A rapid method for detection of genetically modified organisms based on magnetic separation and surface-enhanced Raman scattering

In this study, a new method combining magnetic separation (MS) and surface-enhanced Raman scattering (SERS) was developed to detect genetically modified organisms (GMOs). An oligonucleotide probe which is specific for 35 S DNA target was immobilized onto gold coated magnetic nanospheres to form oligonucleotide-coated nanoparticles. A self assembled monolayer was formed on gold nanorods using 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) and the second probe of the 35 S DNA target was immobilized on the activated nanorod surfaces. Probes on the nanoparticles were hybridized with the target oligonucleotide. Optimization parameters for hybridization were investigated by high performance liquid chromatography. Optimum hybridization parameters were determined as: 4 μM probe concentration, 20 min immobilization time, 30 min hybridization time, 55 °C hybridization temperature, 750 mM buffer salt concentration and pH: 7.4. Quantification of the target concentration was performed via SERS spectra of DTNB on the nanorods. The correlation between the target concentration and the SERS signal was found to be linear within the range of 25-100 nM. The analyses were performed with only one hybridization step in 40 min. Real sample analysis was conducted using Bt-176 maize sample. The results showed that the developed MS-SERS assay is capable of detecting GMOs in a rapid and selective manner.     

Photoinduced rearrangement of aromatic N-chloroamides to chloroaromatic amides in the solid state: inverted Π(N)-Σ(N) occupational stability of amidyl radicals

We report a solid-state photochemical rearrangement reaction by which aromatic N-chloroamides exposed to UV light or sunlight are rapidly and efficiently converted to chloroaromatic amides. The course, the intermediate (nascent chlorine vs dichlorine) and the outcome of the reaction depend on the excitation (exposure time, wavelength, and intensity) and on inherent structural factors (the directing role of the substituents and, as demonstrated by the different reactivity of two polymorphs of N-chlorobenzanilide, the supramolecular structure). The photolysis of the chloroamides provides facile photochemical access to arylamidyl radicals as intermediates, which in the absence of strong hydrogen bond donors are stabilized in the reactant crystals by C-H/N-Cl···π interactions, thus, providing insight into their structure and chemistry. Thorough theoretical modeling of the factors determinant to the stability and the nature of the spin-hosting orbital evidenced that although the trans-Π(||) state (Np spin) of the amidyls is normally preferred over the trans-Σ(⊥) configuration (Nsp(2) spin), stabilization by aromatic conjugation, steric and geometry factors, as well as by electronic effects from the substituents can decrease the Π-Σ gap in these intermediates significantly, resulting in similar and, in the case of the orthogonal amide-phenyl disposition, even reversed population of the unpaired electron in the two orbitals. Quantitative correlation established that the inverted occupational spin stability and the Π(N)-Σ(N) crossover are collectively facilitated by the conformation, valence angle, and disposition of the amide group relative to the aromatic system. The stabilization and detection of a trans-Σ(⊥) radical was experimentally accomplished by steric locking of the orthogonal trans-amide conformation with double ortho-tert-butyl substitution at the phenyl ring. The effects of the single para-phenyl substituents on the relative occupational stability of the arylamidyl radical states point out to non-Hammett behavior. By including cumulative electronic effects from multiple substitutions, four distinct families of the aromatic amidyl radicals were identified. The Π(∥) state is the most stable structure of the N-phenylacetamidyl radical and of most of the substituted arylamidyls, although the Σ(⊥) and Π(⊥) states can also be stabilized by introducing tert-butyl and nitro groups, respectively.     

Amperometric Phenol Biosensor Based on Horseradish Peroxidase Entrapped PVF and PPy Composite Film Coated GC Electrode

Polyvinylferrocene (PVF) was used as a mediator for the fabrication of a horseradish peroxidase (HRP)-modified electrode to detect phenol derivatives via a composite polymeric matrix of conducting polypyrrole (PPy). Through an electropolymerization process, enzyme HRP was entrapped with PPy in a three-electrode system onto a glassy carbon electrode previously covered with PVF, resulting in a composite polymeric matrix. Steady-state amperometric measurements were performed at ?200 mV vs. Ag/AgCl in aqueous phosphate buffer containing NaCl 0.1 M (pH 6.8) in the presence of hydrogen peroxide. The response of the HRP-modified PVF electrode was investigated for various phenol derivatives, which were 4-chlorophenol, phenol, catechol, hydroquinone, 2-aminophenol, pyrogallol, m-cresol, and 4-methoxyphenol. Analytical parameters for the fabricated PVF electrode were obtained from the calibration curves. The highest sensitivity was obtained from the calibration of 4-chlorophenol as 29.91 nA/μM. The lowest detection limit was found to be 0.22 μM (S/N?=?3) for catechol, and the highest detection limit was found to be 0.79 μM (S/N?=?3) for 4-methoxyphenol among the tested derivatives. The biosensor can reach 95% of steady-state current in about 5 min. The electrode is stable for 2 months at 4 °C.     

Structure elucidation of two new unusual monoterpene glycosides from Euphorbia decipiens, by 1D and 2D NMR experiments

Two new unusual monoterpene glycosides, (Z)-3,6-dimethyl-3-(β-D-O-glucosylmethylene)cyclohept-4-ene-1-one (1) and 3,6-dimethyl-3-(β-D-O-glucosylmethylene)cycloheptanone (2) have been isolated along with five known compounds, 3-hydroxy-4-methoxybenzoic acid, 6,7-dihydroxycoumarin, luteolin, apigenin 5-O-αl-L-rhamnoside, and pinocembrin-7-O-rutinoside from ethyl acetate extract of Euphorbia decipiens. The structures of the isolated compounds were elucidated by extensive 1D- and 2D-NMR, and mass spectroscopic analyses.     

Experimental analysis of true left-handed behaviour and transmission properties of composite metamaterials

We report the true left-handed transmission of a composite metamaterial (CMM) consisting of periodically stacked split-ring resonator (SRR) and wire elements. The negative permeability (μ < 0) gap is demonstrated explicitly by comparing SRR and closed-ring resonator structures. We confirm experimentally that the plasma cut-off frequency of the CMM is determined by the combined dielectric response of SRR and wire elements, and it is much lower than that of the wire-only medium. This is crucial to identify the left-handed transmission bands of the CMM. We further investigate the effect of intralayer and interlayer disorder on the transmission spectrum of CMM arising from misaligned fabrication and stacking of the SRR layers. We found that the intralayer disorder affects the μ < 0 gap of SRRs and the left-handed transmission band of CMM significantly, whereas the SRR transmission is rather immune to interlayer disorder.     

Crystal and molecular structure of 3‐phenyl‐4‐(p‐chlorobenzylamino)‐4,5‐dihydro‐1‐H‐1,2,4‐triazol‐5‐on

The structure of the title compound, C₁₅H₁₃N₄OCl was determined by single crystal X‐ray diffraction technique. The structure consists of a p‐chlorobenzylamino moiety and triazol and phenyl rings. The title compound crystallizes in the monoclinic space group P2₁/c with a = 14.368(3), b = 6.255(3), c = 17.631(3) Å, β = 113.24(3)°, Z = 4, V = 1455.8(8) ų and D_x = 1.372 gcm^‐3. The structure was solved by direct methods and refined by full‐matrix least‐squares method (R=0.0477). The dihedral angle between the triazole moiety and the phenyl ring is 28.8(3)°. The molecular packing is stabilized by N‐H…N and N‐H…O types of inter molecular hydrogen bonds. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)