reversible process
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2021 ◽  
Author(s):  
Niamh Mac Fhionnlaoich ◽  
Stephen Schrettl ◽  
Nicholas B. Tito ◽  
Ye Yang ◽  
Malavika Nair ◽  
...  

The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase leads to the assembly of individual nanometre-sized particles into arrays of micrometre-sized aggregates, whose size and characteristic spacing can be tuned by varying the cooling rate. This fully reversible process offers hierarchical control over structural order on the molecular, nanoscopic, and microscopic level and is an interesting model system for the programmable patterning of nanocomposites with access to micrometre-sized periodicities.


2021 ◽  
Author(s):  
Leila Reyes Ruiz ◽  
Kathleen King ◽  
Elizabeth M Garrett ◽  
Rita Tamayo

The opportunistic nosocomial pathogen Clostridioides difficile exhibits phenotypic heterogeneity through phase variation, a stochastic, reversible process that modulates expression. In C. difficile, multiple sequences in the genome undergo inversion through site-specific recombination. Two such loci lie upstream of pdcB and pdcC, which encode phosphodiesterases (PDEs) that degrade the signaling molecule c-di-GMP. Numerous phenotypes are influenced by c-di-GMP in C. difficile including cell and colony morphology, motility, colonization, and virulence. In this study, we aimed to assess whether PdcB phase varies, identify the mechanism of regulation, and determine the effects on intracellular c-di-GMP levels and regulated phenotypes. We found that expression of pdcB is heterogeneous and the orientation of the invertible sequence, or pdcB switch, determines expression. The pdcB switch contains a promoter that when properly oriented promotes pdcB expression. Expression is augmented by an additional promoter upstream of the pdcB switch. Mutation of nucleotides at the site of recombination resulted in phase-locked strains with significant differences in pdcB expression. Characterization of these mutants showed that the pdcB locked-ON mutant has reduced intracellular c-di-GMP compared to the locked-OFF mutant, consistent with increased and decreased PdcB activity, respectively. These alterations in c-di-GMP had concomitant effects on multiple known c-di-GMP regulated processes. These results indicate that phase variation of PdcB allows C. difficile to coordinately diversify multiple phenotypes in the population to enhance survival.


2021 ◽  
Vol 37 (4) ◽  
pp. 833-846
Author(s):  
Selvaraj Shunmugaperumal ◽  
Saranya Dhasarathan ◽  
Kamatchi Selvaraj. P ◽  
Ilango Kaliappan

New unsymmetrical Schiff bases containing azomethine moiety with simple aromatic section in one side and ferrocene fragment attached imine on the other side have beensynthesized. Advent of metal-to-ligand charge transfer band for the coordination of Cu2+ ions with receptors and appropriate changes in UV-Visible spectra for other metal ion combination with the sensor is reported. Observed extravagant ΔEpvalues suggest quasi-reversible process. The ΔIpa amount calculated from the anodic current Ipa value noticed for receptor solution and different metal ion added sensor solution discloses the concentration of metal ions required for effective sensing. The synthesized ligands were subjected to antimicrobial activity against four bacterial and two fungal stains and the zone of inhibition (in mm) was calculated. Further molecular docking study was carried out and the binding energy (Kcal.mol-1) for the synthesized ligand (R1 and R2) with the selected protein was intended.


Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 925
Author(s):  
Chang Liu ◽  
Jinglong Liang ◽  
Hui Li ◽  
Hongyan Yan ◽  
Sijia Zheng ◽  
...  

The electrochemical reduction process of ZnFe2O4 in NaCl-CaCl2 melts was studied. Thermodynamic analysis shows that the reduction process of ZnFe2O4 is carried out in multiple steps, and it is difficult to reduce Fe3+ to Fe in one step. Electrochemical tests revealed that the reduction process of ZnFe2O4 includes three steps: First, Fe3+ is reduced to Fe in two steps, then Zn2+ is reduced to Zn in one step. The reduction of Fe3+ on the Mo electrode is a reversible process controlled by diffusion, while the reduction of Zn2+ is an irreversible process controlled by diffusion. The influence of electrolysis voltage and temperature on the process of electric deoxidation has also been studied. It is indicated that properly increasing the temperature is conducive to the diffusion of oxygen ions, thereby increasing the deoxidation rate. With the gradual increase of voltage, the reduction process of ZnFe2O4 is ZnFe2O4 → FeO + ZnO → Fe + ZnO → Fe + Zn.


Author(s):  
Hui Xu ◽  
Shuang Li ◽  
You-Shuo Liu

Vascular aging is a pivotal risk factor promoting vascular dysfunction, the development and progression of vascular aging-related diseases. The structure and function of endothelial cells (ECs), vascular smooth muscle cells (VSMCs), fibroblasts, and macrophages are disrupted during the aging process, causing vascular cell senescence as well as vascular dysfunction. DNA methylation, an epigenetic mechanism, involves the alteration of gene transcription without changing the DNA sequence. It is a dynamically reversible process modulated by methyltransferases and demethyltransferases. Emerging evidence reveals that DNA methylation is implicated in the vascular aging process and plays a central role in regulating vascular aging-related diseases. In this review, we seek to clarify the mechanisms of DNA methylation in modulating ECs, VSMCs, fibroblasts, and macrophages functions and primarily focus on the connection between DNA methylation and vascular aging-related diseases. Therefore, we represent many vascular aging-related genes which are modulated by DNA methylation. Besides, we concentrate on the potential clinical application of DNA methylation to serve as a reliable diagnostic tool and DNA methylation-based therapeutic drugs for vascular aging-related diseases.


Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 810
Author(s):  
David Sands

The Carnot cycle and the attendant notions of reversibility and entropy are examined. It is shown how the modern view of these concepts still corresponds to the ideas Clausius laid down in the nineteenth century. As such, they reflect the outmoded idea, current at the time, that heat is motion. It is shown how this view of heat led Clausius to develop the entropy of a body based on the work that could be performed in a reversible process rather than the work that is actually performed in an irreversible process. In consequence, Clausius built into entropy a conflict with energy conservation, which is concerned with actual changes in energy. In this paper, reversibility and irreversibility are investigated by means of a macroscopic formulation of internal mechanisms of damping based on rate equations for the distribution of energy within a gas. It is shown that work processes involving a step change in external pressure, however small, are intrinsically irreversible. However, under idealised conditions of zero damping the gas inside a piston expands and traces out a trajectory through the space of equilibrium states. Therefore, the entropy change due to heat flow from the reservoir matches the entropy change of the equilibrium states. This trajectory can be traced out in reverse as the piston reverses direction, but if the external conditions are adjusted appropriately, the gas can be made to trace out a Carnot cycle in P-V space. The cycle is dynamic as opposed to quasi-static as the piston has kinetic energy equal in difference to the work performed internally and externally.


Author(s):  
David Sands

The Carnot cycle and the attendant notions of reversibility and entropy are examined. It is shown how the modern view of these concepts still correspond to the ideas Clausius laid down in the nineteenth century. As such, they reflect the outmoded idea current at the time that heat is motion. It is shown how this view of heat led Clausius to develop the entropy of a body based on the work that could be done in a reversible process rather than the work that was actually done. In consequence, Clausius built into entropy a conflict with energy conservation, which is concerned with actual changes in energy. In this paper, a macroscopic formulation of internal mechanisms of damping based on rate equations for the distribution of energy within a gas. It is shown that work processes involving a step-change in external pressure, however small, are intrinsically irreversible. However, under idealised conditions of zero damping the gas inside a piston expands and traces out a trajectory through the space of equilibrium states. Therefore, the entropy change due to heat flow from the reservoir matches the entropy change of the equilibrium states. This trajectory can traced out in reverse as the piston reverses direction, but if the external conditions are adjusted appro-priately, the gas can be made to trace out a Carnot cycle in P-V space. The cycle is dynamic as opposed to quasi-static as the piston has kinetic energy equal in difference to the work done in-ternally and externally.


2021 ◽  
Vol 162 (22) ◽  
pp. 884-888
Author(s):  
Szandra Boldizsár ◽  
János Rottek ◽  
Tamás Schneider ◽  
Fatima Varga ◽  
Erika Szaleczky

Összefoglaló. Az eltűnőepeút-szindróma ritka, rossz prognózisú kórkép. Az epeutak progresszív destrukciójával, az intrahepaticus epeutak eltűnésével jár, epepangáshoz, biliaris cirrhosishoz, végül májelégtelenséghez vezet. A háttérben álló kiváltó okok között infekciók, ischaemia, gyógyszermellékhatások, illetve daganatos megbetegedések szerepelhetnek. A malignitások közül a leggyakrabban a Hodgkin-lymphomához társult formájával találkozhatunk. Cikkünkben egy fiatal, Hodgkin-lymphomás betegünk esetét szeretnénk bemutatni, akinél az icterus hátterében eltűnőepeút-szindróma igazolódott, melyet egyéb okok kizárását követően szövettani mintavétellel igazoltunk. A két ciklus ABVD-protokoll szerinti kezelést követő PET/CT az alapbetegség tekintetében komplett metabolikus remissziót igazolt. A klinikai javuláshoz azonban hosszú hónapokra volt szükség. Végül az epeúteltűnés esetünkben reverzibilis folyamatnak bizonyult, az alapbetegség tekintetében a komplett metabolikus remisszió elérésével az epeút-károsodás megállítható volt. Orv Hetil. 2021; 162(22): 884–888. Summary. destruction and loss of the intrahepatic bile ducts leading to cholestatis, biliar chirrosis and finally liver failure. It has been described in different pathologic conditions including infections, ischemia, adverse drug reactions and malignancies. The Hodgkin’s lymphoma-associated type occurs most frequently among the forms of the disease of malignant origin. In this report, we introduce the case of a 32-year-old male patient with Hodgkin’s lymphoma, diagnosed with vanishing bile duct syndrome upon liver biopsy as a root cause behind his icterus. The PET/CT has proven complete metabolic remission after 2 cycles of ABVD chemoterapy. Clinical improvement, however, occurred only after several months. Finally the loss of bile ducts proved to be a reversible process, the complete metabolic remission of Hodgkin’s lymphoma resulted in the regeneration of the bile ducts. Orv Hetil. 2021; 162(22): 884–888.


2021 ◽  
Author(s):  
Hernando Lopez-Bertoni ◽  
Amanda Johnson ◽  
Yuan Rui ◽  
Bachchu Lal ◽  
Johnathan Coulter ◽  
...  

Abstract DNA methylation is a reversible process catalyzed by the ten-eleven translocation (TET) family of enzymes (TET1, TET2, TET3) that convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Altered patterns of 5hmC and 5mC are widely reported in human cancers and loss of 5hmC correlates with poor prognosis. Understanding the mechanisms leading to 5hmC loss and its role in oncogenesis will advance the development of epigenetic-based therapeutics. We show that TET2 loss associates with GBM stem cells and correlates with poor survival of GBM patients. We further identify a SOX2:miR-10b-5p:TET2 axis that represses TET2 expression, represses 5hmC, increases 5mC levels and induces GBM cell stemness and tumor-propagating potential. In vivo delivery of a miR-10b-5p inhibitor that normalizes TET2 expression and 5hmC levels inhibits tumor growth and prolongs survival of animals bearing pre-established orthotopic GBM xenografts. These findings highlight the importance of TET2 and 5hmC loss in Sox2-driven oncogenesis and their potential for therapeutic targeting.


2021 ◽  
Vol 11 ◽  
Author(s):  
Xin-Yuan Dai ◽  
Liang Shi ◽  
Zhi Li ◽  
Hai-Yan Yang ◽  
Ji-Fu Wei ◽  
...  

Among the over 150 RNA modifications, N6-methyladenosine (m6A) is the most abundant internal modification in eukaryotic RNAs, not only in messenger RNAs, but also in microRNAs and long non-coding RNAs. It is a dynamic and reversible process in mammalian cells, which is installed by “writers,” consisting of METTL3, METTL14, WTAP, RBM15/15B, and KIAA1429 and removed by “erasers,” including FTO and ALKBH5. Moreover, m6A modification is recognized by “readers,” which play the key role in executing m6A functions. IYT521-B homology (YTH) family proteins are the first identified m6A reader proteins. They were reported to participate in cancer tumorigenesis and development through regulating the metabolism of targeted RNAs, including RNA splicing, RNA export, translation, and degradation. There are many reviews about function of m6A and its role in various diseases. However, reviews only focusing on m6A readers, especially YTH family proteins are few. In this review, we systematically summarize the recent advances in structure and biological function of YTH family proteins, and their roles in human cancer and potential application in cancer therapy.


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