Measuring temperature gradients in evaporating multicomponent alcohol/water droplets

We demonstrate that temperature gradients can be investigated in evaporating volatile water/alcohol droplets by characterising the volume averaged temperature by laser induced fluorescence and the near-surface temperature by cavity enhanced Raman scattering. In the former technique, the fluorescence spectrum from Rhodamine B can be used to determine the droplet temperature with an accuracy of +/-1 K. The latter technique uses the band width of the OH stretching Raman band to determine the temperature change within the near-surface volume in which whispering gallery modes propagate with an accuracy of +/-4 K. We demonstrate that the temperatures measured with varying evaporation time, buffer gas pressure, droplet size and composition are consistent with the predictions from a quasi-steady theoretical treatment of the evaporation rate and can be used to investigate temperature gradients within evaporating droplets.     

Correlating sideband patterns with powder patterns for accurate determination of chemical shift parameters in solid-state NMR

Powder patterns and sideband patterns have different strengths when it comes to using them to determine chemical shift parameters. Here, we show that chemical shift parameters can be determined with high accuracy by analysing the correlation pattern from a 2D experiment which correlates a powder pattern in the indirect dimension with a sideband pattern in the direct dimension. The chemical shift parameters so determined have greater accuracy than those obtained by analysing a sideband or powder pattern alone, for the same signal-to-noise ratio. This method can be applied for both resolved correlation patterns and to cases where two components share similar isotropic chemical shifts. The methodology is demonstrated in this paper, both theoretically and experimentally, on the (31)P signals of the bis-phosphonate drug, pamidronate.     

Synthesis, characterisation and structures of thio-, seleno- and telluro-ether complexes of gallium(III)

The reactions of GaX3 (X = Cl, Br or I) with SMe2, SeMe2 and TeMe2 (L) in non-coordinating solvents produces only the pseudo-tetrahedral [GaX3L], which have been characterised by IR, Raman and multinuclear NMR (1H, 71Ga, 77Se or 125Te) spectroscopy, and by the crystal structure of [GaCl3(SeMe2)]. The 71Ga NMR resonances show small low frequency shifts for fixed halides as the neutral donors change from S --> Se --> Te. Bidentate ligands including MeS(CH2)2SMe, PhS(CH2)2SPh, MeSe(CH2)2SeMe, nBuSe(CH2)2Se(n)Bu and MeTe(CH2)3TeMe (L-L) also produce complexes with 4-coordinate gallium centres, [(GaX3)2(mu-L-L)], confirmed by the crystal structures of [(GaI3)2(mu-MeS(CH2)2SMe)], [(GaCl3)2(mu-PhS(CH2)2SPh)] and [(GaCl3)2(mu-nBuSe(CH2)2Se(n)Bu)]. The structural data are consistent with the weaker Lewis acidity of the gallium as the halide co-ligands become heavier. Multinuclear NMR studies suggest that in chlorocarbon solutions partial dissociation of the ligands occur, which increases with the halide co-ligand Cl < Br < I. The o-xylyl dithioether, o-C6H4(CH2SMe)2, despite being pre-organised for chelation, also forms [(GaCl3)2(mu-L-L)]. The corresponding diselenoether complex decomposes in solution with C-Se bond cleavage to form the selenonium salt [o-C6H4CH2Se(Me)CH2][GaCl4], which was structurally characterised. The ditelluroether o-C6H4(CH2TeMe)2 undergoes rapid C-Te bond fission and rearrangement upon reaction with GaCl3, and the telluronium species [o-C6H4CH2Te(Me)CH2]+ and [MeTe(CH2(o-C6H4)CH2TeMe)2]+ have been identified by ES+ mass spectrometry from their characteristic isotope patterns.     

Tannin fingerprinting in vegetable tanned leather by solid state NMR spectroscopy and comparison with leathers tanned by other processes

Solid state 13C-NMR spectra of pure tannin powders from four different sources--mimosa, quebracho, chestnut and tara--are readily distinguishable from each other, both in pure commercial powder form, and in leather which they have been used to tan. Groups of signals indicative of the source, and type (condensed vs. hydrolyzable) of tannin used in the manufacture are well resolved in the spectra of the finished leathers. These fingerprints are compared with those arising from leathers tanned with other common tanning agents. Paramagnetic chromium (III) tanning causes widespread but selective disappearance of signals from the spectrum of leather collagen, including resonances from acidic aspartyl and glutamyl residues, likely bound to Cr (III) structures. Aluminium (III) and glutaraldehyde tanning both cause considerable leather collagen signal sharpening suggesting some increase in molecular structural ordering. The 2?Al-NMR signal from the former material is consistent with an octahedral coordination by oxygen ligands. Solid state NMR thus provides easily recognisable reagent specific spectral fingerprints of the products of vegetable and some other common tanning processes. Because spectra are related to molecular properties, NMR is potentially a powerful tool in leather process enhancement and quality or provenance assurance.     

Facile Tuning of Luminescent Platinum(II) Schiff Base Complexes from Yellow to Near‐Infrared: Photophysics,Electrochemistry, Electrochemiluminescence and Theoretical Calculations

The photophysical and related properties of platinum(II) Schiff base complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. A series of such complexes, differing only in the number and positioning of methoxy substituents on the phenoxy ring, were synthesised and their photophysical, electrochemical and electrochemiluminescent (ECL) properties investigated. Theoretical calculations were performed in order to gain further insight into the relationship between structure and properties in these materials. By positioning methoxy groups para and/or ortho to either the imine or the oxygen group on the ligand, electron density could be directed selectively toward the LUMO or HOMO as required. This allowed the emission colour (both photoluminescent and electrochemiluminescent) to be tuned over a wide range between 587 and 739 nm. The variation in orbital energies was also manifested in the positions of the absorption bands and the redox properties of the complexes, as well as in the NMR shifts for the uncoordinated ligands. All reported complexes displayed intense electrochemiluminescence (ECL), which could be initiated either by annihilation or co‐reactant pathways. The relationship between the electrochemical and photophysical properties and the efficiency of the ECL is discussed. For two of the complexes solid‐state ECL could be generated from electrodeposited layers of the complex.     

Towards the development of an immuno MALDI (iMALDI) mass spectrometry assay for the diagnosis of hypertension

The renin-angiotensin-aldosterone system (RAAS) plays an essential role in the regulation of plasma volume and arterial blood pressure. One of the most common diseases of the RAAS is the autonomous production of aldosterone by the adrenal glands, caused by either bilateral adrenal hyperplasia or an aldosterone-producing adenoma. This condition, known as primary aldosteronism, is a treatable and often curable form of hypertension. The measurement of plasma renin activity (PRA), as determined by radioimmunoassay for angiotensin I is essential to the diagnosis of primary aldosteronism. However, accurate determination of PRA is often hampered by low plasma concentrations of angiotensin I. Here, we report the use of immuno-MALDI (iMALDI) as a highly sensitive and specific method for the absolute quantitation of angiotensin I in plasma. iMALDI permits concentration determination by affinity-capture of angiotensin I and a stable-isotopically labeled standard (SIS) peptide on immobilized anti-peptide antibodies. The affinity beads are placed on the MALDI target, permitting automated analysis of large numbers of patient samples. Pretreatment of the plasma is not required, and this method is suitable for the accurate determination of angiotensin I in whole plasma. The calibration curve generated using this method was linear over a 50-fold concentration range in plasma, with a correlation coefficient of 0.984. MS/MS sequence confirmation provides absolute specificity. The iMALDI angiotensin I assay, therefore, has the potential to be developed into a method for determining PRA that has advantages in time, in specificity, and in safety.     

Taking TiF4 complexes to extremes--the first examples with phosphine co-ligands

The first soft donor adducts of TiF(4), [TiF(4)(diphosphine)] (diphosphine = o-C(6)H(4)(PMe(2))(2), R(2)P(CH(2))(2)PR(2), R = Me or Et) have been prepared from [TiF(4)(MeCN)(2)] and the diphosphines in rigorously anhydrous CH(2)Cl(2), as extremely moisture sensitive yellow solids, and characterised by multinuclear NMR ((1)H, (31)P, (19)F), IR and UV/vis spectroscopy. The crystal structure of [TiF(4){Et(2)P(CH(2))(2)PEt(2)}] has been determined and shows a distorted six-coordinate geometry with disparate Ti-F(transF) and Ti-F(transP) distances and long Ti-P bonds. Weaker soft donor ligands including Ph(3)P, Ph(2)P(CH(2))(2)PPh(2), o-C(6)H(4)(PPh(2))(2), Ph(2)As(CH(2))(2)AsPh(2), o-C(6)H(4)(AsMe(2))(2) and (i)PrS(CH(2))(2)S(i)Pr do not form stable complexes with TiF(4), although surprisingly, fluorotitanate(IV) salts of the previously unknown doubly protonated ligand cations [LH(2)][Ti(4)F(18)] (L = o-C(6)H(4)(PPh(2))(2), o-C(6)H(4)(AsMe(2))(2) and (i)PrS(CH(2))(2)S(i)Pr) are formed in some cases as minor by-products. The structure of [o-C(6)H(4)(PPh(2)H)(2)][Ti(4)F(18)] shows the first authenticated example of a diprotonated o-phenylene-diphosphine. The synthesis and full spectroscopic characterisation are reported for a range of TiF(4) adducts with hard N- or O-donor ligands for comparison purposes, along with crystal structures of [TiF(4)(thf)(2)], [TiF(4)(Ph(3)EO)(2)]·2CH(2)Cl(2) (E = P or As), and [TiF(4)(bipy)].     

Halometallate Complexes of Germanium(II) and (IV): Probing the Role of Cation,Oxidation State and Halide on the Structural and Electrochemical Properties

The Ge^IV chlorometallate complexes, [EMIM]₂[GeCl₆], [EDMIM]₂[GeCl₆] and [PYRR]₂[GeCl₆] (EMIM=1‐ethyl‐3‐methylimidazolium; EDMIM=2,3‐dimethyl‐1‐ethylimidazolium; PYRR=N‐butyl‐N‐methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single‐crystal X‐ray diffraction. The imidazolium chlorometallates exhibited significant C?H???Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution ¹H NMR data also showed cation–anion association. The synthesis and characterisation of Ge^II halometallate salts [EMIM][GeX₃] (X=Cl, Br, I) and [PYRR][GeCl₃], including single‐crystal X‐ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic‐voltammetry experiments on the Ge^IV species in CH₂Cl₂ solution showed two distinct, irreversible reduction waves attributed to Ge^IV–Ge^II and Ge^II–Ge⁰, whereas the Ge^II species exhibited one irreversible reduction wave. The potential for the Ge^II–Ge⁰ reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from Ge^IV to Ge^II does have an effect; for a given cation, reduction from the [GeCl₃]^? salts occurred at a less cathodic potential. The nature of the halide co‐ligand also has a marked influence on the reduction potential for the Ge^II–Ge⁰ couple, such that the reduction potentials for the [GeX₃]^? salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.     

Crystallization and orientation of isotactic poly(propylene) in cylindrical nanopores

The crystallization of polymers in cylindrical geometries is important as interest in polymer nanowires and nanostructures grows. Here, semicrystalline isotactic poly(propylene) (iPP) is shown to crystallize in a homogeneous, low‐dimensional fashion when confined in cylindrical pores as small as 15 nm. A strong dependence on pore diameter is demonstrated. Isothermal crystallization studies suggest a reduced Avrami exponent as pore diameter decreases and as crystallization time increases. Complementary X‐ray diffraction with tilt (texture analysis) reveals one‐dimensional ordering of iPP crystals within pores of 40 nm diameter or less in which crystals preferentially orient, perpendicular to the pore wall. These findings demonstrate that the origin of this orientation is related to the impingement of crystals against the pore wall, thus “freezing out” polymer crystallizing in nonpreferred directions. These results show that curvature‐directed crystallization is one potential means to control a polymer's crystallization rate and orientation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1412–1419     

Femtosecond electron-transfer reactions in mono- and polynucleotides and in DNA

Quenching of redox active, intercalating dyes by guanine bases in DNA can occur on a femtosecond time scale both in DNA and in nucleotide complexes. Notwithstanding the ultrafast rate coefficients, we find that a classical, nonadiabatic Marcus model for electron transfer explains the experimental observations, which allows us to estimate the electronic coupling (330 cm(-1)) and reorganization (8070 cm(-1)) energies involved for thionine-[poly(dG-dC)](2) complexes. Making the simplifying assumption that other charged, pi-stacked DNA intercalators also have approximately these same values, the electron-transfer rate coefficients as a function of the driving force, DeltaG, are derived for similar molecules. The rate of electron transfer is found to be independent of the speed of molecular reorientation. Electron transfer to the thionine singlet excited state from DNA obtained from calf thymus, salmon testes, and the bacterium, micrococcus luteus (lysodeikticus) containing different fractions of G-C pairs, has also been studied. Using a Monte Carlo model for electron transfer in DNA and allowing for reaction of the dye with the nearest 10 bases in the chain, the distance dependence scaling parameter, beta, is found to be 0.8 +/- 0.1 A(-1). The model also predicts the redox potential for guanine dimers, and we find this to be close to the value for isolated guanine bases. Additionally, we find that the pyrimidine bases are barriers to efficient electron transfer within the superexchange limit, and we also infer from this model that the electrons do not cross between strands on the picosecond time scale; that is, the electronic coupling occurs predominantly through the pi-stack and is not increased substantially by the presence of hydrogen bonding within the duplex. We conclude that long-range electron transfer in DNA is not exceptionally fast as would be expected if DNA behaved as a "molecular wire" but nor is it as slow as is seen in proteins, which do not benefit from pi-stacking.