napff was prepared as described elsewhere.6 ,  17 all other chemicals were purchased from sigma  aldrich and used as received . to prepare a solution of napff , solid napff was weighed into a 14  ml vial and an appropriate amount of d2o added , followed by standardised naod ( ca . the mixture was then stirred for 24  h to yield a clear , slightly viscous solution with a pd of between 12.1 and 12.6 before being transferred in aliquots ( 560  l ) to nmr tubes ( 5  mm ) by pipette . the samples were then aged for between 6 and 8 days at ( 2953 )  k before analysis or gel preparation . analysis by h  nmr and polarised optical microscopy suggested that the solutions reached a steady state after 5 days ( figures  s26 and s27 in the supporting information ) . to prepare cacl2-triggered gels , cacl2 solution ( 0.75  m , 40  l ) was added to the top of the napff solution in the nmr tube using a long needle . the sample was then immediately transferred to the nmr spectrometer held at ( 2980.5 )  k , or , for gels prepared away from the magnetic field , a water bath held at ( 2980.3 )  k. after 60  h , the samples prepared in the magnetic field were removed from the spectrometer and placed in the water bath . all samples were left to stand for at least 7 days following cacl2 addition prior to analysis . the height of the 560  l solution in the nmr tube ( 41  mm ) is sufficient so that , when first placed in the spectrometer , the sample adjacent to the radiofrequency coils of the spectrometer is completely free from the added cacl2 , which slowly diffuses down the tube into the nmr - active region . glucono--lactone ( gdl)-triggered gels were prepared as for cacl2-triggered gels , but with solid gdl ( 34  mg ) added to the top of the napff solution using a pasteur pipette . where noted , the napff solutions were doped with dioxane - d8 ( 0.05  vol  % , 6  mm ) to act as an additional probe for deuterium nmr .
the magnetic - field - induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator , and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of cacl2 or upon a reduction in solution ph is reported . 
 utilising the switchable nature of the magnetic field coupled with the slow diffusion of cacl2 , it is possible to precisely control the extent of anisotropy across a hydrogel , something that is generally very difficult to do using alternative methods . 
 the approach is readily extended to other compounds that form viscous solutions at high ph . 
 it is expected that this work will greatly expand the utility of such low - molecular - weight gelators ( lmwg ) in areas where alignment is key .