Disposable pipette tips extraction: Fundamentals,applications and state of the art

Disposable pipette tips extraction consists of a solid‐phase extraction in which the sorbent is poorly dispersed in a pipette tip, which allows a quick and dynamic contact between the aspirated analyte from the sample and the solid phase. It is a technique used particularly in food and forensic analysis, since it requires a small amount of sample and solvent. This article highlights the principles, advantages and disadvantages of the disposable pipette tips extraction method and reviews recent applications.     

13C NMR determination of the microstructure of polypropylene obtained with the DADNi(NCS)2/methylaluminoxane catalyst system

A complete ¹³C NMR characterization of a polymer synthesized with a new Ni‐diimine complex [DADNi(NCS)₂, where DAD = 2,6‐iPr? C₆H₃? N?C(Me)? C(Me)? N? 2,6‐iPr? C₆H₃] activated by methylaluminoxane by homopolymerization of propylene is presented. The amorphous material was made up mainly of blocks of syndiotactic polypropylene and ethylene–propylene copolymer. Some degree of propylene inversion (<1.2 mol %) and of long isobutyl and 2‐methyl hexyl branching (<1 mol %) were assigned and quantified. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2171–2178, 2004     

Lipid composition-dependent incorporation of multiple membrane proteins into liposomes

Membrane proteins from bacteria Pasteurella multocida were used as a model for studying its incorporation into liposomes. An important step to achieve efficient high yield protein incorporation in proteoliposomes is the study of the more suitable lipid composition. To this end, we compared the amount of total protein, reconstituted by co-solubilization methods, into liposomes of phospholipids with different polar head groups and acyl chain lengths. The liposomes and proteoliposomes were characterised by isopycnic centrifugation in sucrose gradient and by dynamic light scattering. Experimental and theoretical results were compared considering the effects exerted through the hydrocarbon chain length, volume, and optimal cross-sectional area of the phospholipid (combined in the geometrical critical packing parameter, lipid–protein matching), critical spontaneous radius of curvature of the bilayer vesicle, phase transition temperature of the lipid and ratio of lipid–protein molecules present in the vesicles. The highest incorporation of multiple proteins was found with dipalmitoylphosphatidylcholine (DPPC), reaching a yield of 93% compared to the lower relative amounts incorporated in proteoliposomes of the other lipids. The incorporation of multiple proteins induces a proportional enhancement of vesicular dimension, since DPPC–proteoliposomes have an average diameter of 1850 Å, compared to the 1430 Å for pure DPPC vesicles.     

119Sn-Mössbauer spectroscopic studies on organoheterobimetallic half sandwich ruthenium–tin containing derivatives

A series of heterobimetallic complexes containing Ru–Sn bonds, of general formula [RuCp(L)₂SnX₂Y] [L = PPh₃, 1/2 dppe = 1,2-bis(diphenylphosphino)ethane; X, Y = F, Cl and Br], was prepared and studied by elemental analysis, ¹¹⁹Sn-Mössbauer spectroscopy, i.r. and ¹H-, ¹³C-, ¹⁹F-, ³¹P- and ¹¹⁹Sn-n.m.r. spectroscopy. ¹¹⁹Sn-Mössbauer studies allowed determination of the coordination number of the Sn^II center as well as the group electronegativity of the organometallic fragment [RuCp(L)₂]⁺. These results, supported by multinuclear n.m.r. data suggested that the electronic charge distribution between the Ru^II and Sn^II centers are strongly dependant upon the nature of L and the electronegativity of X and Y.     

Non-linear correlations between formal potential and Hammett parameters of substituted iron phthalocyanines and catalytic activity for the electro-oxidation of hydrazine

The activity of the different iron phthalocyanines was examined using the complexes adsorbed on graphite electrodes. The effect of the Fe(II)/(I) formal potential of iron phthalocyanines on the their catalytic activity for the electro-oxidation of hydrazine was investigated. A plot of log k (rate constant at constant potential) versus the Fe(II)/(I) formal potential gives a volcano curve. The rate of the reaction increases with the driving force of the catalyst (measured as its formal potential) and then decreases for higher driving forces. A similar graph is obtained with a plot of log k versus the sum of the Hammett parameters of the substituents on the periphery of the phthalocyanine ligand. A maximum activity is obtained for a complexes having an M(II)/(I) redox potential close to –0.6 V which agrees with previous studies conducted with phthalocyanines of different metals and with cobalt phthalocyanines bearing different substituents.Dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry.     

Synthesis and characterization of [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*] and [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*] BF4

[Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*]ⁿ⁺ (Cp*=pentamethylciclopentadiene, n=0, 1), respectively named complexes V and VI, were synthesized and characterized. The X-ray structure has been solved and ¹H-, ¹³C-NMR and elemental analysis were performed for the n=0 complex. Cyclic voltammetry showed a potential difference of 360 mV within the two redox peaks. An absorption band at 850 nm was assigned to an intervalence band. The Mössbauer investigations show a uniform Fe²⁺ environment for the neutral compound and two sites, assigned to Fe²⁺ and Fe³⁺ for the monoxidized compound. The information gathered by all the previously mentioned techniques indicates that the studied binuclear compound belongs to the mixed valence class II using Robin and Day classification.     

Tin(IV) derivatives of 2,6-pyridinedicarboxylate: A Sn Mössbauer spectroscopic investigation

A series of organotin(IV) derivatives of 2,6-pyridinedicarboxylate has been investigated by Mössbauer spectroscopy in order to elucidate aspects concerning bonding and structural features in the solid state. A geometrical pattern of five-fold coordination at the metal centre has been revealed for SnCl₃Bu and SnClBu₃ derivatives. Trans stereochemistry for the butyl and vinyl groups of SnCl₂Bu₂ and SnCl₂(Vin)₂ derivatives has also been identified by this method. The isomer shift for the divinyl derivative is concurrent to a 7-coordinate metal centre contrasting to that for the dibutyl one. Although there is a discrepancy in isomer shift between these compounds, both have seven-fold coordination at the Sn(IV) nucleus. The resulting data has given evidence that 2,6-pyridinedicarboxylate is acting as a tridentate ligand through pyridil and carbolxylate moiety to all derivatives except for SnClBu₃. For the latter, the coordination mode occurs via carboxylate groups. The overall data support distorted geometrical pattern to all complexes in solid state.     

Almost Summing Polynomials

This paper introduces the class of almost summing homogeneous polynomials between Banach spaces. A characterization by means of vector‐valued sequences is proved, connections with the theory of absolutely summing polynomials are established and several examples are given. Some composition and coincidence theorems are obtained and the case of spaces with type or cotype is also investigated.     

Carbon-13 and proton NMR assignments of a new agathisflavone derivative

The (1)H and (13)C NMR spectra of 5-acetyl-7,4'-dimethoxyflavone-(6-8')-5'-acetyl-7',4'-dimethoxyflavone, a new agathisflavone derivative, were completely assigned on the basis of 1D and 2D NMR techniques.     

Linearization of multipolynomials and applications

We prove that every multipolynomial between Banach spaces is the composition of a canonical multipolynomial with a linear operator, and that this correspondence establishes an isometric isomorphism between the spaces of multipolynomials and linear operators. Applications to composition ideals of multipolynomials and to multipolynomials that are of finite rank, approximable, compact, and weakly compact are provided.