Curve fitting to asymmetrical chromatograms by the extended Kalman filter in frequency domain

An algorithm is presented to perform curve fitting on the basis of the Fourier transform of a signal. The curve fitting has been done with the exponentially modified Gaussian model, obtained when convolving a Gaussian distribution and an exponential decay function. The parameter estimation has been carried out by means of the two-dimensional extended Kalman filter. The goodness-of-fit has been characterized by the trace of the covariance matrix of the estimated parameters. The precision of the estimated parameters obtained by fitting either in time or frequency domain is compared.     

Benzoxadiazocines,benzothiadiazocines and benzotriazocines-IV : Ring closure of 1-(2-[n-(2-chloroethyl and 2-hydroxyethyl)-n-methylamino]phenyl)-3-phenylthioureas. tetrahydroquinoxaline vs.dihydro-3,1,6-benzothiadiazocine and hexahydro-1,3,6-benzotriazocinethione formation

While base induced ring closure of 1-(2-[N-(alkylsulfonyl and arylsulfonyl)-N-(2-chloroethyl)amino]phenyl)-3-phenylthioureas 1 had furnished the corresponding type 2 dihydro-3,1,6-benzothiadiazocine derivatives rather than the isomeric hexahydro-1,3,6-benzotriazocinethiones (3) or tetrahydroquinoxalines (4), base induced ring closure of the related N-(2-chloroethyl)-N-Me derivatives 9a-9c, 10a and lOb furnishes type 14 tetrahydroquinoxalines. 14a is obtained also by treating the N-(2-hydroxyethyl)-N-Me derivative 11 with the triphenylphosphine-diethyl azodicarboxylate (DEAD) reagent. In situ replacement of the chlorine atom of compound 9a by iodine in the absence of base as well as treatment of 1-(2-[N-(2-hydroxyethyl)-N-methylamino]phenyl)-1-methyl-3-phenylthiourea (18) with the triphenyl-phosphine-DEAD reagent furnishes the benzimidazole derivatives 16 and 22, respectively, whose formation may be rationalised by assuming the intermediacy of the dihydro- and tetrahydro-3,1,6-benzothiadiazocine derivatives 12a · HI and 20, respectively, and their subsequent ring contraction.     

Chemical imaging of biological systems with the scanning electrochemical microscope

A brief overview on recent advances in the application of scanning electrochemical microscopy (SECM) to the investigation of biological systems is presented. Special emphasis is given to the mapping of local enzyme activity by SECM, which is exemplified by relevant original systems.     

Intrinsic metrics preserving maps on Abelian lattice-ordered groups

Swamy studied the natural metric ¦x–y¦ on Abelian lattice-ordered groupsG, and he proved that the stable isometries which preserve this metric have to be automorphisms ofG. Holland proved that the only intrinsic metrics on lattice-ordered groups, i.e., invariant and symmetric metrics, are the multiples n¦x –y¦ for some integern. We show that iff is an arbitrary surjection from an Abelian lattice-ordered groupG ₁ onto an Archimedean Abelian lattice-ordered groupG ₂ such that f(0)]0 and, for some non-zero intrinsic metricsD andd, D(f(x),f(y)) depends functionally on d(x,y), thenf is a homomorphism of G₁ onto G₂.Presented by R. S. Pierce.     

Structure Determination of Zinc Complexes of Iminodiacetamide Ionophores in Solution and in the Solid State

It is shown by extensive NMRinvestigation that hexa-coordinatedZn²⁺-complexes containing two tridentateiminodiacetamide ligands adopt a solutionconformation with two different kinds ofZn–O bonds possessing a center ofinversion. In contrast, the complexmolecules are chiral in the solid state asdetermined by CP-MAS ¹³C NMR spectroscopy.     

Interaction of Pesticides with a β-Cyclodextrin Derivative Studied by Reversed-phase Thin-layer Chromatography and Principal Component Analysis

The interaction of 18 pesticides with a water-soluble -cyclodextrin polymer (BCDP) was studied by reversed-phase thin-layer chromatography and principal component analysis (PCA) was employed for the elucidation of the relationship between the relative strength of interaction and the calculated surface parameters of the guest molecules. Except for penconazole the lipophilicity of the pesticides decrease in the presence of BCDP. PCA indicated that apolar surface parameters are highly positively correlated with the strength of interaction. The data indicate that the agrochemical characteristics (adsorption, leakage, decomposition, etc) of complexed pesticide molecules can be different from those of uncomplexed onesresulting in modified efficacy.     

Arsenic speciation in xylem sap of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 μmol dm⁻³ arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment, and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite.     

Preparation and Spectroscopic Characterization of (9Z,9′Z)‐Lutein (Neolutein C)

The preparation of pure, crystalline (9Z,9′Z)‐lutein (neolutein C; 2 ) by I₂‐catalyzed photoisomerization of (all‐E)‐lutein ( 1 ) is described. The structure of 2 was unambiguously determined by UV/VIS, CD, and NMR spectroscopy, as well as by mass spectrometry, and the complete assignment of the ¹³C‐NMR spectrum of this carotenoid is presented for the first time.     

Synthesis of new tricyclic ring systems containing the pyrimido[5, 4-b][1, 4]oxazine skeleton

Synthesis of derivatives 4 and 6 of two novel tricyclic ring systems, 1, 2, 4-triazolo[3, 4-c]pyrimido[5, 4-b]-[1, 4]oxazine and imidazo[1, 2-c]pyrimido[5, 4-b][1, 4]oxazine, respectively is described. Although the parent pyrimido[5, 4-b]oxazines possess positive inotropic activity, the tricyclic compounds are practically inactive.     

Synthesis,analytical characterization and use of octakis(2,3-di-O-methyl-6-O-sulfo)-gamma-cyclodextrin,a novel,single-isomer,chiral resolving agent in low-pH background electrolytes

The third member of the family of single-isomer, sulfated gamma-cyclodextrins, the sodium salt of octakis(2,3-di-O-methyl-6-O-sulfo)-gamma-cyclodextrin has been synthesized, analytically characterized and used for the capillary electrophoretic separation of the enantiomers of nonionic, weak acid and weak base analytes in low-pH aqueous background electrolytes. Though octakis(2,3-di-O-methyl-6-O-sulfo)-gamma-cyclodextrin complexes less strongly with many of the analytes tested than the other members of the single-isomer, 6-O-sulfo gamma-cyclodextrin family, such as octa(6-O-sulfo)-gamma-cyclodextrin and octakis(2,3-di-O-acetyl-6-O-sulfo)-gamma-cyclodextrin, it offers excellent separation selectivities, often complementary to those of both the single-isomer, 6-O-sulfo beta-cyclodextrins and 6-O-sulfo gamma-cyclodextrins. Rapid, efficient enantiomer separations were observed for a large number of structurally diverse analytes in acidic aqueous background electrolytes.