Half-maximum Peak Height Research Articles

Intrinsic Properties of immunoglobulin IgG1 Isotype-Switched B Cell Receptors Promote Microclustering and the Initiation of Signaling

Memory B cells express high-affinity, immunoglobulin GB cell receptors (IgG BCRs) that enhance B cell responses, giving rise to the rapid production of high-affinity, IgG antibodies. Despite the central role of IgG BCRs in memory responses, the mechanisms by which the IgG BCRs function to enhance B cell responses are not fully understood. Using high-resolution live-cell imaging, we showed that IgG1 BCRs dramatically enhanced the earliest BCR-intrinsic events that followed within seconds of B cells' encounter with membrane bound antigen, including BCR oligomerization and BCR microcluster growth, leading to Syk kinase recruitment and calcium responses. The enhancement of these early events was dependent on a membrane proximal region of the IgG1 cytoplasmic tail not previously appreciated to play a role in IgG1 BCR signaling. Thus, intrinsic properties of the IgG1 BCR enhance early antigen-driven events that ultimately translate into heightened signaling.

Petroleomics: Chemistry of the underworld

Each different molecular elemental composition-e.g., C(c)H(h)N(n)O(o)S(s)-has a different exact mass. With sufficiently high mass resolving power (m/Deltam(50%) approximately 400,000, in which m is molecular mass and Deltam(50%) is the mass spectral peak width at half-maximum peak height) and mass accuracy (<300 ppb) up to approximately 800 Da, now routinely available from high-field (>/=9.4 T) Fourier transform ion cyclotron resonance mass spectrometry, it is possible to resolve and identify uniquely and simultaneously each of the thousands of elemental compositions from the most complex natural organic mixtures, including petroleum crude oil. It is thus possible to separate and sort petroleum components according to their heteroatom class (N(n)O(o)S(s)), double bond equivalents (DBE = number of rings plus double bonds involving carbon, because each ring or double bond results in a loss of two hydrogen atoms), and carbon number. "Petroleomics" is the characterization of petroleum at the molecular level. From sufficiently complete characterization of the organic composition of petroleum and its products, it should be possible to correlate (and ultimately predict) their properties and behavior. Examples include molecular mass distribution, distillation profile, characterization of specific fractions without prior extraction or wet chemical separation from the original bulk material, biodegradation, maturity, water solubility (and oil:water emulsion behavior), deposits in oil wells and refineries, efficiency and specificity of catalytic hydroprocessing, "heavy ends" (asphaltenes) analysis, corrosion, etc.

Thermal behavior of a bentonite

Abstract The mineralogical composition of the Kutahya calcium bentonite (CaB) from Turkey was obtained as mass% of 60% calcium rich smectite (CaS), 30% opal-CT (OCT), trace amount illite (I), and some non-clay impurities by using chemical analysis (CA), X-ray diffraction (XRD), and thermal analysis (TG-DTA) data. The crystallinity, porosity, and surface area of the samples heated between 25–1300°C for 2 h were examined by using XRD, TG, DTA and N2-adsorption-desorption data. The position of the 001 reflection which is the most characteristic for CaS does not affect from heating between 25–600°C and then disappeared. The decrease in relative intensity (I/I 0) from 1.0 to zero and the increase in full width at half-maximum peak height (FWHM) from 0.25 to 1.0° of the 001 reflection show that the crystallinity of the CaS decreased continuously by rising the heating temperature from 25 to 900°C and then collapsed. The most characteristic 101 reflection for opals intensifies greatly between 900 and 1100°C with...

The effect of heat treatment on the paracrystallinity of an opal-CT found in a bentonite

To investigate temperature dependence of paracrystallinity for opal-CT, a bentonite containing approximately 34% by mass opal-CT have been used as material. Since opal-CT can not be separated entirely, the bentonite samples have been heated at different temperatures in the interval from 200 °C to 1300 °C for 2 h, and at 1050 °C for different time intervals changing from 2 h to 24 h. The X-ray diffraction (XRD) patterns of the original and heated samples have been obtained. The increase in the paracrystallinity has been discussed according to the thermal behavior of the relative intensity ( I/ I 0), relative full width at half-maximum peak height (FWHM/FWHM 0 ≡ W) and d-value of the most characteristics XRD peak for opal-CT between 0.405 nm and 0.410 nm region. The increase in I/ I 0 from 1 to 3, and in d(l 0 1) spacing from 0.4050 to 0.4095 and decrease in W from 1 to 0.6 show that there is an increase in paracrystallinity for opal-CT by rising the temperatures between 800 °C and 1300 °C. The increase, of I/ I 0 value from 1 to 5 by heating at 1050 °C while time increases from 2 h to 24 h shows that the paracrystallinity of opal-CT increase by time and reaches steady state condition approximately 1300 °C.

Atmospheric Pressure Photoionization Proton Transfer for Complex Organic Mixtures Investigated by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

To further clarify the role of dopant solvent in proton transfer in atmospheric pressure photoionization (APPI), we employ ultrahigh-resolution FT-ICR mass analysis to identify M(+*), [M + H](+), [M - H](-), and [M + D](+) species in toluene or perdeuterotoluene for an equimolar mixture of five pyrrolic and pyridinic nitrogen heterocyclic model compounds, as well as for a complex organic mixture (Canadian Athabasca bitumen middle distillate). In the petroleum sample, the protons in the [M + H](+) species originate primarily from other components of the mixture itself, rather than from the toluene dopant. In contrast to electrospray ionization, in which basic (e.g., pyridinic) species protonate to form [M + H](+) positive ions and acidic (e.g., pyrrolic) species deprotonate to form [M - H](-) negative ions, APPI generates ions from both basic and acidic species in a single positive-ion mass spectrum. Ultrahigh-resolution mass analysis (in this work, m/Deltam(50%) = 500,000, in which Deltam(50%) is the mass spectral peak full width at half-maximum peak height) is needed to distinguish various close mass doublets: (13)C versus (12)CH (4.5 mDa), (13)CH versus (12)CD (2.9 mDa), and H(2) versus D (1.5 mDa).

Preparation and characterization of acid-activated bentonite powders

The Kütahya calcium bentonite (CaB) from Turkey shows significant changes in crystal structure, chemical composition and porosity with H 2SO 4 activation realized by heating its acidic aqueous suspension at 97 °C for 6 h. The acid content was changed from zero to 70% by mass, based on the dry bentonite–acid mixture. It was estimated from chemical analysis (CA) and X-ray diffraction (XRD) data that the CaB contains 65% calcium montmorillonite (CaM) and 30% opal-CT (OCT) by mass, and also illite (I) and other impurities in lower extents. The decrease in crystallinity of the CaM by the activation was discussed as regards to the decrease in the relative intensity ( I / I 0) and increase in the full width at half-maximum peak height (FWHM) of the 001 XRD peak for CaM with the H 2SO 4%. The CA data reveals that the relative content of the undissolved cations in the CaB increase in the order of Ca 2+, Na +, Mg 2+, Fe 2+,3+, Al 3+, K +, Si 4+, and Ti 4+ with H 2SO 4%. The specific micropore volume ( V mi) and specific mesopore volume ( V me) of the samples were estimated from N 2-adsorption and desorption data, by standard methods. The V me shows a ‘zig-zag’ increase from 0.104 cm 3g − 1 to a maximum of 0.232 cm 3g − 1 at 40% and then decrease to 0.149 cm 3g − 1 at 70% H 2SO 4, respectively. The V mi increases about from zero to 0.055 cm 3g − 1 at 10% H 2SO 4 and then stayed approximately constant.

Characterization of silica polymorphs in kaolins by X-ray diffraction before and after phosphoric acid digestion and thermal treatment

To characterize silica polymorphs (silicas) in some kaolins, orthophosphoric acid digestion (240 °C, 15 min), and thermal treatment (1050 °C, 24 h) were applied to eight samples. The original, digested, and heated samples were examined by X-ray diffraction (XRD). Crystalline silica quartz (SiO 2) was identified from the standard XRD patterns of the original kaolins; all contained quartz. On the other hand, hydrated partially crystalline silicas (SiO 2· nH 2O), such as well-ordered opal-C and opal-CT, were not readily distinguished from high-temperature crystalline silica, α-cristobalite, using standard XRD patterns of the original kaolins because, sharp and intense characteristic XRD peaks ( h k l = 1 0 1) centered near 0.4 nm for opal-C, opal-CT, and α-cristobalite coincided. In order to distinguish these silicas the XRD patterns of the digested and heated samples were evaluated. It was observed that the 1 0 1 peaks disappear and sharpen in the course of digestion and heating, respectively. Because, the crystallinity of α-cristobalite does not change by these treatments, it was concluded that the kaolins contain opal-C and opal-CT or their mixtures in amorphous opal-A (SiO 2· nH 2O), but not α-cristobalite, which is probably human carcinogen. Because, the crystallinity increases in order opal-CT and opal-C, the narrowing in width at half-maximum peak height (FWHM) 1 0 1 must be more for opal-CT than opal-C by heating. Therefore, to distinguish opal-CT and opal-C from each other, the FWHM values before and after the heating process, were examined. Based on the results, it was estimated that six kaolins contain opal-CT in opal-A matrix, one kaolin contains only opal-A in a trace amount, and one kaolin contains non-opals.

ESI FT-ICR mass spectral analysis of coal liquefaction products

We have applied electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze the pyridine soluble fraction of a distillation resid and a further processed liquid product in a coal liquefaction process. The inherent high resolving power ( m/Δ m 50%>300,000, in which Δ m 50% is full mass spectral peak width at half-maximum peak height) and mass accuracy (<1 ppm) of FT-ICR MS makes it possible to resolve and identify polar heteroatomic species. The resid contains more heteroatomic compounds and a higher molecular weight distribution whereas the liquid sample is lower in average mass and more saturated. The data confirms that the liquefaction process produces lower mass, hydrogenated liquid product whereas the resid (highly aromatic and of high heteroatom content) must be recycled to reduce its heteroatom content and increase its degree of saturation.

Resolution and Identification of Elemental Compositions for More than 3000 Crude Acids in Heavy Petroleum by Negative-Ion Microelectrospray High-Field Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Although crude acids are minor constituents in petroleum, they have significant implications for crude oil geochemistry, corrosion, and commerce. We have previously demonstrated that a single positive-ion electrospray ionization (ESI) high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) experiment can resolve and identify 3000 chemically different elemental compositions of bases (basic nitrogen compounds) in a crude oil. Here, we show that negative-ion ESI high-field FT-ICR MS can selectively ionize and identify naphthenic acids without interference from the hydrocarbon background. When combined with prechromatographic separation, ESI FT-ICR MS reveals an even more detailed acid composition. An average mass resolving power, m/Δm50% ≥ 80 000 (Δm50% is mass spectral peak full width at half-maximum peak height) across a wide mass range (200 < m/z < 1000), distinguishes as many as 15 distinct chemical formulas within a 0.26 Da mass window. Collectively, more than 3000 chemically different elemental compositions containing O2, O3, O4, and O2S, O3S, and O4S were determined in a South American heavy crude. Our data indicates that the crude acids consist of a mixture of structures ranging from C15−C55 with cyclic (1−6 rings) and aromatic (1−3 ring) structures. The acid composition appears to be simpler than that of the corresponding hydrocarbon analogues.

Phase correction for collision model analysis and enhanced resolving power of fourier transform ion cyclotron resonance mass spectra.

Phase correction of FT-ICR data yields an absorption spectrum that offers a gain by up to a factor of 2 in mass resolving power (at half-maximum peak height), compared to conventional magnitude-mode display. That improvement is equivalent to doubling the applied magnetic field strength, without loss in signal-to-noise (S/N) ratio, provided that the time-domain data are padded with an equal number of zeroes before FFT. Our simple, visual, user-interactive algorithm quickly corrects for zero-order and first-order variation of phase with frequency. We find that the theoretical mass resolving power enhancement for pressure-limited absorption-mode over magnitude-mode line shape depends on the collision mechanism: factor of 1.40 for hard sphere vs 3(1/2) for Langevin (ion: induced dipole). Thus, the experimental enhancement in mass resolving power (factor of 1.43 +/- 0.09) for isotopically resolved peaks in the FT-ICR mass spectra of electrosprayed bovine carbonic anhydrase (approximately 29 kDa) directly supports the hard-sphere collision model. Optimal implementation of phasing requires the following: (a) a delay between excitation and detection of less than half of one sampling interval to avoid baseline "roll" and Gibb's oscillations; (b) accurate analog-to-digital conversion; (c) a sufficiently long acquisition period to yield several data points per absorption-mode peak width at half-maximum peak height; and (d) avoidance of FT-ICR apodization functions (e.g., Hamming and Hanning) that suppress the initial time-domain data. Pulsed single-frequency excitation (duration much less than the reciprocal of the Nyquist bandwidth) can eliminate higher than first-order variation of phase with frequency. Phased FT-ICR spectra should prove especially desirable for analysis of complex mixtures, for resolving isotopic distributions in electrosprayed multiply charged macromolecules and for characterizing ion collisions (and thus ion size and shape).

Action potentials and frequency-dependent secretion in the mouse neurohypophysis.

The frequency-dependence of secretion of arginine vasopressin (AVP) from the mouse neural lobe in vitro was studied and found to be comparable to that reported for the rat neural lobe in vitro. For a stimulus train of 600 pulses, the secretion of AVP per pulse (i.e., facilitation) increased to a maximum at 20 Hz. Compound intracellular action potentials were recorded from the mouse neural lobe using optical recording methods and potentiometric dyes. These extrinsic optical signals reflect the true time courses of transmembrane potential changes (e.g., action potentials), and the action potentials recorded from mouse neural lobes had a duration of 5 ms; at half-maximum peak height. Optical recordings during repetitive stimulation showed that significant spike broadening occurred in each subsequent spike at 10 and 16 Hz stimulation. These data are consistent with a spike broadening hypothesis of frequency-dependent facilitation in the neural lobe. However, 4-aminopyridine, a drug which causes spike broadening in neural tissues by blocking potassium channels, did not produce an increase in secretion of AVP per stimulus from the mouse neural lobe.

Phenanthrimidazoles as fluorescent derivatives in the analysis of fatty acids by high-performance liquid chromatography

In methyl polyphosphate, prepared in chloroform, fatty acids condense with 9,10-diaminophenanthrene to form 2-substituted phenanthrimidazoles. The reaction proceeds to completion within 3–6 min at 85° to give, in general, yields reproducibly in excess of 95%. Exceptions are linolenic acid, from which the yield is reproducibly 91%, and formic acid, from which no derivative is obtained under these conditions. When the 2-substituent is unconjugated with the nucleus the mean quantum yield of fluorescence from derivatives of seventeen different acids under conditions relevant to the derivatives' chromatography (methanolic solvents) is 0.68 in nitrogen-purged solvents and 0.31 in aerated solvents, both with standard deviations of 0.02. The fluorescence emission exhibits overlapping maxima at 367 and 382 nm, with a width at half maximum peak height of 3120 cm -1. Under nitrogen, but not in the presence of air, quantum yields vary negligibly with the water content of the solvent over the chromatographically useful range. At higher concentrations of water the formation of weakly fluorescent micelles may occur. Above the acetic derivative the molar absorptivities in methanolic solvents are independent of the substituent in the sixteen unconjugated derivatives examined. At 254–255 nm the man value is 90133. Other weaker absorbance maxima are available at various points up to 354 nm. From these results the intrinsic fluorescence sensitivity value of the derivatives is greater than that of the 4-hydroxymethyl-7-methoxycoumarin ester derivatives by a factor of 12. The reaction mixture may be injected directly on to reversed-phase (octadecylsilyl) columns. Of the nineteen acids examined, up to erucic in molecular weight, the derivatives of all except the pair n-butyric and crotonic are separated from one another in aqueous methanol containing 0.01 M ammonium carbonate. On gradient elution, equimolar amounts of different acids give essentially constant peak areas, in contrast to the methoxycoumarins.

Utilizing an intrinsic 31P NMR probe in studies of cobalamin ligation

Phosphorous 31 nuclear magnetic resonance spectroscopy has been employed to observe changes in axial ligation in hydroxycobalamin solutions. The naturally occurring phosphorous nucleus in the benzimidazole side “arm” of the corrin is shown to exhibit different chemical shifts depending upon whether the benzimidazole is coordinated to the cobalt (III) ion or whether it has been displaced. The phosphorous resonance's linewidth at half maximum peak height seems also to be an indicator of the cobalt oxidation state, exhibiting a twenty fold larger width in the coblt (II) complex. The implications of these findings for future studies on certain coenzyme B 12 dependent enzymes is discussed.