Replacement of Poly(vinyl pyrrolidone) by Thiols: A Systematic Study of Ag Nanocube Functionalization by Surface-Enhanced Raman Scattering

In this work, we used surface-enhanced Raman scattering (SERS) to monitor the replacement of poly(vinyl pyrrolidone) (PVP) on Ag nanocubes by cysteamine, thiol-terminated PEG, and benzenedithiol. PVP is widely used as a colloidal stabilizer and capping agent to control the shape of Ag (as well as many other noble metals) nanocrystals during synthesis, and to stabilize the final colloidal suspension. However, the surface chemistry of Ag nanocrystals often needs to be tailored for specific applications, so the PVP coating must be removed and/or replaced by other ligands. By monitoring the signature peak from the carbonyl groups of PVP, we show, for the first time, that the PVP adsorbed on the surface of Ag nanocubes was completely replaced by the thiol molecules at room temperature over the course of a few hours. We observed the same trend no matter if the Ag nanocubes were suspended in an aqueous solution of the thiol or supported on a silicon substrate and then immersed in the thiol solution.     

Formation of 4-N-Arylamino-1-butanol Derivatives from Aromatic Nitro Compounds via a Novel Palladium-Catalyzed Tetrahydrofuran Ring-Opening Reaction

Abstract

4-N-Arylamino-1-butanol derivatives are produced via a palladium-catalyzed tetrahydrofuran ring-opening reaction. This reaction occurs during the reduction of aromatic nitro groups with polymethylhydrosiloxane (PMHS) and potassium fluoride in the presence of hydrogen peroxide. This represents a novel route for the synthesis of 4-N-arylamino-1-butanols.     

Monitoring of progestins: Development of immunochemical methods for purification and detection of levonorgestrel

A polyclonal antibody (Ab) for the progestin levonorgestrel (LNG) was generated, and immunochemical assays for its detection, clean-up and concentration were developed. A highly specific microplate diagnostic assay for the detection of LNG was developed that used the enzyme linked immunosorbent assay (ELISA) method. The LNG ELISA developed was sensitive and reproducible; it exhibited I₅₀ and I₂₀ values of 3.3 ± 1.8 ng mL⁻¹ and 0.6 ± 0.4 ng mL⁻¹, respectively, and the Abs did not cross react with any of the tested steroid hormones. The above Abs were used to develop a sol-gel-based immunoaffinity purification (IAP) method for concentration and clean-up of LNG that is compatible with subsequent immunochemical or instrumental chemical analytical procedures, such as liquid chromatography followed by mass spectrometry (LC-MS/MS). Development of the columns included successful entrapment of Abs within a tetramethoxysilane (TMOS)-based SiO₂ polymer network. The Abs could bind the free analyte from solution, and the bound analyte could be easily eluted from the sol-gel matrix at high recoveries. The Ab selectivity towards the antigen was high, in both ELISA and the sol-gel columns, but the entrapped Abs cross-reacted with two other steroid hormones - ethynylestradiol (EE2) and nortestosterone (NT) - which share similar epitopes with LNG, despite the lack of cross reactivity in the ELISA. The validity of the method was investigated by LC-MS/MS and a good analytical correlation was obtained.     

Lattice Poisson-Boltzmann simulations of electro-osmotic flows in microchannels

This paper presents the numerical results of electro-osmotic flows in micro- and nanofluidics using a lattice Poisson-Boltzmann method (LPBM) which combines a potential evolution method on discrete lattices to solve the nonlinear Poisson equation (lattice Poisson method) with a density evolution method on discrete lattices to solve the Boltzmann-BGK equation (lattice Boltzmann method). In an electrically driven osmotic flow field, the flow velocity increases with both the external electrical field strength and the surface zeta potential for flows in a homogeneous channel. However, for a given electrical field strength and zeta potential, electrically driven flows have an optimal ionic concentration and an optimum width that maximize the flow velocity. For pressure-driven flows, the electro-viscosity effect increases with the surface zeta potential, but has an ionic concentration that yields the largest electro-viscosity effect. The zeta potential arrangement has little effect on the electro-viscosity for heterogeneous channels. For flows driven by both an electrical force and a pressure gradient, various zeta potential arrangements were considered for maximize the mixing enhancement with a less energy dissipation.     

Photoinduced 1,4-additions of indoles to enones

[reaction: see text] A photoinduced procedure for the 1,4-addition of indoles to enones is described. This reaction occurs with modest to excellent yield for cyclic and some acyclic enones. This reaction is experimentally simple, requiring only irradiation (UVA lamps, ca. 350 nm) of the reagents in a CH2Cl2 solution at room temperature, and avoids the necessity to use a Lewis acid. An important solvent effect was noticed, with CH2Cl2 and CHCl3 being the optimal solvents. Various substituents are tolerated on the indole moiety and an electronic trend was noticed, as electron-withdrawing groups can suppress this reaction. A mechanism involving single electron transfer between the enone triplet excited state and the indole is proposed and accounts for all experimental observations.     

Detection of a single DNA base-pair mismatch using an anthracene-tagged fluorescent probe

A novel anthracene-tagged oligonucleotide can discriminate between a fully-matched DNA target sequence and one with a single mismatching base-pair through a remarkable difference in fluorescence emission intensity upon duplex formation.     

Absolute net charge and the biological activity of oligopeptides

Sequences of human proteins are frequently prepared as synthetic oligopeptides to assess their functional ability to act as compounds modulating pathways involving the parent protein. Our objective was to analyze a set of oligopeptides, to determine if their solubility or activity correlated with features of their primary sequence, or with features of properties inferred from three-dimensional structural models derived by conformational searches. We generated a conformational database for a set of 78 oligopeptides, derived from human proteins, and correlated their 3D structures with solubility and biological assay activity (as measured by platelet activation and inhibition). Parameters of these conformers (frequency of coil, frequency of turns, the degree of packing, and the energy) did not correlate with solubility, which was instead partly predicted by two measures obtained from primary sequence analysis, that is, the hydrophobic moment and the number of charges. The platelet activity of peptides was correlated with a parameter derived from the structural modeling; this was the second virial coefficient (a measure of the tendency for a structure to autoaggregate). This could be explained by an excess among the active peptides of those which had either a large number of positive charges or in some cases a large number of negative charges, with a corresponding deficit of peptides with a mixture of negative and positive charges. We subsequently determined that a panel of 523 commercially available (and biologically active) peptides shared this elevation of absolute net charge: there were significantly lower frequencies of peptides of mixed charges compared to expectations. We conclude that the design of biologically active peptides should consider favoring those with a higher absolute net charge.     

Valence-bond states: Link models

An isotropic anti-ferromagnetic quantum state on a square lattice is characterized by symmetry arguments only. By construction, this quantum state is the result of an underlying valence bond structure without breaking any symmetry in the lattice or spin spaces. A detailed analysis of the correlations of the quantum state is given (using a mapping to a 2D classical statistical model and methods in field theory like mapping to the non-linear sigma model or bosonization techniques) as well as the results of numerical treatments (regarding exact diagonalization and variational methods). Finally, the physical relevance of the model is motivated. A comparison of the model to known anti-ferromagnetic Mott–Hubbard insulators is given by means of the two-point equal-time correlation function obtained (i) numerically from the suggested state and (ii) experimentally from neutron scattering on cuprates in the anti-ferromagnetic insulator phase.     

An allylstannane reagent on non-cross-linked polystyrene support

[reaction: see text] A new allylstannane reagent on non-cross-linked polystyrene was developed for the first time. This support differs markedly from standard cross-linked polymers because it is completely soluble in organic solvents; moreover, the reactions can be conveniently monitored directly by standard 1H NMR methods. The allylstannane underwent a free radical reaction with an alkyl halide to form a new allyl appendage. Tin byproducts can be easily recovered from cold methanol as white crystalline solids.     

On the degree of groups of polynomial subgroup growth

Let be a finitely generated residually finite group and let denote the number of index subgroups of . If for some and for all , then is said to have polynomial subgroup growth (PSG, for short). The degree of is then defined by .

Very little seems to be known about the relation between and the algebraic structure of . We derive a formula for computing the degree of certain metabelian groups, which serves as a main tool in this paper. Addressing a problem posed by Lubotzky, we also show that if is a finite index subgroup, then .

A large part of the paper is devoted to the structure of groups of small degree. We show that is bounded above by a linear function of if and only if is virtually cyclic. We then determine all groups of degree less than , and reveal some connections with plane crystallographic groups. It follows from our results that the degree of a finitely generated group cannot lie in the open interval .

Our methods are largely number-theoretic, and density theorems à la Chebotarev play essential role in the proofs. Most of the results also rely implicitly on the Classification of Finite Simple Groups.