Six freshwater microturbellarian species (Platyhelminthes) in permanent wetlands of the Coastal plain of southern Brazil: new records, abundance, and distribution

Microturbellarians occur in a wide range of ecosystems, but their diversity and distribution are largely unknown. In this work, we report on the morphology, abundance, and distribution of 6 species of microturbellarians, namely Baicalellia evelinae, Catenula evelinae, C. leuca, C. turgida, Gieysztoria chiqchi, and Stenostomum hemisphericum. We provide photographs and schematic drawings of the specimens in vivo. Three of them were known only for their type localities. Most species showed low to moderate abundance and were found in a single wetland in this study. Gieysztoria chiqchi is reported from Brazil for the first time. All records extend the ranges of the species at least 800 km to the southeast.Facultad de Ciencias Naturales y Muse

An ab initio study of the photodissociation of CH2I and CH2I+

8 pags., 5 figs., 4 tabs.Photodissociation of the CH2I radical and the CH2I+ cation is studied by means of high-level ab initio calculations, including spin-orbit effects. Potential-energy curves (PEC) along the dissociating bond distances involved in some fragmentation pathways of these species are computed for the ground and several excited electronic states. Based on the PECs obtained, the possible photodissociation mechanisms are analyzed and suggested. Significant differences are found between the fragmentation dynamics of the neutral radical and that of the cation. While a relatively simple dissociation dynamics is predicted for CH2I, more complex fragmentation mechanisms involving internal conversion and couplings between different excited electronic states are expected for CH2I+. The species studied here are relevant to atmospheric chemistry, and the present work can help to understand better how their photodissociation may affect chemical processes in the atmosphere.This work was funded by the Ministerio de Ciencia e Innovación (MICINN, Spain), grant no. PGC2018-096444-B-I00, PID2019-107115GB-C21, PID2021-122549NB-C21, PID2021-122796NB-I00, and PID2021- 122839NB-I00. A. B. acknowledges funding from the I-COOP program from CSIC, grant no. COOPB20364, which made possible a research stay at Instituto de Fısica Fundamental, CSIC. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie SkłodowskaCurie grant agreement no. 872081, and from the COST Action CA21101 (COSY). The Centro de Supercomputacion de Galicia (CESGA, Spain) is acknowledged for the use of its resources.Peer reviewe

Correlation Analysis of TEM Images of Nanocrystal Molecules

Quantitative characterizataion of images of naocrystals and nanostructures is a challenging but important task. The development and optimization of methods for the construction of complex nanostructures rely on imaging techniques. Computer programs were developed to quantify TEM images of nanocrystal/DNA nanostructures, and results are presented for heterodimers annd trimers of gold nanocrystals. The programs presented here have also been used to analyze more complex trimers and tetramers linked by branched DNA, as well as for structures made from attaching gold nanocrystals to CdSe/ZnS core-shell quantum dots. This work has the additional goal of enabling others to quickly and easily adapt the methods for their own use

Chirality in Bare and Passivated Gold Nanoclusters

Chiral structures have been found as the lowest-energy isomers of bare (Au$_{28}$ and Au$_{55}) and thiol-passivated (Au$_{28}(SCH$_{3})$_{16}$and Au$_{38}(SCH_{3})_{24}) gold nanoclusters. The degree of chirality existing in the chiral clusters was calculated using the Hausdorff chirality measure. We found that the index of chirality is higher in the passivated clusters and decreases with the cluster size. These results are consistent with the observed chiroptical activity recently reported for glutahione-passivated gold nanoclusters, and provide theoretical support for the existence of chirality in these novel compounds.Comment: 5 pages, 1 figure. Submitted to PR

A High-level Ab Initio Study of the Destruction of Methanimine under UV Radiation

13 pags., 9 figs., 1 tab. -- Unified Astronomy Thesaurus concepts: Complex organic molecules (2256); Photodissociation reactions (2266)The photodecomposition of methanimine (CH$_2$NH) in the interstellar medium through several possible pathways is investigated by means of high-level multireference configuration interaction {\it ab initio} calculations. Among them are photodissociation pathways involving hydrogen-atom elimination from both the CH$_2$ and NH groups, and fragmentation into CH$_2$ and NH. Potential-energy curves for the ground and several excited electronic states, as well as nonadiabatic couplings between them, are calculated. Possible dissociation mechanisms are discussed for the different pathways. It is found that the minimum excitation energy required for methanimine dissociation is above $7$ eV. By using a two-dimensional representation of methanimine, the CH$_2$NH $\rightarrow$ CHNH$_2$ isomerization is explored as an additional methanimine decomposition pathway. Hydrogen-atom elimination from the CH$_2$ group is also investigated along the isomerization pathway. The results show that the isomerization proceeds by overcoming a transition state that in the first two excited states would require excitation energies similar to or somewhat lower than the typical minimum energies needed for breaking the molecule through the fragmentation pathwys. Therefore, CH$_2$NH $\rightarrow$ CHNH$_2$ isomerization can effectively contribute to methanimine decomposition, competing efficiently with the photodissociation pathways. The radiation content present in the interstellar medium makes possible the occurrence of all the pathways studied.This work was funded by the Ministerio de Ciencia e Innovación (MICINN, Spain), grant Nos. PGC2018-096444-BI00, PID2019-107115GB-C21, PID2021-122549NB-C21, PID2021-122796NB-I00, and PID2021-122839NB-I00. A.B. acknowledges funding from the I-COOP program from CSIC, grant No. COOPB20364, which made possible a research stay at Instituto de Física Fundamental, CSIC. This project has received funding from the European Union’s Horizon 2020 research and innovation program under Marie SkłodowskaCurie Grant Agreement No. 872081. The authors acknowledge the National Plan for Science, Technology and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia, grant No. 2-17-01-001-0061. The Centro de Supercomputación de Galicia (CESGA, Spain) is acknowledged for allowing the use of its resources

Six freshwater microturbellarian species (Platyhelminthes) in permanent wetlands of the Coastal plain of southern Brazil: new records, abundance, and distribution

Microturbellarians occur in a wide range of ecosystems, but their diversity and distribution are largely unknown. In this work, we report on the morphology, abundance, and distribution of 6 species of microturbellarians, namely Baicalellia evelinae, Catenula evelinae, C. leuca, C. turgida, Gieysztoria chiqchi, and Stenostomum hemisphericum. We provide photographs and schematic drawings of the specimens in vivo. Three of them were known only for their type localities. Most species showed low to moderate abundance and were found in a single wetland in this study. Gieysztoria chiqchi is reported from Brazil for the first time. All records extend the ranges of the species at least 800 km to the southeast.Facultad de Ciencias Naturales y Muse