Nonionic surfactant-capped gold nanoparticles as postcolumn reagents for high-performance liquid chromatography assay of low-molecular-mass biothiols

Gold nanoparticles (GNPs) have been stabilized with nonionic surfactant ligands, i.e., Brij 35, and their aggregation could be induced rapidly and selectively by biologically active low-molecular-mass thiols including sulphydryl-containing amino acids (cysteine and homocysteine) and small peptides (glutathione, cysteinylglycine, and glutamylcysteine). A new postcolumn detection method has been developed for high-performance liquid chromatography (HPLC) assay of these small biothiols based on the analyte-induced aggregation of the GNPs. Compared with conventional thiol-reactive probes, the GNP colloids are easier to prepare, much more stable in aqueous solution over a wide pH range and at ambient temperature, and exhibit relatively high selectivity toward small biothiols. The analysis of human urine samples demonstrated that the proposed method is promising in HPLC assay of the small thiol molecules in biological fluids.     

Improving Resolution of Isomeric Flavonoids and Their Glycosides Using Two-Dimensional Liquid Chromatography Coupled With High-Resolution Mass Spectrometry

Chromatographia - The separation of isomers is one of the key issues in analysing complex natural matrices, thus commanding a higher separating power from the applied analytical system. In this...     

Electrophysiological Responses of Bactrocera kraussi (Hardy) (Tephritidae) to Rectal Gland Secretions and Headspace Volatiles Emitted by Conspecific Males and Females

Pheromones are biologically important in fruit fly mating systems, and also have potential applications as attractants or mating disrupters for pest management. Bactrocera kraussi (Hardy) (Diptera: Tephritidae) is a polyphagous pest fruit fly for which the chemical profile of rectal glands is available for males but not for females. There have been no studies of the volatile emissions of either sex or of electrophysiological responses to these compounds. The present study (i) establishes the chemical profiles of rectal gland contents and volatiles emitted by both sexes of B. kraussi by gas chromatography–mass spectrometry (GC–MS) and (ii) evaluates the detection of the identified compounds by gas chromatography–electroantennogram detection (GC–EAD) and –electropalpogram detection (GC–EPD). Sixteen compounds are identified in the rectal glands of male B. kraussi and 29 compounds are identified in the rectal glands of females. Of these compounds, 5 were detected in the headspace of males and 13 were detected in the headspace of females. GC–EPD assays recorded strong signals in both sexes against (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-ethyl-7-mehtyl-1,6-dioxaspiro[4.5]decane isomer 2, (E,Z)/(Z,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, and (Z,Z)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. Male antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-methyl-6-pentyl-3,4-dihydro-2H-pyran, 6-hexyl-2-methyl-3,4-dihydro-2H-pyran, 6-oxononan-1-ol, ethyl dodecanoate, ethyl tetradecanoate and ethyl (Z)-hexadec-9-enoate, whereas female antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and 2-methyl-6-pentyl-3,4-dihydro-2H-pyran only. These compounds are candidates as pheromones mediating sexual interactions in B. kraussi.     

Maximum density space packing with parallel strings of spheres

A string of spheres is a sequence of nonoverlapping unit spheres inR ³ whose centers are collinear and such that each sphere is tangent to exactly two other spheres. We prove that if a packing with spheres inR ³ consists of parallel translates of a string of spheres, then the density of the packing is smaller than or equal to . This density is attained in the well-known densest lattice sphere packing. A long-standing conjecture is that this density is maximum among all sphere packings in space, to which our proof can be considered a partial result. The work of A. Bezdek and E. Makai was partially supported by the Hungarian National Foundation for Scientific Research under Grant Number 1238.     

Synthesis of novel neuroexcitatory amino acids derived from kainic acid

The synthesis of the novel epimeric amino acids $\text{5a}$ and $\text{7a}$ by oxidation of methyl ketones derived from kainic acid is described. On biological testing both compounds exhibit a strong neuroexcitatory activity.     

The molecular conformation of clonidine hydrochloride,an α-adrenergic agonist

The molecular conformation of the antihypertensive drug clonidine hydrochloride [2-(2,6-dichlorophenylimino)-2-imidazole HCl] has been shown by crystallographic studies to have a nearly perpendicular arrangement of the phenyl and imidazole rings as described by the torsion angles C₂-C₁-N₁-C₂= 76 ° and C₁-N₁-C₂-N₁ = 0 °. This conformation is not either of those suggested as the minimum energy form by CNDO/2 calculations for the protonated or free-base models. However, it is consistent with a nonplanar model proposed as the active conformer based on QSAR and spectral studies. The bonding about the imidazole carbon is similar to the guanidinium ion and the three C₂-N distances of the planar imidazole ring are nearly equal. The chloride ion forms strong hydrogen bonds with the amine hydrogen (2.3 Å) and the imidazole (N₁,) hydrogen (2.4 Å). Comparison with -adrenergic agonists shows that this conformation of clonidine fits the proposed pharmacophore model and should compete effectively for the -adrenergic receptors.Presented in part at the American Crystallographic Association Meeting, Clemson, South Carolina, January 1976.     

Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands

A series of novel TIQ based N,N′-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)₃ as the ideal pre-catalyst for this particular reaction.     

Synthesis and luminescence behaviour of novel heterodecanuclear silver(I)-rhenium(I) alkynyl complexes. X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2

A novel series of luminescent heterodecanuclear mixed-metal alkynyl complexes, [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(N--N)(CO)3]4](PF6)2, (N--N = tBu2bpy, Me2bpy, phen, Br2phen), have been successfully synthesized; the X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2 have also been determined.     

Precise Size‐Selective Sieving of Nanoparticles Using a Highly Oriented Two‐Dimensional Supramolecular Polymer

The development of size‐selective membranes with well‐defined nanopores towards the precise separation of nanometer‐sized substances is a challenging task to achieve. Here a supramolecular membrane is presented that comprises a highly oriented, honeycomb‐like, 2D supramolecular polymer on a polycarbonate filter support. It enables precise size‐selective sieving of colloidal nanoparticles (NPs). Owing to the uniform parallel‐aligned nanocavities within the 2D supramolecular polymers, the composite membrane shows a high size‐selectivity with a sub‐nanometer accuracy in the cutoff size of about 4.0 nm. In principle, the species of size‐separable particles are unlimited, as demonstrated by quantum dots, noble metal, and metal oxide NPs. This supramolecular membrane combined with filtration advances the potential of NPs in terms of their monochromatic emission and size monodispersity, and also enables rapid removal of small magnetic NP adsorbents that are otherwise difficult to capture.