170,054 research outputs found
Unprecedented gas-phase chiroselective logic gates
No full textBotta B, Fraschetti C, D'Acquarica I, et al. Unprecedented gas-phase chiroselective logic gates. Organic & Biomolecular Chemistry. 2011;9(6):1717-1719.The gas-phase encounters between 2-aminobutane and proton-bound chiral resorcin[4]arene/nucleoside complexes behave in the gas phase as supramolecular "chiroselective logic gates" by releasing the nucleoside depending on the resorcin[4] arene and the 2-aminobutane configurations
Enantioselective supramolecular devices in the gas phase. Resorcin[4] arene as a model system
No full textFraschetti C, Letzel M, Filippi A, Speranza M, Mattay J. Enantioselective supramolecular devices in the gas phase. Resorcin[4] arene as a model system. Beilstein Journal of Organic Chemistry. 2012;8:539-550.This review describes the state-of-art in the field of the gas-phase reactivity of diastereomeric complexes formed between a chiral artificial receptor and a biologically active molecule. The presented experimental approach is a ligand-displacement reaction carried out in a nano ESI-FT-ICR instrument, supported by a thermodynamic MS-study and molecular-mechanics and molecular-dynamics (MM/MD) computational techniques. The noncovalent ion-molecule complexes are ideal for the study of chiral recognition in the absence of complicating solvent and counterion effects
Substituent effects on the stereochemistry of gas-phase intracomplex nucleophilic substitutions
No full textThe mechanism and stereochemistry of the intracomplex solvolysis of proton-bound complexes [Y center dot center dot center dot H center dot center dot center dot M](+) between M = (CH3OH)-O-18 and Y = 1-arylethanol [(S)-1-(para-tolyl)ethanol (1(S)), (S)-1-(para-chlorophenyl)ethanol (2(S)), (S)-1-(meta-alpha,alpha,alpha-trifluoromethylphenyl)ethanol (3(S)), (S)-1-(Para-alpha,alpha,alpha-trifluoromethylphenyl)-ethanol (4(S)), (R)-1-(pentafluorophenyl)ethanol (5(R)), (R)-alpha-(trifluoromethyl)benzyl alcohol (6(R)), and (R)-1-phenylethanol (7(R))] have been investigated in the gas phase (CH3F; 720 Torr) in the 25-140 degrees C temperature range. Gas-phase solvolysis of [Y center dot center dot center dot H center dot center dot center dot M](+) (Y = 2(S), 3(S), 4(S), and 7(R)) leads to extensive racemization above a characteristic temperature t(#) (e.g. at t(#) > 60 degrees C for 7(R)), whereas below that temperature the reaction displays a preferential retention of configuration. Predominant retention of configuration is instead observed in the intracomplex solvolysis of [Y center dot center dot center dot H center dot center dot center dot M](+) (Y = 1(S), 4(S), 5(R), and 6(R)) with the temperature range investigated (25 <= T <= 120 degrees C). These results indicate that the intracomplex solvolysis proceeds through the intermediacy of the relevant benzylic cations (Bz(+)), which is electrostatically coordinated to a H2O and a (CH3OH)-O-18 molecule (a pure S(N)1 mechanism). The obtained gas-phase mechanism is discussed in the light of related solution data. It is concluded that the stereochemistry of unimolecular solvolytic reactions is determined by the lifetime and the dynamics of the species involved and, if occurring in solution, by the nature and the dynamics of the solvent cage as well
Unprotected Galactosamine as a Dynamic Key for a Cyclochiral Lock.
No full textFraschetti C, Letzel MC, Paletta M, et al. Unprotected Galactosamine as a Dynamic Key for a Cyclochiral Lock. Journal of the American Society for Mass Spectrometry. 2021.The discrimination of d-galactosamine (G), representative of the amino-sugar class of compounds, has been probed through nano-ESI-FT-ICR mass spectrometry by isolating the relevant [C·H·G]+ proton-bound complexes with the enantiomers of the cyclochiral resorcin[4]arene C and allowing them to react toward three primary amines (B = EtNH2, iPrNH2, and (R)- and (S)-sBuNH2). The system under investigation presents several features that help to unveil the behavior of unprotected G in such a supramolecular architecture: (i) the hydrophobic derivatization of the C convex side forces the polar guest G to be coordinated by the cyclochiral concave region; (ii) protonated d-galactosamine exists as an anomeric mixture, dynamically interconverting throughout the experimental time-window; and (iii) different basicities of B allow the experiment to subtly tune the reactivity of the [C·H·G]+ complexes. Three [C·H·G]+ aggregate-types were found to exist, differing in both their origin and reactivity. The most reactive adducts ([C·H·G]ESI+), generated in the electrospray environment, undergo a G-to-B ligand exchange in competition with a partial isomerization to the unreactive [C·H·G]GAS+-type complexes. Finally, the poorly reactive [C·H·G]SOL+ aggregates are formed in solution over an hours-long time scale. A cyclochirality effect on the reactivity was found to depend on the considered [C·H·G]+ aggregate-type
Trophic importance of subtidal metazoan meiofauna: evidence from in situ exclusion experiments on soft and rocky substrates
No full textIn coastal marine ecosystems, predation might affect spatial distribution and population dynamics of benthic assemblages. Here, by means of experimental exclusion of potential predators, we compared the effects of epibenthic predation on metazoan meiofaunal assemblages on soft and rocky substrates. Different patterns of abundance were observed in uncaged versus caged plots, across habitats. In caged soft substrates, the abundance of Nematodes, Copepods and Polychaetes increased by 56, 45, 57%, respectively, in the first 3 months. An increase in the number of meiofaunal taxa was also observed. The exclusion of predators from rocky substrates showed less clear patterns. It did not affect the number of taxa while a decrease in meiofaunal abundance was observed. Our results suggest that the exclusion of epibenthic predators had clear effect on total metazoan meiofaunal abundance and on the number of taxa, only in soft bottoms. The different impact of predation across habitats can be potentially explained by differences in terms of spatial variability and substrate complexity. We estimated that, coarsely, more than 75% of total metazoan meiofaunal production can be channeled to higher trophic levels through predation on soft-bottoms. Among meiofaunal taxa, Polychaetes and Nematodes provided the major contribution to benthic energy transfers. These results suggest the trophic relevance of metazoan meiofauna in coastal food webs and claim for the refinement of further experiments for the quantification of its role in different ecological systems
Meiofauna communities, nematode diversity and C degradation rates in seagrass (Posidonia oceanica L.) and unvegetated sediments invaded by the algae Caulerpa cylindracea (Sonder)
No full textWe investigated meiofauna and sedimentary C cycling in seagrass (Posidonia oceanica) and unvegetated sediments invaded and not invaded by the non-indigenous tropical algae Caulerpa cylindracea. In both habitats, invaded sediments were characterized by higher organic matter contents. No effect was observed for prokaryotes and C degradation rates. In seagrass sediments, C turnover in invaded beds was about half that in not invaded ones. Meiofaunal communities varied significantly among invaded and not invaded grounds only in bare sediments. In both habitats, nematode species richness and assemblage composition were not affected by the algae. The effect of C. cylindracea on the turnover and nestedness components of the Jaccard dissimilarity varied between the two habitats. We show that the presence of C. cylindracea gives rise to variable consequences on meiofauna biodiversity and C cycling in different habitats. We conclude that further studies across different habitats and ecological components are needed to ultimately understand and predict the consequences of C. cylindracea invasion in shallow Mediterranean ecosystem
The enlargement of the Suez Canal and introduction of non-indigenous species to the Mediterranean Sea
No full textThe Suez Canal is one of the most important waterways in the world – during the last year 17,148 ships passed through the Canal – reducing emissions, saving time, and operating costs to shippers. The rapid increase in ship size from the “Post-Suezmax” (> 12,000 TEU) to the latest container vessels (> 19,000 TEU) now requires enlargements of port facilities and canals.
A project of this magnitude, and with potentially negative environmental outcomes, requires a transparent and scientifically sound “Environmental Impact Assessment” (EIA). An explicit obligation on Parties to the Convention on Biological Diversity (https://www.cbd.int/doc/ legal/cbd-en.pdf) was made to consider transboundary impacts on biodiversity, particularly those associated with invasive non-indigenous species
A three-year time series of elemental and biochemical composition of organic matter in subtidal sandy sediments of the Ligurian Sea (northwestern Mediterranean).
No full textVariations in organic matter composition and microphytobenthic biomass were examined in the surface sandy sediments at a water depth of 10 m in the Gulf of Marconi (NW Mediterranean Sea) over a three year period. Seasonal changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter as well as Chi a were assessed in order to provide information about the origin and fate of sedimentary organic matter, the contribution of microphytobenthic biomass, seasonal and interannual variations of food quantity and quality, and factors related to food availability. Data obtained in this three-year study revealed that organic matter determined with a muffle furnace is clearly an overestimate of the organic content of the sediment and is thus of little significance for benthic ecologists studying community dynamics in relation to food availability. Labile organic matter, utilized to estimate the food potentially available for benthic consumers, accounted for only a small percentage (on average less than 10%) of total organic C. The highest labile fraction was observed in spring, whereas minima were recorded in winter. Analysis of elemental and biochemical composition of organic matter showed an inverse relationship between amount of organic matter and its potential availability to consumers; small quantities of high-quality organic matter were replaced by large quantities of refractory material. The labile portion was mostly microphytobenthic (65% of the labile carbon). Protein:carbohydrate ratios were low and confirmed the role of proteins as a potentially limiting factor for consumers. Significant differences in nutritional quality of the sediment organic matter were observed from year to year, changes due to the increase in specific labile compound content
Gas-Phase Enantioselectivity of Chiral N-Linked Peptidoresorc[4]arene Isomers toward Dipeptides
No full textBotta B, Fraschetti C, D'Acquarica I, et al. Gas-Phase Enantioselectivity of Chiral N-Linked Peptidoresorc[4]arene Isomers toward Dipeptides. Journal of Physical Chemistry A. 2009;113(52):14625-14629.The gas-phase enantioselectivity of cone N-linked peptidoresorc[4]arenes (generally symbolized as M) toward the homologue dipeptides (generally symbolized as A) has been evaluated by measuring the kinetics of the A release from the diastereomeric [M center dot H center dot A](+) complexes induced by (R)-(-)-2-butylamine (B). In most cases investigated, the heterochiral [M center dot H center dot A](+) complexes, namely those wherein the configuration of the A guest is opposite to that or the host M pendants, react faster (up to 5 times) than the homochiral analogues, wherein guest A guest has the same Configuration of the host M pendants. The kinetic results, discussed in the light of previous MS and NMR evidence, indicate that both the efficiency and the enantioselectivity of the guest exchange reaction depend essentially on the Structure and the relative stability of the diastereomeric [M center dot H center dot A](+) complexes. These, in turn, depend oil the functional groups and the configuration of both the guest and the host pendants. The absence of any significant effects of the B configuration indicates that, in all systems investigated, the dipeptide guest A is predominantly located outside the host chiral cavity
Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase
No full textFraschetti C, Letzel M, Paletta M, et al. Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase. Journal of Mass Spectrometry. 2012;47(1):72-78.The effect of cyclochirality of rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene (C) on the enantiodiscrimination of a number of chiral bidentate and tridentate aromatic and aliphatic biomolecules (G) has been investigated by nano-electrospray ionization (nano-ESI)-Fourier transform ion cyclotron resonance mass spectrometry. The experimental approach is based on the formation of diastereomeric proton-bound [C center dot H center dot G](+) complexes by nano-ESI of solutions containing an equimolar amount of quasi-enantiomers (C) together with the chiral guest (G) and the subsequent measurement of the rate of the G substitution by the attack of several achiral and chiral amines. In general, the heterochiral complexes react faster than the homochiral ones, except when G is an aminoalcoholic neurotransmitter whose complexes, beyond that, exhibit the highest enantioselectivity. The kinetic results were further supported by both collision-induced dissociation experiments on some of the relevant [C-2 center dot H center dot G](+) three-body species and Density functional theory (DFT) calculations performed on the most selective systems. Copyright (C) 2012 John Wiley & Sons, Ltd
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