Search results for "MOLECULE"
showing 10 items of 5162 documents
Conformational investigation of α,β-dehydropeptides. IX. N-Acetyl-(E)-α,β-dehydrobutyrine N′-methylamide: stereoelectronic properties from infrared a…
2009
The Fourier transform infrared spectra of Ac-(E)-deltaAbu-NHMe were analyzed to determine the predominant solution conformation(s) of this (E)-alpha,beta-dehydropeptide-related compound and the electron density perturbation in its amide groups. The measurements were performed in dichloromethane and acetonitrile in the region of mode vs (N-H), amide I, amide II and vs (C(alpha)=Cbeta). The equilibrium geometrical parameters, calculated by a method based on the density functional theory with the B3LYP functional and the 6-31G* basis set, were used to support spectroscopic interpretation and gain some deeper insight into the molecule. The experimental and theoretical data were compared with th…
The transformation of aromatic molecules into the subspace of their double bonds
1975
A model of new submolecules is presented. As an application some absorptions of aromatic radicals are interpreted in UV and visible spectra. Extension of the model to biological systems is prejudged.
Carbohydrate nanocarriers in biomedical applications: functionalization and construction
2015
The specific targeting of either tumor cells or immune cells in vivo by carefully designed and appropriately surface-functionalized nanocarriers may become an effective therapeutic treatment for a variety of diseases. Carbohydrates, which are prominent biomolecules, have shown their outstanding ability in balancing the biocompatibility, stability, biodegradability, and functionality of nanocarriers. The recent applications of sugar (mono/oligosaccharides and/or polysaccharides) for the development of nanomedicines are summarized in this review, including the application of carbohydrates for the surface-functionalization of various nanocarriers and for the construction of the nanocarrier its…
Chemical conjugation of dexamethasone to a polyaspartamide and in vitro evaluation studies
2004
Two macromolecular conjugates of dexamethasone containing different drug amounts were synthesized using PHEA as the polymeric carrier and a succinic group as spacer. The content of linked drug was equal to 25.3% w/w (conjugate A) and 12.7% w/w (conjugate B). Both polymeric conjugates, unlike the free drug, were water-soluble and the amount of unlinked drug was evaluated to be approximately about 0.01% w/w. Both conjugates were relatively stable in vitro at pH 7.4 whereas in the presence of esterase only the conjugate B was able to release drug under the used experimental conditions. This dissimilar behavior has been attributed to the distinct macromolecular conformations assumed in aqueous …
In situ UV-visible spectroelectrochemistry in the course of oxidative monomer electrolysis
2015
Abstract Novel method to characterize the macromolecuar structure of an electroactive polymer deposited via electrooxidation of the corresponding monomer on the electrode surface has been proposed. It is based on experimental determination of the number of electrons spent for oxidation of an initially solute monomer species which is used to calculate the number of covalent bonds linking each monomer unit with neighboring units inside the polymer. The former parameter is found by tracing simultaneously the variations of instantaneous values of the solute monomer concentration and of the passed charge in the course of the monomer oxidation electrolysis. This monomer concentration is establish…
Merging shuttle reactions and paired electrolysis for reversible vicinal dihalogenations
2021
Vicinal dibromides and dichlorides are important commodity chemicals and indispensable synthetic intermediates in modern chemistry that are traditionally synthesized using hazardous elemental chlorine and bromine. Meanwhile, the environmental persistence of halogenated pollutants necessitates improved approaches to accelerate their remediation. Here, we introduce an electrochemically assisted shuttle (e-shuttle) paradigm for the facile and scalable interconversion of alkenes and vicinal dihalides, a class of reactions that can be used both to synthesize useful dihalogenated molecules from simple alkenes and to recycle waste material through retro-dihalogenation. The reaction is demonstrated…
A theoretical study of neutral and reduced tetracyano-p-quinodimethane (TCNQ)
2004
Abstract The molecular structure of neutral, anionic, and dianionic tetracyano- p -quinodimethane (TCNQ), as well as the electron affinity of TCNQ, have been studied with HF, MP2, and different density functional theory (DFT) procedures. The optimized geometries compare well with the available experimental data, although the C N bond distance is not correctly described at the MP2 level. The calculated parameters are rather insensitive to the basis set employed, and the addition of diffuse functions does not yield significant changes. When the extra electrons are added, the central ring of TCNQ progressively becomes more aromatic. Compared with the CCSD(T) estimate, the value of the adiabati…
A new C–C bond formation model based on the quantum chemical topology of electron density
2014
ELF topological analyses of bonding changes in non-polar, polar and ionic organic reactions involving the participation of CC(X) double bonds make it possible to establish a unified model for C–C bond formation. This model is characterised by a C-to-C coupling of two pseudoradical centers generated at the most significant atoms of the reacting molecules. The global electron density transfer process that takes place along polar and ionic reactions favours the creation of these pseudoradical centers at the most nucleophilic/electrophilic centers of the reacting molecules, decreasing activation energies. The proposed reactivity model based on the topological analysis of the changes in electron…
ChemInform Abstract: A New C-C Bond Formation Model Based on the Quantum Chemical Topology of Electron Density
2014
ELF topological analyses of bonding changes in non-polar, polar and ionic organic reactions involving the participation of CC(X) double bonds make it possible to establish a unified model for C–C bond formation. This model is characterised by a C-to-C coupling of two pseudoradical centers generated at the most significant atoms of the reacting molecules. The global electron density transfer process that takes place along polar and ionic reactions favours the creation of these pseudoradical centers at the most nucleophilic/electrophilic centers of the reacting molecules, decreasing activation energies. The proposed reactivity model based on the topological analysis of the changes in electron…
Light induced processes in thin films of indandione type organic molecules
2007
The optically induced switching of material properties is important for investigations of opto-electronic effects and optomechanical properties. Investigated organic materials contain chromophore dipole consisting of acceptor and donor groups bridged by a delocalized p-electron system. Both calculations and experimental data show a reversible highly dipolar photoinduced intra molecular charge transfer in indandione type molecules (DMABI) accompanied by change of the sign and the value of the dipole moment. Investigations of optical properties of thin host-guest polymer films show that the photoinduced process of DMABI is related to the photoinduced switching between two equally stable state…