Simple and effective in situ sample illumination for electron paramagnetic resonance

Illumination into an electron paramagnetic resonance (EPR) spectrometer is commonly carried out through the optical window, perpendicular to the sample and magnetic field. Here we show that significant improvements can be obtained by using the walls of the EPR tube as a light guide, with the light scattered only around the sample-containing area.

Determining and controlling conformational information from orientationally selective light-induced triplet-triplet electron resonance spectroscopy for a set of bis-porphyrin rulers

We recently reported a new technique, light-induced triplet-triplet electron resonance (LITTER) spectroscopy, which allows quantification of the dipolar interaction between the photogenerated triplet states of two chromophores. Here we carry out a systematic LITTER study, considering orientation selection by the detection pulses, of a series of bis-porphyrin model peptides with different porphyrin-porphyrin distances and relative orientations. Orientation-dependent analysis of the dipolar datasets yields conformational information of the molecules in frozen solution which is in good agreement with density functional theory predictions. Additionally, a fast partial orientational-averaging treatment produces distance distributions with minimized orientational artefacts. Finally, by direct comparison of LITTER data to double electron-electron resonance (DEER) measured on a system with Cu(II) coordinated into the porphyrins, we demonstrate the advantages of the LITTER technique over the standard DEER methodology. This is due to the remarkable spectroscopic properties of the photogenerated porphyrin triplet state. This work sets the basis for the use of LITTER in structural investigations of unmodified complex biological macromolecules, which could be combined with Förster resonance energy transfer and microscopy inside cells.

Hexanuclear Ln6 L6 Complex Formation by Using an Unsymmetric Ligand

Multinuclear, self-assembled lanthanide complexes present clear opportunities as sensors and imaging agents. Despite the widely acknowledged potential of this class of supramolecule, synthetic and characterization challenges continue to limit systematic studies into their self-assembly restricting the number and variety of lanthanide architectures reported relative to their transition metal counterparts. Here we present the first study evaluating the effect of ligand backbone symmetry on multinuclear lanthanide complex self-assembly. Replacement of a symmetric ethylene linker with an unsymmetric amide at the center of a homoditopic ligand governs formation of an unusual Ln6 L6 complex with coordinatively unsaturated metal centers. The choice of triflate as a counterion, and the effect of ionic radii are shown to be critical for formation of the Ln6 L6 complex. The atypical Ln6 L6 architecture is characterized using a combination of mass spectrometry, luminescence, DOSY NMR and EPR spectroscopy measurements. Luminescence experiments support clear differences between comparable Eu6 L6 and Eu2 L3 complexes, with relatively short luminescent lifetimes and low quantum yields observed for the Eu6 L6 structure indicative of non-radiative decay processes. Synthesis of the Gd6 L6 analogue allows three distinct Gd⋯Gd distance measurements to be extracted using homo-RIDME EPR experiments.

Title: experimental realisation of multi-qubit gates using electron paramagnetic resonance

Quantum information processing promises to revolutionise computing; quantum algorithms have been discovered that address common tasks significantly more efficiently than their classical counterparts. For a physical system to be a viable quantum computer it must be possible to initialise its quantum state, to realise a set of universal quantum logic gates, including at least one multi-qubit gate, and to make measurements of qubit states. Molecular Electron Spin Qubits (MESQs) have been proposed to fulfil these criteria, as their bottom-up synthesis should facilitate tuning properties as desired and the reproducible production of multi-MESQ structures. Here we explore how to perform a two-qubit entangling gate on a multi-MESQ system, and how to readout the state via quantum state tomography. We propose methods of accomplishing both procedures using multifrequency pulse Electron Paramagnetic Resonance (EPR) and apply them to a model MESQ structure consisting of two nitroxide spin centres. Our results confirm the methodological principles and shed light on the experimental hurdles which must be overcome to realise a demonstration of controlled entanglement on this system.

Direct Comparison between Förster Resonance Energy Transfer and Light-Induced Triplet-Triplet Electron Resonance Spectroscopy

To carry out reliable and comprehensive structural investigations, the exploitation of different complementary techniques is required. Here, we report that dual triplet-spin/fluorescent labels enable the first parallel distance measurements by electron spin resonance (ESR) and Förster resonance energy transfer (FRET) on exactly the same molecules with orthogonal chromophores, allowing for direct comparison. An improved light-induced triplet-triplet electron resonance method with 2-color excitation is used, improving the signal-to-noise ratio of the data and yielding a distance distribution that provides greater insight than the single distance resulting from FRET.

Frequency swept pulses for the enhanced resolution of ENDOR spectra detecting on higher spin transitions of Gd(III)

Half-Integer High Spin (HIHS) systems with zero-field splitting (ZFS) parameters below 1 GHz are generally dominated by the spin |─1/2>→|+1/2 > central transition (CT). Accordingly, most pulsed Electron Paramagnetic Resonance (EPR) experiments are performed at this position for maximum sensitivity. However, in certain cases it can be desirable to detect higher spin transitions away from the CT in such systems. Here, we describe the use of frequency swept Wideband, Uniform Rate, Smooth Truncation (WURST) pulses for transferring spin population from the CT, and other transitions, of Gd(III) to the neighbouring higher spin transition |─3/2>→|─1/2 > at Q- and W-band frequencies. Specifically, we demonstrate this approach to enhance the sensitivity of ¹H Mims Electron-Nuclear Double Resonance (ENDOR) measurements on two model Gd(III) aryl substituted 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) complexes, focusing on transitions other than the CT. We show that an enhancement factor greater than 2 is obtained for both complexes at Q- and W-band frequencies by the application of two polarising pulses prior to the ENDOR sequence. This is in agreement with simulations of the spin dynamics of the system during WURST pulse excitation. The technique demonstrated here should allow more sensitive experiments to be measured away from the CT at higher operating temperatures, and be combined with any relevant pulse sequence.

Fullerene Complexation in a Hydrogen-Bonded Porphyrin Receptor via Induced-Fit: Cooperative Action of Tautomerization and C-H···π Interactions

A supramolecular chiral hydrogen-bonded tetrameric aggregate possessing a large cavity and tetraarylporphyrin substituents was assembled using alternating 4H- and 2H-bonds between ureidopyrimidinone and isocytosine units, respectively. The aggregation mode was rationally shifted from social to narcissistic self-sorting by changing urea substituent size only. The H-bonded tetramer forms a strong complex with C₆₀ guest, at the same time undergoing remarkable structural changes. Namely, the cavity adjusts to the guest via keto-to-enol tautomerization of the ureidopyrimidinone unit and as a result, porphyrin substituents move apart from each other in a scissor blade-like opening fashion. The rearrangement is accompanied by C-H···π interaction between the alkyl solubilizing groups and the nearby placed porphyrin π-systems. The latter interaction was found to be crucial for the guest complexation event, providing energetic compensation for otherwise costly tautomerization. We showed that only the systems possessing sufficiently long alkyl chains capable of interacting with a porphyrin ring are able to form a complex with C₆₀. The structural rearrangement of the tetramer was quantitatively characterized by electron paramagnetic resonance pulsed dipolar spectroscopy measurements using photogenerated triplets of porphyrin and C₆₀ as spin probes. Further exploring the C-H···π interaction as a decisive element for the C₆₀ recognition, we investigated the guest-induced self-sorting phenomenon using scrambled tetramer assemblies composed of two types of monomers possessing alkyl chains of different lengths. The presence of the fullerene guest has enabled the selective scavenging of monomers capable of C-H···π interaction to form homo-tetrameric aggregates.

Magnetic and Electronic Structural Properties of the S3 State of Nature's Water Oxidizing Complex: A Combined Study in ELDOR-Detected Nuclear Magnetic Resonance Spectral Simulation and Broken-Symmetry Density Functional Theory

ELDOR-detected nuclear magnetic resonance (EDNMR) spectral simulations combined with broken-symmetry density functional theory (BS-DFT) calculations are used to obtain and to assign the ⁵⁵Mn hyperfine coupling constants (hfcs) for modified forms of the water oxidizing complex in the penultimate S₃ state of the water oxidation cycle. The study shows that an open cubane form of the core Mn₄CaO₆ cluster explains the magnetic properties of the dominant S = 3 species in all cases studied experimentally with no need to invoke a closed cubane intermediate possessing a distorted pentacoordinate Mn₄ ion as recently suggested. EDNMR simulations found that both the experimental bandwidth and multinuclear transitions may alter relative EDNMR peak intensities, potentially leading to incorrect assignment of hfcs. The implications of these findings for the water oxidation mechanism are discussed.

Modelling Conformational Flexibility in a Spectrally Addressable Molecular Multi-Qubit Model System

Dipolar coupled multi-spin systems have the potential to be used as molecular qubits. Herein we report the synthesis of a molecular multi-qubit model system with three individually addressable, weakly interacting, spin 1 / 2 ${{ 1/2 }}$ centres of differing g-values. We use pulsed Electron Paramagnetic Resonance (EPR) techniques to characterise and separately address the individual electron spin qubits; Cu^II , Cr₇ Ni ring and a nitroxide, to determine the strength of the inter-qubit dipolar interaction. Orientation selective Relaxation-Induced Dipolar Modulation Enhancement (os-RIDME) detecting across the Cu^II spectrum revealed a strongly correlated Cu^II -Cr₇ Ni ring relationship; detecting on the nitroxide resonance measured both the nitroxide and Cu^II or nitroxide and Cr₇ Ni ring correlations, with switchability of the interaction based on differing relaxation dynamics, indicating a handle for implementing EPR-based quantum information processing (QIP) algorithms.

Erythrosin B as a New Photoswitchable Spin Label for Light-Induced Pulsed EPR Dipolar Spectroscopy

We present a new photoswitchable spin label for light-induced pulsed electron paramagnetic resonance dipolar spectroscopy (LiPDS), the photoexcited triplet state of erythrosin B (EB), which is ideal for biological applications. With this label, we perform an in-depth study of the orientational effects in dipolar traces acquired using the refocused laser-induced magnetic dipole technique to obtain information on the distance and relative orientation between the EB and nitroxide labels in a rigid model peptide, in good agreement with density functional theory predictions. Additionally, we show that these orientational effects can be averaged to enable an orientation-independent analysis to determine the distance distribution. Furthermore, we demonstrate the feasibility of these experiments above liquid nitrogen temperatures, removing the need for expensive liquid helium or cryogen-free cryostats. The variety of choices in photoswitchable spin labels and the affordability of the experiments are critical for LiPDS to become a widespread methodology in structural biology.

Light-induced pulsed dipolar EPR spectroscopy for distance and orientation analysis

Measuring distances in biology at the molecular level is of great importance for understanding the structure and function of proteins, nucleic acids and other biological molecules and their complexes. Pulsed Dipolar Spectroscopy (PDS) offers advantages with respect to other methods as it is uniquely sensitive and specific to electronic spin centers and allows measurements in near-native conditions, comprising the in-cell environment. PDS methods measure the electron spin-spin dipolar interaction, therefore they require the presence of at least two paramagnetic centers, which are often stable radicals. Recent developments have introduced transient triplet states, photo-activated by a laser pulse, as spin labels and probes, thereby establishing a new family of techniques-Light-induced PDS (LiPDS). In this chapter, an overview of these methods is provided, looking at the chromophores that can be used for LiPDS and some of the technical aspects of the experiments. A guide to the choice of technique that can yield the best results, depending on the type of system studied and the information required, is provided. Examples of previous LiPDS studies of model systems and proteins are given. Characterization data for the chromophores used in these studies is tabulated to help selection of appropriate triplet state probes in future studies.

Orientation-Selective and Frequency-Correlated Light-Induced Pulsed Dipolar Spectroscopy

We explore the potential of orientation-resolved pulsed dipolar spectroscopy (PDS) in light-induced versions of the experiment. The use of triplets as spin-active moieties for PDS offers an attractive tool for studying biochemical systems containing optically active cofactors. Cofactors are often rigidly bound within the protein structure, providing an accurate positional marker. The rigidity leads to orientation selection effects in PDS, which can be analyzed to give both distance and mutual orientation information. Herein we present a comprehensive analysis of the orientation selection of a full set of light-induced PDS experiments. We exploit the complementary information provided by the different light-induced techniques to yield atomic-level structural information. For the first time, we measure a 2D frequency-correlated laser-induced magnetic dipolar spectrum, and we are able to monitor the complete orientation dependence of the system in a single experiment. Alternatively, the summed spectrum enables an orientation-independent analysis to determine the distance distribution.

Solvent-Dependent Reactivity and Photochemistry of Dinuclear and Mononuclear Platinum(IV) Azido Triazaolato Complexes

Reaction between the platinum(IV) azido complex trans,trans,trans-[Pt(py)2(N3)2(OH)2] (1) and 1,4-diphenyl-2-butyne-1,4-dione 2 in MeCN produces the intermediate peroxide-bridged dimeric platinum(IV) azido triazolato species (5), which has been characterised by X-ray crystallography. However, if the reaction between 1 and 2 is conducted in MeOH it results in decomposition. Over time in MeCN, dimer (5) converts into mononuclear complexes trans,trans,trans-[Pt(py)2(N3)(triazole)(OH)2] (3 a/3 b), which are in dynamic exchange. If resuspended in protic solvents (MeOH,H2O), 3 a/3 b undergo a slow (22 d) irreversible rearrangement to a cyclised platinum(IV) species 4 which contains a formally N,O-chelated ligand. Conversion of 3 a/3 b to 4 in d 4-MeOH can be accelerated (384x) by irradiation with visible light, although continued irradiation also produces N3 . and OH. radicals, and the [4-N3]+ species can be readily detected by ESI-MS. Solvent choice significantly effects both the cycloaddition reaction between 1 and 2, and the stability of the resultant complexes.

Light-Induced Triplet-Triplet Electron Resonance Spectroscopy

We present a new technique, light-induced triplet-triplet electron resonance spectroscopy (LITTER), which measures the dipolar interaction between two photoexcited triplet states, enabling both the distance and angular distributions between the two triplet moieties to be determined on a nanometer scale. This is demonstrated for a model bis-porphyrin peptide that renders dipolar traces with strong orientation selection effects. Using simulations and density functional theory calculations, we extract distance distributions and relative orientations of the porphyrin moieties, allowing the dominant conformation of the peptide in a frozen solution to be identified. LITTER removes the requirement of current light-induced electron spin resonance pulse dipolar spectroscopy techniques to have a permanent paramagnetic moiety, becoming more suitable for in-cell applications and facilitating access to distance determination in unmodified macromolecular systems containing photoexcitable moieties. LITTER also has the potential to enable direct comparison with Förster resonance energy transfer and combination with microscopy inside cells.

Conformational Flexibility of Hybrid [3]- and [4]-Rotaxanes

The synthesis, structures, and properties of [4]- and [3]-rotaxane complexes are reported where [2]-rotaxanes, formed from heterometallic {Cr₇Ni} rings, are bound to a fluoride-centered {CrNi₂} triangle. The compounds have been characterized by single-crystal X-ray diffraction and have the formulas [CrNi₂(F)(O₂C^tBu)₆]{(BH)[Cr₇NiF₈(O₂C^tBu)₁₆]}₃ (3) and [CrNi₂(F)(O₂C^tBu)₆(THF)]{(BH)[Cr₇NiF₈(O₂C^tBu)₁₆]}₂ (4), where B = py-CH₂CH₂NHCH₂C₆H₄SCH₃. The [4]-rotaxane 3 is an isosceles triangle of three [2]-rotaxanes bound to the central triangle while the [3]-rotaxane 4 contains only two [2]-rotaxanes bound to the central triangle. Studies of the behavior of 3 and 4 in solution by small-angle X-ray scattering and atomistic molecular dynamic simulations show that the structure of 3 is similar to that found in the crystal but that 4 has a different conformation to the crystal. Continuous wave and pulsed electron paramagnetic resonance spectroscopy was used to study the structures present and demonstrate that in frozen solutions (at 5 K) 4 forms more extended molecules than 3 and with a wider range of conformations.

An NMR and MD study of complexes of bacteriophage lambda lysozyme with tetra- and hexa-N-acetylchitohexaose

The X-ray structure of lysozyme from bacteriophage lambda (λ lysozyme) in complex with the inhibitor hexa-N-acetylchitohexaose (NAG6) (PDB: 3D3D) has been reported previously showing sugar units from two molecules of NAG6 bound in the active site. One NAG6 is bound with four sugar units in the ABCD sites and the other with two sugar units in the E'F' sites potentially representing the cleavage reaction products; each NAG6 cross links two neighboring λ lysozyme molecules. Here we use NMR and MD simulations to study the interaction of λ lysozyme with the inhibitors NAG4 and NAG6 in solution. This allows us to study the interactions within the complex prior to cleavage of the polysaccharide. 1 HN and 15 N chemical shifts of λ lysozyme resonances were followed during NAG4/NAG6 titrations. The chemical shift changes were similar in the two titrations, consistent with sugars binding to the cleft between the upper and lower domains; the NMR data show no evidence for simultaneous binding of a NAG6 to two λ lysozyme molecules. Six 150 ns MD simulations of λ lysozyme in complex with NAG4 or NAG6 were performed starting from different conformations. The simulations with both NAG4 and NAG6 show stable binding of sugars across the D/E active site providing low energy models for the enzyme-inhibitor complexes. The MD simulations identify different binding subsites for the 5th and 6th sugars consistent with the NMR data. The structural information gained from the NMR experiments and MD simulations have been used to model the enzyme-peptidoglycan complex.

A visible-light photoactivatable di-nuclear PtIV triazolato azido complex

A novel PtIV triazolato azido complex [3]-[N1,N3] has been synthesised via a strain-promoted double-click reaction (SPDC) between a PtIV azido complex (1) and the Sondheimer diyne (2). Photoactivation of [3]-[N1,N3] with visible light (452 nm) in the presence of 5'-guanosine monophosphate (5'-GMP) produced both PtIV and PtII 5'-GMP species; EPR spectroscopy confirmed the production of both azidyl and hydroxyl radicals. Spin-trapping of photogenerated radicals - particularly hydroxyl radicals - was significantly reduced in the presence of 5'-GMP.

Binding of tetracycline to its aptamer determined by 2D-correlated Mn2+ hyperfine spectroscopy

The tetracycline-binding RNA aptamer (TC-aptamer) binds its cognate ligand the antibiotic tetracycline (TC) via a Mg²⁺ or Mn²⁺ ion with high affinity at high divalent metal ion concentrations (K_D=800pM, ⩾10 mM). These concentrations lie above the physiological divalent metal ion concentration of ca. 1 mM and it is known from literature, that the binding affinity decreases upon decreasing the divalent metal ion concentration. This work uses a Mn²⁺ concentration of 1 mM and 1D-hyperfine experiments reveal two pronounced ³¹P couplings from the RNA besides the ¹³C signal of ¹³C-labeled TC. From these 1D-hyperfine data alone, however, no conclusions can be drawn on the binding of TC. Either TC may bind via Mn²⁺ to the aptamer or TC may form a free Mn-TC complex and some Mn²⁺ also binds to the aptamer. In this work, we show using 2D-correlated hyperfine spectroscopy at Q-band frequencies (34 GHz), that the ¹³C and ³¹P signals can be correlated; thus arising from a single species. We use THYCOS (triple hyperfine correlation spectroscopy) and 2D ELDOR-detected NMR (2D electron electron double resonance detected NMR) for this purpose showing that they are suitable techniques to correlate two different nuclear spin species (¹³C and ³¹P) on two different molecules (RNA and TC) to the same electron spin (Mn²⁺). Out of the two observed ³¹P-hyperfine couplings, only one shows a clear correlation to ¹³C. Although THYCOS and 2D EDNMR yield identical results, 2D EDNMR is far more sensitive. THYCOS spectra needed a time factor of ×20 in comparison to 2D EDNMR to achieve a comparable signal-to-noise.

Light-Induced Pulsed EPR Dipolar Spectroscopy on a Paradigmatic Hemeprotein

Light-induced pulsed EPR dipolar spectroscopic methods allow the determination of nanometer distances between paramagnetic sites. Here we employ orthogonal spin labels, a chromophore triplet state and a stable radical, to carry out distance measurements in singly nitroxide-labeled human neuroglobin. We demonstrate that Zn-substitution of neuroglobin, to populate the Zn(II) protoporphyrin IX triplet state, makes it possible to perform light-induced pulsed dipolar experiments on hemeproteins, extending the use of light-induced dipolar spectroscopy to this large class of metalloproteins. The versatility of the method is ensured by the employment of different techniques: relaxation-induced dipolar modulation enhancement (RIDME) is applied for the first time to the photoexcited triplet state. In addition, an alternative pulse scheme for laser-induced magnetic dipole (LaserIMD) spectroscopy, based on the refocused-echo detection sequence, is proposed for accurate zero-time determination and reliable distance analysis.

A novel Pt(iv) mono azido mono triazolato complex evolves azidyl radicals following irradiation with visible light

A novel Pt^IV azido triazolato complex exists as an equilibrium between two species in d₃-MeCN and evolves azide radicals (but not hydroxide radicals) when irradiated with visible light.

The platinum(iv) azido complex trans,trans,trans-[Pt^IV(N₃)₂(OH)₂(py)₂] (1) undergoes cycloaddition with 1,4-diphenyl-2-butyne-1,4-dione (2) under mild, catalyst-free conditions, affording a number of mono and bis click products. The major mono click product (3) exists in MeCN as an equilibrium mixture between two species; 3a and 3b rapidly interconvert through nucleophilic attack of the axial Pt–OH group at the adjacent Ph–CO group. The kinetic and thermodynamic parameters for this interconversion have been measured by selective saturation-transfer NMR spectroscopic experiments and are consistent with cyclisation at the Pt centre. Complex 3b was also characterised by X-ray crystallography. Visible light irradiation (440–480 nm) of 3 in d₃-MeCN produces azidyl radicals (N₃˙), as demonstrated by EPR spin-trapping with DMPO; no generation of hydroxyl radicals was observed. ¹H–¹⁹⁵Pt HMBC NMR confirmed that the photoproducts were Pt^IV rather than Pt^II species, and HPLC was consistent with these being [3–N₃]⁺ species; no facile photoejection of the triazolato ligand was observed, consistent with MS/MS fragmentation of 3. When 3 was irradiated in the presence of 5′-GMP, no 5′-GMP photoproducts were observed, suggesting that complex 3 is likely to exhibit significantly simplified biological activity (release of azidyl radicals but not DNA binding) compared with complex 1.

A Structural Model of a P450-Ferredoxin Complex from Orientation-Selective Double Electron-Electron Resonance Spectroscopy

Cytochrome P450 (CYP) monooxygenases catalyze the oxidation of chemically inert carbon-hydrogen bonds in diverse endogenous and exogenous organic compounds by atmospheric oxygen. This C-H bond oxy-functionalization activity has huge potential in biotechnological applications. Class I CYPs receive the two electrons required for oxygen activation from NAD(P)H via a ferredoxin reductase and ferredoxin. The interaction of Class I CYPs with their cognate ferredoxin is specific. In order to reconstitute the activity of diverse CYPs, structural characterization of CYP-ferredoxin complexes is necessary, but little structural information is available. Here we report a structural model of such a complex (CYP199A2-HaPux) in frozen solution derived from distance and orientation restraints gathered by the EPR technique of orientation-selective double electron-electron resonance (os-DEER). The long-lived oscillations in the os-DEER spectra were well modeled by a single orientation of the CYP199A2-HaPux complex. The structure is different from the two known Class I CYP-Fdx structures: CYP11A1-Adx and CYP101A1-Pdx. At the protein interface, HaPux residues in the [Fe₂S₂] cluster-binding loop and the α3 helix and the C-terminus residue interact with CYP199A2 residues in the proximal loop and the C helix. These residue contacts are consistent with biochemical data on CYP199A2-ferredoxin binding and electron transfer. Electron-tunneling calculations indicate an efficient electron-transfer pathway from the [Fe₂S₂] cluster to the heme. This new structural model of a CYP-Fdx complex provides the basis for tailoring CYP enzymes for which the cognate ferredoxin is not known, to accept electrons from HaPux and display monooxygenase activity.

Exploiting orientation-selective DEER: determining molecular structure in systems containing Cu(ii) centres

Analysis of orientation-selective DEER measurements using Cu(ii) centres in a series of molecules demonstrates its limits and capabilities in structure elucidation.

Chelate-free metal ion binding and heat-induced radiolabeling of iron oxide nanoparticles

A novel reaction for chelate-free, heat-induced metal ion binding and radiolabeling of ultra-small paramagnetic iron oxide nanoparticles (USPIOs) has been established. Radiochemical and non-radioactive labeling studies demonstrated that the reaction has a wide chemical scope and is applicable to p-, d- and f-block metal ions with varying ionic sizes and formal oxidation states from 2+ to 4+. Radiolabeling studies found that 89Zr-Feraheme (89Zr-FH or 89Zr-ferumoxytol) can be isolated in 93 ± 3% radiochemical yield (RCY) and >98% radiochemical purity using size-exclusion chromatography. 89Zr-FH was found to be thermodynamically and kinetically stable in vitro using a series of ligand challenge and plasma stability tests, and in vivo using PET/CT imaging and biodistribution studies in mice. Remarkably, ICP-MS and radiochemistry experiments showed that the same reaction conditions used to produce 89Zr-FH can be employed with different radionuclides to yield 64Cu-FH (66 ± 6% RCY) and 111In-FH (91 ± 2% RCY). Electron magnetic resonance studies support a mechanism of binding involving metal ion association with the surface of the magnetite crystal core. Collectively, these data suggest that chelate-free labeling methods can be employed to facilitate clinical translation of a new class of multimodality PET/MRI radiotracers derived from metal-based nanoparticles. Further, this discovery is likely to have broader implications in drug delivery, metal separation science, ecotoxicology of nanoparticles and beyond.

Inferential Source Attribution from Dust: Review and Analysis

The analysis of dust allows inference of exposures to geographical areas, environments, activities, and processes. This activity of inferential source attribution is distinguished from that of comparative source attribution, where the focus is on the degree of correspondence between two sources in relation to other possible sources. Review of source attribution efforts in the forensic and broader scientific literature shows that most efforts are limited in one or more of four principal ways, which are classified as: (a) methods based on attribution by direct comparison; (b) methods based on closed-set item classification; (c) analysis using restricted methods and characteristics, and (d) requirement of a large sample size. These limitations provide the context for the requirements of more generalized inferential source attribution. Occurring much more rarely, and almost exclusively in the forensic literature, are individual source attribution case reports that have a microscopical, multidisciplinary perspective. Collectively these are an excellent illustration of potential and their common features demonstrate that (a) a diversity of laboratory expertise and methodology is required in order for source attribution to be successful; (b) different tools need to be applied in different cases, and (c) a process must be in place that allows a facile choice among this diversity of tools, in response to the particular investigative problem and the specifics of the samples that are available. Alternative collaborative mechanisms are considered and recommendations are made for related research and programmatic application.

Lipoprotein complex of equine lysozyme with oleic acid (ELOA) interactions with the plasma membrane of live cells

Recent evidence supports the idea that early aggregates, protein, and lipoprotein oligomers but not large aggregates like fibrils that are formed at late stages of the aggregation process are responsible for cytotoxicity. Oligomers can interact with the cellular plasma membrane affecting its structure and/or dynamics or may be taken up by the cells. In either case, disparate cascades of molecular interactions are activated in the attempt to counteract the disturbance induced by the oligomers. If unsuccessful, cell death follows. Here, we study the molecular and cellular mechanisms underlying PC12 cell death caused by ELOA oligomers. ELOA, a lipoprotein complex formed by equine lysozyme (EL) and oleic acid (OA), induces cell death in all tested cell lines, but the actual mechanism of its action is not known. We have used methods with single-molecule sensitivity, fluorescence correlation spectroscopy (FCS), fluorescence cross-correlation spectroscopy (FCCS), and confocal laser scanning microscopy (CLSM) imaging by avalanche photodiodes (APD), so-called APD imaging, to study ELOA interactions with the plasma membrane in live PC12 cells. We detected ELOA accumulation in the cell surroundings, observed ELOA interactions with the plasma membrane, and local changes in plasma membrane lipid dynamics in the vicinity of ELOA complexes. These interactions resulted in plasma membrane rupture, followed by rapid influx and distribution of ELOA inside the already dead cell. In order to probe the ELOA-plasma membrane interaction sites at the molecular and atomic levels, the ELOA complexes were further studied by photochemically induced dynamic nuclear polarization (photo-CIDNP) spectroscopy, nuclear magnetic resonance (NMR) and atomic force microscopy (AFM). We observed a novel mechanism of oligomer toxicity-cell death induced by continuous disturbance of the plasma membrane, eventually causing permanent plasma membrane damage and identified the sites in ELOA that are potentially involved in the interactions with the plasma membrane.

Responsibility as a dimension of HIV prevention normative beliefs: measurement in three drug-using samples

The concept of responsibility was derived originally from principles of morality, as part of a network of rights, duties and obligations. HIV risk-related studies have suggested that a sense of responsibility for condom use to protect a partner is a potentially important predictor of condom use in drug-using populations. We created a four-item scale measuring Self responsibility to use condoms and Partner's responsibility to use condoms. Data were collected from three drug-using samples: crack smokers, HIV seropositive crack smokers in an intervention study in Houston, Texas, and Tanzanian heroin users in Dar es Salaam. Data indicated that the four responsibility items had high alpha coefficients in each sample, and that there were moderate to high intercorrelations between equivalent self and partner responsibility items. There were significant differences in scale scores between the crack smokers and the HIV positive crack smokers and the Tanzanian samples, but no significant differences between the HIV positive and Tanzanian samples. Comparing within the first crack-smoker sample those who were HIV positive and negative showed significant differences in the direction of higher beliefs in responsibility to use condoms in the HIV positive group. These data suggest that responsibility is measurable, holds similar psychometric properties across three samples differing in culture and HIV serostatus, and that condom use responsibility is conceptualized as a measure of general responsibility rather than as a reciprocal self/partner responsibility.

An investigation of condom use by frequency of sex

OBJECTIVES

To examine the association between condom use and frequency of sex across sexual partner types.

METHODS

Data were collected from African American drug users residing in Washington, DC. Participants were asked to provide the first name of the last three partners with whom they had had vaginal sex, to define the type of relationship, the number of times they had had vaginal sex in the last 30 days with each partner, and whether they had used a condom during their last sexual encounter with each partner. Condom use was examined by frequency of sex in the past 30 days controlling for partner type.

RESULTS

Frequency of sexual encounters varied by partner type. The largest number of sexual encounters was with casual partners, followed by commercial and primary partners, respectively. Within partner types, participants had sex most frequently with primary partners. Condom use was lowest within primary partner relationships. Regardless of partner type, condom use varied consistently depending on the frequency of sex with the same partner.

CONCLUSIONS

Condom use is related to the frequency of sex between partners when partner type is controlled. The association between frequency of sex and condom use is independent of partner type, suggesting that partner type may become less influential in determining condom use as the frequency of sex increases. This finding suggests that contextual factors determining condom use go beyond partner type designations and include other relationship variables.

Crack smokers' intention to use condoms with loved partners: intervention development using the theory of reasoned action, condom beliefs, and processes of change

Prevalence rates of HIV infection acquired through heterosexual contacts have risen steadily since 1982. Crack cocaine smokers are at particular risk of HIV infection due to heterosexual exposure. HIV risk reduction interventions seeking to increase condom use among drug users have met with minimal success, and there is a need for interventions to be strongly grounded in psychosocial models of behaviour change. This study presents the results of an investigation of predictors of intention to use condoms and related therapy processes among heterosexual drug users. Data were analyzed from 586 crack smokers recruited in Washington, DC, Miami, Florida, and Collier County, Florida who reported having both primary and casual sex partners. Participants responded to items derived from the theory of reasoned action, the theory of planned behaviour and the transtheoretical model of change. Condom use beliefs and therapy processes used to initiate and maintain condom use were assessed. Outcome expectancies and normative beliefs were the strongest predictors of intention to use condoms with a primary sexual partner. In turn, beliefs that condoms inhibit sexual romance and decrease sexual pleasure strongly predicted outcome expectancies. Therapy processes found to be associated with these constructs included: self-liberation, counter conditioning and stimulus control/reinforcement. Results suggest that HIV risk reduction interventions using a group format and targeting condom beliefs related to sexual romance and pleasure will decrease negative outcome expectancies about condom use. Also, reinforcing attempts to use condoms with intimate partners should increase positive outcome expectancies and intention to initiate or maintain condoms with a primary sexual partner.

Gender differences in the processes of change for condom use: patterns across stages of change in crack cocaine users

Interventions to increase condom use in crack users have had mixed results. For interventions to achieve greater success, the mechanisms of behavior change in this population need to be understood. One mechanism, the processes of change, was examined across stages of change for condom use. Results from the analysis of variance for males and females revealed that stage of change was associated with different levels of three experiential processes: consciousness raising, social liberation and self-reevaluation. However, these analyses found that male and females seem to have different patterns of behavioral process use. Specifically, females in the preparation stage were different from those in precontemplation, whereas this difference was not pronounced in males. In general, people had high levels of experimental processes in every stage of change. The patterns of behavior process use mimicked patterns found for other behaviors with a linear increase across the stages of change. This may indicate that for maintaining condom use, more emotional and behavioral activities are required throughout the process of acquisition and maintenance than are necessary for other health-related activities. Implications of this research are that interventions for increasing condom use in drug users may target behavioral steps differently for males and females.

Attitudes toward lesbian, gay, and bisexual college students: the contribution of pluralistic ignorance, dynamic social impact, and contact theories

Social psychology theories may be useful in developing new interventions to reduce prejudice against lesbian, gay, and bisexual (LGB) college students. For this preliminary study, the authors surveyed 109 college dormitory residents to determine their personal comfort with LGB students and their perceptions of other students' comfort with these individuals. They found widespread evidence of pluralistic ignorance--the students rated themselves as significantly less anti-gay than either their friends or the typical student. Students' attitudes showed geographic clustering, with the building of residence a significant predictor of students' attitudes. Finally, consistent with the contact hypothesis, the perception that 1 or 2 LGB students lived on the same floor or in the same building was associated with more positive attitudes.

Improving attitudes regarding the elderly population: the effects of information and reinforcement for change

PURPOSE

Altering negative attitudes associated with ageism may be possible by giving people accurate information about older people in conjunction with reinforcement for change.

DESIGN AND METHODS

Ninety-nine college students (35 men, 63 women; mean age = 20 years, SD = 2.78) participated in one of three groups: information only, information plus an innocuous discussion group, and information plus a reinforcement-to-change discussion group. The participants' attitudes toward elderly people were measured before, immediately after the intervention, and at a one-month follow-up. Changes in attitudes across groups and time were analyzed using analysis of variance (ANOVA) and t tests.

RESULTS

Information alone produced initial improvements in attitudes in all groups; however, only the group members who received additional reinforcement for change maintained positive attitude changes at one-month follow-up.

IMPLICATIONS

This study supports the premise that negative attitudes toward older people are amendable; however, the new attitude may be lost without reinforcement for change.

A comparison of the reliability of self-reported drug use and sexual behaviors using computer-assisted versus face-to-face interviewing

The purpose of this study was to assess the reliability of responses to HIV risk behavior questions obtained using a voice-enhanced, computer-administered self-interview (audio-CASI) system with touch-screen response compared with those obtained via face-to-face interviews administered by trained and experienced interviewers. Additionally, the study assessed bias that may be attributable to an audio-CASI data collection format. The design of the study was a four-group crossover design with random assignment to one of four study conditions: (a) audio-CASI interview at both intake and retest, (b) face-to-face interview at both intake and retest, (c) audio-CASI interview at intake and face-to-face interview at retest, and (d) face-to-face interview at intake and audio-CASI interview at retest. The study was conducted with a sample of drug users at risk for HIV infection interviewed in nonclinical settings. Data were collected at intake and 48 hours after intake. Analyses show that data obtained using voice-enhanced computer interviewing with touch-screen response are reliable and are comparable to data obtained using interviewer administered face-to-face interviews. However, bias was found to be associated with data collection format and may be partially attributable to the complexity of the questionnaire.

Reducing children's immunization distress in a primary care setting

The purpose of this study was to compare two brief, inexpensive distraction techniques for children receiving immunizations during a county-sponsored immunization clinic. Preschool children (n = 80) were assigned to a party blower intervention, a pinwheel intervention, or a control group. Nurses were instructed to use "standard instructions" for the control group, and to simply provide the distracter and encourage use, but not to spend time trying to train the child or force them to use it, for the other groups. Results of planned comparisons indicated significant party blower results in the children's ratings of reduced distress (P < .01) and the parents' ratings of having to hold their child less strongly (P = .04), and showed it to be more distracting than the pinwheel (P < .02). The overall pattern of results on all rating scales supports the efficacy of using a party blower for reducing children's immunization distress, with minimal staff training and no procedural delay.

Measuring IQ in schizophrenia research: an update of the Quick Test in estimating IQ decline

The WAIS-R measurement of IQ in schizophrenic patients is problematic: the Quick Test of Ammons and Ammons has been used as an alternative despite variability in the accuracy of its estimation of IQ in other groups. We have updated the Quick Test and compared our new version with the original in 44 schizophrenic patients, and both versions with the WAIS-R in a subgroup of 15 patients. Improving the Quick Test materials led to improvement in performance independent of long-term memory function: both versions overestimated WAISR IQ. A previous finding of very high correlation between WAIS-R IQ and Quick Test IQ estimate in schizophrenic patients was not replicated. IQ decline measured with the NART and the Quick Test was less than that using the NART and the WAIS-R. We conclude that the Quick Test has serious limitations as an estimate of IQ in schizophrenic patients, and will bias the assessment of IQ decline so that its extent is apparently less than in reality.

The acceptability of a computer HIV/AIDS risk assessment to not-in-treatment drug users

The purpose of this paper is to report the results of a study assessing the acceptability of a computer HIV risk assessment instrument administered to not-in-treatment drug users. The study asked three questions related to acceptability: (1) are drug users comfortable responding to HIV risk questions using the computer assessment; (2) do drug users feel that they possess the requisite skill to respond to questions using a computer; and (3) do drug users believe that the responses they provide using the computer assessment will remain private and confidential. This study differs from other assessments of the acceptability of computer assisted data collection in that the population of interest has only limited education and interaction with computers. Furthermore, the study was implemented under field conditions. To conduct the study, an existing HIV risk assessment instrument was adapted for use with the computer. Only slight modifications were made to the content of the instrument. To facilitate data collection with this population, audio enhancement and touch screen were used. Three scales measuring comfort, skill and perceived privacy were developed. Results of analysis showed that drug users are comfortable responding to an HIV risk assessment using computer assisted interviewing. Drug users also perceived that they possessed the requisite skill to successfully complete the interview. And, study participants reported that they believed that their responses using the computer interview would remain private and confidential. Only minor differences in scale scores based on sociodemographic characteristics were found among study participants. Implications of the findings are discussed.

Introduction of HIV into drug injector networks outside AIDS epicentres

Injection drug users (IDUs) continue to be at risk for HIV infection despite high levels of knowledge about how human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) is transmitted. Yet, among not-in-treatment injection drug users, the chances of becoming infected with HIV vary substantially. Information regarding the factors that facilitate the introduction of HIV into networks of drug injectors in low HIV seroprevalence cities is urgently needed. This study examines the factors related to HIV seroprevalence in a large (n=9492), multi-site sample of IDUs recruited in 11 low seroprevalence cities. Univariate and multivariate associations between drug injection and sexual behaviours and travel to an AIDS epicentre were examined. Results show that, next to male-to-male sexual contact, having sex at least twice in an AIDS epicentre was the strongest predictor of HIV infection. Also associated with higher odds of being HIV-positive were racial/ethnic characteristics, daily drug injection, and injecting drugs in an AIDS epicentre. These results confirm that travelling to an AIDS epicentre and having sex or injecting drugs play a large role in the introduction of HIV into drug injector networks in low seroprevalence cities.

Descriptive analysis of eating behavior in school-age children with cystic fibrosis and healthy control children

STUDY OBJECTIVE

To investigate calorie intake, behavioral eating styles, and parent perception of eating behavior of school-age children with cystic fibrosis (CF) compared with healthy peers.

DESIGN

A two-group comparison study.

SETTING

A clinical sample of 28 school-age children with CF and a community sample of 28 healthy peers matched for age (6 to 12 years) and socioeconomic status.

MEASUREMENTS AND MAIN RESULTS

The children with CF consumed more calories per day (2175 cal/d) than the control children (1875 cal/d) and achieved a significantly higher recommended daily allowance (RDA) of energy (128% of the RDA) than the control children (91.61% of the RDA). Fifty-four percent of the CF sample were achieving the CF dietary recommendations of 120% of the RDA. Despite this energy intake, the CF sample was significantly below the control sample on weight (24.56 vs 31.23 kg), height (125.48 vs 133.06 cm), and z score for weight (-0.811 vs 0.528) and height (-0.797 vs 0.371). On measures of behavioral eating style, the CF sample had significantly longer meals (23.90 min) than the control sample (17.34 min) and had a significantly slower pace of eating (43.27% 10-second intervals with bites) than the control sample (51.29% 10-second intervals with bites) but did not differ significantly on the number of calories consumed during dinner. On a measure of parent report of mealtime behaviors, parents of the children with CF rated mealtime behavior problems of "dawdles" and "refuses food" as more intense (mean, 3. 46) than did the parents of control children (mean, 2.67). For the CF sample, a significant correlation was found between the parent intensity ratings of problem behavior in general and meal duration (r = .48), and a significant negative correlation was found between the parent intensity ratings of problem mealtime behaviors and the percentage of intervals with bites (pace of meal) (r = -.533).

CONCLUSIONS

Although the school-age children with CF were consuming more calories per day than their healthy peers, and more than 50% of the children in the CF sample were at or above the CF dietary recommendations, the children in the CF sample were significantly below the control children on measures of weight and height. The behavioral data suggest that increased caloric intake is not without cost, because the CF sample spent an additional 7 minutes per day at dinner and ate their meals at a slower pace than their healthy peers. These data were associated with higher intensity ratings of mealtime behaviors by parents of children with CF. These findings point to the need for individualized assessment of energy needs for school-age children with CF and comprehensive programs that teach parents behavioral strategies to motivate their children to meet these higher energy requirements in an adaptive manner.

An assessment of the risks of syphilis and HIV infection among a sample of not-in-treatment drug users in Houston, Texas

The research presented in this paper details the results of an assessment of the risk factors associated with having a positive syphilis or HIV serology. The study was conducted using a sample of not-in-treatment drug users volunteering to participate in an HIV risk reduction intervention. The sample was composed of individuals who had injected drugs within 30 days or smoked crack cocaine 48 hours prior to participation in the study. Study participants were approximately 75% male and 66% African-American. All participants provided a blood sample to be tested for HIV and syphilis. Analysis of risk was conducted using univariate and multivariate statistical methods. Multivariate analysis of blood results showed that women, African-Americans, and those having a positive blood test for HIV were at higher odds of having a positive syphilis test. Analysis also showed that being a gay or bisexual male, having a history of drug injection, having less than a high-school education, having a history of trading sex for money, being African-American, and having a positive blood test for syphilis significantly increased the odds of a positive HIV test. Implications for HIV and STD prevention are discussed.

HIV risk in intravenous drug users and crack cocaine smokers: predicting stage of change for condom use

This study examined the utility of the Transtheoretical Model of Change and the AIDS Risk Reduction Model for predicting condom use with not-in-treatment crack cocaine smokers and intravenous drug users. The sample included 265 participants; 99 reported having casual partners and 166 reported having main partners. All participants must have used drugs in the preceding 48 hr and received no drug treatment for at least 1 year. Participants were grouped into 3 stages of change; precontemplation, contemplation, and action. Logistic regression analyses indicated that both the benefits of change and condom assertiveness varied across the stages of change for main and casual partners, whereas the costs of change were important for predicting stage only with main partners. Age was a significant predictor of stage with casual partners, whereas ethnicity and nonherpes sexually transmitted diseases significantly predicted stage with main partners. The utility of the stages of change for choosing intervention strategies and the need for more qualitative and longitudinal research to determine additional predictors of intention to use condoms are discussed.

HIV risk in intravenous drug users and crack cocaine smokers: predicting stage of change for condom use

This study examined the utility of the Transtheoretical Model of Change and the AIDS Risk Reduction Model for predicting condom use with not-in-treatment crack cocaine smokers and intravenous drug users. The sample included 265 participants; 99 reported having casual partners and 166 reported having main partners. All participants must have used drugs in the preceding 48 hr and received no drug treatment for at least 1 year. Participants were grouped into 3 stages of change; precontemplation, contemplation, and action. Logistic regression analyses indicated that both the benefits of change and condom assertiveness varied across the stages of change for main and casual partners, whereas the costs of change were important for predicting stage only with main partners. Age was a significant predictor of stage with casual partners, whereas ethnicity and nonherpes sexually transmitted diseases significantly predicted stage with main partners. The utility of the stages of change for choosing intervention strategies and the need for more qualitative and longitudinal research to determine additional predictors of intention to use condoms are discussed.

Eating in preschool children with cystic fibrosis and healthy peers: behavioral analysis

STUDY OBJECTIVE

To investigate calorie intake, behavioral eating styles, and parent perception of eating behavior of preschool children with cystic fibrosis (CF) compared with healthy peers.

DESIGN

A two group comparison study.

SETTING

A clinical sample of 32 preschool children with CF (aged 2 to 5 years) and a community sample of 29 healthy peers matched for age and socioeconomic status.

MEASUREMENTS AND MAIN RESULTS

The two groups did not differ on the total number of calories consumed per day or the percentage of calories derived form fat. The CF sample achieved a significantly higher percent of the recommended daily allowance (RDA) of energy (95% RDA) than the control group (84% RDA), P < .05, but did not achieve the CF dietary recommendations of 120% RDA. On measures of behavioral eating style, the CF sample had significantly longer meals (24.63 min) than the control group (18.57 min), P < .01, but did not differ on pace of eating or calories consumed per bite. On a measure of parent report of mealtime behavior, parents of the CF sample identified mealtime behaviors of "dawdles" and "refuses food" as more problematic (M = .93) than parents of control children (M = .22), P < .05.

CONCLUSIONS

While preschool children with CF consume as much or more than healthy peers, they are not achieving the CF dietary recommendations. Furthermore, there appear to be behavioral differences in eating and parent perception of CF children's eating that may contribute to the failure to achieve dietary recommendations.

Increasing calorie consumption in children with cystic fibrosis: replication with 2-year follow-up

Three mildly malnourished children with cystic fibrosis and their parents participated in a behavioral group-treatment program that focused on promoting and maintaining increased calorie consumption. Treatment included nutritional education, gradually increasing calorie goals, contingency management, and relaxation training, and was evaluated in a multiple baseline design across four meals. Children's calorie intake increased across meals, and total calorie intake was 32% to 60% above baseline at posttreatment. Increased calorie consumption was maintained at the 96-week follow-up (2 years posttreatment). The children's growth rates in weight and height were greater during the 2 years following treatment than the year prior to treatment. Increases in pace of eating and calories consumed per minute were also observed 1 year posttreatment. These findings replicated and extended earlier research supporting the efficacy of behavioral intervention in the treatment of malnutrition in children with cystic fibrosis.

A behavioral approach to increasing calorie consumption in children with cystic fibrosis

To increase calorie consumption of 5 mildly malnourished children with cystic fibrosis (CF), intervention was implemented in multiple baseline fashion across snack and three meals. Intervention involved nutritional education establishing gradually increasing calories goals, teaching parents contingency management strategies, and a reward system for achieving calorie goals. Following 6 treatment sessions, the children's calorie intake increased across meals and total calorie intake was 25 to 43% above baseline. The calorie increase was maintained at 9-month follow-up. Significant changes in weight and height were made during treatment and the year following intervention. The results suggest that the long-term oral intake of children with CF can be modified by a short-term behavioral intervention.