Convenient Estimation for Counterion Dissociation of Cationic Micelles Using Chloride-Sensitive Fluorescence Probe

Chloride-sensitive fluorescence probe provides a new approach to studying the degree of micellar counterion dissociation (α). The fluorescence of N-ethoxycarbonylmethyl-6-methoxyquinolinium bromide (MQAE) is quenched by chloride ion with linear Stern–Volmer plots. Thus the fluorescence intensity can be used to monitor the concentration of free chloride ion in micellar solutions. The Stern–Volmer plot gave a distinct break at critical micelle concentration (CMC) due to the counterion binding to micelles. The estimated α and CMCs of cationic surfactants including fluorocarbon ones were in fair agreement with the reported experimental values. The MQAE has greater sensitivity to bromide ion of CTAB than chloride ion of CTAC. The α of 0.16 for CTAB micelles was almost constant up to 0.2 M CTAB at 35°C. The α values of CTAB micelles decreased with increasing the concentrations of CTAB and NaBr along with micellar growth

Bio-mimetic Control of An Externally powered Prosthetic Forearm Based on EMG Signals

The EMG signals which include information on not only mascle force but operator's intended motion and mechanical impedance property of joints have been often used as control signals of prosthetic arms. Most of previous researches, however, adopted only the ON/OFF control of the prosthetic arms depending on the results of the EMG pattern discrimination, or controlled only a particular joint depending on the torque estimated from the EMG signals. In this paper, we propose a multi-joint control method of a prosthetic forearm using the EMG signals. In order to realize the natural feeling of control similar to that of the human movements, the impedance model of human forearm is introduced to the control system. Also the force level during the motion is estimated from the EMG signals and used as the control command to each joint. It is shown from the experiments that the forearm motions and force levels can be estimated by using the EMG signals, and the prosthetic forearm can be controlled based on the impedance model smoothly

Krafft temperature and enthalpy of solution of N-acyl amino acid surfactants and their racemic modifications: Effect of the counter ion

金沢大学工学部The Krafft temperatures and enthalpies of solution of N-hexadecanoyl alaninate and valinate, and N-tetradecanoyl phenylalaninate were obtained from differential scanning calorimetry. The Krafft temperature of N-acyl amino acid surfactant increased with decreasing size of the counter ion, with some exceptions. The enthalpy of solution was endothermic and increased with decreasing size of the counter ion except for the cases of lithium salt. The results showed that the L-L interaction in the solid state of N-hexadecanoyl amino acid surfactant salt was superior to the D-L interaction for both the alanine and valine systems when the counter ion size increased. However, the D-L interaction was still advantageous for the phenylalanine system with Cs+ as a counter ion. Both Fourier transform infrared spectroscopy studies and theoretical calculations suggested that the difference in magnitudes of the interactions between peptide and counter ion was a dominant factor for the chiral effect

Catalysis of Cu Cluster for NO Reduction by CO: Theoretical Insight into the Reaction Mechanism

Density functional theory calculations here elucidated that Cu₃₈-catalyzed NO reduction by CO occurred not through NO dissociative adsorption but through NO dimerization. NO is adsorbed to two Cu atoms in a bridging manner. NO adsorption energy is much larger than that of CO. N–O bond cleavage of the adsorbed NO molecule needs a very large activation energy (Δ<i>G</i>°^‡). On the other hand, dimerization of two NO molecules occurs on the Cu₃₈ surface with small Δ<i>G</i>°^‡ and very negative Gibbs reaction energy (Δ<i>G</i>°) to form ONNO species adsorbed to Cu₃₈. Then, a CO molecule is adsorbed at the neighboring position to the ONNO species and reacts with the ONNO to induce N–O bond cleavage with small Δ<i>G</i>°^‡ and very negative Δ<i>G</i>°, leading to the formation of N₂O adsorbed on Cu₃₈ and CO₂ molecule in the gas phase. N₂O dissociates from Cu₃₈, and then it is readsorbed to Cu₃₈ in the most stable adsorption structure. N–O bond cleavage of N₂O easily occurs with small Δ<i>G</i>°^‡ and significantly negative Δ<i>G</i>° to form the N₂ molecule and the O atom adsorbed on Cu₃₈. The O atom reacts with the CO molecule to afford CO₂ and regenerate Cu₃₈, which is rate-determining. N₂O species was experimentally observed in Cu/γ-Al₂O₃-catalyzed NO reduction by CO, which is consistent with this reaction mechanism. This mechanism differs from that proposed for the Rh catalyst, which occurs via N–O bond cleavage of the NO molecule. Electronic processes in the NO dimerization and the CO oxidation with the O atom adsorbed to Cu₃₈ are discussed in terms of the charge-transfer interaction with Cu₃₈ and Frontier orbital energy of Cu₃₈

Structural Expansion of Catalytic RNA Nanostructures through Oligomerization of a Cyclic Trimer of Engineered Ribozymes

The multimolecular assembly of three-dimensionally structured proteins forms their quaternary structures, some of which have high geometric symmetry. The size and complexity of protein quaternary structures often increase in a hierarchical manner, with simpler, smaller structures serving as units for larger quaternary structures. In this study, we exploited oligomerization of a ribozyme cyclic trimer to achieve larger ribozyme-based RNA assembly. By installing kissing loop (KL) interacting units to one-, two-, or three-unit RNA molecules in the ribozyme trimer, we constructed dimers, open-chain oligomers, and branched oligomers of ribozyme trimer units. One type of open-chain oligomer preferentially formed a closed tetramer containing 12 component RNAs to provide 12 ribozyme units. We also observed large assembly of ribozyme trimers, which reached 1000 nm in size

Fluorosilane Activation by Pd/Ni→Si–F→Lewis Acid Interaction: An Entry to Catalytic Sila-Negishi Coupling

International audienceA new mode of bond activation involving M→Z interactions is disclosed. Coordination to transition metals as σ-acceptor ligands was found to enable the activation of fluorosilanes, opening the way to the first transition-metal-catalyzed Si-F bond activation. Using phosphines as directing groups, sila-Negishi couplings were developed by combining Pd and Ni complexes with external Lewis acids such as MgBr2. Several key catalytic intermediates have been authenticated spectroscopically and crystallographically. Combined with DFT calculations, all data support cooperative activation of the fluorosilane via Pd/Ni→Si-F→Lewis acid interaction with conversion of the Z-type fluorosilane ligand into an X-type silyl moiety