Crystal Cohesion and Conformational Energies

ISBN-13: 9783642815799 / Angielski / Miękka / 2012 / 154 str.

R. M. Metzger; F. a. Momany; B. D. Silverman

Opis

With the advent of X-ray diffraction and crystal structure determination in 1912 researchers in physics and chemistry began investigating the problem of crystal co hesion, i. e., on the question of what holds crystals together. The names of M. Born, E. Madelung, P. P. Ewald, F. Bloch, E. P. Wigner, and J. E. Mayer are, in particular, associated with the pre-1940 work on the cohesion of inorganic lattices. The advent of digital computers brought along great advances in the detailed understanding of ionic crystals, molecular crystals, and metals. The work of P. O. Lowdin and r A. I. Kitaigorodosky are seminal i these more recent advances. This volume is a collection of specialist reports on a subset of the general problem of crystal cohesion. It is intended for researchers and advanced students in solid-state chemistry and physics, and biochemistry. WILLIAMS reports on the mole cule-independent empirical parameters for dispersion and repulsion that explain, and can predict, the cohesive energy of neutral organic lattices. MOMANY applies similar procedures to the conformational energy problem and shows how they can be used for the pharmacological problems of polypeptide drug design. METZGER uses quantum-mechanical molecule-dependent atom-in-molecule charges, dipole moments, and polarizabilities to study the cohesion of organic ionic (semiconducting) and par tially ionic (metallic) lattices. SILVERMAN emphasizes, with quantum-mechanical dimer calculations, the importance of dispersive interactions for the observed stacking modes in organic metallic lattices."

Spis treści

1. Introduction.- References.- 2. Transferable Empirical Nonbonded Potential Functions.- 2.1 Introductory Comments.- 2.2 Empirical Nonbonded Potential Models.- 2.2.1 The Number of Adjustable Parameters and Heteroatomic Combining Laws.- 2.2.2 The Atomic Hardness Parameters, C.- 2.2.3 The Repulsion Center Shift for Bonded Hydrogen.- 2.2.4 The Net Atomic Charges, q.- 2.3 Nonbonded Interactions in Molecular Crystals.- 2.3.1 Nonbonded Crystal Lattice Energy.- 2.3.2 Mathematical Description of the Crystal Structure.- 2.3.3 The Structural Derivatives of C.- 2.3.4 The Forces and Torques as Functions of the Nonbonded Potential Parameters.- 2.4 Accelerated Convergence of Lattice Sums.- 2.4.1 Fourier Transforms of the Lattice Sum.- 2.4.2 Numerical Examples.- 2.4.3 Lattice Energy Derivatives Including Accelerated Convergence.- 2.5 Derivation of Nonbonded Potential Parameters.- 2.5.1 The Force-Fit Method.- 2.5.2 Application to Hydrocarbons.- 2.5.3 The Direct-Parameter-Fit Method.- 2.6 Extensions of the Potential Model.- 2.6.1 Molecular Rotations and Translations.- 2.6.2 Intramolecular Rotations.- 2.6.3 Thermal Corrections.- 2.6.4 Lattice Vibrations.- 2.6.5 Weak Morse Bond Potential.- 2.6.6 High-Pressure Crystal Structures.- 2.7 Appendix. Derivatives of C.- References.- 3. Conformational Analysis and Polypeptide Drug Design.- 3.1 Introductory Comments.- 3.2 Computational Procedures.- 3.3 Polypeptides and Their Constituents.- 3.3.1 Modifications to the Peptide Backbone.- a) L-Amino Acids.- b) D-Amino Acids.- c) C?-Methyl Analogs.- d) N-Methyl Analogs.- e) Depsipeptides.- f) Reduced Carbonyl. Intercalated Methylene (homo), and Carbazic Acid (?-Aza) Analogs.- 3.3.2 Chain Reversals and Bend Conformations.- a) LL, LD, and DL Bends.- b) Depsipeptide Bend Structures.- 3.3.3 Direction Reversal: Retro, Retroenantiomers, and Retro-all-D-Peptides.- 3.3.4 Bridges: Disulfide Bonds and Carba-Analogs.- 3.3.5 Modifications of Side Chains.- 3.3.6 Abnormal Side-Chain Modifications.- a) ?,?-Dehydro Analogs.- b) 3,4-Dehydroproline, Azetidine, and Thiazolidine.- 3.4 Application of Conformational Information to Drug Design.- 3.4.1 Example Studies: Backbone Substitutions and Conformational Effects.- a) D-Amino Acid Substitution.- Case I: C-terminal of Somatostatin.- Case II: N-terminal of Luteinizing Hormone-Releasing Hormone (LHRH).- Case III: Substitution for Glycine in Enkephalins (EK) and LHRH.- Case IV: L- to D-Conversion in Somatostatin.- Case V: L- to D-Conversions in LHRH Antagonists.- b) N-Methyl and Depsipeptide Results.- Case VI: Eledoisin and [(N-Me)Leu7]-LHRH.- c) L-, D-Combinations.- Case VII: A Conformational Approach to the Design of Growth Hormone Agonist.- 3.5 Conclusions.- References.- 4. Cohesion and Ionicity in Organic Semiconductors and Metals.- 4.1 Introductory Comments.- 4.2 Crystal Cohesive Energies: General Theory.- 4.2.1 Löwdin’s Theory.- 4.2.2 Madelung Energy.- 4.2.3 Charge-Dipole and Dipolar Energies.- 4.2.4 Polarization and Dispersion Energies.- 4.3 Born-Haber Cycles and Criteria for Ionicity.- 4.3.1 Born-Haber Cycles.- 4.3.2 Criteria for Ionicity.- 4.4 Lattice Energy Calculations.- 4.4.1 Lattice Energy Algorithms.- 4.4.2 Madelung Energy-Uniform Lattice.- 4.4.3 Madelung Energy-Wigner Lattice.- 4.4.4 Beyond the Madelung Energy.- References.- 5. Slipped Versus Eclipsed Stacking of Tetrathiafulvalene (TTF) and Tetracyanoquinodimethane (TCNQ) Dimers.- 5.1 Introductory Comments.- 5.2 Geometry of Donor-Acceptor ? Complexes: Slipped Versus Eclipsed Stacking.- 5.3 Molecular-Orbital Calculations.- 5.3.1 Extended-Hückel Calculations.- 5.3.2 CNDO/2 Calculations.- 5.4 Interactions Between Closed-Shell Neutral TTF Molecules: Hard-Sphere Packing and Atom-Atom Potentials in Crystalline TTF.- 5.5 Density-Functional Calculation: Neutral TTF Dimer.- 5.6 Density-Functional Calculation: Open Shell TTF Dimer.- 5.7 Conclusions.- References.