Journal of Toxicology and Environmental Health
ISSN: 0098-4108 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uteh19
Relationship between chlorofluorocarbon chemical structure and their salmonella mutagenicity R. Benigni , M. Cotta‐Ramusino & C. Andreoli To cite this article: R. Benigni , M. Cotta‐Ramusino & C. Andreoli (1991) Relationship between chlorofluorocarbon chemical structure and their salmonella mutagenicity, Journal of Toxicology and Environmental Health, 34:3, 397-407, DOI: 10.1080/15287399109531576 To link to this article: http://dx.doi.org/10.1080/15287399109531576
Published online: 15 Oct 2009.
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Citing articles: 2 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=uteh19 Download by: [University of Florida]
Date: 12 November 2015, At: 15:01
RELATIONSHIP BETWEEN CHLOROFLUOROCARBON CHEMICAL STRUCTURE AND THEIR SALMONELLA MUTAGENICITY R. Benigni
Downloaded by [University of Florida] at 15:01 12 November 2015
Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanita, Rome, Italy M. Cotta-Ramusino Laboratory of Pharmaceutical Chemistry, Istituto Superiore di Sanità, Rome, Italy C. Andreoli Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanita, Rome, Italy
This paper is a quantitative analysis of the relationship between the chemical structure and the Salmonella mutagenicity of a number of chlorofluorocarbons (CFC). The molecules were characterized by both molecular orbital and physical chemical parameters. The results of the analysis indicated that the CFC mutagenicity is correlated with two parameters: the free energy of binding to biological receptors, and the energy of the highest occupied molecular orbital (HOMO). Since these are the same factors that would favor the cytochrome P-450-catalyzed metabolism, it would appear that the CFC mutagenicity is determined more by the rate of initial activation than by the rate of DNA attack.
INTRODUCTION Chlorinated and fluorinated derivatives of methane and ethane are widely used as refrigerants, food packaging agents, aereosol propellants, and intermediate process products. Fully halogenated chlorofluorocarbons (CFC) are very stable chemicals and have been shown to persist in the atmosphere and to interfere with the earth's protective ozone layer. In order to replace them, the environmental impact of alternative CFCs is presently under testing. It should be remarked that a decrease in the CFC effect on the ozone layer can only be achieved by producing compounds with a lesser degree of chemical stability, that is, compounds in which some hydrogens are not replaced by halogens. But the diminished stability may imply a higher potential reactivity with the biological systems, hence potential toxicity. This explains the importance of studies focused on the CFC toxicity. This study is aimed at finding the relationship between CFC struc397 Journal of Toxicology and Environmental Health, 34:397-407, 1991 Copyright © 1991 by Hemisphere Publishing Corporation
398
R. BENIGNI ET AL.
tures, and their mutagenic properties. The Salmonella mutagenicity data reported by Longstaff et al. (1984) were used. The CFC chemical structure was parametereized by quantum and physical chemical parameters. DATA AND ANALYSIS METHODS
Downloaded by [University of Florida] at 15:01 12 November 2015
Data Base
The original genotoxicity data were generated by Longstaff et al. (1984). Table 1 reports the results of CFCs and other chlorocarbons obtained with the Salmonella reverse mutation (Ames) test. The experiments were performed with a protocol specifically designed for testing gases. Compounds were considered to be mutagenic if they induced a mutation frequency greater than twice that of the background (Longstaff et al., 1984). Quantum Calculations
Ab initio molecular orbital calculations were carried out with the GAUSSIAN 80 program package. All the geometries were fully optimized at the STO-3G level with the Murtaugh-Sargent option. The values for the Table 1 compounds are reported in Table 2. Physical Chemical Parameters
The logarithm of the octanol/water partition coefficient (log P) was estimated according to the Leo's fragment constant method (Lyman et al., 1982). For a number of CFCs, experimental log P values were also available (C. Hansch, personal communication) (data not shown). Since the agreement between calculated and experimental values was very good (r = .99), we used for this study the homogeneous set of calculated values. Molar refractivity (MR) was calculated as described in Lyman et al. (1982). The estimation of the average free energy of binding (AC) to biological receptors was calculated according to Andrews et al. (1984). The values of the physical chemical parameters are reported in Table 3. Stepwise Linear Discriminant Analysis
This is an algorithm that constructs a set of linear functions of the original variables; this set is aimed at permitting the maximum discrimination between two classes of objects (Lachenbruch, 1975). RESULTS AND DISCUSSION
The experience of the quantitative structure-activity relationship (QSAR) studies has pointed to a number of principles, or quality criteria, that are important for performing the analysis in a correct way and with reliable results. An incorrect strategy is starting a QSAR study by calculat-
CHLOROFLUOROCARBON STRUCTURE AND MUTAGEN1CITY
399
TABLE 1. Effects of Methane and Ethane Analogs on the Mutation Frequency of Salmonella Tester Strains TA1535 and TA100 in the Presence of S9 Mix
Downloaded by [University of Florida] at 15:01 12 November 2015
Test gas 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Formula
FC11 CCI3F CCI2F2 FC12 CCIF3 FC13 CHCI2F FC21 FC22 CHCIF2 FC23 CHF3 FC31 CH2CIF FC32 CH2F2 Monochloromethane CH3CI Dichloromethane CH 2 CI 2 Trichloromethane CHCI3 Tetrachloromethane CCI 4 CCI2FCCIF2 FC113 CCIF2CCIF2 FC114 CCIF2CF3 FC115 FC123 CHCI2CF3 FC124 CHCIFCF3 FC125 CHF2CF3 FC 133a CH2CICF3 FC134 CHF2CHF2 FC 134a CH2FCF3 CCIF2CH3 FC 142b CHF2CH2F FC143 FC 143a CH3CF3 FC 152a CHF2CH3 Trichloroethane CCI3CH3
TA1535 ratio test/ control reversion frequency
TA100 ratio test/ control reversion frequency
1.1 1.6 1.5 1.4 8.6 1.5 177.7 1.5
0.4 0.8 1.1 1.8 7.9 0.9 52.5 1.8
6.2
7.3
Mutagenic
5.6
2.4
Mutagenic
1.4
1.3
Nonmutagenic
2.4a 2.0
ISSN: 0098-4108 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uteh19
Relationship between chlorofluorocarbon chemical structure and their salmonella mutagenicity R. Benigni , M. Cotta‐Ramusino & C. Andreoli To cite this article: R. Benigni , M. Cotta‐Ramusino & C. Andreoli (1991) Relationship between chlorofluorocarbon chemical structure and their salmonella mutagenicity, Journal of Toxicology and Environmental Health, 34:3, 397-407, DOI: 10.1080/15287399109531576 To link to this article: http://dx.doi.org/10.1080/15287399109531576
Published online: 15 Oct 2009.
Submit your article to this journal
View related articles
Citing articles: 2 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=uteh19 Download by: [University of Florida]
Date: 12 November 2015, At: 15:01
RELATIONSHIP BETWEEN CHLOROFLUOROCARBON CHEMICAL STRUCTURE AND THEIR SALMONELLA MUTAGENICITY R. Benigni
Downloaded by [University of Florida] at 15:01 12 November 2015
Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanita, Rome, Italy M. Cotta-Ramusino Laboratory of Pharmaceutical Chemistry, Istituto Superiore di Sanità, Rome, Italy C. Andreoli Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanita, Rome, Italy
This paper is a quantitative analysis of the relationship between the chemical structure and the Salmonella mutagenicity of a number of chlorofluorocarbons (CFC). The molecules were characterized by both molecular orbital and physical chemical parameters. The results of the analysis indicated that the CFC mutagenicity is correlated with two parameters: the free energy of binding to biological receptors, and the energy of the highest occupied molecular orbital (HOMO). Since these are the same factors that would favor the cytochrome P-450-catalyzed metabolism, it would appear that the CFC mutagenicity is determined more by the rate of initial activation than by the rate of DNA attack.
INTRODUCTION Chlorinated and fluorinated derivatives of methane and ethane are widely used as refrigerants, food packaging agents, aereosol propellants, and intermediate process products. Fully halogenated chlorofluorocarbons (CFC) are very stable chemicals and have been shown to persist in the atmosphere and to interfere with the earth's protective ozone layer. In order to replace them, the environmental impact of alternative CFCs is presently under testing. It should be remarked that a decrease in the CFC effect on the ozone layer can only be achieved by producing compounds with a lesser degree of chemical stability, that is, compounds in which some hydrogens are not replaced by halogens. But the diminished stability may imply a higher potential reactivity with the biological systems, hence potential toxicity. This explains the importance of studies focused on the CFC toxicity. This study is aimed at finding the relationship between CFC struc397 Journal of Toxicology and Environmental Health, 34:397-407, 1991 Copyright © 1991 by Hemisphere Publishing Corporation
398
R. BENIGNI ET AL.
tures, and their mutagenic properties. The Salmonella mutagenicity data reported by Longstaff et al. (1984) were used. The CFC chemical structure was parametereized by quantum and physical chemical parameters. DATA AND ANALYSIS METHODS
Downloaded by [University of Florida] at 15:01 12 November 2015
Data Base
The original genotoxicity data were generated by Longstaff et al. (1984). Table 1 reports the results of CFCs and other chlorocarbons obtained with the Salmonella reverse mutation (Ames) test. The experiments were performed with a protocol specifically designed for testing gases. Compounds were considered to be mutagenic if they induced a mutation frequency greater than twice that of the background (Longstaff et al., 1984). Quantum Calculations
Ab initio molecular orbital calculations were carried out with the GAUSSIAN 80 program package. All the geometries were fully optimized at the STO-3G level with the Murtaugh-Sargent option. The values for the Table 1 compounds are reported in Table 2. Physical Chemical Parameters
The logarithm of the octanol/water partition coefficient (log P) was estimated according to the Leo's fragment constant method (Lyman et al., 1982). For a number of CFCs, experimental log P values were also available (C. Hansch, personal communication) (data not shown). Since the agreement between calculated and experimental values was very good (r = .99), we used for this study the homogeneous set of calculated values. Molar refractivity (MR) was calculated as described in Lyman et al. (1982). The estimation of the average free energy of binding (AC) to biological receptors was calculated according to Andrews et al. (1984). The values of the physical chemical parameters are reported in Table 3. Stepwise Linear Discriminant Analysis
This is an algorithm that constructs a set of linear functions of the original variables; this set is aimed at permitting the maximum discrimination between two classes of objects (Lachenbruch, 1975). RESULTS AND DISCUSSION
The experience of the quantitative structure-activity relationship (QSAR) studies has pointed to a number of principles, or quality criteria, that are important for performing the analysis in a correct way and with reliable results. An incorrect strategy is starting a QSAR study by calculat-
CHLOROFLUOROCARBON STRUCTURE AND MUTAGEN1CITY
399
TABLE 1. Effects of Methane and Ethane Analogs on the Mutation Frequency of Salmonella Tester Strains TA1535 and TA100 in the Presence of S9 Mix
Downloaded by [University of Florida] at 15:01 12 November 2015
Test gas 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Formula
FC11 CCI3F CCI2F2 FC12 CCIF3 FC13 CHCI2F FC21 FC22 CHCIF2 FC23 CHF3 FC31 CH2CIF FC32 CH2F2 Monochloromethane CH3CI Dichloromethane CH 2 CI 2 Trichloromethane CHCI3 Tetrachloromethane CCI 4 CCI2FCCIF2 FC113 CCIF2CCIF2 FC114 CCIF2CF3 FC115 FC123 CHCI2CF3 FC124 CHCIFCF3 FC125 CHF2CF3 FC 133a CH2CICF3 FC134 CHF2CHF2 FC 134a CH2FCF3 CCIF2CH3 FC 142b CHF2CH2F FC143 FC 143a CH3CF3 FC 152a CHF2CH3 Trichloroethane CCI3CH3
TA1535 ratio test/ control reversion frequency
TA100 ratio test/ control reversion frequency
1.1 1.6 1.5 1.4 8.6 1.5 177.7 1.5
0.4 0.8 1.1 1.8 7.9 0.9 52.5 1.8
6.2
7.3
Mutagenic
5.6
2.4
Mutagenic
1.4
1.3
Nonmutagenic
2.4a 2.0
