Synthesis of AB3‐type miktoarm star polymers with steroid core via a combination of “Click” chemistry and ring opening polymerization techniques

Well‐defined AB₃‐type miktoarm star‐shaped polymers with cholic acid (CA) core were fabricated with a combination of “click” chemistry and ring opening polymerization (ROP) methods. Firstly, azide end‐functional poly(ethylene glycol) (mPEG), poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(ε‐caprolactone) (PCL) polymers were prepared via controlled polymerization and chemical modification methods. Then, CA moieties containing three OH groups were introduced to these polymers as the end groups via Cu(I)‐catalyzed click reaction between azide end‐functional groups of the polymers ( mPEG‐N₃ , PMMA‐N₃ , PS‐N₃ , and PCL‐N₃ ) and ethynyl‐functional CA under ambient conditions, yielding CA end‐functional polymers ( mPEG‐Cholic , PMMA‐Cholic , PS‐Cholic , and PCL‐Cholic ). Finally, the obtained CA end‐capped polymers were employed as the macroinitiators in the ROP of ε‐caprolactone (ε‐CL) yielding AB₃‐type miktoarm star polymers ( mPEG‐Cholic‐PCL₃ , PMMA‐Cholic‐PCL₃ , and PS‐Cholic‐PCL₃ ) and asymmetric star polymer [ Cholic‐(PCL)₄ ]. The chemical structures of the obtained intermediates and polymers were confirmed via Fourier transform infrared and ¹H nuclear magnetic resonance spectroscopic techniques. Thermal decomposition behaviors and phase transitions were studied in detail using thermogravimetric analysis and differential scanning calorimetry experiments. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3390–3399     

Synthesis,characterization, electrochromic properties,and electrochromic device application of a novel star polymer consisting of thiophene end‐capped poly(ε‐caprolactone) arms emanating from a hexafunctional cyclotriphosphazene core

Hexa‐armed and thiophene (Thi) end‐capped poly(ε‐caprolactone) star polymer (N₃P₃‐(PCL‐Thi)₆), containing cyclotriphosphazene core, was prepared in a four‐step reaction sequence. Ring‐opening polymerization (ROP) and “click chemistry” techniques were employed in the first and final steps, respectively. Hexa‐armed PCL star polymer (N₃P₃‐(PCL‐OH)₆) was successfully synthesized via ROP of ε‐caprolactone (ε‐CL) by using hekzakis(p‐(hydroxymethyl)phenoxy) cyclotriphosphazene as the multisite initiator and tin(II) 2‐ethylhexanoate (Sn(Oct₂)) as the catalyst in bulk at 115 °C. Further modifications of the N₃P₃‐(PCL‐OH)₆ were accomplished by derivatization of the hydroxyl‐functional chain ends. The obtained N₃P₃‐(PCL‐OH)₆ was then reacted with 2‐bromo‐2‐methylpropanoyl bromide, and this led to a star polymer with bromide end groups, N₃P₃‐(PCL‐Br)₆. In the third step, N₃P₃‐(PCL‐Br)₆ was azidified with sodium azide (NaN₃) in DMF affording N₃P₃‐(PCL‐N₃)₆. Conversion of the azide chain end groups into Thi was quantitatively accomplished via the “click reaction” between N₃P₃‐(PCL‐N₃)₆ and prop‐2‐yn‐1‐yl 3‐thienyl acetate in the final step. Subsequently, the star polymer with six Thi chain ends (N₃P₃‐(PCL‐Thi)₆) was employed in electrochemical copolymerization with both pyrrole and Thi. Electrochromic properties and electrochromic device application of N₃P₃‐(PCL‐Thi)₆/PThi were also investigated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3668–3682, 2010     

Graft copolymerization of butyl acrylate and 2‐ethyl hexyl acrylate from labile chlorines of poly(vinyl chloride) by atom transfer radical polymerization

Trace amounts of labile chlorines present in poly(vinyl chloride) (PVC) were found to act as initiation sites for the preparation of graft copolymers of PVC by copper‐mediated atom transfer radical polymerization (ATRP). High grafting yields were attained during the graft copolymerizations of n‐butyl acrylate (161.8%) and 2‐ethyl hexyl acrylate (51.2%) in 7.5 h. In both cases, the grafting proceeded with first‐order kinetics with respect to the monomer concentrations, this being typical for ATRP. Gel permeation chromatography traces of the resulting products did not exhibit additional peaks attributable to the formation of free homopolymers. The presented procedure offers an efficient means of preparing self‐plasticized PVC structures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3457–3462, 2003     

阴离子对鼠尾草提取物中Ni盐前体绿色合成的NiO纳米粒子磁性和结构性能的影响

采用绿色合成方法,将鼠尾草提取物用作还原和封端剂合成氧化镍纳米颗粒(NiO NPs)。此外,使用各种前驱体合成了NiO NPs,并使用扫描电子显微镜对其形貌进行了分析。利用傅里叶变换红外光谱和粉末X射线衍射(PXRD)对NiO NPs的结构进行了表征,使用振动样品磁强计测量了它们的磁性。PXRD研究表明,所有合成的NiO NPs都表现出具有高结晶度的面心立方相,并且形成了具有高纯度相的NiO。磁化研究结果表明,3种镍盐(乙酸盐、氯化物和硫酸盐)前驱体合成的NiO NPs分别表现出超顺磁、软铁磁和顺磁行为。     

Total production of (R)-3,5-bistrifluoromethylphenyl ethanol by asymmetric reduction of 3,5-bis(trifluoromethyl)-acetophenone in the submerged culture of Penicillium expansum isolate

A total of 82 fungal isolates were screened for their ability to reduce 3,5-bis(trifluoromethyl)-acetophenone 1. Penicillium expansum was found to successfully reduce ketone 1 in the submerged culture. A second screening was performed on the active P. expansum strains identified by the first screening. A number of strains of P. expansum were found to produce (R)-3,5-bistrifluoromethylphenyl ethanol 2 with over 99% enantiomeric excess (ee) from ketone 1. The most productive strain was identified as P. expansum EBK-9, and this strain was selected for further experiments. The total production of 2 was carried out by P. expansum EBK-9 in a laboratory-scale bioreactor employing optimized conditions as determined by our experiments. P. expansum EBK-9 gave 2 with ee >99% and 76% yield. On a large scale, a total of 3.35 g/L of 2 was produced from 1 after 56 h.     

Benchmark solutions of radiative transfer equation for three-dimensional rectangular homogeneous media

Three-dimensional steady-state radiative integral transfer equations (RITEs) for a cubic absorbing and isotropically scattering homogeneous medium are solved using the method of “subtraction of singularity”. Surface integrals and volume integrals are carried out analytically to eliminate singularities, to assure highly accurate solutions, and to reduce the computational time. The resulting system of linear equations for the incident energy is solved iteratively. Six benchmark problems for cold participating media subjected to various combinations of externally uniform/non-uniform diffuse radiation loads are considered. The solutions for the incident energy and the net heat flux components are given in tabular form for scattering albedos of ω=0, 0.5 and 1.     

Hilbert basis of the Lipman semigroup

In this Note, we give a new method to compute the Hilbert basis of the semigroup of certain positive divisors supported on the exceptional divisor of a normal surface singularity. Our approach is purely combinatorial and enables us to avoid the long calculation of the invariants of the ring as it is presented in the work of Alt?nok and Tosun.     

PHOTOREACTIVATION OF KILLING INE. coliK–12 phr- CELLS IS NOT CAUSED BY PYRIMIDINE DIMER REVERSAL

Abstract— Escherichia coli K–12 strains deleted in the phr gene which encodes the apoenzyme of photolyase show significant residual photoreactivation activity after exposure to high photoreactivating light doses. We show that this photoreactivation of killing is not associated with reversal of pyrimidine dimers and conclude that the effect is probably attributable to the direct photoconversion of the6–4 photoproducts to their Dewar isomers (Type III photoreactivation).     

PHOTOREPAIR OF NONADJACENT PYRIMIDINE DIMERS BY DNA PHOTOLYASE

Abstract— Photolyases reverse the harmful effects of UV light on cells by converting pyrimidine dimers (Pyr[]Pyr) into two pyrimidine monomers by utilizing near-UV and visible light. Previous work has shown that photolyase repairs T[c,s]T and T[t,s]T in DNA as well as U[]U in RNA, all of which are formed by joining the two adjacent pyrimidines in a light-dependent reaction. In this report, we show that Pyr[]Pyr formed in nonadjacent pyrimidines are also substrates for DNA photolyase.     

Ultrafast dynamics and anionic active states of the flavin cofactor in cryptochrome and photolyase

We report here our systematic studies of the dynamics of four redox states of the flavin cofactor in both photolyases and insect type 1 cryptochromes. With femtosecond resolution, we observed ultrafast photoreduction of oxidized state flavin adenine dinucleotide (FAD) in subpicosecond and of neutral radical semiquinone (FADH(*)) in tens of picoseconds through intraprotein electron transfer mainly with a neighboring conserved tryptophan triad. Such ultrafast dynamics make these forms of flavin unlikely to be the functional states of the photolyase/cryptochrome family. In contrast, we find that upon excitation the anionic semiquinone (FAD(*-)) and hydroquinone (FADH(-)) have longer lifetimes that are compatible with high-efficiency intermolecular electron transfer reactions. In photolyases, the excited active state (FADH(-)*) has a long (nanosecond) lifetime optimal for DNA-repair function. In insect type 1 cryptochromes known to be blue-light photoreceptors the excited active form (FAD(*-)*) has complex deactivation dynamics on the time scale from a few to hundreds of picoseconds, which is believed to occur through conical intersection(s) with a flexible bending motion to modulate the functional channel. These unique properties of anionic flavins suggest a universal mechanism of electron transfer for the initial functional steps of the photolyase/cryptochrome blue-light photoreceptor family.