The preparation and characterization of a platinum ether complex

The reaction of [Pt((F₃C)CCH(CF₃))(P(C₂H₅)₃)₂CH₃OH]PF₆ with allene in methanol affords a novel metallocyclic ethereal complex [$\text{Pt((F}{}_3\text{C)CHC(CF}{}_3\text{)C(CH}{}_3\text{)CH}{}_2\text{O}$CH₃)(P(C₂H₅)₃)₂]PF₆, which has been characterized by ¹H, ²H, ¹⁹F and ³¹P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P2₁/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R  0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed.     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.     

Detection of mitochondrial DNA mutations using temporal temperature gradient gel electrophoresis

Mitochondrial disorders are a group of clinically and genetically heterogeneous diseases. Common recurrent mitochondrial DNA (mtDNA) point mutations account for the molecular defects of a small proportion of patients. In order to identify mtDNA mutations, comprehensive mutational analysis of the entire mitochondrial genome is necessary. We developed the temporal temperature gradient gel electrophoresis (TTGE) method to screen for mutations in mtDNA. The entire mitochondrial genome was amplified using 32 pairs of overlapping primers followed by TTGE analysis of the DNA fragments. TTGE method was first validated on 200 DNA fragments containing known mutations or polymorphisms. On TTGE, homoplasmic nucleotide substitutions show a single band shift and heteroplasmic mutations show multiple banding patterns. The known mutations or polymorphisms were correctly identified. TTGE was then used to screen for unknown mutations in the mitochondrial genome. DNA banding patterns, deviated from wild-type, suggestive of either homoplasmic or heteroplasmic mutations, were followed by direct DNA sequencing to identify the mutations. Numerous mutations and polymorphisms were detected. The results demonstrated that TTGE detects and distinguishes heteroplasmic mutations from homoplasmic polymorphisms. It also detects heteroplasmic changes in the background of a homoplasmic polymorphism. Overall, TTGE was proven to be a simple, rapid, sensitive, and effective mutation detection method.     

Microwave digestion of fish tissue for selenium determination by differential pulse polarography

In KIO(3)NH(3)NH(4)Cl medium, the selenium complex Se(O)SO(2-)(3), resulted from the reaction of selenite and sulphite in acid solution, gave a catalytic wave, which was applied to the determination of selenium in fish by differential pulse polarography. The sample was decomposed using the HNO(3)/H(2)SO(4)/H(2)O(2) digestion mixture in a closed PTFE digestion vessel with microwave heating. The detection limit was 0.06 mug/dm(3). The calibration curve was linear up to 8 mug/dm(3). Selenate present was reduced with hot hydrochloric acid to selenite. The recoveries of the selenite and selenate in two spiked samples investigated ranged from 91 to 104%. The NIES CRM No. 6 mussel was analyzed and the results obtained agreed well with the reference value (reference value: 1.5 mug/g; found: 1.43 +/- 0.05 mug/g). The results obtained by differential pulse polarography were in good agreement with those found by hydride generation atomic absorption spectrometry.     

Capillary sodium dodecyl sulfate-DALT electrophoresis with laser-induced fluorescence detection for size-based analysis of proteins in human colon cancer cells

Capillary sodium dodecyl sulfate (SDS)-DALT electrophoresis (SDS-DALT-CE) refers to CE separation of proteins based on their size; DALT is the abbreviation for Dalton, the unit used to describe molecular weight. In this work, seven proteins from 18 to 116 kDa were denatured by SDS, labeled by 3-(2-furoyl) quinoline-2-carboxaldehyde, separated by SDS-DALT-CE in polyethylene oxide sieving matrix, and detected by laser-induced fluorescence (LIF) in a sheath flow cuvette. This method was combined with detergent differential fractionation, which is a protein fractionation method using a series of detergent-containing buffers to sequentially extract protein fractions from cells, to analyze the proteins in HT29 human colon adenocarcinoma cells. In addition, on-column labeling was demonstrated for protein analysis by SDS-DALT-CE with LIF, and applied to analysis of proteins in a single HT29 cancer cell. Most proteins had molecular masses from 10 to 120 kDa. Similar protein profiles were obtained for single cells and protein extract of a large cell population.     

Enzymes in Organic Synthesis: Application to the Problems of Carbohydrate Recognition (Part 1)

Carbohydrates on cell surfaces are information molecules. Although only seven or eight monosaccharides are commonly used as building blocks in mammalian systems, the multifunctionality of these monomers can lead to the assembly of an immense variety of complex structures. Millions of different tetrasaccharide structures, for example, can be constructed from this small number of building blocks, if branching, the stereochemistry of glycosidic linkages, and the modification of hydroxyl and amino groups are taken into consideration. Oligosaccharides therefore represent an effective class of biomolecules that code for a vast amount of information required in various biological recognition processes, such as intercellular communication, signal transduction, cell adhesion, infection, cell differentiation, development and metastasis. The pace of development of pharmaceuticals based on carbohydrates has, however, been slower than that based on other classes of biomolecules. Part of the reason is the lack of technologies for the study of complex carbohydrates. There is no method to amplify oligosaccharides for sequence analysis. There is no machine available for automated synthesis of oligosaccharides. In addition, the possibly poor bioavailability and difficulties in the large-scale synthesis of carbohydrates have undoubtedly contributed to this slow pace. The enzymatic and chemoenzymatic methods, especially those based on aldolases and glycosyltransferases, described here appear to be useful for the synthesis of mono- and oligosaccaharides and related molecules. Further advances in glycobiology will probably lead to the development of new technologies for the study of carbohydrate recognition and for the synthesis of bioactive carbohydrates and mimetics to control the recognition processes.     

Enantioselective total syntheses of manzamine a and related alkaloids

As a prelude to undertaking the total syntheses of the complex manzamine alkaloids, a series of model studies were conducted to establish the scope and limitations of intramolecular [4 + 2] cycloadditions of N-acylated vinylogous ureas with the trienic substrates 17a,b, 28a,b, and 34. These experiments clearly demonstrated that the geometry of the internal double bond and the presence of an electron-withdrawing group on the diene moiety were essential for the facile and stereoselective formation of the desired cycloadducts. The enantioselective syntheses of the manzamine alkaloids ircinol A (75), ircinal A (5), and manzamine A (1) were then completed by employing a convergent strategy that featured a novel domino Stille/Diels-Alder reaction to construct the tricyclic ABC ring core embodied in these alkaloids. Thus, the readily accessible chiral dihydropyrrole 58 was first converted in a single chemical operation into the key tricyclic intermediate 60. Two ring-closing metathesis reactions were then used to form the 13- and 8-membered rings leading to Z-72 and 74, the latter of which was quickly elaborated into ircinal A (5) via ircinol A (75). The synthetic 5 thus obtained was converted into manzamine A (1) following literature precedent. This concise synthesis of ircinal A required a total of 24 operations from commercially available starting materials with the longest linear sequence being 21 steps.     

Functionalized platinum(II) terpyridyl alkynyl complexes as colorimetric and luminescence pH sensors

A series of platinum(II) terpyridyl alkynyl complexes that have been derivatized with basic amino functionalities, [Pt(tpy)(C[triple bond]C-C6H4-NR2-4]X (X = OTf-, R = CH3 1, R = CH2CH2OCH3 2, R = H 3; X = Cl-, R = CH3 4, R = CH2CH2OCH3 5, R = H 6) (tpy = 2,2':6',2' '-terpyridine), have been synthesized and characterized. Their photophysical responses at various acid concentrations were studied. The abilities of the complexes to function as colorimetric and luminescence pH sensors were demonstrated with dramatic color changes and luminescence enhancement upon introduction of acid.     

Structures and stabilities of [C3H2]+ ˙ and [C3H2]2+ ions

Ab initio molecular orbital theory using basis sets up to 6-311G^{* *}, with electron correlation incorporated via configuration interaction calculations with single and double substitutions, has been used to study the structures and energies of the C₃H₂ monocation and dication. In agreement with recent experimental observations, we find evidence for stable cyclic and linear isomers of [C₃H₂]^{+ ˙}. The cyclic structure (, a) represents the global minimum on the [C₃H₂]^{+ ˙} potential energy surface. The linear isomer (, b) lies somewhat higher in energy, 53 kJ mol^?1 above a. The calculated heat of formation for [HCCCH]^{+ ˙} (1369 kJ mol^?1) is in good agreement with a recent experimental value (1377 kJ mol^?1). For the [C₃H₂]²⁺ dication, the lowest energy isomer corresponds to the linear [HCCCH]²⁺ singlet (h). Other singlet and triplet isomers are found not to be competitive in energy. The [HCCCH]²⁺ dication (h) is calculated to be thermodynamically stable with respect to deprotonation and with respect to C? C cleavage into CCH⁺ + CH⁺. The predicted stability is consistent with the frequent observation of [C₃H₂]²⁺ in mass spectrometric experiments. Comparison of our calculated ionization energies for the process [C₃H₂]^{+ ˙} → [C₃H₂]²⁺ with the Q_min values derived from charge-stripping experiments suggests that the ionization is accompanied by a significant change in structure.     

Photo- and thermoinduced generation of 1,3-diaryl carbonyl ylides from 2,3-diaryloxiranes 1,3-dipolar cycloadditions to dipolarophiles

A group of symmetrically substituted 2,3-diaryloxiranes have been studied as photoprecursors for carbonyl ylides. The stereochemistry of the adducts obtained upon interception of these 4n pi-transient systems with a variety of dipolarophiles provides information on the mode(s) of electrocyclic opening of the oxiranes to carbonyl ylides, as well as the mechanism of the 4n + 2 cycloaddition process. The stereochemistry of the dipolarophiles is preserved in the cycloadducts, which is consistent with a concerted addition process; however, solvent effects, steric hindrance, and possibly secondary orbital overlap factors all may play a role in determining the product distribution.