Xem 1-20 trên 49 kết quả Hydrogen bonds
  • Lecture Organic chemistry - Chapter 8: Alcohols. The main contents of this chapter include all of the following: Ethanol, cyclic alcohols are called cycloalkanols, physical properties, hydrogen bonding, synthesis of alcohols R-OH,...and other contents.

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  • We present an array of force spectroscopy experiments that aim to identify the role of solvent hydrogen bonds in protein folding and chemical reactions at the single-molecule level. In our experiments we control the strength of hydrogen bonds in the solvent environment by substituting water (H2O) with deuterium oxide (D2O). Using a combination of force protocols, we demonstrate that protein unfolding, protein collapse, protein folding and a chemical reaction are affected in different ways by substituting H2O with D2O.

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  • Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for lifegiving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy.

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  • hort hydrogen bonds are present in many chemical and biological sys-tems. It is well known that these short hydrogen bonds are found in the active site of enzymes and aid enzyme catalysis. This study aims to system-atically characterize all short hydrogen bonds from a nonredundant dataset of protein structures. The study has revealed that short hydrogen bonds are commonly found in proteins and are widely present in different regions of the protein chain, such as the backbone or side chain, and in different secondary structural regions such as helices, strands and turns. ...

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  • A structuring and eventual exclusion of water surrounding backbone hydrogen bonds takes place during protein fold-ing as hydrophobic residues cluster around such bonds. Taken as an average over all hydrogen bonds, the extent of desolvation is nearly a constant of motion, as revealed by re-examination of the longest all-atom trajectory with explicit solvent [Y.Duan & P.A.Kollman (1998)Science 282, 740].Furthermore, this extent of desolvation is pre-served across native soluble proteins, except for cellular prion proteins....

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  • This chapter describes the structure of the water molecule and explores the many ways that polar covalent bonds and hydrogen bonds among water molecules affect organisms and their interactions with their environments. In addition, this chapter discusses topics including concentrations of solutions, hydrogen ion concentration (pH), and buffer solutions.

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  • In this chapter, you will learn: Know why water is polar, understand how water forms H-bonds, understand how H-bonds stabilize the structure of water, understand how water dissolves polar and ionic compounds, understand how water interacts with non-polar compounds, know what is a solvation/hydration shell,...

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  • The creation of Trichet bonds will result in various advantages both in comparison to the present unstable situation and other proposed solutions. First, the long duration of Trichet bonds will eliminate the immediate crisis caused by short term expiration of significant amounts of debt which is looming over Greece, Ireland, Portugal, Spain and possibly other EU countries. Second, the guarantee of the principal with the zero-coupon ECB bond collateral increases the quality of the Trichet Bonds compared to existing sovereign debt.

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  • The structure and dynamics of proteins and enzymatic activity is intrinsically linked to the strength and positions of hydrogen bonds in the system.[1] A hydrogen bond results from an attractive force between an electronegative atom and a hydrogen atom.[2] The hydrogen is attached to a strongly electronegative heteroatom, such as oxygen or nitrogen, termed the hydrogen- bond donor. This electronegative atom decentralizes the electron cloud around the hydrogen nucleus, leaving the hydrogen atom with a positive partial charge.

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  • Host-guest complexation relies on interactions of molecules through secondary chemical bonds. Such complexation can lead to formation of loose associations, as well as to that of very stable adducts. In formation of these addition compounds, important roles are played by hydrogen-bonding and hydrophobic interactions. In certain cases one of the reacting partners will wind up in a relatively enclosed space, embraced by the other reactant this is when the host-guest description is most appropriate.

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  • Drug-Receptor Interaction partial charges. When a hydrogen atom bearing a partial positive charge bridges two atoms bearing a partial negative charge, a hydrogen bond is created. A van der Waals’ bond (B) is formed between apolar molecular groups that have come into close proximity. Spontaneous transient distortion of electron clouds (momentary faint dipole, !!) may induce an opposite dipole in the neighboring molecule. The van der Waals’ bond, therefore, is a form of electrostatic attraction, albeit of very low strength (inversely proportional to the seventh power of the distance).

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  • Meeting the demand for the second edition of this book, which is – despite a reprint in 1990 – no longer available, and considering the progress that has been made during the last decade in the study of solvent e¤ects in experimental and theoretical organic chem-istry, this improved third edition is presented to the interested reader. Following the same layout as in the second edition, all topics retained have been brought up to date, with smaller and larger changes and additions on nearly every page. Two Sections (4.4.7 and 5.5.

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  • The book "Developments in Electrochemistry" contains five feature articles in recent advanced electrochemistry. These selected feature articles emphasize physical phenomena rather than mathematical formalisms of electrochemistry.

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  • Among halogens, fluorine is quite characteristic and specific since it has the largest electronegativity (4.0 vs 3.5 for oxygen) and the sterically second smallest van der Waals' radius (1.35 ~ vs. 1.20/~ for hydrogen). A carbon-fluorine bond is also stronger than a carbon-hydrogen bond (485 kJ/mol vs 414 kJ/mol). Therefore, fluoro organic compounds have unique chemical and physical properties.

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  • The authors and publisher are pleased to present the twentyeighth edition of Harper’s Illustrated Biochemistry. This edition features for the first time multiple color images, many entirely new, that vividly emphasize the ever-increasing complexity of biochemical knowledge. The cover picture of green fluorescent protein (GFP), which recognizes the award of the 2008 Nobel Prize in Chemistry to Martin Chalfie, Roger Y. Tsien, and Osamu Shimomura, reflects the book’s emphasis on new developments.

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  • X-ray crystallography of the nonheme manganese catalase fromLactobacillus plantarum(LPC) [Barynin, V.V., Whit-taker, M.M., Antonyuk, S.V., Lamzin, V.S., Harrison, P.M., Artymiuk, P.J. & Whittaker, J.W. (2001)Structure9, 725–738] has revealed the structure of the dimanganese redox cluster together with its protein environment. The oxidized [Mn(III)Mn(III)] cluster is bridged by two solvent molecules (oxo and hydroxo, respectively) together with a l1,3bridging glutamate carboxylate and is embedded in a web of hydrogen bonds involving an outer sphere tyrosine residue (Tyr42). ...

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  • Tham khảo sách 'harper’s illustrated biochemistry twenty-eighth edition_1', y tế - sức khoẻ, y học thường thức phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả

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  • NA helicases are ubiquitous molecular motor proteins which harness the chemical free energy of ATPhydrolysis to catalyze the unwinding of energetically stable duplex DNA, and thus play important roles in nearly all aspects of nucleic acid metabolism, including replication, repair, recombina-tion, and transcription. They break the hydrogen bonds between the duplex helix and move unidirectionally along the bound strand. All helicases are also translocases and DNA-dependentATPases.Most contain conserved helicase motifs that act as an engine to power DNA unwinding. ...

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  • Cytochrome P450 enzymes promote a number of oxidative biotransformations including the hydroxylation of unacti-vated hydrocarbons.

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  • The complexes of acidic quinine solution with acidic solutions of sulfate-salts of Fe, Zn and Ce have been synthesized. Bonds of Fe-O, Zn-O and Ce-O were formed via the hydroxyl oxygen atom with a preservation of hydrogen bond and have been proved by the infrared spectroscopy.

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