Doctoral students seminar (June 12, 2018)

Nazmul Hasan on “Crystallization of Isotactic Poly(methacrylic acid) at the Air-Water Interface”

and Svetlana Pylaeva on “Effects of Hofmeister Ion Series on Stability of a Salt Bridge”

Location: UL, Linnéstr. 5, SR 225
Time: 3.30pm-5.00pm

Link to Google-Maps

Abstracts

Effects of Hofmeister Ion Series on Stability of a Salt Bridge

S. Pylaeva, M. Brehm, and D. Sebastiani

Salt bridges are defined as an interaction of two aminoacid side chains of opposite charge [1]. Often found exposed to solvent salt bridges a susceptible to interactions with it, primarily with water. As opposite charges attract each other, polar water molecules can counteract, solvating the charges separately and thus breaking the salt bridge – ion pair. Free ions in solution can further influence salt bridge stability by extra shielding of charges and competition for ion pair formation (aminoacid – free ion).

We have investigated effects of Hofmeister ion series on an arginine – aspartic acid salt bridge by means of computer simulations. Changes in thermodynamic properties of a salt bridge and dynamic properties of the solution will be discussed in a talk.

References
[1] J.E. Donald, D.W. Kulp, W.F. DeGrado, Proteins, 79(3), 898 (2011)

Crystallization of Isotactic Poly(methacrylic acid) at the Air-Water Interface

Nazmul Hasan

Acrylic polymers such as poly(methyl methacrylate) (PMMA) or poly(acrylic acid)  (PAA) are amorphous in nature even changing their tacticity, but by employing different treatments  (e.g., solvent treatment,  high-temperature annealing or precipitation), they can be slowly crystallized [1,2].  It has been reported that several weeks of high-temperature annealing are necessary to crystallize i-PMMA which forms a double helix structure[3]. However, using the simple air-water interface employed Langmuir-Blodgett (LB) method; i-PMMA can crystallize quickly[4]. Herein, we have reported the crystallization of another polymer of the acrylic family i.e., isotactic poly(methacrylic acid) (i-PMAA) at the air-water interface. The polymer is dissolved in dimethyl sulfoxide (DMSO) and spread on the water surface of a Langmuir trough. The obtained surface pressure vs. area (π-A) isotherm shows a phase transition plateau at the surface pressure range of (10-14) mN/m. However, this plateau is started to disappear at a subphase pH of 6 and at pH ≥7, no (π-A) is observed. The phase transition is monitored in real time by the infrared reflection absorption spectroscopy (IRRAS). The normalized IRRAS spectra show an increase of αCH₃ (δ_as ≈ 1388 cm^-1) band intensity of iPMAA at the plateau region. The increase of this band intensity is reported as a crystallization process for a thin film of i-PMMA as well as for i-PMAA[5–7]. In addition to IRRAS, Brewster angle (BAM) and epifluorescence microscopy are used to see film morphology on the water surface. However, no film morphology is observed. Therefore, several Langmuir-Blodgett (LB) films are transferred to the mica substrate at different surface pressure before and after the plateau. Atomic force microscopy (AFM) of the LB films transferred at the plateau shows crystalline nano entities with a size of (20-80) nm and the height is between (2-4) nm.  Furthermore, the crystallization is also confirmed by grazing incident X-ray scattering (GIXS) experiment on the LB film.

References: