Role Of Isomers Research Articles

Isomer engineering of benzofuran derived AIE luminogens: Synthesis, mechanochromism, pH responsive fluorescent switching, cell-imaging and Fe3+ sensing

The influence of multiple factors often leads to the unexpected performances of the designed AIEgens. It is difficult to precisely conclude the influence of the substituted sites and role of isomers on the photophysical properties of the AIEgens which therefore brings uncertainty in the molecular design strategies. Isomer engineering of AIEgens is a less explored domain. There are only a few reports that substantiate the effects and positions of the substituents on the AIE properties. The present investigation explores two isomeric benzofuran-derived luminogens GBY-1 and GBY-4, both featuring a TPE moiety and showcasing AIE and AIEE properties respectively inherited from TPE. The isomeric effect resulting from TPE incorporation at different positions across benzofuran significantly influenced their photophysical properties, mechanofluorochromic properties, and AIE effect. Their distinctive luminogenic features were evident in mechanochromic property as well as in cancer cell imaging. GBY-1 was found to be uniformly dispersed in the cytoplasm, not co-localized with the nucleus, while GBY-4 accumulated near the cell membrane. Furthermore, post-functionalization of one of the luminogens, GBY-1, derived another AIEgen, GBY-5 with a dramatic improvement in the PLQE along with its ability to selectively sense Fe3+ in aqueous environments, within a detection limit of 0.00035 mM.

Role of isomers and steric hindrance in the micellization of carboxylated carbosilane surfactants

AbstractA series of carboxylated carbosilane surfactants with methyl, ethyl, branching CH3, phenyl, and cyclohexyl (Me‐Si2C‐COONa, Et‐Si2C‐COONa, Si2C‐La‐COONa, Ph‐Si2C‐COONa, and Cy‐Si2C‐COONa) were prepared. The effect of isomer and steric hindrance on their micellization in aqueous solution was investigated by surface tension, conductivity, transmission electron microscopy (TEM) and dynamic light scattering (DLS). Si2C‐La‐COONa with branching CH3 shows a lower γCMC value and higher the CMC value compared with Et‐Si2C‐COONa. Cy‐Si2C‐COONa with cyclohexyl (41.6 mN m−1) and Ph‐Si2C‐COONa with phenyl (43.9 mN m−1) have larger γCMC values due to the distinct steric hindrance and hydrophobicity. In aqueous solution, the aggregation behavior of Si2C‐La‐COONa, Cy‐Si2C‐COONa, and Ph‐Si2C‐COONa is enthalpy‐driven. However, the micellization process of Me‐Si2C‐COONa and Et‐Si2C‐COONa is governed by the enthalpy‐driven at high temperature and entropy‐driven at low temperature. DLS and TEM results indicate that the carboxylated carbosilane surfactants can self‐assemble into aggregate with hydrodynamic diameters of 50–400 nm.

Vibrational spectroscopy of the hexahydrated sulfate dianion revisited: role of isomers and anharmonicities.

We report on the gas phase vibrational spectroscopy of the hexahydrated sulfate dianion, SO42-(H2O)6, and its fully deuterated isotopologue, SO42-(D2O)6, using infrared photodissociation (IRPD) spectroscopy of the D2-tagged dianions in combination with density-functional-theory calculations on minimum-energy structures as well as finite temperature ab initio molecular dynamics (AIMD) simulations. The IRPD spectra were recorded at an ion trap temperature of 12 K and in the spectral range from 650 to 3800 cm-1, covering the intramolecular modes of the solvent (OH/OD stretches and H2O/D2O bends) at higher energies, those of the solute (sulfate stretches) at intermediate energies and the intermolecular solute librational modes at the lowest energies. Isomer-specific double resonance in combination with messenger-tag dependent IRPD spectra show that only a single isomer is contributing significantly and that this isomer is not the highly symmetric Td but rather the lower symmetry C3 isomer. Temperature-dependent IR multiple photon dissociation spectra of bare SO42-(H2O)6 suggest that the C3 isomer remains the most stable one up to 200 K. The AIMD simulations reveal that the IRPD spectra can only be fully understood when anharmonic effects as well as entropy-driven hydrogen bond network fluctuations are considered.

Late-time emission of prompt fission γ rays

The emission of prompt fission $\ensuremath{\gamma}$ rays within a few nanoseconds to a few microseconds following the scission point is studied in the Hauser-Feshbach formalism applied to the deexcitation of primary excited fission fragments. Neutron and $\ensuremath{\gamma}$-ray evaporations from fully accelerated fission fragments are calculated in competition at each stage of the decay, and the role of isomers in the fission products, before $\ensuremath{\beta}$ decay, is analyzed. The time evolution of the average total $\ensuremath{\gamma}$-ray energy, the average total $\ensuremath{\gamma}$-ray multiplicity, and the fragment-specific $\ensuremath{\gamma}$-ray spectra is presented in the case of neutron-induced fission reactions of $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$, as well as spontaneous fission of $^{252}\mathrm{Cf}$. The production of specific isomeric states is calculated and compared to available experimental data. About 7% of all prompt fission $\ensuremath{\gamma}$ rays are predicted to be emitted between 10 ns and 5 $\ensuremath{\mu}\mathrm{s}$ following fission, in the case of $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}\phantom{\rule{4pt}{0ex}}({n}_{\mathrm{th}},f)$ reactions, and up to 3% in the case of $^{252}\mathrm{Cf}$ spontaneous fission. The cumulative average total $\ensuremath{\gamma}$-ray energy increases by 2% to 5% in the same time interval. Finally, those results are shown to be robust against significant changes in the model input parameters.

Gas phase vibrational spectroscopy of the protonated water pentamer: the role of isomers and nuclear quantum effects.

We use cryogenic ion trap vibrational spectroscopy to study the structure of the protonated water pentamer, H+(H2O)5, and its fully deuterated isotopologue, D+(D2O)5, over nearly the complete infrared spectral range (220-4000 cm-1) in combination with harmonic and anharmonic electronic structure calculations as well as RRKM modelling. Isomer-selective IR-IR double-resonance measurements on the H+(H2O)5 isotopologue establish that the spectrum is due to a single constitutional isomer, thus discounting the recent analysis of the band pattern in the context of two isomers based on AIMD simulations 〈W. Kulig and N. Agmon, Phys. Chem. Chem. Phys., 2014, 16, 4933-4941〉. The evolution of the persistent bands in the D+(D2O)5 cluster allows the assignment of the fundamentals in the spectra of both isotopologues, and the simpler pattern displayed by the heavier isotopologue is consistent with the calculated spectrum for the branched, Eigen-based structure originally proposed 〈J.-C. Jiang, et al., J. Am. Chem. Soc., 2000, 122, 1398-1410〉. This pattern persists in the vibrational spectra of H+(H2O)5 in the temperature range from 13 K up to 250 K. The present study also underscores the importance of considering nuclear quantum effects in predicting the kinetic stability of these isomers at low temperatures.

New perspectives in neurosteroid action: open questions for future research.

New perspectives in neurosteroid action: open questions for future research.

Use of Multi-response Modelling to Investigate Mechanisms of β-Carotene Degradation in Dried Orange-Fleshed Sweet Potato During Storage: from Carotenoids to Aroma Compounds

In order to give insight into β-carotene degradation mechanism during the storage of dried orange-fleshed sweet potato, and particularly into the role of isomers and norisoprenoids formation, multi-response kinetic modelling was applied. Determination of degradation compounds were carried out by HPLD-DAD and SPME-GC-MS as a function of time between 10 and 40 °C and at four water activities from 0.13 to 0.76. Kinetic modelling was developed assuming first-order reactions and by using mass balance. Eight compounds, namely, two isomers (9-cis- and 13-cis-β-carotene), two β-carotene epoxides (β-carotene 5,6 and 5,8 epoxide) and four volatile compounds (β-cyclocitral, β-ionone, 5,6-epoxy-β-ionone and dihydroactinidiolide), were integrated into two theoretical reaction schemes. The different models were discriminated according to goodness of fit to experimental data. This work showed that: (1) the formation of cis-isomers from β-carotene preceded oxidation, (2) β-cyclocitral arose directly from β-carotene scission while the other norisoprenoids resulted from β-carotene epoxide degradation, (3) cis-isomers were high reactive compounds. Temperature had a major influence on reaction rates k while water activities only impacted k at values under 0.51. Therefore, multi-response modelling is not only a tool to predict β-carotene degradation but a interesting way to select the appropriate degradation scheme based on the different options presented in literature.

Do the new cluster sources also produce isomers?

The experimental and theoretical effort in the Chemistry Division of the Naval Research Laboratory in the area of clusters is briefly reviewed. We have focused on the effects of structural isomers and “magic number” structures on distributions of cluster sizes and, more recently, on the role of isomers in chemical reactions. The focus of this work is on whether or not the existence of a magic cluster size precludes there being more than one isomer of that size. Various theoretical methods have been used to study the sometimes magic 9-atom alkali-halide cluster ions. It is possible, but not compelling, that isomers of this cluster size are produced in sputtering sources of clusters. Under certain experimental conditions the relative intensity of the 60-carbon-atom ion appears so great as to suggest that no isomer other than the proposed icosahedral structure can be present. The geometry of this unique structure has been optimized using two local density functionals to predict some of its special properties. For the case of the magic C ion, theoretically the two lowest-lying isomers are clearly linear and monocyclic. Experimentally, both forms are observed with cyclic form predominant.