Search Results (580)

FTIR spectroscopy, attenuated total reflection (ATR), and diffuse reflectance (DRIFT) modalities, along with ICP–AES spectroscopy and correlation analysis, including two-dimensional correlation spectroscopy (2DCOS), were used for the detailed analysis of Kastanozem (chestnut) soils. Microaggregates (20–200 μm) and macroaggregates (200–1000 μm) of characteristic horizons of uncultivated (fallow) and cultivated (arable land) chestnut soils of the same origin were physically fractionated by wet sieving. The combination of these molecular and atomic spectroscopy techniques in combination with correlation analysis was able to find direct correlations between matrix-forming anions and soil organic matter (SOM) of Kastanozems. Humic substances were separated from the corresponding soil samples to reveal SOM contributions more explicitly. Microaggregates of the size fractions of 20–40 μm and 40–60 μm bore the most comprehensive information for both techniques used. Most significant differences between land-use Kastanozem samples were observed in topsoil horizons (arable P versus light-colored humic AJ horizon), and for the next pair of horizons along the profile xerometamorphic BMK horizon to structural metamorphic BM horizon. These differences included carbonate matrix and SOM amounts and composition. Topsoil arable land showed significantly smaller amounts of total organic carbon and a decrease in the share of long-chain hydrocarbons compared to fallow, which has a more distinctive character compared to similar land-use samples of Chernozem. An increase in carbonate contents with soil depth was found for both land-use samples, while the amounts and composition of the silicate matrix remained largely unchanged within the depth profile. The heterospectral 2DCOS comparison of FTIR (between horizons and land-use samples), ICP–AES (between land-use samples), and FTIR–AES (for the same sample) showed the possibility of a more reliable attribution of FTIR absorption bands and revealed the differences in the macro- and micro-aggregate elemental and SOM composition of Kastanozems. Full article

Terpyridines are well-known ligands in coordination chemistry, are valued for their conformational flexibility and strong metal-binding properties, and are also of interest as fluorophores. This study focused on the synthesis and comprehensive investigation of a new class of bis-oxazolo[5,4-b]pyridine derivatives, designed based on their structural similarity to terpyridines. Four novel compounds, 4a–d, were synthesized by cyclization of amide derivatives of 3-aminopyridin-2(1H)-ones using pyridine-2,6-dicarboxylic acid and its dichloride as key acidic components. Their structures and purity were confirmed by melting point analysis, high-resolution mass spectrometry, and ¹H, ¹³C NMR spectroscopy. Compounds 4a–c exhibit UV absorption at 323–357 nm and intense blue to deep-blue fluorescence (357–474 nm, цi ≈ 0.32–0.84) in chloroform, dichloromethane, and acetonitrile, attributed to p–p* transitions within the conjugated ring system. These findings suggest their potential as phosphors for organic electronics. Computational modeling of 4a–c molecules provided insight into their electronic structures, conformational stability, and predicted optical behavior. The most stable conformers (4a–II, 4b–II, 4c–II′) exhibited a progressive decrease in the HOMO–LUMO gap from 4a to 4c, correlated with the enhancement of photoactivity. Among them, compound 4a stands out as the most promising luminophore, displaying the most intense and narrow luminescence band, owing to its high molecular symmetry and stable emission characteristics. Overall, this study lays the foundation for future studies of bis(oxazolo[5,4-b]pyridine) derivatives in coordination chemistry and optoelectronic materials development. Full article

To obtain data on the effects of ozonolysis on the structural and dynamic parameters of ultrafine fibers based on the binary compositions of poly-(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) with varying ratios of polymer components ranging from 0/100 to 100/0 mass%, produced by electrospinning, a study was conducted. The morphology and structural–dynamic characteristics of the ultrafine fibers were examined. Comprehensive research was carried out, combining thermophysical measurements (DSC), dynamic measurements using an electron paramagnetic resonance (EPR) technique, scanning electron microscopy, and infrared spectroscopy. The influence of the mixture’s composition and ozonolysis on the degree of crystallinity of PHB and the molecular mobility of the TEMPO radical (tetramethylpiperidine-1-oxyl) in the amorphous regions of the PHB/PVP fiber material was demonstrated. The low-temperature maximum on the DSC thermograms provided information about the fraction of hydrogen bonds in the mixed compositions, allowing for the enthalpy of thermal destruction of these bonds in both the original and oxidized samples to be determined. The study showed significant changes in the degree of crystallinity of PHB, the enthalpy of hydrogen bond destruction, molecular mobility, moisture absorption of the compositions, and the activation energy of rotational diffusion in the amorphous regions of the PHB/PVP mixed compositions. It was established that within the 50/50% PHB/PVP ratio, an inversion transition occurs from the dispersion material to the dispersion medium. Ozonolysis induces a sharp change in the material’s structure. The conducted research provided the first opportunity to assess the impact of ozonolysis on the structural and dynamic characteristics of PHB/PVP ultrafine fibers at a molecular level. These materials may serve as a therapeutic system for controlled drug delivery. Full article

Organic photovoltaic materials and nonlinear optical materials share inherent commonalities in molecular characteristics—such as strong light absorption, high charge carrier mobility, and tunable energy levels. Therefore, this study selects a bithiophene-fused ring system with photovoltaic application potential as the research subject. Using TTTTB6-2CHO (TB1) and IDTTB6-2CHO (TB2) as comparative molecules, their nonlinear optical properties in the near-infrared region were systematically investigated. Transient absorption spectroscopy results demonstrate that TB1 exhibits strong and persistent excited-state absorption within the spectral range of 650–900 nm, endowing it with excellent two-photon absorption performance (a cross-section of up to 5591 GM at 650 nm) and an ultralow optical limiting threshold (0.00147 J/cm² under 800 nm femtosecond laser irradiation). The findings of this study not only confirm the feasibility of developing nonlinear optical materials from photovoltaic candidate molecules but also highlight the effectiveness of the “thiophene-for-benzene substitution” strategy in significantly enhancing optical nonlinearity. These results provide valuable design principles for the development of multifunctional organic optoelectronic materials, particularly for application scenarios such as laser protection. Full article

In order to improve the utilization of alkali lignin (AL) as an effective component for ultraviolet (UV) shielding, demethylation and acetylation modification were carried out to improve the UV absorption performance of lignin. Then, lignin-based sunscreens were successfully prepared by mixing the modified lignin and commercial cream without UV shielding ingredients. The modified alkali lignin was comprehensively characterized in terms of its molecular weight, functional groups and structural properties by GPC, UV spectroscopy and ³¹P NMR. The results showed that the Mw of all three lignin feedstocks (AL, AL_MeOH and AL_Acetone) was decreased with prolonged demethylation time. Compared to the original feedstock, demethylated AL had a darker color and improved UV absorption performance due to the increased phenolic hydroxyl content (approximately 4.35 mmol/g). ³¹P-NMR spectra showed that the guaiacyl phenolic hydroxyl content decreased rapidly after acetylation, causing the sample color to become lighter. Among all lignin-based sunscreens, DAL_Acetone achieved the highest SPF value of 11.23, a 69.4% increase over its pre-reaction level and a 7.58-fold enhancement compared to the original lignin. In summary, this study opens a promising avenue for repurposing industrial lignin as a sustainable biomaterial in high-value sectors like UV-blocking agents and cosmetic formulations. Full article

A promising direction for the creation of new biologically active derivatives of the alkaloid lupinine is the synthesis of “hybrid molecules” that combine a fragment of the alkaloid and the pharmacophore of 1,2,3-triazole in their structure. From a biological perspective, this work presents the first X-ray diffraction study of a single crystal of (1S,9aR)-1-({4-[4-(Benzyloxy)-3-methoxyphenyl]-1H-1,2,3-triazol-1-yl}methyl)octahydro-2H-quinolizine, a new, recently synthesized 1,2,3-triazole derivative of lupinine. A comparison of theoretically predicted and experimentally observed structural parameters was carried out. The FTIR spectroscopy study and vibrational properties calculations allowed us to interpret the FTIR absorption spectrum and localize specific vibrational modes in quinolizidine, 1,2,3-triazole, and benzene rings. Such information can be fruitful for further characterization of the synthesis process and products. The molecular docking of the compound was performed. It was shown that the studied molecules are capable of interacting with the Mpro binding site via non-covalent and hydrophobic interactions with subsites S3 (Met165, Glu166, Leu167, Pro168) and S5 (Gln189, Thr190, Gln192), which ensure the stabilization of the Mpro substrate. Blocking of the active site of the enzyme in the region of the oxyanion hole does not occur, but stable stacking interactions with the π-system of one of the catalytic amino acids, His41, are observed. Full article

Short linear maltodextrin (SLMD) mixtures, which are modified from starch, comprise approximately 10 linear glucose molecules. In this study, we explored the noncovalent molecular association of SLMD with ferulic acid (FA) in aqueous and solid systems, as well as its applicability to water-in-oil (W/O) emulsion systems. Results showed that SLMD interacts with FA at a 1:1 molar ratio with an average equilibrium constant of 13.3 M⁻¹ in pure water. Changes in ellipticity in the involved circular dichroism absorption spectrum and nuclear magnetic resonance spectroscopy revealed that multipoint direct interactions exist between SLMD and FA suggesting complex formation through inclusion. Complexation does not impede the radical scavenging ability of FA; instead, there is an additive effect with a slight contribution from SLMD. SLMD crystals with a high FA content were obtained for B-type amylose. However, no strong interaction between the solid forms of SLMD and FA was recognized. For both SLMD aq. and W/O emulsions with different FA concentrations, the UV protection effect increased due to the solubility enhancement of FA by SLMD. Overall, this study demonstrates the ability and potential importance of SLMD to associate with functional components in water and solid systems and the applicability to emulsified systems. Full article

Vanadyl octa-(4-tert-butylphenyl)phthalocyanine (VOPc(t-BuPh)₈) and vanadyl octa-(4-tert-butylphenyl)tetrapyrazinoporphyrazine (VOTPyzPz(t-BuPh)₈) complexes were synthesized for the first time and confirmed by IR and UV-Vis spectroscopy and MALDI-TOF spectrometry. The method of synthesis of their precursors, 4,5-bis(4-tert-butylphenyl)phthalonitrile ((t-BuPh)₂PN) and 5,6-bis(4-tert-butylphenyl)pyrazine-2,3-dicarbonitrile ((t-BuPh)₂PDC), was modified, resulting in higher yields. For the vanadyl complexes, the basic properties were studied, and it was found that the red shift in the Q band in the first protonation step is approximately two times greater than that of previously known complexes. An electrochemical study showed the influence of aza-substitution on the redox properties and on the energies of the frontier orbitals of all the compounds presented. For all four considered compounds, quantum chemical calculations of the molecular structure, IR spectra, and electronic absorption spectra were carried out using density functional theory (DFT) and time-dependent density functional theory (TDDFT and simplified sTDDFT) approaches. According to the DFT calculations, vanadyl macrocyclic complexes have dome-shaped distorted structures. Experimental and theoretical IR and electronic absorption spectra were compared and interpreted. Full article

Photodynamic therapy is a cancer treatment that relies on a photosensitizer (PS) to generate reactive oxygen species upon light activation, thereby destroying cancer cells. The photophysical properties of porphyrins make them effective PSs, while nanoparticles (NPs) enhance their delivery and stability. The bioavailability and targeting efficiency of NPs-PS complexes may be improved through transport via human serum albumin (HSA). This study investigates the HSA binding affinity with 5,10,15,20-(Tetra-4-carboxyphenyl)porphyrin (TCPP) and with TiO₂-TCPP complexes. The interactions were analyzed using UV-Vis absorption, laser-induced fluorescence (LIF), and FTIR spectroscopy. Molecular docking was performed and provided consistent binding constant values for the TCPP–HSA complex with UV-Vis absorption measurements. LIF data revealed a slightly lower affinity when compare free porphyrin with TiO₂-TCPP, possibly due to competitive binding between TiO₂ and HSA. Docking simulations indicated that TCPP favorably interacts with amino acid residues located in subdomains IB and IIIA of HSA, supporting a preferential binding near Sudlow site I. FTIR measurements revealed conformational changes in HSA for both its interactions with TCPP and TiO₂-TCPP, including alterations in α-helical content and reorganization of the hydrogen bonding network within the polypeptide backbone. Full article

Organic phase change materials (OPCMs) show immense application potential in solar energy storages owing to high energy storage capacity and latent heat efficiency. However, it is difficult to achieve prolonged energy storage due to the sensitivity of phase change to environmental temperature, and adding other substances will lead to a decrease in total energy density. Herein, azobenzene organic phase change composite (C₁₄Azo-MA) was designed and prepared by doping myristic acid (MA) with an azobenzene derivative (C₁₄Azo) featuring a carbon chain identical to that of the MA matrix. C₁₄Azo-MA was systematically characterized by UV–Visible absorption spectroscopy and differential scanning calorimetry. The results showed that the C₁₄Azo-MA retains the same isomerization properties as the C₁₄Azo dopant. C₁₄Azo-MA, due to its molecular photoisomerization and enhanced intermolecular interactions, establishes a new energy barrier and forms supercooling within C₁₄Azo-MA, thereby allowing the storage of thermal energy below the crystallization temperature of MA. Notably, the C₁₄Azo-MA exhibits a high energy density of 225.08 J g⁻¹, surpassing that of pure MA by 14.42%. This work holds significant potential for solar energy storage applications. Full article

Understanding the influence of solvent environments on the excited-state charge transfer process remains a fundamental question in molecular photophysics and photochemistry. While twisted intramolecular charge transfer (TICT) is crucial in determining fluorescence efficiency and photostability, the combined effects of solvent polarity and hydrogen bonding interactions are still elusive. Here, we employ steady-state and femtosecond transient absorption (fs-TA) spectroscopy with density functional theory (DFT) calculations to investigate the excited-state dynamics of 7-(diethylamino)coumarin-3-carboxylic acid (7-DCCA) in different solvents. Our findings reveal that in highly polar solvents with strong hydrogen-donating and hydrogen-accepting capabilities, 7-DCCA undergoes significant TICT formation, resulting in fluorescence quenching. Conversely, in environments with low polarity or weak hydrogen-bonding interactions, this transformation is largely suppressed. Quantitative correlation analysis utilizing the Kamlet–Taft and Catalán four-parameter models further elucidates the synergistic role of solvent polarity and specific hydrogen-bonding parameters in modulating the steady-state spectral behavior of 7-DCCA. This study provides microscopic insights into solvent–charge transfer interactions and establishes a general framework for enhancing the luminescence efficiency and structural robustness of organic optoelectronic materials through strategic solvent engineering. Full article

Background and Objectives: Elastodontic appliances made of medical-grade silicone are increasingly used in interceptive orthodontics, but prolonged intraoral exposure may affect their stability. This study evaluated structural changes in LM-Activator^TM 2 appliances after clinical use, using Fourier-transform infrared (FTIR) spectroscopy. Materials and Methods: Eight appliances (one unused control and seven worn for 3–24 months) were analyzed by FTIR-ATR in the 4000–650 cm⁻¹ range. Absorption bands characteristic of polydimethylsiloxane (PDMS) were quantified, and indices reflecting backbone crosslinking, side-group retention, hydrophilicity, and relative reduction in methyl-related spectral contributions were calculated. Results: The PDMS backbone remained chemically intact across all samples. However, progressive molecular reorganization was detected with wear duration. The Backbone Dominance Index increased significantly from control to 24 months, while side-group indices decreased, confirming apparent depletion of methyl-related FTIR bands. Hydrophilicity and crosslinking indices rose over time, particularly after 12 months, indicating increased surface polarity and network densification. Conclusions: LM-Activator^TM 2 appliances undergo gradual intraoral aging, marked by backbone crosslinking and apparent reduction in methyl-associated vibrational contributions inferred from FTIR ratio side-groups. These changes, while not compromising the polymer identity, may influence surface properties, biofilm retention, and long-term mechanical behavior. Periodic replacement is recommended to ensure optimal clinical performance. Full article

Azulene-based chromophores are of growing interest due to their unique electronic structures and potential applications as pH-responsive optical materials. In this study, a series of azulene–1,3,6,8-tetraazapyrene (TAP) triads were successfully synthesized and characterized to systematically explore how connectivity between the TAP and azulene units influences their optical and redox properties. UV-Vis absorption spectroscopy and cyclic voltammetry measurements clearly show that the electronic properties depend heavily on the connectivity pattern, as the effective π-conjugation and molecular planarity vary considerably in triads. Remarkably, triads A₂₂ and A₂₆, in which the TAP core is directly connected through the electron-rich five-membered ring, exhibit enhanced π-conjugation and pronounced color changes upon protonation. In contrast, A₆₆, linked via the electron-deficient seven-membered ring, reveals weaker π-conjugation and less pronounced pH-responsiveness. These experimental findings are further supported by DFT calculations. This comprehensive structure–property relationship study provides valuable insights for the rational design of advanced optoelectronic and stimuli-responsive materials. Full article

Produced from the parenchymatous tissue of the stem pith of Tetrapanax papyrifer, the material known as pith paper served as a distinctive support medium for Chinese export paintings during the 19th and early 20th centuries. Today, it is commonly found in collections worldwide. Due to its inherently fragile structure, conservation interventions are often necessary. However, the material’s chemical composition and deterioration mechanisms remain poorly understood, which not only complicates treatment decisions but also undermines preventive conservation efforts. This study presents a systematic investigation into the anatomical structure and ageing behaviour of pith paper using a multi-analytical approach. Optical and scanning electron microscopy revealed a preserved honeycomb-like cellular architecture composed of thin-walled, entirely of non-lignified parenchyma cells, which contributes to the material’s mechanical fragility. Artificial ageing experiments showed a significant loss of flexibility, increased yellowing, and a decline in pH with ageing time. Infrared spectroscopy identified molecular changes consistent with cellulose chain scission, with decreases in O–H and C–O–C absorptions revealing acid-hydrolysis-driven breakdown, while colourimetry pointed to the formation of chromophoric degradation products. These findings offer a foundational understanding of pith paper’s vulnerabilities and provide essential insights for the development of informed conservation and storage strategies. Full article

Low temperatures have a significant impact on the growth, development, and productivity of cucumber plants. The potential of near-infrared spectroscopy and the aquaphotomics approach for investigating chilling stress was studied in Voreas F1 and Gergana cultivars. Changes in the spectral patterns of cucumber plants were compared with physiological and metabolic data. Voreas plants were unable to survive seven days of low-temperature stress due to a drastic increase in electrolyte leakage and a decrease in the net photosynthesis rate, stomatal conductance, and transpiration rate. Gergana plants survived chilling by preserving cell membrane integrity and photosynthesis efficiency. During chilling treatment, the content of most metabolites in both cultivars was reduced compared to the controls, yet it was much more pronounced in Voreas. We observed an increased accumulation of cinnamic acid on the seventh day only in the Gergana cultivar. A MicroNIR spectrometer was used for in vivo spectral measurements of cotyledons and the first two leaves. Differences in absorption spectra were observed among control, stressed, and recovered plants, across different days of stress, and between the studied cultivars. The most significant differences were in the 1300–1600 nm range, much smaller for Gergana than Voreas. Aquagrams of the two cultivars also reveal differences in their responses to low temperatures and changes in water molecular structure in the leaves. The errors of prediction for the days of chilling by using PLS models were from 0.96 to 1.14 days for independent validation, depending on the spectral data of different leaves used. Near-infrared spectroscopy and aquaphotomics can be used as additional tools for early detection of stress and investigation of low-temperature tolerance in cucumber cultivars. Full article