Orbital Steering Research Articles

Coupling Effect of Nonlinear Stiffness of Tape Spring Hinges and Flexible Deformation of Panels during Orbit Maneuvers

Many solar panels for spacecrafts are deployed by Tape Spring Hinges (TSHs) which have changeable stiffness. The stiffness of TSH is small when panels are folded, and it becomes large quickly in its deployed status. Since the solar panel is a thin sheet, flexible deformation is easily generated by orbit maneuvers. The coupling effect between the nonlinear TSHs and the flexible panels generates obvious vibration which affects the operational stability of the satellite. To investigate this coupling effect, non-deformable, linear deformable and nonlinear deformable panels were modelled by rigid body, modal order reduction method (MORM) and finite element method (FEM), respectively. The driving torque of TSH was described as a function of the rotation angle and angular velocity. The nonlinear properties of the TSH were reflected by one angle-stiffness spline multiplied by one stiffness coefficient. Dynamic responses of a satellite in deployment and orbit steering were analyzed by numerical simulations. Analysis results indicate the local deformation of panels keeps the stiffness of the TSH within a large range which accelerates the orbit maneuvers. However, much vibration is generated by the coupling effect if the luck-up status is broken up. The coupling effect affects the sequence of deployment, overshoot phenomenon and acceleration magnitude of the panels. Although the MORM is more efficient than FEM in computation, we propose FEM is better suited in the design of TSH and in studying the precise control of spacecraft with flexible solar panels and TSHs.

Regulating the Interfacial Electronic Coupling of Fe2N via Orbital Steering for Hydrogen Evolution Catalysis

The capability of manipulating the interfacial electronic coupling is the key to achieving on-demand functionalities of catalysts. Herein, it is demonstrated that the electronic coupling of Fe2 N can be effectively regulated for hydrogen evolution reaction (HER) catalysis by vacancy-mediated orbital steering. Ex situ refined structural analysis reveals that the electronic and coordination states of Fe2 N can be well manipulated by nitrogen vacancies, which impressively exhibit strong correlation with the catalytic activities. Theoretical studies further indicate that the nitrogen vacancy can uniquely steer the orbital orientation of the active sites to tailor the electronic coupling and thus benefit the surface adsorption capability. This work sheds light on the understanding of the catalytic mechanism in real systems and could contribute to revolutionizing the current catalyst design for HER and beyond.

Computational fluid dynamic analysis of physical forces playing a role in brain organoid cultures in two different multiplex platforms

BackgroundOrganoid cultivation in suspension culture requires agitation at low shear stress to allow for nutrient diffusion, which preserves tissue structure. Multiplex systems for organoid cultivation have been proposed, but whether they meet similar shear stress parameters as the regularly used spinner flask and its correlation with the successful generation of brain organoids has not been determined.ResultsHere we used computational fluid dynamics (CFD) to simulate two multiplex culture conditions: steering plates on an orbital shaker and the use of a previously described bioreactor. The bioreactor had low speed and high shear stress regions that may affect cell aggregate growth, depending on volume, whereas the computed variables of the steering plates were closer to those of the spinning flask.ConclusionOur protocol improves the initial steps of the standard brain organoid formation, and the produced organoids displayed regionalized brain structures, including retinal pigmented cells. Overall, we conclude that suspension culture on orbital steering plates is a cost-effective practical alternative to previously described platforms for the cultivation of brain organoids for research and multiplex testing.

Design of x-ray diagnostic beam line for a synchrotron radiation source and measurement results

Indus-2 is a 2.5GeV synchrotron radiation source (SRS) operational at the Raja Ramanna Centre for Advanced Technology (RRCAT) in India. We have designed, developed and commissioned x-ray diagnostic beam line (X-DBL) at the Indus-2. It is based on pinhole array imaging (8–18keV). We have derived new equations for online measurements of source position and emission angle with pinhole array optics. Measured values are compared with the measurements at an independent x-ray beam position monitor (staggered pair blade monitor) installed in the X-DBL. The measured values are close to the theoretical expected values within ±12µm (or ±1.5μrad) for sufficiently wide range of the beam movements. So, beside the beam size and the beam emittance, online information for the vertical position and angle is also used in the orbit steering. In this paper, the various design considerations of the X-DBL and online measurement results are presented.

Geometric Restraint Drives On- and Off-pathway Catalysis by the Escherichia coli Menaquinol:Fumarate Reductase

Complex II superfamily members catalyze the kinetically difficult interconversion of succinate and fumarate. Due to the relative simplicity of complex II substrates and their similarity to other biologically abundant small molecules, substrate specificity presents a challenge in this system. In order to identify determinants for on-pathway catalysis, off-pathway catalysis, and enzyme inhibition, crystal structures of Escherichia coli menaquinol:fumarate reductase (QFR), a complex II superfamily member, were determined bound to the substrate, fumarate, and the inhibitors oxaloacetate, glutarate, and 3-nitropropionate. Optical difference spectroscopy and computational modeling support a model where QFR twists the dicarboxylate, activating it for catalysis. Orientation of the C2-C3 double bond of activated fumarate parallel to the C(4a)-N5 bond of FAD allows orbital overlap between the substrate and the cofactor, priming the substrate for nucleophilic attack. Off-pathway catalysis, such as the conversion of malate to oxaloacetate or the activation of the toxin 3-nitropropionate may occur when inhibitors bind with a similarly activated bond in the same position. Conversely, inhibitors that do not orient an activatable bond in this manner, such as glutarate and citrate, are excluded from catalysis and act as inhibitors of substrate binding. These results support a model where electronic interactions via geometric constraint and orbital steering underlie catalysis by QFR.

Comments on orbital steering

Molecular orbital theory has been applied to explore the potential energy surface for several bimolecular reactions. The results of these calculations can be used to assess the rate accelerations that might be achieved in similar optimally oriented reactions. Several of the reactions studied (e.g., CH3O− + H2NCHO) are bimolecular counterparts of intermediate steps in enzyme catalysis (e.g., serine proteinase activity). In these cases the importance of “orbital steering” as a vehicle for enzyme catalysis is assessed.

Daniel E. Koshland, Jr. (1920–2007)

Daniel E. Koshland, Jr. (1920–2007)

An alternative view of enzyme catalysis

Abstract This paper begins with a brief review of theories and concepts that have influenced today's view of enzyme catalysis: transition-state stabilization, entropy, orbital steering, proximity, and intramolecularity. The discussion then launches into the "spatiotemporal" model of enzyme catalysis in which fast intramolecular and enzymatic rates are ascribed to short distances that are imposed rigidly upon the reacting entities. An equation relating rate and distance is set forth, as are experimental and computational data supporting this relationship. Finally, enzyme systems themselves are analyzed in terms of the distance parameter and the so-called "split-site" model in which ground-state geometries play a crucial role. Among the many surprising conclusions is a transition-state stabilization by noncovalent forces (e.g., hydrogen-bonding) that are positioned far away from the actual transition-state chemistry. The model also confronts and dismisses the claim in classical enzymology that the ubiquitous enzyme-substrate complex is either inconsequential or inhibitory to the overall reaction rate.

Ribozyme catalysis via orbital steering

Orbital steering is invoked to explain how the three-dimensional structure of a small self-cleaving RNA, the hammerhead ribozyme, both prevents and enhances RNA autocatalysis. Within the conserved catalytic core of the ribozyme, the position of the 2′ oxygen atom of the G8 ribose is observed to be aligned almost perfectly with the phosphorus atom and the 5′ oxygen atom of the adjacent A9 phosphate group for self-cleavage via an in-line attack mechanism. Despite this apparent near-perfect atomic positioning, no cleavage takes place. The explanation proposed is that a network of hydrogen bonds in the ribozyme core orients or steers the orbitals containing the electron lone pairs of the attacking nucleophile (the 2′ oxygen atom) away from the A9 phosphorus atom, eliminating overlap with the vacant phosphorus d-orbitals despite the near-perfect in-line positioning of the oxygen atom, thus preventing catalysis. Because of the near-perfect atomic positioning of the 2′ oxygen atom relative to the phosphate group, orbital steering effects in this case are fortuitously uncoupled from conformational, distance and orientation effects, allowing an assessment of the catalytic power due purely to orbital steering. In contrast, a conformational change at the cleavage site is required to bring the 2′ oxygen atom and the scissile phosphate group into atomic positions amenable to an in-line attack mechanism. In addition, the conformationally changed structure must then steer the lone-pair orbitals of the correctly positioned 2′ oxygen atom toward the scissile phosphorus atom in order for cleavage to take place. We estimate that fulfilment of each of these two required changes may contribute separately an approximately 1000-fold rate enhancement, potentially accounting for a significant fraction of the catalytic power of this ribozyme. Orbital steering therefore appears to be a general phenomenon that may help to explain catalysis in both ribozymes and protein enzymes in a unified manner.

D-Amino acid oxidase: new findings.

The most recent research on D-amino acid oxidases and D-amino acid metabolism has revealed new, intriguing properties of the flavoenzyme and enlighted novel biotechnological uses of this catalyst. Concerning the in vivo function of the enzyme, new findings on the physiological role of D-amino acid oxidase point to a detoxifying function of the enzyme in metabolizing exogenous D-amino acids in animals. A novel role in modulating the level of D-serine in brain has also been proposed for the enzyme. At the molecular level, site-directed mutagenesis studies on the pig kidney D-amino acid oxidase and, more recently, on the enzyme from the yeast Rhodotorula gracilis indicated that the few conserved residues of the active site do not play a role in acid-base catalysis but rather are involved in substrate interactions. The three-dimensional structure of the enzyme was recently determined from two different sources: at 2.5-3.0 A resolution for DAAO from pig kidney and at 1.2-1.8 A resolution for R. gracilis. The active site can be clearly depicted: the striking absence of essential residues acting in acid-base catalysis and the mode of substrate orientation into the active site, taken together with the results of free-energy correlation studies, clearly support a hydrid transfer type of mechanism in which the orbital steering between the substrate and the isoalloxazine atoms plays a crucial role during catalysis.

A Conserved Negatively Charged Cluster in the Active Site of Creatine Kinase Is Critical for Enzymatic Activity

A Conserved Negatively Charged Cluster in the Active Site of Creatine Kinase Is Critical for Enzymatic Activity

Transition state structure of arginine kinase: implications for catalysis of bimolecular reactions.

Arginine kinase belongs to the family of enzymes, including creatine kinase, that catalyze the buffering of ATP in cells with fluctuating energy requirements and that has been a paradigm for classical enzymological studies. The 1.86-A resolution structure of its transition-state analog complex, reported here, reveals its active site and offers direct evidence for the importance of precise substrate alignment in the catalysis of bimolecular reactions, in contrast to the unimolecular reactions studied previously. In the transition-state analog complex studied here, a nitrate mimics the planar gamma-phosphoryl during associative in-line transfer between ATP and arginine. The active site is unperturbed, and the reactants are not constrained covalently as in a bisubstrate complex, so it is possible to measure how precisely they are pre-aligned by the enzyme. Alignment is exquisite. Entropic effects may contribute to catalysis, but the lone-pair orbitals are also aligned close enough to their optimal trajectories for orbital steering to be a factor during nucleophilic attack. The structure suggests that polarization, strain toward the transition state, and acid-base catalysis also contribute, but, in contrast to unimolecular enzyme reactions, their role appears to be secondary to substrate alignment in this bimolecular reaction.

Orbital steering in the catalytic power of enzymes: small structural changes with large catalytic consequences.

Small structural perturbations in the enzyme isocitrate dehydrogenase (IDH) were made in order to evaluate the contribution of precise substrate alignment to the catalytic power of an enzyme. The reaction trajectory of IDH was modified (i) after the adenine moiety of nicotinamide adenine dinucleotide phosphate was changed to hypoxanthine (the 6-amino was changed to 6-hydroxyl), and (ii) by replacing Mg2+, which has six coordinating ligands, with Ca2+, which has eight coordinating ligands. Both changes make large (10(-3) to 10(-5)) changes in the reaction velocity but only small changes in the orientation of the substrates (both distance and angle) as revealed by cryocrystallographic trapping of active IDH complexes. The results provide evidence that orbital overlap produced by optimal orientation of reacting orbitals plays a major quantitative role in the catalytic power of enzymes.

Matrix synthesis of chiral carboxy derivatives: Aldehyde chiral discrimination due to a two‐point coordination of Mg2+

AbstractTo control stereoselectivity in aldol‐like reactions with chiral carbohydrate templates, we studied the interaction between completely protected dialdo compounds and magnesium enediolates of arylacetic acids. Diastereomeric mixtures of the highly functionalized acids obtained were esterified to isolate individual methyl uronates. It was found that all the diastereomeric esters exhibit Cotton effects of the same positive sign in the 220–230 nm region and so possess the same S configuration of the aryl chiral center C(6). Chiral center C(5) configurational assignments were performed using IR and ORD spectroscopy. We separated and specified four pairs of diastereomeric methyl uronates. It follows that the precursory acids have the same 5R*, 6S (major isomers) and 5S*, 6S (minor isomers) configurations. A tentative mechanism for complexation and possible models of Mg2+ ‐protected dialdose intermediate complexes has been proposed. We have concluded that a kind of orbital steering is realized, accompanied by some “tuning” of molecular assembly conditioned by two‐point coordination between Mg2+ and potential cation‐binding sites in the substrate molecules. Thus it has been demonstrated that reasonable diastereo‐selectivity can be achieved even through the use of small matrix molecules using rather small functional groups, which do not impose any stringent steric requirements. © 1993 Wiley‐Liss, Inc.

ChemInform Abstract: STEREO‐ AND REGIO‐SPECIFICITY IN ORGANIC SYNTHESIS PROMOTED BY METAL IONS

AbstractReview: Bericht über einen Vortrag, der auf dem "26th International Congress of Pure and Applied Chemistry" in Tokyo v. 4.9.

Stereo- and regio-specificity in organic synthesis promoted by metal ions

Abstract

ChemInform Abstract: MOLECULAR ORBITAL STUDIES OF ENZYME ACTIVITY. 2. NUCLEOPHILIC ATTACK ON CARBONYL SYSTEMS WITH COMMENTS ON ORBITAL STEERING

Chemischer InformationsdienstVolume 7, Issue 45 Preparative Organic Chemistry ChemInform Abstract: MOLECULAR ORBITAL STUDIES OF ENZYME ACTIVITY. 2. NUCLEOPHILIC ATTACK ON CARBONYL SYSTEMS WITH COMMENTS ON ORBITAL STEERING S. SCHEINER, S. SCHEINERSearch for more papers by this authorW. N. LIPSCOMB, W. N. LIPSCOMBSearch for more papers by this authorD. A. KLEIER, D. A. KLEIERSearch for more papers by this author S. SCHEINER, S. SCHEINERSearch for more papers by this authorW. N. LIPSCOMB, W. N. LIPSCOMBSearch for more papers by this authorD. A. KLEIER, D. A. KLEIERSearch for more papers by this author First published: November 9, 1976 https://doi.org/10.1002/chin.197645115Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue45November 9, 1976 RelatedInformation

Molecular orbital studies of enzyme activity. 2. Nucleophilic attack on carbonyl systems with comments on orbital steering.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular orbital studies of enzyme activity. 2. Nucleophilic attack on carbonyl systems with comments on orbital steeringSteve Scheiner, William N. Lipscomb, and Daniel A. KleierCite this: J. Am. Chem. Soc. 1976, 98, 16, 4770–4777Publication Date (Print):August 1, 1976Publication History Published online1 May 2002Published inissue 1 August 1976https://doi.org/10.1021/ja00432a014RIGHTS & PERMISSIONSArticle Views195Altmetric-Citations76LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (911 KB) Get e-Alerts Get e-Alerts

“Orbital steering”, entropy, and rate accelerations

Some important conceptual and quantitative differences are described between the “orbital steering” and entropy descriptions of the rate accelerations in intramolecular and enzymic reactions that may be brought about by geometric constraints other than distortion. The treatments differ by a factor of 10 3 – 10 4 in the maximum rate acceleration that may be obtained from these constraints. The estimation of a “proximity factor” without taking adequate account of the translational and overall rotational entropy terms gives a misleading value for this factor. The conclusion is reaffirmed that increasing the probability of reaction by restricting the free translational and rotational movement of reacting groups can play a large role in the catalytic power of enzymes.

A molecular orbital study on the enzymic reaction mechanism of α-chymotrypsm

On the basis of the three-dimensional structure of the active site of α-chymotrypsin determined by X-ray diffraction analysis, we calculated a total energy and delocalization energy by using a molecular orbital method including all valence electrons, i.e. σ- and π-electrons. The calculated potential curve for a hydrolysis by a-chymotrypsin reproduced the experimental curve well, and the relative magnitudes of all steps in the reaction path explain the experimentally obtained activation energies satisfactorily. The validity of the “charge relay system” proposed by Blow and co-workers was investigated from the quantum-chemical point of view, and the possible importance of this structure for the acceleration of the hydrolysis through a proton transfer within the active site was pointed out. Delocalization energy was proved to play an important role in lowering the activation energy, and the effect of “orbital steering” suggested by Koshland and co-workers was also shown to be of importance for the catalytic reaction of α-chymotrypsin.