far-IR Spectra Research Articles

Infrared Spectroscopy of RNA Nucleosides in a Wide Range of Temperatures.

The RNA world hypothesis suggests that early cellular ancestors relied solely on RNA molecules for both genetic information storage and cellular functions. RNA, composed of four nucleosides-adenosine, guanosine, cytidine, and uridine-forms the basis of this theory. These nucleosides consist of purine nucleobases, adenine and guanine, and pyrimidine nucleobases, cytosine and uracil, bonded to ribose sugar. Notably, carbonaceous chondrite meteorites have revealed the presence of these bases and sugar, hinting at the potential existence of nucleosides in space. This study aims to present the infrared spectra of four RNA nucleosides commonly found in terrestrial biochemistry, facilitating their detection in space, especially in astrobiological and astrochemical contexts. Laboratory measurements involved obtaining mid- and far-IR spectra at three temperatures (-180 °C, room temperature, and +180 °C), followed by calculating molar extinction coefficients (ε) and integrated molar absorptivities (ψ) for corresponding bands. These spectral data, along with ε and ψ values, serve to provide quantitative insights into the presence and relative abundance of nucleosides in space and aid in their detection.

Molecular dynamics simulations reliably identify vibrational modes in far-IR spectra of phospholipids.

The properties of self-assembled phospholipid membranes are of essential importance in biochemistry and physical chemistry, providing a platform for many cellular life functions. Far-infrared (far-IR) vibrational spectroscopy, on the other hand, is a highly information-rich method to characterize intermolecular interactions and collective behaviour of lipids that can help explain, e.g., chain packing, thermodynamic phase behaviour, and sequestration. However, reliable interpretation of the far-IR spectra is still lacking. Here we present a molecular dynamics (MD) based approach to simulate vibrational modes of individual lipids and in an ensemble. The results are a good match to synchrotron far-IR measurements and enable identification of the molecular motions corresponding to each vibrational mode, thus allowing the correct interpretation of membrane spectra with high accuracy and resolving the longstanding ambiguities in the literature in this regard. Our results demonstrate the feasibility of using MD simulations for interpreting far-IR spectra broadly, opening new avenues for practical use of this powerful method.

Theoretical terahertz spectroscopy of free radical solutes in solution: an EPR spin probe in water.

Free radical species are used as spin labels in electron paramagnetic resonance (EPR) spectroscopy of biomolecular systems in water, for instance in the frame of Overhauser dynamic nuclear polarization (ODNP) relaxometry to probe the local hydration water dynamics close to protein surfaces in aqueous environments. Widely used in this context are nitroxide spin probes such as TEMPO, PROXYL or MTSL derivatives. Here, we study the THz spectroscopy of HMI (2,2,3,4,5,5-HexaMethylImidazolidin-1-oxyl) in water at ambient conditions which has been recently investigated as to how its EPR properties depend on its solvation pattern in water. To enable theoretical THz spectroscopy of molecular radicals in solution, we have generalized well-established methodologies for THz spectral decomposition of closed-shell systems, namely the supermolecular solvation complex (SSC) and cross-correlation analysis (CCA) techniques, to open-shell polyatomic solute species in water. Based on this methodological advance, we have decomposed and assigned the THz response of HMI including its solvation shell by employing the generalized SSC and CCA methods to cope with the open-shell character of this free radical solute, in particular its unpaired electron localized at the nitroxy group. We reveal that the main modulations of the far-IR spectrum of HMI are dominated by the low-frequency intramolecular modes of the spin probe molecule itself while the solvation of its two hydrogen bonding sites contribute much less intensely in this spectral window. Finally, we have computed THz spectra of HMI with its local solvation water with an aim to provide a theoretical analogue of experimental THz difference spectroscopy. Beyond the specific case, our decomposition methodology that now is able to include open shells can be applied in future work to analyze the low-frequency vibrational response of the solvation shell of other free radicals in solution.

Tracing obscured galaxy build-up at high redshift using deep radio surveys

Context. A fundamental question of extra-galactic astronomy that is yet to be fully understood, concerns the evolution of the star formation rate (SFR) and supermassive black hole (SMBH) activity with cosmic time, as well as their interplay and how it impacts galaxy evolution. A primary focus that could shed more light on these questions is the study of merging systems, comprising highly star-forming galaxies (SFGs) and active galactic nuclei (AGN) at the earliest stages of galactic formation. However, considering the challenges associated with identifying these objects, it is essential to explore complementary selection methods across multiple wavelengths. Aims. The primary objective of this study is to conduct a comprehensive analysis of a sample of high-redshift (z > 3) far-infrared (far-IR) and radio-emitting galaxies in the highest possible spatial resolution. The aim is to study the properties of this population, such as their morphological characteristics, and to explore the interplay of SFR and SMBH activity at this epoch. Methods. In order to select the galactic population of our interest, we employed two selection criteria that have frequently been used as separate methods in the literature. In more detail, we selected galaxies that present relatively compact radio morphologies at 1.4 GHz (i.e., an angular size smaller than 10 arcsec) as well as a far-IR spectrum that peaks in flux at λ ≥ 350 μm (i.e., flux350 μm > flux250 μm). For these selection criteria, we used the COSMOS and ECDF-S fields, two of the most extensively observed astronomical fields currently available, which provide high spectral and spatial resolution at a multi-wavelength scale. By accepting only galaxies that satisfied these selection criteria, we derived a sample of eight galaxies that were identified either photometrically or spectroscopically at z > 3 from literature studies and by our team. Results. A thorough investigation of available optical, near-IR, and millimetre (mm) imaging reveals a possible merging scenario in five out of eight cases in our sample. Additionally, available multi-wavelength photometry strongly suggests active star formation at the 103 M⊙ yr−1 level in massive systems (stellar masses of M⋆ ∼ 1011 M⊙) co-hosting an active SMBH. Conclusions. Comparison of these results with previous studies, suggests that our selection method preferentially identifies galaxies hosting an active SMBH, as well as a strong SFG component, resulting in high SFR and IR luminosity. An additional examination of the efficacy of the radio and far-IR selection criteria provides further support for their combined application in selecting co-evolving AGN and star formation activity at high redshift. In this regard, future use of these selection criteria on radio and far-IR/mm observations of statistically larger galaxy samples is of high interest.

The “Periodic Table” of 1-methylbenzotriazole: Zinc(II) Complexes

In an attempt to fill in the empty Zn position in the “Periodic Table” of 1-methylbenzotriazole (Mebta), reactions between Zn(II) sources and this ligand were carried out. The detailed synthetic studies provided access to complexes [ZnX2(Mebta)2] (X = Cl, 1; X = Br, 3; X = I, 4), (MebtaH)2[ZnCl4] (2), tet-[Zn(NO3)2(Mebta)2] (5), oct-[Zn(NO3)2(Mebta)2] (6), and [Zn(Mebta)4](Y)2 [Y = ClO4, 7; Y = PF6, 8]. Solid-state thermal decomposition of 2 leads to 1 in quantitative yield. The structures of 3, 4, 5, 6, and 7 were determined by single-crystal crystallography. The structures of the remaining complexes were proposed based on spectroscopic evidence. In all compounds, Mebta behaves as monodentate ligand using the nitrogen of the position 3 as donor. Complexes 1–4, 7, and 8 are tetrahedral. Complexes 5 and 6 are isostoichiometric and their preparation in pure forms depends on the reaction conditions; in the former the ZnII atom has a tetrahedral geometry, whereas in the latter the metal ion is octahedral. This case of rare isomerism arises from the monodentate (in 5) vs. bidentate (in 6) coordination of the nitrato groups. Extensive π–π stacking interactions and non-classical H bonds build interesting 3D architectures in the structurally characterized complexes. The compounds were characterized by IR, far-IR, and Raman spectroscopies in the solid state, and the data were interpreted in terms of the structures (known or proposed) of the complexes and the coordination modes of the organic and inorganic ligands involved. The solid-state structures of the complexes are not retained in solution, as proven by NMR (1H, 13C[1H]) spectroscopy and molar conductivity data. The thermal decomposition study of 1 and 3 leads to stable intermediates with 1:1 stoichiometry, i.e., ZnX2(Mebta). Based on far-IR spectra, polymeric tetrahedral structures are possible with simultaneous presence of terminal and bridging X− groups. Liquid-phase ab initio (MP2) and gas-phase DFT calculations, performed on Mebta and the nitrato complexes, respectively, shed light on the tendency of Mebta for N3-coordination, and the existence and relative stabilities of 5 and 6.

Visible and infrared transparent conductive films with passive cooling capabilities

In order to facilitate radiative cooling in optoelectronic devices, it is necessary to employ infrared (IR) transparent conductive films (TCFs) that permit thermal radiation from internal circuits to pass through. This can be accomplished by using TCFs with a wide transparency range that extends into the far-IR spectrum. We have produced hafnium-doped indium oxide (InHfO) TCFs that have a wide transparency range spanning from 400 nm to 20 μm. These TCFs, with a thickness of 120 nm, exhibit a sheet resistance of approximately 200 Ω/□, high visible relative transmittance (90% at 550 nm, comparable to ITO), and IR transparency (66.9% in the 1.35–20 μm range). By replacing commercial ITO TCFs with InHfO TCFs, we successfully decreased the operating temperature of an enclosed resistor from 65.5 °C to 63.6 °C, and potentially to 61.1 °C via radiative cooling. This decrease corresponds to around 5–10% of the temperature difference between the resistor and room temperature. The InHfO TCFs we have prepared are suitable for a range of applications requiring transparency from the visible to the far-IR spectrum and may open up new avenues for optoelectronic applications.

On the solvation structures formed in conditioning-free MMAC-based electrolytes: A theoretical–experimental spectroscopic insight of interest to Mg battery area

The 2.39:1 Mg:MgCl2:AlCl3 (MMAC)-tetrahydrofuran (THF) and 1:1.22 MMAC-diethylene glycol dimethyl ether (G2) electrolytes, which have been already investigated by electrochemical measurements, are studied in the current work by using experimental vibrational spectroscopy allied to ab initio molecular dynamics (AIMD) simulations of spectra. Raman data are practically identical to the 2:1 MgCl2:AlCl3 (MACC)-THF and 3:5 MACC-G2 binary systems, except for a 330 cm−1 band, commonly assigned to [AlCl3(THF)1-2] and/or [AlCl2]+, which is absent for the THF-based ternary system. Subtle changes are also seen in the far-IR spectra, where a band at around 315 cm−1 shows strong dependence on the MgCl2 content and so may be associated to the [Mg2(μ-Cl)3]+ dimer. The monomeric species, [MgCl]+, is also observed in both electrolytes by means of IR bands at 270–285, 300 and 325–330 cm−1. The varied amounts of monomer and dimer seem to be related to the electrochemical activities determined for these ternary systems.

Photoabsorption of Microhydrated Naphthalene and Its Cyano-Substituted Derivatives: Probing Prereactive Models for Photodissociation in Molecular Clouds.

We investigate the photoionization pathways of naphthalene, 1-cyanonaphthalene, and 2-cyanonaphthalene upon complexation with the water dimer, aiming to understand the photodissociation process under conditions of the interstellar medium (ISM). We analyze the intermolecular bonding pattern, equilibrium rotational properties, energy complexation, far-IR spectra, and ionic trends of the possible photoproducts using dispersion-corrected density functional theory (DFT-D) and time-dependent DFT (TD-DFT). For the different configurations, we evaluate the possible charge-transfer (CT) excitations near the photoionization limit. Our results indicate that, in high-radiation regions of the ISM (>8.0 eV), CT excitations occur from localized occupied molecular orbitals (MOs) in the aromatic molecules to mixed unoccupied MOs in the complexes, favoring cationic aromatic species in these conditions. We notice that the photoabsorption spectra depend on the type of intermolecular interaction (H-bonds or O-H···π bonds) in the complexes, as well as the presence and position (1 or 2) of the cyano-functional group in naphthalene. For hydrated naphthalene, the O-H···π complexes assume a more relevant role for photodissociation. In the case of the cyano-substituted derivatives, the H-bonded structures are more favorable to be considered as prereactive models. However, the cyano group at position 2 indicates that CT excitations toward the water dimer are more likely to occur.

Chemical composition of carbonaceous asteroid Ryugu from synchrotron spectroscopy in the mid- to far-infrared of Hayabusa2-returned samples

Context.The current period is conducive to exploring our Solar System's origins with recent and future space sample return missions, which provide invaluable information from known Solar System asteroids and comets The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) recently brought back samples from the surface of the Ryugu carbonaceous asteroid.Aims.We aim to identify the different forms of chemical composition of organic matter and minerals that constitute these Solar System primitive objects, to shed light on the Solar System's origins.Methods.In this work, we recorded infrared (IR) hyper-spectral maps of whole-rock Ryugu asteroid samples at the highest achievable spatial resolution with a synchrotron in the mid-IR (MIR). Additional global far-IR (FIR) spectra of each sample were also acquired.Results.The hyper-spectral maps reveal the variability of the functional groups at small scales and the intimate association of phyl-losilicates with the aliphatic components of the organic matter present in Ryugu. The relative proportion of column densities of the identified IR functional groups (aliphatics, hydroxyl + interlayer and/or physisorbed water, carbonyl, carbonates, and silicates) giving access to the composition of the Ryugu samples is estimated from these IR hyper-spectral maps. Phyllosilicate spectra reveal the presence of mixtures of serpentine and saponite. We do not detect anhydrous silicates in the samples analysed, at the scales probed. The carbonates are dominated by dolomite. Aliphatics organics are distributed over the whole samples at the micron scale probed with the synchrotron, and intimately mixed with the phyllosilicates. The aromatic C=C contribution could not be safely deconvolved from OH in most spectra, due to the ubiquitous presence of hydrated minerals. The peak intensity ratios of the organics methylene to methyl (CH2/CH3) of the Ryugu samples vary between about 1.5 and 2.5, and are compared to the ratios in chondrites from types 1 to 3. Overall, the mineralogical and organic characteristics of the Ryugu samples show similarities with those of CI chondrites, although with a noticeably higher CH2/CH3in Ryugu than generally measured in C1 chondrites collected on Earth, and possibly a higher carbonate content.

DFT and ab initio molecular dynamics simulation study of the infrared spectrum of the protic ionic liquid 2-hydroxyethylammonium formate.

Protic ionic liquids (PILs) typically show a complex band shape in their infrared (IR) spectra in the high-frequency range due to the hydrogen stretching vibrations of functional groups forming rather strong hydrogen bonds (H-bonds). In the low-frequency range, the intermolecular stretching mode of the H-bond leaves a mark in the far-IR spectrum of PILs. In this study, the IR spectrum of the PIL 2-hydroxyethylammonium formate, [HOCH2CH2NH3][HCOO], is investigated in order to identify the different modes that contribute to the high-frequency band shape, i.e. the cation ν(NH), ν(OH), and ν(CH) modes, and the anion ν(CH) mode, as well as the intermolecular mode of the strongest H-bond in the far-IR spectrum. The assignment is validated by quantum chemistry calculations of clusters at the density functional theory (DFT) level for four ionic pairs and by ab initio molecular dynamics (AIMD) simulations of ten ionic pairs. There is good agreement between the vibrational frequencies obtained from DFT and AIMD simulations for both the high- and low-frequency ranges. Based on the calculations, the strong H-bond interaction between the cation -NH3 group and [HCOO]- gives a broad band envelope associated with the ν(NH) mode in the high-frequency range of the IR spectrum on which there are narrower peaks corresponding to the ν(OH) and ν(CH) modes. In the far-IR (FIR) spectrum, the anions' rattling motion gives a broad feature with a maximum at 160 cm-1, while the H-bond's intermolecular NH⋯O stretching mode appears as a peak at 255 cm-1.

ANTIFUNGAL AND ANTIOXIDANT ACTIVITIES OF COBALT AND NICKEL METAL COMPLEXES OF P-AMINO BENZAMIDE

Cobalt and nickel bio-active metal chelates were synthesized using p-aminobenzamide and thiocyanate ion in an equimolar ratio, and they were assessed for conductivity, UV-Visible, IR, and far-IR spectra as well as metal ion estimation identification. Based on their spectral and magnetic characteristics, the complexes were given octahedral geometry. The complexes are paramagnetic, monomeric, and non-electrolyte. With the help of the Agar Disc diffusion method using fluconazole as the reference drug, the antifungal activity of metal chelates through an in-vitro mechanism was compared with p-aminobenzamide against C. albicans. Metal(II) chelates' in-vitro DPPH free radical scavenging ability was tested and contrasted with that of standard ascorbic acid. The complexes appear to have moderate activity, according to the results of the computation of the IC50 values at four distinct concentrations.

INFLUENCE OF SILVER NANOPARTICLES ON TOTAL ABSORPTION FLUXES OF METHYL AMMONIUM LEAD TRI-IODIDE PHOTOCELL

Plasmonic nanoparticles exhibit a great ability to dramatically improve photon harvesting in solar cells. They provide an exceptionally very innovative way of transforming the solar cell and photovoltaic cell industries. In photovoltaic cell research, nano-plasmonics especially noble metal nanoparticles have emerged as a new frontier runner plasmons to be incorporated in photovoltaic structures. These nano plasmons concentrate photons and channel them inside a perovskite layer. However, challenges on its effectiveness have emerged and need to be addressed. These challenges includes the loss in absorption fluxes, increased light trapping band, developing inexpensive fabrication techniques, scaling plasmonics into manufacturing levels and integrating them into perovskite active nanostructures. In this paper, we address the challenge posed by low total absorption fluxes and decreased total enhancement across the whole solar spectrum using silver nanoplasmonics to improve its total absorption fluxes. We therefore document a numerical analysis of total absorption enhancements of a model CH3NH3PbI3 perovskite photocell whose active absorber layer is embedded with spherical plasmonic silver nanoparticles of different diameters at different array spacing. It is still unknown to what extent the organic cation (framework) affects the optical and electronic properties of CH3NH3PbI3 perovskites. Further, there a number of questions that have been raised in relation to the inorganic framework or lattice though computational has suggested that CH3NH3PbI3 is influenced by different geometric parameters related to CH3NH3+ on its nitrogen K-edge (or the nitrogen 1s-orbital electrons). Therefore, new ways in which the organic cation can interact with the inorganic Pb–I lattice is believed to affect its XA spectrum and therefore its electronic structure. It has been suggested that hybridized CH3NH3+ levels in the (lead-and-iodide dominated) valence band appear to dominate in CH3NH3PbI3 crystals and the band gap in CH3NH3PbI3 can change due to the rotation of the CH3NH3+ cation, mostly by affecting the conduction band. The influence of particle size, array spacing and location is analyzed numerically and discussed in a realistic system. Results revealed that when silver nanoparticles are integrated into a CH3NH3PbI3 perovskite layer, total solar absorption enhancement increases by 8% in the infrared (IR) and by 48 % in the far-infrared (far-IR) spectra in layers of 135 nm thicknesses at minimum array spacing and maximum diameter. It was concluded that the total absorption enhancement can be improved by reinforcement from a plasmonic near-field influenced by its total cross sectional scattering effects. In this process absorption in the IR and far IR spectra is influenced in the CH3NH3PbI3 perovskite layer.

Multi-Centered Solid-Phase Quasi-Intramolecular Redox Reactions of [(Chlorido)Pentaamminecobalt(III)] Permanganate—An Easy Route to Prepare Phase Pure CoMn2O4 Spinel

We synthesized and structurally characterized the previously unknown [Co(NH3)5Cl](MnO4)2 complex as the precursor of CoMn2O4. The complex was also deuterated, and its FT-IR, far-IR, low-temperature Raman and UV-VIS spectra were measured as well. The structure of the complex was solved by single-crystal X-ray diffraction and the 3D-hydrogen bonds were evaluated. The N-H…O-Mn hydrogen bonds act as redox centers to initiate a solid-phase quasi-intramolecular redox reaction even at 120 °C involving the Co(III) centers. The product is an amorphous material, which transforms into [Co(NH3)5Cl]Cl2, NH4NO3, and a todorokite-like solid Co-Mn oxide on treatment with water. The insoluble residue may contain {Mn4IIIMnIV2O12}n4n−, {Mn5IIIMnIVO12}n5n− or {MnIII6O12}n6n− frameworks, which can embed 2 × n (CoII and/or CoIII) cations in their tunnels, respectively, and 4 × n ammonia ligands are coordinated to the cobalt cations. The decomposition intermediates decompose on further heating via a series of redox reactions, forming a solid CoIIMIII2O4 spinel with an average size of 16.8 nm, and gaseous N2, N2O and Cl2. The CoMn2O4 prepared in this reaction has photocatalytic activity in Congo red degradation with UV light. Its activity strongly depends on the synthesis conditions, e.g., Congo red was degraded 9 and 13 times faster in the presence of CoMn2O4 prepared at 550 °C (in air) or 420 °C (under N2), respectively.

Nanoscale Cu(II) MOFs Formed via Microemulsion: Vibrational Mode Characterization Performed using a Combined FTIR, Synchrotron Far-IR, and Periodic DFT Approach

Two Cu(II) metal–organic frameworks (MOFs) were prepared on the nanoscale at room temperature using a microemulsion method, namely, [Cu3(BTC)2(H2O)3] (BTC = benzene-1,3,5-tricarboxylate), known as HKUST-1 (1), and [Cu2(OH)(BTC)(H2O)]·2H2O (2). Thermochemical and gas sorption properties of the microporous topologies were characterized by mid- and far-infrared vibrational spectroscopy, supported by periodic density functional theory calculations. The mid-infrared profile of 1 appeared altered in response to gas sorption under variable temperature and pressure conditions. Vibrational mode analysis indicated the most sensitive infrared peaks were associated with the internal vibrations of organic linker moieties indirectly coupled to the Cu(II)–gas coordination site, activated by a lowered symmetry induced by guest interactions. Synchrotron far-infrared spectroscopy was shown to be a useful diagnostic for the microstructure of 1 and 2 where different temperature dependences were displayed in the low-frequency region. The loss of residual water during the activation of 2 at elevated temperature coincides with peaks indicative of free paddle-wheel moieties emerging in the far-IR spectra. As demonstrated for both materials 1 and 2, vibrational mode analysis was effective in screening MOF materials for their propensity toward gas uptake and, inversely, the diffusion of guest species such as adsorbed water from the microporous environments.

Ex-vivo Antimalarial and in-vitro Biological Activities of newly synthesized Co(II) complex with Schiff base

Abstract The first-row transition metal complex of Schiff base has been synthesized and characterized based on physicochemical spectral and biochemical methods. The metal-ligand stoichiometry and molecular formula of the complex assessed by Elemental analysis and metal estimation-neutral, monomeric nature of the complex and paramagnetic nature also predict by the conductance and magnetic moment study. The octahedral environment around Co(II) and metal-imine bond as a whole predicted by atomic IR and Far-IR spectra. In-vitro antibacterial and antifungal activities of the Schiff base and its complexes compared with those for standard (Chloramphenicol & Fluconazole) by agar disc diffusion method. The Ex-vivo antimalarial activity of the Schiff base and its metal complex was found by using Plasmodium falciparum bacteria/fungal.

Combining experimental and theoretical vibrational spectroscopy to study magnesium aluminum chloride complex electrolytes

Measurements of the Far-IR and Raman spectra of 1:1 MACC-ether electrolytes were carried out. [(μ-Cl)2Mg2]2+ is the major dimer in DME solution and the bands at 250 and 222 cm−1 may be used as markers in the respective IR and Raman spectra. On the other hand, [MgCl]+ stands out in the THF-based electrolyte, where an IR band at 286 cm−1 is here reported for the first time in the literature and may be employed as sensor. The [(μ-Cl)3Mg2]+ dimer, which is usually formed at the 2:1 MACC-THF electrolyte and deemed the electrochemically active species on the electrode, is also identified at the 1:1 ratio. AIMD-simulated IR spectra of the dimer and monomer are in good agreement with the experimental data and were pivotal to characterize the [MgCl(THF)5]+ complex. QC calculations helped assign a few bands in the Raman spectra and Gibbs free energies explained the preferential formation of Mg species in each medium.

Synchrotron far-infrared spectra for the characterisation of molecular crystals of forensic interest: Amphetamine, methamphetamine, MDA, MDMA and substituted methcathinones

This combined laboratory and theoretical investigation focussed on a suite of crystalline phenethylamine-class molecules of forensic interest: amphetamine sulfate, levo- and dextro-methamphetamine hydrochloride, 3,4-methyl​enedioxy-methamphetamine (MDMA) hydrochloride, 3,4-methylenedioxy-​amphetamine (MDA) hydrochloride, and the hydrochloride salts of two substituted (4-fluoro and 4-methyl) methcathinones. Far-infrared (far-IR) spectra across the 30–600 cm−1 wavenumber range were recorded at the Australian Synchrotron light source. Resolved absorption profiles enabled vibrational features to be assigned via comparison to periodic density functional theory (p-DFT) performed at the B3LYP-D3/6-311 G(d) level. The calculations accurately reproduce the experimental spectra (frequencies and peak intensities) for ordered molecular crystal-type samples, such as methamphetamine stereoisomers and two substituted methcathinones. Significant band broadening for amphetamine sulfate was observed, likely due to crystal disorder, while MDMA and MDA showed convolved stretching modes from comparatively impure samples. For all seven molecular crystals investigated, previously unpublished peak assignments and relative band intensities have now been systematically compiled; completing the spectral region that lies between the more thoroughly studied terahertz and mid-IR regions. These results can be incorporated in spectral libraries and databases to enable far-IR statistical analyses to be performed on forensic samples of mixed or impure compounds.

Gas-Phase Infrared Spectroscopy of Neutral Peptides: Insights from the Far-IR and THz Domain.

Gas-phase, double resonance IR spectroscopy has proven to be an excellent approach to obtain structural information on peptides ranging from single amino acids to large peptides and peptide clusters. In this review, we discuss the state-of-the-art of infrared action spectroscopy of peptides in the far-IR and THz regime. An introduction to the field of far-IR spectroscopy is given, thereby highlighting the opportunities that are provided for gas-phase research on neutral peptides. Current experimental methods, including spectroscopic schemes, have been reviewed. Structural information from the experimental far-IR spectra can be obtained with the help of suitable theoretical approaches such as dynamical DFT techniques and the recently developed Graph Theory. The aim of this review is to underline how the synergy between far-IR spectroscopy and theory can provide an unprecedented picture of the structure of neutral biomolecules in the gas phase. The far-IR signatures of the discussed studies are summarized in a far-IR map, in order to gain insight into the origin of the far-IR localized and delocalized motions present in peptides and where they can be found in the electromagnetic spectrum.

A Study on Blend Ratio-dependent Far-IR and Low-frequency Raman Spectra and WAXD Patterns of Poly(3-hydroxybutyrate)/poly(4-vinylphenol) Using Homospectral and Heterospectral Two-dimensional Correlation Spectroscopy.

An intensive analysis of far-infrared (far-IR), low-frequency Raman, and wide angle X-ray diffraction (WAXD) data has been performed by two-dimensional correlation spectroscopy (2D-COS) as a function of the blend ratio of poly(3-hydroxybutyrate)/poly(4-vinylphenol) (PHB/PVPh). Homospectral 2D-COS revealed that a weak band at 128 cm-1 in the far-IR spectra appeared more clearly in the 2D correlation spectra. Heterospectral 2D-COS (far-IR/low-frequency Raman and far-IR/WAXD) provided very important results that were hardly detected in the conventional 2D-COS. A far-IR peak at 130 cm-1 in the heterospectral 2D-COS had negative correlations with the peaks in the low-frequency Raman spectra at 81, 100, and 110 cm-1 and WAXD profile 8.78 and 11.01°. These results indicated that those peaks have different origins; the 130 cm-1 peak comes from the intermolecular C=O···H-O hydrogen bond between PHB and PVPh, while those for low-frequency Raman and WAXD peaks are the features of PHB crystalline structure.

The prediction of far-infrared spectra for molecular crystals of forensic interest – Phenylethylamine, ephedrine & pseudoephedrine

Synchrotron far-infrared (far-IR) spectra were measured for a representative set of pharmaceutical-type molecular crystals: phenylethylamine hydrochloride salt, ephedrine base and its hydrochloride salt, and pseudoephedrine base and its hydrochloride salt. Resolved spectral profiles in the 30–600 cm−1 range allowed for comparison of absorption bands to simulated spectra obtained by periodic density function theory (DFT) code. The B3LYP-D3/6-311G(d) level of theory returned highly accurate predictions of the experimental far-IR spectra for well-ordered crystalline samples, including an agreement between relative peak intensities almost unprecedented for organic crystal systems of this size. Simulated far-IR spectra for the phenylethylamine hydrochloride and ephedrine base samples do not match to the same degree; potentially due to higher disorder within the solid-state. These comparisons to theory generally allowed for confident assignment of prominent absorption bands to low-lying vibrational modes. The experimental spectra (including those for related illicit drug compounds: amphetamine sulphate, methamphetamine hydrochloride, MDA hydrochloride, and MDMA hydrochloride), peak assignments, and relative band intensities are compiled and evaluated for their inclusion in spectral libraries and their application to chemometric analysis for mixed compounds of pharmaceutical and forensic interest.