Read by QxMD icon Read


Jozef Lengyel, Christian van der Linde, Michal Fárník, Martin K Beyer
The reaction of dichlorodifluoromethane (CF2Cl2) with hydrated electrons (H2O)n(-) (n = 30-86) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The hydrated electron reacts with CF2Cl2, forming (H2O)mCl(-) with a rate constant of (8.6 ± 2.2) × 10(-10) cm(3) s(-1), corresponding to an efficiency of 57 ± 15%. The reaction enthalpy was determined using nanocalorimetry, revealing a strongly exothermic reaction with ΔHr(CF2Cl2, 298 K) = -208 ± 41 kJ mol(-1)...
September 14, 2016: Physical Chemistry Chemical Physics: PCCP
Amou Akhgarnusch, Wai Kit Tang, Han Zhang, Chi-Kit Siu, Martin K Beyer
The recombination reactions of gas-phase hydrated electrons (H2O)n˙(-) with CO2 and O2, as well as the charge exchange reaction of CO2˙(-)(H2O)n with O2, were studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry in the temperature range T = 80-300 K. Comparison of the rate constants with collision models shows that CO2 reacts with 50% collision efficiency, while O2 reacts considerably slower. Nanocalorimetry yields internally consistent results for the three reactions. Converted to room temperature condensed phase, this yields hydration enthalpies of CO2˙(-) and O2˙(-), ΔHhyd(CO2˙(-)) = -334 ± 44 kJ mol(-1) and ΔHhyd(O2˙(-)) = -404 ± 28 kJ mol(-1)...
September 14, 2016: Physical Chemistry Chemical Physics: PCCP
Y Z Chua, M Tylinski, S Tatsumi, M D Ediger, C Schick
Physical vapor deposition (PVD) has been used to prepare organic glasses with very high kinetic stability and it has been suggested that molecular anisotropy is a prerequisite for stable glass formation. Here we use PVD to prepare glasses of tetrachloromethane, a simple organic molecule with a nearly isotropic molecular structure. In situ AC nanocalorimetry was used to characterize the vapor-deposited glasses. Glasses of high kinetic stability were produced by deposition near 0.8 Tg. The isothermal transformation of the vapor-deposited glasses into the supercooled liquid state gave further evidence that tetrachloromethane forms glasses with high kinetic stability, with the transformation time exceeding the structural relaxation time of the supercooled liquid by a factor of 10(3)...
June 28, 2016: Journal of Chemical Physics
Michael I Recht, Vicki Nienaber, Francisco E Torres
Isothermal titration calorimetry (ITC) provides a sensitive and accurate means by which to study the thermodynamics of binding reactions. In addition, it enables label-free measurement of enzymatic reactions. The advent of extremely sensitive microcalorimeters have made it increasingly valuable as a tool for hit validation and characterization, but its use in primary screening is hampered by requiring large quantities of reagents and long measurement times. Nanocalorimeters can overcome these limitations of conventional ITC, particularly for screening libraries of 500-1000 compounds such as those encountered in fragment-based lead discovery...
2016: Methods in Enzymology
Cristian Rodríguez-Tinoco, Marta Gonzalez-Silveira, Joan Ràfols-Ribé, Aitor F Lopeandía, Javier Rodríguez-Viejo
While ordinary glasses transform into supercooled liquid via a homogeneous bulk mechanism, thin film glasses of higher stability transform heterogeneously by a front propagating from the surface and/or the interfaces. In this work, we use quasi-adiabatic fast scanning nanocalorimetry to determine the heat capacity of thin glassy layers of indomethacin vapor-deposited in a broad temperature range of 110 K below the glass transition temperature. Their variation in fictive temperature amounts to 40 K. We show that a propagating front is the initial transformation mechanism in all cases...
December 14, 2015: Physical Chemistry Chemical Physics: PCCP
Dongwoo Lee, Gi-dong Sim, Kejie Zhao, Joost J Vlassak
Reactive nanolaminates afford a promising route for the low-temperature synthesis of zirconium diboride, an ultrahigh-temperature ceramic with metallic properties. Although the addition of carbon is known to facilitate sintering of ZrB2, its effect on the kinetics of the formation reaction has not been elucidated. We have employed a combined approach of nanocalorimetry and first-principles theoretical studies to investigate the kinetic role of carbon in the synthesis of ZrB2 using B4C/Zr reactive nanolaminates...
December 9, 2015: Nano Letters
Feng Yi, Jeffery B DeLisio, Michael R Zachariah, David A LaVan
We report on measurements integrating a nanocalorimeter sensor into a time-of-flight mass spectrometer (TOFMS) for simultaneous thermal and speciation measurements at high heating rates. The nanocalorimeter sensor was incorporated into the extraction region of the TOFMS system to provide sample heating and thermal information essentially simultaneously with the evolved species identification. This approach can be used to measure chemical reactions and evolved species for a variety of materials. Furthermore, since the calorimetry is conducted within the same proximal volume as ionization and ion extraction, evolved species detected are in a collision-free environment, and thus, the possibility exists to interrogate intermediate and radical species...
October 6, 2015: Analytical Chemistry
Amou Akhgarnusch, Robert F Höckendorf, Martin K Beyer
The reaction of sulfur hexafluoride with gas-phase hydrated electrons (H2O)n(-), n ≈ 60-130, is investigated at temperatures T = 140-300 K by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. SF6 reacts with a temperature-independent rate of 3.0 ± 1.0 × 10(-10) cm(3) s(-1) via exclusive formation of the hydrated F(-) anion and the SF5(•) radical, which evaporates from the cluster. Nanocalorimetry yields a reaction enthalpy of ΔHR,298K = 234 ± 24 kJ mol(-1). Combined with literature thermochemical data from bulk aqueous solution, these result in an F5S-F bond dissociation enthalpy of ΔH298K = 455 ± 24 kJ mol(-1), in excellent agreement with all high-level quantum chemical calculations in the literature...
October 1, 2015: Journal of Physical Chemistry. A
Katherine R Whitaker, M Tylinski, Mathias Ahrenberg, Christoph Schick, M D Ediger
The reversing heat capacity of vapor-deposited o-terphenyl glasses was determined by in situ alternating current nanocalorimetry. Glasses were deposited at substrate temperatures ranging from 0.39 Tg to Tg, where Tg is the glass transition temperature. Glasses deposited near 0.85 Tg exhibited very high kinetic stability; a 460 nm film required ∼10(4.8) times the structural relaxation time of the equilibrium supercooled liquid to transform into the liquid state. For the most stable o-terphenyl glasses, the heat capacity was lower than that of the ordinary liquid-cooled glass by (1 ± 0...
August 28, 2015: Journal of Chemical Physics
Ina Herber, Wai-Kit Tang, Ho-Yin Wong, Tim-Wai Lam, Chi-Kit Siu, Martin K Beyer
Reactions of [M(H2O)n](+), M = Cr, Mn, Fe, Co, Ni, Cu, and Zn, n < 50, with CH3CN are studied in the gas phase by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Sequential uptake of 4-6 acetonitrile molecules is observed for all metals. Rate constants show a weak dependence on both the metal and the number of acetonitrile molecules already in the cluster. Nanocalorimetry yields the enthalpy of the first reaction step. For most metals, this is consistent with a ligand exchange of water against acetonitrile...
June 4, 2015: Journal of Physical Chemistry. A
Manel Molina-Ruiz, Pablo Ferrando-Villalba, Cristian Rodríguez-Tinoco, Gemma Garcia, Javier Rodríguez-Viejo, Inma Peral, Aitor F Lopeandía
The use of a membrane-based chip nanocalorimeter in a powder diffraction beamline is described. Simultaneous wide-angle X-ray scattering and scanning nanocalorimetric measurements are performed on a thin-film stack of palladium/amorphous silicon (Pd/a-Si) at heating rates from 0.1 to 10 K s(-1). The nanocalorimeter works under a power-compensation scheme previously developed by the authors. Kinetic and structural information of the consumed and created phases can be obtained from the combined techniques...
May 2015: Journal of Synchrotron Radiation
Y Z Chua, M Ahrenberg, M Tylinski, M D Ediger, C Schick
Glasses of ethylcyclohexane produced by physical vapor deposition have been characterized by in situ alternating current chip nanocalorimetry. Consistent with previous work on other organic molecules, we observe that glasses of high kinetic stability are formed at substrate temperatures around 0.85 Tg, where Tg is the conventional glass transition temperature. Ethylcyclohexane is the least fragile organic glass-former for which stable glass formation has been established. The isothermal transformation of the vapor-deposited glasses into the supercooled liquid state was also measured...
February 7, 2015: Journal of Chemical Physics
Christian Riekel, Emanuela Di Cola, Michael Reynolds, Manfred Burghammer, Martin Rosenthal, David Doblas, Dimitri A Ivanov
Noble metal nanoparticles with ligand shells are of interest for applications in catalysis, thermo-plasmonics, and others, involving heating processes. To gain insight into the structure-formation processes in such systems, self-assembly of carbohydrate-functionalized gold nanoparticles during precipitation from solution and during further heating to ca. 340 °C was explored by in situ combination of nanobeam SAXS/WAXS and nanocalorimetry. Upon precipitation from solution, X-ray scattering reveals the appearance of small 2D domains of close-packed nanoparticles...
January 13, 2015: Langmuir: the ACS Journal of Surfaces and Colloids
Feng Yi, Il Kyoon Kim, Song Li, David A Lavan
The phase transition evolution with hydration of a model system, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), was investigated with a fast nanocalorimetry system. Using nanocalorimetry, it is possible to measure the gel to liquid phase transitions that occur on millisecond to second time scales and quantify the time to recover the hydrated state. The results show the phase transition occurring in a few milliseconds and the relaxation or recovery time from the dehydrated state back to original hydrated state occurring with times dependent on the local humidity...
November 2014: Journal of Pharmaceutical Sciences
Michael D Grapes, Thomas LaGrange, Lawrence H Friedman, Bryan W Reed, Geoffrey H Campbell, Timothy P Weihs, David A LaVan
Nanocalorimetry is a chip-based thermal analysis technique capable of analyzing endothermic and exothermic reactions at very high heating and cooling rates. Here, we couple a nanocalorimeter with an extremely fast in situ microstructural characterization tool to identify the physical origin of rapid enthalpic signals. More specifically, we describe the development of a system to enable in situ nanocalorimetry experiments in the dynamic transmission electron microscope (DTEM), a time-resolved TEM capable of generating images and electron diffraction patterns with exposure times of 30 ns-500 ns...
August 2014: Review of Scientific Instruments
Julien Boulon, Isabelle Braud, Sébastien Zamith, Pierre Labastie, Jean-Marc L'Hermite
An experimental nanocalorimetric study of mass selected protonated (H2O)nH(+) and deprotonated (H2O)n-1OH(-) water clusters is reported in the size range n = 20-118. Water cluster's heat capacities exhibit a change of slope at size dependent temperatures varying from 90 to 140 K, which is ascribed to phase or structural transition. For both anionic and cationic species, these transition temperatures strongly vary at small sizes, with higher amplitude for protonated than for deprotonated clusters, and change more smoothly above roughly n ≈ 35...
April 28, 2014: Journal of Chemical Physics
Michael I Recht, Vandana Sridhar, John Badger, Pierre-Yves Bounaud, Cheyenne Logan, Barbara Chie-Leon, Vicki Nienaber, Francisco E Torres
Fragment-based lead discovery (FBLD) is a technique in which small, low-complexity chemical fragments of 6 to 15 heavy atoms are screened for binding to or inhibiting activity of the target. Hits are then linked and/or elaborated into tightly binding ligands, ideally yielding early lead compounds for drug discovery. Calorimetry provides a label-free method to assay binding and enzymatic activity that is unaffected by the spectroscopic properties of the sample. Conventional microcalorimetry is hampered by requiring large quantities of reagents and long measurement times...
April 2014: Journal of Biomolecular Screening
Lito P de la Rama, Liang Hu, Zichao Ye, Mikhail Y Efremov, Leslie H Allen
We report a systematic study of melting of layered lamella of silver alkanethiolates (AgSCn). A new synthesis method allows us to independently change the thickness of the crystal in two ways-by modulating chain length (n = 7-18) and by stacking these crystals to a specific layer number (m = 1-10). This method produces magic size lamella, having a well-spaced discrete melting point, Tm, distribution. Nanocalorimetry shows stepwise increases in Tm, as the lamella thickness increases by integer increments of chain length...
September 25, 2013: Journal of the American Chemical Society
John M Gregoire, Kechao Xiao, Patrick J McCluskey, Darren Dale, Gayatri Cuddalorepatta, Joost J Vlassak
We combine the characterization techniques of scanning AC nanocalorimetry and x-ray diffraction to study phase transformations in complex materials system. Micromachined nanocalorimeters have excellent performance for high-temperature and high-scanning-rate calorimetry measurements. Time-resolved X-ray diffraction measurements during in-situ operation of these devices using synchrotron radiation provide unprecedented characterization of thermal and structural material properties. We apply this technique to a Fe0...
May 20, 2013: Applied Physics Letters
Katherine R Whitaker, Daniel J Scifo, M D Ediger, Mathias Ahrenberg, Christoph Schick
In situ AC nanocalorimetry was used to measure the reversing heat capacity of vapor-deposited glasses of decahydronaphthalene (decalin). Glasses with low heat capacity and high kinetic stability, as compared to the corresponding liquid-cooled glass, were prepared from cis-decalin and from several cis/trans-decalin mixtures. This is the first report of highly stable glass formation for molecular mixtures. The 50/50 cis/trans-decalin mixture is the highest fragility material reported to produce an ultrastable glass...
October 24, 2013: Journal of Physical Chemistry. B
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"