Water-Insensitive Synthesis of Poly-β-Peptides with Defined Architecture

Biocompatible and proteolysis-resistant poly-β-peptides have broad applications and are dominantly synthesized via the harsh and water-sensitive ring-opening polymerization of β-lactams in a glovebox or using a Schlenk line, catalyzed by the strong base LiN(SiMe₃)₂. We have developed a controllable and water-insensitive ring-opening polymerization of β-amino acid N-thiocarboxyanhydrides (β-NTAs) that can be operated in open vessels to prepare poly-β-peptides in high yields, with diverse functional groups, variable chain length, narrow dispersity and defined architecture. These merits imply wide applications of β-NTA polymerization and resulting poly-β-peptides, which is validated by the finding of a HDP-mimicking poly-β-peptide with potent antimicrobial activities. The living β-NTA polymerization enables the controllable synthesis of random, block copolymers and easy tuning of both terminal groups of polypeptides, which facilitated the unravelling of the antibacterial mechanism using the fluorophore-labelled poly-β-peptide.     

Degradation of Structurally Defined Graphene Nanoribbons by Myeloperoxidase and the Photo-Fenton Reaction

As an emerging member of the graphene family, structurally defined graphene nanoribbons (GNRs) have shown promising applications in various fields. The evaluation of the degradability of GNRs is particularly important for assessing the persistence level and risk of these materials in living organisms and the environment. However, there is a void in the study of the degradation of GNRs. Here, we report the degradation behavior of GNRs in the presence of human myeloperoxidase (hMPO) or treated with the photo-Fenton (PF) reaction. With the assistance of potassium hydroxide or imidazole, which facilitates the dispersion of GNRs in the aqueous solution, GNRs underwent only partial degradation after 25-hour incubation with hMPO, while, the PF reaction degraded GNRs almost completely after 120 hours. These results indicate that structurally precise GNRs can be efficiently degraded under suitable conditions, providing more opportunities for future applications in different fields.     

Molecular Photochemistry: Recent Developments in Theory

Photochemistry is a fascinating branch of chemistry that is concerned with molecules and light. However, the importance of simulating light‐induced processes is reflected also in fields as diverse as biology, material science, and medicine. This Minireview highlights recent progress achieved in theoretical chemistry to calculate electronically excited states of molecules and simulate their photoinduced dynamics, with the aim of reaching experimental accuracy. We focus on emergent methods and give selected examples that illustrate the progress in recent years towards predicting complex electronic structures with strong correlation, calculations on large molecules, describing multichromophoric systems, and simulating non‐adiabatic molecular dynamics over long time scales, for molecules in the gas phase or in complex biological environments.     

Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts

[reaction: see text] Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation.     

A hierarchy of coupled maps

A large number of logistic maps are coupled together as a mathematical metaphor for complex natural systems with hierarchical organization. The elementary maps are first collected into globally coupled lattices. These lattices are then coupled together in a hierarchical way to form a system with many degrees of freedom. We summarize the behavior of the individual blocks, and then explore the dynamics of the hierarchy. We offer some ideas that guide our understanding of this type of system. (c) 2002 American Institute of Physics.     

Multi-separation, centrifugality and centripetality imply chaos

Let be an interval. need not be compact or bounded. Let be a continuous map, and be a trajectory of with or . Then there is a point such that . A point is called a centripetal point of relative to if or , and is centrifugal if or . In this paper we prove that if there exist centripetal points of in , then has periodic points of some odd () period . In addition, we also prove that if ) is multi-separated by Fix(), or there exists a centrifugal point of in , then is turbulent and hence has periodic points of all periods.

     

Synthesis and characterization of diphenylaminodiphenyl stryl based alternating copolymers

Diphenylaminobiphenylated stryl based alternating copolymers with phenyl or fluorene, which were expected to have a terphenylene vinylene backbone containing an (N,N‐diphenylamino)biphenyl pendant and a phenyl/fluorene/phenylene vinylene backbone containing an (N,N‐diphenylamino)biphenyl pendant, were synthesized by a Suzuki coupling reaction. The obtained copolymers were confirmed with various types of spectroscopy. The alternating copolymers showed good hole‐injection properties because of their low oxidation potential and good solubility and high thermal stability with a high glass‐transition temperature. The alternating copolymers showed blue emissions because of the adjusted conjugation lengths; the maximum wavelength was 460 nm for poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl]vinylene‐alt‐5‐(2′‐ethylhexyloxy)‐2‐methoxybenzene} and 487 nm for poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl] vinylene‐alt‐9,9‐dihexylfluorene}. The maximum brightness of indium tin oxide/poly(3,4‐ethylene dioxythiophene)/polymer/LiF/Al devices with poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl]vinylene‐alt‐5‐(2′‐ethylhexyloxy)‐2‐methoxybenzene} or poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl]vinylene‐alt‐9,9‐dihexylfluorene} as the emitting layer was 250 or 1000 cd/m², respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 341–347, 2007     

掺CdSxSe1-x玻璃波导分布反馈光学双稳器件

本文给出了掺CdS_xSe_1-x玻璃平面波导分布反馈(DFB)光学双稳器件的设计和制备方法,实现了低功耗、快速的本征光学双稳。     

Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity

We theoretically and experimentally investigated the reorganization of cladding modes in high-refractive-index- (HRI-) coated long-period gratings (LPGs), focusing on the influence of refractive-index sensitivity. When azimuthally symmetric nanoscale HRI coatings are deposited along LPG devices, a significant modification of the distribution of cladding modes occurs, depending on the layers' features (refractive index and thickness) and on the external refractive index. In particular, if these parameters are properly chosen, a transition between cladding modes and overlay modes occurs. Numerical and experimental effects of the mode transition on the sensitivity of the surrounding refractive index are described.     

A magnetic resonance device designed via global optimization techniques

In this paper we are concerned with the design of a small low-cost, low-field multipolar magnet for Magnetic Resonance Imaging with a high field uniformity. By introducing appropriate variables, the considered design problem is converted into a global optimization one. This latter problem is solved by means of a new derivative free global optimization method which is a distributed multi-start type algorithm controlled by means of a simulated annealing criterion. In particular, the proposed method employs, as local search engine, a derivative free procedure. Under reasonable assumptions, we prove that this local algorithm is attracted by global minimum points. Additionally, we show that the simulated annealing strategy is able to produce a suitable starting point in a finite number of steps with probability one.This work was supported by CNR/MIUR Research Program Metodi e sistemi di supporto alle decisioni, Rome, Italy.Mathematics Subject Classification (1991):65K05, 62K05, 90C56