Self-assembled nanoribbons and nanotubes in water: energetic vs entropic networks

We present a comparative investigation of two opposite classes of self-assembled fibrillar networks. Ribbons and tubes having cross-sectional dimensions in the nanoscale can be formed in aqueous solutions of steroids derived, respectively, from deoxycholic (DC) and lithocholic (LC) acids. Rheological features distinguish energetic networks of DC ribbons rigidly fixed in cylindrical bundles and entropic transient networks of LC tubes weakly interacting in shear-sensitive suspensions. The two classes are characterized by their frequency sweep profiles, viscoelastic linear domains, scaling laws of the elastic shear modulus vs concentration, kinetics of formation of the networks, and their optical birefringence aspects. A theoretical context for networks of rigid fibers is used to account for the scaling exponents α in the G' (and σ ) ∝Cα laws (α =2.0 and 1.0, respectively, for DC and LC). The evolution observed in DC gels from ribbons to cylindrical fibers with monodisperse sections made up with four ribbons is an indication of an equilibrated balance between face-to-face attractions and untwisting elastic processes of the constitutive ribbons

Microfluidic Assisted Self-Assembly of pH-Sensitive Low-Molecular Weight Hydrogelators Close to the Minimum Gelation Concentration

\u3cp\u3eThe fibrillation and subsequent gelation of low molecular hydrogelators is usually triggered by external stimuli. Generally, strong acids are employed to trigger the self-assembly mechanism in pH-responsive supramolecular systems. However, the generation and design of novel stable gels with performing mechanical properties is a challenging task as a result of the uneven self-assembled networks formed. Here, we report the study of the self-assembly process of a low molecular weight hydrogelator (LMWG) in the proximity of its minimum gelation concentration (MGC = 0.3 mg/ml). At such high dilution, the generation of homogeneous gels with good mechanical properties by turning pH by strong acids is a demanding task as a result of the lack of monodisperse 1D self-assembled rod-like aggregates. A microfluidic device is employed here to gradually and homogeneously change the pH. We show that self-assembly of LMWG in well-defined structures can be enhanced by using the diffusive mixing occurring in the microfluidic reactor channel. For very short mixing times, aggregates with 2 nm cross-section are found in the region adjacent to the focused LMWG solution in contact with the low pH buffer solution streams, where the pH reaches values below the pKa of the LMWG and triggers the supramolecular self-assembly. For longer mixing times, aggregates grow in size and occupy homogeneously the micro channel. The results presented here show that better controlled self-assembly can be achieved using microfluidic mixing devices and early stages of self-assembly can be efficiently studied by coupling synchrotron SAXS with microfluidics.\u3c/p\u3

Using chirality to influence supramolecular gelation

Most low molecular weight gelators are chiral, with racemic mixtures often unable to form gels. Here, we show an example where all enantiomers, diastereomers and racemates of a single functionalized dipeptide can form gels. At high pH, different self-assembled aggregates are formed and these directly template the structures formed in the gel. Hence, solutions and gels with different properties can be accessed simply by varying the chirality. This opens up new design rules for the field

Selective and highly efficient dye scavenging by a pH-responsive molecular hydrogelator

A structurally simple low molecular weight hydrogelator derived from isophthalic acid forms robust pH-responsive hydrogels capable of highly efficient and selective dye adsorption

Improvement of molecular gel formation efficiency by adjusting preorganization of amino acid-derived flexible molecules. A NMR and thermodynamic study

The efficiency of the formation of molecular gels of simple de-rivatives of l-valineand l-isoleucine is greatl yimproved in dif-ferent organic solvents when ahexyl fragment is replaced byabulkier cyclohexyl one. Astudy using NMR and IR spectrosco-py provides information on the preferred conformation softhemolecules, indicat ing that the cyclohexyl moiety preclud es in-tramolecular Hbondingand preorganises the system for inter-molecular interactions, which are responsible for fiber forma-tion. NMR data of the gels provides thermod ynamic data on fi-brillization, revealing that the origin of this effect is mainly en-tropic. Electron microscopy (SEM and TEM) images show fibril-lar and tape-like objects, which are observed commonly inmolecular gels. Rheological measurements revealsignificantdifferences between cyclohexyl and hexyl appendedgelators.These findings could contribute to the rational design of small,flexible, buildingblocks forself-assemblyMinistry of Science and Innovat ionofSpain (grantCTQ2012-37735) and UniversitatJaume I(grant P1.1B2012-25) are thankedfor financial support

Mental Health of Adults Treated in Adolescence with Scoliosis-Specific Exercise Program or Observed for Idiopathic Scoliosis

Objective. To examine general mental health in adult males and females, who in adolescence participated in a scoliosis-specific therapeutic exercise program or were under observation due to diagnosis of scoliosis. Design. Registry-based, cross-sectional study with retrospective data collection. Methods. Sixty-eight subjects (43 women) aged 30.10 (25–39) years, with mild or moderate scoliosis (11–36° Cobb angle), and 76 (38 women) nonscoliotic subjects, aged 30.11 (24–38) years, participated. The time period since the end of the exercise or observation regimes was 16.5 (12-26) years. Beck Depression Inventory (BDI) and General Health Questionnaire (GHQ-28) scores were analyzed with the χ2 and U tests. Multiple regression analyses for confounders were also performed. Results. Intergroup differences of demographic characteristics were nonsignificant. Scoliosis, gender, participation in the exercise program, employment, and marital status were associated with BDI scores. The presence of scoliosis and participation in the exercise program manifested association with the symptoms. Higher GHQ-28 “somatic symptoms” subscale scores interacted with the education level. Conclusions. Our findings correspond to the reports of a negative impact of the diagnosis of scoliosis and treatment on mental health. The decision to introduce a therapeutic program in children with mild deformities should be made with judgment of potential benefits, risks, and harm

Gelation properties of self-assembling N-acyl modified cytidine derivatives

In this study we report the synthesis of new cytidine derived gelators possessing acyl chains of different lengths. These low molecular weight gelators were shown to form self-supporting gels at 0.5 % (w/v) in binary systems of aqueous miscible polar organic solvent and water. The representative gels were studied using rheology and their fibrillar structure confirmed by TEM imaging and FTIR. We further demonstrated the use of these gels as potential drug delivery platforms by monitoring release characteristics of both high and low molecular weight fluorescently labelled tracers

In vitro inhibition of aeromonas hydrophila growth by ethanolic extracts obtained from leaves of various ficus species (Moraceae)

рыбы, болезни рыб, инфекционные болезни рыб, аэромоноз, аэромонады, ингибирование роста, питательные среды, этанольные экстракты, фикус, листь