Quasiclassical Trajectory Study of the Si + SH Reaction on an Accurate Double Many-Body Expansion Potential Energy Surface.

An accurate potential energy surface (PES) for the HSiS system based on MRCI+Q calculations extrapolated to the complete basis set limit is presented. Modeled with the double many-body expansion (DMBE) method, the PES provides an accurate description of the long-range interactions, including electrostatic and dispersion terms decaying as R-4, R-5, R-6, R-8, R-10 that are predicted from dipole moments, quadrupole moments, and dipolar polarizabilities, which are also calculated at the MRCI+Q level. The novel PES is then used in quasiclassical trajectory calculations to predict the rate coefficients of the Si + SH → SiS + H reaction, which has been shown to be a major source of the SiS in certain regions of the interstellar medium. An account of the zero-point energy leakage based on various nonactive models is also given. It is shown that the reaction is dominated by long-range forces, with the mechanism Si + SH → SiSH → SSiH → SiS + H being the most important one for all temperatures studied. Although SSiH corresponds to the global minimum of the PES, the contribution from the direct reaction Si + SH → SSiH → SiS + H is less than 0.5% for temperatures higher than 500 K. The rovibrational distributions of the products are calculated using the momentum Gaussian binning method and show that as the temperature is increased the average vibrational quantum number decreases while the rotational distribution spreads up to larger values.

Optimized Structural Data at the Complete Basis Set Limit via Successive Quadratic Minimizations.

Two variants of a successive quadratic minimization method (SQM and c-SQM) are suggested to calculate the structural properties of molecular systems at the complete basis set (CBS) limit. When applied to H3+, H2O, CH2O, SH2, and SO2, they revealed CBS/(x1, x2) structural parameters that significantly surpass the raw ones calculated at the x2 basis set level. Such a performance has also been verified for the intricate case of the water dimer. Because the c-SQM method is system specific, thus showing somewhat enhanced results relative to the general SQM protocol, it can be of higher cost depending on the level of calibration used. Yet, it hardly surpasses the general quality of the results obtained with the cost-effective SQM method. Since the number of cycles required to reach convergence is relatively small, both schemes are simple to use and easily adaptable to any of the existing extrapolation schemes for the Hartree-Fock and correlation energies.

Accurate DMBE potential-energy surface for CNO(2A″) and rate coefficients in C(3P)+NO collisions.

A realistic double many-body expansion potential energy surface (PES) is developed for the 2A″ state of the carbon-nitrogen-oxygen (CNO) system based on MRCI-F12/cc-pVQZ-F12 ab initio energies. The new PES reproduces the fitted points with chemical accuracy (root mean square deviation up to 0.043 eV) and explicitly incorporates long range energy terms that can accurately describe the electrostatic and dispersion interactions. Thermal rate coefficients were computed for the C(3P) + NO(2Π) reaction for temperatures ranging from 15 K to 10 000 K, and the values are compared to previously reported results. The differences are rationalized, and the major importance of long range forces in predicting the rate coefficients for barrierless reactions is emphasized.

Accurate Potential Energy Surface for Quartet State HN2 and Interplay of N(4S) + NH(X̃3Σ-) versus H + N2(A3Σu+) Reactions.

A global potential energy surface for the lowest quartet state of HN2 is reported for the first time from accurate multireference ab initio calculations extrapolated to the complete basis set limit using the double many-body expansion method. All its stationary points are characterized, with the lowest quartet of HN2 predicted to have a bent global minimum 36 kcal mol-1 below the N(4S) + NH(X̃3Σ-) asymptote, from which it is barrierlessly achievable. The entire set of calculated ab initio points has been fitted for energies up to 1000 kcal mol-1 above the global minimum with an RMSD of 0.89 kcal mol-1, a gap comprising all identified stationary points. Special care is taken in modeling the involved long-range forces and cusps caused by crossing seams. The novel PES prompts for the calculation of rate constants for several unexplored reactions that are relevant for combustion, plasma, and atmospheric chemistry.

Quasiclassical Study of the C(3P) + NO(X2Π) and O(3P) + CN(X2Σ+) Collisional Processes on an Accurate DMBE Potential Energy Surface.

The predicted rate constants for C + NO and O + CN collisions in three potential energy surfaces (PESs) for the 2A' state of the CNO molecule are compared using quasiclassical trajectories. Different temperature dependencies are obtained for the C + NO reaction, which are explained in terms of the long-range properties of the PESs. Recommended values and mechanistic details are also reported. For O + CN collisions, a better agreement between the theoretical results is found, except for temperatures below 100 K.

Two- vs. single-stage anaerobic reactors: evaluation of effluent quality and energy production potential using sucrose-based wastewater.

Two- and single-stage anaerobic treatment systems were assessed for treatment performance and for bioenergy production from sucrose-based wastewater. In the two-stage system, a hydrogen-producing upflow anaerobic sludge blanket reactor (HU reactor) was used in the acidogenic phase. The methanogenic reactor of the two-stage system (MF reactor) and the single-stage reactor (SSF reactor) were structured fixed-bed reactors. The two-stage system showed superior performance, evidenced by lower organic acids, chemical oxygen demand (COD) and suspended solids concentrations in the effluent, and higher biogas methane content and yield. Continuous and stable H2 production was obtained in the acidogenic reactor. At the end of operation, the organic loading rates applied to the two- and single-stage systems were 6.4 and 5.2 gCOD L-1 d-1, respectively. Under these conditions, the effluent soluble COD and volatile suspended solids (VSS) concentrations were 165 and 92 mg L-1 in the two-stage system, and 256 and 244 mg L-1 in the single-stage system, respectively. The energy yield of the two-stage system was 20.69 kJ g-1CODadded, which was 34% higher than the yield of the single-stage system. The sequencing analyses showed that the archaeal distribution changed little between the inoculum and sludge from the MF reactor, in which acetoclastic Methanosaeta was predominant. However, hydrogenotrophic Methanospirillum was found most, followed by Methanosaeta, in the sludge from the SSF reactor.

The O + NO( v) Vibrational Relaxation Processes Revisited.

We have carried out a quasiclassical trajectory study of the O + NO( v) energy transfer process using DMBE potential energy surfaces for the ground-states of the 2A' and 2A″ manifolds. State-to-state vibrational relaxation rate constants have been computed over the temperature range 298 and 3000 K and initial vibrational states between v = 1 and 9. The momentum-Gaussian binning approach has been employed to calculate the probability of the vibrational transitions. A comparison of the calculated state-to-state rate coefficients with the results from experimental studies and previous theoretical calculations shows the relevance of the 1 2A″ potential energy surface to the title vibrational relaxation process.

Accurate Explicit-Correlation-MRCI-Based DMBE Potential-Energy Surface for Ground-State CNO.

We report a new global double many-body expansion potential energy surface for the ground state of the CNO(2A') manifold, calculated by the explicit correlation multireference configuration interaction method. The functional form was accurately fitted to 3701 ab initio points with a root mean squared deviation of 0.99 kcal mol-1. All stationary points reported in previous forms are systematically described and improved, in addition to three new ones and a characterization of an isomerization transition state between the CNO and NCO minima. The novel proposed form gives a realistic description of both short-range and long-range interactions and hence is commended for dynamics studies.

Biohydrogen production at pH below 3.0: Is it possible?

Biological hydrogen production was investigated in continuous acidogenic reactors fed with sucrose at 30 °C without pH control. In the first experimental phase, three reactors were compared: a structured fixed-bed (FB), a granular UASB (UG) and a flocculent UASB (UF-1). They were run at 3.3 h HRT and 33 gCOD L-1d-1 OLR. Hydrogen production occurred throughout the experimental period with an average effluent pH of only 2.8. The FB, UG and UF-1 reactors presented volumetric hydrogen production rates (VHPR) of 95 ± 69, 45 ± 37 and 54 ± 32 mLH2 L-1h-1, respectively; and H2 yields (HY) of 1.5 ± 0.8, 0.8 ± 0.6 and 1.2 ± 0.7 molH2 mol-1 sucroseconsumed, respectively. The UF-1 reactor showed intermediate VHPR and HY, but no declining trend, contrary to what was observed in the FB reactor. Thus, aiming at continuous and long-term H2 production, a flocculent UASB was applied in the second experimental phase. In this phase, the HRT of the acidogenic reactor, which was named UF-2, was raised to 4.6 h, resulting in an OLR of 25 gCOD L-1d-1. The VHPR and the HY increased considerably to 175 ± 44 mLH2 L-1h-1 and 3.4 ± 0.7 molH2 mol-1 sucroseconsumed, respectively. These improvements were accompanied by greater sucrose removal, higher suspended biomass concentration, less production of lactate and more of acetate, and high ethanol concentration. Contradicting the current published literature data that reports strong inhibition of H2 production by dark fermentation at pH less than 4.0, the UF-2 reactor presented stable, long-term H2 production with satisfactory yields at pH 2.7 on average. 16 S rDNA sequencing revealed that two sequences assigned as Ethanoligenens and Clostridium accounted for over 70% of the microbiota in all the reactors. The non-necessity of adding alkalizing agents and the successful H2 production under very acid conditions, demonstrated in this study, open a new field of investigation in biological hydrogen production by dark fermentation towards a more sustainable and feasible technology.

Comparison of Aerobic and Anaerobic Biodegradation of Sugarcane Vinasse.

Vinasse is the main liquid waste from ethanol production, and it has a considerable pollution potential. Biological treatment is a promising alternative to reduce its organic load. The aim of this study was to analyze the biodegradation of sugarcane juice vinasse in aerobic and anaerobic conditions. The content of carbohydrates, proteins and volatile fatty acids was evaluated. Vinasse samples showed a high biodegradability (>96.5 %) and low percentage of inert chemical oxygen demand (COD) (<3.2 %) in both aerobic and anaerobic conditions. The rates of substrate utilization were slightly higher in aerobic reactors, but COD stabilization occurred simultaneously in the anaerobic reactors, confirming its suitability for anaerobic digestion. Inert COD in anaerobic conditions was lower than in aerobic conditions. On the other hand, COD from metabolic products in the anaerobic reactors was higher than in the aerobic ones, indicating an increased release of soluble microbial products (SMPs) by anaerobic microorganisms. The results indicated that carbohydrates were satisfactorily degraded and protein-like substances were the major components remaining after biological degradation of vinasse.

Modeling cusps in adiabatic potential energy surfaces.

A method for modeling cusps on adiabatic potential energy surfaces without the need for any adiabatic-to-diabatic transformation is presented and shown to be successfully applied to the (2)A″ state of NO2. The more complicated case of a system with permutationally equivalent crossing seams is also examined and illustrated by considering the two first (2)A' states of the nitrogen trimer.

Dynamics of the O + ClO reaction: reactive and vibrational relaxation processes.

Classical trajectories have been integrated to study the O + ClO reaction, both reactive and vibrational energy transfer processes, for the range of temperatures 100 ≤ T/K ≤ 500 using momentum Gaussian binning. The employed potential energy surface is the recently proposed single-sheeted double many-body expansion potential energy surface for the (2)A" ground-state of ClO2 based on multireference ab initio data. A capture-type regime with a room-temperature rate constant of (17.8 ± 0.5) × 10(-12) cm(3) s(-1) and temperature dependence of k(T/K)/cm(3) s(-1) = 22.4 × 10(-12) × T(-0.81) exp(-39.2/T) has been found. Although the value reported here is half of the experimental and recommended one, tentative explanations are given. Other dynamical attributes are also examined for the title reaction, with state-to-all and state-to-state vibrational relaxation and excitation rate constants reported for temperatures of relevance in stratospheric chemistry.

Single-sheeted double many-body expansion potential energy surface for ground-state ClO2.

A global single-sheeted double many-body expansion potential energy surface is reported for the ground electronic state of ClO2. The potential energy surface is obtained by fitting 3200 energy points that map all atom-diatom dissociation channels as well as all relevant stationary points, including the well-known OClO and ClOO structures. The ab initio calculations are obtained at the multireference configuration interaction level of theory, employing the cc-pVXZ (X = D, T) Dunning basis sets, and then extrapolated to the complete basis set limit with the generalized uniform singlet- and triplet-pair protocol. The topographical features of the novel global potential energy surface are examined in detail.

Molecular identification of Lactobacillus spp. associated with puba, a Brazilian fermented cassava food.

Puba or carimã is a Brazilian staple food obtained by spontaneous submerged fermentation of cassava roots. A total of 116 lactobacilli and three cocci isolates from 20 commercial puba samples were recovered on de Man, Rogosa and Sharpe agar (MRS); they were characterized for their antagonistic activity against foodborne pathogens and identified taxonomically by classical and molecular methods. In all samples, lactic acid bacteria were recovered as the dominant microbiota (7.86 ± 0.41 log10 CFU/g). 16S-23S rRNA ARDRA pattern assigned 116 isolates to the Lactobacillus genus, represented by the species Lactobacillus fermentum (59 isolates), Lactobacillus delbrueckii (18 isolates), Lactobacillus casei (9 isolates), Lactobacillus reuteri (6 isolates), Lactobacillus brevis (3 isolates), Lactobacillus gasseri (2 isolates), Lactobacillus nagelii (1 isolate), and Lactobacillus plantarum group (18 isolates). recA gene-multiplex PCR analysis revealed that L. plantarum group isolates belonged to Lactobacillus plantarum (15 isolates) and Lactobacillus paraplantarum (3 isolates). Genomic diversity was investigated by molecular typing with rep (repetitive sequence)-based PCR using the primer ERIC2 (enterobacterial repetitive intergenic consensus). The Lactobacillus isolates exhibited genetic heterogeneity and species-specific fingerprint patterns. All the isolates showed antagonistic activity against the foodborne pathogenic bacteria tested. This antibacterial effect was attributed to acid production, except in the cases of three isolates that apparently produced bacteriocin-like inhibitory substances. This study provides the first insight into the genetic diversity of Lactobacillus spp. of puba.

Recurrence of chronic urticaria caused by reinfection by Helicobacter pylori.

OBJECTIVE: To describe a case of chronic urticaria in a female adolescent associated with Helicobacter pylori infection, confirmed in two different occasions, with improvement of urticaria after the antibacterial treatment. CASE DESCRIPTION: A 13-year-old female patient sought medical care with chronic urticaria and epigastric pain unresponsive to medical treatment. Laboratorial tests for further investigation were normal except for the upper gastrointestinal endoscopy with biopsy showing moderate chronic active gastritis associated with Helicobacter pylori. After specific and appropriate treatment, the patient had remission of the symptoms. A new upper gastrointestinal endoscopy to control the treatment after nine months was normal. After five years, the patient returned with recurrence of urticaria and epigastric pain. She was taking antihistamines, without any improvement. It was again submitted to screening protocol for chronic urticaria with normal results. She was submitted to upper gastrointestinal endoscopy, which showed positive urease test. The patient started a new treatment for Helicobacter pylori with disappearance of chronic urticaria and epigastric pain within seven days. COMMENTS: The reported case suggests a causal relationship between the positive diagnosis of Helicobacter pylori and the occurrence of chronic urticaria, showing the remission of symptoms after the institution of effective therapy for this agent. Chronic urticaria is a disease of complex etiology, and although controversial, there is growing evidence of Helicobacter pylori involvement with extraintestinal diseases, including chronic urticaria.

Molecular identification of Lactobacillus spp. associated with puba, a Brazilian fermented cassava food

Puba or carimã is a Brazilian staple food obtained by spontaneous submerged fermentation of cassava roots. A total of 116 lactobacilli and three cocci isolates from 20 commercial puba samples were recovered on de Man, Rogosa and Sharpe agar (MRS); they were characterized for their antagonistic activity against foodborne pathogens and identified taxonomically by classical and molecular methods. In all samples, lactic acid bacteria were recovered as the dominant microbiota (7.86 ± 0.41 log10 CFU/g). 16S-23S rRNA ARDRA pattern assigned 116 isolates to the Lactobacillus genus, represented by the species Lactobacillus fermentum (59 isolates), Lactobacillus delbrueckii (18 isolates), Lactobacillus casei (9 isolates), Lactobacillus reuteri (6 isolates), Lactobacillus brevis (3 isolates), Lactobacillus gasseri (2 isolates), Lactobacillus nagelii (1 isolate), and Lactobacillus plantarum group (18 isolates). recA gene-multiplex PCR analysis revealed that L. plantarum group isolates belonged to Lactobacillus plantarum (15 isolates) and Lactobacillus paraplantarum (3 isolates). Genomic diversity was investigated by molecular typing with rep (repetitive sequence)-based PCR using the primer ERIC2 (enterobacterial repetitive intergenic consensus). The Lactobacillus isolates exhibited genetic heterogeneity and species-specific fingerprint patterns. All the isolates showed antagonistic activity against the foodborne pathogenic bacteria tested. This antibacterial effect was attributed to acid production, except in the cases of three isolates that apparently produced bacteriocin-like inhibitory substances. This study provides the first insight into the genetic diversity of Lactobacillus spp. of puba.

Ab initio-based global double many-body expansion potential energy surface for the first 2A" electronic state of NO2.

An ab initio-based global double many-body expansion potential energy surface is reported for the first electronic state of the NO(2)((2)A") manifold. Up to 1700 ab initio energies have been employed to map the full configuration space of the title molecule, including stationary points and asymptotic channels. The calculated grid energies have been scaled to account for the incompleteness of the basis set and truncation of the MRCI expansion and fitted analytically with a total root-mean-squared-deviation smaller than 1.0 kcal mol(-1). The lowest point of the potential energy surface corresponds to the (2)B(1) linear minimum, which is separated from the C(s) distorted minimum by a C(2v) barrier of ≈9.7 kcal mol(-1). As usual, the proposed form includes a realistic representation of long-range interactions. Preliminary work indicates its reliability for reaction dynamics.

The early days of pandemic (H1N1) 2009 virus infection in the central region of Portugal.

BACKGROUND: The first case of pandemic (H1N1) 2009 virus infection was diagnosed in the central region of Portugal on June 16, 2009, in a woman infected in Canada. METHODS: The aim of our study was, first to characterize the clinical and epidemiologic aspects of all the patients with clinical manifestations included in the definition of case for investigation with samples submitted to diagnosis of the pandemic (H1N1) 2009 virus infection, in the central region of Portugal; second to assess the precision of the case definition of case for investigation considered in the study according to the presence or the absence of fever at the moment of clinical observation. We reviewed the medical records of all the patients presenting with Influenza like-illness classified as case for investigation and the first cases of patients infected with the new pandemic (H1N1) 2009 virus, diagnosed in the central region of Portugal during the pandemic period between June and August, 2009, were analyzed. Real-time reverse-transcriptase polymerase-chain-reaction (RT-PCR) testing was used to confirm the pandemic (H1N1) 2009 virus infection. Data collection was performed on a standardized paper format in agreement with the General Health Directorate. RESULTS AND DISCUSSION: Pandemic (H1N1) 2009 virus infection was confirmed in 255 patients. Overall, median age was 23 years and 42.7 % were included in the category of 20 to 29 years. Confirmed infection in patients with less than 2 years or greater than 50 years was a rare event. The first cases were imported from Europe, namely France, Spain and England. On a second phase, pandemic (H1N1) 2009 virus infection was acquired in the south of Portugal (Algarve), before de diagnosis of the first domestic case. The incidence rate for pandemic (H1N1) 2009 virus infection was 10.7 per 100,000 persons and was different according to the district. It was higher in the district of Coimbra and Guarda were the main roads connecting to Europe are. The median calculated incubation period for the for pandemic (H1N1) 2009 virus infection was 2 days. The length of the clinical manifestations until the patients look for medical observation had a median time of 2 days. All the cases were of mild to moderate severity. No deaths were observed. CONCLUSIONS: The early days of pandemic (H1N1) 2009 virus infection was mild in our region. Most affected patients were young adults, with the extreme categories ages of life being spared. Early detection and diagnosis, combined with stringent isolation and treatment procedures could have slowed the spread of the infection in our region.

Initial in vitro evaluations of the antibacterial activities of glucosinolate enzymatic hydrolysis products against plant pathogenic bacteria.

AIMS: The aim of the study was to evaluate the in vitro antibacterial effects of glucosinolate hydrolysis products (GHP) against plant pathogenic micro-organisms namely Agrobacterium tumefaciens, Erwinia chrysanthemi, Pseudomonas cichorii, Pseudomonas tomato, Xanthomonas campestris and Xanthomonas juglandis. METHODS AND RESULTS: Using a disc diffusion assay, seven different doses of 10 GHP were tested against each bacteria. The results showed that the isothiocyanates were potent antibacterials, whilst the other GHP were much less efficient. Moreover, the antibacterial effects were dose-dependent, increasing with the dose applied; 2-phenylethylisothiocyanate and sulforaphane showed the strongest inhibitory effects. The overall results show a great potential for using the isothiocyanates as an alternative tool to control undesired bacterial growth in plants. CONCLUSIONS: Glucosinolate hydrolysis products and more specifically the isothiocyanates: benzylisothiocyanate, 2-phenylethylisothiocyanate, the isothiocyanate Mix and sulforaphane, were effective phytochemicals against the in vitro growth of the phytopathogenic bacteria. The antibacterial activity exhibited by these phytochemicals reinforces their potential as alternatives to the traditional chemical control of phytopathogenic bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: This current in vitro study is the first providing comparative data on GHP as potential control agents for plant pathogenic bacteria. However, more studies are needed to determine their possible allelopathic impacts e.g. inhibition of plant growth and negative effects on beneficial soil bacteria and fungi (mycorrhizae).

The antimicrobial effects of glucosinolates and their respective enzymatic hydrolysis products on bacteria isolated from the human intestinal tract.

AIMS: The aim of the study was to evaluate the in vitro antibacterial activity of glucosinolates and their enzymatic hydrolysis product against bacteria isolated from the human intestinal tract. METHODS AND RESULTS: Using a disc diffusion bioassay, different doses of intact glucosinolates and their corresponding hydrolysis products were tested. There were clear structure-activity and concentration differences with respect to the in vitro growth inhibition effects as well as differences in the sensitivities of the individual bacteria. The most effective glucosinolate hydrolysis products were the isothiocyanates; sulforaphane and benzyl isothiocyanate were the best inhibitors of growth. Indole-3-carbinol had some inhibitory effects against the Gram-positive bacteria but had no effect, even at the highest dose, against the Gram-negative bacteria. Indole-3-acetonitrile had some inhibitory activity against the Gram-negative bacteria. Glucosinolates, nitriles and amines were ineffective at all the doses used. CONCLUSIONS: Glucosinolate hydrolysis products and specifically the isothiocyanates SFN and BITC have significant antimicrobial activity against Gram-positive and Gram-negative bacteria, and might be useful in controlling human pathogens through the diet. SIGNIFICANCE AND IMPACT OF THE STUDY: This the first major in vitro study demonstrating the potential of these natural dietary chemicals as an alternative to, or in combination with, current antibiotic-based therapies for treating infectious diseases.