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The active site of mammalian purple acid phosphatases (PAPs) have a dinuclear iron site in two accessible oxidation states (FeIII2and FeIIIFeII), and the heterovalent is the active form, involved in the regulation of phosphate and phosphorylated metabolite levels in a wide range of organisms. Therefore, two sites with different coordination geometries to stabilize the heterovalent active form and, in addition, with hydrogen bond donors to enable the fixation of the substrate and release of the product, are believed to be required for catalytically competent model systems. Two ligands and their dinuclear iron complexes have been studied in detail. The solid-state structures and properties, studied by X-ray crystallography, magnetism, and Mössbauer spectroscopy, and the solution structural and electronic properties, investigated by mass spectrometry, electronic, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and Mössbauer spectroscopies and electrochemistry, are discussed in detail in order to understand the structures and relative stabilities in solution. In particular, with one of the ligands, a heterovalent FeIIIFeIIspecies has been produced by chemical oxidation of the FeII2precursor. The phosphatase reactivities of the complexes, in particular, also of the heterovalent complex, are reported. These studies include pH-dependent as well as substrate concentration dependent studies, leading to pH profiles, catalytic efficiencies and turnover numbers, and indicate that the heterovalent diiron complex discussed here is an accurate PAP model system.

This study investigated how to control the rate of photoreduction of metastable AuCl2–at the solid–solution interface of large ZnO nanoparticles (NPs) (50–100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO–Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2–at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO–solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent’s permittivity (ε) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO–solution interface, it was confirmed that low ε solvent mixtures (ε ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 104electrons·particle–1·s–1) compared to solvent mixtures with high ε (ε = 29.9, ∼1.9 × 104electrons·particle–1·s–1). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO–Au NP hybrid. Under conditions where electron discharge was rapid (such as in low ε solvents), AuCl2–precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.

High Speed Sintering is a novel Additive Manufacturing technology that functions by inkjet deposition of a radiation absorbing material directly on to the powder surface followed by the infrared irradiation of the entire build surface. The area deposited with radiation absorbing material absorbs significantly more energy than areas without, sufficient to cause the powder to sinter. Mechanical properties are known to be related to crystallinity, however, no work to date has yet been performed to investigate the relationship between print densities, how this influences crystallinity and the resulting mechanical performance. Dithered patterns were used to vary print density, part crystallinity analysed by Differential Scanning Calorimetry and mechanical properties evaluated by tensile testing. Results showed crystallinity decreased as print density increased. This was reflected by mechanical properties which showed stiffness and tensile strength increased with crystallinity at the expense of ductility. Moreover, High Speed Sintered parts show comparable crystallinity to Laser Sintering indicating the radiation absorbing material has little effect on part microstructure.

Two synthetic derivatives of the naturally occurring cyclic pseudooctapeptides patellamide A–F and ascidiacyclamide, that is, H4pat2, H4pat3, as well as their CuIIcomplexes are described. These cyclic peptide derivatives differ from the naturally occurring macrocycles by the variation of the incorporated heterocyclic donor groups and the configuration of the amino acids connecting the heterocycles. The exchange of the oxazoline and thiazole groups by dimethylimidazoles or methyloxazoles leads to more rigid macrocycles, and the changes in the configuration of the side chains leads to significant differences in the folding of the cyclic peptides. These variations allow a detailed study of the various possible structural changes on the chemistry of the CuIIcomplexes formed. The coordination of CuIIwith these macrocyclic species was monitored by high‐resolution electrospray mass spectrometry (ESI‐MS), spectrophotometric (UV/Vis) and circular dichroic (CD) titrations, and electron paramagnetic resonance (EPR) spectroscopy. Density functional theory (DFT) calculations and molecular mechanics (MM) simulations have been used to model the structures of the CuIIcomplexes and provide a detailed understanding of their geometric preferences and conformational flexibility. This is related to the CuIIcoordination chemistry and the reactivity of the dinuclear CuIIcomplexes towards CO2fixation. The variation observed between the natural and various synthetic peptide systems enables conclusions about structure–reactivity correlations, and our results also provide information on why nature might have chosen oxazolines and thiazoles as incorporated heterocycles.

The synthesis and characterization of a novel dinucleating ligand L (L=4,11‐dimethyl‐1,8‐bis{2‐[N‐(di‐2‐pyridylmethyl)amino]ethyl}cyclam) and its μ‐oxo‐bridged diferric complex [(H2L){FeIII2(O)}(Cl)4]2+are reported. This diiron(III) complex is the first example of a truly functional purple acid phosphatase (PAP) mimic as it accelerates the hydrolysis of the activated phosphomonoester 2,4‐dinitrophenyl phosphate (DNPP). The spectroscopic and kinetic data indicate that only substrates that are monodentately bound to one of the two ferric ions can be attacked by a suitable nucleophile. This is, most probably, a terminal iron(III)‐bound hydroxide. DFT calculations support this assumption and also highlight the importance of secondary interactions, exerted by the protonated cyclam platform, for the positioning and activation of the iron(III)‐bound substrate. Similar effects are postulated in the native enzyme but addressed in PAP mimics for the first time.

The Cu(II) doped MgO system is known to display features indicating behavior intermediate between static and dynamic Jahn−Teller effects at low temperature. The system is interesting as there is a low barrier between equivalent Jahn−Teller distortions in the cubic host lattice. In order to study the geometry of the Cu(II) ion in this system, we have recorded the low temperature magnetic circular dichroism (MCD) and X-ray absorption fine structure (XAFS) spectra. The spectra have been interpreted in terms of the Cu(II) centers distorting the host lattice such that the CuO 6center is a tetragonally elongated octahedron.

The copper(II) coordination chemistry of westiellamide (H3Lwa), as well as of three synthetic analogues with an [18]azacrown‐6 macrocyclic structure but with three imidazole (H3L1), oxazole (H3L2), and thiazole (H3L3) rings instead of oxazoline, is reported. As in the larger patellamide rings, the Nheterocycle‐Npeptide‐Nheterocyclebinding site is highly preorganized for copper(II) coordination. In contrast to earlier reports, the macrocyclic peptides have been found to form stable mono‐ and dinuclear copper(II) complexes. The coordination of copper(II) has been monitored by high‐resolution electrospray mass spectrometry (ESI‐MS), spectrophotometric and polarimetric titrations, and EPR and IR spectroscopies, and the structural assignments have been supported by time‐dependent studies (UV/Vis/NIR, ESI‐MS, and EPR) of the complexation reaction of copper(II) with H3L1. Density functional theory (DFT) calculations have been used to model the structures of the copper(II) complexes on the basis of their spectroscopic data. The copper(II) ion has a distorted square‐pyramidal geometry with one or two coordinated solvent molecules (CH3OH) in the mononuclear copper(II) cyclic peptide complexes, but the coordination sphere in [Cu(H2Lwa)(OHCH3)]+differs from those in the synthetic analogues, [Cu(H2L)(OHCH3)2]+(L=L1, L2, L3). Dinuclear copper(II) complexes ([CuII2(HL)(μ‐X)]+; X=OCH3, OH; L=L1, L2, L3, Lwa) are observed in the mass spectra. While a dipole–dipole coupled EPR spectrum is observed for the dinuclear copper(II) complex of H3L3, the corresponding complexes with H3L (L=L1, L2, Lwa) are EPR‐silent. This may be explained in terms of strong antiferromagnetic coupling (H3L1) and/or a low concentration of the dicopper(II) complexes (H3Lwa, H3L2), in agreement with the mass spectrometric observations.

A new theoretical approach for the calculation of the electronic and molecular structures of octahedrally-coordinated high-spin d 4complexes is described. A prescription for the construction of an effective 3T 1+ 5E ( O) Hamiltonian from the ligand-field matrices of a complex with general trigonal symmetry is given, where the ligand field is parametrized in terms of the angular-overlap model (AOM). The Jahn–Teller matrices for the 3T 1+ ( 5E⊗e) vibronic Hamiltonian are constructed and the lowest eigenvalues are calculated by a numerical method. The model obviates the need to assume a temperature dependence of bonding parameters, inherent to the conventional ligand-field-theory approach and is applicable over the whole range of vibronic-coupling strengths, as demonstrated by example calculations on the [Mn(OD 2) 6] 3+cation and MgO:Cr 2+.

A method for evaluating sample bias in field measurements is presented. Experiments were performed in the field and laboratory to quantify the bias as a function of particle size for the scanning mobility particle sizer and the aerodynamic particle sizer. Sources of bias and sample loss considered in this work were sampling line loss, instrumental differences and inlet efficiencies. Measurement of the bias and sample loss allow for correction of the data acquired in the field, so as to obtain more representative samples of atmospheric concentrations. Substantial losses of fine and ultrafine particle count were observed, with sampling line losses ranging from 10–50 %, dependent on particle size. Only minor line losses were observed for coarse particles (approximately 5 %) because the sampling line was oriented vertically.

A purple acid phosphatase from sweet potato is the first reported example of a protein containing an enzymatically active binuclear Fe-Mn center. Multifield saturation magnetization data over a temperature range of 2 to 200 K indicates that this center is strongly antiferromagnetically coupled. Metal ion analysis shows an excess of iron over manganese. Low temperature EPR spectra reveal only resonances characteristic of high spin Fe(III) centers (Fe(III)-apo and Fe(III)-Zn(II)) and adventitious Cu(II) centers. There were no resonances from either Mn(II) or binuclear Fe-Mn centers. Together with a comparison of spectral properties and sequence homologies between known purple acid phosphatases, the enzymatic and spectroscopic data strongly indicate the presence of catalytic Fe(III)-Mn(II) centers in the active site of the sweet potato enzyme. Because of the strong antiferromagnetism it is likely that the metal ions in the sweet potato enzyme are linked via a μ-oxo bridge, in contrast to other known purple acid phosphatases in which a μ-hydroxo bridge is present. Differences in metal ion composition and bridging may affect substrate specificities leading to the biological function of different purple acid phosphatases.

Real‐time single particle mass spectrometry, or continuous aerosol mass spectrometry, was originally developed in the 1970s for the purpose of identifying the chemical composition of airborne particulate matter in real‐time. Although this technique has continued to evolve throughout the following decades, the fundamental characteristic of this method remains the same, involving the continuous introduction of solid particle or liquid droplets directly into the ion source region of a mass spectrometer. Continuous sample introduction allows for the chemical analysis of single airborne particles in real‐time. A number of mass analyzers have been employed in real‐time single particle mass spectrometry. The original real‐time single particle mass spectrometer used a magnetic sector mass analyzer. Quadrupole, double‐focusing, and ion trap mass spectrometers have also been utilized. The majority of the current real‐time single particle mass spectrometry techniques use time‐of‐flight mass spectrometry. In the literature, a variety of general names have been applied to real‐time single particle mass spectrometry methods. These names include direct‐inlet mass spectrometry, on‐line laser microprobe mass spectrometry, particle analysis by mass spectrometry, particle beam mass spectrometry, and rapid‐single particle mass spectrometry. This review covers real‐time single particle mass spectrometry techniques that were developed from 1973 through 1998, specifically for analyzing airborne particulate matter, including environmental aerosols, biological aerosols, and clean‐room aerosols. Because the majority of the historical and current real‐time single particle mass spectrometers have been employed for atmospheric aerosols, this topic is the primary focus of this review. This review does not include on‐line mass spectrometry methods that are employed as a detector for other instrumental methods, such as liquid chromatography. © 2000 John Wiley & Sons, Inc., Mass Spec Rev 19: 248–274, 2000

Metered dose inhalers produce a fine spray of aerosol particles that are used as an inhalation drug delivery system for a variety of therapeutic purposes. Common analytical methods employed for characterizing the aerosol dosage are typically off-line analyses for both chemical information and particle size distributions, and focus on the bulk aerosol rather than on single particles. Aerosol time-of-flight mass spectrometry offers the capability to analyze the aerosol dose in near real-time, providing both size and chemical information for single particles. Though aerosol time-of-flight mass spectrometry has been used primarily to characterize environmental samples, this is the first demonstration of its bioanalytical capabilities. This paper discusses the characterization of an albuterol metered dose inhaler using both high and low laser power for the desorption/ionization process in order to control the amount of fragmentation observed in the mass spectral analysis. Using high laser power, significant fragmentation occurs with no major ion peaks above mass-to-charge 100 Da. In contrast, lower laser power allows for the observation of protonated and deprotonated parent ion in positive and negative ion analysis respectively. Also, high mass daughter ions are apparent in both positive and negative ion analysis.