Octadecyl phosphoric acid ester has been found to produce oriented, well-ordered monolayers on a flat tantalum(V) oxide surface, via self-assembly from a heptane/propan-2-ol solution. By means of contact angle, optical waveguide lightmode spectroscopy (OWLS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and X-ray photoelectron spectroscopy (XPS) measurements, it has been shown that these layers closely resemble those formed by the corresponding thiol−gold system, with respect to packing density, inclination, and order. The system shows promise as an approach to functionalizing oxide surfaces with well-ordered organic monolayers, with potential applications in the fields of biochemical analysis and sensors.

We use ambient-pressure X-ray photoelectron spectroscopy (APXPS) to study chemical changes, including hydroxylation and water adsorption, at copper oxide surfaces from ultrahigh vacuum to ambient relative humidities of ∼5%. Polycrystalline CuO and CuO surfaces were prepared by selective oxidation of metallic copper foils. For both oxides, hydroxylation occurs readily, even at high-vacuum conditions. Hydroxylation on both oxides plateaus near ∼0.01% relative humidity (RH) at a coverage of ∼1 monolayer. In contrast to previous studies, neither oxide shows significant accumulation of molecular water; rather, both surfaces show a high affinity for adventitious carbon contaminants. Results of isobaric and isothermic experiments are compared, and the strengths and potential drawbacks of each method are discussed. We also provide critical evaluations of the effects of the hot filament of the ion pressure gauge on the reactivity of gas-phase species, the peak fitting procedure on the quantitative analysis of spectra, and rigorous accounting of carbon contamination on data analysis and interpretation. This work underscores the importance of considering experimental design and data analysis protocols during APXPS experiments with water vapor in order to minimize misinterpretations arising from these factors.

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Single crystals of the title compound were obtained from the electrochemical oxidation of ET ( 3 . 5~ lo-' M in a mixture of CH,CI,/CH,CN/H,O 10:2:1) in the presence of the tetrabutylammonium salt of the polyoxoanion [COW,,O,,,-~ 1161 (5 x M in a mixture of CH,CI,/CH,CN 1 :1) in a U-shaped cell with Pt electrodes (0.5 mm diameter) separated by a sintered-glass frit. The intensity of the current was fixed at 1 PA. After 2 or 3 weeks. amber, platelike single crystals of the title compound were collected carefully and air dried.Magnetic measurements were carried out on single crystals with a magnetometer (905 VTS, SEH Corporation) equipped with a SQUID sensor (SQUID = superconducting quantum interference device). EPR measurements of the X band at variable temperature were recorded on a Bruker ER 200D spectrometer equipped with a helium cryostat. In the experiment the static magnetic field is perpendicular to the long axis of the needlelike single crystal. Infrared spectra in the range 400-4700cm-' were made on KBr pellets with a FT-IR interferometer Nicolet MX1. Conductivity measurements were performed using the four-probe method on approximately 4-mm long-needlelike single crystals. O,,] . 5.5: amber platelike crystal: 0.41 x 0.34 x 0.01 mm', Enraf-Nonius CAD4 diffractometer. M = 6081.8, monoclinic.space group f 2 / m with u = 13.971(9), b = 43.117 (7), c =14.042 (5) A, fl = 107.25(3), V = 8078.5 A' . and Z = 2 (pea,cd = 2.496 gem-'; Mo,, radiation, E. = 0.71073 A. p = 96.554 cm-I), structure solved by direct methods and successive Fourier difference synthesis. Refinement of 329 variables with anisotropic thermal parameters (for Co, W and S atoms) gave R ( F ) = 0.068 and Rw(F) = 0.102 by using 2614 absorption corrected reflections with f 2 6rr(I). Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (FRG), on quoting the depository number CSD-57908. the authors, and the journal citation. [8] H. T. Evans, M. T. Pope, Inorg. Chem. 1984, 23, 501. [9] J.Considerable efforts have been made recently in the structural modification of oligonucleotides."] Several properties of the natural 2'-deoxyoligoribonucleotides must be improved for potential therapeutic application of the antisense strategy. For example, the stability of the antisense oligonucleotides towards nucleases must be substantially increased, while the affinity and the specificity for the complementary RNA target is maintained (or even increased). So far, most of the replacements of the phosphodiester linkage that lead to an increased resistance towards nucleases are also connected with a decrease in the affinity for a complementary RNA strand.". ' I Two exceptions to this were recently reported in which either an N-methylhydroxylamine or a thioformacetal unit was used as a PO,We proposed to replace the natural phosphodiester linkage in 1 (Scheme 1) by an amide function (as in 2-4), which offers several advantages compared to previously reported modificat i o n~...

Recent years have witnessed fast advancements in near ambient pressure X-ray photoelectron (NAPP) spectroscopy, which is emerging as a powerful tool for the investigation of surfaces in presence of vapors and liquids. In this paper we present a new chamber for the investigation of solid/vapor interfaces relevant to environmental and atmospheric chemistry that fits to the NAPP endstation at the Swiss Light Source. The new chamber allows for performing X-ray photoelectron spectroscopy (XPS) and electron yield near-edge X-ray absorption fine structure spectroscopy (NEXAFS) using soft, tender and hard X-ray in vacuum and in near-ambient pressures up to 20 mbar at environmentally relevant conditions of temperature and relative humidity. In addition, the flow tube design of the chamber enables the dosing of sticky reactive gases with short pressure equilibration time. The accessible photoelectron kinetic energy ranges from 2 to 7000 eV. This range allows the determination of surface and bulk electronic properties of ice and other environmental materials, such as metal oxides and frozen solutions, which are relevant to understanding atmospheric chemistry. The design of this instrument and first results on systems of great interest to the environmental and atmospheric chemistry community are presented. In particular, nearambient pressure XPS and NEXAFS, coupled to a UV-laser setup, were used to study the adsorption of water on a TiO 2 powder sample. The results are in line with previously proposed adsorption models of water on TiO 2 , and, furthermore, indicate that the concentration of water molecules tends to increase upon UV irradiation. In a second example we illustrate how NEXAFS spectroscopy measurements at the chlorine K-edge can provide new insight on the structures of eutectic and sub-eutectic frozen NaCl solutions at high and low relative humidity, respectively, indicating the formation of solution and solid NaCl phases, respectively. Finally, we demonstrate the assets of this new chamber for the dosing of sticky acidic gases and, in particular, for the investigation of formic acid uptake on ice surfaces.Keywords Metal oxides Á Ice Á Halogens Á X-ray photoelectron spectroscopy (XPS) Á Near-edge X-ray absorption fine structure (NEXAFS) Á Near ambient pressure photoemission (NAPP)

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The interfacial ionization of strong acids is an essential factor of multiphase and heterogeneous chemistry in environmental science, cryospheric science, catalysis research and material science. Using near ambient pressure core level X-ray photoelectron spectroscopy, we directly detected a low surface coverage of adsorbed HCl at 253 K in both molecular and dissociated states. Depth profiles derived from XPS data indicate the results as physisorbed molecular HCl at the outermost ice surface and dissociation occurring upon solvation deeper in the interfacial region. Complementary X-ray absorption measurements confirm that the presence of Cl ions induces significant changes to the hydrogen bonding network in the interfacial region. This study gives clear evidence for nonuniformity across the air-ice interface and questions the use of acid-base concepts in interfacial processes.

The replacement of phosphodiester bonds in natural 2'deoxyoligonucleotides by amide bonds was recently described ['] for their application to the antisense strategy.['] Among the five structural amide isomers we incorporated into oligonucleotides, compounds with modification 2 (Fig. 1) contributed to a slight increase in the thermodynamic stability of the duplexes formed with complementary RNA strands. Moreover, oligonucleotides with alternating phosphodiester and amide linkages showed a largely increased resistance towards endo-and exonucleases.[19] The fate of MPPH after oxidation was determined by treating it with a 30-fold molar excess of cyclohexene in the presence of TiTMCM41 for 16 h. Analysis by GC (without quenching the reaction with PPh,) revealed that the only major MPPH-derived product was the alcohol MPPOH, which was present in roughly similar amounts to the cyclohexene oxide produced (MPP0H:epoxide -1.2:l). This effectively demonstrates that MPPH does not form MPPO radicals, and hence epoxidation does not occur by peroxyl addition to the olefinic double bond followed by loss of the alkoxyl radical (see Scheme 1).[20] Some very recent work by A. Corma et al, yet to be published, demonstrates that the maximum catalytic activity as a function of titanium loading for Ti+MCM41 is different from that forTifMCM41. Therefore, in a "worst case scenario", we could possibly be comparing the most catalytically eficient loading for TiTMCM41 with a poorly efficient loading for Ti-MCM41. I211 Under the same conditions trans-stilbene was not oxidized to trans-stilbene oxide. Since the pore dimensions of the catalyst are large enough to allow free passage of both cis-and trans-stilbene molecules throughout its structure, the lack of oxidation implies that steric effects may be important around the Ti'" centers.[22] H.