Supramolecular Phenomena

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1、5SupramolecularPhenomena5.1ClathratesInterstitialmolecularcomplexes,orclathrates,werefirstobservedbyHumphreyDavywhodescribedthesolidgasclathrateformedbychlorineinclusioninice[1].ThenatureofthisinclusionphenomenonwasfurtherstudiedbyMichaelFaradaywhodemonstratedthatchlorinecouldbelibera

2、tedfromthe‘chlorinehydrate’[2].ThiswaslatershownbyLinusPaulingtobeðH2OÞ72=
Cl2[3].Theclathrate3phenomenonhasalsobeenobservedformanyothersmallmoleculesincludingthenoblegases.Oneofthemoreimportantexamplesistheformationofmethanehydratesingaspipelines.Whenmethaneentersapipeunderpressurea

3、tlowtemperaturesitcancausecrystallizationofanywaterthatispresent.Theresultingclathrateiscomprisedofmethanemoleculesheldwithinahydrogen-bondednetworkoffrozenwatermolecules.Methane,unusuallyforasmallorganicmole-culewithnofunctionalgroups,actuallyactsasatemplatearoundwhichlowdensityicef

4、orms.Intheabsenceofguestmoleculesthemorecommoncompacticestructureresults.Asmightbeexpectedboththeformationandinhibitionofgasclathratehydratesisofgreatindustrialimportance.Methaneclathrates,foundmostlyinoceanfloorsandareasofpermafrost,areattractivesourcesofmethaneitselfduetotheirglobal

5、abundanceandavailability,withperhapsasmuchas1610kgpresentintheEarth’scrust.Theirpresencewasfirstnoticedinpipelinesinthe1930sandtheirnaturedeterminedinthe1960s.Althoughtheirpresencemaycausealarm,theclathratesarenotnecessarilyhazardousinthemselves.Unlesstheyundergodramaticchangesinpress

6、ureortemperature,orareignited,theirdecompositionaround0Cisnotexplosive.Problemsdoarisewhengashydratesforminnaturalgaspipelinesandcauseblockagesthatcanleadtocatastrophicfailure.Tothisendthestructuresofthehydrates,suchasthatshowninFigure5.1,remainanareaofsupramolecularinvestigation[4]

7、.Aswillbeseentheclathratephenomenonisnotrestrictedtothesolidphase.APracticalGuidetoSupramolecularChemistryPeterJ.Cragg#2005JohnWiley&Sons,LtdISBN:0-470-86653-5162SUPRAMOLECULARPHENOMENAFigure5.1Simulationofamethanehydrate[1]Onacombinationofoxymuriaticgasandoxygenegas,H.Davy,Philos.Tr

8、ans.RoyalSoc