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Schorr P, Kovačević B, Volmer DA. Overestimation of 3α- over 3β -25-Hydroxyvitamin D 3 Levels in Serum: A Mechanistic Rationale for the Different Mass Spectral Properties of the Vitamin D Epimers. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:1116-1125. [PMID: 33780622 DOI: 10.1021/jasms.1c00054] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The metabolism of vitamin D3 includes a parallel C-3 epimerization pathway-in addition to the standard metabolic processes for vitamin D3-reversing the stereochemical configuration of the -OH group at carbon-3 (β→α). While the biological function of the 3α epimer has not been elucidated yet, the additional species cannot be neglected in the analytical determination of vitamin D3, as it has the potential to introduce analytical errors if not properly accounted for. Recently, some inconsistent mass spectral behavior was seen for the 25-hydroxyvitamin D3 (25(OH)D3) epimers during quantification using electrospray LC-MS/MS. The present work extends that of Flynn et al. ( Ann. Clin. Biochem. 2014, 51, 352-559) and van den Ouweland et al. ( J. Chromatogr. B 2014, 967, 195-202), who reported larger electrospray ionization response factors for the 3α epimer of 25(OH)D3 in human serum samples as compared to the regular 3β variant. The present work was concerned with the mechanistic reasons for these differences. We used a combination of electrospray ionization, atmospheric pressure chemical ionization, and density functional theory calculations to uncover structural dissimilarities between the epimers. A plausible mechanism is described based on intramolecular hydrogen bonding in the gas phase, which creates a small difference of proton affinities between the epimers. More importantly, this mechanism allows the explanation of the different ionization efficiencies of the epimers based on kinetic control of the ionization process, where ionization initially takes place at the hydroxyl group with subsequent proton transfer to a basic carbon atom. The barrier for this transfer differs between the epimers and is in direct competition with H2O elimination from the protonated hydroxyl group. The "hidden" site of high gas phase basicity was revealed through computational calculations and appears to be inaccessible via direct protonation.
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Affiliation(s)
- Pascal Schorr
- Department of Chemistry, Humboldt University Berlin, 12489 Berlin, Germany
| | - Borislav Kovačević
- Group for Computational Life Sciences, Ruđer Bošković Institute, 10000 Zagreb, Croatia
| | - Dietrich A Volmer
- Department of Chemistry, Humboldt University Berlin, 12489 Berlin, Germany
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Ochiai N, Sasamoto K, Kishimoto T. Development of a Method for the Quantitation of Three Thiols in Beer, Hop, and Wort Samples by Stir Bar Sorptive Extraction with in Situ Derivatization and Thermal Desorption-Gas Chromatography-Tandem Mass Spectrometry. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2015; 63:6698-6706. [PMID: 26166150 DOI: 10.1021/acs.jafc.5b02298] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A method for analysis of hop-derived polyfunctional thiols, such as 4-sulfanyl-4-methylpentan-2-one (4S4M2Pone), 3-sulfanylhexan-1-ol (3SHol), and 3-sulfanylhexyl acetate (3SHA), in beer, hop water extract, and wort at nanogram per liter levels was developed. The method employed stir bar sorptive extraction with in situ derivatization (der-SBSE) using ethyl propiolate (ETP), followed by thermal desorption and gas chromatography-tandem mass spectrometry (TD-GC-MS/MS) with selected reaction monitoring (SRM) mode. A prior step involved structural identification of the ETP derivatives of the thiols by TD-GC-quadrupole-time-of-flight mass spectrometry with parallel sulfur chemiluminescence detection (Q-TOF-MS/SCD) after similar der-SBSE. The der-SBSE conditions of the ETP concentration, buffer concentration, salt addition, and extraction time profiles were investigated, and the performance of the method was demonstrated with spiked beer samples. The limits of detection (LODs) (0.19-27 ng/L) are below the odor threshold levels of all analytes. The apparent recoveries at 10-100 ng/L (99-101%) and the repeatabilities [relative standard deviation (RSD) of 1.3-7.2%; n = 6] are also good. The method was successfully applied to the determination of target thiols at nanogram per liter levels in three kinds of beer samples (hopped with Cascade, Citra, and Nelson Sauvin) and the corresponding hop water extracts and wort samples. There was a clear correlation between the determined values and the characteristics of citrus hop aroma for each sample.
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Affiliation(s)
- Nobuo Ochiai
- †GERSTEL K.K., 1-3-1 Nakane, Meguro-ku, Tokyo 152-0031, Japan
| | - Kikuo Sasamoto
- †GERSTEL K.K., 1-3-1 Nakane, Meguro-ku, Tokyo 152-0031, Japan
| | - Toru Kishimoto
- ‡Asahi Breweries, Limited, 1-21 Midori 1-chome, Moriya-shi, Ibaraki 302-0106, Japan
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Chai Y, Weng G, Shen S, Sun C, Pan Y. The protonation site of para-dimethylaminobenzoic acid using atmospheric pressure ionization methods. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:668-676. [PMID: 25627246 DOI: 10.1007/s13361-014-1069-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Revised: 12/15/2014] [Accepted: 12/15/2014] [Indexed: 06/04/2023]
Abstract
The protonation site of para-dimethylaminobenzoic acid (p-DMABA) was investigated using atmospheric pressure ionization methods (ESI and APCI) coupled with collision-induced dissociation (CID), nuclear magnetic resonance (NMR), and computational chemistry. Theoretical calculations and NMR experiments indicate that the dimethyl amino group is the preferred site of protonation both in the gas phase and aqueous solution. Protonation of p-DMABA occurs at the nitrogen atom by ESI independent of the solvents and other operation conditions under typical thermodynamic control. However, APCI produces a mixture of the nitrogen- and carbonyl oxygen-protonated p-DMABA when aprotic organic solvents (acetonitrile, acetone, and tetrahydrofuran) are used, exhibiting evident kinetic characteristics of protonation. But using protic organic solvents (methanol, ethanol, and isopropanol) in APCI still leads to the formation of thermodynamically stable N-protonated p-DMABA. These structural assignments were based on the different CID behavior of the N- and O-protonated p-DMABA. The losses of methyl radical and water are the diagnostic fragmentations of the N- and O-protonated p-DMABA, respectively. In addition, the N-protonated p-DMABA is more stable than the O-protonated p-DMABA in CID revealed by energy resolved experiments and theoretical calculations.
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Affiliation(s)
- Yunfeng Chai
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, Zhejiang, People's Republic of China
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Ochiai N, Mitsui K, Sasamoto K, Yoshimura Y, David F, Sandra P. Multidimensional gas chromatography in combination with accurate mass, tandem mass spectrometry, and element-specific detection for identification of sulfur compounds in tobacco smoke. J Chromatogr A 2014; 1358:240-51. [PMID: 25087743 DOI: 10.1016/j.chroma.2014.06.106] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Revised: 06/26/2014] [Accepted: 06/30/2014] [Indexed: 01/08/2023]
Abstract
A method is developed for identification of sulfur compounds in tobacco smoke extract. The method is based on large volume injection (LVI) of 10μL of tobacco smoke extract followed by selectable one-dimensional ((1)D) or two-dimensional ((2)D) gas chromatography (GC) coupled to a hybrid quadrupole time-of-flight mass spectrometer (Q-TOF-MS) using electron ionization (EI) and positive chemical ionization (PCI), with parallel sulfur chemiluminescence detection (SCD). In order to identify each individual sulfur compound, sequential heart-cuts of 28 sulfur fractions from (1)D GC to (2)D GC were performed with the three MS detection modes (SCD/EI-TOF-MS, SCD/PCI-TOF-MS, and SCD/PCI-Q-TOF-MS). Thirty sulfur compounds were positively identified by MS library search, linear retention indices (LRI), molecular mass determination using PCI accurate mass spectra, formula calculation using EI and PCI accurate mass spectra, and structure elucidation using collision activated dissociation (CAD) of the protonated molecule. Additionally, 11 molecular formulas were obtained for unknown sulfur compounds. The determined values of the identified and unknown sulfur compounds were in the range of 10-740ngmg total particulate matter (TPM) (RSD: 1.2-12%, n=3).
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Affiliation(s)
- Nobuo Ochiai
- GERSTEL K.K., 1-3-1 Nakane, Meguro-ku, 152-0031 Tokyo, Japan.
| | - Kazuhisa Mitsui
- Japan Tobacco Inc., 6-2 Umegaoka Aoba-ku, Yokohama-shi, 227-8512 Kanagawa, Japan; The United Graduate School of Agricultural Sciences, Ehime University, 3-5-7 Tarumi, 790-8566 Matsuyama, Japan
| | - Kikuo Sasamoto
- GERSTEL K.K., 1-3-1 Nakane, Meguro-ku, 152-0031 Tokyo, Japan
| | - Yuta Yoshimura
- Japan Tobacco Inc., 6-2 Umegaoka Aoba-ku, Yokohama-shi, 227-8512 Kanagawa, Japan
| | - Frank David
- Research Institute for Chromatography, Kennedypark 26, 8500 Kortrijk, Belgium
| | - Pat Sandra
- Research Institute for Chromatography, Kennedypark 26, 8500 Kortrijk, Belgium
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Chai Y, Hu N, Pan Y. Kinetic and thermodynamic control of protonation in atmospheric pressure chemical ionization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:1097-1101. [PMID: 23633014 DOI: 10.1007/s13361-013-0626-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 03/21/2013] [Accepted: 03/21/2013] [Indexed: 06/02/2023]
Abstract
For p-(dimethylamino)chalcone (p-DMAC), the N atom is the most basic site in the liquid phase, whereas the O atom possesses the highest proton affinity in the gas phase. A novel and interesting observation is reported that the N- and O-protonated p-DMAC can be competitively produced in atmospheric pressure chemical ionization (APCI) with the change of solvents and ionization conditions. In neat methanol or acetonitrile, the protonation is always under thermodynamic control to form the O-protonated ion. When methanol/water or acetonitrile/water was used as the solvent, the protonation is kinetically controlled to form the N-protonated ion under conditions of relatively high infusion rate and high concentration of water in the mixed solvent. The regioselectivity of protonation of p-DMAC in APCI is probably attributed to the bulky solvent cluster reagent ions (S(n)H(+)) and the analyte having different preferred protonation sites in the liquid phase and gas phase.
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Affiliation(s)
- Yunfeng Chai
- Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
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Reid GE, Simpson RJ, O'Hair RA. Leaving group and gas phase neighboring group effects in the side chain losses from protonated serine and its derivatives. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2000; 11:1047-1060. [PMID: 11118111 DOI: 10.1016/s1044-0305(00)00189-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The gas phase fragmentation reactions of protonated serine and its YNHCH(CH2X)CO2H derivatives, beta-chloroalanine, S-methyl cysteine, O-methyl serine, and O-phosphoserine, as well as the corresponding N-acetyl model peptides have been examined via electrospray ionization tandem mass spectrometry (MS/MS). In particular, the competition between losses from the side chain and the combined loss of H2O and CO from the C-terminal carboxyl group of the amino acids or H2O or CH2CO from the N-acetyl model peptides are compared. In this manner the effect of the leaving group (Y = H or CH3CO, vary X) or of the neighboring group can be examined. It was found that the amount of HX lost from the side chain increases with the proton affinity of X [OP(O)(OH)2 > OCH3 approximately equals OH > Cl]. The ion due to the side chain loss of H2O from the model peptide N-acetyl serine is more abundant than that from protonated serine, suggesting that the N-acetyl group is a better neighboring group than the amino group. Ab initio calculations at the MP2(FC)/6-31G*//HF/6-31G* level of theory suggest that this effect is due to the transition state barrier for water loss from protonated N-acetyl serine being lower than that for protonated serine. The mechanism for side chain loss has been examined using MS3 tandem mass spectrometry, independent synthesis of proposed product ion structures combined with MS/MS, and hydrogen/deuterium exchange. Neighboring group rather than cis 1,2 elimination processes dominate in all cases. In particular, the loss of H3PO4 from O-phosphoserine and N-acetyl O-phosphoserine is shown to yield a 3-membered aziridine ring and 5-membered oxazoline ring, respectively, and not the dehydroalanine moiety. This is in contrast to results presented by DeGnore and Qin (J. Am. Soc. Mass Spectrom. 1998, 9, 1175-1188) for the loss of H3PO4 from larger peptides, where dehydroalanine was observed. Alternate mechanisms to cis 1,2 elimination, for the formation of dehydroalanine in larger phosphoserine or phosphothreonine containing peptides, are proposed.
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Affiliation(s)
- G E Reid
- Joint Protein Structure Laboratory, The Ludwig Institute for Cancer Research, Royal Melbourne Hospital, Parkville, Victoria, Australia
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Vais V, Etinger A, Mandelbaum A. Intramolecular proton transfers in stereoisomeric gas-phase ions and the kinetic nature of the protonation process upon chemical ionization. JOURNAL OF MASS SPECTROMETRY : JMS 1999; 34:755-760. [PMID: 10407360 DOI: 10.1002/(sici)1096-9888(199907)34:7<755::aid-jms831>3.0.co;2-j] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The isobutane chemical ionization (CI) mass spectra of cis- and trans-1-butyl-3- and -4-dimethylaminocyclohexanols and of their methyl ethers exhibit abundant [MH - H(2)O](+) and [MH - MeOH](+) ions respectively. On the other hand, only the MH(+) ions of the cis-isomers exhibit significant [MH - H(2)O](+) and [MH - MeOH](+) ions under collision-induced dissociation (CID) conditions. The non-occurrence of water and methanol elimination in the CID spectra of the trans-isomers indicates retention of the external proton at the dimethylamino group in the MH(+) ions that survive after leaving the ion source and the first quadrupole of the triple-stage quadrupole ion separating system, and the trans-orientation of the two basic sites does not allow proton transfer from the dimethylamino group to the hydroxyl or methoxyl. Such transfer is allowed in the cis-amino alcohols and amino ethers via internal hydrogen-bonded (proton-bridged) structures, resulting in the elimination of water and methanol from the surviving MH(+) ions of these particular stereoisomers upon CID. The abundant [MH - ROH](+) ions in the isobutane-CI mass spectra of the trans-isomers indicates protonation at both basic sites, affording two isomeric MH(+) ions in each case, one protonated at the dimethylamino group and the other at the less basic oxygen function. These results show that the isobutane-CI protonation of the amino ethers and amino alcohols is a kinetically controlled process, occurring competitively at both basic sites of the molecules, despite the large difference between their proton affinities ( approximately 25 and approximately 35 kcal mol(-1); 1 kcal = 4.184 kJ). Copyright 1999 John Wiley & Sons, Ltd.
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Affiliation(s)
- V Vais
- Department of Chemistry, Technion-Israel Institute of Technology, Haifa, Israel
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8
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Cross GG, Fyles TM. On the Synthesis of Monoamides of 18-Crown-6-tetracarboxylic Acid. J Org Chem 1997. [DOI: 10.1021/jo970707c] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- G. G. Cross
- Department of Chemistry, University of Victoria, Victoria, British Columbia V8W 3P6, Canada
| | - T. M. Fyles
- Department of Chemistry, University of Victoria, Victoria, British Columbia V8W 3P6, Canada
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Bogdanov B, Matimba HE, Ingemann S, Nibbering NM. Chemical ionization of phenyl n-propyl ether and methyl substituted analogs: Propene loss initiated by competing proton transfer to the oxygen atom and the aromatic ring. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 1996; 7:639-652. [PMID: 24203479 DOI: 10.1016/1044-0305(96)00002-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/1995] [Revised: 02/05/1996] [Accepted: 02/05/1996] [Indexed: 06/02/2023]
Abstract
The mechanism of propene loss from protonated phenyl n-propyl ether and a series of mono-, di-, and trimethylphenyl n-propyl ethers has been examined by chemical ionization (CI) mass spectrometry in combination with tandem mass spectrometry experiments. The role of initial proton transfer to the oxygen atom and the aromatic ring, respectively, has been probed with the use of deuterated CI reagents, D2O, CD3OD, and CD3CN (given in order of increasing proton affinity), in combination with deuterium labeling of the β position of the n-propyl group or the phenyl ring. The metastable [M + D](+) ions of phenyl n-propyl ether-formed with D2O as the CI reagent-eliminate C3H5D and C3H6 in a ratio of 10:90, which indicates that the added deuteron is incorporated to a minor extent in the expelled neutral species. In the experiments with CD3OD as the CI reagent, the ratio between the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of phenyl n-propyl ether is 18:82, whereas the ratio becomes 27:73 with CD3CN as the reagent. A similar trend in the tendency to expel a propene molecule that contains the added deuteron is observed for the metastable [M + D](+) ions of phenyl n-propyl ether labeled at the β position of the alkyl group. Incorporation of a hydrogen atom that originates from the aromatic ring in the expelled propene molecule is of negligible importance as revealed by the minor loss of C3H5D from the metastable [M + H](+) ions of C6D5OCH2CH2CH3 irrespective of whether H2O, CH3OH, or CH3CN is the CI reagent. The combined results for the [M + D](+) ions of phenyl n-propyl ether and deuterium-labeled analogs are suggested to be in line with a model that assumes that propene loss occurs not only from species formed by deuteron transfer to the oxygen atom, but also from ions generated by deuteron transfer to the ring. This is substantiated by the results for the methyl-substituted ethers, which reveal that the position as well as the number of methyl groups bonded to the ring exert a marked effect on the relative importances of the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of the unlabeled methyl-substituted species.
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Affiliation(s)
- B Bogdanov
- Institute of Mass Spectrometry, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS, Amsterdam, The Netherlands
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Nakata H, Arakawa N, Mizuno R. Significant differences in site of protonation and extent of fragmentations in chemical ionization and fast atom bombardment mass spectrometry of simple bifunctional compounds. A mechanistic implication for formation of protonated molecules. ACTA ACUST UNITED AC 1994. [DOI: 10.1002/oms.1210290406] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Takayama M, Tanaka Y, Nomura T. Competitive formation of M+˙ and [M + H]+ ions under fast atom bombardment conditions. ACTA ACUST UNITED AC 1993. [DOI: 10.1002/oms.1210281227] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Nakata H, Kadoguchi K, Konishi H, Takeda N, Tatematsu A. Protonation susceptibility and fragmentation capability of functional groups in chemical ionization mass spectrometry of simple bifunctional compounds. Semi-quantitative interpretation of spectra. ACTA ACUST UNITED AC 1993. [DOI: 10.1002/oms.1210280203] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Nakata H. Protonation susceptibility of functional groups: A new parameter for interpreting chemical ionization mass spectra of bifunctional organic compounds. ACTA ACUST UNITED AC 1992. [DOI: 10.1002/oms.1210270607] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Donovan T, Brodbelt J. Selective ion-molecule reactions of 2,5-dimethylpyrrole-γ-butyrolactone with dimethyl ether ions. ACTA ACUST UNITED AC 1992. [DOI: 10.1002/bms.1200210506] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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