The superstructure of carbosilane dendrimers with perfluorinated end groups in bulk and in solution

Carbosilane dendrimers of generation 1 to 4 are functionalized with perfluorinated (-C₆F₁₃) end groups. Extending the spacer between the central Si and the first layer of branching points allows the synthesis of the 4^th generation. The superstructure of these systems in bulk observed with X-ray scattering is the result of the microphase separation between the carbosilane scaffold and the end groups. It varies with generation from a layered to a columnar structure. In dilute solution only the second generation dendrimer shows a tendency for aggregation. The others form compact particles consisting of single molecules with a core shell structure.     

Design and Synthesis of Arylpiperazine Serotonergic/Dopaminergic Ligands with Neuroprotective Properties

Long-chain arylpiperazine scaffold is a versatile template to design central nervous system (CNS) drugs that target serotonin and dopamine receptors. Here we describe the synthesis and biological evaluation of ten new arylpiperazine derivatives designed to obtain an affinity profile at serotonin 5-HT_1A, 5-HT_2A, 5-HT₇ receptor, and dopamine D₂ receptor of prospective drugs to treat the core symptoms of autism spectrum disorder (ASD) or psychosis. Besides the structural features required for affinity at the target receptors, the new compounds incorporated structural fragments with antioxidant properties to counteract oxidative stress connected with ASD and psychosis. All the new compounds showed CNS MultiParameter Optimization score predictive of desirable ADMET properties and cross the blood–brain barrier. We identified compound 12a that combines an affinity profile compatible with antipsychotic activity (5-HT_1A K_i = 41.5 nM, 5-HT_2A K_i = 315 nM, 5-HT₇ K_i = 42.5 nM, D₂ K_i = 300 nM), and compound 9b that has an affinity profile consistent with studies in the context of ASD (5-HT_1A K_i = 23.9 nM, 5-HT_2A K_i = 39.4 nM, 5-HT₇ K_i = 45.0 nM). Both compounds also had antioxidant properties. All compounds showed low in vitro metabolic stability, the only exception being compound 9b, which might be suitable for studies in vivo.     

Bacillus cereus Toxin Repertoire: Diversity of (Iso)cereulide(s)

The emetic Bacillus cereus toxin cereulide (1) poses a significant safety risk in the food industry, causing emesis and nausea after consumption of contaminated foods. Analogously to cereulide, the structures of various isocereulides, namely, isocereulides A–G, have been recently reported and could also be identified in B. cereus-contaminated food samples. The HPLC fractionation of B. cereus extracts allows us to isolate additional isocereulides. By applying MSⁿ sequencing, post-hydrolytic dipeptide, amino acid and α-hydroxy acid analyses using UPLC-ESI-TOF-MS to purify the analytes, seven new isocereulides H–N (2–8) could be elucidated in their chemical structures. The structure elucidation was supported by one-dimensional and two-dimensional NMR spectra of the isocereulides H (2), K (5), L and N (6 + 8) and M (7). The toxicity of 2–8 was investigated in a HEp-2 cell assay to determine their respective 50% effective concentration (EC₅₀). Thus, 2–8 exhibited EC₅₀ values ranging from a 0.4- to 1.4-fold value compared to cereulide (1). Missing structure-activity correlations indicate the necessity to determine the toxic potential of all naturally present isocereulides as single compounds to be able to perform a thorough toxicity evaluation of B. cereus-contaminated foods in the future.     

Quantification of Porous Properties of Shear Crystallized Lipids

The aim of this study was to investigate the impact that shear and composition have on the structural properties associated with the porous phases of lipids. To accomplish this aim, we developed eight main crystallized samples using cocoa butter (CB) or trilaurin (TL) in the presence or absence of monostearate (M) (5% w/w). The samples were sheared at 500 s⁻¹ using random (RS) or laminar (LS) shear at a cooling rate of 2 °C/min. Using the maximal ball (MB) algorithm, several empirical void measurements such as connectivity (z), pore and throat volume weighted radii (R₄₃), and void fraction (v) were quantified using 3D X-ray microcomputed tomography images. Most void features were identified as micropores (R ≥ 10 μm) possibly originating from the crystallization process and post-process crystal growth. Likewise, depending on the applied treatments, mechanisms impacting void formation were found to produce noticeable variation in v (0.019 to 0.139) and to determine whether void morphology was spherical, irregular, and/or highly connected.     

Long-distance rotational echo double resonance measurements for the determination of secondary structure and conformational heterogeneity in peptides.

The utility of rotational echo double resonance (REDOR) NMR spectroscopy for determining the conformations of linear peptides has been examined critically using a series of crystalline and amorphous samples. The focus of the present work was the evaluation of long-distance (> 5 A) interactions using 13C-15N dephasing. Detailed studies of specifically labeled melanostatin and synthetic analogs of the alpha-factor yeast mating hormone show that nitrogen-dephased, carbon-observe REDOR measurements are reliable for distances up to 6.0 A, and that dipolar interactions can be detected for distances up to 7 A. By contrast, nitrogen-observe REDOR gives reliable results only for distances shorter than 5.0 A. To measure distances accurately, REDOR data must be corrected for the effects of natural-abundance spins. These corrections are particularly important for measuring long distances, which are of the greatest value for determining peptide secondary structure. We have developed a spherical shell model for calculating the effect of these background spins. The REDOR studies also indicate that in a lyophilized powder, the tridecapeptide alpha-factor mating pheromone from Saccharomyces cerevisiae (WHWLQLKPGQPMY) probably exists as a distribution of different turn structures around the KPGQ region. This finding revises previous solid-state NMR studies on this peptide, which concluded alpha-factor assumes a distorted type-I beta-turn in the Pro-Gly central region of the molecule [J.R. Garbow, M. Breslav, O. Antohi, F. Naider, Biochemistry, 33 (1994) 10094].     

The use of densimetry and fixed-cell scanning calorimetry to probe solute and solution structure and reactions from 270 K to 400 K

We have used a vibrating-tube densimeter to investigate the densities and volumetric properties of aqueous solutions, and a fixed-cell scanning calorimeter to measure aqueous solution heat capacities. Solutions investigated include sugars, neutral weak acids and bases, neutralized acids and bases, neutral and protonated amino acids, surfactants, and both strong and ion-paired electrolytes. We have made measurements at molalities m from 0.005 mol·kg⁻¹ to 0.5 mol·kg⁻¹, at temperatures T from 278.15 K to 393.15 K, and at the pressure P = 0.35 MPa. We have calculated the apparent molar volumes V_φ and apparent molar heat capacities C_p,φ of the solutions and fit them by regression to equations that describe the surfaces (V_φ, T, m) and (C_p,φ, T, m). These results reflect changes and differences in both solute-solute and solute-solvent interactions. Standard state partial molar volumes V₂° and heat capacities C_p,2° were estimated by extrapolation to the M = 0 mol·kg⁻¹ plane of the fitted surfaces. We have calculated (Δ_r,C_p,m, T, m) surfaces for various proton dissociation reactions, and we have created surfaces representing (Δ_rH_m, T, m) and (pQ_a, T, m) by integration of our (Δ_rC_p,m, T, m) surfaces using values for (Δ_rH_m, m) and (pK_a, m) at a reference T as integration constants. We have also created surfaces representing (Δ_rS_m, T, m) and (Δ_rV_m, T, m) for these dissociation reactions.     

Spectral filtering for ultra-fast mode-locking in the normal dispersive regime

A theoretical model is developed which characterizes the physical process responsible for generating ultra-short, high-energy, mode-locked pulses in a normal GVD laser cavity with spectral filtering. Two physical parameters are critical to achieving optimal performance: the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering allows for the high-energy of typical normal GVD laser cavities to be maintained while the pulse intensity doubles and the FWHM reduces by an order of magnitude. This phenomenon is generic and ubiquitous to normal GVD mode-locking. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of weathered wood-plastic composite surfaces using FTIR spectroscopy, contact angle, and XPS

Much of the current growth of wood-plastic composites (WPCs) is due to increased penetration into the decking market; therefore it has become imperative to understand the durability of WPCs in outdoor applications. In this study, wood flour filled high-density polyethylene (HDPE) composites were manufactured through either injection molding or extrusion. A set of extruded composites were also planed to remove the extruded surface. Composites were weathered in a xenon-arc weathering apparatus. Scanning electron microscopy (SEM) was used to characterize the morphology of the composite surface. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was useful in showing the loss of wood particles from the surface after weathering. Contact angle was higher for the extruded and planed composites compared with the injection molded composites, and was shown using X-ray photoelectron spectroscopy (XPS) to be due to lubricant used as a processing aid.