| 1. |
- Graf, Gesche, et al.
(författare)
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Determination of Sorption Isotherm and Rheological Properties of Lysozyme Using a High-Resolution Humidity Scanning QCM-D Technique
- 2013
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 117:34, s. 10017-10026
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Tidskriftsartikel (refereegranskat)abstract
- The high-resolution humidity scanning QCM-D technique enables investigation of hydration of soft matter films using a quartz crystal microbalance with dissipation monitoring (QCM-D) equipped with a humidity module. Based on a continuous increase of relative humidity, properties of soft matter films can be investigated depending on the water content of the surrounding atmosphere. Determination of complete water sorption isotherms is possible via analysis of the overtone dependence of the resonance frequencies. Rheological properties are monitored via measurement of the dissipation. The glass transition can be identified from the change of viscoelastic properties of the film reflected in changes of the dissipation. A high-resolution water sorption isotherm of lysozyme was measured and compared with results from water sorption calorimetry. Analysis of the rheological behavior during hydration of lysozyme films revealed the presence of two separate sharp transitions at the water activities 0.67 and 0.91, which are connected to the glass transition. In previous works, only the existence of a broad glass transition has been reported so far. Combining the QCM-D data with Raman scattering data presented earlier, a new mechanism of isothermal glass transition in lysozyme is proposed.
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| 2. |
- Meister, Annette, et al.
(författare)
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Temperature-dependent self-assembly and mixing behavior of symmetrical single-chain bolaamphiphiles
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:12, s. 6238-46
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Tidskriftsartikel (refereegranskat)abstract
- The temp.-dependent self-assembly and the mixing behavior of sym. single-chain bolaamphiphiles with different polymethylene chain lengths and different headgroup structures were investigated in water by differential scanning calorimetry (DSC), cryo transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS). The even-numbered polymethylene-1,w-bis(phosphocholines) (PC-Cn-PC) are known to form nanofibers composed of stretched mols. with an all-trans alkyl chain conformation (Drescher, S.; Meister, A.; Blume, A.; Karlsson, G.; Almgren, M.; Dobner, B. Chem.-Eur. J.2007, 13, 5300-5307). The odd-numbered analogs were synthesized to study a possible even-odd effect of these bolaamphiphiles during their aggregation in water. In addn. to these bolaamphiphiles with phosphocholine headgroups, a new series of polymethylene-1,w-bis(phosphodimethylethanolamines) (Me2PE-Cn-Me2PE) with smaller headgroup sizes was synthesized. These bolaamphiphiles show an addnl. fiber-fiber transition when the alkyl chain length exceeds 26 carbon atoms. The mixing behavior of both types of bolaamphiphiles indicates that differences in the alkyl chain length up to six carbon atoms are tolerated within the fiber structure. The mixing of two Me2PE-Cn-Me2PE or PC-Cn-PC type bolaamphiphiles with different alkyl chain lengths offers the possibility to adjust the temp., where the crosslinking of the fibers is disrupted and where the fibers break apart. As a consequence, temp. switchable hydrogels are obtained that can be fine-tuned for drug delivery applications. The comparison with dotriacontane-1,32-diyl-bis[2-(methylammonio)-ethylphosphate] (MePE-C32-MePE), a new bolaamphiphile with even smaller phosphomonomethylammonio headgroups, illustrates the importance of the headgroup size for the aggregation behavior. This bolaamphiphile self-assembles exclusively into lamellar structures, and this aggregate type persists in mixts. with the fiber forming Me2PE-C32-Me2PE.
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