Lability of heavy metal species in aquatic humic substances characterized by ion exchange with cellulose phosphate

Labile metal species in aquatic humic substances (HSs) were characterized by ion exchange on cellulose phosphate (CellPhos) by applying an optimized batch procedure. The HSs investigated were pre-extracted from humic-rich waters by ultrafiltration and a resin XAD 8 procedure. The HS-metal species studied were formed by complexation with Cd(II), Ni(II), Cu(II), Mn(II) and Pb(II) as a function of time and the ratio ions to HSs. The kinetics and reaction order of this exchange process were studied. At the beginning (<3 min), the labile metal fractions are separated relatively quickly. After 3 min, the separation of the metal ions proceeds with uniform half-lives of about 12-14 min, revealing rather slow first-order kinetics. The metal exchange between HSs and CellPhos exhibited the following order of metal lability with the studied HSs: Cu > Pb > Mn > Ni > Cd. The required metal determinations were carried out by atomic absorption spectrometry.

Total Fatty Acids in Murrah Buffaloes Milk on Commercial Farms in Brazil

The objective of this trial was to document the total fatty acids in Murrah buffaloes milk on commercial farms in Brazil. Data from forty lactating Murrah-crossbred buffaloes were collected on five commercial farms located at Sarapui and Pilar do Sul, São Paulo-Brazil. A field survey was done from April to November 2002. In four farms, buffaloes were fed with wet brewers grains (primary concentrate). Only one farm (Farm 4) offered pasture and corn silage. Monthly milk samples were collected and stored at -20 degrees C until analyzed for fatty acid composition. The fatty acids with the highest percentage in total milk fat were C(16:0); C(18:1c9); C(18:0) and C(14:0). The average content observed in C(16:0) varied from 25.4 to 32.5%. Farm 4 (pasture plus corn silage) showed a higher C(16:0) value (32.5%). C(18:1c9) (varied) from 20.6 to 25.1%, C(14:0) varied from 5.9 to 8.9% and CLA content (C(18:2c9t11)) varied from 1.0 to 1.8%. Farm 3 presented higher average of C(18:1c9) (25.1%) and C(18:2c9t11) (1.8%), and lower average of C(14:0) (6.0%). Likewise, unsaturated fatty acids, C(18:1c9) and C(18:2c9t11) were higher on Farm 3. Probably, these results can be due to high CIA intakes derived from wet brewers grain and pasture. Long chain fatty acids varied from 34.2% (Farm 4) to 48.8% (Farm 3). In general, diets based on pasture and corn silage increased the levels of medium chain fatty acids in Murrah buffaloes milk.

Influence of free amino acids on clavulanic acid production by Streptomyces clavuligerus in synthetic medium

The effect of nitrogen source on clavulanic acid production was investigated in shake flasks. Media containing asparagine plus one of several different amino acids or a combination of two amino acids was tested. The best result, ca. 180 mg/L clavulanic acid, CA, in 60 h, was obtained with the lysine-tyrosine pair In an aerated and agitated fermentor this medium led to CA concentrations of ca. 210 mg/L, a remarkable production for synthetic medium utilization. Amino acids analysis during cultivation indicated that, while asparagine was consumed rapidly, lysine and tyrosine were metabolized slowly, promoting CA production.

Synthesis and characterization of solid molybdenum(VI) complexes with glycolic, mandelic and tartaric acids. Photochemistry behaviour of the glycolate molybdenum complex

The complexes (NH4)(2)[ MoO2( C2H2O3)(2)]center dot H2O, (NH4)(2)[MoO2(C8H6O3)(2)] and (NH4)(2) [MoO3(C4H4O6)]center dot H2O were prepared by reaction of MoO3 with glycolic, mandelic and tartaric acids, respectively. The complexes were characterized by elemental and thermal analysis, IR spectroscopy and X- ray diffraction. Crystals of the glycolate and tartarate complexes are orthorhombic and the mandelate complex is monoclinic. Elemental and thermal analysis data showed that the glycolate and tartarate complexes are monohydrated. Hydration water is not present in the structure of the mandelate complex. IR spectra showed COO- is involved in coordination as well as the oxygen atom of the deprotonated hydroxyl group of the alpha-carbon. The glycolate molybdenum complexes with general formula M-2[MoO2(C2H2O3)(2)]center dot nH(2)O, where M is an alkali metal and n=1 or 1/2, were also prepared and characterized. Aqueous solutions of the glycolate complex become blue and mandelate and tartarate complexes change to yellow or brown when exposed to UV- radiation.

Dipole moments in Langmuir monolayers from aromatic carboxylic acids

The three-layer capacitor model proposed by Demchak and Fort [J. Colloid Interface Sci. 46 (1974) 191] is employed to relate measured surface potentials of Langmuir monolayers from a series of polyphenyl carboxylic acids to molecular dipole moments calculated using semiempirical quantum methods. The effective dielectric constant at the air/monolayer interface is 3.0 +/- 0.6, very close to that estimated for aliphatic compounds. Good agreement between theory and experiment is obtained by adopting a dielectric constant of 6.4 for the monolayer/water interface and a contribution from the water reorientation of -0.064 +/- 0.006 D, which shows that the parameters in the DF model are essentially the same as for aliphatic amphiphiles, such as esters, acids, alcohols and ethers. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Carboxylic acids of marine evaporitic oils from Sergipe-Alagoas Basin, Brazil

A. suite of 10 different marine evaporitic oil samples from Sergipe-Alagoas Basin, Brazil was studied for its biomarker content, in particular its acidic constituents. The oils showed different molecular distributions and relative abundances of n-alkanoic, isoprenoid and hopanoic acids. The observed differences were assigned to the incorporation of immature organic matter in the oils and fractionation along the migration pathway. The diagenetic precursor functionality (alcohol/ether or acid) was proposed based on the comparison of the relative abundances of the neutral and acidic biomarkers (hopanoids, isoprenoids, alkyl-steranes, monoaromatic alkyl-steroids). In the acidic fraction, 3 series of steroid-alkanoic acids and monoaromatic steroid-alkanoic acids (steroid-methanoic, ethanoic and propanoic acids and monoaromatic steroid-methanoic, ethanoic and propanoic acids) were detected, while in the neutral fraction only 2 series of each corresponding class could be observed (methyl and ethyl-steranes and monoaromatic methyl and ethyl-steroids). These carbon shifts suggest that decarboxylation is an important process in the formation of the alkyrsteranes and monoaromatic alkyl-steroids, and we infer that carboxylic acids are the diagenetic precursors of these classes of compounds. When alcohol or ether are the diagenetic precursors (isoprenoids and hopanoids), no significant differences in the molecular distributions between neutral and acidic fractions were observed. (C) 2000 Elsevier B.V. Ltd. All rights reserved.

Reduction of mercury(II) by tropical river humic substances (Rio Negro) - Part II. Influence of structural features (molecular size, aromaticity, phenolic groups, organically bound sulfur)

The influence of structural features of tropical river humic substances (HS) on their capability to reduce mercury(II) in aqueous solutions was studied. The HS investigated were conventionally isolated from Rio Negro water-Amazonas State/Brazil by means of the collector XAD 8. In addition, the isolated HS were on-line fractionated by tangential-flow multistage ultrafiltration (nominal molecular-weight cut-offs: 100, 50, 30, 10, 5 kDa) and characterized by potentiometry and UV/VIS spectroscopy. The reduction of Hg(II) ions to elemental Hg by size-fractions of Rio Negro HS was assessed by cold-vapor AAS (CVAAS). UV/VIS spectrometry revealed that the fractions of high molecular-size (F-1 > 100 kDa and F-2: 50-100 kDa) have a higher aromaticity compared to the fractions of small molecular-size (F-5: 5-10 kDa, F-6: < 5 kDa). In contrast, the potentiometric study showed different concentration of functional groups in the studied HS fractions. The reduction of Hg(II) by aquatic HS fractions at pH 5 proceeded in two steps (I, II) of slow first order kinetics (t(1/2) of I: 160 min, t(1/2) of II: 300 min) weakly influenced by the molecular-size, in contrast to the differing degree of Hg(II) reduction (F-5 > F-2 > > F-1 > F-3 > F-4 > > F-6). Accordingly, Hg(II) ions were preferably reduced by HS molecules having a relatively high ratio of phenolic/carboxylic groups and a small concentration of sulfur. From these results a complex 'competition' between reduction and complexation of mercury(II) by aquatic HS occurring in tropical rivers such as the Rio Negro can be suggested. (C) 2003 Elsevier B.V. All rights reserved.

Reduction of mercury(II) by tropical river humic substances (Rio Negro) - A possible process of the mercury cycle in Brazil

The evolution of elemental Hg from its environmental compounds has already been supposed to be an important process within the global mercury cycle. The present study characterizes the abiotic reduction of Hg(II) ions by typical river humic substances (HS) conventionally pre-isolated by the adsorbent XAD 8 from the Rio Negro near Manaus, Brazil. For the investigation of this reduction process a special reaction and Hg(0) trapping unit combined with cold-vapor atomic absorption spectrometry (CVAAS) was developed. Preconcentration of traces of mercury(II), if required, was obtained by a home-made FIA system using microcolumns filled with the Hg(II)-selective collector CheliteS(R) (Serva Company). The effect of environmentally relevant parameters such as the pH value, the Hg(II)/HS ratio and the HS concentration on the I-IE;(II) reduction process was studied as a function of the time. The Hg(0) production was highest at pH 8.0 and in the case of decreasing HS amounts (0.5 mg) when about 65% of initially 1.0 mug Hg(H) was reduced within 50 h. Moreover, the reduction efficiency of HS towards HE;(II) strongly depended on the HS concentration but hardly on the Hg(II)/HS ratio. The reduction kinetics followed a relatively slow two-step first-order mechanism with formal rate constants of about 0.1 and 0.02 h(-1), respectively. Based on these findings the possible relevance of the abiotic evolution of mercury in humic-rich aquatic environments is considered. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Association of free amino acids with caries experience and mutans streptococci levels in whole saliva of children with early childhood caries

Objective: The aim of the present study was to identify the free amino acid content in whole saliva of children with (CE) and without early childhood caries (CF) (ECC), correlating these findings with caries experience and mutans streptococci (MS) levels in saliva.Design: Seventy-eight healthy children, both genders, 6-71 months age, were selected to participate in the study. Following examination for dmft scores calculation, unstimulated whole saliva was collected from all 78 participants, stored at -80 degrees C, and used for amino acid analysis, on a Biochem 20 plus amino acid analyzer. Stimulated whole saliva was collected from 52 children, transported, diluted and plated on MSB agar medium for detection of MS in cfu/mL.Results: Forty different free amino acids were identified in whole saliva, with great variation in their concentration. A statistically significant relation was found between caries experience and the presence of free proline and glycine. While proline (p = 0.0182) was more frequently absent in the CF group, the absence of glycine (p = 0.0397) was more often observed in the CE group. In the presence of higher levels of MS, free glycine reduced the risk of experiencing dental caries (p = 0.0419). Conversely, the presence of proline was found to increase the risk of experiencing the disease (p = 0.0492).Conclusions: The presence of free proline and absence of free glycine in children with ECC, highly contaminated with MS, increased the chances of experiencing dental caries in the present population. Further studies are needed to better understand this phenomenon. (C) 2008 Elsevier Ltd. All rights reserved.

Apparent digestibility of protein, energy, and amino acids in some selected feed ingredients for pacu Piaractus mesopotamicus

The apparent digestibility coefficients (ADCs) of amino acids (AA), protein, and energy in six feed ingredients (Brazilian fish meal, soybean meal, corn gluten meal, alcoholic yeast, corn, and wheat bran) we evaluated for pacu juveniles. In general, all ingredients showed high digestibility values for all AA, and differences among ADCs of individual amino acid were detected (P < 0.01). Corn gluten, soybean, and fish meals had the highest ADCs of AA. The ADCs of protein in fish meal, yeast, and corn gluten meal should not be used as AA digestibility indicators, because those showed differences up to 6.7% between the ADCs of protein and AA. All ingredients had lower ADCs of energy than corn gluten meal (P < 0.01). Lysine was the first limiting amino acid in fish meal, corn gluten meal, wheat bran, and corn, and the second limiting amino acid in soybean meal, as methionine was the first limiting amino acid in soybean meal and yeast. However, the soybean meal was the best quality protein source, as it had the highest digestible essential amino acid index. This demonstrated that digestible amino acid values can be used to formulate practical diets for pacu, preventing potential deficiencies or excess that might cause environmental and economic losses.