Publications by authors named "Freek Ariese"

75 Publications

Characterization of a liquid-core waveguide cell for studying the chemistry of light-induced degradation.

Analyst 2021 May;146(10):3197-3207

Analytical Chemistry Group, van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands and Conservation and Restoration of Cultural Heritage, Amsterdam School for Heritage, Memory and Material Culture, University of Amsterdam, P.O. Box 94552, 1091 GN, Amsterdam, The Netherlands.

Many organic compounds undergo changes under the influence of light. This might be beneficial in, for example, water purification, but undesirable when cultural-heritage objects fade or when food ingredients (e.g., vitamins) degrade. It is often challenging to establish a strong link between photodegradation products and their parent molecules due to the complexity of the sample. To allow effective study of light-induced degradation (LID), a low-volume exposure cell was created in which solutes are efficiently illuminated (especially at low concentrations) while simultaneously analysed by absorbance spectroscopy. The new LID cell encompasses a gas-permeable liquid-core waveguide (LCW) connected to a spectrograph allowing collection of spectral data in real-time. The aim of the current study was to evaluate the overall performance of the LID cell by assessing its transmission characteristics, the absolute photon flux achieved in the LCW, and its capacity to study solute degradation in presence of oxygen. The potential of the LID set-up for light-exposure studies was successfully demonstrated by monitoring the degradation of the dyes eosin Y and crystal violet.
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http://dx.doi.org/10.1039/d1an00272dDOI Listing
May 2021

Multimodal, label-free fluorescence and Raman imaging of amyloid deposits in snap-frozen Alzheimer's disease human brain tissue.

Commun Biol 2021 04 15;4(1):474. Epub 2021 Apr 15.

Department of Physics and Astronomy, LaserLaB Amsterdam, VU Amsterdam, Amsterdam, The Netherlands.

Alzheimer's disease (AD) neuropathology is characterized by hyperphosphorylated tau containing neurofibrillary tangles and amyloid-beta (Aβ) plaques. Normally these hallmarks are studied by (immuno-) histological techniques requiring chemical pretreatment and indirect labelling. Label-free imaging enables one to visualize normal tissue and pathology in its native form. Therefore, these techniques could contribute to a better understanding of the disease. Here, we present a comprehensive study of high-resolution fluorescence imaging (before and after staining) and spectroscopic modalities (Raman mapping under pre-resonance conditions and stimulated Raman scattering (SRS)) of amyloid deposits in snap-frozen AD human brain tissue. We performed fluorescence and spectroscopic imaging and subsequent thioflavin-S staining of the same tissue slices to provide direct confirmation of plaque location and correlation of spectroscopic biomarkers with plaque morphology; differences were observed between cored and fibrillar plaques. The SRS results showed a protein peak shift towards the β-sheet structure in cored amyloid deposits. In the Raman maps recorded with 532 nm excitation we identified the presence of carotenoids as a unique marker to differentiate between a cored amyloid plaque area versus a non-plaque area without prior knowledge of their location. The observed presence of carotenoids suggests a distinct neuroinflammatory response to misfolded protein accumulations.
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http://dx.doi.org/10.1038/s42003-021-01981-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8050064PMC
April 2021

Label-free stimulated Raman scattering imaging reveals silicone breast implant material in tissue.

J Biophotonics 2020 05 23;13(5):e201960197. Epub 2020 Feb 23.

LaserLaB Amsterdam, Department of Physics and Astronomy, Faculty of Sciences Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Millions of women worldwide have silicone breast implants. It has been reported that implant failure occurs in approximately a tenth of patients within 10 years, and the consequences of dissemination of silicone debris are poorly understood. Currently, silicone detection in histopathological slides is based on morphological features as no specific immunohistochemical technique is available. Here, we show the feasibility and sensitivity of stimulated Raman scattering (SRS) imaging to specifically detect silicone material in stained histopathological slides, without additional sample treatment. Histology slides of four periprosthetic capsules from different implant types were obtained after explantation, as well as an enlarged axillary lymph node from a patient with a ruptured implant. SRS images coregistered with bright-field images revealed the distribution and quantity of silicone material in the tissue. Fast and high-resolution imaging of histology slides with molecular specificity using SRS provides an opportunity to investigate the role of silicone debris in the pathophysiology of implant-linked diseases.
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http://dx.doi.org/10.1002/jbio.201960197DOI Listing
May 2020

The search for a unique Raman signature of amyloid-beta plaques in human brain tissue from Alzheimer's disease patients.

Analyst 2020 Mar;145(5):1724-1736

Department of Physics and Astronomy, LaserLaB Amsterdam, VU Amsterdam, The Netherlands.

Definite Alzheimer's disease (AD) diagnosis is commonly done on ex vivo brain tissue using immuno-histochemical staining to visualize amyloid-beta (Aβ) aggregates, also known as Aβ plaques. Raman spectroscopy has shown its potential for non-invasive and label-free determination of bio-molecular compositions, aiding the post-mortem diagnosis of pathological tissue. Here, we investigated whether conventional Raman spectroscopy could be used for the detection of amyloid beta deposits in fixed, ex vivo human brain tissue, taken from the frontal cortex region. We examined the spectra and spectral maps of three severe AD cases and two healthy control cases and compared their spectral outcome among each other as well as to recent results in the literature obtained with various spectroscopic techniques. After hyperspectral Raman mapping, Aβ plaques were visualized using Thioflavin-S staining on the exact same tissue sections. As a result, we show that tiny diffuse or tangled-like morphological structures, visible under microscopic conditions on unstained tissue and often but erroneously assumed to be deposits of Aβ, are instead usually an aggregation of highly auto-fluorescent lipofuscin granulates without any, or limited, plaque or plaque-like association. The occurrence of these auto-fluorescent particles is equally distributed in both AD and healthy control cases. Therefore, they cannot be used as possible criteria for Alzheimer's disease diagnosis. Furthermore, a unique plaque-specific/Aβ spectrum could not be determined even after possible spectral interferences were carefully removed.
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http://dx.doi.org/10.1039/c9an02087jDOI Listing
March 2020

Bioactivity Profiling of Small-Volume Samples by Nano Liquid Chromatography Coupled to Microarray Bioassaying Using High-Resolution Fractionation.

Anal Chem 2019 08 2;91(16):10458-10466. Epub 2019 Aug 2.

Division of BioAnalytical Chemistry, Amsterdam Institute of Molecules, Medicines and Systems , Vrije Universiteit Amsterdam , Amsterdam 1081 HZ , The Netherlands.

High-throughput screening platforms for the identification of bioactive compounds in mixtures have become important tools in the drug discovery process. Miniaturization of such screening systems may overcome problems associated with small sample volumes and enhance throughput and sensitivity. Here we present a new screening platform, coined picofractionation analytics, which encompasses microarray bioassays and mass spectrometry (MS) of components from minute amounts of samples after their nano liquid chromatographic (nanoLC) separation. Herein, nanoLC was coupled to a low-volume liquid dispenser equipped with pressure-fed solenoid valves, enabling 50-nL volumes of column effluent (300 nL/min) to be discretely deposited on a glass slide. The resulting fractions were dried and subsequently bioassayed by sequential printing of nL-volumes of reagents on top of the spots. Unwanted evaporation of bioassay liquids was circumvented by employing mineral oil droplets. A fluorescence microscope was used for assay readout in kinetic mode. Bioassay data were correlated to MS data obtained using the same nanoLC conditions in order to assign bioactives. The platform provides the possibility of freely choosing a wide diversity of bioassay formats, including those requiring long incubation times. The new method was compared to a standard bioassay approach, and its applicability was demonstrated by screening plasmin inhibitors and fibrinolytic bioactives from mixtures of standards and snake venoms, revealing active peptides and coagulopathic proteases.
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http://dx.doi.org/10.1021/acs.analchem.9b01261DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706796PMC
August 2019

Circular Spectropolarimetric Sensing of Vegetation in the Field: Possibilities for the Remote Detection of Extraterrestrial Life.

Astrobiology 2019 10 27;19(10):1221-1229. Epub 2019 Aug 27.

Leiden Observatory, Leiden University, Leiden, The Netherlands.

Homochirality is a generic and unique property of all biochemical life, and the fractional circular polarization of light it induces therefore constitutes a potentially unambiguous biosignature. However, while high-quality circular polarimetric spectra can be easily and quickly obtained in the laboratory, accurate measurements in the field are much more challenging due to large changes in illumination and target movement. In this study, we measured various targets in the field, up to distances of a few kilometers, using the dedicated circular spectropolarimeter TreePol. We show how photosynthetic life can readily be distinguished from abiotic matter. We underline the potential of circular polarization signals as a remotely accessible means to characterize and monitor terrestrial vegetation, for example, for agriculture and forestry. In addition, we discuss the potential of circular polarization for the remote detection of extraterrestrial life.
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http://dx.doi.org/10.1089/ast.2019.2050DOI Listing
October 2019

Circular spectropolarimetric sensing of higher plant and algal chloroplast structural variations.

Photosynth Res 2019 May 23;140(2):129-139. Epub 2018 Aug 23.

Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA, Leiden, The Netherlands.

Photosynthetic eukaryotes show a remarkable variability in photosynthesis, including large differences in light-harvesting proteins and pigment composition. In vivo circular spectropolarimetry enables us to probe the molecular architecture of photosynthesis in a non-invasive and non-destructive way and, as such, can offer a wealth of physiological and structural information. In the present study, we have measured the circular polarizance of several multicellular green, red, and brown algae and higher plants, which show large variations in circular spectropolarimetric signals with differences in both spectral shape and magnitude. Many of the algae display spectral characteristics not previously reported, indicating a larger variation in molecular organization than previously assumed. As the strengths of these signals vary by three orders of magnitude, these results also have important implications in terms of detectability for the use of circular polarization as a signature of life.
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http://dx.doi.org/10.1007/s11120-018-0572-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548066PMC
May 2019

Imaging linear and circular polarization features in leaves with complete Mueller matrix polarimetry.

Biochim Biophys Acta Gen Subj 2018 06 9;1862(6):1350-1363. Epub 2018 Mar 9.

Optical Sensing Lab, Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695, USA.

Spectropolarimetry of intact plant leaves allows to probe the molecular architecture of vegetation photosynthesis in a non-invasive and non-destructive way and, as such, can offer a wealth of physiological information. In addition to the molecular signals due to the photosynthetic machinery, the cell structure and its arrangement within a leaf can create and modify polarization signals. Using Mueller matrix polarimetry with rotating retarder modulation, we have visualized spatial variations in polarization in transmission around the chlorophyll a absorbance band from 650 nm to 710 nm. We show linear and circular polarization measurements of maple leaves and cultivated maize leaves and discuss the corresponding Mueller matrices and the Mueller matrix decompositions, which show distinct features in diattenuation, polarizance, retardance and depolarization. Importantly, while normal leaf tissue shows a typical split signal with both a negative and a positive peak in the induced fractional circular polarization and circular dichroism, the signals close to the veins only display a negative band. The results are similar to the negative band as reported earlier for single macrodomains. We discuss the possible role of the chloroplast orientation around the veins as a cause of this phenomenon. Systematic artefacts are ruled out as three independent measurements by different instruments gave similar results. These results provide better insight into circular polarization measurements on whole leaves and options for vegetation remote sensing using circular polarization.
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http://dx.doi.org/10.1016/j.bbagen.2018.03.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5970099PMC
June 2018

Screening for microplastics in sediment, water, marine invertebrates and fish: Method development and microplastic accumulation.

Mar Pollut Bull 2017 Sep 6;122(1-2):403-408. Epub 2017 Jul 6.

Department of Environment and Health, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands.

Measurements of microplastics in biota and abiotic matrices are key elements of exposure and risk assessments for this emerging environmental pollutant. We investigated the abundance of microplastics in field-collected biota, sediment and water. An improved sediment extraction method, based on density separation was developed. For analysis of microplastics in biota we found that an adapted enzymatic digestion protocol using proteinase K performed best, with a 97% recovery of spiked plastic particles and no observed degradation effects on the plastics in subsequent Raman analysis. Field analysis revealed that 8 of 9 tested invertebrate species from the North Sea and 68% of analyzed individuals of brown trout (Salmo trutta) from the Swedish West Coast had microplastics in them. Based on the number of plastic particles per kg d.w. the microplastic concentrations found in mussels were approximately a thousand-fold higher compared to those in sediment and surface water samples from the same location.
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http://dx.doi.org/10.1016/j.marpolbul.2017.06.081DOI Listing
September 2017

Understanding Ultrafast Dynamics of Conformation Specific Photo-Excitation: A Femtosecond Transient Absorption and Ultrafast Raman Loss Study.

J Phys Chem A 2017 Sep 24;121(35):6538-6546. Epub 2017 Aug 24.

Department of Inorganic and Physical Chemistry, Indian Institute of Science , Bangalore, 560012, India.

Excited state ultrafast conformational reorganization is recognized as an important phenomenon that facilitates light-induced functions of many molecular systems. This report describes the femtosecond and picosecond conformational relaxation dynamics of middle-ring and terminal ring twisted conformers of the acetylene π-conjugated system bis(phenylethynyl)benzene, a model system for molecular wires. Through excitation wavelength dependent, femtosecond-transient absorption measurements, we found that the middle-ring and terminal ring twisted conformers relax at femtosecond (400-600 fs) and picosecond (20-24 ps) time scales, respectively. Actinic pumping into the red flank of the absorption spectrum leads to excitation of primarily planar conformers, and results in very different excited state dynamics. In addition, ultrafast Raman loss spectroscopic studies revealed the vibrational mode dependent relaxation dynamics for different excitation wavelengths. To corroborate our experimental findings, DFT and time-dependent DFT calculations were carried out. The Franck-Condon simulation indicated that the vibronic structure observed in the electronic absorption and the fluorescence spectra are due to progressions and combinations of several vibrational modes corresponding to the phenyl ring and the acetylenic groups. Furthermore, the middle ring torsional rotation matches the room-temperature electronic absorption, in stark contrast to the terminal ring torsional rotation. Finally, we show that the middle-ring twisted conformer undergoes femtosecond torsional planarization dynamic, whereas the terminal rings relax on a few tens of picosecond time scale.
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http://dx.doi.org/10.1021/acs.jpca.7b03893DOI Listing
September 2017

Fast High-Resolution Screening Method for Reactive Surfaces by Combining Atomic Force Microscopy and Surface-Enhanced Raman Scattering.

Appl Spectrosc 2017 Jul 22;71(7):1551-1559. Epub 2016 Dec 22.

2 Philips Lighting, High-Tech Campus, Eindhoven, The Netherlands.

A fast high-resolution screening method for reactive surfaces is presented. Atomic force microscopy (AFM) and surface-enhanced Raman spectroscopy (SERS) are combined in one method in order to be able to obtain both morphological and chemical information about processes at a surface. In order to accurately align the AFM and SERS images, an alignment pattern on the substrate material is exploited. Subsequent SERS scans with sub-micron resolution are recorded in 30 min per scan for an area of 100 × 100 µm and are accompanied by morphological information, supplied by a fast AFM, of the same area. Hence, a complete reactivity overview is obtained within several hours with only a monolayer of reactant. To demonstrate the working principle of this method, a SERS substrate containing the alignment pattern and silver nanoparticle aggregates as catalytic sites is prepared to study the photo-catalytic reduction of p-nitrothiophenol ( p-NTP).
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http://dx.doi.org/10.1177/0003702816683528DOI Listing
July 2017

Altered Adipogenesis in Zebrafish Larvae Following High Fat Diet and Chemical Exposure Is Visualised by Stimulated Raman Scattering Microscopy.

Int J Mol Sci 2017 Apr 24;18(4). Epub 2017 Apr 24.

Institute of Environmental, Health and Societies, Brunel University, UB8 3PH London, UK.

Early life stage exposure to environmental chemicals may play a role in obesity by altering adipogenesis; however, robust in vivo methods to quantify these effects are lacking. The goal of this study was to analyze the effects of developmental exposure to chemicals on adipogenesis in the zebrafish (). We used label-free Stimulated Raman Scattering (SRS) microscopy for the first time to image zebrafish adipogenesis at 15 days post fertilization (dpf) and compared standard feed conditions (StF) to a high fat diet (HFD) or high glucose diet (HGD). We also exposed zebrafish embryos to a non-toxic concentration of tributyltin (TBT, 1 nM) or Tris(1,3-dichloroisopropyl)phosphate (TDCiPP, 0.5 µM) from 0-6 dpf and reared larvae to 15 dpf under StF. Potential molecular mechanisms of altered adipogenesis were examined by qPCR. Diet-dependent modulation of adipogenesis was observed, with HFD resulting in a threefold increase in larvae with adipocytes, compared to StF and HGD. Developmental exposure to TBT but not TDCiPP significantly increased adipocyte differentiation. The expression of adipogenic genes such as , and was altered in response to HFD or chemicals. This study shows that SRS microscopy can be successfully applied to zebrafish to visualize and quantify adipogenesis, and is a powerful approach for identifying obesogenic chemicals in vivo.
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http://dx.doi.org/10.3390/ijms18040894DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5412473PMC
April 2017

Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy.

J Chem Phys 2017 Feb;146(6):064303

Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India.

Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multi-exponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (-C≡C-) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric "molecular wires."
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http://dx.doi.org/10.1063/1.4975174DOI Listing
February 2017

Different Phases of Breast Cancer Cells: Raman Study of Immortalized, Transformed, and Invasive Cells.

Biosensors (Basel) 2016 Nov 28;6(4). Epub 2016 Nov 28.

Molecular Reproduction, Development & Genetics, Indian Institute of Science, Bangalore 560012, India.

Breast cancer is the most prevalent cause of cancer-associated death in women the world over, but if detected early it can be treated successfully. Therefore, it is important to diagnose this disease at an early stage and to understand the biochemical changes associated with cellular transformation and cancer progression. Deregulated lipid metabolism has been shown to contribute to cell transformation as well as cancer progression. In this study, we monitored the biomolecular changes associated with the transformation of a normal cell into an invasive cell associated with breast cancer using Raman microspectroscopy. We have utilized primary normal breast cells, and immortalized, transformed, non-invasive, and invasive breast cancer cells. The Raman spectra were acquired from all these cell lines under physiological conditions. The higher wavenumber (2800-3000 cm) and lower wavenumber (700-1800 cm) range of the Raman spectrum were analyzed and we observed increased lipid levels for invasive cells. The Raman spectral data were analyzed by principal component-linear discriminant analysis (PC-LDA), which resulted in the formation of distinct clusters for different cell types with a high degree of sensitivity. The subsequent testing of the PC-LDA analysis via the leave-one-out cross validation approach (LOOCV) yielded relatively high identification sensitivity. Additionally, the Raman spectroscopic results were confirmed through fluorescence staining tests with BODIPY and Nile Red biochemical assays. Furthermore, Raman maps from the above mentioned cells under fixed conditions were also acquired to visualize the distribution of biomolecules throughout the cell. The present study shows the suitability of Raman spectroscopy as a non-invasive, label-free, microspectroscopic technique, having the potential of probing changes in the biomolecular composition of living cells as well as fixed cells.
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http://dx.doi.org/10.3390/bios6040057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5192377PMC
November 2016

Chemical Swarming: Depending on Concentration, an Amphiphilic Ruthenium Polypyridyl Complex Induces Cell Death via Two Different Mechanisms.

Chemistry 2016 Jul 4;22(31):10960-8. Epub 2016 Jul 4.

Leiden Institute of Chemistry, Leiden University, 2300 RA, Leiden, Netherlands), FAX.

The crystal structure and in vitro cytotoxicity of the amphiphilic ruthenium complex [3](PF6 )2 are reported. Complex [3](PF6 )2 contains a Ru-S bond that is stable in the dark in cell-growing medium, but is photosensitive. Upon blue-light irradiation, complex [3](PF6 )2 releases the cholesterol-thioether ligand 2 and an aqua ruthenium complex [1](PF6 )2 . Although ligand 2 and complex [1](PF6 )2 are by themselves not cytotoxic, complex [3](PF6 )2 was unexpectedly found to be as cytotoxic as cisplatin in the dark, that is, with micromolar effective concentrations (EC50 ), against six human cancer cell lines (A375, A431, A549, MCF-7, MDA-MB-231, and U87MG). Blue-light irradiation (λ=450 nm, 6.3 J cm(-2) ) had little influence on the cytotoxicity of [3](PF6 )2 after 6 h of incubation time, but it increased the cytotoxicity of the complex by a factor 2 after longer (24 h) incubation. Exploring the unexpected biological activity of [3](PF6 )2 in the dark elucidated an as-yet unknown bifaceted mode of action that depended on concentration, and thus, on the aggregation state of the compound. At low concentration, it acts as a monomer, inserts into the membrane, and can deliver [1](2+) inside the cell upon blue-light activation. At higher concentrations (>3-5 μm), complex [3](PF6 )2 forms supramolecular aggregates that induce non-apoptotic cell death by permeabilizing cell membranes and extracting lipids and membrane proteins.
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http://dx.doi.org/10.1002/chem.201600927DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5096026PMC
July 2016

Triplet excited electronic state switching induced by hydrogen bonding: A transient absorption spectroscopy and time-dependent DFT study.

J Chem Phys 2016 Mar;144(11):114301

Inorganic and Physical Chemistry Department, Indian Institute of Science, Bangalore 560012, India.

The solvent plays a decisive role in the photochemistry and photophysics of aromatic ketones. Xanthone (XT) is one such aromatic ketone and its triplet-triplet (T-T) absorption spectra show intriguing solvatochromic behavior. Also, the reactivity of XT towards H-atom abstraction shows an unprecedented decrease in protic solvents relative to aprotic solvents. Therefore, a comprehensive solvatochromic analysis of the triplet-triplet absorption spectra of XT was carried out in conjunction with time dependent density functional theory using the ad hoc explicit solvent model approach. A detailed solvatochromic analysis of the T-T absorption bands of XT suggests that the hydrogen bonding interactions are different in the corresponding triplet excited states. Furthermore, the contributions of non-specific and hydrogen bonding interactions towards differential solvation of the triplet states in protic solvents were found to be of equal magnitude. The frontier molecular orbital and electron density difference analysis of the T1 and T2 states of XT indicates that the charge redistribution in these states leads to intermolecular hydrogen bond strengthening and weakening, respectively, relative to the S0 state. This is further supported by the vertical excitation energy calculations of the XT-methanol supra-molecular complex. The intermolecular hydrogen bonding potential energy curves obtained for this complex in the S0, T1, and T2 states support the model. In summary, we propose that the different hydrogen bonding mechanisms exhibited by the two lowest triplet excited states of XT result in a decreasing role of the nπ(∗) triplet state, and are thus responsible for its reduced reactivity towards H-atom abstraction in protic solvents.
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http://dx.doi.org/10.1063/1.4943514DOI Listing
March 2016

Identification of Multiple Water-Iodide Species in Concentrated NaI Solutions Based on the Raman Bending Vibration of Water.

J Phys Chem A 2016 Feb 29;120(5):709-14. Epub 2016 Jan 29.

Supply Chain, Research & Development, Strategic Research Group Measurement & Analytical Science, AkzoNobel , Zutphenseweg 10, 7418 AJ Deventer, The Netherlands.

The influence of aqueous electrolytes on the water bending vibration was studied with Raman spectroscopy. For all salts investigated (NaI, NaBr, NaCl, and NaSCN), we observed a nonlinear intensity increase of the water bending vibration with increasing concentration. Different lasers and a tunable frequency-doubled optical parametric oscillator system were used to achieve excitation wavelengths between 785 and 374 nm. Focusing on NaI solutions, the relative enhancement of the water bending vibration was found to increase strongly with excitation photon energy, in line with a preresonance effect from the iodide-water charge-transfer transition. We used multivariate curve resolution (MCR) to decompose the measured Raman spectra of NaI solutions into three interconverting spectral components assigned to bulk water and water molecules interacting with one (X···H-O-H···O) and two (X···H-O-H···X) iodide ions (X = I(-)). The Raman spectrum of solid sodium iodide dihydrate supports the assignment of the latter. Using the MCR results, relative Raman scattering cross sections of 4.0 ± 0.6 and 14.0 ± 0.1 were calculated for the mono- and di-iodide species, respectively (compared to that of bulk water set to unity). In addition, it was found that at relatively low concentrations each iodide ion affects the Raman spectrum of roughly 22 surrounding water molecules, indicating that the influence of iodide extends beyond the first solvation shell. Our results demonstrate that the Raman bending vibration of water is a sensitive probe, providing new insights into anion solvation in aqueous environments.
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http://dx.doi.org/10.1021/acs.jpca.5b10102DOI Listing
February 2016

Using ferrule-top opto-mechanical probes as a new tool in VCSEL reliability experiments.

Opt Express 2015 Nov;23(23):30318-28

Today, vertical cavity surface emitting lasers (VCSELs) are used in many high-end applications, for which the laser lifetime is a critical parameter. Changes in the spatial distribution of the various emission modes of the VCSEL can be used as an early sign of device degradation, enhancing the speed and detail of failure mode analysis. We have developed a ferrule-top combined atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) probe that can be used to analyze the transverse mode pattern of the 850 nm radiation at a <200 nm spatial resolution. During accelerated lifetime testing, the newly developed method shows that small local changes in the optical output can already be detected before any sign of device degradation is observed with conventional methods.
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http://dx.doi.org/10.1364/OE.23.030318DOI Listing
November 2015

Raman and infra-red microspectroscopy: towards quantitative evaluation for clinical research by ratiometric analysis.

Chem Soc Rev 2016 Apr;45(7):1879-900

Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bengaluru 560 012, India. and Department of Instrumentation and Applied Physics, Indian Institute of Science, Bengaluru 560 012, India.

Biomolecular structure elucidation is one of the major techniques for studying the basic processes of life. These processes get modulated, hindered or altered due to various causes like diseases, which is why biomolecular analysis and imaging play an important role in diagnosis, treatment prognosis and monitoring. Vibrational spectroscopy (IR and Raman), which is a molecular bond specific technique, can assist the researcher in chemical structure interpretation. Based on the combination with microscopy, vibrational microspectroscopy is currently emerging as an important tool for biomedical research, with a spatial resolution at the cellular and sub-cellular level. These techniques offer various advantages, enabling label-free, biomolecular fingerprinting in the native state. However, the complexity involved in deciphering the required information from a spectrum hampered their entry into the clinic. Today with the advent of automated algorithms, vibrational microspectroscopy excels in the field of spectropathology. However, researchers should be aware of how quantification based on absolute band intensities may be affected by instrumental parameters, sample thickness, water content, substrate backgrounds and other possible artefacts. In this review these practical issues and their effects on the quantification of biomolecules will be discussed in detail. In many cases ratiometric analysis can help to circumvent these problems and enable the quantitative study of biological samples, including ratiometric imaging in 1D, 2D and 3D. We provide an extensive overview from the recent scientific literature on IR and Raman band ratios used for studying biological systems and for disease diagnosis and treatment prognosis.
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http://dx.doi.org/10.1039/c5cs00540jDOI Listing
April 2016

Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10-Phenanthrenequinone. A Time-Resolved Resonance Raman Study.

J Phys Chem A 2015 Oct 28;119(40):10147-57. Epub 2015 Sep 28.

Inorganic and Physical Chemistry Department, Indian Institute of Science , Bangalore 560012, India.

The photochemistry of aromatic ketones plays a key role in various physicochemical and biological processes, and solvent polarity can be used to tune their triplet state properties. Therefore, a comprehensive analysis of the conformational structure and the solvent polarity induced energy level reordering of the two lowest triplet states of 9,10-phenanthrenequinone (PQ) was carried out using nanosecond-time-resolved absorption (ns-TRA), time-resolved resonance Raman (TR(3)) spectroscopy, and time dependent-density functional theory (TD-DFT) studies. The ns-TRA of PQ in acetonitrile displays two bands in the visible range, and these two bands decay with similar lifetime at least at longer time scales (μs). Interestingly, TR(3) spectra of these two bands indicate that the kinetics are different at shorter time scales (ns), while at longer time scales they followed the kinetics of ns-TRA spectra. Therefore, we report a real-time observation of the thermal equilibrium between the two lowest triplet excited states of PQ, assigned to nπ* and ππ* of which the ππ* triplet state is formed first through intersystem crossing. Despite the fact that these two states are energetically close and have a similar conformational structure supported by TD-DFT studies, the slow internal conversion (∼2 ns) between the T(2)(1(3)nπ*) and T(1)(1(3)ππ*) triplet states indicates a barrier. Insights from the singlet excited states of PQ in protic solvents [ J. Chem. Phys. 2015 , 142 , 24305 ] suggest that the lowest nπ* and ππ* triplet states should undergo hydrogen bond weakening and strengthening, respectively, relative to the ground state, and these mechanisms are substantiated by TD-DFT calculations. We also hypothesize that the different hydrogen bonding mechanisms exhibited by the two lowest singlet and triplet excited states of PQ could influence its ISC mechanism.
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http://dx.doi.org/10.1021/acs.jpca.5b07972DOI Listing
October 2015

Ascorbate protects neurons against oxidative stress: a Raman microspectroscopic study.

ACS Chem Neurosci 2015 Nov 19;6(11):1794-801. Epub 2015 Aug 19.

LaserLaB, Faculty of Sciences, VU University Amsterdam , 1081 HV Amsterdam, The Netherlands.

Oxidative stress due to excessive accumulation of reactive oxygen or nitrogen species in the brain as seen in certain neurodegenerative diseases can have deleterious effects on neurons. Hydrogen peroxide, endogenously generated in neurons under normal physiological conditions, can produce an excess of hydroxyl radical via a Fenton mediated mechanism. This may induce acute oxidative injury if not scavenged or removed effectively by antioxidants. There are several biochemical assay methods to estimate oxidative injury in cells; however, they do not provide information on the biochemical changes as the cells get damaged progressively under oxidative stress. Raman microspectroscopy offers the possibility of real time monitoring of the chemical composition of live cells undergoing oxidative stress under physiological conditions. In the present study, a hippocampal neuron coculture was used to observe the acute impact of hydroxyl radicals generated by hydrogen peroxide in the presence of Fe(2+) (Fenton reaction). Raman peaks related to nucleic acids (725, 782, 1092, 1320, 1340, 1420, and 1576 cm(-1)) showed time-dependent changes over the experimental period (60 min), indicating the breakdown of the phosphodiester backbone as well as nuclear bases. Interestingly, ascorbic acid (a potent antioxidant) when cotreated with Fenton reactants showed protection of cells as inferred from the Raman spectra, presumably by scavenging hydroxyl radicals. Little or no change in the Raman spectra was observed for untreated control cells and for cells exposed to Fe(2+) only, H2O2 only, and ascorbate only. A live-dead assay study also supported the current observations. Hence, Raman microspectroscopy has the potential to be an excellent noninvasive tool for early detection of oxidative stress that is seen in neurodegenerative diseases.
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http://dx.doi.org/10.1021/acschemneuro.5b00106DOI Listing
November 2015

Raman Spectroscopic Techniques for Planetary Exploration: Detecting Microorganisms through Minerals.

Astrobiology 2015 Aug 17;15(8):697-707. Epub 2015 Jul 17.

1 LaserLaB, Faculty of Sciences, VU University Amsterdam , Amsterdam, the Netherlands .

Raman spectroscopy can provide highly specific chemical fingerprints of inorganic and organic materials and is therefore expected to play a significant role in interplanetary missions, especially for the search for life elsewhere in our solar system. A major challenge will be the unambiguous detection of low levels of biomarkers on a mineral background. In addition, these biomarkers may not be present at the surface but rather inside or underneath minerals. Strong scattering may prevent focusing deeper into the sample. In this paper, we report the detection of carotenoid-containing microorganisms behind mineral layers using time-resolved Raman spectroscopy (TRRS). Two extremophiles, the bacterium Deinococcus radiodurans and the cyanobacterium Chroococcidiopsis, were detected through translucent and transparent minerals using 440 nm excitation under resonance conditions to selectively enhance the detection of carotenoids. Using 3 ps laser pulses and a 250 ps gated intensified CCD camera provided depth selectivity for the subsurface microorganisms over the mineral surface layer and in addition lowered the contribution of the fluorescent background. Raman spectra of both organisms could be detected through 5 mm of translucent calcite or 20 mm of transparent halite. Multilayered mineral samples were used to further test the applied method. A separate tunable laser setup for resonance Raman and a commercial confocal Raman microscope, both with continuous (non-gated) detection, were used for comparison. This study demonstrates the capabilities of TRRS for the depth-selective analysis through scattering samples, which could be used in future planetary exploration to detect microorganisms or biomarkers within or behind minerals.
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http://dx.doi.org/10.1089/ast.2015.1329DOI Listing
August 2015

Tissue phantoms to compare spatial and temporal offset modes of deep Raman spectroscopy.

Analyst 2015 Apr;140(7):2504-12

LaserLaB, VU University, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

Time-resolved and spatially offset Raman spectroscopies have previously been demonstrated for depth analysis through strongly scattering, non-transparent materials. In this study, several series of tissue phantoms were created with varied compositions and thicknesses to compare the potential of these different Raman techniques for biomedical applications. Polydimethylsiloxane (PDMS) phantoms were made with TiO2 particles suspended as a scattering agent, mimicking the scattering properties of biological tissues. The phantom layers contained embedded biomineral simulating inclusions (sphere or layer-shaped) with varied carbonate to phosphate ratios. The tissue phantoms were studied using Time Resolved Raman Spectroscopy (TRRS), Spatially Offset Raman Spectroscopy (SORS), and their combination, using a single instrumental setup with picosecond pulsed excitation at 720 nm and two different detectors. A comparison is made of the efficiency of these techniques to resolve chemical information from these heterogeneous scattering phantom samples. Measurements with continuous wave detection were found to offer a better signal-to-noise ratio than with TRRS, and in SORS measurements ratios of target to matrix signal were found to vary depending on the structural geometry and optical properties of the phantoms. Anomalous SORS behaviour, in which the relative contribution from the target decreases with offset, was observed in cases where the target was highly scattering and the top layer was relatively transparent. Time gating with an intensified charge-coupled device (ICCD) detector can yield more direct information on the depth of the hidden material.
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http://dx.doi.org/10.1039/c4an01889cDOI Listing
April 2015

Fluorescence behavior of (selected) flavonols: a combined experimental and computational study.

Phys Chem Chem Phys 2013 Aug;15(30):12572-81

Amsterdam Center for Multiscale Modelling (ACMM), Section Theoretical Chemistry, VU University Amsterdam, Amsterdam, The Netherlands.

In this article, results of (time-dependent) density functional theory (DFT and TDDFT) calculations are combined with experimental absorption and fluorescence measurements to explain fluorescence properties of a series of flavonols. The well-understood fluorescence properties of 3- and 5-hydroxyflavone are revisited and validate our combined experimental and theoretical approach. The accuracy of the computational data (energy differences for selected points at the PES, excitation energies and oscillator strengths) allows us to understand quite different experimentally observed fluorescence spectra in the presence of only subtle structural differences. We show that for flavonols with additional hydroxyl groups not the neutral molecule but rather anions lead to fluorescence and that solvation molecules need to be included explicitly in the theoretical calculations to obtain a sufficient accuracy-enabling the understanding and prediction of experimental data for flavonols belonging to different sub-classes.
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http://dx.doi.org/10.1039/c3cp44267eDOI Listing
August 2013

Binding of naproxen enantiomers to human serum albumin studied by fluorescence and room-temperature phosphorescence.

Spectrochim Acta A Mol Biomol Spectrosc 2013 Mar 14;105:67-73. Epub 2012 Dec 14.

Biomolecular Analysis and Spectroscopy, LaserLaB, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

The interaction of the enantiomers of the non-steroidal anti-inflammatory drug naproxen (NPX) with human serum albumin (HSA) has been investigated using fluorescence and phosphorescence spectroscopy in the steady-state and time-resolved mode. The absorption, fluorescence excitation, and fluorescence emission spectra of (S)-NPX and (R)-NPX differ in shape in the presence of HSA, indicating that these enantiomers experience a different environment when bound. In solutions containing 0.2M KI, complexation with HSA results in a strongly increased NPX fluorescence intensity and a decreased NPX phosphorescence intensity due to the inhibition of the collisional interaction with the heavy atom iodide. Fluorescence intensity curves obtained upon selective excitation of NPX show 8-fold different slopes for bound and free NPX. No significant difference in the binding constants of (3.8±0.6)×10(5) M(-1) for (S)-NPX and (3.9±0.6)×10(5) M(-1) for (R)-NPX was found. Furthermore, the addition of NPX quenches the phosphorescence of the single tryptophan in HSA (Trp-214) based on Dexter energy transfer. The short-range nature of this mechanism explains the upward curvature of the Stern-Volmer plot observed for HSA: At low concentrations NPX binds to HSA at a distance from Trp-214 and no quenching occurs, whereas at high NPX concentrations the phosphorescence intensity decreases due to dynamic quenching by NPX diffusing into site I from the bulk solution. The dynamic quenching observed in the Stern-Volmer plots based on the longest phosphorescence lifetime indicates an overall binding constant to HSA of about 3×10(5) M(-1) for both enantiomers.
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http://dx.doi.org/10.1016/j.saa.2012.12.007DOI Listing
March 2013

Looking inside catalyst extrudates with time-resolved surface-enhanced Raman spectroscopy (TR-SERS).

Appl Spectrosc 2012 Oct;66(10):1179-85

Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.

Raman spectroscopy is one of the major characterization methods employed over the last few decades as a nondestructive technique for the study of heterogeneous catalysts and related catalytic reactions. However, the promise of practical applicability on millimeter-sized catalyst bodies, such as extrudates, has not been fulfilled completely. Large fluorescence signals and the highly scattering nature of the extrudates often hamper its practical usage. Different approaches to overcome this problem were examined, including the use of time-resolved Raman spectroscopy (TRRS), spatially offset Raman spectroscopy (SORS), surface-enhanced Raman spectroscopy (SERS), and combinations of these techniques. This paper demonstrates that especially TRRS can provide chemical information at depth within catalyst bodies, overcoming fluorescence background signals and allowing for visualization of analytes at different depths. It also examines the application of time-resolved SERS within catalyst bodies to gain insight into localized activity. With these options a wider applicability of Raman spectroscopy for industrial catalysis research becomes within reach.
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http://dx.doi.org/10.1366/12-06698DOI Listing
October 2012

Stereoselective binding of flurbiprofen enantiomers and their methyl esters to human serum albumin studied by time-resolved phosphorescence.

Chirality 2012 Oct 21;24(10):840-6. Epub 2012 Jun 21.

Department of Biomolecular Analysis and Spectroscopy, LaserLaB, VU University Amsterdam, The Netherlands.

The interaction of the nonsteroidal anti-inflammatory drug flurbiprofen (FBP) with human serum albumin (HSA) hardly influences the fluorescence of the protein's single tryptophan (Trp). Therefore, in addition to fluorescence, heavy atom-induced room-temperature phosphorescence is used to study the stereoselective binding of FBP enantiomers and their methyl esters to HSA. Maximal HSA phosphorescence intensities were obtained at a KI concentration of 0.2 M. The quenching of the Trp phosphorescence by FBP is mainly dynamic and based on Dexter energy transfer. The Stern-Volmer plots based on the phosphorescence lifetimes indicate that (R)-FBP causes a stronger Trp quenching than (S)-FBP. For the methyl esters of FBP, the opposite is observed: (S)-(FBPMe) quenches more than (R)-FBPMe. The Stern-Volmer plots of (R)-FBP and (R)-FBPMe are similar although their high-affinity binding sites are different. The methylation of (S)-FBP causes a large change in its effect on the HSA phosphorescence lifetime. Furthermore, the quenching constants of 3.0 × 10(7) M(-1) s(-1) of the R-enantiomers and 2.5 × 10(7) M(-1) s(-1) for the S-enantiomers are not influenced by the methylation and indicate a stereoselectivity in the accessibility of the HSA Trp to these drugs.
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http://dx.doi.org/10.1002/chir.22080DOI Listing
October 2012

Complementary fluorescence and phosphorescence study of the interaction of brompheniramine with human serum albumin.

J Phys Chem B 2012 Jun 4;116(24):7033-9. Epub 2012 Jun 4.

Department of Biomolecular Analysis and Spectroscopy, LaserLaB, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

Binding of the antihistamine drug brompheniramine (BPA) to human serum albumin (HSA) is studied by measuring quenching of the fluorescence and room temperature phosphorescence (RTP) of tryptophan. The modified Stern-Volmer equation was used to derive association constants and accessible fractions from the steady-state fluorescence data. Decay associated spectra (DAS) revealed three tryptophan fluorescence lifetimes, indicating the presence of three HSA conformations. BPA causes mainly static quenching of the long-living, solvent-exposed conformer. RTP spectra and lifetimes, recorded under deoxygenated conditions in the presence of 0.2 M KI, provided additional kinetic information about the HSA-BPA interactions. Fluorescence DAS that were also recorded in the presence of 0.2 M KI revealed that the solvent-exposed conformer is the major contributor to the RTP signal. The phosphorescence quenching is mostly dynamic at pH 7 and mostly static at pH 9, presumably related to the protonation state of the alkylamino chain of BPA. This provides direct insight into the binding mode of the antihistamine drug, as well as kinetic information at both the nanosecond and the millisecond time scales.
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http://dx.doi.org/10.1021/jp300055cDOI Listing
June 2012

Identification of inorganic pigments used in porcelain cards based on fusing Raman and X-ray fluorescence (XRF) data.

Appl Spectrosc 2011 Nov;65(11):1281-90

Ghent University, Research group Raman spectroscopy, Department of Analytical Chemistry, Ghent, Belgium.

Raman spectroscopy and X-ray fluorescence (XRF) spectroscopy are often used as complementary techniques that are well suited for the analysis of art objects because both techniques are fast, sensitive, and noninvasive and measurements can take place in situ. In most of these studies, both techniques are used separately, in the sense that the spectra are evaluated independently and single conclusions are obtained, considering both results. This paper presents a data fusion procedure for Raman and XRF data for the characterization of pigments used in porcelain cards. For the classification of the analyzed points of the porcelain cards principal component analysis (PCA) was used. A first attempt was made to develop a new procedure for the identification of the pigments using a database containing the fused Raman-XRF data of 24 reference pigments. The results show that the classification based on the fused Raman-XRF data is significantly better than the classifications based on the Raman data or the XRF data separately.
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http://dx.doi.org/10.1366/11-06368DOI Listing
November 2011
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