CuO particles from ionic liquid/water mixtures: evidence for growth via Cu(OH)2 nanorod assembly and fusion

Tetrabutylammonium hydroxide/water mixtures are efficient reaction media for the fabrication of nanoscale metal oxides and hydroxides. Uniform CuO nanoplates, among others, can be grown on a large scale. This work shows that after 30 s at temperatures above 40 degrees C, CuO formation is already essentially complete. X-ray diffraction and transmission electron microscopy (TEM) show that the resulting plates form via a two-step process, where Cu(OH) 2 rods precipitate first. These rods aggregate and fuse into plates with a width/height ratio of about 1.9. High-resolution TEM and electron diffraction show that the plates are single crystals and exhibit only some defects, which most likely originate from the assembly and fusion of the primary rods.     

Structured electrodeposition in magnetic gradient fields

Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.     

Water soluble photoactive cellulose derivatives: synthesis and characterization of mixed 2-[(4-methyl-2-oxo-2H-chromen-7-yl)oxy]acetic acid–(3-carboxypropyl)trimethylammonium chloride esters of cellulose

Photoactive derivatives of cellulose were prepared by a mild esterification of the biopolymer with 2-[(4-methyl-2-oxo-2H-chromen-7-yl)oxy]acetic acid via the activation of the carboxylic acid with N,N′-carbonyldiimidazole. Subsequently, modification with the cationic carboxylic acid (3-carboxypropyl)trimethylammonium chloride was carried out. Thus, water soluble polyelectrolytes decorated with high amounts of photochemically active chromene moieties were obtained. The structures of the novel polysaccharide esters and the polyelectrolytes were evaluated by means of NMR and IR spectroscopy. Moreover, the light triggered photodimerization of the chromene moieties of the photoactive polyelectrolytes was studied by means of UV–Vis spectroscopy in the dissolved state. The photochemistry observed may be used to control the properties of the new polysaccharide derivatives and are thus of interest in the design of smart materials.     

Modulating Guest Uptake in Core–Shell MOFs with Visible Light

A two‐component core–shell UiO‐68 type metal–organic framework (MOF) with a nonfunctionalized interior for efficient guest uptake and storage and a thin light‐responsive outer shell was prepared by initial solvothermal MOF synthesis followed by solvent‐assisted linker exchange. The bulky shell linker features two tetra‐ortho‐fluorinated azobenzene moieties to exploit their advantageous photoisomerization properties. The obtained perfect octahedral MOF single crystals can be switched repeatedly and with an unprecedented efficiency between E‐ and Z‐rich states using visible light only. Due to the high photoswitch density per pore of the shell layer, its steric demand and thus molecular uptake (and release) can be conveniently modulated upon green and blue light irradiation. Therefore, the “smart” shell acts as a light‐controlled kinetic barrier or “gate” for the diffusion of cargo molecules in and out of the MOF crystals.     

Prediction of human dietary δ15N intake from standardised food records: validity and precision of single meal and 24-h diet data

Natural stable isotope ratios (δ¹⁵N) of humans can be used for nutritional analyses and dietary reconstruction of modern and historic individuals and populations. Information about an individual’s metabolic state can be obtained by comparison of tissue and dietary δ¹⁵N. Different methods have been used to estimate dietary δ¹⁵N in the past; however, the validity of such predictions has not been compared to experimental values. For a total of 56 meals and 21 samples of 24-h diets, predicted and experimental δ¹⁵N values were compared. The δ¹⁵N values were predicted from self-recorded food intake and compared with experimental δ¹⁵N values. Predicted and experimental δ¹⁵N values were in good agreement for meals and preparations (r?=?0.89, p?r?=?0.76, p?δ¹⁵N was mainly determined by the amount of fish, whereas the contribution of meat to dietary δ¹⁵N values was less pronounced. Prediction of human dietary δ¹⁵N values using standardised food records and representative δ¹⁵N data sets yields reliable data for dietary δ¹⁵N intake. A differentiated analysis of the primary protein sources is necessary when relating the proportion of animal-derived protein in the diet by δ¹⁵N analysis.     

Self-supporting isotopic chromium thin films

Chromium is a shiny, hard and malleable metal, which can be cold rolled in good quality to a thickness below a micrometer. Thinner foils can be obtained by electron-beam gun evaporation or by electroplating. Isotopically enriched material typically has not the quality for cold rolling processes. As ⁵⁰Cr has a natural abundance of only 4.5 % the enriched material is rather expensive so electron-beam deposition is not a good option because of the inherently low yield of the method. In this contribution we present the preparation of self-supporting ⁵⁰Cr thin films by thermal evaporation out of a tantalum crucible as an alternative to electrodeposition. With the described method we obtained self-supporting films with a thickness between 250 and 620 μg/cm².     

Planning and combining of isochronous stability studies of CRMs

The first part of this paper discusses some critical factors in planning and evaluation of isochronous stability studies. Recommendations on the number of time-points, number of items, and number of replicates to be measured on each unit are given. In general, more than two time-points should be used. The effect of batch heterogeneity can be eliminated by spreading the results over more units. An approach for combining two or more isochronous stability studies is developed in the second part. This approach includes a potential correction of the earlier stability study, pooling of data of the stability studies, and an uncertainty evaluation taking into consideration the uncertainty of the initial correction. The statistical basis for this approach is developed and equations for evaluation of the uncertainty of stability of the combined study are given.     

On the distribution of trace elements in human skeletons

Instrumental neutron activation analysis and flameless atomic absorption spectrometry have been used to study the occurence and distribution with a maximum of 25 elements in multiple sites of a skeleton and in the iliac crest of 69 ancient human skeletons. To study the distribution of trace elements between the different bone fractions the material of each sampling site was chemically treated to separate the collagen and the mineral from one another. Losses or contamination during the extraction procedure have been controled in detail by balance calculations. The elements can be subdivided into several groups due to the balance calculation and their association with the mineral. The analysis of the skeleton showed that the trace elements are distributed in varying degrees within a bone and throughout the skeleton their variation seems to be related to functional and structural conditions of the sampling site. The element content was observed to be higher at epiphyseal areas of long bones than in the shaft and higher in trabecular than in cortical bones. It was found that the element content of a single bone sample depends largely on the mass ratio spongiosa/compacta at the sampling site. By investigating an ancient population group, information about the “natural levels” and biological variation of trace elements was obtained. The results for F, Pb, Sr, and Zn in particular suggest that these elements could be useful in the study of health problems in man which involves the bone tissue.     

Combination of neutron activation analysis and argon plasma emission spectrocopy in the elemental analysis of biological materials

Trace elements and major constituents are analyzed in solid biological material and body fluids in order to compare the range of application of instrumental neutron activation analysis and plasma emission spectroscopic techniques. It is demonstrated that both methods should be regarded as complementary analytical techniques. In separate or sequential combination of both techniques the elemental coverage in the analysis of biological material is extended.