Understanding the geometrical preferences in chemical reactions is crucial for advancing the field of organic chemistry and improving synthetic strategies. One such preference, the Bürgi-Dunitz ...angle, is central to nucleophilic addition reactions involving carbonyl groups. This study successfully employs a novel two-dimensional Distortion-Interaction/Activation-Strain Model in combination with a two-dimensional Energy Decomposition Analysis to investigate the origins of the Bürgi-Dunitz angle in the addition reaction of CN– to (CH3)2CO. We constructed a 2D potential energy surface defined by the distance between the nucleophile and carbonylic carbon atom and by the attack angle, followed by an in-depth exploration of energy components, including strain and interaction energy. Our analysis reveals that the Bürgi-Dunitz angle emerges from a delicate balance between two key factors: strain energy and interaction energy. High strain energy, as a result of the carbonyl compound distorting to avoid Pauli repulsion, is encountered at high angles, thus setting the upper bound. On the other hand, interaction energy is shaped by a dominant Pauli repulsion when the angles are lower. This work emphasizes the value of the 2D Energy Decomposition Analysis as a refined tool, offering both quantitative and qualitative insights into chemical reactivity and selectivity.
An Au(I)‐catalyzed cyclization/semipinacol rearrangement cascade of 1,6‐enynes has been developed for the construction of spiro4.5decanes and 7‐azaspiro4.5decanes. The use of JohnPhosAuCl/NaBARF as a ...catalyst afforded functionalizable spirocyclic products with good diastereoselectivities of 6.7:1 to >20:1 dr. A plausible reaction mechanism has also been proposed on the basis of previous literature and our experimental results.
This comprehensive handbook covers the diverse aspects of chemical vapor transport reactions from basic research to important practical applications. The book begins with an overview of models for ...chemical vapor transport reactions and then proceeds to treat the specific chemical transport reactions for the elements, halides, oxides, sulfides, selenides, tellurides, pnictides, among others. Aspects of transport from intermetallic phases, the stability of gas particles, thermodynamic data, modeling software and laboratory techniques are also covered. Selected experiments using chemical vapor transport reactions round out the work, making this book a useful reference for researchers and instructors in solid state and inorganic chemistry.
Ideal for newcomers and established researchers in the field Reaction Mechanisms of Metal Complexes in Solution is a complete treatment of the area covering advanced topics with relevance to ...biomedical applications, extraction metallurgy, food chemistry and a wealth of other industrial processes and research areas.
•A method for designing a family of multi-loop deployable mechanisms is proposed.•Several overconstrained parallel mechanisms and loop-coupled mechanisms are obtained.•All the mechanisms obtained ...have one DOF in the deploying mode.•The loop-coupled mechanism based on 8R linkages has an additional 3 DOF mode.•The parallel mechanism based on 10R linkages has an additional 2 DOF 5R planar mode.
This paper is to propose a novel construction method for constructing a family of over-constrained multi-loop deployable mechanisms by connecting orthogonal single-loop linkages using spherical (S) joints. An orthogonal single-loop linkage refers to a linkage with an even number of identical links with orthogonal revolute (R)-joint axes and no offset. Two types of multi-loop mechanisms are obtained, including parallel mechanisms (PMs) and loop-coupled mechanisms (LCMs) by connecting orthogonal Bricard linkage, 8R or 10R linkage platforms. The mechanisms constructed by orthogonal Bricard linkages only have one degree-of-freedom (DOF). The volume of the PM is calculated, which indicates that the mechanisms have a high ratio of stowed-to-deployed diameter, without considering link interference. The mechanisms designed using orthogonal 8R or 10R linkages have multiple motion modes and can switch between different modes through singular positions. Finally, the method has been extended to the PMs and LCMs composed of loops that the axes of two adjacent R joints are not perpendicular to each other.
Thymus-derived lymphocytes protect mammalian hosts against virus- or cancer-related cellular alterations through immune surveillance, eliminating diseased cells. In this process, T cell receptors ...(TCRs) mediate both recognition and T cell activation via their dimeric αβ, CD3ϵγ, CD3ϵδ, and CD3ζζ subunits using an unknown structural mechanism. Here, site-specific binding topology of anti-CD3 monoclonal antibodies (mAbs) and dynamic TCR quaternary change provide key clues. Agonist mAbs footprint to the membrane distal CD3ϵ lobe that they approach diagonally, adjacent to the lever-like Cβ FG loop that facilitates antigen (pMHC)-triggered activation. In contrast, a non-agonist mAb binds to the cleft between CD3ϵ and CD3γ in a perpendicular mode and is stimulatory only subsequent to an external tangential but not a normal force (∼50 piconewtons) applied via optical tweezers. Specific pMHC but not irrelevant pMHC activates a T cell upon application of a similar force. These findings suggest that the TCR is an anisotropic mechanosensor, converting mechanical energy into a biochemical signal upon specific pMHC ligation during immune surveillance. Activating anti-CD3 mAbs mimic this force via their intrinsic binding mode. A common TCR quaternary change rather than conformational alterations can better facilitate structural signal initiation, given the vast array of TCRs and their specific pMHC ligands.
Animal Vigilance builds on the author's previous publication with Academic Press ( Social Predation: How Group Living Benefits Predators and Prey ) by developing several other themes including the ...development and mechanisms underlying vigilance, as well as developing more fully the evolution and function of vigilance. Animal vigilance has been at the forefront of research on animal behavior for many years, but no comprehensive review of this topic has existed. Students of animal behavior have focused on many aspects of animal vigilance, from models of its adaptive value to empirical research in the laboratory and in the field. The vast literature on vigilance is widely dispersed with often little contact between models and empirical work and between researchers focusing on different taxa such as birds and mammals. Animal Vigilance fills this gap in the available material. * Tackles vigilance from all angles, theoretical and empirical, while including the broadest range of species to underscore unifying themes * Discusses several newer developments in the area, such as vigilance copying and effect of food density * Highlights recent challenges to assumptions of traditional models of vigilance, such as the assumption that vigilance is independent among group members, which is reviewed during discussion of synchronization and coordination of vigilance in a group * Written by a top expert in animal vigilance
This reprint aims to disseminate the latest research achievements, findings, and ideas in the robotics field, with particular focus on the Italian scenario. It covers a range of topics related to the ...theory, design, practice, and applications of robots, such as robot design and kinematics, dynamics of robots and multi-body systems, linkages and manipulators, control of robotic systems, trajectory planning and optimization, innovative robots and applications, industrial robotics, collaborative robotics, medical robotics, assistive robotics, and service robotics. The reprints contributions include (but are not limited to) revised and substantially extended versions of selected papers that were presented at the 2nd International Conference of IFToMM, Italy (IFIT 2018).
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