What controls the melting properties of DNA-linked gold nanoparticle assemblies?

We report a series of experiments and a theoretical model designed to systematically define and evaluate the relative importance of nanoparticle, oligonucleotide, and environmental variables that contribute to the observed sharp melting transitions associated with DNA-linked nanoparticle structures. These variables include the size of the nanoparticles, the surface density of the oligonucleotides on the nanoparticles, the dielectric constant of the surrounding medium, target concentration, and the position of the nanoparticles with respect to one another within the aggregate. The experimental data may be understood in terms of a thermodynamic model that attributes the sharp melting to a cooperative mechanism that results from two key factors: the presence of multiple DNA linkers between each pair of nanoparticles and a decrease in the melting temperature as DNA strands melt due to a concomitant reduction in local salt concentration. The cooperative melting effect, originating from short-range duplex-to-duplex interactions, is independent of DNA base sequences studied and should be universal for any type of nanostructured probe that is heavily functionalized with oligonucleotides. Understanding the fundamental origins of the melting properties of DNA-linked nanoparticle aggregates (or monolayers) is of paramount importance because these properties directly impact one's ability to formulate high sensitivity and selectivity DNA detection systems and construct materials from these novel nanoparticle materials.     

A concise synthesis of (2S,4R)- and (2S,4S)-4-methylglutamic acid

A concise, multi-gram scale method for producing the bioactive and enantiomerically pure epimers, (2S,4R)- and (2S,4S)-glutamic acids, in a single synthetic scheme is described.     

Addition of grignard reagents to aryl acid chlorides: an efficient synthesis of aryl ketones

[chemical reaction: see text]. Direct addition of Grignard reagents to acid chlorides in the presence of bis[2-(N,N-dimethylamino)ethyl] ether proceeds selectively to provide aryl ketones in high yields. A possible tridentate interaction between Grignard reagents and bis[2-(N,N-dimethylamino)ethyl] ether moderates the reactivity of Grignard reagents, preventing the newly formed ketones from nucleophilic addition by Grignard reagents.     

Waterborne polyurethane assembly multifunctional coating for hydrophobic and antibacterial fabrics

Surface modification of fabrics is a powerful strategy that can endow fabrics with desired effects while keeping the intrinsic properties. Herein, an ordinary strategy, dipping-drying based layer-by-layer self-assembly (LbL) coating, is reported to functionalize fabrics’ surfaces. Firstly, the novel cation waterborne polyurethanes (QAHDPU) and anion waterborne polyurethanes (HDPU) are successfully designed and synthesized. By incorporating targeted molecule, hydantoin diol (HD) and quaternary ammonium salt with long alkyl chain (DOQA), the QAHDPU are antibacterial and hydrophobically functionalized. Taking advantage of strong adhesion, waterborne polyurethanes (WPUs) are physically bonded to surfaces of fabrics to generate durable antibacterial and hydrophobic fabrics. The QAHDPU with long alkyl chain combined with rough and porous fabric surface fabricates hydrophobic fabric surface, which can prevent bacteria from adhering to the fabrics. Furthermore, the coated fabrics present excellent antibacterial properties after chlorination, forming a second barrier against bacteria. The chlorinated coated fabrics, can inactivate 85.0–99.9% of Staphylococcus aureus and 85.0–97.7% of Escherichia coli with contact time of 60 min. The hydrophobic properties of coated fabrics are greatly improved with water contact angles of 122.0°–141.1°. In addition, the proposed method is applicable for a variety of fibers and expected to be used for industrial production.

Graphical abstract

     

Quantitative determination of glutathione in single human erythrocytes by capillary zone electrophoresis with electrochemical detection

Glutathione (GSH) in single human erythrocytes is determined by capillary zone electrophoresis with end-column amperometric detection at a gold/mercury amalgam microelectrode. A capillary of 10 microm inner diameter is suitable for determination of GSH in an individual erythrocyte with a good signal-to-noise ratio. The limit of detection is 1 x 10(-7) mol/L or 26 amol and the linear dynamic range is 2 x 10(-7) to 2 X 10(-5) mol/L for the capillary. In this method, the calibration line is obtained with a capillary adsorbed before a certain amount of hemoglobin can be used for the quantification of GSH in the external standardization. The whole cell injection and the lack of necessity of a derivatization reaction lead to more accurate and precise results, which are closer to the macroscopic values of glutathione in human red blood cell (i.e., hemolysate) than those determined by indirect laser-induced fluorescence detection.     

Synthesis of Enantiomerically Pure Carbohydrate-Derived Annulated Cyclopentadienes and Ferrocenes

The cyclopentadienes 3a/b/c, 8b/c, 12a/b/d , and 16a/b/d were prepared as mixtures of regioisomers from the D -mannitol-derivatives 1,6,10 , and 14 and transformed into the ferrocenes 17, 18 , and 19 (73%; 38:17:45), 23, 24 , and 25 (70%; 6:42 :52), 26 (31%), and 27 (27%), respectively. Deprotection of 17–19 with HCl/MeOH gave the H₂O-soluble ferrocenes 20–22 ; chloromercuration and iodination of 17 via 29 led to the C₂-symmetric diiodo-ferrocene 30 . The mono(chloromercurio) derivative 28 , obtained as a by-product, was also transformed into 29 . The structure of the ferrocenes 18 and 19 , and of the bis(chloromercurio)ferrocene 29 has been established by X-ray analysis. The starting cyclopentadienes 3 were obtained in 50% yield from 1 by dialkylation of CpNa, followed by thermolysis of the spiro-annulated 2 . Similarly, dimesylate 6 (from 4 ) gave the spiro-annulated diene 7 and the annulated dienes 8 in about equal amounts; thermolysis transformed 7 into 8 (62%). The dienes 12 were prepared in 15% yield from the ditriflate 10 via 11 , the dimesylate 9 proving insufficiently reactive, and the dienes 16 (49%) from 14 via 15 .     

Direct injection of plasma to determine pseudoephedrine by high performance liquid chromatography with column switching

An HPLC method has been developed for the determination of pseudoephedrine in plasma using column switching. Preparation of the sample was simple in that only 1000 microL of water was added to 200 microL of plasma before injection. A 900 microL aliquot was injected onto the precolumn. Double distilled water was used to elute and remove proteins and polar components in the sample. The components retained on the precolumn were flushed forward onto the analytical column by the mobile phase (acetonitrile-0.2 mol/L ammonium sulphate, 10:90 v/v) with automated column switching. The limit of determination of pseudoephedrine in plasma was 12 ng/mL. The relative standard deviations of intra- and inter-assay for the determination of pseudoephedrine in plasma were 1.2-9.8% over the concentration range 1020-21.8 ng/mL. The mean recovery by on-line solid phase extraction was 94.76% (RSD = 1.1%).     

Kinetic theory of reacting systems

In this paper transport processes of reacting systems are investigated, based on the Boltzmann equations. The Boltzmann equations are solved by means of Grad's moment method to thirteen moments and some formal results are obtained for transport properties. It is shown that the rate coefficients are quadratic functions of hydrodynamic fluxes and are in the form

where

are the scalar moments associated with the reaction and q, J, Π are heat flux, material flux and traceless symmetric stress tensor. k⁽⁰⁾_i is the usual local equilibrium formula for reaction rate constant. Iterative solutions for the equations of change for

, q, J and Π are obtained from which transport coefficients are calculated for the reacting system. It is shown that the solutions, when specialized to nonreacting mixtures, lead to results for the transport coefficients which are exactly in agreement with the Chapman-Enskog theory results. The modifications of the transport coefficients due to reactions are obtained from the iterative solutions and the bracket integrals necessary for their calculations are explicitly given in an appendix.     

Study on osmotic pressures for aqueous lysozyme and alpha-chymotrypsin-electrolyte solutions with two Yukawa potentials

The equation of state (EOS) of Duh and Mier-y-Terán for one Yukawa potential is expanded to two Yukawa potentials to describe the nonidealities of the charged lysozyme and alpha-chymotrypsin solutions. Instead of the classical DLVO theory, the attractive dispersion and double-layer repulsion interactions are represented by two Yukawa potentials, respectively. For the aqueous lysozyme solutions, the only adjustable dispersion energy parameter epsilon/k is regressed and the average deviation is 1.76%. For the aqueous alpha-chymotrypsin solutions, two adjustable parameters (the molecular weight and dispersion energy parameter) are regressed and the average deviation is 7.62%. Some correlation and prediction results are discussed.     

Single-isomer sulfated alpha-cyclodextrins for capillary electrophoresis. Part 2. Hexakis(6-O-sulfo)-alpha-cyclodextrin: synthesis, analytical characterization, and initial screening tests

The second member of the family of single-isomer sulfated alpha-cyclodextrins, the sodium salt of hexakis(6-O-sulfo)-alpha-cyclodextrin (HxS), has been synthesized, analytically characterized, and used as the resolving agent for the capillary electrophoretic separation of the enantiomers of nonionic, weak-acid and weak-base analytes present in our initial screening kit. HxS interacted less strongly with many of the analytes tested than the larger-ring analogs, heptakis(6-O-sulfo)-beta-cyclodextrin (HS) and octakis(6-O-sulfo)-gamma-cyclodextrin (OS). For some of the analytes, the separation selectivities obtained with HxS were complementary to those observed with hexakis(2,3-di-O-acetyl-6-O-sulfo)-alpha-cyclodextrin (HxDAS), HS, and OS. For all analytes, the effective mobilities and separation selectivities as a function of the background electrolyte concentration of HxS followed the trends that were found for HxDAS, HS, and OS.