Tunable all-optical delays via Brillouin slow light in an optical fiber

We demonstrate a technique for generating tunable all-optical delays in room temperature single-mode optical fibers at telecommunication wavelengths using the stimulated Brillouin scattering process. This technique makes use of the rapid variation of the refractive index that occurs in the vicinity of the Brillouin gain feature. The wavelength at which the induced delay occurs is broadly tunable by controlling the wavelength of the laser pumping the process, and the magnitude of the delay can be tuned continuously by as much as 25 ns by adjusting the intensity of the pump field. The technique can be applied to pulses as short as 15 ns. This scheme represents an important first step towards implementing slow-light techniques for various applications including buffering in telecommunication systems.     

Optimization of a high speed countercurrent chromatograph for analytical separations

The analytical capability of the high speed countercurrent chromatograph model 4000 (HSCCC-4000) has been improved by optimizing the dimensions of the multilayer coiled column. Using a two-phase solvent system of n-hexane – ethyl acetate – methanol – water (1:1:1:1) and a set of indole auxins as test samples, a series of studies was conducted to evaluate performance of coiled columns with i.d.s ranging from 0.1 to 0.55 mm. The studies on the stationary phase retention indicated that multilayer coils of 0.55 mm and 0.30 mm i.d. provide satisfactory retention of the stationary phase while the 0.10 mm i.d. column fails to yield reproducible retention. The best partition efficiencies were obtained from the 0.30 mm i.d. multilayer coil with a 6 ml capacity which produced theoretical plate numbers ranging from 5500 to 10500 with a resolution factor of 2.30. The feasibility of interfacing the HSCCC-4000 with a mass spectrometer is briefly discussed.     

Efficient synthesis of carbopeptoid oligomers: insight into mimicry of β-peptide

The ready access to a new class of carbohydrate mimetics was demonstrated by the synthesis of tetrameric carbopeptoids, in which glycosidic bonds were replaced with amide linkages. We herein describe the detailed synthetis method of β(1→2)- and β(1→6)-linked carbopeptoids starting from each d-glucosamine and d-glucose derivative. The building blocks were polymerized using BOP reagent and DIEA to form a homooligomer. These produced carbopeptoids are resistant to glycosidases and have interesting biological activity. With conformational analysis by molecular modeling calculation, β(1→2)-linked decamer showed a typical 16-helix form as a mimic of β-peptide. Therefore, our polysaccharide analogues have potential as peptide foldamers.     

Determination of Backbone Amide Hydrogen Exchange Rates of Cytochrome c Using Partially Scrambled Electron Transfer Dissociation Data

The technological goal of hydrogen/deuterium exchange-mass spectrometry (HDX-MS) is to determine backbone amide hydrogen exchange rates. The most critical challenge to achieve this goal is obtaining the deuterium incorporation in single-amide resolution, and gas-phase fragmentation may provide a universal solution. The gas-phase fragmentation may generate the daughter ions which differ by a single amino acid and the difference in deuterium incorporations in the two analogous ions can yield the deuterium incorporation at the sub-localized site. Following the pioneering works by Jørgensen and Rand, several papers utilized the electron transfer dissociation (ETD) to determine the location of deuterium in single-amide resolution. This paper demonstrates further advancement of the strategy by determining backbone amide hydrogen exchange rates, instead of just determining deuterium incorporation at a single time point, in combination with a wide time window monitoring. A method to evaluate the effects of scrambling and to determine the exchange rates from partially scrambled HDX-ETD-MS data is described. All parent ions for ETD fragmentation were regio-selectively scrambled: The deuterium in some regions of a peptide ion was scrambled while that in the other regions was not scrambled. The method determined 31 backbone amide hydrogen exchange rates of cytochrome c in the non-scrambled regions. Good fragmentation of a parent ion, a low degree of scrambling, and a low number of exchangeable hydrogens in the preceding side chain are the important factors to determine the exchange rate. The exchange rates determined by the HDX-MS are in good agreement with those determined by NMR.

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Phase transition of a single sheet of sashlike polydiacetylene atomic sash on a solid surface

The phase transition of sashlike polydiacetylene (PD) atomic sash in an extrathin (0.4 nm) vapor-deposited monolayer on a graphite (0001) surface has been observed by in-situ scanning tunneling microscopy (STM). The conformation of the atomic sash composed of a row of lying alkyl chains stitched up with a PD chain is different around the crossing points of the alkyl and PD chains in the two phases, and hence the contrast of the STM image is different in the middle of the sashes. The difference is associated with the color transition of bulk PDs.     

Electrochemistry of sinapine and its detection in medicinal plants

Sinapine (O-sinapoyl choline) is a crucial component, with much medicinal value, of many dietary and medicinal plants. It has been found that sinapine gives an electrochemical response at a pyrolytic graphite electrode. The electrochemical properties of sinapine have been investigated. The peak current in the cyclic voltammogram is linear in the concentration range 1.9×10^–6–2.5×10^–4 mol L^–1 and the limit of detection is 9.9×10^–7 mol L^–1. These properties can be applied to the determination of sinapine in extracts from three kinds of medicinal plant. The electrochemical method reported here is highly selective, sensitive, and stable.     

A prodrug of NMDA/glycine site antagonist, L-703,717, with improved BBB permeability: 4-acetoxy derivative and its positron-emitter labeled analog

4-Acetoxy derivative (1) of L-703,717, a high-affinity (IC50=4.5 nM) antagonist for the glycine site of NMDA receptors, was synthesized and its brain uptake was examined using a carbon-11 labeled analog ([11C]1). Initial radioactivity in the brain after intravenous injection of [11C]1 was a 2-fold that of [11C]L-703,717 in mice. Rapid bioconversion of [11C]1 into [11C]L-703,717 was demonstrated by metabolite analyses of rat brain after [11C]1 injection. Ex vivo autoradiography of [11C]1 in rat brain showed the same cerebellar localization of radioactivity as [11C]L-703,717. These results indicate that 1 is a promising pharmacological tool as a prodrug of L-703,717 with improved BBB permeability.     

Design and efficient synthesis of 2 alpha-(omega-hydroxyalkoxy)-1 alpha,25-dihydroxyvitamin D3 Analogues, including 2-epi-ED-71 and their 20-epimers with HL-60 cell differentiation activity

A concise and efficient synthetic approach to 2 alpha-(omega-hydroxyalkoxy)-1 alpha,25-dihydroxyvitamin D(3) (4a-c), including 2-epi-ED-71, was developed starting from D-glucose as a chiral template for the construction of the 2 alpha-modified A-ring precursors (11a-c). It was found that the best ligand for the bovine thymus vitamin D receptor (VDR) in this series is 4b, which has 1.8 times greater binding affinity for the bovine thymus VDR than that of the natural hormone 1. Interestingly, potency in the induction of HL-60 cell differentiation for 4a-c was almost the same or weaker than that of 1 despite the strong binding affinity for the VDR. Next, we were interested in the "double modification"of 1 based on 4a-c with C20-epimerization, affording 2 alpha-(omega-hydroxyalkoxy)-20-epi-1 alpha,25-dihydroxyvitamin D(3) (20-epi-4a-c). All three 2 alpha-substituted 20-epi analogues of 1 (20-epi-4a-c) exhibited stronger binding affinities for the VDR, and their conformations in the ligand binding domain of VDR were analyzed by molecular modeling. Double-modified analogues of 20-epi-4a-c showed marked HL-60 cell differentiation activity, and 20-epi-4a possesses an activity 58-fold higher than that of the natural hormone 1.     

Fast atom bombardment mass spectral study of tetracycline antibiotics

In the fast atom bombardment mass spectra of tetracyclines, ammonia elimination fragment ions, [M + H – NH₃]⁺ and [M + H – NH₃ – H₂O]⁺, appeared with considerable abundances. A plausible mechanism for the loss of ammonia from [M + H]⁺ was discussed based on results by measurements on various types of tetracyclines and benzamides as the model compounds and B/E linked scanning. The results indicated that the loss of ammonia occurred in the carboxyamide moiety in the A ring and was accelerated by an ortho-hydroxy group. The same fragmentations were observed in the electrospray mass spectra of tetracyclines with a skimmer-capillary voltage differential of 150 V.     

Effects of electrospray capillary temperature on amide hydrogen exchange

Amide hydrogen/deuterium (H/D) exchange coupled with proteolysis, high-perfeomance liquid chromatographic (HPLC) separation and mass spectrometry (MS) has become a powerful tool to study protein dynamics in solution. Prior to the execution of H/D exchange experiments, various experimental parameters have to be set, including proteolysis, HPLC, and MS conditions. Here we investigate the effects of electrospray capillary temperature on deuterium retention in backbone amides of various pepsin-generated cytochrome c peptides. Lower capillary temperature generally helps retain more deuterium than higher capillary temperature. When the capillary temperature was 150 degrees C, on average 26% more deuterium was retained than when the capillary temperature was set at 250 degrees C. The effects of capillary temperature varied depending on the ions monitored. There was little difference in deuterium retention among different charge state species of the same peptide at 150 degrees C. However, a lower charge state ion loses more deuterium atoms going from 150 degrees C to 250 degrees C than the corresponding higher charge state species. These results indicate that the capillary temperature should be optimized not only to maximize the signal-to-noise of each ion followed in H/D exchange experiments, but also to minimize the deuterium loss of the ions. Also the loss of deuterium in several ions, especially lower charge state ones, should be monitored in the optimization, as the temperature effects vary among ions and are more significant for lower charge state ions.