Synthesis and characterization of polyurethanes containing cholesterol and phosphatidylcholine analogous moieties

Several new polyurethanes containing cholesterol and phosphatidylcholine analogous moieties were synthesized by addition polymerization of 2-[bis(2-hydroxyethyl)methylammonio]ethyl 5-cholesten-3β-yl phosphate ( 2 ) with diisocyanates such as hexamethylene diisocyanate (HDI), 2,4-tolylene diisocyanate (TDI), 4,4′-methylenediphenyl diisocyanate (MDI) and m-xylylene diisocyanate (XDI), respectively. They were characterized by their IR and ¹H NMR spectral data and elemental analyses. Preliminary studies suggest that these polyurethanes show the viscosity behavior of common polyelectrolytes.     

Expansion of time window for mass spectrometric measurement of amide hydrogen/deuterium exchange reactions

Backbone amide hydrogen exchange rates can be used to describe the dynamic properties of a protein. Amide hydrogen exchange rates in a native protein may vary from milliseconds (ms) to several years. Ideally, the rates of all amide hydrogens of the analyte protein can be determined individually. To achieve this goal, monitoring of a wider time window is critical, in addition to high sequence coverage and high sequence resolution. Significant improvements have been made to hydrogen/deuterium exchange mass spectrometry methods in the past decade for better sequence coverage and higher sequence resolution. On the other hand, little effort has been made to expand the experimental time window to accurately determine exchange rates of amide hydrogens. Many fast exchanging amide hydrogens are completely exchanged before completion of a typical short exchange time point (10–30 s) and many slow exchanging amide hydrogens do not start exchanging before a typical long exchanging time point (1–3 h). Here various experimental conditions, as well as a quenched‐flow apparatus, are utilized to monitor cytochrome c amide hydrogen exchange behaviors over more than eight orders of magnitude (0.0044–1 000 000 s), when converted into the standard exchange condition (pH 7 and 23°C). Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and biological activities of 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand, and its metabolically stable ether-linked analogues

We synthesized 2-arachidonoylglycerol (1), an endogenous cannabinoid receptor ligand, and its metabolically stable ether-linked analogues. Compound 1 was synthesized from 1,3-benzylideneglycerol (6) and arachidonic acid in the presence of N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine followed by treatment with boric acid and trimethyl borate. An ether-linked analogue of 2-arachidonoylglycerol (2) was synthesized from 6 and 5,8,11,14-eicosatetraenyl iodide (9). The ether-linked analogues of 2-palmitoylglycerol (4) and 2-oleoyglycerol (5) were synthesized from 6 and hexadecyl iodide (12) and 9-octadecenyl iodide (14), respectively. We confirmed that 1 stimulates NG108-15 cells to induce rapid transient elevation of the intracellular free Ca2+ concentrations through a CB1 receptor-dependent mechanism. Noticeably, 2 exhibited appreciable agonistic activity, although its activity was significantly lower than that of 1. Compound 2 would be a useful tool in exploring the physiological significance of 1, because this compound is resistant to hydrolyzing enzymes in contrast to 1. On the other hand, the ether-linked analogues of either 4 or 5 failed to act as a CB1 receptor agonist. Compounds 4 and 5 would also be valuable as control molecules in experiments where 2 is employed.     

Semiconductor laser with curved deep-etched distributed Bragg reflectors supporting a planar Gaussian mode

A compact integration-compatible semiconductor laser supporting a planar Gaussian mode is demonstrated. Curved deep-etched distributed Bragg reflectors (DBR's), contouring the phase front of the Gaussian wave, act as feedback elements. The DBR's are 0.5 microm deep and have two first-order air gaps separated by a third-order semiconductor spacer. Low-threshold current (10 mA) is achieved for a 90-microm-long laser with a waist of 2 microm. Lasing in a planar Gaussian mode is observed up to 1.7 times the threshold current, whereas at higher currents the mode behavior degrades because of spatial hole burning.     

Compatibility between methanol and water in the three-dimensional cage formation of large-sized protonated methanol-water mixed clusters

Infrared spectra of large-sized protonated methanol-water mixed clusters, H(+)(MeOH)(m)(H(2)O)(n) (m=1-4, n=4-22), were measured in the OH stretch region. The free OH stretch bands of the water moiety converged to a single peak due to the three-coordinated sites at the sizes of m+n=21, which is the magic number of the protonated water cluster. This is a spectroscopic signature for the formation of the three-dimensional cage structure in the mixed cluster, and it demonstrates the compatibility of a small number of methanol molecules with water in the hydrogen-bonded cage formation. Density functional theory calculations were carried out to examine the relative stability and structures of selected isomers of the mixed clusters. The calculation results supported the microscopic compatibility of methanol and water in the hydrogen-bonded cage development. The authors also found that in the magic number clusters, the surface protonated sites are energetically favored over their internal counterparts and the excess proton prefers to take the form of H(3)O(+) despite the fact that the proton affinity of methanol is greater than that of water.     

Über die Annäherung analytischer Funktionen. II.

Ohne Zusammenfassung     

Temperature dependence of soliton density in the incommensurate phase of [N(CH3)4]2ZnCl4 crystals

The successive phase transitions of [N(CH₃)₄]₂ZnCl₄ have been investigated by EPR in a Mn²⁺ doped-sample. The temperature change in the resonance line shape near the commensurate-incommensurate transition temperature was analysed by a one-dimensional phase soliton model, so that the soliton density, modulation amplitude and initial phase were determined. The discommensuration phenomenon was also observed and discussed in terms of the domain wall resulting from the soliton.     

Ignition limits of short-term overloaded electric wires in microgravity

Ignition phenomena of electric wires carrying short-term excess electric currents were investigated in microgravity with experiments and calculations. Microgravity experiments were conducted in 100 m and 50 m drop towers and calculations were carried out with a one dimensional cylindrical coordinate system. The experimental results showed that the limiting oxygen concentration (LOC) under a given electric current was much lower in microgravity than that in normal gravity except for extremely large electric current overload cases. According to the calculations, the supplied electric current, the Joule energy supplied to the wire, determined the amount of pyrolysis gas from the insulation and the resulting thickness of the gaseous fuel layer around the sample in gas phase increased. The increased fuel layer thickness resulted in a longer ignition delay, which leads to lower LOC. The changes in the estimated LOC changed as a function of supplied energy and agreed well with the experimental results. Further, the minimum ignition energy causing ignition (ignition limit) is nearly constant under a constant oxygen concentration, which supports experimental findings in previous research.