Disinfectant-Assisted Preparation of Hierarchical ZSM-5 Zeolite with Excellent Catalytic Stabilities in Propane Aromatization.

A series of quaternary ammonium or phosphonium salts were applied as zeolite growth modifiers in the synthesis of hierarchical ZSM-5 zeolite. The results showed that the use of methyltriphenylphosphonium bromide (MTBBP) could yield nano-sized hierarchical ZSM-5 zeolite with a "rice crust" morphology feature, which demonstrates a better catalytic performance than other disinfect candidates. It was confirmed that the addition of MTBBP did not cause discernable adverse effects on the microstructures or acidities of ZSM-5, but it led to the creation of abundant meso- to marco- pores as a result of aligned tiny particle aggregations. Moreover, the generation of the special morphology was believed to be a result of the coordination and competition between MTBBP and Na+ cations. The as-synthesized hierarchical zeolite was loaded with Zn and utilized in the propane aromatization reaction, which displayed a prolonged lifetime (1430 min vs. 290 min compared with conventional ZSM-5) and an enhanced total turnover number that is four folds of the traditional one, owing to the attenuated hydride transfer reaction and slow coking rate. This work provides a new method to alter the morphological properties of zeolites with low-cost disinfectants, which is of great potential for industrial applications.

Energy minimization segmentation model based on MRI images.

Introduction: Medical image segmentation is an important tool for doctors to accurately analyze the volume of brain tissue and lesions, which is important for the correct diagnosis of brain diseases. However, manual image segmentation methods are time-consuming, subjective and lack of repeatability, it needs to develop automatic and reliable methods for image segmentation. Methods: Magnetic Resonance Imaging (MRI), a non-invasive imaging technique, is commonly used to detect, characterize and quantify tissues and lesions in the brain. Partial volume effect, gray scale in homogeneity, and lesions presents a great challenge for automatic medical image segmentation methods. So, the paper is dedicated to address the impact of partial volume effect and multiple sclerosis lesions on the segmentation accuracy in MRI. The objective function of the improved model and the post-processing method of lesion filling are researched based on the fuzzy clustering space and energy model. Results: In particular, an energy-minimized segmentation algorithm is proposed. Through experimental verification, the AR-FCM algorithm can better overcome the problem of low segmentation accuracy of the RFCM algorithm for tissue boundary voxels and improve the segmentation accuracy of this algorithm. Meanwhile, a multi-channel input energy-minimization segmentation method with lesion filling and anatomical mapping is further proposed. Discussion: The feasibility of the lesion filling strategy using post-processing can be confirmed and the segmentation accuracy is increased by comparison experiments.

Fibrillar seeds alleviate amyloid-ß cytotoxicity by omitting formation of higher-molecular-weight oligomers.

Amyloid-ß (Aß) peptides can exist in distinct forms including monomers, oligomers and fibrils, consisting of increased numbers of monomeric units. Among these, Aß oligomers are implicated as the primary toxic species as pointed by multiple lines of evidence. It has been suggested that toxicity could be rendered by the soluble higher-molecular-weight (high-n) Aß oligomers. Yet, the most culpable form in the pathogenesis of Alzheimer's disease (AD) remains elusive. Moreover, the potential interaction among the insoluble fibrils that have been excluded from the responsible aggregates in AD development, Aß monomers and high-n oligomers is undetermined. Here, we report that insoluble Aß fibrillar seeds can interact with Aß monomers at the stoichiometry of 1:2 (namely, each Aß molecule of seed can bind to two Aß monomers at a time) facilitating the fibrillization by omitting the otherwise mandatory formation of the toxic high-n oligomers during the fibril maturation. As a result, the addition of exogenous Aß fibrillar seeds is seen to rescue neuronal cells from Aß cytotoxicity presumably exerted by high-n oligomers, suggesting an unexpected protective role of Aß fibrillar seeds.

Selective recognition induced nanostructures in a cucurbit[7]uril-based host-guest system: micelles, nanorods and nanosheets.

The selective recognition between CB[7] and hexadecyl dimethyl benzyl ammonium chloride (HDBAC) was investigated using ITC and NMR. The long alkyl-bearing surfactant can form micelles when dispersed in water. We found that progressive addition of CB[7] into the HDBAC dispersion induced the transformation of micelles into various self-organized structures including nanorods and nanosheets as evidenced by DLS, TEM, AFM and SAXS. A rational mechanism is proposed to illustrate the host-guest interaction induced transformation process.

Stepwise ordering of imidazolium-based cationic surfactants during cooling-induced crystallization.

Surfactants bearing imidazolium cations represent a new class of building blocks in molecular self-assembly. These imidazolium-based cationic surfactants can exhibit various morphologies during phase transformations. In this work, we studied the self-assembly and phase behavior of 1-hexadecyl-3-methylimidazolium chloride (C(16)mimCl) aqueous dispersions (0.5-10 wt %) by using isothermal titration calorimetry, differential scanning calorimetry, synchrotron small- and wide-angle X-ray scattering, freeze-fracture electron microscopy, optical microscopy, electrical conductance, and Fourier transform infrared spectroscopy. It was found that C(16)mimCl in aqueous solutions can form two different crystalline phases. At higher C(16)mimCl concentrations (>6 wt %), the initial spherical micelles convert directly to the stable crystalline phase upon cooling. At lower concentrations (0.5 or 1 wt %), the micelles first convert to a metastable crystalline phase upon cooling and then transform to the stable crystalline phase upon further incubation at low temperature. The electrical conductance measurement reveals that the two crystalline phases have similar surface charge densities and surface curvatures. Besides, the microscopic and spectroscopic investigations of the two crystalline phases suggest that the metastable crystalline phase has preassembled morphology and a preordered submolecular packing state that contribute to the final stable crystalline structure. The formation of a preordered structure prior to the final crystalline state deepens our understanding of the crystallization mechanisms of common surfactants and amphiphilic ionic liquids and should thus be widely recognized and explored.

Comparative studies on the crystalline to fluid phase transitions of two equimolar cationic/anionic surfactant mixtures containing dodecylsulfonate and dodecylsulfate.

In this work, a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), and an anionic surfactant, sodium dodecylsulfonate (SDSO(3)) or sodium dodecylsulfate (SDSO(4)), were mixed in an equimolar ratio to prepare SDSO(3)-DTAB and SDSO(4)-DTAB binary mixtures. The phase behavior, structure, and morphology of these two surfactant mixtures were investigated by differential scanning calorimetry, synchrotron X-ray scattering, freeze-fracture electron microscopy, and Fourier transform infrared spectroscopy. It was found that upon heating, both of the two systems transform from multilamellar crystalline phase to liquid crystalline (or fluid) phase. It is interesting to find that, although SDSO(3) has a lower molecular weight, the crystalline phase of SDSO(3)-DTAB shows much higher thermostability as compared with that of SDSO(4)-DTAB. Other than this, we observed a large difference in the repeat distances of the two crystalline phases. More interestingly, at 60 °C in the fluid phases, cylindrical micelles formed in the SDSO(3)-DTAB system, while spherical micelles were observed in the SDSO(4)-DTAB system. Our present work demonstrates that a subtle difference in the headgroup structure of the anionic component markedly affects the thermostability, packing structure, and morphology of the surfactant mixtures, which suggests the importance of the match of the head-head and tail-tail interactions between the cationic and anionic surfactants.

Denaturation behaviors of two-state and non-two-state proteins examined by an interruption-incubation protocol.

We established an interruption-incubation protocol to study the denaturation and aggregation behaviors of two-state and non-two-state proteins, represented by hen egg-white lysozyme (lysozyme) and bovine serum albumin (BSA), by differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy. After incubation at selected interrupting temperatures (T(int)), the onset temperature (T(onset)) and denaturation temperature (T(d)) of the reheating scans were found to pose distinct contrasts between the two proteins. BSA shows increasing T(onset) and T(d) as T(int) increases, whereas lysozyme exhibits invariable T(onset) and T(d). After long-time incubation, the reheating scans of BSA still show residual peaks in the DSC curves. Moderate aggregation upon incubation restricts the refolding of the thermodynamically stable unfolding intermediates in the denaturation of BSA. On the contrary, prolonged incubation at selected T(int) causes complete denaturation of lysozyme. The results were also supported by FTIR experiments. It is concluded that the variable T(onset) and T(d) indicate the unfolding of the "trapped" intermediates in the second heating scans, and the invariable T(onset) and T(d) values indicate the nonexistence of such intermediates. The examination of two additional proteins, ribonuclease A and γ-globulin, shows a similar phenomenon. The results may represent the general features of two-state and non-two-state denaturations and the protocol would serve to study protein denaturation cooperativity.

Mechanism of the fast exchange between bound and free guests in cucurbit[7]uril-guest systems.

The fast exchange is found to be due to the mismatch between the hydrophobic interaction inside the CB[7] cavity and the ion-dipole/hydrogen-bonding interactions in the port region of the CB[7]. This mismatch also induces the multi-step separation process between guest and CB[7] molecules, as elucidated by molecular dynamics simulation.

Interaction of synthetic HPV-16 capsid peptides with heparin: thermodynamic parameters and binding mechanism.

Capsid proteins binding cell surface proteoglycans is a key early event in human papillomavirus (HPV) infection. The positively charged sequences at the C-terminus of the L1 protein and the N- and C-termini of the L2 protein of HPV-16 can efficiently bind to heparin receptors, which were characterized in the present study by quantitative isothermal titration calorimetry experiments primarily, fluorescence spectroscopy, and static right-angle light scattering. The binding constant, K, was at an order of magnitude of 10(7) M(-1) for the two peptides at the N- and C-termini of HPV-16 L2 and segment b at the C-terminus of HPV-16 L1, while that for other L1 analogues were of a smaller order, illustrating that the heparin binding is a typical sequence-specific and -dependent phenomenon. These results suggest that, in addition to L1, the L2 protein may participate in cell surface attachment during HPV infection. Furthermore, the calorimetry results demonstrated that hydrophobic interactions and hydrogen bonding are involved in peptide binding to heparin in addition to the essential electrostatic interactions. Meanwhile, circular dichroism spectroscopy revealed that binding to heparin does not induce obvious secondary structural changes in the peptides.

Nonsynchronicity phenomenon observed during the lamellar-micellar phase transitions of 1-stearoyllysophosphatidylcholine dispersed in water.

Knowledge on the synchronicity or cooperativity of changes in different parts of the amphiphilic molecules is important to understand the molecular mechanisms of phase transformations of self-assembled aggregates. A long-standing and challenging question is to understand the roles individual groups/portions in an amphiphilic molecule play during phase transitions. To address this question, we selected a lysophospholipid, 1-stearoyllysophosphatidylcholine (SLPC), to study the transition mechanisms between its lamellar phase and micellar phase by using differential scanning calorimetry, small-angle X-ray scattering, Fourier transform infrared spectroscopy, and two-dimensional correlation analysis. It was found that during the lamellar to micellar transition the interfacial C=O groups and the lipid acyl tails change evidently with the former changing a little earlier, but the lipid headgroups remain unchanged in the hydration and conformation state. This means that the head, interface, and tail of SLPC molecules change nonsynchronously. Moreover, the results show that the lamellar to micellar transition is initiated by the interfacial groups. The molecular mechanism of the slow formation kinetics of the lamellar state from the micellar state was also discussed in the context of the nonsynchronicity phenomenon. The markedly different behaviors of the head and interface/tail groups during phase transitions are explained as the retention of the intermolecular attractive forces between the neighboring polar headgroups of the amphiphiles.