LECTUR : Water “ the solvent for biochemical reaction “ DOCTOR : Nabil Amer DONE BY : Hiba Adel

1. LECTUR : Water “ the solvent for biochemical reaction “ DOCTOR : Nabil Amer DONE BY : Hiba Adel EDITED BY : Hamza Alzoubi PERIOD : MID-TERM DATE : 26-JUNE-2018

2. Learning Objectives

3. Chemical Formula Chemical Formula: uses the chemical symbols to represent the atoms of the elements and their ratios in the chemical compound. H2O 2:1 ratio of H to O . Note : 1 molecule of O 2 molecules of H www.brooklyn.cuny.edu

4. when electrons are shared but shared unequally POLAR COVALENT BONDS H2O

5. www.bennett29j.k12.co.us

6. The Properties of Water Affect the Bonding Abilities of Biomolecules The strength and specificity of weak interactions are highly dependent on the medium in which they take place, and the majority of biological interactions take place in water. Two properties of water are especially important biologically:

7. *Water is essential for the interactions in our body. *60-70% is the percentage of water in the human body. -water is essential for movement of molecules ,metabolism,blood and actions of enzyme. *about 75% of the earth’s surface is water-covered.

8. water is a polarmolecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

9. Water is a polar molecule . The water molecule is bent, not linear, and so the distribution of charge is asymmetric. The oxygen nucleus draws electrons away from the hydrogen nuclei, which leaves the region around the hydrogen nuclei with a net positive charge. The water molecule is thus an electrically polar structure.

10. Fig. 2-1, p.35

11. The structure of water. Oxygen has a partial negative charge, and the hydrogens have a partial positive charge. The uneven distribution of charge gives rise to the large dipole moment of water. The dipole moment in this figure points in the direction from negative to positive, the convention used by physicists and physical chemists; organic chemists draw it pointing in the opposite direction.

12. Water is highly cohesive Water molecules interact strongly with one another through hydrogen bonds. These interactions are apparent in the structure of ice . Networks of hydrogen bonds hold the structure together; similar interactions link molecules in liquid water and account for the cohesion of liquid water, although, in the liquid state, some of the hydrogen bonds are broken. The highly cohesive nature of water dramatically affects the interactions between molecules in aqueous solution.

13. Structure of Ice. Hydrogen bonds (shown as dashed lines) are formed between water molecules.

14. The polarity and hydrogen-bonding capability of water make it a highly interacting molecule. Water is an excellent solvent for polar molecules. The reason is that water greatly weakens electrostatic forces and hydrogen bonding between polar molecules by competing for their attractions. • For example, consider the effect of water on hydrogen bonding between a carbonyl group and the NH group of an amide.

15. A hydrogen atom of water can replace the amide hydrogen atom as a hydrogen-bond donor, whereas the oxygen atom of water can replace the carbonyl oxygen atom as a hydrogen-bond acceptor. Hence, a strong hydrogen bond between a CO group and an NH group forms only if water is excluded.

16. Water is called the "universal solvent" because it dissolves more substances than any other liquid. *anything we want to dissolve at first we try it in water then in hot water then in acids and bases.

17. You just have to know the highest one (o) and the Lowest one (H).

19. Water and Ammonia are very close in molecular weight. Note the number of b.p and m.p. NH3 and CH4 are gases.

20. Moreover, the presence of water with its polar nature permits another kind of weak interaction to take place, one that drives the folding of proteins and the formation of cell boundaries .

21. However, the organization visible in a cell or a molecule arises from biological events that are subject to the same physical laws that govern all processes—in particular, the laws of thermodynamics.

22. Fig. 2-2, p.35

23. 1- Sodium chloride (NaCl) dissolves when water molecules continuously attack the NaCl crystal, pulling away the individual sodium (Na+) and chloride (Cl–) ions. 2- When we have more solid , does not dissolve in water , we reach the state of saturation . 3- Hydration shells surrounding ions in solution. Unlike charges attract. The partial negative charge of water is attracted to positively charged ions. Likewise, the partial positive charge on the other end of the water molecule is attracted to negatively charged ions.

24. Fig. 2-3, p.36

25. Ion–dipole and dipole–dipole interactions help ionic and polar compounds dissolve in water. (a) Ion–dipole interactions with water. (b) Dipole–dipole interactions of polar compounds with water. The examples shown here are an alcohol (ROH) and a ketone (R2CAO).

26. Table 2-2, p.37

27. 1-Fatty acids surrounded by water 2-they will not dissolve in water . معلومهعامه : لماتعملمخللاخراشيبحطوازيتعشانيعزلهعنالهواءالخارجي Fig. 2-4, p.37

28. The previous slide ; An amphiphilic molecule: sodium palmitate. Amphiphilic molecules are frequently symbolized by a ball and zigzag line structure, where the ball represents the hydrophilic polar head and the zigzag line represents the nonpolar hydrophobic hydrocarbon tail.

29. That’s what happen when we put a drop of oil in the water:  A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle centre. 

30. Fig. 2-5, p.37

31. Micelle formation by amphipathic molecules in aqueous solution. When micelles form, the ionized polar groups are in contact with the water, and the nonpolar parts of the molecule are protected from contact with the water.

32. 2.3 What Are Titration Curves? In an aqueous solution, the relative concentrations of a weak acid and its conjugate base can be related to the titration curve of that acid. In the region of the titration curve in which the pH changes very little upon addition of acid or base, the acid/base concentration ratio varies within a fairly narrow range (10:1 at one extreme and 1:10 at the other).

33. Fig. 2-13a, p.46

34. We have a relative abundance of acetic acid and acetate ion , and alkaline solution (محلولقلوي : يعنيقاعدييحتويعلىايونالهيدروكسيد ) • CH3COO- : conjugated base . • PH at which acid = base called inflection point .

35. Fig. 2-13b, p.46

36. At this region , when the PH = 4.76, the addition of base will not affect PH . Note that there is a region near the Pka at which the titration curves is relatively flat .In the other words , the PH changes very little as the base is added in this region . In the middle no change in the PH PH will change from 4.76 to 6.8 .

37. FROM TEXT BOOK : CAMPLLE PAGE NUMBER 51 Titration is an experiment in which measured amount of base are added to measure amount of acid . The point in the titration at which the acid in exactly neutralized is called the equivalence point . An inflection point in the titration curve is reached when the PH equals the Pka of acetic acid . Equal concentration at this point . pKa is the acid dissociation constant at logarithmic scale. It is used to measure the strength of an acid in solution. On the contrary, pH is a measure of concentration of hydrogen ions in an aqueous solution.( from google ).

38. 2.1 What Makes Water a Polar Molecule? The properties of the water molecule have a direct effect on the behavior of biomolecules. Water is a polar molecule, with a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. There are forces of attraction between the unlike partial charges. Polar substances tend to dissolve in water, but nonpolar substances do not.

39. 2.2 What Is a Hydrogen Bond? A hydrogen bond is a special case of dipole–dipole interactions. In both the liquid state and the solid state, water molecules are extensively hydrogen-bonded to one another. Hydrogen bonding between water and polar solutes takes place in aqueous solutions. The three-dimensional structures of many important biomolecules, including proteins and nucleic acids, are stabilized by hydrogen bonds.

40. A comparison of linear and nonlinear hydrogen bonds. Nonlinear bonds are weaker than bonds in which all three atoms lie in a straight line. Fig. 2-6, p.38

41. Fig. 2-7, p.39

42. A comparison of the numbers of hydrogen bonding sites in HF, H2O, and NH3. (Actual geometries are not shown.) Each HF molecule has one hydrogen-bond donor and three hydrogen-bond acceptors. Each H2O molecule has two donors and two acceptors. Each NH3 molecule has three donors and one acceptor.

43. Fig. 2-8, p.39

44. Tetrahedral hydrogen bonding in H2O . An array of H2O molecules in an ice crystal . Each H2O molecule is hydrogen-bond to 4 others .

45. Example of H bonding between polar group and water; Fig. 2-9, p.41

46. Table 2-5, p.41

47. p.42

48. The ionization of water. Fig. 2-10, p.43

49. The hydration of hydrogen ion in water. Fig. 2-11, p.43

50. Table 2-6, p.45