A Rhizavidin Monomer with Nearly Multimeric Avidin‐Like Binding Stability Against Biotin Conjugates

Developing a monomeric form of an avidin‐like protein with highly stable biotin binding properties has been a major challenge in biotin‐avidin linking technology. Here we report a monomeric avidin‐like protein—enhanced monoavidin—with off‐rates almost comparable to those of multimeric avidin proteins against various biotin conjugates. Enhanced monoavidin (eMA) was developed from naturally dimeric rhizavidin by optimally maintaining protein rigidity during monomerization and additionally shielding the bound biotin by diverse engineering of the surface residues. eMA allowed the monovalent and nonperturbing labeling of head‐group‐biotinylated lipids in bilayer membranes. In addition, we fabricated an unprecedented 24‐meric avidin probe by fusing eMA to a multimeric cage protein. The 24‐meric avidin and eMA were utilized to demonstrate how artificial clustering of cell‐surface proteins greatly enhances the internalization rates of assembled proteins on live cells.     

pH/potential-responsive large aggregates from the spontaneous self-assembly of a triblock copolymer in water

A simple triblock copolymer, mPEG750-aniline pentamer-mPEG750, was prepared by condensation polymerization. The solubility of aniline pentamer in this kind of copolymer was improved in common solvents especially in aqueous solution, and the electroactivity of this copolymer was confirmed by UV-vis and CV in aqueous solution. When aniline pentamer was in its emeraldine state, the copolymer spontaneously self-assembled into large spheres (with diameters up to 1000 nm) in acidic aqueous solution (pH < 3), and into microspheres (with diameters of about 300 nm) in alkali aqueous solution, while the size of the aggregates decreased with the increase of pH. For reversible transition between the large spheres and microspheres under the change of the pH and potential, which changed the doping state and the oxidation state, respectively, the copolymer has potential applications in sensors, controlled drug release, and so forth.     

Study the property of double-ended fluoroalkyl poly(ethylene glycol) hydrogel as a depot for hydrophobic drug delivery using electron paramagnetic resonance technique and cell proliferation assay

Hydrogel formed by fluoroalkyl double-ended polyethylene glycol (R_f-PEG) micelles was studied to assess its properties to encapsulate a hydrophobic electron spin labeled drug, Chlorambucil–Tempol adduct (CT), and to control and sustain the drug release. The drug loaded hydrogel samples were characterized with variable-temperature dependent EPR experiment, and EPR theoretical lineshape analysis. It was found that CT molecules reside in the hydrophobic R_f-cores/IPDU shells of the R_f-PEG micelles and the maximum molecular-level loading capacity was estimated to be 18.8 mg per gram of the R_f-PEG. It has been known that R_f-PEG hydrogel with certain molecular masses for the fluoroalkyl group and the PEG chain shows properties of sol/gel phase coexistence and surface erosion, which represent the favorable condition for a pharmaceutical depot to control the kinetics of drug release. To evaluate the R_f-PEG’s biocompatibility and kinetics of the drug release, a cell proliferation assay was carried out on human oropharyngeal carcinoma (KB) cells. The results show that R_f-PEG is biocompatible and able to release CT to the cell media with a constant equilibrium concentration independent of the amount of CT loaded hydrogel.     

Pd(II) complexes of N,S-heterocyclic carbenes with pendant and coordinated allyl function and their Suzuki coupling activities

3-(2-Propenyl)benzothiazolium bromide () provides a direct and simple entry to Pd(ii) complexes with N,S-heterocyclic carbene (NSHC) ligands functionalized with an allyl pendant with hemilabile potential. Addition of salt to Pd(OAc)(2) eliminates HOAc and affords the bis(carbene) complexes cis-[PdBr(2)(NHSC)(2)] (cis-, NSHC = 3-(2-propenyl)benzothiazolin-2-ylidene) and trans-[PdBr(2)(NHSC)(2)] (trans-) along with the monocarbene complexes [PdBr(2)(NSHC)] () and trans-[PdBr(2)(benzothiazole-kappaN)(NSHC)] () as minor side products. Salt-metathesis of cis- with AgO(2)CCF(3) yields the mixed dicarboxylato-bis(carbene) complex cis-[Pd(O(2)CCF(3))(2)(NSHC)(2)] (). Complexes cis-, trans- and were characterized by multinuclear NMR spectroscopies, ESI mass spectrometry and elemental analysis. The molecular structures of complexes cis-, and have been determined by X-ray single crystal diffraction. Complexes cis- and as well as an in situ mixture of Pd(OAc)(2) and salt are active toward Suzuki-Miyaura coupling of aryl bromides and activated aryl chlorides giving good conversions.     

New synthesis of zinc tetrakis(arylethynyl)porphyrins and substituent effects on their redox chemistry

Sonogashira coupling of zinc 5,10,15,20-tetraethynylporphyrin with various phenyl iodides under mild conditions afforded good yields of the corresponding zinc porphyrins. This method is applicable to a variety of aryl iodides including meso-substituted iodoporphyrin to form a conjugated star-shaped multiporphyrin. The UV-Vis spectra show that peak broadening, red shifts, and changes in the oscillator strength of absorptions increase with the extension of pi-conjugation. In the electrochemical measurements, the first oxidation of porphyrins 4-9 occurs at potentials in the range +0.89 to +1.08 V, which are comparable to that of ZnTPP (TPP = tetraphenylporphyrin). The first reduction was observed at potentials from -0.73 to -0.89 V, which is anodically shifted by 390-550 mV as compared to that of ZnTPP, and the second reduction occurs at potentials in the range -1.12 to -1.33 V. The para-substituted tetrakis(phenylethynyl)porphyrins show substituent effects on their redox chemistry and exhibit only slight substituent effects in their emission and absorption maxima.     

Novel and Efficient Procedure for the Regiocontrolled Preparation of α‐(Phenylsulfanyl) Carbonyl Compounds

A new procedure for the regiocontrolled synthesis of α‐(phenylsulfanyl) carbonyl compounds has been developed, making use of lithium naphthalenide induced reductive sulfenylation of α‐cyano carbonyl compounds as a key operation. Through this protocol, a variety of á‐(phenylsulfanyl) carbonyl compounds has been prepared in moderate to high yields. The completely regioselective sulfenylation was observed in most of the cases.     

Anion photoelectron spectroscopy of C(5)H(-)

Anion photoelectron spectroscopy is performed on the C(5)H(-) species. Analogous to C(3)H(-) and C(3)D(-), photodetachment transitions are observed from multiple, energetically close-lying isomers of the anion. A linear and a cyclic structure are found to have electron binding energies of 2.421+/-0.019 eV and 2.857+/-0.028 eV, respectively. A cyclic excited state is also found to be 1.136 eV above the linear (2)Pi C(5)H ground state. Based on our assignments of the observed transitions and previous calculations on the energetics of neutral C(5)H isomers, the cyclic (1)A(1) anion state is found to lie 0.163 eV below the (3)A linear anion.     

Photoinduced energy transfer in bichromophoric co-assemblies based on amphiphilic poly(amidoamine) dendrons

Spherical co-assemblies were generated from an equivalent-molar-ratio mixture of amphiphilic poly(amidoamine) dendrons that were modified with focal carbazole and/or pyrene chromophores from the first to the third generation (DnCz I and DnPy, where n=1, 2, 3 denotes the generation of dendrons) in water at a concentration of 3.0 x 10(-6) M, lower than the individual critical aggregation concentrations (CAC) of either DnCz I or DnPy. UV-vis absorption and fluorescence emission spectra indicated that fluorescence resonance energy transfer (FRET) from carbazole to pyrene units occurred efficiently within the co-assemblies. Further study implied that part of the carbazole and/or pyrene units stacked homogeneously in the co-assemblies via pi-pi stacking and the dendritic branches served as connectors due to the hydrogen-bonding interaction.     

Dimolybdenum Complex Containing N–H···Mo Interactions. Synthesis and Structure of cis-[Mo2(HDpyF)2(CH3CN)4](BF4)4 and its Transformation to [Mo2(DpyF)2(py)4](BF4)2 [HDpyF?=?Bis(2-pyridyl)formamidine; py?=?pyridine]

The complex cis-[Mo₂(HDpyF)₂(CH₃CN)₄](BF₄)₄, 1, was prepared by the reaction of Mo₂(DpyF)₄ with HBF₄ in CH₃CN, in which new bonding mode of the HDpyF ligand and axial N–H···Mo interactions are observed. Reaction of 1 with pyridine afforded the complex trans-[Mo₂(DpyF)₂(py)₄](BF₄)₂, 2. In complex 1, the neutral bidentate HDpyF ligands bridge the metal centers through one of the amine nitrogen atoms and the adjacent pyridyl nitrogen atom, resulting in the s-trans-anti-s-trans conformation. The anionic DpyF⁻ ligands of 2 adopt the s-trans,s-trans conformation and are coordinated to the Mo centers in bidentate fashions through the two central nitrogen atoms and the two terminal nitrogen atoms are not coordinated. Dedicated to the memory of Professor F. A. Cotton, a great mentor and friend.     

Certification of standard reference materials containing bitter orange

A suite of three dietary supplement standard reference materials (SRMs) containing bitter orange has been developed, and the levels of five alkaloids and caffeine have been measured by multiple analytical methods. Synephrine, octopamine, tyramine, N-methyltyramine, hordenine, total alkaloids, and caffeine were determined by as many as six analytical methods, with measurements performed at the National Institute of Standards and Technology and at two collaborating laboratories. The methods offer substantial independence, with two types of extractions, two separation methods, and four detection methods. Excellent agreement was obtained among the measurements, with data reproducibility for most methods and analytes better than 5% relative standard deviation. The bitter-orange-containing dietary supplement SRMs are intended primarily for use as measurement controls and for use in the development and validation of analytical methods. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.