A direct solid‐phase assay specific for heavy‐metal toxicity. II. Assessment of heavy‐metal immobilization in soils and bioavailability to plants

We have used the solid‐phase MetPLA TE, an enzyme assay that is specific for heavy‐metal toxicity, to investigate metal toxicity of soils that have been amended with urban wastewater sludges or contaminated with dry deposition from metal‐plating industries. We have shown that soil toxicity, using MetPLA TE, ranged from 21 to 72.5% inhibition of enzyme activity. Evin soil, which displayed the highest toxicity, also had the highest concentrations of Pb and Zn. Metal uptake studies with ryegrass grown on Evin soil, showed Zn, Cd, and Pb accumulation in the plant that exceeds the standard levels reported for grasses

Solid‐phase MetPLA TE was also used as a tool to study the reduction of heavy‐metal toxicity following soil amendments to immobilize metals in soil and thus reduce their toxicity. It was found that the addition of 1% hydrated manganese oxide significantly reduced dissolved metals in soil, their accumulation by ryegrass, and soil toxicity as shown by MetPLA TE.     

A direct solid‐phase assay specific for heavy metal toxicity. I. methodology

We have developed a direct toxicity assay for soils, sediments and sludges that is specific for heavy‐metal toxicity. In the assay, a β‐galactosidase‐producingstrain of Escherichia coll is mixed with the solids sample together with a small volume (1.0 ml/0.5 to 1.0 g of solids) of eluent Extraction of metals from the solids sample is not required. Controls run with the assay eliminate interference due to indigenous β‐ga‐lactosidase activity or interaction between the solid matrix and the chromaphore. Use of 0.1 M sodium nitrate as eluent was found to yield somewhat higher sensitivity to heavy metals in solid‐phase samples than MilliQ water. Application of the assay to a diverse array of soils, sludges, and sediments indicated that samples from industrial sites were generally more toxic than those from residential or commercial sites. Heavy‐metal toxicity was correlated with the copper and zinc content of solids samples, but toxicity varied considerably at the lower range of metal contents. The proposed solid‐phase assay should prove useful as a screening test for heavy‐metal toxicity in soils, sediments, and sludges. It can also help distinguish between heavy metals and organic chemicals as the cause of toxicity in solid‐phase samples.     

Molecular electrostatic potentials of DNA base–base pairing and mispairing

An understanding of why adenine (A) pairs with thymine (T) and cytosine (C) with guanine (G) in DNA is very useful in the design of sensors and other related devices. We report the use of dissociation energies, geometries and molecular electrostatic potentials (MEPs) to justify the canonical (AT and CG) Watson-Crick pairs. We also analyze all mismatches in both configurations—cis and trans—with respect to their glycoside bonds. As expected, we found that the most stable pair configuration corresponds to CG, providing an energy criterion for that preferred configuration. The reason why A gets together with T is much more difficult to explain as the energy of this pair is smaller than the energy of some other mismatched pairs. We tested MEPs to see if they could shed light on this problem. Interestingly, MEPs yield a unique pattern (shape) for the two canonical cases but different shapes for the mismatches. A tunnel of positive potential surrounded by a negative one is found interconnecting the three H-bonds of CG and the two of AT. This MEP tunnel, assisted partially by energetics and geometrical criteria, unambiguously determine a distinctive feature of the affinity between A and T as well as that between G and C.     

Kinetics and equilibria of metal‐containing materials: Ramifications for aquatic toxicity testing for classification of sparingly soluble metals,inorganic metal compounds and minerals

The concentration of soluble metal more closely reflects the bioavailable fraction than does the total or “nominal”; concentration which includes the undissolved portion of the compound being tested. Consideration of metal species would provide a better estimation of bioavailability of the metal. Because the solubility of sparingly soluble metals, metal compounds and minerals depends on the dissolution conditions, aquatic toxicity tests may produce different results depending on the protocol used for the preparation of the test solutions. This paper considers critical aspects of the physical and chemical processes associated with dissolution. The kinetics and equilibria associated with the dissolution of sparingly soluble metals, metal compounds and minerals are reviewed, with special reference to the influence of grinding of materials. This is of importance in the regulatory classification of sparingly soluble compounds. A protocol that is appropriate for preparation of solutions for aquatic toxicity testing of sparingly soluble metals, metal compounds and minerals is recommended. The appropriateness of the results obtained using the proposed protocol for determining environmental risk is carefully considered, and the importance of considering both the actual concentrations of metal that would be in the environment and the bioavailability of the metal species present is highlighted.     

Acyclonucleoside Iron Chelators of 1‐(2‐Hydroxyethoxy)methyl‐2‐alkyl‐3‐hydroxy‐4‐pyridinones: Potential Oral Iron Chelation Therapeutics

The method of synthesizing acyclonucleoside iron chelators is both convenient and cost effective compared to that of synthesizing ribonucleoside iron chelators. The X‐ray crystal structural analysis shows that the 2‐hydroxyethoxymethyl group does not affect the geometry of the iron chelating sites. Therefore, the iron binding and removal properties of the acyclonucleoside iron chelators should remain similar to the ribonucleoside iron chelators, which is confirmed by the titration and competition reaction of the acyclonucleoside chelators with iron and ferritin, respectively. The acyclonucleoside iron chelators are more lipophilic with measured n‐octanol and Tris buffer distribution coefficients than ribonucleoside iron chelators.     

Phytotoxicity and metal leaching in EDDS‐assisted phytoextraction from pyrite wastes with Ethiopian mustard and fodder radish

Abstract

This study examines the influence of a low‐persistent chelator, [S,S]‐EDDS (ethylene diamine disuccinic acid), on the growth of Ethiopian mustard (Brassica carinata A. Braun) and fodder radish (Raphanus sativus L. var. oleiformis) and on metal leaching (ML) in As–Co–Cu–Pb–Zn‐contaminated pyrite wastes. Plants were grown in pots for 75 days with test doses of 2.5 and 5 mmol EDDS per kg of soil applied through irrigation one week before harvest, and 1 mmol EDDS per kg of soil repeated five times at 5‐ and 10‐day intervals, in comparison with untreated controls. Fodder radish treated with 1 mmol at the five‐day interval was also irrigated with 1 mg IBA (indole‐3‐butyric acid) per kg of soil every 10 days. Shoot biomass, leaf area and root growth were generally reduced by EDDS in both species, particularly in repeated applications and in radish, regardless of IBA supply, with root biomass being more affected than length and electrical capacitance (EC). EDDS generally improved shoot concentrations of Cu, Co, Zn and Pb, but repeated treatments caused significant ML (mainly of Cu), explained by a multivariate relationship (R ² = 0.52) including the integral over time of both leaf area (R ² = 0.43) and root EC (R ² = 0.09). We conclude that roots play a secondary role in preventing ML, because of the prevailing effect of leaf transpiration in controlling percolation. The best metal phytoextraction was achieved with EDDS applied at harvest – a safe ML strategy, especially at the low dose of 2.5 mmol per kg of soil.

Abbreviations: DTPA, diethylene triamine pentaacetic acid; EC, electrical capacitance; EDDS, ethylene diamine disuccinic acid; EDTA, ethylene diamine tetraacetic acid; HM, heavy metals; IAA, indoleacetic acid; IBA, indolebutyric acid; ICP‐OES, inductively coupled plasma optical emission spectroscopy; LA, leaf area; ML, metal leaching     

Modelling interactions of acid–base balance and respiratory status in the toxicity of metal mixtures in the American oyster Crassostrea virginica

Heavy metals, such as copper, zinc and cadmium, represent some of the most common and serious pollutants in coastal estuaries. In the present study, we used a combination of linear and artificial neural network (ANN) modelling to detect and explore interactions among low-dose mixtures of these heavy metals and their impacts on fundamental physiological processes in tissues of the Eastern oyster, Crassostrea virginica. Animals were exposed to Cd (0.001–0.400 μM), Zn (0.001–3.059 μM) or Cu (0.002–0.787 μM), either alone or in combination for 1 to 27 days. We measured indicators of acid–base balance (hemolymph pH and total CO₂), gas exchange (Po₂), immunocompetence (total hemocyte counts, numbers of invasive bacteria), antioxidant status (glutathione, GSH), oxidative damage (lipid peroxidation; LPx), and metal accumulation in the gill and the hepatopancreas. Linear analysis showed that oxidative membrane damage from tissue accumulation of environmental metals was correlated with impaired acid–base balance in oysters. ANN analysis revealed interactions of metals with hemolymph acid–base chemistry in predicting oxidative damage that were not evident from linear analyses. These results highlight the usefulness of machine learning approaches, such as ANNs, for improving our ability to recognize and understand the effects of sub-acute exposure to contaminant mixtures.     

Synthesis of Oligoribonucleotides Containing 4‐Thiouridine Using the Convertible Nucleoside Approach and the 1‐(2‐Fluorophenyl)‐4‐Methoxypiperidin‐4‐yl Group

Oligoribonucleotides containing 4‐thiouridine were prepared using the Fpmp group for protection of the 2′‐OH. Two uridine derivatives with the 1,2,4‐triazolyl and the 2‐nitrophenyl groups at position 4 were used to obtain 4‐thiouridine by postsynthetic substitution with sodium hydrogen sulfide. Both uridine derivatives allow the preparation of the desired oligonucleotides in good yields.     

Design,Efficient Synthesis,and Anti‐HIV Activity of 4′‐C‐Cyano‐ and 4′‐C‐Ethynyl‐2′‐deoxy Purine Nucleosides

Some 4′‐C‐ethynyl‐2′‐deoxy purine nucleosides showed the most potent anti‐HIV activity among the series of 4′‐C‐substituted 2′‐deoxynucleosides whose 4′‐C‐substituents were methyl, ethyl, ethynyl and so on. Our hypothesis is that the smaller the substituent at the C‐4′ position they have, the more acceptable biological activity they show. Thus, 4′‐C‐cyano‐2′‐deoxy purine nucleosides, whose substituent is smaller than the ethynyl group, will have more potent antiviral activity. To prove our hypothesis, we planned to develop an efficient synthesis of 4′‐C‐cyano‐2′‐deoxy purine nucleosides (4′‐CNdNs) and 4′‐C‐ethynyl‐2′‐deoxy purine nucleosides (4′‐EdNs). Consequently, we succeeded in developing an efficient synthesis of six 2′‐deoxy purine nucleosides bearing either a cyano or an ethynyl group at the C‐4′ position of the sugar moiety from 2′‐deoxyadenosine and 2,6‐diaminopurine 2′‐deoxyriboside. Unfortunately, 4′‐C‐cyano derivatives showed lower activity against HIV‐1, and two 4′‐C‐ethynyl derivatives suggested high toxicity in vivo.     

The season‐of‐birth paradox

Abstract

Vital statistics data show a remarkably consistent seasonality in U.S. birth patterns, with peaks in late summer and winter months, and a valley in the spring. An attitude survey of college students suggests that peaks in the actual birth distribution occur in unpopular months in which to give birth; the valley in the actual birth distribution occurs in popular months. This paradoxical finding is named the Season‐of‐Birth Paradox. Explanations to resolve the paradox include biological and psychological components. A psychological mechanism—named the Misinformed Reproducer Hypothesis—is tested using NSFG data from the 1973–75 and 1979–81 cycles. Results suggest that women stop contracepting with the expectation that they will get pregnant almost immediately. When it takes several months on the average for a successful conception to occur, the actual birth distribution is shifted away from the preferred birth distribution. These results suggest that psychological as well as biological mechanisms underlie the consistent seasonality patterns in U.S. births.     

An Efficient Route to Novel 4,5‐Di‐ and 2,4,5‐Tri Substituted Imidazoles from Imidazo[1,5‐a]‐1,3,5‐triazine (5,8‐Diaza‐7,9‐dideazapurine) Derivatives

Two new types of imidazole derivatives: N‐(2‐R¹‐5‐R²‐1H‐imidazol‐4‐yl) thioureas 7a–g and N‐(2‐R¹‐5‐R²‐1H‐imidazol‐4‐yl) formamides 8b,c,g were obtained in high yields by the hydrolytic degradation of 6‐R¹‐8‐R²‐2‐thioxo‐2,3‐dihydroimidazo[1,5‐a]‐1,3,5‐triazin‐4(1H)‐ones 5a–g and 6‐R¹‐8‐R²‐imidazo[1,5‐a]‐1,3,5‐triazin‐4(3H)‐ones 6b,c,d, respectively. The tautomeric preferences of the new imidazoles were determined.     

Synthesis and Biological Evaluation of Novel Apio Nucleosides with Thiazole‐4‐carboxamide and 1,2,4‐Triazole‐3‐carboxamide

In view of biological activities of azole nucleosides and apio‐dideoxynucleoside, novel apio nucleoside analogues (1 and 2) with thiazole and triazole base moiety were synthesized using 2,3‐O‐isopropylidene‐apio‐β‐d‐furanose (3), which was prepared from d‐mannose.     

Biological versus geochemical control and environmental change drivers of the base metal budgets of a tropical montane forest in Ecuador during 15 years

To assess the susceptibility of the base metal budget of a remote tropical montane forest in Ecuador to environmental change, we determined the extent of biological control of base metal fluxes and explored the impact of atmospheric inputs and precipitation, considered as potential drivers of ecosystem change, on the base metal fluxes. We quantified all major base metal fluxes in a ca. 9.1 ha forested catchment from 1998 to 2013. Mean (±s.d.) annual flux to the soil via throughfall + stemflow + litterfall was 13800 ± 1500 mg m^?2 Ca, 19000 ± 1510 mg m^?2 K, 4690 ± 619 mg m^?2 Mg and 846 ± 592 mg m^?2 Na of which 22 ± 6, 45 ± 16, 39 ± 10 and 84 ± 33%, respectively, were leached to below the organic layer. The mineral soil retained 79–94% of this Ca, K and Mg, while Na was released. Weathering rates estimated with three different approaches ranged from not detected (ND) to 504 mg m^?2 year^?1 Ca, ND-1770 mg m^?2 year^?1 K, 287–597 mg m^?2 year^?1 Mg and 403–540 mg m^?2 year^?1 Na. The size of mainly biologically controlled aboveground fluxes of Ca, K and Mg was 1–2 orders of magnitude larger than that of mainly geochemically controlled fluxes (sorption to soil and weathering). The elemental catchment budgets (total deposition ? streamflow) were positive for Ca (574 ± 893 mg m^?2) and K (1330 ± 773 mg m^?2), negative for Na (?370 ± 1300 mg m^?2) and neutral for Mg (1.89 ± 304 mg m^?2). Our results demonstrate that biological processes controlled element retention for Ca, K and Mg in the biological part of the ecosystem. This was different for Na, which was mainly released by weathering from the study catchment, while the biological part of the ecosystem was Na-poor. The deposition of base metals was the strongest driver of their budgets suggesting that the base metal cycling of the study ecosystem is susceptible to changing deposition.     

Synthesis of D‐Altritol Nucleosides with a 3′‐O‐Tert‐Butyldimethylsilyl Protecting Group

Four D‐altritol nucleosides with a 3′‐O‐tert‐butyldimethylsilyl protecting group are synthesized (base moieties are adenine, guanine, thymine and 5‐methylcytosine). The nucleosides are obtained by ring opening reaction of 1,5:2,3‐dianhydro‐4,6‐O‐benzylidene‐D‐allitol. Optimal reaction circumstances (NaH, LiH, DBU, phase transfer, microwave irridation) for the introduction of the heterocycles are base‐specific. For the introduction of the 3′‐O‐silyl protecting group, long reaction times and several equivalents of tert‐butyldimethylsilyl chloride are needed.     

Thiosugars. XII. Synthesis of New 3′‐O‐Substituted 2′,5′‐Anhydro‐2′‐thio‐α‐d‐pentofuranosyl Nucleoside Analogues

Methyl 2,5‐anhydro‐3‐O‐(2‐methoxyethyl)‐2‐thio‐β‐d‐arabinofuranoside and methyl 2,5‐anhydro‐3‐O‐(2‐fluorobenzyl)‐2‐thio‐α‐d‐lyxofuranoside were transformed into the corresponding uridine, thymidine, cytidine and adenosine analogues, which exclusively exhibited the α‐configuration irrespective of the anomeric configuration of the donor. The structure, configuration, and conformation of the products was elucidated by X‐ray structure analyses. The nucleoside analogues were tested for antiviral activities.     

Design and synthesis of 4,5,6,7‐tetrahydro‐1H‐1,2‐diazepin‐7‐one derivatives as a new series of Phosphodiesterase 4 (PDE4) inhibitors

Phosphodiesterase 4 (PDE4) inhibitors have attractive therapeutic potential in respiratory, inflammatory, metabolic and CNS disorders. The present work details the design, chemical exploration and biological profile of a novel PDE4 inhibitor chemotype. A diazepinone ring was identified as an under-represented heterocyclic system fulfilling a set of PDE4 structure-based design hypotheses. Rapid exploration of the structure activity relationships for the series was enabled by robust and scalable two/three-steps parallel chemistry protocols. The resulting compounds demonstrated PDE4 inhibitory activity in cell free and cell-based assays comparable to the Zardaverine control used, suggesting potential avenues for their further development.     

Second Generation of cycloSal‐Pronucleotides with Esterase‐Cleavable Sites: The ”Lock‐In”‐Concept

A conceptual extension of the cycloSal‐pronucleotide approach is presented. The characteristic feature of the new cycloSal‐derivatives of the anti‐HIV active nucleoside analogue d4T 1 is the incorporation of an enzymatically cleavable carboxylic ester moiety with the intention to trap the triesters inside cells (”lock‐in”‐concept). CycloSal‐triesters bearing different ester groups in the 3‐or 5‐position of the cycloSal‐moiety are described. Surprisingly, only acetyl‐and levulinyl esters are cleaved readily in CEM cell extracts while alkyl esters were found to be stable. Nevertheless, in in‐vitro anti‐HIV assays most of the compounds achieve the thymidine–kinase bypass, thus proving that they act at least as nucleotide delivery systems.