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Excited state of biological molecules
BIOCHEMICAL EDUCATION
July 1976
Vol. 4
No. 3
57
SALVATORE F. RUSSO UNITS FOR ABSORPTIVITY COEFHCIENTS
Chemistry Department W e s t e r n W a s h i n g t o n S t a t e College Bellingham W a s h i n g t o n 98225, U S A
In a research paper (Lin, Means, and Feeney, 1969) and later in a laboratory manual (Rendina, 1971) the assumption is made that a molar absorptivity of 13,000M -~ cm-1 for trinitrophenyl a-amino acids may be expressed as 13,000 moles "l cm 2. The following unit analysis will show that m o l e s - t cm z is not correct for a molar absorptivity but is valid for a kilomolar absorptivity. Beer's law is utilized in the form A=EMIC where A is absorbance, EM is the molar absorptivity, l is the path length, and C is molar concentration. If the path length (l) is in cm and the concentration (C) in moles/liter it follows that E M will have units of M -1 cm -1 since absorbance is a unitless parameter. Consider now that for molar concentration mole _ mole liter 1000 ml
--
.001 mole ~
=
mmole
assuming that 1 ml = 1 cm 3. It then follows that A
=
//mmole'~ = mmole E M c m ~ . cm---~j--) E M cm2
It follows that EM =
A cm2 mmole
(1000mole) mole \
or
cm 2 1000EKM = 1 0 0 0 A m o l e
= A 1000 cm2 mole /
= EM
The above clearly shows that E M, the molar absorptivity, is equal to 1000 EKM, where EKM is the kilomolar absorptivity. The point to remember is that the molar absorptivity is defined in terms of the absorbance of a molar siluation. Although kilomolar absorptivity has units of cm z mole"1 it is not equivalent to molar absorptivity despite the fact that mole "~ appears as part of its units. The kilomolar absorptivity is often chosen as the mode of expression in microchemical work (Kolthoff, et al., 1969).
Kolhoff, I. M., Sandell, E. B., Meehan, E. J., and Bruckenstein, S. (1969). Qualitative chemical analysis, 4th edition, p. 970. London: Collier-Macmillan Limited.
kmole = ( 1000 moles ) mole liter \ l~Om-1 = cm 3
Lin, Y., Means, G. E., and Feeney, R. E. (1969). The action of proteolytie enzymes on N,N-dimethyl proteins. Journal of Biological Chemistry, 244, 789-793.
mole mole A = EKM cm ~5-m3 = EKM cm2
Rendina, G. (1971). Experimental methods in modern biochemistry, pp. 215-218. Philadelphia: W. B. Saunders Company.
where EKM is the kilomolar absorptivity.
BOOK REVIEWS
I
Exeited State of Biologleal Molecules E d i t e d b y J. B. Birks. J o h n Wiley a n d Sons, 1976. P p 652. £18.50 o r $40.70. This volume contains the proceedings of an international conference held at the Calouste Gulbenkian Foundation Centre in Lisbon in 1974. It contains accounts of both plenary lectures and contributed papers, about eighty in all, although some are presented in abbreviated or abstract form. The material is divided up into six main sections, the rehearsal of which gives a good indication of the broad coverage: (a) excited states of organic molecules, which includes some general background material; (b) DNA and nucleotides; (c) photosynthetic pigments; (d) proteins and amino acids; (e) visual pigments; and (f) energy transfer in biological molecules. This is a good survey of recent work in photobiology, with an emphasis on the photophysical aspects of the subject. The monograph emerges as a handsome book, with author and subject indices. Nevertheless, in its very nature it is somewhat disjointed overall, and one cannot but wonder how long our libraries can continue to afford the purchase of such expensive conference proceedings when the material should be (and generally is) available in the primary and review literature. Department of Chemistry Queen Mary College University of London.
EKM = A cm2 mole
REFERENCES
cm 2 EM = A - mmole For kilomolar concentration and
and
Thus
R. Bonnett
ltistochemistry of Amyloid, General Considerations, Light Microscopical and Ultrastruetural Examinations. Experimental Pathology, Suppl. 1. D. Stiller a n d D. K a t e n k a m p . V. E. B. G u s t a v F i s c h e r V e r l a g . J e n a . (pp 1-116; 27 Illustrations). 1975. Price 41.50M. Interest waxes and wanes in Amyloid as theories to explain its appearance in various pathological tissues are produced and subsequently refuted. Over the years, however, a mass of solid information has accumulated which defines and characterizes this material which apparently arises from the degradation of immunoglobins. This monograph, the first in a new series of supplements published by Experimental Pathology describes the evidence, both chemical, histochemical and serological, on the basis of which the protein, polysaccharide and lipid components of amyloid have been identified. Since amyioid is normally located in tissues by the marked fluorescence which results following staining with Congo red or thiofiavine, it is not surprising that the book is well illustrated with photomicrographs, some of them in colour. It will no doubt prove a useful adjunct to the less complete accounts of amyloid which appear in the usual text books of pathology, although on occasion the meaning is slightly obscured by odd lapses of English. David A. Hall Department of Medicine University of Leeds, U.K.
July 1976
Vol. 4
No. 3
57
SALVATORE F. RUSSO UNITS FOR ABSORPTIVITY COEFHCIENTS
Chemistry Department W e s t e r n W a s h i n g t o n S t a t e College Bellingham W a s h i n g t o n 98225, U S A
In a research paper (Lin, Means, and Feeney, 1969) and later in a laboratory manual (Rendina, 1971) the assumption is made that a molar absorptivity of 13,000M -~ cm-1 for trinitrophenyl a-amino acids may be expressed as 13,000 moles "l cm 2. The following unit analysis will show that m o l e s - t cm z is not correct for a molar absorptivity but is valid for a kilomolar absorptivity. Beer's law is utilized in the form A=EMIC where A is absorbance, EM is the molar absorptivity, l is the path length, and C is molar concentration. If the path length (l) is in cm and the concentration (C) in moles/liter it follows that E M will have units of M -1 cm -1 since absorbance is a unitless parameter. Consider now that for molar concentration mole _ mole liter 1000 ml
--
.001 mole ~
=
mmole
assuming that 1 ml = 1 cm 3. It then follows that A
=
//mmole'~ = mmole E M c m ~ . cm---~j--) E M cm2
It follows that EM =
A cm2 mmole
(1000mole) mole \
or
cm 2 1000EKM = 1 0 0 0 A m o l e
= A 1000 cm2 mole /
= EM
The above clearly shows that E M, the molar absorptivity, is equal to 1000 EKM, where EKM is the kilomolar absorptivity. The point to remember is that the molar absorptivity is defined in terms of the absorbance of a molar siluation. Although kilomolar absorptivity has units of cm z mole"1 it is not equivalent to molar absorptivity despite the fact that mole "~ appears as part of its units. The kilomolar absorptivity is often chosen as the mode of expression in microchemical work (Kolthoff, et al., 1969).
Kolhoff, I. M., Sandell, E. B., Meehan, E. J., and Bruckenstein, S. (1969). Qualitative chemical analysis, 4th edition, p. 970. London: Collier-Macmillan Limited.
kmole = ( 1000 moles ) mole liter \ l~Om-1 = cm 3
Lin, Y., Means, G. E., and Feeney, R. E. (1969). The action of proteolytie enzymes on N,N-dimethyl proteins. Journal of Biological Chemistry, 244, 789-793.
mole mole A = EKM cm ~5-m3 = EKM cm2
Rendina, G. (1971). Experimental methods in modern biochemistry, pp. 215-218. Philadelphia: W. B. Saunders Company.
where EKM is the kilomolar absorptivity.
BOOK REVIEWS
I
Exeited State of Biologleal Molecules E d i t e d b y J. B. Birks. J o h n Wiley a n d Sons, 1976. P p 652. £18.50 o r $40.70. This volume contains the proceedings of an international conference held at the Calouste Gulbenkian Foundation Centre in Lisbon in 1974. It contains accounts of both plenary lectures and contributed papers, about eighty in all, although some are presented in abbreviated or abstract form. The material is divided up into six main sections, the rehearsal of which gives a good indication of the broad coverage: (a) excited states of organic molecules, which includes some general background material; (b) DNA and nucleotides; (c) photosynthetic pigments; (d) proteins and amino acids; (e) visual pigments; and (f) energy transfer in biological molecules. This is a good survey of recent work in photobiology, with an emphasis on the photophysical aspects of the subject. The monograph emerges as a handsome book, with author and subject indices. Nevertheless, in its very nature it is somewhat disjointed overall, and one cannot but wonder how long our libraries can continue to afford the purchase of such expensive conference proceedings when the material should be (and generally is) available in the primary and review literature. Department of Chemistry Queen Mary College University of London.
EKM = A cm2 mole
REFERENCES
cm 2 EM = A - mmole For kilomolar concentration and
and
Thus
R. Bonnett
ltistochemistry of Amyloid, General Considerations, Light Microscopical and Ultrastruetural Examinations. Experimental Pathology, Suppl. 1. D. Stiller a n d D. K a t e n k a m p . V. E. B. G u s t a v F i s c h e r V e r l a g . J e n a . (pp 1-116; 27 Illustrations). 1975. Price 41.50M. Interest waxes and wanes in Amyloid as theories to explain its appearance in various pathological tissues are produced and subsequently refuted. Over the years, however, a mass of solid information has accumulated which defines and characterizes this material which apparently arises from the degradation of immunoglobins. This monograph, the first in a new series of supplements published by Experimental Pathology describes the evidence, both chemical, histochemical and serological, on the basis of which the protein, polysaccharide and lipid components of amyloid have been identified. Since amyioid is normally located in tissues by the marked fluorescence which results following staining with Congo red or thiofiavine, it is not surprising that the book is well illustrated with photomicrographs, some of them in colour. It will no doubt prove a useful adjunct to the less complete accounts of amyloid which appear in the usual text books of pathology, although on occasion the meaning is slightly obscured by odd lapses of English. David A. Hall Department of Medicine University of Leeds, U.K.