Nd[Al(iPrO)4]3, a novel tetranuclear alkoxide forming merohedrally twinned crystals

The new tetranuclear alkoxide hexa‐μ₂‐isopropoxy‐1:2κ⁴O;1:3κ⁴O;1:4κ⁴O‐hexaisopropoxy‐2κ²O,3κ²O,4κ²O‐trialumin­ium(III)­neodymium(III), [Nd{Al(C₃H₇O)₄}₃], has a metal–oxy­gen NdAl₃O₁₂ core which consists of four metal atoms arranged in an approximately planar triangular geometry. The central Nd atom is six‐coordinated by O atoms and the Al atoms are four‐coordinated by O atoms.     

Simulation of hydroforming of steel tube made of metastable stainless steel

The Olson–Cohen model for strain-induced deformation, further developed by Stringfellow and others, has been calibrated together with a flow stress model for the plastic deformation of metastable stainless steel. Special validation tests for checking one of the limitations of the model have also been carried out. The model has been implemented into a commercial finite element code using a staggered approach for integrating the stress–strain relations with the microstructure model. Results from a thermo-mechanical coupled simulation of hydroforming of a tube have been compared with corresponding experiments. The agreement between experimental results of radial expansion and martensite fraction and the corresponding computed results is good.     

Biosynthetic 13C labeling of aromatic side chains in proteins for NMR relaxation measurements

Site-specific 13C labeling offers a desirable means of eliminating unwanted relaxation pathways and coherent magnetization transfer in NMR relaxation experiments. Here we use [1-13C]-glucose as the sole carbon source in the growth media for protein overexpression in Escherichia coli. The approach results in specific incorporation of 13C at isolated positions in the side chains of aromatic amino acids, which greatly simplifies the measurements and interpretation of 13C relaxation rates in these spin systems. The method is well suited for characterization of chemical exchange by CPMG or spin-lock relaxation methods. We validated the method by acquiring 13C rotating-frame relaxation dispersion data on the E140Q mutant of the C-terminal domain of calmodulin, which reveal conformational exchange dynamics with a time constant of 71 mus for Y138.     

Stability indicating methods for the determination of some fluoroquinolones in the presence of their decarboxylated degrades

Two stability-indicating methods, namely densitometric TLC and derivative spectrophotometry for the determination of the fluoroquinolone antibacterials lomefloxacin (Lfx), moxifloxacin (Mfx), and sparfloxacin (Sfx) in the presence of their acid degrades are described. Acid degradation was adopted and the main decarboxylated product separated by TLC. Degradation products were identified confirming a previously mentioned degradation scheme. The densitometric method is based on the separation of the intact drug from its acid degradation product on silica gel G plates using different mobile phases and the spots of the intact drugs were scanned at 288, 290, and 292 nm for Lfx, Mfx, and Sfx, respectively. The derivative spectrophotometric method utilizes first derivative D(1) UV spectrophotometry with zero crossing points at 295.2 nm for Lfx, 280.4 and 303.4 nm for Mfx, and 280.8 nm for Sfx. Regression analysis of Beer's plots showed good correlation in the concentration ranges 0.2-1.2, 0.1-1.4, and 0.5-2.0 microg/spot for Lfx, Mfx, and Sfx, respectively, in the densitometric method and 2-16 microg/ml for all drugs in the derivative spectrophotometric method. The proposed methods were successfully applied for the determination of the investigated drugs in bulk powder with mean percentage accuracy ranges from 98.93 to 101.25% for the TLC method and from 98.18 to 100.35% for the D(1) method. The proposed methods were also applied for the determination of the investigated drugs in their pharmaceutical dosage forms and their validity was assessed using the standard addition technique with mean percentage recovery ranging from 100.25 to 101.70% in the TLC method and from 99.27 to 102.12% in the D(1) method. The selectivity of the proposed methods was tested by the analysis of laboratory-prepared mixtures containing different percentages of the studied drugs and their acid degrades. The proposed methods were found selective for the determination of the intact drugs in the presence of up to 90% of their degrades in the TLC method and 70% for Lfx and 90% for Mfx and Sfx in the D(1) method.     

Synthesis,redox properties,and EPR spectroscopy of manganese(III) complexes of the ligand N,N-bis(2-hydroxybenzyl)-N'-2-hydroxybenzylidene-1,2-diaminoethane: formation of mononuclear,dinuclear, and even higher nuclearity complexes

The synthesis and characterization of the title trisphenolate ligand are described. From its reaction with manganese(III) three complexes were isolated. The crystal structures revealed one pentacoordinate monomer and two similar dimers with different solvents of crystallization. In the dimers the metal ions are hexacoordinate and connected through bridging of two phenolates. A combination of electrochemistry and EPR spectroscopy showed that, in acetonitrile, the isolated batches were all identical and mainly monomeric, indicating that the mononuclear complex is in equilibrium with the dimer and perhaps also with complexes of higher nuclearity, as suggested by the detection of both the trimer and the tetramer by electrospray ionization mass spectrometry (ESI-MS). The successful use of the monomer batch as an epoxidation catalyst indicated that a high-valent manganese-oxo species can be formed, although it is probably short-lived. This is also suggested by EPR studies of the species formed by electrochemical oxidation of the complex. Upon one-electron oxidation, a manganese(IV) species was formed, which was at least partly converted to another species containing a phenoxy radical.     

Approximately central matrix units and the structure of noncommutative tori

The property of approximate divisibility forC*-algebras is introduced and studied. Simple approximately divisibleC*-algebras are shown to have nice nonstableK-theory properties. Non-rational noncommutative tori are shown to be approximately divisible. It follows that every simple noncommutative torus (in particular, every irrational rotation algebra) has stable rank one and real rank zero.     

Some preliminary investigations by means of gas adsorption on sintered porous membranes for the separation of the uranium isotopes by gaseous diffusion

Colloid and Polymer Science - An introductory investigation of the pore structure of a new type of porous membrane, manufactured by a new method, has been performed. The membranes are suitable for...     

Solvent affects the conformation of virginiamycin M1 (pristinamycin IIA, streptogramin A)

The streptogramins are antibiotics which act by binding two different components at separate nearby sites on the bacterial 50S ribosome, inhibiting protein synthesis. The first component, a macrolactone, is common to many of the streptogramin antibiotics and, thus, is referred to by many names including virginiamycin M1(VM1), pristinamycin IIA, ostreogrycin A and streptogramin A. X-Ray crystallographic studies of VM1 bound to ribosomes and to a deactivating enzyme show a different conformation to that of VM1 in chloroform solution. We now report the results of high resolution 2D NMR experiments that show that the conformation of VM1 in dimethyl sulfoxide and methanol differs from both that in chloroform solution and in the bound form. The 3D structure and the 1H NMR and 13C NMR chemical shifts of VM1 in dimethyl sulfoxide and methanol are described.     

A purely infinite AH-algebra and an application to AF-embeddability

We show that there exists a purely infinite AH-algebra. The AH-algebra arises as an inductive limit ofC*-algebras of the formC ₀([0, 1),M _k ) and it absorbs the Cuntz algebra ctive limit of the finite and elementaryC*-algebrasC ₀([0, 1),M _k ). As an application we give a new proof of a recent theorem of Ozawa that the cone over any separable exactC*-algebra is AF-embeddable, and we exhibit a concrete AF-algebra into which this class ofC*-algebras can be embedded.     

Unified treatment of fluorescence and raman scattering processes near metal surfaces

We present a general model study of surface-enhanced resonant Raman scattering and fluorescence focusing on the interplay between electromagnetic effects and the molecular dynamics. Our model molecule is placed close to two Ag nanoparticles and has two electronic levels. A Franck-Condon mechanism provides electron-vibration coupling. Using realistic parameter values for the molecule we find that an electromagnetic enhancement by 10 orders of magnitude can yield Raman cross sections sigma(R) of the order 10(-14) cm(2). We also discuss the dependence of sigma(R) on incident laser intensity.