Journal of Magnetic Resonance

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Journl of Mgnetic Resonnce 205 (2010) 242 246 Contents lists ville t ScienceDirect Journl of Mgnetic Resonnce journl homepge: www.elsevier.

Wemmer,c, Alexnder Pines,c, * Mterils Sciences Division, Lwrence Berkeley Ntionl Lortory, Berkeley, CA 94720, USA Physicl Biosciences Division, Lwrence Berkeley Ntionl Lortory, Berkeley, CA 94720,

1 Journl of Mgnetic Resonnce 205 (2010) Contents lists ville t ScienceDirect Journl of Mgnetic Resonnce journl homepge: Xenon-sed moleculr sensors in lipid suspensions Tyler Meldrum,c, Leif Schröder,c,1, Philipp Denger d, Dvid E. Wemmer,c, Alexnder Pines,c, * Mterils Sciences Division, Lwrence Berkeley Ntionl Lortory, Berkeley, CA 94720, USA Physicl Biosciences Division, Lwrence Berkeley Ntionl Lortory, Berkeley, CA 94720, USA c Deprtment of Chemistry, University of Cliforni, Berkeley, CA 94720, USA d Atlg. Medizinische Physik in der Rdiologie (Division of Medicl Physics in Rdiology), Deutsches Kresforschungszentrum, Im Neuenheimer Feld 280, Heidelerg, Germny rticle info strct Article history: Received 9 Mrch 2010 Revised 7 My 2010 Aville online 13 My 2010 Keywords: Biosensors Cryptophne Host guest systems Lipid vesicles Xenon There hve een mny proposls to use xenon-sed moleculr sensors in iologicl settings. Fundmentl to understnding the properties of these sensors in vivo is chrcterizing their ehvior in lipid environments. We report the investigtion of xenon-sed moleculr sensors in suspensions of lipid vesicles with size comprle to cells. We detil spectroscopic properties of sensors ssocited with lipid vesicles s well s those in equilirium in the surrounding solution. We chrcterize the dependence of the spectrl prmeters on temperture, relevnt for studies t physiologicl tempertures. We lso demonstrte the ility to perform selective sturtion trnsfer (Hyper-CEST) etween sensor, oth lipid ound nd unound, nd the ulk solution. Lstly, we demonstrte the pplicility of sturtion trnsfer in the heterogeneous medium s n imging modlity. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Xenon-sed moleculr sensors re host molecules tht re designed to give unique mgnetic resonnce (MR) signl from xenon tom tht is temporrily encpsulted [1]. These sensors, often referred to s xenon iosensors, cn e conjugted with moiety tht confers chemicl specificity for inding to prticulr nlyte; exmples of such inding moieties re iotin or vidin [1], oligonucleotides or ptmers [2,3], or enzyme sustrtes [4]. Binding to moleculr trget cuses locliztion of the sensor in regions contining the nlyte, mking it possile to imge the trget of chemicl interest [5]. While there is gret potentil in using these sensors for trgeted moleculr imging in vivo, for exmple, in the determintion of distriutions of cell surfce receptors [3], their non-specific interctions with mny iologicl mterils re poorly understood. Some interction etween the hydrophoic xenon-inding moiety ( cryptophne molecule) tht hs een trgeted to cell surfce receptor nd the hydrophoic interior of the cell memrne is likely. Studies hve een conducted on cryptophnes in hydrophoic orgnic solvents [6,7] nd in humn plsm [8], ut there hs een no previous report on the interction of cryptophnes with lipid vesicles. We investigted interctions etween cryptophne nd lipid vesicles tht re comprle in size nd composition to cell memrnes [9] using xenon NMR; the system is shown schemticlly in Fig. 1. Lipid vesicles hve een successfully used s crrier gents for xenon (without cryptophne-sed sensors) in MR ngiogrphy [9] nd in MR imging of the rt rin [10]; these nd other reports [11,12] indicte tht xenon is more solule in lipids thn in wter. In ddition, we hypothesized tht cryptophne, hydrophoic molecule, would show greter soluility in lipid emulsion thn in pure wter. The incresed soluility of oth xenon nd the sensor is dvntgeous in mximizing signl. Furthermore, we hoped to resolve the signls corresponding to free xenon dissolved in oth queous nd lipid environments, s well s the signls corresponding to xenon ound in the sensor in oth queous nd lipid environments. We wnted to extend previous work involving the temperture dependence of the chemicl shift vlues for these signls. Lstly, we predicted tht we could selectively imge the sensor in queous nd lipid environments, illustrting the ppliction of xenon-sed moleculr sensors to trgeted imging in iologicl mixtures. 2. Results nd discussion 2.1. Lipid suspensions vs. queous solutions * Corresponding uthor t: Mterils Sciences Division, Lwrence Berkeley Ntionl Lortory, Berkeley, CA 94720, USA. Fx: E-mil ddress: pines@erkeley.edu (A. Pines). 1 Present ddress: Moleculr Imging Group, Leiniz-Institut für Molekulre Phrmkologie, Roert-Rössle-Str. 10, Berlin, Germny. In ll experiments reported here, we used vrint of cryptophne-a cge (inset in Fig. 1) s xenon host. This cge molecule hs cette groups chemiclly ttched to its exterior, conferring prtil soluility in the queous phse of the suspension; we refer /$ - see front mtter Ó 2010 Elsevier Inc. All rights reserved. doi: /j.jmr

T. Meldrum et l. / Journl of Mgnetic Resonnce 205 (2010) 242 246 243 H = Me Me Me Me Fig. 1. A schemtic of the vrious pools of xenon in this study.

2 T. Meldrum et l. / Journl of Mgnetic Resonnce 205 (2010) H = Me Me Me Me Fig. 1. A schemtic of the vrious pools of xenon in this study. Xe lipid (green) nd Xe q (red) correspond to unound xenon. Xe@cge lipid (drk lue) nd Xe@cge q (yellow) pper 130 ppm upfield of the Xe q pek. The cge is represented y the light lue hexgon. The modified cryptophne cge used in these studies, shown in the inset, is termed dicid cge. The introduction of two cette groups confers some wter soluility to this otherwise hydrophoic molecule. to this cryptophne compound s dicid cge. A sturted queous solution hs 15 ± 5 lm of the dicid cge, s determined y UV vis sornce (e 287nm = 8000 M 1 cm 1 ) [13]. The NMR spectrum of xenon uled into pure wter shows peks corresponding to gseous xenon (referenced to 0 ppm) nd to xenon dissolved in wter (Xe q ) t 189 ppm. Fig. 2 shows the xenon-nmr spectrum of dicid cge in wter (lck), with resonnces t 62 nd 189 ppm, corresponding to xenon ound in the cryptophne cge in n queous environment (Xe@cge q ) nd free 196 0% lipid 1% lipid 10% lipid H xenon in queous solution (Xe q ), respectively. These shifts re consistent with those reported elsewhere [1]. The spectrum of dicid cryptophne in 1% lipid suspension (red in Fig. 2) showed three resonnces: the two found in the pure queous solution nd third resonnce t 73 ppm. We ttriute this third resonnce to tht of xenon ound in the cryptophne cge in lipid environment (Xe@cge lipid ). The integrted res of the Xe@cge peks in the 1% lipid suspension give reltive signl intensities of 1:2 (Xe@cge lipid :Xe@cge q ). Becuse this rtio is much lrger thn the lipid/wter volume rtio (1:100), we estimte tht dicid cge is t lest 50 times more solule in lipid thn in wter. As previous dt show tht the inding ffinity of xenon for the cge in wter is greter thn in n polr solvent [14], it is unlikely tht the 1:2 rtio of the Xe@cge lipid :Xe@cge q signls cn e explined y greter frction of cges contining xenon in the lipid phse. With 5% nd 2% lipid suspensions, oth Xe@cge q nd the Xe@cge lipid peks were clerly visile, ut when the lipid content ws incresed to 10%, only one pek ws oserved: Xe@ cge lipid t 73 ppm (lue in Fig. 2). The rtio of pek intensities, Xe@cge lipid :Xe@cge q, for the 2% nd 5% lipid suspensions ws 0.9:1 nd 1.6:1, respectively. This increse of the Xe@cge lipid q rtio with lipid content verifies the preferentil prtitioning of cge nd xenon into the liphtic lipid environment. Beyond the chnges in the Xe@cge peks due to lipid content, we note tht the pek t 189 ppm shifts downfield nd is rodened upon ddition of the lipid. We fitted this region of the spectrum using two Lorentzin curves, representing the Xe q nd Xe lipid peks. These fits show rod pek 1 ppm downfield of nrrower, more intense pek. We ttriute the more intense pek to Xe q ecuse it hs chemicl shift vlue closer to tht of Xe q from the 0% lipid solution. The chemicl shift vlue for the Xe q pek increses with incresing lipid content; this effect, reported previously with proteins [15], is result of wek surfce interctions etween xenon toms nd other molecules in solution. The oservtion of distinct Xe q nd Xe lipid peks indictes tht these two pools exchnge slowly on the chemicl shift timescle. While the integrted res of the solvent peks do not show quntittive reltionship with the lipid content of given smple, trend of incresing Xe lipid pek re with incresing lipid content is oserved. The lck of quntittive greement is proly due to error in the fits resulting from the lrge difference in the intensities of the two fitted peks. Nevertheless, the fit prmeters yield systemtic trend for the chemicl shift vlues of oth the Xe q nd Xe lipid peks, supporting the vlidity of the fits, which re provided s Supporting Informtion. Interestingly, we note tht the chemicl shift seprtion etween the xenon signls in queous nd lipid environments without the cge (1 ppm) is ten times smller thn the seprtion with the cge (10 ppm). This ility of host molecule to mplify the chemicl shift seprtion my e useful in determining the locl chemicl environment of the cge nd other molecules to which the cge my e ound Temperture dependence frequency [ppm] Fig. 2. Xenon NMR spectr of the dicid cge in smples of 0% (lck), 1% (red), nd 10% (lue) lipid content. The peks t 190 ppm correspond to the Xe q nd Xe lipid peks, while the peks t 63 nd 73 ppm correspond to Xe@cge q nd Xe@cge lipid, respectively. (For interprettion of the references to color in this figure legend, the reder is referred to the we version of this rticle.) We explored the temperture dependence of xenon-sed moleculr sensors in lipid suspensions t tempertures from 5 C to 40 C. Following initil equilirtion t room temperture, smples were llowed to equilirte for 5 min. t ech temperture point efore dt cquisition. At tempertures elow 25 C, the Xe lipid peks for the 1%, 2%, nd 5% lipid suspensions were distinguishle from the Xe q peks, s shown in Fig. S2. However, t tempertures ove 25 C the peks overlpped nd could not e fitted unmiguously. Generlly, the position of the Xe q pek vried qudrticlly with temperture, s hs een reported previously [16], while the position of the Xe lipid pek decresed with incresing temperture. The chemicl shift vlues of the Xe@cge q

244 T. Meldrum et l. / Journl of Mgnetic Resonnce 205 (2010) 242 246 nd Xe@cge lipid peks showed liner increse with temperture the slope of the Xe@cge q shift ws consistent with previous results t 0.

3 244 T. Meldrum et l. / Journl of Mgnetic Resonnce 205 (2010) nd Xe@cge lipid peks showed liner increse with temperture the slope of the Xe@cge q shift ws consistent with previous results t 0.31 ± 0.01 ppm C 1 [17], nd tht of the Xe@cge lipid pek ws 0.18 ± 0.03 ppm C 1. Plots of chemicl shift vlues t different tempertures re ville s Supporting Informtion Sturtion trnsfer Tle 1 Integrted pek res of xenon-nmr spectrum of 1% lipid suspension following sturtion t vrious frequencies. Letters designting the sturtion frequency correspond to the spectr in Fig. 3. Sturtion frequency Xe lipid Xe q Xe@cge lipid Xe@cge q ( ppm) (49.7 ppm) c (59.4 ppm) c d (64.3 ppm) e (69.1 ppm) d f (88.6 ppm) All pek res normlized to this vlue. No oservle pek t this frequency. c This frequency corresponds to Xe@cge q. d This frequency corresponds to Xe@cge lipid. When using xenon-sed moleculr sensors in mixed queous/ lipid environments, exchnge mong four distinct xenon pools ffects the system, illustrted schemticlly in Fig. 1. To qulittively chrcterize these exchnge pthwys etween the different pools, we used the pproch termed Hyper-CEST [18], nlogous to Xenon Polriztion Trnsfer Contrst (XTC) [19], in which decrese in the Xe q signl following sturtion t the Xe@cge frequency occurs in the presence of the moleculr sensor. In our experiments, sturtion pulses were 500 ms in durtion, much longer thn the 30 ms residence time of xenon toms reported for cryptophne cge in wter [13], nd were designed to hve ndwidth of 1.8 ppm (150 Hz) [20]. As shown in Fig. 3, when sturtion pulse ws pplied t frequency fr off resonnce from the Xe@cge signls (spectrum f), no chnge ws oserved in the signl intensity of ny pek. When the pulse ws pplied t frequencies t or ner the Xe@cge peks, sturtion ws oserved to vrying degrees in other peks. The results of these sturtion trnsfer experiments re summrized in Tle 1. The trnsfer of sturtion etween the lipid nd queous pools indictes chemicl exchnge of xenon etween these two environments on the time scle of the pplied sturtion pulse (500 ms). The difference in the degree of sturtion s result of pulses pplied t the Xe@cge q vs. Xe@cge lipid frequencies indictes more rpid exchnge of xenon in nd out of the cge in the lipid phse thn in wter. This oservtion is consistent with the linewidths of the Xe@cge peks; the linewidth of the Xe@cge lipid pek, property indictive of the exchnge rte, is two to five times wider thn tht of the Xe@cge q pek in oth the 1% nd 2% lipid smples (see Supporting Informtion). Ultimtely, higher concentrtions of oth xenon nd cge in the lipid environment, together with more rpid exchnge, result in more efficient Hyper-CEST sturtion in lipid environments using xenon-sed moleculr sensors. This incresed sturtion efficiency could e used to improve xenon NMR detection sensitivity in lipophilic systems Imging To demonstrte the pplicility of frequency-selective Hyper- CEST detection to imging, we comined sturtion with phseencoded imging, s shown in Fig. 4. When wek sturtion pulses were pplied resonnt with either Xe@cge lipid or Xe@cge q, the response ws totl sturtion of the Xe q nd Xe lipid peks, verifying the presence of dicid cge (Fig. 4 nd c). In contrst, when sturtion ws pplied t frequency directly etween those of the two cge peks, insufficient contrst ws generted to verify off-resonnt sturtion on-resonnt sturtion f c d e [mm] c frequency [ppm] Fig. 3. The xenon NMR spectr following Hyper-CEST sturtion t different sturtion frequencies s indicted y the smll rrows. Sturtion is most pprent when sturting directly on the Xe@cge peks (spectr nd d), especilly the Xe@cge lipid pek. When sturting the Xe@cge lipid pek (spectrum ), the individul Xe q nd Xe lipid peks ecome pprent due to the reduction in pek intensity [mm] [ppm] Fig. 4. A demonstrtion of the selectivity of Hyper-CEST for imging with the dicid cge in lipid suspension. When sturtion is pplied to either the Xe@cge q () or Xe@cge lipid (c) pek, the response is diminished in the on-resonnt cse. When sturtion is pplied t frequency etween the two Xe@cge peks (), there is no pprent sturtion in the imge. The pplied rdio frequency field in these imging experiments is pproximtely one-fifth the mplitude of tht used in Fig. 3, giving incresed selectivity.

4 T. Meldrum et l. / Journl of Mgnetic Resonnce 205 (2010) the presence of cge in the Hyper-CEST imges (Fig. 4). This demonstrtes the utility of frequency-selective sturtion for detecting multiple moleculr sensors with smll frequency seprtions. Bsed on the unique response of the Xe@cge q nd Xe@cge lipid signls to sturtion, we nticipte the development of multiplexing using xenon-sed moleculr sensors. Incorporting multiplexing with previously reported work on the detection of low concentrtions of sensor [17] my provide fcile wy to chrcterize n nlyte with NMR in wy nlogous to multiplexed opticl detection using fluorophores. 3. Conclusion The NMR signl enhncement resulting from incresed mounts of xenon nd sensor in lipid environments reduces sensitivity requirements for detection of nlytes typiclly found in lipophilic medi. The response of the Xe q nd Xe lipid peks to sturtion t frequencies corresponding to Xe@cge q nd Xe@cge lipid reduces these sensitivity requirements even further. In ddition, differences in the chemicl shift of xenon in the presence of moleculr sensor fcilitte the discrimintion of the chemicl environment of xenon, either queous or lipid, with greter frequency resolution thn in the sence of sensor. Interestingly, xenon-sed moleculr sensors in lipid emulsions show quntittive dependence on temperture; it is possile tht similr dependence on other solvent properties, for exmple, ph, will emerge in future experiments. By exploiting the response to oth mgnetiztion trnsfer nd to physicl nd chemicl properties of the locl environment, sensors could e designed tht simultneously nlyze severl properties of system of interest, for exmple, iologicl or other chemicl mrkers, tht pper in different concentrtions in lipophilic nd hydrophilic regions of the ody. 4. Experimentl Dilute suspensions of lipid vesicles were prepred from phrmceuticl grde lipid suspension (Intrlipid Ò 20%, Phrmci) tht contins vesicles nm in dimeter [10]. Lipid emulsion ws diluted with wter/d 2 (minimum 30% D 2 for frequency locking in the spectrometer) to 1%, 2%, 5%, nd 10% lipid content. To ech liquot of this dilute lipid suspension (4.0 ml) ws dded vrint of cryptophne-a (2.0 ± 0.4 mg), termed dicid cge, with two methoxy groups ech replced y methyl croxylic cid groups for incresed wter soluility. The concentrtion of dicid cge in the lipid suspension could not e directly mesured during smple preprtion ecuse the lipid vesicles strongly sctter light. By llowing the smple to settle for 10 min fter shking nd y pipetting from the top of the suspension, we voided introducing powder into the NMR smple tues; thus, the mount of dissolved cge ws fixed for ny given lipid concentrtion. Dt were recorded on 7.05 T NMR spectrometer (Vrin, Plo Alto, CA) using 5 mm nd 10 mm (spectroscopy) nd 30 mm (imging) proes. Hyperpolrized xenon (P 4%) [21,22] ws generted with XenoSpin polrizer (Amershm Helth, Durhm, NC) from gs mixture of 89% He, 10% N 2, nd 1% xenon with nturl-undnce isotopes (Prxir) t 70 psi. Gs contining hyperpolrized xenon ws uled (15 20 s, 0.45 stndrd liters per minute) into the NMR tues contining smple (2.5 ml for the 10 mm proe, 1.0 ml for the 5 mm proe). Gs flow ws interrupted using stopped-flow system [23], followed y dely (5 15 s) to llow the ules to dissipte. The temperture of the system ws controlled using the vrile temperture unit of the spectrometer. The Hyper-CEST experiments (5 mm proe) were conducted using continuous wve (cw) sturtion period (500 ms, pplied rdio frequency field strength B 1 = 2.23 lt), followed y hrd 90 pulse nd redout of free induction decy (50 ms). After Fourier trnsformtion (FT) nd ppliction of n podiztion filter, the xenon gs pek ws referenced to 0 ppm in ech spectrum for which gs pek ws present. All other spectr used the sme reference for 0 ppm. Peks were fitted to the dt using the uilt-in fit routines in the IGR Pro 6.1 softwre pckge (WveMetrics Inc., Lke swego, R). Imging experiments were conducted using grdient coil ssemly (Resonnce Reserch Inc., Billeric, MA) for sptil encoding. Two 10 mm NMR tues were ech connected to the gs delivery system nd plced side-y-side in 30 mm NMR proe. When using two phntoms, the flow output of the polrizer ws incresed to 0.65 stndrd liters per minute. No ttempt ws mde to compenste for differences in polriztion output with incresed flow. Hyper-CEST imges were cquired using cw sturtion pulse (6 s, pplied field strength B 1 = 0.44 lt) nd slice-selective 90 pulse long the z-dimension (1.2 ms, sinc shpe, 13.5 mm slice-thickness) with susequent 2-dimensionl phse encoding (15 30 mm 2 field-of-view, mtrix size 4 8). Ech point in k-spce ws red out once for 1024 ms with 5 khz spectrl width. Post-processing using MATLAB Ò (The MthWorks Inc., Ntick, MA) included two-dimensionl FT for sptil reconstruction fter zero-filling to n 8 16 dtset nd one-dimensionl FT for spectrl reconstruction. Imges showing the sptil distriution of the xenon signl t d 190 ppm were generted y summtion of the signl intensity over five dt points (0.74 ppm) in the solute spectrum nd susequent color-encoding of these vlues. Acknowledgments Reserch ws supported y the Director, ffice of Science, ffice of Bsic Energy Sciences, Mterils Sciences nd Engineering Division nd Physicl Biosciences Division of the US Deprtment of Energy under Contrct No. DE-AC02-05CH11231 [TM, LS, DEW, nd AP], y the Deutsche Forschungsgemeinschft through Emmy Noether Fellowships (SCHR 995/1-1 nd SCHR 995/2-1) [LS], y the Europen Reserch Council through Strting Grnt Biosensor Imging under ERC Grnt Agreement No [LS], nd y fellowship of the Germn Cncer Reserch Center [PD]. Appendix A. Supplementry mteril Supplementry dt ssocited with this rticle cn e found, in the online version, t doi: /j.jmr References [1] M. Spence, S. Ruin, I. Dimitrov, E. Ruiz, D. Wemmer, A. Pines, S. Yo, F. Tin, P. Schultz, Functionlized xenon s iosensor, Proc. Ntl. Acd. Sci. 98 (2001) [2] V. Roy, T. Brotin, J.-P. Dutst, M.-H. Chrles, T. Delir, F. Mllet, G. Huer, H. Desvux, Y. Boulrd, P. Berthult, A cryptophne iosensor for the detection of specific nucleotide trgets through xenon NMR spectroscopy, Chem. Phys. Chem. 8 (2007) [3] G.K. Sewrd, Q. Wei, I.J. Dmochowski, Peptide-medited cellulr uptke of cryptophne, Bioconjugte Chem. 19 (2008) [4] J.A. Aron, J.M. Chmers, K.M. Jude, L. Di Costnzo, I.J. Dmochowski, D.W. Christinson, Structure of 129Xe-cryptophne iosensor complexed with humn cronic nhydrse II, J. Am. Chem. Soc. 130 (2008) [5] C. Hilty, T.J. Lowery, D.E. Wemmer, A. Pines, Spectrlly resolved mgnetic resonnce imging of xenon iosensor, Angew. Chem. Int. Ed. 45 (2006) [6] K. Brtik, M. Luhmer, J. Dutst, A. Collet, J. Reisse, 129Xe nd 1H NMR study of the reversile trpping of xenon y cryptophne-a in orgnic solution, J. Am. Chem. Soc. 120 (1998) [7] G. Huer, L. Beguin, H. Desvux, T. Brotin, H. Fogrty, J.-P. Dutst, P. Berthult, Cryptophne xenon complexes in orgnic solvents oserved through NMR spectroscopy, J. Phys. Chem. A 112 (2008) [8] P.A. Hill, Q. Wei, R.G. Eckenhoff, I.J. Dmochowski, Thermodynmics of xenon inding to cryptophne in wter nd humn plsm, J. Am. Chem. Soc. 129 (2007)

5 246 T. Meldrum et l. / Journl of Mgnetic Resonnce 205 (2010) [9] H.E. Möller, M. Chwl, X.J. Chen, B. Driehuys, L.W. Hedlund, C.T. Wheeler, G.A. Johnson, Mgnetic resonnce ngiogrphy with hyperpolrized 129Xe dissolved in lipid emulsion, Mgn. Reson. Med. 41 (1999) [10] G. Duhmel, P. Choquet, E. Grillon, L. Lmlle, J.-L. Leviel, A. Ziegler, A. Constntinesco, Xenon-129 MR imging nd spectroscopy of rt rin using rteril delivery of hyperpolrized xenon in lipid emulsion, Mgn. Reson. Med. 46 (2001) [11] R. Smith, E. Porter, K. Miller, The soluility of nesthetic gses in lipid ilyers, Biochim. Biophys. Act 645 (1981) [12] A. Venktesh, L. Zho, D. Blmore, F. Jolesz, M. Alert, Evlution of crrier gents for hyperpolrized xenon MRI, NMR Biomed. 13 (2000) [13] M. Spence, E. Ruiz, S. Ruin, T. Lowery, Development of functionlized xenon iosensor, J. Am. Chem. Soc. 126 (2004) [14] G. Huer, T. Brotin, L. Duois, H. Desvux, J.-P. Dutst, P. Berthult, Wter solule cryptophnes showing unprecedented ffinity for xenon: cndidtes s NMR-sed iosensors, J. Am. Chem. Soc. 128 (2006) [15] S. Ruin, M. Spence, I. Dimitrov, E.J. Ruiz, A. Pines, D.E. Wemmer, Detection of conformtionl chnge in mltose inding protein y 129Xe NMR spectroscopy, J. Am. Chem. Soc. 123 (2001) [16] A. Cheruini, A. Bifone, Hyperpolrised xenon in iology, Prog. Nucl. Mgn. Reson. Spectrosc. 42 (2003) [17] L. Schröder, T. Meldrum, M. Smith, T. Lowery, D.E. Wemmer, A. Pines, Temperture response of 129Xe depolriztion trnsfer nd its ppliction for ultr-sensitive NMR detection, Phys. Rev. Lett. 100 (2008) (4). [18] L. Schröder, T. Lowery, C. Hilty, D. Wemmer, A. Pines, Moleculr imging using trgeted mgnetic resonnce hyperpolrized iosensor, Science 314 (2006) [19] K. Ruppert, J. Brookemn, K. Hgspiel, J. Mugler III, Proing lung physiology with xenon polriztion trnsfer contrst (XTC), Mgn. Reson. Med. 44 (2000) [20] VS Bjj, T. Meldrum, D.E. Wemmer, A. Pines, Appliction of multiple-pulse sturtion trnsfer sequences to hyperpolrized 129Xe, J. Mgn. Reson., sumitted for puliction. [21] W. Hpper, E. Miron, S. Schefer, D. Schreier, W. Vn Wijngrden, X. Zeng, Polriztion of the nucler spins of nole-gs toms y spin exchnge with opticlly pumped lkli-metl toms, Phys. Rev. A 29 (1984) [22] T. Wlker, W. Hpper, Spin-exchnge opticl pumping of nole-gs nuclei, Rev. Mod. Phys. 69 (1997) [23] S.-I. Hn, S. Grci, T.J. Lowery, E.J. Ruiz, J.A. Seeley, L. Chvez, D.S. King, D.E. Wemmer, A. Pines, NMR-sed iosensing with optimized delivery of polrized 129Xe to solutions, Anl. Chem. 77 (2005)

A FACTORIAL STUDY ON THE EFFECTS OF β CYCLODEXTRIN AND POLOXAMER 407 ON THE SOLUBILITY AND DISSOLUTION RATE OF PIROXICAM

IJRPC 20, (3) Chowdry et l. ISSN: 223 278 INTERNATIONAL JOURNAL OF RESEARCH IN PHARMACY AND CHEMISTRY Aville online t www.ijrpc.com Reserch Article A FACTORIAL STUDY ON THE EFFECTS OF β CYCLODEXTRIN AND