Our scientific research is organized around two themes (A and B):

A)    Development of new methodology to determine crystal structures from diffraction data and the actual application of these methods to experimental diffraction data.
Current research projects focus on the crystal-structure determination from powder-diffraction data, in particular larger organic and organo-metallic compounds.
           
B)    The static and dynamic aspects of (partly) crystalline material during melting, crystallization, phase transitions and other structural changes in relation to the (changes in ) macroscopic behavior of the  material. Current research projects involve the melting, crystallization and structural properties of natural fats (cocoa butter, palm kernel oil) and their constituent triglycerides. (Time-resolved) X-ray powder diffraction is an important tool in this research.


Current research projects

Crystal-structure determination using powder-diffraction data


X-ray diffraction is one of the most important and powerful techniques to characterize solid materials and to determine their crystal structure at the atomic level. Although single-crystal X-ray diffraction is commonly used for this latter purpose, many materials crystallize only as conglomerate of very small crystallites and, for precisely this reason, they are employed in such a polycrystalline (powder) form, for example pharmaceuticals (optimal solubility properties), catalysts (increased surface area), pigments (increase dispersibility), triglycerides (fats and oils). 
   Crystal-structure determination from powder-diffraction data is one of the research specialisms of the Laboratory for Crystallography (UvA) and encompasses both the development of methodological improvements as well as the actual crystal-structure determinations on the basis of experimental powder-diffraction data (see projects below and Publications).
   

• Development of low-resolution structural models in ab initio structure-determination techniques

Netherlands Foundation for Scientific Research (NWO) project 332-023
Start 01-08-2001 ; End 01-08-2005
Personnel: V. Brodski M Sc

• Structure determination of Fe(II) spin-crossover complexes from powder-diffraction data 

University of Amsterdam  project
Start  1999  ; End  2003
Personnel: Dr. E. Dova (PhD at 10-09-2003)

• Melting, crystallization and structural properties of natural fats and their constituent triglycerides as they occur in food products (e.g. chocolate, milk etc.)

Background:


Many consumer products, such as food (e.g. confectionary products, chocolate, margarines), personal care products (ointments, crèmes) and medicines, contain fats and oils.  Fats and oils consist mainly of triglycerides (also called triacylglycerols). They supply firmness to the product (in case of fats), they carry flavour or other active components and, last but not least, they provide nutritional, sensory and physiological values to the product. 
    Triglycerides are glycerol esters of fatty acids.The long hydrocarbon chains of the latter can pack in different ways, leading to different crystalline phases (polymorphs) as function of time and temperature. In order of increasing stability, four main phase classes may be observed, an unstable γ phase, an unstable α phase, a β’ (beta-prime) phase, characterized by small (1 μm) needle-shaped crystals, and a β phase that grows into much larger (20 μm) platelet-like crystals.  The phase sequence γ => α  => β’  => β is irreversible although for some triglycerides and fats (e.g. milkfat) the β phase is never observed. Because of the difference in crystal morphology between the β’ and β phases, and other processes that may take place during the phase transitions (Ostwald ripening, phase segregation), phase control is essential in industry. For example, the presence of (larger) β crystals in margarine gives the product a sandy mouth feeling (sandiness).
    Cocoa butter, a main ingredient used in the confectionery industry, is a complex mixture of about thirty different types of triglycerides while, in addition, also small amounts of di- and monoacylglycerols and some other minor components are present. However, compared to other natural fats and oils (e.g. butterfat, palm oil), its composition, melt- and crystallization behaviour is largely dominated by three triglycerides:  nearly three quarters of any cocoa butter consists of the three mono-cis-unsaturated triglycerides: SOS (1,3-distearoyl-2-oleoylglycerol; C₅₇H₁₀₈O₆; ~ 25%), POS (2-oleoyl-1-palmitoyl-3-stearoylglycerol; C₅₅H₁₀₄O₆; ~ 35%) and POP (1,3-dipalmitoyl-2-oleoylglycerol; C₅₃H₁₀₀O₆; ~ 15%). This unique composition confers the manufactured chocolate product not only taste and nutritional value but it also determines valuable physical characteristics such as brittleness (the ‘snap’ when chocolate breaks) and a fast and complete melting at body temperature that provides a cooling effect (‘mouth feeling’). In chocolate, the β phase is responsible for these effects and the β’ phase is not wanted because a β’ => β phase transition after moulding the chocolate product leads to a poorer quality product. The β phase actually consists of two sub phases, the so called β (V) and β(VI). The occurrence of a grayish layer on chocolate (‘fat bloom’), for example because it has been stored too long storage at a too high temperature, is commonly related to the phase transition β(V) => β(VI) in the cocoa butter. The γ, the α and the β’ phases can be obtained by cooling a completely molten mass of chocolate (or cocoa butter). The β phases, however, can be obtained only via heating the β’ phase or from cooling a molten mass that still contains liquid β-crystalline seeds, so in effect a recrystallization of the β phase (see publications below)  
    In the Laboratory for Crystallography (UvA), in a series of projects (see below), the crystallization properties of chocolate, cocoa butter and other lipid mixtures are being investigated.  Also crystal structure determination using powder diffraction data plays an important role in this research. Publications concerning our fat research (1999 - ). See ESRF-higlights-2004



Current and previous projects in fat research

• Effect of additives on the phase behaviour of lipids.

Netherlands Technology Foundation (STW) project 349-5616
Start 01-05-2001 ; End 01-05-2005
Personnel: Dr. M.M. Pop
Users: Unilever Research (UK) and Loders Croklaan/IOI(Wormerveer)

• Phase behaviour of fats in dynamic systems, in relation to the atomic structure of triacylglycerols

Netherlands Technology Foundation (STW) project 349-5405
Start 01-04-2001 ; End 01-04-2005
Personnel: Dr. D.J.A. De Ridder and Ing. J.B. van Mechelen (Ph-D student)
Users: ADM Cocoa ( Koog a/d Zaan, NL), Nestlé Nederland (Nunspeet, NL), Gerkens Cacao BV( Wormerveer, NL) and Barry Callebaut Belgium BV (Wieze, B) 

See ESRF-highlights-2004

• The relation between the threedimensional structure of fat crystals and the polymorphic phase behaviour of fats. 

Netherlands Technology Foundation (STW) project ACH 3794
Start 01-04-1996 ; End 01-11-2000.
Personnel:  Dr. K.F. van Malssen
                   Dr. A. van Langevelde (PhD on 19-10-2000)
Users:  ADM Cocoa ( Koog a/d Zaan, NL), Nestlé Nederland (Nunspeet, NL), Gerkens Cacao BV( Wormerveer, NL), Barry Callebaut Nederland BV (Bussum, NL) and Koninklijke de Ruijter/Heinz Co (Baarn, NL)

See ESRF-highlights-2004

Other projects

• Scientific analysis of historical paint

University of Amsterdam project
Start 1999   ; End 2003
Personnel:  Dr J. Dik (PhD on 04-03-2003)

• Time-resolved X-ray diffraction using a twodimensional detector

Netherlands Technology Foundation (STW) project 349- 3799
Start april 1996  End may 2001
Personnel : Dr. C. Kiers, Dr. M.M. Pop
Users: Enraf-Nonius (now part of Bruker-Nonius), Hoogovens (now part of Corus)

Goal: Adaptation of the hard- and software of the two-dimensional area-detector FAST to enable the recording of a complete two-dimensional diffraction pattern in 40 ms.

Contacts.

René Peschar, J/K-1.43
tel +31 (0) 20 - 525 7040 E-mail René Peschar

Kees Goubitz, J/K-1.45
tel  +31 (0) 20 - 525 7038 E-mail Kees Goubitz

Rob Helmholdt, J/K-1.47
tel +31 (0) 20 - 525 7033 E-mail Rob Helmholdt