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Pseudomonas putida F1 utilizes p-cymene (p-isopropyltoluene) by an 11-step pathway through p-cumate (p-isopropylbenzoate) to isobutyrate, pyruvate, and acetyl coenzyme A. The cym operon, encoding the conversion of p-cymene to p-cumate, is located just upstream of the cmt operon, which encodes the further catabolism of p-cumate and is located, in turn, upstream of the tod (toluene catabolism) operon in P. putida F1. The sequences of an 11,236-bp DNA segment carrying the cym operon and a 915-bp DNA segment completing the sequence of the 2,673-bp DNA segment separating the cmt and tod operons have been determined and are discussed here. The cym operon contains six genes in the order cymBCAaAbDE. The gene products have been identified both by functional assays and by comparing deduced amino acid sequences to published sequences. Thus, cymAa and cymAb encode the two components of p-cymene monooxygenase, a hydroxylase and a reductase, respectively; cymB encodes p-cumic alcohol dehydrogenase; cymC encodes p-cumic aldehyde dehydrogenase; cymD encodes a putative outer membrane protein related to gene products of other aromatic hydrocarbon catabolic operons, but having an unknown function in p-cymene catabolism; and cymE encodes an acetyl coenzyme A synthetase whose role in this pathway is also unknown. Upstream of the cym operon is a regulatory gene, cymR. By using recombinant bacteria carrying either the operator-promoter region of the cym operon or the cmt operon upstream of genes encoding readily assayed enzymes, in the presence or absence of cymR, it was demonstrated that cymR encodes a repressor which controls expression of both the cym and cmt operons and is inducible by p-cumate but not p-cymene. Short (less than 350 bp) homologous DNA segments that are located upstream of cymR and between the cmt and tod operons may have been involved in recombination events that led to the current arrangement of cym, cmt, and tod genes in P. putida F1.
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PMID:p-Cymene catabolic pathway in Pseudomonas putida F1: cloning and characterization of DNA encoding conversion of p-cymene to p-cumate. 915 Feb 11

Photodynamic treatment of the gram-negative bacteria Escherichia coli B and Acinetobacter baumannii and the gram-positive bacterium Staphylococcus aureus was performed using two newly devised and synthesized antioxidant carrier photosensitizers (antioxidant carrier sensitizers-2 [ACS-2] and antioxidant carrier sensitizers-3 [ACS-3]), which are butyl hydroxy toluene and propyl gallate substituted haematoporphyrins, respectively. It was found that ACS-2 is less reactive than other photosensitizers previously used for the same purpose, whereas ACS-3 is very effective against the multidrug-resistant bacterium A. baumannii, causing its complete eradication at a low fluence (approximately 7.5 J/cm2) of blue light (407-420 nm) and a low concentration (10 microM). At a higher fluence (approximately 37.5 J/cm2) complete eradication of E. coli B can be obtained under the same conditions. Furthermore, X-ray microanalysis and ultrastructural changes indicate that ACS-3, especially in the case of photodynamic treatment of A. baumannii, interferes with membrane functions and causes the inactivation of the bacterium. ACS-3 may be suggested as a specific photosensitization agent for photoinactivation of gram-negative bacteria.
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PMID:Photodynamic effects of antioxidant substituted porphyrin photosensitizers on gram-positive and -negative bacterial. 1278 58

Here we describe the chemiresistive sensing of volatile organic compounds (VOCs) with films of chemically synthesized approximately 4 nm diameter Au and AuAg alloy nanoparticles (NPs) stabilized by a surfactant, tetraoctylammonium bromide (TOABr). The chemiresistive sensing properties were measured over a concentration range of 100 to 0.04% saturation for methanol (MeOH), ethanol (EtOH), 2-propanol (IPA), and toluene (Tol) vapor analytes and compared directly to the chemiresistive sensing properties of films of 1.6 nm diameter hexanethiolate (C6S)-coated Au monolayer-protected clusters (MPCs). Films of TOABr-stabilized Au NPs exhibit the opposite response compared to those of C6S-coated Au MPCs. The details are unclear, but the mechanism likely involves changes in capacitive charging in the film or improved conductive pathways through the Au NPs upon incorporation of VOCs into the film for the former as opposed to the well-known change in electron hopping conductivity for the latter. This leads to a decrease in resistance in the presence of VOCs for TOABr Au as opposed to an increase for C6S Au. The TOABr Au sensors are more sensitive, especially for polar analytes, and have greater long-term stability compared to C6S Au. The limit of detection (LOD) for films of TOABr-coated Au NPs is 3, 2, 12, and 37 ppm for IPA, MeOH, EtOH, and Tol, respectively, as compared to 106, 326, 242, and 48 for C6S Au. Films of TOABr-stabilized AuAg alloy NPs exhibit the same type of response, but the sensitivity decreases dramatically with increasing Ag content, showing that the metal composition of the NPs in the film plays a role in the sensing properties, which has not been well-recognized in the literature.
ACS Nano 2008 Aug
PMID:Chemiresistive sensing of volatile organic compounds with films of surfactant-stabilized gold and gold-silver alloy nanoparticles. 1920 57

We report the construction of lipid-quantum dot (L-QD) bilayer vesicles by incorporation of the smallest (2 nm core size) commercially available CdSe/ZnS QD within zwitterionic dioleoylphosphatidylcholine and cationic 1,2-dioleoyl-3-trimethylammonium-propane lipid bilayers, self-assembling into small unilamellar vesicles. The incorporation of QD in the acyl environment of the lipid bilayer led to significant enhancement of their optical stability during storage and exposure to UV irradiation compared to that of QD alone in toluene. Moreover, structural characterization of L-QD hybrid bilayer vesicles using cryogenic electron microscopy revealed that the incorporation of QD takes place by hydrophobic self-association within the biomembranes. The L-QD vesicles bound and internalized in human epithelial lung cells (A549), and confocal laser scanning microscopy studies indicated that the L-QD were able to intracellularly traffick inside the cells. Moreover, cationic L-QD vesicles were injected in vivo intratumorally, leading to enhanced retention within human cervical carcinoma (C33a) xenografts. The hybrid L-QD bilayer vesicles presented here are thought to constitute a novel delivery system that offers the potential for transport of combinatory therapeutic and diagnostic modalities to cancer cells in vitro and in vivo.
ACS Nano 2008 Mar
PMID:Lipid-quantum dot bilayer vesicles enhance tumor cell uptake and retention in vitro and in vivo. 1920 64

The preparation of wavelength-specific Bragg mirrors was realized by an effective and reproducible spin-coating approach using colloidal suspensions of functionalized mesoporous silica nanoparticles and titania sols. Due to the small particle size and the resulting low surface roughness, the formation of multilayers was possible without transmitting defects on the surface with every following coating step. The Bragg reflectors show sensitivity toward specific relative pressures of organic vapors such as toluene, giving rise to optically encoded adsorption properties as a function of solvent pressure and, thus, to optical adsorption isotherms.
ACS Nano 2009 Jul 28
PMID:Vapor-sensitive bragg mirrors and optical isotherms from mesoporous nanoparticle suspensions. 1953 64

Carbon nitride materials have extraordinary potential in various applications, including catalysts, filled-particles, and superhard materials. Carbon nitride nanoclusters have been prepared under mild solvothermal conditions by a reaction between 1,3,5-trichlotriazine and sodium azide in toluene. The bulk material formed has a C(3)N(4) composition and consists of spheres with diameters ranging from approximately 1 nm to 4 mum. Nanometer-sized clusters of C(3)N(4) stoichiometry have been isolated on surfaces by sublimation or simple physicochemical methods. The clusters have then been characterized by atomic force microscopy and X-ray photoelectron spectroscopy. The laser desorption ionization mass spectra show peaks assignable to the C(12)N(16), C(21)N(28), and C(33)N(44) molecules which could correspond to cage structures with 4, 7, and 11 units of the C(3)N(4) subunit, respectively. The structure and stability of these new nitrogen-rich carbon nitride nanocages has been investigated using density functional theory calculations.
ACS Nano 2009 Nov 24
PMID:Azafullerene-like nanosized clusters. 1986 Mar 86

We present a mesoporous hole-conducting polymer film resulting from spontaneous block copolymer self-assembly based on a simple spin-coating protocol. A diblock copolymer consisting of a triphenylamine side group polymer and a poly(d,l-lactide) block (PSTPA-b-PLA) is shown to microphase separate to form ordered 13 nm cylindrical PLA microdomains embedded in the semiconducting PSTPA matrix. Partially ordered and film-spanning PLA domains could be identified in films immediately after spin coating from toluene solutions on conducting substrates. Selective mild etching of the minority PLA domains (in weak aqueous base) leads to a mesoporous hole-conducting polymer matrix. The pore structure is replicated electrochemically in platinum, demonstrating the viability of this approach to producing nano-organized heterojunction structures in thin films.
ACS Nano 2010 Feb 23
PMID:Soft-etch mesoporous hole-conducting block copolymer templates. 2009 66

We demonstrate here two-terminal, charge-based memory from C60 films inside vertical 7 nm silicon nanogap devices. This testbed structure eliminated the possibility of metal migration in the nanostructure because the two electrodes are made solely of silicon; hence, the often troublesome and confusing possibility of filamentary metal formation is obviated. Saturated solutions of C60 in toluene, mesitylene, and 1-methylnaphthalene were each used to deposit these films at elevated temperatures. Electrical I-V measurements reveal a high yield (67%) of devices demonstrating bipolar, switchable hysteresis from both the mesitylene- and 1-methylnaphthalene-deposited devices, while the toluene-grafted devices display no such behavior. Pulse-based memory measurements of switching devices indicate high ON/OFF ratios (maximum approximately 1500), good stability (>100 cycles without device degradation) for molecular devices, and low operating currents (approximately 10(-11) A) in room temperature testing.
ACS Nano 2010 Apr 27
PMID:Two-terminal molecular memories from solution-deposited C60 films in vertical silicon nanogaps. 2023 44

High-quality approximately 16 nm c-In2O3 nanoctahedra and approximately 6 nm Pd spherical nanoparticles were synthesized via a high-temperature wet-chemical approach, and their electrophoretic mobilities in toluene were investigated, respectively. Opposite electrical charge-induced 2D binary nanoparticle superlattice patterns containing two such nanocomponents were prepared, for the first time. Three types of c-In2O3-skeleton-structure-contained assembly patterns were identified as well. It was further observed that the vertices of c-In2O3 nanoctahedra could have higher electrical charge density than that on edge or plane and the small Pd nanoparticles were "suspended" on the middle plane of the c-In2O3 nanoctahedra, apparently well above the substrate surface (support film) rather than sitting on it. The assembly structure study indicates that Coulomb forces resulted from the opposite electrical charges are the dominative driving forces to induce the formation of such nanoctahedra-nanospheres 2D binary nanoparticle superlattices.
ACS Nano 2010 Apr 27
PMID:Assembling nonspherical 2D binary nanoparticle superlattices by opposite electrical charges: the role of Coulomb forces. 2034 38

The new metalloporphyrin Pt(tptnp), where tptnp = tetraphenyltetranaphtho[2,3]porphyrin, has been prepared and subjected to photophysical and electrooptical device studies. In degassed toluene solution at room temperature Pt(tptnp) features efficient phosphorescence emission with lambda(max) 883 nm with a quantum efficiency of 0.22. The complex has been used as the active phosphor in polymer and organic light-emitting diodes. Polymer light-emitting diodes based on a spin-coated emissive layer consisting of a blend of Pt(tptnp) doped in poly(9-vinylcarbazole) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole exhibit near-IR emission with lambda(max) 896 nm, with a maximum external quantum efficiency (EQE) of 0.4% and a maximum radiant emittance of 100 muW/cm(2). Organic light-emitting diodes prepared via vapor deposition of all layers and that feature an optimized multilayer hole injection and electron blocking layer heterostructure with an emissive layer consisting of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) doped with Pt(tptnp) exhibit a maximum EQE of 3.8% and a maximum radiant emittance of 1.8 mW/cm(2). The polymer and organic light-emitting diodes characterized in this study exhibit record high efficiency for devices that emit in the near-IR at lambda >800 nm.
ACS Appl Mater Interfaces 2009 Feb
PMID:Efficient near-infrared polymer and organic light-emitting diodes based on electrophosphorescence from (tetraphenyltetranaphtho[2,3]porphyrin)platinum(II). 2035 14


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