Evaluation of parameters critical to observing proteins inside living Escherichia coli by in-cell NMR spectroscopy

Our recently developed in-cell NMR procedure now enables one to observe protein conformations inside living cells. Optimization of the technique demonstrates that distinguishing the signals produced by a single protein species depends critically on protein overexpression levels and the correlation time in the cytoplasm. Less relevant is the selective incorporation of (15)N. Poorly expressed proteins, insoluble proteins, and proteins that cannot tumble freely due to associations within the cell cannot yet be observed. We show in-cell NMR spectra of bacterial NmerA and human calmodulin and discuss limitations of the technique as well as prospects for future applications.     

Resolution of a paradox in the electrophoresis of DNA in agarose gels

A paradox was observed in a previous study of the electrophoresis of linear DNA fragments in agarose gels (D. L. Holmes and N. C. Stellwagen, Electrophoresis 1990, 11, 5-15). The pore size of the agarose matrix was more accurately determined if the root-mean-square radius of gyration was used to measure DNA macromolecular size. However, the Ogston equations were obeyed and other gel parameters such as the apparent fiber radius and fiber volume appeared to be better described if the geometric mean radius was used to measure DNA size. This paradox can be resolved if relative mobilities (with respect to the smallest DNA molecule in the data set) are used to construct the Ferguson plots, instead of absolute mobilities. Using relative mobilities and the root-mean-square radius of gyration, the Ogston equations are obeyed and the pore size of the matrix is consistent with values determined by other methods.     

Dehydrogenation of propane on aluminoplatinum catalysts modified with Re,Zr, Sc,and Sn

The effect of addition of Re, Zr, Sc, and Sn on an aluminoplatinum catalyst in the reaction of dehydrogenation of propane was investigated. It was shown that addition of 0.2–0.5% Zr, Sc, or Re virtually does not alter the catalytic properties of the aluminoplatinum catalyst (APC); addition of 0.2% Sn increases the activity, selectivity, and stability of Pt/Al₂O₃. The amount of coke deposited on the APC after the first 5 min of work decreases by three times in the presence of Sn. The coke is more enriched with hydrogen than the other systems formed on the surface of Pt-Sn/Al₂O₃.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 765–771, April, 1991.     

Vanadium oxide surface studies

The vanadium oxides can exist in a range of single and mixed valencies with a large variety of structures. The large diversity of physical and chemical properties that they can thus possess make them technologically important and a rich ground for basic research. Here we assess the present status of the microscopic understanding of the physico-chemical properties of vanadium oxide surfaces. The discussion is restricted to atomically well-defined systems as probed by surface techniques. Following a brief review of the properties of the bulk oxides the electronic and geometric structure of their clean single crystal surfaces and adsorption studies, probing their chemical reactivity, are considered. The review then focuses on the growth and the surface properties of vanadium oxide thin films. This is partitioned into films grown on oxide substrates and those on metal substrates. The interest in the former derives from their importance as supported metal oxide catalysts and the need to understand the two-dimensional overlayer of the so-called “monolayer” catalyst. On the single crystal metal substrates thin oxide layers with high structural order and interesting properties can be prepared. Particular attention is given to ultrathin vanadium oxide layers, so-called nano-layers, where novel phases, stabilised by the substrate, form.     

A criterion for the uniform distribution of sequences in compact metric spaces

LetX be a compact metric space, le μ be a non-negative normalized Borel measure onX and letf be a measurable bounded real-valued function defined onX such thatf is μ-almost everywhere continuous and different from zero. It is proved that a sequence (x _n ),n=1,2, … of points inX is μ-uniformly distributed if and only if for every Borel setE?X with μ(Bd(E))=0 we have \(\mathop {\lim }\limits_{N \to \infty } \frac{1}{N}\sum\limits_{n = 1}^N {f(x_n )} 1_E (x_n ) = \int\limits_E {f(x)d\mu (x)} ,\) where 1 _E denotes the characteristic function ofE andbdE the boundary ofE. Furthermore some quantitative aspects and generalizations of this theorem are discussed.     

Beryllium diffusion across GaAs/(Al,Ga)As heterojunctions and GaAs/AlAs superlattices during MBE growth

Beryllium diffusion during MBE growth of (Al, Ga)As layers, (Al, Ga)As/GaAs heterojunctions and GaAs/AlAs superlattices has been studied by electrochemical C-V and secondary ion mass spectrometry (SIMS) concentration profiling, in conjunction with transmission electron microscopy. Diffusion times were comparatively short since they were limited to part of the growth sequence, so non-equilibrium effects had a significant influence. The results are consistent with an interstitial-substitutional mechanism in which lattice site incorporation becomes more difficult with increasing band gap enthalpy. Incorporation involves a kick-out reaction which leads to the observed disordering of the superlattices.