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Modiba P, Matoetoe M, Crouch AM. Kinetics study of transition metal complexes (Ce–DTPA, Cr–DTPA and V–DTPA) for redox flow battery applications. Electrochim Acta 2013. [DOI: 10.1016/j.electacta.2013.01.081] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Weldegergis BT, Villiers AD, McNeish C, Seethapathy S, Mostafa A, Górecki T, Crouch AM. Characterisation of volatile components of Pinotage wines using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC–TOFMS). Food Chem 2011. [DOI: 10.1016/j.foodchem.2010.11.157] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Chamier J, Leaner J, Crouch AM. Photoelectrochemical determination of inorganic mercury in aqueous solutions. Anal Chim Acta 2010; 661:91-6. [DOI: 10.1016/j.aca.2009.11.062] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 11/20/2009] [Accepted: 11/27/2009] [Indexed: 10/20/2022]
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Klink MJ, Crouch AM. Preparation of low temperature nano-structured ZnO and RhO2 on titanium substrates, and evaluation for phenol electro-catalytic oxidation. Mikrochim Acta 2009. [DOI: 10.1007/s00604-009-0157-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Weldegergis BT, Crouch AM. Analysis of volatiles in Pinotage wines by stir bar sorptive extraction and chemometric profiling. J Agric Food Chem 2008; 56:10225-10236. [PMID: 18939846 DOI: 10.1021/jf8015706] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A fast, simple, cost-effective, and reliable method based on stir bar sorptive extraction (SBSE) in the headspace mode was used for the analysis of 39 volatile components in Pinotage wines. The method was sensitive, with LODs ranging from 50.0 pg/L to 281 ng/L and LOQs between 180 pg/L and 938 ng/L. Precision was between 6 and 20%. The intermediate precision was within the acceptable range. Moreover, good calibration curves with R(2) > 0.99 for all compounds were achieved. The method was successfully applied for the analysis of 87 young Pinotage wines of vintages 2005 and 2006 collected from various South African regions. To characterize the results based on vintage and origin, the obtained concentrations of the compounds were subjected to chemometric analysis. Exploratory factor analysis (FA), principal component analysis (PCA), and analysis of variance (one-way ANOVA) were consecutively done. The chemometrics approach revealed a reasonable correlation among the volatile components of these wines, as well as with respect to their year of production.
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Affiliation(s)
- Berhane T Weldegergis
- Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, Stellenbosch, South Africa
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Weldegergis BT, Tredoux AGJ, Crouch AM. Application of a headspace sorptive extraction method for the analysis of volatile components in South African wines. J Agric Food Chem 2007; 55:8696-8702. [PMID: 17927151 DOI: 10.1021/jf071554p] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A headspace sorptive extraction (HSSE) in combination with thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) method for the analysis of volatile components (alcohols, esters, carbonyls, acids, phenols and lactones) in wine samples was developed. Extraction conditions such as salting-out effects, sorption time, stirring speed, phase ratio, extraction temperature, and effect of pH were thoroughly evaluated as part of method validation. The method was very sensitive with LODs and LOQs between 50 pg/L to 299 microg/L and 0.2 ng/L to 0.996 microg/L, respectively. Repeatability for all the compounds was between 3 and 22%. The intermediate repeatability was obtained within the acceptable range. Out of 39 volatile compounds selected, 37 were detected and quantitated. The method was found to be simple, cost-effective, sensitive, and use a small sample volume. The method was successfully applied for the routine analysis of 79 young red and white wine samples from various South African districts.
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Affiliation(s)
- Berhane T Weldegergis
- Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, Stellenbosch, South Africa
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Stopforth A, Burger BV, Crouch AM, Sandra P. The analysis of estrone and 17β-estradiol by stir bar sorptive extraction–thermal desorption–gas chromatography/mass spectrometry: Application to urine samples after oral administration of conjugated equine estrogens. J Chromatogr B Analyt Technol Biomed Life Sci 2007; 856:156-64. [PMID: 17581803 DOI: 10.1016/j.jchromb.2007.05.025] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2006] [Revised: 03/29/2007] [Accepted: 05/21/2007] [Indexed: 11/27/2022]
Abstract
The development of a sensitive and solvent-free method for the measurement of estrone (E(1)) and 17beta-estradiol (17beta-E(2)) in human urine samples is described. The deconjugated estrogens were derivatized in situ with acetic acid anhydride and the derivatives were extracted directly from the aqueous samples using stir bar sorptive extraction (SBSE). The compounds containing a secondary alcohol function are further derivatized by headspace acylation prior to thermal desorption and gas chromatography/mass spectrometry (GC/MS). A number of experimental parameters, including salt addition, temperature and time, were optimized to increase the recovery of E(1) and 17beta-E(2) by SBSE. The derivatization reactions were also optimized to obtain the highest yields of the acylated estrogens. Detection limits of 0.02 and 0.03 ng mL(-1) were obtained for E(1) and 17beta-E(2), respectively. The method was applied to determine the effect of conjugated equine estrogen intake on the excretion of E(1) and 17beta-E(2) in human urine samples. Increased levels of the endogenous estrogens were detected after administering a standard dose of Premarin to a female volunteer. Routine monitoring of estrogen levels is recommended to avoid a high urinary excretion of E(1) and 17beta-E(2), nowadays enlisted as endocrine disrupting chemicals (EDCs), during hormone replacement therapy.
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Affiliation(s)
- Adriana Stopforth
- Department of Chemistry, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
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Stopforth A, Grobbelaar CJ, Crouch AM, Sandra P. Quantification of testosterone and epitestosterone in human urine samples by stir bar sorptive extraction – thermal desorption – gas chromatography/mass spectrometry: Application to HIV-positive urine samples. J Sep Sci 2007; 30:257-65. [PMID: 17390621 DOI: 10.1002/jssc.200600280] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A simple method is described for the measurement of testosterone (T) and epitestosterone (ET) in human urine samples. The deconjugated steroids were extracted directly from the samples by stir bar sorptive extraction (SBSE) and derivatized in situ on the stir bar by headspace acylation prior to thermal desorption and GC/MS. Extraction and derivatization parameters, namely salt addition, temperature, and time, were optimized to improve the recovery of T and ET by SBSE. The limits of quantification (S/N 10) were 0.9 ng/mL for T and 2.8 ng/mL for ET. Quantification of the steroids in urine samples was performed using standard addition to avoid the influence of matrix effects. The method was applied for the measurement of urinary T and ET in a group of healthy volunteers and HIV+ patients. Decreased levels of T were detected in the HIV+ group, whereas the excretion of ET was comparable for the two groups. Further clinical research is required to elucidate the biomarker significance of the T/ET ratio in HIV infection.
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Affiliation(s)
- Adriana Stopforth
- Department of Chemistry, University of Stellenbosch, Matieland, South Africa
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Nagaraju V, Goje T, Crouch AM. Determination of Copper and Iron Using [S,S']-Ethylenediaminedisuccinic Acid as a Chelating Agent in Wood Pulp by Capillary Electrophoresis. ANAL SCI 2007; 23:493-6. [PMID: 17420559 DOI: 10.2116/analsci.23.493] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A capillary electrophoresis (CE) method is described for the simultaneous determination of copper and iron after complexation with a readily biodegradable chelating agent, [S,S']-ethylenediaminedisuccinic acid (EDDS), in wood pulp. CE separation was performed in a fused-silica capillary (50 microm i.d.; total length, 65 cm) with an electrolyte containing 25 mM borate buffer and 0.5 mM CTAB at pH 7.0 and an applied voltage of -25 kV. The samples were introduced by applying a 50 mbar pressure for 2 s, and detection of the complexes was monitored at 245 nm. The methodology performance of the methods was evaluated in terms of the linearity, limit of detection (LOD), limit of quantitation (LOQ) and reproducibility. The applicability of the method was demonstrated for the analysis of copper and iron in wood pulp.
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Affiliation(s)
- Velupula Nagaraju
- Department of Chemistry and Polymer Science, University of Stellenbosch, South Africa
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Katata L, Nagaraju V, Crouch AM. Determination of ethylenediaminetetraacetic acid, ethylenediaminedisuccinic acid and iminodisuccinic acid in cosmetic products by capillary electrophoresis and high performance liquid chromatography. Anal Chim Acta 2006; 579:177-84. [PMID: 17723741 DOI: 10.1016/j.aca.2006.07.024] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Revised: 07/11/2006] [Accepted: 07/11/2006] [Indexed: 10/24/2022]
Abstract
A capillary electrophoresis (CE) and a high performance liquid chromatography (HPLC) method are described for the simultaneous determination of ethylenediaminetetraacetic acid (EDTA), S,S'-ethylenediaminedisuccinic acid (EDDS) and R,S-iminodisuccinic acid (IDS) complexing agents as their Fe(III) complexes in cosmetics like shower cream and foam bath. The non-biodegradable EDTA is used in combination with biodegradable analogues like EDDS and IDS in many commercial products. The HPLC method involves separation by reversed-phase ion pair chromatography on a C(18) column using methanol-formate buffer (20 mM tetrabutylammonium hydrogen sulfate, 15 mM sodium formate adjusted to pH 4.0 with formic acid) (10:90, v/v) as mobile solvent at a flow rate of 0.8 mL min(-1) at 24 degrees C using UV detection at 240 nm. The CE separation was performed in a fused silica capillary of 50 microm i.d. with the total length of 50 cm with a 10 mM MES and MOPSO (pH 5.5) at an applied voltage of -25 kV. The samples were introduced by applying a 50 mbar pressure for 2s. Absorbances at 215 and 225 nm were monitored for the detection of the complexes. The methodology performance of the two methods was evaluated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ) and reproducibility. The LOD values obtained from HPLC are low when compared with CE. The applicability of both the methods was demonstrated for the analysis of cosmetic products such as shower cream and foam bath. The results obtained by both CE and HPLC were found to be comparable and in good agreement.
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Affiliation(s)
- L Katata
- Department of Chemistry, University of Stellenbosch, Private Bag No. XI, Stellenbosch 7602, South Africa
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Stopforth A, Burger BV, Crouch AM, Sandra P. Urinalysis of 4-hydroxynonenal, a marker of oxidative stress, using stir bar sorptive extraction–thermal desorption–gas chromatography/mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci 2006; 834:134-40. [PMID: 16520098 DOI: 10.1016/j.jchromb.2006.02.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 02/20/2006] [Accepted: 02/21/2006] [Indexed: 10/24/2022]
Abstract
A simple and fast method for the measurement of 4-hydroxynonenal (4HNE), a highly toxic end-product of lipid peroxidation, in urine samples is described. The method combines stir bar sorptive extraction (SBSE) with two derivatization steps, followed by thermal desorption and GC/MS. 4HNE is derivatized in situ with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine and the oxime is extracted from the aqueous phase with SBSE. The 4HNE-oxime is further acylated by headspace derivatization prior to thermal desorption. Derivatization reactions and extraction were optimized in terms of reagent quantities, temperature and time. The method is linear over a concentration range of 0.5-5 ng mL(-1) with a correlation coefficient of 0.997. The limit of detection and limit of quantitation are 22 and 75 pg mL(-1) urine, respectively. The high sensitivity of the method allows the measurement of physiological concentrations of 4HNE in urine samples.
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Affiliation(s)
- Adriana Stopforth
- Department of Chemistry, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
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Henley WH, Wilburn RT, Crouch AM, Jorgenson JW. Flow Counterbalanced Capillary Electrophoresis Using Packed Capillary Columns: Resolution of Enantiomers and Isotopomers. Anal Chem 2005; 77:7024-31. [PMID: 16255605 DOI: 10.1021/ac050742g] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A method with the ability to increase greatly both the resolution and efficiency of a given capillary electrophoretic system is described. This method differs from traditional capillary electrophoresis (CE) in that a counterflow is induced in the direction opposite to the electrokinetic migration of the analyte. This has the effect of extending not only the time the analytes migrate in the electric field but also the effective length and the effective applied voltage of the system. Previous work in our group with flow counterbalanced capillary electrophoresis has utilized an open tube of small inner diameter to reduce peak broadening caused by hydrodynamic flow. Narrow-diameter capillaries (5-10 microm) restricted analysis to fluorescent analytes and laser-induced fluorescence detection. The method described here uses a capillary of much larger inner diameter (75 microm) that has been packed with nonporous silica particles. The packing material reduces the amount of band broadening caused by pressure-induced flow relative to that experienced in an open tube. A larger diameter capillary allows the detection of analytes by UV absorption, not only eliminating the need to tag analytes with fluorescent tags but also allowing for the detection of a much broader range of analytes. The system was evaluated by studying the separations of several enantiomers using only beta-cyclodextrin as the chiral selector. The system was also used to resolve the two naturally occurring isotopes of bromine and to resolve phenylalanine from phenylalanine-d8. Relative to traditional CE, large improvements in resolution and separation efficiency have been achieved with this method.
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Affiliation(s)
- W Hampton Henley
- Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599-3290, USA
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Raubenheimer HG, du Toit A, du Toit M, An J, van Niekerk L, Cronje S, Esterhuysen C, Crouch AM. Anionic Fischer-type carbene complexes as bidentate (N,O) ligandsElectronic supplementary information (ESI) available: molecular structures of 4b, 5, 7 and 8. See http://www.rsc.org/suppdata/dt/b3/b316998g/. Dalton Trans 2004:1173-80. [PMID: 15252657 DOI: 10.1039/b316998g] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
New polynuclear complexes, (L1)3M2 [M2 = Cr(III) (4a,4b), Fe(III) (5), Co(III) (8)], (L1)2M2(L2)2 [M2 = Co(II) (7), Ni(II) (9)], (L1)2M2(O)L2 [M2 = V(IV) (6)] and L1M2Cp2 [M2 = Ti(III) (10)] with L1 = (CO)5M1=C[C=NC(CH3)=CHS](O-)(M1 = Cr or W) and L2 = 4-methylthiazole or THF, are described. The molecular structures of these complexes determined by X-ray diffraction show that the Fischer-type carbene complexes act as bidentate ligands towards the second metal centre, coordinating through C(carbene)-attached O-atoms and imine N-atoms of the thiazolyl groups to form five-membered chelates with the oxygen atoms in the mer configuration. Isostructural complexes have similar characteristic band patterns in their far-IR spectra. Cyclic voltammetry of selected complexes reveals the oxidation of the carbene complex ligand between 1.01 and 1.29 V. Oxidation of the central metal (M2) takes place at 0.56 and 0.86 V for 7 and 9, respectively. Three stepwise reductions of Cr(III) to Cr(0) occur for 4a and 4b in the region -0.51 to -1.58 V. These new ligand types and other variants thereof should find application in ligand design with the first metal -- and other ligands attached thereto -- in the carbene complex ligand, playing an important role.
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Affiliation(s)
- Helgard G Raubenheimer
- Department of Chemistry, University of Stellenbosch, Private Bag X1, Matieland 7602, Stellenbosch, South Africa.
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Crouch AM, Langford CH, Lawrence MF, Ordonez I. Dark electrochemistry and photoelectrochemistry of molecularly doped ion-exchange polymer blends. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100332a043] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Maisela LL, Crouch AM, Darkwa J, Guzei IA. Bidentate aryldichalcogenide complexes of [(diphosphino)ferrocene]palladium(II) and [(diphosphino)ferrocene]platinum(II). Synthesis, molecular structures and electrochemistry. Polyhedron 2001. [DOI: 10.1016/s0277-5387(01)00923-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Nevondo FA, Crouch AM, Darkwa J. Synthesis and characterisation of thiolato Schiff base nickel(II) complexes. X-Ray structures of Ni(η5-C5H5)(PPh3)(SC6H4NCHC6H4Br-4′) and Ni(η5-C5H5)(PBu3)(SC6H4NCHC6H4CH3-4′) ‡. ACTA ACUST UNITED AC 2000. [DOI: 10.1039/a906949f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Archer SJ, Harvey GA, Moss JR, Crouch AM. A comparison of the dinuclear diacyl complexes FpC(O)(CX2)3C(O)Fp (X F or H; Fp η5-C5H5Fe(CO)2) and the molecular structure of the compound where X F. Inorganica Chim Acta 1992. [DOI: 10.1016/s0020-1693(00)85000-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Archer SJ, Finch KP, Friedrich HB, Moss JR, Crouch AM. Synthesis and properties of the heterodinuclear complexes [Cp(CO)2Fe(CH2)nRu(CO)2Cp] (where n=3–6; Cp=η5-C5H5). Inorganica Chim Acta 1991. [DOI: 10.1016/s0020-1693(00)90148-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Crouch AM, Sharma DK, Langford CH. Kinetics of charge transfer from zinc tetraphenylporphyrin to an axially co-ordinated pyridine. ACTA ACUST UNITED AC 1988. [DOI: 10.1039/c39880000307] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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