Energy conversion by autonomous regulation of chaos: dynamical mechanism of loose coupling

Inspired by recent experiments of molecular motors, a dynamical systems model for a flexible machine is proposed which converts injected energy to output directional motion. The output amount is distributed broadly, and thus the coupling between input energy and output motion is loose, as in the experiments. This energy conversion is shown to be robust against the change of surrounding environment. Stability analysis on the fixed point solutions of the model is presented, which suggests that transient chaotic motion, induced by temporal three-body motion, is relevant to the energy conversion.     

Measurement of 15N chemical shift anisotropy in a protein dissolved in a dilute liquid crystalline medium with the application of magic angle sample spinning

The chemical shifts of nuclei that have chemical shielding anisotropy, such as the 15N amide in a protein, show significant changes in their chemical shifts when the sample is altered from an isotropic state to an aligned state. Such orientation-dependent chemical shift changes provide information on the magnitudes and orientation of the chemical shielding tensors relative to the molecule's alignment frame. Because of the extremely high sensitivity of the chemical shifts to the sample conditions, the changes in chemical shifts induced by adding aligned bicelles do not arise only from the protein alignment but should also include the accumulated effects of environmental changes including protein-bicelle interactions. With the aim of determining accurate 15N chemical shielding tensor values for solution proteins, here we have used magic angle sample spinning (MAS) to observe discriminately the orientation-dependent changes in the 15N chemical shift. The application of MAS to an aligned bicelle solution removes the torque that aligns the bicelles against the magnetic field. Thus, the application of MAS to a protein in a bicelle solution eliminates only the molecular alignment effect, while keeping all other sample conditions the same. The observed chemical shift differences between experiments with and without MAS therefore provide accurate values of the orientation-dependent 15N chemical shifts. From the values for ubiquitin in a 7.5% (w/v) bicelle medium, we determined the 15N chemical shielding anisotropy (CSA) tensor. For this evaluation, we considered uncertainties in measuring the 1H-15N dipolar couplings and the 15N chemical shifts and also structural noise present in the reference X-ray structure, assuming a random distribution of each NH bond vector in a cone with 5 degrees deviation from the original orientation. Taking into account these types of noise, we determined the average 15N CSA tensor for the residues in ubiquitin as Delta sigma=-162.0+/-4.3 ppm, eta=0.18+/-0.02, and beta=18.6+/-0.5 degrees, assuming a 1H-15N bond length of 1.02 A. These tensor values are consistent with those obtained from solid-state NMR experiments.     

Highly sodium-selective fluoroionophore based on conformational restriction of oligoethyleneglycol-bridged biaryl boron-dipyrromethene

A non-PET and non-PCT fluoroionophore has been designed and synthesized based on the combination of a biaryl boron-dipyrromethene fluorophore with an oligoethyleneglycol bridge. A specific red-shift response of absorption for NaClO4 in acetonitrile was demonstrated based on conformational restriction triggered by cation recognition at the bridge. The concentration of Na+ can be determined accurately using fluorescence due to a high extinction coefficient (epsilon = 50 000), a high fluorescence quantum yield (Phif = 0.68), and the sharpness of absorption and emission peaks of the boron-dipyrromethene derivative.     

Blocks of central -group extensions

Let and be finite groups that have a common central -subgroup for a prime number , and let and respectively be -blocks of and induced by -blocks and respectively of and , both of which have the same defect group. We prove that if and are Morita equivalent via a certain special -bimodule, then such a Morita equivalence lifts to a Morita equivalence between and .

     

Two new dimeric acridone alkaloids from Glycosmis citrifolia

Two new acridone dimers, glycobismines-F (1) and -G (2), were isolated from the roots of Glycosmis citrifolia collected in Taiwan. The structures of the new compounds were determined based on spectral analysis.     

Absolute configurational assignments of secondary amines by CD-sensitive dimeric zinc porphyrin host

A general chiroptical protocol for determination of absolute configuration of secondary amines including acyclic and cyclic aliphatic amines, aromatic amines, amino acids, and amino alcohols is described. The chiral substrate is linked to the achiral carrier moiety (3-N-Boc-amino-propyl-N-Boc-amino)acetic acid 1 (BocHNCH(2)CH(2)CH(2)BocNCH(2)COOH), which after deprotection, yields a bidentate conjugate, capable of forming a 1:1 host/guest complex with dimeric zinc porphyrin host 2. As in the cases of primary amines and secondary alcohols reported earlier, the complexation of secondary amine conjugates to porphyrin tweezer host 2 represents a stereodifferentiating process, where the large (L) group at the stereogenic center (assigned on the basis of conformational energies A value) protrudes from the porphyrin binding pocket. This leads to formation of host/guest complexes with a preferred porphyrin helicity that exhibit intense exciton split CD spectra. It was found that the chiral sense of porphyrin twist is clearly controlled by the stereogenic center despite the Z/E conformational complexity around the tertiary amide bond of secondary amine conjugates that has greatly hampered previous configurational assignments. Thus, in cases where there is no ambiguity regarding the relative steric size of substituents, the observed CD couplet can be applied for straightforward assignment of absolute configurations. In addition, to extend the application to more difficult cases a molecular mechanics calculation approach using the Merck Molecular Force Field (MMFFs) was developed; this provides conformational information of host/guest complexes and leads to prediction of preferred porphyrin helicity independent of conformational A values. This chiroptical protocol in combination with molecular modeling represents a general method for configurational assignments of secondary amines.     

Formal total synthesis of (+)-macrosphelide A based on regioselective hydrolysis using lipase

Three kinds of seco-macrosphelide A congeners, (4R,5S,10R,11S,15S)-6, (4R,5S,9S,14R,15S)-7 and (3S,8R,9S,14R,15S)-8 were chemically synthesized, and they were exposed to the lipase OF-360 from Candida rugosa to give three hydroxy carboxylic acids, respectively. Macrolactonization of the hydroxy acid (4R,5S,10R,11S)-18 derived from (4R,5S,10R,11S,15S)-6 gave 12-membered lactone (19) in 47% overall yield from 6, while that of the seco-acid (4) derived from (4R,5S,9S,14R,15S)-7 afforded (-)-dibenzyl macrosphelide A (25) in 27% overall yield from 7. Macrolactonization of the hydrolysis product, seco-acid (5) derived from (3S,8R,9S,14R,15S)-8, provided (-)-dibenzyl macrosphelide A (25) (5% overall yield from 8) and 12-membered lactone (19) (20% overall yield from 8) concurrently.     

A New Crystal Form,Polymorphism, and Multi‐Morphology in Biodegradable Poly(3‐hydroxypropionate)

Summary: A new crystal morphology (δ form) of poly(3‐hydroxypropionate) (PHP) is found in cast and melt‐crystallized PHPs with low molecular weight, in which the PHP chains possibly adopt a 2₁ helix rather than the trans conformation found in the β or γ form. The fusion temperature‐ and the crystallization temperature‐dependent polymorphism are responsible for the dual morphologies and the unique growth kinetics of spherulites in the melt‐crystallized PHPs.

a) A dual‐morphology developed at 70 °C in PHP films after melting at 117 °C and b) that formed during cooling at a rate of 1 °C · min⁻¹ from 130 °C.     

A Simple and Versatile Method for the Construction of Nearly Ideal Polymer Networks

Polymer networks usually contain numerous inhomogeneities that deteriorate their physical properties and should be eliminated to create reliable, high‐performance materials. A simple method is introduced for the production of nearly ideal networks from various vinyl polymers through controlled polymerization and subsequent crosslinking. Monodisperse star polymers with bromide end groups were synthesized by atom‐transfer radical polymerization and end‐linked with dithiol linkers using thiol–bromide chemistry. This simple procedure formed nearly ideal polymer networks, as revealed from elasticity of the formed gel and model conjugation reactions involving linear polymers. The versatility of this method was demonstrated by preparing networks of common vinyl polymers, including polyacrylates, polymethacrylate, and polystyrene. This method can be used to prepare multiple functional nearly ideal gels and elastomers and to explore fundamental aspects of polymer networks.