Phase Stability Improvement of a γ-CsPbI3 Perovskite Solar Cell Utilizing a Barium Bis(trifluoromethanesulfonimide) Solution

The cesium lead iodide (CsPbI3) perovskite solar cell possesses a wide band gap ranging from 1.65 to 1.75 eV, which is suitable for integration into a tandem structure along with a low-band-gap silicon solar cell. Moreover, CsPbI3 has received considerable attention as a potential solution for the prevalent issues of low thermal stability of organic-inorganic perovskite solar cells and phase segregation encountered in conventional mixed halide wide-band-gap perovskite solar cells. Through the implementation of volatile additives, CsPbI3 has demonstrated substantial advancements in efficiency, process temperature, and stability. This study introduces a novel approach for barium (Ba)-doping by spraying an antisolvent containing barium bis(trifluoromethanesulfonimide) during the spin-coating process. By incorporating Ba2+ through this spraying technique, the formation of the delta phase in CsPbI3 is significantly suppressed; thereby, a power conversion efficiency of 18.56% is achieved, and a remarkable 93% of the initial efficiency is maintained after 600 h.

Constraining the ^{30}P(p, γ)^{31}S Reaction Rate in ONe Novae via the Weak, Low-Energy, β-Delayed Proton Decay of ^{31}Cl

The ^{30}P(p,γ)^{31}S reaction plays an important role in understanding the nucleosynthesis of A≥30 nuclides in oxygen-neon novae. The Gaseous Detector with Germanium Tagging was used to measure ^{31}Cl β-delayed proton decay through the key J^{π}=3/2^{+}, 260-keV resonance. The intensity I_{βp}^{260}=8.3_{-0.9}^{+1.2}×10^{-6} represents the weakest β-delayed, charged-particle emission ever measured below 400 keV, resulting in a proton branching ratio of Γ_{p}/Γ=2.5_{-0.3}^{+0.4}×10^{-4}. By combining this measurement with shell-model calculations for Γ_{γ} and past work on other resonances, the total ^{30}P(p,γ)^{31}S rate has been determined with reduced uncertainty. The new rate has been used in hydrodynamic simulations to model the composition of nova ejecta, leading to a concrete prediction of ^{30}Si:^{28}Si excesses in presolar nova grains and the calibration of nuclear thermometers.

Tunable broadband terahertz polarizer using graphene-metal hybrid metasurface

We demonstrate an electrically tunable polarizer for terahertz (THz) frequency electromagnetic waves formed from a hybrid graphene-metal metasurface. Broadband (>3 THz) polarization-dependent modulation of THz transmission is demonstrated as a function of the graphene conductivity for various wire grid geometries, each tuned by gating using an overlaid ion gel. We show a strong enhancement of modulation (up to ∼17 times) compared to graphene wire grids in the frequency range of 0.2-2.5 THz upon introduction of the metallic elements. Theoretical calculations, considering both plasmonic coupling and Drude absorption, are in good agreement with our experimental findings.

Effects of age and strain on small intestinal and hepatic antioxidant defense enzymes in Wistar and Fisher 344 rats

Age- and strain-associated alterations in intestinal and hepatic antioxidant defense enzymes including superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), and glutathione-S-transferase (GST), and lipid peroxidation were examined in Wistar and F344 rats of both strains aged 2 weeks, 2.5, 10 and 23 months. In the small intestine, activities of SOD and GSH-PX and lipid peroxidation were not affected by age or strain difference. Intestinal GST activity was noticeably increased with age in both strains, but somewhat different pattern of age-related changes occurred between two strains. Wistar rats aged 23 months had a significantly higher intestinal GST activity than corresponding age of F344 rats. In the liver, cytosolic SOD activity was not affected by age and strain, whereas GSH-PX and GST activities and lipid peroxidation were markedly influenced by age or strain difference. In particular, hepatic GSH-PX in Wistar rats resulted in a significant increase after 10 months of age and stayed at this level till 23 months of age we examined. Also, Wistar rats showed a higher lipid peroxidation in the liver of 2.5 months old when compared with corresponding age of F344 rats. However, F344 rats did not show any significant age-dependent changes in GSH-PX and lipid peroxidation. In contrast, the GST activity did show much of an age-associated alteration in both strains. Age-associated change in GST activity of Wistar rats was much greater than that observed in F344 rats, especially late in the lifetime (23 months old). It is concluded from our results that age has profound impact on development of some antioxidant enzymes in the small intestine and liver and also strain-related difference in development of antioxidant defense system was observed at least some time of rat life.

Three-dimensional quantitative structure-activity relationship study of nonsteroidal estrogen receptor ligands using the comparative molecular field analysis/cross-validated r2-guided region selection approach

A newly developed comparative molecular field analysis (CoMFA) technique, the cross-validated r2-guided region selection (CoMFA/q2-GRS) method, has been used to build a quantitative structure-activity relationship (3D-QSAR) for nonsteroidal estrogen receptor (ER) ligands. Ligands included in this study belong to a series of diethylstilbestrol (DES) and indenestrol analogues whose affinities for the mouse ER (mER) have been determined in our laboratory. The final model utilized 30 compounds and yielded a q2GRS (cross-validated r2, guided region selection) of 0.796, as compared to a q2 of 0.720 for conventional CoMFA, with a standard error of prediction of 0.594 at 3 principal components. This model was used to visualize steric and electrostatic features of the ligands that correspond with ER binding affinity. Results obtained from the CoMFA steric and electrostatic plots of this model have also been compared to information from the ER binding affinities of substituted estradiol analogues. This is in an effort to determine structural features of compounds in the CoMFA analysis that may correspond to those of the estradiol analogues and to further clarify the mode of binding of nonsteroidal ER ligands.

Separation of indenestrol A and B isomers and enantiomers by high-performance liquid chromatography

High-performance liquid chromatography (HPLC) methods have been developed for the separation of substituted indenestrol A and B isomers on different columns. The isomers were separated by normal-phase liquid chromatography with a silica gel column. Enantiomers of these compounds were separated by chiral HPLC and the most successful separations were achieved with a Chiralcel OJ column.

Estrogen-dependent gene regulation by an oxidative metabolite of diethylstilbestrol, diethylstilbestrol-4',4"-quinone

Diethylstilbestrol (DES) is a well-characterized carcinogen in humans and animals although its mechanisms of carcinogenicity are not yet known. While the estrogenic activity of DES is important, there is evidence that oxidative metabolism also plays an important role for its toxicity. DES is oxidatively metabolized in vivo and in vitro to a number of compounds including diethylstilbestrol-4',4"-quinone (DQ), an unstable and reactive intermediate, and Z,Z-dienestrol (ZZ-DIEN). Estrogen receptor (ER) binding assays with mouse uterine cytosol indicate that DES, DQ and ZZ-DIEN have relative binding affinities of 286, 3.6 and 0.3, respectively, relative to estradiol as 100. In addition, DQ binds irreversibly and specifically to ER suggesting that DQ may be biologically active despite its rapid metabolism and lower binding affinity compared to DES. To test this, COS-1 cells were transfected with an estrogen responsive reporter construct containing of VitA2 estrogen response element (ERE) with or without an ER expression vector. In the presence of ER, treatments with DES, DQ and ZZ-DIEN resulted in 11, 10, and 2-fold induction of chloramphenicol acetyltransferase (CAT) activity, respectively. This induction was mediated by estrogen receptor since it was suppressed by pretreatment with a 10-fold excess of the pure antiestrogen ICI 182,780. These data indicate that DQ is a biologically active intermediate that is capable of transactivation of estrogen responsive genes through the ER. Furthermore, the data suggest that the ability of DQ to irreversibly bind ER may result in persistent stimulation of ER. This persistent stimulation may be related to the carcinogenicity of DES.

Mouse steroid sulfotransferases: substrate specificity and preliminary X-ray crystallographic analysis

Three mouse cytosolic sulfotransferases were expressed in Escherichia coli cells in order to study their substrate specificities toward natural as well as synthetic steroid hormones. The Km and Vmax values confirmed the high substrate specificity of estrogen and hydroxysteroid sulfotransferases toward estradiol and dehydroepiandrosterone, respectively. In sharp contrast, the synthetic estrogen diethylstilbestrol was metabolized efficiently by both enzymes to its disulfate ester. These sulfotransferases display highly stereospecific sulfotransferase activity for sulfating only the trans-isomer of diethylstilbestrol. Crystals suitable for high-resolution structure determination of estrogen sulfotransferase were grown with polyethylene glycol. The crystals belong to the orthorhombic space group P2(1)2(1)2, and diffracted to 2.5 A.

Ligand-based identification of environmental estrogens

Comparative molecular field analysis (CoMFA), a three-dimensional quantitative structure-activity relationship (3D-QSAR) paradigm, was used to examine the estrogen receptor (ER) binding affinities of a series of structurally diverse natural, synthetic, and environmental chemicals of interest. The CoMFA/3D-QSAR model is statistically robust and internally consistent, and successfully illustrates that the overall steric and electrostatic properties of structurally diverse ligands for the estrogen receptor are both necessary and sufficient to describe the binding affinity. The ability of the model to accurately predict the ER binding affinity of an external test set of molecules suggests that structure-based 3D-QSAR models may be used to supplement the process of endocrine disruptor identification through prioritization of novel compounds for bioassay. The general application of this 3D-QSAR model within a toxicological framework is, at present, limited only by the quantity and quality of biological data for relevant biomarkers of toxicity and hormonal responsiveness.

Assessing environmental chemicals for estrogenicity using a combination of in vitro and in vivo assays

Because of rampant concern that estrogenic chemicals in the environment may be adversely affecting the health of humans and wildlife, reliable methods for detecting and characterizing estrogenic chemicals are needed. It is important that general agreement be reached on which tests to use and that these tests then be applied to the testing of both man-made and naturally occurring chemicals. As a step toward developing a comprehensive approach to screening chemicals for estrogenic activity, three assays for detecting estrogenicity were conducted on 10 chemicals with known or suspected estrogenic activity. The assays were 1) competitive binding with the mouse uterine estrogen receptor, 2) transcriptional activation in HeLa cells transfected with plasmids containing an estrogen receptor and a response element, and 3) the uterotropic assay in mice. The chemicals studied were 17 beta-estradiol, diethylstilbestrol, tamoxifen, 4-hydroxytamoxifen, methoxychlor, the methoxychlor metabolite 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), endosulfan, nonylphenol, o,p'-DDT, and kepone. These studies were conducted to assess the utility of this three-assay combination in the routine screening of chemicals, or combinations of chemicals, for estrogenic activity. Results were consistent among the three assays with respect to what is known about the estrogenic activities of the chemicals tested and their requirements for metabolic activation. By providing information on three levels of hormonal activity (receptor binding, transcriptional activation, and an in vivo effect in an estrogen-responsive tissue), an informative profile of estrogenic activity is obtained with a reasonable investment of resources.

Estrogen receptor stereochemistry: ligand binding orientation and influence on biological activity

Racemic (Rac) 4'- and 5-deoxyindenestrol A (4'-DIA and 5-DIA), monohydroxyl analogs of the diethylstilbestrol (DES) oxidative metabolite indenestrol A (IA), were synthesized, and their enantiomers were resolved and isolated. Each compound was then tested for estrogen receptor (ER) binding affinity, uterotropic activity, and nuclear ER levels, to further define the stereochemical preference of the ER and to structually evaluate the function of each IA hydroxyl group for binding and biological activity. Competitive binding to cytosolic ER determined the relative binding affinity of racemic mixtures of 4'- and 5-DIA as 1.3 and 3.7, respectively, compared with that of DES, 286. The ER exhibited a binding preference for the S-enantiomer of both compounds, with relative binding affinities of 4'-DIA-R, 0.2; 4'-DIA-S, 1.8; 5-DIA-R, 0.9; and 5-DIA S, 5.6. 4'-DIA-Rac produced 3 times the in vivo stimulation of 5-DIA-Rac in the uterotropic bioassay (with mouse uterine doubling doses of 302.4 and 800 micrograms/kg, respectively). Nuclear ER levels measured 1 hr after in vivo treatment with either 160 micrograms/kg 4'-DIA or 80 micrograms/kg 5-DIA showed a maximum binding level of 2 (4'-DIA) and 1.5 (5-DIA) times saline control, with these doses producing levels nearly equal to that caused by a 10 micrograms/kg dose of IA. Metabolic studies were carried out by treating mice with [3H]4'- and [3H]5-DIA-Rac, to determine the differential binding affinity and biological stimulation of 4'-DIA and 5-DIA. The in vivo metabolism of the [3H]DIA compounds showed formation of [3H]IA-Rac in urine extracts, as analyzed by chiral high performance liquid chromatography. Furthermore, in vitro incubation of unlabeled 4'- and 5-DIA-Rac with mouse liver microsomes showed stereospecific metabolism, with IA-S primarily formed from 4'-DIA-Rac and IA-R from 5-DIA-Rac. Metabolism of 4'-DIA-Rac to the more active IA S-enantiomer and of 5-DIA-Rac to the less active IA R-enantiomer contributes to the different biological activities, because the ER exhibits a chiral preference for these compounds. The higher binding affinity of 5-DIA indicates that the phenyl ring hydroxyl group is required for high affinity binding; however, both hydroxyl groups are needed for subsequent biological activity. These data further suggest that the ER demonstrates stereochemical ligand binding and that IA binds in an orientation relative to 17 beta-estradiol in which the IA phenyl ring corresponds to the estradiol A-ring.

Estrogen receptor stereochemistry: ligand binding and hormonal responsiveness

Estrogen stimulation of the uterus produces a spectrum of biochemical responses that are customarily linked together. This report is an overview of a series of studies by our laboratory investigating the role of different ligand structures in eliciting hormonal responses. Diethylstilbestrol (DES) and certain structural analogs, indenestrol A (IA), indenestrol B (IB), and pseudo-DES, were used as probes to segregate various genomic responses previously considered interrelated, most notably the events of specific protein synthesis and DNA synthesis. These compounds have weak uterotrophic activity; however, they interact with high affinity specifically with mouse uterine estrogen receptors (ERs). All of them produce stoichiometrically similar amounts of ER complex in the nucleus. Indenestrol A and IB possess a single chiral carbon atom and exist as a mixture of enantiomers (ENTs). Competitive binding assays of pure ENTs and cytosolic ERs demonstrated a stereochemical chiral preference for the IA isomer but not IB. This preference was also evident from nuclear ER occupancy experiments. Biologic activity of the IA ENTs also demonstrated differences as seen by receptor binding. Ornithine decarboxylase (ODC) activity was stimulated 600% by DES and partially by IA (rac). All of the ODC activity produced by IA (rac) was due to the IA(C3)-S ENT. Uterine DNA synthesis was measured after treatment with the IA compounds. Indenestrol A (rac) increased DNA synthesis to 40% of the level seen with DES. The weak ENTs showed no activity and the active ENTs were weaker than the IA racemic. These compounds should be useful probes for studying the individual responses involved in estrogen-induced uterine growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple estrogen binding sites in the uterus: stereochemistry of receptor and non-receptor binding of diethylstilbestrol and its metabolites

Indenestrol A (IA), an oxidative metabolite of the synthetic estrogen diethylstilbestrol (DES), has high binding affinity for estrogen receptor in mouse uterine cytosol but possesses weak biological activity. Racemic mixture of optically active [3H]indenestrol A (IA-Rac) was separated and purified into individual enantiomers on a semi-preparative scale by HPLC with a Chiralpak OP(+) column. The structure-activity relationship was investigated among the [3H]IA enantiomers (IA-R and IA-S) and [3H]DES through direct saturation binding assays using mouse uterine cytosol. Specific binding curves and Scatchard plots were obtained for each [3H]ligand; DES, IA-Rac, IA-R and IA-S. IA-S enantiomer (Kd = 0.67) binds to the estrogen receptor with the same affinity as DES (Kd = 0.71) and four times higher affinity than IA-R (Kd = 2.56). The number of binding sites for IA-S is approximately the same as estradiol, DES and IA-Rac while IA-R binds far fewer sites than the other ligands. Saturation binding assays indicated that [3H]DES and [3H]IA enantiomers exhibited a higher level of non-specific binding to the cytosol receptor compared to estradiol which has a low level of non-specific binding. These binding studies led to the detection of an additional binding component for the stilbestrol compounds in estrogen target tissue cytosol preparations. Sucrose density gradient separation assays under low salt conditions showed that both [3H]DES and [3H]IA compounds bound to the 8S form of the receptor, the same as E2. But, in addition both DES and IA bound to another binding component in 4S region. The binding to the 4S component were partially displaced by the addition of excess unlabeled E2 and DES. Further characterization of the 4S component is described.

Diethylstilbestrol metabolites and analogs. Stereochemical probes for the estrogen receptor binding site

Indenestrol A (IA) and indenestrol B (IB) are analogs and metabolites of diethylstilbestrol (DES). These compounds have high binding affinity with the estrogen receptor (ER) but possess weak uterotropic activity. Due to their chemical structures, IA and IB exist as mixtures of enantiomers. We investigated whether the poor biological activity of these compounds was due to differential activity of the enantiomers. We also utilized these compounds as probes to determine the extent of stereochemical sensitivity in the ER ligand binding site. The IA and IB enantiomers were separated to greater than 98% purity using a chiral high pressure liquid chromatography column. Their enantiomeric nature was confirmed by mass spectrometry and NMR. The purified IA enantiomer peak 1 was derivatized with 4-bromobenzoyl chloride. The resulting di(4-bronobenzoate) IA was analyzed by x-ray crystallography and the absolute enantiomeric conformation assigned is C(3)-R. The IA enantiomers designated IA-R and A-S were assayed by competitive binding to cytosolic ER. The competitive binding index was estradiol, 100; DES, 286; IA-Rac (racemic mixture of IA), 143; IA-R, 3; and IA-S, 285; the index showed that ER demonstrates a stereochemical chiral preference. The IB enantiomers did not show a binding preference: IB, 145; IB-1, 100; and IB-2, 143. The differences in the IA enantiomer binding were shown to be due to competitive interactions by Lineweaver-Burk analysis of saturation binding of estradiol to ER in the presence of 1-, 5-, and 10-fold molar excess of competitor. Differences in binding affinity of the enantiomers could be partially explained by differences in the association rate constant (k+1) determined by association rate inhibition studies in which IA-S was 15 times more active than IA-R. Nuclear estrogen receptor levels were measured 1 h after in vivo treatment with doses of 5-20 micrograms/kg. The IA-Rac produced only 60% of the levels is compared with DES. Nuclear ER levels were checked every 30 min up to 2 h with no apparent difference, indicating that the low early levels were not due to a delayed estrogen receptor retention. When the enantiomers were tested individually only a dose of 10 micrograms/kg IA-S translocated ER to a level comparable to DES, while IA-R showed low levels at several doses. These results suggest that the poor biological activity of IA may be related to the differential ER interaction of its enantiomers.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular complexes of thyroid hormone tyrosyl rings with aromatic donors. Possible relationship to receptor protein interactions

Several lines of evidence have indicated that thyroid hormones share common molecular properties (accessible planar face and lateral halogenation) with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds of environmental importance and can modulate their toxicity. Binding of dioxin to a soluble intracellular protein (dioxin or Ah receptor) appears to be the initial step in their mechanism of toxicity and a stacking interaction model has been proposed at the molecular level. It has also been recognized that the Ah receptor and the triiodothyronine nuclear receptor share certain physical and chemical properties important in their binding interactions. In this work, we examined the possibility that thyroid hormones might also be able to bind by a stacking complexation mechanism. By use of methods based on nuclear magnetic resonance spectroscopy, selected, structurally distinct thyroid hormone analogues with widely different hormonal activities were shown to function as electron acceptors in molecular complexes with aromatic donors involving the nonphenolic or tyrosyl ring. Binding free energies for these complexes correlated well with those previously reported for the triiodothyronine (L-T3) nuclear receptor binding interaction with the same compounds. This included preference for L-T3 over thyroxine (L-T4), very favorable binding of 3,5,3'-triiodothyroacetic acid (Triac), and marked preference for L-T3 over D-T3. These results suggest that a considerable part of the structural specificity in thyroid hormone action may be mediated by the tyrosyl ring interaction. Binding ligands for the triiodothyronine nuclear receptor and the Ah receptor may share common molecular parameters in the expression of their binding activities.

Estrogen receptor-binding activity of polychlorinated hydroxybiphenyls: conformationally restricted structural probes

A series of polychlorinated hydroxybiphenyls (PCBs) has been tested for their binding activity to soluble uterine estrogen receptor protein. Competitive binding analysis was performed on 0-40% ammonium sulfate-enriched uterine cytosol receptor preparations which improved the binding activity for the PCB compounds by a factor of 10-40, by decreasing the nonspecific binding. The binding activities have been correlated to molecular properties supported by molecular modeling studies which emphasize the importance of conformational restriction. The estrogen receptor bound 4-hydroxy-2',4',6'-trichlorobiphenyl (4H2',4',6'TCB) with the greatest affinity, with the concentration of unlabeled inhibitor yielding half-maximal specific binding relative to estradiol (C50) being approximately 42 compared to estradiol, C50 approximately 1.0. PCB compounds that demonstrated appreciable receptor-binding activity were also active in vivo in stimulating uterine weight increases, whereas weak binders were inactive. The 4H2',4',6'TCB compound represents a high degree of conformational restriction around the interring bond due to the presence of two ortho-chlorine atoms. The other PCBs in this series, which show lower receptor-binding activity, vary in position of chlorine substituents and can assume multiple low energy conformations as a result of less hindrance to rotation around the interring bond.

Polychlorinated biphenyls and related compound interactions with specific binding sites for thyroxine in rat liver nuclear extracts

Thyroid hormone analogues, polychlorinated biphenyls (PCBs), and their derivatives were shown to bind specifically to thyroxine-specific binding sites in rat liver nuclear extracts. The structure-binding relationship for thyroxine binding prealbumin was qualitatively similar to that for the nuclear receptor. In general for both binding proteins, increased binding affinity was seen for the more linear and in some cases rectangular shaped (as opposed to the angular shaped thyroid hormones) chlorinated aromatic hydrocarbons with chlorine concentrated in lateral positions (3,3',5,5'-substitution on biphenyl nucleus). However two groups of compounds showed distinct quantitative differences. The relatively less polar and more lipophilic nonhydroxylated PCBs bound the nuclear receptor with significantly lower affinities while two compounds that are structurally related by the potential for equilibrium interconversion to a rigid planar structure bound with significantly higher affinities. This latter class of compounds represents soluble dioxin (TCDD) approximate isosteres and has an extended (polarizable) pi-system brought about by a planar structure (or conversion to the same) and lateral halogenation. These structure requirements are maximally expressed in 3,3',5,5'-tetrachlorodiphenoquinone (TCDQ), which shows a remarkably high affinity (Ka = 1.84 X 10(11) M-1) for the nuclear receptor. Thus, the nuclear receptor shows the expected structural specificity and sensitivity for possible involvement in the high toxicity of these classes of compounds. The physiological significance of these binding results is supported by the dose-dependent regulation (increase) of the thyroxine nuclear receptor number by dioxin, although the mechanism responsible for this increase is not clear. The nuclear binding component was further analyzed by sucrose density gradient centrifugation and was found to have a sedimentation coefficient of 4.3 S under high salt conditions. A crude estimate of the molecular weight (45,200) was obtained from a linear plot of standard globular protein fraction number (sedimentation coefficient) vs. log molecular weight. Although direct evidence is not provided, the thyroxine nuclear receptor may cooperate with a second receptor in binding the TCDQ type ligand or exists as a multimeric species with binding properties of both prealbumin and the dioxin (or Ah) receptor.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) as a potent and persistent thyroxine agonist: a mechanistic model for toxicity based on molecular reactivity

TCDD and thyroxine have common molecular reactivity properties which enable them to present a planar face and lateral halogens in interactions with proteins. These molecular properties are consistent with the structure-toxicity relationship for TCDD and related compounds. Biological evidence is discussed including preliminary studies on the effects of TCDD exposure on tadpole growth and development which is consistent with the possible thyroxine-like activity of TCDD. The work suggests the possibility that toxicity is at least in part the expression of potent and persistent thyroid hormone activity (responses induced by TCDD which qualitatively correspond to those mediated by thyroid hormones). A mechanism for toxicity is proposed which involves receptor proteins; the planar aromatic system controls binding to cytosolic proteins and halogen substituents regulate binding to nuclear proteins. This simple model based on molecular reactivity sheds light on the diversified effects of TCDD and related compound toxicity and on certain thyroid hormone action. The model also permits predictions to be made with regard to the toxicity and thyroid hormone activity of untested compounds. In addition, the model suggests a general mechanism for hormone action based on metabolically regulated differential and cooperative protein receptor binding events in cellular compartments which can explain agonism, antagonism and potentiation within the framework of receptor occupancy theory.

Structure-induction versus structure-toxicity relationships for polychlorinated biphenyls and related aromatic hydrocarbons

A comparison of the structure-induction (involving rat and mouse Ah receptor binding) and structure-toxicity (in vivo guinea pig toxicity) relationships suggests that two receptors with structurally distinct binding properties may be involved. This is supported by demonstration of potentiated toxicity through a mechanism believed to involve the Ah receptor as a site of loss with respect to toxicity. Theoretical and working models are proposed for these separate receptors to aid in the search for other relevant binding proteins. The findings suggest that polychlorinated biphenyls that are relatively low in toxicity may have modulating properties on the action of highly toxic compounds with which they are normally found in the environment.

Molecular interactions of toxic chlorinated dibenzo-p-dioxins and dibenzofurans with thyroxine binding prealbumin

The interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds with prealbumin, a model for the nuclear thyroid hormone receptor, have been studied with use of computer graphics and predictions made regarding relative binding affinities for such structures. These modeling predictions were tested by experimentally measuring the binding affinities of dioxin and furan analogues. The results were in general agreement with the modeling predictions and demonstrated that such compounds could be effective competitive binding ligands for thyroxine-specific binding sites in prealbumin. The computer modeling work also demonstrates the importance of lateral chlorine substitution in the binding of these toxic compounds. The prealbumin interaction model should be of use in investigating the structure-toxicity relationships of these classes of toxic compounds. Thus, if prealbumin is a model for the nuclear thyroid hormone receptor, this work would also have major implications bearing on the mechanism of dioxin toxicity and the potential of these compounds to function as potent and persistent thyroxine agonists. A new cooperative receptor mechanism for dioxin toxic action is proposed.

In vitro metabolism of mono-2-ethylhexyl phthalate by microsomal enzymes. Similarity to omega- and (omega-1) oxidation of fatty acids

Mono-2-ethylhexyl pthalate (MEHP) is oxidized to omega-, omega-1-, and omega-2-hydroxylation products as well as (very slightly) to a dicarboxylic acid by washed microsomes from rat liver and kidney, and rabbit but not rat lung. The reactions involve molecular oxygen, are strongly inhibited by carbon monoxide and oxidized cytochrome c, and NADPH is preferred over NADH. Piperonyl butoxide inhibits hydroxylation of MEHP, but clofibrate does not. The differential effects of inducers (phenobarbital and clofibrate) and inhibitors (sodium laurate, n-decane, metyrapone) on terminal and subterminal hydroxylation as well as differences in apparent Km for the two suggest that rat liver contains at least two different MEHP hydroxylases. Comparisons of tissue distribution, susceptibility to inhibitors, and induction properties suggest that the hydroxylation of MEHP is more likely to be mediated by the P-450 isozymes associated with omega- and (omega-1)-hydroxylation of fatty acids than with those that utilize hydrocarbons as substrates.

A screening assay for the tetrachlorodibenzo-p-dioxin receptor using the [125I]iodovaleramide derivative of trichlorodibenzo-p-dioxin as the binding ligand

A relatively simple assay method for the putative cytosolic 'receptor' that binds 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds is described. The assay is based on specific binding of [125I]dioxin to cytosol 'receptor' protein. Saturation is ensured by competition experiments in which unlabeled TCDD and other competitors displace the radiolabeled ligand from specific binding sites. This assay has been applied to estimation of levels of 'receptor' in cytosol.

The relationship between metabolism of 2,3,4,5,3',4',5'-heptachlorobiphenyl and its ability to induce both cytochromes P-448 and P-450

Male CD rats received i.p. injections of 2,3,4,5,3',4',5'-heptachlorobiphenyl (7CB) under conditions resulting in induction of both benzphetamine demethylase (cytochrome P-450-dependent) and ethoxyresorufin deethylase (cytochrome P-448-dependent) activities. To test the possibility that one class of induction (P-450) was due to the parent compound and the other (P-448) to a metabolite, liver, adipose, bile, urine and feces were analyzed for the presence of 3,4,5,3',4',5'-hexachlorobiphenyl (6CB) (the major photolysis product of 7CB) and/or 3-hydroxy-3,4,5,3',4',5'-hexachlorobiphenyl (OH-6CB), another known P-448 inducer. To allow for the possibility that 6CB might be a transient intermediate. The results supported the hypothesis that 7CB is a true 'mixed inducer', nor requiring metabolic alteration for its dual activity.

A new synthesis of tetrachlorofluorodibenzo-p-dioxin

The 1,2,3,4-tetrachloro-7-fluorodibenzo-p-dioxin has been synthesized via condensation of 4-fluorocatechol and pentachloronitrobenzene. This compound could be used as an internal standard for the analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin by chromatographic methods.

Radioimmunoassay for mono-(2-ethylhexyl) phthalate in unextracted plasma

We report a radioimmunoassay for mono-(2-ethylhexyl) phthalate that has been coupled to a protein carrier as a radioligand. Competitive interference tests with a variety of related compounds indicated the assay to be highly specific. Quantitative comparison of mono-(2-ethylhexyl) phthalate values in plasma and serum samples between the radioimmunoassay and gas chromatographic procedures indicated a high reliability. Because this potentially toxic compound can leach into plasma from polyvinyl plastics, this assay should be particularly useful for those involved in the manufacture or use of medical devices made of them.

Radioimmunoassay for mono-(2-ethylhexyl) phthalate in unextracted plasma

We report a radioimmunoassay for mono-(2-ethylhexyl) phthalate that has been coupled to a protein carrier as a radioligand. Competitive interference tests with a variety of related compounds indicated the assay to be highly specific. Quantitative comparison of mono-(2-ethylhexyl) phthalate values in plasma and serum samples between the radioimmunoassay and gas chromatographic procedures indicated a high reliability. Because this potentially toxic compound can leach into plasma from polyvinyl plastics, this assay should be particularly useful for those involved in the manufacture or use of medical devices made of them.