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At least 235 records · Page 13Linked to original sources
PubMed1997

Novel Resorcinarene Cavitand-Based CMP(O) Cation Ligands: Synthesis and Extraction Properties.

Tetrafunctionalized resorcinarene cavitands (4-6) have been synthesized starting from tetrakis(bromomethyl)cavitand 3. New cavitand-based cation ligands with (carbamoylmethyl)phosphonate (CMP) and -phosphine oxide (CMPO) moieties (8a,b and 9a,b) were prepared via two different routes in good (45-86%) overall yields. The ligands (8a,b and 9b) are very effective europium extractants. Ph(2)CMPON(Pr)-cavitand 8b has the highest extraction constant, determined with radiotracer experiments, for 1:1 complexation with Eu(picrate)(3) (K(ex)(1) = 2.7 x 10(12) M(-)(4)). The steric preorganization of the four CMP(O) moieties on the resorcinarene cavitand improves the efficiency and selectivity [of Eu(III) over UO(2)(II) and Fe(III)] of the metal extraction processes, compared to simple CMP(O) extractants.

Journal Article↗
PubMed1999

An Intramolecular Nitrone-Olefin Dipolar Cycloaddition-Based Approach to Total Synthesis of the Cylindricine and Lepadiformine Marine Alkaloids.

A synthetic route to the cylindricine skeleton as well as to the reported structure of the marine alkaloid lepadiformine has been achieved using an intramolecular nitrone/1,3-diene dipolar cycloaddition as the key step. The synthesis began with sequential alkylations of acetone oxime to afford key intermediate oxime 30, which contains all of the carbons necessary to form the tricyclic skeleton of the alkaloids. Nitrone 40, available from oxime 30 by standard transformations, underwent an intramolecular 1,3-dipolar cycloaddition to provide isoxazolidine 43. Related 1,3-dipolar cycloadditions were also explored on two additional nitrone-olefin substrates 41 and 42, which were prepared in a manner similar to that of 40. The tricyclic alkaloid core 52 was formed stereoselectively by a tandem oxidation-Michael addition of amino alcohol 49 derived from isoxazolidine 43. Cleavage of the O-phenyl ether of 52 provided 2-epi-cylindricine C (53). Several unsuccessful attempts were made to convert 52 to cylindricine C by epimerization at C2. Tricyclic ketone 52 was deoxygenated to give amine 59, whose structure and relative stereochemistry were confirmed by single-crystal X-ray analysis of its picrate salt. Removal of the O-phenyl protecting group from 59 provided tricyclic amino alcohol 60 having the putative structure of lepadiformine, but whose NMR data did not correspond to those of the natural product.

Journal Article↗
PubMed2006

Mechanism of a four-phase liquid membrane oscillator containing hexadecyltrimethylammonium bromide.

The oscillatory behavior of a nitromethane based liquid membrane oscillator was investigated to contribute to the oscillation mechanism at the molecular level. At the beginning the system contains three phases: the aqueous donor phase in which the cationic surfactant, hexadecyltrimethylammonium bromide and ethanol are present and the aqueous acceptor phase made up by sucrose solution separated by the liquid membrane containing a constant amount of picric acid. During experiment a new phase x is created between the liquid membrane and acceptor phase. It was established that the oscillations take place at the membrane/phase x and the phase x/acceptor phase interfaces. Five basic regions can be distinguished in the oscillation pattern. The molecular events provoking the oscillations of electric potential difference between the two aqueous phases involve essentially the diffusion of hexadecyltrimethylammonium bromide and ion pairs formed by the cation of the surfactant and the picrate anion to the vicinity of the membrane/phase x interface, sudden adsorption of these ion pairs at this interface in noncatalytic and autocatalytic steps, desorption of ion pairs from the membrane/phase x interface into phase x, diffusion of ion pairs to the vicinity of phase x/acceptor phase interface, and sudden adsorption at this interface followed by desorption to the aqueous acceptor phase. It is shown by numerical simulations that the proposed mechanism may account for the observed oscillations and for the species distribution throughout the system as found experimentally. This four-phase system behaves like two coupled oscillators.

Cetrimonium↗
PubMed2000

Design and synthesis of a new class of nonmacrocyclic alkali metal host compounds

A new class of nonmacrocyclic metal ion hosts has been examined that features a polyspirocyclic framework that offers a 1,3,5-triaxial presentation of ligating centers. These compounds are easily synthesized and exploit stereoelectronic influences to preorganize the metal ion binding site. While compounds bearing oxygen substituents (X = OH, OMe) failed to show appreciable binding of alkali metals, the aminated host (X = NHBn) exhibitied strong binding with association constants (K(a)) greater than 10(7)-10(8) as measured by picrate extraction analysis.

Journal Article↗
PubMed2000

A lead-filled G-quadruplex: insight into the G-Quartet's selectivity for Pb(2+) over K(+)

The lipophilic nucleoside, G 1, extracts Pb(2+) picrate from water into organic solvents to give structures based on the hydrogen-bonded G-quartet. Crystal structures indicate important differences between (G 1)(8)-Pb(2+) and (G 1)(8)-K(+). The divalent Pb(2+) templates a smaller G(8) cage than does K(+), as judged by the M-O6 bond length, O6-O6 diagonal distance, and inter-tetramer separation. The more compact Pb(2+) octamer correlates with NMR data indicating that N2-N7 hydrogen bonds in (G 1)(8)-Pb(2+) are kinetically more stable than in (G 1)(8)-K(+).

Journal Article↗
PubMed2001

Anion-dependent dimerization of a guanidiniocarbonyl pyrrole cation in DMSO.

With spherical counteranions such as chloride or hexafluorophosphate, the glycine-derived guanidiniocarbonyl pyrrole cation 1 self-assembles into discrete dimers in DMSO, as can be seen by NMR and ESI mass spectral analysis. According to concentration- and temperature-dependent NMR studies, the dimerization is endothermic and therefore entropy driven. Molecular modeling suggests that the dimers are held together by hydrogen bonding in combination with pi-pi interactions. In the presence of picrate anions, dimerization of cation 1 does not occur, probably due to the formation of pi-stacked ion pairs.

Algorithms↗
PubMed1989

Kinetic and chemometric studies of the determination of creatinine using the Jaffé reaction. Part I. Kinetics of the reaction: analytical conclusions.

A kinetic-spectrophotometric study of the Jaffé reaction was carried out and the kinetic behaviour, calibration step and interfering effect of albumin on creatinine standard solutions were studied. It was concluded that there is a variation in the kinetic behaviour of the system when higher concentrations of creatinine, picrate or sodium hydroxide are tested. The experimental conditions for quantifying creatinine must be chosen so that the kinetic behaviour is the same in the dynamic concentration range. Changes in the absorbance (delta A) versus concentration equations were chosen as the most suitable for calibration graphs. It was also shown that creatinine results will have a proportional bias error if the interfering effect of albumin is not taken into consideration.

Creatinine↗
PubMed1989

Kinetic and chemometric studies of the determination of creatinine using the Jaffé reaction. Part 2. Application to human serum samples: kinetic behaviour and chemometric evaluation of the determination.

The kinetic behaviour of the reaction of alkaline picrate with creatinine in human serum samples was found to be similar to that for standard creatinine solutions containing albumin. A chemometric evaluation of the kinetic determination of creatinine using the Jaffé reaction was carried out. The analysis of variance (ANOVA) method applied to the delta A45,180 values, obtained from two replicates of three different serum samples over a period of 10 d, showed that the between-day and between-replicate variations added a component to the total variability, the residual error (delta R2) being 5 X 10(-5). A study of the accuracy of the determination was carried out by means of percentage recovery experiments, Youden's method and the standard additions method. Percentage recovery experiments showed that albumin has a marked effect on the results obtained. The application of Youden's method to four serum samples indicated that the method does not have a constant bias error, but, by applying the standard additions method it was concluded that the method has a proportional bias error. The recovery factor, defined as the ratio of the slope of the standard additions graph to that of the standard response graph, was also calculated for the four serum samples. The best values were obtained with different standard response graphs (7.7, 15.4 and 25.6 g l-1 of albumin) for each sample. A modification of the routine procedure used in clinical laboratories is proposed. This modification is based on the principles of the standard additions method and gives better results for creatinine content than those obtained with the routine procedure.

Creatinine↗
PubMed1994

Application of a picrolonate ion-selective electrode to the assay of calcium and piperazine in pharmaceuticals and serum.

The construction and some analytical applications of a liquid picrolonate (Picrl-) ion-selective electrode based on the tris(phenanthrolinato)iron(II) (ferroin) picrolonate salt, dissolved in 2-nitrotoluene, are described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to picrolonate anions in the concentration range from 5 x 10(-2) to 5 x 10(-2) mol l-1. The response is virtually unaffected by pH changes in the range 3-10. Major interferents are picrates, 4-nitrophenolates, 3,5-dinitrosalicylates and 2,4-dinitrophenolates. In analytical applications direct potentiometric methods for the determination of picrolonates and indirect methods for the determination of calcium and piperazine are described. Calcium in the ranges 4-24 and 50-90 mg l-1, under specified experimental conditions, can be determined with mean relative errors of 1.1 and 1.4%, respectively. The method is applicable to soluble samples, pharmaceuticals and industrial and real human serum. Piperazine in the ranges 1-10 and 13-20 mg can be determined with a mean relative error of 1.2% in soluble salts and pharmaceutical formulations, respectively. An accuracy of better than 1.5% and a reproducibility (relative standard deviation) of 0.1% were achieved in the analysis of pharmaceutical products.

Calcium↗
PubMed2003

On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines.

2,3-Diaminophenol 4, 3,4-diaminophenol 5, 4-methoxy-1,2-diaminobenzene 6, 3,4-diaminobenzenethiol 7, 2,3-diaminobenzoic acid 8, and 3,4-diaminobenzoic acid 9 were reacted with 2,4-pentanedione to yield the corresponding benzo[b][1,4]diazepinium salts, respectively. The hydroxy-benzo[b][1,4]diazepinium salts 17 and 18 do not form mesomeric betaines (MB) on deprotonation. Instead, they are converted into the diimines 24 and 25. By contrast, the 7-mercaptobenzo[b][1,4]diazepinium salt 20 yields the corresponding thiolate on increasing the pH of the solution. This MB, which possesses 4n pi-electrons, does not fit into the classification system of heterocyclic mesomeric betaines accepted today. Deprotonation of the betaine results in the formation of an instable anionic thiolate 31 which oxidizes immediately to the disulfide 32. The carboxy derivatives 21 and 22 readily form cross-conjugated mesomeric betaines. Whereas the diimine 34 proved to be instable, the sodium salt of the diimine 36 was unambiguously characterized. An X-ray single crystal analysis of 22 as its picrate is presented in order to gain additional insights into these 4n pi-electron systems.

Journal Article↗
PubMed2004

Design and coordination behavior of the first selective recognition ligand of 147Pm(III).

A new amide tripodal ligand, 6-[2-(2-diethylamino-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide (4) has been designed and synthesized for the recognition of rare earth ions. Three representative complexes of trivalent lighter (La), middle (Gd), and heavier (Er) rare earth ions with 4 were synthesized and characterized by X-ray crystallography. In the complex, the heptadentate forms a cup-like coordination cavity encapsulating the central ion. Different supramolecular complex dimers are constructed by pi-pi interaction and van der Waals forces in accordance with the lanthanide contraction. The differences of the cavity and dimer structures were investigated further by assessing the separation efficiency of in multitrace solvent extraction of rare earth ions from picrate acid solution and the ligand has the best separation factor for 147Pm(III).

Crystallography, X-Ray↗
PubMed2004

Azidocryptands-synthesis, structure, and complexation properties.

Cryptands bearing an intraannular azido substituent have been synthesized and characterized spectroscopically. Their complexation properties were investigated by picrate extraction analysis. The oxygen-containing cryptands were found to be good ligands for alkali cations, with a preference for Li(+) and Na(+). The molecular structure of the complex with KBr was determined by X-ray crystallography. In this, the first structurally characterized complex of an aryl azide bound to a metal cation, the potassium cation was found to show ninefold coordination to four oxygen atoms and two nitrogen atoms of the crown ether moiety, to the bromide anion and to N1 of the azido group, as well as C1 of the benzene ring.

Journal Article↗
PubMed1997

Urinary IGF and IGF binding protein-3 in children with disordered growth. The North West Paediatric Endocrine Group.

OBJECTIVE: Both IGF-I and IGFBP-3 reflect spontaneous GH secretion in healthy individuals. We have evaluated the clinical usefulness of urinary IGF-I and IGFBP-3 measurements in the diagnosis of children with disordered growth. DESIGN: Serum IGF-I and IGFBP-3 radioimmunoassays (RIA) were developed, and modified for quantitation in urine. The relationship between serum and urine levels, and the performance of these tests in the diagnosis of GH deficiency (GHD) were examined. PATIENTS: Sixty-nine children (age 9.5 +/- 3.6 years; 37 boys, 32 girls) provided a timed overnight urine collection and a serum sample collected on the same morning. Subjects were defined as GHD (n = 22) or short normal (SN; n = 47) on the basis of medical history, clinical examination, auxology and peak response to a GH stimulation test (< 20 mU/L in GHD patients). MEASUREMENTS: IGF-I and IGFBP-3 in serum and urine were measured by RIA, urinary GH (uGH) by immunoradiometric assay (IRMA) after dialysis and urinary creatinine by the alkaline picrate method. Urine results were expressed as total amount excreted (tulGFBP-3 (microgram), tulGF-1 (ng), tuGH (ng), tuCrt (mmol). RESULTS: Urine IGF-I and IGFBP-3 excretion correlated significantly to serum levels of IGF-I and IGFBP-3 and also to tuGH excretion. There was a strong positive relationship between both urinary peptides and tuCrt, which suggested that renal filtration was the source of these peptides in urine. In addition, there were significant correlations with age, bone age and height SD score, of similar magnitude to those for tuGH. In prepubertal children, serum IGF-I and IGFBP-3 were significantly lower in GHD compared with SN children, while in puberty only serum IGFBP-3 was significantly lower in GHD. There was no difference however, in tulGF-I or tulGFBP-3 between GHD and SN children either prepubertally or in puberty with near complete overlap of the values between groups. CONCLUSIONS: Measurements of tulGF-I and tulGFBP-3 have no place in the diagnosis of childhood GHD. Nonetheless, the significant correlations between serum and urinary IGF-I and IGFBP-3 levels and their correlation to uGH indicate that these peptides could be used as non-invasive physiological markers of the GH-IGF axis.

Adolescent↗
PubMed1999

Elevated creatinine after ingestion of model aviation fuel: interference with the Jaffe reaction by nitromethane.

A 2 years 9 month-old-boy who ingested model aviation fuel was found to have an elevated serum creatinine concentration of 0.53 mmol/L (normal range 0.02-0.05 mmol/L) by the Jaffe (alkaline picrate) reaction. However, when the creatinine concentration was measured using a specific enzymatic assay, it was within the normal range. It was shown that nitromethane, a constituent of aviation fuel, interferes with the Jaffe reaction, leading to a falsely elevated creatinine reading. This phenomenon has been reported only once previously and, despite its potential clinical importance, nitromethane does not appear in published lists of substances that interfere with the Jaffe reaction.

Aircraft↗
PubMed2006

Sodium dodecyl sulphate as a rapid clearing agent for studying the hard parts of monogeneans and nematodes.

Hard structures of helminths have often been used for taxonomic identification but are usually not clearly defined when treated with conventional methods such as ammonium picrate-glycerin for monogeneans and glycerin for nematodes. The present study reports a rapid and simple technique to better resolve the hard parts of selected monogeneans and nematodes using 5-10% alkaline sodium dodecyl sulphate (SDS). In comparison with established methods, SDS-treated worms become more transparent. In monogeneans treated with SDS, clear details of the hooks, hook filaments, anchors, bars and the sclerotized copulatory organs could be observed. In SDS-treated nematodes, spicules and ornamentations of the buccal capsules could be clearly seen.

Animals↗
PubMed1995

Paraquat and diquat interference in the analysis of creatinine by the Jaffé reaction.

Paraquat and diquat were shown to interfere significantly in the measurement of plasma creatinine by the alkaline picrate (Jaffé) reaction in a young man who ingested a massive dose of a mixture of the 2 herbicides. It is likely that these bipyridylium compounds react in a manner similar but at different rates compared with creatinine in the Jaffé reaction.

Adult↗
PubMedDate not supplied

Synthesis and characterization of new chiral calix[4]arenes.

The unique chiral calixarenes were successfully synthesized by the following two methods: the Williamson ether synthesis and a stepwise ether cleavage with a mild Lewis acid. The high regioselectivity is recognized by the latter stepwise method. The ionophores having oligoethylene glycol unit efficiently extracted larger alkali metal ions like K+, Rb+, and Cs+ than smaller ones like Li+ and Na+. Their ion selectivity apparently changed by the chain length of crown ether. All racemates obtained could be resolved to each enantiomer by HPLC using a chiral column. The calixarenes with planar chirality recognized the chirality of guest molecules. Thus, the (-)-receptor resolved strongly forms 1:1 complex with (R)-(+)-alpha-phenylethylammonium picrate.

Journal Article↗