Gene/Protein Disease Symptom Drug Enzyme Compound
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Tremendous research efforts have been spent on thiolated gold nanoparticles and self-assembled monolayers of thiolate (RS-) on gold, but thiolated gold nanowires have received almost no attention. Here we computationally design two such one-dimensional nanosystems by creating a linear chain of Au icosahedra, fused together by either vertex sharing or face sharing. Then neighboring Au icosahedra are bridged by five thiolate groups for the vertex-sharing model and three RS-Au-SR motifs for the face-sharing model. We show that the vertex-sharing thiolated gold nanowire can be made either semiconducting or metallic by tuning the charge, while the face-sharing one is always metallic. We explain this difference between the two nanowires by examining their band structures and invoking a previously proposed electron-count rule. Implications of our findings for previous experimentation of gold nanowires are discussed, and a potential way to make thiolated gold nanowires is proposed.
ACS Nano 2009 Aug 25
PMID:Thiolated gold nanowires: metallic versus semiconducting. 1960 60

The atomic scale details of single-walled carbon nanotube (SWNT) nucleation on metal catalyst particles are elusive to experimental observations. Computer simulation of metal-catalyzed SWNT nucleation is a challenging topic but potentially of great importance to understand the factors affecting SWNT diameters, chirality, and growth efficiency. In this work, we use nonequilibrium density functional tight-binding molecular dynamics simulations and report nucleation of sp(2)-carbon cap structures on an iron particle consisting of 38 atoms. One C(2) molecule was placed every 1.0 ps around an Fe(38) cluster for 30 ps, after which a further 410 ps of annealing simulation without carbon supply was performed. We find that sp(2)-carbon network nucleation and annealing processes occur in three sequential and repetitive stages: (A) polyyne chains on the metal surface react with each other to evolve into a Y-shaped polyyne junction, which preferentially form a five-membered ring as a nucleus; (B) polyyne chains on the first five-membered ring form an additional fused five- or six-membered ring; and (C) pentagon-to-hexagon self-healing rearrangement takes place with the help of short-lived polyyne chains, stabilized by the mobile metal atoms. The observed nucleation process resembles the formation of a fullerene cage. However, the metal particle plays a key role in differentiating the nucleation process from fullerene cage formation, most importantly by keeping the growing cap structure from closing into a fullerene cage and by keeping the carbon edge "alive" for the addition of new carbon material.
ACS Nano 2009 Nov 24
PMID:Quantum chemical molecular dynamics simulation of single-walled carbon nanotube cap nucleation on an iron particle. 1982 61

We demonstrate by molecular dynamics simulations that graphene sheets could be hosted in the hydrophobic interior of biological membranes formed by amphiphilic phospholipid molecules. Our simulation shows that these hybrid graphene--membrane superstructures might be prepared by forming hydrated micelles of individual graphene flakes covered by phospholipids, which can be then fused with the membrane. Since the phospholipid layers of the membrane electrically isolate the embedded graphene from the external solution, the composite system might be used in the development of biosensors and bioelectronic materials.
ACS Nano 2010 Jan 26
PMID:Sandwiched graphene--membrane superstructures. 2002 67

Efficient delivery of nanosized drug formulations to the desired body sites is not always reached despite the rapid development of pharmaceutical nanotechnologies. In spite of the undoubted effect of the size for increased bioavailability and controlled drug delivery, submicrometer formulations also require a deeper level of design. The surface properties of the particles determine the stability of the particles, interactions with the body, and targeting potentials of drugs. Thus, the efficacy of the drug can be increased utilizing the surface layer of the nanoparticles. Influencing the surface characters of the drug is the main focus of the present work, which introduces a method for preparing nanoparticles with functional sites from low-solubility drugs using hydrophobin (HFB) proteins. Particles were prepared by precipitating a lipophilic drug (beclomethasone dipropionate) in water in the presence of the HFB proteins. Particle size below 200 nm could easily be reached with increasing HFB concentration. The particles were shown to be stable for at least 5 h in suspension, and they could be stored for longer periods of time after freeze-drying. Labeling studies using green fluorescent protein (GFP) genetically fused to a HFB clearly demonstrated that the surface of the nanoparticles was covered with the hydrophobins and that the surface could be further modified by utilizing fusion proteins. This provides a template for a variety of different functional surface-bound groups that could be tailored by modifying the hydrophilic side of the HFB via protein bioengineering. In this study, the combination of proteins and traditional pharmaceutical technology was used to synthesize functionalized protein-coated nanoparticles for drug delivery purposes.
ACS Nano 2010 Mar 23
PMID:Multifunctional hydrophobin: toward functional coatings for drug nanoparticles. 2021 Mar 3

Mutations in myocilin cause an inherited form of open angle glaucoma, a prevalent neurodegenerative disorder associated with increased intraocular pressure. Myocilin forms part of the trabecular meshwork extracellular matrix presumed to regulate intraocular pressure. Missense mutations, clustered in the olfactomedin (OLF) domain of myocilin, render the protein prone to aggregation in the endoplasmic reticulum of trabecular meshwork cells, causing cell dysfunction and death. Cellular studies have demonstrated temperature-sensitive secretion of myocilin mutants, but difficulties in expression and purification have precluded biophysical characterization of wild-type (wt) myocilin and disease-causing mutants in vitro. We have overcome these limitations by purifying wt and select glaucoma-causing mutant (D380A, I477N, I477S, K423E) forms of the OLF domain (228-504) fused to a maltose binding protein (MBP) from E. coli . Monomeric fusion proteins can be isolated in solution. To determine the relative stability of wt and mutant OLF domains, we developed a fluorescence thermal stability assay without removal of MBP and provide the first direct evidence that mutated OLF is folded but less thermally stable than wt. We tested the ability of seven chemical chaperones to stabilize mutant myocilin. Only sarcosine and trimethylamine N-oxide were capable of shifting the melting temperature of all mutants tested to near that of wt OLF. Our work lays the foundation for the identification of tailored small molecules capable of stabilizing mutant myocilin and promoting secretion to the extracellular matrix, to better control intraocular pressure and to ultimately delay the onset of myocilin glaucoma.
ACS Chem Biol 2010 May 21
PMID:Rescue of glaucoma-causing mutant myocilin thermal stability by chemical chaperones. 2033 47

Solution-phase pyridine treatment displaced oleic acid capping ligands from the surface of PbSe nanocrystals. During ligand displacement the nanostructure morphology dramatically changed from well-stabilized, individual nanocrystals to form crystallographically connected nanocrystal networks. The network morphology was governed by the diameter of the constituent nanocrystals. Larger nanocrystals showed dipolar alignment but maintained individual nanocrystal character, while smaller nanocrystals crystallographically fused along the <100> axis. Optical studies of nanocrystal thin films showed that pyridine ligand displacement quenches the nanocrystal photoluminescence. Blends of nanocrystals and conjugated polymer showed photoluminescence quenching of the polymer with increasing nanocrystal content. The extent of photoluminescence quenching was only weakly dependent on the nanocrystal size or surface chemistry, suggesting that the interaction between nanocrystal and polymer is mostly in the form of energy transfer rather than charge transfer.
ACS Appl Mater Interfaces 2009 Feb
PMID:PbSe nanocrystal network formation during pyridine ligand displacement. 2035 9

5,7,12,14-Tetrachloro-6,13-diaza-6,13-dihydropentacene (TCDAHP) and 5,7,12,14-tetrachloro-6,13-diazapentacene (TCDAP) were synthesized and assessed as the active channel materials for thin-film transistor applications. Analyses of the crystal structures of these molecules revealed that both exhibited slipped pi-pi stacking of the long and fused aromatic moiety. Although the packing features of the two compounds are basically identical, their highest occupied molecular orbitals, which are relevant to hole transport, are very different. Better mobility was predicted for TCDAHP over TCDAP based on the dimeric structure in the X-ray coordinates. The morphologies of thin films of TCDAHP and TCDAP prepared by thermal evaporation depend critically on the substrate on which the molecules were deposited: from the amorphous state on a SiO(2)/Si surface to the crystalline state on a pentacene buffer layer surface. The performance of thin-film transistors prepared on various substrate surfaces was studied. While no field-effect mobility was observed for these films deposited on SiO(2)/Si, a high mobility of 1.4 cm(2)/(V s) for the TCDAHP film was achieved when deposited on a pentacene buffer layer prepared on a rubbed monolayer of n-nonyltrichlorosilane on a SiO(2)/Si surface. A similar device prepared from TCDAP gave a mobility of 0.13 cm(2)/(V s).
ACS Appl Mater Interfaces 2009 Sep
PMID:Diazapentacene derivatives as thin-film transistor materials: morphology control in realizing high-field-effect mobility. 2035 35

Three new fused-ring pyrazine derivatives end-functionalized with trifluoromethylphenyl groups have been synthesized. The effect of a fused-ring pyrazine core on the thermal, electronic, optical, thin film morphology, and organic field-effect transistor (OFET) properties was investigated both experimentally and theoretically. Electrochemistry measurements and density functional theory calculations suggest that the pyrazine core plays a significant role in tuning the electron affinities of these compounds. The optical absorption and fluorescence properties are also sensitive to the pyrazine core. The OFET devices based on the fused-ring pyrazine compounds exhibit electron mobilities as high as ca. 0.03 cm(2) V(-1) s(-1) under nitrogen, and their performance is sensitive to the pyrazine core. The larger pyrazine core leads to a lower LUMO level and lower reorganization energy, to more ordered thin film morphology with larger grain size, and finally to higher mobilities.
ACS Appl Mater Interfaces 2009 May
PMID:Fused-ring pyrazine derivatives for n-type field-effect transistors. 2035

A new amorphous semiconducting polymer containing dodecylthiophene rings and a rigid thieno[3,2-b]thiophene ring, poly(2,5-bis(3'-dodecyl-2,2'-bithiophen-5-yl)thieno[3,2-b]thiophene) (NAP), was synthesized via a microwave-assisted Stille coupling reaction. The presence of the flexible unsubstituted thiophene ring units next to the rigid fused thiophene ring caused NAP to have an amorphous structure. This structure was confirmed by XRD, AFM, and computational calculations. In particular, the out-of-plane XRD patterns of NAP thin films exhibited no reflection peaks before or after the annealing process, indicating that the films had amorphous microstructures. In addition, AFM images of the NAP thin films showed amorphous surface morphologies with very small root-mean-square (rms) surface roughnesses of 0.3-0.5 nm, independent of surface treatment or heat treatment. Computational calculations performed to investigate the preferred conformation of the polymer confirmed the amorphous characteristics of the NAP structure. On the basis of these findings, we propose how an amorphous NAP semiconductor can maintain high carrier mobility. A NAP-based TFT device exhibited a very high carrier mobility of 0.02 cm(2) V(-1) s(-1) with an on/off ratio of 1 x 10(5) and a very small threshold voltage of -2.0 V. This carrier mobility is the highest yet reported for TFTs based on amorphous semiconductors. Thus, the present findings suggest that an amorphous semiconductor layer comprised of NAP would be suitable for use in high-performance organic TFTs fabricated via simple processes in which neither surface treatment nor heat treatment is necessary.
ACS Appl Mater Interfaces 2010 Apr
PMID:A new amorphous semiconducting polythiophene for high-performance organic thin-film transistors. 2038 57

Split-inteins can be used to generate backbone cyclized peptide as a source of new bioactive molecules. In this work we show that cysteine-mediated splicing can be performed in the oxidative environment of the periplasm of Escherichia coli. Cyclization of the TEM-1 beta-lactamase and of small randomized peptides was demonstrated using an artificially permuted version of the DnaB mini-intein from Synechocystis sp. PCC6803 strain fused to a signal sequence. For small peptides, a signal sequence that promotes cotranslational translocation had to be used. Efficient backbone cyclization was observed for more than 50% of combinatorial peptides featuring a fully randomized sequence inserted between a serine and glycine that are necessary for fast splicing. Furthermore, by coexpressing a mutant of the pIV outer membrane pore protein of fd bacteriophage, we showed that peptides can diffuse in the extracellular medium. These results open new routes for searching compounds acting on new targets such as exported and membrane proteins or pathogen microorganisms.
ACS Chem Biol 2010 Jul 16
PMID:Intein-mediated cyclization of randomized peptides in the periplasm of Escherichia coli and their extracellular secretion. 2052 81


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