RESUMEN

The aluminum content of concentrated (27 wt%) sodium chloride solutions could be crucial for large-scale chlor-alkali-based industries applying membrane cell electrolysis. Thus, a facile method which enables a fast and reliable protocol to determine the Al content of these solutions on ppb scale in industrial environments is fundamentally important. It was demonstrated that the increased sensitivity of colorful Al-ECR (eriochrome cyanine R) complex by the use of a cationic surfactant and specific biological buffers could effectively indicate the Al content in an extended pH interval of a concentrated saline medium under industrial conditions. The dependence of the analytical protocol on pH, temperature, time, wavelength, and the salinity of the medium was investigated. It was shown that the absorbance-based measurements of the solution should be performed at least 2-4 h after its preparation. By applying the selected two Good's buffers (HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, MOPS: 3-(N-morpholino)-propanesulfonic acid) and Tris (tris(hydroxymethyl)aminomethane), 32.8-38.1 % increase in the sensitivity was achieved for saturated NaCl solutions. Moreover, the limits of detection and quantification (LOD, LOQ) were also lowered by 19.0-29.8 %, and the salinity dependence of the calibration was also reduced.

RESUMEN

To date, the commonly used methods for diffusion coefficient measurements have some hurdles that prevent them from being widely applied in pharmaceutical laboratories. This study aimed to modify a method developed by di Cagno et al. based on the use of a UV-Vis spectrometer and apply the method to investigate the effect of dissolution media on the diffusivity of small molecules and proteins. A total of five small molecules and two proteins in different aqueous media and polymer solutions were investigated in this study. By attaching a 3D-printed cover with an open slit to a standard UV-Vis cuvette, the incident UV light could only pass through the open slit to measure the local drug concentration. During the diffusion experiment, drug molecules diffused from the cuvette bottom to the slit. According to the concentration measured as a function of time, diffusion coefficient was calculated based on Fick's law of diffusion using the analytical and numerical approaches. As a result, diffusion coefficients could be accurately measured with high reproducibility. The results also suggested that different media could affect the diffusion coefficients of small molecules by < 10% and proteins by < 15%. Since the UV-Vis spectrometer is a routine instrument, this method can potentially be employed by many pharmaceutical laboratories for diffusion coefficient measurements.

RESUMEN

Silver nanotriangles (AgNTs) were successfully synthesized as a colorimetric probe for selective and sensitive histidine detection in aqueous media within a 15-100 µM range and a detection limit of 330 nM using UV-Vis spectroscopy. The interaction of HgCl2 with AgNTs would lead to the formation of disk-shaped Ag/Hg amalgam as observed from the transmission electron images and X-ray diffraction patterns. Histidine prevents these structural and morphological changes and accordingly, the detection approach was developed based on the correlation between the histidine concentration and the in-plane dipole plasmon resonance (DPR) intensity.

RESUMEN

This work aims at studying why azodicarbonamide (ADCA), a formally apolar compound with good hydrogen bond (HB) acceptors, is soluble only in polar aprotic solvents like dimethyl sulfoxide (DMSO) but not in water. Solubility measurements, as well as quantum mechanical and classical molecular dynamics simulations, were employed to tackle the problem. We found that in the liquid phase a polar conformer of ADCA (µ = 8.7 D), unreported to date, is favoured under the enthalpic drive provided by a highly polar solvent. At the same time, the very high hydrogen bond propensity of water with itself prevents this solvent from providing an effective hydrogen bond-mediated solvation. Solvents bearing good HB acceptors, while lacking strong HB donors, contribute to further stabilizing solute-solvent adducts through weak and fluxional HBs that involve the amide groups of ADCA. Implications for the solubility of ADCA down to µM concentrations were evaluated, also with the aid of classical simulations of solution nanodroplets.

RESUMEN

Expanding on earlier observations, we show that many melanin materials, in vitro synthesized from a wide range of precursors, can be fractionated into a dark-colored precipitate and a near-colorless, dispersible fraction. The dispersible fractions exhibited absorbance in the UVA and UVB range of the electromagnetic spectrum, but none in the visible range. In addition, fluorescent properties were associated with all dispersible fractions obtained. FT-IR spectroscopic analyses were performed to compare both types of fractions. Overall, it appears that some of the properties associated with melanin (UV absorbance, fluorescence) may not necessarily reside in the dark-colored portion of melanin, but in a colorless fraction of the material. It remains to be seen whether any of these in vitro observations have any relevance in vivo. However, we raise the possibility that the presence of a colorless fraction within melanin materials and their associated properties may have received inadequate attention. Given the important association between melanin, UV protection, and skin cancer, it is worthwhile to consider this additional aspect of melanin chemistry.

Asunto(s)

RESUMEN

Porphyrins are intermediate metabolites in the biosynthesis of vital molecules, including heme, cobalamin, and chlorophyll. Bacterial porphyrins are known to be proinflammatory and have been associated with biofilm production. This study investigated porphyrin production by strains of Corynebacterium diphtheriae using emission spectroscopy, high-performance liquid chromatography with fluorescence detection, a diode array detector, and mass spectrometry. Emission spectroscopy revealed characteristic porphyrin emission spectra in all strains, with coproporphyrin III predominating. Qualitative analysis via different chromatography methods revealed identified coproporphyrin III, uroporphyrin I, and protoporphyrin IX in all the strains. Quantitative analysis revealed strain-dependent coproporphyrin III production. More studies are needed to investigate the relationship between porphyrin production and the virulence potential of Corynebacterium diphtheriae.

RESUMEN

Parallel-stranded G-quadruplex structures are found to be common in the human promoter sequences. We tested highly fluorescent 9-methoxyluminarine ligand (9-MeLM) binding interactions with different parallel G-quadruplexes DNA by spectroscopic methods such as fluorescence and circular dichroism (CD) titration as well as UV melting profiles. The results showed that the studied 9-MeLM ligand interacted with the intramolecular parallel G-quadruplexes (G4s) with similar affinity. The binding constants of 9-methoxyluminarine with different parallel G4s were determined. The studies upon oligonucleotides with different flanking sequences on c-MYC G-quadruplex suggest that 9-methoxyluminarine may preferentially interact with 3'end of the c-MYC promoter. The high decrease in 9-MeLM ligand fluorescence upon binding to all tested G4s indicates that 9-methoxyluminarine molecule can be used as a selective fluorescence turn-off probe for parallel G-quadruplexes.

Asunto(s)

RESUMEN

4-Nitroquinoline-N-oxide (NQO) and 4-nitropyridine-N-oxide (NPO) are important precursors for the synthesis of substituted heterocycles while NQO is a popular model mutagen and carcinogen broadly used in cancer research; intermolecular interactions are critical for their reactions or functioning in vivo. Herein, the effects of the coordination of N-oxide's oxygen atom to Lewis acids on multicenter donor-acceptor bonding were explored via a combination of experimental and computational studies of the complexes of NQO and NPO with a typical π-electron donor, pyrene. Coordination with ZnCl2 increased the positive electrostatic potentials on the surfaces of these π-acceptors and lowered the energy of their LUMO. Analogous effects were observed upon the protonation of the N-oxides' oxygen or bonding with boron trifluoride. The interaction of ZnCl2, NPO, or NQO and pyrene resulted in the formation of dark co-crystals comprising π-stacked Zn-coordinated N-oxides and pyrene similar to that found with protonated or (reported earlier) BF3-bonded N-oxides. Computational studies indicated that the coordination of N-oxides to zinc(II), BF3, or protonation led to the strengthening of the multicenter bonding of the nitro-heterocycle with pyrene, and this effect was related both to the increased electrostatic attraction and molecular-orbital interactions in their complexes.

RESUMEN

Butin and butein are significant bioactive flavanones derived from plants, existing as tautomers of each other. However, their physicochemical attributes, such as their spectral profiles under varying experimental conditions in aqueous solutions and established chromatographic methods for distinguishing between them, remain undetermined. In this study, we determined the basic properties of butin and butein using conventional spectroscopic, reversed-phase, and chiral HPLC analyses. The spectra of the synthesized butin and butein were analyzed using a UV-Vis spectrophotometer in several solvents with different polarities as well as in aqueous solutions at various pH values. Furthermore, the behavior of the measured spectra was reproduced by calculations to reveal the effects of the solvent and pH on the spectra of butin and butein in organic and aqueous solutions. Subsequently, we assessed the structural stability of butin and butein using reversed-phase HPLC, which revealed that butein is unstable compared with butin in a general culture medium. The synthesized butin was effectively separated into R- and S-isomers with positive and negative Cotton effects, respectively, via HPLC using a chiral column. These findings will aid in uncovering the individual properties of both butin and butein that may have been concealed by their tautomerism and enable the synthesis of S-butin, which is typically challenging and time-consuming to isolate.

Asunto(s)

RESUMEN

A spectroscopic setup for isomerization quantum yield determination is reported. The setup combines fiber-coupled LEDs, a commercially calibrated thermopile detector for measurement of the photon flux, and a fiber-coupled UV-vis spectrometer. By solving the rate equations numerically, isomerization quantum yields can be obtained from the UV-vis absorption spectra. We show that our results for the prototypical photoswitch azobenzene are in excellent agreement with the literature. The analysis of the errors showed that the quantum yields determined using this method are in the same order of magnitude as when using actinometry, thus demonstrating the reliability of our setup.

RESUMEN

BACKGROUND: The phenolic polymer lignin is one of the primary chemical constituents of the plant secondary cell wall. Due to the inherent plasticity of lignin biosynthesis, several phenolic monomers have been shown to be incorporated into the polymer, as long as the monomer can undergo radicalization so it can participate in coupling reactions. In this study, we significantly enhance the level of incorporation of monolignol ferulate conjugates into the lignin polymer to improve the digestibility of lignocellulosic biomass. RESULTS: Overexpression of a rice Feruloyl-CoA Monolignol Transferase (FMT), OsFMT1, in hybrid poplar (Populus alba x grandidentata) produced transgenic trees clearly displaying increased cell wall-bound ester-linked ferulate, p-hydroxybenzoate, and p-coumarate, all of which are in the lignin cell wall fraction, as shown by NMR and DFRC. We also demonstrate the use of a novel UV-Vis spectroscopic technique to rapidly screen plants for the presence of both ferulate and p-hydroxybenzoate esters. Lastly we show, via saccharification assays, that the OsFMT1 transgenic p oplars have significantly improved processing efficiency compared to wild-type and Angelica sinensis-FMT-expressing poplars. CONCLUSIONS: The findings demonstrate that OsFMT1 has a broad substrate specificity and a higher catalytic efficiency compared to the previously published FMT from Angelica sinensis (AsFMT). Importantly, enhanced wood processability makes OsFMT1 a promising gene to optimize the composition of lignocellulosic biomass.

RESUMEN

Creatinine is the end product of the catabolism of creatine and creatine phosphate. Creatine phosphate serves as a reservoir of high-energy phosphate, especially in skeletal and cardiac muscle. Besides typical known changes in serum and urinary creatinine concentrations, rare cases associated with changes in serum and urinary creatine levels have been described in the literature in humans. These cases are mostly linked to an excessive intake of creatine ethyl ester or creatine monohydrate, often resulting in increased urine creatinine concentrations. In addition, it is known that at such elevated creatinine concentrations, creatinine crystallisation may occur in the urine. Analysis of crystals and urinary concrements, often of heterogenous chemical composition, may provide diagnostic and therapeutic hints to the benefit of the patient. The aim of the present work was to analyze urine crystals of unclear composition with microscopic and spectroscopic techniques. On routine microscopic analysis of urine, a preliminary suspicion of uric acid or creatinine crystals was expressed. The crystals were of a cuboid shape and showed polarization effects in microscopy. The dried urine sample was whitish-orange in colour, odourless and dissolved well in water. Protein concentration in dry weight (DW) urine was about 0.3 mg/mg. The measured zinc content in the studied sample was approximately 660 µg/g DW sample and copper content was approximately 64 µg/g DW sample. A lead signal of around 10 µg/g DW sample was also observed. UV-Vis analysis showed a maximum creatine peak around 220 nm, compatible with the spectrum of creatinine with a maximum peak of 230 nm. Using HPLC technique, an extreme high ratio of creatine to creatinine of about 38 was measured, which led to the conclusion of the occurrence of rare creatine crystals in urine.

Asunto(s)

RESUMEN

Novel (N-arylamino)phenothiazinium dyes containing meta-substituted-arylamine auxochrome units were successfully obtained by applying a sonochemical protocol designed for a more efficient energy usage in the preparation of methylene blue (MB) analogues. Single crystal X-ray diffraction analysis revealed the spatial arrangement in aggregated crystalline state of (N-(meta-bromoaryl)amino)phenothiazinium dye with minor variances induced by the nature of the halogenide counterion (iodide or chloride). The optical UV-vis properties of the novel (N-arylamino)phenothiazinium dyes were comparable to those of the parent MB, with the longest wavelength absorption maxima situated in the visible range (640-680 nm), large molar extinction coefficients (log ε = 4.5-5.1) and weak solvatochromism in polar solvents. Their fluorescence emission in solid state was evidenced by One Photon Excited Fluorescence Lifetime Imaging (OPE-FLIM) and Two Photon Excited Fluorescence Lifetime Imaging (TPE-FLIM) experiments. Theoretical calculations based on Time Dependent-Density Functional Theory (TD-DFT) at B3PW91 and CAM-B3LYP/def2-SV(P) level of theory predicted absorption and fluorescence emission wavelength maxima in reasonable agreement with experimental data. Computational results suggest that the electronic excitations imply a departure from the planar molecular ground state towards geometrically rearranged excited states disfavoring the vibronic couplings due to a high degree of flexibility induced by the conformational motion of the N-arylamino auxochromes. Preliminary studies regarding the dyes' relevance in biological environment indicated lipophilicity (log P octanol/water 0.5-2.3), no aggregation tendency in diluted solutions in the concentration range 10-50 microM and ability for cytoplasmatic staining of D407 human retinal pigment epithelial cells.

RESUMEN

Spectroscopic properties are commonly used in the experimental evaluation of ground- and excited-state aromaticity in expanded porphyrins. Herein, we investigate if the defining photophysical properties still hold for a diverse set of hexaphyrins with varying redox states, topologies, peripheral substitutions, and core-modifications. By combining TD-DFT calculations with several aromaticity descriptors and chemical compound space maps, the intricate interplay between structural planarity, aromaticity, and absorption spectra is elucidated. Our results emphasize that the general assumption that antiaromatic porphyrinoids exhibit significantly attenuated absorption bands as compared to aromatic counterparts does not hold even for the unsubstituted hexaphyrin macrocycles. To connect the spectroscopic properties to the hexaphyrins' aromaticity behaviour, we analyzed chemical compound space maps defined by the various aromaticity indices. The intensity of the Q-band is not well described by the macrocyclic aromaticity. Instead, the degeneracy of the frontier molecular orbitals, the HOMO-LUMO gap, and the |ΔHOMO-ΔLUMO|2 values appear to be better indicators to identify hexaphyrins with enhanced light-absorbing abilities in the near-infrared region. Regions with highly planar hexaphyrin structures, both aromatic and antiaromatic, are characterized by an intense B-band. Hence, we advise using a combination of global and local aromaticity descriptors rooted in different criteria to assess the aromaticity of expanded porphyrins instead of solely relying on the absorption spectra.

RESUMEN

Molybdenum disulfide (MoS2) quantum dots (QDs) based therapeutic approaches hold great promise for biomedical applications, necessitating a thorough evaluation of their potential effects on biological systems. In this study, we systematically investigated the impact of MoS2 QDs coated with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethyleneglycol)-2000](DPSE-PEG) linked with (3-carboxypropyl)triphenyl-phosphonium-bromide (TPP) on molecular structures of hepatic tissue lipids and proteins through a multifaceted analysis. The DSPE-PEG-TPP-MoS2 QDs were prepared and administered to the mice daily for 7 weeks. Liver tissues were subjected to a comprehensive examination using various techniques, including Fourier-transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, and liver function tests. FTIR revealed subtle changes in the lipid composition of liver tissues, indicating potential modifications in the cell membrane structure. Also, the (CH stretching and amides I and II regions) analysis unveiled tiny alterations in lipid chain length and fluidity without changes in the protein structures, suggesting a minor influence of DSPE-PEG-TPP-MoS2 QDs on the liver's cellular membrane and no effect on the protein structures. Further scrutiny using UV-vis spectroscopy demonstrated that DSPE-PEG-TPP-MoS2 QDs had no discernible impact on the absorbance intensities of aromatic amino acids and the Soret band. This observation implies that the treatment with SPE-PEG-TPP-MoS2 QDs did not induce significant alterations in helical conformation or the microenvironment surrounding prosthetic groups in liver tissues. The liver function tests, including ALP, ALT, AST, and BIL levels, revealed no statistically significant changes in these key biomarkers despite minor fluctuations in their values, indicating a lack of significant liver dysfunction. This study provides a detailed understanding of the effects of DSPE-PEG-TPP-MoS2 QDs on hepatic lipids and proteins, offering valuable insights into the biocompatibility and limited impact on the molecular and functional aspects of the liver tissue. These findings could be essential for the application of MoS2 QDs-based therapies.

Asunto(s)

RESUMEN

We employ UV/Vis Diffuse Reflectance spectroscopy directly coupled with a packed bed flow reactor to extract quantitative kinetic information. We use as a show-case the CuII/CuI redox dynamics during the reduction half cycle of the NH3-Selective Catalytic Reduction (SCR) on Cu-CHA catalysts. Our measurements enable quantification of the fraction of oxidized Cu, reconstructed by Multivariate Curve Resolution (MCR) together with monitoring of the gas-phase evolution during the reaction. These data both on the dynamics of the gas-phase and of the active site oxidation state have been used to assess the reduction half cycle rate equation and estimate the rate constant. Our results in terms of reaction orders and kinetic constant are in line with previous findings in the literature. Overall, our results demonstrate that the combined analysis of the UV spectra and of the gas-phase dynamics provides converging and unparalleled kinetic insight: this approach effectively resolves ambiguities concerning RHC kinetics and mechanism. More in general, this work provides evidence that operando spectroscopy can be used to extract quantitative kinetic information on catalytic cycles.

RESUMEN

Time elapsed since bloodstain deposition is a crucial aspect in forensic investigations, where non-destructive spectroscopic methods play a pivotal role. While extensive research has been conducted by UV-Vis spectroscopy, showcasing its utility in specific cases, there is still a paucity of studies based on NIR spectroscopy, which has the potential to overcome the limitations of the UV-Vis-based methods. To compensate for this disequilibrium, the present study aimed to evaluate the NIR applicability for estimating the age of forensic bloodstains and develop a performance comparison with UV-Vis spectroscopy methods. Capillary blood was sampled and subjected to a 16-day aging, during which it was repeatedly analyzed using both spectroscopic methods. Subsequently, chemometric analysis was applied to process the spectral data and independently assess the methods' performance. Classical preprocessing transforms (i.e., Savitzky-Golay derivatives and SNV transform) were used together with more targeted strategies, such as class centering, whose benefit was highlighted by PCA. Lastly, PLS regression models were computed to evaluate the effectiveness of both spectroscopic methods in estimating the time elapsed since blood trace deposition. Comparable root mean square errors in prediction (RMSEP) - 40 and 55 h for UV-Vis and NIR spectroscopy, respectively - were observed for both techniques, featuring an improvement with respect to the existing literature for NIR spectroscopy. Data fusion strategies for a multi-instrumental platform were also explored, evaluating advantages and disadvantages of low-level and mid-level approaches. The results indicated that NIR spectroscopy integrated with adequate chemometric strategies deserves increased appreciation in forensic bloodstain dating.

Asunto(s)

RESUMEN

The development of in situ techniques to quantitatively characterize the heterogeneous reactions is essential for understanding physicochemical processes in aqueous phase. In this work, a new approach coupling in situ UV-vis spectroscopy with a two-step algorithm strategy is developed to quantitatively monitor heterogeneous reactions in a compact closed-loop incorporation. The algorithm involves the inverse adding-doubling method for light scattering correction and the multivariate curve resolution-alternating least squares (MCR-ALS) method for spectral deconvolution. Innovatively, theoretical spectral simulations are employed to connect MCR-ALS solutions with chemical molecular structural evolution without prior information for reference spectra. As a model case study, the aqueous adsorption kinetics of bisphenol A onto polyamide microparticles are successfully quantified in a one-step UV-vis spectroscopic measurement. The practical applicability of this approach is confirmed by rapidly screening a superior adsorbent from commercial materials for antibiotic wastewater adsorption treatment. The demonstrated capabilities are expected to extend beyond monitoring adsorption systems to other heterogeneous reactions, significantly advancing UV-vis spectroscopic techniques toward practical integration into automated experimental platforms for probing aqueous chemical processes and beyond.

RESUMEN

Cyclo-meta-phenylenes doped with nitrogen atoms at the periphery were designed and synthesized. The syntheses of the macrocyclic structures were achieved with one-pot Suzuki-Miyaura coupling to arrange phenylene rings and pyridinylene rings in an alternating fashion. Analyses with UV-vis spectroscopy showed changes in the photophysical properties with nitrogen doping, and X-ray crystallographic analyses experimentally revealed the presence of biased charges on the peripheral nitrogen atoms.

RESUMEN

In this study, UV-vis spectroscopy was employed to investigate the interaction between formylphenoxyacetic acid (FPAA) and its derivatives (chalcone and flavones) with ionic surfactants (SDS, CTAB, and DTAB) in different physiological environments. Changes in the physiochemical properties of FPAA chalcone and flavones including binding constants, partitioning constants, and Gibbs free energy were observed which were influenced by the presence of ionic surfactants computed using mathematical models. The solubilization of the targeted compounds in the ionic surfactants was determined through the binding constant (Kb). The results of the present study indicated that electrostatic interactions played a significant role in the solubilization of the targeted compounds in SDS, CTAB, and DTAB. At pH 4.1, FPAA chalcone exhibited stronger binding affinity with SDS compared to CTAB and DTAB. However, at pH 7.4, chalcone showed stronger binding with DTAB compared to SDS, while negligible interaction with CTAB was observed at pH 7.4. The flavones demonstrated stronger binding with DTAB at pH 7.4 compared to SDS and CTAB and it exhibited strong bonding with CTAB at pH 4.1. The negative values of the Gibbs free energy for binding (ΔGb˚) and partitioning (ΔGp˚) constants displayed the spontaneity of the process. However, FPAA chalcone with SDS and FPAA flavones with DTAB furnished positive ΔGb˚, indicating a non-spontaneous process.

Asunto(s)