bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of magnetic spinel ferrite CoFe2O4 nanoparticles from ferric salt and characterization of the size-dependent superparamagnetic properties
Authors: Liu Chao , Rondinone Adam J. , Zhang Z. John
Published: October 2007

The CoFe2O4 nanoparticles have been synthesized by using a stable ferric salt of FeCl3 with a micellar microemulsion method. The normal micelles are formed by sodium dodecyl sulfate (NaDS) in aqueous solutions. The mean size of the nanoparticles can be controlled from less than 4 nm to about 10 nm through controlling the concentrations of the reagents. The neutron diffraction in combination with the Rietveld refinement shows that these CoFe2O4 nanoparticles have a high degree of inversion with 66% of the tetrahedral sublattice occupied by Fe3+. Magnetic measurements and neutron diffraction studies demonstrate the superparamagnetic nature of these CoFe2O4 nanoparticles. The size-dependent superparamagnetic properties of CoFe2O4 nanoparticles have also been systematically studied. The blocking temperature and coercive field of the nanoparticles increase with increasing size of the nanoparticles. The superparamagnetic behaviors of CoFe2O4 nanoparticles are consistent with the Stoner-Wohlfarth theory of single domain particles.
Fabrication and physical properties of self-organized silver nanocrystals
Authors: Pileni M. P.
Published: October 2007

A simple method is used to prepare highly monodispersed silver nanoparticles in the liquid phase, which starts from an initial synthesis in functionalized AOT reverse micelles. To narrow the particle size distribution from 43 to 12.5% in dispersion, the particles are extracted from the micellar solution. The size-selected precipitation method is used. The nanocrystallites dispersed in hexane are deposited on a support. A monolayer made of nanoparticles with spontaneous compact hexagonal organization is observed. The immersion of the support on the solution yields to the formation of organized multilayers arranged as microcrystal in a face-centered-cubic structure.

We compare the optical properties of spherical particles organized in a two- and three-dimensional structure with isolated and disordered particles. When particles, deposited on cleaved graphite, are arranged in a hexagonal array, the optical measurements under p-polarization show a new high-energy resonance, which is interpreted as a collective effect, resulting from optical anisotropy due to the mutual interactions between particles. We support this interpretation by numerical calculations performed for finite-size clusters of silver spheres. For disordered particles, a low-energy resonance appears instead of the high-energy resonance observed for spherical and organized particles. This is interpreted as optical shape anisotropy due to the asymmetrical arrangement of particles.

The tip of a scanning tunneling microscope (STM) may be used as an extremely localized source of low-energy electrons to locally excite photon emission from a variety of metal films. The detection of locally excited luminescence at the junction of an STM tip provides access to electron dynamic properties at the surface, which makes it possible to study luminescence phenomena of nanometer-sized structures.

The photon intensity emitted from electrically isolated silver nanoparticles self-organized as a 2D network on a gold (111) substrate is analyzed. We observed unexpectedly strong variations of photon-emission efficiency from isolated nanoparticles, depending on how tightly they are embedded within the network site. The quenching site observed in the STM photon emission map is interpreted as an enhanced interaction of electrons with surface photon modes.
Redox-active polymer-nanoparticle hybrid materials
Authors: Watson Keith J. , Zhu Jin , Nguyen SonBinh T. , Mirkin Chad A.
Published: October 2007

Ring-opening metathesis polymerization was used to modify organic soluble gold nanoparticles with redox-active polymers. A gel-permeation chromatography study revealed that each nanoparticle is modified with approximately 11 polymer chains. Electrochemical studies of nanoparticles modified with block copolymers of two different redox-active groups revealed that each monomer is electrochemically accessible, while no current rectification was observed.
Binary cooperative complementary nanoscale interfacial materials
Authors: Jiang L. , Wang R. , Yang B. , Li T. J. , Tryk D. A. , Fujishima A. , Hashimoto K. , Zhu D. B.
Published: October 2007

Binary cooperative complementary nanoscale interfacial materials, i.e, materials with two complementary properties on the nanoscale, are introduced as a new concept for the design of functional materials. The concept is based on the generation of nanostructures with mutually compensating properties on the surface of a solid. Under certain coordinating conditions, unexpected properties may often appear at these kinds of interfaces, creating a huge potential for applications and theoretical research. Recent research indicates that the binary cooperative complementary concept is extremely useful for the design and creation of nanoscale functional materials.
Phototransformation of Alkanethiol-derivatized Noble Metal Nanoparticle
Authors: Ah Chil Seong , Han Hyouk Soo , Kim Kwan , Jang Du-Jeon
Published: October 2007

Photon-initiated shape transformation of n-alkanethiol-derivatized noble metal nanoparticles has been studied with variations of metal, alkanethiol, and solvent. Silver nanoparticles undergo fragmentation upon irradiation while gold ones barely do. Silver/gold composite particles follow the case of silver with a reduced efficiency. The efficiency decreases as alkanethiol length or solvent dipole moment increases. Following the conduction of thermalized photon energy, alkanethiol can dissociate in a period of heat dissipation, and some of dethiolated particles fragment within the recombination time. Prior to the thermal conduction, shape transformation via melt and vaporization also occurs for both metals but this effect is less apparent for silver because of more notable fragmentation followed. The difference in the transformation of two metals is ascribed to the differences in work function, oxidation potential, atomization enthalpy, and particle size. Smaller fragmentation efficiency with more polar solvent or longer alkanethiol is attributed mainly to relatively smaller dissociation rate compared with heat dissipation rate.
Synthesis and characterization of Cu x S nanoparticles. Nature of the infrared band and charge-carrier dynamics
Authors: Brelle M. C. , Torres-Martinez C. L. , McNulty J. C. , Mehra R. K. , Zhang J. Z.
Published: October 2007

CuxS (x = 1,2) nanoparticles have been synthesized utilizing different capping molecules including polyethyleneglycol (PEG), polyvinylpyrrolidone (PVP), casein hydrolysate-enzymatic (CAS), and bovine serum albumin (BSA). The ground-state electronic absorption spectra of the CuxS nanoparticles show three distinct types of CuxS formed: a green type assigned as crystalline CuS, and two brown types assigned as crystalline Cu2S and amorphous Cu2S. The brown types exhibit a steady increase in absorption toward shorter wavelengths starting at around 650 nm, while the green type shows the same steady increase in absorption, but with an additional absorption band in the infrared (IR). The IR band is attributed to an electron-acceptor state lying within the bandgap. ESR measurements of free Cu(II) ions in solution for all samples show the presence of Cu(II) in the brown amorphous samples, but not in the green or brown crystalline samples. Ultrafast dynamics of photoinduced electrons have been measured for all samples using femtosecond-transient absorption/bleach spectroscopy. In all brown Cu2S samples studied, the early time-transient profiles feature a pulse-width-limited (<150 fs) rise followed by a fast decay (1.1 ps) and a slow decay (>80 ps). These decay dynamics were found to be independent of pump power and stabilizing agent. The fast 1.1 ps decay is attributed to charge carrier trapping, while the long decay may be due to either recombination or deep trapping of the charge carriers. The green CuxS samples studied showed interesting power-dependent behavior. At low excitation intensities, the green CuxS samples showed a transient bleach signal, while at high intensities, a transient absorption signal has been observed. The increased transient absorption over bleach at high intensities is attributed to trap-state saturation. A kinetic model has been developed to account for the main features of the electronic relaxation dynamics.
One-dimensional growth of rock-salt PbS nanocrystals mediated by surfactant/polymer templates
Authors: Yang Shihe , Wang Suhua , Fung K. K.
Published: October 2007

A novel method has been developed for the synthesis of compound semiconductor nanorods (PbS). This method consists of using a functionalized lead(II) salt Pb(AOT)2 as the precursor and a polymer (PVB) as both a matrix and a stabilizer. The PbS nanocrystallites prepared using this method are all oriented with their (100) lattice planes parallel to the substrate surface. Possible mechanisms are briefly discussed for the growth of the rod-shaped PbS nanocrystals with the preferred orientation in the polymer film.
Preparation of II-VI group semiconductor nanowire arrays by dc electrochemical deposition in porous aluminum oxide templates
Authors: Xu Dongsheng , Chen Dapeng , Xu Yajie , Shi Xuesong , Guo Guolin , Gui Linlin , Tang Youqi
Published: October 2007

II-VI group compound semiconductors such as CdS, CdSe, and CdTe nanowire arrays have been prepared by direct current electrodeposition in porous anodic aluminum oxide template from nonaqueous electrolyte. SEM and TEM results show that these nanowires have a highly anisotropic structure of aligned nanowires with diameters of 15-200 nm, which are consistent with the diameters of the templates used. Electron diffraction and HREM investigations demonstrate that the crystalline structures of these nanowires are uniform hexagonal single crystal. This approach can be used to fabricate single crystal nanowire arrays of a wide range of semiconductors and other materials.
Control of morphology in synthesizing mesoporous silica
Authors: Mou Chung-Yuan , Lin Hong-Ping
Published: October 2007

Mesoporous silica can be synthesized by either the alkaline route or the acidic route, both using surfactants as templates. Morphological transformations of mesoporous silica can produce various hierarchical orders. Different morphologies are produced under different synthetic conditions. In the alkaline route, the surfactant/silicate liquid crystal system undergoes phase transformation to form vesicles and further transforms to the hexagonal phase. The results are tubule-within-tubule and hollow pillar-within-sphere structures depending on cosurfactant/surfactant composition. Using nitric acid in the acidic route, one can obtain hierarchical ropes or gyroids depending on stirring conditions. Ammonia hydrothermal treatment can induce further morphological transformation to nanotubes of mesoporous silica.
Polymeric nanostructured composite films
Authors: Shen Jiacong , Sun Junqi , Zhang Xi
Published: October 2007

This research news describes the construction of polymeric nanostructured composite film based on a variety of interactions, such as hydrophobic–hydrophilic effect, electrostatic interaction, hydrogen bonding, etc. The work focused on developing strategies to solve the basic problems in the area of ultrathin film research, such as stability, improving the interface quality, creating patterned interface, and techniques to construct nanolayered structure. With in-depth study of the relationship between the microscopic layered architecture and macroscopic function of supramolecular assemblies, it is anticipated that one could obtain miniature devices or machines of high efficiency through integration of the assembling process and device fabrication.
Processible nanomaterials with high conductivity and magnetizability. Preparation and properties of maghemite/polyaniline nanocomposite films
Authors: Tang Ben Zhong , Geng Yanhou , Sun Qunhui , Zhang Xi Xiang , Jing Xiabin
Published: October 2007

A versatile process employing anionic surfactants has been developed for the preparation of processible nanocomposite films with electrical conductivity and magnetic susceptibility. Maghemite (γFe2O3) nanoclusters (~10 nm in size) are coated with 4-dodecyl-benzenesulfonic acid, and polyaniline (PAn) chains are doped with 10-camphorsulfonic acid. The coated nanoclusters and doped polymers are soluble in common solvents, and casting the solutions readily gives free-standing nanocomposite films with nanocluster contents as high as ~50 wt %. The γFe2O3/PAn nanocomposites show high conductivity (82–237 S cm -1 ) and magnetizability (up to ~35 emu/g γFe2O3).
High-density femtosecond transient absorption spectroscopy of semiconductor nanoparticles. A tool to investigate surface quality
Authors: Burda C. , El-Sayed Mostafa A.
Published: October 2007

At the high laser excitation intensities used in our experiments, more than 50 electron-hole pairs are formed in colloidal semiconductor nanoparticles used in our studies. At this density of charge carriers, new transient absorptions are observed in the femtosecond transient spectra in the 450 to 700 nm region with unresolved fast rise (<100 fs) and two decay components of 660 fs and >150 ps. The absorption at 510 nm could be quenched with the adsorption of electron acceptors (e.g., benzoquinone, 1,2-naphthoquinone), whereas the low-energy transient absorption was not affected. For CdS NPs, we found that passivation eliminated most of the transient absorption. The transient absorptions are thus proposed to result from either trap-state absorption, trapped dimers (or complexes) and/or Stark-shifted exciton absorption resulting from surface electric field of the uncompensated trapped electron-hole pairs. All these possibilities require effective surface trapping at these high levels of excitation.
Chemistry and photophysics of thiol-stabilized II-VI semiconductor nanocrystals
Authors: Eychmüller Alexander , Rogach Andrey L.
Published: October 2007

The chemical and physical properties of thiol-stabilized semiconductor nanocrystals are reviewed. The materials prepared include cadmium and mercury chalcogenides with sizes ranging between 1.4 and about 8 nm. In this size regime, the optical properties of the particles are governed by the size-quantization effect. All nanocrystals synthesized belong to the cubic crystal structure. Some applications of this class of materials are outlined.
Distribution and shape of self-assembled InAs quantum dots grown on GaAs (001)
Authors: Zhang K. , Falta J. , Schmidt Th. , Heyn Ch. , Materlik G. , Hansen W.
Published: October 2007

Grazing incidence small angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) experiments are employed to study self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) on GaAs (001). The GISAXS spectra show pronounced non-specular diffuse scattering satellite peaks with high diffraction orders up to ±3 along [110], [1-10], and [100] sample azimuthal orientations with respect to the incoming beam, indicating a lateral ordering of the InAs QDs. The correlation lengths of the lateral dot distribution are found to be identical along [110] and [1-10] but smaller along [100] direction. The ratio of the mean dot-dot distances along [100] and [1-10] azimuths is determined to be 1.13, indicating the anisotropic ordering of QD distribution. Broad diffraction peaks are observed at larger scattering angles and associated to dot facet crystal truncation rods (CTR). We determine {111}-like facets along [110] and [1-10] sample azimuths, and {101}-like facets along [100] azimuth.
A complementary study of surface-enhanced Raman scattering and metal nanorod arrays
Authors: Yao J. L. , Pan G. P. , Xue K. H. , Wu D. Y. , Ren B. , Sun D. M. , Tang J. , Xu X. , Tian Z. Q.
Published: October 2007

The two-dimensional arrays of various metal nanowires with diameters ranging from 15 to 70 nm have been fabricated by electrodepositing metals of Cu, Ag, Au, Ni, and Co into the nanoholes of the anodic aluminum oxide (AAO) films, followed by partial removal of the film. The strong surface-enhanced Raman scattering (SERS) effects were observed from the metal nanowire arrays including Ni, Co metals that were normally considered to be non-SERS active substrates. It has been shown that metal nanowire arrays can serve as very good SERS active substrates, especially for transition metals. The SERS intensity of the probe molecule adsorbed at the nanowires depends critically on the length of the nanowires explored at the surface. And the band frequency is very sensitive to the diameter, which reflects the change in the electronic property of metal nanowires. Applying this probe molecule strategy, SERS could develop into a diagnostic tool of metal nanowires (nanorods).
A gold nanoparticle/latex microsphere-based colorimetric oligonucleotide detection method
Authors: Reynolds Robert A. , Mirkin Chad A. , Letsinger Robert L.
Published: October 2007

An exceptionally simple and effective DNA detection methodology based on latex microsphere and gold nanoparticle probes has been developed. The latex and gold particle probes, which were functionalized with separate oligonucleotide sequences, undergo hybridization in the presence of target strands that are complementary to both of the probes. Duplex formation thus results in linking of gold nanoparticles to the latex microspheres and a corresponding white-to-red color change, which, because of the particularly large extinction coefficient of the gold nanoparticles, is clearly visible to the naked eye. Background signal caused by unbound gold nanoparticles is significantly reduced by filtering the solution containing the sample and probes through a size-selective cellulose acetate membrane. The unbound gold probes move freely through this membrane while the larger latex particles are trapped. Therefore, if the latex and gold nanoparticles are joined together via the target oligonucleotides, the membrane appears red, indicating a positive test result. If no hybridization takes place, the membrane appears white, indicating a negative result. The lower detection limits for this system are 500 pM for a 24 base single-stranded target and 2.5 nM for a duplex target oligonucleotide.
Colloidal nanocrystals for telecommunications. Complete coverage of the low-loss fiber windows by mercury telluride quantum dot
Authors: Harrison M. T. , Kershaw S. V. , Burt M. G. , Rogach A. L. , Kornowski A. , Eychmüller Alexander , Weller H.
Published: October 2007

Optical fibers have revolutionized the telecommunications industry to such an extent that the network capacity available today was unthinkable 20 years ago. Even so, with the advent of the datawave, and the exponential increase of network traffic predicted to continue indefinitely, the generation of bandwidth remains a challenge. One of the major limitations to the implementation of future high-capacity, ultra-broadband optical networks is the expansion of the fiber bandwidth beyond that available from the current state-of-the-art signal amplification device--the erbium-doped fiber amplifier (EDFA). Although there is currently a large effort to expand the flat-gain bandwidth of the EDFA, most of these efforts involve sophisticated engineering, exotic glass fibers, or multicomponent cascaded systems. In a radically different approach, we are attempting to use the unique properties of semiconductor nanocrystals, or quantum dots, as "designer atoms" in order to produce an ultra-broadband optical amplifier with complete coverage of the telecommunications wavelengths. In this paper we review the synthesis of thiol-stabilized mercury chalcogenide nanocrystals via an aqueous colloidal route, which demonstrate extremely intense photoluminescence all the way across the spectral region of interest, i.e., from 1000 to over 1700 nm.
Multiply coated microspheres. A platform for realizing fields-induced structural transition and photonic bandgap
Authors: Sheng Ping , Wen Weijia , Wang Ning , Ma Hongru , Lin Zhifang , Zhang W. Y. , Lei X. Y. , Wang Z. L. , Zheng D. G. , Tam Wing Yim , Chan C. T.
Published: October 2007

Under crossed electric and magnetic fields, multiply coated microspheres form columnar crystallites with an internal structure that transforms from body-centered-tetragonal to face-centered-cubic as the ratio between the magnetic and the electric fields exceeds a minimum value. The observed transition scenario is in excellent agreement with calculations. These multiply coated microspheres also serve as building blocks for photonic crystals. Robust photonic gaps exist in any periodic structure built from such spheres when the filling ratio of the spheres exceeds a threshold.
Effect of nanostructured supports on catalytic methane decomposition
Authors: Ji L. , Tang S. , Chen P. , Zeng H. C. , Lin J. , Tan K. L.
Published: October 2007

Carbon deposition from catalytic methane decomposition has drawn increasing interest recently. Previously, we have found the carbon formation depends on the crystalline structure of the support, following the trend of Ni/CeO2 > Ni/CaO > Ni/MgO, because Ni supported on MgO is uniformly dispersed and can stabilize high-x CH x intermediates. We have also found that the addition of Pt can inhibit the carbon deposition on Co/Al2O3 because the alloying between Pt and Co results in the better dispersion of Co on the support. Furthermore, it was revealed that by judging the Ni/Mg molar ratio from 1 to 0.25 we could reduce the diameter of deposited carbon nanotubes from 20 to 12 nm, with substantially smaller production rate. All of these previous studies indicated that better dispersion of the supported metal would benefit the decreasing of carbon deposition. Here we present our recent investigation of the effect of support particle size on the carbon deposition. Three different types of 10 wt% Co/Al2O3 catalysts were prepared: Co on commercial Al2O3 (Cat 1), Co on sol-gel-processed Al2O3 (Cat 2), and sol-gel-made homogeneous Co-in-Al2O3 (Cat 3). TEM showed that the diameter of the Co3O4 particles in sol-gel Al2O3 is only around 6 nm, while it is 20-40 nm in the commercial catalyst. By using XRD and FTIR, Co was identified as crystalline Co3O4 in the as-prepared Cat 1 sample, CoAl2O4 in Cat 2, and amorphous Al2O3 in Cat 3, indicating the best dispersion in Cat 3. Methane CO2 reforming was studied on the three catalysts. Longer lifetime was measured for Cat 3 as compared to those on Cat 1 and Cat 2 (>20 h vs. 1 h). The support size effect is discussed.
The chelate effect in binding, catalysis, and chemotherapy
Authors: Breslow Ronald , Belvedere Sandro , Gershell Leland , Leung David
Published: October 2007

Cyclodextrin (CD) dimers bind amino acid side chains, and such binding can dissociate aggregated proteins, including citrate synthase (dimer) and lactic dehydrogenase (tetramer). A CD dimer can bind a hydrophobic photosensitizer that, upon irradiation, generates singlet oxygen. This cleaves the dimer and releases the photosensitizer. CD dimers in a cytochrome P-450 mimic steer catalyzed hydroxylation to a bound steroid with geometric control. Chelate binding has also led to a group of cytodifferentiating agents whose mechanism has been recently established. They have promising anticancer properties, and are currently entering human trials as therapeutic agents.
Chemical etiology of nucleic acid structure
Authors: Eschenmoser A. , Krishnamurthy R.
Published: October 2007

The synthesis of potentially natural nucleic acid alternatives and comparison of some of their chemical properties with those of RNA and DNA have led to findings that we consider to be relevant in the context of a chemical etiology of nucleic acid structure.
Novel reagents and reactions for drug design
Authors: Baker T. J. , Rew Y. , Goodman M.
Published: October 2007

In this presentation, we cover new results from two of our synthetic endeavors: guanidinylation reagents and novel bridged opioids. In the first part, we describe the applications of the diurethane-triflylguanidines to prepare target bioactive structures including peptides, heterocyclic drugs, and aminoglycoside derivatives. The formation of novel guanidinoglycosides led to a family of effective binders to the RNA recognition element of the HIV-1 Rev protein. In the second part, the syntheses of sulfur and amine-bridged cyclic opioids is described. These analogs exhibit enhanced binding, both in vitro and in vivo. Specifically, H-Tyr-c[d-Vall-Gly-Phe-d/l-Alal]-OH (Vall and Alal denote the lanthionine amino acid ends linked by a monosulfide bridge) is potent and highly δ -receptor selective while Tyr-c[(Nγ CH3 )-d-A2 bu-Gly-Phe-NHCH2CH2 -] though nonselective is one of the most potent opioids prepared to date. These molecules are representative of our design of novel peptidomimetic opioids.
Tissue-specific peptide pools. Generation and function
Authors: Ivanov Vadim T. , Yatskin Oleg N. , Kalinina Olga A. , Philippova Marina M. , Karelin Andrei A. , Shemyakin-Ovchinnikov Elena Yu. Blishchenko
Published: October 2007

Systematic analysis of several tissue extracts for peptide components followed by bioactivity studies leads to formulation of the concept of "tissue-specific peptide pools". According to that concept the endogenous proteolysis of proteins with well-established functions, such as hemoglobin, actin, and cellular enzymes in tissues leads to formation of the sets (or pools) of bioactive peptides. The sets are tissue-specific on one hand and conservative in a given tissue at normal conditions on the other. The content and the composition of pool components are sensitive both to pathologies linked with alterations of tissue metabolism and to prolonged physiological changes. In vivo formation of fragments of functional proteins includes several consecutive proteolytic stages inside the cells and further release of bioactive compounds into the surrounding medium. The effects of pool components take place predominantly at tissue and cellular levels, their effects being related to stimulation or inhibition of cell growth, induction of cell differentiation, and death. The above-mentioned features lead to the proposal that the main in vivo function of components of tissue-specific peptides is maintenance of tissue homeostasis, i.e., the normal ratio of functional, dividing, differentiating, and dying cells of tissues. Components of tissue-specific peptide pools display several features distinguishing them from "classical" peptide hormones and neuromediators. Summarizing, a novel peptidergic regulatory system is considered.
Designer cyclopeptides for self-assembled tubular structures
Authors: Ranganathan Darshan , Lakshmi C. , Haridas V. , Gopikumar M.
Published: October 2007

A simple design strategy for a facile and direct entry into hydrogen-bonded peptide nanotubes is delineated with polymethylene-bridged cystine-based macrocycles. The key feature of the design is the placement of a pair of self-complementary hydrogen-bonding (NH–CO or NH–CO–NH) groups at almost opposite poles of the ring. A large variety of cyclobisamides and bisureas prepared in a single step by direct condensation of commercially available 1,ω-alkane dicarbonyl dichloride or diisocyanate with either cystine diOMe or its extended bispeptide were examined by X-ray crystallography and shown to possess an inherent property of self-assembling into hydrogen-bonded, open-ended, hollow tubular structures. The totally hydrophobic interior of the cyclobisamide tubes creates a micro environment capable of solubilizing highly lipophilic substances in water. The cyclic bisurea tubes are demonstrated to act as excellent receptors for selective binding to 1,ω-alkane dicarboxylates. The scope of the design is extended to the creation of tubular structures by stacking of rings through aromatic π-π interactions.
Use of inhibitors to study reactions catalyzed by enzymes requiring pyridoxal phosphate as coenzyme
Authors: Adams Benjamin , Axelsson B. Svante , Beresford Kenneth J. M. , Church Nicola J. , Spencer Philip A. , Whyte Sheena M. , Young Douglas W.
Published: October 2007

The stereochemistry of a variety of pyridoxal phosphate-mediated enzymic reactions has been studied using enzyme inhibitors that are stereospecifically labeled in the β-position with deuterium. A versatile synthesis has been developed to prepare a wide variety of stereospecifically labeled d- and l-amino acids and inhibitors. Investigation of the "turnover" of β-chloro-d-alanine and d- and l-serine-O-sulfate by d-amino acid aminotransferase and l-aspartate aminotransferase respectively has shown that reaction within the active site of the former enzyme occurs with retention of stereochemistry. Although l-aspartate aminotransferase is an enzyme of the α-family, when it was incubated with β-chloro-l-alanine in the presence of 2-mercaptoethanol, β-substitution occurred. This was shown to involve retention of stereochemistry, an outcome typical of reactions catalyzed by enzymes of the β-family that have little or no homology with enzymes of the α-family. Formation of the "Schnackerz intermediate" has been studied as has the d-amino acid oxidase catalyzed reaction of the naturally occurring inhibitor d-propargylglycine.
Biological monitoring for exposure to volatile organic compounds (VOCs) (IUPAC Recommendations 2000)
Authors: Heinrich-Ramm R. , Jakubowski M. , Heinzow B. , Christensen J. Molin , Olsen E. , Hertel O.
Published: October 2007

This paper deals with the appropriate application of biological monitoring (BM) for exposure to volatile organic compounds (VOCs). Sampling guidelines, approved analytical procedures, quality control systems, detailed aspects for the interpretation of biomonitoring data, a compilation of international biological action values for VOC exposure at the workplace (e.g., BAT, BEI®), and state of the art reference values are outlined or referred to in this review for recommendation as guidelines for health professionals in occupational and environmental settings.

VOCs are frequently encountered at the workplace, in daily routines and widely used consumer products. They cover a broad spectrum of chemical classes with different physicochemical and biological properties. Inhalation is a prominent route of exposure due to their volatility but many VOCs can quite readily be absorbed through the skin. BM allows assessment of the integrated exposure by different routes including inhalation and concomitant dermal and oral uptake—a helpful tool for relating exposure to body burden and possible health effects. Because of the different toxicological profiles of VOCs, no uniform approach for BM can be recommended. VOCs in blood and urinary VOC metabolites are most often applied for BM. Limit values for workplace exposure have been established for many VOCs. In this field, profound analytical methodology and extensive experience exist in numerous international scientific laboratories for reliable routine application. Contamination and loss of VOCs during specimen collection, storage and sample treatment, and applied calibration procedure are the most important uncertainties for analytical quantification of VOCs in blood. For interpretation of the analytical results appropriate time of sampling, according to toxicokinetics of the compound, is crucial due to VOC elimination with short but differing biological half-lives. Lifestyle factors (such as smoking habits, alcohol consumption, and dietary habits), workload, personal working habits, exposure to VOC mixtures and endogeous factors (as genetic polymorphism for VOC metabolizing enzymes, body mass) contribute to BM results and have to be considered in detail. Future analytical work should focus on the improvement of analytical methodology of VOC determination in body fluids at low-level environmental exposure and evaluation of corresponding reference intervals.
Properties and units in the clinical laboratory sciences. Part VIII. Properties and units in clinical microbiology (Technical Report) (IFCC-IUPAC 1999)
Authors: Forsum U. , Olesen H. , Frederiksen W. , Persson B.
Published: October 2007

The document describes the use of the concept property and the presentation of results in clinical microbiology. Systematic names in clinical microbiology require the use of a nominal-scale kind-of-property to describe taxonomy. For this purpose the kind-of-property "taxon" is introduced. The document further lists properties commonly used in clinical microbiology. The documents follows the IUPAC-IFCC systematic syntax, and this creates a basis for integration of the format of clinical microbiology laboratory reports in the general clinical laboratory sciences laboratory reports format.
p53 mutations as fingerprints of environmental carcinogens
Authors: Cetin-Atalay Rengul , Ozturk Mehmet
Published: October 2007

Mutations of the p53 tumor suppressor gene occur in a great majority of human cancers. The protein product of p53 gene is involved in DNA damage response. Consequently, p53 gene may be a preferred target for environmental carcinogens, which also act as DNA-damaging agents. This is probably why p53 mutations are frequent in cancers linked to environmental carcinogens. Moreover, these carcinogens leave molecular fingerprints on the p53 gene. Thus, the study of p53 mutation spectra has been a useful approach to implicate suspected carcinogens to different human cancers. This review provides further insight into the significance of p53 mutation spectra in ten common human malignancies (skin, liver, lung, bladder, breast, head and neck, esophagus, stomach and colorectal cancers, and hematological malignancies), in relation with environmental carcinogens.
Recent advances in metal carcinogenicity
Authors: Hartwig A.
Published: October 2007

The carcinogenicity of nickel, chromium, arsenic, cobalt, and cadmium compounds has long been recognized. Nevertheless, the mechanisms involved in tumor formation are not well understood. The carcinogenic potential depends on metal species; major determinants are oxidation state and solubility. Two modes of action seem to be predominant: the induction of oxidative DNA damage and the interaction with DNA repair processes, leading to an enhancement of genotoxicity in combination with a variety of DNA-damaging agents. Nucleotide excision repair (NER) is inhibited at low, non-cytotoxic concentrations of nickel(II), cadmium(II), cobalt(II), and arsenic(III); the repair of oxidative DNA base modifications is disturbed by nickel(II) and cadmium(II). One reason for repair inhibition appears to be the displacement of zinc(II) and magnesium(II). Potentially sensitive targets are so-called zinc finger structures present in several DNA repair enzymes such as the mammalian XPA protein and the bacterial formamidopyrimidine-DNA glycosylase (Fpg protein); detailed studies revealed that each zinc finger protein exerts unique sensitivities toward toxic metal ions. Taken together, toxic metal ions may lower the genetic stability by inducing oxidative DNA damage and by decreasing the repair capacity towards DNA lesions induced by endogenous and exogenous mutagens, which may in turn increase the risk of tumor formation.
A review of human and sub-human primate toxicity of hexachlorobenzene
Authors: Jarrell John , Gocmen Ayhan
Published: October 2007

The inadvertent exposure of a large cohort of individuals to hexachlorobenzene (HCB) in the mid-1950s in southeastern Turkey remains an environmental disaster that continues to fascinate and provide interesting observations concerning this ubiquitous chemical. A brief history of the exposure is presented with particular reference to the initial presentation of Pembe Yara and Porphyria Cutanea Tarda and later to reproductive performance in humans and sub-human primates. Differential toxicity is present in the oocytes of monkeys, with more severe damage identified in primordial germ cells rather than in growing oocytes. However, this observation did not express itself in women, as there was no increased incidence of premature menopause among those exposed. Germ cell toxicity remains a possible outcome of exposure, however. The serum HCB levels measured in exposed individuals predicted the lifetime risk of spontaneous abortion, not only in exposed individuals but also in the control populations, indicating that a possible population effect is present.
Use of genetically altered animal models in understanding the role of metallothionein in cadmium toxicity
Authors: Klaassen Curtis D. , Choudhuri Supratim
Published: October 2007

Acute Cd exposure produces liver injury, whereas chronic Cd exposure damages the kidney but not the liver. Previous experiments suggest that the low-molecular-weight, metal-binding protein metallothionein (MT) in liver protects against liver injury, but is responsible for the kidney injury observed after chronic Cd exposure. Thus, prior to the development of MT-transgenic and MT-knockout mice models, MT's role was always assumed to be a toxicological paradox, hepatoprotection but nephrotoxicity. The development of MT-transgenic and MT-knockout mice models has reconfirmed MT's protective role against Cd-induced hepatotoxicity, but it has challenged MT's suggested role in Cd-induced nephrotoxicity. In this communication, recent data using these genetically altered mice models indicate that MT protects against not only the Cd-induced hepatotoxicity, but also nephrotoxicity, hematotoxicity, immunotoxicity, and bone damage.
Environmental specimen banking. Herring gull eggs and breams as bioindicators for monitoring longterm and spatial trends of chlorinated hydrocarbons
Authors: Marth P. , Martens D. , Schramm K.-W. , Schmitzer J. , Oxynos K. , Kettrup A.
Published: October 2007

The German Environmental Specimen Bank (GESB) has been an important tool in contaminant monitoring and ecotoxicological research for more than one decade. The annual monitoring program provides a long-term database to determine trends in contaminant burdens in biota samples. Results of ten years of experience in the determination of chlorinated hydrocarbons (CHCs) in herring gull eggs collected in the North Sea and the Baltic Sea are presented. In addition, the study reports CHC concentrations in bream livers from the River Elbe between 1993-1997. Most of the compounds studied show a significant decline over time, especially in samples from East Germany. For specimens taken in West Germany, only small decreases or no changes of CHC levels were observed.
Role of catecholamines and cyclic AMP systems in phencyclidine and morphine dependence. Study of mutant mice
Authors: Nabeshima Toshitaka , Mamiya Takayoshi , Noda Yukihiro
Published: October 2007

To investigate an involvement of catecholamines and/or the cyclic adenosine monophosphate (cAMP) systems in the development of drug dependence, we examined whether phencyclidine (PCP) and morphine dependence were developed in tyrosine hydroxylase (TH) heterozygous (TH+/-) and cAMP response element binding protein (CREB) binding protein (CBP) heterozygous (CBP+/-) mice. PCP (8 mg/kg) induced place preference in wild-type mice pretreated with PCP (10 mg/kg/day for 28 days) and increased the level of cAMP in the striatum, but not in the thalamus/hypothalamus. In TH+/- and CBP+/- mice, however, we could not find PCP-induced place preference. The increased level of cAMP in the striatum was observed in CBP+/-, but not TH+/- mice. When wild-type mice pretreated with morphine (10 mg/kg) twice a day for 5 days were challenged with naloxone (5 mg/kg), they showed increased jumping, rearing, and forepaw tremor counts as a sign of withdrawal and an increased level of cAMP in the thalamus/hypothalamus, but not in the striatum. In TH+/- and CBP+/- mice, however, jumping and forepaw tremor counts were decreased compared to in wild-type mice. An increase in the level of cAMP in the thalamus/hypothalamus in CBP+/-, but not in TH+/- mice was observed. These results suggest that catecholamines and CBP are involved in the development of PCP and morphine dependence, and that changes in catecholaminergic and/or cAMP systems induced by repeated PCP and morphine treatments play an important role in the addiction to PCP and morphine.
The mechanism of the releasing action of amphetamine. Uptake, superfusion, and electrophysiological studies on transporter-transfected cells
Authors: Pifl C. , Sitte H. H , Reither H. , Singer E. A.
Published: October 2007

Amphetamine analogues are able to induce signs of neurotoxicity in the brain. In order to understand this type of neurotoxicity, the interaction of amphetamine with its molecular targets must be elucidated. These molecular targets are plasmalemmal and vesicular monoamine transporters. We investigated the interaction of amphetamine with these transporters in cells transfected with the respective cDNA. Superfusion and whole-cell, patch-clamp experiments were performed, and the toxicity of substrates of the transporters was studied. Amphetamine was taken up by dopamine transporter-expressing cells in a sodium-dependent and cocaine-blockable manner. Furthermore, it elicited inward currents in these cells concentration-dependently. Correlation of uptake, release, and patch-clamp experiments suggest that ion fluxes induced by substrate-gating on transporters may significantly contribute to the releasing action of amphetamine and of other transporter substrates. Dopamine accumulation into serotoninergic terminals depleted of serotonin by 3,4-methylenedioxymethamphetamine was discussed as a mechanism of Ecstasy-toxicity. This is in agreement with a toxic effect of intracellular dopamine which could be demonstrated on our transporter-overexpressing cells. These results, apart from their relevance for the toxicity by amphetamine analogues, may also have bearings on the mechanisms in neurodegenerative diseases affecting monoamine transmitters.
Atom efficiency and catalysis in organic synthesis
Authors: Sheldon Roger A.
Published: October 2007

The key to waste minimization in fine chemicals manufacture is the widespread substitution of classical organic syntheses employing stoichiometric amounts of inorganic reagents with cleaner, catalytic alternatives. The E factors (by waste per kg product) of chemical processes increase dramatically on going downstream from bulk to fine chemicals and pharmaceuticals, mainly owing to the use of "stoichiometric" methods. The concept of atom efficiency is a useful tool for rapid evaluation of the amount of waste generated by alternative processes. The general theme of atom-efficient, catalytic processes is illustrated with industrially relevant examples. These include catalysis by solid acids and bases, catalytic reductions and oxidations, catalytic C_C bond formation, asymmetric catalysis, biocatalysis, and catalysis in novel media (aqueous and fluorous biphasic systems, supercritical fluids, and ionic liquids).
Use of the life-cycle assessment (LCA) toolbox for an environmental evaluation of production processes
Authors: Herrchen Monika , Klein Werner
Published: October 2007

Green chemistry not only emphasizes the central production process of the "green" chemical, but it ultimately requires a life-cycle conceptual approach for each chemical product. A life-cycle conceptual approach comprises the consideration of all stages along the life cycle of a chemical (i.e., raw material extraction, pre-production, production, use, recycling, and disposal) as well as the consideration of environmental impacts caused by by-products and auxiliaries (such as solvents and additives, but also technical facilities which have to be provided to produce the green chemical). A significant improvement in the evaluation of green chemical products can be approached by the complementary use of the methodologies of life-cycle assessment (LCA) and risk assessment. The use and combination of both methodologies can be performed by a separate use of the instruments (depending on the scope, definition, and application of LCA), an iterative use of LCA and risk assessment, or a complete integration of both instruments. Pros and cons of these approaches are discussed.
Fats and oils as oleochemical raw materials
Authors: Hill Karlheinz
Published: October 2007

Vegetable oils and fats are important constituents of human and animal foodstuffs. Certain grades are industrially used and, together with carbohydrates and proteins, are important renewable resources compared to fossil and mineral raw materials, whose occurrence is finite. In concepts for new products, the price, performance, and product safety criteria are equally important and have a correspondingly high importance right at the start of product development. To ensure a high degree of product safety for consumers and the environment, renewable resources have often been shown to have advantages when compared with petrochemical raw materials and can therefore be regarded as being the ideal raw material basis. Results from oleochemistry show that the use of vegetable fats and oils allows the development of competitive, powerful products, which are both consumer-friendly and environment-friendly. Recently developed products, which fit this requirement profile, are the anionic surfactants cocomonoglyceride sulfate and the nonionic sugar surfactant alkyl polyglycoside. These products are used especially as mild surfactants in cosmetic formulations. In polymer applications derivatives of oils and fats, such as epoxides, polyols, and dimerizations products based on unsaturated fatty acids, are used as plastic additives or components for composites or polymers like polyamides and polyurethanes. In the lubricant sector fatty acid-based esters have proven to be powerful alternatives to conventional mineral oil products.
Utilization of TiO2 photocatalysts in green chemistry
Authors: Anpo Masakazu
Published: October 2007

Environmental pollution and destruction on a global scale have drawn attention to the vital need for totally new environmentally friendly, clean chemical technologies and processes, the most important challenge facing chemical scientists in the field of green chemistry. Strong contenders as environmentally harmonious catalysts are photocatalysts that operate at room temperature and in a clean manner, while applications of such safe photocatalytic systems are urgently desired for the purification of polluted water, the decomposition of offensive atmospheric odors as well as toxins, the fixation of CO2, and the decomposition of NOx and chlorofluorocarbons on a huge global scale. To address such enormous tasks, photocatalytic systems that are able to operate effectively and efficiently not only under UV light but also under the most environmentally ideal energy source, sunlight, must be established. To this end, we are moving in a positive direction with various practical applications already at hand, as is described.

The present report involves 1) new approaches in the design and development of second-generation titanium oxide photocatalysts which can operate effectively under visible light and/or solar beam irradiation, 2) practical industrial applications of titanium oxide photocatalysts in Japan, and 3) recent advances in green chemistry in Japan.
Oxidation reactions in the synthesis of fine and intermediate chemicals using environmentally benign oxidants and the right reactor system
Authors: Hoelderich Wolfgang F. , Kollmer Felix
Published: October 2007

This review outlines several approaches for designing new and environmentally friendly heterogeneously catalyzed oxidation processes for the synthesis of fine and intermediate chemicals. Environmentally benign oxidants such as molecular oxygen, hydrogen peroxide or nitrous oxide can be activated on suitable heterogeneous catalysts showing high activity and selectivity toward the desired oxygenated products. Several examples illustrate that features known from the synthesis of bulk chemicals can successfully be applied for manufacturing intermediate and specialty chemicals applying conventional industrial reactor systems. Direct oxidation of isoprenol, b-picoline, and benzene are chosen as examples for continuous gas-phase processes, oxidation of pinene and propylene as examples for semi-continuous or batchwise processes in the liquid phase.