A tetrafluorophenyl activated ester self-assembled monolayer for the immobilization of amine-modified oligonucleotides

A tetrafluorophenyl (TFP) ester-terminated self-assembled monolayer (SAM) for the fabrication of DNA arrays on gold surfaces is described. Activated ester SAMs are desirable for biomolecule array fabrication because they readily react with amine-containing molecules to form a stable amide linkage. N-Hydroxysuccinimide (NHS) ester SAMs are commonly used for this purpose but are subject to a competing hydrolysis side reaction, limiting their effectiveness under basic conditions. TFP was evaluated here as an alternative activated ester leaving group with a potentially greater stability under basic conditions. It is shown that TFP SAMs are much more stable to basic pH than their NHS analogs and are also more hydrophobic, which is an advantage in the fabrication of high-density spotted arrays. DNA arrays prepared on TFP SAMs at pH 10 have a 5-fold greater surface density of DNA molecules, reduced fluorescence background, and smaller spot radii than those prepared on NHS SAM analogs.     

Study on the photostability of guaiazulene by high-performance liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry

The photostability of guaiazulene (1,4-dimethyl-7-isopropylazulene; GA), a natural azulenic compound used in cosmetic and health-care products, as well as in pharmaceutical preparations, was investigated in solution (methanol, ethanol, acetonitrile), by different techniques: gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography combined with atmospheric pressure chemical ionization mass spectrometry and UV detection (LC/APCI-MS and HPLC/UV). A solar simulator (xenon-arc lamp) was used as UV-A radiation source. The study involved: monitoring compound decomposition, identifying products of photodegradation (PPs), assessing the role of oxygen and evaluating the kinetics of the process. Minor PPs are volatile compounds and were characterized by GC/MS, while oligomeric polyoxygenated compounds, tentatively characterized on the basis of MS and MS/MS spectra, were found to be the main photoproducts. The photodegradation was found to be enhanced by the presence of oxygen; nevertheless, determination of the singlet oxygen quantum yield for GA gave a lower value than that for the reference standard Rose Bengal. The obtained results and the developed stability-indicating methods (GC/MS and LC/MS) are of interest for stability studies and/or quality control purposes of GA as raw material or cosmetic products.     

On the nature of the Brønsted acidic groups on native and functionalized mesoporous siliceous SBA-15 as studied by benzylamine adsorption from solution

The concentration and Br?nsted acidity of surface silanol groups on mesoporous silica (SBA-15) has been studied by following the adsorption of benzylamine, BA, from water as a function of pH. The adsorbed amount of BA from water was compared to the maximum amount of BA that could be adsorbed from cyclohexane. Furthermore, the surface concentration and acidity of carboxylic acid functions on surface-functionalized SBA-15 was also studied, which allowed the relative surface concentration of remaining silanols to be obtained. Two types of silanols can be identified, where about 1/5 of the silanols have a pKa 相似文献   

Temperature effect on the complex formation between tricyclic antidepressant drugs (amitriptyline or imipramine) and hydroxypropyl-β-cyclodextrin in water

The molecular encapsulation of two tricyclic antidepressants (TCA) drugs, amitriptyline and imipramine, by a glycosidic receptor, 6-hydroxypropyl-β-cyclodextrin (HPBCD), has been carried out in water solution by means of conductometric studies at different temperatures ranging from 15 °C to 45 °C. Conductivity measurements of aqueous solutions of the drug were performed: (i) in the absence of HPBCD, as a function of drug concentration; and (ii) in the presence of HPBCD, as a function of HPBCD concentration. Both drugs, amitriptyline and imipramine, form inclusion complexes characterized by a 1:1 stoichiometry and an association constant () in the range of 500–1200 M⁻¹. The ionic molar conductivities at infinite dilution of the free () and complexed () drugs have been calculated from these conductivity data as well. From the dependency of the association constant on temperature, changes on the enthalpy, ΔH ⁰, entropy, ΔS ⁰, and heat capacity at constant pressure, , have been determined. This thermodynamic information, which reveals that the complexes formed by HPBCD and the antidepressant drugs, AMYTPH⁺ and IPRH⁺, are enthalpy driven at T ≥ 25 °C but entropy driven at T < 25 °C, points to the contribution of van der Waals interactions, hydrophobic effect and solvent reorganization, as the main driven forces promoting the interaction. The analysis of these association processes was also used to elucidate the potential viability of using HPBCD as a vector of these antidepressant drugs.     

Dinuclear zinc(II) complexes of symmetric Schiff-base ligands with extended quinoline sidearms

The synthesis of two 2-formylquinolines is reported via the Skraup method followed by SeO(2) oxidation. Each aldehyde is condensed with (1R,2R)-diaminocyclohexane and (R)-BINAM, yielding four enantiomerically-pure bis(imine-quinoline) ligands. The neutral ligands are reacted with ZnCl(2) to give complexes with bis(bidentate) coordination of ZnCl(2) units. X-Ray structural characterization of three complexes shows them to have a single-stranded helical motif, with M helicity, except in one case where a 1:1 mixture of M and P helices is seen. The ligands and complexes are further characterized spectroscopically by solution (1)H and (13)C NMR, UV-vis and ECD.     

Proton solvation and transport in aqueous and biomolecular systems: insights from computer simulations

The excess proton in aqueous media plays a pivotal role in many fundamental chemical (e.g., acid-base chemistry) and biological (e.g., bioenergetics and enzyme catalysis) processes. Understanding the hydrated proton is, therefore, crucial for chemistry, biology, and materials sciences. Although well studied for over 200 years, excess proton solvation and transport remains to this day mysterious, surprising, and perhaps even misunderstood. In this feature article, various efforts to address this problem through computer modeling and simulation will be described. Applications of computer simulations to a number of important and interesting systems will be presented, highlighting the roles of charge delocalization and Grotthuss shuttling, a phenomenon unique in many ways to the excess proton in water.     

Solvochromic effects in model eumelanin compounds

We have created an indolic compound which is ideally suited to the study of the relationship between structure and function in eumelanin formation. N-methyl-5-hydroxy-6-methoxyindole (MHMI) is stable in solid and liquid states, highly soluble in a variety of solvents and forms a dimer only through the 4-4' positions. The limited binding possibilities are due to functional groups strategically placed to inhibit chemical interactions through the 2 and 7 positions. It forms a crystal structure with a remarkable packing arrangement, with four monomers grouped in parallel pairs spaced 3.5 A apart within each unit cell. Optical spectra reveal a multi-peaked absorbance profile similar to 5,6-dihydroxyindole (DHI) and N-acetyl-tryptophanamide (NATA), and strong fluorescence emission with radiative quantum yields of 29% and 33% in benzene and acetonitrile, respectively. The quantum yield is similar to that of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and shows that solvent aromaticity by itself does not affect the yield. Solution in chloroform results in an almost complete quenching of the fluorescence but an increase in emission is observed with photoactivation. Crystallographic results shown here suggest new structural possibilities for eumelanin and the controlled binding possibilities make this an excellent model for monitoring changes in function with increasing oligomer size in eumelanin formation.     

Electrochemically controlled hydrogen bonding. Electrolyte effects in an oxidation-based arylurea-amide system

Oxidation of a dimethylaminophenyl-substituted urea leads to a > 2000-fold increase in binding strength between the urea and a diamide guest in 0.1 M NBu4B(C6F5)4/CH2Cl2. The strength of this interaction is obscured when NBu4ClO4 or NBu4PF6 is used as the electrolyte due to competition between the neutral guest and the electrolyte anion for H-bonding to the urea cation.     

Cell-electronic sensing of particle-induced cellular responses

We report a new technique for the continuous and real-time measurement of microparticle-induced cellular responses using a real-time cell-electronic sensing (RT-CES) technology. The method involves the use of microelectrode-embedded microwells seeded with one of two lung cancer carcinoma cell lines (A549 and SK-MES-1), allowing for continuous measurements of impedance. The change in impedance that is automatically converted to the cell index is linearly correlated with the numbers of the seeding cells during the log phase, providing quantitative measurement of cytotoxicity. After 24 h of initial incubation in 96 microwells, the cultures are treated with microparticles, and changes in the cell index are monitored in real time. Multiple data, including dose response curves, IC(50) (a concentration inhibiting 50% cell growth), and cell-specific and particulate-specific cell responses, are obtained from a single set of experiments. SK-MES-1 cells consistently showed more severe effects and lower IC(50) values than A549 cells when they were treated with quartz particle suspensions. The different effects detected using the RT-CES technique were related to morphological change and apoptosis, supported by the scanning electronic microscopy and flow cytometry results. The method is further used to test the cytotoxicity of two PM(10) standard reference materials of urban air dust and diesel particulates, demonstrating the potential application of this new technique for biomonitoring of air particulates.