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Rate of a Click Chemistry reaction under catalysis by trace-amounts of copper as evaluated by NMR spectroscopy
No full textSince its introduction,click chemistry revolutionized many fields of synthetic chemistry such as material science and molecular
biology. It is considered the ‘ cream of the crop ’ of synthesis because of its speed and success rate. This notwithstanding, many kinetic and thermodynamic aspects of the typical Cu+ -catalysed [3+ 2] azide – alkyne cycloaddition (CuAAC) remain vaguely characterized at the present time. There are a number of studies focusing also on the kinetics of typical CuAAC reactions, showing how these follow first-order
or, in some chain reaction mechanisms, second-order kinetics and no regioselectivity is observed. In the absence of any Cu+
catalyst, it was established that a cycloaddition reaction between azide and alkyne groups may only occur by using high
temperatures ( > 70 °C) which are capable of overcoming the relatively high-energy activation barrier by increasing the collision energy between these groups. In such instances, second-order kinetics are observed.
Conversely, owing to the introduction of a Cu+ catalyst, the cycloaddition step follows a different mechanism which requires a lower activation energy. Specifically, the Cu+ catalyst binds with the alkyne group in the initial step and facilitates conjugation of the azido group to the Cu
+ – alkyne complex in the subsequent step. This alternative mechanism operates at milder temperatures (~40 °C) and follows first-order kinetics. Furthermore, the reaction implies a preferential orientation of the ligands of the azide and the alkyne to minimize steric hindrance, thereby yielding a regioselective product.
One of the most critical disadvantages deriving from a no-catalyst approach is represented by the costs of heating required
to improve the rate of cycloaddition and the loss of regioselectivity.
Conversely, the catalytic approach brings the advantage of milder reaction temperatures, albeit with the requirement of a costly and
time consuming Cu+ removal step, which is necessary in most cases. This conundrum, however, may be overcome by a method
using very low amounts of catalyst, only for those applications where traces of Cu+in the final product are acceptable. Therefore,
we hereby report the reaction rate, monitored through NMR spectroscopy, of a [3 + 2] cycloaddition reaction between a water-
soluble alkynol and a poly(ethylene glycol) oligomer, capped with an azido and an amine group at each end of the chain, and
catalysed by trace amounts of copper (Scheme 1). Here, we aimed to demonstrate that despite the relevantly low amount of catalyst,
the cycloaddition reaction may be carried out maintaining regioselectivity and at acceptable rates under the same mild temperature conditions as ordinarily used for click chemistry
Reduced complexity of multidimensional and diffusion NMR spectra of soil humic fractions as simplified by Humeomics
No full textUnveiling the molecular composition of the unextractable soil organic fraction (humin) by humeomics
No full textUnveiling the molecular composition of the unextractable soil organic fraction (humin) by humeomics
No full textWe applied humeomics to a soil unextractable humin fraction (HUM1) and its derived humin (HUM2) after removal of minerals by an HF/HCl treatment. Humeomics implies progressive separation and structural characterization of molecules released from complex humin matrices as (i) unbound, (ii) weakly ester-bound, (iii) strongly ester-bound, and (iv) ether-bound. Molecular characterization of fractions was achieved by GC-MS, thermochemolysis-GC-MS, and 13C-CPMAS-NMR. Both weight and chromatographic yields were higher for the clay-depleted HUM2 than those for HUM1, and this increased molecular detection in HUM2. Saturated and unsaturated alkanoic, α,ω-alkanedioic, hydroxyalkanoic acids, alkanols, and hydrocarbons were found in both HUM1 and HUM2. Abundant odd-C numbered n-alkanoic acids in unbound fractions indicated accumulation of free microbial metabolites, whereas plant-derived acids remained in fractions more tightly bound to the humin matrix. Unsaturated, n-alkanedioic, and hydroxyalkanoic acids were detected after hydrolysis of complex esters. The aromatic character in humin residues progressively increased with humeomics sequential steps, while alkyl and hydroxy-alkyl compounds were reduced. Humins contained similar components as a humic acid extracted from the same soil, implying that traditional humic pools differed in supramolecular arrangement rather than in molecular composition. The humeomic approach enables the determination of the molecular composition of humic matter and may improve knowledge of the structure-activity relations of organic matter in soil
Humeomics: A key to unravel the humusic pentagram
Full text linkHumeomics is a sequential chemical fractionation that applies organic solvent extraction, transesterification with boron trifluoride in methanol, methanolic alkaline hydrolysis, and cleavage of ether and glycosidic bonds with HI. The procedure revealed a series of unique humic fractions with specific molecular composition. The technique can provide molecular identification compound classes that are found inside the soil humus, thus revealing concomitant information on the original conformation of these substances in the humus matrix. Thus, humeomics can serve as an analytical tool to unfold the complexity of the soil humeome, peering into parts of organic matter that were previously unexplored
Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid
No full textSIRT1 Activation by Natural Phytochemicals: An Overview
No full textSirtuins are class III histone deacetylases, whose enzymatic activity is dependent on NAD+ as a cofactor. Sirtuins are reported to modulate numerous activities by controlling gene expression, DNA repair, metabolism, oxidative stress response, mitochondrial function, and biogenesis. Deregulation of their expression and/or action may lead to tissue-specific degenerative events involved in the development of several human pathologies, including cancer, neurodegeneration, and cardiovascular disease. The most studied member of this class of enzymes is sirtuin 1 (SIRT1), whose expression is associated with increasing insulin sensitivity. SIRT1 has been implicated in both tumorigenic and anticancer processes, and is reported to regulate essential metabolic pathways, suggesting that its activation might be beneficial against disorders of the metabolism. Via regulation of p53 deacetylation and modulation of autophagy, SIRT1 is implicated in cellular response to caloric restriction and lifespan extension. In recent years, scientific interest focusing on the identification of SIRT1 modulators has led to the discovery of novel small molecules targeting SIRT1 activity. This review will examine compounds of natural origin recently found to upregulate SIRT1 activity, such as polyphenolic products in fruits, vegetables, and plants including resveratrol, fisetin, quercetin, and curcumin. We will also discuss the potential therapeutic effects of these natural compounds in the prevention and treatment of human disorders, with particular emphasis on their metabolic impact
Decomposition of bio-degradable plastic polymer in a real on-farm composting process
No full textBackground: The current wide diffusion of bio-degradable plastic made up by starch-based polymeric composite has focused the attention on the allocation of bio-polymers for the direct recycling in composting processes. Actually, the acknowledged current methods to estimate the bio-degradability are mainly based on laboratory tests and measurements under controlled conditions, while scarce information are available on the effective transformation of bio-film derivatives in real composting facilities. The aim of this paper was to determine at molecular level the decomposition of specific starch-based thermoplastic mulching film for horticultural crops, in a real on-farm composting system for the attainment of mature compost for agricultural application. Results: The initial and final molecular composition of both bulk biomasses and bio-plastic composite were evaluated through13C solid-state CPMAS-NMR spectroscopy and off-line thermochemolysis—gas chromatography–mass spectrometry. The effective decomposition of the bio-polymer was shown by mono-dimensional and pseudo-2D NMR experiments that revealed the alteration of the intermolecular linkages among the monomeric constituents, while the thermochemolysis confirmed the complete decomposition of starch components. Concomitantly, the molecular characterization of bulk compost indicated the typical selective preservation of hydrophobic components currently found in aerobic composting processes, with a significant increase (+50 %) for the yields of aromatic lignin derivatives and recalcitrant aliphatic compounds. Conclusion: In addition to the classical testing methodologies, the detailed analytical investigation represents a powerful methodology to elucidate the molecular composition and modification of plastic bio-polymers thereby providing a valuable contribution to further promote the composting process as viable way to recycle the biodegradable polymeric materials
Gene transactivation and transrepression in myc-driven cancers
No full textMYC is a proto-oncogene regulating a large number of genes involved in a plethora of cellular functions. Its deregulation results in activation of MYC gene expression and/or an increase in MYC protein stability. MYC overexpression is a hallmark of malignant growth, inducing self-renewal of stem cells and blocking senescence and cell differentiation. This review summarizes the latest advances in our understanding of MYC-mediated molecular mechanisms responsible for its oncogenic activity. Several recent findings indicate that MYC is a regulator of cancer genome and epigenome: MYC modulates expression of target genes in a site-specific manner, by recruiting chromatin remodeling co-factors at promoter regions, and at genome-wide level, by regulating the expression of several epigenetic modifiers that alter the entire chromatin structure. We also discuss novel emerging therapeutic strategies based on both direct modulation of MYC and its epigenetic cofactors
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