Quantitative electrochemical SERS of flavin at a structured silver surface

In situ electrochemical surface enhanced Raman spectra (SERS) for an immobilized monolayer of a flavin analogue (isoalloxazine) at nanostructured silver surfaces are reported. Unique in the present study, the flavin is not directly adsorbed at the Ag surface but is attached through a chemical reaction between cysteamine adsorbed on the Ag surface and methylformylisoalloxazine. Even though the flavin is held away from direct contact with the metal, strong surface enhancements are observed. The nanostructured silver surfaces are produced by electrodeposition through colloidal templates to produce thin (<1 microm) films containing close-packed hexagonal arrays of uniform 900 nm sphere segment voids. The sphere segment void (SSV) structured silver surfaces are shown to be ideally suited to in situ electrochemical SERS studies at 633 nm, giving stable, reproducible surface enhancements at a range of electrode potentials, and we show that the SER spectra are sensitive to subfemtomole quantities of immobilized flavin. Studies of the SER spectra as a function of the electrode potential show clear evidence for the formation of the flavin semiquinone at the electrode surface at cathodic potentials.     

Morphological wetting transitions at chemically structured surfaces

Chemically structured surfaces are discussed which consist of patterns of lyophilic and lyophobic surface domains. Wetting layers on top of these surfaces attain a variety of morphologies and undergo morphological wetting transitions. One convenient way to explore these transitions experimentally is by changing the total volume of the wetting layer.     

Xylyl isocyanide platinum and palladium complexes

Bis(cycloocta-1,5-diene)platinum reacts with isopropyl isocyanide to give the trinuclear complex [Pt₃(CNPrⁱ)₆]. A related palladium compound was prepared by treating either [Pd(dba)₂] or [Pd₂(dba)₂CHCl₃] with 2,6-dimethylphenyl isocyanide. Reactions of the cluster [Pt₃(CNC₆H₃-2,6-Me₂)₆] and its presumed palladium analogue with the olefins (NC)₂C:C(CN)₂, F₂C:CFCl and (CN)₂C:C(CF₃)₂, give the compounds [M(olefin)(CNC₆H₃-2,6-Me₂)₂] (M  Pt, Pd) in which the metals are η²-bonded to the coordinated olefins. The compound [Pd₃(CNC₆H₃-2,6-Me₂)₆] reacts with F₂C:CFBr and with F₂C:CFCl to give the trans complexes [Pd(X)(C₂F₃)(CNC₆H₃-2,6-Me₂)₂] (X  Br, Cl). Similar compounds [M(L)-(CNC₆H₃-2,6-Me₂)₂] (M  Pt, Pd), (L  MeO₂CHC:CHCO₂Me, OOCH: CHCOO) have also been prepared, and characterised. Two platinum complexes [Pt(CH:NC₆H₃-2,6-Me₂)(SiMePh₂)(CNC₆H₃-2,6-Me₂)₂] and [Pt₂(μ-(PhC)₂CO)(CNC₆H₃-2,6-Me₂) ₄] hav been synthesized by treating the complex [Pt₃(CNC₆H₃-2,6-Me₂)₆] with HSiMePh₂ and cyclopropenone, respectively. NMR and IR data for the new species are reported and discussed.     

Bioinspired structured surfaces

Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. Various natural objects which provide functionality of commercial interest have been characterized to understand how a natural object provides functionality. We have modeled and fabricated structures in the lab using nature's route and developed optimum structures. Once it is understood how nature does it, optimum structures have been fabricated using smart materials and fabrication techniques. This feature article provides an overview of four topics: Lotus effect, rose petal effect, gecko feet, and shark skin.     

Surface properties of platinum and palladium

Surface energies, defect formation heats and activation energies of atom self-diffusion on Pt and Pd (111), (100) and (110) planes have been estimated by the interacting bond method.

---

, , (111), (100), (110) Pt Pd.

     

New findings on CO electrooxidation at platinum nanoparticle surfaces

Different unsupported platinum nanoparticles are synthesized via water-in-oil microemulsion and colloidal methods (PAA). TEM, adatom adsorption and cyclic voltammetry measurements give very coherent results concerning the surface structure of the crystallites. The combination of these results with CO stripping experiments leads us to assign the oxidation peak multiplicity to surface structure rather than to pure size effect.     

Nitrate complexes of divalent palladium and platinum

Conclusions Some nitrate complexes of Pd(II) and Pt(II) were synthesized. The absorption bands of the nitrate groups in the IR spectra of the obtained complexes were studied in the 900–1700 cm^–1 region. A study was also made of the NMR spectra of the nitrate complexes of Pt(II) in D₂O.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1677–1679, July, 1977.     

Triphenylphosphine carboxylate complexes of platinum and palladium

Conclusions Some carboxylate complexes of platinum and palladium of type (Ph₃P)₂M(OOCR)₂ were obtained by the reaction of organic acids with the complexes (Ph₃P)₄Pt and (Ph₃P)₄Pd.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 946–947, April, 1973.     

New titrimetric methods for palladium and platinum

Palladium(III) is reduced to the metal by a reducing sugar in alkaline medium, and the metal is then dissolved in a solution of iron(III). The iron(II) produced is titrated oxidimetrically. Platinum is determined by precipitating it with ferrocyanide and titrating the excess of ferrocyanide added. Halides and the platinum and coinage metals interfere.     

Superwetting of structured surfaces

Superwetting of structured surfaces, sometimes referred to as hemi-wicking, was studied both experimentally and theoretically. Structured substrates with regular arrays of square pillars or frustra were machined from graphite blocks and then treated to render them lyophilic. Liquids spread over these surfaces to produce noncircular wetting areas. If the channels between the features were made shallower or narrower, liquids wicked more and spread over a larger area. The inherent wettability of the graphite was relatively unimportant; large differences in the contact angles had little influence on the spreading. Practically, this means that, to achieve extensive coverage, near-zero contact angles are not required. A combination of the appropriate surface structure and moderate inherent wettability can effectively flatten liquids, spreading them over very large areas.     

Voltammetric approach to multicomponent electrochemical systems at platinum electrode surfaces

Adsorption interactions of different systems on electrodispersed and smooth platinum electrodes were explored through anodic stripping voltammetry using a conventional flow cell technique at 25°C. A first adsorbate was formed at the platinum electrode in contact with the solution containing the adsorbable species I, and subsequently the platinum—adsorbate I system was put into contact with a solution containing the adsorbable species II, where I CO, CH₃OH and reduced CO₂, and II C₂H₄, C₂H₂ and CO, and vice versa. The anodic stripping voltammograms revealed either a total or partial displacement of adsorbate I by adsorbate II, or chemical interactions among adsorbed residues I and Il. The following decreasing platinum—adsorbate interaction sequence was established C₂H₂-2 > CO > C₂H₄ > CH₃OH ≈ CO₂.     

Polymer-supported palladium and platinum species as hydrogenation catalysts

The synthesis of new hydrogel copolymers and their use for anchoring Pd and Pt species is described. The supported catalysts are effective for the reduction of alkenes, dienes, alkynes, and nitroaromatics under mild conditions. The catalysts have been characterized by chemical analysis, particle size measurement, IR, TGA, and x-ray photoelectron spectra. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, particle size of the catalysts, and partial pressure of hydrogen have been determined. The kinetics of hydrogenation have been analyzed using concepts useful under slurry reaction conditions. The recycling efficiencies of the catalysts and product analysis to establish selectivities have been assessed. © 1992 John Wiley & Sons, Inc.     

Determination of palladium and platinum by atomic absorption

Palladium and platinum are determined by atomic absorption after fire-assay concentration into a gold bead. The limit of determination is ~0.06 ppm in a 20-g sample. Serious depressive interelement interferences are removed by buffering the solutions with a mixture of cadmium and copper sulphates with cadmium and copper concentrations each at 0.5%. Substantial amounts of Ag, Al, Au, Bi, Ca, Co, Cr, Fe, Hg, K, La, Mg, Mn, Mo, Na, Ni, Pb, Te, Ti, V, Y, Zn, and the platinum metals do not interfere in the atomic-absorption determination.     

Halo-carbonyl complexes of palladium,platinum and gold

In this review we summarize some recent literature data concerning synthetic procedures, properties, structure, reactivity and applications of halo-carbonyl complexes of palladium, platinum and gold, taking into consideration that the organometallic chemistry of these metals, with a particular attention to the halo-carbonyls, has been reviewed 20 years ago [F. Calderazzo, J. Organomet. Chem. 400 (1990) 303]. A brief overview of the early studies is provided.     

Paramagnetic complexes of platinum and palladium with acetamide

Summary Direct reaction of K₂MCl₄ (M=Pt or Pd) with acetamide leads reproducibly to complexes which can be formulated as [Pt(C₂H₄ON)₂Cl]_n and Pd₄(C₂H₄ON)₇(OH)₂. Analytical and spectroscopic (i.r., n.m.r. and e.p.r.) data support the existence of polynuclear structures involving bridging ligands and partially oxidized metal centres.     

Synthesis and characterization of platinum and palladium pyrrolidinedithiocarbamate complexes

Treatment of (PPh₃)₂MCl₂ (M = Pd or Pt) with ammonium pyrrolidinedithiocarbamate (NH₄S₂CNC₄H₈) in a 1:1 molar ratio gave (PPh₃)M(Cl)(κ ² S,S-S₂CNC₄H₈) [M = Pt (1), Pd (2)]. On the other hand, the interaction of these compounds in a 1:2 [M:L] molar ratio gave (PPh₃)Pt(κS-S₂CNC₄H₈)(κ ² S,S-S₂CNC₄H₈) (3), which contains both terminal and chelated dithiocarbamato ligands, or a yellow insoluble solid for M = Pd. The bis(diphenylphosphino)ethane platinum or palladium dichlorides [(dppe)MCl₂] reacted with the same ligand to give the salts [(dppe)M(κ ² S,S-S₂CNC₄H₈)]Cl (M = Pt (4), Pd (5) which have only one chelating dithiocarbamato ligand. The new compounds were characterized by ¹H-, ¹³C{¹H}- and ³¹P-n.m.r. spectroscopy, mass spectrometry, elemental analysis and X-ray single crystal structure analysis.     

Extraction chromatography of palladium and platinum complexes with nitroso-R-salt

The retention of palladium and platinum complexes with nitroso-R-salt on silica gel treated with Aliquat 336 has been investigated. The complexation of platinum with nitroso-R-salt (NRS) requires heating of H₂PtCl₆ with an excess of NRS at 100°. The affinity of the complexes for an Aliquat 336 stationary phase increases in the following order: PdCl₄²⁻ ˜ Pt-NRS < PtCl₆²⁻ Pd-NRS. The complexes of palladium and platinum can be separated by column chromatography on silica treated with Aliquat 336 and eluted with 0.25M perchloric acid (Pt) and 1M perchloric acid (Pd).