Relative lability of trace metals complexed in aquatic humic substances using ion-exchanger cellulose-hyphan

The purpose of this paper is to characterize the lability/inertness metal fractions complexed by aquatic humic substances (HS) in relation to pH, complexation time, and HS concentration. HS were preconcentrated by ultrafiltration and complexed with bivalent metal ions. These fractions were characterized by ion exchange with the chelating collector cellulose Hyphan by applying batch procedure. The metals were determined by atomic absorption spectrometry. The results show that the distribution coefficients, Kd, decreased with HS presence, and that the relative lability of metal fractions complexed by HS is dependent on variables such as pH, complexation time, and HS concentration. Until c.a. 15 min, the metal change between aquatic HS and ion exchanger occurs following a 2 order reaction. Afterwards, the remaining metal fraction in the HS reacts following a 1st order reaction. For traces of metal ions bound to dissolved HS, the lability orderPb > Mn > Cd, Ni > Cu is revealed. ©1997 Soc. Bras. Química.

An alternative methodology for the extraction of humic substances from organic soils

The present study reports on an alternative methodology for the extraction of Humic Substances (HS) from the soil. The extractions were carried out with 0.5 M KOH for 3 h, at a ratio of 1:20 (m/v) under a nitrogen atmosphere. The HS were separated by centrifugation based on their solubility in alcaline solution. This methodology was compared with the usual procedure in three different soil samples and in one sample from vermicompost. The yield, E4/E6 ratio, ash content, and the elemental composition (C, H, O, N) of the extracted HS have been determined. The functional groups were identified by Fourier-transform infrared spectroscopy. This novel procedure adds a new perspective to the extraction of humic substances due to the short time and high performance of the extraction in relation to the usual procedure.

Interaction of mercury(II) with humic substances from the Rio Negro (Amazonas State, Brazil) by means of an ion exchange procedure

The aquatic humic substances (HS) investigated in this study with respect to their binding capability towards mercury(II) were isolated from the river Rio Negro, Amazonas State - Brazil, by means of the adsorbent XAD 8. Labile/inert fractions of inorganic Hg(II) complexes formed with these HS were characterized using an ion-exchange batch and column technique, respectively, based on Chelite S. This collector exhibits high Hg(II) distribution coefficients, Kd, up to the order of 104 decreasing, however, in the case of small Hg(II)/HS ratios (< 0.1 μg Hg(II) / mg HS). The influence of different complexation parameters (ratio of Hg(II)/HS, pH, contact time, complexing time) relevant for Hg(II) binding in aquatic environments was assessed. The Hg(II) lability in dissolved HS is mainly influenced by the mass ratio of Hg(II)/HS and the ageing of Hg(II)-HS species formed. This is particularly obvious in the case of low Hg(II) loading of HS where slow transformation processes of freshly formed Hg(II)-HS species significantly decrease their lability, leading to incomplete recoveries (< 20%) of the total Hg(II) bound to HS.

Influence of antimicrobial subinhibitory concentrations on hemolytic activity and bacteriocin-like substances in oral: Fusobacterium nucleatum

Fusobacterium nucleatum is considered for its role in colonization of initial and late microorganisms in dental plaque and for its coaggregation with other bacterial species. It is known that action of different antimicrobial substances may interfere with either virulence factors or with host-bacteria interaction. The goal of this study was to examine the influence of subinhibitory concentrations of chlorhexidine, triclosan , penicillin G and metronidazole on hemolytic activity and bacteriocin-like substance production of oral F. nucleatum. A high resistance to penicillin G was observed and 63% of the isolates were β-lactamase positive. All the tested isolates were susceptible to metronidazole. F. nucleatum isolates grown with or without antimicrobials were alpha-hemolytics. Bacteriocin-like substance production was increased in isolates grown with penicillin G. Impaired production of hemolytic or antagonic substances can suggest a role in the regulation of oral microbiota.

A new application of humic substances: Activation of supports for invertase immobilization

Invertase was immobilized on aminopropyl silica (APTS-SiO2) activated with humic substances (APTS-SiO2-HS) and on aminopropyl silica activated with glutaraldehyde (APTS-SiO2-GA). The resulting activity of both systems was compared. Humic substances (HS) used for the activation of the silica were extracted from soil of Cananéia, São Paulo State, Brazil, according to the procedure recommended by the International Humic Substances Society. Activity was determined by measuring the rate of formation of reduced sugars using the reaction with dinitrosalicylic acid (DNS). The amount of HS bound on the APTS-SiO2 was equal to 50 mg. The maximum amount of invertase immobilized on APTS-SiO2-HS was 15200 U/g while in the system APTS-SiO2-GA it was 13400 U/g. The experimental enzymatic activity was 3700 and 3300 U/g, for the systems APTS-SiO2-HS and APTS-SiO2-GA, respectively. Considering the increased amount and activity of immobilized enzyme compared with the glutaraldehyde method, it was concluded that this technique opens a new perspective in the preparation of supports for enzyme immobilization employing humic substances. © Springer-Verlag 2000.

Competition between humic substances and α-amino acids by metal species

The aim of the present work was to carry out experimental comparison between humic substances (HS) and representative α-amino acids (methionine, methionine sulfoxide and cysteine hydrochloride) in relation to the complexation of biologically active trace elements (Al, Cu, Pb, Mn, Zn, Cd and Ni). A mobile time-controlled tangential-flow UF technique was applied to differentiate between HS-metal and α-aminoacids-metal complexes. Metal determinations were conventionally carried out using a ICP-OES. The results showed that HS may be considered as a selective complexing agents with higher metal bonding capability in relation to Al, Cu and Pb, the fact that may be clinically important.

Studies on the interaction between humic substances and conducting polymers for sensor application

The interaction between humic substances and poly(o-ethoxyaniline) (POEA), a conducting polymer, was investigated for both solution and self-assembled films. The results have shown that the humic substances induce a doping of POEA by protonation, as indicated by UV-Vis and Raman spectroscopies. The atomic force microscopy (AFM) studies on the self-assembled films have shown that the average roughness of the polymer film has increased after exposing it to humic substances (fulvic and humic acids), consistent with the interaction between POEA and humic substances. However, this change in morphology is reversible by washing the films with water in agreement with the electrical data allowing using this system in sensor applications. Here, the sensor formed by an array of different sensing units was able to detect and distinguish humic substances in aqueous solution, as shown by multivariate analysis (principal component analysis). The motivation to detect humic substance comes due to its importance in terms of quality control of water or soil. ©2005 Sociedade Brasileira de Química.

Oral toxicity of chemical substances found in Dimorphandra mollis (Caesalpiniaceae) against honeybees (Apis mellifera) (Hymenoptera: Apidae)

Dimorphandra mollis is a characteristic plant from Brazilian saP vanna-like vegetation. The pollen of this species could be toxic to bees and the objective of the present investigation was to study the toxicity of methanolic extracts obtained from the flowers, peduncles and stem bark of D. mollis to Apis mellifera workers. For the study, the extracts were incorporated into the diet of the bees for later evaluation of mortality rates. The substances isolated: neoisoastilbin, catechin, astilbin and tannins were tested on adult workers and only catechin did not cause toxic effects. The data obtained in the toxicity bioassays were analyzed statistically by Log Rank test and all methanolic extracts showed significant (p<0.0001) toxic effects. Astilbin is also the major component of pollen grains, and is probably responsible for honeybee mortality during blooming periods.

The role of workers in transferring queen substances and the differences between worker castes in the leaf-cutting ant, Acromyrmex subterraneus brunneus (Hymenoptera: Formicidae)

The present study focused on the relationship between the queen and workers in Acromyrmex subterraneus brunneus colonies mediated by the possible transfer of substances from the fertile to the sterile caste. The queens were submitted to different situations of physical limitation, i.e., they were kept isolated in cages with holes that only permitted the entry of workers but left the queen isolated. A tracer (water-soluble dye) was applied to the pronotum and gaster of the queen and its dispersal among workers was analyzed. The results demonstrated that the minor sub caste (0.7-0.9 mm) passed on the dye through allogrooming and self-grooming, or transferred the dye through trophallaxis to the major sub caste (1.2-2.0 mm) when they were not in direct contact with the queen. These findings indicate the communication and probable transfer of substances from the queen to the workers, as well as a substance transfer between workers.

Interaction between humic substances and metallic ions: A selectivity study of humic substances and their possible therapeutic application

The complexation capacity of humic substances extracted from peat samples taken from the Mogi River in Ribeirao Preto, SP, Brazil, was determined using metal ions (Al(III), Pb(II), Cr(VI) and Cd(II)), yielding the following order of affinity: Cr(VI)< Cd(II)substances are nontoxic up to a maximum concentration of 512 mg kg-1. These findings reinforce the possibility of using humic substances as a metal detoxicant. ©2007 Sociedade Brasileira de Química.

The influence of seasonalness on the structural characteristics of aquatic humic substances extracted from Negro River (Amazon state) waters: Interactions with Hg(II)

In this work, humic substances were extracted from water samples collected monthly from the Negro River basin in the Amazon state (Brazil) to study their properties in the Amazonian environment and interactions with the mercury ion considering the influence of seasonalness in this formation. The C/H, C/N and C/O atomic ratio parameters, functional groups, concentration of semiquinone-type free radicals, pH, pluviometric and fluviometric indices, and mercury concentrations were interpreted using hierarchical cluster analysis (HCA) and principal component analysis (PCA). The statistical analyses showed that when the pluviometric index was greater and the fluviometric index was smaller, the degree of humification of aquatic substances was greater. The following decreasing order of the degree of humification of the AHS collected monthly was established: Nov/02 to Feb/03 > Mar/02 to May/02 > Jun/02 to Oct/02. The greatest concentrations of mercury were detected in more humidified samples. These results suggest that due to inter and/or intra-molecular rearrangements, the degree of humification of aquatic humic substances is related to its affinity for Hg(II) ions. ©2007 Sociedade Brasileira de Química.

Solvent capacity of different substances on gutta-percha and resilon

The aim of this study was to evaluate the effectiveness of 3 solvents (eucalyptol, orange oil, and xylol) on 2 types of gutta-percha (conventional and thermoplastic) and Resilon. Specimens (10 mm diameter × 1 mm thick; n=7 per condition) were prepared and maintained at 37°C for 48 h. Each specimen was weighed on a precision scale every 24 h until its mass was stable, at which time the initial mass was determined. Specimens (n=7) were then immersed in the solvent solutions and, after 48 h at 37°C, they were reweighed at 24- h intervals, until stabilization (final mass). The difference between the final and the initial mass determined the solvent capacity of each solvent. Data were subjected to analysis of variance and Tukey's test at 5% significance level. The results demonstrated that xylol was the most effective, especially on conventional gutta-percha and Resilon (p<0.05). Eucalyptol and orange oil were more effective on thermoplastic gutta-percha than the other materials (p<0.05). It was concluded that all evaluated substances presented solvent action, but xylol was the most effective on both gutta-percha or Resilon.

In vitro antimicrobial activity of auxiliary chemical substances and natural extracts on Candida albicans and Enterococcus faecalis in root canals

Objective: The aim of this study was to evaluate the antimicrobial activity of auxiliary chemical substances and natural extracts on Candida albicans and Enterococcus faecali's inoculated in root canals. Material and Methods: Seventy-two human tooth roots were contaminated with C. albicans and E. faecalis for 21 days. The groups were divided according to the auxiliary chemical substance into: G1) 2.5% sodium hypochlorite (NaOCl), G2) 2% chlorhexidine gel (CHX), G3) castor oil, G4) glycolic Aloe vera extract, g5) glycolic ginger extract, and G6) sterile saline (control). The samples of the root canal were collected at different intervals: confirmation collection, at 21 days after contamination; 1st collection, after instrumentation; and 2nd collection, seven days after instrumentation. Microbiological samples were grown in culture medium and incubated at 37°C for 48 hours. Results: The results were submitted to the Kruskal-Wallis and Dunn (5%) statistical tests. NaOCl and CHX completely eliminated the microorganisms of the root canals. Castor oil and ginger significantly reduced the number of CFU of the tested bacteria. Reduction of CFU/mL at the 1st and 2nd collections for groups G1, G2, G3 and G4 was greater in comparison to groups G5 and G6. Conclusion: It was concluded that 2.5% sodium hypochlorite and 2% chlorhexidine gel were more effective in eliminating C. albicans and E. faecalis, followed by the castor oil and glycolic ginger extract. The Aloe vera extract showed no antimicrobial activity.

Fat body, hemolymph and ovary routes for delivery of substances to ovary in Melipona quadrifasciata anthidioides: Differences among castes through the use of electron-opaque tracers

The yolk protein precursor, vitellogenin (Vg), in bees is synthesized in the fat body trophocytes, delivered to the hemolymph and ultimately absorbed from there during the vitellogenic phase of oocytes in the active ovary. The routes tracing the material exchange that occurs between the trophocytes and the hemolymph, in addition to the transportation from the hemolymph to the ovarian follicles, were marked by alkaline phosphatase and lanthanum nitrate (LN). Active ovaries from nurse workers and physogastric queens, as well as inactive ovaries of virgin queens, were examined by transmission electron microscopy. The LN permitted better visualization of the routes of exchanges between the organs and the hemolymph. Both methods demonstrate the apparent differences between the phases of the ovary and the bee caste. In inactive ovaries of the virgin queens, the routes from the follicular epithelium to the oocyte remain closed; conversely, they are open in active ovaries of the nurse workers and physogastric queens. The differences between the methods and classes of bees are discussed. © The Author 2013. Published by Oxford University Press [on behalf of The Japanese Society of Microscopy]. All rights reserved.