Determination of surface charge properties of PC-12 cells by electrophoresis

The electrophoretic behavior of pheochromocytoma (PC-12) cells was investigated both experimentally and theoretically. Cell mobility in aqueous media at different pHs and ionic concentrations was measured, and a model, which assumed that the cell surface contains both acidic and basic functional groups, was proposed. As a result, it was revealed that the experimental data gathered can be described satisfactorily by assuming that the cell surface contains two types of monovalent acidic functional groups and one basic functional group. The values of the dissociation constants of the acidic and basic groups are found to be close to those of acidic amino acids, which indicates that the acidic amino acids may play an important role in the surface electrical properties of PC-12 cells.     

Pulsed remote Raman system for daytime measurements of mineral spectra

A remote Raman system has been developed utilizing a 532nm pulsed laser and gated intensified charged couple device (ICCD) detector in the oblique geometry. When the system is set for 50m sample distance it is capable of measuring Raman spectra of minerals located at distances in the range of 10-65m from the telescope. Both daytime and nighttime operations are feasible and the spectra of minerals can be measured in a short period of time, of the order of a few seconds. In oblique geometry, measured sampling depth is more than 30m, during which the system maintains very high performance without any adjustments. Much longer sampling depth (0.1-120m) has been observed when the system is configured in the coaxial geometry. Clear advantages of using a gated detection mode over the continuous (CW) mode of operation in reducing the background signal and eliminating long-lived fluorescence signals from the Raman spectra are presented. The performance of the pulsed Raman system is demonstrated by measuring spectra of Raman standards including benzene (C(6)H(6)) and naphthalene (C(10)H(8)), a low Raman cross section silicate mineral muscovite (KAl(2)(Si(3)Al)O(10)(OH)(2)), and a medium Raman cross section mineral calcite (CaCO(3)).     

Sensitive high-performance liquid chromatographic determination of famotidine in plasma. Application to pharmacokinetic study.

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of famotidine in human plasma is described. Clopamide was used as the internal standard. Plasma samples were extracted with diethyl ether to eliminate endogenous interferences. Plasma samples were then extracted at alkaline pH with ethyl acetate. Famotidine and the internal standard were readily extracted into the organic solvent. After evaporation of ethyl acetate, the residue was analysed by HPLC. The chromatographic separation was accomplished with an isocratic mobile phase consisting of acetonitrile-water (12:88, v/v) containing 20 mM disodium hydrogenphosphate and 50 mM sodium dodecyl sulphate, adjusted to pH 3. The HPLC microbore column was packed with 5 microns ODS Hypersil. Using ultraviolet detection at 267 nm, the detection limit for plasma famotidine was 5 ng/ml. The calibration curve was linear over the concentration range 5-500 ng/ml. The inter- and intra-assay coefficients of variation were found to be less than 10%. Applicability of the method was demonstrated by a bioavailability/pharmacokinetic study in normal volunteers who received 80 mg famotidine orally.     

Novel design of a pentacyclic scaffold as structural mimic of saframycin A

The design, synthesis and evaluation of a pentacyclic scaffold, CWO-324 to mimic saframycin A is described. CWO-324 is readily synthesized in five steps from 1,4-diacetyl-piperazine-2,5-dione and 2,5-dimethoxybenzaldehyde. CWO-324 was found to scission DNA, binds to bases 69-83(5′-GCAGTCAGG CACCGT-3′) of Hind III/Rsa I from plasmid pBR322 DNA in a foot-printing study and possesses anti-tumor activity.     

Surface-initiated growth of poly d(A-T) by Taq DNA polymerase

In this paper, we report surface-initiated d(A-T) polymerization by Taq DNA polymerase as a method for constructing DNA-tethered surfaces using an enzyme. The enzymatic polymerization was conducted successfully via two steps: tethering of oligo d(A-T)s onto the surface presenting carboxylic acids by amide coupling and surface-initiated polymerization using Taq DNA polymerase. In this enzymatic polymerization process, the design and construction of carboxylic acid-presenting surfaces were found to be an important factor: DNA growth did not occur on the gold surface coated only with the self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA), but effectively proceeded on the surfaces presenting mixed SAMs of MHDA and 1-pentadecanethiol. The coupling of oligo d(A-T)s and the subsequent DNA polymerization reaction were characterized by polarized infrared external reflectance spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy.     

Temperature dependence of the distribution of the first passage time: results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Gō-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T(opt). The optimal folding temperature T(opt) is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T(opt) and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T(opt) and start to diverge when the temperature is lower than T(opt). The distribution of FPT is close to a log-normal-like distribution at T > or = T(opt). At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.     

Nouvelle méthode de détermination des taux de réativité des copolymères par résonance magnétique nucléaire: Application aux poly(méthacrylate de méthyle–chlorure de vinylidène)

Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by ¹H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction.     

Carbon fibre electrodes in flow potentiometric stripping analysis

The construction of carbon fibre flow electrodes suitable for use in connection with potentiometric and constant-current stripping is described, and the fibre electrodes are compared with a glassy carbon disc thin layer cell. The signal-to-background ratio is approximately 1.6 times higher for an 8–10 μm carbon fibre compared to the glassy carbon disc electrode. If an Ag/AgCl tube is used as both counter and reference electrode, the signal-to-noise ratio of the fibre electrode is approximately five times better than for a glassy carbon disc electrode with a calomel reference; the latter electrode design, however, gives slightly better precision. The dead volume and internal potential drop of the fibre electrodes are more than one order of magnitude smaller than for the glassy carbon disc electrode. Because of the simplicity of the manufacturing process and low material cost, the fibre cells can be used as disposable electrodes and the polishing process necessary in connection with glassy carbon disc electrodes can be omitted.     

Aminonaphthalic anhydrides as red-emitting materials: electroluminescence, crystal structure, and photophysical properties

The red and orange emitters (ANA-1-3) consisting of a 4-amino-1,8-naphthalic anhydride group were synthesized. The lowest absorption band of these ANA molecules centered at approximately 450 nm is assigned to be a charge-transfer transition with emission at 514-536 nm in nonpolar solvents such as n-hexane and at approximately 590-640 nm in polar solvents such as THF and CH(2)Cl(2) and in the solid states. Emission lifetimes are measured with time-correlated single photon counting. Shorter lifetimes are observed for the ANA molecules when dissolved in polar solvents compared with those in nonpolar solvents. Strong dipole-dipole interaction of ANA molecules with solvents is indicated. At high concentrations the measured emission lifetimes, generally shortened from self-quenching, are found to remain about the same order of magnitude in ANAs. This implies that the exciton states of aggregates are formed and they exhibit a relatively long lifetime. Crystallographic data of 4-(phenyl antracen-9-yl) (ANA-2) and 4-(phenyl-2-naphthyl) amino-1,8-naphthalic anhydrides (ANA-3) show that the molecules exist as dimeric structures with antiparallel head-to-tail stacking of naphthalic anhydride planes in addition to other pi-pi stacking. The strong dipole-dipole interactions and the pi-pi stacking account for the observed red-shifted emissions of ANAs in the powders. For films prepared from vacuum sublimation, a structure similar to that in the crystal but with less crystalline order is expected based on the emission wavelength. Several electroluminescent devices based on these ANAs are reported here; they emit orange-red light at 602-628 nm with high brightness and steady external quantum efficiency.