Modulating the poly-l-lysine structure through the control of the protonation–deprotonation state of l-lysine

Abstract

Designing the architecture of l-lysine-based polymeric structures is a highly challenging task that requires careful control of the amino acid reactive groups. Conventional processes to obtain branched polylysine need several steps and the addition of specific catalysts. In the present work, to gain a better understanding and control of the formation of l-lysine-based polymers, we have investigated the correlation between the protonation state of l-lysine and the corresponding hydrothermally grown structures. The samples have been characterized by combining optical spectroscopies, such as UV–Vis, fluorescence, and synchrotron radiation circular dichroism with structural analysis by Nuclear Magnetic Resonance, Fourier Transform Infrared spectroscopy, and dynamic light scattering. We have observed that aqueous precursor solutions with alkaline pHs promote the formation of branched structures. In contrast, high pHs favour the reactivity of the ε-amino groups leading to linear structures, as shown by circular dichroism analyses. On the other hand, acidic conditions trigger the branching of the amino acid. Interestingly, the polymeric forms of l-lysine emit in the blue because the increasing number of intermolecular hydrogen bonds promote the intermolecular charge transfer responsible for the emission. Understanding the correlation between the l-lysine charged states and the polymeric structures that could form controlling the protonation–deprotonation states of the amino acid opens the route to a refined design of polypeptide systems based on l-lysine.

In Vitro Antiviral Activity of Hyperbranched Poly-L-Lysine Modified by L-Arginine against Different SARS-CoV-2 Variants

“…This trend suggests that the signal was due to the α-CH 2 groups next to the amide bonds of L-lysine. In particular, the rise in the signals at 4.15 and 4.25 ppm indicates the formation of a hyperbranched polymeric structure via amide bonding, which was in agreement with FTIR analysis and previously published data [20,21].…”

Design of Dual-Emitting Nonaromatic Fluorescent Polymers through Thermal Processing of l-Glutamic Acid and l-Lysine

“…2,6 Moreover, these properties have also been explored on homopolymers achieved through a hydrothermal procedure by controlling the protonation state of Lys. 11 The present work aimed instead at investigating the PL properties of heteropolymers obtained by coupling different molar ratios of Lys with another biologically very important AB 2 amino acid, Glu, which, as mentioned above, is somehow the counterpart of Lys. After the synthesis, we compared the optical properties of the Glu−Lys heteropolymer with those of the two separated homopolymers: hyperbranched polylysine (PolyLys) 2 and polyglutamic acid (PGA).…”

“…The optical properties of Lys homopolymers obtained through a solventless thermal procedure, and in particular the photoluminescence (PL), have been largely investigated by our group, with and without the support of boric acid as an amidation catalyst. , Moreover, these properties have also been explored on homopolymers achieved through a hydrothermal procedure by controlling the protonation state of Lys . The present work aimed instead at investigating the PL properties of heteropolymers obtained by coupling different molar ratios of Lys with another biologically very important AB 2 amino acid, Glu, which, as mentioned above, is somehow the counterpart of Lys.…”

“…At physiological conditions, Lys assumes a zwitterionic form with protonated amino and deprotonated carboxyl groups. In the solid state, Lys is a neutral zwitterion 11 (Scheme 1).…”

Ultrahigh power output and durable flexible all-polymer triboelectric nanogenerators enabled by rational surface engineering

“…To this end, we proposed to use PLL or cPLL as the surface modification layer for the PEDOT:PSS electrode. Briefly, cPLL was obtained by the protonation of the amino group of PLL under acidic conditions, 32 as shown in Fig. 1a.…”