Synthesis and micellization of amphiphilic poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride) block copolymers

Amphiphilic biodegradable block copolymers [poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride)] were synthesized by the melt polycondensation of poly(ethylene glycol) and sebacic anhydride prepolymers. The chemical structure, crystalline nature, and phase behavior of the resulting copolymers were characterized with ¹H NMR, Fourier transform infrared, gel permeation chromatography, and differential scanning calorimetry. Microphase separation of the copolymers occurred, and the crystallinity of the poly(sebacic anhydride) (PSA) blocks diminished when the sebacic anhydride unit content in the copolymer was only 21.6%. ¹H NMR spectra carried out in CDCl₃ and D₂O were used to demonstrate the existence of hydrophobic PSA domains as the core of the micelle. In aqueous media, the copolymers formed micelles after precipitation from water‐miscible solvents. The effects on the micelle sizes due to the micelle preparation conditions, such as the organic phase, dropping rate of the polymer organic solution into the aqueous phase, and copolymer concentrations in the organic phase, were studied. There was an increase in the micelle size as the molecular weight of the PSA block was increased. The diameters of the copolymer micelles were also found to increase as the concentration of the copolymer dissolved in the organic phase was increased, and the dependence of the micelle diameters on the concentration of the copolymer varied with the copolymer composition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1271–1278, 2006     

Electrochemical characteristics of gatifloxacin and its interaction with DNA.

The electrochemical behavior of gatifloxacin (GTFX) and its interaction with natural calf thymus DNA (ctDNA) is investigated by differential pulse voltammetry (DPV) on a carbon paraffined electrode. According to the suggested electrochemical equation, a binding constant of 1.7058 x 10(5) (mol L(-1))(-1) and binding sizes s = 3.09 (base pairs) of GTFX with ctDNA are obtained by nonlinear fit analysis of electrochemical data. The results demonstrate that GTFX has the properties of an intercalative binder.     

Chiral separation of synthetic vicinal diol compounds by capillary zone electrophoresis with borate buffer and beta-cyclodextrin as buffer additive.

The investigation on capillary electrophoretic enantioseparation of six synthetic compounds containing vicinal diol groups has been undertaken to acquire the optimum conditions using native beta-cyclodextrin (beta-CD) as chiral selector and borate as a background electrolyte. The separation was carried out in an uncoated capillary (58.5 cm x 75 microm i.d., effective length 48.5 cm) and the effects of several important factors were investigated in detail. The results showed that beta-CD as a chiral selector exhibited good enantioselectivity and that the enantioseparation was greatly influenced by the structure of the diols, the borate concentration and the buffer pH. The optimum performance was obtained for the chiral vicinal diols under the conditions of 200 mM borate buffer of pH 9.8 containing 1.7% beta-CD at an applied voltage of 15 kV and a capillary temperature of 20 degrees C. Under the conditions, four diols were baseline separated with fast analysis time and the good theoretical plate numbers (above 10 x 10(4)) and favorable migration-time reproducibilities (RSDs below 3.0%) were obtained. The separation results were satisfactory.     

Experimental and computational studies of intracomplex reactions in Mg+(primary, secondary alkylamine) complexes induced by photoexcitation of Mg+

We report herein a comprehensive study of photoinduced reactions in complexes of Mg+ with primary (n-propyl- and isopropylamine) and secondary amines (dipropyl- and diisopropylamine) in the spectral range of 230-440 nm. Similar to the methyl- and ethylamine complexes studied previously, N-H bond activation of these complexes is very unfavorable. Instead, the C(alpha)-C, C-N, and C(alpha)-H bond-cleavage photoproducts are observed after photoexcitation of the Mg+ complexes (3(2)P<--3(2)S). For Mg+(primary amine) complexes, for example, Mg+-NH2CH2CH2CH3, and Mg+-NH2CH(CH3)2, the photoproducts resulting from C(alpha)--C rupture prevail after P(z) and charge-transfer excitations, whereas the Mg+ photofragment is predominant upon P(x,y) excitation. However, with further N-alkyl substitution, as in Mg+(secondary amine) complexes, for example, Mg+-NH(CH2CH2CH3)2 and Mg+-NH[CH(CH3)2]2, a novel intracomplex C-C coupling photoreaction dominates on P(x,y) excitation of Mg+, which is believed to arise from Mg+* insertion into the C-N bond. With P(z) and charge-transfer excitation, the Mg-R elimination photoproducts, arising from C(alpha)-C bond cleavage, predominate. The energetics and possible mechanisms of the intracomplex photoreactions are analyzed in detail with the help of extensive quantum mechanics calculations.     

Analysis of bufadienolides in the Chinese drug ChanSu by high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry

The qualitative analysis of bufadienolides in the Chinese drug ChanSu was performed using high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS). Bufadienolides are the major bioactive constituents of ChanSu, which is used to treat heart failure and cancer in traditional Chinese medicine. The APCI-MS fragmentation behavior of bufadienolides was studied. For bufadienolides with only hydroxyl substituents, the fragmentation was characterized by successive eliminations of H(2)O and CO molecules, and the profile of MS/MS product ions was correlated with the number of hydroxyl groups. If a C-16 acetoxyl group was present, the fragmentation of [M+H](+) ions was triggered by initial loss of 60 Da (HOAc). The elimination of CO was significant for bufadienolides with a 19-formyl group, and the 19-hydroxyl group could be characterized by the loss of 30 Da (HCHO). These fragmentation rules were applied to the identification of bufadienolides in a methanolic extract of ChanSu, which was separated on a C(18) column with gradient elution. A total of 35 bufadienolides were identified, including four new constituents. The method established here facilitated the convenient and rapid quality control of ChanSu crude drug and its pharmaceutical preparations.     

Dual analyte flow injection fluorescence immunoassays using thiophilic gel reactors and synchronous scanning detection

Heterogeneous fluorescence immunoassays have been automated using flow injection manifolds incorporating thiophilic gel solid phase reactors to separate antibody-bound and unbound analyte molecules. Antibody elution is achieved by changes in ionic strength, thus allowing the use of pH sensitive fluorescent labels. This facilitates the development of dual analyte systems, in which two competitive immunoassays with separate labels are monitored in parallel. Detection of the fluorophores by high speed synchronous fluorescence scanning while the flow is briefly stopped utilises either one synchronous interval which detects both fluorophores, or two separate scans at different wavelength intervals, one for each fluorophore. Simultaneous analyses of serum albumin and transferrin exemplify these novel approaches. Spectroscopic interferences are very small, analyte recoveries are close to 100%, with a relative standard deviation of 5-6% and a sampling rate of 20 h-1.     

Observation of isomeric states in197Bi

The high spin states of¹¹⁹Te, populated in¹¹⁰Pd(¹³C,4n) and¹¹⁰Pd(¹²C,3n) reactions, have been studied through -ray spectroscopy. The level scheme has been established upto a spin of 55/2. Three-quasiparticle states, based on g² _7/2h_11/2 and g_7/2d_5/2h_11/2 configurations, have been identified. The 35/2 and 39/2 states are suggested to be the fully aligned states constituted by five valence h_11/2 ³, g_7/2, d_5/2 quasiparticles.     

Theoretical study of thermal diffusivity of superlattices in measurements using “mirage” technique

A complete theoretical treatment for the determination of thermal diffusivity of superlattices by the mirage technique has been performed. An effective medium approximation model of the thermal conductivity and thermal diffusivity of both sublayers is presented, which is different from the simple models with the thermal diffusivity or thermal conductivity in series or parallel. The numerical calculation of the transverse component of the probe beam deflection in the mirage effect shows that the results obtained from the complete thermal-wave theory and the medium approximation model, for the optically and thermally thick superlattices, are in good agreement with each other. However, the further study on the thermally thin superlattices shows that either the series or the parallel model of the thermal conductivity should be chosen according to whether the thermal impedance of the superlattice is larger or less than that of substrate, respectively.     

Optical spectra of an intracavity two-photon medium with sequeezed inputs

We consider an ensemble of three-level configuration atoms in an optical cavity, interacting through two-photon transitions with a cavity mode, driven by a broad-band squeezed input of finite amplitude. The atom-cavity system is coupled to reservoirs to describe the losses of the atoms and the cavity. Optical spectra in the transmitted and the reflected field are calculated and analysed in the good cavity limit, for the purely absorptive resonant case and the general case, respectively.     

TheΛ b →Λ c decay form factors

The recently measured cross-sections for diffractive dissociation of nuclei in high-energy proton nucleus (pA) collisions show a strikingA ^1/3 dependence on the target massA. Such a dependence emerges from an optical model which incorporates a simple mechanism to produce the absorption fluctuations required for inelastic diffraction. The observed momentum transfer (t) dependence of the differential cross-section, dσ/dt∝ exp(?B|t|), is described in terms of a correlation length \(R_F = \sqrt {2B} \) of the absorption fluctuations which turns out to be of the size of a nucleon. The excitation massM dependence, dσ/dM ²∝M ^?2, is explained by a bremsstrahlung mechanism.