uva-dare (digital academic repository) triacylglycerol ...chapterr 6 structuree of cncn+2cn-type...

23
UvA-DARE is a service provided by the library of the University of Amsterdam (http://dare.uva.nl) UvA-DARE (Digital Academic Repository) Triacylglycerol Structures and Cocoa-butter Crystallization. van Langevelde, A.J. Link to publication Citation for published version (APA): van Langevelde, A. J. (2000). Triacylglycerol Structures and Cocoa-butter Crystallization. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 26 May 2020

Upload: others

Post on 24-May-2020

2 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

UvA-DARE is a service provided by the library of the University of Amsterdam (http://dare.uva.nl)

UvA-DARE (Digital Academic Repository)

Triacylglycerol Structures and Cocoa-butter Crystallization.

van Langevelde, A.J.

Link to publication

Citation for published version (APA):van Langevelde, A. J. (2000). Triacylglycerol Structures and Cocoa-butter Crystallization.

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s),other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons).

Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, statingyour reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Askthe Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam,The Netherlands. You will be contacted as soon as possible.

Download date: 26 May 2020

Page 2: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

Chapte rr 6

Structur ee of CnCn+2Cn-typ e

(#ii = even ) p'-triacylglycerol s

acceptedd for publication in Acta Cryst. B

Abstract t Thee crystal structures of the 3' phase of CLC (l,3-didecanoyl-2-dodecanoyl-glycerol) and

MPMM (l,3-ditetradecanoyl-2-hexadecanoyI-glycerol) have been determined trom single-crystal X-rayy diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals aree orthorhombic with space group Ibal and Z = 8. The unit-cell parameters of P'-CLC are a = 57.368(6),, b = 22.783(2) and c = 5.6945(6) A and the final R value is 17.5 %. The unit-cell parameterss of P'-MPM are a = 76.21(4), b = 22.63(1) and c = 5.673(2) A and the final R ̂value is 5.77 %. Both the P'-CLC and fT-MPM molecules are crystallized in a chair conformation being bend att the glycerol moiety. The zigzag planes of the acyl chains are orthogonal packed as is typical for a P'' phase. Furthermore, unit-cell parameters of some other members of the C^C^C.-type triacylglyceroll series have been refined on their high-resolution X-ray powder diffraction pattern. Finally,, the crystal structures are compared with the currently known structures and models of triacylglycerols. .

91 1

Page 3: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6 6

6.11 Introductio n Triacylglycerolss (TAGs) are esterifications of three long-chain fatty acids with glycerol. Many

differentt types of TAGs exist because the three fatty acids can all differ in chain length and degree off saturation. Natural oils and fats are complex mixtures of these various TAG types and are applied inn a wide range of consumer products such as foods, cosmetics and medicine. Typical physical propertiess of TAG mixtures such as solidification, melting and polymorphic behaviour give each productt its own characteristics (Sato, 1996). For example, spreadability of butter and lipstick, hardnesss of chocolate, quality of ointments, consistency of whipped cream are all determined by the polymorphicc phase of the fat component. Likewise, temperature-dependent polymorphic phase transitionss are held responsible for product degradation, e.g. fat-bloom formation at the chocolate surface.. To understand the complex crystallization processes and totally control the manufacturing processes,, crystal-structure information of various TAG polymorphs is indispensable.

TAGss and their mixtures crystallize in the different polymorphic phases a, P and/or p' and sometimess several different P' and/or p polymorphs exist (Simpson and Hagemann, 1982; Arishima andd Sato, 1989). Phase transformations of most TAGs (a -> P', a -> P' -> p or a -+ P) are monotropicc resulting in only one stable phase, P' or P, depending on the TAG type (Hagemann, 1988).. For QC^C^type (« = even) TAGs the most stable phase is p, whereas for C.C^C,, and CaCfl+4Cfl+2-typee (n = even) TAG series the p'-phase is the most stable (De Jong, 1980). Furthermore, relativee phase stability is determined by the degree of saturation.

X-rayy powder diffraction (XRPD) is commonly used to distinguish between the various polymorphs,, since each polymorph has its own characteristic powder-diffraction pattern originating fromfrom the typical packing of the long hydrocarbon chains. However, for complete structure informationn single crystals are essential and these are difficult to grow. Therefore, only crystal structuress of the p polymorph of CCC, IXL , PPP and CLBrC (2-ll-bromoundecanoyl-l,3-didecanoyl-glycerol)) are known (Doyne and Gordon, 1968; Gibon et al, 1984; Jensen and Mabis, 19633 and 1966; Larsson, 1965a; Van Langevelde et al, 1999a). They crystallize in space group PI, havingg an asymmetric 'tuning-fork' conformation, characterized by the two outer acyl chains (I) and (III )) pointing in one direction and the middle one (11) in opposite direction (Fig. 6.1). The molecules aree packed like stacked chairs and the zigzag planes of all hydrocarbon chains are parallel, which is typicall for a p polymorph (Abrahamsson et al, 1978). Recently, Van Langevelde et al. (1999a) confirmedd the structural correspondence in the P-CnC„C„-type (n = even) TAG series. Even the crystall structure of CLBrC, a heavy-atom analogue of the C„C-+2C1,-type (n = even) and therefore expectedd to be P'-stable was crystallized in the p polymorph (De Jong and Van Soest, 1978).

Soo far, efforts made to determine the crystal structure of TAGs in the p' phase were not successful.. Growing of reasonable single crystals and the typical diffraction character were major problemss in most trials. Nevertheless, unit-cell parameters and space groups of P'-LLL, P'-PSP, P'-CnCnC,,, and p'-LML were determined from single-crystals (Birker et al, 1991; Hernqvist, 1988; Hemqvistt and Larsson, 1982; Larsson, 1965b). On basis of packing arguments acyl chains were suggestedd to be tilted with respect to the methyl end-group plane. The direction of this tilt was expectedd to alternate between successive chain layers. Recently, from powder-diffraction data cell parameterss and space group Ibal were determined for the p' polymorph of the C„C 2̂CB-type (n =

92 2

Page 4: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure of C„C„ t,C„-type (n = even) P'-triacylglycerols

even)) TAG series (Van Langevelde et al. 1999b). Based on this information it was argued that straightt TAG molecules without chain tilts may result in a plausible model for the structure of the P' polymorph.. However, all these P'-models are packing models only and provide no definite structural detail. .

Upp til l now, the only crystal-structure model of a P' polymorph at the atomic level was publishedd by Van de Streek et al. (1999). They constructed a model for the P' polymorph of CLC originatingg from the crystal structures of n-C28H58 (octacosane; Boistelle et al., 1976) and PP2 (1,2-dihexadecanoyl-3-acetyl-.sw-glycerol;; Goto et al., 1992). Since the structure of n-C28H5g has the desiredd chain packing and the structure of PP2 the desired chair conformation, parts of both structuress were combined in one model. The calculated powder diagram of this model is in good agreementt with the experimental one.

Heree we report the first experimental crystal structure of a TAG in the P' polymorph. The structuree of P'-CLC, a C„C„+2C„-type (n = even) TAG, has been determined from single-crystal X-rayy diffraction data. Furthermore, the crystal structure of P'-MPM, another series member, has been determinedd from high-resolution XRPD data. Finally, these structures are compared with existing P'-models. .

HI I

II a

\\ II

II b

FIGUREE 6.1 (a) Schematic representation of a tuning-fork conformation, (b) Schematic representation of a chairr conformation. In both (a) and (b) the orientation of carbonyl and the zigzag planes are randomly chosen. .

Il l l

93 3

Page 5: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6 6

6.22 Materials and methods

6.2.16.2.1 Samples, sample preparation and data collection

AA series of C.C^C.-type (« = even) TAGs (CLC, LML, MPM and PSP) was obtained from Unileverr Research Laboratory (Vlaardingen, The Netherlands) where the TAGs have been synthesizedd and, subsequently, purified with the Midget Rapid Zone Refiner X-521 (Enraf Nonius, Delft,, The Netherlands).

Manyy small crystals of the purified CLC were obtained from the melt using a cold finger. Thesee small crystals were used as seeds mounted on a metal wire to induce crystallization from moltenn CLC which was kept a few degrees below its melting point. Among the many crystals obtainedd via this method only a few turned out to be good enough for use in a single-crystal diffractionn experiment.

X-rayy diffraction data of a CLC single crystal (0.8 x 0.04 x 0.005 mm3) was collected at beamlinee ID 11 (ESRF, Grenoble, France; Kvick and Wulff, 1992) using a monochromatic beam withh a fixed wavelength of 0.5061 A. Images having a maximal J-spacing resolution of 0.936 A weree made at room temperature using a Siemens CCD camera with an exposure time of 3 s. The crystall was rotated over a q> range of 0 - 360° with a stepsize of 0.3° at co of 160° and 340°. The spots,, which were collected from the images, were indexed using the program SMART (Braker AXS Inc.,, 1998) resulting in an orthorhombic cell with axis lengths a = 57.368(6), b = 22.783(2) and c = 5.6945(6)) A, and space group Iba2. With 8 molecules in the unit cell having a volume of 7443(1) A3

thiss result in a calculated density of 1.04 g cm"3. The data was integrated using the program SAINT (Brukerr AXS Inc., 1996) resulting in a total of 5706 reflections within the range -52 <, h <, 51, -20 < kk < 20 and -6 < / < 5, corresponding with a (sin 0)/X range of 0.0236 - 0.5344 A'1. Merging equivalentt and Friedel reflections yielded 1642 unique reflections, which is a completeness of 66 %. Off these, 824 reflections were above the significance level of 3.5 a(F) and were treated as observed. Thee intensity of the strongest reflections could not be determined accurately since they exceeded the dynamicc range of the detector.

XRPDD patterns of LML, MPM and PSP were obtained with the high-resolution powder diffractometerr at beamline BM16 (ESRF, Grenoble, France; Fitch, 1996) using a monochromatic beamm with a fixed wavelength of 0.650515(1) A for MPM and 0.445348(1) A for LML, MPM and PSP.. XRPD data was collected from capillaries with a diameter of 1.5 mm filled with powdered TAGG which were rotating during exposure. Continuous scans were made of an MPM sample at roomm temperature from 0.0 to 37.0° 2 $ with 0.5° 20 min*1 and a sampling time of 50 ms. After data collectionn this scan was binned at 0.003° 20. LML, MPM and PSP samples were scanned at a temperaturee of 250 K from 0.0 to 52.0° 20 with 0.5° 20 min"1 and a sampling time of 50 ms. After dataa collection these scans were binned at 0.005° 20.

6.2.26.2.2 Structure determination ofjS'-CLCfrom single-crystal data

Attemptss to solve the crystal structure of CLC with standard structure-determination packages weree unsuccessful due to the small number of available reflections at atomic resolution and the

94 4

Page 6: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure ofCmCm+£„-type (n = even) fi'-triacylgfycerols

uncommonn ratio between the cell axes. Finally, employing all 1642 unique reflections, a partial trial structuree was generated using the macromolecular stmcture-detemiination program Shake-and-Bake vl.55 (Miller et ai, 1994) and manual interference. This incomplete model (25 atoms) was refined usingg the unrestrained maximum-likelihood method REFMA C (Murshudov et a/., 1997) as available inn the CCP4 package (The CCP4 suite, 1994). The structure was manually updated using the visualizationn program O (Jones et ai, 1991) employing ImF^DF ̂ electron-density maps. Using thiss procedure the structure was completed after three cycles. The structure was further refined usingg Xtal (Hall et ai, 1995) with an isotropic block-diagonal least-squares refinement on \F] employingg 824 observed reflections. The refinement converged to an R value of 17.5 % and a maximumm A/crof 0.24. Soft bond and angle restraints on all non-H atoms were used ending up with aa total of 167 variables. H atoms with U= 0.1 A2 were calculated at 1.0 A of their carrier atom and keptt fixed during refinement. A final AF synthesis revealed a residual electron density between -1.2 andd 1.1 e/A3 in the vicinity of the glycerol moiety.

6.2.36.2.3 Structure determination of other series members from powder data

Celll parameters of p'-LML, p*-MPM and P'-PSP, as determined by Van Langevelde et al. (1999b;; Table 5.2), were refined on their synchrotron diffraction patterns using the program UnitCellUnitCell (Holland and Redfern, 1997).

Too obtain accurate reflection intensities a full-pattern decomposition (FPD) procedure was appliedd for the orthorhombic crystallized ji'-MPM (Table 6.6). The high-resolution synchrotron powder-diffractionn pattern was fitted employing a split-type pseudo-Voigt peak-profile function (Toraya,, 1986) and decomposed using the program MRIA (Zlokazov and Chernyshev, 1992). Since thee molecular structure of the QC^Cj.-type (n = even) TAGs differ by the length of the acyl chains only,, and since the melting points of their p* polymorphs lie on a smooth curve (Birker et al, 1991), thiss series can be considered as homologous. Therefore, a structure model for P'-MPM has been madee using the program Cerius2™ (Molecular Simulations Inc., 1995), starting from the crystal structuree of P'-CLC. The terminating H-atoms of all acyl chains were replaced by a -(CH2-CH2)2-H fragment.. To position this possible model in the asymmetric unit of the refined unit cell with space groupp Ibal, a grid-search procedure (Chernyshev and Schenk, 1998) was applied using the reflectionn intensities obtained from the FPD procedure. The obtained translational and rotational parameterss were refined followed by a bond-restrained Rietveld refinement (RR). During refinementt soft restraints were applied to the atomic distances (a is ~1 % of the ideal bond lengths). Underr these restrictions the coordinates of all atoms (O, C and H) as well as isotropic atomic-displacementt parameters (C4J were refined. The U ̂ values of all C atoms were coupled as well as thee t/iso values for all O atoms, the U ̂ values for H atoms were fixed at 0.05 A2. The preferred orientationn was refined using the nine coefficients of the symmetrized harmonics-expansion method (Ahteee et al., 1989; JSrvinen, 1993).

Thee crystal structure of P'-MPM has been compared with the structure of P'-CLC in order to determinee their structural correspondence. Therefore, matching was performed by minimizing the distancee between corresponding C and O atoms, resulting in an overall r.m.s. (root mean square) valuee expressing the quality of the fit.

95 5

Page 7: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

6.2.46.2.4 Comparison of J3' structures with models

Thee crystal structure of P'-CLC has been compared with the packing model by Van Langeveldee et al. (1999b; Chapter 5) and with the recently published atomic model by Van de Streekk et al. (1999). The atomic coordinates of the last one were obtained from Jacco van de Streek (CAOS/CAMMM Center, Nijmegen, The Netherlands). A comparison was also made between crystal structuress of (3 and P' polymorphs. For the p polymorph the atomic coordinates of the crystal structuree of p-PPP were used (Table 2.4; Van Langevelde et al., 1999a).

Forr visualization and structural comparison of the structures version 3.0a of the program PLUVAPLUVA (Driessen et al., 1988) was used. Drawings of molecular structures were made using the programm PLATON(Spek, 2000).

6.33 Results and discussion

6.3.16.3.1 Structure of P'-CLC from single-crystal data

Thee chemical structure diagram and a PLATON (Spek, 2000) representation of the crystal structuree of P'-CLC are shown in Fig. 6.2. The fractional atomic coordinates and isotropic atomic-displacementt parameters (ADPs) are listed in Table 6.1. Under the experimental conditions given in §6.2.11 P'-CLC crystallizes in space group Ibal in a chair conformation, characterized by two neighbouringg acyl chains (II) and (III ) pointing in one direction. The other (I) makes an angle of -130°° with chains (II) and (III) . Bond lengths and angles are listed in Table 6.2. The molecules are bendd at the glycerol moiety and packed with the chains along each other as imposed by the Ibal symmetryy resulting in a layered structure (Fig. 6.3). Layers of chains are succeeded by either planes off methyl-end groups or by planes of glycerol moieties. The layers are parallel to the be plane. The directionn of the 65° tilt of the chains with respect to the methyl end-group plane is changing per chainn layer. The zigzag planes of the acyl chains are orthogonal packed as is typical for a P' polymorphh (Abrahamsson et al, 1978).

H H H2CC C CH2

II I I OO O o o ^^ o ^ o = ^

(CH2)pp (CH2)q (CH2)r

II I I CH33 CH3 CH,

FIGUREE 6.2a Chemical structural diagram of CLC (p = r = 8 and q = 10), LML (p = r = 10 and q = 12), MPMM (p = r = 12 and q = 14) and PSP (p = r = 14 and q = 16).

96 6

Page 8: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure ofC„C„ t:C„-type (it = even) P'-triacylglyceroh

FIGUREE 6.2b PLATON (Spek, 2000) representation of the crystal structure of P'-CLC.

FIGUREE 6.3 (a) Packing diagram of P'-CLC perpendicular to the ac plane showing the bending of the molecules,, (b) Packing diagram of P'-CLC perpendicular to the ab plane showing the chain packing.

Page 9: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

TABLEE 6.1 Fractional atomic coordinates and isotropic atomic-displacement parameters (A') for fi'-CLC

Celll parameters of P'-CLC: a = 57.368(6), b = 22.783(2), c = 5.6945(6) A. The volume is 7443(1) A3 and thee space group is Iba2, with Z = 8 resulting in a density of 1.04 g cm"3.

Atom m

CI I C2 2 C3 3 Ola a Cla a 02a a C2a a C3a a C4a a C5a a C6a a C7a a C8a a C9a a ClOa a Olb b Clb b 02b b C2b b C3b b C4b b C5b b C6b b C7b b C8b b C9b b ClOb b CII lb C12b b Olc c Clc c 02c c C2c c C3c c C4c c C5c c C6c c C7c c C8c c C9c c ClOc c

X X

0 . 2 6 0 6 2 ( 1 5) ) 0 . 2 3 7 3 6 ( 1 3) ) 0 . 2 3 0 1 2 ( 1 3) ) 0 . 2 7 6 6 ( 6) ) 0 . 2 9 9 1 8 ( 1 8) ) 0 . 3 0 5 8 ( 1 3) ) 0 . 3 1 7 1 8 ( 1 5) ) 0 . 3 3 9 0 5 ( 1 4) ) 0 . 3 5 3 1 6 ( 1 4) ) 0 . 3 7 8 9 2 ( 1 4) ) 0 . 3 9 3 7 8 ( 1 4) ) 0 . 4 1 8 8 8 ( 1 5) ) 0 . 4 3 3 8 5 ( 1 4) ) 0 . 4 5 8 4 2 ( 1 5) ) 0 . 4 7 3 3 5 ( 9) ) 0 . 2 3 8 ( 5) ) 0 . 2 2 7 ( 2) ) 0 . 2 1 9 ( 6) ) 0 . 2 2 3 2 6 ( 9} } 0 . 2 1 0 5 1 ( 1 5) ) 0 . 1 8 5 0 6 ( 1 5) ) 0 . 1 6 9 5 4 ( 1 4) ) 0 . 1 4 5 7 8 ( 1 5) ) 0 . 1 3 0 3 9 ( 1 4) ) 0 . 1 0 5 5 8 ( 1 4) ) 0 . 0 9 1 1 1 ( 1 4) ) 0 . 0 6 7 3 2 ( 1 4) ) 0 . 0 5 2 7 8 ( 1 5) ) 0 . 0 2 8 9 5 ( 1 1) ) 0 . 2 0 7 0 ( 1 0) ) 0 . 1 9 6 9 ( 1 0) ) 0 . 2 0 6 ( 3) ) 0 . 1 7 4 9 1 ( 1 3) ) 0 . 1 6 0 9 2 ( 1 4) ) 0 . 1 3 7 8 1 ( 1 4) ) 0 . 1 2 4 5 6 ( 1 4) ) 0 . 1 0 0 2 2 ( 1 4) ) 0 . 0 8 6 7 0 ( 1 3) ) 0 . 0 6 4 7 7 ( 1 4) ) 0 . 0 5 0 1 8 ( 1 5) ) 0 . 0 2 6 6 5 ( 1 1) )

y y

0 . 4 2 4 0 ( 2) ) 0 . 3 9 8 4 ( 7) ) 0 . 4 1 8 9 ( 2) ) 0 . 4 0 5 ( 1 1) ) 0 . 4 1 7 ( 4) ) 0 . 4 4 1 ( 1 3) ) 0 . 3 9 0 9 ( 2) ) 0 . 4 3 0 3 ( 2) ) 0 . 4 1 3 5 ( 2) ) 0 . 4 2 9 7 ( 2) ) 0 . 4 0 9 9 ( 2) ) 0 . 4 3 0 6 ( 2) ) 0 . 4 0 6 4 ( 2) ) 0 . 4 3 2 9 ( 2) ) 0 . 4 0 1 3 ( 2) ) 0 . 3 3 2 ( 1 3) ) 0 . 3 0 1 6 ( 1 6) ) 0 . 3 2 2 ( 6) ) 0 . 2 3 7 0 ( 3) ) 0 . 2 3 0 5 ( 2) ) 0 . 2 4 6 2 ( 2) ) 0 . 2 2 9 4 ( 2) ) 0 . 2 5 1 6 ( 2) ) 0 . 2 3 0 2 ( 2) ) 0 . 2 5 2 5 ( 2) ) 0 . 2 3 0 7 ( 2) ) 0 . 2 5 7 1 ( 2) ) 0 . 2 3 1 9 ( 2) ) 0 . 2 5 4 9 ( 2) ) 0 . 4 0 4 ( 7) ) 0 . 4 2 3 ( 3) ) 0 . 4 6 1 ( 1 0) ) 0 . 3 8 9 1 ( 2) ) 0 . 4 2 9 8 ( 2) ) 0 . 3 9 9 8 ( 2) ) 0 . 4 2 8 7 ( 2) ) 0 . 4 0 2 6 ( 2) ) 0 . 4 2 9 3 ( 2) ) 0 . 3 9 5 3 ( 2) ) 0 . 4 2 8 2 ( 2) ) 0 . 4 0 7 2 ( 2) )

z z

- 0 . 2 9 7 8 ( 1 0) ) - 0 . 2 3 3 1 ( 1 3) )

0 . 0 1 0 0 ( 1 2) ) - 0 . 1 3 ( 3) ) - 0 . 1 6 5 ( 8) ) - 0 . 3 5 ( 3) )

0 . 0 1 7 5 ( 1 0) ) 0 . 0 0 4 8 ( 1 1} } 0 . 2 1 9 1 ( 1 1) ) 0 . 1 8 8 4 ( 1 1) ) 0 . 3 9 4 6 ( 1 1) ) 0 . 3 6 5 1 ( 1 0) ) 0 . 5 5 6 8 ( 1 0) ) 0 . 5 3 8 8 ( 1 0) ) 0 . 7 0 7 7 ( 1 0) )

- 0 . 2 1 ( 6) ) - 0 . 3 7 2 ( 1 3) ) - 0 . 5 5 ( 3) ) - 0 . 3 1 1 3 ( 1 2) ) - 0 . 0 7 1 3 ( 1 1) ) - 0 . 1 2 0 4 ( 1 0) )

0 . 0 9 3 1 ( 1 1) ) 0 . 0 6 1 0 ( 1 0) ) 0 . 2 6 6 6 ( 1 0) ) 0 . 2 4 9 3 ( 1 1) ) 0 . 4 5 6 4 ( 1 1) ) 0 . 4 4 7 9 ( 1 1) ) 0 . 6 5 0 4 ( 1 0) ) 0 . 6 1 9 3 ( 8) ) 0 . 0 3 9 ( 1 6) ) 0 . 2 3 0 ( 9) ) 0 . 3 5 ( 3) ) 0 . 3 1 7 6 ( 1 1) ) 0 . 4 9 6 4 ( 1 1) ) 0 . 5 3 2 3 ( 1 1) ) 0 . 7 2 5 6 ( 1 1) ) 0 . 7 4 5 4 ( 1 1) ) 0 . 9 5 7 4 ( 1 1) ) 0 . 9 9 8 3 ( 1 1) ) 1 . 1 8 2 2 ( 1 0) ) 1 . 1 5 4 6 ( 8) )

u„ u„ 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 0 9 ( 1 9) ) 0 . 0 9 ( 1 2) ) 0 . 0 8 ( 1 8) ) 0 . 1 1 ( 1 5) ) 0 . 2 ( 3} } 0 . 0 5 ( 1 4) ) 0 . 0 7 ( 1 7) ) 0 . 0 9 ( 1 9) ) 0 . 0 9 ( 1 9) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 2 ( 4) ) 0 . 2 ( 4) ) 0 . 0 6 ( 1 0) ) 0 . 1 ( 2) ) 0 . 1 0 ( 1 3) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 0 8 ( 1 8) ) 0 . 0 6 ( 1 6) ) 0 . 0 6 ( 1 5) ) 0 . 1 ( 2) ) 0 . 1 ( 3) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 1 ( 3) ) 0 . 3 ( 5) ) 0 . 0 6 ( 1 0) ) 0 . 1 ( 2) ) 0 . 0 9 ( 1 2) ) 0 . 2 ( 4) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 1 ( 2) ) 0 . 2 ( 3) ) 0 . 2 ( 5) ) 0 . 3 ( 5) )

98 8

Page 10: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure ofCBC„+,CK-type (n = even) f}'-triacylgfycerols

TABLEE 6.2 Selected geometric parameters (A, °)for fi'-CLC

CII — C l --C 2 --C 2 --C 3 --01a--Cla--Cla--C2a--C3a--C4a--C5a--C6a--C7a--C8a--C9a--Olb--Clb --Clb --C2b--

01a--01b--01b--C l --Olc--Cla--02a a 02a--Ola--Cla--C4a--C5a--C4a--C7a--C8a--C7a--ClOa a Clb --02b--02b--01b--Clb--

01a a C2 2 01b b C3 3 01c c

- C l a a - 0 2a a -C2a a ~C3a a -C4a a -C5a a -C6a a -C7a a -C8a a -C9a a -ClOa a - C l b b - 0 2b b -C2b b -C3b b

- C l --- C 2 --- C 2 ---C22 — - C 33 — - O l a --~ C l a--- C l a --- C l a --- C 2 a--- C 3 a--- C 4 a--- C 5 a--- C 6 a--- C 7 a---C8a~ ~ —— C9a - 0 1 b--- C l b --- C l b --- C l b --- C 2 b--

C2 2 -CI -CI -C3 3 C3 3 C2 2

-C I I -O l a a -C2a a -C2a a -C3a a -C2a a -C3a a -C6a a -C5a a -C6a a -C9a a —— C8a - C 2 2 - O l b b -C2b b -C2b b -C3b b

1 . 3 9 ( 1 4) ) 1 . 5 0 2 ( 1 2) ) 1 . 5 ( 3) ) 1 . 5 1 9 ( 1 1) ) 1 . 3 8 ( 7) ) 1 . 3 4 ( 7) ) 1 . 2 ( 2) ) 1 . 5 8 ( 5) ) 1 . 5 4 4 ( 1 0) ) 1 . 5 1 4 ( 9) ) 1 . 5 3 3 ( 1 1) ) 1 . 5 2 0 ( 1 0) ) 1 . 5 2 4 ( 1 1) ) 1 . 4 9 4 ( 9) ) 1 . 5 3 7 ( 1 1) ) 1 . 4 7 5 ( 8) ) 1 . 3 ( 3) ) 1 . 2 ( 2) ) 1 . 5 3 ( 4) ) 1 . 5 5 7 ( 9) )

1 0 7 ( 6) ) 113 (11) ) 104 (13) ) 1 1 0 . 3 ( 8) ) 1 0 7 ( 4) ) 1 1 8 ( 1 4) ) 1 2 1 ( 9) ) 1 2 1 ( 5) ) 1 1 7 ( 9) ) 1 0 6 ( 2) ) 1 0 4 . 5 ( 5) ) 1 1 1 . 3 ( 5) ) 1 1 2 . 4 ( 5) ) 1 1 0 . 7 ( 5) ) 1 1 0 . 4 ( 5) ) 1 0 9 . 5 ( 5) ) 1 0 7 . 3 ( 4) ) 1 1 7 ( 2 2) ) 1 2 5 ( 1 6) ) 1 2 1 ( 1 0) ) 1 1 5 ( 1 4) ) 1 1 1 ( 3) )

C3b--C4b--C5b--C6b--C7b--C8b--C9b--ClOb--Cllb --0 1 c--C l c --C l c --C2c--C3c--C4c--C5c--C6c--C7c--C8c--C9c--

C2b--C5b--C4b--C7b--C8b--C7b--C8b--C9b--C12b b C l c --0 2 c--0 2 c--O l c --C3c--C4c--C3c--C6c--C5c--C8c--C7c--ClOc--

-C4b b -C5b b -C6b b -C7b b -C8b b -C9b b -ClOb b - C II lb -C12b b -Clc c -02c c -C2c c -C3c c -C4c c -C5c c -C6c c -C7c c -C8c c -C9c c -ClOc c

- C 3 b--- C 4 b--- C 5 b--- C 6 b--- C 7 b--- C 8 b--- C 9 b---ClOb--—— Cll b - 0 1 c---Cl cc — - C l c --- C l c ---C2cc — -C3cc — -C4cc — -C5cc — - C 6 c---C7cc — — -C8cc — — - C 9 c--

-C4b b -C3b b -C6b b -C5b b -C6b b -C9b b -ClOb b - C l l b b —— ClOb -C3 3 -01c c -C2c c -C2c c Clc c C2c c C5c c

c c -C7c c C6c c C9c c

-C8c c

1 . 5 2 9 ( 1 2) ) 1 . 5 5 5 ( 1 0) ) 1 . 4 6 5 ( 1 1) ) 1 . 5 4 5 ( 9) ) 1 . 5 1 4 ( 1 1) ) 1 . 5 2 5 ( 9) ) 1 . 4 9 2 ( 1 1) ) 1 . 5 3 5 ( 9) ) 1 . 4 7 5 ( 1 0) ) 1 . 3 1 ( 1 1) ) 1 . 2 ( 2) ) 1 . 5 6 ( 6) ) 1 . 5 9 4 ( 9) ) 1 . 5 0 6 ( 1 1) ) 1 . 4 9 1 ( 9) ) 1 . 5 2 2 ( 1 1) ) 1 . 5 5 9 ( 9) ) 1 . 4 9 6 ( 1 0) ) 1 . 5 3 6 ( 9) ) 1 . 4 4 1 ( 1 0) )

1 0 5 . 4 ( 5) ) 1 1 0 . 3 ( 5) ) 1 1 0 . 5 ( 5) ) 1 0 9 . 2 ( 5) ) 1 1 2 . 4 ( 5) ) 1 1 0 . 6 ( 5) ) 1 1 0 . 0 ( 5) ) 1 0 8 . 8 ( 5) ) 1 0 6 . 3 ( 5) ) 1 1 6 ( 8) ) 121 (10) ) 1 2 1 ( 9) ) 1 1 7 ( 7) ) 1 0 9 ( 2) ) 1 0 5 . 4 ( 4) ) 1 1 0 . 4 ( 5) ) 1 1 0 . 5 ( 5) ) 1 1 1 . 2 ( 5) ) 1 0 9 . 7 ( 5) ) 1 0 8 . 2 ( 5) ) 1 0 5 . 9 ( 5) )

99 9

Page 11: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

Sincee the molecular structure fits the 2mF0-DFcak electron-density map very well, it can be concludedd that this crystal structure indeed expresses the measured intensity values (Fig. 6.4). Althoughh a rather high R value remains after refinement, no significant maxima were observed in thee AF synthesis. Furthermore, refinement in monoclinic space group TZ with two molecules in the asymmetricc unit did not lead to more accurate results. The ADP values of P'-CLC are somewhat largerr than ADPs for comparable structures, such as P-PPP (Table 2.4; Van Langevelde et ai, 1999a).. Especially at the end of the acyl chains the APDs are large, denoting a larger mobility of the chainn ends.

6.3.26.3.2 Structure of other series members from powder data

Thee cell parameters of P'-MPM measured at room temperature were refined to a = 76.21(4), b == 22.63(1) and c = 5.673(2) A resulting in a cell volume of 9784(8) A3. Like for p'-CLC the space groupp for P'-MPM is Ibal. With eight C^H^O,* molecules in the unit cell the calculated density is 1.0200 g cm"3. The FPD applied to 1.5 - 24.0° 26>of the synchrotron pattern resulted in an /?p of 7.9 %,, an R ̂ of 11.4 % and a %2 of 4.86. Rietveld refinement applied to a 2orange from 2.0 to 27.0° resultedd in a final fit between the calculated and experimental powder pattern with an Rp value of 5.77 %, an R ̂ of 7.4 %, an flBragg of 12.6 % and a x2 of 2.92 (Fig. 6.5). Without correction for preferredd orientation the Rp value was 7.3 %, the R ̂ 10.2 %, the RBngg value 15.5 % and the x2 was 4.1.. The refined preferred-orientation parameters are listed in Table 6.3. The refined crystal structuree of P'-MPM is shown in Fig. 6.6. Fractional atomic coordinates and geometric parameters aree listed in Tables 6.4 and 6.5, respectively. P'-MPM is crystallized in a chair conformation and the zigzagg planes of the acyl chains are orthogonal packed. The structure of P'-MPM is almost identical too the structure of P'-CLC as expressed by an overall r.m.s. value of 0.095.

1&&0&0Ó 1&&0&0Ó

FIGUREE 6.4 2mF0-DFeak electron-density map of p'-CLC contoured at a 2a level superposed with the final structurall model.

100 0

Page 12: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure ofC,C ofC,Cmm+£,-type+£,-type (n = even) fi'-triacylgfycerols

TABL EE 63 Refined preferred-orientation coefficients offi'-MPM

UP UP

20+ + 22+ + 40+ + 42+ + 444 + 60+ + 622 + 64+ + 66+ +

djp djp

- 0 . 0 54 4 0 . 1 25 5

- 0 . 4 05 5 - 0 . 5 52 2 - 0 . 1 42 2

0 . 5 93 3 - 0 . 0 60 0 - 0 . 2 85 5 - 0 . 0 41 1

Thee unit-cell parameters of P'-LML, P'-MPM and P'-PSP as refined from the high-resolution XRPDD data (A, = 0.445348(1) A) obtained at T = 250 K, show that LML and MPM at this temperaturee are crystallized in a monoclinic lattice and PSP in an orthorhombic lattice (Table 6.6). Sincee the b axis has been chosen as unique, the orthorhombic unit cells (CLC from single-crystal data,, MPM from powder data at room temperature and PSP from powder data at T = 250 K) were transformed.. For P'-LML the symmetry-related reflections (hkl and hk!) are significantly split resultingg in a fi of 90.4°, whereas for p'-MPM these reflections are just broadened resulting in a fi of 90.2°.. For p'-PSP broadening of these reflections is hardly noticeable and fi refined to 90.00(2)°. Thee XRPD patterns of all these TAGs show identical extinction conditions corresponding to the orthorhombicc space group Ic2a (or Icma). However, this space group is impossible for a monoclinic latticee and therefore the correct space group for the monoclinic ones is 72. In contrast to earlier work (Tablee 5.2 and Fig. 5.3; Van Langevelde et al, 1999b) a linear increase of the c axis and unit-cell volumee with increasing acyl-chain length is observed (Table 6.6 and Fig. 6.7).

Itt is remarkable that P'-MPM measured at room temperature was undoubtedly crystallized in ann orthorhombic lattice, whereas the jff parameter of p'-MPM measured at T = 250 K significantly deviatess from 90.0°. Furthermore, deviation from orthorhombic symmetry is decreasing with increasingg acyl-chain length (Table 6.6). Therefore, we conclude that the crystal structure of p'-PSP att T = 250 K is an isomorphic homologue of P'-CLC and orthorhombic p'-MPM. So p'-PSP may bee obtained by extrapolation from P'-MPM as is described for the P-C,C,,C„-type (n = even) TAGs seriess (Van Langevelde et al, 1999a). Since monoclinic p*-LML and p'-MPM differ from the series byy a small deviation in the /7 parameter only, also their structures seem to be similar to P'-CLC and orthorhombicc p'-MPM. Possibly, the chain-end mobility, as observed at the crystal structure of p'-CLC,, is less for the lower-temperature measurements and the positions of the chain-end atoms deviatee slightly from their corresponding atomic positions in orthorhombic symmetry. This small deviationn may force the symmetry to be monoclinic. Since this deviation becomes smaller with increasingg chain length, it is assumed that the orthogonal-lateral chain packing of the TAG moleculess is more stable at longer chain lengths, preventing considerable chain-end mobility.

101 1

Page 13: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

TABLEE 6.4 Fractional atomic coordinates offi'-MPM after Rietveld refinement

Celll parameters of p'-MPM: a = 76.21(4), b = 22.63(1), c = 5.673(2) A. The volume is 9784(8) A3 and the spacee group is Iba2, with Z - 8 resulting in a density of 1.02 g cm'\

Atom m £/*,(A2) )

Cl l C2 2 C3 3 Ola a Cla a 02a a C2a a C3a a C4a a C5a a C6a a C7a a C8a a C9a a ClOa a Cll a a C12a a C13a a C14a a Olb b Clb b 02b b C2b b C3b b C4b b C5b b C6b b C7b b C8b b C9b b ClOb b Cll b b C12b b C13b b C14b b C15b b C16b b Olc c Clc c 02c c C2c c C3c c C4c c C5c c C6c c C7c c C8c c C9c c ClOc c Cll c c C12c c C13c c C14c c

0.242 2 0.259 9 0.264 4 0.229 9 0.213 3 0.208 8 0.199 9 0.182 2 0.172 2 0.153 3 0.142 2 0.123 3 0.113 3 0.095 5 0.083 3 0.065 5 0.053 3 0.035 5 0.023 3 0.258 8 0.267 7 0.273 3 0.270 0 0.280 0 0.298 8 0.310 0 0.328 8 0.339 9 0.358 8 0.368 8 0.386 6 0.397 7 0.416 6 0.426 6 0.444 4 0.455 5 0.473 3 0.281 1 0.289 9 0.281 1 0.305 5 0.316 6 0.333 3 0.343 3 0.361 1 0.372 2 0.388 8 0.399 9 0.418 8 0.429 9 0.448 8 0.459 9 0.478 8

0.074 4 0.100 0 0.081 1 0.094 4 0.081 1 0.055 5 0.111 1 0.071 1 0.090 0 0.073 3 0.094 4 0.071 1 0.095 5 0.066 6 0.096 6 0.067 7 0.096 6 0.067 7 0.097 7 0.167 7 0.197 7 0.178 8 0.262 2 0.269 9 0.251 1 0.268 8 0.245 5 0.267 7 0.244 4 0.267 7 0.241 1 0.267 7 0.244 4 0.267 7 0.239 9 0.261 1 0.231 1 0.095 5 0.077 7 0.041 1 0.110 0 0.070 0 0.099 9 0.071 1 0.096 6 0.070 0 0.104 4 0.072 2 0.095 5 0.068 8 0.090 0 0.064 4 0.088 8

-0 .839 9 -0 .772 2 -0 .528 8 -0 .681 1 -0 .713 3 -0 .896 6 -0 .550 0 -0 .558 8 -0 .348 8 -0 .366 6 -0 .157 7 -0 .174 4 0.025 5 0.023 3 0.206 6 0.201 1 0.381 1 0.373 3 0.555 5

-0 .757 7 -0 .923 3 -1 .103 3 -0 .871 1 -0 .633 3 -0 .679 9 -0 .468 8 -0 .496 6 -0 .294 4 -0 .306 6 -0 .101 1 -0 .109 9 0.094 4 0.080 0 0.293 3 0.291 1 0.505 5 0.505 5

-0 .498 8 -0 .303 3 -0 .174 4 -0 .222 2 -0 .039 9 -0 .009 9 0.185 5 0.200 0 0.410 0 0.443 3 0.629 9 0.615 5 0.813 3 0.790 0 0.987 7 0.960 0

0.018 8 0.018 8 0.018 8 0.011 1 0.018 8 0.011 1 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.011 1 0.018 8 0.011 1 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.011 1 0.018 8 0.011 1 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8 0.018 8

102 2

Page 14: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure of CmCn+jCm-type (n = even) fi'-triacylglycerols

TABLEE 6.5 Selected geometric parameters (A3, °)for fi'-MPM

CI—Ola a C l—— C2 C22 — Olb C22 — C3 C33 —Olc Olaa —Cla Claa — 02a Claa —C2a C2aa — C3a C3aa —C4a C4aa —C5a C5aa — C6a C6aa — C7a C7aa —C8a C8aa —C9a C9aa —ClOa ClOaa —Cl l a Cll aa —C12a C12aa —C13a C13aa —C14a Olbb —Clb Clbb —02b Clbb —C2b C2bb —C3b C3bb —C4b C4bb —C5b Olaa —CI — Olbb — C2 — Olbb —C2 —

C2 2 CI I C3 3

CI—C22 —C3 Olcc — C3 — Claa —Ola — 02aa — C l a-02aa — C l a-Olaa —Cla — Claa — C2a — C4aa —C3a — C5aa —C4a — C4aa — C5a — C7aa — C6a — C8aa — C7a — C7aa — C8a — ClOaa — C9a-Cll la— ClOa ClOaa —Cl l a C13aa —C12a C14aa —C13a Clbb — O l b -02bb — C l b-02bb — C l b-Olbb —Clb -Clbb — C 2 b-C2bb — C 3 b-C5bb — C 4 b-

C2 2 -CI I -Ola a -C2a a -C2a a C3a a C2a a C3a a C6a a C5a a C6a a C9a a

-C8a a —— C9a —— CI 2a —— Clla —— CI 2a -C2 2 -Olb b -C2b b -C2b b -C3b b -C4b b -C3b b

1.36 6 1.50 0 1.51 1 1.51 1 1.36 6 1.33 3 1.23 3 1.57 7 1.53 3 1.50 0 1.52 2 1.51 1 1.51 1 1.48 8 1.52 2 1.54 4 1.53 3 1.53 3 1.53 3 1.53 3 1.33 3 1.20 0 1.52 2 1.54 4 1.52 2 1.54 4 109 9 113 3 104 4 111 1 108 8 120 0 119 9 121 1 118 8 106 6 104 4 113 3 113 3 111 1 110 0 109 9 110 0 110 0 110 0 110 0 109 9 117 7 127 7 117 7 116 6 110 0 105 5 110 0

C5bb —C6b C6bb —C7b C7bb —C8b C8bb —C9b C9bb —ClOb ClObb —Cl l b Cll bb —C12b C12bb — C13b C13bb —C14b C14bb —C15b C15bb —C16b Olc—Clc c Clcc —02c Clcc —C2c C2cc — C3c C3cc —C4c C4cc —C5c C5cc — C6c C6cc —C7c C7cc — C8c C8cc — C9c C9cc —ClOc ClOcc —Cl l c Cll cc —C12c C12c—— C13c C13c—— C14c C4bb — C5b — C7bb —C6b — C8bb — C7b — C7bb — C8b — C8bb — C9b — C9bb —ClOb-C12bb — Cl lb Cll bb —C12b C14bb —C13b C15bb —C14b C16bb —C15b Clcc —Olc— 02cc — Clc — 02cc —Clc— Olcc —Clc— C3cc — C2c — C4cc — C3c — C3cc — C4c — C6cc — C5c — C5cc — C6c — C8cc — C7c — C7cc — C8c — ClOc—— C9c-C9cc —ClOc-C12cc —Cl l c Cll cc —C12c C14cc —C13c

C6b b C5b b C6b b C9b b ClOb b

- C l l b b —— ClOb —— CI 3b —— C12b —— C13b —— C14b C3 3 Olc c C2c c C2c c Clc c C2c c C5c c C4c c C7c c C6c c C9c c -C8c c -C l l c c —— ClOc —— C13c —— C12c

1.45 5 1.53 3 1.50 0 1.51 1 1.48 8 1.52 2 1.54 4 1.53 3 1.53 3 1.53 3 1.53 3 1.30 0 1.23 3 1.54 4 1.58 8 1.49 9 1.48 8 1.51 1 1.54 4 1.48 8 1.53 3 1.54 4 1.53 3 1.53 3 1.53 3 1.53 3 111 1 109 9 113 3 111 1 110 0 108 8 109 9 111 1 109 9 109 9 109 9 116 6 122 2 121 1 116 6 109 9 105 5 112 2 112 2 111 1 109 9 107 7 109 9 111 1 109 9 110 0 109 9

103 3

Page 15: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

Intensityy (a.u.)

(V) )

Cfc> >

U\ U\

O O

II L L

L L

FIGUREE 6.5 Synchrotron powder-diffraction pattern (X = 0.650515(1) A) of orthorhombic P'-MPM (upper), thee pattern as calculated from the refined crystal structure (middle) and the difference between these patternss (lower).

104 4

Page 16: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure ofC„C„+,C„-type (n = even) fi'-triacylglycerols

J^HWWHHK K FIGUREE 6.6 PLATON (Spek, 2000) representation of the crystal structure of P'-MPM.

TABL EE 6.6 Refined cell parameters offi'-C„C„ +2C„-type TAGs

Inn order to compare these cell parameters easier, the unit cells have been transformed to an unique

bb axis.

aa (A) b(k) b(k) c(A) )

Off O

PO PO r(°) ) FF (A3) Spacee group Chemical l formula a Z Z A* fc(gcm-3) )

** data collection \*V /

P'-CLC(0) )

22.783(2) ) 5.6945(6) ) 57.368(6) ) 90.0 0 90.0 0 90.0 0 7443(1) ) Icla Icla CCiiii HH6666006 6

8 8 1.04 4 295 5

P'-LML(6) )

22.650(2) ) 5.6513(4) ) 67.183(6) ) 90.0 0 90.391(7) ) 90.0 0 8599.3(9) ) 72 2

GUHTSOS S

8 8 1.03 3 250 0

P,-MPM(4) )

22.63(1) ) 5.673(2) ) 76.21(4) ) 90.0 0 90.0 0 90.0 0 9784(8) ) Icla Icla

*-47^9o'-'6 6

8 8 1.02 2 295 5

P'-MPIVr"" "

22.660(2) ) 5.6261(7) ) 76.217(8) ) 90.0 0 90.18(1) ) 90.0 0 9717(1) ) 72 2

^W^W^t ^W^W^t

8 8 1.03 3 250 0

p..pSpW W

22.829(4) ) 5.5946(8) ) 85.48(2) ) 90.0 0 90.00(2) ) 90.0 0 10917(3) ) 7c2a a

^53"l02^-'6 6

8 8 1.02 2 250 0

(a)) Determined from single-crystal data; (b) determined from high-resolution powder data.

Thee characteristic powder-diffraction pattern of P'-TAGs originates from the orthogonal laterall chain packing denoted by Ox (Abrahamsson et ah, 1978). Since many scatterers are at the latticee planes which are (nearly) parallel to the acyl chains, this results in strong reflections in the X-rayy powder diagram (Fig. 6.8 and Table 6.7). The lattice-plane distances for the lattice planes (nearly)) parallel to the acyl chains show that reflections with identical indices of different series memberss do not have exactly the same rf-spacing values (Table 6.7). As a result, the characteristic regionn of the XRPD pattern and the lateral chain packing is slightly different for each series member off this P'-stable TAG series.

105 5

Page 17: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

5 5 to o

1 1

90--

80--

70--

60--

50--

400 -

CLC C LML L MPM M

Trigfyceride e series s

PSP P

-- 13000

-- 12000

-- 11000 —

-- 10000 |

.90000 °

-- 8000

-- 7000

FIGUREE 6.7 The length of the c axis (black squares) and the unit-cell volume (open circles) of P'-CLC, P' LML ,, P'-MPM and P'-PSP (Table 6.6)

6.3.36.3.3 (Dis)similarities between P'-structures and models

Thee unit-cell parameters and space group of P'-CLC and P'-MPM correspond well to the ones determinedd from Guinier data previously (Table 5.2; Van Langevelde et al, 1999b). However, in contrastt with their P'-CLC packing model, having intramolecular parallel acyl-chain zigzag planes, P'-CLCC adopts an 0 lateral chain packing with intramolecular orthogonal zigzag planes. Since at thatt moment straight asymmetric tuning-fork conformations were available only, this type of TAG moleculess was used for their packing model. As a result, no til t of the acyl chains with respect to the methyl-endd group plane has been found. In retrospect, the assumption that the P'-C„C„+2C„-type (n = even)) TAG molecules are in a straight asymmetric tuning-fork conformation was incorrect though it wass already recognised that with TAG molecules in a chair conformation the relative phase stability off the P' polymorph can be explained.

TABLEE 6.7 Characteristic d spacings (A) for fl'-C„C„ +2Cn-type (n = even) TAG series

P'-CLC"" " P'-LMLW W

P'-MPM"" " P'-MPM"" " P'-PSP"" "

d(id(i 1 4)

4.342 2

4.373 3

4.411 1

4.392 2

4.410 0

d(3d(3 1 4)

4.342 2

4.364 4

4.411 1

4.389 9

4.410 0

rf(3rf(3 1 6)

4.113 3

4.201 1

4.270 0

4.254 4

4.298 8

d(3d(3 1 6)

4.113 3

4.189 9

4.270 0

4.249 9

4.298 8

d(3d(3 1 8)

3.845 5

3.990 0

4.094 4

4.081 1

4.153 3

d(id(i 1 8)

3.845 5

3.976 6

4.094 4

4.075 5

4.153 3

d(6d(6 0 0)

3.797 7

3.775 5

3.772 2

3.777 7

3.805 5

(a)) Orthorhombic lattice; (b) monoclinic lattice. See Table 6.6 for unit-cell parameters

106 6

Page 18: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure ofC„C„.,C„-type (n = even) fi'-triacylglycerols

} } d(3d(3 1 6)

} } d(3d(3 1 6)

d(6d(6 0 0)

FIGUREE 6.8 Crystal structure of P'-CLC (transformed to a unique b axis) with the acyl chains perpendicular too the plane of the paper. The lattice planes responsible for the characteristic d spacings are indicated (Tabless 6.6 and 6.7).

Thee crystal-structure model by Van de Streek et al. (1999) accommodates most of the characteristicc elements of the P'-CLC crystal structure. Their TAG molecules are bent at the glyceroll moiety, adopt an 0L lateral chain packing with intramolecular orthogonal zigzag planes and aree in a chair conformation. Consequently, their calculated X-ray powder diffractogram is in good agreementt with the experimental one. However, some deviations between their model and the experimentall crystal structure can be observed. The conformation of their glycerol moiety is not completelyy correct, which results in a significant difference (~4 A) between the c axis of their model andd the experimental one. Furthermore, the orientations of the acyl-chain zigzag planes with respect too the axes through the chains differ 90° with the experimental ones. Since this orientation differs 90°° for all three acyl chains, the overall 0L chain packing of their model is still the same as the chainn packing in the experimental crystal structure, but the carbonyl moiety of the second chain pointss just in the opposite direction.

Thee crystal structures of the known p and P' polymorphs differ in three major aspects: i) the moleculess of the p polymorph are straight whereas the molecules of the P' polymorph are bent at thee glycerol moiety, ii) the p polymorph has intramolecular parallel zigzag planes whereas the P' polymorphh has intramolecular orthogonal zigzag planes, and Hi) the p polymorph is crystallized in ann asymmetric tuning-fork conformation whereas the P' polymorph adopts a chair conformation. Alll these differences affect the conformation of the glycerol moiety (Fig. 6.9). The typical conformationn of the glycerol moiety in the p polymorph is a consequence of a straight structure

107 7

Page 19: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

havingg intramolecular parallel zigzag planes and an asymmetric tuning-fork conformation. Similarly,, the typical conformation of the glycerol moiety in the P' polymorph is a consequence of a bentt structure having intramolecular orthogonal zigzag planes and a chair conformation. Since the relativee stability of the polymorphic phases is determined by differences in chain length and saturationn (De Jong, 1980), the crystallizing polymorph is not determined by the typical glycerol moietyy of the (5 and P' polymorphs.

Fromm the crystal structures of these P' and p polymorphs the relative stability of the P' polymorphh for the C„C„+2C„-type (n = even) TAG series can be explained. Since the crystal structure off these series members are in a chair conformation a solid-state transformation to a p polymorph, typicallyy crystallized in a tuning-fork conformation, is impossible. Therefore, it is expected that the crystall structure of a P' polymorph of p-stable TAGs wil l differ from the structures reported here.

Thee investigations were supported by the Netherlands Foundation for Chemical Research (NWO/CW)) with financial aid from the Netherlands Technology Foundation (STW). The authors thankk Unilever Research Laboratory (Vlaardingen, The Netherlands) for providing CLC crystals. Thee authors also thank the ESRF (Grenoble, France) for the opportunity to perform the synchrotron experiments,, and Prof. Dr. A. Kvick and Dr. A. N. Fitch for their invaluable help at ID 11 (single-crystall diffraction measurements) and BM16 (high-resolution powder diffraction measurements), respectively.. Bruker AXS is kindly thanked for making available their single-crystal software packages.. Jacco van de Streek is thanked for providing the coordinates of his P'-CLC structure model. .

FIGUREE 6.9 PLATON (Spek, 2000) representation of the glycerol moiety of the crystal structure of (a) p'-CLCC and (b) P-PPP (Table 2.4; Van Langevelde et ai, 1999a).

108 8

Page 20: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

StructureStructure qfCMC^jCK-type (n = even) fi'-triacylgfycerols

References s Abrahamsson,, S., Dahlen, B., Löfgren, H. and Pascher, I. (1978). Lateral packing of hydrocarbon chains.

Progr.Progr. Chem. Fats Other Lipids 16, 125-143.

Ahtee,, M., Nurmela, M., Suortti, P. and JSrvinen, M. (1989). Correction for preferred orientation in Rietveld refinement.. J. Appl. Cryst. 22,261-268.

Arishima,, T. and Sato, K. (1989). Polymorphism of POP and SOS. Dl. Solvent crystallization of p2 and p, polymorphs.. J. Am. OH Chem. Soc. 66,1614-1617.

Birker,, P. J. M. W. L., De Jong, S., Roijers, E. C. and Van Soest, T. C. (1991). Structural investigations of p' triacylglycerols:: an X-ray diffraction and microscopic study of twinned p' crystals. J. Am. Oil Chem. Soc.Soc. 68,895-906.

Boistelle,, R., Simon, B. and Pèpe, G. (1976). Polytypic structures of n-C^ln (octacosane) and n-C^i14

(hcxatriacontane).. Acta Cryst. B32,1240-1243.

Brukerr AXS Inc. (1996). SAINT. Version 4.0. Bruker AXS Inc., Madison, Wisconsin, USA.

Brukerr AXS Inc. (1998). SMART. Version 5.0. Bruker AXS Inc., Madison, Wisconsin, USA.

Chernyshev,, V. V. and Schenk, H. (1998). A grid search procedure of positioning a known molecule in an unknownn crystal structure with the use of powder diffraction data. Z Kristallogr. 213,1-3.

Dee Jong, S. (1980). Triacylglycerol crystal structures and fatty acid conformations - A theoretical approach. PhDPhD thesis. University of Utrecht, The Netherlands.

Dee Jong, S. and Van Soest, T. C. (1978). Crystal structures and melting points of saturated triglycerides in thee p-2 phase. Acta Cryst. B34,1570-1583.

Doyne,, T. H. and Gordon, J. T. (1968). The crystal structure of a diacid triglyceride. J. Am. Oil Chem. Soc. 45,333-334. .

Driessen,, R. A. J., Loopstra, B. O., De Bruijn, D. P., Kuipers, H. P. C. E. and Schenk, H. (1988). Crystallographicc modelling. J. Comput.-AidedMol. Des. 2,225-233.

Fitch,, A. N. (1996). The high resolution powder diffraction beamline at ESRF. Materials Science Forum, Vol.. 228, edited by R. J. Cernik, R. Delhez and E. J. Mittemeijcr, pp. 219-222. Aedermannsdorf: Transs Tech Publications.

Gibon,, V., Blanpain, P., Norberg, B. and Durant, F. (1984). New data about molecular structure of P-trilaurin.. Bull. Soc. Chim. Belg. 93,27-34.

Goto,, M., Kodali, D. R., Small, D. M., Honda, K., Kozawa, K. and Uchida.T. (1992). Single crystal structuree of a mixed-chain triacylglycerol: l,2-dipalmitoyl-3-acetyl-5«-glycerol. Proc. Nat. Acad. Sci. USAUSA 89,8083-8086.

Hagemann,, J. W. (1988). Thermal behavior and polymorphism of acylglycerides, in Crystallization and polymorphismpolymorphism of fats and fatty acids edited by N. Garti and K. Sato. (Marcel Dekker Inc., New York andd Basel) 9-96.

Hall,, S. R., King, G. S. D. and Stewart, J. M. (1995). Xtal. Version 3.5. Universities of Western Australia, Australia,, Geneva, Switzerland, and Maryland, USA.

Hemqvist,, L. (1988). On the crystal structure of the P',-form of triglycerides and the mechanism behind the P',-»pp transition of fats. Fat Sci Technol. 90,451-454.

109 9

Page 21: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt

ChapterChapter 6

Hernqvist,, L. and Larsson, K. (1982). On the crystal structure of the P'-form of triglycerides and structural changess at the phase transitions LIQ—wx—»P'—>p. Fette Seifen Anstrichm. 84,349-354.

Holland,, T. J. B. and Redfern, S. A. T. (1997). Unit cell refinement from powder diffraction data: The use of regressionn diagnostics. Mineral Mag. 61,65-77.

JSrvinen,, M. (1993). Application of symmetrized harmonics expansion to correction of the preferred orientationn effect. J. Appl. Cryst. 26, 525-531.

Jensen,, L. H. and Mabis, A. J. (1963). Crystal structure of P-tricaprin. Nature 197,681-682.

Jensen,, L. H. and Mabis, A. J. (1966). Refinement of the structure of P-tricaprin. Acta Cryst. 21,770-781.

Jones,, T. A., Zou, J. Y., Cowan, S. W. and Kjeldgaard, M. (1991). Improved methods for building protein modelss in electron density maps and the location of errors in these models. Acta Cryst. A47,110-119.

Kvick,, A. and Wulff, M. (1992). The materials science and Laue diffraction beamlines at the European Synchrotronn Radiation Facility. Rev. Sci. Instrum. 63,1073-1076.

Larsson,, K. (1965a). The crystal structure of the P-form of trilaurin. ArkivKemi 23,1-15.

Larsson,, K. (1965b). Solid state behaviour of glycerides. Arkiv Kemi 23, 35-56.

Miller,, R., Gallo, S. M., Khalak, H. G. and Weeks, C. M. (1994). SnB: Crystal structure determination via Shake-and-Bake.. J. Appl. Cryst. 27,613-621.

Molecularr Simulation Inc. (1995). Cerius2. Release 2.0. Biosym/Molecular Simulations Inc., San Diego, USA. .

Murshudov,, G. N., Vagin, A. A. and Dodson, E. J. (1997). Refinement of macromolecular structures by the maximum-likelihoodd method. Acta Cryst. D53,240-255.

Sato,, K. (1996). Polymorphism of pure triacylglycerols and natural fats. Adv. Appl. Lipid Res. 2,213-268.

Simpson,, T. D. and Hagemann, J. W. (1982). Evidence of two P' phases in tristearin. J. Am. Oil Chem. Soc. 59,, 169-171.

Spek,, A. L. (2000). PLATON, a multipurpose crystallographic tool. Utrecht University, Utrecht, The Netherlands. .

Thee CCP4 suite: Programs for protein crystallography. (1994). Acta Cryst. D50,760-763.

Toraya,, H. (1986). Whole-powder-pattern fitting without reference to a structural model: application to X-rayy powder diffractometer data. J. Appl. Cryst. 19, 440-447.

Vann de Streek, J., Verwer, P., De Gelder, R. and Hollander, F. (1999). Structural analogy between P' triacylglycerolss and n-alkanes. Toward the crystal structure of p'-2 p.p+2.p triacylglycerols. J. Am. OilOil Chem. Soc. 76,1333-1341.

Vann Langevelde, A., Van Malssen, K., Hollander, F., Peschar, R. and Schenk, H. (1999a). Structure of mono-acidd even-numbered p-triacylglycerols. Acta Cryst. B55,114-122.

Vann Langevelde, A., Van Malssen, K., Sonneveld, E., Peschar, R. and Schenk, H. (1999b). Crystal packing off a homologous series p'-stable triacylglycerols. J. Am. Oil Chem. Soc. 76, 603-609.

Zlokazov,, V. B. and Chernyshev, V. V. (1992). MRIA - A program for a full profile analysis of powder multiphasee neutron-diffraction time-of-flight (direct and fourier) spectra. J. Appl. Cryst. 25,447-451.

110 0

Page 22: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt
Page 23: UvA-DARE (Digital Academic Repository) Triacylglycerol ...Chapterr 6 Structuree of CnCn+2Cn-type (#ii = even) p'-triacylglycerols accepteddforpublicatio ni n Acta Cryst. B Abstractt