Electrochemical plasmonic sensors

The enormous progress of nanotechnology during the last decade has made it possible to fabricate a great variety of nanostructures. On the nanoscale, metals exhibit special electrical and optical properties, which can be utilized for novel applications. In particular, plasmonic sensors including both the established technique of surface plasmon resonance and more recent nanoplasmonic sensors, have recently attracted much attention. However, some of the simplest and most successful sensors, such as the glucose biosensor, are based on electrical readout. In this review we describe the implementation of electrochemistry with plasmonic nanostructures for combined electrical and optical signal transduction. We highlight results from different types of metallic nanostructures such as nanoparticles, nanowires, nanoholes or simply films of nanoscale thickness. We briefly give an overview of their optical properties and discuss implementation of electrochemical methods. In particular, we review studies on how electrochemical potentials influence the plasmon resonances in different nanostructures, as this type of fundamental understanding is necessary for successful combination of the methods. Although several combined platforms exist, many are not yet in use as sensors partly because of the complicated effects from electrochemical potentials on plasmon resonances. Yet, there are clearly promising aspects of these sensor combinations and we conclude this review by discussing the advantages of synchronized electrical and optical readout, illustrating the versatility of these technologies.     

129Xe NMR study of the localization of PdCl2 supported on carbon nanotubes

Localization of PdCl₂ clusters supported on multi-wall carbon nanotubes (MWCNT) has been investigated using ¹²⁹Xe NMR of adsorbed xenon. As-made MWCNTs with channels initially inaccessible for adsorption and ball-milled MWCNTs with the totally accessible internal surface were used as supports. The observed ¹²⁹Xe NMR spectra were determined by the dynamics of xenon exchange between the aggregate pores and nanotube channels. No considerable changes of the ¹²⁹Xe NMR spectrum with the concentration of supported PdCl₂ were observed for the as-made MWCNT, while an additional resonance appeared for the ball-milled nanotubes. The ¹²⁹Xe NMR experiments evidenced the supported species to be localized on the internal surface of the ball-milled MWCNT.     

Rearrangement of Derivatives of 1,3-Dithian-5-amineinto Bicyclic 2-Thiazolidines. Crystal Structures of cis- and trans-1-(2-Aryl-1,3-dithain-5-yl)-2-thioureas and cis- and trans-5-Aryl-3-imino-7,7a-dihydro-1H,3H,5H-thiazolo[3,4-c]thiazoles

Under conditions normally applied to transform thioureas into the corresponding carbodiimides, cis- and trans-1-(2-aryl-1,3-dithian-5-yl)-2-thioureas 7 and 8 undergo a rearrangement to 5-aryl-3-imino-7,7a-dihydro-1H, 3H, 5H-thiazolo[3,4-c]thiazoles 9/10 with cis- and trans-fused rings, respectively. The structures of these novel heterocycles were established by X-ray analysis of compounds 9a , 9d , and 10d . The cis-fused compounds 9 are the thermodynamically more stable ones. The stereochemical outcome of the rearrangement depends on the carbenium ion stabilizing capability of the aryl moiety and on the reagent system applied. With Ar = Ph, p-Cl-Ph, p-O₂N-Ph, the reaction can be directed to deliver mainly either the cis-thiazolothiazoles 9 or the trans-thiazolothiazoles 10 . With Ar = 5-methyl-4-imidazolyl or p-Me₂N-Ph, formation of the cis-thiazolothiazoles ( 9a and 9b , resp.) is strongly favored independently of the reaction conditions, In contrast to it 2-aryl analogs, (1,3-dithian-5-yl)-2-thiourea 7g can be transformed into the carbodiimide 11 . Under rigorous conditions, 11 also undergoes rearrangement to the corresponding thiazolothiazole 9g . Mechanisms explaining the above findings are discussed. Reaction of trans-2-phenyl-1,3-dithian-5-amine 6d with phosgene or trichloromethyl chloroformate gives the 5-phenyl-7,7a-dihydro-1H,3H,5H-thiazolo[3,4-c]-thiazol-3-ones 12 and 13 , whereas the amine 5g lacking an aryl substitutent forms the sable isocyanate 14 . Compound 14 is transformed into the corresponding thiazolothiazolone 15 by refluxing in diglyme. Syntheses are described for the 1,3-dithian-5-amines 5 / 6 and the thioureas 7 / 8 derived therefrom. The relative configuration of 7d and 8d was determined by X-ray analysis. NMR data then allowed to assign the configurations of all compounds of types 7 and 8 .     

Separation methods in the chemistry of humic substances

Separation methods are widely used to isolate humic substances (HSs), to fractionate them before further investigation, and to obtain information about their structure and properties. Among the chromatographic methods, techniques based on a size-exclusion effect appear to be most useful, as they allow us to relate elution data to the molecular mass distribution of HSs. The limitations of this approach are discussed in this review. Gas chromatography with mass spectrometric detection is typically used to identify the products of pyrolysis or thermochemolysis of HSs; this technique is considered most important in the structural investigation of HSs. Electrophoretic methods (especially capillary zone electrophoresis) provide detailed characterization of HSs, but it is very difficult to relate the electrophoretic data to any specific subfraction, structure or properties of HSs. The electrophoretic patterns are often called "fingerprints" and can potentially be used for the identification and classification of HSs. This is limited, however, by the great diversity of the procedures employed and by the low degree of harmonization--no data on reproducibility and between-laboratory comparability are available. The same holds true, to a certain degree, for most methods utilized for the characterization of HSs. Separation methods play an important role in the examination of the interactions of HSs with heavy metals and other chemical pollutants. They allow us to determine binding constants and other data necessary to predict the mobility of chemical pollutants in the environment.     

In-situ analysis of stepwise self-assembled 1,6-hexanedithiol multilayers by surface plasmon resonance measurements

1,6-Hexandithiol (HDT) forms 6.9 +/- 1.0 A thick defect-free monolayers on gold substrates if the solution is purged by argon during the adsorption while long term (> 1000 min) exposure of the substrate to alcoholic HDT results in the stepwise formation of multilayers in the absence of argon purging.     

Interconnecting carbon nanotubes with an inorganic metal complex

Intermolecular carbon nanotube junctions were formed through amide linkage of amino functionalized multiwall carbon nanotubes and [Ru (dcbpy)(bpy)2](PF6)2, an inorganic metal complex. Nanotube interconnects were visualized using atomic force microscopy. Absorption and emission spectroscopy showed significant changes between starting products and the resulting ruthenium nanotube complex, indicative of successful chemical modification.     

Treatment of multiexponential decay data by the method of zero determinants

The principles of a new method, the method of zero determinants, are described which can be used for the determination of the number of exponentials in accurate, multiexponential decay curves, as well as for the smoothing of multiexponential experimental data. It is based on the idea that the determinant of an overdetermined data matrix for accurate data is zero. The method is not limited by mathematical approximations, and thus uncovers the decay curve hidden in the data set.     

Catechol-O-methyltransferase-Inhibiting Pyrocatechol Derivatives: Synthesis and Structure-Activity Studies

3-Nitro- and 3-cyanopyrocatechols bearing electron-withdrawing substituents at C(5) have been found to inhibit the enzyme catechol-O-methyltransferase. Structure-activity studies are discussed on the basis of the pharmocological data of 50 compounds (cf, Chapt. 4, Tables 1–7). Some 3-nitro-5-aroylpyrocatechols (Type A², Table 1) fulfil the requirements for a clinical candidate, being orally active, specific, reversible, and relatively short-acting. The chemical work involved is illustrated by describing a choice of exemplary syntheses, dealing with compounds 9, 11, 14, 18, 22, 24, 25, 35, 41 , and 42 (Chapt. 5, Schemes 1–10).     

A simple method for estimating activation energies using the fragmentation yield: Collision-induced dissociation of iron(II)-phenanthroline complexes in an electrospray ionization mass spectrometer

The gas-phase stabilities of Fe(Phi)3(2+) complexes, where Phi represents the 1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline ligands were investigated by collision-induced dissociation (CID) in the capillary-first skimmer region upon changing the voltage difference between the capillary and the skimmer. The loss of only one ligand from the Fe(Phi)3(2+) complexes was observed with each of the phenanthroline ligands studied. An increase in the voltage difference between the capillary and the skimmer resulted in a higher fragmentation yield as calculated from the intensity of the precursor and the fragment ion. The fragmentation yield versus capillary-skimmer voltage difference plots were evaluated by means of the Arrhenius and the Rice-Ramsperger-Kassel (RRK) model by fitting the model parameters to the experimental data. Both models yielded practically the same results. In addition, if the internal energy gained through the capillary-skimmer region is estimated correctly, the approximate value of the critical energy (activation energy) for fragmentation can be extracted from the fragmentation yield versus capillary-skimmer voltage difference plots. It was found that the gas-phase stabilities of the Fe(Phi)3(2+) complexes are nearly identical except for the more stable Fe(II)-4,7-diphenyl-1,10-phenanthroline complex. The critical energy for fragmentation was estimated to be approximately 1.2 and 0.9 eV for the Fe(II)- 4,7-diphenyl-1,10-phenanthroline, and the other complexes, respectively.