反应工程课件chap7

Chapter7ReactionMechanisms,Pathways,Bioreactions,andBioreactorsJ.W.Gibbs:"Oneoftheprincipalobjectsoftheoreticalresearchistofindthepointofviewfromwhichthesubjectappearsinitsgreatestsimplicity."OverviewPseudo-steady-statehypothesis(PSSH)ActiveintermediatesRatelawsforbothchemicalandbiologicalreactionsEnzymaticreactions,Michaelis-Mentenequation,organismgrowthkineticsBioreactors7.1Activeintermediates&NonelementaryratelawsExp.1Exp.2ActiveintermediateAhigh-energymoleculethatreactsvirtuallyasfastasitisformed.PresentinverysmallconcentrationsA*:Unstablemolecule,i.e.,activeintermediatesFreeradicals,e.g.,CH3•Ionicintermediates,e.g.,carboniumionEnzyme-substratecomplexes1922,F.A.LindermannFrederickAlexanderLindemann

(5April1886–3July1957)Caltech'sAhmedZewail

Wins1999NobelPrizeInChemistryScienceDaily(Oct.13,1999)—Dr.AhmedH.Zewailhaswonthe1999NobelPrizeinchemistryforhisgroundbreakingworkinviewingandstudyingchemicalreactionsattheatomiclevelastheyoccur.

Zewail,anativeofEgypt,isLinusPaulingProfessorofChemicalPhysicsandprofessorofphysicsattheCaliforniaInstituteofTechnology.Heisinternationallyrecognizedforhiseffortsinafieldhepioneeredknownasfemtochemistry.Thistechniqueusesultrafastlaserstoprobechemicalreactionsastheyactuallyoccurinrealtime."forshowingthatitispossiblewithrapidlasertechniquetoseehowatomsinamoleculemoveduringachemicalreaction."Zewailseekstounderstandbetterthewaythatchemicalbondsformandbreak."forhisstudiesofthetransitionstatesofchemicalreactionsusingfemtosecondspectroscopy"飞秒：10-15

秒；皮秒：10-12

秒；纳秒：10-9

秒；微秒：10-6

秒7.1.1Pseudo-Steady-StateHypothesis(PSSH)positionoftheactiveintermediatedoesnotoccurinstantaneouslyafterinternalactivationofthemoleculeThereisatimelag,althoughinfinitesimallysmall,duringwhichthespeciesremainsactivatedPSSHIftheactiveintermediateappearsinnreactions,thenExample:Azomethane(AZO)Experiments:Pressure>1atmPressure<50mmHgProposedmechanism:(1)(2)(3)PSSH

ratelawPSSH:NetrateofAZO*=0LowAZOconcentration:HighAZOconcentration:ApparentfirstorderApparentsecondorderRatelaw:Symbolically:Activation:Deactivation:position:M:inertFirst-orderratelawforanonelementaryreactionExample:7.1.2SearchingforamechanismGeneralconsiderations:Rulesofthumbfordevelopmentofamechanism1.Specieshavingtheconcentration(s)appearinginthedenominatoroftheratelawprobablycollidewiththeactiveintermediate,2.Ifaconstantappearsinthedenominator,oneofthereactionstepsisprobablythespontaneouspositionoftheactiveintermediate,3.Specieshavingtheconcentration(s)appearinginthenumeratoroftheratelawprobablyproducetheactiveintermediateinoneofthereactionsteps,Findingthereactionmechanism:Stepstodeducearatelaw1.Assumeanactiveintermediate(s)2.Postulateamechanism,utilizingtheratelawobtainedfromexperimentaldata,ifpossible3.Modeleachreactioninthemechanismsequenceasanelementaryreaction4.Afterwritingratelawsfortherateofformationofdesiredproduct,writetheratelawsforeachoftheactiveintermediates5.UsethePSSH6.EliminatetheconcentrationoftheintermediatespeciesintheratelawsbysolvingthesimultaneousequationsdevelopedinSteps4and57.Ifthederivedratelawdoesnotagreewithexperimentalobservation,assumeanewmechanismand/orintermediatesandgotoStep3.Astrongbackgroundinorganicandinorganicchemistryishelpfultopredictingtheactivatedintermediatesforthereactionunderconsideration.ThereactionhasanelementaryratelawExample:

Whydoestheratelawdecreasewithincreasingtemperature?However...Lookwhathappenstotherateasthetemperatureisincreased.Mechanism:

(1)(2)(3)

PSSH:Thisresultshowswhytheratedecreasesastemperatureincreases.Example:TheStern-VolmerequationPleaserefertothebook,P268.7.1.3ChainreactionsStepsinachainreaction:1.Initiation:formationofanactiveintermediate2.Propagationorchaintransfer:interactionofanactiveintermediatewiththereactantorproducttoproduceanotheractiveintermediate3.Termination:deactivationoftheactiveintermediatetoformproductsExample:PSSHappliedtothermalcrackingofethaneInitiation:(1)Propagation:(2)(3)(4)Termination:(5)7.1.4ReactionpathwaysEthanecrackingC2H6C2H5•CH3•CH4C4H10H2C2H4H•k5k1k2k4k3SmogformationNONO2O3O2HCHOROO•RO•RCHOO2R••CHORCH=CHRCH2=CHCH=CH2CH2=CHCH2CHOOk7k6k5k1k2k3k4hvMetabolicpathwaysC2H5OHCH3CHOCH3COO-Acetyl-PNAD+NADHNAD+NADHATPADPAlcoholdehydrogenaseAcetaldehydedehydrogenaseAcetatekinase7.2EnzymaticreactionfundamentalsAnenzymeisahigh-molecular-weightproteinorprotein-likesubstancethatactsonasubstrate(reactantmolecule)totransformitchemicallyatagreatlyacceleratedrate,usually103to1017timesfasterthantheuncatalyzedrate.Enzymesareusuallypresentinsmallquantitiesandarenotconsumedduringthecourseofthereactionnordotheyaffectthechemicalreactionequilibrium.Lowactivationenergy.Enzyme-substratecomplex:activeintermediateEnzymeSpecific:oneenzymecatalyzesonetypeofreactionProducedonlybylivingorganisms.

CommercialenzymesaregenerallyproducedbybacteriaWorkundermildconditionsNamedintermsofthereactions7.2.1Enzyme-substratecomplexBinding:substratetoenzyme

hydrogenbonding,hydrophobic,ionic,andLondonvanderWaalsforcesTwomodelsforsubstrate-enzymeinteractions:

thelockandkeymodel

theinducedfitmodel

Therearesixclassesofenzymesandonlysix.1.Oxidoreductases2.Transferases3.Hydrolases4.Isomerases5.Lyases6.Ligases,（氧化还原酶）（转移酶）（水解酶）（异构酶）（连接酶）（裂解酶）7.2.2MechanismsE:Enzyme;S:Substrate;W:Water;ES:enzyme-substratecomplex;P:productsPSSH:ThenetrateofdisappearanceofsubstrateThenetrateofformationofenzyme-substratecomplex(E)cannotbemeasuredIntheabsenceofenzymedenaturization7.1.2SearchingforamechanismGeneralconsiderations:Rulesofthumbfordevelopmentofamechanism1.Specieshavingtheconcentration(s)appearinginthedenominatoroftheratelawprobablycollidewiththeactiveintermediate,2.Ifaconstantappearsinthedenominator,oneofthereactionstepsisprobablythespontaneouspositionoftheactiveintermediate,3.Specieshavingtheconcentration(s)appearinginthenumeratoroftheratelawprobablyproducetheactiveintermediateinoneofthereactionsteps,7.3.1Michaelis-MentenequationWaterinexcessMichaelis-MentenequationturnovernumberMichaelisconstant(affinityconstant)（亲合力常数）Michaelis-MentenplotInterpretationofMichaelisconstantCS-rSVmaxVmax/2KMLineweaver-BurkplotProduct-enzymecomplexPSSHtoboth(E•S)and(E•P):Briggs-Haldaneequation7.2.4BatchreactorcalculationforenzymereactionsMolebalance(Liquidphase)RatelawCombineIntegrateMichaelis-MentenequationintermsofthesubstrateconcentrationIntercept=Vmax/KM(S0-S)/t[ln(S0/S)]/t0Slope=-1/KMEvaluatingVmaxandKMEffectoftemperatureTVmax7.3InhibitionofenzymereactionsFactors

temperature

solutionpH

inhibitorInhibitor

speciesthatinteractwithenzymesandrendertheenzymeineffectivetocatalyzeitsspecificreactionReversibleinhibitions:

competitive,petitive,petitive（竞争）（无竞争）（非竞争）7.3.1CompetitiveinhibitionCompetitiveinhibitionpathwayI+E•IKIReactionsteps(1)(2)(3)(4)(5)PSSHLineweaver-BurkplotforcompetitiveinhibitionNoinhibition1/(-rs)1/SCompetitiveinhibitionIncreasinginhibitorconcentration(I)7.3.2petitiveinhibitionI+E•S•IKI(1)(2)(3)(4)(5)petitiveinhibitionpathwayReactionstepsLineweaver-BurkplotforpetitiveInhibition1/(-rs)1/SIncreasinginhibitorconcentration(I)petitiveinhibitionNoinhibition7.3.3petitiveinhibition

(Mixedinhibition)I+E•S•I(1)(2)(3)(4)(5)MixedinhibitionpathwayReactionstepsIE•I+S+Lineweaver-Burkplotforpetitiveenzymeinhibition1/(-rs)1/SIncreasinginhibitorconcentration(I)Noinhibitionpetitive(bothslopeandinterceptchange)petitive(interceptchanges)Competitive(slopechanges)Noinhibition1/(-rs)1/SLineweaver-BurkplotsforthreetypesofenzymeinhibitionSummaryplotoftypesofinhibition7.3.4SubstrateinhibitionLowsubstrateconcentrationSmaxHighsubstrateconcentrationSOptimumsubstrateconcentration-rS7.3.5MultipleenzymeandsubstratesystemsEnzymeregenerationOverall,Glucose(Sr)-gluconolactone(P1)G.O.(Eo)G.O.H2(Er)H2O2(P2)O2(S2)EnzymecofactorsAlcoholdehydrogenaseAcetaldehyde(S1)Ethanol(P1)NADH(S2)NAD+(S2*)H+7.4BioreactorsCellgrowthanddivisionCulturemediaconditions(pH,temperature,etc).CellmultiplicationGrowthofanaerobicorganism:7.4.1CellgrowthPhaseI:Lagphase,littleincreaseincellconcentrationPhaseII:Exponentialgrowthphase,cellgrowthproportionaltothecellconcentrationPhaseIII:Stationaryphase,netgrowthrateiszeroasaresultofthedepletionofnutrientsandessentialmetabolitesPhaseIV:Deathphase,whereadecreaseinlivecellconcentrationoccursIIIIIIIV7.4.2RatelawsCells+SubstrateMorecells+ProductMonodequationforexponentialgrowth::specificgrowthrate,s-1Ks:TheMonodconstant,g/dm3MonodequationKs:smallWhenproductinhibitstherateofgrowth:EmpiricalformofMonodequationforproductinhibitionProductconcentrationatwhichallmetabolismceases,g/dm3Forglucose-to-ethanolfermentationTessierequationMoserequationCelldeathrateDoublingtimes:thetimerequiredforamassofanorganismtodouble.

AmeasureofmicrobialgrowthratesEffectoftemperatureTI’7.4.3StoichiometryCells+SubstrateMorecells+ProductGrowthassociatedproductformationNongrowthassociatedproductformationCellmaintenanceNeglectingcellmaintenanceAtypicalvalue:Yieldcoefficients:SubstrateutilizationSubstrateaccountingNetrateofsubstrateconsumption=Rateconsumedbycells+Rateconsumedtoformproduct+RateconsumedformaintenanceGrowthassociatedproductformationinthegrowthphaseNongrowthassociatedproductformationInthestationaryphaseInthestationaryphase,theconcentrationoflivecellsisconstant.NeglectscellmaintenanceLuedeking-Piretequationfortherateofproductformationwith7.4.4MassbalancesCellbalance:Substratebalance:BatchoperationCellSubstrateGrowthphaseStationaryphaseProductBatchstationarygrowthphase7.4.5ChemostatsChemostats:CSTRsthatcontainmicroorganismsOneofthemostimportantfeaturesofthechemostatisthatitallowstheoperatorstocontrolthecellgrowthrate,byadjustingthevolumetricfeedra