近红外光谱NIR在分子结构、分子间相互作用研究的应用进展

AdvancesinMolecularStructureandInteractionStudiesUsingNearInfraredSpectroscopy

近红外光谱NIR在分子结构、分子间相互作用研究的应用进展IntroductionofNIRSpectroscopy

#1.BriefHistory

1880s1930s1940s1950sHowever，insufficientspectrometerssuitablefortheNIRregiondifficultyinthespectralanalysis

1960s

Anagriculturalengineer--KarlNorris--“fatherofNIRspectroscopy”

1970s-1990sChemometric--2Dcorrelationanalysis，quantumchemicalcalculations.

近红外区的波段范围为12500−4000cm−1(800−2500nm)，近红外区域是由电子跃迁加上振动和转动跃迁引起的，它也是倍频和组频区。

#2.PrinciplesofNIRSpectroscopy

Near-infrared(NIR)spectralregion:12500−4000cm−1(800−2500nm)

NIRspectroscopyisconcernedwithbothelectronicandvibrationaltransitions.bothovertonesandcombinationmodes.

NIRstimulatesstudiesonovertonesandcombinationmodesandtheiranharmonicitiesmolecularstructures,interactions,reactions,andproperties.

NIRabsorptionbandintensitiesaremuchweakerthanthoseofMIR.

Somebandsduetoovertonesandcombinationmodesoverlapeachother.

Bandsascribedtofunctionalgroups(e.g.,OH,CH,NH)

containingahydrogenatomdominatetheNIRspectra.

XHstretchingbands(X=O,N)arebetterseparatedintheNIRregionthanMIR.

TheshiftfortheovertonebandsismuchlargerthanthatofMIRbands.

BandsascribedtothefirstovertonesoftheXHofmonomericspeciesexhibitmuchgreaterintensitythanbandsofpolymericspecies.

SixCharacteristics#3.ImportanceandAdvantages--PhysicalChemistry

MIRNIRItcanbeusedtoeasilyidentifyfreespecies.

CAN：BandsduetoovertonesandcombinationmodesofXH(X=C,O,N)groups.

CAN’T：BandsduetoovertonesandcombinationmodesofC-XandC=X(X=C,N,O)groups,exceptforthesecondovertoneoftheC=Ostretchingmode.

SpectralAnalysisinNIRregion

Differencespectra差谱Derivativespectra导数光谱Fourierself-deconvolution傅里叶自解卷积

Asampleissubjectedtoanperturbation(controlledchange)→T,P,pH,concentration…whileallotherparametersarekeptsame.Theperturbationwhichinducestheselectiveintensitychangesatindividualwavenumbers.

Classicalmetheds2DCorrelationSpectroscopy

Chemometrics

PrincipalComponentAnalysis(PCA)主元分析EvolvingFactorAnalysis(EFA)探索性因子分析MultivariateCurveResolution(MCR)多元曲线分辨率

MultivariateCalibration多元校正方法

Water

TEXTHEREApplicationsOfNIRSpectroscopy

ν2+ν3

(5100−5300cm−1)

ν1+ν3

(6800−7200cm−1)

v1v2v31,3-aminopropanol

ethyleneglycol

n-butylalcohol

BinarymixturesofwaterwithX

Hence,byusingNIRspectroscopy,onecanexaminethestateofwaterinOH-containingsolventssuchasalcoholsordiols.

Ⅰ.StructureofBulkWater.

Thestructureofliquidwatercanbedividedintotwogroups:mixturemodelscontinuummodels

Anequilibriumconsistingofafewspecificstructuralunits,

(mostlytwoorthree).

Anetworkoftetrahedrallyhydrogen-bondedmoleculesofwaterwithacontinuousdistributionofdistances,angles,andenergies.

Andthismodelwhichassumesthepresenceofweakandstronghydrogen-bondedoscillators.

Thefixedstructuremaybedimers,trimers,tetramers…butmostlythesubstructuresarediffererentintheaveragenumberofhydrogenbondsperwatermolecule.

AnalysisoftheNIRregion:theovertonesandcombinationmodes.

ThemajorityofclassicalMIRandRamanstudiesonthestructureofwatersupportthevalidityofthemixturemodel.

TheRamanspectraofliquidH2O,D2O,andHDOinsolution

(10%)…wereinterpretedintermsofacontinuummodel.

ν2+ν3

ν1+ν3

νCorrespondingrawspectraMCR-ALSanalysisCrossingtemperatureRevealsthepresenceoftwostructuralconstituentsofwaterwiththelinearintensitychangesinoppositedirections.

Atlowandhightemperaturesthestructureofwaterisdominatedbyoneofthesetwocomponents:Strongerhydrogen-bondWeakerhydrogen-bond

A2DIR-NIRanalysisshowsthethreekindsofwaterwith

differentdegreesofhydrogenbonding.

Thetemperature-andpressure-inducedchangesinthesolubilityphenomenaof

aqueoussolutionsresultfromvariationsinwaterstructureandhydrogenbonding.

Theauthorsstresstheadvantagesofspectralmeasurementsintheovertoneregionoverthefundamentalone.

Ⅱ.InteractionofWaterwithOtherMolecules.

Theν2+ν3combinationbandofwaterinNIRregionappearsfreefromanyothersignificantabsorption.

Theshapeandpositionofthisbandindicatethenumberofhydrogenbondscreatedbymoleculesofwatertotheothermolecules.

Binarymixturesofwaterwith2-propanol

Normalizedspectraofbulk2-propanol

NormalizedspectraOfbulkwater

2-propanolobtainedfromspectraofmixture

waterobtainedfromspectraofmixture

①.Theadditionofasmalltomoderateamountofwaterhasanegligibleeffectonthestructureoftheorganicphase.

②.ν2+ν3

combinationbandofbulkwaterisblue-shiftedwithrespecttothatinthespectralprofileofwaterinthemixture.

HydrogenBondingandMolecularInteraction

以温度T为变量的异步二维相关谱A.Temperature-dependentasynchronous2DNIRcorrelationspectra

n-butylalcohol

sec-butylalcohol

iso-butylalcohol

tert-butylalcohol

TheintensityofthebondedOHdecreasesongoingfrom1-butanoltotert-butanol,whereastheintensityofthefreeOHisseentoincrease.。

n-butylalcohol

sec-butylalcohol

iso-butylalcohol

tert-butylalcohol

Powerspectra

(diagonalofthesynchronousspectrum)

FreeOH

Thestrongerhydrogenbondingis,themorered-shiftedisthebandduetothebondedOH.Incontrast,thebandpositionofthefreeOHshowstheoppositetrend(blue-shift).

BondedOH

Comparisonofresultsfordifferentaliphaticalcoholsrevealsthatstrengthofthehydrogenbondingweakenswithanincreaseinboththealcoholorderandthechainlength.

--Thegroupscanbebothacceptorsanddonors,suchasOHoramine.

B.

Intra-intermolecularinteraction

MIR+NIR:Withconcentration,Thepopulationofthemoleculeswiththe

intramolecularhydrogenbondsattheexpenseofthemoleculesinvolvedintheintermolecularhydrogenbonding.

DFTcalculations+NIRmeasurements:

1,2-aminoalcohols

1,3-aminoalcohols

IntramolecularN−H···Obond

IntermolecularO−H···Nbond

IntermolecularO−H···Nbond

DFTcalculationsshow:ThedimerswiththeO−H···Nbondsareabout1.4kcal/molmorestablethanthosewiththeN−H···Obonds.

Twodimerso