Benchmarking the ACEnano Toolbox for Characterisation of Nanoparticle Size and Concentration by Interlaboratory Comparisons

ACEnano is an EU-funded project which aims at developing, optimising and validating methods for the detection and characterisation of nanomaterials (NMs) in increasingly complex matrices to improve confidence in the results and support their use in regulation. Within this project, several interlaboratory comparisons (ILCs) for the determination of particle size and concentration have been organised to benchmark existing analytical methods. In this paper the results of a number of these ILCs for the characterisation of NMs are presented and discussed. The results of the analyses of pristine well-defined particles such as 60 nm Au NMs in a simple aqueous suspension showed that laboratories are well capable of determining the sizes of these particles. The analysis of particles in complex matrices or formulations such as consumer products resulted in larger variations in particle sizes within technologies and clear differences in capability between techniques. Sunscreen lotion sample analysis by laboratories using spICP-MS and TEM/SEM identified and confirmed the TiO₂ particles as being nanoscale and compliant with the EU definition of an NM for regulatory purposes. In a toothpaste sample orthogonal results by PTA, spICP-MS and TEM/SEM agreed and stated the TiO₂ particles as not fitting the EU definition of an NM. In general, from the results of these ILCs we conclude that laboratories are well capable of determining particle sizes of NM, even in fairly complex formulations.     

Chiral Transformation in Protonated and Deprotonated Adipic Acids through Multistep Internal Proton Transfer

Protonated and deprotonated adipic acids (PAA: HOOC? (CH₂)₄? COOH₂⁺ and DAA: HOOC? (CH₂)₄? COO^?) have a charged hydrogen bond under the influence of steric constraint due to the molecular skeleton of a circular ring. Despite the similarity between PAA and DAA, it is surprising that the lowest energy structure of PAA is predicted to have (H₂O???H???OH₂)⁺ Zundel‐like symmetric hydrogen bonding, whereas that of DAA has H₃O⁺ Eigen‐like asymmetric hydrogen bonding. The energy profiles show that direct proton transfer between mirror image structures is unfavorable. Instead, the chiral transformation is possible by subsequent backbone twistings through stepwise proton transfer along multistep intermediate structures, which are Zundel‐like ions for PAA and Eigen‐like ions for DAA. This type of chiral transformation by multistep intramolecular proton transfers is unprecedented. Several prominent OH???O short hydrogen‐bond stretching peaks are predicted in the range of 1000–1700 cm^?1 in the Car–Parrinello molecular dynamics (CPMD) simulations, which show distinctive signatures different from ordinary hydrogen‐bond peaks. The O? H? O stretching peaks in the range of 1800–2700 cm^?1 become insignificant above around 150 K and are almost washed out at about 300 K.     

Linear optical coherence tomography system with a downconverted fringe pattern

Linear optical coherence tomography (LOCT) systems are a simple and robust alternative to time-domain optical coherence tomography systems, but a detector with approximately 10(4) pixels is needed for an imaging depth of 2 mm. We present a new system for LOCT with a special mask attached to the image sensor. The mask essentially performs a downconversion of the spatial frequencies by multiplication with a second spatial frequency. This reduces the fringe frequency of the optical coherence tomography signal so that the signal can be sampled with fewer pixels.     

Linear optical coherence tomography system with extended measurement range

Optical coherence tomography (OCT) sensors traditionally use scanning optical delay lines with moving parts and a single detector. OCT systems with a linear detector array (linear OCT or L-OCT) are simple and robust, but a detector with approximately 10,000 pixels is needed for an imaging depth of 2mm, which is necessary for most biomedical applications. We present a new optical setup for L-OCT with an increased measurement range. An additional grating performs a reduction of the spatial frequencies of the fringe pattern on the detector without loss in the signal-to-noise ratio, so the signal can be sampled with a minimal number of pixels. The theory for this approach is addressed and the first measurements are presented.     

Novel Cofacial Porphyrin-Based Homo- and Heterotrimetallic Complexes of Transition Metals

We present a straightforward and generally applicable synthesis route for cofacially linked homo- and heterotrimetallic trisporphyin complexes. The protocol encompasses synthesising the first aryl-based, trans-o-phenylene trisporphyrin starting from pyrrole and benzaldehyde with an overall yield of 3.6 %. It also allows investigating the respective cis-isomer as the first conformationally restricted planar-chiral trisporphyrin. The free-base ligand was used in subsequent metalation reactions to afford the corresponding homotrimetallic Mn(III)-, Fe(III)-, Ni(II)-, Cu(II)-, Zn(II)- and Pd(II) complexes – additionally, a small adaptation of the protocol resulted in the defined Ni(II)Fe(III)Ni(II) complex in a total yield of 2.3 %. By monitoring Ni(II) insertion into the empty trimeric ligands, we affirmed that the outer porphyrin rings are filled before the internal ring. The molecular species were characterised by ¹H NMR, UV-Vis, photoluminescence, IR, MS, CID, and high-resolution IMS measurements.     

Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis,spectroscopy and static quantum chemistry

In spite of intense, recent research efforts, luminescent transition metal complexes with Earth-abundant metals are still very rare owing to the small ligand field splitting of 3d transition metal complexes and the resulting non-emissive low-energy metal-centered states. Low-energy excited states decay efficiently non-radiatively, so that near-infrared emissive transition metal complexes with 3d transition metals are even more challenging. We report that the heteroleptic pseudo-octahedral d²-vanadium(iii) complex VCl₃(ddpd) (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-yl-pyridine-2,6-diamine) shows near-infrared singlet → triplet spin–flip phosphorescence maxima at 1102, 1219 and 1256 nm with a lifetime of 0.5 μs at room temperature. Band splitting, ligand deuteration, excitation energy and temperature effects on the excited state dynamics will be discussed on slow and fast timescales using Raman, static and time-resolved photoluminescence, step-scan FTIR and fs-UV pump-vis probe spectroscopy as well as photolysis experiments in combination with static quantum chemical calculations. These results inform future design strategies for molecular materials of Earth-abundant metal ions exhibiting spin–flip luminescence and photoinduced metal–ligand bond homolysis.

Vanadium is an abundant and cheap metal but near-infrared luminescent vanadium complexes are extremely rare with largely unexplored photophysics and photochemistry. We delineate the photodynamics of VCl₃(ddpd) to infer novel design strategies.     

On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes

We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO₂)₂H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M₁M₂dcpm₂(HOx)]⁺ with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM]⁺ . These structures are established by comparison of isomer-selective experimental vibrational band patterns displayed by the cryogenically cooled and N₂-tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end-on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side-on docking). Within each class, there are additional isomeric variations according to the orientation of the OH group. This behavior indicates that HOx undergoes strong and directional coordination to [CuCu]⁺ but adopts a more flexible coordination to [AgAg]⁺ . Infrared spectra of the bare ions, fragmentation thresholds and ion mobility measurements are reported to explore the behaviors of the complexes at ambient temperature.     

Mn12-Acetate Complexes Studied as Single Molecules

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn₁₂ coordination clusters of general formula [Mn^III₈Mn^IV₄O₁₂(RCOO)₁₆(H₂O)₄] had been exemplified by bulk samples of the archetypal [Mn^III₈Mn^IV₄O₁₂(CH₃COO)₁₆(H₂O)₄] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn₁₂ system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn₁₂O₁₂(CH₃COO)₁₅(CH₃CN)]⁺ (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn₁₂O₁₂(CH₃COO)₁₅(CH₃CN)]⁺ (1) , [Mn₁₂O₁₂(CH₃COO)₁₆] (2) , [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄] (3) , and the complex in bulk geometry [Mn^III₈Mn^IV₄O₁₂(CH₃COO)₁₆(H₂O)₄] (5) . The found magnetic fingerprints – experiment and theory alike – are of a remarkable robustness: The Mn^IV₄ core bears almost no magnetic anisotropy while the surrounding Mn^III₈ ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn₁₂ core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects.