Glucocorticoids contribute to metabolic and liver impairments induced by lactation overnutrition in male adult rats.

Introduction: Lactation overnutrition is a programming agent of energy metabolism, and litter size reduction leads to the early development of obesity, which persists until adulthood. Liver metabolism is disrupted by obesity, and increased levels of circulating glucocorticoids are pointed as a possible mediator for the obesity development, since bilateral adrenalectomy (ADX) can reduce obesity in different models of obesity. Methods: This study aimed to evaluate the effects of glucocorticoids on metabolic changes and liver lipogenesis and insulin pathway induced by lactation overnutrition. For this, on the postnatal day 3 (PND), 3 pups (small litter-SL) or 10 pups (normal litter-NL) were kept with each dam. On PND 60, male Wistar rats underwent bilateral adrenalectomy (ADX) or fictitious surgery (sham), and half of ADX animals received corticosterone (CORT- 25 mg/L) diluted in the drinking fluid. On PND 74, the animals were euthanized by decapitation for trunk blood collection, and liver dissection and storage. Results and Discussion: SL rats presented increased corticosterone, free fatty acids, total and LDL-cholesterol plasma levels, without changes in triglycerides (TG) and HDL-cholesterol. The SL group also showed increased content of liver TG, and expression of fatty acid synthase (FASN), but decreased expression of PI3Kp110 in the liver, compared to NL rats. In the SL group, the ADX decreased plasma levels of corticosterone, FFA, TG and HDL cholesterol, liver TG, and liver expression of FASN, and IRS2, compared to sham animals. In SL animals, CORT treatment increased plasma levels of TG and HDL cholesterol, liver TG, and expression of FASN, IRS1, and IRS2, compared with the ADX group. In summary, the ADX attenuated plasma and liver changes observed after lactation overnutrition, and CORT treatment could reverse most ADX-induced effects. Thus, increased circulating glucocorticoids are likely to play a pivotal role in liver and plasma impairments induced by lactation overnutrition in male rats.

Lactation overnutrition-induced obesity impairs effects of exogenous corticosterone on energy homeostasis and hypothalamic-pituitary-adrenal axis in male rats.

AIMS: Litter size reduction on the first days of life results in increased body weight and adiposity, with higher levels of circulating glucocorticoids. Obese rodents are more sensitive to the anabolic effects of glucocorticoids and less responsive to glucocorticoids feedback on hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to evaluate effects of the treatment with corticosterone on metabolic responses and HPA axis in adult male rats reared in small litters. MAIN METHODS: From postnatal day (PND) 60 to 88, adult male rats of normal (NL- 10 pups/dam) and small (SL- 3 pups/dam) litters received oral treatment with Corticosterone (CORT-15 mg/L) in the drinking water or no treatment, composing the four experimental groups (NL-water; NL-CORT; SL-water and SL-CORT), for the evaluation of energy homeostasis and HPA axis. KEY FINDINGS: Male rats of SL-water group presented on PND88: glucose intolerance, higher adiposity, plasma triglycerides, free fatty acids, total and low-density lipoprotein (LDL) cholesterol and corticosterone. SL-water animals showed increased mRNA of corticotrophin-releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN) and proopiomelanocortin (POMC) in the pituitary, with decreased mRNA expression of PVN mineralocorticoid receptor. NL-CORT animals presented glucose intolerance, increased body weight, food intake, total and LDL cholesterol. Glucocorticoid treatment reduced corticosterone levels and adrenal cortex thickness in NL group, associated with increased mRNA of PVN CRH and pituitary POMC, without effects on SL animals. SIGNIFICANCE: Lactation overnutrition promotes hyperreactivity of HPA axis and reduces the responsiveness to glucocorticoids effects on energy balance and negative feedback of HPA axis in adult male rats.

The Effect of Goethites on the Polymerization of Glycine and Alanine Under Prebiotic Chemistry Conditions.

After pre concentration of monomers, polymerization is the second most important step for molecular evolution. The formation of peptides is an important issue for prebiotic chemistry and consequently for the origin of life. In this work, goethite was synthesized by two different routes, named goethite-I and goethite-II. Although both samples are goethite, Far-FT-IR spectroscopy and EPR spectroscopy showed differences between them, and these differences had an effect on the polymerization of glycine and alanine. For the amino acid polymerization, three protocols were used, that resembled prebiotic Earth conditions: a) amino acid plus goethite were mixed and heated at 90 °C for 10 days in solid state, b) a wet impregnation of the amino acid in the goethite, with subsequent heating at 90 °C for 10 days in solid state, and c) 10 wet/dry cycles each one for 24 h at 90 °C. Experiments with glycine plus goethite-II, using protocols B and C, produced only Gly-Gly. In addition, for the C protocol the amount of Gly-Gly synthesized was 3 times higher than the amount of Ala-Ala. Goethite-I presented a decrease in the EPR signal, when it was submitted to the protocols with and without amino acids. It is probable the decrease in the intensity of the EPR signal was due to a decrease in the imperfections of the mineral. For all protocols the mixture of alanine plus goethite-I or goethite-II produced c(Ala-Ala). However, for wet/dry cycles, protocol C presented higher yields (p < 0.05). In addition, Ala-Ala was produced using protocols A and C. The c(Ala-Ala) formation fitted a zero-order kinetic equation model. The surface areas of goethite-I and goethite-II were 35 m2 g-1 and 37 m2 g-1, respectively. Thermal analysis indicated that the mineral changes the thermal behavior of the amino acids. The main reactions for the thermal decomposition of glycine were deamination and dehydration and for alanine was deamination.

Unexpected Thiocyanate Adsorption onto Ferrihydrite Under Prebiotic Chemistry Conditions.

The most crucial role played by minerals was in the preconcentration of biomolecules or precursors of biomolecules in prebiotic seas. If this step had not occurred, molecular evolution would not have occurred. Thiocyanate is an important molecule in the formation of biomolecules as well as a catalyst for prebiotic reactions. The adsorption of thiocyanate onto ferrihydrite was carried out under pH and ion composition conditions in seawater that resembled those of prebiotic Earth. The seawater used in this work had high Mg2+, Ca2+ and SO42- concentrations. The most important result of this work was that ferrihydrite adsorbed thiocyanateata pH value (7.2 ± 0.2) that usually does not adsorb thiocyanate. The high adsorptivity of Mg2+, Ca2+ and SO42-onto ferrihydrite showed that seawater ions can act as carriers of thiocyanate to the ferrihydrite surface, creating a huge outer-sphere complex. Kinetic adsorption and isotherm experiments showed the best fit for the pseudo-second-order model and an activation energy of 23.8 kJ mol-1forthe Langmuir-Freundlich model, respectively. Thermodynamic data showed positive ΔG values, which apparently contradict the adsorption isotherm data and kinetic data that was obtained. The adsorption of thiocyanate onto ferrihydrite could be explained by coupling with the exergonic SO42- adsorption onto ferrihydrite. The FTIR spectra showed no difference between the C≡N stretching peaks of adsorbed thiocyanate and free thiocyanate, corroborating the formation of an outer-sphere complex. All the results demonstrated the importance of the artificial seawater composition for the adsorption of thiocyanate and for understanding prebiotic chemistry.

Interaction between glyphosate and montmorillonite in the presence of artificial seawater.

Glyphosate (N- (phosphonomethyl) glycine) is one of the most widely used herbicides in the world. In the literature, there are several studies describing the interaction between glyphosate and clay minerals. However, there is a lack of data of this interaction in marine environments. In this research, we examined the adsorption of glyphosate onto montmorillonite in the presence of artificial seawater. Mössbauer data showed that the interaction of the phosphonate group of glyphosate with Fe2+ of montmorillonite prevents its oxidation to Fe3+. X-ray diffractograms showed that glyphosate adsorption takes place only onto the montmorillonite surface and not in its interlayers. Infrared spectroscopy data demonstrate that the interaction between glyphosate and montmorillonite could be through the amino group. FT-IR spectra of aqueous solutions of salts of seawater showed that Ca2+ interacts with glyphosate of the phosphonate group, thus causing an increase in its adsorption onto montmorillonite. However, glyphosate dissolved in 0.50 mol L-1 NaCl and 0.034 mol L-1MgCl2 solutions showed the lowest adsorption onto montmorillonite. In addition, the adsorption of glyphosate onto montmorillonite decreased when the NaCl concentration increased. The results fitted the Sips isotherm model, probably because the Ca2+ interacts with glyphosate, making the adsorption process more homogeneous. Thus, n values for Freundlich and Sips isotherm models decreased with an increase in ionic strength. Glyphosate and ions of artificial seawater increased the pHpzc of montmorillonite.

Interference of goethite in the effects of glyphosate and Roundup® on ZFL cell line.

Goethite (α-FeOOH) brings important perspectives in environmental remediation, as, due to its physicochemical properties, this iron oxide can adsorb a wide variety of compounds, including glyphosate. This study aimed to evaluate the effects of goethite nanoparticles (NPs), glyphosate (Gly), Roundup® (Rd), and co-exposures (Gly + NPs and Rd + NPs) on zebrafish liver cell line (ZFL). ZFL cells were exposed to NPs (1, 10, and 100 mg L-1), Gly (3.6 mg L-1), Rd (10 mg L-1), and co-exposures (Gly + NPs and Rd + NPs), or only to saline for 1, 6, and 12 h. Cell viability was assessed by Trypan blue, MTT, and neutral red assays. The generation of reactive oxygen species and total antioxidant capacity were also determined, while genotoxicity was quantified by the comet assay. Both NPs and Rd in isolation produced cytotoxic effects at 6 h and genotoxic effects at 1 and 6 h. Rd + NPs resulted in synergistic effects, intensifying the toxicity. Cells exposed to Gly did not present toxic effects and Gly + NPs resulted in the suppression of toxic effects observed for NPs. The presence of other components in Roundup® seems to favor its toxicity compared to the active ingredient. In conclusion, according to the in vitro model, the concentrations used were not safe for the ZFL lineage.

Can maternal treatment with metformin during gestation and lactation cause metabolic and cardiovascular disorders in rat offspring?

Objective: The aim was to evaluate if maternal treatment with metformin (MET) during pregnancy and lactation could be safe for metabolic and cardiovascular parameters of adult male and female offspring.Materials and methods: Wistar female rats were treated with MET (293 mg/kg/d) or tap water, by gavage during gestation (METG or CTRG) or gestation and lactation (METGL or CTRGL).Results: At 75 days of life, male and female MET offspring presented similar blood pressure when compared with their CTR. The heart rate of female METGL was higher than in the CTRGL. The insulin sensitivity, basal glycaemia, body weight, Lee index of obesity, plasmatic concentration of triglycerides, total cholesterol and fat acid of male and female MET were similar to CTR groups. Lower fat pad deposition was observed in female METG and METGL.Conclusion: MET exposure during gestational and lactation does not program cardiovascular and metabolic alterations in adult offspring life.

Adenine Adsorbed onto Montmorillonite Exposed to Ionizing Radiation: Essays on Prebiotic Chemistry.

Most adsorption and radiolysis experiments related to prebiotic chemistry studies are performed in distilled water or sodium chloride solutions. However, distilled water and sodium chloride solutions do not represent the composition of the primitive seas of Earth. In this work, an artificial seawater with ion abundances Mg2+ > Ca2+ >> Na+ ≈ K+ and SO42- >> Cl- was used, one that is different from the average composition of seawater today. This artificial seawater is named seawater 4.0 Ga, since it better represents the composition of the major constituents of seawater of primitive Earth. The radiolysis of adenine adsorbed onto montmorillonite was studied. The most important result is that adenine is adsorbed onto montmorillonite, when it is dissolved in artificial seawater 4.0 Ga, and the clay protects adenine against gamma radiation decomposition. However, desorption of adenine from montmorillonite was possible only with 0.10 mol L-1 of KOH. This result indicates that adenine was strongly bonded to montmorillonite. Fourier transform infrared spectroscopy showed that NH2 group and electrostatic interactions, between negatively charged montmorillonite and positively charged adenine, are responsible for adsorption of adenine onto montmorillonite. In addition, X-ray diffractograms showed that adenine enters in the interlayer space of montmorillonite.

Sex differences in glucocorticoids-induced anabolic effects in rats.

Glucocorticoids (GC) increase food intake and body weight in humans and rodents and chronic stress and GC treatment-induced enhancement of the plasma concentration of GC lead to obesity and metabolic changes. In response to hypercaloric treatment, males were shown to be more susceptible to obesity than females, demonstrating that sex differences may affect energy homeostasis. The objective of the current study was to evaluate the effects of prolonged (28 days) treatment with dexamethasone or corticosterone on food intake and body weight gain in intact rats, both male and female. Also examined were Lee index, weights and area of adipocytes of retroperitoneal and perigonadal+perirenal adipose tissues, glucose tolerance test (GTT) and plasma concentrations of free fatty acids, cholesterol and triglycerides. Treatment with dexamethasone was able to increase body weight, food intake, area of adipocytes and weight of retroperitoneal adipose tissue in males. Prolonged treatment with corticosterone also stimulated body weight gain and food intake in males. In addition, it induced an increase in the area of adipocytes and weight of perirenal+perigonadal adipose tissue and higher glycemia after GTT in these animals, without changes on Lee index and plasma parameters after both GC treatments. No parameter was changed by dexamethasone or corticosterone treatment in female rats. Thus, it can be concluded that male rats are more susceptible to the anabolic effects of glucocorticoids than female rats, and these responses can be due to the protective effects of circulating estrogens in females, and/or the difference between males and females in the expression/activity of corticosteroids receptors.

Solid adenine and seawater salts exposed to gamma radiation: An FT-IR and EPR spectroscopy analysis for prebiotic chemistry.

Solids of adenine obtained from distilled water and seawater lyophilized solutions were γ irradiated at a 94.52 kGy dose. Results indicate that pure solid adenine had a low degradation rate, likewise the solid containing seawater salts. However, EPR spectroscopy analysis suggests a high interaction of the radiation with seawater salts, by radical formation in sulfate ions. These outcomes are of interest for prebiotic chemistry, since ions could have played important roles in chemical evolution. In addition, Martian soil is rich in sulphate salts, thus these salts could protected organic molecules being degraded by γ-radiation.

The effect of pH and ionic strength on the adsorption of glyphosate onto ferrihydrite.

Although, glyphosate (N-(phosphonomethyl) glycine) is one of the most widely used herbicides in the world, its interaction with poorly crystalline iron oxides, such as ferrihydrite, is not well studied. In this research, we examined the adsorption of glyphosate onto ferrihydrite using infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR), adsorption kinetic models and adsorption isotherm models. The effect of pH and sodium chloride concentration on the adsorption of glyphosate onto ferrihydrite as well as the effect of extractors (CaCl2 0.010 mol L-1 and Mehlich) on the desorption of glyphosate were also evaluated. There are two important findings described in this work. First, 84% of adsorbed glyphosate strongly interacted to ferrihydrite as an inner-sphere complex and phosphate and amine groups are involved in this interaction. Second, an increase of sodium chloride salt concentration increased the adsorption of glyphosate onto ferrihydrite. The non-linear Langmuir model and pseudo second order model showed a good agreement of theoretical limit of glyphosate adsorbed onto ferrihydrite, 54.88 µg mg-1 and 48.8 µg mg-1, respectively. The adsorption of glyphosate onto ferrihydrite decreased when the pH increased. Under the conditions used in this work, EPR spectra did not show dissolution of ferrihydrite. Surface area, pore volume and pHpzc of ferrihydrite decreased after adsorption of glyphosate.

WITHDRAWN: Sex differences in glucocorticoids-induced anabolic effects on energy balance.

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. This error bears no reflection on the article or its authors. The publisher apologizes to the authors and the readers for this unfortunate error.

Estradiol protects against ovariectomy-induced susceptibility to the anabolic effects of glucocorticoids in rats.

Glucocorticoids increase appetite and body weight gain in rats and ovariectomy (OVX) induces obesity, while estrogen (E) replacement attenuates OVX-induced changes. It is known that animals with obesity are more responsive to glucocorticoids anabolic effects than lean ones. This study aimed to evaluate the effects of ovariectomy and the protective role of estradiol on the responses induced by prolonged treatment with corticosterone or dexamethasone on energy homeostasis. For this, female Wistar rats subjected to SHAM or OVX surgery, composing the SHAM, OVX, and OVX + E groups, received water/ETOH or corticosterone (15 mg/l) and water or dexamethasone (0.5 µg/l) as drinking fluid for 28 days. The OVX + E group, since the first day, was daily treated with estradiol (10 µg/0.2 ml/rat SC). OVX induced enhancement of body weight gain, food intake, area of the adipocytes and weight of retroperitoneal adipose tissue, plasma cholesterol and glucose intolerance, with reduction on uterus weight. In OVX animals, treatment with glucocorticoids induced increases on body weight gain, food intake, weight of retroperitoneal adipose tissue, area of adipocytes of retroperitoneal and perigonadal + perirenal fat depots, plasma triglycerides (corticosterone), and glycemic response after GTT (dexamethasone), with minor effects on SHAM group. Estradiol treatment to OVX rats prevented these effects induced by glucocorticoids, in addition to decrease body weight gain, fat accumulation and glucose intolerance, and to increase weight of uterus, triglycerides and free fatty acids plasma levels. These data demonstrate that protection against glucocorticoids-induced anabolic responses in females is eliminated by ovariectomy and estradiol can prevent these responses.

Salinity Effects on the Adsorption of Nucleic Acid Compounds on Na-Montmorillonite: a Prebiotic Chemistry Experiment.

Any proposed model of Earth's primitive environments requires a combination of geochemical variables. Many experiments are prepared in aqueous solutions and in the presence of minerals. However, most sorption experiments are performed in distilled water, and just a few in seawater analogues, mostly inconsistent with a representative primitive ocean model. Therefore, it is necessary to perform experiments that consider the composition and concentration of dissolved salts in the early ocean to understand how these variables could have affected the absorption of organic molecules into minerals. In this work, the adsorption of adenine, adenosine, and 5'AMP onto Na+montmorillonite was studied using a primitive ocean analog (4.0 Ga) from experimental and computational approaches. The order of sorption of the molecules was: 5'AMP > adenine > adenosine. Infrared spectra showed that the interaction between these molecules and montmorillonite occurs through the NH2 group. In addition, electrostatic interaction between negatively charged montmorillonite and positively charge N1 of these molecules could occur. Results indicate that dissolved salts affect the sorption in all cases; the size and structure of each organic molecule influence the amount sorbed. Specifically, the X-ray diffraction patterns show that dissolved salts occupy the interlayer space in Na-montmorillonite and compete with organic molecules for available sites. The adsorption capacity is clearly affected by dissolved salts in thermodynamic terms as deduced by isotherm models. Indeed, molecular dynamic models suggest that salts are absorbed in the interlamellar space and can interact with oxygen atoms exposed in the edges of clay or in its surface, reducing the sorption of the organic molecules. This research shows that the sorption process could be affected by high concentration of salts, since ions and organic molecules may compete for available sites on inorganic surfaces. Salt concentration in primitive oceans may have strongly affected the sorption, and hence the concentration processes of organic molecules on minerals.

Oxytocin participates on the effects of vasoactive intestinal peptide on food intake and plasma parameters.

Vasoactive intestinal peptide (VIP) is a neurotransmitter with anorectic effect that acts in the hypothalamus to regulate food intake. Oxytocin is a neuropeptide produced in the hypothalamus that controls energy homeostasis and has an inhibitory role on food intake. Thus, the present study aims at verifying the role of oxytocin as a mediator of VIP on energy homeostasis. For this purpose, intracerebroventricular microinjection of oxytocin receptor antagonist (vasotocin, OVT) or vehicle (NaCl 0.9%) was carried out in male rats, and after 15 min, VIP or saline was microinjected. After 15 min of the second microinjection, food intake was evaluated or euthanasia was undertaken for blood collection. There was a reduction on food intake after VIP microinjection and the pretreatment with OVT partially reversed this effect. Hyperglycemia was observed after VIP microinjection, and pretreatment with OVT partially blocked this effect. Plasma corticosterone concentration was significantly increased after VIP or OVT. Plasma levels of free fatty acids were decreased by VIP, but not when VIP was microinjected after OVT. Thus, OVT partially reversed VIP-induced hypophagia and changes on plasma metabolic parameters, suggesting a role for oxytocin as a mediator of VIP effects on energy homeostasis.

Interaction, at Ambient Temperature and 80 °C, between Minerals and Artificial Seawaters Resembling the Present Ocean Composition and that of 4.0 Billion Years Ago.

Probably one of the most important roles played by minerals in the origin of life on Earth was to pre-concentrate biomolecules from the prebiotic seas. There are other ways to pre concentrate biomolecules such as wetting/drying cycles and freezing/sublimation. However, adsorption is most important. If the pre-concentration did not occur-because of degradation of the minerals-other roles played by them such as protection against degradation, formation of polymers, or even as primitive cell walls would be seriously compromised. We studied the interaction of two artificial seawaters with kaolinite, bentonite, montmorillonite, goethite, ferrihydrite and quartz. One seawater has a major cation and anion composition similar to that of the oceans of the Earth 4.0 billion years ago (ASW 4.0 Ga). In the other, the major cations and anions are an average of the compositions of the seawaters of today (ASWT). When ASWT, which is rich in Na+ and Cl-, interacted with bentonite and montmorrilonite structural collapse occurred on the 001 plane. However, ASW 4.0 Ga, which is rich in Mg2+ and SO42-, did not induce this behavior. When ASW 4.0 Ga was reacted with the minerals for 24 h at room temperature and 80 °C, the release of Si and Al to the fluid was below 1 % of the amount in the minerals-meaning that dissolution of the minerals did not occur. In general, minerals adsorbed Mg2+ and K+ from the ASW 4.0 Ga and these cations could be used for the formation of polymers. Also, when the minerals were mixed with ASW 4.0 Ga at 80 °C and ASWT at room temperature or 80 °C it caused the precipitation of CaSO4∙2H2O and halite, respectively. Finally, further experiments (adsorption, formation of polymers, protection of molecules against degradation, primitive cell wall formation) performed under the conditions described in this paper will probably be more representative of what happened on the prebiotic Earth.

The adsorption of amino acids and cations onto goethite: a prebiotic chemistry experiment.

Few prebiotic chemistry experiments have assessed the adsorption of biomolecules by iron oxide-hydroxides. The present work investigated the effects of cations in artificial seawaters on the adsorption of Gly, α-Ala and ß-Ala onto goethite, and vice versa. Goethite served to concentrate K and Mg cations from solution; these effects could have played important roles in peptide nucleoside formation. Goethite showed low adsorption of Gly and α-Ala. On the other hand, ß-Ala (a non-protein amino acid) was highly adsorbed by goethite. Because Gly and α-Ala are the most common amino acids in living beings, and iron oxide-hydroxides are widespread on Earth, additional iron oxides should be studied. Increased ionic strength in artificial seawaters decreased the adsorption of amino acids by goethite. Because Na was highly abundant in the artificial seawater, it showed the highest effect on amino acid adsorption. ß-Ala increased the adsorption of K and Ca by goethite, this effect could have been important for peptide synthesis.

Characterization of the Adsorption of Nucleic Acid Bases onto Ferrihydrite via Fourier Transform Infrared and Surface-Enhanced Raman Spectroscopy and X-ray Diffractometry.

Minerals could have played an important role in concentration, protection, and polymerization of biomolecules. Although iron is the fourth most abundant element in Earth's crust, there are few works in the literature that describe the use of iron oxide-hydroxide in prebiotic chemistry experiments. In the present work, the interaction of adenine, thymine, and uracil with ferrihydrite was studied under conditions that resemble those of prebiotic Earth. At acidic pH, anions in artificial seawater decreased the pH at the point of zero charge (pHpzc) of ferrihydrite; and at basic pH, cations increased the pHpzc. The adsorption of nucleic acid bases onto ferrihydrite followed the order adenine >> uracil > thymine. Adenine adsorption peaked at neutral pH; however, for thymine and uracil, adsorption increased with increasing pH. Electrostatic interactions did not appear to play an important role on the adsorption of nucleic acid bases onto ferrihydrite. Adenine adsorption onto ferrihydrite was higher in distilled water compared to artificial seawater. After ferrihydrite was mixed with artificial seawaters or nucleic acid bases, X-ray diffractograms and Fourier transform infrared spectra did not show any change. Surface-enhanced Raman spectroscopy showed that the interaction of adenine with ferrihydrite was not pH-dependent. In contrast, the interactions of thymine and uracil with ferrihydrite were pH-dependent such that, at basic pH, thymine and uracil lay flat on the surface of ferrihydrite, and at acidic pH, thymine and uracil were perpendicular to the surface. Ferrihydrite adsorbed much more adenine than thymine; thus adenine would have been better protected against degradation by hydrolysis or UV radiation on prebiotic Earth.

A Prebiotic Chemistry Experiment on the Adsorption of Nucleic Acids Bases onto a Natural Zeolite.

There are currently few mechanisms that can explain how nucleic acid bases were synthesized, concentrated from dilute solutions, and/or protected against degradation by UV radiation or hydrolysis on the prebiotic Earth. A natural zeolite exhibited the potential to adsorb adenine, cytosine, thymine, and uracil over a range of pH, with greater adsorption of adenine and cytosine at acidic pH. Adsorption of all nucleic acid bases was decreased in artificial seawater compared to water, likely due to cation complexation. Furthermore, adsorption of adenine appeared to protect natural zeolite from thermal degradation. The C=O groups from thymine, cytosine and uracil appeared to assist the dissolution of the mineral while the NH2 group from adenine had no effect. As shown by FT-IR spectroscopy, adenine interacted with a natural zeolite through the NH2 group, and cytosine through the C=O group. A pseudo-second-order model best described the kinetics of adenine adsorption, which occurred faster in artificial seawaters.

An experimental and theoretical vibrational study of interaction of adenine and thymine with artificial seawaters: A prebiotic chemistry experiment.

Nucleic acid bases play important roles in living beings. Thus, their interaction with salts the prebiotic Earth could be an important issue for the understanding of origin of life. In this study, the effect of pH and artificial seawaters on the structure of adenine and thymine was studied via parallel determinations using FT-IR, Raman spectroscopy and theoretical calculations. Thymine and adenine lyophilized in solutions at basic and acidic conditions showed characteristic bands of the enol-imino tautomer due to the deprotonation and the hydrochloride form due to protonation, respectively. The interaction of thymine and adenine with different seawaters representative of different geological periods on Earth was also studied. In the case of thymine a strong interaction with Sr(2+) promoted changes in the Raman and infrared spectra. For adenine changes in infrared and Raman spectra were observed in the presence of salts from all seawaters tested. The experimental results were compared to theoretical calculations, which showed structural changes due to the presence of ions Na(+), Mg(2+), Ca(2+) and Sr(2+) of artificial seawaters. For thymine the bands arising from C4=C5 and C6=O stretching were shifted to lower values, and for adenine, a new band at 1310cm(-1) was observed. The reactivity of adenine and thymine was studied by comparing changes in nucleophilicity and energy of the HOMO orbital.