CHE 141 1st Edition Lecture 26Outline of Current Lecture- Biomolecules: Chlorins and Porphyrins- Biomolecules: Heme- Biomolecules: Drugs and Therapeutic Agents- Thermochemistry - Spontaneous and Nonspontaneous Processes- Entropy- Macrostates and Microstates- Entropy and Probability- The 2nd Law of ThermodynamicsCurrent LectureBiomolecules: Chlorins and Porphyrins- Metal ions essential to human health need to be present in foods the body can absorb- Biological polydentate ligands help metal ions participate in biological process- Chlorophyll is the pigment which allows plants to absorb energy from light- It appears green as it absorbs in the blue and red region of the electromagnetic spectrumThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- All molecules of chlorophyll contain ring-shaped tetradentate ligands called chlorins- The structure of chlorins is similar to polyphyrins, another important class of tetradentate ligands found in biological systems- Chlorins and porphyrins have 4 N donor atoms- The lone pair of e- on the N atoms can occupy either the four equatorial coordination sites in an octahedral complex ion or all four coordination sites in a square planar complex ion- In octahedral complexes, each central metal ion still has its two axial sites available for bonding to other ligands- Macrocyclic ligand : a ring containing multiple electron-pair donors that bind to a metal ion- Chlorin and porphyrin are heterocyclic macrocycles as they have atoms of at leasttwo different elements as members of its rings- When they form a coordinate bond with Mn+, the two hydrogen atoms ionize giving the ring a charge of 2- and the complex ion an overall charge of (n-2)+Biomolecules: Heme- Heme is a porphyrin complex which eneables hemoglobin to transport O2 in the blood- The four nitrogen atoms in the porphyrin ring of a heme group occupy equatorial positions in an octahedral complex of an Fe2+ ion- Below the porphyrin ring, a fifth bond is formed between the Fe2+ ion and a lone pair of e- on a nitrogen atom in the hemoglobin protein- The sixth ligand, located above the ring is typically a molecule of O2- The four nitrogen atoms in heme occupy equatorial positions in an octahedral complex in which the central metal ion is Fe2+- Hemoglobin contains four heme groups, each of which is bound to a protein chain- Each O2 molecule can act as a Lewis base and donate one of its lone pairs of e- tothe iron in heme- Forms a covalent coordinate bond strong enough to carry oxygen from lungs to cells and weak enough to break easily when the oxygen reaches a cell- When oxygen is released, it is replaced by a water molecule then the hemoglobin travels back to the lungs to repeat the cycle- Other ligands of similar size to O2 easily binds to the sixth Fe2+ binding cite, such as CO- CO binds about 200 times more strongly than O2 which is why CO poisoning is deadlyBiomolecules: Drugs and Therapeutic Agents- Diamminedichloroplatinum(II) is square planar and forms geometric iosmers cis- and trans-- Cisplatin is an effective anticancer treatment as it attaches itself to the cancer cellsDNA and replaces the Cl- ligands with donor atoms from DNA strands- The cis arrangement of the Cl- corresponds to the geometry required to bind to theDNA strands- The trans isomer does not have the correct geometrical arrangements of Cl- ligandto bind to the DNA strands- Cisplatin and other closely related platinum (II) complexes are commonly used in chemotherapyThermochemistry - The system is the part of the universe under examination, such as a chemical reaction- The surroundings is the rest of the universe- For any given process, such as a chemical reactions or change of state, the sign of the overall energy change delta energy tells us the direction of net energy flow- Thermochemistry is the study of energy and its transformations, in short, the relationship between heat, energy, and work- 1st law of thermodynamics: energy cannot be created or destroyed- however we can observe:o energy naturally spreads out and becomes less concentrated over timeo to gather it up again to do useful work would require more energy input than it would recover, hence this energy is effectively lost- enthalpy is a measure of the total energy of a thermodynamic system and is measured in joules- enthalpy change is the flow of energy into or out of a system during a chemical reaction or physical change carried out at constant pressure- standard molar enthalpy of formation is the enthalpy change f a chemical reaction in which one mole of a substance is formed from its constituent elements in their standard states measured in joules per mole - if delta H<0 the system gives off heat, this is an exothermic process whereby energy flows from a system into its surroundings- if delta H>0 the system absorbs heat, this is an endothermic process whereby energy flows from the surroundings into the systemSpontaneous and Nonspontaneous Processes- a spontaneous process occurs without any ongoing outside intervention, iron exposed to water ad oxygen forms rust- a non-spontaneous process may only occur if energy is continually added to the system, a rusty nail will not spontaneously return to its former state however Fe2O3 can be converted to Fe(s) via electrolysis which requires electrical energy input- spontaneity is not the same as speed- a reaction may be thermodynamically spontaneous but kinetically slow- a catalyst increases the rate of spontaneous reaction, however it cannot make a nonspontaneous process spontaneous - just because a reaction/process is nonspontaneous, that doesn’t mean it is impossible, just that it requires a supply of energy- a mechanical system proceeds in the direction of lowest potential energy, so does a chemical system proceed in the direction of lowest enthalpynope, if this was the case all exothermic reactions would be spontaneous and all endothermic reactions would be nonspontaneous- although a lot of spontaneous processes are exothermic, there are also plenty of spontaneous processes that are endothermic - inside instant cold pack, a spontaneous endothermic reaction is happening,- the evaporation of liquid water spilled on the floor is also endothermic and spontaneousEntropy- entropy is a measure of the randomness or disorder of a system, a disordered state has a large entropy, a more ordered system has a small