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Fluorescence spectra of metal chelates
Rpectrochimica Acta, 1960, Tol. 16, pp. 236 to 243. Pergamon Press Ltd. Printed in Northern Ireland
RESEARCH NOTES
Fluorescence spectra of metal chelates (Received 21
JuEy 1959)
A report on the spectral characteristics of certain metal chelates [l] a few of the cases cited showed only approximate correlation of absorption and excitation spectra. These have been re-examined with the use of the Aminco-Bowman spectrophotofluorometer and better correction factors applied. The intensity of the exciting light from 250 m ,uto 350 m p was evaluated with the iron-III oxalate actinometer [2], from 350 to 550 my with a Radio Corporation of America 7200 photomultiplier tube, and from 550 to 585 m ,u with a thermopile (Kipp No. E20). In the chemical-actinometer method a 0.006 M solution of potassium iron-III oxalate (0.1 N in sulfuric acid) was placed in the 1 cm fused silica cell of the instrument and exposed for 15 min to the radiation from the xenon arc through the excitation monochromator. During this time the solution was stirred with a stream of carbon dioxide gas. The amount of iron-II produced was determined by the standard o-phenanthroline method. This procedure in the 1 cm cell gave reproducible results from 250 to 400 mp. At longer wavelengths more concentrated solutions and longer cells were necessary, hence consistent results were more difficult to obtain. The spectral response curve of the 7200 photomultiplier tube which covered the range from 250 to 580 rnp was purchased from the manufacturer. This tube has a quartz envelope and the spectral response showed a smooth curve except for a minor peak in the 250 to 280 m ,urange. The radiation from the xenon arc was measured directly on the 7200 tube, at a distance of 73 cm with the photometer of the instrument. Except for the region from 250 to 280 m,u the 7200 tube and the chemical actinometer gave the same results. Since this wavelength region was near the lower limit of the tube the chemical actinometer was considered a more accurate measure of the radiation from 250 to 280 m,u. The correction factors from the 7200 tube were considered inaccurate above 550 rnp and a thermopile was chosen for measurement of the radiation above this point. The response curve of the xenon arc measured on the thermopile closely paralleled those of the chemical actinometer and the 7200 tube. The validity of the correction factors is supported by the fact that after correction the quinine sulfate and sodium fluorescein excitation curves showed maxima corresponding to their respective absorbance curves. The results from these measurements on the chelates showed a very close correlation of absorption and excitation spectra in all cases. In the case of the zirconium-flavonol complex the previous results had failed to show an absorption peak at 389 rnp. This peak was shown on the excitation spectra and has now been found in the absorption spectra with a Beckman DKl spectrophotometer and proper concentrations of the chelate (0.5 pmole of flavonol with 2 pmole of ZrIV in 25 ml). The photomultiplier tubes used to measure the emission spectra on the Aminco-Bowman spectrophotofluorometer were evaluated with a standardized 500 W projection lamp. Some minor revisions in the original fluorescent band peaks have also been necessary from IN
[l] [2]
C. G. HATCHARD and C. A. PARKER, Proc. Roy. Sot. A 235, 518 (1956). C. E. WHITE, D. C. HOFFMAN and J. 8. MAGEE, Spectl-ochim. Acta 9, 105 (1957).
236
Research notes
these measurements. Table 1 gives the data from the above measurements on solutions containing 4 pmoles of metal ion and 1 ,umole of reagent in 25 ml except in the cases of the zirconium-flavonol complex which is given above and the lithium-oxine complex. The absorption values for the lithium-oxine complex at the two lower wavelengths were obtained from 3.25 pmoles of oxine and 20 pmoles of Li+ in 25 ml and the two higher Table 1
, Acidity
Complex
(PH)
Maximum excitation wavelengths
Absorption
~ band peaks (m/l)
265,415-420
4.63
(m/l)
(m/i)
I Al-morin Al-2:2’-dihydroxy-l:l’-azonaphthalene-4-sulphonic acid, sodium salt Al-2:4:2’-trihydroxyazobenzene-5’sulphonic acid, sodium salt Be-morin Be-1:4-dihydroxyanthraquinone Be-l-amino-4hydroxyanthraquinone Th-1-amino-4hydroxyanthraquinone Zr-flavonol BPbenzoin Li-oxme
Fluorescence band peaks
1
265.415
~
505-510
I 4.63
) 335, 530-565
4.63
270, 350,480
-11
280, 320,430
j
330, 545-560
630-640
270, 350, 485-490 285, 320, 430
575-585
j
530-540
I
-11 -11 -2.3 0.2 N H,SO, alk.+thanol alk.-et’hanol
530,575
I
1 530-535, 570
’ 585, 630-635
545, 580-585
540, 585
630-650
545,585 254, 328, 389 370 245, 255, 323, 340-370 (shoulder)
545-560,585 265, 330, 390 365 365
650-660 460-465 480 540
Because of the limitations of the apparaones from twenty-five times these concentrations. tus and the weak fluorescence of the lithium complex we have reported only one excitation range. However our experiments indicate that 254 mp is a strong excitation point for this complex. The excitation and emission values in the table are probably within an accuracy of about 5 m p. Ac~,~aolcledgenle?lts-The writers wish to express their appreciation to the National Science Foundation and the University of Maryland Research Board for partial support of this project.
C. E. WIIITE M. Ho E. Q. WEIMER
Departwzext of Chemistry University of Masylnnd College Park, Md.
Infrared-transparent
plates of alumina aerogel
(Received 14 October1959) INFRARED studies of hydroxyl groups and adsorbed molecules on solid adsorbents are of wide current interest [l]. Solids used to date have imposed serious limitations on such [l] R. P. EISCHENS and W. A. PLISKIN, Advances in Catalysis
237
10,1 (1958).
RESEARCH NOTES
Fluorescence spectra of metal chelates (Received 21
JuEy 1959)
A report on the spectral characteristics of certain metal chelates [l] a few of the cases cited showed only approximate correlation of absorption and excitation spectra. These have been re-examined with the use of the Aminco-Bowman spectrophotofluorometer and better correction factors applied. The intensity of the exciting light from 250 m ,uto 350 m p was evaluated with the iron-III oxalate actinometer [2], from 350 to 550 my with a Radio Corporation of America 7200 photomultiplier tube, and from 550 to 585 m ,u with a thermopile (Kipp No. E20). In the chemical-actinometer method a 0.006 M solution of potassium iron-III oxalate (0.1 N in sulfuric acid) was placed in the 1 cm fused silica cell of the instrument and exposed for 15 min to the radiation from the xenon arc through the excitation monochromator. During this time the solution was stirred with a stream of carbon dioxide gas. The amount of iron-II produced was determined by the standard o-phenanthroline method. This procedure in the 1 cm cell gave reproducible results from 250 to 400 mp. At longer wavelengths more concentrated solutions and longer cells were necessary, hence consistent results were more difficult to obtain. The spectral response curve of the 7200 photomultiplier tube which covered the range from 250 to 580 rnp was purchased from the manufacturer. This tube has a quartz envelope and the spectral response showed a smooth curve except for a minor peak in the 250 to 280 m ,urange. The radiation from the xenon arc was measured directly on the 7200 tube, at a distance of 73 cm with the photometer of the instrument. Except for the region from 250 to 280 m,u the 7200 tube and the chemical actinometer gave the same results. Since this wavelength region was near the lower limit of the tube the chemical actinometer was considered a more accurate measure of the radiation from 250 to 280 m,u. The correction factors from the 7200 tube were considered inaccurate above 550 rnp and a thermopile was chosen for measurement of the radiation above this point. The response curve of the xenon arc measured on the thermopile closely paralleled those of the chemical actinometer and the 7200 tube. The validity of the correction factors is supported by the fact that after correction the quinine sulfate and sodium fluorescein excitation curves showed maxima corresponding to their respective absorbance curves. The results from these measurements on the chelates showed a very close correlation of absorption and excitation spectra in all cases. In the case of the zirconium-flavonol complex the previous results had failed to show an absorption peak at 389 rnp. This peak was shown on the excitation spectra and has now been found in the absorption spectra with a Beckman DKl spectrophotometer and proper concentrations of the chelate (0.5 pmole of flavonol with 2 pmole of ZrIV in 25 ml). The photomultiplier tubes used to measure the emission spectra on the Aminco-Bowman spectrophotofluorometer were evaluated with a standardized 500 W projection lamp. Some minor revisions in the original fluorescent band peaks have also been necessary from IN
[l] [2]
C. G. HATCHARD and C. A. PARKER, Proc. Roy. Sot. A 235, 518 (1956). C. E. WHITE, D. C. HOFFMAN and J. 8. MAGEE, Spectl-ochim. Acta 9, 105 (1957).
236
Research notes
these measurements. Table 1 gives the data from the above measurements on solutions containing 4 pmoles of metal ion and 1 ,umole of reagent in 25 ml except in the cases of the zirconium-flavonol complex which is given above and the lithium-oxine complex. The absorption values for the lithium-oxine complex at the two lower wavelengths were obtained from 3.25 pmoles of oxine and 20 pmoles of Li+ in 25 ml and the two higher Table 1
, Acidity
Complex
(PH)
Maximum excitation wavelengths
Absorption
~ band peaks (m/l)
265,415-420
4.63
(m/l)
(m/i)
I Al-morin Al-2:2’-dihydroxy-l:l’-azonaphthalene-4-sulphonic acid, sodium salt Al-2:4:2’-trihydroxyazobenzene-5’sulphonic acid, sodium salt Be-morin Be-1:4-dihydroxyanthraquinone Be-l-amino-4hydroxyanthraquinone Th-1-amino-4hydroxyanthraquinone Zr-flavonol BPbenzoin Li-oxme
Fluorescence band peaks
1
265.415
~
505-510
I 4.63
) 335, 530-565
4.63
270, 350,480
-11
280, 320,430
j
330, 545-560
630-640
270, 350, 485-490 285, 320, 430
575-585
j
530-540
I
-11 -11 -2.3 0.2 N H,SO, alk.+thanol alk.-et’hanol
530,575
I
1 530-535, 570
’ 585, 630-635
545, 580-585
540, 585
630-650
545,585 254, 328, 389 370 245, 255, 323, 340-370 (shoulder)
545-560,585 265, 330, 390 365 365
650-660 460-465 480 540
Because of the limitations of the apparaones from twenty-five times these concentrations. tus and the weak fluorescence of the lithium complex we have reported only one excitation range. However our experiments indicate that 254 mp is a strong excitation point for this complex. The excitation and emission values in the table are probably within an accuracy of about 5 m p. Ac~,~aolcledgenle?lts-The writers wish to express their appreciation to the National Science Foundation and the University of Maryland Research Board for partial support of this project.
C. E. WIIITE M. Ho E. Q. WEIMER
Departwzext of Chemistry University of Masylnnd College Park, Md.
Infrared-transparent
plates of alumina aerogel
(Received 14 October1959) INFRARED studies of hydroxyl groups and adsorbed molecules on solid adsorbents are of wide current interest [l]. Solids used to date have imposed serious limitations on such [l] R. P. EISCHENS and W. A. PLISKIN, Advances in Catalysis
237
10,1 (1958).