Subsequent Spectroscopic Analysis Research Articles

Opuntia ficus-indica (L.) Mill. and Opuntia stricta (Haw.) Haw. Mucilage-Based Painting Binders for Conservation of Cultural Heritage

The possibility of using materials from the waste of agricultural products for the conservation of cultural and artistic heritage has led to important technological developments on mortars, plasters, colors, and other applications. In this experimental work, we investigated the binding properties of mucilage obtained from two different species of the genus Opuntia, both collected in Sicily, Italy: Opuntia ficus-indica (L.) Mill. and Opuntia stricta (Haw.) Haw. Through chemical acid hydrolysis, and subsequent spectroscopic analysis conducted at 13C-NMR, the main monosaccharide composition of both mucilage was studied, identifying considerable compositional differences. In fact, the mucilage of O. ficus indica had similar total amounts of arabinose (23.65%), galactose (20.87%), and glucose isomers (23.89%), while that of O. stricta was characterized by significant amounts of arabinose (36.48%) and galactose (32.31%) units. The samples were obtained by dispersing pigments on the mucilage and applying the obtained tempera by a brush onto both paper and chalk supports, in order to observe if the colors changed with different substrates. Colorimetric analysis, measuring ΔE, showed how the same pigment modifies its aspect depending on the binder used. After a two-week UV ageing process, pigments that had dispersed in O. stricta changed their aspect more than those dispersed in O. ficus-indica. Overall, it is also evident how ΔE data for organic pigments are higher than those for inorganic ones.

Structural Changes in Insulin at a Soft Electrochemical Interface.

Understanding the interaction of proteins at interfaces, which occurs at or within cell membranes and lipoprotein vesicles, is central to our understanding of protein function. Therefore, new experimental approaches to understand how protein structure is influenced by protein-interface interactions are important. Herein we build on our previous work exploring electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) to investigate changes in protein secondary structure that are modulated by protein-interface interactions. The ITIES provides an experimental framework to drive protein adsorption at an interface, allowing subsequent spectroscopic analysis (e.g., Fourier transform infrared spectroscopy) to monitor changes in protein structure. Here, we reveal that the interaction between insulin and the interface destabilizes native insulin secondary structure, promoting formation of α helix secondary structures. These structural alterations result from protein-interface rather than protein-protein interactions at the interface. Although this is an emerging approach, our results provide a foundation highlighting the value of the ITIES as a tool to study protein structure and interactions at interfaces. Such knowledge may be useful to elucidate protein function within biological systems or to aid sensor development.

Gas-Phase Structural Analysis of Supramolecular Assemblies.

Ion mobility spectrometry and gas-phase IR action spectroscopy are two structure-sensitive mass-spectrometric methods becoming more popular recently. While ion mobility spectrometry provides collision cross sections as a size and shape dependent parameter of an ion of interest, gas-phase spectroscopy identifies functional groups and is capable of distinguishing different isomers. Both methods have recently found application for the investigation of supramolecular assemblies. We here highlight several aspects.Starting with the characterization of switching states in azobenzene photoswitches as well as redox-switchable lasso-type pseudorotaxanes, structures of isomers can be distinguished and mechanistic details analyzed. Ion mobility mass spectrometry in combination with gas-phase H/D-exchange reactions unravels subtle structural details as described for the chiral recognition of crown ether amino acid complexes. Gas-phase IR spectroscopy allows identification of details of the binding patterns in dimeric amino acid clusters as well as the serine octamer. This research can be extended into the analysis of peptide assemblies that are of medical relevance, for example, in Alzheimer's disease, and into a general hydrophobicity scale for natural as well as synthetic amino acids. The development of ultracold gas-phase spectroscopy that for example makes use of ions trapped in liquid helium droplets provides access to very well resolved spectra. The combination of ion mobility separation of ions with subsequent spectroscopic analysis even permits separation of different isomers and studying them separately with respect to their structure. This represents a great advantage of these gas-phase methods over solution experiments, in which the supramolecular complexes under study typically equilibrate and thus prevent a separate investigation of different isomers. At the end of this overview, we will discuss larger and more complex supramolecules, among them giant halogen-bonded cages and complex intertwined topologies such as molecular knots and Solomon links.

Electrochemical preconcentration coupled with spectroscopic techniques for trace lead analysis in olive oils

In this paper we present a novel combined electrochemical-spectroscopic approach suitable to monitor trace levels of heavy metals directly in edible oils. The method is based on the electrochemical preconcentration/extraction of the analyte from the tested real matrix by cathodic deposition onto a Pt working electrode, then transfer and anodic re-oxidation of the metallic deposit to a “clean” aqueous solution, suitable for the subsequent spectroscopic analysis. The procedure has been here focused to the determination of lead in extra virgin olive oil (EVOO), performed by applying ICP-QMS or GFAAS techniques. To this aim, the EVOO samples were mixed with proper amounts of the room temperature ionic liquid (RTIL) [P14,6,6,6]+[NTf2]-, in order to obtain a non-aqueous supporting electrolyte suitable for the electrodeposition process. The feasibility and performance of the analytical strategy were at first tested in standard solutions of Pb(II) in RTIL, produced by anodic dissolution of lead in the RTIL, as well as in olive oil samples mixed with 0.5 M RTIL and spiked with known amounts of Pb(II). The optimisation of the electrochemical parameters was achieved by applying a D-Optimal Design, properly set up to optimise the efficiency of the deposition and re-oxidation steps, quantitative recovery and measurement time. Finally, the analytical procedure was applied to the determination of Pb content in some Italian EVOOs, without any need of performing mineralization pretreatments. Data obtained with the proposed procedure satisfactorily agree with those achieved by ICP-QMS analysis after microwave digestion, being differences between the two approaches within 10%, with the advantage of reducing to half the pretreatment time, operating at room temperature and avoiding the use of aggressive solvents.

Mechanistic study of the role of hydrogen bond donors in the two-component organocatalysis of the ring-opening reaction of epoxides

The ring-opening reaction of epoxides is an essential step in CO2 conversion into value-added heterocyclic carbonates. There has been an increasing focus on developing organocatalysts composed by a nucleophile and a hydrogen bond donor (HBD), so that CO2 conversion can occur at ambient conditions, with the rationale that HBD can aid epoxide’s ring-opening. Nevertheless, it is not clear what is the real role of HBDs on this reaction. Herein, it was employed a combined spectroscopic and theoretical approach to obtain mechanistic insight into the ring-opening of a model epoxide, when catalyzed by pyridine and different HBDs. While the pyridine-HBD system decreased the activation barrier from ˜60 to ˜22–23 kcal mol−1, by itself pyridine decreased it to ˜27 kcal mol−1. This shows that HBDs present a small effect on the activation energy. Furthermore, it was found that water molecules can act as HBD with similar results to other molecules. This helps to explain why catalytic amounts of water have found to be advantageous in CO2 conversion. Further work found that the activation barrier is mainly controlled by steric contributions. Subsequent spectroscopic analysis showed that the obtained rate constants follow the same trend found in the theoretical calculations, while these reactions lead to the formation of the same products in similar ratios. It was also found that one pyridine molecule can catalyze the opening of two epoxides, resulting in a trimeric structure. Finally, the addition of electron-donating groups to pyridine increases the catalytic properties of the system.

High resolution study of the ν2 and ν5 rovibrational fundamental bands of thionyl chloride: Interplay of an evolutionary algorithm and a line-by-line analysis.

The ν2 and ν5 fundamental bands of thionyl chloride (SOCl2) were measured in the 420 cm-1-550 cm-1 region using the FT-far-IR spectrometer exploiting synchrotron radiation on the AILES beamline at SOLEIL. A straightforward line-by-line analysis is complicated by the high congestion of the spectrum due to both the high density of SOCl2 rovibrational bands and the presence of the ν2 fundamental band of sulfur dioxide produced by hydrolysis of SOCl2 with residual water. To overcome this difficulty, our assignment procedure for the main isotopologues 32S16O35Cl2 and 32S16O35Cl37Cl alternates between a direct fit of the spectrum, via a global optimization technique, and a traditional line-by-line analysis. The global optimization, based on an evolutionary algorithm, produces rotational constants and band centers that serve as useful starting values for the subsequent spectroscopic analysis. This work helped to identify the pure rotational submillimeter spectrum of 32S16O35Cl2 in the v2=1 and v5=1 vibrational states of Martin-Drumel et al. [J. Chem. Phys. 144, 084305 (2016)]. As a by-product, the rotational transitions of the v4=1 far-IR inactive state were identified in the submillimeter spectrum. A global fit gathering all the microwave, submillimeter, and far-IR data of thionyl chloride has been performed, showing that no major perturbation of rovibrational energy levels occurs for the main isotopologue of the molecule.

Intrinsic surface areas and bond site concentrations of silica aerogels of different densities

Silica aerogels were investigated to determine the relationship of density, surface area, and the concentration of molecular absorption bonding sites. Aerogel surface areas were measured, by Brunauer–Emmett–Teller (BET), for densities ranging from 35mg/cm3 to 200mg/cm3. Chlorosilanes were chosen as the test adsorbates for this study, as they do not physisorb in multiple layers on the mesoporous silica surface. Trimethylchlorosilane (TMCS) was selected as the primary adsorbate because of its high vapor pressure at ambient conditions. Aerogel samples were exposed to TMCS vapors until saturation. Complete infiltration was verified by Raman spectroscopy of a cross-sectioned sample. The total amount of adsorbate at saturation was determined through the weight gain using a microbalance. The cumulative TMCS surface area at saturation, calculated from the footprint of the TMCS molecule and the total number of molecules derived from the weight gain, is significantly smaller than the intrinsic surface area measured by BET. This implies that chemisorption, and not physisorption, governs the saturation phenomenon. This hypothesis was verified with chlorosilanes with larger molecules – phenyldimethylchlorosilane and diphenylmethylchlorosilane. The gained weight per unit volume in the silica aerogels scaled as the molecular mass of the radicals, bonded to the silica network, and did not scale as the footprint area of the different chlorosilane molecules. This work provides fundamental information for understanding the capabilities of aerogels to collect and concentrate organic molecules for subsequent spectroscopic analysis.

Optical levitation in a Bessel light beam

A vertically oriented zero order Bessel light beam is shown to create a one-dimensional array of trapped particles over extended (millimeter) distances. The particles take up equilibrium positions over the entire length of the beam and this is a consequence of the interplay between optical scattering and the self-healing properties of the Bessel beam. This work has analogies to recent studies of optically bound matter and allows for the simple creation of one-dimensional particle chains and their subsequent spectroscopic analysis.

Exploiting π shielding interactions in a η6 arene-complexed chiral auxiliary

The origin of asymmetric induction in a chiral auxiliary derived from isomannide was probed using a series of η6 arene chromium carbonyl complexes. Diastereoselectivity as high as 99% was attainable, and subsequent spectroscopic analysis shed light on the role of π–π interactions.

Thermal Volatilization Analysis: A Versatile Platform for Spectroscopic Investigations of Polymer Degradation Processes

The thermal volatilization analysis (TVA) and subambient thermal volatilization analysis (SATVA) techniques are described. In addition to rate profiling of the volatile product flux of thermal degradation under high-vacuum conditions through measurement of pressure in the vacuum line as a function of sample temperature, the TVA technique is shown to afford a convenient method for an isolation, on the basis of volatility under high-vacuum conditions, of product fractions of thermal degradation for subsequent spectroscopic analysis. The capacity and flexibility of TVA as a platform for these analyses are illustrated in a case study format by degrading poly(bisphenol A, 2-hydroxy propylether). The overall degradation process is quantified, and most significant pathways of thermolysis are identified through subsequent spectroscopic analysis of products of decomposition. The design and construction of a modified vacuum-tight long-path gas IR cell, as an interface allowing for the application of Fourier transform infrared spectroscopy (FT-IR) for the on-line analysis of volatile products of polymer degradation, is detailed. Proof of concept and application of this new analytical technique, subsequently referred to as TVA/FT-IR, is illustrated through the examination of appropriate aspects of the thermal degradation of polymethyl methacrylate polymers.

Compositional heterogeneity in pectic polysaccharides: NMR studies and statistical analysis

AbstractPectins are a class of heterogeneous polysaccharides used in the food industry as a result of their ability to form gels. They are primarily composed of a (1ŕ4)‐α‐D‐galactopyranosyluronic acid backbone where the carboxylic acid group is methyl esterified at a level which depends on the source of the pectin and processing conditions used to isolate the material. Of considerable interest is the distribution of the free acid and methyl ester groups along this polymer chain. NMR spectroscopy, coupled with statistical analysis, is a powerful technique for the study of sequence distribution of monomers. Experimental conditions (temperature, pD) are reported which are appropriate for the analysis of pectic polysaccharides. Results are presented from a study of sequence distribution in native, modified, and fractionated pectins using 1H and 13C solution NMR methods. The triad sequence information was examined using Bernoullian and Markovian probability models in conjunction with continuous Gaussian distribution and discrete models. Intermolecular heterogeneity in pectins results in triad frequencies which reflect the distribution of acid and ester monomers for native and base saponified pectins. Fractionation of pectin through physicochemical methods and subsequent spectroscopic analysis provide insight into this heterogeneity. Segregation into discrete polymer populations shows a structural diversity best approximated by a 3‐component statistical model.

Shpol'skii fluorimetry as an independent identification method to upgrade routine HPLC analysis of polycyclic aromatic hydrocarbons

High Performance Liquid Chromatography combined with fluorescence detection is routinely used in the Dutch Water Quality Survey to determine the Polycyclic Aromatic Hydrocarbons (PAH) contents of marine sediment samples. In this paper Shpol'skii spectroscopy is utilized to ascertain the identity and the purity of the peaks in the chromatogram by collection of several eluting fractions and subsequent spectroscopic analysis. The low temperature Shpol'skii technique provides high-resolution fluorescence spectra of PAHs that can serve as fingerprints. Thus, information concerning peak purity was obtained and the number of components identified was roughly doubled.

Photochemistry and photopolymerization activity of novel perester derivatives of fluorenone

The photochemistry and photopolymerization activity of three novel t-butylperester derivatives of fluorenone have been examined and compared with unsubstituted fluorenone and a tetra-t-butylperester of benzophenone. The longest wavelength absorption bands of all three derivatives are blue-shifted from that of fluorenone itself with a marked increase in the corresponding extinction coefficients, associated with the electron withdrawing effect of the peroxyester groups and a concurrent increase in the charge transfer content of the molecule due to substitution. The fluorescence quantum yields of the fluorenone derivatives are also greater than those of fluorenone in a range of solvent systems; this effect is associated with an increase in the degree of charge transfer content in the lowest excited singlet state. Photoreduction quantum yields are also higher in 2-propanol solvent, that for the bis-perester derivative being twice that of the monoperester. The presence of a tertiary amine (triethylamine) enhances the photoreduction quantum yields due to an increase in the probability of electron abstraction. Conventional micro-second flash photolysis in 2-propanol solution indicates that free radical formation occurs from an upper excited triplet n-π ∗ state. Rates of photopolymerization in bulk poly(methyl methacrylate) on a percentage basis are also higher for the three perester derivatives with those for the monoesters being greater than for the bisperester. The latter is associated with a much higher probability of self termination reactions. The presence of methyldiethanolamine enhances the rate of photopolymerization with both fluorenone and the monoperester derivatives but reduces that with the 2-t-butylperester, 7-nitro and bisperester derivatives due to competitive termination reactions. The results are discussed on the basis of the photophysical data and subsequent spectroscopic analysis of the polymer samples by second-order derivative u.v. spectroscopy and fluorescence analysis, both of which are shown to be valuable methods for the determination of chromophoric initiator fragments.

Isolation and Identification of the Major Component of Setal Exudate from Corythucha ciliata

Isolation and Identification of the Major Component of Setal Exudate from Corythucha ciliata

Determining the permeability of polycyclic aromatic hydrocarbons through polymer films

A laboratory bench apparatus was developed to determine the permeability of polycyclic aromatic hydrocarbons (PAH) through various polymer films, which is based on the recovery of PAH by fabric and liquid filters and subsequent spectroscopic analysis according to fluorescence quasi-line spectra at low temperature. The apparatus enables investigations to be carried out in the temperature range of 293–423°K with an error of determining the permeability factor of the order of 4%. Permeability factors were obtained for anthracene for a cellulose hydrate film in the temperature range of 303–373°K.