THz Absorption Spectra Research Articles

Terahertz spectra of proteinuria and non-proteinuria.

In clinical practice, proteinuria detection is of great significance in the diagnosis of kidney diseases. Dipstick analysis is used in most outpatient settings to semi-quantitatively measure the urine protein concentration. However, this method has limitations for protein detection, and alkaline urine or hematuria will cause false positive results. Recently, terahertz time-domain spectroscopy (THz-TDS) with strong hydrogen bonding sensitivity has been proven to be able to distinguish different types of biological solutions, which means that protein molecules in urine may have different THz spectral characteristics. In this study, we performed a preliminary clinical study investigating the terahertz spectra of 20 fresh urine samples (non-proteinuria and proteinuria). The results showed that the concentration of urine protein was positively correlated with the absorption of THz spectra at 0.5-1.2THz. At 1.0 THz, the pH values (6, 7, 8, and 9) had no significant effect on the THz absorption spectra of urine proteins. The terahertz absorption of proteins with a high molecular weight (albumin) was greater than that of proteins with a low molecular weight (β2-microglobulin) at the same concentration. Overall, THz-TDS spectroscopy for the qualitative detection of proteinuria is not affected by pH and has the potential to discriminate between albumin and β2-microglobulin in urine.

Nondestructive identification of wood species by terahertz spectrum

AbstractTerahertz time‐domain spectroscopy (THz‐TDS) has become an emerging nondestructive detection technique due to the unique properties of THz waves; it offers safety, penetrability, and fingerprint identification, especially for commonly used non‐polar materials. Here, we measure the differences in THz spectra of four wood blocks (manglietia, amur linden, black walnut, and ebony) in the frequency range of 0.1–0.9 THz. In addition, we demonstrate the principal components analysis (PCA) applied in THz absorption spectra; the principal components extracted from original data by PCA can replace the original absorption coefficient data and can clearly distinguish the wood types. Results show that THz‐TDS combined with PCA can be used as an effective nondestructive identification method in the field of public security, food detection, and customs anti‐smuggling initiatives.

Designing luminescent diimine-Cu(i)–phosphine complexes by tuning N-ligand and counteranions: correlation of weak interactions, luminescence and THz absorption spectra

π–π stacking interactions and C–H⋯X (X = O, F) interactions formed by counteranions help to enhance the rigidity of these structures and further improve their luminescence quantum yields.

Terahertz spectroscopy of the helium endofullerene He@C60.

We studied the quantized translational motion of single He atoms encapsulated in molecular cages by terahertz absorption. The temperature dependence of the THz absorption spectra of 3He@C60 and 4He@C60 crystal powder samples was measured between 5 and 220 K. At 5 K there is an absorption line at 96.8 cm-1 (2.90 THz) in 3He@C60 and at 81.4 cm (2.44 THz) in 4He@C60, while additional absorption lines appear at higher temperature. An anharmonic spherical oscillator model with a displacement-induced dipole moment was used to model the absorption spectra. Potential energy terms with powers of two, four and six and induced dipole moment terms with powers one and three in the helium atom displacement from the fullerene cage center were sufficient to describe the experimental results. Excellent agreement is found between potential energy functions derived from measurements on the 3He and 4He isotopes. One absorption line corresponds to a three-quantum transition in 4He@C60, allowed by the anharmonicity of the potential function and by the non-linearity of the dipole moment in He atom displacement. The potential energy function of icosahedral symmetry does not explain the fine structure observed in the low temperature spectra.

Selection rules and dynamic magnetoelectric effect of the spin waves in multiferroic BiFeO3

We report the magnetic field dependence of the THz absorption and non-reciprocal directional dichroism spectra of BiFeO$_3$ measured on the three principal crystal cuts for fields applied along the three principal directions of each cut. From the systematic study of the light polarization dependence we deduced the optical selection rules of the spin-wave excitations. Our THz data, combined with small-angle neutron scattering results showed that i) an in-plane magnetic field rotates the $\mathbf{q}$ vectors of the cycloids perpendicular to the magnetic field, and ii) the selection rules are mostly determined by the orientation of the $\mathbf{q}$ vector with respect to the electromagnetic fields. We observed a magnetic field history dependent change in the strength and the frequency of the spin-wave modes, which we attributed to the change of the orientation and the length of the cycloidal $\mathbf{q}$ vector, respectively. Finally, we compared our experimental data with the results of linear spin-wave theory that reproduces the magnetic field dependence of the spin-wave frequencies and most of the selection rules, from which we identified the spin-polarization coupling terms relevant for the optical magnetoelectric effect.

Facile high yield, excellent catalytic performance of polyoxometalate-based lanthanide phosphine oxide complexes: Syntheses, structures, photocatalysis and THz spectra

Water pollution, which continuously threatens human health and the sustainable development of society, has become a major concern. Photocatalytic degradation is an effective strategy to remove organic dyes from wastewater. For this strategy, it is crucial to select the appropriate catalyst. Using triphenylphosphine oxide (OPPh3) as the ligand, phosphomolybdic acid as the anion template, three new lanthanide complexes [Ln(OPPh3)4(H2O)3](PMo12O40)∙4C2H5OH (1–3) (Ln = Sm, Gd, Tb) were synthesized. The raw materials for the reaction are cheap and readily available. The convenient synthesis method is environmentally friendly, with high yield (70%–80%). Complexes 1–3 are all seven-coordinated mononuclear structures centered on lanthanide ions, [PMo12O40]3- anions and solvent molecules are not coordinated with metal ions. These mononuclear structures eventually form complicated 3D supramolecular structures through hydrogen bonds, Mo–O … π or C–H … π weak interactions. Complexes 1–3 photocatalytic degradation of MB have high removal rates, as catalysts have enough stability to be reused, and can be used as excellent catalysts for the degradation of dye molecules in sewage. Among them, the removal rate of MB by photodegradation of complex 2 was highest (99.50%). In addition, the effects of different initial concentrations of MB solution and different types of organic dyes on the photocatalysis experiment were investigated. The photocatalytic reaction mechanism of complexes 1–3 was also studied. Due to the similar structures of complexes 1–3, they have almost the same THz absorption spectra with different absorption intensity, which may be attributed to the difference of the number of weak interactions. Therefore, terahertz spectroscopy can be used as a sensitive method to distinguish and determine small differences between lanthanide-organic complexes. This is the first time that this spectrum has been used to characterize lanthanide phosphine oxide complexes modified by [PMo12O40]3-.

Terahertz and Raman Spectroscopic Investigation of Monohydrate Cocrystal of Antitubercular Isoniazid with Protocatechuic Acid.

Pharmaceutical cocrystal provides an alternative modification strategy for the formulation development of drugs owning to their potential ability to improve the physicochemical properties of active pharmaceutical ingredients (APIs) efficiently by changing inter-molecular interactions between raw materials. Isoniazid (INH) is an indispensable main drug for the treatment of tuberculosis, but its tablet formulation is unstable and prone to degradation. In the present study, the monohydrate cocrystal of INH and protocatechuic acid (PA) was prepared by solvent evaporation using PA as cocrystal former to optimize the properties of INH. The parent materials and corresponding 1:1 molar ratio INH-PA monohydrate cocrystal have been characterized by the terahertz time-domain (THz-TDS) and Raman spectroscopy. The THz absorption spectra displayed that there were obvious differences between the peaks of experimental cocrystal and the parent materials, and the same situation was found in Raman vibrational spectra. In addition, density functional theory (DFT) was applied to simulating and optimizing the structure of INH-PA monohydrate cocrystal and supplied corresponding vibrational modes. Our results provided a unique method to characterize the formation of INH-PA monohydrate cocrystal at the molecular-level and a lot of information about cocrystal structure and intra-molecular and/or inter-molecular hydrogen bond interactions in the emerging pharmaceutical cocrystal fields.

Various Characteristics of Severely Aged Flame‐Retardant Cross‐Linked Polyolefin

Flame‐retardant cross‐linked polyolefin (FR‐XLPO), is widely used as insulators for electric cables. Several cables installed in nuclear power plants must be functional even when they suffer a severe accident. Therefore, sheets of FR‐XLPO were exposed to heat, gamma rays, and high‐temperature steam. Before and after such aging treatments, samples' mechanical and thermal properties and infrared and THz absorption spectra were measured. As a result, it has become clear that FR‐XLPO is fairly resistant to superheated steam with no oxygen, although it is easily degraded thermally if oxygen is present. It is also resistant to gamma rays to a certain extent. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Analysis of Intermolecular Weak Interactions and Vibrational Characteristics for Vanillin and Ortho-Vanillin by Terahertz Spectroscopy and Density Functional Theory

In this article, the characteristic absorption spectra of Vanillin and ortho-Vanillin were investigated by terahertz time-domain spectroscopy (THz-TDS) in the range of 0.4–2.0 THz. Using quantum chemistry tools, density functional theory calculations were performed to obtain the theoretical THz spectra. To better understand the THz absorption spectra on a molecular level and to systematically and comprehensively interpret the origin of the characteristic absorption peaks, the vibrational characteristics and the intermolecular weak interactions of these two compounds were analyzed using a cluster model. We used the vibrational mode automatic relevance determination method to assign the vibrational modes of all absorption peaks and provide the percentage contribution of these modes. The vibrational modes of Vanillin and ortho-Vanillin were mainly dihedral angle torsion. The intermolecular weak interactions were analyzed using the independent gradient model based on Hirshfeld partition of molecular density method. The results indicated that the weak interaction types of Vanillin and ortho-Vanillin were dominated by van der Waals interaction. This work has demonstrated that using THz-TDS combined with quantum chemical calculations is an effective way to identify and investigate isomers. This method has significant potential applications for exploring the relationship between the biomolecular structure and the material performance.

Terahertz and Raman Spectroscopic Investigation of Anti-tuberculosis Drug-Drug Cocrystallization Involving 4-aminosalicylic Acid and Pyrazinamide

Drug-drug cocrystals can enhance the dissolution rate, oral bioavailability as well as increase their stability and hygroscopicity. In this paper, the anti-tuberculosis drug-drug cocrystal between pyrazinamide (PZA) and 4-aminosalicylic acid (PASA) was prepared with the water-assisted grinding approach. The parent materials and corresponding 1:1 molar ratio binary PASA-PZA cocrystal have been characterized by applying the terahertz time-domain (THz-TDS) and Raman spectroscopy. The THz absorption spectra presented that there were significantly different peaks between the parent materials and the drug-drug cocrystal. Raman spectral results also indicated the differences of such cocrystal compared with the starting compounds. In addition, density functional theory (DFT) calculations were employed for simulating the structure of PASA-PZA cocrystal and provide its vibrational modes assignment. All of our results offered a unique means to characterize the conformation of specific PASA-PZA drug-drug cocrystals at the molecule-level, providing a great deal of information about the cocrystals’ formation and also both intramolecular and/or inter-molecular hydrogen bond interactions within the emerging solid-state pharmaceutical fields.

Broadband Terahertz Spectroscopy of Glutathione

Abstract The conformation of glutathione is of great significance for its biological function. In this study, the absorption spectra of reduced (GSH) and oxidized (GSSG) glutathione in the frequency range of 0.5–12.0 THz were obtained by air plasma terahertz time-domain spectroscopy (THz-TDS). The results demonstrated that GSH had rich characteristic absorption peaks in the THz region, while GSSG presented a monotonous absorption spectrum without obvious peaks. Combined with powder X-ray diffraction (PXRD), GSH had a certain crystal structure and GSSG was amorphous, suggesting that the THz spectroscopy was sensitive to the molecular structure and crystal form. The density functional theory (DFT) calculation based on the GSH crystal structure was performed to simulate the THz absorption spectrum and analyze the vibrational property. The result showed that GSH molecule could form rich inter- and intramolecular hydrogen bonds which helped to constrain flexible peptide. Lattice vibrations and hydrogen bonds of GSH could effectively resonate with THz waves. The different THz absorption peaks of GSH corresponded to different collective or local molecular vibrations which were closely related to the hydrogen bonding interactions. The study may help to deepen the understanding of GSH molecular conformation and weak interactions.

Qualitative and Quantitative Analyses of Potassium Sorbate in Milk Powder using Terahertz Spectra

Using the terahertz time-domain spectroscopy system (THz-TDS), the potassium sorbate content in milk powder has been investigated. Firstly, the THz time-domain spectra of the samples were transformed into frequency spectra by Fourier transform, and then, through a set of simplified formulas of the optical parameters, the THz absorption spectra and refractive index spectra were obtained. Based on the characteristic absorption peak of potassium sorbate, a quantitative analysis model of potassium sorbate in milk powder was constructed using ordinary least squares (OLS) linear regression. In the case of low content (<1%) of potassium sorbate, a special THz absorption band (0.887–1.000 THz) was selected to construct a partial least squares (PLS) model that is called Sub-PLS. In addition, for qualitative analysis, we used partial least squares discrimination analysis (PLS-DA). Experimental results show that the proposed Sub-PLS model is superior to the PLS model based on full spectrum in accuracy, and the proposed PLS-DA is superior to other nonlinear regression methods such as support vector machine and neural network.

Vibrational Spectroscopic Investigation into Novel Ternary Eutectic Formed between Pyrazinamide, Fumaric Acid, and Isoniazid.

To improve the efficacy of anti-tuberculosis (anti-TB) therapy, drug–drug co-crystallization stands for an alternative approach to settle the tuberculosis problem. Directly co-crystallizing two typical parent anti-TB drugs (pyrazinamide, PZA and isoniazid, INH) into a single binary co-crystal could not be obtained successfully. Multicomponent eutectic are highly effective and useful for enhancing the dissolution rate, bioavailability, and physical stability of the poorly water-soluble active pharmaceutical ingredient (API) drugs, when the attempts of forming a binary co-crystal have failed. Therefore, the ternary eutectic composition conception was proposed in this study, in which fumaric acid (FA) was chosen as the molecule to connect two first-line anti-tubercular drugs. First of all, three starting materials (including PZA, INH, and FA) were grinded at a 1:1:1 molar ratio, the eutectic composition was investigated through vibrational spectroscopic techniques, including terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy. Additionally, the density functional theory (DFT) was utilized to simulate the optimized structures and vibrational modes of two possible theoretical eutectic composition forms. The THz absorption spectrum of the theoretical form I shows much more consistency with the experimental results than that of form II. Raman spectra also help to characterize the differences in vibrational modes between the eutectic composition and the starting parent compounds. The results provide us with both structural information and intermolecular hydrogen bonding interactions within specific multicomponent eutectic composition formulations based on Raman and terahertz vibrational spectroscopic techniques in combination with theoretical calculations.

Terahertz spectroscopic diagnosis of early blast-induced traumatic brain injury in rats.

The early diagnosis of blast-induced traumatic brain injury (bTBI) is of great clinical significance for prognostication and treatment. Here, we report a new strategy for early bTBI diagnosis through serum and cerebrospinal fluid (CSF) based on terahertz time-domain spectroscopy (THz-TDS). The spectral differences of serum and CSF for different degrees of experimental bTBI in rats have been demonstrated in the early period. In addition, the THz spectra of total protein in the hypothalamus and hippocampus were investigated at different time points after blast exposure, which both showed clear differences with time increasing compared with that in the normal brain. This might help to explain the neurological symptoms caused by bTBI. Moreover, based on the THz absorption spectra of serum and CSF, the principal component analysis and machine learning algorithms were performed to automatically identify the degree of bTBI. The highest diagnostic accuracy was up to 95.5%. It is suggested that this method has potential as an alternative method for high-sensitive, rapid, label-free, economical and early diagnosis of bTBI.

Qualitative differences in the calculated THz absorption spectra of linear and branched polymers as exemplifed in amylose and amylopectin

Qualitative absorption spectra of the amylose and the amylopectin molecules were calculated in the THz frequency range within the framework of a simple model of coupled oscillators. The simulations revealed that the absorption of the linear molecule (amylose) was approximately twice as strong as that of the branched molecule (amylopectin) with the same molecular weight. The differences in the fine structure of the obtained spectra were also described. The results can be used to determine the degree of polymer branching using THz spectroscopy.

Fingerprint characterization of M-EDTA complexes and iron compounds using terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy (THz-TDS) provides a novel approach for the coordination compounds characterization. In this paper, the THz absorption spectra of iron complexes and M-EDTA (M = Cd2+, Cu2+, Ni2+, Co2+, Fe2+, Fe3+, Mn2+, Cr3+) complexes were investigated. Comparing to the infrared (IR) spectra of those compounds, the THz spectra can provide unique chemical and intermolecular vibrational information. The M − O and M − N vibrational modes in the THz-TDS spectra of M-EDTA complexes reveal the vibrational information of intermolecular interactions. Characteristic absorption bands in the THz spectra of various complexes and ligands are observed. THz absorption spectra of iron complexes and different ligands exhibited characteristic absorption bands in 0–2.2 THz region. These characteristic bands can be used to characterize and identify different complexes and ligands. The molecular vibrational information in the THz spectral band provides the unique fingerprint for further study of coordination compounds identification and structure characterization.

High-Precision Continuous-Wave Terahertz Spectroscopy Based on a Photomixing Technique for Identifying Pearls.

We present the accurate terahertz spectra of between imitation and cultured pearls using continuous-wave terahertz (CW-THz) spectroscopy. Using Fourier transform infrared (FT-IR) spectroscopy and optical coherence tomography (OCT) measurements, cultured pearls can be distinguished from imitation pearls by observing distinct absorption peaks and discriminative boundaries. The THz absorption spectra up to 0.3 THz obtained from CW-THz spectroscopy show several absorption peaks at specific frequencies with the cultured pearls but no peaks with the imitation pearls, which results from the existence of the nacre polymorph of cultured pearls. Hence, it is expected that the CW-THz system proposed herein will be applicable to fast, nondestructive spectrum analysis including pearl identification.

Identification of vibrational modes in thymine bases by broadband far-infrared absorption spectroscopy

Far-infrared and THz absorption spectra were obtained for thymine bases. Quantum chemical calculations were also conducted to simulate the far-infrared spectrum using density functional theory. Three models were used for the simulations. In one model, a thymine monomer was assumed. The second model assumed a thymine dimer, where two pyrimidine rings were aligned antiparallel. The last model assumed a thymine trimer, in which four hydrogen bonds were formed in three pyrimidine rings placed on the same plane. By comparing the measurements and simulations, almost all the absorption peaks appearing from 100 to 600 cm−1 could be assigned to torsional or skeletal vibrations of a pyrimidine ring. On the other hand, absorption peaks appearing in the THz range from 16.7 to 167 cm−1 were assigned to intermolecular vibrations.

Characterization of Nucleobases in Broadband Terahertz Spectra from 0.5 to 10 THz with the Air-Biased-Coherent-Detection Technique.

Terahertz time-domain spectroscopy (THz-TDS) is an effective coherent detection technique for deeply understanding the structures and functions of biomolecules. However, generally not full information in the whole THz range can be obtained due to the limited detection bandwidth (usually less than 5 THz) of the traditional THz-TDS systems. In this paper, effective THz absorption spectra in 0.5–10 THz range of five typical nucleobases of DNA/RNA are characterized with a super broadband THz detection technique, called the air-biased- coherent-detection (THz-ABCD) technique. Few unexpected characteristic absorption peaks appeared in the low-frequency region and meanwhile a series of anticipated characteristic absorption peaks are found in the high-frequency region. The fingerprint spectra of these nucleobases are helpful for further analysis on the vibration and twisting behavior of hydrogen bonds, van der Waals and electrostatic forces etc. between and within DNA/RNA biomolecules.

Inspecting human colon adenocarcinoma cell lines by using terahertz time-domain reflection spectroscopy.

Techniques to inspect and analyze human colorectal cancer cell lines by using terahertz time-domain attenuated total reflection spectroscopy (THz TD-ATR) were investigated. The characteristics of THz absorption spectra of two colorectal cancer cell lines DLD-1 and HT-29 in aqueous solutions with different concentrations were studied. Different spectral features were observed compared to normal cell line. Identification results based on different parameters including absorption coefficient, refractive index, real and imaginary parts of complex permittivity, dielectric loss tangent were discussed. This research may be promising for quick and instant inspection of liquid samples by using THz time-domain spectroscopy in medical applications.