Formation, structure, and reactivity of amino-terminated organic films on silicon substrates

Amino-functionalized organic films were prepared by self-assembling 3-aminopropyltriethoxysilane (APTES) on silicon wafers in either anhydrous toluene or phosphate-buffered saline (PBS) for varied deposition times. Fourier transform infrared spectroscopy (FTIR) and ellipsometry have shown that the structure and thickness of APTES films are governed by the deposition time and reaction solution. Deposition from an anhydrous toluene solution produces APTES films ranging from 10 to 144 A in thickness, depending on the reaction time. FTIR spectra indicate that film growth initially proceeds by adsorption of APTES to the silicon surface followed by siloxane condensation, and after an extended period of time APTES molecules accumulate on the underlying APTES film by either covalent or noncovalent interactions. In contrast, spectroscopically indistinguishable APTES films in thickness ranging from 8 to 13 A were formed when deposition was conducted in aqueous solutions. Measured water contact angles indicate that APTES films deposited in aqueous solutions are more hydrophilic compared to those prepared in toluene solutions. Fluorescence measurements revealed that APTES films prepared in toluene solutions contain more reactive surface amino groups by ca. 3 to 10 times than those prepared in aqueous solutions for the identical reaction time.     

Simultaneous Analysis of Lipid-Soluble Constituents of Erxian Decoction by GC–MS

Erxian Decoction (EXD), a traditional Chinese medicine formula mainly composed of six Chinese herbs, was originally developed for menopausal syndromes and had been practiced since the 1950s in China. Previous studies only focused on the water-soluble compounds involved in EXD by LC or TLC. This study analyzed the whole profile of the volatile constituents contained in EXD to supplement its quality evaluation method. Several EXD samples were extracted with chloroform and ethyl acetate, respectively, to get the lipid-soluble chloroform and ethyl acetate fractions and compared their gas chromatographic profiles by GC–MS. The EXD samples were hydrolyzed with hydrochloric acid in a water-bath at 100 °C, neutralized with 40% NaOH, and finally extracted with ethyl acetate and chloroform for the quantification of the total sarsasapogenins contained in EXD. A total of 56 compounds belonging to a variety of natural product categories such as aromatic phenols, terpenes, fatty acids, ketones, esters, and aldehydes, etc. were identified from the chloroform and ethyl acetate extracts by using the online EI–MS characterization. The GC–MS method showed a linear response for sarsasapogenin quantification with r = 0.994. The intra-day and inter-day variations of precision and accuracy of the assay were less than 5%. This developed GC–MS method could thus be successfully applied for the identification of lipid-soluble constituents derived from EXD, and also for the accurate quantification of the total sarsasapogenins contained in the acid hydrolyzed EXD samples.     

Characterizations of inverse M-matrices with special zero patterns

In this paper, we provide some characterizations of inverse M-matrices with special zero patterns. In particular, we give necessary and sufficient conditions for k-diagonal matrices and symmetric k-diagonal matrices to be inverse M-matrices. In addition, results for triadic matrices, tridiagonal matrices and symmetric 5-diagonal matrices are presented as corollaries.     

Protein dynamics measurements by TROSY-based NMR experiments

The described TROSY-based experiments for investigating backbone dynamics of proteins make it possible to elucidate internal motions in large proteins via measurements of T(1), T(2), and NOE of backbone (15)N nuclei. In our proposed sequences, the INEPT sequence is eliminated and the PEP sequence is replaced by the ST2-PT sequence from the HSQC-based experiments. This has the benefit of shortening the pulse sequences by 5.4 ms (=1/2J) and results in an increase in the intrinsic sensitivity of the proposed TROSY-based experiments. The TROSY-based experiments are on average of 13% more sensitive than the corresponding HSQC-based experiments on a uniformly (15)N-labeled Xenopus laevis calcium-bound calmodulin sample on a 750-MHz spectrometer at 5 degrees C. The amide proton linewidths of the TROSY-based experiments are 2-13 Hz narrower than those of the HSQC experiments. More sensitivity gain and higher resolution are expected if the protein sample is deuterated.     

Zeta-potential measurement using the Smoluchowski equation and the slope of the current-time relationship in electroosmotic flow

The zeta -potential of a solid-liquid interface is an important surface characterization quantity for applications ranging from the development of biomedical polymers to the design of microfluidic devices. This study presents a novel experimental technique to measure the zeta -potentials of flat surfaces. This method combines the Smoluchowski equation with the measured slope of current-time relationship in electroosmotic flow. This method is simple and accurate in comparison with the traditional streaming potential and electrophoresis techniques. Using this method the zeta -potentials of glass and poly(dimethylsiloxane) (PDMS) coated surfaces in KCl and LaCl3 aqueous solutions were measured using several flow channels ranging from 200 to 300 microm in height. The zeta -potential was found to vary from -88 to -66 mV for glass surface and -110 to -68 mV for PDMS surfaces depending on the electrolyte and the ionic concentration. The measured values of the zeta -potential are found to be independent of the channel size and the applied driving voltage and generally are repeatable within +/-6%.     

A 31P-NMR. Study of Some Phosphite Complexes of Platinum (0)

³¹P-NMR. spectra for a series of phosphite complexes of platinum (0) have been measured. Low temperature studies have revealed the existence in solution of the mixed complexes Pt[PPh₃]₂[P(OPh₃)₃]₂ and Pt[PPh₃][P(OPh)₃]₃ of which the former is isolable.     

Vibrational spectral studies of ion-ion and ion-solvent interactions. III. Zinc nitrate in water/acetonitrile mixtures

Raman and some infrared line parameters of Zn(NO ₃ ) ₂ /H ₂ O/CH ₃ CN systems spanning a range of both solute and mixed solvent compositions are reported. It is concluded that the first cosphere of the zinc cation contains H ₂ O, CH ₃ CN, and NO ₃ ^–, the relative amounts of which are dependent on the composition. From an intensity analysis the relative amounts of these species in the first cosphere have been obtained. As the CH ₃ CN/H ₂ O ratio increases, a signal at 2263 cm ^–1 , attributed to CH ₃ CN in the second cosphere binding to water in the first cosphere, increases. For a solvent composition of 4 moles water to 1 mole acetonitrile, an ion-pair association constant for Zn ²⁺ (NO ₃ )^– of 0.090 M ^–1 (25°C) was measured. Evidence that the tetrahedral four-coordinate species [Zn(NO ₃ ) ₂ (CH ₃ CN) ₂ ] is the major constituent in acetonitrile-rich mixed solvents is presented.     

Chemical immobilization of azido cellulose phenylcarbamate onto silica gel via Staudinger reaction and its application as a chiral stationary phase for HPLC

Azido cellulose phenylcarbamate (AzCPC) was synthesized regioselectively and chemically immobilized onto aminized silica gel to afford urea-bonded chiral stationary phases (CSPs). The obtained CSPs showed good enantioselectivity in HPLC towards various racemates using normal phase eluants (hexane/2-propanol, hexane/chloroform or hexane/2-propanol/chloroform).