Correlations between Van der Waals' volume and retention index general equation applicable to different homologous series

Summary Correlations between retention index (R_I) and Van der Waals' volume (V_W) in homologous series of n-alcohols, n-aldehydes and esters are studied on the stationary phases Carbowax 1540 and squalane. Influence of functional groups is quantified and a method for obtaining one general equation, valid for an indeterminate number of homologous series, is proposed.     

Reactions of thiosemicarbazones derived from beta-keto amides and beta-keto esters with Zn(II) and Cd(II) acetates: influence of metal, substitution, reagent ratio and temperature on metal-induced cyclization

Zinc(II) and cadmium(II) acetates were reacted in methanol under various experimental conditions with thiosemicarbazones derived from beta-keto amides or beta-keto esters (HTSC). Some of these reactions afforded thiosemicarbazonate complexes [M(TSC)2] with IR and NMR spectra compatible with N,S-coordination, but most gave complexes [ML2], where HL is a substituted 2,5-dihydro-5-oxo-1H-pyrazole-1-carbothioamide resulting from cyclization of the HTSC. Some of these pyrazolonates and two of the HL ligands were studied by X-ray diffractometry, and their structures are discussed. Surprisingly, the reactions of zinc(II) acetate with HTSC in 1:1 mol ratio usually gave a third, previously unreported type of complex with a dideprotonated ligand, [Zn(L-H)], which was also formed when [ZnL2] and Zn(OAc)2 interacted at room temperature in 1:1 mol ratio. These L-H complexes are highly insoluble in all common solvents, which hinders their characterization but suggests that they are polymeric in nature.     

Derivative spectrophotometric resolution of mixtures of the food colourants Tartrazine, Amaranth and Curcumin in a micellar medium

A study of the absorption spectra of the food colourants Tartrazine (E-102), Amaranth (E-123) and Curcumin (E-100) in various organic solvents and pH media, have been carried out. In addition, the spectral behaviour in aqueous micellar systems of anionic, cationic and non-ionic surfactants, as well as beta-cyclodextrin, was investigated. Analytical methods are proposed for the determination of the three dyes in mixtures without any prior separation step, by the application of the derivative technique to the normal absorption spectra, based on the use of cetyltrimethylammonium bromide (CTAB) in 0.1 M NaOH, over the concentration range 2-50 mug ml(-1). The methods are applied for determining the three dyes in commercial food products.     

A simple and very sensitive spectrophotometric method for the direct determination of copper ions

A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (epsilon) was 3.92x10(4) L mol(-1) cm(-1), and Beer's law was obeyed up to 3 mg L(-1) of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L(-1) Cu(II). The limit of detection was 2.5 micro g L(-1) and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%.     

Epoxides,cyclic sulfites,and sulfate from natural pentacyclic triterpenoids: theoretical calculations and chemical transformations

Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical (13)C and (1)H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and (3)J(H,H) coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and alpha- or beta-epoxide configurations together with 4-aza or 3-aza structures.     

Infrared Study of Solid Dispersions of β-Cyclodextrin with Naphthalene Derivitaves

The inclusion complexes of β-cyclodextrin (β-CD) with naphthalene and some of its derivatives in the solid state have been studied by infrared spectroscopy. Digital subtraction, deconvolution and curve fitting have been used to investigate the interactions between the naphthalene derivatives andβ-CD. Several preparation methods for the solid dispersions have been tested, using FTIR as an effective tool to evaluate the interactions at the molecular level. The effects of temperature and humidity on the spectra have been also analyzed. A carbonyl moiety in the guest molecule can increase the stability of the complex by establishing specific interactions with the hydroxyl groups of the CD cavity rims. The stability of the complexes is higher for 2-naphthylacetate than that for 1-naphthyl acetate, andso is the degree of association of its carbonyl groups. On the other hand, 2-acetylnaphthaleneforms very stable inclusioncomplexes although its carbonyl groups appear to be significantly less associated.     

An effective enantioselective approach to the securinega alkaloids: total synthesis of (-)-norsecurinine

[reaction: see text] A highly versatile approach to the enantioselective synthesis of securinega alkaloids is presented. Crucial steps are a palladium-catalyzed enantioselective imide alkylation, a vinylogous Mannich reaction, and a ring-closing metathesis process. Through this strategy, the synthesis of (-)-norsecurinine has been accomplished in nine steps and 11% overall yield.     

Determination of Benzo[a]pyrene in smoking-flavour agents (water-soluble liquid smoke) by second derivative constant-wavelength synchronous spectrofluorimetry

We have developed a simple, rapid, inexpensive method for the determination of benzo[a]pyrene (BP, a known carcinogen) in smoking-flavour agents (water-soluble liquid smoke; WSLS). After purification of the WSLS by a single passage through a Sep Pak C18 Plus cartridge, BP in the hexane eluate was determined by second derivative constant-wavelength synchronous spectrofluorimetry. Method precision (RSD < 6%) and recovery ( approximately 92%) were satisfactory, and the detection and quantification limits (1.05 and 2.28 mug kg(-1) respectively) indicated that the current maximum permissible concentration of BP in smoke flavourings (10 mug kg(-1)) can be monitored by this method.     

Coupled-column liquid chromatography method with photochemically induced derivatization for the direct determination of benzoylureas in vegetables

The coupled-column (LC-LC) system, consisting of a first column packed with internal surface reversed phase (ISRP) (50 x 4.6mm ID) and a Chrompack C18 (100 x 4.6 mm ID) as second column, allowed the simultaneous determination of five benzoylurea insecticides in dichloromethane (CH2Cl2) extracts of vegetable samples without any clean-up step. This system was combined with a photochemically induced fluorescence (PIF) post-column derivatization in order to provide strongly fluorescent photoproducts from the non-fluorescent benzoylureas. Limits of detection ranged from 0.21 to 0.98 microg L(-1) of pesticide (equivalent to 0.14-0.65 microg kg(-1) in vegetable samples) and limits of determination ranged from 4.0 to 10.0 microg L(-1) (equivalent to 2.7-6.7 microg kg(-1)). Linearity of the method was established between 2 and 1800 microg L(-1), depending upon the compound. Validation of the total method was performed by randomly analyzing recoveries of four vegetable samples (aubergine, cucumber, green bean, and tomato) spiked at two levels of concentration (10.0 and 33.3 microg kg(-1)). The combination of the LC-LC system with PIF detection provides a sensitive, selective, and rapid method for the determination of pesticides in vegetable samples at levels lower than the maximum residue levels (MRLs) established for these compounds by Spanish legislation.     

Use of highly efficient Draper-Lin small composite designs in the formal optimisation of both operational and chemical crucial variables affecting a FIA-chemiluminescence detection system

A new formal strategy in the multidimensional optimisation of the experimental variables affecting the chemiluminescence (CL) detection in flow injection analysis (FIA) is proposed here. The strategy implies several steps, being the most significant: selection of the variables to be studied and their experimental domain; use of a screening design to detect significant variables and interactions into the experimental region; study of the main effect of variables and second-order interactions; and finally application of a Draper-Lin small composite design (orthogonal) to obtain the optimum values of the significant variables. The methodology is applied to the determination of methylamine by FIA based on the use of the peroxyoxalate CL (PO-CL) reaction. Considering the high number of experiments required due to the different chemical and instrumental variables to be taken account and their adequate compatibility to obtain maximum sensitivity, the methodology offers a rigorous study of the main effects and interactions, achieving a reduction of experimental work.