Hydrogen bonding multiple

A solution leading to a successful algorithm was recently found for the folding of ribonucleic acid (RNA) [36], Natural RNA polymers (figure C2.14.1) are mainly made up from four different bases . A, C, G and U. As with DNA, multiple hydrogen bonding favours the fonnation of G-C and A-U pairs [16, 37, 38] which leads to the appearance of certain characteristic stmctures. Loop closure is considered to be the most important folding event. 

All of these functions are made possible by the characteristic chemical features of carbohydrates (1) the existence of at least one and often two or more asymmetric centers, (2) the ability to exist either in linear or ring structures, (3) the capacity to form polymeric structures via glyeosidie bonds, and (4) the potential to form multiple hydrogen bonds with water or other molecules in their environment. 

FIGURE 7.29 Like cellulose, chitin, man-nan, and poly(D-mannuronate) form extended ribbons and pack together efficiently, taking advantage of multiple hydrogen bonds. 

Primary structures are stabilized by covalent peptide bonds. Higher orders of structure are stabilized by weak forces—multiple hydrogen bonds, salt (electrostatic) bonds, and association of hydrophobic R groups. 

Fig. 18.—Structure of Maltitol, Showing Multiple Hydrogen-bonding. " [Key , more acidic possible hydrogen-bond.]...

Gonzales, L., Mo, O., Yanez, M., 1996, High Level Ab Initio Versus DFT Calculations on (H202)2 and H202-H20 Complexes as Prototypes of Multiple Hydrogen Bonded Systems , J. Comput. Chem., 18, 1124. 

Zhang, Q., Bell, R., Truong, T. N., 1994, Ab Initio and Density Funcional Theory Studies of Proton Transfer Reactions in Multiple Hydrogen Bond Systems , J. Phys. Chem., 99, 592. 

Crystal Engineering Using Multiple Hydrogen Bonds A. D. Burrows... 

On the other hand, the over-the-center coordination in a carousel copper(II)-triazine complex (Fig. 14) [92] appears to be the result of multiple hydrogen bonding and steric effects. 

Burrows AD (2004) Crystal Engineering Using Multiple Hydrogen Bonds 108 55-96 Bussmann-Holder A, Dalai NS (2007) Order/Disorder Versus or with Displacive Dynamics in Ferroelectric Systems. 124 1-21... 

Polyethers have high water solubilities because of their ability to form multiple hydrogen bonds to water molecules. 

Tominaga, M Konishi, K. Aida, T. Catalysis of Nudeo-base via Multiple Hydrogen-Bonding Interactions Accderation of Aminolysis of 6-Chloropurine Derivatives by Uradls J. Am Chem Soc 1999,121,7704-7705. 

The phosphonium salt 21 having a multiple hydrogen-bonding site which would interact with the substrate anion was applied to the phase transfer catalyzed asymmetric benzylation of the p-keto ester 20,[18 191 giving the benzylated P-keto ester 22 in 44% yield with 50% ee, shown in Scheme 7 Although the chemical yield and enantiomeric excess remain to be improved, the method will suggest a new approach to the design of chiral non-racemic phase transfer catalysts. 

K. Manabe, Asymmetric Phase-Transfer Alkylation Catalyzed by a Chiral Quaternary Phosphonium Salt with a Multiple Hydrogen-Bonding Site , Tetrahedron Lett. 1998, 39, 5807-5810. 

K. Manabe, Synthesis of Nobel Chiral Quaternary Phosphonium Salts with a Multiple Hydrogen-Bonding Site, and Their Application to Asymmetric Phase-Transfer Alkylation , Tetrahedron 1998, 54, 14465-14476. 

Scheme 26 Anion directed synthesis of [5]pseudorotaxane 57. Structural characterisation of this species has demonstrated that the PF< anion is located at its centre forming multiple hydrogen bonds to 57 s components... 

Addition of 81-SH to 80-SS-81 led to formation of the homodisulfide compounds and an equilibrium, with an exchange constant of 1.8, was established. The presence of the templating (D)Pro(L)Val(D)Val tri-peptide in this mixture, shifted the equilibrium dramatically and the formation of the homodisulfide 80-SS-80 was amplified with a Keq=32. Since the templating tri-peptide was supported on polymer beads, the isolation of receptor 80-SS-80 (in 97% purity) was achieved easily by extraction of the beads. The formation of multiple hydrogen bonds between the template and the components of the DCL, led to the isolation of the best possible receptor available from the building blocks present in the equilibrated mixture. 

The catalysts (or template) is able to bind two reactants forming a ternary complex via multiple hydrogen bonds. In this complex, the reactants are brought in close proximity accelerating the nucleophilic attack that yields the final product. 

Wang and Sutherland95 communicated an autocatalytic Diels-Alder reaction in which the adduct of diene 113 and olefin 114 catalyzed its own formation. This was accomplished through binding of both reactants in a pre-organized fashion by means of multiple hydrogen bonding (see complex below structures 113 and 114 overleaf). 

---