Changes In Absorption Spectra Research Articles

Exploiting Hydrogen Interaction of Drugs and Biodegradable Scaffolds Using Nanoparticles Loaded Nanofibers

AbstractThis study presents a detailed investigation of the structural and surface modifications of Fe3O4 nanoparticles (NPs). Fourier Transform Infrared (FTIR) spectroscopy was utilized to analyze the distinct characteristic peaks of Fe3O4 NPs and their subsequent modifications with stearic acid (ST) layers. The FTIR analysis revealed characteristic peaks at 580 cm−1, and 441 cm−1, corresponding to the Fe‐O stretching vibrations of the bulk Fe3O4 NPs. The successful loading of stearic acid onto the Fe3O4 NPs was confirmed by the appearance of new peaks at 1413 cm−1 and 2908 cm−1, indicative of the asymmetric CH2 stretch and CH3 umbrella vibration modes of stearic acid. UV‐Vis spectroscopy further corroborated the efficient loading of tetracycline and ibuprofen onto Fe3O4/DST nanoparticles, as evidenced by changes in absorption spectra. N2 adsorption‐desorption isotherms illustrated the presence of micro and meso pores on the surface of Fe3O4 NPs, with alterations in pore volume and diameter post‐surface modification and drug loading. Evaluation of magnetic properties indicated a reduction in saturation magnetization after surface modification and drug loading, attributed to changes in homogeneity and surface moments. Differential Reflectance Spectroscopy (DRS) and Raman spectroscopy elucidated distinctive peaks and shifts in spectra, confirming the composition and structural changes in drug‐loaded nanofibers.

Spectroscopic behavior of bufotenine and bufotenine N-oxide: Solvent and pH effects and interaction with biomembrane models

Bufotenine is a fluorescent analog of Dimethyltryptamine (DMT) that has been widely studied due to its psychedelic properties and biological activity. However, little is known about its spectroscopic properties in different media. Thus, we present in this work, for the first time, the spectroscopic behavior of bufotenine and bufotenine N-oxide by means of their fluorescence properties. Both molecules exhibit changes in optical absorption and emission spectra with variations in pH of the medium and in different solvents. Assays in the presence of biomembranes models, like micelles and liposomes, were also performed. In surfactants titration experiments, the spectral shift observed in fluorescence shows the interaction of both molecules with pre-micellar structures and with micelles. Steady state anisotropy measurements show that both bufotenine and bufotenine N-oxide, in the studied concentration range, interact with liposomes without causing changes in the fluidity of the lipid bilayer. These results can be useful in studies that aim at searching for new compounds, inspired by bufotenine and bufotenine N-oxide, with relevant pharmacological activities and also in studies that use these molecules as markers of psychiatric disorders.

An Introduction to Processing, Fitting, and Interpreting Transient Absorption Data.

Transient absorption (TA) spectroscopy is a powerful time-resolved spectroscopic method used to track the evolution of excited-state processes through changes in the system's absorption spectrum. Early implementations of TA were confined to specialized laboratories, but the evolution of commercial turn-key systems has made the technique increasingly available to research groups across the world. Modern TA systems are capable of producing large datasets with high energetic and temporal resolution that are rich in photophysical information. However, processing, fitting, and interpreting TA spectra can be challenging due to the large number of excited-state features and instrumental artifacts. Many factors must be carefully considered when collecting, processing, and fitting TA data in order to reduce uncertainty over which model or set of fitting parameters best describes the data. The goal of data preparation and fitting is to reduce as many of these extraneous factors while preserving the data for analysis. In this method, beginners are provided with a protocol for processing and preparing TA data as well as a brief introduction to selected fitting procedures and models, specifically single wavelength fitting and global lifetime analysis. Commentary on a number of commonly encountered data preparation challenges and methods of addressing them is provided, followed by a discussion of the challenges and limitations of these simple fitting methods.

A sensor array based on a nanozyme with polyphenol oxidase activity for the identification of tea polyphenols and Chinese green tea

Green tea is popular among consumers because of its high nutritional value and unique flavor. There is often a strong correlation among the type of tea, its quality level and the price. Therefore, the rapid identification of tea types and the judgment of tea quality grades are particularly important. In this work, a novel sensor array based on nanozyme with polyphenol oxidase (PPO) activity is proposed for the identification of tea polyphenols (TPs) and Chinese green tea. The absorption spectra changes of the nanozyme and its substrate in the presence of different TPs were first investigated. The feature spectra were scientifically selected using genetic algorithm (GA), and then a sensor array with 15 sensing units (5 wavelengths × 3 time) was constructed. Combined with the support vector machine (SVM) discriminative model, the discriminative rate of this sensor array was 100% for different concentrations of typical TPs in Chinese green tea with a detection limit of 5 μM. In addition, the identification of different concentrations of the same tea polyphenols and mixed tea polyphenols have also been achieved. Based on the above study, we further developed a facile and efficient new method for the category differentiation and adulteration identification of green tea, and the accuracy of this array was 96.88% and 100% for eight types of green teas and different adulteration ratios of Biluochun, respectively. This work has significance for the rapid discrimination of green tea brands and adulteration.

One-pot polycondensation and characterization of melamine-based polymer for mercury and sodium hypochlorite sensing

A porous, low-cost, organic, amorphous and carbon-nitride functionalized polymer was synthesized using melamine and 5-bromo-2-thiophenecarboxaldehyde. One-pot polycondensation method was opted, to yield hyper-crosslinked polyaminal network which was used for the detection of NaOCl and Hg2+. Reaction proceeds in single step without addition of any catalyst and gives promising yield. The authenticity of the synthesized polymer MB was established using X-Ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) and Energy-dispersive spectroscopy (EDS). However, the morphology and thermal stability of MB was studied using X-Ray diffraction (XRD) & Scanning electron microscopy (SEM) and Thermogravimetric analysis (TGA) & Differential thermal analysis (DTA) respectively. BET studies were carried out to analyze the porous structure of MB. The pore diameter is centred at 6.2851 nm with specific surface area of 24.348 m2 g–1 and pore volume of 0.038258 cm3 g–1. The TGA curve showed that it has a good thermal stability (250°C). The synthesized compound was checked for its sensing behaviour with different analytes (metal ions: Cu2+, Cr2+, Mg2+, Cd2+, Mn2+, Zn2+, Pb2+, Hg2+; acids: HCl, H2SO4, HNO3 and ROS: t-BuOOH, KO2, NaOCl) in deionized water and was found to show significant change in intensity with NaOCl and Hg2+. The change in absorption spectra was observed at varied concentrations of NaOCl and Hg2+ solutions in deionized water using UV-Vis. Spectrophotometer.

Unveiling structural and energetic characterization of the emissive RNA alphabet anchored in the methylthieno[3,4-d]pyrimidine heterocycle core.

This study presents a comprehensive theoretical exploration of the fluorescent non-natural emissive nucleobases- mthA, mthG, mthC, and mthU derived from the methylthieno[3,4-d]pyrimidine heterocycle. Our calculations, aligning with experimental findings, reveal that these non-natural bases exert minimal influence on the geometry of classical Watson-Crick base pairs within an RNA duplex, maintaining H-bonding akin to natural bases. In terms of energy, the impact of the modified bases, but for mthG, is also found to be little significant. We delved into an in-depth analysis of the photophysical properties of these non-natural bases. This investigation unveiled a correlation between their absorption/emission peaks and the substantial impact of the modification on the energy levels of the highest unoccupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbital (LUMO). Notably, this alteration in energy levels resulted in a significant reduction of the HOMO-LUMO gap, from approximately 5.4-5.5 eV in the natural bases, to roughly 3.9-4.7 eV in the modified bases. This shift led to a consequential change in absorption and emission spectra towards longer wavelengths, elucidating their bathochromic shift.

Self-indicating polymers: a pathway to intelligent materials.

Self-indicating polymers have emerged as a promising class of smart materials that possess the unique ability to undergo detectable variations in their physical or chemical properties in response to various stimuli. This article presents an overview of the most important mechanisms through which these materials exhibit self-indication, including aggregation, phase transition, covalent and non-covalent bond cleavage, isomerization, charge transfer, and energy transfer. Aggregation is a prevalent mechanism observed in self-indicating polymers, where changes in the degree of molecular organization result in variations in optical or electrical properties. Phase transition-induced self-indication relies on the transformation between different phases, such as liquid-to-solid or crystalline-to-amorphous transitions, leading to observable changes in color or conductivity. Covalent bond cleavage-based self-indicating polymers undergo controlled degradation or fragmentation upon exposure to specific triggers, resulting in noticeable variations in their structural or mechanical properties. Isomerization is another crucial mechanism exploited in self-indicating polymers, where the reversible transformation between the different isomeric forms induces detectable changes in fluorescence or absorption spectra. Charge transfer-based self-indicating polymers rely on the modulation of electron or hole transfer within the polymer backbone, manifesting as changes in electrical conductivity or redox properties. Energy transfer is an essential mechanism utilized by certain self-indicating polymers, where energy transfer between chromophores or fluorophores leads to variations in the emission characteristics. Furthermore, this review article highlights the diverse range of applications for self-indicating polymers. These materials find particular use in sensing and monitoring applications, where their responsive nature enables them to act as sensors for specific analytes, environmental parameters, or mechanical stress. Self-indicating polymers have also been used in the development of smart materials, including stimuli-responsive coatings, drug delivery systems, food sensors, wearable devices, and molecular switches. The unique combination of tunable properties and responsiveness makes self-indicating polymers highly promising for future advancements in the fields of biotechnology, materials science, and electronics.

Ultrafast spectroscopy of the hydrophilic carotenoid crocin at various pH.

This study delves into the pH-dependent effects on the excited-state behavior of crocin, a hydrophilic carotenoid with diverse functions in biological systems. Steady-state spectroscopy demonstrates notable changes in absorption and fluorescence spectra, characterized by a pH-dependent blue shift and altered resolution of vibrational bands. Transient absorption spectra further elucidate these effects, highlighting a significant blue shift in the S1-Sn peak with increasing pH. Detailed kinetic analysis shows the pH-dependent dynamics of crocin's excited states. At pH 11, a shortening of effective conjugation is observed, resulting in a prolonged S1/ICT lifetime. Conversely, at pH 9, our data suggest a more complex scenario, suggesting the presence of two distinct crocin species with different relaxation patterns. This implies structural alterations within the crocin molecule, potentially linked to the deprotonation of hydroxyl groups in crocin and/or saponification at high pH.

Enhanced intramolecular charge transfer and near-infrared fluorescence in 4-dimethylamino-chalcone analogues through extended conjugation: synthesis, photophysical properties, and theoretical modelling.

The distinctive characteristics of near-infrared fluorescent organic molecules render them indispensable across diverse applications, from energy harvesting to bioimaging and sensing technologies. In this work, we continue our investigation on the chalcone derivative, 4-dimethylamino-2'-hydroxychalcone (nDHC, n = 1; where n is the number of olefinic bonds), by expanding the number of central double bonds (n = 2 (2DHC) and n = 3 (3DHC)). Additionally, we also synthesized the structurally related chalcones lacking the OH group (DC, 2DC, 3DC) in order to obtain a comprehensive understanding of their effects on the intramolecular charge transfer (ICT). The results show remarkable bathochromic shifts in absorption and fluorescence peaks in solution as n increases. These shifts, 20 nm and 35 nm for absorption and 100 nm and 200 nm for fluorescence in 2DHC and 3DHC, respectively, signify enhanced ICT and a significant increase in the excited state's dipole moment. The presence of OH groups notably amplifies these shifts due to additional electron donation, influencing solute-solvent interactions in solution. Femtosecond fluorescence upconversion and transient absoprtion techniques unraveled distinct dynamics in these derivatives, exhibiting the dominance of vibrational cooling, solvation, and intramolecular motions, particularly in the larger conjugated systems 3DHC and 3DC. The observed changes in the femtosecond transinet absorption spectra suggest the existence of new active states in extended conjugation systems, indicating diverse intramolecular conformational states contributing to their relaxation dynamics. The results of this study provide invaluable insights into excited-state spectroscopy, offering a roadmap for tailoring chalcone derivatives for specific applications.

An ultrafast and highly sensitive fluorescent probe for the detection of HSO3− and its application in food samples and SO2 gas

SO2 is one of the main components of air pollution gas, its derivatives HSO3− and SO32− were considerable used as food additive because of their antiseptic and bacteriostatic effects. Excessive intake of HSO3− is harmful to human health, so it is extremely important to detect the content of HSO3− in food sample by effective method. In this work, a small molecular fluorescence probe TPE-O based on tetraphenylethene fluorophore was designed and synthesized. The probe showed ultrafast (< 3 s) and obvious colorimetric response to HSO3− with high selectivity and sensitivity (LOD = 210 nM). The possible Michael-type addition of HSO3− on the activated C = C bond blocked the π-conjugated system, thus lead to changes in fluorescence and absorption spectra. Probe TPE-O not only can detect the content of HSO3− in sugar and wine, but also can be loaded on agarose hydrogel to detect SO2 gas. Therefore, this work provided a powerful tool for the detection of HSO3− in food samples and SO2 gas.

Pore Nanoarchitectonics of Carbon Nitrides for the Excited‐State Deactivation of Confined Methylene Blue

AbstractThe confinement of organic chromophores within mesoporous material architectures can exert a considerable alteration on their physico‐chemical properties. This study presents a detailed spectroscopic investigation of methylene blue (MB) entrapped in mesoporous polymeric carbon nitrides (mPCNs) with different pore architecturesusing transient absorption spectroscopy (TAS). The spatial confinement of MB molecules results in a prominent change in absorption spectra, characterized by both redshifts and the appearance of additional shoulder peaks, arising from the formation of MB dimers (MB2) concomitant with a distortion of the MB structure. Upon photoexcitation, entrapped MB molecules exhibit a notable altered excited‐state absorption feature, along with a drastic excited‐state quenching within 2 ns compared to molecues in bulk solutions. In contrast to the ultrafast quenching of sole MB2 with a lifetime of ~3.6 ps in highly concentrated solutions, the concentration‐dependent quenching behavior of MB aggregates in confined environments suggests the effect is caused by excimers formed in close proximity. The findings of this work highlight the impact of constrained environments and intermolecular interactions on the relaxation pathways of the excited states in photoactive molecules.

Arthrospira cell residue valorization: A study on protein hydrolysate production by limited enzymatic hydrolysis

Arthrospira cell residue (ACR) is a byproduct of the spirulina industry that can be valorized into protein hydrolysates. In this study, we used alkaline protease to hydrolyze ACR and evaluated the effects of hydrolysis time on the properties and functionalities of the hydrolysates. We measured the degree of hydrolysis (DH), particle size, fluorescence, UV‒visible absorption, surface hydrophobicity, emulsification, solubility, and antioxidant activity of the hydrolysates. The DH reached a maximum of 10.2% ± 0.6% after 240 min. Hydrolysis also altered the structure and conformation of the ACR protein, as shown by changes in fluorescence, UV-visible absorption, and FTIR spectra. Hydrolysis enhanced the solubility, surface hydrophobicity, and emulsifying activity of the hydrolysates but not the emulsion stability. The hydrolysates also exhibited higher antioxidant activity than ACR. These results indicate that enzymatic hydrolysis can convert ACR into valuable protein hydrolysates.

Upconversion luminescence nanosensor for detection of Fe3+ and phosphate ion based on the inner-filter effect.

In this work, an upconversion luminescence (UCL) nanosensor for fast detection of ferric ion (Fe3+) and phosphate ion (Pi) is developed based on the inner-filter effect (IFE) between NaYF4:Yb/Er upconversion nanoparticles (UCNPs) and Fe3+-hypocrellin B (HB) complex. Fe3+-HB complex has strong absorption band (450-650nm), which overlaps with the green emission peak of UCNPs at 545nm. By adding Fe3+ and Pi, the UCNPs-HB system produces the red-shift change of absorption spectrum, which leads to the "on-off-on" process of IFE. So, with the specific recognition ability of HB for Fe3+ and the competitive complexation of Pi for Fe3+, the proposed nanosensor utilizes the UCL change to achieve the detection of the targets. For the detections of Fe3+, the linear range is 10-600μM with a limit of detection (LOD) of 2.62μM, and for Pi, the linear range is 5-100μM with a LOD of 1.25μM. The results for selectivity, precision, and recovery test are also satisfactory. Furthermore, the real sample detection shows that the proposed nanaosensor has a great potential in environmental and biological systems. An upconversion luminescence (UCL) nanosensor based on the inner-filter effect (IFE) between upconversion nanoparticles (UCNPs) and Fe3+-hypocrellin B (HB) complex for the detection of Fe3+ and phosphate ion has been proposed, which is promising to be a convenient and sensitive assay for monitoring Fe3+ and phosphate ion in different environments and biological systems.

A graphene-metal hybrid biosensor for SEIRA spectroscopy applications

Detecting the building blocks of all living organisms plays a vital role in medical diagnosis and biological research. Infrared (IR) spectroscopy is one of the techniques for detecting biomolecules, such as DNA, RNA, and lipids, through their vibrational fingerprints. IR spectroscopy provides biosensing by directly measuring changes in absorption spectra; however, nanometric-size molecules reveal a weak signal-to-noise ratio with IR light, which is a disadvantage for sensitive bio-detection. Surface-Enhanced Infrared Spectroscopy (SEIRA) based on different structures and materials has been widely used to overcome this problem. In this study, a SEIRA platform based on a hybrid graphene-metal nanoantenna array is designed by combining the enhanced sensitivity of graphene with its electrical tunability and strong-field enhancement with metallic structures. The plasmonic resonance of graphene nano-slit is dynamically tuned to detect fingerprints of protein monolayer at different frequencies. The same detection behavior has been statically demonstrated by metallic antennas. Our results indicate that the sensitivity of the SEIRA sensor platform is quite high due to the combination of graphene and metal hybrid structure compared to the metal resonator alone because of the strong light confinement in the graphene layer. The proposed biosensor can detect the Amid-I and Amid-II bonds, which create relatively strong vibrational fingerprints, as well as the Amide-III bond, which is a very weak bond of a monolayer protein-goat-mouse Immunoglobulin (IgG) protein. It can also be a very useful characterization tool for identifying the molecular fingerprints of unknown chemicals and molecules with its capability to span a large spectral range either dynamically or statically. The strong light absorption via metallic structures compensates for the large areal coverage of graphene sheets, which is quite a challenge for dynamic tuning in real applications.

Orange Carotenoid Protein in Mesoporous Silica: A New System towards the Development of Colorimetric and Fluorescent Sensors for pH and Temperature.

Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs-containing echinenone or canthaxanthin as carotenoids-is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λMAX shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λMAX shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors.

Terahertz dual-tunable absorber based on hybrid gold-graphene-strontium titanate-vanadium dioxide configuration

A terahertz dual-tunable polarization-independent metamaterial absorber based on hybrid gold-graphene-strontium titanate (STO)-vanadium dioxide (VO2) configuration is proposed. The results show that the absorption rate of absorber can achieve 98.3% at 0.2 THz. Moreover, both the absorption frequency and absorption rate of the absorber can be dual-tuned by varying the chemical potential of graphene and temperature of STO and VO2. Additionally, the performance of the absorber is theoretically analyzed by using the coupled mode theory (CMT) and impedance matching theory (IMT). Finally, the changes in the absorber's absorption spectra are discussed when the depth of STO and VO2 layers is modified. This work provides a theoretical basis for the designs of dual-tunable absorbers and filters, and also offers a new method for switching and modulation of THz radiation.

Effect of Chloride, Sulfate, and Ferrate Salts on Electronic Energy Levels of Anthracene Proving it a Potential Candidate as an ON and ON-OFF UV-Vis Sensor.

Anthracene molecule possesses remarkable optical activity and till today this molecule is of special interest of scientists. Present study is focused on the study of effects of Chloride, Sulfate, Nitrate and Ferrate salts on absorption and emission spectra of targeted fluorophore in carbontetrachloride, chloroform, dichloromethane and methanol. Prominent solvatochromic effects shows dependence of HOMO-LUMO orbitals on solvent polarity. Anthracene molecules exhibits changes in absorption and emission spectra, and show both ON and ON-OFF behavior on addition of said ions. Based on experimental results it was concluded that fluorophore molecule could be used more effectively as UV-Visible (UV-V) sensors in comparison to the emission sensor.

Synthesis and characterization of azulene-based BO-doped heteroaromatics

Simultaneously incorporating heteroatoms and nonbenzenoid aromatic hydrocarbons, such as azulene, into polycyclic aromatic hydrocarbons, offers a robust strategy for designing molecules with aesthetic appeal and unique properties. This study presents the successful synthesis and characterization of a series of azulene-based BO-doped heteroaromatics. Investigation into their optical and electrochemical properties, through UV–vis absorption, cyclic voltammetry, and DFT calculations, reveal their sensitivity to fluoride ions, making them promising candidates for chemosensor applications. Notably, unlike the parent azulene, which is sensitive to acid, these new compounds show negligible changes in absorption and NMR spectra when exposed to excess trifluoroacetic acid. This observation suggests that the introduction of BO unit effectively restrains the protonation of azulene moiety.

Solution Studies of a Water-Stable, Trivalent Antimony Pnictogen Bonding Anion Receptor with High Binding Affinities for CN-, OCN-, and OAc.

The solution phase anion binding behavior of a water-stable bidentate pnictogen bond donor was studied. A modest change in the visible absorption spectrum allowed for the determination of the binding constants. High binding constants were observed with cyanide, cyanate, and acetate, and these were corroborated with density functional theory (DFT) calculations. The receptor could be recovered free from the anion following treatment with methyl triflate, confirming that it remains intact. The tight binding of cyanide and water stability were exploited to use this system as a supramolecular catalyst in a phase-transfer Strecker reaction, further demonstrating the utility of pnictogen bonding as a tool in noncovalent catalysis.

Imidazole-based optical sensors as a platform for bisulfite sensing and BSA/HSA interaction study. An experimental and theoretical investigation

The fluorescent lapachones were obtained from lapachol, a natural product extracted from the heartwood of Tabebuia sp. (Tecoma). The extracted lapachol was oxidized and cyclized to obtain the compounds β-lapachone and nor-β-lapachone, and treatment with terephthalaldehyde led to the final products with ∼ 60% yield. The photophysical studies showed absorption maxima in the violet region (∼400 nm) and fluorescence emission maxima depending on the solvent, ranging from 430 to 575 nm with a relatively large positive solvatochromism, confirmed by the Lippert-Mataga plot. Theoretical calculations corroborate the experimental observations regarding the ICT mechanism. The imidazoles showed a selective response to bisulfite ion (HSO3−) over other common anions, displaying a large change in both fluorescence and absorption spectra immediately after the addition of bisulfite, proving their potential application in tracing the bisulfite in future biological systems. The binding capacity of the imidazoles with human or bovine serum albumin (HSA and BSA, respectively) is spontaneous, weak (102–103 M−1 range), and subdomains IIA (Site I) and IB (Site III) are the main binding regions for the imidazoles depending on the nature of the metabolite or drug previously complexed with the albumin structure. Overall, both albumins have the same capacity to interact with the imidazoles under study.