Nitric Oxide Adsorption and Reduction Reaction Mechanism on the Rh₇⁺ Cluster: A Density Functional Theory Study

The transition metal rhodium has been proved the effective catalyst to convert from NOx to N2. In the present work, we are mainly focused on the NO adsorption and decomposition reaction mechanism on the surface of the Rh7+ cluster, and the calculated results suggest that the reaction can proceed via three steps. First, the NO can adsorb on the surface of the Rh7+ cluster; second, the NO decomposes to N and O atoms; finally, the N atom reacts with the second adsorbed NO and reduces to a N2 molecule. The N–O bond breaks to yield N and O atoms in the second step, which is the rate-limiting step of the whole catalytic cycle. This step goes over a relatively high barrier (TS12) of 39.6 kcal/mol and is strongly driven by a large exothermicity of 55.1 kcal/mol during the formation of stable compound 3, accompanied by the N and O atoms dispersed on the different Rh atoms of the Rh7+ cluster. In addition, the last step is very complex due to the different possibilities of reaction mechanism. On the basis of the calculations, in contrast to the reaction path II that generates N2 from two nitrogen atoms coupling, the reaction path I for the formation of intermediate N2O is found to be energetically more favorable. Present work would provide some valuable fundamental insights into the behavior of the nitric oxide adsorption and reduction reaction mechanism on the Rh7+ cluster

Mechanism and Substrate-Dependent Rate-Determining Step in Palladium-Catalyzed Intramolecular Decarboxylative Coupling of Arenecarboxylic Acids with Aryl Bromides: A DFT Study

The mechanism of palladium-catalyzed intramolecular decarboxylative coupling of arenecarboxylic acids with aryl bromides has been studied computationally with the aid of density functional theory. Full free-energy profiles have been computed for all ether- and amine-containing substituted substrates. The calculations indicate that the rate-determining step is indeed substrate dependent, as reflected in free energy profiles; the oxidative addition, decarboxylation, or reductive elimination step can become the rate-determining step for the full catalytic cycle due to the different substituents on the substrates. In addition, we also demonstrate the preference of NCH₃- over NH-containing amine substrates for the decarboxylation process. The calculations are in good agreement with the experimental observations

Explore the Catalytic Reaction Mechanism in the Reduction of NO by CO on the Rh₇⁺ Cluster: A Quantum Chemical Study

Rhodium has been proved to possess unique reactivity to convert NO_<i>x</i> into N₂ with high conversion efficiency and selectivity. In this study, we have carried out DFT calculations on the reaction mechanism in the reduction of NO by CO on the surface of the Rh₇⁺ cluster. The calculated results suggest that the reaction proceeds via three steps. First, the NO and CO are adsorbed on the Rh₇⁺ cluster, then the adsorbed NO decomposes to N and O atoms. The O atom reacts with the adsorbed CO leading to the formation of CO₂ molecule. Second, another NO is adsorbed on the rhodium cluster and decomposes to N and O atoms, then the two N atoms couple with each other to yield N₂ molecule. Finally, the second CO can be adsorbed on the Rh₁ or Rh₇ atom of the Rh₇⁺ cluster and oxidized to CO₂ molecule. On the basis of present calculations from gas-phase Gibbs free energy profiles, the reaction path related to CO adsorption on the Rh₇ atom is energetically more favorable. The second adsorbed NO generating N and O atoms in the second step is the rate-limiting step of whole catalytic cycle. The high activation barrier (TS₆₇) of 56.6 kcal/mol can be driven by large exergonic reaction. Our work would provide some valuable fundamental insights into the reaction mechanism between NO and CO on the rhodium surface, which is vitally important to decrease NO emissions in automotive exhaust gas

Micellization Parameters of Six Gemini Quaternary Ammonium Surfactants from Measurements of Conductivity and Surface Tension

The micellization of six Gemini quaternary ammonium surfactants aqueous solutions has been investigated from measurements on specific conductivity as a function of surfactant concentration at different temperatures from (298.15 to 323.15) K. The micellization parameters such as the critical micellar concentration (CMC) and the degree of counterion dissociation (β), Gibbs free energy (Δ<i>G</i>_mic), enthalpy (Δ<i>H</i>_mic), and entropy (Δ<i>S</i>_mic) of micellization are then obtained. It is shown that the conductometry measurements provide agreement of the CMC values at 298.15 K with the surface tension studies. With the rise of temperature, the values of CMC and β increase, while Δ<i>G</i>_mic changes little. The linear plots of <i>T</i>Δ<i>S</i>_mic versus Δ<i>H</i>_mic show the effects of enthalpy–entropy compensation. The length of alkyl chain and the spacer group of the Gemini surfactant have significant influences on micellization parameters

Antibacterial Activity, <i>in Vitro</i> Cytotoxicity, and Cell Cycle Arrest of Gemini Quaternary Ammonium Surfactants

Twelve gemini quaternary ammonium surfactants have been employed to evaluate the antibacterial activity and <i>in vitro</i> cytotoxicity. The antibacterial effects of the gemini surfactants are performed on <i>Escherichia coli</i> (<i>E. coli</i>) and <i>Staphylococcus aureus</i> (<i>S. aureus</i>) with minimum inhibitory concentrations (MIC) ranging from 2.8 to 167.7 μM. Scanning electron microscopy (SEM) analysis results show that these surfactants interact with the bacterial cell membrane, disrupt the integrity of the membrane, and consequently kill the bacteria. The data recorded on C6 glioma and HEK293 human kidney cell lines using an MTT assay exhibit low half inhibitory concentrations (IC₅₀). The influences of the gemini surfactants on the cell morphology, the cell migration ability, and the cell cycle are observed through hematoxylin-eosin (HE) staining, cell wound healing assay, and flow cytometric analyses, respectively. Both the values of MIC and IC₅₀ decrease against the growth of the alkyl chain length of the gemini surfactants with the same spacer group. In the case of surfactants 12-<i>s</i>-12, the MICs and IC₅₀s are found to decrease slightly with the spacer chain length changing from 2 to 8 and again to increase at higher spacer length (<i>s</i> = 10–12). All of the gemini surfactants show great antibacterial activity and cytotoxicity, and they might exhibit potential applications in medical fields

Mechanisms and Origins of Switchable Regioselectivity of Palladium- and Nickel-Catalyzed Allene Hydrosilylation with N‑Heterocyclic Carbene Ligands: A Theoretical Study

The mechanisms and origins for the Pd- and Ni-catalyzed regioselective hydrosilylation of allene have been investigated by means of density functional theory (DFT) calculations. The free-energy profiles of Pd- and Ni-catalyzed reactions with small and bulky N-heterocyclic carbene (NHC) ligands are calculated to determine the mechanism for regioselectivities. The calculation results show that different metals (Ni vs Pd) lead to regiochemical reversals for the hydrosilylation of allene. The allylsilane is the major product via palladium catalysis with small NHC ligand, while the vinylsilane is the major product via nickel catalysis with bulky NHC ligand. Both electronic and steric factors play a key role in the regioselectivities for the hydrosilylation of allene via Pd and Ni catalysts. The calculation results are in good agreement with observed regioselectivities and could provide insights into the design of new catalysts for the regioselectivity of hydrosilylation reactions

Formation of Novel Aqueous Two-Phase Systems with Piperazinium-Based Ionic Liquids and Anionic Surfactants: Phase Behavior and Microstructure

Two novel aqueous two-phase systems (ATPSs) involving protic piperazinium-based ionic liquids (ILs) and anionic surfactants were found in the 1-ethylpiperazinium tetrafluoroborate ([C₂pi]­[BF₄]) + sodium dodecyl sulfate (SDS) + H₂O system and the 1-phenylpiperazinium tetrafluoroborate ([Phpi]­[BF₄]) + sodium dodecyl benzenesulfonate (SDBS) + H₂O system. The ATPS regions in the ternary phase diagrams were determined, and the compositions and the microstructures of the conjugated phases were analyzed by UV–vis, ¹H NMR, DLS, and cryogenic TEM measurements. The results demonstrate size-enhanced micelles for both ATPSs. The strong electrostatic interactions between the cationic moiety of IL and the anionic surfactant play a very important role in the assembly of the large aggregates, and the cation−π interactions are involved in the [Phpi]­[BF₄] + SDBS + H₂O ATPS. In addition, the small cationic moiety of [C₂pi]­[BF₄] can be packed in the micelles, while the larger hydrophilic cationic moiety of [Phpi]­[BF₄] makes it difficult to get into the micelles, leading to the different size enhancement effects. The driving force of phase separation is the formation and distribution of the large aggregates in the aqueous solutions. This work presents a novel nonaromatic ATPS formed by a piperazinium-based IL and an anionic surfactant, in which considerable size enhancement of aggregates takes place without the assistance of aromaticity in contrast to the other aromatic ATPSs

Densities and Viscosities for the Ternary System of Decalin + Methylcyclohexane + Cyclopentanol and Corresponding Binaries at <i>T</i> = 293.15 to 343.15 K

Densities (ρ) and viscosities (η) for the ternary system of decalin (1) + methylcyclohexane (2) + cyclopentanol (3) and three corresponding binary systems have been measured over the whole composition range at 11 temperature points from 293.15 K to 343.15 K under atmospheric pressure (0.1 MPa). The excess molar volumes (VmE) and viscosity deviations (Δη) of binary systems have been calculated and further fitted with the Redlich–Kister equation, while corresponding physical data of the ternary system have been correlated via the Clibuka, Singh, Nagata-Tamura, and Redlich–Kister equations. The VmE values are negative for the binary system of decalin (1) + methylcyclohexane (2) with a minimum when the moles of the two components are similar. For the system of decalin (1) + cyclopentanol (2), the VmE values are always positive with a maximun at about x1 = 0.6. At the same time, a sigmoid curve can be observed for the system of methylcyclohexane (1) + cyclopentanol (2). The minimum and maximum appear around x1 = 0.2 and x1 = 0.9, respectively. The Δη values of the three binary systems are all negative and the absolute values decrease with increase in temperature. For the ternary system, the VmE values are partially negative and the Δη values are negative over the entire concentration range. The nonideal behaviors of the mixtures are discussed in the perspective of intermolecular interaction and structural effect

Conformational Isomerism Influence on the Properties of Piperazinium Bis(trifluoromethylsulfonyl)imide

Investigation of conformational isomerism of ring compounds can help us get a clear comprehension of the ring structure and reveal significant structure–activity relationship. In this study, conformational isomerism of the cationic moiety of ionic liquid 1-ethyl-1,4-dimethylpiperazinium bis­(trifluoromethylsulfonyl)­imide ([C₂C₁C₁⁴pi]­[NTf₂]) has been investigated by means of ¹H nuclear magnetic resonance spectra. The energy levels for different conformations of the cationic moiety [C₂C₁C₁⁴pi]⁺ are obtained via density functional theory calculations. The predominant cis-conformer in [C₂C₁C₁⁴pi]­[NTf₂] at its liquid state is observed under ambient conditions, where the ethyl group locates at the equatorial position of quaternary nitrogen atom, consistent with the calculated results. The trans-conformer minorities in the IL convert to the cis-conformers when [C₂C₁C₁⁴pi]­[NTf₂] is well crystallized. Besides, the addition of polar solvents, such as ethanol, leads to a convenient and complete transformation from the trans-form to the recognizable cis-form. The phase-transition behaviors have been measured by means of differential scanning microcalorimetry (DSC), and the DSC results can be highly affected by the initial state of the IL. Density and viscosity measurements for mixtures of [C₂C₁C₁⁴pi]­[NTf₂] with ethanol or 1-propanol at different temperatures <i>T</i> = (293.15 to 323.15) K are performed. Conformational isomerism affects the excess molar volumes of [C₂C₁C₁⁴pi]­[NTf₂] + alcohol systems more significantly than the viscometric property. The behaviors, as comparison, for the mixtures of 1-<i>n</i>-pentyl-1,4-dimethyl-piperazinium bis­(trifluoromethylsulfonyl)­imide ([C₅C₁C₁⁴pi]­[NTf₂]) with ethanol are observed with the same phenomena as the common binary systems. On the basis of the experimental and calculated results of the ILs, it can be concluded that conformational isomerism in the cation of [C₂C₁C₁⁴pi]­[NTf₂] is quite significant, and it should be taken into account when sensitive properties are evaluated

Derivative of Epigallocatechin-3-gallatea Encapsulated in ZIF8 with Polyethylene GlycolFolic Acid Modification for Target and pH-Responsive Drug Release in Anticancer Research

Epigallocatechin-3-gallatea (EGCG), a key component of tea, has been found to have anticancer activity but poor stability. To improve its antioxidative stability and widen the application of EGCG in anticancer therapy, a kind of EGCG derivative, EGCG palmitate (PEGCG), was synthesized and encapsulated in ZIF-8 nanoparticles with functionalization of folic acid (FA), which is commonly used as pH-responsive drug carrier. PEGCG encapsulated in polyethylene glycol (PEG)–FA/ZIF-8 nanoparticles (PEG–FA/PEGCG@ZIF-8 NPs) exhibits sixfold improvement of stability compared to that of free PEGCG. With target recognition between folic acid (FA) on the surface of NPs and overexpressed FA receptor (FR) in cancer cells, the NPs can be efficiently internalized into cells and present targeted effects of inhibition growth on HeLa cells (cancer cells) compared with HEK 293 cells (normal cells), consistent with the regulation of reactive oxygen species (ROS) level and the induction of autophagy. The detection of autophagy flux and the measurement of autophagy marked proteins in cells suggest that autophagy flux and the autophagosome formation are appreciably induced when the cells were treated with PEG–FA/PEGCG@ZIF-8 NPs. It indicates that pH-responsive PEG–FA/PEGCG@ZIF-8 NPs with target identification for cancer cells can be used as highly efficient drug carriers in targeting cancer chemotherapy