The role of entanglements on the stability of microphase separated diblock copolymers in shear flow

Various possible orientations of lamellar structures of diblock copolymers under shear are investigated with respect to their stability. A Brownian dynamics model is put forward in which each diblock is modeled as a dumbbell. The blobs in each dumbbell are held together by a finite extendable nonlinear elastic (FENE) potential and interact with all surrounding blobs by soft dissipative particle dynamics (DPD) potentials. In addition to this, the blobs have the possibility to entangle with each other. The corresponding interactions lead to large viscosities, which, however, quickly diminish with increasing shear rate. This fact turns out to be crucial for the stabilization of structures with the lamellae parallel to the velocity-vorticity plane. As a second result it is found that asymmetry in the entanglement interactions stimulates the actual reorientation into this state.     

Plant elemental composition and portable X‐ray fluorescence (pXRF) spectroscopy: quantification under different analytical parameters

Emergence of portable X‐ray fluorescence (pXRF) systems presents new opportunities for rapid, low‐cost plant analysis, both as a lab system and in situ system. Numerous studies have extolled the virtues of using pXRF for a wide range of plant applications, however, for many such applications, there is need for further assessment with regards to analytical parameters for plant analysis. While pXRF is a potential powerful research tool for elemental composition analysis, its successful use in plant analysis is made more likely by having an understanding of X‐ray physics, calibration process, and ability to test a variety of homogenous and well‐characterized materials for developing a matrix‐specific calibration. Because potential pXRF users may often underestimate the complexity of proper analysis, this study aims at providing a technical background for plant analysis using pXRF. The focus is on elemental quantification under different analytical parameters and different methods of sample presentation: direct surface contact under vacuum, placement in a sample cup with prolene as a seal, and without the aid of a vacuum. Direct analysis on the surface of a pXRF provided highest sensitivity and accuracy (R² > 0.90) for light elements (Mg to P). Sulfur, K, and Ca can be reliably measured without the aid of a vacuum (R² > 0.99, 0.97, and 0.93 respectively), although lower detection limits may be compromised. pXRF instruments provide plant data of sufficient accuracy for many applications and will reduce the overall time and budget compared with the use of conventional techniques. Sensitivity and accuracy are dependent on the instrument's settings, make, and model. © 2015 The Authors. X‐Ray Spectrometry published by John Wiley & Sons, Ltd.     

Bioisosteric Exchange of C ‐Chloro and Methyl Substituents: Synthesis and Initial Biological Studies of Atpenin A5 Analogues

Asymmetric synthesis and initial biological studies of two analogues of a naturally occurring chlorinated antifungal agent, atpenin A5, are described. These analogues were selected on the basis of Cl→CH₃ or H₃C→Cl exchanges in the side‐chain of atpenin A5. The interchange of chloro and methyl substituents led to complex II inhibitors with equal IC₅₀ values. This suggests that Cl?Me bioisosteric exchange can be realized in aliphatic settings.     

Synthesis and Biological Evaluation of Bromo‐ and Fluorodanicalipin A

We disclose the syntheses of (+)‐bromodanicalipin A as well as (±)‐fluorodanicalipin A. The relative configuration and ground‐state conformation in solution of both molecules was secured by J‐based configuration analysis which revealed that these are identical to natural danicalipin A. Furthermore, preliminary toxicological investigations suggest that the adverse effect of danicalipin A may be due to the lipophilicity of the halogens.     

Anharmonic vibrational calculations modeling the raman spectra of intermediates in the photoactive yellow protein (PYP) photocycle

The role of anharmonic effects in the vibrational spectroscopy of the dark state and two major chromophore intermediates of the photoactive yellow protein (PYP) photocycle is examined via ab initio vibrational self-consistent field (VSCF) calculations and time-resolved resonance Raman spectroscopy. For the first time, anharmonicity is considered explicitly in calculating the vibrational spectra of an ensemble consisting of the PYP chromophore surrounded by model compounds used as mimics of the important active-site residues. Predictions of vibrational frequencies on an ab initio corrected semiempirical potential energy surface show remarkable agreement with experimental frequencies for all three states, thus shedding light on the potential along the reaction path. For example, calculated frequencies for vibrational modes of the red-shifted intermediate, PYPL, exhibit an overall average error of 0.82% from experiment. Upon analysis of anharmonicity patterns in the PYP modes we observe a decrease in anharmonicity in the C8-C9 stretching mode nu29 (trans-cis isomerization marker mode) with the onset of the cis configuration in PYPL. This can be attributed to the loss of the hydrogen-bonding character of the adjacent C9-O2 to the methylamine (Cys69 backbone). For several of the modes, the anharmonicity is mostly due to mode-mode coupling, while for others it is mostly intrinsic. This study shows the importance of the inclusion of anharmonicity in theoretical spectroscopic calculations, and the sensitivity of experiments to anharmonicity. The characterization of protein active-site residues by small molecular mimics provides an acceptable chemical structural representation for biomolecular spectroscopy calculations.     

Oligothiophene-linked bisnaphthopyrans: sequential and temperature-dependent photochromism

Photochromic bisnaphthopyrans linked with oligothiophenes were synthesized and their photochromic behavior studied. Sequential and temperature-dependent photochromism was observed in the oligothiophene linked bisnaphthopyrans. The kinetics of photo and thermal processes in bisnaphthopyrans in comparison with naphthopyrans were studied. Substituent and linking effects on the photochromic properties are discussed. We demonstrate that the cross-talk between the two photochromophores is dependent on the length of the oligothiophene linker. The presence of the bithiophene linker led to high colorability and high quantum yield of coloration.     

Improved high-performance liquid chromatography-diode array detection method for the determination of phenolic compounds in leaves and peels from different apple varieties

Hydroxycinnamic acids derivatives, monomeric and oligomeric flavan-3-ols, flavonols, and dihydrocalcones are four of the major polyphenolic groups found in apples leaves and peels. A simple extraction with minimal pre-treatment and a high-performance liquid chromatography-diode array detection determination are optimized and validated, in order to identify and quantitate the polyphenolic profile of leaves and peels of four apples varieties (Gala, Topaz, Golden Delicious, and Florina). The improved chromatographic method has led to better separation of some known polyphenols in a single course, and diode-array detection has been used for the previsional identification of some polyphenolic compounds not available as standards. Because the mobile phase and the chromatographic column are compatible with a mass spectrometer, this method could investigate the unknown flavanols, flavonols, hydrocinnamic acid derivatives, and chalcone-related compounds found in apple leaves and peel extracts analyzed.     

Synthesis and micellar properties of surface-active ionic liquids: 1-alkyl-3-methylimidazolium chlorides

A series of surface-active ionic liquids, RMeImCl, has been synthesized by the reaction of purified 1-methylimidazole and 1-chloroalkanes, RCl, R=C(10),C(12),C(14), and C(16), respectively. Adsorption and aggregation of these surfactants in water have been studied by surface tension measurement. Additionally, solution conductivity, electromotive force, fluorescence quenching of micelle-solubilized pyrene, and static light scattering have been employed to investigate micelle formation. The following changes resulted from an increase in the length of R: an increase of micelle aggregation number; a decrease of: minimum area/surfactant molecule at solution/air interface; critical micelle concentration, and degree of counter-ion dissociation. Theoretically-calculated aggregation numbers and those based on quenching of pyrene are in good agreement. Gibbs free energies of adsorption at solution/air interface, DeltaG(ads)(0), and micelle formation in water, DeltaG(mic)(0), were calculated, and compared to those of three surfactant series, alkylpyridinium chlorides, RPyCl, alkylbenzyldimethylammonium chlorides, RBzMe(2)Cl, and benzyl(3-acylaminoethyl)dimethylammonium chlorides, R(')AEtBzMe(2)Cl, respectively. Contributions to the above-mentioned Gibbs free energies from surfactant methylene groups (in the hydrophobic tail) and the head-group were calculated. For RMeImCl, the former energy is similar to that of other cationic surfactants. The corresponding free energy contribution of the head-group to DeltaG(mic)(0) showed the following order: RPyCl approximately RBzMe(2)Cl>RMeImCl>R(')AEtBzMe(2)Cl. The head-groups of the first two surfactant series are more hydrophobic than the imidazolium ring of RMeImCl, this should favor their aggregation. Micellization of RMeImCl, however, is driven by a relatively strong hydrogen-bonding between the chloride ion and the hydrogens in the imidazolium ring, in particular the relatively acidic H2. This interaction more than compensates for the relative hydrophilic character of the diazolium ring. As indicated by the corresponding DeltaG(mic)(0), micellization of R(')AEtBzMe(2)Cl is more favorable than that of RMeImCl because the CONH group of the former surfactant series forms hydrogen bonds to both the counter-ion and the neighboring molecules in the micelle.     

Solubilization of Paclitaxel (taxol) by peptoad self-assemblies

A molecular dynamics simulation was carried out involving a paclitaxel molecule, 987 peptoad molecules, and 35 938 water molecules (conditions shown experimentally to effect paclitaxel solubilization in water). The peptoads are shown to form large clumps, the centers of which are dry and thus favorable to hydrogen bonding between paclitaxel and peptoads. Hydrogen-bonding equilibrium among the peptoads themselves in the developing clumps is achieved in 2 ns. The number and position of hydrogen bonds between the paclitaxel and peptoads fluctuate randomly from two to six within a 2-5 ns time frame. Hydrophobic association between the peptoad chains and the apolar paclitaxel groups does not seem to be an important element of the solubilization. Instead, the hydrophobic chains of the peptoads encasing the paclitaxel extend outward into the dry interior of the peptoad clump where other chains in the clump are located. One hopes that studies such as this will ultimately allow rational predictions when designing new and specific drug solubilizers.