Search

In this first article of the two-article series, we focus on the major systems of units in physics. Different systems of units, besides the SI, are commonly used, depending on the domain of interest. Conversion of equations and units across systems that differ in the number of base dimensions often poses learning difficulties. This article aims to clarify this somewhat neglected topic in college physics instruction. [ABSTRACT FROM AUTHOR]

Contaminants of emerging concern (CECs) in the environment undergo various transformations, leading to the formation of transformation products (TPs) with a modified ecological risk potential. Although the environmental significance of TPs is increasingly recognized, there has been relatively little research to understand the influences of such transformations on subsequent ecotoxicological safety. In this study, we used four pairs of CECs and their methylated or demethylated derivatives as examples to characterize changes in bioaccumulation and acute toxicity in Daphnia magna, as a result of methylation or demethylation. The experimental results were further compared to quantitative structure-activity relationship (QSAR) predictions. The methylated counterpart in each pair generally showed greater acute toxicity in D. magna, which was attributed to their increased hydrophobicity. For example, the LC50 values of methylparaben (34.4 ± 4.3 mg L-1) and its demethylated product (225.6 ± 17.3 mg L-1) differed about eightfold in D. magna. The methylated derivative generally exhibited greater bioaccumulation than the demethylated counterpart. For instance, the bioaccumulation of methylated acetaminophen was about 33-fold greater than that of acetaminophen. In silico predictions via QSARs aligned well with the experimental results and suggested an increased persistence of the methylated forms. The study findings underline the consequences of simple changes in chemical structures induced by transformations such as methylation and demethylation and highlight the need to consider TPs to achieve a more holistic understanding of the environmental fate and risks of CECs.

Background: The available in vitro evidences suggest the inherent instability and interconvertibility of [6]-gingerol and [6]-shogaol. However, limited data on their in vivo interconversion hinder understanding of their influence on the pharmacokinetic profiles. Purpose: This study presents the first comprehensive in vivo investigation aiming to determine the interconversion pharmacokinetics in rats, and elucidate the oral bioavailability, target distribution, biotransformation, and excretion profiles of the key ginger constituents, [6]-gingerol, [6]-shogaol, and zingerone. Methods: The pharmacokinetics was investigated through single intravenous (3 mg/kg) or oral (30 mg/kg) administration of [6]-gingerol, [6]-shogaol, or zingerone, followed by the determination of their tissue distribution after oral dosing (30 mg/kg). Intravenous pharmacokinetics was leveraged to evaluate the interconversion, circumventing potential confounders associated with the oral route. Results: All rats tolerated these compounds throughout the pharmacokinetic study. The parent compounds exhibited rapid but partial absorption, and extensive organ distribution with substantial biotransformation, thereby limiting the oral bioavailability of each compound to below 2% when administered as pure compounds. Conversion of [6]-gingerol to [6]-shogaol after intravenous administration, demonstrated a significantly larger clearance compared to the reverse conversion ([6]-shogaol to [6]-gingerol). The irreversible metabolic clearance for both compounds was significantly greater than their reversible bioconversions. Furthermore, [6]-gingerol underwent biotransformation to zingerone. Conjugated glucuronides were eliminated partly through renal excretion, with minimal fecal excretion. Conclusion: This in vivo investigation demonstrates the influence of interconversion on the disposition kinetics of [6]-gingerol, [6]-shogaol, and zingerone, as evidenced by the findings in the systemic circulation. The study further highlights the importance of considering this interconversion and tissue distribution when determining the administration dosage of ginger constituent combinations for therapeutic benefits and clinical applications. [ABSTRACT FROM AUTHOR]

Obesity, characterized by the excessive accumulation of adipose tissue, has emerged as a major public health concern worldwide. To develop effective strategies for treating obesity, it is essential to comprehend the biological properties of different adipose tissue types and their respective roles in maintaining energy balance. Adipose tissue serves as a crucial organ for energy storage and metabolism in the human body, with functions extending beyond simple fat storage to encompass the regulation of energy homeostasis and the secretion of endocrine factors. This review provides an overview of the key characteristics, functional differences, and interconversion processes among white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue. Moreover, it delves into the molecular mechanisms and recent research advancements concerning the browning of WAT, activation of BAT, and whitening of BAT. Although targeting adipose tissue metabolism holds promise as a potential approach for obesity treatment, further investigations are necessary to unravel the intricate biological features of various adipose tissue types and elucidate the molecular pathways governing their interconversion. Such research endeavors will pave the way for the development of more efficient and targeted therapeutic interventions in the fight against obesity. [ABSTRACT FROM AUTHOR]

BackgroundThe available in vitro evidences suggest the inherent instability and interconvertibility of [6]-gingerol and [6]-shogaol. However, limited data on their in vivo interconversion hinder understanding of their influence on the pharmacokinetic profiles.PurposeThis study presents the first comprehensive in vivo investigation aiming to determine the interconversion pharmacokinetics in rats, and elucidate the oral bioavailability, target distribution, biotransformation, and excretion profiles of the key ginger constituents, [6]-gingerol, [6]-shogaol, and zingerone.MethodsThe pharmacokinetics was investigated through single intravenous (3 mg/kg) or oral (30 mg/kg) administration of [6]-gingerol, [6]-shogaol, or zingerone, followed by the determination of their tissue distribution after oral dosing (30 mg/kg). Intravenous pharmacokinetics was leveraged to evaluate the interconversion, circumventing potential confounders associated with the oral route.ResultsAll rats tolerated these compounds throughout the pharmacokinetic study. The parent compounds exhibited rapid but partial absorption, and extensive organ distribution with substantial biotransformation, thereby limiting the oral bioavailability of each compound to below 2% when administered as pure compounds. Conversion of [6]-gingerol to [6]-shogaol after intravenous administration, demonstrated a significantly larger clearance compared to the reverse conversion ([6]-shogaol to [6]-gingerol). The irreversible metabolic clearance for both compounds was significantly greater than their reversible bioconversions. Furthermore, [6]-gingerol underwent biotransformation to zingerone. Conjugated glucuronides were eliminated partly through renal excretion, with minimal fecal excretion.ConclusionThis in vivo investigation demonstrates the influence of interconversion on the disposition kinetics of [6]-gingerol, [6]-shogaol, and zingerone, as evidenced by the findings in the systemic circulation. The study further highlights the importance of considering this interconversion and tissue distribution when determining the administration dosage of ginger constituent combinations for therapeutic benefits and clinical applications.

Cancer cells, especially cancer stem cells (CSCs), share many molecular features with induced pluripotent stem cells (iPSCs) that enable the derivation of induced pluripotent cancer cells by reprogramming malignant cells. Conversely, normal iPSCs can be converted into cancer stem-like cells with the help of tumor microenvironment components and genetic manipulation. These CSC models can be utilized in oncogenic initiation and progression studies, understanding drug resistance, and developing novel therapeutic strategies. This review summarizes the role of pluripotency factors in the stemness, tumorigenicity, and therapeutic resistance of cancer cells. Different methods to obtain iPSC-derived CSC models are described with an emphasis on exposure-based approaches. Culture in cancer cell-conditioned media or cocultures with cancer cells can convert normal iPSCs into cancer stem-like cells, aiding the examination of processes of oncogenesis. We further explored the potential of reprogramming cancer cells into cancer-iPSCs for mechanistic studies and cancer dependencies. The contributions of genetic, epigenetic, and tumor microenvironment factors can be evaluated using these models. Overall, integrating iPSC technology into cancer stem cell research holds significant promise for advancing our knowledge of cancer biology and accelerating the development of innovative and tailored therapeutic interventions. [ABSTRACT FROM AUTHOR]

The structure and assembly properties of ferritin derived from aquatic products remain to be explored. Constructing diverse three-dimensional (3D) protein architectures with the same building blocks has important implications for nutrient delivery, medicine and materials science. Herein, ferritin from Asterias forbesii (AfFer) was prepared, and its crystal structure was resolved at 1.91 Å for the first time. Notably, different from the crystal structure of other reported ferritin, AfFer exhibited a BCT lattice arrangement in its crystals. Bioinspired by the crystal structure of AfFer, we described an effective approach for manufacturing 3D porous, crystalline nanoarchitectures by redesigning the shared protein interface involved in different 3D protein arrays. Based on this strategy, two 3D superlattices of body-centered tetragonal and simple cubicwere constructed with ferritin molecules as the building blocks. This study provided a potentially generalizable strategy for constructing different 3D protein-based crystalline biomaterials with the same building blocks. [ABSTRACT FROM AUTHOR]

The conversion between the relaxation modulus and creep compliance is a traditional research topic in viscoelastic materials. Generally, different methods have been used to solve the numerical solution based on convolution theory. However, the initial relaxation modulus (relaxation modulus at t = 0) has been difficult to obtain. This paper aimed to propose a fast calculation method to derive the initial relaxation modulus from the creep compliance. First, three groups of uniaxial static creep tests of asphalt mixtures were conducted to determine the creep compliance of the experimental data. Then, the calculation of the initial relaxation modulus from the creep compliance by three inversion methods (midpoint method, approximate method, and Laplace numerical inversion method) was evaluated. The results indicate that approximate method and Laplace numerical inversion method cannot calculate the initial relaxation modulus value, and the calculation results of the midpoint method can only approach the exact value infinitely, for which calculating the relaxation modulus at 0.0005 s requires 2000 s. The results can only approach the exact value infinitely and take a lot of computing time. Finally, a fast calculation method for the initial relaxation modulus is proposed and verified by Laplace initial value theorem, and this method can directly derive a simple expression for calculating the initial relaxation modulus without requiring computational time. The proposed calculation methods of the initial relaxation modulus for various viscoelastic models were then put forward. The research results provide an effective tool for obtaining the initial relaxation modulus accurately. [ABSTRACT FROM AUTHOR]

Soai's asymmetric autocatalysis represents a highly remarkable example for spontaneous symmetry breaking and enantioselective amplification in the enantioselective alkylation of pyrimidine‐5‐carbaldehydes to the corresponding chiral pyrimidine alcohols. Recently, zinc hemiacetalate complexes, formed from pyrimidine‐5‐carbaldehydes and the chiral product alcohol, were identified by in situ high‐resolution mass spectrometric measurements as highly active transient asymmetric catalysts in this autocatalytic transformation. To study the formation of such hemiacetals and their stereodynamic properties, we focused on the synthesis of coumarin homolog biaryl systems with carbaldehyde and alcohol substituents. Such systems are able to form hemiacetals by intramolecular cyclization. An interesting feature of the substituted biaryl backbone is that tropos and atropos systems can be obtained, enabling or disabling the intramolecular cyclization to hemiacetals. Biaryl structures with various functional groups were synthesized, and the equilibrium and stereodynamics between the closed and open structures were investigated by dynamic enantioselective HPLC (DHPLC). The enantiomerization barriers ΔGǂ and activation parameters ΔHǂ and ΔSǂ were determined from temperature dependent kinetic measurements. [ABSTRACT FROM AUTHOR]

Obesity, characterized by the excessive accumulation of adipose tissue, has emerged as a major public health concern worldwide. To develop effective strategies for treating obesity, it is essential to comprehend the biological properties of different adipose tissue types and their respective roles in maintaining energy balance. Adipose tissue serves as a crucial organ for energy storage and metabolism in the human body, with functions extending beyond simple fat storage to encompass the regulation of energy homeostasis and the secretion of endocrine factors. This review provides an overview of the key characteristics, functional differences, and interconversion processes among white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue. Moreover, it delves into the molecular mechanisms and recent research advancements concerning the browning of WAT, activation of BAT, and whitening of BAT. Although targeting adipose tissue metabolism holds promise as a potential approach for obesity treatment, further investigations are necessary to unravel the intricate biological features of various adipose tissue types and elucidate the molecular pathways governing their interconversion. Such research endeavors will pave the way for the development of more efficient and targeted therapeutic interventions in the fight against obesity.

Potential roles for anthocyanins in preventing various chronic diseases have been reported. These compounds are highly sensitive to external conditions and are susceptible to degradation, which increases the complexity of their metabolism in vivo. This review discusses anthocyanin metabolism in the digestive tract, phase I and II metabolism, and enterohepatic circulation (EHC), as well as their distribution of anthocyanins in blood, urine, and several organs. In the oral cavity, anthocyanins are partly hydrolyzed by microbiota into aglycones which are then conjugated by glucuronidase. In stomach, anthocyanins are absorbed without deglycosylation via specific transporters, such as sodium-dependent glucose co-transporter 1 and facilitative glucose transporters 1, while in small intestine, they are mainly absorbed as aglycones. High polymeric anthocyanins are easily degraded into low-polymeric forms or smaller phenolic acids by colonic microbiota, which improves their absorption. Anthocyanins and their derivatives are modified by phase I and II metabolic enzymes in cells and are released into the blood via the gastrovascular cavity into EHC. Notably, interconversion can be occurred under the action of enzymes such as catechol-O-methyltransferase. Taking together, differences in anthocyanin absorption, distribution, metabolism, and excretion largely depend on their glycoside and aglycone structures. [ABSTRACT FROM AUTHOR]

Entangled (M3L2)n polyhedral complexes represent a unique class of supramolecular architectures that are stabilized by relatively weak metal–acetylene interactions in cooperation with conventional metal–pyridyl coordination. Counter‐anion exchange of these complexes with a nitrate (NO3−) ion triggered formal metal insertion between the metal centers, and a heteroleptic ternary coordination mode with acetylenic, pyridyl, and nitrate donors was generated on the metal centers. As a result, the main frameworks of the polyhedral complexes M18L12 and M12L8 were formally extended into a new series of concave polyhedra having the compositions M21L12 and M13L8, respectively. This transformation also resulted in the local disconnection of the highly entangled trifurcate topology of the framework, providing clues toward the skeletal editing of extended and complex three‐dimensional (3D) architectures. [ABSTRACT FROM AUTHOR]

Cancer cells, especially cancer stem cells (CSCs), share many molecular features with induced pluripotent stem cells (iPSCs) that enable the derivation of induced pluripotent cancer cells by reprogramming malignant cells. Conversely, normal iPSCs can be converted into cancer stem-like cells with the help of tumor microenvironment components and genetic manipulation. These CSC models can be utilized in oncogenic initiation and progression studies, understanding drug resistance, and developing novel therapeutic strategies. This review summarizes the role of pluripotency factors in the stemness, tumorigenicity, and therapeutic resistance of cancer cells. Different methods to obtain iPSC-derived CSC models are described with an emphasis on exposure-based approaches. Culture in cancer cell-conditioned media or cocultures with cancer cells can convert normal iPSCs into cancer stem-like cells, aiding the examination of processes of oncogenesis. We further explored the potential of reprogramming cancer cells into cancer-iPSCs for mechanistic studies and cancer dependencies. The contributions of genetic, epigenetic, and tumor microenvironment factors can be evaluated using these models. Overall, integrating iPSC technology into cancer stem cell research holds significant promise for advancing our knowledge of cancer biology and accelerating the development of innovative and tailored therapeutic interventions.

The structure and assembly properties of ferritin derived from aquatic products remain to be explored. Constructing diverse three-dimensional (3D) protein architectures with the same building blocks has important implications for nutrient delivery, medicine and materials science. Herein, ferritin from Asterias forbesii (AfFer) was prepared, and its crystal structure was resolved at 1.91 Å for the first time. Notably, different from the crystal structure of other reported ferritin, AfFer exhibited a BCT lattice arrangement in its crystals. Bioinspired by the crystal structure of AfFer, we described an effective approach for manufacturing 3D porous, crystalline nanoarchitectures by redesigning the shared protein interface involved in different 3D protein arrays. Based on this strategy, two 3D superlattices of body-centered tetragonal and simple cubicwere constructed with ferritin molecules as the building blocks. This study provided a potentially generalizable strategy for constructing different 3D protein-based crystalline biomaterials with the same building blocks.

The conversion between the relaxation modulus and creep compliance is a traditional research topic in viscoelastic materials. Generally, different methods have been used to solve the numerical solution based on convolution theory. However, the initial relaxation modulus (relaxation modulus at t = 0) has been difficult to obtain. This paper aimed to propose a fast calculation method to derive the initial relaxation modulus from the creep compliance. First, three groups of uniaxial static creep tests of asphalt mixtures were conducted to determine the creep compliance of the experimental data. Then, the calculation of the initial relaxation modulus from the creep compliance by three inversion methods (midpoint method, approximate method, and Laplace numerical inversion method) was evaluated. The results indicate that approximate method and Laplace numerical inversion method cannot calculate the initial relaxation modulus value, and the calculation results of the midpoint method can only approach the exact value infinitely, for which calculating the relaxation modulus at 0.0005 s requires 2000 s. The results can only approach the exact value infinitely and take a lot of computing time. Finally, a fast calculation method for the initial relaxation modulus is proposed and verified by Laplace initial value theorem, and this method can directly derive a simple expression for calculating the initial relaxation modulus without requiring computational time. The proposed calculation methods of the initial relaxation modulus for various viscoelastic models were then put forward. The research results provide an effective tool for obtaining the initial relaxation modulus accurately.

Self-assembled supramolecular coordination complexes can take on a wide range of three-dimensional architectures with varying ratios of metal-to-ligand. Control over which architecture will be adopted can be difficult to maintain, as many may form from the starting materials and conditions present. Characterizing the resulting architectures formed can be challenging, in particular when discerning between lower or higher ordered structures of identical stoichiometry. Here we report the synthesis and characterization of a Ti2L3 football-like or pill-shaped capsule, unexpectedly formed from attempts to synthesize variations on a Ti4L6 tetrahedron. The two anionic cores are formed from identical stoichiometric ratios of organic linkers and metal nodes. The high symmetry of the structures, and identical m/z ratios, posed characterization challenges. Crystallization was the only method that allowed for precise structural determination. In the presence of appropriate counter ion guests, the Ti2L3 capsule converts into the Ti4L6 tetrahedron at elevated temperatures over several days. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chirally structured alkaloids have diverse metabolic and physiological properties. • This method can accurately detect 10 kinds of alkaloids and isomers in complex substrates. • Overcoming the difficulties in separating multiple chiral enantiomers in complex matrices. • The study firstly analyzes isomers ratio of alkaloids, and speculates the interconversion mechanism. Multiple chiral enantiomer separation poses challenges in analyzing complex matrices like natural plant materials. Currently, there is no straightforward method for simultaneous separation and analysis of ten alkaloids and enantiomers, mainly due to most of their low levels. Here, we present an improved chiral liquid chromatography-tandem mass spectrometry method for accurate quantification of ten alkaloids and enantiomers. This method exhibits recoveries of 92.3 to 118.1 %, intra-day precisions of 0.6 to 4.7 %, and inter-day precisions of 1.2 to 4.5 %, with detection limits ranging from 0.03 to 3.0 ng/mL. Successfully applied to the ten alkaloids and enantiomers quantification in precursor tobacco materials and aerosols from traditional cigarettes and heated tobacco products, our results show higher concentrations of ten alkaloids in traditional cigarette aerosol compared to heated tobacco products aerosol. During aerosol formation, (R)-cotinine, N-methylanabasine, and β-nornicotyrine were produced. Notably, high temperatures during aerosol formation favored the (R)-enantiomer of several chiral alkaloids, and lead to the formation of new secondary alkaloids. This proposed mechanism represents the first attempt to elucidate the interconversion of alkaloids during aerosol formation. [ABSTRACT FROM AUTHOR]

Purpose: Exploration of the chemical, analytical and pharmacokinetic properties of the API, RO7304898, an allosteric EGFR inhibitor, intended to be developed as a mixture of two rapidly interconverting diastereoisomers with composition ratio of approximately 1:1. Methods: Assessment of diastereoisomer stereochemistry, interconversion rates, binding to EGFR protein, metabolic stability and in vivo PK in Wistar-Han rats was conducted. Results: The two diastereoisomers of the API undergo fast interconversion at physiologically relevant pH and direct EGFR binding studies revealed diastereoisomer B to be the active moiety. Pharmacokinetic studies in rat revealed a low-moderate total plasma clearance of the API along with similar plasma concentration-time profiles for diastereoisomers A and B, and the diastereoisomeric ratio reached stable equilibrium favoring formation of the potent diastereoisomer B. In in vitro incubations, the API was metabolically stable in plasma and hepatocyte suspension incubations in all species tested except that of rat hepatocytes. Additionally, only small species differences in the A:B composition were observed in vitro with the potent diastereoisomer B being the predominant form. Conclusions: We demonstrated that the API, a mixture of two diastereoisomers; A (impotent) and B (potent), undergoes rapid interconversion which is faster than the apparent distribution and elimination rates of the individual diastereoisomers in vivo in rat, serving to diminish concerns that separate diastereoisomer effects may occur in subsequent pharmacologic and pivotal toxicological studies. Whilst vigilant monitoring of the diastereoisomeric ratio will need to be continued, this data adds confidence on the development pathway for this API to the clinic. [ABSTRACT FROM AUTHOR]

Using the density functional theory methods, quantum chemical calculations of the excited states of monosubstituted and disubstituted meso-nitro derivatives of octaethylporphyrin (OEP) and their Zn complexes are performed. The obtained data indicate that the charge transfer states are located substantially higher than the locally excited states and do not play a considerable role in the fluorescence quenching of these compounds, which was assumed earlier. It is shown that conformational dynamics take place for all studied compounds in the triplet state, which gives rise to the formation of structures with a common conjugated system of bonds between the porphyrin macrocycle and the nitro group. It is characterized by a small activation barrier (<200 cm–1) of structural rearrangement and a noticeable decrease in the Δ(T1–S0) energy gap between the ground and lower triplet states. The obtained data indicate that H2-α-NO2-OEP, H2‑α,γ‑(NO2)2-OEP, and Zn-α,γ-(NO2)2-OEP in the triplet state in toluene solutions have conformations with the Δ(T1–S0) energy gap noticeably less than 7800 cm–1. This makes it possible to explain the decrease in the quantum yield of interconversion of these compounds when estimating from the results of measuring the luminescence intensity of singlet oxygen. The fact that the sum of the interconversion and fluorescence quantum yields for the compounds under study is not equal to unity can be explained by conformational transformations in the excited states, which can have an effect on the probability of internal conversion in the singlet state and the accuracy of determining the interconversion quantum yield by different methods. [ABSTRACT FROM AUTHOR]

Estrogens are known to have an adverse impact on the reproductive functions of aquatic animals in natural waters. However, the estrogen levels are usually below the detection limits and vary drastically in the surface water, making it difficult to assess the environmental exposure in watershed management. While dynamic models are useful to bridge the data gaps on estrogen levels in surface water, the complex interconversion among estrogens hinders the accurate calculation of estrogens levels. To address the issue, we developed a kinetic model consisting of three first-order ordinary differential equations to track the concentration change of three key estrogens, estrone (E1), 17α-estradiol (E2α), and 17β-estradiol (E2β) with time resulting from the complex interconversion process. The model was solved by the matrix method and applied to 15 sets of lab data measured both in anaerobic and aerobic conditions as well as in aqueous solutions and solids with various initial estrogen concentrations from earlier studies. The coefficient of determination (R2) values for those datasets range between 0.842 and 0.989, indicating very good accuracy for the application to the natural environment. This kinetic model can help managers to assess the environmental exposure in watershed management and make determinations on effective solutions. [ABSTRACT FROM AUTHOR]

In the present work, a comparative study on the capability of two approaches to successfully interconvert linear viscoelastic functions is performed. The main concept arises from our previous works, where a polymeric material is treated as a collection of meso‐regions, each one of them with a specific energy barrier. The linking between meso‐regions and their rearrangements leads to a time‐dependent constitutive equation. A crucial issue is the distribution of the energy barriers of the meso‐regions, revealing the importance of the distributed nature of the polymeric structure. In this work, the effect of the distribution type was examined by assuming either a Gaussian distribution function or a normalized loss modulus distribution, which can be evaluated from the loss modulus experimental data. Four different polymers were examined and it was proved that both treatments can satisfactorily predict the creep and relaxation function, once the model parameters are evaluated on the basis of dynamic moduli experimental data. [ABSTRACT FROM AUTHOR]

The quantitative double self-sorting between the three-component rectangle [Cu4(1)2(2)2]4+ and the four-component sandwich complex [Cu2(1)(2)(4)]2+ is triggered by inclusion and release of DABCO (4). The fully reversible and clean switching between two multicomponent supramolecular architectures can be monitored by fluorescence changes at the zinc porphyrin sites. The structural changes are accompanied by a huge spatial contraction/expansion of the zinc porphyrin–zinc porphyrin distances that change from 31.2/38.8 Å to 6.6 Å and back. The supramolecular interconversion was used for the highly selective detection of DABCO in a mixture of other similar compounds.

• Hederagenin and gypsogenin have been isolated from plant material. • Both compounds can be interconverted in good yields. • Oxidation of gypsogenin followed by decarboxylation led to 4- epi -hedragonic acid. Gypsogenin (1) and hederagenin (2) were isolated by extracting the powdered roots of Saponaria officinalis and the pericarp of Sapindus saponaria , respectively. While the gypsophila derived saponin can be obtained easily and in large quantities as a technical product, the plant material from Sapindus saponaria is difficult to obtain in Europe and the North-Americas, whereas in Latin America it is readily available (unlike the gypsophila saponin). In order to achieve a better accessibility of both aglycones, gypsogenin (1) and hederagenin (2), a simple synthesis for their interconversion was developed. Modification of the reaction conditions led to the first synthesis of 4- epi -hedragonic acid (3). [ABSTRACT FROM AUTHOR]

A new efficient method for the synthesis of a high ratio of E -alkenes from E / Z mixtures of alkenes with B2 pin2 in the presence of a rhodium catalyst is described. This reaction features mild reaction conditions, broad functional group tolerance, and highly great application potential. [ABSTRACT FROM AUTHOR]

The ring inversion of cyclohexane is a classic textbook example in organic chemistry of large-scale intramolecular interconversion. Early work by Luz using deuterated cyclohexane has shown how the interconversion rate can be studied. Here the complex proton NMR spectrum of cyclohexane is reported. We apply liquid-crystal 1H NMR spectroscopy as a function of temperature to study the interconversion rate process. For low temperatures interconversion is slow, at higher temperatures the fast interconversion limit is approached. For intermediate temperatures significant line broadening is observed as the signature of the interconversion process. [ABSTRACT FROM AUTHOR]

This work provides the accurate reference data for structural and energetic properties relevant for computational studies of amino acids and polypeptides. Glycine due to its small size allows for detailed theoretical explorations of its whole conformational space. The reference energies are computed at the CCSD(T)/CBS+CV level on the best estimated geometries of all local minima and the transition states. For the minima, we complete the set of reference structures reported in Phys. Chem. Chem. Phys., 2013, 15, 10094, by determining the CCSD(T)/(CBS+CV)MP2 quality geometries for the two highest energy conformers VIIp/tcc and VIIIn/gtc. These data stand as the reference to asses reliability and accuracy of less expensive computational models, with particular focus on dispersion-corrected hybrid and double-hybrid DFT approaches, considering several basis sets of double- and triple-ζ quality. Based on results for minima the B2LYP-D3(BJ)/aug-cc-pVTZ level is set as the reference for transition states geometries. Considering accuracy of both single point energies and structural parameters B2PLYP(-D3BJ) and DSDPBEP86 in conjunction with aug-cc-pVTZ basis set can be recommended for reference studies of amino-acids and small poly-peptides, while B3LYP(-D3(BJ)) shown to be the most robust from considered hybrid DFT approaches. [ABSTRACT FROM AUTHOR]

Many contaminants of emerging concern (CECs) have reactive functional groups and may readily undergo biotransformations, such as methylation and demethylation. These transformations have been reported to occur during human metabolism and wastewater treatment, leading to the propagation of CECs. When treated wastewater and biosolids are used in agriculture, CECs and their transformation products (TPs) are introduced into soil-plant systems. However, little is known about whether transformation cycles, such as methylation and demethylation, take place in higher plants and hence affect the fate of CECs in terrestrial ecosystems. In this study, we explored the interconversion between four common CECs (acetaminophen, diazepam, methylparaben, and naproxen) and their methylated or demethylated TPs in Arabidopsis thaliana cells and whole wheat seedlings. The methylation-demethylation cycle occurred in both plant models with demethylation generally taking place at a greater degree than methylation. The transformation rate of demethylation or methylation was dependent on the bond strength of R-CH 3 , with demethylation of methylparaben or methylation of acetaminophen being more pronounced. Although not explored in this study, these interconversions may exert influences on the behavior and biological activity of CECs, particularly in terrestrial ecosystems. The study findings demonstrated the prevalence of transformation cycles between CECs and their methylated or demethylated TPs in higher plants, contributing to a more complete understanding of risks of CECs in the human-wastewater-soil-plant continuum.

The study addresses the physical background and modeling of linear viscoelastic response functions and their reasonable relationships to the Caputo-Fabrizio fractional operator via the Prony (Dirichlet series) series decomposition. The problem of interconversion with power-law and exponential (single and multi-term functions) has been discussed. Special attentions have been paid on the Prony series decomposition approach, the related interconversion problems and the expression of the viscoelastic constitutive equations in terms of Caputo-Fabrizio fractional operator.

We present a cryogenic infrared spectroscopy study of protonated 3,4-methylenedioxymethampetamine (MDMA) and some of its metabolites. The IR spectra are sufficiently well resolved to give distinct vibrational signatures for each molecule, as well as indicate common functional groups in some of the variants. A more detailed analysis reveals that the spectral interpretation is more complex. The overly rich IR spectra already betray the existence of a number of conformers, which are assigned by comparison to quantum-chemical calculations. An attempt to quantify the various conformers for MDMA was not successful, strongly suggesting that the conformers can freely interconvert at these cryogenic temperatures. Image 1 • Cryogenic IR ion spectroscopy reveals common features held by MDMA metabolites. • Increased resolution at cryogenic temperatures disambiguates key spectral features. • Complexity of spectra indicates a number of trapped conformers. • Attempts at conformer quantitation provide evidence for rapid interconversion. [ABSTRACT FROM AUTHOR]

Abstract A first modeling approach was used to understand the behavior of folate in cowpea seeds during soaking at different temperatures (30 °C, 60 °C and 95 °C). Folic acid, 10-formylfolic acid, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate were quantified in both the seeds and the soaking water during the process. A 2D-axisymmetric seed soaking simulator was then built considering these 4 folate vitamers to simultaneously describe diffusion, oxidation and interconversion of the single vitamers. The model adjustments revealed the predominance of folate diffusion at 60 °C and 95 °C (apparent diffusivity 2–3 × 10−11 m2 s−1) whereas at 30 °C enzymatic interconversions of all vitamers into 5-methyltetrahydrofolate were observed (reaction rate of 8.0 × 10−5 s−1 for 5-formyltetrahydrofolate). The results of this study allow us to recommend a preliminary soaking step to retain folate in seeds and to improve the bioavailability of folates for human nutrition. Highlights • Our model describes the behavior of folates during soaking-cooking of cowpea. • The apparent diffusivity of folate increased with temperature. • Folate diffusion was confirmed by immunostaining of 5-CH 3 H 4 folate. • At 30 °C, all folate vitamers were interconverted into 5-CH 3 H 4 folate. • Our results allow us to recommend how to preserve folate during soaking-cooking. [ABSTRACT FROM AUTHOR]

Highlights • Single-laboratory validation of a new method for folate quantification in food. • The single-enzymatic extraction step is used for folate analyses in food. • A plant origin hydrolase enables folate deglutamylation within 1 h. • Conversion between 10-HCO-PteGlu, 5,10-CH+=H 4 folate and 5-HCO-H 4 folate is studied. • 50% of 5,10-CH+=H 4 folate is converted into 5-HCO-H 4 folate during folate analysis. Abstract A rapid, sensitive and reproducible method for analysis of naturally-occurring folates and folic acid in food has been developed and validated. A single-enzyme extraction step, in which a pure recombinant enzyme of plant origin (Arabidopsis thaliana) was used, enabled fast and reproducible deglutamylation during folate extraction within the incubation time of 1 h. Six commonly occurring folate forms (tetrahydrofolate, 5,10-methenyltetrahydrofolate, 10-formylfolic acid, 5-formyltetrahydrofolate, folic acid and 5-methyltetrahydrofolate) were detected and quantified in 9 min using liquid chromatography-tandem mass spectrometry (LC–MS/MS). 13C 5 -labeled 5-formyltetrahydrofolate, 13C 5 -labeled folic acid and 13C 5 -labeled 5-methyltetrahydrofolate were used as internal standards for the quantification. The method is described by a calibration curve (R2>0.99 and trueness 85–115%), a limit of quantification at 0.1 μg/100 g, trueness at 80–120% in spiked samples and certified reference materials, and a precision <10%. However, the precision in quantification of tetrahydrofolate was not within the acceptable limits due to the lack of use of the corresponding internal standard. An interconversion study of unstable formyl forms was performed which showed that 50% of 5,10-methenyltetrahydrofolate is converted to 5-formyltetrahydrofolate during the analysis. The developed LC–MS/MS method is a candidate for a future standard method for folate analysis in food. [ABSTRACT FROM AUTHOR]

In this work, the capacity of the generalized fractional Maxwell (GFMM) and Kelvin-Voigt (GFKM) models for the interconversion of dynamic to static (creep and relaxation) functions, with regard to appropriate experimental data of various polymeric structures, is examined. The analysis is executed within the frame of linear viscoelasticity. Furthermore, a comparative study with the results produced by the implementation of the fractional Zener model has been performed. A good approximation of the generated viscoelastic functions by GFKM and GFMM model was postulated. Concerning the fractional Zener model, it can be extracted that its effectiveness to the interconversion of the viscoelastic functions is dependent on the specific material's viscoelastic response, and the wideness of the time/frequency region examined. It was found that the incorporation of a correction factor in the calculation procedure of the creep compliance function can result in significantly better results, regardless of the model used. Graphical abstract [ABSTRACT FROM AUTHOR]

An axle molecule 12+ containing one viologen nucleus and two identical p‐toluic acid sides was synthesized. The sequential binding of the Q[7] wheels to the 12+ axle leads to the formation of a molecular shuttle and then a homowheel, [3]pseudorotaxane. The [3]pseudorotaxane can reversibly transform to [2]pseudorotaxane by acid‐base control. On the other hand, the initially formed molecular shuttle can also transform to [2]pseudorotaxane directly and reversibly under pH control. As a whole, a molecular shuttle and [3]/[2]pseudorotaxanes constructed a pH‐controlled multiple interconvertible system. Spare wheels: A pH‐controlled multiple interconvertible system is described. It comprises a molecular shuttle, [3]pseudorotaxane and [2]pseudorotaxane based on cucurbit[7]uril was established. [ABSTRACT FROM AUTHOR]

In the study of resistive random access memory using GeTeOx film as the switching layer, the device performed excellent property of bipolar resistive switching (BRS), which could be gradually transformed to the complementary resistive switching (CRS) by varying SET process current compliance. The conductive filament conduction mechanism of BRS could be verified by electrical characteristics and reliable data fitting. Through increasing current compliance of the SET process, CRS could be achieved due to higher activity of oxygen vacancies originated from the intensified thermal effect. This paper was beneficial to understand the switching mechanisms of BRS and CRS and provide a method to realize interconversion. Moreover, it was also a potential and promising device to be applied in the neurosynaptic biomimetic field. [ABSTRACT FROM AUTHOR]

Abstract The reaction between Re 2 O 7 and K 2 S 2 O 7 in the molten phase is studied by Raman spectroscopy under static equilibrium oxidative conditions at temperatures of 260–470 °C and in the full composition range, X R e 2 O 7 0 = 0 − 1. Raman band intensity correlations are adequate for inferring a 1:1 stoichiometry for the complex formation reaction. Depending on temperature and on composition of the mixture, two isomeric ReVII-oxosulfato complexes are formed: (a) ReO 3 SO 4 −, prevalent at low temperature (T<300 °C), where penta-coordinated ReVII takes on a tri-oxo termination configuration; and (b) (ReO 2) 2 O 2 (SO 4) 2 2-, dominant at high temperature (T>360 °C), with hexa-coordinated ReVII in di-oxo termination configuration. The characteristic symmetric and antisymmetric stretching modes (ν s / ν a s) of the Re(=O) 3 + and Re(=O) 2 3+ cores are found at 975/938 cm-1 and 989/944 cm-1 for the tri-oxo and di-oxo sites, respectively. A fully reversible temperature-dependent 2ReO 3 SO 4 −(l) ↔ (ReO 2) 2 O 2 (SO 4) 2 2-(l) interconversion equilibrium is evidenced. Consistent molecular structural models are proposed for the ReO 3 SO 4 − and (ReO 2) 2 O 2 (SO 4) 2 2- complexes as well as for their associated/polymeric counterparts, (ReO 3 SO 4) n n- and ((ReO 2) 2 O 2 (SO 4) 2) n 2n-. Molten Re 2 O 7 reacts with K 2 SO 4 according to Re 2 O 7 (l) + 2SO 4 2- → ReO 4 −(l) + S 2 O 7 2-(l). The ReVII-oxosulfato complexes and their configurational, structural and vibrational properties are of interest as references for inferring corresponding properties for dispersed amorphous oxo-ReVII species in supported rhenia catalysts. [ABSTRACT FROM AUTHOR]

The intestinal epithelium is a rapidly renewing cellular compartment. This constant regeneration is a hallmark of intestinal homeostasis and requires a tightly regulated balance between intestinal stem cell (ISC) proliferation and differentiation. Since intestinal epithelial cells directly contact pathogenic environmental factors that continuously challenge their integrity, ISCs must also actively divide to facilitate regeneration and repair. Understanding niche adaptations that maintain ISC activity during homeostatic renewal and injury-induced intestinal regeneration is therefore a major and ongoing focus for stem cell biology. Here, we review recent concepts and propose an active interconversion of the ISC niche between homeostasis and injury-adaptive states that is superimposed upon an equally dynamic equilibrium between active and reserve ISC populations. Highlights The homeostatic niche maintains the activity of Lgr5+ intestinal stem cells and the relative quiescence of reserve ISCs. Upon injury, the ISC niche undergoes substantial adaptation to effect epithelial repair, potentially by activating reserve ISC populations. The intestinal stroma, epithelium, and paracrine signals may all underlie niche adaptations to injury. Microbes, viruses, diet, and inflammation are external factors that impact the integrity of ISCs, thus affecting intestinal epithelial health in homeostasis and influencing recovery upon injury. [ABSTRACT FROM AUTHOR]

Understanding and modeling the viscoelastic behavior of polymers and polymer-based materials for a wide range of quasistatic and high strain rates is of great interest for applications in which they are subjected to mechanical loads over a long time of operation, such as the self-weight or other static loads. The creep compliance and relaxation functions used in the characterization of the mechanical response of linear viscoelastic solids are traditionally determined by conducting two separate experiments—creep tests and relaxation tests. This paper first reviews the steps involved in conducting the interconversion between creep compliance and relaxation modulus in the time domain, illustrating that the relaxation modulus can be obtained from the creep compliance. This enables the determination of the relaxation modulus from the results of creep tests, which can be easily performed in pneumatic equipment or simple compression devices and are less costly than direct relaxation tests. Some existing methods of interconversion between the creep compliance and the relaxation modulus for linear viscoelastic materials are also presented. Then, a new approximate interconversion scheme is introduced using a convenient Laplace transform and an approximated Gamma function to convert the measured creep compliance to the relaxation modulus. To demonstrate the accuracy of the fittings obtained with the method proposed, as well as its ease of implementation and general applicability, different experimental data from the literature are used.

DLS Microrheology involves tracking the time dependent motion or mean square displacement of dispersed tracer particles of known size using Dynamic Light Scattering (DLS) in order to determine viscoelastic properties of the dispersion medium. The viscoelastic moduli are calculated using a generalised form of the Stokes-Einstein equation which requires Fourier Transformation of the MSD. An alternative approach for estimating the viscoelastic moduli uses a modified algebraic form of the generalized Stokes-Einstein equation, which employs a power law expression to describe the local change in MSD with time. Since the mean square displacement is linearly related to the creep compliance, it can be shown that the same algebraic approach can also be applied to creep measurements made on a rotational rheometer, giving access to the low frequency moduli in a fraction of the time required for oscillatory testing. Furthermore, the quality of the conversion process can be improved by fitting a Burgers model to the time domain data prior to conversion thus minimising errors associated with local differentiation, which is fundamental to the conversion approach.

As the metabolites of tetrabromobisphenol A (TBBPA), tetrabromobisphenol A mono- and di-methyl ethers (TBBPA MME and TBBPA DME) have been detected in various environmental media. However, knowledge of the contribution of plants to their environmental fates, especially to the interactions between TBBPA DME and TBBPA, is quite limited. In this study, the metabolism and behaviors of TBBPA DME was studied with pumpkin plants through 15-day hydroponic exposure. The TBBPA were also studied separately using in-lab hydroponic exposure for comparison. The results showed that more TBBPA DME accumulated in pumpkin roots and translocated up to stems and leaves compared with TBBPA. Transformation of TBBPA DME occurred later and more slowly than that of TBBPA. Interconversion between TBBPA DME and TBBPA was verified in intact plants for the first time. Namely, TBBPA DME can be biotransformed to TBBPA MME (transformation ratio in mole mass, TRMM 0.50%) and to TBBPA (TRMM 0.53%) within pumpkin; and TBBPA can be biotransformed to TBBPA MME (TRMM 0.58%) and to TBBPA DME (TRMM 0.62%). In addition, two single benzene-ring metabolites, 2,6-dibromo-4-(2-(2-hydroxyl)-propyl)-anisole (DBHPA, TRMM 3.4%) with an O -methyl group and 2,6-dibromo-4-(2-(2-hydroxyl)-propyl)-phenetole (DBHPP, TRMM 0.57%) with an O -ethyl group, were identified as the transformation products in the TBBPA exposure experiments. The transformation and interconversion from TBBPA DME back to TBBPA is reported as a new pathway and potential source for TBBPA in the environment. [ABSTRACT FROM AUTHOR]

It may happen under the conditions employed that enantiomers interconvert to each other. In this case, obviously, the kinetics of the process is to be examined. When enantiomers dynamically interconvert to each other during the separation process, a plateau is observed between the adjacent peaks (so-called Batman peak appears). The peak shape depends on the rate constant of this dynamic reaction. A novel stochastic model was derived which takes both the separation and the interconversion into account at the molecular level – thus the effects of the parameters affecting the separation can be investigated. The novel model was used for the study of quetiapine, a drug molecule that interconverts during the separation to evaluate the rate constant based on the enantiomerization. Various flow rates and temperatures were used, and good agreement was obtained with the rate constant obtained from optical rotation experiments and with the software written by Trapp [1] . The most important result we concluded is the need of mild conditions during the separation to ascertain the rate constant the most accurately (low flow rates and temperatures where the enantiomerization process is limited to a few interconversions). The comparison of the rate constants of the on-column and the off-column experiments should be done by considering the stationary phase effects that are absent in the off-column experiments. [ABSTRACT FROM AUTHOR]

A variety of methods applicable to the interconversion of static (creep) and dynamic (relaxation) functions, with regard to appropriate experimental data of various polymers is investigated and compared. The effectiveness of the selected methods was verified by a series of creep experimental data of various polymeric structures. While most of the employed methods are well established in the literature, some further modifications have been introduced for an improvement of the conversion procedure. Furthermore, a new approach is also employed, which is based on the stretched-exponential function, usually applied to represent both relaxation and retardation functions. It is seen that the examined methods produce a similar result, concerning the creep compliance function, having as a beginning storage and loss modulus experimental data. The same observation applies to the retardation spectra, pointing the fact that discrete spectra deviates significantly from the continuous spectra. As a result, it is shown that the creep compliance function, or the relaxation modulus function, can be predicted using experimental dynamic data (relaxation or creep, respectively), as well as anyone of the examined interconversion methods, with an accuracy close to 5%. The use of approximate or exact relations in the whole procedure was proved not to have a significant effect on the final result (referring mostly to the retardation spectra). [ABSTRACT FROM AUTHOR]

The interconversion relations for viscoelastic functions are derived with the consideration of the time-dependent bulk modulus, K(t), for both traditional and fractional Prony series representations of viscoelasticity. The application of these relations is to replace the fitting parameters of Young’s relaxation modulus, E(t), by the unknown parameters of K(t) and the known parameters of the shear relaxation modulus, G(t), and to fit the E(t) to the experimental data for obtaining the parameters of K(t). The fitting results show that only two experiments for measuring the viscoelastic functions of an isotropic material are not enough to determine the other viscoelastic functions. However, if we consider the relaxation rates of K(t) and G(t), we may conclude that the constant bulk modulus is a more reasonable assumption, and the corresponding Poisson’s ratio, ν(t), is a monotonic-increasing function. [ABSTRACT FROM AUTHOR]

In the present work, a time-dependent constitutive equation, established in the literature, is further elaborated to describe a variety of viscoelastic functions. The viscoelastic model under investigation is based on the assumption that the network of chains is thought to be an ensemble of meso-regions, linked to each other. The neighboring chains on the basis of cooperative motions, change their positions, and the time-dependent response is determined by the distribution of meso‑regions with varying energy barriers. In the present work, the Gaussian distribution was selected to be followed by the activation energies. The constitutive equation was solved for dynamic mechanical, stress-relaxation and creep experiments. It has been shown that starting from one viscoelastic function in the frequency (time) domain, all viscoelastic functions in the time (frequency) domain could hereafter be evaluated, with the same parameter values. The proposed treatment was proved to be flexible enough, to predict viscoelastic functions of various polymeric materials and polymer nanocomposites. [ABSTRACT FROM AUTHOR]