Binding Of Aniline Research Articles

Electrochemical Surface-Enhanced Raman Spectroscopy for Aniline Adsorbed on Silver Electrodes: A DFT Study of the Anharmonic Effects of Amino Wagging Vibrational Modes

Aniline molecules exhibit a special amino wagging vibrational mode on the surface of the silver electrode. The corresponding Raman peak not only displays enhanced Raman signals in surface-enhanced Raman spectroscopy (SERS) experiments but also shows a shift toward higher wavenumbers. This work adopts a molecule-metal cluster model to investigate the normal Raman spectra of aniline molecules and their SERS spectra adsorbed on silver electrode surfaces by density functional theory (DFT) approaches. Based on the harmonic approximation, the influence of anharmonic effects on the normal Raman and SERS spectra of aniline is further considered. Our calculated results of the anharmonic Raman spectra of free aniline molecules show that their anharmonic effect mainly comes from the amino wagging vibrational mode. Then, the anharmonic Raman spectra of aniline binding to neutral and positively charged silver clusters were calculated and compared with the harmonic Raman spectra. It was found that the coupling effect between vibrational modes also greatly affects the Raman spectral characteristics. Finally, the excited state energy gap and pre-resonance Raman spectra of the aniline–silver cluster complexes are studied, and it is believed that there may be a charge-transfer enhancement mechanism.

Interpretation of cytochrome P450 monooxygenase kinetics by modeling of thermodynamic activity

The experimentally determined Michaelis constant Kmc results from a combination of two effects: the recognition of the substrate by the enzyme and the molecular interactions between substrate and solvent. By separating substrate recognition from solvent effects, the thermodynamic activity-based Michaelis constant Kma allows for an unambiguous comparison of how different substrates fit into the substrate binding site. Kma of a poorly water-soluble substrate is calculated from the experimentally determined concentration-based Michaelis constant Kmc and its activity coefficient at infinite dilution γ∞. Comparing the Kma of different substrates instead of the experimentally determined Kmc prevents misinterpretations of the molecular basis of enzyme-substrate interactions. While n-octane showed the lowest Kmc value of six P450BM-3 substrates, its Kma was 500 fold higher than aniline, indicating that the binding of n-octane is mainly driven by its low water solubility, while binding of aniline is driven by its shape complementarity. For three substrates (aniline, oct-1-yne, n-octane), γ∞ was reliably calculated by molecular dynamics simulations, either in binary substrate-water mixtures or in ternary mixtures including DMSO as cosolvent. It is demonstrated that the widely used DMSO has a considerable effect on the measured Kmc value. Depending on the substrate, addition of 10% v/v DMSO increases Kmc by up to a factor of 11. To make biocatalytic experiments reproducible, it is therefore of utmost importance to carefully report the reaction conditions. The reliable simulation of activity coefficients in complex mixtures allows for an unambiguous comparison of enzyme-substrate interactions and provides a predictive tool for the design of biocatalytic processes.

Base–acid-induced translational isomerism in a branched [4]rotaxane

A branched [4]rotaxane containing three switching arms with both secondary ammonium cation and aniline binding sites for threaded crown ethers was prepared. 1H NMR spectroscopy was used to show the translational isomerisation of the [4]rotaxane, and different absorption maxima and the oxidation potential for the [4]rotaxane possessing a 1,3,5-tris(4-aminophenyl)benzene centre were monitored by ultraviolet spectroscopy and electrochemical studies, respectively, as the [4]rotaxane was exposed to encircling dibenzo[24]crown-8 species.

Enzymatic polymerization of pyrrole with Trametes versicolor laccase and dioxygen in the presence of vesicles formed from AOT (sodium bis-(2-ethylhexyl) sulfosuccinate) as templates

The oxidative polymerization of pyrrole with the enzyme Trametes versicolor laccase (TvL) and dioxygen (O2) in aqueous solution at pH 3.5 was investigated and found to be regulated by anionic vesicles formed from sodium bis-(2-ethylhexyl) sulfosuccinate (AOT). The polymeric products obtained in the presence of the vesicular templates have high absorption at λ≈450 and 1000nm, which is indicative for polypyrrole (PPy) in its conductive bipolaron state. Absence of unpaired electrons in the bipolaronic PPy product obtained was supported by EPR measurements. Furthermore, the FTIR spectrum of isolated PPy is comparable with the FTIR spectrum reported in literature for chemically or electrochemically synthesized PPy. Under optimal reaction conditions in the presence of the vesicles, i.e., 6.0mM AOT, 8.0mM pyrrole, 3.7μM TvL, pH 3.5 (0.1M sodium dihydrogenphosphate solution), a pyrrole conversion of about 84% was obtained after 7 days reaction time at T≈25°C. Most of the dark green PPy products remained dispersed in the aqueous medium thanks to the vesicles, while the products obtained without vesicles or in presence of sodium di-n-butylsulfosuccinate (6.0mM) had a very different UV/vis/NIR absorption spectrum and almost completely precipitated from the solution. 2H NMR measurements of pyrrole-d5 and MD simulations of an AOT bilayer fragment, solvated into a sodium dihydrogenphosphate solution containing pyrrole, indicate partitioning of pyrrole at pH 3.5 into the region of the AOT membrane before pyrrole oxidation was initiated; however, a preferential binding and specific orientation of pyrrole in the vicinity of the AOT head group could be excluded. Binding of pyrrole to AOT bilayers at pH 3.5 was also compared with the binding of aniline to the same type of bilayers (vesicles) at pH 4.3. This comparison was made since it is known from previous work that aniline can also be polymerized enzymatically in the presence of AOT vesicles. The behavior of the two monomers is, however, quite different. Contrary to pyrrole, in the case of aniline at pH 4.3, anilinium cations were clearly shown by both methodologies – MD simulations and NMR measurements – to bind extensively to the vesicle surface, where the sulfonate group of AOT is localized. Therefore, it can be concluded that a specific pre-orientation of the monomers, before oxidation and polymerization are initiated by the enzymes, is not a common key feature of the two template-assisted reactions and, therefore, cannot be taken as a general explanation for the observed regulating effect of the vesicles. The origin of the vesicle template effect still needs to be elucidated.

Conducting Polymer Films Fabricated by Oxidative Graft Copolymerization of Aniline on Poly(acrylic acid) Grafted Poly(ethylene terephthalate) Surfaces

A conductive polyaniline/poly(ethylene terephthalate) (PANI/PET) composite film was fabricated via the oxidative graft copolymerization of aniline (ANI) onto the plasma-induced poly(acrylic acid) (PAAc) grafted PET surface. The attenuated total reflectance Fourier transform infrared spectroscopy spectra (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) results confirmed that PANI was successfully grafted onto the surface of the PAAc-g-PET films. The effects of the experimental conditions on the percentage of PANI grafted onto the PAAc-g-PET films were extensively investigated. A very high grafting percentage of ANI can be obtained through the acid-base reaction between the aniline monomer and PAAc on the PAAc-g-PET surface at high temperature. As a result, the grafting percentage of PANI can be increased to as high as 12.18 wt %, which causes the surface resistance of the PANI-g-PAAc-g-PET film to be reduced to about 1000 Omega/sq. We predicted that this is because of the high flexibility of the PAAc molecular chains and high solubility of aniline, both of which facilitate the binding of aniline to PAAc during this high temperature acid-base reaction. It was observed by atomic force microscopy (AFM) that the PANI-modified PET surface exhibits higher size irregularity and surface roughness, which further indicated that a much greater number of aniline molecules can be reactively bonded to and distributed along the grafted AAc chains and that the PANI-g-PAAc-g-PET surface resulting from the sequential oxidative graft copolymerization can possess higher electrical conductivity.

Elucidating the Mechanism of the Asymmetric Aza‐Michael Reaction

The mechanism of the palladium-catalysed asymmetric aza-Michael addition of aniline to alpha,beta-unsaturated N-imide was examined from several aspects using a combination of techniques, including X-ray crystallography, mass spectrometry, NMR, UV/Vis spectroscopy, and kinetic studies. The binding of aniline to the dicationic palladium(II) metal centre was found to occur in two consecutive steps: The binding of the first aniline is fast and reversible, whereas the binding of the second aniline is slower and irreversible. This occurs in competition with the binding of the N-imide, which forms a planar six-membered chelate ring with the metal centre; coordinating through the 1,3-dicarbonyl moiety. Isotopic labelling revealed that the addition of N-H occurs in a highly stereoselective manner, allowing the synthesis of optically active beta(2)- and beta(2,3)-amino acid derivatives. The stereochemistry of the addition is postulated to be syn. In situ kinetic studies provided evidence for product inhibition. The binding of the N-imide to the catalyst was found to be the rate-limiting step. Aniline was found to be an inhibitor of the pre-catalyst. The study culminated in the design of a new reaction protocol. By maintaining a low concentration of the aniline substrate during the course of the reaction, significant enhancement of yield and enantioselectivity can be achieved.

Binding of 2,4,6-trinitrotoluene, aniline, and nitrobenzene to dissolved and particulate soil organic matter.

The distribution of TNT* (the sum of TNT and its degradation products), aniline, and nitrobenzene between particulate organic matter (POM), dissolved soil organic matter (DOM), and free compound was studied in controlled kinetic (with and without irradiation) and equilibrium experiments with mixtures of POM and DOM reflecting natural situations in organic rich soils. The binding of TNT* to POM was fast, independent of irradiation, and adsorption isotherms had a great linear contribution (as determined by a mixed model), indicative of a hydrophobic partitioning mechanism. The binding of TNT* to DOM was slower, strongly enhanced under nonirradiated conditions, and adsorption isotherms were highly nonlinear, indicative of a specific interaction between TNT derivatives and functional groups of DOM. Nitrobenzene was associated to both POM and DOM via hydrophobic partitioning, whereas aniline binding was dominated by specific binding to POM and DOM functional groups. On the basis of nitrobenzene and TNT* adsorption parameters determined by a mixed Langmuir + linear model, POM had 2-3 times greater density of hydrophobic moieties as compared to DOM. This difference was reflected by a greater (O + N)/C atomic ratio for DOM. The sum of C-C and C-H moieties, as determined by X-ray photoelectron spectroscopy (XPS), and the sum of aryl-C and alkyl-C, as determined by solid-state cross-polarization magic-angle spinning (CP-MAS) 13C NMR, could only qualitatively account for differences in adsorption parameters. Aliphatic C was found to be more important for the hydrophobic partitioning than aromatic C. On the basis of nonlinear adsorption parameters,the density of functional groups reactive with aniline and TNT derivatives was 1.3-1.4 times greater in DOM than in POM, which was in fair agreement with 13C NMR and XPS data for the sum of carboxyl and carbonyl groups as potential sites for electrostatic and covalent bonding. We conclude that in contaminated soils characterized by continuous leaching of DOM, formation of TNT derivatives (via biotic and abiotic reductive degradation) and their preference for specific functional groups in DOM may contribute to a significant transportation of potentially toxic TNT compounds into surface waters and groundwaters.

Involvement of Singlet Oxygen in Cytochrome P450-Dependent Substrate Oxidations

Cytochrome P450 (P450)-dependent p-hydroxylation of aniline and o-deethylation of 7-ethoxycoumarin were examined in rat liver microsomes in the presence of radical scavengers. The addition of β-carotene, a quencher of singlet oxygen species (1O2), suppressed the aniline hydroxylation, while the addition of sodium azide (NaN3) (1O2 quencher) enhanced the reaction. No other reactive oxygen scavengers or chelating agents such as superoxide dismutase, catalase, dimethylsulfoxide, or deferoxamine altered the reaction. In contrast, the microsomal o-deethylation of 7-ethoxycoumarin was suppressed by the addition of NaN3. 1O2 was detectable during the reaction of microsomes and NADPH by ESR spin-trapping when 2,2,6,6-tetramethyl-4-piperidone (TMPD) was used as a spin trap, and the 1O2 was quenched by the additions of β-carotene, NaN3, aniline, and 7-ethoxycoumarin. The enhancement effect of NaN3 in the hydroxylation of aniline appeared to be due to the conformational change of P450 protein, which in turn enhances the binding of aniline to P450 in terms of the spectral dissociation constant (Ks). In contrast, 1O2 appeared to be active in the o-deethylation of 7-ethoxycoumarin. On the basis of the results, the involvement of 1O2 in P450-dependent substrate oxygenations is proposed.

Covalent Binding of Aniline to Humic Substances. 1. Kinetic Studies

The reaction kinetics for the covalent binding of aniline with reconstituted IHSS humic and fulvic acids, unfractionated DOM isolated from Suwannee River water, and whole samples of Suwannee River water have been investigated. The reaction kinetics in each of these systems can be adequately described by a simple second-order rate expression. The effect of varying the initial concentration of aniline on reaction kinetics suggested that approximately 10% of the covalent binding sites associated with Suwannee River fulvic acid are highly reactive sites that are quickly saturated. Based on the kinetic parameters determined for the binding of aniline with the Suwannee River fulvic and humic acid isolates, it was estimated that 50% of the aniline concentration decrease in a Suwannee River water sample could be attributed to reaction with the fulvic and humic acid components of the whole water sample. Studies with Suwannee River fulvic acid demonstrated that the rate of binding decreased with decreasing pH, whic...

Covalent Binding of Aniline to Humic Substances. 2. 15N NMR Studies of Nucleophilic Addition Reactions

Aromatic amines are known to undergo covalent binding with humic substances in the environment. Although previous studies have examined reaction conditions and proposed mechanisms, there has been no direct spectroscopic evidence for the covalent binding of the amines to the functional groups in humic substances. In order to further elucidate the reaction mechanisms, the Suwannee River and IHSS soil fulvic and humic acids were reacted with 15N-labeled aniline at pH 6 and analyzed using 15N NMR spectrometry. Aniline underwent nucleophilic addition reactions with the quinone and other carbonyl groups in the samples and became incorporated in the form of anilinohydroquinone, anilinoquinone, anilide, imine, and heterocyclic nitrogen, the latter comprising 50% or more of the bound amine. The anilide and anilinohydroquinone nitrogens were determined to be susceptible to chemical exchange by ammonia. In the case of Suwannee River fulvic acid, reaction under anoxic conditions and pretreatment with sodium borohydri...

Effects of acetone administration on cytochrome P-450-dependent monooxygenases in hamster liver, kidney, and lung

The effects of acetone on liver, kidney, and lung monooxygenases were studied using hamsters administered 8% acetone in drinking water. Binding of aniline to liver microsomes induced a type II difference spectrum, and the spectral binding was enhanced in hamsters pretreated with acetone. Administration of acetone caused significant increases of cytochrome P-450 and cytochrome b5 contents in liver microsomes. The increases of the hemeproteins were associated with induction of monooxygenase activities toward test substrates, aniline, N-nitrosodimethylamine, benzphetamine, benzo(a)pyrene, and 7-ethoxycoumarin. In the kidneys, acetone administration increased microsomal contents of the hemeprotein and monooxygenase activities toward aniline. N-nitrosodimethylamine, and 7-ethoxycoumarin, but not benzphetamine or benzo(a)pyrene. In the lungs, acetone pretreatment increased aniline hydroxylase activity without affecting the levels of N-nitrosodimethylamine demethylase, cytochromes P-450 and b5. In marked contrast to the inductive effects in the liver, acetone administration markedly decreased lung microsomal benzo(a)pyrene hydroxylase and 7-ethoxycoumarin O-deethylase activities. Gel electrophoresis of liver and kidney microsomes from control and acetone-treated hamsters revealed that acetone treatment enhanced the intensity of a protein band(s) in the cytochrome P-450 molecular weight region. Immunoblotting of the microsomal proteins showed that the protein band induced by acetone in hamster liver, kidney and lung was cross-reactive with antibody raised against ethanol-inducible human liver cytochrome P-450. These results demonstrate that acetone has the ability to uniformly induce a specific form of cytochrome P-450, designated as IIE1, and to cause differential changes of monooxygenase activities in the hamster tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Occurrence of a cytochrome P-450-containing mixed-function oxidase system in the pond snail,Lymnaea stagnalis

1. The occurrence of an as yet unidentified cytochrome P-450 in the microsomal fraction of the digestive gland of the snail, Lymnaea stagnalis was studied. 2. Studies in vivo and in vitro (digestive gland homogenates or the 170,000g fraction) of the cytochrome P-450-mediated metabolism of substrates such as biphenyl, pentoxy- and ethoxy-resorufin and aminopyrine have been made. 3. Cytochrome P-450 concentration in the digestive gland calculated from CO-difference spectra was 0.30 +/- 0.05 nmol/g tissue. This amount was not increased either by phenobarbital or by 3-methylcholanthrene. 4. Aniline binding spectra resembled normal type II spectra, while type I model substrates such as hexobarbital and 2,2'-dichlorobiphenyl showed type II- or reversed type I-like spectra. 5. O-Deethylation of 7-ethoxyresorufin did not occur, but 7-pentoxyresorufin O-depentylation activity (80.4 +/- 28.6 pmol resorufin/g per hour) and aminopyrine N-demethylation activity (375 +/- 96 pmol formaldehyde/g per minute) were demonstrated. 6. 4-Hydroxybiphenyl was the major metabolite of biphenyl, while minor amounts of 2-hydroxybiphenyl were formed (in vivo: 63.7 nmol 4-hydroxybiphenyl and 3.33 nmol 2-hydroxybiphenyl per snail per 24 h, after an oral dose of 778.2 nmol biphenyl; in vitro 118 +/- 21 pmol and 21 +/- 9 nmol, respectively (digestive gland homogenate/mg protein, per hour). 7. The results indicate that the isoenzymes involved in the observed MFO activities resemble isoenzymes P-450b/e.

Morphological modification of polyaniline using polyelectrolyte template molecules

We report modification of polymer morphology for polyaniline by using different electrolytes to dissolve the aniline monomer before polymerization. Aqueous HCl, poly(vinylsulfonic acid), poly(acrylic acid), and poly(styrenesulfonic acid) were used as electrolytes for electrochemical polymerization of aniline. We found the morphology is strongly modified by using these polymer acids a electrolytes to replace the conventional aqueous HCl electrolyte. The observed variation in morphology among different polyelectrolytes is consistent with variation in binding of aniline to different polymer acids. The polymer acids appear to serve as a templates for polymerization.

Ferriprotoporphyrin IX Oxygen Activation/Insertion Reactions: The Nature of the Interaction between Ferriprotoporphyrin IX and Aniline (Substrate)

The interaction between aniline and ferriprotoporphyrin IX in alkaline solution has been investigated using pyridine and the N-methyl pyridinium ion as site-specific inhibitors of oxygen activation. Pyridine inhibits oxygen activation in a noncompetitive manner with respect to aniline ( K 1 = 1.24 mol −1 dm 3 at 30°C) while the N-methyl pyridinium ion inhibited in a manner consistent with two sites for aniline binding, only one of which was competitively inhibited ( K 1 = 317mol -l dm 3 at 30°C). A comprehensive reinvestigation of the interaction of pyridine and N-methyl pyridinium ions with alkaline ferriprotoporphyrin IX has shown that two molecules of each ligand bind per hemin dimer in a strongly cooperative manner. The association constant for the first pyridinium ion bound is K 1a = 176 mol −1 dm 3 at 30°C, while that for the first pyridine molecule bound is K 1a = 0.580 mol −1 dm 3 at 30°C; these are both close to the observed inhibition association constants ( K 1). Thermodynamic parameters for the interactions have been evaluated and compared to previous literature values. On the basis of these results a model is proposed for aniline interaction with the ferriprotoporphyrin dimer IX which involves the binding of two molecules of aniline to the ferriprotoporphyrin IX tetrapyrrole ring system by planar π bonding interactions with the rings having the propionate groups attached.

Monooxygenase activity of human hemoglobin: NMR demonstration of different modes of substrate binding corresponding to different activities of hemoglobin derivatives.

In the accompanying paper [Ferraiolo, B. L., Onady, G. M., & Mieyal, J. J. (1984) Biochemistry (preceding paper in this issue)] we reported different aniline hydroxylase activities for ferrihemoglobin, its isolated subunits, and the converse pair of valency hybrids alpha 3+2(beta 2+-CO)2 and (alpha 2+-CO)2 beta 3+2 in a reconstituted system containing reduced nicotinamide adenine dinucleotide phosphate (NADPH) and cytochrome P-450 reductase. To investigate the molecular basis for the different activities, 1H NMR T1 relaxation studies of aniline were performed in the absence and presence of each of the hemoglobin (Hb) species. The paramagnetic contribution of the ferric heme iron atoms of each Hb derivative to the enhanced relaxation of the proton nuclei of aniline was determined relative to control experiments in which the hemoproteins had been converted fully to the corresponding (carbonmonoxy)ferrous forms, which are diamagnetic. According to the known distance dependence of the paramagnetic effect and the relative changes in T1 for the upfield and downfield signals in the spectrum of aniline, it was ascertained that aniline binds in the same manner to the beta-ferric hybrid and to ferrihemoglobin. These two forms displayed equivalent hydroxylase activities that were the highest among the Hb derivatives for the same aniline concentration. The T1 changes observed with the alpha-ferric hybrid suggest a different orientation for aniline in that complex. The T1 data for the isolated subunits alpha 3+ and beta 3+4 would indicate that overall binding of aniline includes a component of direct aniline-heme ligation in each case.(ABSTRACT TRUNCATED AT 250 WORDS)

SORPTION OF ANILINE ON SELECTED ALFISOLS FROM THE EASTERN COAL REGION

The sorptive behavior of aniline was investigated in two Alfisols from eastern coal regions. Batch adsorption/desorption studies (soil/solution ratio 1:5, aniline concentration 25 to 400 ..mu..g/ml) were performed on the prominent genetic horizons of each soil. Sorption was evaluated as a function of equilibrium pH and ionic strength (Na/sub 2/SO/sub 4/) of the supporting electrolyte and on selected horizons treated to remove organic materials (H/sub 2/O/sub 2/ oxidation) and secondary iron components (oxalate and DCB-extractable). The behavior of aniline in the B horizons was concentration-dependent, and at higher concentrations (>75 ..mu..g/ml) sorption exceeded that of the upper or A horizons and was reversible. Aniline sorption was pH-dependent, reflecting different mechanisms and sites of sorption in the A and B horizons. Binding of aniline in the A horizons was greater below the compound pKa; maximum sorption in B horizons occurred above the pKa. Sorption in the A horizon was controlled primarily by partially irreversible interaction with organic materials; the high degree of sorption in the lower horizons may have resulted from proton transfer reactions and binding of the anilinium ion to interlayer areas of phyllosilicate minerals. 39 references, 5 figures, 2 tables.

Effect of acute and repeated chlordimeform treatment on rat hepatic microsomal drug metabolizing enzymes

The effect of chlordimeform (CDM) treatment on the hepatic microsomal drug metabolizing enzymes was examined in male and female rats following either acute or repeated treatment. After acute administration of chlordimeform (100 mg/kg, i.p., 1 hour before killing) differential effects were observed in various parameters of the hepatic microsomal mixed function oxidase system with significant decreases in ethylmorphine metabolism, cytochrome P-450 content, NADPH cytochrome c reductase, and in the spectral binding of hexobarbital and aniline while no changes were found in the metabolism of aniline or p-nitroanisole. Durations of zoxazolamine-induced paralysis and pentobarbital-induced hypnosis were increased significantly after acute CDM administration. Following repeated administration of CDM (75 mg/kg, i.p., for 4 days) to adult male rats, a decrease was observed in zoxazolamine-induced paralysis time while pentobarbital-induced hypnosis was not altered. Metabolism studies using isolated hepatic microsomal fractions showed a decreased rate of biotransformation of ethylmorphine and aniline while the activity of p-nitroanisole O-demethylase was not changed. No differences were found in cytochrome P-450 levels whereas microsomal spectral binding of hexobarbital was reduced while that of aniline was not affected. Following acute or repeated administration of CDM to adult female rats, decreases in the hepatic microsomal metabolism of aniline, but not ethylmorphine or p-nitroanisole, were observed. Addition of CDM to microsomal suspensions yielded a Type I binding curve.

Effect of indole on the mono-oxygenase system in rat liver microsomes.

The effect of indole on the mono-oxygenase systems was studied in liver microsomes from control, indole-, phenobarbital- and 3-methylcholanthrene-treated rats. No induction was observed by indole of either cytochrome P-450 or the mono-oxigenase activities. It was, however, a potent competitive inhibitor of aniline hydroxylase (Ki=0.03 ~ 0.04 mM). A spectroscopic study showed that this competition occurred at the aniline binding site on cytochrome P-450. The inhibitory effect was observed on aminopyrine N-demethylase with less efficiency (Ki=Q.l~0.5 mM) and on benzo[a]pyrene hydroxylase. These inhibitions were also observed in the systems of mice, rabbits and monkeys. The physiological effect of indole on liver drug metabolism was also discussed.

Tolerance development to cadmium-induced decrease in hepatic oxidative xenobiotic metabolism and cytochrome P-450 content in the male rat

Cadmium, in dose of 0.84 mg/kg (ip), produces a marked inhibition in hepatic oxidative xenobiotic metabolism which results from a decreased cytochrome P-450 content in the male rat. The inhibitions in microsomal metabolism of aniline, ethylmorphine, or p-nitroanisole were not elicited by the 0.84 mg/kg cadmium dose in rats which had been pretreated (72 hours prior) with a lower dose of cadmium (0.21 mg Cd/kg, ip). Likewise, the decreases in both microsomal cytochrome P-450 content and in microsomal spectral binding of hexobarbital or aniline produced by the 0.84 mg/kg cadmium dose were not elicited in the rats pretreated with the low cadmium dose. The 0.21 mg/kg cadmium dose produced an increase (370%) in the cadmium-binding capacity as well as an increase (395%) in total hepatic metallothionein. These data are consistent with the hypothesis that the pretreatment of animals with relatively low cadmium doses produces an increase in the cellular levels of metallothionein which can then bind and ameliorate the toxicological effects of a subsequently administered toxic dose of cadmium.

1H nuclear relaxation study of the aniline-binding site in human hemoglobin

Hemoglobin-catalyzed hydroxylation of aniline may be taken as a model for similar reactions catalyzed by cytochrome P-450. Using ultraviolet-difference spectroscopy and 1H nuclear relaxation techniques, the binding of aniline to hemoglobin was examined. From the magnitude of paramagnetic effects of ferric iron on aniline protons, using the correlation time determined from the magnetic field dependence of water proton relaxation rates, aniline was found to bind to methemoglobins such that the aromatic protons are 8.5 ± 0.7 A, away from the high-spin Fe3+. A mode of binding is proposed where the aniline molecule is hydrogen bonded to the distal histidine of hemoglobin.