The Study of Polyphosphate Hydrolysis Using 31P NMRKenneth RobertsonAustin Peay State UniversityClarksville, TNINTRODUCTIONl Orthophosphates and PolyphosphatesOPOOO-3HOPOO(OP)OONaNanOPOOHONaINTRODUCTIONl Several examples of polyphosphatesl Pyrophosphate -l Tripolyphosphate -l Trimetaphosphate -l Hexametaphosphate –16-20 P atoms in a chainPPOOOOOHOHOHPOHOHOPPOOOOHOHOHOHPOPOPOOOOOHOHOHINTRODUCTIONl Used in paint strippers, soft drinks, toothpaste, and baking powderl Phosphates are added to municipal water systems to prevent corrosion in pipesl Polyphosphates hydrolyze into orthophosphates over timel Little published literature concerning kinetics of the degradationINTRODUCTIONl31P NMR used to monitor polyphosphate hydrolysisl NMR can provide:l Qualitative data: Peaks in 31P NMR spectral Quantitative data: Areas under peaks in 31P NMR spectraINTRODUCTION -NMRl NMR data collected in previous research contained variability and lacked reproducibilityl External reference standard of orthophosphate used in an attempt to improve datal Areas of phosphate peaks were normalized to standard’s peak areal Normalized and unnormalized data were compared to evaluate validityINTRODUCTION -Kineticsl Rate law of hydrolysis is an important area of studyl Most researchers agree that polyphosphate hydrolysis is a first-order process.l If reaction is first-order, then the phosphate chain or ring is split randomly.l Using steady-state approximation, equations can be derived for kinetic modelingl Trimetaphosphate hydrolysis will be used as an example to derive equationsINTRODUCTION -Kineticsl Trimeta degradation is a three step processl The first order rate law is integrated to obtain an expression for the trimeta concentrationOPOPTPTPTMKKK2321→+→→[][][][][][][][]tkTMTMteTMTMdtkTMTMdTMkdtTMd100011−=−=−=∫∫INTRODUCTION -Kineticsl Orthophosphate is produced through two mechanismsl Assuming steady-state approximation…l Expression for orthophosphate concentration [][][]TPkPkdtOd232 +=[][][][] []TMkkTPTPkTMkdtTPd21210=−==[][][][] []TPkkPPkTPkdtPd32320=−==[][]TMkdtOd13=andINTRODUCTION -Kineticsl The first order rate law for orthophosphate is integrated to obtain an expression for orthophosphate concentrationl By using steady-state approximation, kinetic equations for orthophosphate and polyphosphate concentrations can be derived[][][][][][][][]()tkOOttktkeTMOdteTMkOdeTMkdtOd10111333000101−−−−===∫∫PROCEDURE – Sample Preparationl Four polyphosphates were studied:l Pyrophosphate (Na4P2O7)l Tripolyphosphate (Na5P3O10)l Trimetaphosphate (Na3P3O9)l Hexametaphosphate (16-20 P atoms in chain)l Solutions of each phosphate were prepared at pH’s of 1 and 7PROCEDURE – Sample Preparationl Deuterated solvents were used so the solvent would not interfere with the molecular spin of the samplel Approximately 35 mg of phosphate were added to 1 mL of deuterated water (D2O) for every solutionl Deuterated nitric acid (DNO3) and deuterated sodium hydroxide (NaOD) were used to control pH of solutionPROCEDURE – Sample Preparationl External reference standards were added to all pH 1 solutionsl Approximately 50 mg sodium orthophosphate added to 1 mL D2Ol pH of standard was adjusted to 9 so its peak would separate from the solution’s orthophosphate peakl Standard was placed in NMR tube insert, which was then fit into standard NMR tubePROCEDURE – NMR Testingl 250 MHz Bruker Nuclear Magnetic Resonance Spectrometerl Operated at P resonant frequency of 100 MHzl Relaxation delay –5 secondsl 64 scans takenPROCEDURE – Data Analysisl NMR generates FIDsl PCNMR for Windows used to convert FIDs to spectral Spectra contained peaks that represented P atoms in different magnetic environmentsl Area under peaks proportional to number of P atoms that peak representedl Chemical shifts of peaks obtained from NMR spectra plotterPROCEDURE – Data Analysisl Hydrolysis data was fit to first-order kinetics models using Graphical Analysis for Windowsl Polyphosphate concentration –1storder model:l Orthophosphate concentration –consecutive 1storder reaction model:l Areas under phosphate peaks graphed according to these models[][]ktepolypoly−=0[][]()kteAOrtho−−= 10PROCEDURE – Data Analysisl Rate constants (k) were produced by these modelsl 0.693 was divided by polyphosphate rate constant to determine polyphosphate half-livesl Error in polyphosphate rate constant calculated using linear regressionSPECTRAPPOOOOHOHOHOHSPECTRAPOPOPOOOOOHOHOHHYDROLYSIS GRAPHS –pH 1Pyrophosphate - pH 0.96 - Normalized00.511.522.533.5020406080100120140Time (Hours)OrthoPolyPPOOOOHOHOHOHHYDROLYSIS GRAPHS –pH 1Trimetaphosphate - pH 1.03 - Normalized0246810120102030405060Time (Hours)Normalized Peak AreaOrthoTerminal PolyTrimetaInternal PolyPOPOPOOOOOHOHOHHYDROLYSIS GRAPHS –pH 7Hexametaphosphate - pH 6.80 - Normalized0246810120102030405060708090100Time (days)Normalized Peak AreaOrthoTerminal PolyInternal PolyTRIMETA –POLY CURVE-FITSNormalizedUnnormalizedk=7.5 x 10-11/hrk=5.1 x 10-11/hrTRIMETA -ORTHO CURVE-FITSNormalizedUnnormalizedk=3.1 x 10-21/hrk=3.9 x 10-11/hrAverage 1stOrder Rate Constants and Half-Lives for Polyphosphate HydrolysesPolyphosphatespH± 0.2Poly 1stOrder Rate Constants Half-LivesOverall 1stOrder Rate ConstantsNa-Pyrophosphate 710-3/ day <1000 days 10-1 / dayNa-Tripolyphosphate 710–3/ day <1000 days 10-1/ dayNa-Trimetaphosphate 7Too much variability to model data 10-3/ dayNa-Hexametaphosphate 710-3/ day <1000 days 10-2/ dayNORMALIZEDNa-Pyrophosphate 12.3 x 10-2/ hr 30 hr 3.9 x 10-2/ hrNa-Tripolyphosphate 13.2 x 10-2/ hr 22 hr 1.1 x 10-2/ hrNa-Trimetaphosphate 170. x 10-2/ hr 1 hr 3.3 x 10-2/ hrNa-Hexametaphosphate 12.7 x 10-2/ hr 26 hr 2.6 x 10-2/ hrUNNORMALIZEDNa-Pyrophosphate 12.7 x 10-2/ hr 26 hr 12 x 10-2/ hrNa-Tripolyphosphate 13.2 x 10-2/ hr 22 hr 7.2 x 10-2/ hrNa-Trimetaphosphate 155 x 10-2/ hr 1 hr 44 x 10-2/ hrNa-Hexametaphosphate 14.2 x 10-2/ hr 17 hr 7.8 x 10-2/ hrAverage Errors in Polyphosphate Rate ConstantsErrors greater for all unnormalized rate constantsPolyphosphateNormalized PolyphosphateUnnormalized PolyphosphateRate Constant(1/hr)Error (1/hr)Rate Constant(1/hr)Error (1/hr)Pyrophosphate –pH 12.3 x 10-20.1 x 10-22.7 x 10-20.2 x 10-2Tripolyphosphate –pH 13.2 x 10-20.6 x 10-23.2 x 10-20.8 x 10-2Trimetaphosphate –pH 170. x 10-25 x 10-255 x 10-28 x 10-2Hexametaphosphate –pH 12.7 x 10-20.2 x 10-24.2 x 10-20.6 x 10-2Chemical Shifts of