Pavel Matousek

This proof of concept study demonstrates the application of transmission Raman spectroscopy (TRS) to the non-invasive and non-destructive quantification of low levels (0.62-1.32% w/w) of an active pharmaceutical ingredient's polymorphic forms in a pharmaceutical formulation. Partial least squares calibration models were validated with independent validation samples resulting in prediction RMSEP values of 0.03-0.05% w/w and a limit of detection of 0.1-0.2% w/w. The study further demonstrates the ability of TRS to quantify all tablet constituents in one single measurement. By analysis of degraded stability samples, sole transformation between polymorphic forms was observed while excipient levels remained constant. Additionally, a beam enhancer device was used to enhance laser coupling to the sample, which allowed comparable prediction performance at 60 times faster rates (0.2s) than in standard mode.

This article reviews emerging Raman techniques for deep, non-invasive characterisation of biological tissues. As generic analytical tools, the new methods pave the way for a host of new applications including non-invasive bone disease diagnosis, chemical characterisation of 'stone-like' materials in urology and cancer detection in a number of organs.

We demonstrate that picosecond time-resolved photoelectron angular distributions (PADs) provide a sensitive probe of an evolving alignment in an excited polyatomic molecule. Such an evolving alignment can be caused by pure rotational recurrences or by rotation-vibration coupling. If a molecule is chosen for which the rotational recurrence times are well-known the method provides a means of establishing the mechanism of intramolecular vibrational energy redistribution (IVR). In the case of S1 para-difluorobenzene we observe striking alignment changes as a function of pump-probe time delay which we attribute to rotationally mediated IVR.

The lowest allowed electronic transition of fac-[Re(Cl)(CO)3(bopy)2] (bopy ) 4-benzoylpyridine) has a Re f bopy MLCT character, as revealed by UV-vis and stationary resonance Raman spectroscopy. Accordingly, the lowestlying, long-lived, excited state is Re f bopy 3MLCT. Electronic depopulation of the Re(CO)3 unit and population of a bopy ð* orbital upon excitation are evident by the upward shift of î(CtO)

In the present study, the possibility of employing spatially offset Raman spectroscopy (SORS) in the qualitative and quantitative characterization of quality parameters of salmon through the skin has been explored. A laboratory-based SORS setup comprising an 830 nm laser was employed, and intact samples and model samples made of salmon tissue constituents were used to investigate the penetration of Raman signals through the dark and light part of salmon skin. Intact salmon samples with both dark and light skin were measured at different spatial offsets. When using spatial offsets in the range of 5-6 mm, the results clearly show that information regarding fatty acid composition and carotenoid content could be obtained from both dark and light parts of the skin. Similar information could not be obtained using conventional backscattering Raman spectroscopy. Model samples of ground salmon spiked with either solutions of carotenoids or a range of vegetable oils were also measured, and at a spatial offset of 5 mm, a clear relationship between Raman carotenoid band intensities and carotenoid concentrations in the model samples was revealed. In addition, high correlations for the estimation of iodine values (i.e., fatty acid unsaturation) could be obtained for SORS measurements through light and dark parts of the salmon skin. A crude estimate suggested that information from around 5 mm beneath the surface area of the salmon skin could be obtained. The choice of a laser line in the near-infrared region is a major prerequisite for successful through-skin analysis of salmon. This feasibility study could pave the way for future Raman analysis of intact salmon.

A simple procedure for the recovery of deep subsurface Raman spectra in stratified turbid samples by defocusing a conventional Raman instrument is presented. The method is based on effects present with spatially offset Raman spectroscopy (SORS) and, although not as efficient as the standard SORS approach, it permits a simple way of recovering subsurface Raman spectra from less challenging samples. Demonstration of the effect is performed using a standard SORS device and a commercial Raman instrument on the noninvasive measurement of paracetamol tablets held within a nontransparent white plastic bottle.

A recently developed micrometer-scale spatially offset Raman spectroscopy (μ-SORS) method provides a new analytical capability for investigating non-destructively the chemical composition of sub-surface, micrometer-scale thickness, diffusely scattering layers at depths beyond the reach of conventional confocal Raman microscopy. Here, we demonstrate experimentally, for the first time, the capability of μ-SORS to determine whether two detected chemical components originate from two separate layers or whether the two components are mixed together in a single layer. Such information is important in a number of areas, including conservation of cultural heritage objects, and is not available, for highly turbid media, from conventional Raman microscopy, where axial (confocal) scanning is not possible due to an inability to facilitate direct imaging within the highly scattering sample. This application constitutes an additional capability for μ-SORS in addition to its basic capacity to determine the overall chemical make-up of layers in a turbid system.

The results of electrochemical measurements, density-functional theory calculations, emission and time-resolved IR (TRIR) spectroscopic studies for fac-[ReCl(CO)3(dppz-X2)], (dppz = dipyrido[3,2-a:2',3'-c]phenazine; X = CH3, H, F, Cl, CF3) are reported. For all complexes the calculations show that the lowest unoccupied molecular orbital (LUMO) is a phenazine based orbital localized on the dppz ligand. We observe that three different excited states, IL pi pi*, metal-to-ligand charge-transfer (MLCT) (phen), and MLCT (phz), are formed depending upon the substituent on the dppz ligand and on the nature of the solvent. This means that both the energy and the nature of the photophysically active state(s) can be tuned by both chemical modification of dppz ligand and solvent properties. The excited-state dynamics in these systems is directly related to the mechanism of the "light switch effect", and ps-TRIR has allowed a deeper insight into this mechanism by being able to directly monitor the change in the population of the higher lying emissive phen-type (3)MLCT and IL pi pi* states and the dark (3)MLCT (phz) state depending on the different environmental factors.

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.

Here we propose and demonstrate a new analytical method for the noninvasive measurement of subsurface temperatures within diffusely scattering (turbid) media in combination with high chemical selectivity. The method is based upon the first combination of Stokes/anti-Stokes light scattering measurements and the recently developed spatially offset Raman spectroscopy (SORS). This approach has been conceptually demonstrated by measuring material-specific temperatures within a turbid sublayer of poly(tetrafluoroethylene) (PTFE) through a highly diffusely scattering overlayer of poly(oxymethylene) POM (3 mm thick). Root-mean-square errors (RMSEs) of 0.16-0.71 °C were achieved when measuring temperatures over ranges between 24 and 45 °C. This unique capability complements the array of existing, predominantly surface-based, temperature measurement techniques. It paves the way for a wide range of topical applications including subsurface, chemically specific, noninvasive temperature measurem...

We demonstrate the potential of Raman spectroscopy to detect cocaine concealed inside transparent glass bottles containing alcoholic beverages. A clear Raman signature of cocaine with good signal-to-noise was obtained from a approximately 300 g solution of adulterated cocaine (purity 75%) in a 0.7 L authentic brown bottle of rum with 1 s acquisition time. The detection limit was estimated to be of the order of 9 g of pure cocaine per 0.7 L (approximately 0.04 moles L(-1)) with 1 s acquisition time. The technique holds great promise for the fast, non-invasive, detection of concealed illicit compounds inside beverages using portable Raman instruments, thus permitting drug trafficking to be combated more effectively.

Raman Spectroscopy has become an important technique for assessing the composition of excised sections of bone, and is currently being developed as an in vivo tool for transcutaneous detection of bone disease using spatially offset Raman spectroscopy (SORS). The sampling volume of the Raman technique (and thus the amount of bone material interrogated by SORS) depends on the nature of the photon scattering in the probed tissue. Bone is a complex hierarchical material and to date little is known regarding its diffuse scattering properties which are important for the development and optimization of SORS as a diagnostic tool for characterizing bone disease in vivo. SORS measurements at 830 nm excitation wavelength are carried out on stratified samples to determine the depth from which the Raman signal originates within bone tissue. The measurements are made using a 0.38 mm thin Teflon slice, to give a pronounced and defined spectral signature, inserted in between layers of stacked 0.60 mm thin equine bone slices. Comparing the stack of bone slices with and without underlying bone section below the Teflon slice illustrated that thin sections of bone can lose appreciable number of photons through the unilluminated back surface. The results show that larger SORS offsets lead to progressively larger penetration depth into the sample; different Raman spectral signatures could be retrieved through up to 3.9 mm of overlying bone material with a 7 mm offset. These findings have direct impact on potential diagnostic medical applications; for instance on the detection of bone tumors or areas of infected bone.

Raman spectroscopy was used to show that across 10 cm of diaphyseal (mid-shaft) cortical bone the phosphate-to-amide I ratio (a measure of the mineral to collagen ratio) can vary by as much as 8%, and the phosphate-to-carbonate ratio (a measure of carbonate inclusion in mineral crystals) by as much as 5%. The data are preliminary but are important because they reveal a spatial variation at a scale that is much larger than many of the spectral maps reported in the literature to date. Thus they illustrate natural variation in chemical composition that could have been overlooked in such studies or could have appeared as an undue error where the overall composition of the bone was investigated. Quantifying the variation in mid-shaft cortical bone at the millimeter/centimeter scale reduces the possibility of natural heterogeneity obscuring the average bone composition, or being mistaken for experimental signal, and results in an improvement in the sampling accuracy analogous to that obta...

Raman spectroscopy has recently seen major advances in the area of deep non-invasive characterisation of diffusely scattering samples; this progress is underpinned by the emergence of spatially offset Raman spectroscopy and associated renaissance of transmission Raman spectroscopy permitting the characterisation of diffusely scattering samples at depths not accessible by conventional Raman spectroscopy. Examples of emerging research activities include non-invasive diagnosis of bone disease and cancer, rapid quality control of pharmaceutical formulations and security screening of explosives and counterfeit drugs through unopened translucent bottles. This article reviews this field focusing on recent developments with high societal relevance.

The triplet metal-to-ligand charge transfer ((3)MLCT) dynamics of two structurally characterized Re(I)(CO)(3)(phen)(HisX)-modified (phen = 1,10-phenanthroline; X = 83, 109) Pseudomonas aeruginosa azurins have been investigated by picosecond time-resolved infrared (TRIR) spectroscopy in aqueous (D(2)O) solution. The (3)MLCT relaxation dynamics exhibited by the two Re(I)-azurins are very different from those of the sensitizer [Re(I)(CO)(3)(phen)(im)](+) (im = imidazole). Whereas the Re(I)(CO)(3) intramolecular vibrational relaxation in Re(I)(CO)(3)(phen)(HisX)Az (4 ps) is similar to that of [Re(I)(CO)(3)(phen)(im)](+) (2 ps), the medium relaxation is much slower ( approximately 250 vs 9.5 ps); the 250-ps relaxation is attributable to reorientation of D(2)O molecules as well as structural reorganization of the rhenium chromophore and nearby polar amino acids in each of the modified proteins.

ABSTRACT We present the picosecond time-resolved resonance Raman (ps-TR3) spectra of the first excited singlet state (S1) of cis-stilbene (d0), fully deuterated cis-stilbene (d12) and α,α′-d2-cis-stilbene (d2) measured in hexane at pump and probe wavelengths 267 and 630 nm, respectively. The main observation is that in the lower wavenumber region the spectra are dominated by a second-order overtone progression originating from a 229 cm−1 fundamental band for the S1d0cis-stilbene. The observed low-wavenumber modes of the excited cis-stilbene are substantially more resonantly enhanced than the modes around 1600 cm−1. Copyright © 2003 John Wiley & Sons, Ltd.

The synthesis of a cyclometallated Pt(II) thiolate carbonyl complex Pt(thpy)(CO)(mts), (thpy = 2-(2'-thienyl)-pyridinate, mts = methylthiosalicylate) is reported. A combination of emission and time-resolved infrared (TRIR) techniques revealed for both Pt(thpy)(CO)(mts) and its chloride analogue Pt(thpy)(CO)Cl the predominant intra 2-(2'-thienyl)-pyridinate 3pi pi* character of the lowest electronic excited state. The unusually short lifetime (780 ps) of the intraligand 3pi pi* lowest excited state of Pt(thpy)(CO)(mts) indicates that this electronic state is influenced by another close-lying excited state, probably charge-transfer in origin.

The photophysics of fac-[(dppz-12-NO2)Re(CO)3(4-Me2Npy)]+ in CH3CN have been investigated using picosecond time-resolved IR (ps-TRIR) spectroscopy, to reveal the first example of a Re(I)-dppz complex with a charge separated lowest-lying excited state.