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Ion/ion reactions with "onium" reagents: an approach for the gas-phase transfer of organic cations to multiply-charged anions.
Gilbert JD, Prentice BM, McLuckey SA
(2015) J Am Soc Mass Spectrom 26: 818-25
MeSH Terms: Alkylation, CME-Carbodiimide, Catalysis, Chelating Agents, Cross-Linking Reagents, Edetic Acid, Energy Transfer, Hot Temperature, Indicators and Reagents, Models, Molecular, Oligopeptides, Organophosphorus Compounds, Protein Conformation, Quaternary Ammonium Compounds, Spectrometry, Mass, Electrospray Ionization, Static Electricity, Sulfonium Compounds, Tandem Mass Spectrometry, Tetraethylammonium, Volatilization
Show Abstract · Added August 17, 2016
The use of ion/ion reactions to effect gas-phase alkylation is demonstrated. Commonly used fixed-charge "onium" cations are well-suited for ion/ion reactions with multiply deprotonated analytes because of their tendency to form long-lived electrostatic complexes. Activation of these complexes results in an SN2 reaction that yields an alkylated anion with the loss of a neutral remnant of the reagent. This alkylation process forms the basis of a general method for alkylation of deprotonated analytes generated via electrospray, and is demonstrated on a variety of anionic sites. SN2 reactions of this nature are demonstrated empirically and characterized using density functional theory (DFT). This method for modification in the gas phase is extended to the transfer of larger and more complex R groups that can be used in later gas-phase synthesis steps. For example, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) is used to transfer a carbodiimide functionality to a peptide anion containing a carboxylic acid. Subsequent activation yields a selective reaction between the transferred carbodiimide group and a carboxylic acid, suggesting the carbodiimide functionality is retained through the transfer process. Many different R groups are transferable using this method, allowing for new possibilities for charge manipulation and derivatization in the gas phase.
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20 MeSH Terms
Assessment of MRI issues at 7 T for 28 implants and other objects.
Dula AN, Virostko J, Shellock FG
(2014) AJR Am J Roentgenol 202: 401-5
MeSH Terms: Artifacts, Equipment Safety, Hot Temperature, Humans, Magnetic Resonance Imaging, Metals, Prostheses and Implants, Risk Assessment
Show Abstract · Added March 27, 2014
OBJECTIVE - Metallic implants are currently a contraindication for volunteer subjects and patients referred for 7-T examinations because of concerns related to magnetic field interactions and MRI-related heating. Artifacts may also be problematic. Therefore, the purpose of this investigation was to evaluate these MRI issues for 28 implants and other objects in association with a 7-T MR system.
MATERIALS AND METHODS - Tests were performed at 7 T using standardized procedures to evaluate magnetic field interactions (translational attraction and torque) for all 28 items. MRI-related heating and artifacts were assessed using spin-echo and gradient-echo pulse sequences, respectively, for two aneurysm clips located within a transmit-receive head radiofrequency coil.
RESULTS - Eight of the 28 items showed magnetic field interactions at levels that could pose risks to human subjects. The two aneurysm clips exhibited heating, but the temperature rise did not exceed 1°C. Artifacts were dependent on the material and dimensions of each aneurysm clip.
CONCLUSION - These findings show that certain implants and objects may be acceptable for human subjects undergoing MRI examinations at 7 T, whereas others may involve possible risks. This information has important implications for individuals referred for MRI examinations at 7 T.
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8 MeSH Terms
Molecular characterization of larval peripheral thermosensory responses of the malaria vector mosquito Anopheles gambiae.
Liu C, Zwiebel LJ
(2013) PLoS One 8: e72595
MeSH Terms: Animals, Anopheles, Arthropod Antennae, Female, Gene Expression, Hot Temperature, Humans, Insect Proteins, Insect Vectors, Larva, Locomotion, Organ Specificity, Thermosensing, Transient Receptor Potential Channels
Show Abstract · Added May 27, 2014
Thermosensation provides vital inputs for the malaria vector mosquito, Anopheles gambiae which utilizes heat-sensitivity within a broad spectrum of behaviors, most notably, the localization of human hosts for blood feeding. In this study, we examine thermosensory behaviors in larval-stage An. gambiae, which as a result of their obligate aquatic habitats and importance for vectorial capacity, represents an opportunistic target for vector control as part of the global campaign to eliminate malaria. As is the case for adults, immature mosquitoes respond differentially to a diverse array of external heat stimuli. In addition, larvae exhibit a striking phenotypic plasticity in thermal-driven behaviors that are established by temperature at which embryonic development occurs. Within this spectrum, RNAi-directed gene-silencing studies provide evidence for the essential role of the Transient Receptor Potential sub-family A1 (TRPA1) channel in mediating larval thermal-induced locomotion and thermal preference within a discrete upper range of ambient temperatures.
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14 MeSH Terms
Three-dimensional molecular imaging with photothermal optical coherence tomography.
Skala MC, Crow MJ, Wax A, Izatt JA
(2013) Methods Mol Biol 1026: 85-92
MeSH Terms: Cell Line, Tumor, Darkness, Gold, Hot Temperature, Humans, Imaging, Three-Dimensional, Immunoconjugates, Metal Nanoparticles, Molecular Imaging, Tissue Culture Techniques, Tomography, Optical Coherence
Show Abstract · Added March 11, 2014
Optical coherence tomography (OCT) is a three-dimensional optical imaging technique that has been successfully implemented in ophthalmology for imaging the human retina, and in studying animal models of disease. OCT can nondestructively visualize structural features in tissue at cellular-level resolution, and can exploit contrast agents to achieve molecular contrast. Photothermal OCT relies on the heat-producing capabilities of antibody-conjugated gold nanoparticles to achieve molecular contrast. A pump laser at the nanoparticle resonance wavelength is used to heat the nanoparticles in the sample, and the resulting changes in the index of refraction around the nanoparticles are detected by phase-sensitive OCT. Lock-in detection of the pump beam amplitude-modulated frequency and the detector frequency allow for high-sensitivity images of molecular targets. This approach is attractive for nondestructive three-dimensional molecular imaging deep (approximately 2 mm) within biological samples. The protocols described here achieve a sensitivity of 14 parts per million (weight/weight) nanoparticles in the sample, which is sufficient to differentiate EGFR (epidermal growth factor receptor)-overexpressing cells from minimally expressing cells in three-dimensional cell constructs.
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11 MeSH Terms
A Wang-Landau study of a lattice model for lipid bilayer self-assembly.
Gai L, Maerzke K, Cummings PT, McCabe C
(2012) J Chem Phys 137: 144901
MeSH Terms: Algorithms, Hot Temperature, Lipid Bilayers, Models, Molecular, Molecular Conformation, Monte Carlo Method
Show Abstract · Added May 3, 2017
The Wang-Landau (WL) Monte Carlo method has been applied to simulate the self-assembly of a lipid bilayer on a 3D lattice. The WL method differs from conventional Monte Carlo methods in that a complete density of states is obtained directly for the system, from which properties, such as the free energy, can be derived. Furthermore, from a single WL simulation, continuous curves of the average energy and heat capacity can be determined, which provide a complete picture of the phase behavior. The lipid model studied consists of 3 or 5 coarse-grained segments on lattices of varying sizes, with the empty lattice sites representing water. A bilayer structure is found to form at low temperatures, with phase transitions to clusters as temperature increases. For 3-segment chains, varying lattice sizes were studied, with the observation that the ratio of chain number to lattice area (i.e., area per lipid) affects the phase transition temperature. At small ratios, only one phase transition occurs between the bilayer and cluster phases, while at high lipid ratios the phase transition occurs in a two-step process with a stable intermediate phase. This second phase transition was not observed in conventional Metropolis Monte Carlo simulations on the same model, demonstrating the advantage of being able to perform a complete scan of the whole temperature range with the WL method. For longer 5-segment chains similar phase transitions are also observed with changes in temperature. In the WL method, due to the extensive nature of the energy, the number of energy bins required to represent the density of states increases as the system size increases and so limits its practical application to larger systems. To improve this, an extension of the WL algorithm, the statistical-temperature Monte Carlo method that allows simulations with larger energy bin sizes, has recently been proposed and is implemented in this work for the 3-segment lattice model. The results obtained are in good agreement with the original WL method and appear to be independent of the energy bin size used.
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6 MeSH Terms
Depletion of the C. elegans NAC engages the unfolded protein response, resulting in increased chaperone expression and apoptosis.
Arsenovic PT, Maldonado AT, Colleluori VD, Bloss TA
(2012) PLoS One 7: e44038
MeSH Terms: Animals, Caenorhabditis elegans, Endoplasmic Reticulum, Gene Expression Regulation, Developmental, Heat-Shock Proteins, Hot Temperature, Intestinal Mucosa, Lysosomes, Molecular Chaperones, RNA Interference, Stress, Physiological, Unfolded Protein Response, Up-Regulation
Show Abstract · Added April 25, 2013
The nascent polypeptide-associated complex (NAC) is a highly conserved heterodimer important for metazoan development, but its molecular function is not well understood. Recent evidence suggests the NAC is a component of the cytosolic chaperone network that interacts with ribosomal complexes and their emerging nascent peptides, such that the loss of the NAC in chaperone-depleted cells results in an increase in misfolded protein stress. We tested whether the NAC functions similarly in Caeonorhabditis (C.) elegans and found that its homologous NAC subunits, i.e. ICD-1 and -2, have chaperone-like characteristics. Loss of the NAC appears to induce misfolded protein stress in the ER triggering the unfolded protein response (UPR). Depletion of the NAC altered the response to heat stress, and led to an up-regulation of hsp-4, a homologue of the human chaperone and ER stress sensor GRP78/BiP. Worms lacking both ICD-1 and the UPR transcription factor XBP-1 generated a higher proportion of defective embryos, showed increased embryonic apoptosis and had a diminished survival rate relative to ICD-1-depleted animals with an intact UPR. Up-regulation of hsp-4 in NAC-depleted animals was specific to certain regions of the embryo; in embryos lacking ICD-1, the posterior region of the embryo showed strong up-regulation of hsp-4, while the anterior region did not. Furthermore, loss of ICD-1 produced prominent lysosomes in the gut region of adults and embryos putatively containing lipofuscins, lipid/protein aggregates associated with cellular aging. These results are the first set of evidence consistent with a role for C. elegans NAC in protein folding and localization during translation. Further, these findings confirm C. elegans as a valuable model for studying organismal and cell-type specific responses to misfolded protein stress.
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13 MeSH Terms
Development of a simultaneous cryo-anchoring and radiofrequency ablation catheter for percutaneous treatment of mitral valve prolapse.
Boronyak SM, Merryman WD
(2012) Ann Biomed Eng 40: 1971-81
MeSH Terms: Animals, Catheter Ablation, Hot Temperature, Mitral Valve Prolapse, Swine
Show Abstract · Added February 12, 2015
Mitral valve prolapse (MVP) is one subtype of mitral valve (MV) disease and is often characterized by enlarged leaflets that are thickened and have disrupted collagen architecture. The increased surface area of myxomatous leaflets with MVP leads to mitral regurgitation, and there is need for percutaneous treatment options that avoid open-chest surgery. Radiofrequency (RF) ablation is one potential therapy in which resistive heating can be used to reduce leaflet size via collagen contracture. One challenge of using RF ablation to percutaneously treat MVP is maintaining contact between the RF ablation catheter tip and a functioning MV leaflet. To meet this challenge, we have developed a RF ablation catheter with a cryogenic anchor for attachment to leaflets in order to apply RF ablation. We demonstrate the effectiveness of the dual-energy catheter in vitro by examining changes in leaflet biaxial compliance, thermal distribution with infrared (IR) imaging, and cryogenic anchor strength. We report that 1250 J of RF energy with cryo-anchoring reduced the determinant of the deformation gradient tensor at systolic loading by 23%. IR imaging revealed distinct regions of cryo-anchoring and tissue ablation, demonstrating that the two modalities do not counteract one another. Finally, cryogenic anchor strength to the leaflet was reduced but still robust during the application of RF energy. These results indicate that a catheter having combined RF ablation and cryo-anchoring provides a novel percutaneous treatment strategy for MVP and may also be useful for other percutaneous procedures where anchored ablation would provide more precise spatial control.
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5 MeSH Terms
Netrin (UNC-6) mediates dendritic self-avoidance.
Smith CJ, Watson JD, VanHoven MK, Colón-Ramos DA, Miller DM
(2012) Nat Neurosci 15: 731-7
MeSH Terms: Animals, Animals, Genetically Modified, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Cell Adhesion Molecules, Cell Movement, Cloning, Molecular, Dendrites, Hot Temperature, Luminescent Proteins, Membrane Proteins, Microscopy, Confocal, Models, Molecular, Mutation, Nerve Tissue Proteins, Netrins, Nociceptors, Signal Transduction, Time Factors, Time-Lapse Imaging
Show Abstract · Added February 3, 2014
Dendrites from a single neuron may be highly branched but typically do not overlap. Self-avoidance behavior has been shown to depend on cell-specific membrane proteins that trigger mutual repulsion. Here we report the unexpected discovery that a diffusible cue, the axon guidance protein UNC-6 (Netrin), is required for self-avoidance of sister dendrites from the PVD nociceptive neuron in Caenorhabditis elegans. We used time-lapse imaging to show that dendrites fail to withdraw upon mutual contact in the absence of UNC-6 signaling. We propose a model in which the UNC-40 (Deleted in Colorectal Cancer; DCC) receptor captures UNC-6 at the tips of growing dendrites for interaction with UNC-5 on the apposing branch to induce mutual repulsion. UNC-40 also responds to dendritic contact through another pathway that is independent of UNC-6. Our findings offer a new model for how an evolutionarily conserved morphogenic cue and its cognate receptors can pattern a fundamental feature of dendritic architecture.
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Treatment of amphibians infected with chytrid fungus: learning from failed trials with itraconazole, antimicrobial peptides, bacteria, and heat therapy.
Woodhams DC, Geiger CC, Reinert LK, Rollins-Smith LA, Lam B, Harris RN, Briggs CJ, Vredenburg VT, Voyles J
(2012) Dis Aquat Organ 98: 11-25
MeSH Terms: Animals, Antifungal Agents, Antimicrobial Cationic Peptides, Anura, Chytridiomycota, Female, Hot Temperature, Itraconazole, Larva, Male, Mycoses, Probiotics, Time Factors, Treatment Failure
Show Abstract · Added May 20, 2014
Amphibian conservation goals depend on effective disease-treatment protocols. Desirable protocols are species, life stage, and context specific, but currently few treatment options exist for amphibians infected with the chytrid fungus Batrachochytrium dendrobatidis (Bd). Treatment options, at present, include antifungal drugs and heat therapy, but risks of toxicity and side-effects make these options untenable in some cases. Here, we report on the comparison of several novel treatments with a more generally accepted antifungal treatment in experimental scientific trials to treat Bd-infected frogs including Alytes obstetricans tadpoles and metamorphs, Bufo bufo and Limnodynastes peronii metamorphs, and Lithobates pipiens and Rana muscosa adults. The experimental treatments included commercial antifungal products (itraconazole, mandipropamid, steriplantN, and PIP Pond Plus), antimicrobial skin peptides from the Bd-resistant Pelophylax esculentus, microbial treatments (Pedobacter cryoconitis), and heat therapy (35°C for 24 h). None of the new experimental treatments were considered successful in terms of improving survival; however, these results may advance future research by indicating the limits and potential of the various protocols. Caution in the use of itraconazole is warranted because of observed toxicity in metamorphic and adult frogs, even at low concentrations. Results suggest that rather than focusing on a single cure-all, diverse lines of research may provide multiple options for treating Bd infection in amphibians. Learning from 'failed treatments' is essential for the timely achievement of conservation goals and one of the primary aims for a publicly accessible treatment database under development.
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14 MeSH Terms
Differential fMRI activation to noxious heat and tactile stimuli in parasylvian areas of new world monkeys.
Chen LM, Dillenburger BC, Wang F, Tang CH
(2012) Pain 153: 158-69
MeSH Terms: Animals, Brain Mapping, Hot Temperature, Magnetic Resonance Imaging, Pain, Physical Stimulation, Saimiri, Somatosensory Cortex
Show Abstract · Added June 26, 2014
Emerging evidence supports an important role of posterior parasylvian areas in both pain and touch processing. Whether there are separate or shared networks for these sensations remains controversial. The present study compared spatial patterns of brain activation in response to unilateral nociceptive heat (47.5°C) or innocuous tactile stimulation (8-Hz vibration) to digits through high-resolution functional magnetic resonance imaging (fMRI) in squirrel monkeys. In addition, the temporal profile of heat-stimulus-evoked fMRI Blood Oxygenation Level Dependent (BOLD) signal changes was characterized. By examining high-resolution fMRI and histological measures at both the individual and the group levels, we found that both nociceptive heat and tactile stimuli elicited activation in bilateral secondary somatosensory and ventral parietal areas (S2/PV) and in ipsilateral ventral somatosensory areas (VS) and retroinsula (Ri). Bilateral posterior insular cortex (pIns) and area 7b responded preferentially to nociceptive heat stimulation. Single voxels within each activation cluster showed robust BOLD signal changes during each block of nociceptive stimulation. Across animals (n=11), nociceptive response magnitudes of contralateral VS and pIns and ipsilateral Ri were significantly greater than corresponding areas in the opposite hemisphere. In sum, both distinct and shared areas in regions surrounding the posterior sylvian fissure were activated in response to nociceptive and tactile inputs in nonhuman primates.
Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
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8 MeSH Terms