Distal charge transport in peptides

Biological systems often transport charges and reactive processes over substantial distances. Traditional models of chemical kinetics generally do not describe such extreme distal processes. In this Review, an atomistic model for a distal transport of information, which was specifically developed for peptides, is considered. Chemical reactivity is taken as the result of distal effects based on two-step bifunctional kinetics involving unique, very rapid motional properties of peptides in the subpicosecond regime. The bifunctional model suggests highly efficient transport of charge and reactivity in an isolated peptide over a substantial distance; conversely, a very low efficiency in a water environment was found. The model suggests ultrafast transport of charge and reactivity over substantial molecular distances in a peptide environment. Many such domains can be active in a protein.     

Anion binding and transport by steroid-based receptors

The steroid nucleus is well-established as a scaffold for anion receptors. The bile acids are especially useful, providing inexpensive starting points with helpful substitution patterns. This article describes developments since an earlier review in 2003. Included are podand and cyclic structures, uncharged and positive receptors, and various arrays of H-bond donor and other binding functionality. Applications have been found in anion sensing, selective extractions, transport across bilayer membranes, and the discovery of antibiotics.     

Sequence dependence of charge transport properties of DNA

The electrical conduction through three short oligomers (26 base pairs, 8 nm long) with differing numbers of GC base pairs was measured. One strand is poly(A)-poly(T), which is entirely devoid of GC base pairs. Of the two additional strands, one contains 8 and the other 14 GC base pairs. The oligomers were adsorbed on a gold substrate on one side and to a gold nanoparticle on the other side. Conducting atomic force microscope was used for obtaining the current versus voltage curves. We found that in all cases the DNA behaves as a wide band-gap semiconductor, with width depending on the number of GC base pairs. As this number increases, the band-gap narrows. For applied voltages exceeding the band-gap, the current density rises dramatically. The rise becomes sharper with increasing number of GC base pairs, reaching more than 1 nA/nm2 for the oligomer containing 14 GC pairs.     

Silsesquioxane-based nanocomposite dendrimers with photo-luminescent and charge transport properties

The synthesis and characterization of octavinylsilsesquioxane (OVS)-based nanocomposite dendrimers with luminescent and charge transport properties are reported. The nanocomposite dendrimers were prepared in high yield using mild Heck chemistry of mono-haloaromatic compounds with the peripheral vinylsilane groups of OVS. Attachment of 2-naphthalene, 2-(9,9-dimethyl)fluorene, and 2-(4-phenyl)-5-(1-naphthyl)-1,3,4-oxadiazole resulted in materials with blue-violet emission (360-380 nm) and photo-luminescent quantum efficiencies (PLQEs) from 1 to 26%. Blue-green emission was observed for attachment of 1-pyrene, 9-anthracene, and N1-(4-phenyl)-N1,N4,N4-triphenylbenzene-1,4-diamine with PLQEs ranging from 23 to 50%. Despite the planar characteristics of the organic dendrons, the nanocomposite dendrimers are completely amorphous and have high glass transition temperatures (Tg) ranging from 115 to 186 degrees C with decomposition temperatures (Td) exceeding 450 degrees C. Matrix-assisted laser desorption ionization-time of flight shows that unlike traditional Heck chemistry, haloaromatic compounds are adding twice across the vinylsilane groups. Finally, organic light emitting diodes using the aromatic amine-based dendrimer as hole injection layers show 55% improvement in device efficiency over traditional materials (5.16 vs. 3.24 cd A(-1)) with brightness levels exceeding 40,000 cd m(-2).     

Phenanthrene derivatives combined charge transport properties and strong solid-state emission

Science China Chemistry - As bifunctional materials, phenanthrene derivatives 2,7-diphenylphenanthrene and 2,7-di(styryl)phenanthrene (DPPa and DSPa) were designed and studied. Both materials show...     

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

The Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method using KOs₂O₆ as a host. The composition was identified as Na_1.4Os₂O₆·H₂O by electron probe micro-analysis, thermogravimetric analysis, and structural analysis using synchrotron X-ray diffraction. Na_1.4Os₂O₆·H₂O crystallizes in a regular pyrochlore structure with some defects (space group: Fd-3m, a=10.16851(1) Å). Electrical resistivity, heat capacity, and magnetization measurements clearly showed absence of superconductivity down to 2 K, being in large contrast to what was found for the β-type pyrochlore superconductor AOs₂O₆ (A=Cs, Rb, and K). The Sommerfeld coefficient is 22 mJ K⁻² mol⁻¹, being the smallest among AOs₂O₆. A magnetic anomaly at ∼57 K and associated magneto-resistance (+3.7% at 2 K in 70 kOe) were found.     

两种四噻吩并萘分子晶体电荷传输性质的理论研究

采用密度泛函理论(DFT)方法结合不相干的电荷跳跃模型和随机Monte Carlo模拟,研究了2种四噻吩并萘晶体(AT1和AT2)的分子结构、电子性质及电荷载流子传输参数,并预测了这2种晶体室温下空穴和电子迁移率的各向异性.结果表明标题化合物具有近似平面的刚性骨架结构,电荷传输过程中分子的结构弛豫相当小.基于绝热势能面法计算的AT1和AT2分子空穴/电子传输内重组能分别为9.300×10~(-2)/1.100×10~(-1)eV和1.020×10~(-1)/1.290×10~(-1) eV,外重组能分别为1.835×10~(-2)/1.711×10~(-2) eV和1.857×10~(-2)/1.747×10~(-2) eV.利用Monte Carlo随机模拟方法预测的2种分子晶体室温(300K)下空穴/电子迁移率平均值分别为4.976×10~(-3)/2.766×10~(-2) cm~2 V~(-1)s~(-1)和3.857×10~(-3)/1.478×10~(-2)cm~2 V~(-1)s~(-1).此外,迁移率的角度依赖性研究表明2种载流子在AT1和AT2晶体aob平面传输时表现出显著的各向异性,其最大值均沿着电荷传输积分最大的方向,为制备高性能场效应晶体管器件提供了参考.     

Interaction between amphiphilic peptides and phospholipid membranes

This brief review aims at providing some illustrative examples on the interaction between amphiphilic peptides and phospholipid membranes, an area of significant current interest. Focusing on antimicrobial peptides, factors affecting peptide–membrane interactions are addressed, including effects of peptide length, charge, hydrophobicity, secondary structure, and topology. Effects of membrane composition are also illustrated, including effects of membrane charge, nature of the polar headgroup, and presence of cholesterol and other sterols. Throughout, novel insights on the importance of peptide adsorption density on membrane stability are emphasized, as is the correlation between peptide adsorption, peptide-induced leakage in model liposome systems, peptide-induced lysis of bacteria, and bacteria killing.     

DNA-mediated charge transport by minor groove-binding polyamide

A novel polyamide-modified electrode was fabricated successfully by surface synthesis. The DNA-mediated charge transport by minor groove-binding polyamide was observed for the first time with a [Ru(NH₃)₆]^2+/3+ probe. Two control experiments on HSC₁₁H₂₂NH₂ SAM/Au electrode, with and without DNA adsorption, confirmed that polyamide–DNA complex was a medium of charge transport. Four different DNA sequences were employed to investigate the effect of the charge transport of the polyamide–DNA complex in the minor groove. The peak current and a positive shift of peak potential were enhanced with the affinity increase between polyamide and DNA sequences. The experimental result offers a powerful tool for exquisite recognition of different sequences of base-pairs in double-stranded DNA.     

Suppression of DNA-mediated charge transport by BamHI binding

A guanine radical cation produced by one-electron DNA oxidation migrates over long distances through the DNA pi-stack. Fundamental questions regarding the likelihood of charge transport in genomic DNA, the effects of protein binding, and its biological consequences arise as the next issues of study. Electronic effects of protein binding on the efficiency of charge transport were investigated for the endonuclease BamHI-DNA complex. Direct contact of a positively charged guanidium group of BamHI to guanines in the recognition sequence 5'-GGATCC-3' completely suppressed one-electron oxidation of the guanine in the protein binding site and dramatically lowered the charge transport efficiency through the sequence. Electronically insulated guanines, by the hydrogen bonding contact of a guanidium group in BamHI, no longer function as a stepping stone in the charge transport through the DNA pi-stack.     

Influence of charge state and amino acid composition on hydrogen transfer in electron capture dissociation of peptides

Although conventional N-Cα bond cleavage in electron capture dissociation (ECD) of multiply-charged peptides generates a complementary c′ and z′ fragment pair, the N-Cα cleavage followed by hydrogen transfer from c′ to z′ fragments produces other fragments, namely c′ and z′. In this study, the influence of charge state and amino acid composition on hydrogen transfer in ECD is described using sets of peptides. Hydrogen transferred ionic species such as c′ and z′ were observed in ECD spectra of doubly-protonated peptides, while the triply-protonated form did not demonstrate hydrogen transfer. The extent of hydrogen transfer in ECD of doubly-protonated peptides was dependent on constituent amino acids. The ECD of doubly-protonated peptides possessing numerous basic sites showed extensive hydrogen transfer compared with ECD of less basic peptides. The extent of hydrogen transfer is discussed from the viewpoints of the structure of peptide ions, the possibility of internal hydrogen bonding and intermediate lifetime of complex [c′+z′].     

Low band gap thiophene-perylene diimide systems with tunable charge transport properties

Perylenediimide-pentathiophene systems with varied architecture of thiophene units were synthesized. The photophysical, electrochemical, and charge transport behavior of the synthesized compounds were studied. Both molecules showed a low band gap of ～1.4 eV. Surprisingly, the molecule with pentathiophene attached via β-position to the PDI unit upon annealing showed a predominant hole mobility of 1 × 10(-4) cm(2) V(-1) s(-1) whereas the compound with branched pentathiophene attached via β-position showed an electron mobility of 9.8 × 10(-7) cm(2) V(-1) s(-1). This suggests that charge transport properties can be tuned by simply varying the architecture of pentathiophene units.     

The role of molecular recognition in charge transport properties of doped polyaniline

Molecular recognition plays a significant role in the counterion-induced processibility, morphological features, and physical properties of doped polyaniline (PANI). The interaction of the counterion and solvent controls the chain conformation and, as a result, the formation of extended and localized electronic states; hence, it holds the key for tuning a wide range of electrical and optical properties of doped PANI. The combined effects of counterion, solvent, and processing conditions tune the metal-insulator transition, temperature dependence of conductivity, magnetoresistance, and so forth in doped PANI. The typical examples are shown in the case of PANI doped by camphor sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, and dodecylbenzoyl sulfonic acid.     

Efficient and clean charge derivatization of peptides for analysis by mass spectrometry

Charge derivatization with succinimidyloxycarbonylmethyl tris(2,4,6‐trimethoxyphenyl)phosphonium bromide (TMPP‐Ac‐OSu) has great potential in several aspects of proteomics, such as peptide de novo sequencing, PTM analysis, etc. However, the excess reagent and its side products greatly limited its scope of use. Here, we report an improved method to perform charge derivatization of peptides by TMPP‐Ac‐OSu without interference from the excess reagent and corresponding side products. Briefly, the protein was first separated on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) or coagulated with the gel. The protein in‐gel was then incubated with a high concentration of reagent, followed by extensive washing. Afterwards, the protein was in‐gel digested with trypsin according to the routine protocol. The mainly resultant peptides were attached with one positive tag on the N‐termini or Lys‐ε‐NH₂. The process has been successfully applied to 2‐DE resolved protein spots. Compared to the native proteins, the derivatized counterparts have higher rates of PMF identification and more straightforward tandem mass spectra. This promising method should pave the way for the practical use of charge derivatization in proteomics. Copyright © 2010 John Wiley & Sons, Ltd.     

Optoelectronic and charge transport properties of the complex of carbon nanotube with perylene bisimide

In the present study we carried out an investigation on the structure and properties of the complex formed by adsorbing perylene bisimide (PBI) on the surface of (6,6) carbon nanotube (CNT) by employing different dispersion-corrected density functionals (B97D, B3LYP-GD3, and ωB97XD), which showed the complex as stable. The contribution of various components of interaction energy follows the order: dispersion > electrostatic > induction. The lower ionization energy of CNT and the higher electron affinity of PBI revealed that they constitute a donor-acceptor system. Electron density distribution of the frontier molecular orbitals of complex confirmed the photoinduced charge transfer. The charge transport properties of the complex indicated higher hole mobility than electron mobility making it suitable to be used as p-type transistor. The absorption spectrum of the complex showed absorption in the near ultraviolet-visible-near infrared regions of the electromagnetic spectrum suggesting it useful for solar cells.     

Anion binding properties of indolylmethanes

The anion binding properties of the indolylmethanes (1) were investigated by ¹H-NMR spectroscopy in CDCl₃. Tris(3-methylindol-2-yl)methane (1a) selectively bound a chloride anion the over other tested anions (Br^?, I^?, HSO ₄ ^? , and NO ₃ ^? ). In contrast, analogous compounds, phenyl bis(3-methylindol-2-yl)methane (1b), 2-hydroxyphenyl bis(3-methylindol-2-yl)methane (1c), tri(indol-3-yl)methane (1d), and phenyl di(indol-2-yl)methane (1e), showed a low anion binding ability and selectivity. These results indicate that the number and a position of the binding sites (indole NH protons) of the indolylmethanes are important factors for the formation of the complex with an anion. The high binding ability and selectivity of 1a toward a chloride anion is attributed to the proper size of the binding pocket for a chloride anion and the formation of multiple hydrogen bonds between the three indole NH protons and a chloride anion. The anion affinity of 1a was significantly affected by the cation component of quaternary ammonium salts, indicating that it is ion pair binding and not solely anion binding.     

Cyclic transmembrane charge transport mediated by pyrylium and thiopyrylium ions

Transient spectroscopy revealed that 2,4,6-trimethylpyrylium, 2,4,6-triphenylpyrylium, and 2,4,6-triphenylthiopyrylium ions oxidatively quench excited triplet [5,10,15,20-tetrakis(4-sulfonatophenyl)porphinato]zinc(II) to form the corresponding neutral radicals and the zinc porphyrin pi-cation. The measured quenching rate constants were proportional to the pyrylium one-electron reduction potentials, that is, the reaction driving force. In the presence of anionic dihexadecyl phosphate vesicles, only the fraction of pyrylium not bound to the vesicle was capable of reacting with the photoexcited zinc porphyrin. Nonetheless, the pyrylium radicals mediated highly efficient transmembrane reduction of tris(2,2'-bipyridine)cobalt(III) contained within the inner aqueous core of the vesicles with apparent quantum yields that approached unity. Permeability coefficients (P) determined for the pyrylium radicals, pyrylium cations, and the proton were 10(-4)-2 x 10(-5) cm/s, 10(-10) cm/s, and < 5 x 10(-7) cm/s, respectively, so that only the neutral radicals are membrane-permeable on the time scale of the transmembrane redox reactions. However, each electron carrier was demonstrated to transport up to 200 electrons, at which point the internal pool of electron acceptors was exhausted. Since the cations are membrane-impermeable, a reaction cycle is proposed that includes hydrolysis of the pyrylium cations formed within the aqueous core to the corresponding 1,5-diketones which, as neutral molecules, can diffuse across the bilayer. According to this mechanism, while undergoing redox cycling the pyrylium ions function as cyclical antiporters of OH(-) and the electron, thereby maintaining electroneutrality in the reaction compartments.     

The optical and charge transport properties of discotic materials with large aromatic hydrocarbon cores

The optical absorption and charge transport properties of a series of discotic molecules consisting of peripherally alkyl-substituted polycyclic aromatic cores have been investigated for core sizes, n, of 24, 42, 60, 78, 96, and 132 carbon atoms. In dilute solution, the wavelength maximum of the first absorption band increases linearly with n according to lambda(max) = 280 + 2n and the spectral features become increasingly broadened. The two smallest core compounds display a slight red-shift and increased spectral broadening in spin-coated films. For derivatives with n = 24, 42, 60, and 96, the one-dimensional, intracolumnar charge mobility, Sigma mu(1D), was determined using the pulse-radiolysis time-resolved microwave conductivity technique. For the compounds which were crystalline solids at room temperature, Sigma mu(1D) lay within the range 0.4-1.0 cm(2)/Vs. In the discotic mesophases at ca. 100 degrees C, Sigma mu(1D) was somewhat lower and varied from 0.08 to 0.38 cm(2)/Vs. The mobility values in both phases are considerably larger than the maximum values found previously for discotic triphenylene derivatives. However, the recently proposed trend toward increasing mobility with increasing core size is not substantiated by the results on the present series of increasingly large aromatic core compounds.     

Self-assembling porphyrins and phthalocyanines for photoinduced charge separation and charge transport

Large π-conjugated compounds are promising building blocks for organic thin-film electronics such as organic light-emitting diodes, organic field-effect transistors, and organic photovoltaics. Utilization of porphyrins and phthalocyanines for this purpose is highly fascinating because of their excellent electric, photophysical, and electrochemical properties as well as intense self-assembling abilities arising from π-π stacking interactions. This paper focuses on fundamental aspects of self-assembled structures that have been obtained from porphyrin and phthalocyanine building blocks and more complex composites for photoinduced charge separation and charge transport toward the potential applications to organic thin-film electronics.     

Cyclic transmembrane charge transport mediated by low-potential pyrylium ions

We have investigated the capacity of a series of N-dialkylaminophenyl-substituted pyrylium and thiopyrylium ions to act as photosensitizers and redox mediators between reactants separated by bilayer membranes. These studies were prompted by earlier results indicating that simple trimethy- and triphenyl-substituted analogues could promote efficient photosensitized transmembrane redox between vectorially organized reactants by an electroneutral e(-)/OH(-) antiport mechanism. Unlike the dyes used in the earlier studies, the ions investigated herein absorb strongly throughout the visible absorption region and are therefore potentially useful in solar photoconversion processes. We demonstrate that these ions can carry out cyclic electron transport between phase-separated electron donors and occluded Co(bpy)(3)(3+) in several transversely organized vesicles. The quantum yields obtained were relatively low, but were independent of the membrane microviscosity, suggesting that transmembrane diffusion was not rate-limiting. Triphenylpyrylium and triphenylthiopyrylium ions were shown to be capable of acting as combined photosensitizers/redox relays, apparently by direct oxidation of either solvent (water) or buffer (acetate) ions from their triplet-excited state. These reactions did not require addition of separate photosensitizers and electron donors; as such, they represent a minimal photochemical scheme for effecting transmembrane charge separation. The low-potential visible-absorbing pyrylium ions were unable to function in this dual capacity, consistent with thermodynamic limitations. However, redox titrations established that the pyranyl radicals of these dyes should be capable of reducing H(+) to H(2) in weakly acidic solutions. Consistent with their strongly reducing nature, these dyes were shown to be capable of forming methyl viologen radical in photoinitiated transmembrane redox reactions.