The binding of Mg(II) and Ni(II) to synthetic polynucleotides

Equilibria and kinetics of the interactions of Mg2+ and Ni2+ with poly(U), poly(C) and poly(I) have been investigated at 25 degrees C, an ionic strength of 0.1 M, and pH 7.0 or 6.0. Analogous studies involving poly(A) were reported earlier. All binding equilibria were studied by means of the (usually small) absorbance changes in the ultraviolet range. This technique yields apparent binding constants which are fairly large for the interaction of Ni2+ with poly(A) (K = 0.9 X 10(4) M-1) and poly(I) (K approximately equal to 2 X 10(4) M-1) but considerably lower for the corresponding Mg2+ systems, Mg2+-poly(A) (K = 2 X 10(3) M-1) and Mg2+-poly(I) (K = 280 M-1). Each of the two pyrimidine nucleotides binds both metal ions with about the same strength (K approximately equal to 65 M-1 for poly(U) and K near 600 M-1 for poly(C]. In the case of poly(C) the spectral changes deviate from those expected for a simple binding equilibrium. In addition, the binding of Ni2+ to the four polynucleotides was measured by using murexide as an indicator of the concentration of free Ni2+. The results obtained by this technique agree or are at least consistent with those derived from the ultraviolet spectra. Complications are encountered in the binding studies involving poly(I), particularly at higher metal ion concentrations, obviously due to the formation of aggregated poly(I) species. Kinetic studies of the binding processes were carried out by the temperature-jump relaxation technique. Measurable relaxation effects of time constants greater than 5 microseconds were observed only in the systems Ni2+-poly(A) and Ni2+-poly(I). Such not-too-fast reaction effects are expected for processes which include inner-sphere substitution steps at Mg2+ or Ni2+. The relaxation process in Ni2+-poly(I) is characterized by (at least) four time constants. Obviously, the complicated kinetics again include reactions of aggregated poly(I). The absence of detectable relaxation effects in all other systems (except Mg2+-poly(I), the kinetics of which was not investigated) indicates that inner-sphere coordination of the metal ions to specific sites of the polynucleotides (site binding) does not occur to a significant extent. Rather, the metal ions are bound in these systems mainly by electrostatic forces, forming a mobile cloud. The differences in binding strength which are nevertheless observed are attributed to differences in the conformation of the polynucleotides which result in different charge densities.     

Cost-effective copper removal by electrosorption powered by microbial fuel cells

This work studied a cost-effective electrosorption that driven by microbial fuel cells (MFC-sorption) to remove Cu²⁺ from wastewater without an external energy supply. The impact factors, adsorption isotherms and kinetics of the novel process were investigated. It indicated that a low electrolyte concentration and a high solution pH could enhance the Cu²⁺ removal efficiency, while the adsorption capacity increased with the increase of numbers of MFCs in series and the initial Cu²⁺ concentration. The adsorption isotherms study indicated that the monolayer adsorption in MFC-sorption was dominant. The kinetics study suggested the increase of initial Cu²⁺ concentration could enhance the initial adsorption rate. The electrode characterizations verified the existence of Cu₂O and Cu on the electrode surface of active carbon fibers (ACFs), suggesting that MFC-sorption was not only an adsorption process, but also a redox reaction process.     

磁珠固定化结核分枝杆菌二氢叶酸还原酶及其表征

比较Ni~(2+)-NTA磁珠和羧基磁珠固定结核分枝杆菌二氢叶酸还原酶(Mycobacteriumtuberculosis dihydrofolate reductase,Mt DHFR),探索适合小分子配体混合物库筛选的Mt DHFR固定化方法。重组表达带6×His标签Mt DHFR,纯化后表征酶学性质,比较用Ni~(2+)-NTA磁珠和羧基磁珠固定化时相应固定化容量、保留活性、稳定性及对抑制剂响应。结果表明,Ni~(2+)-NTA磁珠对Mt DHFR固定化容量为(93±12)mg/g磁珠(n=3),但酶比活保留不超过32%,Ni~(2+)明显抑制酶活性,EDTA与Ni~(2+)呈协同抑制效应,Fe~(3+)无显著干扰。羧基磁珠活化固定Mt DHFR的容量(8.6±0.6) mg/g磁珠(n=3),固定化酶比活保留(87±4)%(n=3)。在含50 mmol/L KCl的100 mmol/L HEPES (pH 7.0)中,游离和固定化Mt DHFR在0℃保存16 h活性都无显著改变,但在25℃保存16 h,游离酶活性下降近60%而羧基磁珠固定化Mt DHFR活性下降仅35%。甲氨喋呤对游离Mt DHFR和固定化Mt DHFR的IC50无显著差异(P0.05)。综上,Ni~(2+)-NTA磁珠不适合固定化Mt DHFR;羧基磁珠固定化Mt DHFR能保留活性、热稳定性及对抑制剂的响应,该固定化方法有望用于快速筛选其配体混合物库。     

镉在黑土和棕壤中吸附行为比较研究

比较研究了重金属镉在黑土和棕壤中的吸附热力学和动力学行为.结果表明,在实验设定的浓度范围内,黑土和棕壤对Cd²⁺吸附量随溶液中Cd²⁺浓度的增加而增加.黑土对Cd²⁺的吸附固定能力明显强于棕壤.在平衡液浓度为20 mg·kg^-1时,黑土对Cd²⁺的吸附量为1 485.2 mg·kg^-1、棕壤为700.6 mg·kg^-1.两种土壤对Cd²⁺的吸附等温线与Langmuir、Freundlich和Henry方程均有较好的拟合性,而Temkin方程不适合用来描述Cd²⁺在两种土壤中的等温吸附.根据Langmuir的拟合结果,Cd²⁺在黑土和棕壤中的最大吸附量分别可达5 939.3和2 790 mg·kg^-1.黑土较高的吸附能力与其高的有机质含量和粘粒含量有关.黑土和棕壤中Cd²⁺的吸附是一个快速反应过程,2 min内能达到平衡吸附量的90%,15～30 min左右达到吸附平衡.一级动力学方程是拟合Cd²⁺在黑土和棕壤中吸附动力学过程的最优方程,其次为Elovich方程和双常数方程.随着初始浓度的增加,Cd²⁺在土壤中的吸附速率也不断增大.随着吸附量的增大和反应时间的延长,吸附速率不断下降.在较低的初始浓度下,Cd²⁺在黑土中的下降趋势要快于棕壤.     

Effect of light on the attachment of cyanophage AS-1 to Anacystis nidulans.

The effect of illumination on the extent and kinetics of the adsorption of cyanophage AS-1 to the blue-green alga (cyanobacterium) Anacystis nidulans was studied by using 32P-labeled phage. The initial rate of adsorption was not significantly affected by light. However, at Na+ levels used ordinarily to culture the alga ([Na+] = 11.7 mM), the total amount of phage adsorbed was doubled in the illuminated cultures, as compared with the dark-grown ones, over a wide range of multiplicities of infection (0.05 to 20). Upon a 10-fold increase in Na+ concentration in the medium ([Na+] = 0.11 M), the dark adsorption of the phage increased to the level of light adsorption found in low Na+ medium. The effects on phage adsorption of high Na+ concentration and light were not additive.     

Biosorption of copper,lead and nickel on immobilized Bacillus coagulans using experimental design methodologies

Biosorption of copper, lead and nickel onto immobilized Bacillus coagulans (IBC) from aqueous solution in single- and multi-metal systems was investigated. The results of scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDXA) and Fourier transform infrared (FTIR) spectrometry demonstrated the importance of surface morphology and identified the active groups involved in adsorption. In batch studies, the most significant factors were screened by Minimum Run Res V Design. The Simplex Lattice Mixture Design was then successfully applied to explore the maximum adsorption capacity of the three metals (75.3 mg/g for copper, 118.3 mg/g for lead and 68.4 mg/g for nickel) and the preferential adsorption of IBC followed the order: Pb (II)?>?Cu (II)?>?Ni (II). Furthermore, adsorption kinetics and adsorption isotherms of single-, binary-, and ternary-metal systems were studied and the experimental data was found to fit well to the Freundlich isotherm and pseudo-second-order kinetics.     

重金属对盐生草光合生理生长特性的影响

以盐生草幼苗为试验材料,分别设置0(CK)、50、100、200、400μg?g-1的Ni2+、Cu2+处理,研究重金属Ni2+和Cu2+对盐生草光合生理特性的影响.结果表明:盐生草叶片光合色素含量、净光合速率(Pn)、气孔导度Gs、蒸腾速率Tr、PSⅡ最大光化学效率Fv/Fm、非光化学猝灭系数qN及生长指标(株高、地上部干重和鲜重)在50μg?g-1的Ni2+处理时均达到最大值,后随Ni2+浓度继续增加,其叶片叶绿素a、叶绿素b、Pn、Gs、Tr、Fv/Fm、PSⅡ电子传递量子产率ΦPSⅡ、光化学猝灭系数qP、qN及各项生长指标逐步下降并低于对照水平,而细胞间隙CO2浓度(Ci)较对照呈增加趋势.在50μg?g-1的Cu2+处理时,盐生草叶片光合色素含量、Pn、Gs、Tr、Ci、Fv/Fm、ΦPSⅡ、qP、qN及各项生长指标均达峰值;在100μg?g-1Cu2+处理时,光合色素含量、Pn、Gs、Tr、Fv/Fm、ΦPSⅡ、qN及各项生长指标较对照仍有增加,而后随Cu2+浓度继续增加,其叶绿素a、叶绿素b、各光合参数、叶绿素荧光参数及生长指标均逐步降低并低于对照.可见,盐生草Pn在Ni2+胁迫下的下降主要是由非气孔限制所致,而Cu2+胁迫下的下降主要是由气孔限制所致;低浓度Ni2+和Cu2+对盐生草生长具有一定促进作用,过高浓度Ni2+和Cu2+则会通过抑制盐生草叶片叶绿素合成,影响其光合作用,从而抑制植株生长.     

Accommodation of mouse DRG growth cones to electrically induced collapse: Kinetic analysis of calcium transients and set-point theory

Electrical stimulation causes growth cones of mouse dorsal root ganglion neurons to collapse. During chronic stimulation, however, growth cones resume motility. In addition, these growth cones are now resistant to the collapsing effects of subsequent stimulation, a process we term accommodation. We compared the kinetics of electrically induced Ca²⁺ transients in naive and accommodated growth cones in order to determine whether the accommodation process results from a change in the Ca²⁺ transient, or a change in the Ca²⁺ sensitivity of the growth cones. Three kinetics were determined: (1) the initial increase to peak Ca²⁺ levels produced by 10 Hz stimulation; (2) recovery from peak Ca²⁺ levels during stimulus trains lasting 15 min; and (3) clearing of Ca²⁺ from growth cones after terminating the stimulus. These kinetics were analyzed using single exponential fits to changes in fura-2 fluorescence ratios. The electrically evoked increase in Ca²⁺ was significantly slower in accommodated growth cones (τ = 6.0 s) compared to naive growth cones (τ = 1.4 s). Desptie the slower increase of [Ca²⁺]_i in accommodated growth cones, peak [Ca²⁺]_i was similar to that reached in naive growth cones, and the steady-state Ca²⁺ level was significantly elevated after chronic stimulation. Thus, accommodated growth cones maintained outgrowth at [Ca²⁺]_i that caused collapse initially. Time course experiments show that accommodation is a slow process (t_1/2 = about 3 h). Accommodation did not induce measurable changes in the rates of Ca²⁺ homeostasis during or after stimulus trains. The kinetics of Ca²⁺ recovery during (τ = 90 s) and after 15 min of stimulation (τ = 8.5 s) was not significantly different in accommodated versus naive growth cones. Rates of ⁴⁵Ca²⁺ efflux were also similar in both types of growth cones. These results suggest two regulatory processes contributing to growth cone motility during chronic stimulation: (1) recovery of [Ca²⁺]_i to levels permissive to neurite outgrowth, and (2) an increase in the range of optimal [Ca²⁺]_i for growth cone motility. These adaptive responses of mammalian growth cones to chronic stimulation could be involved in the modulation of CNS development by electrical activity of neurons. © 1993 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Activated carbon prepared from biomass as adsorbent: elimination of Ni(II) from aqueous solution.

Activated carbon (AC) prepared from waste Parthenium was used to eliminate Ni(lI) from aqueous solution by adsorption. Batch mode adsorption experiments are carried out, by varying contact time, metal ion concentration, carbon concentration, pH and desorption to assess kinetic and equilibrium parameters. They allowed initial adsorption coefficient, adsorption rate constant and maximum adsorption capacities to be computed. The adsorption data were modeled by using both Langmuir and Freundlich classical adsorption isotherms. The adsorption capacity (Q0) calculated from the Langmuir isotherm was 54.35 mg Ni(II)/g of AC at initial pH of 5.0 and 20 degrees C, for the particle size 250-500 microm. Increase in pH from 2 to 10 increased percent removal of metal ion. The regeneration by HCl of Ni(II)-saturated carbon by HCl, allowed suggestion of an adsorption mechanism by ion-exchange between metal ion and H+ ions on the AC surfaces. Quantitative recovery of Ni(II) was possible with HCl.     

Vinyl imidazole carrying metal-chelated beads for reversible use in yeast invertase adsorption

Poly(ethylene glycol dimethacrylate-n-vinyl imidazole) [poly(EGDMA–VIM)] hydrogel (average diameter 150–200 μm) was prepared copolymerizing ethylene glycol dimethacrylate (EGDMA) with n-vinyl imidazole (VIM). Poly(EGDMA–VIM) beads had a specific surface area of 59.8 m²/g. Poly(EGDMA–VIM) beads were characterized by swelling studies and scanning electron microscope (SEM). Cu²⁺ ions were chelated on the poly(EGDMA–VIM) beads (452 μmol Cu²⁺/g), then the metal-chelated beads were used in the adsorption of yeast invertase in a batch system. The maximum invertase adsorption capacity of the poly(EGDMA–VIM)–Cu²⁺ beads was observed as 35.2 mg/g at pH 4.5. The adsorption isotherm of the poly(EGDMA–VIM)–Cu²⁺ beads can be well fitted to the Langmuir model. Adsorption kinetics data were tested using pseudo-first- and -second-order models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The value of the Michaelis constant K_m of invertase was significantly larger upon adsorption, indicating decreased affinity by the enzyme for its substrate, whereas V_max was smaller for the adsorbed invertase. The optimum temperature for the adsorbed preparation of poly(EGDMA–VIM)–Cu²⁺-invertase at 50 °C, 10 °C higher than that of the free enzyme at 40 °C. Storage stability was found to increase with adsorption. Adsorbed invertase retains an activity of 82% after 10 batch successive reactions, demonstrating the usefulness of the enzyme-loaded beads in biocatalytic applications.     

盐土粘细菌NUST03的非活性菌体对重金属离子的吸附研究

研究盐土粘细菌NUST03对Cu2+、Cr3+、Ni2+的吸附能力及不同条件下菌体对离子的吸附。实验表明盐土粘细菌NUST03对Cu2+、Cr3+、Ni2+吸附能力为Cu2+>Cr3+>Ni2+,pH值对菌体吸附Cu2+、Ni2+影响较大,氯化钙和氯化镁的存在对菌体吸附Cu2+、Ni2+、Cr3+有一定的抑制作用。     

Chemical modification of Nitzschia panduriformis's frustules for protein and viral nanoparticle adsorption

The frustule of diatoms, through appropriate chemical modification, can be developed for a high adsorption level of recombinant proteins and viral nanoparticles. Field emission scanning electron microscopy (FE-SEM) analysis of clean frustules revealed a 3D loculate areolae structure (valvar phase porous pattern of the siliceous cell wall). Isocyanatopropyl triethoxysilane (IPS) and iminodiacetic acid (IDA) were used to immobilize Cu²⁺ ions (an average Cu²⁺ adsorption capacity about 190 μmol of Cu²⁺/ml of the Cu²⁺-coupled biosilica reached). FE-SEM, energy dispersion X-ray spectroscopy (EDS) and Fourier transform infrared (FT-IR) were used to confirm the chemical modification of the Cu²⁺-coupled biosilica. Protein adsorption was confirmed with the detection of a recombinant (His)₆-tagged green fluorescent protein binding using fluorescent microscopy. Infectious bursal disease virus VP2-441 subviral particles (SVPs) were found to bind to the Cu²⁺-coupled biosilica (approximately 3 × 10^?9 mol of VP2-441 SVPs/ml of modified frustules), a level higher than the previously obtained 9 × 10^?10 mol/ml for SVP binding using a commercial Ni–NTA resin. These give diatom frustules the potential to be developed into a material useful in viral nanoparticle purification systems or as a biosensor for the detection of viruses.     

Using pretreated chestnut endothelium to adsorb lead and cadmium ions from water

The nature chestnut endothelium, as waster source from chestnut (Castaneamollissima) has pigment effecting the process of adsorbing heavy metalions, and the decolorized endothelium has low adsorption capacity. In order to raise the adsorption capacity of heavy metal ions, the discolor endothelium was pretreated by acidic formaldehyde, cis-butenedioic acid and irradiation. Thermodynamic and kinetics model was fitted to the adsorption of Pb (II) and Cd(II) ions onto modified chestnut endothelium by cis-butenedioic acid. Three independent variables including pH, adsorption time and contact temperature were selected as affecting factors to Response Surface. The modified experiment results showed adsorption rate of Pb(II) and Cd(II) ions on the chestnut endothelium modified by 0.5?mol/L cis-butenedioic acid was higher than other modified methods. Thermodynamic and kinetics model was fitted with Langmuir and Pseudo-second-order kinetic model, respectively. 59.23?°C of the adsorption temperature, the 5.72?h of adsorption time and the 6.16 of pH are the optimized conditions of the adsorption rate of Pb²⁺ on modified chestnut endothelium. 55.93?°C of the adsorption temperature, the 4.43?h of adsorption time and the 6.06 of pH are the optimized adsorption conditions of Cd²⁺. Under the optimized condition, the experiment value of the adsorption of Pb²⁺ and Cd²⁺ was 99.76% and 98.90%, respectively, which are close to the predicted value. The FTIR indicated that CO, OH and CH involved in the adsorption process of Pb²⁺ and Cd²⁺.     

Magnesium transport in Salmonella typhimurium: 28Mg2+ transport by the CorA, MgtA, and MgtB systems.

Three loci in Salmonella typhimurium (corA, mgtA, and mgtB) code for components of distinct Mg2+ transport systems (S. P. Hmiel, M. D. Snavely, J. B. Florer, M. E. Maguire, and C. G. Miller, J. Bacteriol. 171:4742-4751, 1989). Strains carrying one wild-type and two mutant alleles of the three loci were constructed to study the kinetics and specificity of ion transport of each system in isolation. The transport systems had different Km and Vmax values for Mg2+ uptake, and each was inhibited by other divalent cations in a distinct rank order of potency: for CorA, Mg2+ greater than Mn2+ greater than Co2+ greater than Ni2+ greater than Ca2+; for MgtA, Zn2+ greater than or equal to Mg2+ greater than Ni2+ approximately Co2+ greater than Ca2+; and for MgtB, Mg2+ approximately Ni2+ approximately Ni2+ greater than Mn2+ much greater than Ca2+. Other differences among the three systems were apparent. The CorA transport system functioned as a Mg2+-Mg2+ exchange system, mediating both efflux and influx of Mg2+. Neither the MgtA nor the MgtB system could mediate Mg2+ efflux. Transport via the MgtB system was very temperature sensitive; Mg2+ was transported at 37 degrees C but not at 20 degrees C. The MgtA and the MgtB transport systems were found to be regulated by the extracellular concentration of Mg2+.     

Adsorption and Desorption of Nickel(II) Ions from Aqueous Solution by a Lignocellulose/Montmorillonite Nanocomposite

A new and inexpensive lignocellulose/montmorillonite (LNC/MMT) nanocomposite was prepared by a chemical intercalation of LNC into MMT and was subsequently investigated as an adsorbent in batch systems for the adsorption-desorption of Ni(II) ions in an aqueous solution. The optimum conditions for the Ni(II) ion adsorption capacity of the LNC/MMT nanocomposite were studied in detail by varying parameters such as the initial Ni(II) concentration, the solution pH value, the adsorption temperature and time. The results indicated that the maximum adsorption capacity of Ni(II) reached 94.86 mg/g at an initial Ni(II) concentration of 0.0032 mol/L, a solution pH of 6.8, an adsorption temperature of 70°C, and adsorption time of 40 min. The represented adsorption kinetics model exhibited good agreement between the experimental data and the pseudo-second-order kinetic model. The Langmuir isotherm equation best fit the experimental data. The structure of the LNC/MMT nanocomposite was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), whereas the adsorption mechanism was discussed in combination with the results obtained from scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectroscopy analyses (FTIR). The desorption capacity of the LNC/MMT nanocomposite depended on parameters such as HNO₃ concentration, desorption temperature, and desorption time. The satisfactory desorption capacity of 81.34 mg/g was obtained at a HNO₃ concentration, desorption temperature, and desorption time of 0.2 mol/L, 60 ºC, and 30 min, respectively. The regeneration studies showed that the adsorption capacity of the LNC/MMT nanocomposite was consistent for five cycles without any appreciable loss in the batch process and confirmed that the LNC/MMT nanocomposite was reusable. The overall study revealed that the LNC/MMT nanocomposite functioned as an effective adsorbent in the detoxification of Ni(II)-contaminated wastewater.     

The kinetics and divalent cation inhibition of plasma membrane ATPase in the yeast Candida albicans

The kinetics of ATP hydrolysis and cation effects on ATPase activity in plasma membrane from Candida albicans ATCC 10261 yeast cells were investigated. The ATPase showed classical Michaelis-Menten kinetics for the hydrolysis of Mg X ATP, with Km = 4.8 mM Mg X ATP. Na+ and K+ stimulated the ATPase slightly (9% at 20 mM). Divalent cations in combination with ATP gave lower ATPase activity than Mg X ATP (Mg greater than Mn greater than Co greater than Zn greater than Ni greater than Ca). Divalent cations inhibited the Mg X ATPase (Zn greater than Ni greater than Co greater than Ca greater than Mn). Free Mg2+ inhibited Mg X ATPase weakly (20% inhibition at 10 mM). Computed analyses of substrate concentrations showed that free Zn2+ inhibited Zn X ATPase, mixed (Zn2+ + Mg2+) X ATPase, and Mg X ATPase activities. Zn X ATP showed high affinity for ATPase (Km = 1.0 mM Zn X ATP) but lower turnover (52%) relative to Mg X ATP. Inhibition of Mg X ATPase by (free) Zn2+ was noncompetitive, Ki = 90 microM Zn2+. The existence of a divalent cation inhibitory site on the plasma membrane Mg X ATPase is proposed.     

Purification of recombinant nucleocapsid protein of Newcastle disease virus from unclarified feedstock using expanded bed adsorption chromatography

In the present work, a single-step purification of recombinant nucleocapsid protein (NP) of the Newcastle disease virus (NDV) directly from unclarified feedstock using an expanded bed adsorption chromatography (EBAC) was developed. Streamline 25 column (ID = 25 mm) was used as a contactor and Streamline chelating adsorbent immobilized with Ni2+ ion was used as affinity adsorbent. The dynamic binding capacity of Ni2+ -loaded Streamline chelating adsorbent for the NP protein in unclarified feedstock was found to be 2.94 mg ml(-1) adsorbent at a superficial velocity of 200 cm h(-1). The direct purification of NP protein from unclarified feedstock using expanded bed adsorption has resulted in a 31% adsorption and 9.6% recovery of NP protein. The purity of the NP protein recovered was about 70% and the volume of processing fluid was reduced by a factor of 10. The results of the present study show that the IMA-EBAC developed could be used to combine the clarification, concentration and initial purification steps into a single-step operation.     

Co does not replace Ni with respect to urease activity in zucchini (Cucurbita pepo convar. giromontiina) and soybean (Glycine max)

In order to evaluate whether Co can functionally replace Ni in urease, as suggested by Watanabe et al. (Soil Sci. Plant Nutr. (1994) 40, 545–548), zucchini and soybean plants were grown in purified nutrient solutions containing nitrate and ammonium as sole N source supplemented either with 0.05 mmol m-3 Ni or Co or with no supplementation (control). In addition, isolated soybean cotyledons were incubated axenically with either 1 mmol m-3 Ni or Co supplements. Plant growth was not affected by the Ni and Co additions, but urease activity was only detected in Ni-supplemented tissue, and in no case did Co raise the urease activity level. Only Ni-deprived plants (–Ni – Co and –Ni + Co) accumulated appreciable amounts of urea in the leaves. These results strongly suggest, that Co does not replace Ni with respect to functional urease.     

XPS evidence for the formation of Ni(II) complexes on treated activated carbon

X-ray photoelectron spectroscopy (XPS) was applied to a solid-state investigation on adsorbed systems obtained by contacting different samples of an activated carbon (Chemviron Filtrasorb 400) with solutions containing (a) 1,10-phenanthroline (phen); (b) NiCl₂·6H₂O. (c) Ni²⁺ ions and phen in a 1:3 molar ratio.XPS results on these systems are discussed with particular regard to the chemical state of the ligand (interaction of functional groups with the substrate) and of the metal ions on carbon (assessment of Ni oxidation state; detection of Ni complexes on carbon and information on their stoichiometries and structures). Various effects of successive chemical treatments on the above reported carbon species were also revealed by XPS, such as:(i) the formation of a ‘carbon–ligand’ system (activated carbon with ligand firmly present on it) after acid elution of the activated carbon treated with Ni–phen complexes in solution, and (ii) the adsorption of Ni²⁺ ions on this ‘carbon–ligand’ system, with fomation of Ni–phen complexes on carbon.