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PubMed1996

The interaction of antitumor-active anthraquinones with biologically important redox couples: I. Spectrophotometric investigation of the interaction of carminic acid and mitoxantrone with the iron (II, III) and copper (I, II) redox couples.

Studying the interaction of antitumor-active anthraquinones with biologically important redox couples is important in understanding the possible reductive or oxidative mode of metabolism of these antineoplastic agents coupled with the formation of free radicals. The interactions of such anthraquinones, i.e., carminic acid (CA) and mitoxantrone (Mx) with iron(II, III) and copper(I, II) redox couples in oxygenated and deaerated solutions, were investigated by UV-Visible and IR-spectroscopy. The superoxide radical reagent, nitroblue tetrazolium (NBT), was added to the metal and anthraquinone solutions and their binary mixtures at varying pH. Formazan, the reduction product of NBT, was produced mainly as a result of Fe(II)-NBT and Fe(II)-Mx-NBT interactions. The ternary mixtures of the lower valencies of iron and copper with CA and NBT exhibited intensive charge-transfer bands in the visible region, while metal-Mx-NBT combinations did not produce such bands, possibly due to the blockage of the redox-active aminoethanolamine side-chains of Mx through coordination with the metals. Copper-Mx combinations showed an oxygen sensitivity as spectral evidence was obtained for the oxidative transformation of Mx to the cyclic primary metabolite. The results were evaluated in regard to the possible oxidative activation of the studied anthracenediones with iron and copper systems.

Anthraquinones↗
PubMed1992

Phenoloxidase catalyzed coupling of catechols. Identification of novel coupling products.

Phenoloxidases from insect cuticle as well as from other sources oxidize catechols resulting in the formation of various coupling products. The two dominating products from 4-methylcatechol and the main product from N-acetyldopamine were purified and identified by means of plasma desorption and electron impact mass spectrometry and by 1H- and 13C-NMR spectroscopy. The main product from both catechols has a quinoid trihydroxybiphenyl structure, indicating oxidative coupling between a catechol and the corresponding trihydroxy derivative. The second product from 4-methylcatechol is a biphenyltetrol derivative, indicating oxidative coupling between two catechols.

Animals↗
PubMed2005

Selenium speciation in Agaricus bisporus and Lentinula edodes mushroom proteins using multi-dimensional chromatography coupled to inductively coupled plasma mass spectrometry.

In this study, selenium species from Se containing proteins in mushrooms (Agaricus bisporus and Lentinula edodes) were investigated with size-exclusion liquid chromatography coupled to UV and inductively coupled plasma mass spectrometry (ICP-MS). Different protein extraction protocols were investigated. Variability of the fractionation patterns with three extraction media (0.1M NaOH, 30 mM Tris-HCl, and enzymatic digestions) was evaluated for both mushroom types. A 24 h Tris-HCl extraction followed by acetone addition was found to be optimal for protein precipitation. Presumably protein bound selenoamino acids were released using enzymes (proteinase K, protease XIV and trypsin). The selenium speciation of the proteolytic extract of the water soluble proteins fraction was carried out by using reversed-phase ion-pairing high performance liquid chromatography (RP-HPIPC) coupled on-line to ICP-MS for selenium specific detection. Selenocystine, selenomethionine, methylselenocysteine and inorganic selenium were established in both samples utilizing retention time standards and standard additions to the sample.

Agaricus↗
PubMed1996

Donor insemination: a comparison of lesbian couples, heterosexual couples and single women.

OBJECTIVE: To compare single women, lesbian couples, and heterosexual couples receiving therapeutic donor insemination (TDI). DESIGN: Chart review followed by anonymous mail questionnaires to donor insemination recipients and their partners. SETTING: Infertility clinic in a university hospital. PATIENTS: One hundred fifteen women receiving donor insemination were identified by chart review. RESULTS: Too few single women responded for reliable comparison. Lesbian women were similar to married women in age, education, duration, and outcome of donor insemination. When considering alternatives to TDI, married women were more likely to consider adoption and lesbians were most likely to consider using a known semen donor or having intercourse with a man aware of their desire to have a child. Married couples were less likely to tell others, including the child, about conception by donor insemination. They were also less likely to support disclosing identifying data about the donor to the child. Lesbians were more likely to report stress in their relationships as a result of TDI. Married men were most likely to support mandatory counseling before TDI initiation.

Adoption↗
PubMed2002

Endocytosis of G protein-coupled receptors: roles of G protein-coupled receptor kinases and beta-arrestin proteins.

Sequestration of G protein-coupled receptors from the cell surface is a commonly observed phenomenon following agonist-stimulation. This process is now believed to be important for receptor resensitization as well as for signal transduction. Over the years, numerous studies have aimed at understanding the molecular mechanisms underlying internalization. Proteins such as the G protein-coupled receptor kinases (GRKs) and the beta-arrestins, which were initially characterized as desensitizing molecules, have been shown to be important regulators of the endocytic process. Recently, numerous interacting partners have been identified for each of these two classes of proteins. However, the details regarding the sequence of these interactions and the cross-talk between signaling pathways containing the different protein complexes are just beginning to be uncovered. In this review, we summarize these findings and discuss the role of GRKs and beta-arrestins, two families of key regulatory proteins that regulate G protein-coupled receptor endocytosis.

Animals↗
PubMed1998

Capillary electrophoresis-mass spectrometry coupling versus micro-high-performance liquid chromatography-mass spectrometry coupling: a case study.

Capillary zone electrophoresis (CZE) and micro-high-performance liquid chromatography (mu-HPLC) coupled to electrospray ionisation (ESI) mass spectrometry were compared with respect to their applicability to problems arising in pharmaceutical drug research and development. Both techniques, which are similar with regard to their operational parameters, were coupled to an API III plus triple quadrupole mass spectrometer using laboratory-built interfaces. The results achieved with the two combinations were compared for sensitivity and general applicability to the quantitative analysis of pharmaceuticals in biological fluids. Midazolam, the 8-chloro-6-(2-fluoro-phenyl)-1-methyl-4H-imidazo-[1,5-a][1,4]-benzodiaze pine, and three of its metabolites were used as test compounds, either as standard solution or after sample clean-up from human plasma. Following different sample preparation routes, liquid-liquid extraction or solid-phase extraction, differences in detection limits as well as robustness in CZE or mu-HPLC coupled with ion spray mass spectrometry (IS-MS) were investigated. Detection limits of about 500 pg/ml for the drug and 2 ng/ml for the metabolites were achieved, using 1 ml of human plasma, only when liquid-liquid extraction was used for sample preparation. Sample preparation using the simpler and faster solid-phase extraction route resulted in deterioration of the separation or clogging of the columns. In all cases, when standard solutions or sample extracts were used, CZE-ESI-MS provided both different selectivity and greater sensitivity.

Chromatography, High Pressure Liquid↗
PubMed2003

Broadband coupling into a single-mode, electroactive integrated optical waveguide for spectroelectrochemical analysis of surface-confined redox couples.

A single-mode, electroactive waveguiding platform capable of measuring spectroelectrochemical responses of surface-adsorbed redox-active molecules over a broad spectral bandwidth has been created. This new planar waveguide spectrometer is a combination of the previously developed electroactive integrated optical waveguide (EA-IOW; Dunphy, D. R.; Mendes, S. B.; Saavedra, S. S.; Armstrong, N. R. Anal. Chem. 1997, 69, 3086-3094) with a recently reported simplified approach to broadband coupling (Bradshaw, J. T.; Mendes, S. B.; Saavedra, S. S. Anal. Chem. 2002, 74, 1751-1759). With the use of a commercially available prism as an incoupling element, the EA-IOW can now guide visible light from at least 500 to 700 nm, improving upon its previously demonstrated monochromatic nature. Coupling profiles of various laser lines along with transmission spectra of narrow band-pass filters at various potentials are used to demonstrate the optical characteristics of this broadband EA-IOW and to compare its response to that of a conventional transmission instrument. Assessment of spectral resolution, performed by measuring the fwhm of various laser lines, ranges from 0.6 to 0.8. To demonstrate the capabilities of this technology, we show the acquisition of absorbance spectra of two different adsorbates, cytochrome c and ferrocenedicarboxylic acid, as a function of applied potential. Subtleties in the redox chemistries of adsorbed molecules, which were difficult to monitor with a monochromatic waveguide, are readily apparent when using the broadband coupling scheme.

Electrochemistry↗
PubMed2005

On-line coupling of gel electrophoresis and inductively coupled plasma-sector field-mass spectrometry for the determination of dsDNA fragments.

The on-line coupling of gel electrophoresis (GE) and inductively coupled plasma-mass spectrometry (ICPMS) is described for the first time. The new method combines the separation power of GE for large biomolecules and the high sensitivity and elemental selectivity of ICPMS. This coupling has been achieved by means of gels housed in glass tubes (length 2.5-20 cm; i.d. 0.5-5 mm). The gel is fixed by glass frits permeable for the analytes. After the electrophoretic separation at voltages up to 500 V, the analytes are transferred to the nebulizer of the ICPMS by an eluent stream, which is separated from the electrode chamber by a membrane. This filter blocks molecules with molecular masses larger than 500 Da. Using double-stranded DNA fragments, commercially available standard solutions were analyzed with on-line GE-ICPMS for the first time by monitoring (31)P(+) with a double-focusing mass spectrometer at a mass resolution of 4000.

Calibration↗
PubMed1998

NMR Coupling versus NMR Chemical Shift Information in Metallobiochemistry. High-Resolution One-Bond (1)H-(13)C Coupling Constants Obtained by a Sensitive Reverse Detection Method.

Imidazole rings are involved in acid/base chemistry, catalysis, H-bonding, and metal complexation throughout biochemistry; these rings are frequently targets for anticancer drugs and carcinogens. However, interpreting the changes in (13)C NMR shifts of these rings is often difficult. We explore the use of high-resolution one-bond (1)H-(13)C coupling constants ((1)J(CH)) for the identification of electronic changes within imidazole rings of samples containing (13)C in natural abundance. The reverse detection method used, called J-coupled heteronuclear multiple quantum coherence (JHMQC) spectroscopy, employs a modified HMQC pulse sequence. The method was evaluated with B(12) models of the type Me(3)BzmCo(DH)(2)(R or X), where Me(3)Bzm = 1,5,6-trimethylbenzimidazole and DH = the monoanion of dimethylglyoxime. (1)J(CH) values of Me(3)BzmCo(DH)(2)CH(3) obtained from both JHMQC and standard coupled 1D (13)C NMR spectra led to similar values, but the JHMQC method gave better resolution and much higher signal-to-noise ratios. The (1)J(CH) values for the endocyclic carbons and the N-methyl group of the Me(3)Bzm in five models fell between those of the free and protonated Me(3)Bzm ligands. Thus, donation of electron density from Me(3)Bzm to the Co center typically increases (1)J(CH) values with respect to the free ligand. Values of (1)J(CH) for several (13)C NMR signals correlated with both EP, a reported measure of electron-donating ability of R or X, and Co-N bond lengths from X-ray structures. For the assessment of electronic properties of the metal center, the (1)J(CH) values appear to be more reliable parameters than the traditionally used (13)C shifts, especially for C's close to the metal. Moreover, (1)J(CH) values for the (13)C signals for Co-(13)C were observed in several models; the (13)C signals for these carbons attached to the quadrupolar cobalt are too broad for (1)J(CH) determination by the traditional 1D method. The JHMQC method developed here is thus very versatile and can provide information on any type of molecule showing resolved CH signals.

Journal Article↗
PubMed2003

Palladium(0)-catalyzed amination, Stille coupling, and Suzuki coupling of electron-deficient aryl fluorides.

The amination of 2-fluoronitrobenzene was Pd(0) catalyzed at 65 degrees C in DMF, and the effectiveness of the catalysis was ligand-dependent. Among the five catalyst systems investigated, Pd(PPh3)4 was the most effective catalyst. The control experiments revealed that Pd(OAc)2 or PPh3 was not responsible for the catalysis. 4-Fluoro-3-nitro-benzonitrile and 4-fluoro-3-nitro-benzaldehyde also underwent Stille coupling and Suzuki coupling in the presence of Pd(PPh3)4, and the reactions afforded the coupling products in 28-86% yields. The control experiments showed no sign of reaction in the absence of palladium. These results were in agreement with the oxidative addition/reductive elimination pathway, where the oxidative addition could conceivably proceed via the SNAr mechanism.

Journal Article↗
PubMed2004

Electronic structure of the water-oxidation catalyst [(bpy)2(OHx)RuORu(OHy)(bpy)2]z+: weak coupling between the metal centers is preferred over strong coupling.

High-level DFT calculations indicate that the singlet ground state of the water-oxidizing blue Ru dimer [(bpy)2(OH2)RuIIIORuIII(OH2)(bpy)2]4+ is not due to a strong coupling of the excess electrons from each of the low-spin d5 RuIII centers across the Ru-O-Ru moiety, as has been assumed to date. Instead, broken symmetry orbital calculations suggest that a weak antiferromagnetically (AF) coupled singlet state is energetically more favorable by 10-35 kcal/mol. Experimentally observed redox potentials can only be reproduced if antiferromagnetic coupling is invoked.

Journal Article↗
PubMed1999

Intramolecular Anodic Olefin Coupling Reactions: The Use of Allylsilane Coupling Partners with Allylic Alkoxy Groups.

Intramolecular anodic olefin coupling reactions having an alkoxy substituent on the allylic carbon of an allylsilane moiety have been studied. These substrates were examined as part of an effort to determine the compatibility of the anodic olefin coupling reaction with the presence of very acid-sensitive functional groups and the construction of functionalized five-membered rings. In the initial experiment reported, an enol ether moiety was coupled to a trisubstituted allylsilane to afford a five-membered ring product without loss of the allylic alkoxy group. The reaction was stereoselective and could be used to generate a five-membered ring with three contiguous asymmetric centers. The stereochemical outcome of the reaction was best explained by a "pseudoequatorial" alkoxy group in the transition state; an argument that implied the reaction was under kinetic control. This suggestion was tested with the use of two electrolysis substrates that led to identical products through different transition states. The two substrates led to much different product ratios, proving that the reactions were not controlled by thermodynamics but rather governed by kinetic control. This observation was opposite to the conclusion reached with earlier vinylsilane-based substrates. Finally, the reactions were shown to be compatible with the presence of the alkoxy group even when challenged to form a fused bicyclic ring skeleton and a quaternary carbon. As in the initial case, the reaction to form a quaternary carbon was also highly stereoselective.

Journal Article↗
PubMed2003

Coupling-isomerization-coupling sequences switched on by propargyl alcohol-enone-isomerization.

The coupling-isomerization-reaction (CIR) of an electron-deficient halide 1 with 1-(p-bromo phenyl) propyne-1-ol (2) leads to an in-situ activation of the carbon-bromine bond towards oxidative addition and has been elaborated to a consecutive CIR-coupling sequence where subsequent palladium catalyzed coupling reactions such as Sonogashira, CIR, Heck, or Suzuki reactions allow a rapid construction of more complex frameworks in a one-pot reaction and in moderate to good yields.

Alcohols↗
PubMed1974

The kinetics of coupled enzyme reactions. Applications to the assay of glucokinase, with glucose 6-phosphate dehydrogenase as coupling enzyme.

1. A theory is developed to account for the kinetics of coupled-enzyme reactions without assuming that the second reaction follows first-order kinetics. 2. A simple procedure is described for applying the theory to the practical design of enzyme assays. 3. The validity of the theory is confirmed for the assay of glucokinase with glucose 6-phosphate dehydrogenase as coupling enzyme. 4. The possibility of extending the theory to three or more coupled reactions is discussed.

Animals↗
PubMed1993

Selective coupling of methotrexate to peptide hormone carriers through a gamma-carboxamide linkage of its glutamic acid moiety: benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate activation in salt coupling.

A convenient synthetic method is described for the preparation of peptide-methotrexate (MTX) conjugates in which MTX is coupled selectively through the gamma-carboxyl group of its glutamic acid moiety to a free amino group in peptide analogs. The syntheses of a somatostatin analog-MTX conjugate (MTX-D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2) (AN-51) and two conjugates of analogs of luteinizing hormone-releasing hormone (LH-RH) with MTX [Glp-His-Trp-Ser-Tyr-D-Lys(MTX)-Leu-Arg-Pro-Gly-NH2] (AJ-04) and [Ac-Ser-Tyr-D-Lys(MTX)-Leu-Arg-Pro-NH-Et] AJ-51 are presented as examples. Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP reagent) was used in the synthesis for activation of 4-amino-4-deoxy-N10-methylpteroic acid, which reacted with the potassium salt of glutamic acid alpha-tert-butyl ester in dimethyl sulfoxide to form the suitably protected MTX derivative. This synthesis provides an example of the high suitability of BOP reagent for the salt-coupling method. The selectively protected MTX derivative was then coupled to the different peptide carriers and deprotected under relatively mild conditions by trifluoroacetic acid. The conjugates of MTX with hormonal analogs are suitable for targeting to various tumors that possess receptors for the peptide moieties.

Amino Acid Sequence↗
PubMed1999

Unusually high standard redox potential of acrylyl-CoA/propionyl-CoA couple among enoyl-CoA/acyl-CoA couples: a reason for the distinct metabolic pathway of propionyl-CoA from longer acyl-CoAs.

The standard redox potential of acrylyl-CoA/propionyl-CoA couple (C(3)) was determined to be 69 mV (vs. standard hydrogen electrode) at pH 7 and 25 degrees C. This value implies that the 2, 3-dehydrogenation of propionyl-CoA is thermodynamically much more unfavorable than that of longer acyl-CoAs because the standard redox potentials of crotonyl-CoA/butyryl-CoA (C(4)), octenoyl-CoA/octanoyl-CoA (C(8)), and hexadecenoyl-CoA/palmitoyl-CoA (C(16)) are all about -10 mV. The unusually high standard redox potential of the acrylyl-CoA/propionyl-CoA couple is thought to be one of the reasons that in mammals propionyl-CoA is not metabolized by beta-oxidation as in the case of longer acyl-CoAs, but by a methylmalonyl-CoA pathway. The obvious structural difference between C(3) and C(4) (and longer) is whether an H or the C(4) atom is connected to -C(3)H=C(2)H-C(1)O-S-CoA. The molecular orbital calculations (MOPAC) for the enoyl and acyl forms of C(3) and C(4) revealed that this structural feature is the main cause for the higher standard redox potential of the C(3) couple. That is, the C(4)-C(3) bond is stabilized by the dehydrogenation to a greater degree than the H-C(3) bond.

Acyl Coenzyme A↗
PubMed1976

Enzyme coupled immunoassay of insulin using a novel coupling reagent.

A novel coupling reagent, meta-maleimidobenzoyl N-hydroxysuccinimide ester was synthesized. Using this reagent, insulin was conjugated very easily with beta-D-galactosidase [EC 3.2.1.23] in neutral, aqueous solution. No reduction of the enzyme activity was observed during the coupling procedure. The competitive bindings of the conjugate and insulin to anti-insulin serum were tested. The results indicated that the conjugate has enough immune reactivity for use in enzyme coupled immunoassay. Using this assay 20-800 pg of insulin were detectable.

Binding, Competitive↗