肽链的刚性结构对氮-(ω-三甲基硅甲基)聚肽链邻苯二甲酰胺单电子转移环化反应的影响

在光诱导下,激发态的氮-(ω-三甲基硅甲基)聚肽链邻苯二甲酰胺经单电子转移形成1,ω-双自由基,其耦合形成聚肽环化物。1,ω-双自由基的1位和ω位间距离与环化物的产率有关:距离愈大,自由基碰撞机率越小,环化物产率越低。肽链的刚性弯曲结构使双自由基1位和ω位的距离呈不规则的变化,从而使聚肽环化物的产率呈不规则的变化。     

Synthesis of 4‐tert‐butyldimethylsilyloxystyrene and its copolymerization with styrene using (η5‐indenyl)trichlorotitanium in the presence of methylaluminoxane

Poly(styrene‐co‐4‐tert‐butyldimethylsilyloxystyrene) as a precursor of hydroxyl‐functionalized syndiotactic polystyrene was successfully synthesized via (η⁵‐indenyl)trichlorotitanium (IndTiCl₃)‐catalyzed copolymerization of styrene with 4‐tert‐butyldimethylsilyloxystyrene in toluene at 25°C in the presence of methylaluminoxane (MAO) ([Al]/[Ti] = 2 000). The amount of styrene derivative incorporated into the polymeric chain for a 20,7 : 1 mole feed ratio of styrene to 4‐tert‐butyldimethylsilyloxystyrene was found to be 1,8 mol‐% from a ¹H NMR analysis. The styrene derivative was successfully prepared from 4‐hydroxybenzaldehyde via first protecting the hydroxyl group using tert‐butyldimethylchlorosilane followed by the ‘Wittig‐type’ reaction with the ‘Tebbe’ reagent. The yield was about 82 wt.‐% on the basis of the initial amount of 4‐hydroxybenzaldehyde used.     

Cu Crystal Growth on a Chelating Fiber with Different Amine Chain Lengths

Summary: Poly(acryloamidino ethyleneamine) (PAEA) and poly(acryloamidino diethylene diamine) (PADD) have been synthesized for the observation of Cu^II complex and Cu(OH)₂ crystal‐growth on the surface of different numbers of amino groups immobilized on polyacrylonitrile (PAN) fibers. The shape of Cu^II crystal growth depends on the amine chain length of the chelating fiber; Cu(OH)₂ crystals grow on the surface of the chelating fiber after Cu^II adsorption.

     

Electrochemical oxygen reduction on nitrogen doped graphene sheets in acid media

Nitrogen doped graphene were prepared via exfoliated graphite oxide. This graphene exhibited significantly high oxygen reduction activity. High electric conductivity, high surface area, large amount of edge sites and pyridinic N site in rGS (reduced graphene sheets) contribute to the high ORR (oxygen reduction reaction) activity. The rGS showed a potential to replace expensive Pt for oxygen reduction reaction in PEMFC.     

Synthesis of 2-azaspiro[4.4]nonan-1-ones via phosphine-catalysed [3+2]-cycloadditions

The phosphine-catalyzed [3+2]-cycloaddition of the 2-methylene γ-lactams 4 and 5 and the acrylate 6 with the ylides derived from the ethyl ester, the amide or the chiral camphor sultam derivative of 2-butynoic acid (7a-c) give directly, or indirectly after reductive cyclization, spiro-heterocyclic products. The acid 32 underwent Curtius rearrangement and then acid hydrolysis to give two novel spiro-cyclic ketones, 41 and 42.     

Engineering of a bis-chelator motif into a protein α-helix for rigid lanthanide binding and paramagnetic NMR spectroscopy

Attachment of two nitrilotriacetic acid-based ligands to a protein α-helix in an i, i + 4 configuration produces an octadentate chelating motif that is able to bind paramagnetic lanthanide ions rigidly and with high affinity, leading to large pseudocontact shifts and residual dipolar couplings in the NMR spectrum.     

Gas‐forming poly(ethylene glycol)‐b‐poly(L‐lactic acid) micelles

In this study, a novel drug‐carrying micelle composed of methoxy poly(ethylene glycol) (mPEG)‐b‐poly(L‐lactic acid) (PLLA) with gas‐forming carbonate linkage was fabricated. Here, the gas‐forming carbonate linkage was formed by the chemical coupling of the terminal hydroxyl group of the PLLA block and benzyl chloroformate (BC). mPEG‐b‐PLLA‐BC was self‐organized in aqueous solution: the PEG block on the hydrophilic outer shell and the PLLA‐BC block in the hydrophoboic innor core. The cleavage of carbonate linkage by hydrolysis and formation of carbon dioxide nanobubbles in the micellar core enabled an accelerated release of the encapsulated anticancer drug (doxorubicin: DOX) from the mPEG‐b‐PLLA‐BC micelles. The amount of drug (DOX) released from the mPEG‐b‐PLLA‐BC micelle was higher than that from the conventional mPEG‐b‐PLLA micelle, which allowed for increased in vitro toxicity against KB tumor cells. Copyright © 2013 John Wiley & Sons, Ltd.     

Computational studies of bacterial resistance to β-lactam antibiotics: mechanism of covalent inhibition of the penicillin-binding protein 2a (PBP2a)

β-Lactam resistance of methicillin-resistant Staphylococcus aureus (MRSA), a pathogenic bacterium that causes staph infections, represents a serious threat to public health. This arises primarily due to the inability of β-lactam antibiotics to inhibit the transpeptidase activity of penicillin-binding protein 2a (PBP2a). Effective inhibition of PBP2a to prevent the bacterial cell wall biosynthesis is of great importance for the treatment of a variety of clinically challenging infectious diseases caused by MRSA. To gain fundamental insights into the mode of covalent inhibition of the enzyme, we have carried out computational studies of the acylation reactions between small β-lactam molecules (methicilin and nitrocefin) and PBP2a using the B3LYP/6-31G* and ONIOM(B3LYP/6-31G*:AMBER) hybrid quantum mechanical/molecular mechanical methods. Our calculations show that the acylation involves two transition states and that methicilin and nitrocefin undergo acylation in slightly different manners. The acylation of nitrocefin is more facile, which is attributed to the larger release of ring strain and the larger resonance stabilization gained upon ring opening. We suggest that, in addition to the nonbonded interactions between the ligand and the protein, these quantum chemical factors, which are associated with efficiency of the acylation step, should be taken into account and carefully controlled in designing novel β-lactam inhibitors of PBP2a.