Structural Conversion Research Articles

Parallel-Connected Voltage Source Converters With a DC Common Mode and an AC Differential Mode PWM Filter

Two 3-phase converters can be connected in parallel using a range of inductor types. Coupled inductors used together with interleaved pulsewidth modulated (PWM) techniques can produce a high-quality multilevel PWM line output voltage. These inductors can be designed to have a high inductance between the two converter outputs to control circulating currents, combined with a low per-phase output inductance. Since the 3-phase PWM voltage between the two converters consists of two components, a differential mode and common mode, two inductor types can be used to separately filter the circulating currents produced by these two components. The inductor types presented places one coupled inductor between the 3-phase output terminals of the two converters, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-limb CI</i> , and a second coupled inductor located between the two converter dc input terminals, a dc coupled inductor or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc choke</i> . The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-limb CI</i> filters circulating currents due to the differential mode PWM voltage and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc choke</i> filters circulating currents due to the common mode PWM voltage. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc choke</i> uses four windings in contrast to the six required of an equivalent common mode 3-phase ac choke. The two converters are operated with a filter capacitor across their dc input terminals. The 3-phase output of the two parallel converters is located at the center tap of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-limb CI</i> windings in each phase and a very low effective per-phase output inductance is obtained. Consequently, the converter structure can supply very high-frequency fundamental output voltages with high-quality multilevel PWM line voltages. The performance of the coupled inductors presented is compared with a conventional coupled inductor and designs show that they can be 13% smaller with 16% lower losses. The parallel converter structure presented is suitable for high-power high-speed electric drives with applications in aerospace and electric vehicles where lightweight magnetics is required. Simulations and experimental results are presented for an 8 kW (300 Vdc, 208 Vac/22A) prototype operating with a fundamental frequency of 60 Hz –1.1 kHz.

Theatres of Belief: Music and Conversion in the Early Modern City ed. by Marie-Alexis Colin, Iain Fenlon, and Matthew Laube

Reviewed by: Theatres of Belief: Music and Conversion in the Early Modern City ed. by Marie-Alexis Colin, Iain Fenlon, and Matthew Laube Paul G. Feller-Simmons Theatres of Belief: Music and Conversion in the Early Modern City. Edited by Marie-Alexis Colin, Iain Fenlon, and Matthew Laube. (Collection "Épitome musical.") Turnhout: Brepols, 2022. [ 312 p. ISBN 9782503598871 (paperback), €70; ISBN 9782503598888 (e-book), €55.] Music examples, tables, illustrations, index. The essay collection Theatres of Belief is the result of a collaborative project between a transnational group of musicologists who share interest in the convergence of religion, sound, and early modern urban spaces. Eleven chapters by different authors provide multiple case studies drawn from cities located in Europe and the Americas between the sixteenth and eighteenth centuries. These studies showcase a variety of approaches to religious confession, conversion, and soundscape. A leading thread of this volume is interactions between sound and confessionalization in the early modern world. In this regard, the authors' tendency to eschew the overarching narratives that have conflated local experience with universal developments related to religious change is a potentially generative model. Many chapters demonstrate how confessionalization traversed dynamic and distinctly localized trajectories. For instance, Philip Hahn considers the incremental introduction of Lutheran music culture in Ulm following its Reformation in 1531. The chapter advances that the city became an exemplary case of a long, acoustic Reformation. Lutheran theologians tried to introduce church [End Page 395] musical practices in a way that conflicted with Ulm's Zwinglian history and thus repeatedly found resistance. Hahn then challenges a unidirectional model for the cultural development of the Reformation that has tended to sideline the realities of sacred music in many regions of central Europe. In discussing the distinction between opposition to musical performance in urban and rural areas surrounding Ulm, Hahn addresses issues of sonic conversion between social boundaries. In a state of pluriform religious cultures, sacred music served to "experience and express religious belonging" (p. 169). Alexander Fisher also explores the role that sound and music played in the strategies of conversion of confessional spaces in southern Germany. Fisher focuses on sonic conversions within worship spaces and the reconfiguration of space particularly delimited by bell signals, processions, and popular singing. Whereas Protestants demarcated confessional boundaries through the sounding of sermons in the vernacular and congregational singing, Catholics responded by producing orthodox songs for the laity and reconfiguring church architecture. As Hahn shows to be the case in Ulm, Fisher demonstrates that polemics surrounding the control of the soundscape were rooted in confessional politics that functioned as markers of social identity. For example, while processions in Catholic locations such as Munich sacralized the public space, they could also serve as a medium of religious confrontation and negotiation. The sonic conversion of physical structures and the interdependence of landscape and soundscape features most strongly in Iain Fenlon's contribution. He provides a chronological exposition of the Christianization of Cordova, Spain, through architectural, ritual, and musical conversions between the fifteenth and sixteenth centuries. In the wake of the reconquista, the construction of a cathedral and royal chapel on the site of the old mosque and the reorganization of the liturgy and music chapel forcefully changed the urban soundscape. Echoing ideas developed by Hahn and Fisher, Fenlon proposes that public music and ritual were functional to displaying Catholic identity and monarchical loyalty in Cordova. In this instance, polyphony performed by the musical forces of the cathedral's chapel gained growing importance in processions throughout the sixteenth century. This "spectacular display of civic and religious belief" (p. 60) thus provided a sonified distinguishability to Catholic devotional identity. Emilio Ros-Fábregas also illustrates how sonic practices identify a Catholic community, albeit in the form of networks interconnected through devotional practices. His chapter focuses on a 1661 publication of Jesuit spiritual exercises dedicated to the Blessed Sacrament based on the traditions of Perpignan and Barcelona. The source provides details about the music that accompanied these exercises and includes an unexpected reference to Juan de Palafox y Mendoza that leads Ros-Fábregas to propose a further connection to Madrid. The chapter frames the source as a key to understanding the extent of the international...

Practical considerations for adaptive strategies by US grazing land managers with a changing climate

AbstractWe outline practical considerations for grazing land adaptations with a changing climate, with an emphasis on the ranch operation scale and specific attention to directional climate changes and increased climate variability. These adaptive strategies fall into two themes: flexibility and learning under uncertainty. Ranches and livestock operations with greater land, social, or other capital resources may have more flexibility. Risk can be reduced for managers (ranchers, farmers, operators, and livestock managers) through participation in conservation or farm policy programs and/or market‐based approaches. Bolstering adaptive capacity across landscapes and time can originate from social capital of operators and strategic collaborations among managers and scientists. As climate diverges from historical baselines and the realm of managers’ experiential knowledge, new conceptual frameworks are needed to structure conversations, influence research relevancy and impact, and drive imaginative solutions among researchers, managers, and local communities for socio‐ecological systems. We provide simplified frameworks to help guide conversation, future research, and new imaginative solutions for systems‐scale knowledge needs and adaptation to address increasingly uncertain and complex change at multiple scales. Practical considerations for adaptive strategies by grazing land managers with a changing climate will be accelerated through (1) collaborative efforts among managers and explicitly with science–management partnerships becoming more mainstream, (2) co‐produced research with managers and researchers at ranch scales, (3) development of communities of practice and associated learning opportunities, and (4) continued co‐development and advancement of technologies and tools that result in high uptake adoption by ranch managers.

1차 측 제어 플라이벅 컨버터의 정전류 및 정전압 제어

In this paper, a constant current(CC) and constant voltage(CV) control method using a primary-side regulated(PSR) fly-buck converter is proposed. Because the primary-side structure of the fly-buck converter is the same as that of the synchronous buck converter, it always operates in continuous conduction mode(CCM). Therefore, in the proposed method, the load information on the secondary side can always be easily estimated by measuring the primary inductor current at the midpoint of the switch-on period. An accurate CC/CV control can be achieved through simple calculations based on this estimated information. Consequently, the proposed method is advantageous for optimizing the control performance of the PSR converter. The validity of the proposed control was verified using a 5 W prototype of a PSR fly-buck converter. The experimental results confirmed that the current reference of 500 mA was followed within the error range of 1.2%, and that the voltage reference of 12 V was followed within the error range of 1.8% despite the indirect control of the load current and output voltage from the primary side.

Boosting the Electrostatic MEMS Converter Output Power by Applying Three Effective Performance-Enhancing Techniques.

This current study aims to enhance the electrostatic MEMS converter performance mainly by boosting its output power. Three different techniques are applied to accomplish such performance enhancement. Firstly, the power is boosted by scaling up the technology of the converter CMOS accompanied circuit, the power conditioning, and power controlling circuits, from 0.35 µm to 0.6 µm CMOS technology. As the converter area is in the range of mm2, there are no restrictions concerning the scaling up of the accompanied converter CMOS circuits. As a result, the maximum voltage of the system for harvesting energy, Vmax, which is the most effective system constraint that greatly affects the converter's output power, increases from 8 V to 30 V. The output power of the designed and simulated converter based on the 0.6 µm technology increases from 2.1 mW to 4.5 mW. Secondly, the converter power increases by optimizing its technological parameters, the converter thickness and the converter finger width and length. Such optimization causes the converter output power to increase from 4.5 mW to 11.2 mW. Finally, the converter structure is optimized to maximize its finger length by using its wasted shuttle mass area which does not contribute to its capacitances and output power. The proposed structure increases the converter output power from 11.2 mW to 14.29 mW. Thus, the three applied performance enhancement techniques boosted the converter output power by 12.19 mW, which is a considerable enhancement in the converter performance. All simulations are carried out using COMSOL Multiphysics 5.4.

Single‐switch coupled‐inductors‐based high step‐up converter with reduced voltage stress

AbstractThis paper proposes a non‐isolated DC‐DC high step‐up converter. To achieve a high voltage conversion ratio and overcome the problems related to near unity duty‐cycle of the conventional boost converter in high step‐up applications, coupled‐inductors along with switch‐capacitor techniques are merged in this topology. The proposed converter provides continuous input current with low ripple without using any current ripple cancellation method and the voltage across the switch is limited inherently. In order to reduce the control circuit complexity, the proposed converter uses only one switch. These features decrease the complexity of the proposed converter structure. The voltage stress of the semiconductor components is reduced significantly; thus, high‐quality elements (fast power MOSFET switches with low on‐state resistance and Schottky diodes with low forward voltage drop along with low power losses) can be used, which minimizes the switching and conduction losses and improves the converter efficiency. To confirm the converter operation and theoretical analysis, a 200‐W prototype converter with 24‐to‐200‐V input and output voltages operating at 100‐kHz is implemented in the laboratory.

A comparison of the electrochemical performance of graphitized coal prepared by high-temperature heating and flash Joule heating as an anode material for lithium and potassium ion batteries

Natural graphite, commonly used in energy storage applications such as the battery industry, is marked as a supply-risk material due to the elevated demand and limited resources. The synthetic graphite process is inefficient, so there is a highly required for alternative methods of making graphite as anode material. In this study, we report two efficient methods for catalytic graphitization of coal using high-temperature heating and flash Joule heating (FJH). Using both methods, the structure and morphology characterizations have demonstrated the successful structural conversion of coal from an amorphous structure into a crystalline structure. When the obtained graphitized coal samples via the high-temperature heating method (HTC) and via the FJH method (FHC) were used as anodes for lithium-ion batteries (LIBs) and potassium-ion batteries (PIBs), the HTC and FHC presented outstanding rate capability and remarkable stable cycling performance. The HTC and FHC anodes delivered initial charge capacities of 322.5 and 321.3 mAh·g−1, respectively, at a current density of 0.1C. for LIBs. When used as anodes in PIBs, the HTC and FHC delivered initial charge capacities of 265.4 and 262.2 mAh·g−1 at 0.1C current density. These results make the HTC and FHC promising materials for developing energy storage applications. Therefore, this work exploited the low price of coal and its abundant reserves, combined with the FJH technique, which is an effective method for saving energy and time, to produce high-quality graphitized coal materials, which can make this process green and economically attractive.

Structural Symmetry Impressing Carrier Dynamics of Halide Perovskite

AbstractMetal halide perovskites (MHPs) have been one of the most promising materials for the photoelectric, electro‐optical, and all‐optical conversion devices, thanks to their excellent energy conversion. To investigate the energy conversion induced by structural symmetry, herein, the carrier dynamics and dielectric properties in MHPs are surveyed and reviewed as the microscopic and macroscopic bridge, respectively. The intrinsic correlations between the structural symmetry broken, carrier dynamics, and energy conversion performance are systematically analyzed by considering the energy band structures and dielectric constants. The internal energy conversion mechanisms are elucidated to pave the way for the perovskite advanced applications.

Boosting sodium storage performance of hard carbons by regulating oxygen functionalities of the cross-linked asphalt precursor

Pre-oxidation treatment is a key process to produce carbon anodes for sodium ion batteries from pitch because it governs the orientation of carbon layers during subsequent carbonization. However, the relationship between the oxygen functionalities in the oxidized pitch and the evolution of carbon structure during carbonization remains unclear. Herein, cross-linked asphalts with differentiated oxygen functionalities such as C–O and C(O)–O (ester group and anhydride), are synthesized to explore their effects on the evolution of carbon structure. The planar cross-linked structures constructed by thermally stable C–O fail to prevent the sliding of carbon layer, leading the formation of short-range order carbon structures with lager lateral size. In contrast, the three-dimensional cross-linked structures constructed by C(O)–O effectively prevent the rearrangement of asphalt at early pyrolysis. Owing to the gas generated by C(O)–O removal during subsequent carbonization, the as-formed more disorder carbon structures with small microcrystalline sizes can generate more closed pores and ultra-micropores, which enhances the low-voltage plateau capacity from 96.06 to 132.2 mAh g−1. The insights for the differentiated oxygen functionalities in regulating the carbon structural conversion pave the way for further development of pitch-based hard carbons with higher performance and their practical applications in SIBs.

A markerless beam's eye view motion monitoring algorithm based on structure conversion and demons registration in medical image with partial data.

To propose a markerless beam's eye view (BEV) motion monitoring algorithm, which works with the inferior quality megavolt (MV) images with multi-leaf collimator (MLC) occlusion-compatible. A thorax phantom was used to verify the accuracy of the algorithm. Lung tumor quality assurance (QA) plans were generated for the phantom, and delivered 10 times on the linear accelerator with manually treatment offsets in various directions. The algorithm was used to register 753 electronic portal imaging device (EPID) images with the appropriate digitally reconstructed radiograph (DRR), calculating a registration offset that was compared with the actual offset to determine the monitoring errors. Image similarity measure was used as an independent check. Additionally, patient data of 21 lung tumor treatment plans were gathered. A total of 533 pairs of patient images were acquired for motion monitoring study, to offer quantifiable data of the tumor position change during treatment. The monitoring algorithm can process various degrees (10%-80%) of image loss, and performs well when dealing with non-rigid registration for partial data images. About 86.8% of the monitoring errors are less than 3mm in the algorithm verification of the phantom study, and about 80% of the errors are under than 2mm. Normalized Mutual Information (NMI) of phantom images changes from 1.182±0.026 to 1.202±0.027, with p<0.005, and the Hausdorff-Distance (HD) changes from 3.506±0.417mm to 3.466±0.473mm, with p<0.005. Translation with a displacement range of -6.0mm to 6.2mm is the predominant change of the patient target during treatment. NMI of patient images changes from 1.216±0.031 to 1.225±0.031, with p<0.005, and HD changes from 3.131±0.876mm to 3.118±0.038mm, with p<0.005. The dice index of target before and after registration is 0.264±0.336, indicating the presence of non-negligible non-rigid deformation. The study provides a robust markerless motion monitoring algorithm for multi-modal, partial data and inferior quality image processing.

Nonisolated Topology for High Step-Up DC–DC Converters

A new dc–dc converter structure with high voltage gain is proposed in this paper. The proposed converter consists of two switches that are turned on and off simultaneously. In addition, the two switched-capacitor cells and one energy storage cell are utilized in the structure of the proposed converter. These result in high voltage gains at low values of the duty cycle. Besides, the voltage stress across the power devices is low and below half of the output voltage. Therefore, the MOSFET switches with low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm {DS-on}}$ </tex-math></inline-formula> and devices with reduced nominal voltage can be used in the proposed converter which in turn reduces the conduction and turn-on losses. The operating principles of the proposed topology are explained, and the analysis of voltage and current stresses of the devices is accomplished. The circuit performance is compared with other solutions in the literature in terms of voltage gain and normalized voltage stress of switches and diodes. Eventually, in order to verify the theoretical analysis, the experimental results are provided.

Two-step structural changes in M3 muscarinic receptor activation rely on the coupled G protein cycle.

G protein-coupled receptors (GPCRs) regulate diverse intracellular signaling pathways through the activation of heterotrimeric G proteins. However, the effects of the reversible activation-deactivation cycle of G protein on the conformational changes of GPCRs remains unknown. By developing a new Förster resonance energy transfer (FRET) tool for human M3 muscarinic acetylcholine receptor, we found that a single-receptor FRET probe can display the consecutive structural conversion of a receptor by G protein cycle. Our results revealed that the G protein activation evokes a two-step change in the hM3R structure, including the fast step mediated by Gq protein binding and the subsequent slower step mediated by the physical separation of the Gαq and Gβγ subunits. We also found that the separated Gαq-GTP forms a stable complex with the ligand-activated hM3R and phospholipase Cβ. In sum, the present study uncovered the real-time conformational dynamics of innate hM3R during the downstream Gq protein cycle.

Structural conversion and characterization of Camellia oleifera shell lignin based on mechanochemical-assisted pretreatment

Camellia oleifera shells (COS), are the by-product of Camellia oleifera seed oil processing, and possess a high lignin content (38.6%). However, information on the fundamental chemistry of this lignin is limited. Herein, mechanochemical strategies combining ball-milling with mild acetosolv or alkaline treatment are presented to compare the structural evolution of COS lignins. The mechanochemical processes significantly improve the lignin yield, releasing lignins with high molecular weights (Mw ≈ 7000 mol/g). The COS lignins are GS-type lignins, and G units account for 71.9% of MWL. The synergistic combination of ball-milling and acetosolv treatment led to the cleavage of β-O-4 linkages. In contrast, the alkaline lignin fractions retained a large number of β-O-4 linkages (50.67/100 Ar) and a low phenolic OH content (1.56 mmol/g), indicating that the ball-milling process had little effect on the alkaline lignin structures (typical substructures). In summary, understanding the structural conversion and characteristics of lignins during the combined pretreatments of COS would facilitate the optimization of the pretreatment process and the deconstruction of COS.

A Pilot Study of the Serious Illness Conversation Guide in a Dialysis Clinic.

Clinician-led conversations about future care priorities occur infrequently with end-stage renal disease (ESRD) patients on dialysis. This was a pilot study of structured serious illness conversations using the Serious Illness Conversation Guide (SICG) in a single dialysis clinic to assess acceptability of the approach and explore conversation themes and potential outcomes among patients with ESRD. Twelve individuals with ESRD on dialysis from a single outpatient dialysis clinic participated in this study. Participants completed a baseline demographics survey, engaged in a clinician-led structured serious illness conversation, and completed an acceptability questionnaire. Conversations were recorded, transcribed and thematically analyzed. The average age of participants was 68.8years. The conversations averaged 20:53 in length. Ten participants (83%) felt that the conversation was held at the right time in their clinical course and eleven participants (91%) felt that it was worthwhile. Most participants (73%) reported neutral feelings about clinician use of a printed guide. Eleven participants (91%) reported no change in anxiety about their illness following the conversation, and five participants (42%) reported that the conversation increased their hopefulness about future quality of life. Thematic analysis revealed common perspectives on dialysis including that participants view in-center hemodialysis as temporary, compartmentalize their kidney disease, perceive narrowed life experiences and opportunities, and believe dialysis is their only option. This pilot study suggests that clinician-led structured serious illness conversations may be acceptable to patients with ESRD on dialysis. The themes identified can inform future serious illness conversations with dialysis patients.

Metamorphism in TDP-43 prion-like domain determines chaperone recognition

The RNA binding protein TDP-43 forms cytoplasmic inclusions via its C-terminal prion-like domain in several neurodegenerative diseases. Aberrant TDP-43 aggregation arises upon phase de-mixing and transitions from liquid to solid states, following still unknown structural conversions which are primed by oxidative stress and chaperone inhibition. Despite the well-established protective roles for molecular chaperones against protein aggregation pathologies, knowledge on the determinants of chaperone recognition in disease-related prions is scarce. Here we show that chaperones and co-chaperones primarily recognize the structured elements in TDP-43´s prion-like domain. Significantly, while HSP70 and HSP90 chaperones promote TDP-43 phase separation, co-chaperones from the three classes of the large human HSP40 family (namely DNAJA2, DNAJB1, DNAJB4 and DNAJC7) show strikingly different effects on TDP-43 de-mixing. Dismantling of the second helical element in TDP-43 prion-like domain by methionine sulfoxidation impacts phase separation and amyloid formation, abrogates chaperone recognition and alters phosphorylation by casein kinase-1δ. Our results show that metamorphism in the post-translationally modified TDP-43 prion-like domain encodes determinants that command mechanisms with major relevance in disease.

On Analogies in Proton-Transfers for Pyrimidine Bases in the Gas Phase (Apolar Environment)—Cytosine Versus Isocytosine

Inter- and intra-molecular proton-transfers between functional groups in nucleobases play a principal role in their interactions (pairing) in nucleic acids. Although prototropic rearrangements (intramolecular proton-transfers) for neutral pyrimidine bases are well documented, they have not always been considered for their protonated and deprotonated forms. The complete isomeric mixtures in acid-base equilibria and in acidity–basicity parameters have not yet been examined. Taking into account the lack of literature and data, research into the question of prototropy for the ionic (protonated and deprotonated) forms has been undertaken in this work. For the purposes of this investigation, two isomeric pyrimidine bases (C—cytosine and iC—isocytosine) were chosen. They exhibit analogous (symmetrical) general acid-base equilibria (intermolecular proton-transfers). Being similar polyfunctional tautomeric systems, C and iC possess two labile protons and five conjugated tautomeric sites. However, positions of exo groups are different. Consequently, structural conversions such as prototropy, rotational, and geometrical isomerism of exo groups (=O/−OH and =NH/−NH2) and their intramolecular interactions with endo groups (=N−/&gt;NH) possible in neutral C and iC and in their ionic forms lead to some differences in compositions of isomeric mixtures. By application of quantum–chemical methods to the isolated (in vacuo) species, stability of all possible neutral and ionic isomers has been examined and the candidate isomers selected. The complete isomeric mixtures have been considered for the first time for di-deprotonated, mono-deprotonated, mono-protonated, and di-protonated forms. Protonation–deprotonation reactions have been analyzed in the gas phase that models non-polar environment. The gas-phase microscopic (kinetic) and macroscopic (thermodynamic) acidity–basicity parameters have been estimated for each step of acid-base equilibria. When proceeding from di-anion to di-cation in four steps of protonation–deprotonation reaction, the macroscopic proton affinities for C and iC differ by less than 10 kcal mol−1. Their DFT-calculated values are as follows: 451 and 457, 340 and 339, 228 and 224, and 100 and 104 kcal mol−1, respectively. Differences between the microscopic proton affinities for analogous isomers of C and iC seem to be larger for the exo than endo groups. Owing to variations of relative stabilities for neutral and ionic isomers, in some cases they are even larger than 10 kcal mol−1.

Multistep sequence-controlled supramolecular polymerization by the combination of multiple self-assembly motifs

The precise sequence control of polymer chain is an important research topic of polymer chemistry. Although some methods such as iterative synthesis and supramolecular polymerization have been developed to fabricate sequence-controllable polymer, it is still a great challenge to consecutively prepare multiple supramolecular polymers with different sequence structures. In this work, through the reasonable utilization of assembly motifs, we integrated multiple host-guest recognitions and metal coordination interactions to prepare different sequence-controlled supramolecular polymers by a multistep assembly strategy. This research provides inspiration for the design and preparation of supramolecular polymers with different sequence structures.

Structural and Mechanistic Basis for the Inactivation of Human Ornithine Aminotransferase by (3S,4S)-3-Amino-4-fluorocyclopentenecarboxylic Acid.

Ornithine aminotransferase (OAT) is overexpressed in hepatocellular carcinoma (HCC), and we previously showed that inactivation of OAT inhibits the growth of HCC. Recently, we found that (3S,4S)-3-amino-4-fluorocyclopentenecarboxylic acid (5) was a potent inactivator of γ-aminobutyric acid aminotransferase (GABA-AT), proceeding by an enamine mechanism. Here we describe our investigations into the activity and mechanism of 5 as an inactivator of human OAT. We have found that 5 exhibits 10-fold less inactivation efficiency (kinact/KI) against hOAT than GABA-AT. A comprehensive mechanistic study was carried out to understand its inactivation mechanism with hOAT. pKa and electrostatic potential calculations were performed to further support the notion that the α,β-unsaturated alkene of 5 is critical for enhancing acidity and nucleophilicity of the corresponding intermediates and ultimately responsible for the improved inactivation efficiency of 5 over the corresponding saturated analogue (4). Intact protein mass spectrometry and the crystal structure complex with hOAT provide evidence to conclude that 5 mainly inactivates hOAT through noncovalent interactions, and that, unlike with GABA-AT, covalent binding with hOAT is a minor component of the total inhibition which is unique relative to other monofluoro-substituted derivatives. Furthermore, based on the results of transient-state measurements and free energy calculations, it is suggested that the α,β-unsaturated carboxylate group of PLP-bound 5 may be directly involved in the inactivation cascade by forming an enolate intermediate. Overall, compound 5 exhibits unusual structural conversions which are catalyzed by specific residues within hOAT, ultimately leading to an enamine mechanism-based inactivation of hOAT through noncovalent interactions and covalent modification.

Density functional theory simulation of heterogeneous polymerization reactions during biomass hydrothermal carbonization

AbstractCarbonaceous microspheres formed through heterogeneous polymerization reactions during hydrothermal carbonization of biomass showed a considerable effect on the mass yield and physicochemical properties of hydrochar. In exploring the growth mechanism of carbonaceous microspheres, the heterogeneous polymerization reaction of four typical organic components (5‐hydroxymethylfurfural, furfural, phenol, and p‐xylene) with the surficial functional groups of carbonaceous microspheres was investigated using density functional theory (DFT). Nucleophilic addition and dehydration are the main forms of polymerization reactions, and the former shows a lower reaction energy barrier than the latter by 100 kJ/mol, indicating that the nucleophilic addition reactions likely occur compared to dehydration reactions. And phenol likely promotes the growth of microspheres. In addition, the surficial furan ring structure of carbonaceous microspheres opened through ring opening, hydrogen atom transfer, and molecular space structure conversion in sequence. Among these reaction steps, the furan ring opening through hydration was the rate‐limiting reaction step, which showed the highest energy barrier with a value of 394.51 kJ/mol. However, the ring opening of furan rings could form more active sites, such as carbonyl groups, for subsequent polymerization reactions, indicating an increased potential for further reactions with aqueous‐phase organic components.

A Review of Non-isolated High Step-up DC-DC Converter Structures and Simulation Analysis of a High Gain Quadratic Converter

A Review of Non-isolated High Step-up DC-DC Converter Structures and Simulation Analysis of a High Gain Quadratic Converter