Community Structure,Geochemical Characteristics and Mineralogy of a Hypersaline Microbial Mat,Cabo Rojo,PR

Seasonal variations in precipitation changed the community composition and microbial activity in a hypersaline, tropical microbial mat, in Cabo Rojo, PR. Using a combination of dissection, light, and transmission electron microscopy, terminal restriction fragment length polymorphism (T-RFLP), in situ microelectrode studies, and ³⁵ S isotope incubations, we documented the major differences between wet and dry seasons. During the wet season (precipitation 177 mm), cyanobacterial (green layer) and anoxyphototrophic (pink layer) communities, as well as the black FeS layer were well-developed, and T-RFLP patterns indicated a diverse community. The rate of oxygenic photosynthesis was 49 μ M min ^{? 1} . Aerobic respiration was 29 μ M min ^{? 1} , and sulfate reduction was 264 nmol cm ^{? 3} h ^{? 1} . During the dry season (precipitation 51 mm), cyanobacteria and anoxyphototrophs were less diverse and abundant, and T-RFLP patterns were less complex. The O ₂ production rate was reduced to 9 μ M min ^{? 1} , as was O ₂ consumption (7 μ M min ^{? 1} ) and sulfate reduction (26 nmol cm ^{? 3} h ^{? 1} ). Aragonite, calcite, halite, and quartz were the predominant minerals. Seasonal differences were found in the green and pink layers for both halite and quartz. Gypsum was not observed, likely due to a sample handling artifact. The fluctuations in community composition and metabolic activity, principally reflected in fluctuations in binding and trapping potential of the uppermost mat community, might be responsible for the observed differences in mineralogy.     

A Novel Zeolite Coating for Protection of Concrete Sewers from Biological Sulfuric Acid Attack

Microbial growth inhibition and resistance to biological deterioration of concrete specimens coated with silver-loaded zeolite was evaluated by measuring the time course of bacterial growth, biological sulfur oxidation, and sulfate production using Acidithiobacillus thiooxidans as a corrosive agent. Live bacterial cells declined from an initial inoculum concentration of 1.1 × 10₄ cell ml_-1 to zero in 10 days, during which only 0.5–1% of the initial sulfur concentration of 10 g l_-1 was biologically oxidized, corresponding to sulfate production rates of 35–42 mg SO ₄ ^{2 ?} g ^{? 1} S ^{? 1} . Leaching coefficients of calcium and silicon in the specimens coated with silver-loaded zeolite of 1.6 × 10 ^{? 4} to 4.6 × 10 ^{? 2} cm ² d ^{? 1} respectively, were only 0.8% and 1% of the uncoated specimens.     

CALB-catalyzed kinetic resolution of (RS)-3-benzoylthio-2-methylpropyl azolides: kinetic and thermodynamic analysis

Abstract

Zofenopril as an ACE inhibitor expired recently was found to have a favourable safety profile in comparison with other ACE inhibitors in treating high blood pressure, congestive heart failure, and acute myocardial infarction. It can be synthesised from the key building blocks of (S)-3-benzoylthio-2-methylpropanoic acid and (4S)-phenylthio-L-proline. In this report, an efficient hydrolytic resolution via Candida antarctic lipase B (CALB) for preparing the former block in isopropyl ether (IPE) containing (RS)-3-benzoylthio-2-methylpropyl pyrazolide (1) and water was developed. Quantitative improvements of the enzyme activity and enantioselectivity in terms of k_2SK_mS^?1?=?5.726?L h^?1 g^?1 and E?=?217 at 45?°C were found from the kinetic analysis. Insights into the CALB performance via thermodynamic analysis were then addressed and compared with those by using (RS)-3-benzoylthio-2-methylpropyl 1,2,4-triazolide (2) as the substrate. A putative thermodynamic model was moreover hypothesised for elucidating the more enthalpy reduction of 68.92-70.86?kJ mol^?1 from the acyl part of (S)-1 and (S)-2 as well as that of 23.69-25.63?kJ mol^?1 from the triad imidazolium to Ser105 and leaving 1,2,4-triazole moiety of (R)-2 and (S)-2 on stabilising the corresponding transition states.     

Synthesis and biodistribution of an 18F-labelled resveratrol derivative for small animal positron emission tomography

Summary. Resveratrol (3,4′,5-trihydroxy-trans-stilbene) is a naturally occurring phytoalexin and polyphenol existing in grapes and various other plants, and one of the best known ‘nutriceuticals’. It shows a multiplicity of beneficial biological effects, particularly, by attenuating atherogenic, inflammatory, and carcinogenic processes. However, despite convincing evidence from experimental and clinical studies, data concerning the role of resveratrol and other members of the large polyphenols family for human health is still a matter of debate. One reason for this is the lack of suitable sensitive and specific methods, which would allow direct assessment of biodistribution, biokinetics, and the metabolic fate of these compounds in vivo. The unique features of positron emission tomography (PET) as a non-invasive in vivo imaging methodology in combination with suitable PET radiotracers have great promise to assess quantitative information on physiological effects of polyphenols in vivo. Herein we describe the radiosynthesis of an ¹⁸F-labelled resveratrol derivative, 3,5-dihydroxy-4′-[¹⁸F]fluoro-trans-stilbene ([¹⁸F]-1), using the Horner-Wadsworth-Emmons reaction as a novel radiolabelling technique in PET radiochemistry for subsequent functional imaging of polyphenol metabolism in vivo. In a typical “three-step/one-pot” reaction, ¹⁸F-labelled resveratrol derivative [¹⁸F]-1 could be synthesized within 120–130 min including HPLC separation at a specific radioactivity of about 90 GBq/μmol. The radiochemical yield was about 9% (decay-corrected) related to [¹⁸F]fluoride and the radiochemical purity exceeded 97%. First radiopharmacological evaluation included measurement of biodistribution ex vivo and positron emission tomography (PET) studies in vivo after intravenous application of [¹⁸F]-1 in male Wistar rats using a dedicated small animal PET camera with very high spatial resolution. Concordantly with data on bioavailability and metabolism of native resveratrol from the literature, these investigations revealed an extensive uptake and metabolism in the liver and kidney, respectively, of [¹⁸F]-1. This study represents the first investigation of polyphenols in vivo by means of PET.     

Ribosylation of the Base Residue of Inosine Derivatives by Phase-Transfer Catalysis

Abstract

Reaction of 2′,3′,5′-O-silylated inosine derivative 1 with 2, 3-O-isopropylidene-5-O-tritylribosyl chloride (3) in a two-phase (CH₂Cl₂-aq. NaOH) system in the presence of Bu₄NBr gave three products, i. e., 6-O-α-, 6-O-β-, and N ¹-β-isomers of glycosides 4, 5a, and 5b. A similar PTC reaction of 1 with 2, 3, 5-tri-O-benzylribosyl bromide (9) gave four regio- and stereo-isomers involving the N¹-β-glycoside 10. Reaction of 1 with 2, 3, 5-tri-O-benzoylribosyl bromide (11) afforded three products involving the desired N¹-β-glycoside 12b, which could be deprotected to give N ¹-ribosylinosine (15b) as a useful intermediate for the synthesis of cIDPR.

     

Sorption of Cadmium and Lead by Bacteria–Ferrihydrite Composites

The sorptive behavior of bacteria—iron oxide composites was investigated in batch metal sorption assays using ferrihydrite in isolation (0.13 and 0.14 g/L ferrihydrite in cadmium and lead systems, respectively) as well as in combination with Bacillus subtilis (0.25 g/L adsorbent mixture) and Escherichia coli (0.27 g/L adsorbent mixture). A pH range from 3.0 to 6.5 was studied using total metal concentrations of 1.0 × 10 ^{? 4.0} and 3.2 × 10 ^{? 5} M with adsorbent mixtures proportioned on a 1:1 mass/volume basis. The log of the apparent surface complex formation constants (log K ^S _M ) and sorption capacity (S _max ) values were determined by fitting the experimental data to one-site Langmuir sorption isotherms. The one-site model effectively described the sorption data (r ² > 0.9), where Cd ^{2 +} exhibited somewhat lower sorption affinities (log K ^S _M = ?3 for ferrihydrite, ?1.7 for B. subtilis–ferrihydrite, and ?1.1 for E. coli–ferrihydrite) than Pb ^{2 +} (log K ^S _M = ?0.9 for ferrihydrite, ? 0.2 forB. subtilis–ferrihydrite, and –0.1 for E. coli–ferrihydrite). The corresponding S _max values for Cd ^{2 +} and Pb ^{2 +} on ferrihydrite were 0.78 mmole/g and 1.34 mmole/g, respectively. For the B. subtilis–ferrihydrite composites, Cd ^{2 +} and Pb ^{2 +} S _max values were lower at 0.29 mmole/g and 0.5 mmole/g, respectively. Similar values were determined for the E. coli–ferrihydrite composites (0.15 mmole/g and 0.68 mmole/g for Cd ^{2 +} and Pb ^{2 +} , respectively). The sorption of Cd ^{2 +} and Pb ^{2 +} by each of the sorbent systems exhibited a strong dependence on pH with sorption edges in the range of pH 4.0 to 7.3. The observed S _max of the composites were lower than values predicted upon available site additivity (Cd ^{2 +} _{B. subtilis ?ferrihydrite} : 0.29 mmole/g (observed) < 0.57 mmole/g (calculated); Cd ^{2 +} _{E. coli ?ferrihydrite} : 0.15 mmole/g (observed) < 0.44 mmole/ g (calculated); Pb ^{2 +} _{B. subtilis ?ferrihydrite} : 0.5 mmole/g (observed) < 0.805 mmole/g (calculated); Pb ^{2 +} _{E. coli –ferrihydrite} : 0.68 mmole/g (observed) < 0.775 mmole/g (calculated)), implying that a masking of reactive surface sites by attachment had occurred between the bacteria and ferrihydrite. Electrophoretic mobility analysis indicated that the ferrihydrite surface properties dominate the net surface charge for each composite system with lesser contributions from the bacteria.     

Genome analysis of species in the genus Hystrix (Triticeae; Poaceae)

Genomic in situ hybridisation (GISH) and Southern genomic hybridisation were applied in order to gain further knowledge regarding generic delimitation of the genus Hystrix as well as to clarify the genomes of the Hystrix species H. patula, H. longearistata, H. coreana, H. duthiei and H. komarovii. The hybridisation intensity of different genomic probes was compared among the Hystrix species and with other Triticeae species. The Southern- and GISH results confirm that H. patula contains the StH genome and show that H. komarovii most likely has a variant of this StH genome. The other Hystrix species under study, i.e. H. longearistata, H. coreana and H. duthiei, contain an Ns basic genome, and most probably two variants of this basic genome, Ns ¹ Ns ² . The genus Hystrix is thus not a monophyletic group of species.     

Methanogenesis and Methanogen Diversity in Three Peatland Types of the Discontinuous Permafrost Zone,Boreal Western Continental Canada

Because recent patterns of permafrost collapse in boreal peatlands appear to enhance emissions of CH ₄ to the atmosphere, we examined methanogenesis and methanogen diversity in peat soil from peatlands with and without permafrost in two peatland complexes situated in continental western Canada. Peat soil from the active layer of permafrost bogs had very low rates of CH ₄ production (ca. 10 nmol g ^?1 day ^?1 ), and we were unable to PCR-amplify 16s rRNA gene sequences using Archaea-specific primers in four peat samples. Surface peat soil from continental bogs with no permafrost supported moderate rates of CH ₄ production (20–600 nmol g ^?1 day ^?1 ), with maximum rates in soil located close to the mean water table level. Additions of ethanol stimulated CH ₄ production rates, suggesting metabolic substrate limitations. Peat from internal lawns, which have experienced surface permafrost degradation in the past 150 years, had very rapid rates of CH₄ production (up to 800 nmol g ^?1 day ^?1 ) occurring within the soil profile. Concomitant rates of anaerobic CO ₂ production were greater in continental bogs (ca. 6 μmol g ^?1 day ^?1 ) than in internal lawns (ca. 4 μ mol g ^?1 day ^?1 ) or in permafrost bogs (2.8 μ mol g ^?1 day ^?1 ). Analysis of the 16s rRNA gene for Archaea in the continental bog indicated mostly sequences associate with Methanobacteriales and RC-I with a Methanosarcinaceae sequence in the deepest peat soil. In the internal lawn, Methanosarcinaceae were most common in peat soil with a Methanosaetaceae sequence in the deepest peat soil. This study showed that patterns of discontinuous permafrost and ongoing permafrost degradation in boreal regions create patchy soil environments for methanogens and rates of methanogenesis.     

Microwave accelerated solvent-free synthesis and antifungal evaluations of flavanones

Microwave irradiation of 2-hydroxy chalcones under solvent-free conditions resulted in a “green-chemistry” procedure for the preparation of flavanones in good yields, using an unmodified household microwave oven and silica as solid support. By irradiation of 2-hydroxy chalcones with trifluoroacetic acid over silica gel, 11 known flavanones were prepared in high yields. The synthesised compounds were characterised using spectroscopic techniques, namely, ¹H NMR, ¹³C NMR and IR, and screened for their antifungal activity in vitro against Sclerotium rolfsii and Rhizoctonia solani by poisoned food technique. The compounds tested were found to be more active against R. solani, whereas against S. rolfsii, moderate activity was observed, as evident from LC₅₀ values. The most potent compound 2-(4-fluorophenyl)-2,3-dihydrochromen-4-one (4a) had LC₅₀ value of 12.0 mg L^?1 followed by 11, 11a, 3a, 9a, 8a, 10a and 10 having LC₅₀ values 18.21, 18.3, 32.9, 50.7, 88.8, 118.8 and 119.7 mg L^?1, respectively.     

1-Deaza-3′-O-methyladenosine: A Nucleoside with the Syn-conformation in the Solid State and in Solution

Abstract

The 2′-O-methyl (2) and the 3′-O-methyl (3) derivatives of 1-deazaadenosine (1) were prepared. Single crystal X-ray analysis as well as ¹H and ¹³C NMR studies were performed on the 3′-O-methyl-1-deazaadenosine 3. In the solid state, the glycosyl torsion angle (χ = 64.7°) is in the syn-range which is caused by an intramolecular (5′)CH2OH…N(3) hydrogen bond. The ribofuranose moiety adopts a ² E (C-3′-exo; S) conformation and the orientation of the exocyclic C(4′)-C(5′) bond is + sc (γ^(+)g). The conformation in solution was found to be very similar to that in solid state. Whereas the 2′-O-methyl derivative of 1 is a strong inhibitor of adenosine deaminase the 3′-O-methyl derivative is neither inhibitor nor substrate.     

Organometallic indolo[3,2-c]quinolines versus indolo[3,2-d]benzazepines: synthesis, structural and spectroscopic characterization, and biological efficacy

The synthesis of ruthenium(II) and osmium(II) arene complexes with the closely related indolo[3,2-c]quinolines N-(11H-indolo[3,2-c]quinolin-6-yl)-ethane-1,2-diamine (L ¹ ) and N′-(11H-indolo[3,2-c]quinolin-6-yl)-N,N-dimethylethane-1,2-diamine (L ² ) and indolo[3,2-d]benzazepines N-(7,12-dihydroindolo-[3,2-d][1]benzazepin-6-yl)-ethane-1,2-diamine (L ³ ) and N′-(7,12-dihydroindolo-[3,2-d][1]benzazepin-6-yl)-N,N-dimethylethane-1,2-diamine (L ⁴ ) of the general formulas [(η⁶-p-cymene)M^II(L ¹ )Cl]Cl, where M is Ru (4) and Os (6), [(η⁶-p-cymene)M^II(L ² )Cl]Cl, where M is Ru (5) and Os (7), [(η⁶-p-cymene)M^II(L ³ )Cl]Cl, where M is Ru (8) and Os (10), and [(η⁶-p-cymene)M^II(L ⁴ )Cl]Cl, where M is Ru (9) and Os (11), is reported. The compounds have been comprehensively characterized by elemental analysis, electrospray ionization mass spectrometry, spectroscopy (IR, UV–vis, and NMR), and X-ray crystallography (L ¹ ·HCl, 4·H₂O, 5, and 9·2.5H₂O). Structure–activity relationships with regard to cytotoxicity and cell cycle effects in human cancer cells as well as cyclin-dependent kinase (cdk) inhibition and DNA intercalation in cell-free settings have been established. The metal-free indolo[3,2-c]quinolines inhibit cancer cell growth in vitro, with IC₅₀ values in the high nanomolar range, whereas those of the related indolo[3,2-d]benzazepines are in the low micromolar range. In cell-free experiments, these classes of compounds inhibit the activity of cdk2/cyclin E, but the much higher cytotoxicity and stronger cell cycle effects of indoloquinolines L ¹ and 7 are not paralleled by a substantially higher kinase inhibition compared with indolobenzazepines L ⁴ and 11, arguing for additional targets and molecular effects, such as intercalation into DNA.     

An Improved Synthesis of N6-(6-Aminohexyl)FAD

Abstract

We report an improved synthesis of N ⁶-(6-aminohexyl)FAD (1) using an efficient one-pot conversion of inosine to the N-trifluoroacetyl protected N ⁶-(6-aminohexyl)adenosine 3. The 5′-O-phosphorylated AMP derivative 4, activated as the imidazolide, was coupled with commercial sodium riboflavin phosphate by using 18-crown-6 in DMF.     

Antifungal activity of a novel chromene dimer

The activity on Aspergillus spp. growth and on ochratoxin A production of two novel chromene dimers (3) was evaluated. The results of the bioassays indicate that the chromene dimer 3a inhibited mycelia growth by approximately 50% (EC₅₀) at 140.1 μmol L⁻¹ for A. niger, 384.2 μmol L⁻¹ for A. carbonarius, 69.1 μmol L⁻¹ for A. alliaceus and 559.1 μmol L⁻¹ for A. ochraceus. When applied at concentrations of 2 mmol L⁻¹, 3a totally inhibited the growth of all Aspergillus spp. tested. Furthermore, ochratoxin A production by A. alliaceus was reduced by about 94% with a 200 μmol L⁻¹ solution of this compound. A moderate inhibitory effect was observed for the analogous structure 3b on ochratoxin A production but not in mycelia growth. No inhibition was registered for compounds 2a and 2b, used as synthetic precursors of the dimeric species 3.     

2,4,5-Triphenylisothiazol-3(2H)-one 1,1-dioxides as inhibitors of human leukocyte elastase

A series of substituted 2,4,5-triphenylisothiazol-3(2H)-one 1,1-dioxides 9 was synthesized and investigated as inhibitors of human leukocyte elastase (HLE). All compounds were found to inhibit HLE in a time-dependent manner and most of them exhibited k_obs/[I] values > 300 M^{? 1}s^{? 1}. The most potent 3-oxosultam of this series was 9l (k_obs/[I] = 2440 M^{? 1}s^{? 1}). Kinetic investigations performed with 9g and different substrate concentrations did not allow to clearly distinguish between a competitive or noncompetitive mode of inhibition. A more complex interaction is supported by the failure of a linear dependency of k_obs values on the inhibitor concentration.     

Synthesis of N-Arylinosines

Abstract

2′,3′,5′-Tri-O(tetrahydropyran-2-yl)inosine 1 was treated with iodobenzene or 2-bromopyridine in the presence of cuprous oxide in pyridines to give the N¹ -aryl derivatives 2a, b. Deprotection of the products afforded N¹ -arylinosines 3a, b.     

DNA binding,prominent photonuclease activity and antibacterial PDT of cobalt(II) complexes of phenanthroline based photosensitizers

Abstract

The chemistry of Co(II) complexes showing efficient light induced DNA cleavage activity, binding propensity to calf thymus DNA and antibacterial PDT is summarized in this article. Complexes of formulation [Co(mqt)(B)₂]ClO₄ 1–3 where mqt is 4-methylquinoline-2-thiol and B is N,N-donor heterocyclic base, viz. 1,10-phenanthroline (phen 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz 3) have been prepared and characterized. The DNA-binding behaviors of these three complexes were explored by absorption spectra, viscosity measurements and thermal denaturation studies. The DNA binding constants for complexes 1, 2 and 3 were determined to be 1.6?×?10³?M^?1, 1.1?×?10⁴?M^?1 and 6.4?×?10⁴?M^?1 respectively. The experimental results suggest that these complexes interact with DNA through groove binding mode. The complexes show significant photocleavage of supercoiled (SC) DNA proceeds via a type-II process forming singlet oxygen as the reactive species. Antimicrobial photodynamic therapy was studied using photodynamic antimicrobial chemotherapy (PACT) assay against E. coli and all complexes exhibited significant reduction in bacterial growth on photoirradiation.     

Homo-C-Nucleoside Analogs† II. Synthesis and Anomeric Configuration of 4-(2,5-Anhydro-D-Gluco-PEntitol-1-YL)-2-Phenyl2H-1,2,3-Triazole††

Abstract

Treatment of 4-(D-gluco-pentitol-l-y1)-2-pheny1–2H-1,2,3-triazole (1) with p-toluenesulfonyl chloride in pyridine solution, afforded the homo-C-nucleoside analog, 4-(2,5-anhydro-D-gluco-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole (2) as well as its partial p-toluenesulfonyl derivative (3). 4-(5-Chloro-5-deoxy-D-gluco-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole (8), was isolated as a byproduct from the reaction. The structure and anomeric configuration of 2 was determined by acylation, ¹H, ¹³C NMR, and NOE, spectroscopy as well as mass spectrometry.

     

Metal-based ethanolamine-derived compounds: a note on their synthesis,characterization and bioactivity

Abstract

Metal-based ethanolamines, (L¹)–(L⁴) coordinated with Co(II), Cu(II), Ni(II) and Zn(II) metals in 1:2 (metal:ligand) molar ratio to produce new compounds have been reported. These compounds were screened for their bactericidal/fungicidal activity against a number of bacterial (Escherichia coli, Shigella flexneri, Pseudomonas aeruginosa, Salmonella typhi, Staphylococcus aureus and Bacillus subtilis) and fungal strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata) alongside against a shrimp species known as Artemia salina. The screening results indicated that metal complexes have significantly higher activity than uncomplexed ligands against one or more bacterial/fungal species due to chelation. The ligand (L⁴) displayed good bacterial and fungal activity as compared to other ligands. The antibacterial results revealed that the Zn(II) complex (16) of (L⁴) was found to be the most active complex and Co(II) complex (14) of the same ligand (L⁴), demonstrated the highest antifungal activity.     

Honokiol and Magnolol Increase the Number of [3H]Muscimol Binding Sites Three-Fold in Rat Forebrain Membranes In Vitro Using a Filtration Assay,by Allosterically Increasing the Affinities of Low-Affinity Sites

1. The bark of the root and stem of various Magnolia species has been used in Traditional Chinese Medicine to treat a variety of disorders including anxiety and nervous disturbances. The biphenolic compounds honokiol (H) and magnolol (M), the main components of the Chinese medicinal plant Magnolia officinalis, interact with GABA_A receptors in rat brain in vitro. We compared the effects of H and M on [³H]muscimol (MUS) and [³H]flunitrazepam (FNM) binding using EDTA/water dialyzed rat brain membranes in a buffer containing 150 mM NaCl plus 5 mM Tris-HCl, pH 7.5 as well as [³⁵S]t-butylbicyclophosphorothionate (TBPS) in 200 mM KBr plus 5 mM Tris-HCl, pH 7.5. H and M had similar enhancing effects on [³H]MUS as well as on [³H]FNM binding to rat brain membrane preparations, but H was 2.5 to 5.2 times more potent than M. 2. [ ³ H]FNM binding. GABA alone almost doubled [³H]FNM binding with EC₅₀ = 450 nM and 200 nM using forebrain and cerebellar membranes, respectively. In the presence of 5 M H or M the EC₅₀ values for GABA were decreased to 79 and 89 nM, respectively, using forebrain, and 39 and 78 nM, using cerebellar membranes. H and M potently enhanced the potentiating effect of 200 nM GABA on [³H]FNM binding with EC₅₀ values of 0.61 M and 1.6 M using forebrain membranes, with maximal enhancements of 33 and 47%, respectively. Using cerebellar membranes, the corresponding values were 0.25 and 1.1 M, and 22 and 34%. 3. [ ³ H]MUS binding. H and M increased [³H]MUS binding to whole forebrain membranes about 3-fold with EC₅₀ values of 6.0 and 15 M. Using cerebellar membranes, H and M increased [³H]MUS binding ~68% with EC₅₀ values of 2.3 and 12 M, respectively. Scatchard analysis revealed that the enhancements of [³H]MUS binding were due primarily to increases in the number of binding sites (B_max values) with no effect on the high affinity binding constants (K_d values). The enhancing effect of H and M were not additive. 4. [ ³⁵ S]TBPS binding. H and M displaced [³⁵S]TBPS binding from sites on whole rat forebrain membranes with IC₅₀ values of 7.8 and 6.0 M, respectively. Using cerebellar membranes, the corresponding IC₅₀ values were 5.3 and 4.8 M. These inhibitory effects were reversed by the potent GABA_A receptor blocker R5135 (10 nM), suggesting that H and M allosterically increase the affinity of GABA_A receptors for GABA and MUS by binding to sites in GABA_A receptor complexes. 5. Two monophenols, the anesthetic propofol (2,6-diisopropylphenol, P) and the anti-inflammatory diflunisal (2,4-difluoro-4-hydroxy-3-biphenyl carboxylic acid, D) also enhanced [³H]MUS binding, decreased the EC₅₀ values for GABA in enhancing [³H]FNM binding and potentiated the enhancing effect of 200 nM GABA on [³H]FNM binding, although enhancements of [³H]MUS binding for these monophenols were smaller than those for H and M, using forebrain and cerebellar membranes. The enhancing effect of P and D on [³H]MUS binding were almost completely additive. 2,2-biphenol was inactive on [³H]MUS and [³H]FNM binding. These, and other preliminary experiments, suggest that appropriate ortho (C2) and para (C4) substitution increases the GABA-potentiating activity of phenols. 6. The potentiation of GABAergic neurotransmission by H and M is probably involved in their previously reported anxiolytic and central depressant effects.