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Linking optical and chemical signatures of dissolved organic matter in the southern Argentine shelf: Distribution and bioavailability
摘要： Fluorescence spectroscopy is commonly used to investigate the distribution and dynamics of dissolved organic matter (DOM) in marine systems. However, the direct comparison with chemical signatures is essential to substantiate the molecular composition of specific fluorescent components. Here we report the relation between optical and chemical signatures of DOM in waters of the Beagle Channel (BCW) (south-east of Tierra del Fuego, in the southern Argentine shelf) at the Pacific-Atlantic connection and neighboring coastal (CW) and oceanic (OW) waters (54.75-55.75°S, 64-68°W). The relationships among concentrations of total dissolved carbohydrates (TDCHO) and amino acids (TDAA), and fluorescent DOM (FDOM), including terrestrial “humic-like” (FDOMC) and “protein-like” compounds (FDOMT), and bioavailability of DOM components were assessed from field measurements acquired in the austral summer 2012. The maximal concentrations of TDCHO, dissolved organic carbon (DOC) and FDOMc intensities were found in BCW, while the minima in OW, displaying a negative correlation with salinity. This spatial distribution of biogeochemical signals suggests that humic compounds contributed by continental runoff contain refractory carbohydrates, and FDOMC resulted as a reliable tracer of carbon pathways in the Pacific-Atlantic connection. Conversely, TDAA and FDOMT showed the opposite distributional trend, with minimal concentrations in BCW and the maxima in CW and OW. The significant positive correlation of TDAA with salinity suggests open water sources of these components, however, phytoplankton biomass (Chla) in CW and OW was significantly lower than in BCW, ruling out the assumption of autochthonous source in open waters. TDAA were negatively correlated with the abundance of heterotrophic bacteria (HB), which displayed a consistent decrease from BCW towards OW, suggesting high bacterial uptake of TDAA in the BCW. This bacterial uptake is supported by the observed variation in carbon contribution of TDAA to DOC (amino acids carbon yield, in %), which is an indicator of DOM lability. The negative correlation found between amino acids carbon yield and HB abundance reflects intense bacterial activity in BCW, where phytoplankton biomass was maximum. Hence, higher DOM “freshness” occurs in the BCW, suggesting a tight coupling between microbial production and consumption.
关键词： Pacific-Atlantic connection.,amino acids,fluorescent dissolved organic matter,carbohydrates
更新于2025-11-14 15:26:12
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Novel BODIPY-conjugated amino acids: Synthesis and spectral properties
摘要： Three BODIPY-based conjugates with lysine, methionine, and tryptophan bound via amino group were synthesized and characterized. Spectral properties of the compounds were studied and a number of photophysical characteristics were obtained. Bioconjugates investigated are water soluble, which makes them promising markers for various bioobjects.
关键词： conjugation,fluorescence,BODIPY,amino acids,markers
更新于2025-11-14 15:14:40
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Photooxidase-mimicking nanovesicles with superior photocatalytic activity and stability based on amphiphilic amino acid and phthalocyanine co-assembly
摘要： Enzyme mimics have broad applications in catalysis and can assist elucidation of the catalytic mechanism of natural enzymes. However, challenges arise from the design of catalytic sites, the selection of host molecules and their integration into active three-dimensional structures. Herein, we develop a mimic photooxidase by synergetic molecular self-assembly. 9-Fluorenylmethyloxycarbonyl-L-histidine in combination with phthalocyanine shows efficient co-assembly into nanovesicles with flexibly tunable particle size and membrane thickness. The obtained nanovesicles are capable of reactive oxygen-mediated photosensitive oxidation with improved efficiency and stability. This work highlights the co-assembly of simple building blocks into a supramolecular photocatalyst, which might give insight into possible evolutionary paths of photocatalytic membraneous systems and will allow the facile transfer into photosensitive nanoreactors or artificial organelles.
关键词： self-assembly,photooxidase,amino acids,nanovesicles,phthalocyanines
更新于2025-09-23 15:23:52
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Rapid Identification of Functional Pyrrolysyl-tRNA Synthetases via Fluorescence-Activated Cell Sorting
摘要： The orthogonal pyrrolysyl-tRNA synthetase/tRNACUA pair and their variants have provided powerful tools for expanding the genetic code to allow for engineering of proteins with augmented structure and function not present in Nature. To expedite the discovery of novel pyrrolysyl-tRNA synthetase (PylRS) variants that can charge non-natural amino acids into proteins site-specifically, herein we report a streamlined protocol for rapid construction of the pyrrolysyl-tRNA synthetase library, selection of the functional PylRS mutants using fluorescence-activated cell sorting, and subsequent validation of the selected PylRS mutants through direct expression of the fluorescent protein reporter using a single bacterial strain. We expect that this protocol should be generally applicable to rapid identification of the functional PylRS mutants for charging a wide range of non-natural amino acids into proteins.
关键词： non-natural amino acids,flow cytometry,mutagenesis,amber codon suppression,genetic code expansion
更新于2025-09-23 15:23:52
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Chirality Inversion on the Carbon Dot Surface via Covalent Surface Conjugation of Cyclic α-Amino Acid Capping Agents
摘要： Manipulating the chiroptical properties at the nanoscale is of great importance in stereoselective reactions, enantioseparation, self-assembly, and biological phenomena. In recent years, carbon dots have garnered great attention because of their favorable properties such as tunable fluorescence, high biocompatibility, and facile, scalable synthetic procedures. Herein, we report for the first time the unusual behavior of cyclic amino acids on the surface of carbon dots prepared via microwave-based carbonization. Various amino acids were introduced on the surface of carbon dots via EDC/NHS conjugation at room temperature. Circular dichroism results revealed that although most of the surface conjugated amino acids can preserve their chirality on negatively charged, “bare” carbon dots, the “handedness” of cyclic α-amino acids can be flipped when covalently attached on carbon dots. Moreover, these chiroptical carbon dots were found to interact with the cellular membrane or its mimic in a highly selective manner due to their acquired asymmetric selectivity. A comprehensive inhibitor study was conducted to investigate the pathway of cellular trafficking of these carbon dots. Overall, it was concluded that the chirality of the amino acid on the surface of carbon dots could regulate many of the cellular processes.
关键词： cyclic amino acids,chiroptical properties,chirality inversion,carbon dots,cellular interaction
更新于2025-09-23 15:21:01
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Stereoselective Sensing of <scp>l</scp> - and <scp>d</scp> -Amino Acids: Development of a Fluorescence-Array Based on Readily Available Chiral Phosphoric Acids
摘要： A chiral sensor-array for the identification of amino-acids was developed, using six readily available bis- and tris-phosphoric acids in combination with Ni2 + and Eu3 +, resulting in a fluorescence-based array with twelve sensors. This array was successfully applied for the chemoselective identification of 19 amino-acids, but also for the enantioselective discrimination between the l- and d-enantiomers.
关键词： amino-acids,chiral sensor-array,fluorescence-based array,enantioselective discrimination,chemoselective identification
更新于2025-09-23 15:21:01
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Stress Physiology of Tea in the Face of Climate Change || Molecular and Physiological Adaptations of Tea Plant in Response to Low Light and UV Stress
摘要： The sensory quality, economic value, and health functions of tea liquor depend on several metabolites in leaves of tea (Camellia sinensis L.), such as polyphenols (the most representative quality- and function-related compounds, especially catechins), caffeine, amino acids, aroma compounds, vitamins, and carbohydrates. The biosynthesis of these molecules is significantly affected by both management practices in the field and environmental factors, such as shading and ultraviolet (UV) stress. In this chapter, therefore, we review existing literature reporting the effects of shade and UV irradiances on tea plants with the aim to reappraise morphological, biochemical, physiological, and molecular responses found in this species. Cultivation of tea plants under shade can (i) induce anatomical and ultrastructural adaptations; (ii) influence leaf color, providing characteristic vivid greenness due to incremented chlorophyll content; (iii) decrease the risk of photoinhibition; and finally (iv) improve the quality of tea beverages by causing the reduction of the concentration of phenylpropanoids and caffeine (which contribute to astringency) while increasing the level of amino acids (the compounds that contribute to sweetness). However, the shade practice in tea is still subjected to controversy, and the correct managing of the shade practice is essential. Elevated UV irradiances, especially UV-B, can alter the plant morphology and affect several biochemical and physiological processes; most plant species respond to UV in a dose dependent manner. Protracted exposition to low UV-B doses (similar to UV peaks actually perceive by plants in the ambient) leads to an enhancement of phenylpropanoid metabolism and in particular stimulates the biosynthesis of UV-protecting flavonoids (mainly catechins). Conversely, UV-B doses much higher than those usually experienced in natural environment lead to the downregulation of the phenylpropanoid metabolism likely due to irreversible (to some extent) UV-triggered damages. The understandings of the reactions of tea plants to different light conditions, including situations of low light and high UV, are of pivotal importance to enhance both plant yield and tea quality by “driving” the accumulation of desired compounds in tea leaves.
关键词： Caffeine,UV stress,Amino acids,Low light,Catechins,Flavonoids,Tea plant
更新于2025-09-23 15:21:01
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Stress Physiology of Tea in the Face of Climate Change || UV-B Radiation-Induced Changes in Tea Metabolites and Related Gene Expression
摘要： UV-B radiation is an inevitable abiotic stress, which could induce a series of changes in metabolites and related metabolisms in plants. UV-B-induced metabolic changes in leaves of Camellia sinensis affect the tea quality. This review summarizes the recent investigations into UV-B radiation-induced changes in tea metabolites and their related gene expression, involving in flavonoids, amino acids, and volatile compounds. UV-B radiation induces flavonoid accumulation by increasing expression of key genes in general phenylpropanoid pathway and flavonoid pathway. The UV-B radiation-induced gene expressions in flavonoid biosynthesis pathway also are affected by transcription factors and endogenous phytohormones signaling pathway. Changes of individual amino acids under UV-B radiation exhibit significant variation among different plants, and their responses to UV-B radiation dose are different. These regulations involve in modulation of gene expressions related to GABA shunt and tricarboxylic acid cycle (TCA). Volatile compounds in Camellia sinensis under UV-B radiation are regulated by both metabolites biosynthesis and volatile glycosidic-precursors hydrolysis. In a word, UV-B radiation influences metabolisms in tea in a rather complex way. More researches on UV-B-induced transcriptional regulation, endogenous-phytohormone signal regulation, metabolisms diversions regulation, etc. are needed in the future.
关键词： Gene expression,Signal regulation,Amino acids,Volatile compounds,Tea polyphenols,UV-B radiation
更新于2025-09-23 15:21:01
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Terahertz Spectral of Enantiomers and Racemic Amino Acids by Time-Domain-Spectroscopy Technology
摘要： The absorption spectra of four amino acids were studied. These spectra are obtained by terahertz time-domain spectroscopy (TDS) technique. The four amino acids are alanine, methionine, leucine, and valine, respectively. The spectra of their enantiomers (L-, D-) and racemic compounds (DL-) were investigated. Although the two isomers have very similar structures, their absorption spectra are obviously different. The absorption coefficient of each structure is calculated by the density functional theory (DFT), and the simulated spectra of each structure are obtained. It is shown that the number of the calculated peaks is in good agreement with the experimental ones. The experimental spectra were compared with the theoretical spectra. The differences between the absorption spectra of isomers are presented, and the reasons for the differences were analyzed. The vibratory spectra of biomolecules were studied, and the correlation between molecular structure and function was further understood.
关键词： collective vibration,isomers,amino acids,density functional theory,terahertz time-domain spectroscopy
更新于2025-09-23 15:21:01
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Photoinduced Proton-Coupled Electron Transfer in Supramolecular Sn <sup>IV</sup> Di( <scp>l</scp> -tyrosinato) Porphyrin Conjugates
摘要： Proton-coupled electron transfer (PCET) plays a key role in many biological processes, and a thorough comprehension of its subtle mechanistic complexity requires the synthesis and characterization of suitable artificial systems capable of mimicking this fundamental, elementary step. Herein, we report on a detailed photophysical investigation of conjugate 1, based on a tin(IV) tetraphenylporphyrin (SnTPP) chromophore bound to two L-tyrosinato amino acids, in CH2Cl2 in combination with organic bases of different strength and the preparation of a novel conjugate 3, based on a tin(IV) octaethylporphyrin (SnOEP) in place of the tetraphenyl analogue, and its photophysical characterization in CH2Cl2 in the presence of pyrrolidine. In the case of compound 1 with all bases examined, quenching of both the singlet and triplet excited states is observed and attributed to the occurrence of concerted proton?electron transfer (CPET). Rates and quenching yields decrease with the strength of the base used, consistent with the decrease of the driving force for the CPET process. Conjugate 3 with pyrrolidine is quenched only at the triplet level by CPET, albeit with slower rates than its parent compound 1, ascribable to the smaller driving force as a result of SnOEP being more difficult to reduce than SnTPP. For both systems, the quenching mechanism is confirmed by suitable blank experiments, specific kinetic treatments, and the observation of kinetic isotope effects (KIEs). Differently from what has been previously proposed, a detailed reinvestigation of the triplet quenching of 1 with pyrrolidine shows that no long-lived radical pair state is formed, as diradical recombination is always faster than formation. This is true for both 1 and 3 and for all bases examined. The kinetics of the CPET pathways can be well described according to Marcus theory and point toward the involvement of substantial reorganization energy as typically observed for PCET processes of concerted nature.
关键词： tin(IV) porphyrin,photophysical characterization,L-tyrosinato amino acids,CPET,PCET,Proton-coupled electron transfer,kinetic isotope effects,concerted proton?electron transfer,Marcus theory
更新于2025-09-23 15:19:57