Non-enzymatic browning-induced water plasticization

An exotherm, observed in differential scanning calorimetry (DSC) scans of amorphous food materials above their glass transition temperature,T _g, may occur due to sugar crystallization, nonenzymatic browning, or both. In the present study, this exothermal phenomenon in initially anhydrous skim milk and lactose-hydrolyzed skim milk was considered to occur due to browning during isothermal holding at various temperatures above the initialT _g. The nonenzymatic, Maillard browning reaction produces water that in amorphous foods, may plasticize the material and reduceT _g. The assumption was that quantification of formation of water from theT _g depression, which should not be observed as a result of crystallization under anhydrous conditions, can be used to determine kinetics of the nonenzymatic browning reaction. The formation of water was found to be substantial, and the amount formed could be quantified from theT _g measured after isothermal treatment at various temperatures using DSC. The rate of water formation followed zero-order kinetics, and its temperature dependence well aboveT _g was Arrhenius-type. Although water plasticization of the material occurred during the reaction, and there was a dynamic change in the temperature differenceT–T _g, the browning reaction was probably diffusioncontrolled in anhydrous skim milk in the vicinity of theT _g of lactose. This could be observed from a significant increase in activation energy. The kinetics and temperature dependence of the Maillard reaction in skim milk and lactose-hydrolyzed skim milk were of similar type well above the initialT _g. The difference in temperature dependence in theT _g region of lactose, but above that of lactose-hydrolyzed skim milk, became significant, as the rate in skim milk, but not in lactose-hydrolyzed skim milk, became diffusion-controlled. The results showed that rates of diffusion-controlled reactions may follow the Williams-Landel-Ferry (WLF) equation, as kinetic restrictions become apparent within amorphous materials in reactions exhibiting high rates at the same temperature under non-diffusion-controlled conditions.     

Specimen transfer from the electrolyte to the UHV in a closed system and some examinations of the double layer on Cu

A transfer system is described which permits the electrochemical preparation of specimens in a purified argon atmosphere and their transport into the UHV for surface analysis. This transfer prevents contamination and oxide formation on semi-noble metals. Reactive metals from only a few monolayers of oxide. This permits examination of electrochemically prepared metal surfaces, which is otherwise not possible. For hydrophobic copper surfaces, the composition of the electrical double layer may be studied. The extraction of the electrode strips the electrolyte off in the vicinity of the Helmholtz layer. For NaClO₄ solutions, the amount of Na⁺ ions and the excess charge decrease linearly with the electrode potential in agreement with a constant electrode capacity. The formation of a prepassive and passive layer leads to a pronounced increase of adsorbed Na⁺ ions. For Cs₂SO₄, specific and co-adsorption of both ions is observed with a minimum in the region of the potential of zero charge.     

A short and versatile route to chiral spiroketal skeletons

Different chiral spiroketal skeletons are obtained, in a versatile manner, by iterative alkylations of acetone N,N-dimethylhydrazone with iodides 2 followed by a one-pot deprotection/spirocyclization sequence. This methodology has been applied successfully to the synthesis of 1,7-dioxaspiro[5.5]undecane and 1,6-dioxaspiro[4.5]decane systems.     

Preparation and characterization of nanometer‐thin freestanding polymer foils for laser‐ion acceleration

We report on the production and characterization of polymer‐based ultra‐thin (sub 10 nm) foils suited for experiments on laser‐ion acceleration in the regime of radiation pressure acceleration. Beside the remarkable mechanical stability compared with commonly used diamond‐like‐carbon foils, a very homogeneous layer thickness and a small surface roughness have been achieved. We describe the technical issues of the production process as well as detailed studies of the mechanical stability and surface roughness tests. The capability of producing uniform targets of large area is essential for advanced laser‐ion acceleration projects which are dealing with high repetition rate and extended measurement series, but might also be useful for other applications which require ultra‐thin and freestanding substrates of high quality. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1355–1360     

Schur multiplicators of infinite pro-<Emphasis Type="Italic">p</Emphasis>-groups with finite coclass

Let G be an infinite pro-p-group of finite coclass and let M(G) be its Schur multiplicator. For p > 2, we determine the isomorphism type of Hom(M(G), ℤ_p), where ℤ_p denotes the p-adic integers, and show that M(G) is infinite. For p = 2, we investigate the Schur multiplicators of the infinite pro-2-groups of small coclass and show that M(G) can be infinite, finite or even trivial.     

Energising the E-factor: The E+-factor

The E-factor has become an important measure for the environmental impact of (bio)chemical reactions. However, summing up the obvious wastes generated in the laboratory neglects energy-related wastes (mostly greenhouse gases) which are generated elsewhere. To estimate these wastes, we propose to extend the E-factor by an energy-term (E⁺-factor). At the example of a lab-scale enzyme fermentation, we demonstrate that the E⁺-factor can constitute a multiple of the classical E-factor and therefore must not be neglected striving for a holistic estimation of the environmental impact.     

Infrared crystallography for framework and linker orientation in metal–organic framework films

Pore alignment and linker orientation influence diffusion and guest molecule interactions in metal–organic frameworks (MOFs) and play a pivotal role for successful utilization of MOFs. The crystallographic orientation and the degree of orientation of MOF films are generally determined using X-ray diffraction. However, diffraction methods reach their limit when it comes to very thin films, identification of chemical connectivity or the orientation of organic functional groups in MOFs. Cu-based 2D MOF and 3D MOF films prepared via layer-by-layer method and from aligned Cu(OH)₂ substrates were studied with polarization-dependent Fourier-transform infrared (FTIR) spectroscopy in transmission and attenuated total reflection configuration. Thereby, the degrees for in-plane and out-of-plane orientation, the aromatic linker orientation and the initial alignment during layer-by-layer MOF growth, which is impossible to investigate by laboratory XRD equipment, was determined. Experimental IR spectra correlate with theoretical explanations, paving the way to expand the principle of IR crystallography to oriented, organic–inorganic hybrid films beyond MOFs.

Polarization-dependent infrared spectroscopy of oriented metal organic framework films fills the information gap left by diffraction methods and gives access to the orientation of the aromatic linker and initial orientation of ultra-thin films.