Capillary electrophoresis analysis of glucooligosaccharide regioisomers

Complex gluco-oligosaccharide mixtures of two regioisomer series were successfully separated by CE. The gluco-oligosaccharide series were synthesized, employing a dextransucrase from Leuconostoc mesenteroides NRRL B-512F, by successive glucopyranosyl transfers from sucrose to the acceptor glucose or maltose. The glucosyl transfer to both acceptors, occurring through the formation of alpha1-->6 linkages, differed for the two series only in the glucosidic bond to the reducing end namely alpha1-->6 or alpha1-->4 bond for glucose or maltose acceptor, respectively. Thus, the combination of the two series results in mixed pairs of gluco-oligosaccharide regioisomers with different degrees of polymerization (DP). These regioisomer series were first derivatized by reductive amination with 9-aminopyrene-1,4,6-trisulfonate (APTS). Under acidic conditions using triethyl ammonium acetate as electrolyte, the APTS-gluco-oligosaccharides of each series were separated enabling unambiguous size determination by coupling CE to electrospray-mass spectrometry. However, neither these acidic conditions nor alkaline buffer systems could be adapted for the separation of the gluco-oligosaccharide regioisomers arising from the two combined series. By contrast, increased resolution was observed in an alkaline borate buffer, using differential complexation of the regioisomers with the borate anions. Such conditions were also successfully applied to the separation of glucodisaccharide regioisomers composed of alpha1-->2, alpha1-->3, alpha1-->4, and alpha1-->6 linkages commonly synthesized by glucansucrase enzymes.     

Fission of a multiphase membrane tube

A common mechanism for intracellular transport is the use of controlled deformations of the membrane to create spherical or tubular buds. While the basic physical properties of homogeneous membranes are relatively well known, the effects of inhomogeneities within membranes are very much an active field of study. Membrane domains enriched in certain lipids, in particular, are attracting much attention, and in this Letter we investigate the effect of such domains on the shape and fate of membrane tubes. Recent experiments have demonstrated that forced lipid phase separation can trigger tube fission, and we demonstrate how this can be understood purely from the difference in elastic constants between the domains. Moreover, the proposed model predicts time scales for fission that agree well with experimental findings.     

Cryptophanols,new versatile compounds for the synthesis of functionalized cryptophanes and polycryptophanes

After deprotection with a palladium catalyst, mono-allylated cryptophane-A (1, 2) and cryptophane-E (3) gave the new cryptophanols 4, 5 and 6, respectively, which are important key compounds for the preparation of monofunctionalized cryptophanes as well as for the design of large supramolecular hosts such as the bis-cryptophanes 7 and 8.     

Reassigning hydrogen-bond centering in dense ice

Hydrogen bonds in H2O ice change dramatically upon compression. Thereby a hydrogen-bonded molecular crystal, ice VII, is transformed to an atomic crystal, ice X. Car-Parrinello simulations reproduce the features of the x-ray diffraction spectra up to about 170 GPa but allow for analysis in real space. Starting from molecular ice VII with static orientational disorder, dynamical translational disordering occurs first via creation of ionic defects, which results in a systematic violation of the ice rules. As a second step, the transformation to an atomic solid and thus hydrogen-bond centering occurs around 110 GPa at 300 K and no novel phase is found up to at least 170 GPa.     

Direct investigation of spin Hamiltonians DS2z by measuring magnetization during intense pulsed fields

We describe a new method for investigating the DS²_z spin Hamiltonians (D > 0) using intense pulsed magnetic fields at low temperature: the level crossings occuring during the pulse result in sharp increases in the magnetization. By this method, we measured D = 12.2 ± 0.2 cm^-1 in ferrous fluosilicate.     

Photomechanical control of the electronic properties of linear pi-conjugated systems

Photodynamic molecular architectures have been synthesized by covalent fixation of a photoisomerizable dimethylazobenzene group at two fixed points of conformationally flexible pi-conjugated quater- and sexithiophene chains. Theoretical geometry optimization shows, in excellent agreement with crystallographic structures, that the mode of fixation of the azo group plays a determining role in the geometry of the final molecular architecture and on its ability to perform the expected photoinduced molecular motion. Thus, covalent fixation of meta-dimethylazobenzene on a quaterthiophene chain results in a conformationally locked system in which photoisomerization of the azo group is hindered. However, the experimental results of optical, (1)H NMR spectroscopic, and electrochemical investigations show that when an azobenzene group is connected at the para positions of the phenyl rings, trans-to-cis photoisomerization of the azo group induces a conformational transition and dimensional changes in the underlying pi-conjugated oligothiophene chain. These experimental results unequivocally show that the photochemically induced geometrical changes produce in turn an increase in the HOMO level and a narrowing of the HOMO-LUMO gap. This therefore provides the first evidence of photomechanical control of the electronic properties of linear pi-conjugated systems.     

Performance of radar absorbing materials by waveguide measurements for X- and Ku-band frequencies

In this work, samples consisting of an elastomeric matrix containing different kinds of active materials in particulate form were prepared for reflectivity measurements. The materials individually used in weight contents of 80% in polychloroprene matrix were: carbonyl-iron (CI) and doped ferrite powders. The microwave reflectivity levels were determined from the magnetic and dielectric properties of the elastomeric composites obtained from scattering data, by fitting the samples in a waveguide, for measurements in the frequency range from 8 to 16 GHz. Better microwave absorption for X-band was obtained for CI while doped ferrite absorbed at higher frequencies (Ku-band).     

Magnetic properties and specific heat of garnet Ca3Fe2Ge3O12

Owing to a four-sublattice molecular field model we have found a good agreement between various experimental results of susceptibility, magnetization and magnetic specific heat obtained on the garnet Ca₃Fe₂Ge₃O₁₂.     

Production of high power tunable UV laser emission by second-harmonic generation fro, a rhodamine 6G dye laser

The generation of tunable UV radiation in the 280–310 nm range by doubling the output frequency of a flashlamp-excited Rhodamine 6 G dye laser is described. By using KDP and ADP crystals, conversion efficiencies of respectively 9.4% and 8.4% are obtained with UV output energies up to 50 mJ.     

Reversible Guest Uptake/Release by Redox‐Controlled Assembly/Disassembly of a Coordination Cage

Controlling the guest expulsion process from a receptor is of critical importance in various fields. Several coordination cages have been recently designed for this purpose, based on various types of stimuli to induce the guest release. Herein, we report the first example of a redox‐triggered process from a coordination cage. The latter integrates a cavity, the panels of which are based on the extended tetrathiafulvalene unit (exTTF). The unique combination of electronic and conformational features of this framework (i.e. high π‐donating properties and drastic conformational changes upon oxidation) allows the reversible disassembly/reassembly of the redox‐active cavity upon chemical oxidation/reduction, respectively. This cage is able to bind the three‐dimensional B₁₂F₁₂^2? anion in a 1:2 host/guest stoichiometry. The reversible redox‐triggered disassembly of the cage could also be demonstrated in the case of the host–guest complex, offering a new option for guest‐delivering control.