Characterization of self-assembled monolayers of porphyrins bearing multiple thiol-derivatized rigid-rod tethers

A series of multithiol-functionalized zinc porphyrins has been prepared and characterized as self-assembled monolayers (SAMs) on Au. The molecules, designated ZnPS(n) (n = 1-4), contain from one to four [(S-acetylthio)methyl]phenylethynylphenyl groups appended to the meso-position of the porphyrin; the other meso-substituents are phenyl groups. For the dithiol-functionalized molecules, both the cis- and the trans-appended structures were examined. The ZnPS(n) SAMs were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and various electrochemical methods. The studies reveal the following characteristics of the ZnPS(n) SAMs. (1) The ZnPS(n) molecules bind to the Au surface via a single thiol regardless of the number of thiol appendages that are available per molecular unit. (2) The porphyrins in the ZnPS(3) and ZnPS(4) SAMs bind to the surface in a more upright orientation than the porphyrins in the ZnPS(1), cis-ZnPS(2), and trans-ZnPS(2) SAMs. The porphyrins in the ZnPS(3) and ZnPS(4) SAMs are also more densely packed than those in the cis-ZnPS(2) and trans-ZnPS(2) SAMs. The packing density of the ZnPS(3) and ZnPS(4) SAMs is similar to that of the ZnPS(1) SAMs, despite the larger size of the molecules in the former SAMs. (3) The thermodynamics and kinetics of electron transfer are generally similar for all of the ZnPS(n) SAMs. The general similarities in the electron-transfer characteristics for all of the SAMs are attributed to the similar binding motif.     

Composition of the essential oil of <Emphasis Type="Italic">Stachys acerosa</Emphasis> growing in central Iran

The essential oil of aerial parts of Stachys acerosa, which belongs to the Lamiaceae family and grows in central Iran, was obtained by a hydrodistileation method and analyzed by GC and GC-MS apparatus. Fourteen compounds representing 98.8% of the oil were identified. Among them N-methylisatin (30%), α-pinene (25%), sabinene (12.3%), and 2-hydroxyacetophenone (11.2%) were the major constituents of the oil, which was obtained in 0.1% yield. Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 32–34, January–February, 2007.     

Regioselective and high-yielding bromination of aromatic compounds using hexamethylenetetramine-bromine

A regioselective and highly efficient method for bromination of aromatic compounds in the presence of a stoichiometric amount of hexamethylenetetramine-bromine (HMTAB) as an efficient reagent in dichloromethane is reported. The selectivity depends on the temperature and nature of the substituent on the substrate. The reactivity of this reagent was increased by supporting it to silica gel for bromination of less activated compounds.     

19F and 31P NMR characterisation of the phosphaalkene,CF3 P=CF2, intermediate in the alkaline hydrolysis of bis(trifluoromethyl)phospine

The previously postulated phosphaalkene intermediate CF₃ P=CF₂ in the alkaline hydrolyses of (CF₃)₂ PH has been trapped and characterised by its ¹⁹F and ³¹P NMR spectra.     

Catalytic homologation of vinyltributylstannane to allyltributylstannane by Mo(IV) complexes in the presence of ethylene

We have found that CH2=CHSnBu3 is converted into CH2=CHCH2SnBu3 catalytically in the presence of Mo(IV) olefin complexes such as Mo(NAr)(CH2CH2)[biphen] (where Ar = 2,6-i-Pr2C6H3 and [biphen]2- = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate). The proposed mechanism involves formation of a metalacyclopentane (MC4) complex from ethylene and CH2=CHSnBu3, "contraction" of this MC4 complex to a metalacyclobutane (MC3) complex, and finally metathesis of the MC3 complex to give CH2=CHCH2SnBu3 and Mo(NAr)(CH2)[biphen]. These new findings suggest (inter alia) that contraction of an MC4 ring to an MC3 ring may be a much more common mode of decomposition of metalacyclopentane rings in d0 complexes than previously believed.     

Development, validation, and standardization of polymerase chain reaction-based detection of E. coli O157

A diagnostic polymerase chain reaction assay was developed for the detection of E. coli O157 as the first part of a multicenter validation and standardization project. The assay is based on amplification of sequences of the rfbE O157 gene and includes an internal amplification control. The selectivity of the assay was evaluated against 155 strains, including 32 E. coli O157, 38 E. coli non-O157, and 85 non-E. coli. It was shown to be highly inclusive (100%) and exclusive (100%). The assay has a 100% detection probability of approximately 2 x 10(3) cells per reaction.     

Essential oil variation of Salvia officinalis aerial parts during its phenological cycle

In this paper the variation in the quantity and quality of the essential oil of Salvia officinalis during its life cycle stages is reported. The oils were obtained by hydrodistillation of air-dried samples. The yield of essential oil (w/w %) in different stages was in the order: floral budding (0.9%) > vegetative (0.7%) > flowering (0.5%) > immature fruit (0.4%) > ripen fruit (0.2%). The essential oils were analyzed by GC and GC-MS. In total, 36, 41, 40, 38, and 41 constituents were identified and quantified in the subsequent stages, respectively. Oxygenated monoterpenes were the main group of compounds in the fruiting set (56.9%), vegetative (48.5%), flowering (47.7%), and floral budding (45.3%) stage. 1,8-cineole as one of the major constituents of all samples was lower in the vegetative stage and gradually increased in subsequent harvesting times to reach a maximum in flowering and then decreased in the fruiting set. In contrast, the globulol content was higher in the first stage and decreased drastically during fruit maturation. Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 16–19, January–February, 2006.     

Identification and structural characterisation of carboxy-terminal polypeptides and antibody epitopes of Alzheimer's amyloid precursor protein using high-resolution mass spectrometry

Alzheimer's disease (AD) is the most common cause for human age-related dementia, characterised by formation of diffuse plaques in brain that are directly involved in AD pathogenesis. The major component of AD plaques is beta-amyloid, a 40 to 42 amino acid polypeptide derived from the amyloid precursor protein (APP) by proteolytic degradation involving the specific proteases, beta-and gamma-secretase acting at the N- and C- terminal cleavage site, respectively. In this study we have prepared polypeptides comprising the carboxy-terminal and transmembrane sequences of APP, by bacterial expression and chemical synthesis, as substrates for studying the C-terminal processing of APP and its interaction with the gamma-secretase complex. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used as a major tool for structure analysis. Immunisation of transgenic mouse models of AD with Abeta42 has been recently shown to be effective to inhibit and disaggregate Abeta-fibrils, and to reduce AD-related neuropathology and memory impairments. However, the mechanism underlying these therapeutic effects has been as yet unclear. Using proteolytic epitope excision from immune complexes in combination with FT-ICR-MS, we identified the epitope recognised by the therapeutically active antibody as the N-terminal Abeta(4-10) sequence; this soluble, nontoxic epitope opens new lead structures for AD vaccine development. A monoclonal antibody (Jonas; JmAb) directed against the cytosolic APP domain was used in studies of APP biochemistry and metabolism. Here we report the identification of the epitope recognised by the JmAb, using the combination of epitope excision and peptide mapping by FT-ICR-MS. The epitope was determined to be located at the C-terminal APP(740-747) sequence; it was confirmed by ELISA binding assays and authentic synthetic peptides and will be an efficient tool in the development of new specific vaccines. These results demonstrate high-resolution FT-ICR-MS as a powerful method for characterising biochemical pathways and molecular recognition structures of APP.     

Molecular complexation of free base meso-tetraarylporphyrins with antimony(III) chloride in free solvent media

The reaction of meso-tetraarylporphyrins (H₂t(Xp)p) with SbCl₃ under free solvent conditions affords green complexes with a 1:1 H₂t(X)pp:SbCl₃ ratio. These complexes have dimeric structures with a (μ-Cl)₂bridge. UV–VIS, ¹H NMR and ¹³C NMR spectra data show that the porphyrin core of [(H₂t(Xp)p)₂Sb₂Cl₆], similar to 1:2 (donor:acceptor) molecular complexes of meso-tetraarylporphyrins and porphyrin diacid, is distorted, thus two nitrogen atoms of pyrrolenine in a side of the porphyrin plane act as electron donors to an antimony atom of SbCl₃. Molecular complexation of meso-tetraarylporphyrins with SbCl₃ produces a large downfield shift for the NH signal, although there is no hydrogen bonding present.     

The effect of pH and ionic strength on the transport of alumina nanofluids in water-saturated porous media

Alumina nanofluids are one of the most useful nanofluids, especially for increasing the thermal conductivity. Due to importance of porous media in the improvement of heat transfer, this study investigates the transport and retention of gamma alumina/water nanofluid in the water-saturated porous media. For this purpose, alumina nanofluids were introduced to the porous media consisting of water-saturated glass beads possessing various pH values (4, 7 and 10) and different ionic strengths (0.001 M of KCl, CaCl₂, AlCl₃, K₂SO₄, CaSO₄, Al₂(SO₄)₃, K₂CO₃ and CaCO₃). Then the break through curve of each experiment was drawn and modeled by combining classical filtration theory with advection–dispersion equation. Single collector efficiency (η₀) and attachment efficiency (α) were calculated by classical filtration theory. Also curve fitting of experiments and modeling was achieved by minimizing the sum of squared residuals, to calculate retardation factor (R) and hydrodynamic dispersion coefficient (D) of each experiment. According to the results, in general, increase in pH and ionic strength will enhance the removal rate coefficient, retardation factor and retention while decreasing the steady-state break through concentration and the hydrodynamic dispersion coefficient. The opposite of this rule was observed and analyzed for aluminum salts. The lowest retention of nanoparticles at 31.04% can be related to their transport in background solution with pH = 4 [α = \(3.87 \times 10^{ - 2}\), K_att = \(3.33 \times 10^{ - 3}\) (min⁻¹), R = 3.93, D = 0.91 (cm² min⁻¹)], and the highest retention in nanoparticle content of 94.29% was observed in background solution containing CaCO₃ [α = \(14.33 \times 10^{ - 2}\), K_att = \(137.82 \times 10^{ - 3}\) (min⁻¹), R = 12.02, D = 0.62 (cm² min⁻¹)]. Therefore, chemistry of water plays an important role in transport and retention parameters. The classical filtration theory and the advection–dispersion model are able to perfectly model and quantify the parameters of the alumina nanofluid transport in saturated porous media.