Characterisation and classification of automotive clear coats with Raman spectroscopy and chemometrics for forensic purposes

The clear coats from a collection of automotive paint samples of 139 vehicles, covering a range of Australian and international vehicle manufacturers and sold in Western Australia, were characterised using FT‐Raman spectroscopy. Principal component analysis (PCA) revealed 19 distinct classes that were associated with the vehicles' manufacturer and model, and in the case of Australian manufacturers, the years of manufacture. Linear discriminant analysis based on the PCA groupings gave excellent discrimination between the groups with 96.9% of the calibration set and 97.6% of the validation set being correctly classified. Although the sample set comprised only vehicles available in Australia, the methodology used is universal and hence applicable in any jurisdiction that is willing and able to generate a statistically significant data set and maintain and update it as new vehicles appear on the market. A FT‐Raman spectroscopy‐based database would rapidly provide information regarding vehicle origin and manufacture and hence generate investigative leads for questioned paint samples found at incident sites. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparison of quartz and Teflon filters for simultaneous collection of size-separated ultrafine aerosol particles and gas-phase zero samples

In this research, the two most common filter media, quartz and Teflon, were tested to obtain information about the possible adsorption of gas-phase compounds onto filters during long sample collection of atmospheric aerosols. Particles of nanometer-size for off-line chemical characterization were collected using a recently introduced differential mobility analyzer for size separation. Samples were collected at an urban site (Helsinki, SMEARIII station) during spring 2010. Sampling time was 4 to 10 days for particles 50, 40, or 30 nm in diameter. Sample air flow was 4 L/min. The sampling setup was arranged so that two samples were obtained for each sampling period almost simultaneously: one containing particles and adsorbed gas-phase compounds and one containing adsorbed gas-phase compounds only. Filters were extracted and analyzed for the presence of selected carboxylic acids, polyols, nitrogen-containing compounds, and aldehydes. The results showed that, in quartz filter samples, gas-phase adsorption may be responsible for as much as 100% of some compound masses. Whether quartz or Teflon, simultaneous collection of gas-phase zero samples is essential during the whole sampling period. The dependence of the adsorption of gas-phase compounds on vapor pressure and the effect of adsorption on the deposited aerosol layer are discussed.     

Regioselective acylation of aminoresorcinarenes

The acid catalyzed hydrolytic cleavage of the oxazine rings in the readily available tetraoxazine derivatives of resorcinarenes results in tetraaminoresorcinarenes. A similar process applied to C₂-symmetrical bisoxazine resorcinarene tetratosylates affords C_2v-symmetrical resorcinarenediamines. The mild acylation of these resorcinareneamines with BOC-anhydride or para-nitrophenyl ester proceeds selectively at the nitrogen atoms without affecting the hydroxyl groups. Most of the resulting resorcinareneamides are thus obtained in preparative yields and can be easily purified by simple crystallizations. In the crystalline state the compounds obtained are found to bind chloride anions through hydrogen bonds and electrostatic interactions and to display a chiral arrangement of hydrogen bonded functional groups at the wide rim of the macrocycle.     

Preparation of dimethoxyborane and analysis by Fourier transform infrared spectroscopy

Dimethoxyborane was prepared by the reaction of trimethoxyboroxine, sodium borohydride and trimethyl borate in diethylene glycol dimethyl ether solvent at 70°C under atmospheric pressure followed by distillation to increase the purity and analyzed in liquid phase by FT-IR. The concentration of dimethoxyborane was identified by hydrolysis with water, which yields boric acid, methanol and hydrogen, whereas the generated hydrogen was analyzed by the mass detector of a volumetric flow apparatus. The FT-IR absorbance peak area showed a linear dependence on dimethoxyborane concentration in the wavenumber range 873 to 950 cm⁻¹ for samples with dimethoxyborane concentrations 0 to 6.2 wt% in trimethyl borate. Data fitting using the least square method gave an R ² value of 97%.     

Photodissociation of formyl fluoride in rare gas matrixes

Photodissociation of formyl fluoride (HCOF) is studied in Ar, Kr, and Xe matrixes at 248 and 193 nm excitation by following spectral changes in the infrared absorption spectra. In all matrixes, the main photodissociation products are CO/HF species, including CO-HF and OC-HF complexes and thermally unstable CO/HF species (a distorted CO/HF complex or a reaction intermediate), which indicate negligible cage exit of atoms produced via the C-F and C-H bond cleavage channels. However, the observation of traces of H, F, CO, CO(2), F(2)CO, FCO, and HRg(2)(+) (Rg = Kr or Xe) in Kr and Xe matrixes would imply some importance of other reaction channels too. The analysis of the decay curves of the precursor shows that dissociation efficiency of HCOF increases as Ar < Kr < Xe, the difference being the factor of 10 between Ar and Xe. Moreover, HCOF dissociates 20-50 times faster at 193 nm compared to 248 nm. Interestingly, whereas the CO/HF species are stable with respect to photolysis in Ar, they photobleach in Kr and Xe matrixes at 248 and 193 nm, even though the first excited states of CO and HF are not energetically accessible with 193 and 248 nm photons. In krypton matrix, the photodissociation of CO/HF species at 248 nm is observed to be a single photon process. Quantum chemical calculations of electronic excitation energies of CO-HF and OC-HF complexes show that the electronic states of HF and CO mostly retain their diatomic nature in the pair. This clearly demonstrates that photodissociation of CO/HF complexes is promoted by the surrounding rare gas lattice.     

High Accuracy Protein Structures from Minimal Sparse Paramagnetic Solid‐State NMR Restraints

There is a pressing need for new computational tools to integrate data from diverse experimental approaches in structural biology. We present a strategy that combines sparse paramagnetic solid‐state NMR restraints with physics‐based atomistic simulations. Our approach explicitly accounts for uncertainty in the interpretation of experimental data through the use of a semi‐quantitative mapping between the data and the restraint energy that is calibrated by extensive simulations. We apply our approach to solid‐state NMR data for the model protein GB1 labeled with Cu²⁺‐EDTA at six different sites. We are able to determine the structure to 0.9 Å accuracy within a single day of computation on a GPU cluster. We further show that in some cases, the data from only a single paramagnetic tag are sufficient for accurate folding.     

Subcomponent Self-Assembly of a Cyclic Tetranuclear FeII Helicate in a Highly Diastereoselective Self-Sorting Manner

An enantiomerically pure diamine based on the 4,15-difunctionalized [2.2]paracyclophane scaffold and 2-formylpyridine self-assemble into an optically pure cyclic metallosupramolecular Fe₄L₆ helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self-assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple-stranded helicate, and hence, leads to the larger strain-free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic chiral self-sorting manner given the fact that the assembly contains ten stereogenic elements, which can in principle give rise to 149 different diastereomers. The metallosupramolecular aggregates could be characterized by NMR, UV/Vis and CD spectroscopy, mass spectrometry, and X-ray crystallography.