Polyelectrolyte Complexes

Complexes of polyelectrolytes (PECs) are oppositely charged polymers assemblies held together by electrostatic interaction. As the non-covalent assembly of macromolecules/colloids in solution has been thoroughly investigated over the last decade with a particular emphasis put on the morphology of the final aggregates as a function of the building blocks-chemistry, the objective of this thesis is to come to a better understanding of the influence of interaction strength between polyelectrolytes on complexes morphologies, as well as kinetics and thermodynamics of the complexation. For this study, weakly and strongly interacting systems given rise to coacervate and precipitate phases has been elected. Those systems have been studied on a wide charge ratio scale (Z[+]/[-]) to span several physical states of the PECs (soluble and colloidal PECs, dense phases). Morphologies of assemblies are assessed by microscopy (optical, fluorescence, atomic force) and scattering techniques (neutron, light). Kinetics and thermodynamics of the complexation process are studied by use of a stopped-flow mixing device and an isothermal titration calorimeter. Results gave us keys to discriminate strongly interacting systems from weakly interacting ones. In particular, the ‘strong systems’ are showed to be non-equilibrium assemblies, ie. the formulation pathway or the way these different macromolecules are coming into contact is then a key step. Another important aspect that could explain the complexation process behavior is the hydration energy of the polyelectrolytes. Calorimetry measurements have been performed for numerous polyelectrolytes and then correlated to complexes properties.

PEMBENTUKAN SPONTAN KOMPLEK POLIELEKTROLIT FIBROIN SUTERA DENGAN ALGINAT SEBAGAI MODEL PENGHANTARAN OBAT (Gita Cahya Eka Darma) Fibroin Sutera (SF) dan Alginat (ALG) merupakan biomaterial yang memiliki efek terapeutik dalam pengobatan luka yaitu hemostatik, dan kemampuannya dalam menyerap eksudat luka. Agen terapetik alami memiliki banyak keunggulan daripada penggunaan obat sintetik kimiawi, sehingga menjadikannya sebagai alternatif pilihan yang baik dalam pengobatan. Penelitian ini bertujuan membuat model penghantaran untuk pengobatan luka yaitu berupa membran serat hasil kompleksasi polielektrolit (PEC) melalui metode koaservasi. SF dari kepompong ulat sutera (Bombyx mori Linn) digunakan sebagai agen polikation, ALG sebagai agen polianion dan Kloramfenikol (CHL) sebagai model obatnya. Karakterisasi membran serat PEC yang dilakukan meliputi analisis gugus fungsi (FTIR), derajat kristalinitas (XRD), sifat termal (DSC), mikroskopik (SEM). Kemudian, dilakukan perhitungan perolehan koaservat (coacervation yield), uji keabuhan (swelling), dan uji pelepasan CHL secara in‒vitro. SDS PAGE digunakan untuk mengidentifikasi protein. Penelitian ini telah menghasilkan SF dengan karakteristik baru yang lebih baik, sehingga diperoleh membran serat PEC yang sesuai sebagai model penghantaran untuk pengobatan luka pada kulit. Membran serat PEC merupakan hasil modifikasi dari koaservat SF‒ALG berbentuk hidrogel. SF dalam membran berada pada konformasi strukturnya yang stabil yaitu Silk II dengan derajat kristalinitas dari SF maupun ikat‒silang elektrostatik SF‒ALG yang baik, sehingga membran serat ini dapat mengembang atau larut bergantung pada pH sistem. Analisis karakteristik membran telah membuktikan bahwa terjadi ikat‒silang elektrostatik antara SF dengan ALG, bentuk polimorf serta derajat kristalinitas SF dan membran dapat dikendalikan sehingga menentukan hasil akhir membran. Membran serat PEC responsif terhadap kondisi keasaman sistem, pada pH < 3 membran mengembang sementara pH > 3‒5,5 membran melarut sehingga dapat disesuaikan dengan kondisi pH tempat pelepasannya. Profil keabuhan meningkat dari pH 1 menuju pH 3 dengan persentase paling rendah adalah 414,3% (F3) dan paling tinggi adalah 844,4% (F2). Profil pelepasan CHL dari F1‒F3 berturut-turut adalah 91,33; 98,88; 81,94% selama 30 menit. Pelepasan paling cepat diperoleh dari formula dengan jumlah ALG lebih besar, sebaliknya pada jumlah SF lebih besar maka pelepasannya lebih lama sehingga rasio ini dapat menentukan jenis pelepasan yang diinginkan. Kata kunci: Fibroin sutera, natrium alginat, koaservasi, komplek polielektrolit, membran serat -------------------------------------------------------------------------------------------------------------------------------------------
SELF-ASSEMBLED POLYELECTROLYTE COMPLEX OF SILK FIBROIN WITH ALGINATE AS DRUG DELIVERY MODEL (Gita Cahya Eka Darma) Silk Fibroin (SF) and Alginate (ALG) are biomaterial that have therapeutic efect in wound dressing which is hemostatic, and the ability upon absorption of wound exudates. Natural therapeutic agents has many advantages than the use of chemical synthetic drugs, so that making it a good alternative in the medication. This research aims to make delivery model for wounds dressing in the form of fiber membrane results from polyelectrolyte complexation (PEC) through coacervation method. SF from silkworm cocoons (Bombyx mori Linn) used as polycations agent, ALG as polyanions agent and Chloramphenicol (CHL) as drug model. Characterization of PEC fiber membranes are conducted with analysis of the functional groups (FTIR), crystallinity degree (XRD), thermal properties (DSC), microscopic (SEM). Then, the study continued to the measurement of coacervation yield, swelling test, and in-vitro drug release test. SDS PAGE was used to verify the protein. This research has gained SF with better new characteristics, in order to obtain the appropriate PEC fiber membrane as delivery models for the treatment of skin wounds. PEC fiber membrane is a modified version from hydrogel-forming of SF‒ALG coacervate. SF in the membrane is in the stable conformation structure (Silk II) with a proper cystallinity degrees of SF and the SF‒ALG electrostatic crosslinking, so this fiber membrane can swelling or dissolve depending on the pH of the system. Characterization analysis of the membrane shown that the electrostatic bonds occurs between SF with ALG, polymorphic forms of the protein fibroin and crystallinity degree of SF and membrane can be controlled to determine the final result of the membrane. PEC fiber membrane is responsive to pH, at pH < 3 swelling occurs while at pH > 3‒5,5 it dissolved, this condition could be adjusted to the pH condition of the site released. The swelling profile increased from pH 1 upto pH 3 with the lowest percentage is 414,3% (F3) and the highest is 844,4% (F2). The CHL release profile of F1‒F3 respectively are 91,33; 98,88; 81,94% during 30 minute. The fastest drug release profile obtained from the formula with a higher amount of ALG, and otherwise on the formula that SF amounts is higher then the release is slower, this ratio can determine the type of release as required. Keywords: Silk fibroin, sodium alginate, coacervation, polyelectrolyte complex, fiber membrane

An overview of the interaction between charged macromolecules in aqueous solution is presented.
The starting point is the dielectric continuum model and the Debye-H¨uckel equation.
The usefulness of the simple theory is emphasized in particular for biological macromolecules,
whose net charge or surface charge density often is low. With more highly charged macromolecules
or aggregates it may be necessary to go beyond the simple Debye-H¨uckel theory and
invoke the non-linear Poisson-Boltzmann equation or even to approach an exact solution using
Monte Carlo simulations or similar techniques. The latter approach becomes indispensable
when studying systems with divalent or multivalent (counter)-ions. The long range character of
the electrostatic interactions means that charged systems of varying geometry - spheres, planes,
cylinders... - often have many properties in common. Another consequence is that the detailed
charge distribution on a macromolecule is less important. Many biological macromolecules contain
titratable groups, which means that the net charge will vary as a consequence of solution
conditions. This gives an extra attractive contribution to the interaction between two macromolecules,
which might be particularly important close to their respective isoelectric points.
The treatment of flexible polyelectrolytes/polyampholytes requires some extra efforts in order
to handle the increasingly complex geometry. A theoretical consequence is that the number of
parameters - chain length, charge density, polydispersity etc - prohibits the presentation of a
simple unified picture. An additional experimental, and theoretical, difficulty in this context
is the slow approach towards equilibrium, in particular with high molecular weight polymers.
A few generic situations where polyelectrolytes can act both as stabilizers and coagulants can,
however, be demonstrated using simulation techniques.

Complexation between anionic and cationic polyelectrolytes results in solid-like precipitates or liquid-like coacervate depending on the added salt in the aqueous medium. However, the boundary between these polymer-rich phases is quite broad and the associated changes in the polymer relaxation in the complexes across the transition regime are poorly understood. In this work, the relaxation dynamics of complexes across this transition is probed over a wide timescale by measuring viscoelastic spectra and zero-shear viscosities at varying temperatures and salt concentrations for two different salt types. We find that the complexes exhibit time-temperature superposition (TTS) at all salt concentrations, while the range of overlapped-frequencies for time-temperature-salt superposition (TTSS) strongly depends on the salt concentration (C s) and gradually shifts to higher frequencies as C s is decreased. The sticky-Rouse model describes the relaxation behavior at all C s. However, collective relaxation of polyelectrolyte complexes gradually approaches a rubbery regime and eventually exhibits a gel-like response as C s is decreased and limits the validity of TTSS.

A complexação entre biomoléculas é um tópico importante em vários campos, desde a Bioquímica, às indústrias farmacêutica, alimentar e de cosméticos. A capacidade de descrever e controlar os mecanismos responsáveis por esses processos, em termos de uma descrição molecular, é um desafio para muitas aplicações práticas. Através da modelação molecular e simulações Monte Carlo, descrevemos aqui um mecanismo peculiar: a regulação de cargas em função do equilíbrio ácido-base. Tal fenómeno é responsável por forças mesoscópicas atractivas em sistemas (bio)coloidais, capazes de explicar a complexação de macropartículas com carga do mesmo sinal. Tal é aqui demonstrado através dos complexos lactoferrina-pectina e pectinametilesterase de cenoura-pectina, os quais ilustram este mecanismo geral que pode ser observado em vários outros sistemas coloidais.

Despite their utmost critical significance, marine gels are have remained, for a long time, understudied in oceanography research. Compared to Dissolved Organic Matter (DOM), Particulate Organic Matter (POM), including marine gels, composes just a small fraction of the reduced carbon stock present in the ocean. Accordingly, compared to the breadth and strength of publications of the geochemistry of DOM, marine gels have received limited attention. However, we now know that these two pipes of marine carbon flux are not independent, and that they are, indeed, interconnected. Because of their polyelectrolyte nature, marine biopolymers—which make the bulk of DOM—can readily self-assemble, forming gels (Nature, 1998). To date, the body of information we possess is still small. Nonetheless, it points out that gels might be the crossing bridge that connects the marine living world to the supramolecular world present in the ocean. This bet was first put on the table by the pioneering work of Farooq Azam (Science, 1998). Yet, the focus has remained on quantitation, fluctuations, distribution, and the particular chemical structural changes that might make DOM species recalcitrant, not on their quaternary structure, shape, size, Z potential, and hydrophobicity, for instance, features required to understand their interactions to form the supramolecular arrays that constitute the matrix of marine gels.
Eighteen years have passed since we last made a special visit to the oceanic gel phase at the University of Washington Friday Harbor Labs, which was published in Marine Chemistry in 2004. Since then, the understanding of where and how marine gels are formed, their interaction with bacteria and pollutants, and the fascinating discovery that they can function as a nucleating source for cloud formation is attracting the interest of a new cohort of specialists, including colleagues in atmospheric sciences. Yet, this is the beginning of a set of fundamental questions that are likely to have profound significance in marine sciences. This Marine Gels Special Issue aims to broaden the community of talent, theory, and technology required to advance our understanding of supramolecular dynamics in the ocean. We need to attract colleagues that hold the power of physics, of first principles, to thoroughly interrogate the complex dynamics of biopolymer interactions in seawater. How susceptible are marine biopolymer dynamics to the consequence of an atmospheric CO2 overload that will certainly not cease to increase in the coming years? This is indeed a fundamental question. Decisions regarding the consequences of catastrophic economic policies are beyond our remit; however, it is in our territory to understand its effects, addressing not only symptomatic particular issues, such as species, regions, and depth, but also mechanisms operating at the deep macromolecular level where changes can affect every aspect of this complex system. It is important that we understand the fundamental laws that govern the behavior of macro-polyelectrolytes, to investigate the physical rules that underlie marine gel dynamics.
In short, this issue is an effort to alert oceanographers to the remarkable predicting power of polymer physic laws. We also aim to persuade polymer physicists, who constitute the main readership of Gels, that the ocean represents an urgent challenge for the survival of our planet, to respond not to the siren appeal from Mars, Jupiter, or distant galaxies, but the urgent call of our own planet.
To his end, we invited one of the best young polymer physicists to write a tutorial on polyelectrolyte dynamics, and a small but outstanding group of colleagues to outline the many complex challenges that remain to be addressed.
Finally,I want to thank my colleagues, who placed their trust in our editorial effort to bring their
outstanding contributions to the press.

Polyelectrolyte complexes (PECs) of biopolymers have been used for many applications, including emulsion stabilization and improvements in the properties of biopolymers, such as interfacial tension. The enhance of interfacial activity of biocompatible compounds is essential to the development of new natural stabilizers. Thus, the aim of this study was to understand how modifications on chitosan structure affect the interfacial tension of PECs. Positive, neutral and negative PECs were formed by varying chitosan or chitosan oligomers: whey protein isolate (WPI) mass ratios. Hydrolysis reduced chitosan size and increased zeta potential. FT-IR, H NMR analyses and crystallinity index confirmed structure modification. Chitosan oligomers showed lower crystallinity index and higher deacetylation degree than native chitosan. Positive
chitosan PEC showed the lowest interfacial tension, suggesting a strong adsorption at interface oil-water and better interfacial stabilization than other PECs. Therefore, changes on chitosan structures enhance PECs interfacial properties and its use as emulsion stabilizer.

A model linear oppositely charged polyelectrolyte complex exhibits phase separation upon heating consistent with lower critical solution temperature (LCST) behavior. The LCST coexistence curves narrow with increasing monovalent salt concentration (Cs) that reduces the polymer concentration (Cp) in the polymer-rich phase. The polymer-rich phase exhibits less hydration with increasing temperature, while an increase in Cs increases the hydration extent. The apparent critical temperature, taken as the minimum in the phase diagram, occurs only for a narrow range of Cs. Mean field theory suggests an increasing Bjerrum length with temperature can lead to an electrostatic-driven LCST; however, the temperature dependence of the Flory-Huggins interaction parameter and solvation effects must also be considered.