Chapter 1 : nucleobases with designed patterns of hydrogen bonding

The chemistry used in key bond-forming steps to prepare nucleobases with designed patterns of hydrogen bonding is surveyed. Incorporation of the nucleobases into DNA and RNA oligomers is achieved either chemically using building blocks such as nucleoside phosphoramidites or enzymatically using nucleotide triphosphates. By varying the hydrogen bonding pattern within nucleobases, and by incorporating additional substituents, new structures have been designed that "reach over" so that contacts with both strands in targeted duplex DNA can be made in antigene strategies to control gene expression. Various new base-pairing systems have been evaluated that expand the genetic alphabet beyond Watson-Crick base pairs A.T and G.C. For example, benzo-homologated analogs of the natural DNA bases represent a new genetic set of orthogonal, size-expanded derivatives that have been shown to encode amino acids of a protein in a living organism.

Production, purification and characterization of recombinant, full-length human claudin-1

The transmembrane domain proteins of the claudin superfamily are the major structural components of cellular tight junctions. One family member, claudin-1, also associates with tetraspanin CD81 as part of a receptor complex that is essential for hepatitis C virus (HCV) infection of the liver. To understand the molecular basis of claudin-1/CD81 association we previously produced and purified milligram quantities of functional, full-length CD81, which binds a soluble form of HCV E2 glycoprotein (sE2). Here we report the production, purification and characterization of claudin-1. Both yeast membrane-bound and detergent-extracted, purified claudin-1 were antigenic and recognized by specific antibodies. Analytical ultracentrifugation demonstrated that extraction with n-octyl-ß-d-glucopyranoside yielded monodispersed, dimeric pools of claudin-1 while extraction with profoldin-8 or n-decylphosphocholine yielded a dynamic mixture of claudin-1 oligomers. Neither form bound sE2 in line with literature expectations, while further functional analysis was hampered by the finding that incorporation of claudin-1 into proteoliposomes rendered them intractable to study. Dynamic light scattering demonstrated that claudin-1 oligomers associate with CD81 in vitro in a defined molar ratio of 1:2 and that complex formation was enhanced by the presence of cholesteryl hemisuccinate. Attempts to assay the complex biologically were limited by our finding that claudin-1 affects the properties of proteoliposomes. We conclude that recombinant, correctly-folded, full-length claudin-1 can be produced in yeast membranes, that it can be extracted in different oligomeric forms that do not bind sE2 and that a dynamic preparation can form a specific complex with CD81 in vitro in the absence of any other cellular components. These findings pave the way for the structural characterization of claudin-1 alone and in complex with CD81.

Nonaqueous capillary zone electrophoresis of synthetic organic polypeptides

Poly(Nε-trifluoroacetyl-l-lysine) was used as a model solute to investigate the potential of nonaqueous capillary electrophoresis (NACE) for the characterization of synthetic organic polymers. The information obtained by NACE was compared to that derived from size exclusion chromatography (SEC) experiments, and the two techniques were found to be complimentary for polymer characterization. On one hand, NACE permitted (i) the separation of oligomers according to their molar mass and (ii) the separation of the polymers according to the nature of the end groups. On the other hand, SEC experiments were used for the characterization of the molar mass distribution for higher molar masses. Due to the tendency of the solutes (polypeptides) to adsorb onto the fused-silica capillary wall, careful attention was paid to the rinsing procedure of the capillary between runs in order to keep the capillary surface clean. For that purpose, the use of electrophoretic desorption under denaturating conditions was very effective. Optimization of the separation was performed by studying (i) the influence of the proportion of methanol in a methanol/acetonitrile mixture and (ii) the influence of acetic acid concentration in the background electrolyte. Highly resolved separation of the oligomers (up to a degree of polymerization n of ∼50) was obtained by adding trifluoroacetic acid to the electrolyte. Important information concerning the polymer conformations could be obtained from the mobility data. Two different plots relating the effective mobility data to the degree of polymerization were proposed for monitoring the changes in polymer conformations as a function of the number of monomers.

Pseudoperiodic "Living" and/or controlled cationic ring-opening copolymerization of oxetane with tetrahydropyran:microstructure of polymers vs kinetics of chain growth

The "living" and/or controlled cationic ring-opening bulk copolymerization of oxetane (Ox) with tetrahydropyran (THP) (cyclic ether with no homopolymerizability) at 35°C was examined using ethoxymethyl-1 -oxoniacyclohexane hexafluoroantimonate (EMOA) and (BF3 · CH3OH)THP as fast and slow initiator, respectively, yielding living and nonliving polymers with pseudoperiodic sequences (i.e., each pentamethylene oxide fragment inserted into the polymer is flanked by two trimethylene oxide fragments). Good control over number-average molecular weight (Mn up to 150000 g mol-1) with molecular weight distribution (MWD ∼ 1.4-1, 5) broader than predicted by the Poison distribution (MWDs > 1 +1/DPn) was attained using EMOA as initiating system, i.e., C 2H5OCH2Cl with 1.1 equiv of AgSbF6 as a stable catalyst and 1.1 equiv of 2,6-di-tert-butylpyridine used as a non-nucleophilic proton trap. With (BF3 · CH 3OH)THP, a drift of the linear dependence M n(GPC) vs Mn(theory) to lower molecular weight was observed together with the production of cyclic oligomers, ∼3-5% of the Ox consumed in THP against ∼30% in dichloromethane. Structural and kinetics studies highlighted a mechanism of chains growth where the rate of mutual conversion between "strain ACE species" (chain terminated by a tertiary 1-oxoniacyclobutane ion, Al) and "strain-free ACE species" (chain terminated by a tertiary 1-oxoniacyclohexane ion, Tl) depends on the rate at which Ox converts the stable species T1 (kind of "dormant" species) into a living "propagating" center A1 (i.e., k aapp[Ox]). The role of the THP solvent associated with the suspension of irreversible and reversible transfer reactions to polymer, when the polymerization is initiated with EMOA, was predicted by our kinetic considerations. The activation -deactivation pseudoequilibrium coefficient (Qt) was then calculated in a pure theoretical basis. From the measured apparent rate constant of Ox (kOxapp) and THP (kTHPapp = ka(endo)app) consumption, Qt and reactivity ratio (kp/kd, k a(endo)/ka(exo), and ks/ka(endo) were calculated, which then allow the determination of the transition rate constant of elementary step reactions that governs the increase of Mu with conversion. © 2009 American Chemical Society.

Amyloid β 1-42 induces hypometabolism in human stem cell-derived neuron and astrocyte networks

Alzheimer's disease (AD) is the most common form of dementia, affecting more than 35 million people worldwide. Brain hypometabolism is a major feature of AD, appearing decades before cognitive decline and pathologic lesions. To date, the majority of studies on hypometabolism in AD have used transgenic animal models or imaging studies of the human brain. As it is almost impossible to validate these findings using human tissue, alternative models are required. In this study, we show that human stem cell-derived neuron and astrocyte cultures treated with oligomers of amyloid beta 1-42 (Aβ1-42) also display a clear hypometabolism, particularly with regard to utilization of substrates such as glucose, pyruvate, lactate, and glutamate. In addition, a significant increase in the glycogen content of cells was also observed. These changes were accompanied by changes in NAD+ /NADH, ATP, and glutathione levels, suggesting a disruption in the energy-redox axis within these cultures. The high energy demands associated with neuronal functions such as memory formation and protection from oxidative stress put these cells at particular risk from Aβ-induced hypometabolism. Further research using this model may elucidate the mechanisms associated with Aβ-induced hypometabolism.

Oxidised LDL-lipids alter redox ratio, lipid raft formation and increase amyloid beta production by SHSY-5Y cells

Elevated cholesterol in mid-life has been associated with increased risk of dementia in later life. We have previously shown that low density lipoprotein (LDL) is more oxidised in the plasma of dementia patients although total cholesterol levels remained unchanged [1]. We have investigated the hypothesis that amyloid beta production and neurodegeneration can be driven by oxidised lipids derived from LDL following the loss of blood brain barrier integrity with ageing. Therefore, we have investigated amyloid beta formation in SHSY5Y cells treated with LDL, minimally modified (ox) LDL, and lipids extracted from both forms of LDL. LDL-treated SHSY-5Y cell viability was not significantly decreased with up to 8 μg LDL/2 × 104 cells compared to untreated cells. However, 8 μg oxLDL protein/2 × 104 cells decreased the cell viability significantly by 33.7% (P < 0.05). A more significant decrease in cell viability was observed when treating cells with extracted lipids from 8 μg of LDL (by 32.7%; P < 0.01) and oxLDL (by 41%; P < 0.01). In parallel, the ratio of reduced to oxidised GSH was decreased; GSH concentrations were significantly decreased following treatment with 0.8 μg/ml oxLD-L (7.35 ± 0.58;P < 0.01), 1.6 μg/ml (5.27 ± 0.23; P < 0.001) and 4 μg/ml (5.31 ± 0.31; P < 0.001). This decrease in redox potential was associated with an increase acid sphingomyelinase activity and lipid raft formation which could be inhibited by desipramine; SHSY5Y cells treated with oxLDL, and lipids from LDL and oxLDL for 16 h showed significantly increased acid sphingomyelinase activity (5.32 ± 0.35; P < 0.05, 5.21 ± 0.6; P < 0.05, and 5.58 ± 0.44; P < 0.01, respectively) compared to control cells (2.96 ± 0.34). As amyloid beta production is driven by the activity of beta secretase and its association with lipid rafts, we investigated whether lipids from ox-LDL can influence amyloid beta by SHSY-5Y cells in the presence of oxLDL. Using ELISA and Western blot, we confirmed that secretion of amyloid beta oligomers is increased by SHSY-5Y cells in the presence of oxLDL lipids. These data suggest a mechanism whereby LDL, and more significantly oxLDL lipids, can drive amyloid beta production and cytotoxicity in neuronal cells. [1] Li L, Willets RS, Polidori MC, Stahl W, Nelles G, Sies H, Griffiths HR. Oxidative LDL modification is increased in vascular dementia and is inversely associated with cognitive performance. Free Radic Res. 2010 Mar; 44(3): 241–8.

The development of functional astrocyte-neuron networks derived from stem cells

There is currently great scientific and medical interest in the potential of tissue grown from stem cells. These cells present opportunities for generating model systems for drug screening and toxicological testing which would be expected to be more relevant to human outcomes than animal based tissue preparations. Newly realised astrocytic roles in the brain have fundamental implications within the context of stem cell derived neuronal networks. If the aim of stem cell neuroscience is to generate functional neuronal networks that behave as networks do in the brain, then it becomes clear that we must include and understand all the cellular components that comprise that network, and which are important to support synaptic integrity and cell to cell signalling. We have shown that stem cell derived neurons exhibit spontaneous and coordinated calcium elevations in clusters and in extended processes, indicating local and long distance signalling (1). Tetrodotoxin sensitive network activity could also be evoked by electrical stimulation. Similarly, astrocytes exhibit morphology and functional properties consistent with this glial cell type. Astrocytes also respond to neuronal activity and to exogenously applied neurotransmitters with calcium elevations, and in contrast to neurons, also exhibited spontaneous rhythmic calcium oscillations. Astroctyes also generate propagating calcium waves that are gap junction and purinergic signalling dependent. Our results show that stem cell derived astrocytes exhibit appropriate functionality and that stem cell neuronal networks interact with astrocytic networks in co-culture. Using mixed cultures of stem cell derived neurons and astrocytes, we have also shown both cell types also modulate their glucose uptake, glycogen turnover and lactate production in response to glutamate as well as increased neuronal activity (2). This finding is consistent with their neuron-astrocyte metabolic coupling thus demonstrating a tractable human model, which will facilitate the study of the metabolic coupling between neurons and astrocytes and its relationship with CNS functional issues ranging from plasticity to neurodegeneration. Indeed, cultures treated with oligomers of amyloid beta 1-42 (Aβ1-42) also display a clear hypometabolism, particularly with regard to utilization of substrates such as glucose (3). Both co-cultures of neurons and astrocytes and purified cultures of astrocytes showed a significant decrease in glucose uptake after treatment with 2 and 0.2 μmol/L Aβ at all time points investigated (p <0.01). In addition, a significant increase in the glycogen content of cells was also measured. Mixed neuron and astrocyte co-cultures as well as pure astrocyte cultures showed an initial decrease in glycogen levels at 6 hours compared with control at 0.2 μmol/L and 2 μmol/L P <0.01. These changes were accompanied by changes in NAD+/NADH (P<0.05), ATP (P<0.05), and glutathione levels (P<0.05), suggesting a disruption in the energy-redox axis within these cultures. The high energy demands associated with neuronal functions such as memory formation and protection from oxidative stress put these cells at particular risk from Aβ-induced hypometabolism. As numerous cell types interact in the brain it is important that any in vitro model developed reflects this arrangement. Our findings indicate that stem cell derived neuron and astrocyte networks can communicate, and so have the potential to interact in a tripartite manner as is seen in vivo. This study therefore lays the foundation for further development of stem cell derived neurons and astrocytes into therapeutic cell replacement and human toxicology/disease models. More recently our data provides evidence for a detrimental effect of Aβ on carbohydrate metabolism in both neurons and astrocytes. As a purely in vitro system, human stem cell models can be readily manipulated and maintained in culture for a period of months without the use of animals. In our laboratory cultures can be maintained in culture for up to 12 months months thus providing the opportunity to study the consequences of these changes over extended periods of time relevant to aspects of the disease progression time frame in vivo. In addition, their human origin provides a more realistic in vitro model as well as informing other human in vitro models such as patient-derived iPSC.

Antidepressant/anxiolytic and anti-nociceptive effects of novel 2-substituted 1,4-benzodiazepine-2-ones

Oxazepam (4a) has been used as overall starting material in the synthesis of novel 2-substituted 1,4-benzodiazepines. By reacting Oxazepam 4a with commercially available hydrazines, hydrazides, semicarbazide, aminoguanidine and N,N-dimethylamino aniline in ethanol under acetic conditions, a series of diazenyl-1,4-benzodiazepines 5a-5i and 2-amino- 1,4-benzodiazepine 5k were obtained in good yields. These novel compounds served as new chemical entities (NCE) for testing in mice. The diazo-benzodiazepine 5d has shown a promising antidepressant effect in initial experiments in vivo at a dose of 5 mg/kg. The highly coloured 2-aminobenzodiazepine derivative 5k showed over a dose range from 5-50 mg/kg an analgesic effect in mice. © Singh et al.

Binding of small molecules to DNA junctions

Previous results in our laboratory suggest that the (CG) 4 segments whether present in a right-handed or a left-handed conformation form distinctive junctions with adjacent random sequences. These junctions and their associated sequences have unique structural and thermodynamic properties that may be recognized by DNA-binding molecules. This study probes these sequences by using the following small ligands: actinomycin D, 1,4-bis(((di(aminoethyl)amino)ethyl)amino)anthracene-9,10-dione, ametantrone, and tris(phenanthroline)ruthenium (II). These ligands may recognize the distinctive features associated to the (CG)4 segment and its junctions and thus interact preferentially near these sequences. Restriction enzyme inhibition assays were used to determine whether or not binding interactions took place, and to approximate locations of these interactions. These binding studies are first carried out using two small synthetic oligomers BZ-III and BZ-IV. The (5meCG)4 segment present in BZ-III adopts the Z-conformation in the presence of 50 m M Co(NH3)63+. In BZ-IV, the unmethylated (CG)4 segment changes to a non-B conformation in the presence of 50 m M Co(NH3)63+. BZ-IV, containing the (CG)4 segment, was inserted into a clone plasmid then digested with the restriction enzyme Hinf I to produce a larger fragment that contains the (CG)4 segment. The results obtained on the small oligomers and on the larger fragment for restriction enzyme Mbo I indicate that 1,4-bis(((di(aminoethyl)amino)ethyl)amino)anthracene-9,10-dione binds more efficiently at or near the (CG)4 segment. Restriction enzymes EcoRV, Sac I and Not I with cleavage sites upstream and downstream of the (CG)4 insert were used to further localize binding interactions in the vicinity of the (CG)4 insert. RNA polymerase activity was studied in a plasmid which contained the (CG)4 insert downstream from the promoter sites of SP6 and T7 RNA polymerases. Activities of these two polymerases were studied in the presence of each one of the ligands used throughout the study. Only actinomycin D and spider, which bind at or near the (CG)4 segment, alter the activities of SP6 and T7 RNA polymerases. Surprisingly, enhancement of polymerase activity was observed in the presence of very low concentrations of actinomycin D. These results suggest that the conformational features of (CG) segments may serve in regulatory functions of DNA. ^

Role of calcium in inflammation: Relevance to Alzheimer's disease

Alzheimer’s disease (AD) is neuropathologically characterized by excessive beta -amyloid (Aβ) plaques and neurofibrillary tangles composed of hyperphosphorylated tau in the brain. Although the etiology of genetic cases of AD has been attributed to mutations in presenilin and amyloid precursor protein (APP) genes, in most sporadic cases of AD, the etiology is still unknown and various predisposing factors could contribute to the pathology of AD. Predominant among these possible predisposing factors that have been implicated in AD are age, hypertension, traumatic brain injury, diabetes, chronic neuroinflammation, alteration in calcium levels and oxidative stress. Since both inflammation and altered calcium levels are implicated in the pathogenesis of AD, we wanted to study the effect of altered levels of calcium on inflammation and the subsequent effect of selective calcium channel blockers on the production of pro-inflammatory cytokines and chemokines. Our hypothesis is that Aβ, depending on it conformation, may contribute to altered levels of intracellular calcium in neurons and glial cells. We wanted to determine which conformation of Aβ was most pathogenic in terms of increasing inflammation and calcium influx and further elucidate the possibility of a link between altered calcium levels and inflammation. In addition, we wanted to test whether calcium channel blockers could inhibit the inflammation mediated by the most pathogenic form of Aβ, by antagonizing the calcium influx triggered by Aβ. Our results in human glial and neuronal cells demonstrate that the high molecular weight oligomers are the most potent at stimulating the release of pro-inflammatory cytokines IL-6 and IL-8 as well as increasing intracellular levels of calcium compared to other conformations of Aβ. Further, L-type calcium channel blockers and calmodulin kinase inhibitors are able to significantly reduce the levels of IL-6 and IL-8. These results suggest that Aβ-induced alteration of intracellular calcium levels contributes to its pro-inflammatory effect.

Avaliação da aplicabilidade de correlações matemáticas e redes neurais na predição de parâmetros de especificação do diesel

Diesel fuel is one of leading petroleum products marketed in Brazil, and has its quality monitored by specialized laboratories linked to the National Agency of Petroleum, Natural Gas and Biofuels - ANP. The main trial evaluating physicochemical properties of diesel are listed in the resolutions ANP Nº 65 of December 9th, 2011 and Nº 45 of December 20th, 2012 that determine the specification limits for each parameter and methodologies of analysis that should be adopted. However the methods used although quite consolidated, require dedicated equipment with high cost of acquisition and maintenance, as well as technical expertise for completion of these trials. Studies for development of more rapid alternative methods and lower cost have been the focus of many researchers. In this same perspective, this work conducted an assessment of the applicability of existing specialized literature on mathematical equations and artificial neural networks (ANN) for the determination of parameters of specification diesel fuel. 162 samples of diesel with a maximum sulfur content of 50, 500 and 1800 ppm, which were analyzed in a specialized laboratory using ASTM methods recommended by the ANP, with a total of 810 trials were used for this study. Experimental results atmospheric distillation (ASTM D86), and density (ASTM D4052) of diesel samples were used as basic input variables to the equations evaluated. The RNAs were applied to predict the flash point, cetane number and sulfur content (S50, S500, S1800), in which were tested network architectures feed-forward backpropagation and generalized regression varying the parameters of the matrix input in order to determine the set of variables and the best type of network for the prediction of variables of interest. The results obtained by the equations and RNAs were compared with experimental results using the nonparametric Wilcoxon test and Student's t test, at a significance level of 5%, as well as the coefficient of determination and percentage error, an error which was obtained 27, 61% for the flash point using a specific equation. The cetane number was obtained by three equations, and both showed good correlation coefficients, especially equation based on aniline point, with the lowest error of 0,816%. ANNs for predicting the flash point and the index cetane showed quite superior results to those observed with the mathematical equations, respectively, with errors of 2,55% and 0,23%. Among the samples with different sulfur contents, the RNAs were better able to predict the S1800 with error of 1,557%. Generally, networks of the type feedforward proved superior to generalized regression.

Potencialidade do tratamento eletroquímico oxidativo associado à adsorção para remediação de corantes têxteis

This study aimed to evaluate the potential of oxidative electrochemical treatment coupled with adsorption process using expanded perlite as adsorbent in the removal of textile dyes, Red Remazol and Novacron Blue on synthetic effluent. Dyes and perlite were characterized by thermogravimetry techniques (TG), Differential Scanning Calorimetry (DSC), Spectroscopy infrared (IR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. Electrochemical treatments used as anodes, Ti/Pt and Pb/PbO2 under different conditions: 60 minutes, current density 20, 40 e 60 mAcm-2, pH 1, 4.5 e 8 and temperature variation 20, 40 e 60 ºC. In the case of adsorption tests, contact time of 30 minutes for the Remazol Red dye and 20 minutes for Novacron Blue were established, while pH 1, 4.5 e 8, 500 mg adsorbent and temperature variation 20, 40 e 60 ºC were used for both treatments. The results indicated that both treatments, electroxidation/adsorption and the adsorption/electroxidation, were effective for removing color from synthetic solutions. The consumption of electricity allowed to evaluate the applicability of the electrochemical process, providing very acceptable values, which allowed us to estimate the cost. Total organic carbon (TOC) and Gas Chromatography linked mass spectrometer (GC-MS) analyzes were performed, showing that the better combination for removing organic matter is by Pb/PbO2 and perlite. Meanwhile, GC-MS indicated that the by-products formed are benzoic acid, phthalic acid, thiocarbamic acid, benzene, chlorobenzene, phenol-2-ethyl and naphthalene when Remazol Red was degraded. Conversely, aniline, phthalic acid, 1, 6 - dimethylnaphthalene, naphthalene and ion hidroxobenzenosulfonat was detected when Novacron Blue was studied. Analyses obtained through atomic absorption spectrometry showed that there was release of lead in the electrochemical oxidation of analyzes that were performed with the anode Pb/PbO2, but these values are reduced by subjecting the effluent to adsorption analysis. According to these results, sequential techniques electroxidation/adsorption and adsorption/electroxidation are to treat solutions containing dyes.

Potencialidade do tratamento eletroquímico oxidativo associado à adsorção para remediação de corantes têxteis

This study aimed to evaluate the potential of oxidative electrochemical treatment coupled with adsorption process using expanded perlite as adsorbent in the removal of textile dyes, Red Remazol and Novacron Blue on synthetic effluent. Dyes and perlite were characterized by thermogravimetry techniques (TG), Differential Scanning Calorimetry (DSC), Spectroscopy infrared (IR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. Electrochemical treatments used as anodes, Ti/Pt and Pb/PbO2 under different conditions: 60 minutes, current density 20, 40 e 60 mAcm-2, pH 1, 4.5 e 8 and temperature variation 20, 40 e 60 ºC. In the case of adsorption tests, contact time of 30 minutes for the Remazol Red dye and 20 minutes for Novacron Blue were established, while pH 1, 4.5 e 8, 500 mg adsorbent and temperature variation 20, 40 e 60 ºC were used for both treatments. The results indicated that both treatments, electroxidation/adsorption and the adsorption/electroxidation, were effective for removing color from synthetic solutions. The consumption of electricity allowed to evaluate the applicability of the electrochemical process, providing very acceptable values, which allowed us to estimate the cost. Total organic carbon (TOC) and Gas Chromatography linked mass spectrometer (GC-MS) analyzes were performed, showing that the better combination for removing organic matter is by Pb/PbO2 and perlite. Meanwhile, GC-MS indicated that the by-products formed are benzoic acid, phthalic acid, thiocarbamic acid, benzene, chlorobenzene, phenol-2-ethyl and naphthalene when Remazol Red was degraded. Conversely, aniline, phthalic acid, 1, 6 - dimethylnaphthalene, naphthalene and ion hidroxobenzenosulfonat was detected when Novacron Blue was studied. Analyses obtained through atomic absorption spectrometry showed that there was release of lead in the electrochemical oxidation of analyzes that were performed with the anode Pb/PbO2, but these values are reduced by subjecting the effluent to adsorption analysis. According to these results, sequential techniques electroxidation/adsorption and adsorption/electroxidation are to treat solutions containing dyes.

A model for the modular evolution of rna addressing open questions on the origin of life

A main unsolved problem in the RNA world scenario for the origin of life is how a template-dependent RNA polymerase ribozyme emerged from short RNA oligomers generated by random polymerization of ribonucleotides (Joyce and Orgel 2006). Current estimates establish a minimum size about 165 nt long for such a ribozyme (Johnston et al. 2001), a length three to four times that of the longest RNA oligomers obtained by random polymerization on clay mineral surfaces (Huang and Ferris 2003, 2006). To overcome this gap, we have developed a stepwise model of ligation-based, modular evolution of RNA (Briones et al. 2009) whose main conceptual steps are summarized in Figure 1. This scenario has two main advantages with respect to previous hypotheses put forward for the origin of the RNA world: i) short RNA....

Enhanced Volatile Organic Compounds emissions and organic aerosol mass increase the oligomer content of atmospheric aerosols

Secondary organic aerosol (SOA) accounts for a dominant fraction of the submicron atmospheric particle mass, but knowledge of the formation, composition and climate effects of SOA is incomplete and limits our understanding of overall aerosol effects in the atmosphere. Organic oligomers were discovered as dominant components in SOA over a decade ago in laboratory experiments and have since been proposed to play a dominant role in many aerosol processes. However, it remains unclear whether oligomers are relevant under ambient atmospheric conditions because they are often not clearly observed in field samples. Here we resolve this long-standing discrepancy by showing that elevated SOA mass is one of the key drivers of oligomer formation in the ambient atmosphere and laboratory experiments. We show for the first time that a specific organic compound class in aerosols, oligomers, is strongly correlated with cloud condensation nuclei (CCN) activities of SOA particles. These findings might have important implications for future climate scenarios where increased temperatures cause higher biogenic volatile organic compound (VOC) emissions, which in turn lead to higher SOA mass formation and significant changes in SOA composition. Such processes would need to be considered in climate models for a realistic representation of future aerosol-climate-biosphere feedbacks.