Intensity calibration for monochromated Al Kα XPS instruments using polyethylene

We describe a method for the intensity calibration of XPS instruments using polyethylene as the reference material. Previous methods have employed noble metals, such as gold, silver, and copper. Polyethylene has a number of advantages over these. It has far fewer photoelectron and Auger electron peaks than such metals, ie, the spectrum largely comprises inelastic background over a wide and continuous range of kinetic energies. The XPS spectrum can be described by a mathematical function enabling simple and noise-free implementation of the reference spectrum. Polyethylene can be cleaned ex situ using a sharp knife or razor blade to remove trace oxygen and, due to its chemical composition, should not be affected by adventitious carbon contamination. Thus, an ion source for sputter cleaning is not required, although an electron flood source for charge compensation is required. The drawback to using polyethylene is that the photoelectron yield is far lower than gold or silver, and this necessitates longer acquisition times and removal of dark noise. Longer acquisition times carry the risk of damaging the polyethylene surface, and we show that, even if damage does occur, it has a negligible effect on the XPS background intensity. The reference spectrum is valid for monochromated Al Kα XPS instruments with a monochromator-sample-analyser angle close to 60°.     

Complexes of HArF and AuX (X = F,Cl, Br,I). Comparison of H-bonds,halogen bonds,F-shared bonds and covalent bonds

The various sorts of complexes in which HArF and AuX (X = F, Cl, Br, I) can engage are probed by MP2/aug-cc-pVTZ calculations. The most weakly bound are those containing a halogen bond (XB) of the AuX⋯FArH sort, with binding energies less than 8 kcal/mol. H-bonded dimers FArH⋯XAu are a little stronger, held together by some 12 kcal/mol. Being the most strongly bound places the F atom of HArF roughly midway between Ar and Au in an F-shaped structure, bound by some 43–54 kcal/mol. The last sort of product involves atomic rearrangements wherein the H atom migrates from Ar to Au, followed by formation of a covalent Ar–Au bond. The resulting molecular unit is stabilized by 30–40 kcal/mol relative to the original HArF and AuX reactants. The H-bonded dimers are held together by an unusually large polarization component, surpassing electrostatic attraction, while dispersion predominates for the halogen bonds. Perturbations of the geometries and stretching frequencies offer a ready means of distinguishing the different types of complexes by spectroscopic techniques.     

Solution epitaxy of patterned ZnO nanorod arrays by interference lithography

Aligned ZnO nanorods with controllable size and tunable pattern pitch were grown at 90 °C in aqueous solutions by employing a nano-pattern fabricated by interference lithography. This method gave perfectly c-axis aligned ZnO nanorods arrays. The optical properties are significantly enhanced by a post-growth treatment combining thermal and plasma treatments. The photoluminescence intensity of the UV emission peak is increased more than 100 times after the post-growth treatments which also led to the occurrence of lasing from the nanorods.     

Resolving Entangled JH-H-Coupling Patterns for Steroidal Structure Determinations by NMR Spectroscopy

For decades, high-resolution ¹H NMR spectroscopy has been routinely utilized to analyze both naturally occurring steroid hormones and synthetic steroids, which play important roles in regulating physiological functions in humans. Because the ¹H signals are inevitably superimposed and entangled with various J_H–H splitting patterns, such that the individual ¹H chemical shift and associated J_H–H coupling identities are hardly resolved. Given this, applications of thess information for elucidating steroidal molecular structures and steroid/ligand interactions at the atomic level were largely restricted. To overcome, we devoted to unraveling the entangled J_H–H splitting patterns of two similar steroidal compounds having fully unsaturated protons, i.e., androstanolone and epiandrosterone (denoted as 1 and 2, respectively), in which only hydroxyl and ketone substituents attached to C3 and C17 were interchanged. Here we demonstrated that the J_H–H values deduced from 1 and 2 are universal and applicable to other steroids, such as testosterone, 3β, 21-dihydroxygregna-5-en-20-one, prednisolone, and estradiol. On the other hand, the ¹H chemical shifts may deviate substantially from sample to sample. In this communication, we propose a simple but novel scheme for resolving the complicate J_H–H splitting patterns and ¹H chemical shifts, aiming for steroidal structure determinations.     

Determination of myo-inositol (free and bound as phosphatidylinositol) in infant formula and adult nutritionals by liquid chromatography/pulsed amperometry with column switching: first action 2011.18

Myo-inositol is a 6-carbon cyclic polyalcohol also known as meso-inositol, meat sugar, inosite, and i-inositol. It occurs in nature in both free (myo-inositol) and bound (inositol phosphates and phosphatidylinositol) forms. For the determination of free myo-inositol, samples are mixed with dilute hydrochloric acid to extract myo-inositol and precipitate proteins, diluted with water, and filtered. For the determination of myo-inositol bound as phosphatidylinositol, samples are extracted with chloroform, isolated from other fats with silica SPE cartridges, and hydrolyzed with concentrated acid to free myo-inositol. Prepared samples are first injected onto a Dionex CarboPac PA1 column, which separates myo-inositol from other late-eluting carbohydrates. After column switching, myo-inositol is further separated on a CarboPac MA1 column using a 0.12% sodium hydroxide mobile phase; strongly retained carbohydrates are eluted from the PA1 column with a 3% sodium hydroxide mobile phase. Eluant from the CarboPac MA1 analytical column passes through an electrochemical detector cell where myo-inositol is detected by pulsed amperometry using a gold electrode. The method showed appropriate performance characteristics versus selected established standard method performance requirement parameters for the determination of myo-inositol: linear response; repeatability (RSDr) of 2%; and intermediate precision (RSDir) of 2.5%. Instrument LOD and LOQ were 0.0004 and 0.0013 mg/100 mL, respectively, and correspond to a free myo-inositol quantitation limit of 0.026 mg/100 g and a phosphatidylinositol quantitation limit of 0.016 mg/100 g. Correlation with the reference microbiological assay was good. The proposed method has been accepted by the Expert Review Panel as an AOAC First Action Method, suitable for the routine determination of myo-inositol in infant formula and adult nutritionals.     

Electron transfer across modular oligo-p-phenylene bridges in Ru(bpy)2(bpy-ph(n)-DQ)4+ (n = 1-5) dyads. Unusual effects of bridge elongation

A series of dyads of general formula Ru(bpy)(2)(bpy-ph(n)-DQ)(4+) (n = 1-5), based on a Ru(II) polypyridine unit as photoexcitable donor, a set of oligo-p-phenylene bridges with 1-5 modular units, and a cyclo-diquaternarized 2,2'-bipyridine (DQ(2+)) as electron acceptor unit, have been synthesized. Their spectroscopic and photophysical properties have been investigated in CH(3)CN and CH(2)Cl(2) by time-resolved emission and absorption spectroscopy in the nanosecond and picosecond time scale. The experimental study has also been complemented with a computational investigation carried out on the whole series of dyads. The absorption spectra of the dyads show new spectroscopic transitions, in addition to those characteristic of the donor, bridge, and acceptor fragments. DFT calculations suggest the assignment of such bands as bridge-to-acceptor (π ph(n)) → (π* DQ) charge-transfer transitions. This assignment is consistent with the solvatochromic and spectroelectrochemical behavior of the new bands. For all the dyads at room temperature in fluid solution, the typical (3)MLCT luminescence of the Ru(II) polypyridine unit is strongly (>90%) quenched, supporting the occurrence of an efficient intramolecular photoinduced electron transfer. The study has revealed, however, that the photophysical mechanism is actually more complex than presumed on the basis of a simple photoinduced electron-transfer scheme. For n = 1, very fast (few picoseconds) photoinduced electron transfer from the MLCT state localized on the substituted bpy ligand to the DQ unit has been observed, followed by slower interligand hopping and charge recombination. For n = 2-5, MLCT excited-state quenching takes place without transient detection of charge-separated product, indicating that charge recombination is faster than charge separation. This behavior can be rationalized in terms of the superexchange couplings expected through this type of bridges for the two processes. The kinetics of MLCT quenching in the dyads with n = 1-5 does not follow the usual exponential falloff with bridge length: after a regular decrease for n = 1-3, the rate constants become almost insensitive to bridge length for n = 3-5. The rationale of this uncommon behavior, as suggested by DFT calculations, lies in a switch in the MLCT quenching mechanism with increasing bridge length, from oxidative quenching by the DQ acceptor to reductive quenching by the bridge.