Role of cell attachment in leaching of chalcopyrite mineral by Thiobacillus ferrooxidans

Summary Experiments on the leaching of copper from chalcopyrite mineral by the bacterium Thiobacillus ferrooxidans show that, in the presence of adequate amounts of sulphide, iron-grown bacteria preferentially oxidise sulphur in the ore (through direct attachment) rather than ferrous sulphate in solution. At 20% pulp density, the leaching initially takes place by a predominantly direct mechanism. The cell density in the liquid phase increases, but the Fe²⁺ is not oxidised. However, in the later stages when less solid substrate is available and the cell density becomes very high, the bacteria start oxidising Fe²⁺ in the liquid phase, thus contributing to the indirect mechanism of leaching. Contrary to expectations, the rate of leaching increased with increasing particle size in spite of the decreasing specific surface area. This has been found to be due to increasing attachment efficiency with increase in particle size. Offprint requests to: R. Kumar     

The iron-quinone acceptor complex in Rhodospirillum rubrum chromatophores studied by EPR

A new EPR signal is reported in Rhodospirillum rubrum chromatophores. The signal is attributed to Q⁻_BFe²⁺, the semiquinone-iron complex of the secondary quinone electron acceptor, on the basis of the following observations. (1) It is induced by a single laser flash given a room temperature and is stable. (2) It is present after odd-numbered flashes and absent after even-numbered flashes when a series of flashes is given. (3) When it is already present, low-temperature illumination results in the disappearance of the signal due to formation of the Q⁻_AFe²⁺Q⁻_B state. (4) Its formation is inhibited by the presence of orthophenanthroline at normal values of pH. The Q⁻_BFe²⁺ signal has two main features, one at g = 1.93 and the other at g = 1.82. The two features have different microwave power and temperature dependences, with the g = 1.82 signal being more difficult to saturate and requiring lower temperatures to be observable. Raising the pH leads to an increase in the g = 1.82 feature, while the g = 1.93 signal decreases in amplitude. It is suggested that the two parts of the signal may represent two EPR forms due to structural heterogeneity. The low-field feature of the Q⁻_BFe²⁺ signal shifts to lower field as the pH is raised and a pK for this change seems to occur at pH 9.4. The Q⁻_AFe²⁺ signal at g = 1.88 also shifts as the pH is increased; however, the shift is less marked than that seen for Q⁻_BFe²⁺, the shift is to higher field and the range over which it occurs is wider and depends upon the temperature of Q⁻_AFe²⁺ formation. This effect may be due to a pK on a protein group being shifted to higher pH by the presence of Q⁻_A. ortho-Phenanthroline broadens and shifts the Q⁻_AFe²⁺ signal. The inhibition of electron transfer between Q⁻_A and Q_B by ortho-phenanthroline becomes less effective at high pH. The new Q⁻_BFe²⁺ signal is unlike other semiquinone-iron signals reported in the literature in bacteria; however, it is remarkably similar to the Q⁻_BFe²⁺ signal reported in Photosystem II.     

Mineralogical controls on the bacterial oxidation of refractory Barberton gold ores

Abstract: The effect of mineralogical characteristics of gold ore minerals on the nature of sulphide oxidation during a bacterial leaching process was investigated. Three different ore types from the South African goldmines were used, i.e. an arsenopyritic-pyritic ore (Sheba goldmine), a pyritic ore (Agnes goldmine) and a loellingitic-arsenopyritic ore (New Consort goldmine). Detailed mineralogical characterization of each ore was performed. Thereafter, polished sections of the sulphides were suspended in a bacterial leach pulp in an air-stirred vessel for various periods of time. The effect of bacterial oxidation on the sulphides was monitored. Different types of gold-bearing arsenopyrite exist, each type having its own characteristic behaviour during the bacterial oxidation process. The rate of oxidation is controlled by the amount of defects in the crystal structure, and the amount of defects is again controlled by the composition of the arsenopyrite crystal. The distribution of refractory gold in the sulphide minerals can be correlated with the presence of compositional zones and structural deviations. These same mineralogical features also control the sites and rates of bacterial oxidation. Thus. refractory gold occurs at sites which are preferentially leached by the bacteria. The rate of gold liberation from sulphides is therefore being enhanced during the early stages of bacterial oxidation. Defects in a crystal structure influence the rate of bio-oxidation, and can be related directly to the crystal structure of the sulphide mineral, the crystallographic orientation of the exposed surfaces, and differences in chemical compositional and mechanical deviations in the crytals. A combination of all of these mineralogical factors influences the bacterial oxidation process. To optimize and to understand the leaching of an individual ore it is important to establish its controlling factors.     

Oxidation of gold-antimony ores by a thermoacidophilic microbial consortium

Antimony leaching from sulfide ore samples by an experimental consortium of thermoacidophilic microorganisms, including Sulfobacillus, Leptospirillum, and Ferroplasma strains was studied. The ores differed significantly in the content of the major metal sulfides (%): Sb_S, 0.84 to 29.95; Fe_S, 0.47 to 2.5, and As_S, 0.01 to 0.4. Independent of the Sb_S concentration in the experimental sample, after adaptation to a specific ore and pulp compaction, the microorganisms grew actively and leached/oxidized all gold-antimony ores at 39 ± 1°C. The lower was the content of iron and arsenic sulfides, the higher was antimony leaching. For the first time the investigations conducted with the use of X-ray microanalysis made it possible to conclude that, in a natural high-antimony ore, Sb inhibits growth of only a part of the cell population and that Ca, Fe, and Sb may compete for the binding centers of the cell.     

Arsenic precipitation in the bioleaching of enargite by Sulfolobus BC at 70 °C

Enargite (Cu₃AsS₄) was leached at 70°C by Sulfolobus BC in shake-flasks. The highest copper dissolution (52% after 550 h of leaching) was obtained with bacteria and 1 g l^–1 ferric ion. In the absence of ferric ion, Sulfolobus BC catalyzes the bioleaching of enargite through a direct mechanism after adhesion onto the mineral surface. In ferric bioleaching, arsenic precipitated as ferric arsenate and arsenic remained associated to the solid residues, preventing the presence of a high dissolved arsenic concentration in the leaching solution. About 90% inhibition of bacterial growth rate and activity was observed for dissolved arsenic concentrations above 600 mg l^–1 for As(III) and above 1000 mg l^–1 for As(V). Arsenic-bearing copper ores and concentrates could be leached by Sulfolobus BC in the presence of ferric iron due to the favourable precipitation of arsenic ion as ferric arsenate, avoiding significant bacterial inhibition.     

Uniform Pomegranate‐Like Nanoclusters Organized by Ultrafine Transition Metal Oxide@Nitrogen‐Doped Carbon Subunits with Enhanced Lithium Storage Properties

Uniform pomegranate‐like nanoclusters (NCs) organized by ultrafine transition metal oxide@nitrogen‐doped carbon (TMO@N–C) subunits (diameter ≈ 4 nm) are prepared on a large scale for the first time through a facile, novel, and one‐pot approach. Taking pomegranate‐like Fe₃O₄@N–C NCs as an example, this unique structure provides short Li⁺/electron diffusion pathways for electrochemical reactions, structural stability during cycling, and high electrical conductivity, leading to superior electrochemical performance. The resulting pomegranate‐like Fe₃O₄@N–C NCs possess a high specific capacity (1204.3 mA h g^?1 at 0.5 A g^?1 over 100 cycles), a stable cycle life (1063.0 mA h g^?1 at 1 A g^?1, 98.4% retention after 1000 cycles), and excellent rate capacities (606.0 mA h g^?1 at 10 A g^?1, 92.0% retention; 417.1 mA h g^?1 at 20 A g^?1, 91.7% retention after 1000 cycles).     

Arsenic Release from a Natural Rock under Near‐natural Oxidizing Conditions

The effects of carbonate concentration and the presence of iron hydroxide phases on the process of arsenic release from an ore material were investigated under experimental oxic conditions and in the pH range from 6.0 to 9.0. These experimental conditions are pertinent to arsenic leaching from tailings and mining wastes. The leaching tests lasted for ≤ 99 days and were performed with materials of five different particle sizes (≤ 2 mm). Carbonate ions were produced in‐situ by dolomite dissolution or were contained in used waters (0 to 30 mM as HCO₃^–). Iron hydroxide phases were formed in situ by oxidative dissolution of metallic iron (Fe⁰) or pyrite (FeS₂). Non‐disturbed batch experiments and air‐homogenized experiments were conducted with a constant amount (10 g/L) of an arsenic‐bearing rock (ore material) of a given particle size and different types of water (deionized, tap and mineral water). For comparison, experiments were conducted with 0.1 M EDTA, 0.1 M Na₂CO₃, and 0.1 M H₂SO₄. Neither the use of dolomite nor the use of water containing various carbonate (HCO₃^–) concentrations could confirm the recent results on the favorable role of As^III‐carbonate complexes on the arsenic transport in the environment. On the other hand, iron hydroxide phases (from Fe⁰ and FeS₂) univocally delayed the As release in both experimental procedures. Furthermore, the theoretically expected effects of the particle size of the ore material was observed. If one takes into consideration that the used HCO₃^– concentrations were up to six times larger then those of natural surface waters (≤ 5.5 mM) but up to five times lower than those currently used in the literature (≥ 100 mM), it is concluded that the reported conflicting results for As leaching from sediments may be a misinterpretation of processes occurring in the sediment and yielding increased As release with increasing HCO₃^–/CO₃^2– concentration.     

Use of heterotrophic microorganisms in mineral biotechnology

A process for biological removal of iron from quartz sands, kaolins and clays was developed in which these industrial minerals were leached at 90°C with lixiviant produced as a result of the cultivation of acid-producing heterotrophic microorganisms, mainly strains of Aspergillus niger, at 30°C in a nutrient medium containing molasses as a source of carbon and energy. The lixiviant, i.e. the fermentation fluid, contained oxalic and citric acids as main components and after the cultivation was acidified to a pH of 0.5 by means of hydrochloric acid. The leaching was carried out in mechanically stirred acid-resistant vats for a period of from 1 to 5 hours. The iron content of some sands treated by this method was lowered from 0.035–0.088 to below 0.012% Fe₂O₃ making them suitable for the preparation of high quality glass. The iron content of different kaolins was lowered from 0.65–1.49 to 0.44–0.75% Fe₂O₃ and as a result of this their whiteness was increased from 55–87 to 86–92%. The iron content of a clay was lowered from 6.25 to 1.85% Fe₂O₃ and this increased the fireproofness of the clay from 1 670 to 1 750°C. Similar process was used for leaching of aluminium from aluminosilicates, mainly clays and kaolins. However, after the cultivation the fermentation fluid was acidified either by means of sulfuric or hydrochloric acid or by means of different mixtures of inorganic acids. For enhancing aluminium solubilization the aluminosilicates were heated before leaching at 600–650°C for 1–2 hours. Over 90% of the aluminium present in different clays and kaolins was leached within 3–6 hours in this way. “Silicate” bacteria related to the species Bacillus circulans and B. mucilaginosus were used to leach silicon from low-grade bauxite ores containing aluminosilicates as impurities. The bacterial action was connected with the formation of mucilaginous capsules consisting of expolysaccharides. The solid residues after leaching were characterized by higher values of alumina content and were suitable for processing by means of the BAYER process for recovering aluminium. Heterotrophic bacteria were used to leach manganese from oxide ores using different organic compounds as reducing agents.     

The Blue Water Footprint of Primary Copper Production in Northern Chile

Water consumption related to the life cycle of metals is seldom reported, even though mines are often situated in very dry regions. In this study we quantified the life cycle consumption of groundwater and fresh surface water (blue water footprint [WF_blue]) for the extraction and production of high‐grade copper refined from both a copper sulfide ore and a copper oxide ore in the Atacama Desert of northern Chile. Where possible, we used company‐specific data. The processes for extracting copper from the two types of ore are quite different from each other, and the WF_blue of the sulfide ore refining process is 2.4 times higher than that of the oxide ore refining process (i.e., 96 cubic meters per metric ton [tonne] of copper versus 40 cubic meters per tonne of copper). Most of the water consumption (59% of WF_blue) in the sulfide ore process occurred at the concentrator plant, via seepage, accumulation, and also by evaporation. In the oxide ore process, the main user of water is the heap‐leaching process, with 45% of WF_blue. The crushing and agglomeration operations, electrowinning cells, and solution pools are also significant contributors to the total consumption of water in the oxide ore process. Most of the water consumed in the oxide ore process was lost to evaporation. The WF_blue of the oxide ore process can be reduced by preventing water evaporation and using more sophisticated devices during irrigation of the leaching heaps. The WF_blue of the sulfide ore refining process can be reduced by improving water recovery (i.e., reducing seepage, accumulation, and evaporation) from the tailings dam at the concentrator plant. Using seawater in the production of copper is also a promising option to reduce the WF_blue by up to 62%.     

Estuarine sediment hydrocarbon-degrading microbial communities demonstrate resilience to nanosilver

Little is currently known about the potential impact of silver nanoparticles (AgNPs) on estuarine microbial communities. The Colne estuary, UK, is susceptible to oil pollution through boat traffic, and there is the potential for AgNP exposure via effluent discharged from a sewage treatment works located in close proximity. This study examined the effects of uncapped AgNPs (uAgNPs), capped AgNPs (cAgNPs) and dissolved Ag₂SO₄, on hydrocarbon-degrading microbial communities in estuarine sediments. The uAgNPs, cAgNPs and Ag₂SO₄ (up to 50 mg L⁻¹) had no significant impact on hydrocarbon biodegradation (80–92% hydrocarbons were biodegraded by day 7 in all samples). Although total and active cell counts in oil-amended sediments were unaffected by silver exposure; total cell counts in non-oiled sediments decreased from 1.66 to 0.84 × 10⁷ g⁻¹ dry weight sediment (dws) with 50 mg L⁻¹ cAgNPs and from 1.66 to 0.66 × 10⁷ g⁻¹ dws with 0.5 mg L⁻¹ Ag₂SO₄ by day 14. All silver-exposed sediments also underwent significant shifts in bacterial community structure, and one DGGE band corresponding to a member of Bacteroidetes was more prominent in non-oiled microcosms exposed to 50 mg L⁻¹ Ag₂SO₄ compared to non-silver controls. In conclusion, AgNPs do not appear to affect microbial hydrocarbon-degradation but do impact on bacterial community diversity, which may have potential implications for other important microbial-mediated processes in estuaries.     

High Volumetric Capacitance,Ultralong Life Supercapacitors Enabled by Waxberry‐Derived Hierarchical Porous Carbon Materials

Supercapacitors with fast charge/discharge rate and long cycling stability (>50 000 cycles) are attractive for energy storage and mobile power supply. In this paper, a facile strategy is developed to fabricate an Fe₂O₃/FeS‐decorated N, S‐codoped hierarchical porous carbon hybrid. Its microstructure and compositions can be readily controlled through adjusting the hydrothermal reaction between waxberry and iron sulfate. The constructed supercapacitors with the as‐prepared carbon materials from this reaction are able to exhibit outstanding capacitive performance with a superfast charge/discharge rate (<1 s), ultralong cycle life (>50 000 cycles, 80 A g⁻¹), ultrahigh volumetric capacitance (1320.4 F cm⁻³, 0.1 A g⁻¹), and high energy density (100.9 W h kg⁻¹, 221.9 W h L⁻¹). The outstanding performance makes it one of the best biomass‐derived supercapacitors. The superior capacitive behavior is likely to arise from the N and S codoping on the surface/edge/skeleton of the carbon microspheres and nanosheet composites coupled with the fast redox reaction of Fe₂O₃/FeS. Overall, this research presents a new avenue for developing the next generation of sustainable high‐performance energy storage device.     

Fe3O4 and bimetal–organic framework Zn/Mg composite peroxide-like catalyze luminol chemiluminescence for specific measurement of atropine in Datura plant

Atropine (AT) is an anticholinergic drug. AT is abundantly in Datura plant seeds. Fe₃O₄@Zn/Mg MOF (Fe₃O₄@MOF) composite was synthesized. The compound had a high peroxidase-like activity in a chemiluminescence (CL) reaction. Addition of AT quenched CL. The linear range and limit of detection were 5–600 μg L⁻¹ and 2 × 10⁻² μg L⁻¹. This method is fast, reversible, and selective, without biodegradability effects, high accuracy, and precision for measuring AT in the Datura plant.     

Microbiological Leaching of Metallic Sulfides

The percentage of chalcopyrite leached in percolators by Thiobacillus ferrooxidans was dependent on the surface area of the ore but not on the amount. Typical examples of ore leaching, which demonstrate the role of the bacteria, are presented. In stationary fermentations, changes in KH(2)PO(4) concentration above or below 0.1% decreased copper leaching as did reduction in the MgSO(4).7H(2)O and increase in the (NH(4))(2)SO(4) concentration. Bacterial leaching of chalcopyrite was more effective than nonbiological leaching with ferric sulfate; ferric sulfate appeared to retard biological leaching, but this effect was likely caused by formation of an insoluble copper-iron complex. Ferrous sulfate and sodium chloride singly accentuated both bacterial and nonbiological leaching of chalcocite but jointly depressed bacterial action. Sodium chloride appeared to block bacterial iron oxidation without interfering with sulfide oxidation. Bacterial leaching of millerite, bornite, and chalcocite was greatest at pH 2.5. The economics of leaching a number of British Columbia ore bodies was discussed.     

Optimization of staged bioleaching of low-grade chalcopyrite ore in the presence and absence of chloride in the irrigating lixiviant: ANFIS simulation

In this investigation, copper was bioleached from a low-grade chalcopyrite ore using a chloride-containing lixiviant. In this regard, firstly, the composition of the bacterial culture media was designed to control the cost in commercial application. The bacterial culture used in this process was acclimated to the presence of chloride in the lixiviant. Practically speaking, the modified culture helped the bio-heap-leaching system operate in the chloridic media. Compared to the copper recovery from the low-grade chalcopyrite by bioleaching in the absence of chloride, bioleaching in the presence of chloride resulted in improved copper recovery. The composition of the lixiviant used in this study was a modification with respect to the basal salts in 9 K medium to optimize the leaching process. When leaching the ore in columns, 76.81 % Cu (based on solid residues of bioleaching operation) was recovered by staged leaching with lixiviant containing 34.22 mM NaCl. The quantitative findings were supported by SEM/EDS observations, X-ray elemental mapping, and mineralogical analysis of the ore before and after leaching. Finally, Adaptive neuro-fuzzy inference system (ANFIS) was used to simulate the operational parameters affecting the bioleaching operation in chloride–sulfate system.     

Gene expression modulation by chalcopyrite and bornite in Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a mesophilic, acidophilic, chemolithoautotrophic bacterium that obtains energy from the oxidation of ferrous iron (Fe²⁺), elemental sulfur and reduced sulfur compounds. The industrial interest in A. ferrooxidans resides in its capacity to oxidize insoluble metal sulfides into soluble metal sulfates, thus allowing the recovery of the desired metals from low-grade sulfide ores. In the present work, RNA arbitrarily primed PCR (RAP-PCR) was performed to identify cDNAs differentially expressed in A. ferrooxidans cells grown in the presence of Fe²⁺ and cells maintained for 24 h in the presence of the copper sulfides bornite and chalcopyrite. Eighteen cDNAs corresponding to genes with known function were identified, and their relative expression was further characterized by real-time quantitative PCR. Bornite had a mild effect on the expression of the 18 genes analyzed. None of these genes was down-regulated and among the few genes up-regulated, it is worth mentioning lepA and def-2 that are involved in protein synthesis. Chalcopyrite presented the most significant changes. Five genes related to protein processing were down-regulated, and another 5 genes related to the transport system were up-regulated. The up- and down-regulation of these genes in the presence of bornite and chalcopyrite could be due to alterations in the ideal pH, presence of copper ions in solution and nutrient limitation. The results suggest that gene expression modulation might be important for the A. ferrooxidans early response to copper sulfides.     

Metabolic rates in harvestmen (Arachnida, Opiliones): the influence of running activity

Abstract. Metabolic rates of adult Lophopilio palpinalis (Herbst, 1799) (Arachnida, Opiliones, Phalangioidea) and Paranemastoma quadripunctatum (Perty, 1833) (Arachnida, Opiliones, Troguloidea) are measured during rest and activity. Carbon dioxide release during rest is continuous in both species. Mean values at 20 °C are 4.2 µL min⁻¹ g⁻¹ for the males of P. quadripunctatum, 4.1 µL min⁻¹ g⁻¹ for the males of L. palpinalis and 4.7 µL min⁻¹ g⁻¹ for the females of L. palpinalis, thus being significantly higher in the egg-producing females. In L. palpinalis, respiratory quotient at rest is 0.84. Spontaneous walking activity with speeds of 15–30 cm min⁻¹ raises the metabolic rate by up to three-fold in both species. Lophopilio palpinalis is made to undertake constant running on a treadmill with speeds of 60, 72 and 96 cm min⁻¹. Enforced activity causes the animals to raise their metabolic rates by up to five-fold above resting rates. Animals reach a steady state of CO₂ release on the treadmill and show a fast t_1/2 on-response, indicating aerobic exercise. The minimum cost of locomotion is determined to be 2.5 × 10⁻³ J cm⁻¹ g⁻¹, thus fitting the predicted values for terrestrial locomotion.     

Cadmium-induced formation of sulphide and cadmium sulphide particles in the aquatic hyphomycete Heliscus lugdunensis

Freshwater fungi which can survive under metal exposure receive increasing scientific attention. Enhanced synthesis of sulphide and glutathione but no phytochelatin synthesis in response to cadmium (up to 80 μM Cd²⁺ in the medium) was measured in the aquatic hyphomycete Heliscus lugdunensis. Up to 25 μmol g⁻¹ dry mass the fungus formed sulphide in an exponentially Cd²⁺-concentration-dependent manner. Using light microscopy, precipitates were observed outside of the hyphae which could be determined as amorphous particles by X-ray diffraction (XRD). Energy dispersive X-ray spectroscopy (EDS) analysis indicated that these particles were mainly composed of Cd and S with an atomic ratio of 1:1, but some elements of the culture medium such as P and Cl were also present. Fungal cells exposed to Cd²⁺ accumulated 12–28 μmol metal g⁻¹ dry mass over a period of 7–28 days. The results may indicate that sulphide could sequester excess Cd²⁺ under oxygen deprived conditions and thereby reduce its toxicity via an additional avoidance mechanism of this fungus.     

Nutrient status of black spruce (Picea mariana [Mill.] BSP) forest soils dominated by Kalmia angustifolia L.

A study was conducted to determine soil chemistry in an uncut black spruce (Picea mariana) forest with and without the ericaceous understory shrub Kalmia angustifolia, as well as on a cut black spruce forest currently dominated by Kalmia. The organic (humus) and mineral (Ae, upper and lower B horizons) soils associated with Kalmia from uncut and cut forests, and non-Kalmia soils from uncut forest, were analyzed for selected soil properties. In general, mineral soils (B horizon) associated with Kalmia in uncut forest have lower values for organic matter (3.25%), organic nitrogen (0.66 mg·g⁻¹), Fe³⁺ (95.4 μg·g⁻¹) and Mn²⁺ (9 μg·g⁻¹), and higher values for pH (4.12) and Ca²⁺ (27 μg·g⁻¹) compared to non-Kalmia (organic matter, 3.43%; organic-N, 1.15 mg·g⁻¹; Fe³⁺, 431 μg·g⁻¹; Mn²⁺, 23.2 μg·g⁻¹; pH, 3.14; Ca²⁺, 15.6 μg·g⁻¹) and cut black spruce-Kalmia (organic matter, 3.74%; organic-N, 0.94 mg·g⁻¹; Fe³⁺, 379 μg·g⁻¹; Mn²⁺, 27 μg·g⁻¹; pH, 2.87; Ca²⁺, 25.2 μg·g⁻¹) forest. The high C:N ratio in Kalmia mineral soil from upper B (29.73) and lower B (identified as B+) (33.08) in uncut black spruce forest was recorded compared to non-Kalmia soils in B (18.17) and B+ (17.05) horizons in uncut black spruce forest. Phenolics leached out from Kalmia litter were lower in Kalmia associated soils than the non-Kalmia soils from the uncut forest, and Kalmia associated soils from the cut forest area. Results indicate that soils associated with Kalmia were nutrient poor particularly for nitrogen, phosphorus, iron and manganese, and provide some basis for the hypothesis that Kalmia has dominated microsites that were nutrient poor prior to Kalmia colonization.     

Proliferation inhibition of novel diphenylamine derivatives

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most widely used drugs in the world but some NSAIDs such as diclofenac and tolfenamic acid display levels of cytotoxicity, an effect which has been attributed to the presence of diphenylamine contained in their structures. A novel series of diphenylamine derivatives were synthetised and evaluated for their cytotoxic activities and proliferation inhibition. The most active compounds in the cytotoxicity tests were derivative 6g with an IC₅₀ value of 2.5 ± 1.1 × 10⁻⁶ M and derivative 6f with an IC₅₀ value of 6.0 ± 3.0 × 10⁻⁶ M (L1210 cell line) after 48 h incubation. The results demonstrate that leukemic L1210 cells were much more sensitive to compounds 6f and 6g than the HEK293T cells (IC₅₀ = 35 × 10⁻⁶ M for 6f and IC₅₀ > 50 × 10⁻⁶ M for 6g) and NIH-3T3 (IC₅₀ > 50 × 10⁻⁶ M for both derivatives). The IC₅₀ values show that these substances may selectively kill leukemic cells over non-cancer cells. Cell cycle analysis revealed that a primary trend of the diphenylamine derivatives was to arrest the cells in the G₁-phase of the cell cycle within the first 24 h. UV–visible, fluorescence spectroscopy and circular dichroism were used in order to study the binding mode of the novel compounds with DNA. The binding constants determined by UV–visible spectroscopy were found to be in the range of 2.1–8.7 × 10⁴ M⁻¹. We suggest that the observed trend for binding constant K is likely to be a result of different binding thermodynamics accompanying the formation of the complexes.     

Bacterial and chemical leaching pattern on copper ores of sandstone and limestone type

Thin polished sections of copper sulphide ore were placed as an energy source in stationary cultures of wild strains and Thiobacillus neapolitanus at pH 7.5. Scanning electron microscopy revealed characteristic leaching patterns that depended on the type of leaching process and time of bioleaching. In some cases, a biological film on the ore surface was observed. Close contact between bacterial cells and ore seems necessary for leaching in some cases.M. Ostrowski and A. Skodowska are with the Department of Photo and Image Information, University of Warsaw, ul.Nowy wiat 67, 00-046 Warsaw, Poland.