Quantitative analysis of continuous-variation plots with a comparison of several methods: Spectrophotometric study of organic and inorganic 1:1 stoichiometry complexes

Bruneau, E.; Lavabre, D.; Levy, Gabor B.; Micheau, J. C.

doi:10.1021/ed069p833

Cited by 56 publications

(35 citation statements)

References 8 publications

(9 reference statements)

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“…This substitution gives the following expressions: 0.592 = 4.916 c Cr III + 4.769 c Co II (6) 0.296 = 12.461 c Cr III + 0.649 c Co II (7) which are then solved mathematically. Calculated molarities of c Co II = 1.05 × 10 ᎑1 M and c Cr III = 1.83 × 10 ᎑2 M are in excellent agreement with the so-called "true" values of c Co II = 1.05 × 10 ᎑1 M and c Cr III = 1.80 × 10 ᎑2 M. Based upon our past experiences, students should be able to get within 1-2% of the correct values.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

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Bilinear Regression Analysis as a Means To Reduce Matrix Effects in Simultaneous Spectrophotometric Determination of Cr(III) and Co(II): A Quantitative Analysis Laboratory Experiment

et al. 1998

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UV-visible absorption spectroscopy provides a very convenient experimental means for determining percentage compositions and solution concentrations of unknown samples, measuring reaction rate constants, and determining both the stoichiometry and equilibrium constant of metalligand complexes. Over the past few years many experimental spectroscopic methods have appeared in this Journal (1-10) and in standard laboratory manuals for use in general chemistry, physical chemistry, or quantitative analysis.Spectroscopic methods are based upon application of the Beer-Lambert law, which states that the measured absorbance, A, is directly proportional to the molar concentration of the light-absorbing species i:where b is the path length (in cm) through the solution and ε is the molar absorptivity (in M ᎑1 cm ᎑1 ) at the absorption wavelength. When two light-absorbing species are present, then the individual absorbances are additive:assuming that no reaction or interaction occurs between components i and j. Absorbance measurements at two wavelengths provide two equations in two unknowns. By solving both equations simultaneously, concentrations of the two components can be obtained. The four ε values needed in this computation are calculated from Beer-Lambert Law plots (or linear least squares analysis) for the separate components using standard solutions of known concentrations. This method has been used numerous times in our instrumental analysis course to determine Co II and Cr III concentrations in unknown liquid mixtures. The two wavelengths selected for these analyses were 510 nm and 575 nm, which correspond to wavelengths of near maximum absorbances for Co II and Cr III , respectively. During the past two years we have continuously upgraded the laboratory experiments students perform in our undergraduate quantitative analysis and instrumental analysis courses, to incorporate as much as possible new analytical methods and data treatments. One of the experiments designed utilized an interesting bilinear regressional analysis to reduce matrix effects in the simultaneous spectrophotometric determination of Cr III and Co II in unknown mixtures. Unlike published laboratory experiments (11), in our method standard solutions contain both ions. Numerical values of the four molar absorptivities are calculated from a least squares analysis of eq 2.From an educational standpoint, our modification gives students greater exposure to standard curve-fitting techniques and provides a convenient means to introduce computer programming and spreadsheet computations into the laboratory portion of the course. Most standard analytical textbooks (12-15) include a fairly detailed discussion of linear least squares analysis, which can be extended to solutions containing two light-absorbing chromophores. Several textbooks (for example Harris [12]) now include instructions regarding spreadsheet computations. The bilinear data treatment through the origin, like the standard linear least squares analysis (y = slope × x + intercept) requires simult...

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Section: Discussion Of Resultsmentioning

confidence: 99%

“…Over the past few years many experimental spectroscopic methods have appeared in this Journal (1)(2)(3)(4)(5)(6)(7)(8)(9)(10) and in standard laboratory manuals for use in general chemistry, physical chemistry, or quantitative analysis.…”

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confidence: 99%

Bilinear Regression Analysis as a Means To Reduce Matrix Effects in Simultaneous Spectrophotometric Determination of Cr(III) and Co(II): A Quantitative Analysis Laboratory Experiment

et al. 1998

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“…Due to a contribution at this wavelength from the free ligand (bipy(GCN4bd) 2 and terpy(GCN4bd) 2 ), the absorbance values were corrected to account for this. [60] The fraction of peptide conjugates, c bipy(GCN4bd) 2 and c terpy-(GCN4bd) 2 , are defined as the ratio C p /(C p +C m ).…”

Section: Uv-visible Spectroscopymentioning

confidence: 99%

Metal‐Ion‐Regulated Miniature DNA‐Binding Proteins Based on GCN4 and Non‐native Regulation Sites

Oheix

Peacock

2014

Chemistry A European J

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The design of artificial peptide dimers containing polypyridine switching domains, for which metal-ion coordination is shown to regulate DNA binding, is reported. Short peptides, based on the basic domain of the GCN4 transcription factor (GCN4bd), dimerised with either 2,2'-bipyridine (bipy(GCN4bd) 2 ) or 2,2':6',2''-terpyridine (terpy(GCN4bd) 2 ) linker units, undergo a conformational rearrangement on Cu II and Zn II coordination. Depending on the linker substitution pattern, this is proposed to alter the relative alignment of the two peptide moieties, and in turn regulate DNA binding. Circular dichroism and UV-visible spectroscopy reveal that Cu II and Zn II coordination promotes binding to DNA containing the CRE target site, but to a differing and opposite degree for the two linkers, and that the metal-ion affinity for terpy(GCN4bd) 2 is enhanced in the presence of CRE DNA. Binding to DNA containing the shorter AP1 target site, which lacks a single nucleobase pair compared to CRE, as well as half-CRE, which contains only half of the CRE target site, was also investigated. Cu II and Zn II coordination to terpy(GCN4bd) 2 promotes binding to AP1 DNA, and to a lesser extent half-CRE DNA. Whereas, bipy(GCN4bd) 2 , for which interpeptide distances are largely independent of metal-ion coordination and less suitable for binding to these shorter sites, displays allosteric ineffective behaviour in these cases. These findings for the first time demonstrate that biomolecular recognition, and specifically sequence-selective DNA binding, can be controlled by metal-ion coordination to designed switching units, non-native regulation sites, in artificial biomolecules. We believe that in the future these could find a wide range of applications in biotechnology.

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“…Over the past few years many experimental spectroscopic methods have appeared in this Journal (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) and in standard laboratory manuals for use in general chemistry, physical chemistry, or quantitative analysis. Two of the cited experiments (13,14 ), involving the simultaneous determination of Cr(III) and Co(II) in mixtures, are performed by students in our Instrumental Analysis course.…”

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confidence: 99%

Selection of an Analysis Wavelength: An Interesting Example Involving Solvatochromism and the Zwitterionic Dimroth-Reichardt's Betaine ET-30 Dye

Deng

Acree

1999

J. Chem. Educ.

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Quantitative analysis of continuous-variation plots with a comparison of several methods: Spectrophotometric study of organic and inorganic 1:1 stoichiometry complexes

Abstract: Use and applications of continuous-variation plots.

Cited by 56 publications

References 8 publications

Bilinear Regression Analysis as a Means To Reduce Matrix Effects in Simultaneous Spectrophotometric Determination of Cr(III) and Co(II): A Quantitative Analysis Laboratory Experiment

Bilinear Regression Analysis as a Means To Reduce Matrix Effects in Simultaneous Spectrophotometric Determination of Cr(III) and Co(II): A Quantitative Analysis Laboratory Experiment

Metal‐Ion‐Regulated Miniature DNA‐Binding Proteins Based on GCN4 and Non‐native Regulation Sites

Selection of an Analysis Wavelength: An Interesting Example Involving Solvatochromism and the Zwitterionic Dimroth-Reichardt's Betaine ET-30 Dye

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