and lower apparent axonal density (DBSI-FF) in multiple WM tracts suggesting a neuroinflammatory component in the pathophysiology of Mn neurotoxicity. Caudate DBSI-NRF was positively associated with both cumulative Mn exposure and clinical parkinsonism, indicating a possible dose-dependent effect on extracellular edema with associated motor effects.

Striatal dopamine synthesis and cognitive flexibility differ between hormonal contraceptive users and nonusers

In rodents and nonhuman primates, sex hormones are powerful modulators of dopamine (DA) neurotransmission. Yet less is known about hormonal regulation of the DA system in the human brain. Using positron emission tomography (PET), we address this gap by comparing hormonal contraceptive users and nonusers across multiple aspects of DA function: DA synthesis capacity via the PET radioligand 6-[18F]fluoro-m-tyrosine ([18F]FMT), baseline D2/3 receptor binding potential using [11C]raclopride, and DA release using methylphenidate-paired [11C]raclopride. Participants consisted of 36 healthy women (n = 15 hormonal contraceptive users; n = 21 naturally cycling/non users of hormonal contraception), and men (n = 20) as a comparison group. A behavioral index of cognitive flexibility was assessed prior to PET imaging. Hormonal contraceptive users exhibited greater DA synthesis capacity than NC participants, particularly in dorsal caudate, and greater cognitive flexibility. Furthermore, across individuals, the magnitude of striatal DA synthesis capacity was associated with cognitive flexibility. No group differences were observed in D2/3 receptor binding or DA release. Analyses by sex alone may obscure underlying differences in DA synthesis tied to women's hormone status. Hormonal contraception (in the form of pill, shot, implant, ring, or intrauterine device) is used by ~400 million women worldwide, yet few studies have examined whether chronic hormonal manipulations impact basic properties of the DA system. Findings from this study begin to address this critical gap in women's health.

Thermal analysis by variable temperature infrared spectroscopy with a button sample holder and Peltier heating/cooling

An apparatus and methodology for variable temperature infrared spectroscopy measurements of neat samples contained in a button sample holder are described. Sample heating and cooling are achieved by applying voltage to stacked Peltier thermoelectric devices. Between 0 and 150 °C, samples can be heated and cooled at 2 °C s^-1 rates, facilitating temperature step heating/cooling profiles with minimal delay between isothermal infrared spectrum measurements. Examples of correlating temperature-dependent spectral variations with specific sample changes are provided for α-quartz heating/cooling, ibuprofen melting, and acetylsalicylic acid thermal decomposition. Trends in α-quartz infrared spectra obtained with a step heating/cooling temperature profile are used to evaluate spectrum measurement reproducibility. Detection of vibration band intensity variations of less than 1% resulting from a 10 °C sample temperature increment illustrates the measurement sensitivity. By comparing infrared spectra obtained at different temperatures, reversible and irreversible sample changes are identified. Infrared spectra acquired during linear ramp heating are employed to determine the ibuprofen melting point, which confirms the temperature measurement accuracy of the apparatus. Selective analysis is demonstrated by determining isoconversion effective activation energies for processes involved in the thermal decomposition of the acetylsalicylic acid component of a commercial pharmaceutical tablet.

Multiple path length mid-infrared spectra of liquids obtained by using a modified button sample holder

A modified mesh button sample holder is characterized by examining the effects of multiple absorption path lengths on infrared spectra. Unlike transmission cells, which are designed to provide a single radiation penetrating distance, reflections by the button stainless-steel mesh result in a wide distribution of absorption path lengths. Consequently, detector signals represent radiation traversing different distances through the sample. Higher absorptivity bands are measured with shorter effective path lengths than lower absorptivity bands. Therefore, band intensity ratios in measured infrared spectra differ from their relative absorptivities. In addition, overlapping band shapes are retained in spectral regions that would be opaque in transmission cell measurements. Wavenumber dependent effective path lengths can be systematically and reproducibly varied by changing the volume of liquid added to the button reservoir. Although Beer's law is not applicable, absorbance is proportional to concentration when sample volumes are constant, facilitating quantitative analyses.

Discrimination of commercial ibuprofen tablets by using a button sample holder and mid-infrared spectroscopy

Infrared spectra obtained from commercial ibuprofen tablets are categorized by using principal component analysis. A stainless steel abrasive button is used to sample the coatings and interiors of ibuprofen tablets with three different formulations. Rubbing the button wire mesh surface across tablet surfaces removes material for analysis. Small fragments are retained within mesh void spaces and larger fragments are swept away prior to analyses. Infrared spectra for tablet coatings exhibit significant differences and can be used for identification. Tablet interior compositions consisting primarily of ibuprofen from different manufacturers are more distinguishable from pre-processed spectra than from spectrum second derivatives. The speed and sensitivity afforded by this methodology suggests that rapid detection of counterfeit pharmaceuticals based on mid-infrared spectroscopy measurements of microgram quantities of material removed with a button sample holder is feasible.

Mid-infrared spectroscopy of liquids by using a modified button sample holder

A new approach for mid-infrared spectroscopy measurements of liquids is described. Thin layers of liquid samples are analyzed by using a modified button sample holder that incorporates a reservoir. To obtain spectra, buttons containing liquid samples are placed at the infrared beam focus of a praying mantis diffuse reflection optical system. Infrared radiation absorption path lengths can be adjusted by changing the quantity of liquid added to the reservoir. Thin film transflection spectra are similar to those obtained by transmission measurements. Transflection spectra of thicker layer liquids also resemble transmission measurements, but with increased relative intensities for low absorptivity peaks. Unlike transmission measurements, transflection spectra retain overlapping peak profiles for highly absorbing vibration bands due to multiple path length dynamic range effects. For a fixed effective path length (i.e. constant liquid volume), linear calibration plots of absorbance or integrated absorbance versus concentration are obtained. The button sample holder provides a methodology that is complementary to the transmission cell and attenuated total reflection (ATR) techniques for infrared analyses of neat solids and liquids, and is especially useful for characterizing thick samples and high absorptivity bands.

Enhancing dopamine tone modulates global and local cortical perfusion as a function of COMT val158met genotype

The cognitive effects of pharmacologically enhancing cortical dopamine (DA) tone are variable across healthy human adults. It has been postulated that individual differences in drug responses are linked to baseline cortical DA activity according to an inverted-U-shaped function. To better understand the effect of divergent starting points along this curve on DA drug responses, researchers have leveraged a common polymorphism (rs4680) in the gene encoding the enzyme catechol-O-methyltransferase (COMT) that gives rise to greater (Met allele) or lesser (Val allele) extracellular levels of cortical DA. Here we examined the extent to which changes in resting cortical perfusion following the administration of two mechanistically-distinct dopaminergic drugs vary by COMT genotype, and thereby track predictions of the inverted-U model. Using arterial spin labeling (ASL) and a double-blind, within-subject design, perfusion was measured in 75 healthy, genotyped participants once each after administration of tolcapone (a COMT inhibitor), bromocriptine (a DA D2/3 agonist), and placebo. COMT genotype and drug interacted such that COMT Val homozygotes exhibited increased prefusion in response to both drugs, whereas Met homozygotes did not. Additionally, tolcapone-related perfusion changes in the right inferior frontal gyrus correlated with altered performance on a task of executive function. No comparable effects were found for a genetic polymorphism (rs1800497) affecting striatal DA system function. Together, these results indicate that both the directionality and magnitude of drug-induced perfusion change provide meaningful information about individual differences in response to enhanced cortical DA tone.

Fragmentation reactions of protonated α,ω-diamino carboxylic acids: The importance of functional group interactions

Protonated members of a homologous series of biologically significant α,ω-diamino carboxylic acids were subjected to collision induced dissociation (CID). The resulting fragmentation patterns were studied using isotopic labeling, quantum mechanical computations, and pseudo MS³ experiments conducted primarily on an ion trap mass spectrometer. Each protonated α,ω-diamino acid showed a primary neutral loss of either ammonia or water; a clear explanation was developed for the observed variation of the two losses within the series. Protonated 2,3-diaminopropanoic acid, 2,4-diaminobutanoic acid, and 2,7-diaminoheptanoic acid gave secondary losses of water, carbon monoxide, and a loss of water plus carbon monoxide, respectively. In the parallel pathways characterized for the fragmentations of protonated ornithine and lysine, the α-nitrogen of the diamino acid was maintained in the cyclic iminium product formed by successive losses of NH₃ and (H₂ O + CO), whereas the side-chain nitrogen was retained by consecutive losses of H₂ O and (CO, NH₃ ). The 1-piperideine ion from protonated lysine was fragmented further, losing ethylene from carbons 4 and 5. Protonated 2,6-diaminopimelic acid fragmented by analogous reactions. Detailed mechanistic schemes for the fragmentation of both protonated 2,3-diaminopropanoic and ornithine were generated from MP2/DFT computations. This work highlights the participation of the side-chain amino group, which distinguishes the gas-phase chemistry of protonated α,ω-diamino acids from the well-documented fragmentation reactions of protonated α-amino acids bearing a hydrogen atom or an alkyl side chain. In general, the results further illustrate the importance of intramolecular separations affecting the specific interactions between functional groups leading to the fragmentation of multifunctional ions.

A high sensitivity variable temperature infrared spectroscopy investigation of kaolinite structure changes

A new approach for thermal analysis based on variable temperature infrared spectroscopy is described and evaluated. Diffuse reflection optics are employed with a sample heating system that does not employ a sealed environmental chamber. Rather than using a sample cup, a thin layer of solid particles is loaded into a "button" sample holder. The new design minimizes spectral artifacts and provides enhanced optical throughput compared to other designs, but necessitates a more restrictive sample heating temperature range. Results obtained while monitoring solid-state temperature-dependent changes are used to assess the sensitivity of the method. Infrared spectrum changes associated with reversible and irreversible kaolinite structure changes are described and characterized. Subtle temperature-dependent sample changes are revealed by positive and negative difference spectrum residuals, which are obtained by subtracting infrared spectra obtained at different temperatures. Scan-to-scan infrared spectrum relative standard deviations at 30 and 150 °C were less than 1.0%, which was slightly higher than the ambient temperature reproducibility.

A variable temperature infrared spectroscopy study of NaY zeolite dehydration

Variable temperature diffuse reflection infrared spectroscopy is used to monitor molecular vibration changes associated with water molecules and zeolite framework during thermal dehydration of NaY zeolite. Absorbance bands are assigned to three unique water molecule environments. These three water types exhibit different temperature-dependent band intensity profiles. A band at 3700 cm^-1 is assigned to framework acid sites. The intensity of this band was found to vary with temperature in a manner consistent with the occupancy of sodium cations in II' unit cell locations. Specific framework vibrations exhibit temperature-dependent intensity change profiles. Band intensities at 1190, 1060, and 960 cm^-1, associated with Si-O-Si and Si-O-Al asymmetric stretching vibrations, are sensitive to water content. Band intensity at 800 cm^-1, assigned to Si-O-Si symmetric stretching, is inversely correlated with temperature-dependent unit cell volume changes. All framework band intensity changes detected during heating are reversible after re-hydration during sample cooling.

Little Change in Functional Brain Networks Following Acute Levodopa in Drug-Naïve Parkinson's Disease

OBJECTIVE

The objective of this study was to investigate the effects of levodopa on functional brain networks in Parkinson's disease.

METHODS

We acquired resting state functional magnetic resonance imaging in 30 drug-naïve participants with Parkinson's disease and 20 age-matched healthy controls. Each participant was studied following administration of a single oral dose of either levodopa or placebo in a randomized, double-blind, crossover design.

RESULTS

The greatest observed differences in functional connectivity were between Parkinson's disease versus control participants, independent of pharmacologic intervention. By contrast, the effects of levodopa were much smaller and detectable only in the Parkinson's disease group. Moreover, although levodopa administration in the Parkinson's disease group measurably improved motor performance, it did not increase the similarity of functional connectivity in Parkinson's disease to the control group.

CONCLUSIONS

We found that a single, small dose of levodopa did not normalize functional connectivity in drug-naïve Parkinson's disease. © 2019 International Parkinson and Movement Disorder Society.

Diffuse reflection mid-infrared spectroscopy of neat powders by using a wire mesh "Button" sample holder

A new approach for neat powder mid-infrared spectroscopy measurements is described. Powder thin layers are created and supported by wire meshes attached to stainless steel backings, or buttons. Stainless steel buttons are durable, resistant to corrosion, and are easily cleaned and reused. To obtain spectra, buttons containing neat samples are placed at the infrared beam focus of a praying mantis diffuse reflection optical system. Wire diameter and mesh opening size dictate the powder particle size range that can be accommodated and maximum sample layer thicknesses, which determine radiation penetration path lengths. For powder layer thicknesses of several microns, infrared spectra that are free of artifacts can be obtained without dilution in a non-absorbing matrix. Nanogram detection limits are demonstrated for a benzoic acid coating prepared by evaporating an aqueous solution from a button surface.

Effects of Dopaminergic Drugs on Cognitive Control Processes Vary by Genotype

Dopamine (DA) has been implicated in modulating multiple cognitive control processes, including the robust maintenance of task sets and memoranda in the face of distractors (cognitive stability) and, conversely, the ability to switch task sets or update the contents of working memory when it is advantageous to do so (cognitive flexibility). In humans, the limited specificity of available pharmacological probes has posed a challenge for understanding the mechanisms by which DA, acting on multiple receptor families across the PFC and striatum, differentially influences these cognitive processes. Using a within-subject, placebo-controlled design, we contrasted the impact of two mechanistically distinct DA drugs, tolcapone (an inhibitor of catechol-O-methyltransferase [COMT], a catecholamine inactivator) and bromocriptine (a DA agonist with preferential affinity for the D2 receptor), on the maintenance and switching of task rules. Given previous work demonstrating that drug effects on behavior are dependent on baseline DA tone, participants were stratified according to genetic polymorphisms associated with cortical (COMT Val158Met) and striatal (Taq1A) DA system function. Our results were partially consistent with an inverted-U-shaped relationship between tolcapone and robust rule maintenance (interaction with COMT genotype) and between bromocriptine and cued rule switching (interaction with Taq1A genotype). However, when task instructions were ambiguous, a third relationship emerged to explain drug effects on spontaneous task switching (interaction of COMT genotype and bromocriptine). Together, this pattern of results suggests that the effects of DA drugs vary not only as a function of the DA system component upon which they act but also on subtle differences in task demands and context.

A variable temperature infrared spectroscopy study of CaA zeolite dehydration and carbonate formation

Variable temperature diffuse reflection infrared spectroscopy is used to monitor the dehydration of calcium enriched Linde type A zeolite (CaA). Infrared spectrum changes indicate that the energy imparted to the zeolite by heating causes water desorption and also facilitates reactions between water and zeolite framework, yielding SiOHAl acid sites. Water also reacts with ambient carbon dioxide producing carbonic acid, which readily dissociates to form carbonate. Three types of carbonate species are reported. The most thermally stable carbonate is coordinated to Ca²⁺ as a monodentate ligand. A second carbonate-containing species may be simultaneously interacting with Ca²⁺ and the zeolite framework. The third type of carbonate is characterized by infrared absorption consistent with a highly symmetric configuration, suggesting weak interactions with the local environment. Temperature-dependent infrared spectrum variations suggest that protons from carbonic acid dissociations react with framework and Ca(OH)⁺ moieties, altering internal CaA pore structure configurations.

Fragmentation pathways arising from protonation at different sites in aminoalkyl-substituted 3-hydroxy-1,2,5-oxadiazoles (3-hydroxyfurazans)

RATIONALE

The gas-phase fragmentation chemistry of multifunctional cations is highly influenced by the site of protonation. Possible relationships between protonation site and fragmentation processes were studied using 4-aminoalkyl-3-hydroxyfurazans. For these heterocyclic amines, the starting points for competing fragmentation pathways varied with protonation at multiple sites in two tautomers.

METHODS

Mass spectra were acquired using electrospray ionization (positive mode) coupled to triple quadrupole and ion trap mass spectrometers; precursor-product ion relationships were studied by collision-induced dissociation. Quantum mechanical computations were performed at the MP2/6-311++G(2d,p)//ωB97X-D/6-311+G(d) level of theory.

RESULTS

Prominent successive losses of NO and CO and competing losses of CH₂ =NH or NH₃ were observed as fragmentation processes. The lowest barrier computed for the initial step in a fragmentation pathway was associated with the [M + H]⁺ ion protonated at N5 in the heterocyclic ring, whereas an alternative ring cleavage leading to complementary product ions was initiated by protonation of the ring at N2. Side-chain protonation led to loss of NH₃ without cleavage of the 3-hydroxyfurazan ring.

CONCLUSIONS

The product ions obtained by the competing fragmentation processes varied with the site of protonation. Interestingly, the most abundant product ions observed at low collision energies were formed by cleavage of protonated molecules possessing more internal energy than other isomers.

Chemistry at Dalhousie circa 1868

This article describes details of classes at Dalhousie University in 1868–1869, of the life of George Lawson, the first Professor of Chemistry and Mineralogy, and of the wide range of chemical concepts known at that time. A comprehensive set of lecture notes from Lawson’s chemistry course, written by a student, Alexander Russell, and held in the Dalhousie University Archives, offers a wonderful insight into the state of chemical knowledge and how it was taught at that time. Lawson began with general chemical principles followed by a detailed discussion of the nonmetals. The second half of the class covered a range of metals followed by a small section on mineralogy and a large section on organic and biological chemistry. Lawson used an older set of atomic masses in which many, but not all, of the elements had masses one-half of the accepted values today. When corrected for these errors, Lawson’s formulae, even for complex molecules such as morphine, mostly agreed with contemporary usage. Examples of nomenclature, chemical formulae, preparations, processes, and properties are presented. A few examination questions are given also. Even though the concepts involved in understanding chemical structure were just being developed, the breadth and depth of descriptive chemical knowledge at that time was remarkable.

Reduction of Fumarate to Succinate Mediated by Fusobacterium varium

Accumulation of succinate as a fermentation product of Fusobacterium varium was enhanced when the anaerobic bacterium was grown on complex peptone medium supplemented with fumarate. Residual substrates and fermentation products were determined by proton NMR spectroscopy. Cells collected from the fumarate-supplemented medium (8-10 h after inoculation) supported the conversion of fumarate to succinate when suspended with fumarate and a co-substrate (glucose, sorbitol, or glycerol). Succinate production was limited by the availability of fumarate or reducing equivalents supplied by catabolism of a co-substrate via the Embden-Meyerhof-Parnas (EMP) pathway. The choice of reducing co-substrate influenced the yield of acetate and lactate as side products. High conversions of fumarate to succinate were achieved over pH 6.6-8.2 and initial fumarate concentrations up to 300 mM. However, at high substrate concentrations, intracellular retention of succinate reduced extracellular yields. Overall, the efficient utilization of fumarate (≤ 400 mM) combined with the significant extracellular accumulation of succinate (corresponding to ≥ 70% conversion) indicated the effective utilization of fumarate as a terminal electron acceptor by F. varium and the potential of the methodology for the bioproduction of succinate.

Ghosts in the Machine II: Neural Correlates of Memory Interference from the Previous Trial

Previous memoranda interfere with working memory. For example, spatial memories are biased toward locations memorized on the previous trial. We predicted, based on attractor network models of memory, that activity in the frontal eye fields (FEFs) encoding a previous target location can persist into the subsequent trial and that this ghost will then bias the readout of the current target. Contrary to this prediction, we find that FEF memory representations appear biased away from (not toward) the previous target location. The behavioral and neural data can be reconciled by a model in which receptive fields of memory neurons converge toward remembered locations, much as receptive fields converge toward attended locations. Convergence increases the resources available to encode the relevant memoranda and decreases overall error in the network, but the residual convergence from the previous trial can give rise to an attractive behavioral bias on the next trial.

Abstract P2-10-04: Using the 21-gene assay from core needle biopsies to choose neoadjuvant therapy for breast cancer: A multi-center trial

Neoadjuvant systemic therapy (NST) can facilitate breast conserving surgery (BCS) for large cancers. While hormone receptor positive (HR+) cancers respond to neoadjuvant chemotherapy (NCT), pathologic complete responses (pCR) are unlikely. Neoadjuvant hormonal therapy (NHT) may make BCS possible with less toxicity than NCT. We hypothesized that the Oncotype Dx® 21-gene Recurrence Score (RS), could guide the decision to treat with NHT versus NCT to facilitate BCS. This hypothesis is based on the ability of the RS to identify ER+ patients (pts) likely to benefit from adjuvant CT vs unlikely to benefit, as well as prior studies showing that pts with a low RS have no pCRs when receiving NCT (Yardley, et al 2015).

Methods: This prospective multi-center study enrolled pts with HR+, HER2-negative, invasive breast cancers not suitable for BCS (size ≥ 2 cm). Diagnosis was made by core needle biopsy (bx). Tissue blocks from the bx's were sent to Genomic Health for RS testing. Pts whose tumors had a RS &lt; 11 were to receive NHT; pts with RS &gt;25 tumors were to receive NCT; pts with midrange RS of 11-25 were randomized to NHT or NCT.

The primary objective was the feasibility of randomizing pts with RS values 11-25 between NHT and NCT. The primary endpoint was whether 1/3 or more of randomized pts would refuse assigned treatment. Secondary endpoints included: clinical partial and complete response (cPR, cCR) rates, overall clinical response rates (CR), pCR in the breast, pCR in the breast and nodes and successful BCS. One-sample binomial test was used to compare the observed refusal rate with 1/3, along with its 95% CI. Fisher's exact test, logistic regression (for a binary endpoint), and/or ordinal regression (for an ordinal endpoint) were used to compare the 4 treatment groups for secondary endpoints.

Results: Seven US and Canadian centers enrolled 64 pts; 5 were excluded (1 delay in RS result, 1 lost block, 1 HR testing discrepancy, 2 not eligible). Of 33 pts with RS 11-25, 5 (15%; 95% CI =2.9% - 27.4%) refused assignment to NCT (2 chose NHT and finished the study). This was significantly lower than the 33% target (binomial test, p=0.0292). Results for other endpoints are shown in the Table (according to treatment received); the total number of pts for the analyses is 55; 1 pt had missing data for clinical response.

Results According to TreatmentTreatment GroupRS&lt;11 NHTRS 11-25 NHTRS 11-25 NCTRS&gt;25 NCTOverall PNN=12N=18N=11N=14 cCR8.3%22.2%36.4%28.6%0.0422cPR75%27.8%36.4%64.3% CR (cCR + cPR)83.3%50%72.7%92.9%0.0490pCR Breast8.3%6%021.4%NSpCR Breast + Nodes00014.3%NSSuccessful BCS75%72.2%63.6%57.1%NS

Conclusions:This pilot showed the feasibility of using the RS to guide NST, with only a 15% refusal rate of randomly assigned treatment. Of greater interest is the finding that pts with a RS &lt;11 had a high CR rate with NHT and that pts with a RS 11-25 who received NHT had a similar rate of BCS success as the pts with RS &lt;11. Conversely, pts with RS&gt;25 treated with NCT had the highest CR (cCR + pCR) and pCR rates. These results demonstrate that conducting a similarly designed larger trial is feasible and suggests that for pts with a low RS, NHT is a potentially effective strategy.

Citation Format: Bear HD, Wan W, Robidoux A, Rubin P, Limentani S, White, Jr. RL, Granfortuna J, Hopkins JO, Oldham D, Rodriguez A, Sing AP. Using the 21-gene assay from core needle biopsies to choose neoadjuvant therapy for breast cancer: A multi-center trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-10-04.

Variable Temperature Infrared Spectroscopy Studies of Aromatic Acid Adsorbate Effects on Montmorillonite Dehydration

Molecular interactions between benzoic, salicylic, and acetylsalicylic acids and water contained within montmorillonite clay interlayer spaces are characterized by using variable temperature diffuse reflection infrared Fourier transform spectroscopy (VT-DRIFTS). By using sample perturbation and difference spectroscopy, infrared (IR) spectral variations resulting from the removal of interlayer water are used to characterize aromatic acid local environment changes. Difference spectra features representing functional group perturbations are correlated with changes in IR absorptions associated with -O-H and -C = O stretching vibrations. Results suggest that adsorbate carboxylic acid functionalities participate in extensive hydrogen bonding and that the strengths of these interactions are diminished when clays are dehydrated. The nature of these interactions and their temperature-dependent properties are found to depend on adsorbate structure and concentration as well as the clay interlayer cation.

Competing fragmentation processes of β-substituted propanoate ions upon collision-induced dissociation

RATIONALE

When subjected to collisional activation, gas-phase carboxylate ions typically undergo decarboxylation. However, alternative fragmentation processes dominate when the carboxylate group is located within certain structural motifs. In this work, the fragmentation processes of β-substituted carboxylate ions are characterized to improve correlations between reactivity and structure.

METHODS

Mass spectra were collected using both ion trap and triple quadrupole mass spectrometers operating in the negative ion mode; collision-induced dissociation (CID) of ions was used to study the relationship between product ions and the structures of their precursor ions. Quantum mechanical computations were performed on a full range of reaction geometries at the MP2/6-311++G(2d,p)//B3LYP/6-31++G(2d,p) level of theory.

RESULTS

For a series of β-substituted carboxylate ions, a product ion corresponding to the anion of the β-substituent was obtained upon CID. Detailed computations indicated that decarboxylative elimination and at least one other fragmentation mechanism had feasible energetics for the formation of substituent anions differing in their gas-phase basicities. Predicted energetics for anti- and synperiplanar alignments in the transition structures for decarboxylative elimination correlated with the positions of crossover points in breakdown curves acquired for conformationally constrained ions.

CONCLUSIONS

The feasibility of more than one mechanism was established for the fragmentation of β-substituted propanoates. The contribution of each mechanistic pathway to the formation of the substituent anion was influenced by structural variations and conformational constraints, but mostly depended on the nature of the substituent. Copyright © 2016 John Wiley & Sons, Ltd.

Phenyl group participation in rearrangements during collision-induced dissociation of deprotonated phenoxyacetic acid

RATIONALE

The identification of trace constituents in biological and environmental samples is frequently based on the fragmentation patterns resulting from the collision-induced dissociation (CID) of gas-phase ions. Credible mechanistic characterization of fragmentation processes, including rearrangements, is required to make reliable assignments for structures of precursor and product ions.

METHODS

Mass spectra were collected using both ion trap and triple quadrupole mass spectrometers operating in the negative ion mode. Precursor ion scans and CID of ions generated in-source were used to establish precursor-product ion relationships. Density functional theory (DFT) computations were performed at the MP2/6-311++G(2d,p)//B3LYP/6-31++G(2d,p) level of theory.

RESULTS

Product ions at m/z 93 and 107 obtained upon CID of phenoxyacetate were attributed to phenoxide and o-methylphenoxide, respectively. An isotopic labeling experiment and computations showed that the phenoxide ion was formed by intramolecular displacement with formation of an α-lactone and also by a Smiles rearrangement. Rearrangement of phenoxyacetate via the ion-neutral complex formed in the α-lactone displacement pathway gave the isomeric o-hydroxyphenylacetate ion which yielded o-methylphenoxide upon decarboxylation. Computations provided feasible energetics for these pathways.

CONCLUSIONS

Previously unrecognized and energetically favorable rearrangements during the collision-induced fragmentation of phenoxyacetate have been characterized using isotopic labeling and DFT computations. Notably, the phenyl substituent plays an indispensable role in each rearrangement process resulting in multiple pathways for the fragmentation of phenoxyacetate.

Variable Temperature Infrared Spectroscopy Investigations of Benzoic Acid Desorption from Sodium and Calcium Montmorillonite Clays

Processes involved in thermal desorption of benzoic acid from sodium and calcium montmorillonite clays are investigated by using variable temperature diffuse reflection Fourier transform infrared spectroscopy (DRIFTS). By monitoring the temperature dependence of infrared absorbance bands while heating samples, subtle changes in molecular vibrations are detected and employed to characterize specific benzoic acid adsorption sites. Abrupt changes in benzoic acid adsorption site properties occur for both clay samples at about 125 °C. Difference spectra absorbance band frequency variations indicate that adsorbed benzoic acid interacts with interlayer cations through water bridges and that these interactions can be disrupted by the presence of organic anions, in particular, benzoate.

Heterocyclic ring cleavage upon collision-induced dissociation of deprotonated 3-hydroxy-1,2,5-oxadiazoles (3-hydroxyfurazans)

A series of 4-substituted 3-hydroxyfurazans were subjected to electrospray ionization tandem mass spectrometry. At low collision energy, oxyisocyanate ([O=C=N-O](-), m/z 58) was formed as the predominant product ion from each deprotonated 3-hydroxyfurazan, indicating cleavage of the heterocyclic ring. The facile energetics of this characteristic fragmentation process was confirmed by density functional computations.

Variable Temperature Infrared Spectroscopy Investigation of Benzoic Acid Interactions with Montmorillonite Clay Interlayer Water

Molecular interactions between benzoic acid and cations and water contained in montmorillonite clay interlayer spaces are characterized by using variable temperature diffuse reflection infrared Fourier transform spectroscopy (VT-DRIFTS). Using sample perturbation and difference spectroscopy, infrared spectral changes resulting from removal of interlayer water and associated changes in local benzoic acid environments are identified. Difference spectra features can be correlated with changes in specific molecular vibrations that are characteristic of benzoic acid molecular orientation. Results suggest that the carboxylic acid functionality of benzoic acid interacts with interlayer cations through a bridging water molecule and that this interaction is affected by the nature of the cation present in the clay interlayer space.

Rearrangements leading to fragmentations of hydrocinnamate and analogous nitrogen-containing anions upon collision-induced dissociation

Tandem mass spectrometry (MS/MS) confirmed decarboxylation as the major collision-induced dissociation (CID) pathway of deprotonated hydrocinnamic acid (C6H5CH2CH2CO2H), N-phenylglycine (C6H5NHCH2CO2H) and 3-pyridin-2-ylpropanoic acid (C5H4NCH2CH2CO2H). The structure and stability of isomeric precursor and product anions were examined using density functional theory and ab initio methods. Geometry optimizations and frequency calculations were performed using the B3LYP/6-31++G(2d,p) level of theory and basis set with additional single point energies calculated at the MP2/6-311++G(2d,p) level. The formation of a delocalized product anion by carboxyl group-mediated migration of a benzylic proton to the ortho position of the ring and subsequent Cα-CO2(-) bond cleavage was energetically more favorable than direct decarboxylation and rearrangements of anions within ion-neutral complexes with carbon dioxide. The energy barrier for rearrangement of the delocalized product anion to the more stable benzylic anion was lowest in the fragmentation pathway of 3-pyridin-2-ylpropanoate. More energetically demanding fragmentation processes were indicated by the formation of other product anions at higher collision energy. Computations supported the feasibility of the formation of hydroxycarbonyl, styrene, and phenide ions from the benzylic anion of hydrocinnamate and the corresponding product anions from the nitrogen-containing analogues. The loss of dihydrogen from decarboxylated 3-pyridin-2-ylpropanoate was characterized computationally as hydride abstraction of an aryl proton. Overall, the results highlight the importance of exploring rearrangements in the fragmentation pathways of ions formed by electrospray ionization (ESI).

Characterization of multiple fragmentation pathways initiated by collision-induced dissociation of multifunctional anions formed by deprotonation of 2-nitrobenzenesulfonylglycine

The correlation of anion structure with the fragmentation behavior of deprotonated nitrobenzenesulfonylamino acids was investigated using tandem mass spectrometry, isotopic labeling and computational methods. Four distinct fragmentation pathways resulting from the collision-induced dissociation (CID) of deprotonated 2-nitrobenzenesulfonylglycine (NsGly) were characterized. The unusual loss of the aryl nitro substituent as HONO was the lowest energy process. Subsequent successive losses of CO, HCN and SO2 indicated that an ortho cyclization reaction had accompanied loss of HONO. Other pathways involving rearrangement of the ionized sulfonamide group, dual bond cleavage and intramolecular nucleophilic displacement were proposed to account for the formation of phenoxide, arylsulfinate and arylsulfonamide product ions at higher collision energies. The four distinct fragmentation pathways were consistent with precursor-product relationships established by CID experiments, isotopic labeling results and the formation of analogous product ions from 2,4-dinitrobenzenesulfonylglycine and the Ns derivatives of alanine and 2-aminoisobutyric acid. The computations confirmed a low barrier for ortho cyclization with loss of HONO and feasible energetics for each reaction step in the four pathways. Computations also indicated that three of the fragmentation pathways started from NsGly ionized at the carboxyl group. Overall, the pathways identified for the fragmentation of the NsGly anion differed from processes reported for anions containing a single functional group, demonstrating the importance of functional group interactions in the fragmentation pathways of multifunctional anions.

Abstract P1-02-11: Flat epithelial atypia on breast core biopsy: Is excision warranted?

Columnar cell lesions of the breast are common findings in core biopsies for mammographically indeterminate calcifications. Atypical columnar cell lesions, also referred to as flat epithelial atypia (FEA), confer a mildly increased risk of subsequent carcinoma and are often co-localized with other patterns of atypia. The management of FEA diagnosed on core biopsy remains controversial with studies reporting carcinoma on excisional biopsy in 13 to 67% of cases. We report the frequency of carcinoma in excision specimens after a diagnosis of FEA on core biopsy over a nine year period at Carolinas Medical Center.

Cases were identified from our files for the period from January 2004 through October 2012. Core biopsies with FEA as the most “advanced” lesion were included. Exclusion criteria included another pattern of atypia, carcinoma in situ, or invasive carcinoma in ipsilateral core biopsies performed concurrently or within four months of the core biopsy with FEA alone. The pathology reports for excision specimens following a core biopsy with FEA alone were retrieved. For each core biopsy with pure FEA, the histologic and mammographic findings were correlated.

A total of 116 cases with a diagnosis of FEA on core biopsy were identified. Two (2) cases were ultrasound core biopsies, 1 was MRI-guided, and the remaining 113 cases were stereotactic core biopsies performed for calcifications. FEA was the most advanced lesion in 53 cases (46%), corresponding to 55 core biopsies. In the 63 cases with FEA and a more advanced lesion, 34 (29%) contained atypical ductal hyperplasia, 6 (5%) atypical lobular hyperplasia, 4 (3%) atypical ductal and lobular hyperplasia, 11 (10%) ductal carcinoma in situ, 2 (2%) lobular carcinoma in situ, and 6 (5%) invasive carcinoma. Of the 55 core biopsies with FEA alone, excision pathology reports were unavailable for 11 cases, and an ipsilateral core biopsy contained a more advanced lesion in 6 cases. Of the 38 remaining cases, 4 excision specimens (11%) contained carcinoma and 8 specimens (21%) contained another, higher risk pattern of atypia (atypical ductal hyperplasia or atypical lobular hyperplasia). Excision results are summarized in the table below: 10 (26%) contained no residual atypia, 16 (42%) residual FEA, 7 (18%) atypical ductal hyperplasia, 1 (3%) atypical lobular hyperplasia, 3 (8%) ductal carcinoma in situ, and 1 (3%) invasive carcinoma.

Excision Findings after Pure FEA on Core BiopsyTotalNo AtypiaFEAADHALHDCISInvasive3810 (26%)16 (42%)7 (18%)1 (3%)3 (8%)1 (3%)

The data from a nine year period at our institution demonstrate an 11% upgrade rate to carcinoma for patients with a diagnosis of FEA on core biopsy. The higher risk patterns of atypia (atypical ductal hyperplasia or atypical lobular hyperplasia) found in 21% of cases also impact risk stratification and future clinical and radiographic follow-up. In total, future clinical management was altered in 32% of patients based on excision specimen results. The findings support performing an excisional biopsy for a core biopsy containing FEA.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-02-11.

Synthesis and tandem mass spectrometry of chlorinated triacylglycerols

The incorporation of 9,10-dichlorooctadecanoyl groups using enzyme-catalyzed acylation and protecting group strategies yielded specific regioisomers of di- and tetrachlorinated triacylglycerols. Hexachloro- and hexabromotriacylglycerols were synthesized by addition of chlorine or bromine to tri-(cis-9-octadecenoyl)glycerol. Upon electrospray ionization and tandem mass spectrometry, the sodium adduct ions of all compounds containing a 9,10-dichlorooctadecanoyl group readily lost two molecules of HCl when subjected to collision-induced dissociation. A mechanism describing sequential HCl losses and the formation of a conjugated diene is proposed for the loss of both vicinal chlorine atoms from an alkyl chain. This characteristic fragmentation behavior and the availability of characterized standards will facilitate the development of quantitative analytical methods for the determination of chlorinated triacylglycerols in lipid mixtures isolated from marine and other biological sources.

Correlations of ion structure with multiple fragmentation pathways arising from collision-induced dissociations of selected α-hydroxycarboxylic acid anions

Under conditions of collision-induced dissociation (CID), anions of α-hydroxycarboxylic acids usually fragment to yield the distinctive hydroxycarbonyl anion (m/z 45) and/or the complementary product anion formed by neutral loss of formic acid (46 u). Further support for the known two-step mechanism, involving an ion-neutral complex for the formation of the hydroxycarbonyl anion from the carboxyl group, is herein provided by tandem mass spectrometric results and density functional theory computations on the glycolate, lactate and 3-phenyllactate ions. A fourth, structurally related α-hydroxycarboxylate ion, obtained by deprotonation of mandelic acid, showed only loss of carbon dioxide upon CID. Density functional theory computations on the mandelate ion indicated that similar energy inputs were required for a direct, phenyl-assisted decarboxylation and a postulated novel rearrangement to a carbonate ester, which yielded the benzyl oxide ion upon loss of CO2. Rearrangement of the glycolate ion led to expulsion of carbon monoxide, whereas the 3-phenyllactate ion showed the loss of water and formation of the benzyl anion and the benzyl radical as competing processes. The fragmentation pathways proposed for lactate and 3-phenyllactate are supported by isotopic labeling. The relative computed energies of saddle points and product ions for all proposed fragmentation pathways are consistent with the energies supplied during CID experiments and the observed relative intensities of product ions. The diverse reaction pathways characterized for this set of four α-hydroxycarboxylate ions demonstrate that it is crucial to understand the effects of structural variations when attempting to predict the gas-phase reactivity and CID spectra of carboxylate ions.

Risk factors for posttreatment edema in patients treated with stereotactic radiosurgery for meningiomas

BACKGROUND

Peritumoral edema is a recognized complication following stereotactic radiosurgery (SRS).

OBJECTIVE

To evaluate the risk of posttreatment peritumoral edema following SRS for intracranial meningiomas and determine predictive factors.

METHODS

Between 2002 and 2008, 173 evaluable patients underwent CyberKnife or Gamma Knife SRS for meningiomas. Eighty-four patients (49%) had prior surgical resections, 13 patients had World Health Organization grade II (atypical) meningiomas, and 117 patients had a neurological deficit before SRS. Sixty-two tumors were in parasagittal, parafalcine, and convexity locations. The median tumor volume was 4.7 mL (range, 0.1-231.8 mL). The median prescribed dose and median prescribed biologically equivalent dose were 15 Gy (range, 9-40 Gy) and 67 Gy (range, 14-116 Gy), respectively. Ninety-seven patients were treated with single-fraction SRS, 74 received 2 to 5 fractions, and 2 received >5 fractions.

RESULTS

The median follow-up was 21.0 months. Thirteen patients (8%) developed symptomatic peritumoral edema, with a median onset time of 4.5 months (range, 0.2-9.5 months). The 3-, 6-, 12-, and 24-month actuarial symptomatic edema rates were 2.9%, 4.9%, 7.7%, and 8.5%, respectively. The crude tumor control rate was 94%. On univariate analysis, large tumor volume (P = .01) and single-fraction SRS (P = .04) were predictive for development of posttreatment edema.

CONCLUSION

SRS meningioma treatment demonstrated a low incidence of toxicity; however, large tumor volumes and single-fraction SRS treatment had an increased risk for posttreatment edema. Risk factors for edema should be considered in meningiomas treatment.

Glutamate racemization and catabolism in Fusobacterium varium

The pathways of glutamate catabolism in the anaerobic bacterium Fusobacterium varium, grown on complex, undefined medium and chemically defined, minimal medium, were investigated using specifically labelled (13)C-glutamate. The metabolic end-products acetate and butyrate were isolated from culture fluids and derivatized for analysis by nuclear magnetic resonance and mass spectrometry. On complex medium, labels from L-[1-(13)C]glutamate and L-[4-(13)C]glutamate were incorporated into C1 of acetate and equally into C1/C3 of butyrate, while label derived from L-[5-(13)C]glutamate was not incorporated. The isotopic incorporation results and the detection of glutamate mutase and 3-methylaspartate ammonia lyase in cell extracts are most consistent with the methylaspartate pathway, the best known route of glutamate catabolism in Clostridium species. When F. varium was grown on defined medium, label from L-[4-(13)C]glutamate was incorporated mainly into C4 of butyrate, demonstrating a major role for the hydroxyglutarate pathway. Upon addition of coenzyme B(12) or cobalt ion to the defined medium in replicate experiments, isotope was located equally at C1/C3 of butyrate in accord with the methylaspartate pathway. Racemization of D-glutamate and subsequent degradation of L-glutamate via the methylaspartate pathway are supported by incorporation of label into C2 of acetate and equally into C2/C4 of butyrate from D-[3-(13)C]glutamate and the detection of a cofactor-independent glutamate racemase in cell extracts. Together the results demonstrate a major role for the methylaspartate pathway of glutamate catabolism in F. varium and substantial participation of the hydroxyglutarate pathway when coenzyme B(12) is not available.

Metabolic footprinting of the anaerobic bacterium Fusobacterium varium using 1H NMR spectroscopy

Metabolic footprinting of the anaerobic bacterium Fusobacterium varium demonstrated the accumulation of six carboxylic acids as metabolic end-products and revealed specific growth requirements and utilization capabilities towards amino acids. Guided by (1)H NMR determinations of residual amino acids in spent medium, a modified chemically defined minimal medium (CDMM*) was developed by minimizing the amino acid composition while satisfying nutritional requirements to support abundant growth of F. varium. Quantitative determinations of carboxylate salts and residual substrates were readily performed by (1)H NMR analysis of lyophilized residues from CDMM* cultures without interference from initial medium components. Only small concentrations of alanine, arginine, glycine, isoleucine, leucine, methionine, proline and valine were required to support growth of F. varium, whereas larger quantities of aspartate, asparagine, cysteine, glutamine, glutamate, histidine, lysine, serine and threonine were utilized, most likely as energy sources. Both bacterial growth and the distribution of carboxylate end-products depended on the composition of the chemically defined medium. In cultures provided with glucose as the primary energy source, the accumulation of butyrate and lactate correlated with growth, consistent with the regeneration of reduced coenzyme formed by the oxidative steps of glucose catabolism.

The Role of Next-Nearest Neighbors in The Neel Model of Surface Anisotropy for BCC Crystals

We have extended the Neél model of surface anisotropy in b.c.c. crystals to include next nearest neighbor interaction. Fitting the experimental data for Fe (001) and (110) surfaces leads to some pradoxes which cast doubt on the Neél surface anisotropy as the dominant source of surface anisotropy in thin films.

Identification of reaction products from reactions of free chlorine with the lipid-regulator gemfibrozil

High global consumption rates have led to the occurrence of pharmaceutically active compounds (PhACs) in wastewater. The use of chlorine to disinfect wastewater prior to release into the environment may convert PhACs into uncharacterized chlorinated by-products. In this investigation, chlorination of a common pharmaceutical, the antihyperlipidemic agent gemfibrozil, was documented. Gemfibrozil (2,2-dimethyl-5-(2,5-dimethylphenoxy)pentanoic acid) was reacted with sodium hypochlorite and product formation was monitored by gas chromatography-mass spectrometry (GC-MS). The incorporation of one, two or three chlorine atoms into the aromatic region of gemfibrozil was demonstrated using negative-ion electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). Further analysis using (1)H nuclear magnetic resonance (NMR) spectroscopy identified the reaction products as 4'-ClGem (5-(4-chloro-2,5-dimethylphenoxy)-2,2-dimethylpentanoic acid) 4',6'-diClGem (5-(4,6-dichloro-2,5-dimethylphenoxy)-2,2-dimethylpentanoic acid), and 3',4',6'-triClGem (5-(3,4,6-trichloro-2,5-dimethylphenoxy)-2,2-dimethylpentanoic acid), products consistent with electrophilic aromatic substitution reactions. The rapid reaction of gemfibrozil with free chlorine at pH conditions relevant to water treatment indicates that a mixture of chlorinated gemfibrozils is likely to be found in wastewater disinfected with chlorine.

Microfabricated magnetic sifter for high-throughput and high-gradient magnetic separation

A microfabricated magnetic sifter has been designed and fabricated for applications in biological sample preparation. The device enables high-throughput, high-gradient magnetic separation of magnetic nanoparticles by utilizing columnar fluid flow through a dense array (~5000/mm(2)) of micropatterned slots in a magnetically soft membrane. The potential of the sifter for separation of magnetic nanoparticles conjugated with capture antibodies is demonstrated through quantitative separation experiments with CD138-labelled MACS nanoparticles. Capture efficiencies ranging from 28-37% and elution efficiencies greater than 73% were measured for a single pass through the sifter.

Improved partition equilibrium model for predicting analyte response in electrospray ionization mass spectrometry

A previously proposed partition equilibrium model for quantitative prediction of analyte response in electrospray ionization mass spectrometry is modified to yield an improved linear relationship. Analyte mass spectrometer response is modeled by a competition mechanism between analyte and background electrolytes that is based on partition equilibrium considerations. The correlation between analyte response and solution composition is described by the linear model over a wide concentration range and the improved model is shown to be valid for a wide range of experimental conditions. The behavior of an analyte in a salt solution, which could not be explained by the original model, is correctly predicted. The ion suppression effects of 16:0 lysophosphatidylcholine (LPC) on analyte signals are attributed to a combination of competition for excess charge and reduction of total charge due to surface tension effects. In contrast to the complicated mathematical forms that comprise the original model, the simplified model described here can more easily be employed to predict analyte mass spectrometer responses for solutions containing multiple components.

Reducing glycerophosphocholine lipid matrix interference effects in biological fluid assays by using high-turbulence liquid chromatography

Matrix interferences can severely affect quantitative assays of biological samples when electrospray ionization (ESI) is employed with liquid chromatography/tandem mass spectrometry (LC/MS/MS). A major source of matrix interferences for plasma sample analyses is the presence of glycerophosphocholine (GPCho) lipids. The efficiency of online high-turbulence liquid chromatography (HTLC) extraction for eliminating these lipids is evaluated and the interfering effects of endogenous lipids on human plasma assays are measured for pharmaceutical compounds having a wide variety of chemical properties. It is found that GPCho lipids, represented by 16:0, 18:1 and 18:0 LPC (lysophosphatidylcholine) and 16:0-18:2 PC, cause variations for hydrophobic compound analyses even when optimal online HTLC extraction conditions are employed. The efficiency for lipid removal depends on the organic content of the transfer solvent, but turbulent flow loading has no significant effect.

Giant Magnetoresistive Sensors for DNA Microarray

Giant magnetoresistive (GMR) sensors are developed for a DNA microarray. Compared with the conventional fluorescent sensors, GMR sensors are cheaper, more sensitive, can generate fully electronic signals, and can be easily integrated with electronics and microfluidics. The GMR sensor used in this work has a bottom spin valve structure with an MR ratio of 12%. The single-strand target DNA detected has a length of 20 bases. Assays with DNA concentrations down to 10 pM were performed, with a dynamic range of 3 logs. A double modulation technique was used in signal detection to reduce the 1/f noise in the sensor while circumventing electromagnetic interference. The logarithmic relationship between the magnetic signal and the target DNA concentration can be described by the Temkin isotherm. Furthermore, GMR sensors integrated with microfluidics has great potential of improving the sensitivity to 1 pM or below, and the total assay time can be reduced to less than 1 hour.

Giant magnetoresistive biochip for DNA detection and HPV genotyping

A giant magnetoresistive (GMR) biochip based on spin valve sensor array and magnetic nanoparticle labels was developed for inexpensive, sensitive and reliable DNA detection. The DNA targets detected in this experiment were PCR products amplified from Human Papillomavirus (HPV) plasmids. The concentrations of the target DNA after PCR were around 10 nM in most cases, but concentrations of 10 pM were also detectable, which is demonstrated by experiments with synthetic DNA samples. A mild but highly specific surface chemistry was used for probe oligonucleotide immobilization. Double modulation technique was used for signal detection in order to reduce the 1/f noise in the sensor. Twelve assays were performed with an accuracy of approximately 90%. Magnetic signals were consistent with particle coverage data measured with Scanning Electron Microscopy (SEM). More recent research on microfluidics showed the potential of reducing the assay time below one hour. This is the first demonstration of magnetic DNA detection using plasmid-derived samples. This study provides a direct proof that GMR sensors can be used for biomedical applications.