Azo dye oxidation with hydrogen peroxide catalysed by manganese 1,4,7-triazacyclononane complexes in aqueous solution

A kinetic and mechanistic study is reported of the oxidation of a number of azonaphthol dyes with hydrogen peroxide in aqueous solution, catalysed by some mono and dinuclear manganese(IV) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN). The results of UV-Vis investigations, augmented by EPR and ESI-MS studies, are described for a series of experiments in which concentrations, pH and ionic strength have been varied. The reactions are characterised by an induction period followed by a relatively rapid oxidation. For the dinuclear manganese complex 2, these are consistent with an initial perhydrolysis of the manganese complex involving both the dye anion and HO2-, to give mononuclear manganese species and the operation of a catalytic cycle incorporating MnIIIL(OH)3, O = MnVL(OH)2 and MnIVL(OH)3 (L = Me3TACN) (cf. the reactions of peroxidase enzymes). ESI-MS results provide evidence for the formation and reaction (with the dye) of MnIVL(OH)3. With the mononuclear manganese complex MnIVL(OMe)3, there is a short lag-phase attributed to perhydrolysis by HO2- followed by the same catalytic cycle.     

Evidence for gravity's influence on molecules at a solid-solution interface

Yoshimoto et al. [Anal. Chem. 2002, 74, 4306-4309] reported that a quartz crystal microbalance or QCM changed its response to sucrose solutions according to its angle of immersion. The effect was tentatively attributed to gravity-caused stress on the viscous interface between the oscillator and the bulk solution. The present work reports results from QCM experiments carried out so that any effect of gravity on the interfacial region would be magnified. This permitted use of a lower-frequency, less-sensitive QCM. Molecules of DNA were tethered to a functionalized QCM surface and then extended in steps, via sandwich hybridization, to produce DNA of uniform and known length. This feature allowed both the effect of QCM immersion angle and the relationship between frequency and molecular length to be investigated simultaneously. Comparison of acoustic wave damping at 0 degrees and 180 degrees immersion angles offers compelling evidence that the interfacial region expands when the active face of the QCM is down and contracts when it is up. This is apparently a consequence of the interfacial region being more dense than the bulk solution. The results are consistent with (a) slow gravity-driven movement of molecules away from a down-facing QCM, (b) rapid hybridization-driven movement away from an up-facing QCM, and (c) a QCM frequency response that decreases according to a simple exponential function of the tethered molecules' radius of gyration.     

Analysis of urinary nucleosides. III. Identification of 5'-deoxycytidine in urine of a patient with head and neck cancer

Modified nucleosides in the urine have been postulated to be diagnostic indices of disease, particularly of cancer. The urine of a patient with terminal head and neck cancer has been found to contain a modified nucleoside with a protonated molecule of m/z 228. By means of high-performance liquid chromatography/ion trap mass spectrometry (HPLC/ITMS) and capillary liquid chromatography/triple quadruple mass spectrometry (CapLC/TQMS) we have identified the compound as 5'-deoxycytidine. This is the first report of 5'-deoxycytidine in man: in addition to the elucidation of its structure, its possible origins and the potential significance of its occurrence are discussed.     

Study of the mass spectrometric fragmentation of pseudouridine: comparison of fragmentation data obtained by matrix-assisted laser desorption/ionisation post-source decay, electrospray ion trap multistage mass spectrometry, and by a method utilising electrospray quadrupole time-of-flight tandem mass spectrometry and in-source fragmentation

Many nucleosides and their modified forms have been studied by mass spectrometry elaborating the detailed fragmentation pathways under MS2 and MS(n) conditions. Although the C-nucleoside pseudouridine has been fragmented and studied briefly, usually amongst many other nucleosides, it has not been investigated to the same extent as other nucleosides. In this report a number of different mass spectrometric techniques are applied to obtain a fuller picture of pseudouridine fragmentation. At the same time this study is used to compare different tandem mass spectrometric techniques, including a novel methodology utilising a quadrupole time-of-flight (Q-ToF) instrument for MS(n) analysis comparable with that available with an ion trap mass spectrometer.     

Identification of butyryl derivatives of cyclic nucleotides by positive ion fast atom bombardment mass spectrometry and mass-analysed ion kinetic energy spectrometry

The syntheses of the dibutyryl derivatives of the 3′,5′-cyclic monophosphates of adenosine, guanosine and cytidine are described. The fast atom bombardment mass spectra of these compounds are discussed, together with the mass-analysed ion kinetic energy spectra of their protonated molecular ions and of diagnostic fragments. A protocol for the identification of the derivatives is reported which includes criteria for confirming retention of the cyclic phosphodiester moiety, substitution of both heterocyclic base and ribose ring, and butyrylation of the 2′-O-position. The origins of significant fragments in the spectra are discussed.     

Crystal and molecular structure of 1-epi-delphisine and nmr assignments for delphisine, 1-epi-delphisine and delphinine

The crystal and molecular structure of the norditerpenoid alkaloid 1-epi-delphisine (5), C₂₈H₄₃NO₈, M _r 521.66, has been confirmed by as X-ray diffraction study using the SIR 88 analysis program. The alkaloid crystallizes in the space groupP2₁ with cell parameters:a=11.853(1)Å,b=10.511(1)Å,c=11.854(1)Å,=112.58(1),V=1363.61(0)ų,Z=2,D _calc=1.27 g/cm³, (CuK)=1.54184 Å, (CuK=7.2 cm^–1,F(000)=564, temperature 23°C,R=0.052, for 2907 reflections. Ring A of 1-epi-delphisine exists in a chair conformation. By comparison, delphisine which bears a C-1 hydroxyl group, has ring A in a boat conformation stabilized by an intramolecular N----H-O hydrogen bond. Ring D of both of these alkaloids exists in a boat form. Unambiguous proton and carbon-13 nmr assignments for delphisine, 1-epi-delphisine and delphinine have been made by a detailed analysis of the DEPT, COSY, HETCOR, COLOC, DIFNOE, and selective INEPT nmr techniques.Dedicated to the memory of Dr. K. Krishna Bhandary (1946–1992).     

Adsorption of Cu(II) and Co(II) complexes on a silica gel surface chemically modified with 2-mercaptoimidazole

The isotherms of adsorption of MeX₂ (Me = Cu²⁺, Co²⁺; X = Cl^–, Br^–, ClO ₄ ^– ) by silica gel chemically modified with 2-mercaptoimidazole (SiMI) were studied in acetone and ethanol solutions, at 25 °C. Covalently attached 2-mercaptoimidazole molecule to silica gel surface adsorbs MeX₂ from solvent by forming a surface complex. The metal is bonded to the surface through the nitrogen atom of attached 2-mercaptoimidazole. At low loading, the electronic and ESR spectral parameters indicated that the Cu²⁺ complexes are in a distorted-tetragonal symmetry field. The d-d electronic transition spectra showed that for Cu(ClO₄)₂ complex, the peak of absorption did not change for any degree of metal loading and for Cl^– and Br^– complexes, the peak maxima shifted to higher energy with lower metal loading. The CoX₂(X = Cl^–, Br^–, ClO ₄ ^– ) analogues possess a distorted-tetrahedral field.     

Vortex Motion and the Geometric Phase. Part II. Slowly Varying Spiral Structures

Summary. We derive formulas for the long time evolution of passive interfaces in three ``canonical' incompressible, inviscid, two-dimensional flow models. The point vortex models, introduced in Part 1 [1] are (i) a ``restricted' three-vortex problem, (ii) a vortex and a particle in a closed circular domain, and (iii) a particle in the flowfield of a mixing layer model undergoing a vortex pairing instability. In each configuration, it was shown in Part 1 that the passive particle exhibits a geometric or Hannay-Berry phase over long time periods induced by the slowly varying periodic background field. In this paper we show how the formula for the evolution of a passive interface driven by the dynamics of the vortices inherits this geometric phase effect. The interface wraps into a spiral formation around the ``parent' vortex, with a slowly varying component induced by the farfield vorticity. The length formula for the long time growth of the slowly rotating spiral decomposes into a ``dynamic' part and a ``geometric' part. The dynamic part is the length in the ``unperturbed' system—i.e., in the absence of the background field—and the geometric part is the contribution of the geometric phase θ _g for a passive particle in the flow. We derive the following simple formula for an interface along a smooth curve joining two arbitrary particles labelled A and B . Define as the difference in interface lengths between the ``unperturbed' system and the ``perturbed' slowly varying system at the end of the long time period T . In each case, , where ξ is the radial coordinate parametrizing the interface at t=0 . Received September 4, 1997; second revision received January 16, 1998; accepted January 27, 1998     

Branching by reactive end groups. III. Synthesis,branching, and analysis of m‐ethynylphenol/p‐t‐butylphenol‐coterminated bisphenol a polycarbonates

The use of m‐ethynylphenol (m‐EP) and p‐t‐butylphenol (PTBP) as coterminators for bisphenol A polycarbonates (BA PCs) provided long‐chain‐branched PCs, partially crosslinked PCs, or both after the thermal reaction of the terminal m‐EP groups, depending on the molar ratio of the chain terminators. Linear m‐EP/PTBP PCs were prepared by solution phosgenation of BA and the two coterminators. Differential scanning calorimetry showed the onset of the m‐EP‐end‐group reaction at about 250 °C by the appearance of a reaction exotherm. The enthalpy (ΔH) of this reaction was roughly proportional to the amount of m‐EP in the PC and to an extent could be used to monitor the progress of the reaction and estimate its kinetics. A complete m‐EP‐end‐group reaction was evident from gel permeation chromatography analysis upon heating under N₂ to 380 °C for 10 min or 360 °C for 60 min. The amount, if any, of gel formed after the m‐EP‐end‐group reaction depended on X_EP; those PCs with a X_EP value less than or equal to 0.33 had little or no gel. The maximum X_EP that precluded the formation of gels after branching was estimated to be about 0.45–0.48. The molecular weight of m‐EP/PTBP PCs increased after branching, as evidenced by gel permeation chromatography analysis. Assuming that the terminal m‐EP groups had a statistical distribution on the polymer chain ends and that they underwent only homopolymerization, the average reacted m‐EP‐group functionality according to estimated gel‐point composition was about 2.8–3.0. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2352–2358, 2000     

Static fluid spheres admitting Karmarkar condition

We explore a new relativistic anisotropic solution of the Einstein field equations for compact stars based on embedding class one condition.For this purpose,we use the embedding class one methodology by employing the Karmarkar condition.Employing this methodology,we obtain a particular differential equation that connects both the gravitational potentials e^λ and e^ν.We solve this particular differential equation choosing a simple form of generalized gravitational potential grr to describe a complete structure of the space-time within the stellar configuration.After determining this space-time geometry for the stellar models,we discuss thermodynamical observables including radial and tangential pressures,matter density,red-shift,velocity of sound,etc.,in the stellar models.We also perform a complete graphical analysis,which shows that our models satisfy all the physical and mathematical requirements of ultra-high dense collapsed structures.Further,we discuss the moment of inertia and M-R curve for rotating and non-rotating stars.