A new cationic poly(ester-anhydride): Synthesis, structure characterization, and biological properties

To improve the cytotoxicity and biocompatibility of cationic polymers used as gene carriers, new cationic poly(ester-anhydride) copolymers (Pea-PAs) bearing a quaternary ammonium group in the backbone were synthesized through a reaction between an aminoester dicarboxylic acid with a tertiary amine in the backbone and excess acetyl chloride. Their structure was characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectrometry (FTIR), and gel permeation chromatography (GPC). They degraded hydrolytically in 20 mM HEPES buffer at pH 7.4 at 37°C with a half-life of more than 70 h. Their cytotoxicity was substantially lower than that of PEI. The blood clotting index (BCI) and haemolysis ratio (HR) also showed that these newly synthesized Pea-PA polymer are biopolymers with good blood compatibility.     

Alternating copolymers incorporating cyclopenta[2,1‐b:3,4‐b′]dithiophene unit and organic dyes for photovoltaic applications

We have synthesized six p‐type copolymers, CPDT ‐ co ‐ TPADCN , CPDT ‐ co ‐ TPADTA , CPDT ‐ co ‐ TPATCN , CPDT ‐ co ‐ DFADCN , CPDT ‐ co ‐ DFADTA , and CPDT ‐ co ‐ DFATCN , consisting of a cyclopenta[2,1‐b:3,4‐b′]dithiophene (CPDT) unit and an organic dye in an alternating arrangement. Triphenylamine (TPA) or difluorenylphenyl amine (DFA) units serve as the electron donors, whereas dicyanovinyl (DCN), 1,3‐diethyl‐2‐thiobarbituric acid, or tricyanovinyl (TCN) units act as the electron acceptors in the dyes. The target polymers were prepared via Stille coupling, followed by postfunctionalization to introduce the electron acceptors to the side chains. Because of the strongest withdrawing ability of TCN acceptor to induce efficient intramolecular charge transfer, CPDT ‐ co ‐ TPATCN and CPDT ‐ co ‐ DFATCN exhibit the broader absorption spectra covering from 400 to 900 nm and the narrower optical band gaps of 1.34 eV. However, the CPDT ‐ co ‐ TPATCN :PC₇₁BM and CPDT ‐ co ‐ DFATCN :PC₇₁BM based solar cells showed the power conversion efficiencies (PCEs) of 0.22 and 0.31%, respectively, due to the inefficient exciton dissociation. The DFA‐based polymers possess deeper‐lying HOMO energy levels than the TPA‐based polymer analogues, leading to the higher V_oc values and better efficiencies. The device based on CPDT ‐ co ‐ DFADTA :PC₇₁BM blend achieved the best PCE of 1.38% with a V_oc of 0.7 V, a J_sc of 4.57 mA/cm², and a fill factor of 0.43. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Crystallization and annealing effects of sputtered tin alloy films on electromagnetic interference shielding

Sn, Al and Cu not only possess electromagnetic interference (EMI) shield efficiency, but also have acceptable costs. In this study, sputtered Sn-Al thin films and Sn-Cu thin films were used to investigate the effect of the crystallization mechanism and film thickness on the electromagnetic interference (EMI) characteristics. The results show that Sn-xAl film increased the electromagnetic interference (EMI) shielding after annealing. For as-sputtered Sn-xCu films with higher Cu atomic concentration, the low frequency EMI shielding could not be improved. After annealing, the Sn-Cu thin film with lower Cu content possessed excellent EMI shielding at lower frequencies, but had an inverse tendency at higher frequencies. For both the Sn-xAl and Sn-xCu thin films after crystallization treatment, the sputtered films had higher electrical conductivity, however the EMI shielding was not enhanced significantly.     

5-Methylcytosine Substantially Enhances the Thermal Stability of DNA Minidumbbells

Minidumbbell (MDB) is a recently identified non-B DNA structure that has been proposed to associate with genetic instabilities. It also serves as a functional structural motif in DNA nanotechnology. DNA molecular switches constructed using MDBs show instant and complete structural conversions with easy manipulations. The availability of stable MDBs can broaden their applications. In this work, we found that substitutions of cytosine with 5-methylcytosine could lead to a significant enhancement in the thermal stabilities of MDBs. Consecutive methylations of cytosine in MDBs brought about cumulative stabilization with a drastic increase in the melting temperature by 23 °C. NMR solution structures of two MDBs containing 5-methylcytosine residues have been successfully determined and revealed that the enhanced stabilities resulted primarily from favorable hydrophobic contacts, more stable base pairs and enhanced base-base stackings involving the methyl group of 5-methylcytosine.     

Control synchronization and parameter identification of two different chaotic systems

In this paper, control synchronization between two chaotic systems governed by different formulas is studied. Based on the techniques of adaptive control and parameters modulation, the response system is controlled to coincide with the drive system without the prior knowledge of parameters. When synchronization is achieved, the unknown parameters of the drive system are well approximated simultaneously. The effect of control parameters on the degree of synchronization is also discussed.