Control over size, shape, and photonics of self-assembled organic nanocrystals.

The facile fabrication of free-floating organic nanocrystals (ONCs) was achieved via the kinetically controlled self-assembly of simple perylene diimide building blocks in aqueous medium. The ONCs have a thin rectangular shape, with an aspect ratio that is controlled by the content of the organic cosolvent (THF). The nanocrystals were characterized in solution by cryogenic transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering. The ONCs retain their structure upon drying, as was evidenced by TEM and atom force microscopy. Photophysical studies, including femtosecond transient absorption spectroscopy, revealed a distinct influence of the ONC morphology on their photonic properties (excitation energy transfer was observed only in the high-aspect ONCs). Convenient control over the structure and function of organic nanocrystals can enhance their utility in new and developed technologies.

Duration of first vaginal birth following cesarean: Is stage of labor at previous cesarean a factor?

OBJECTIVE: Parturients in second delivery undergoing vaginal birth after cesarean (VBAC) are divided to those who had their cesarean delivery (CD) while in labor as opposed to those who had an elective CD. We aimed to study if the stage of labor that was present during the primary CD is associated with the duration of subsequent spontaneous VBAC. METHODS: A retrospective study (2006-2014). Multiparas in second delivery with a history of a CD (P2-VBAC) were sub-grouped based on stage of labor at which the CD was performed in the first delivery; elective, latent, first or second stage of labor, Duration of labor was compared between P2-VBAC (as one group and further as the sub-groups) to primiparas (P1), multiparas in second (P2) and third (P3) vaginal delivery (VD). A Cox regression analysis was performed including maternal age, preterm-delivery, regional anesthesia, oxytocin augmentation, birthweight and neonatal gender. RESULTS: A total of 58,028 parturients were included in the study. Mean duration of labor was significantly longer in parturients with a first VD (P1 and P2-VBAC) compared to repeat VD (P2 and P3), 6.0 versus 2.5 h, respectively, (P < 0.001). Analyzing duration of labor by the sub-groups of P2-VBAC revealed that spontaneous VD following a second-stage CD was associated with shorter duration of labor when compared with spontaneous VD following elective, latent and active first stage CD 4.2 versus 6.3, 7.0, 6.9 h respectively, p<0.001. CONCLUSION: Second stage CD shortens duration of the following VBAC compared to those who underwent cesarean in earlier stages of labor.

Precrystalline Aggregates Enable Control over Organic Crystallization in Solution.

Understanding and controlling organic crystallization in solution is a long-standing challenge. Herein, we show that crystallization of an aromatic amphiphile based on perylene diimide in aqueous media involves initially formed amorphous spherical aggregates that evolve into the crystalline phase. The initial appearance of the crystalline order is always confined to the spherical aggregates that are precursors for crystalline evolution. The change in the solvation of the prenucleation phase drives the crystallization process towards crystals that exhibit very different structure and photofunction. The initial molecular structure and subsequent crystal evolution can be regulated by tuning the hydrophobicity at various stages of crystallization, affording dissimilar crystalline products or hindering crystallization. Thus, the key role of the precrystalline states in organic crystal evolution enables a new strategy to control crystallization by precrystalline state manipulation.

Self-assembly of light-harvesting crystalline nanosheets in aqueous media.

A methodology leading to facile self-assembly of crystalline aromatic arrays in dilute aqueous solutions would enable efficient fabrication and processing of organic photonic and electronic materials in water. In particular, soluble 2D crystalline nanosheets may mimic the properties of photoactive thin films and self-assembled monolayers, covering large areas with ordered nanometer-thick material. We designed such solution-phase arrays using hierarchical self-assembly of amphiphilic perylene diimides in aqueous media. The assemblies were characterized by cryogenic transmission electron microscopy (cryo-TEM), revealing crystalline order and 2D morphology (confirmed by AFM studies). The order and morphology are preserved upon drying as evidenced by TEM and AFM. The 2D crystalline-like structures exhibit broadening and red-shifted absorption bands in UV-vis spectra, typical for PDI crystals and liquid crystals. Photophysical studies including femtosecond transient absorption spectroscopy reveal that two of the assemblies are superior light-harvesters due to excellent solar spectrum coverage and fast exciton transfer, in one case showing exciton diffusion comparable to solid-state crystalline systems based on perylene tetracarboxylic dianhidride (PTCDA).

Hollow V(2)O(5) nanoparticles (fullerene-like analogues) prepared by laser ablation.

Nanoparticles of materials with layered structure are able to spontaneously form closed-cage nanostructures such as nested fullerene-like nanoparticles and nanotubes. This propensity has been demonstrated in a large number of compounds such as WS(2), NiCl(2), and others. Layered metal oxides possess a higher ionic character and consequently are stiffer and cannot be evenly folded. Vanadium pentoxide (V(2)O(5)), a layered metal oxide, has received much attention due to its attractive qualities in numerous applications such as catalysis and electronic and optical devices and as an electrode material for lithium rechargeable batteries. The synthesis by pulsed laser ablation (PLA) of V(2)O(5) hollow nanoparticles, which are closely (nearly) associated with inorganic "fullerene-like" (NIF-V(2)O(5)) nanoparticles, but not quite as perfect, is reported in the present work. The relation between the PLA conditions and the NIF-V(2)O(5) morphology is elucidated. A new mechanism leading to hollow nanostructure via crystallization of lower density amorphous nanoparticles is proposed. Transmission electron microscopy (TEM) is used extensively in conjunction with structural modeling of the NIF-V(2)O(5) in order to study the complex 3-D structure of the NIF-V(2)O(5) nanoparticles. This structure was shown to be composed of facets with their low-energy surfaces pointing outward and seamed by defective domains. These understandings are used to formulate a formation mechanism and may improve the function of V(2)O(5) in its many uses through additional morphological control. Furthermore, this study outlines which properties are required from layered compounds to fold into perfectly closed-cage IF nanoparticles.

Surface functionalization of WS2 fullerene-like nanoparticles.

WS(2) belongs to a family of layered metal dichalcogenide compounds that are known to form cylindrical (inorganic nanotubes-INT) and polyhedral nanostructures--onion or nested fullerene-like (IF) particles. The outermost layers of these IF nanoparticles can be peeled under shear stress, thus IF nanoparticles have been studied for their use as solid lubricants. However, the IF nanoparticles tend to agglomerate, presumably because of surface structural defects induced by elastic strain and curvature, a fact that has a deleterious effect on their tribological properties. In the present work, chemical modification of the IF-WS(2) surface with alkyl-silane molecules is reported. The surface-modified IF nanoparticles display improved dispersion in oil-based suspensions. The alkyl-silane coating reduces the IF-WS(2) nanoparticles' tendency to agglomerate and consequently improves the long-term tribological behavior of oil formulated with the IF additive.

Inhibition of pectin methyl esterase activity by green tea catechins.

Pectin methyl esterases (PMEs) and their endogenous inhibitors are involved in the regulation of many processes in plant physiology, ranging from tissue growth and fruit ripening to parasitic plant haustorial formation and host invasion. Thus, control of PME activity is critical for enhancing our understanding of plant physiological processes and regulation. Here, we report on the identification of epigallocatechin gallate (EGCG), a green tea component, as a natural inhibitor for pectin methyl esterases. In a gel assay for PME activity, EGCG blocked esterase activity of pure PME as well as PME extracts from citrus and from parasitic plants. Fluorometric tests were used to determine the IC50 for a synthetic substrate. Molecular docking analysis of PME and EGCG suggests close interaction of EGCG with the catalytic cleft of PME. Inhibition of PME by the green tea compound, EGCG, provides the means to study the diverse roles of PMEs in cell wall metabolism and plant development. In addition, this study introduces the use of EGCG as natural product to be used in the food industry and agriculture.