A Tandem Mass Spectrometry Study of [C,H2,X2,Si]+• Ions (X = H, D, Cl) and the Generation of Their Neutral Counterparts

2000 ◽  
Vol 6 (2) ◽  
pp. 89-96 ◽  
Author(s):  
Dmitri V. Zagorevski ◽  
Christiane Aubry ◽  
John L. Holmes
Keyword(s):  
Gas Phase ◽  
Mass Spectra ◽  
Appearance Energy ◽  
Time Frame ◽  
Heat Of Formation ◽  
Ion Source ◽  
Collision Induced Dissociation ◽  
Mass Spectrometry Study ◽  
Time Frames ◽  
Positively Charged

Two [Si,C,H4]+• isomers, having similar stabilities and a relatively low barrier for their interconversion, have been separately generated in mass spectrometric experiments. CH2SiD2+• and D2-CH3SiH+• ions were produced from the same ionic precursor, namely ionized 1,1-dideutero-silacyclobutane (D2-I). Dissociation of the latter in the ion source resulted in the silaethene structure, whereas metastable dissociation gave rise to the dideuterated methylsilylene. Appearance energy measurements confirmed the formation of the two [Si,C,H2,D2]+• isomers, whose heats of formation were estimated to be 1017 and 1038 kJ mol−1 for CH3SiH+• and CH2SiH2+•, respectively. Both ion-source and metastable dissociations of ionized D2-I resulted in [Si,C,H3,D]+• and [Si,C,H4]+• ions possessing the methylsilylene structure. The collision-induced dissociation (CID) and neutralization–reionization (NR) mass spectra of CH2SiD2+• and D2-CH3SiH+• ions were distinctively different. The characteristic dissociation channel for the CH2SiD2 structure was the loss of CH2. Some dissociations of the ionized silaethene involved the formation of the methylsilylene intermediate. However, CH3SiH+• ions produced by this isomerization appeared to be unstable and did not survive neutralization–reionization. As a result, the CID mass spectra of CH2SiD2+• ions prior to neutralization and surviving the NR event were almost identical. Strong recovery signals in the NR mass spectra were consistent with the intrinsic stability of neutral silaethene and methylsilylene. The interconversion of these structures generated by neutralization of their positively-charged counterparts seems to be very unlikely. The CID, NR and NR/CID mass spectra of [Si,C,H2,Cl2]+• ions produced from various precursors and in different time frames were indistinguishable. They corresponded to the CH2SiCl2 connectivity of the atoms. The heat of formation for CH2SiCl2+• ions was estimated to be ∼732 kJ mol−1, based on appearance energy measurements. The presence of a strong recovery signal in the NR mass spectra was consistent with the formation of stable neutral 1,1-dichlorosilaethene in the gas phase on the microsecond time frame.

Differentiation of Ionised Benzimidazole from its Isomeric α-Distonic Ion by Collision-Induced Dissociation and Neutralisation—Reionisation Mass Spectrometry

2005 ◽  
Vol 11 (4) ◽  
pp. 381-387 ◽  
Author(s):  
Thanasis Karapanayiotis ◽  
Richard D. Bowen
Keyword(s):  
Mass Spectra ◽  
Radical Cations ◽  
Time Frame ◽  
Careful Consideration ◽  
Collision Induced Dissociation ◽  
Doubly Charged Ions ◽  
Doubly Charged ◽  
Ion Collision ◽  
Charged Ions ◽  
Distonic Ion

Ionised benzimidazole and its isomeric α-distonic ion (or ionised ylid) have been examined by recording their metastable ion, collision-induced dissociation and neutralisation–reionisation mass spectra. These tautomers may be distinguished by careful consideration of key features of the collision-induced dissociation spectra, with or without prior neutralisation and reionisation. Formation of doubly-charged ions by charge stripping occurs preferentially when the α-distonic ion is subjected to collision. This α-distonic ion survives neutralisation and reionisation, thus establishing that the corresponding ylid is stable on the microsecond time frame. The effects of benzannulation on the ease of differentiation of classical and distonic radical cations derived from biologically important heterocycles are considered.

Tautomerism of uracil and related compounds: A mass spectrometry study

2017 ◽  
Vol 24 (2) ◽  
pp. 214-224 ◽  
Author(s):  
Diego D Colasurdo ◽  
Matías N Pila ◽  
Dacio A Iglesias ◽  
Sergio L Laurella ◽  
Danila L Ruiz
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Mass Spectra ◽  
Tautomeric Form ◽  
Ion Trap ◽  
Theoretical Calculations ◽  
Ion Trap Mass Spectrometry ◽  
Mass Spectrometry Study ◽  
Related Compounds ◽  
Substituted Uracils

It has been demonstrated that uracil has a preponderant tautomeric form, but it is also known that different tautomers co-exist in this equilibrium. In this work, mass spectrometry is used as a helpful tool to analyse the equilibria, using derivative compounds to forbid the presence of some tautomers and ion trap mass spectrometry to follow relevant fragmentation pathways. Theoretical calculations were performed to confirm tautomers abundance by energy minimization in gas phase. Analysis of mass spectra of uracil, three methyl-substituted uracils, 2-thiouracil and three benzouracils suggest that uracil exists mainly as three tautomers in gas phase: one major structure that corresponds to the classical structure of uracil (pyrimidine-2,4(1H,3H)-dione) bearing two carbonyls and two NH moieties, and two minor enolic forms (4-hydroxypyrimidin-2(1H)-one and 2-hydroxypyrimidin-4(1H)-one). Such tautomeric distribution is supported by theoretical calculations, which show that they are the three most stable tautomers.

Tautomerization and Dissociation of Dimethyl Phosphonate Ions(CH3O)2P(H)=O•+:Theory and Experiment in Concert

2001 ◽  
Vol 215 (2) ◽  
Author(s):  
L.N. Heydorn ◽  
Y. Ling ◽  
G. de Oliveira ◽  
J.M.L: Martin ◽  
C. Lifshitz ◽  
...  
Keyword(s):  
Gas Phase ◽  
Mass Spectra ◽  
Low Energy ◽  
Collision Induced Dissociation ◽  
Potential Energy Profile ◽  
Time Resolved ◽  
Gas Phase Chemistry ◽  
Dissociation Chemistry ◽  
Phase Chemistry ◽  
Theory And Experiment

The unimolecular gas phase chemistry of the title ion,(CHThe identity of the ions was probed by tandem mass spectrometry methods. These include MI (metastable ion) or CID (collision induced dissociation) spectra, consecutive MI/CID and CID/CID spectra, NRMS (neutralization-reionization mass spectra), NR/CID and CIDI (collision induced dissociative ionization) spectra, time-resolved CID spectra and deuterium labelling. The energetics of the CHTheory and experiment yield a consistent potential energy profile that describes the isomerization and low energy dissociation chemistry of ions

Effects of Momentary Affect on Satisfaction Judgments

2020 ◽  
Vol 41 (2) ◽  
pp. 61-67
Author(s):  
Marko Tončić ◽  
Petra Anić
Keyword(s):  
Linear Models ◽  
Time Frame ◽  
Hierarchical Linear Models ◽  
Curvilinear Relationship ◽  
Positive And Negative Affect ◽  
Transient Events ◽  
Time Frames ◽  
Events Data ◽  
Level Satisfaction ◽  
Source Of Information

Abstract. This study aims to examine the effect of affect on satisfaction, both at the between- and the within-person level for momentary assessments. Affect is regarded as an important source of information for life satisfaction judgments. This affective effect on satisfaction is well established at the dispositional level, while at the within-person level it is heavily under-researched. This is true especially for momentary assessments. In this experience sampling study both mood and satisfaction scales were administered five times a day for 7 days via hand-held devices ( N = 74 with 2,122 assessments). Several hierarchical linear models were fitted to the data. Even though the amount of between-person variance was relatively low, both positive and negative affect had substantial effects on momentary satisfaction on the between- and the within-person level as well. The within-person effects of affect on satisfaction appear to be more pronounced than the between-person ones. At the momentary level, the amount of between-person variance is lower than in studies with longer time-frames. The affect-related effects on satisfaction possibly have a curvilinear relationship with the time-frame used, increasing in intensity up to a point and then decreasing again. Such a relationship suggests that, at the momentary level, satisfaction might behave in a more stochastic manner, allowing for transient events/data which are not necessarily affect-related to affect it.

scholarly journals A Volatility Estimator of Stock Market Indices Based on the Intrinsic Entropy Model

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 484
Author(s):  
Claudiu Vințe ◽  
Marcel Ausloos ◽  
Titus Felix Furtună
Keyword(s):  
Stock Market ◽  
Time Frame ◽  
Data Sets ◽  
Entropy Model ◽  
Daily Data ◽  
Volatility Models ◽  
Derivative Instruments ◽  
Securities Industry ◽  
Time Frames ◽  
Financial Securities

Grasping the historical volatility of stock market indices and accurately estimating are two of the major focuses of those involved in the financial securities industry and derivative instruments pricing. This paper presents the results of employing the intrinsic entropy model as a substitute for estimating the volatility of stock market indices. Diverging from the widely used volatility models that take into account only the elements related to the traded prices, namely the open, high, low, and close prices of a trading day (OHLC), the intrinsic entropy model takes into account the traded volumes during the considered time frame as well. We adjust the intraday intrinsic entropy model that we introduced earlier for exchange-traded securities in order to connect daily OHLC prices with the ratio of the corresponding daily volume to the overall volume traded in the considered period. The intrinsic entropy model conceptualizes this ratio as entropic probability or market credence assigned to the corresponding price level. The intrinsic entropy is computed using historical daily data for traded market indices (S&P 500, Dow 30, NYSE Composite, NASDAQ Composite, Nikkei 225, and Hang Seng Index). We compare the results produced by the intrinsic entropy model with the volatility estimates obtained for the same data sets using widely employed industry volatility estimators. The intrinsic entropy model proves to consistently deliver reliable estimates for various time frames while showing peculiarly high values for the coefficient of variation, with the estimates falling in a significantly lower interval range compared with those provided by the other advanced volatility estimators.

“The surprise questions” using variable time frames in hospitalized patients with advanced cancer

2021 ◽  
pp. 1-5
Author(s):  
Sun Hyun Kim ◽  
Sang-Yeon Suh ◽  
Seok Joon Yoon ◽  
Jeanno Park ◽  
Yu Jung Kim ◽  
...  
Keyword(s):  
Palliative Care ◽  
Advanced Cancer ◽  
Time Frame ◽  
Hospitalized Patients ◽  
Advanced Cancer Patients ◽  
Multicenter Cohort Study ◽  
Prediction Of Survival ◽  
Sensitivity Specificity ◽  
Surprise Question ◽  
Time Frames

Abstract Objective Several studies supported the usefulness of “the surprise question” in terms of 1-year mortality of patients. “The surprise question” requires a “Yes” or “No” answer to the question “Would I be surprised if this patient died in [specific time frame].” However, the 1-year time frame is often too long for advanced cancer patients seen by palliative care personnel. “The surprise question” with shorter time frames is needed for decision making. We examined the accuracy of “the surprise question” for 7-day, 21-day, and 42-day survival in hospitalized patients admitted to palliative care units (PCUs). Method This was a prospective multicenter cohort study of 130 adult patients with advanced cancer admitted to 7 hospital-based PCUs in South Korea. The accuracy of “the surprise question” was compared with that of the temporal question for clinician's prediction of survival. Results We analyzed 130 inpatients who died in PCUs during the study period. The median survival was 21.0 days. The sensitivity, specificity, and overall accuracy for the 7-day “the surprise question” were 46.7, 88.7, and 83.9%, respectively. The sensitivity, specificity, and overall accuracy for the 7-day temporal question were 6.7, 98.3, and 87.7%, respectively. The c-indices of the 7-day “the surprise question” and 7-day temporal question were 0.662 (95% CI: 0.539–0.785) and 0.521 (95% CI: 0.464–0.579), respectively. The c-indices of the 42-day “the surprise question” and 42-day temporal question were 0.554 (95% CI: 0.509–0.599) and 0.616 (95% CI: 0.569–0.663), respectively. Significance of results Surprisingly, “the surprise questions” and temporal questions had similar accuracies. The high specificities for the 7-day “the surprise question” and 7- and 21-day temporal question suggest they may be useful to rule in death if positive.

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