ABSTRACT
Novel biobased films consisting of alginate blends with poly (octanoic acid 2-thiophen-3-yl-ethyl ester) (POTE), a conducting polymer, were prepared by solution casting, and their optical, morphological, thermal, and surface properties were studied. Using UV-visible spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM), the effects of tetrahydrofuran solvent vapors on the optical properties and surface morphology of biobased films with different POTE contents were studied. Results indicate that morphological rearrangements of POTE take place during the process of solvent exposure. Specifically, the solvent vapor induced the formation of POTE small crystalline domains, which allows envisioning the potential of tuning UV-visible absorbance and wettability behavior of biobased films. Finally, theoretical electronic calculations (specifically frontier molecular orbitals analysis) provided consistent evidence on POTE's preferential orientation and selectivity toward the THF-vapor medium.
Subject(s)
Alginates/chemistry , Polymers/chemistry , Solvents , Surface Properties , WettabilityABSTRACT
In quest of a Zintl ion-based Lewis superacids, Al(Ge9L3)3 {L= H, CH3, CHO and CN} compounds have been designed and their properties have been studied within the framework of conceptual density functional theory-based reactivity descriptors. Superacid property has been identified for these complexes as per the fluoride ion affinity (FIA) values. Studies reveal that Al[Ge9(CN)3]3 and Al[Ge9(CH3)3]3 behave like superacids as their FIA exceeds the value of SbF5, which is considered as the strongest Lewis acid. It has been observed that the ligand plays an important role in reactivity as well as in Lewis acidic property.
ABSTRACT
Fourth generation polyamidoamine dendrimer (PAMAM, G4) modified with fluorescein units (F) at the periphery and Pt nanoparticles stabilized by L-ascorbate were prepared. These dendrimers modified with hydrophobic fluorescein were used to achieve self-assembling structures, giving rise to the formation of nanoaggregates in water. The photoactive fluorescein units were mainly used as photosensitizer units in the process of the catalytic photoreduction of water propitiated by light. Complementarily, Pt-ascorbate nanoparticles acted as the active sites to generate H2. Importantly, the study of the functional, optical, surface potential and morphological properties of the photosensitized dendrimer aggregates at different irradiation times allowed for insights to be gained into the behavior of these systems. Thus, the resultant photosensitized PAMAM-fluorescein (G4-F) nanoaggregates (NG) were conveniently applied to light-driven water photoreduction along with sodium L-ascorbate and methyl viologen as the sacrificial reagent and electron relay agent, respectively. Notably, these aggregates exhibited appropriate stability and catalytic activity over time for hydrogen production. Additionally, in order to propose a potential use of these types of systems, the in situ generated H2 was able to reduce a certain amount of methylene blue (MB). Finally, theoretical electronic analyses provided insights into the possible excited states of the fluorescein molecules that could intervene in the global mechanism of H2 generation.
ABSTRACT
A new magnetic superalkali/superhalogen molecule based on the sandwich complex manganocene is reported. The hydrogen atoms of the cyclopentadienyl rings are periodically substituted with electron-donating and electron-withdrawing ligands (or both) to design substituted manganocene complexes. The substituted manganocene complexes exhibit the properties of superalkali and/or superhalogen depending on the nature of the substituents. The substituents, therefore, act as "switches" that can modify the properties of the parent manganocene moiety by keeping its magnetic nature intact. The substituted complexes also show marked nonlinear optical behavior.
ABSTRACT
Molecular dynamics (MD) is currently one of the preferred techniques employed to understand hydrogelation processes for its ability to include large amounts of atoms in computational calculations, since substantial amounts of solvent molecules are involved in gel formation. MD studies have helped to rationalize experimental outcomes that in many occasions were not well understood based on experimental observations. Additionally, MD has been used to study changes in gel physical properties triggered by variations in reaction conditions or gelator structures. Changes in many physical properties were understood using MD, including molecular diffusion, hydrogel swelling and volume transitions. All the examples gathered in this review might help the reader to discover the current state of the art in MD studies carried out to study hydrogelation processes as well as the pioneering studies that paved the way to introduce MD in the field of gels.
Subject(s)
Hydrogels/chemistry , Molecular Dynamics Simulation , HumansABSTRACT
Methyl transfer reactions play an important role in biology and are catalyzed by various enzymes. Here, the influence of the molecular environment on the reaction mechanism was studied using advanced ab initio methods, implicit solvation models and QM/MM molecular dynamics simulations. Various conceptual DFT and electronic structure descriptors identified different processes along the reaction coordinate e.g. electron transfer. The results show that the polarity of the solvent increases the energy required for the electron transfer and that this spontaneous process is located in the transition state region identified by the (mean) reaction force analysis and takes place through the bonds which are broken and formed. The inclusion of entropic contributions and hydrogen bond interactions in QM/MM molecular dynamics simulations with a validated DFTB3 Hamiltonian yields activation barriers in good agreement with the experimental values in contrast to the values obtained using two implicit solvation models.
ABSTRACT
In this study, we present an atomic decomposition, in principle exact, at any point on a given reaction path, of the molecular energy, reaction force and reaction flux, which is based on Bader's atoms-in-molecules theory and on Pendás' interacting quantum atoms scheme. This decomposition enables the assessment of the importance and the contribution of each atom or molecular group to these global properties, and may cast the light on the physical factors governing bond formation or bond breaking. The potential use of this partition is finally illustrated by proton transfers in model biological systems.
ABSTRACT
The mechanism of Menshutkin reaction, NH(3) + CH(3)Cl = [CH(3)-NH(3)]+ + Cl-, has been thoroughly studied in both gas and solvent (H(2)O and cyclohexane) phase. It has been found that solvents favor the reaction, both thermodynamically and kinetically. The electronic activity that drives the mechanism of the reaction was identified, fully characterized, and associated to specific chemical events, bond forming/breaking processes, by means of the reaction electronic flux. This led to a complete picture of the reaction mechanism that was independently confirmed by natural bond-order analysis and the dual descriptor for chemical reactivity and selectivity along the reaction path.
ABSTRACT
In this work, we present a theoretical study of the mechanism of double proton transfer in formamide, formamide-thioformamide and thioformamide dimers. The reaction mechanisms were analyzed in terms of the energy profile and novel concepts such as the reaction force profile and reaction electronic flux, along with local electronic properties such as NBO analysis. All systems were characterized computationally using DFT/B3LYP 6-311G** on Gaussian09. These results show that the electronic processes take place mostly in the transition state for all the systems; in the formamide and thioformamide dimers, electron transfer has a synchronic nature, while the electron transfer is asynchronic in the formamide-thioformamide dimer.
