Differential scanning calorimetry study of the hydrophobic hydration of the elastin-based polypentapeptide, poly(VPGVG), from deficiency to excess of water

Bilayer Hydrogel Composed of Elastin-Mimetic Polypeptides as a Bio-Actuator with Bidirectional and Reversible Bending Behaviors

Biologically derived hydrogels have attracted attention as promising polymers for use in biomedical applications because of their high biocompatibility, biodegradability, and low toxicity. Elastin-mimetic polypeptides (EMPs), which contain a repeated amino acid sequence derived from the hydrophobic domain of tropoelastin, exhibit reversible phase transition behavior, and thus, represent an interesting starting point for the development of biologically derived hydrogels. In this study, we succeeded in developing functional EMP-conjugated hydrogels that displayed temperature-responsive swelling/shrinking properties. The EMP-conjugated hydrogels were prepared through the polymerization of acrylated EMP with acrylamide. The EMP hydrogel swelled and shrank in response to temperature changes, and the swelling/shrinking capacity of the EMP hydrogels could be controlled by altering either the amount of EMP or the salt concentration in the buffer. The EMP hydrogels were able to select a uniform component of EMPs with a desired and specific repeat number of the EMP sequence, which could control the swelling/shrinking property of the EMP hydrogel. Moreover, we developed a smart hydrogel actuator based on EMP crosslinked hydrogels and non-crosslinked hydrogels that exhibited bidirectional curvature behavior in response to changes in temperature. These thermally responsive EMP hydrogels have potential use as bio-actuators for a number of biomedical applications.

Structural and Dynamical Properties of Elastin-Like Peptides near Their Lower Critical Solution Temperature

Elastin-like peptides (ELPs) are artificially derived intrinsically disordered proteins (IDPs) mimicking the hydrophobic repeat unit in the protein elastin. ELPs are characterized by a lower critical solution temperature (LCST) in aqueous media. Here, we investigate the sequence GVG(VPGVG)₃ over a wide range of temperatures (below, around, and above the LCST) and peptide concentrations employing all-atom molecular dynamics simulations, where we focus on the role of intra- and interpeptide interactions. We begin by investigating the structural properties of a single peptide that demonstrates a hydrophobic collapse with temperature, albeit moderate, because the sequence length is short. We observe a change in the interaction between two peptides from repulsive to attractive with temperature by evaluating the potential of mean force, indicating an LCST-like behavior. Next, we explore dynamical and structural properties of peptides in multichain systems. We report the formation of dynamical aggregates with coil-like conformation, in which valine central residues play an important role. Moreover, the lifetime of contacts between chains strongly depends on the temperature and can be described by a power-law decay that is consistent with the LCST-like behavior. Finally, the peptide translational and internal motion are slowed by an increase in the peptide concentration and temperature.

Energetic electron assisted synthesis of highly tunable temperature-responsive collagen/elastin gels for cyclic actuation: macroscopic switching and molecular origins

Thermoresponsive bio-only gels that yield sufficiently large strokes reversibly and without large hysteresis at a well-defined temperature in the physiological range, promise to be of value in biomedical application. Within the present work we demonstrate that electron beam modification of a blend of natural collagen and elastin gels is a route to achieve this goal, viz. to synthesize a bioresorbable gel with largely reversible volume contractions as large as 90% upon traversing a transition temperature that can be preadjusted between 36 °C and 43 °C by the applied electron dose. Employing circular dichroism and temperature depending confocal laser scanning microscopy measurements, we furthermore unravel the mechanisms underlying this macroscopic behavior on a molecular and network level, respectively and suggest a stringent picture to account for the experimental observations.

Surface functionalization superparamagnetic nanoparticles conjugated with thermoresponsive poly(epsilon-lysine) dendrons tethered with carboxybetaine for the mild hyperthermia-controlled delivery of VEGF

Vascular endothelial growth factor (VEGF) is the growth factor responsible for the triggering of angiogenesis, the process of blood vessel formation supporting the long-term viability of any repaired or regenerated tissue. As the growth factor is effective only when concentration gradients are generated, new shuttles need to be developed that ensure both the control of gradients at the site of tissue repair and the release of VEGF at physiological levels. Magnetic hyperthermia is the production of heat induced by magnetic materials through their exposure to an external oscillating magnetic field. In this paper, magnetic nanoparticles capable of generating controllable hyperthermia were functionalised with hyperbranched poly(epsilon-lysine) peptides integrating in their core parallel thermoresponsive elastin-like peptide sequences and presenting an uppermost branching generation tethered by the zwitterionic amino acid carboxybetaine. The results show that these functionalised magnetic nanoparticles avidly bind VEGF and release it only upon generation of mild-hyperthermic pulses generated by oscillating magnetic filed. The VEGF release occurred in a temperature range at which the elastin-like peptides collapse. It is proposed that, through the application of an external magnetic field, these magnetic carriers could generated gradients of VEGF in vivo and allow its tuned delivery in a number of clinical applications.

STATEMENT OF SIGNIFICANCE

The present paper for the first time reveals the possibility to control the delivery of VEGF through mild hyperthermia stimuli generated by a oscillating magnetic field. To this purpose, magnetic nanoparticles of high size homogeneity and coated with a thin coating of poly(acrylic acid) were functionalised with a novel class of poly(epsilon lysine) dendrimers integrating in their structure a thermoresponsive amino acid sequence mimicking elastin and exposing at high density a zwitterionic modified amino acid, the carboxybetaine, known to be able to bind macromolecules. Physicochemical and biochemical characterisation elegantly show the link between the thermal properties of the nanoparticles and of the dendrimer change of conformation and how this enable the release of VEGF at temperature values compatible with the growth factor stability.

Combined effects of solvation and aggregation propensity on the final supramolecular structures adopted by hydrophobic, glycine-rich, elastin-like polypeptides

Previous work on elastin-like polypeptides (ELPs) made of hydrophobic amino acids of the type XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu) has consistently shown that differing dominant supramolecular structures were formed when the suspending media were varied: helical, amyloid-like fibers when suspended in water and globules evolving into "string of bead" structures, poly(ValGlyGlyValGly), or cigar-like bundles, poly(ValGlyGlyLeuGly), when suspended in methyl alcohol. Comparative experiments with poly(LeuGlyGlyValGly) have further indicated that the interface energy plays a significant role and that solvation effects act in concomitance with the intrinsic aggregation propensity of the repeat sequence. Continuing our investigation on ELPs using surface (X-ray photoelectron spectroscopy, atomic force microscopy) and bulk (circular dichroism, Fourier transform infrared spectroscopy) techniques for their characterization, here we have compared the effect of suspending solvents (H(2)O, dimethylsulfoxide, ethylene glycol, and MeOH) on poly(ValGlyGlyValGly), the polypeptide most inclined to form long and well-refined helical fibers in water, searching for the signature of intermolecular interactions occurring between the polypeptide chains in the given suspension. The influence of sequence specificities has been studied by comparing poly(ValGlyGlyValGly) and poly(LeuGlyGlyValGly) with a similar degree of polymerization. Deposits on substrates of the polypeptides were characterized taking into account the differing evaporation rate of solvents, and tests on their stability in ultra high vacuum were performed. Finally, combining experimental and computational studies, we have revaluated the three-dimensional modeling previously proposed for the supramolecular assembly in water of poly(ValGlyGlyValGly). The results were discussed and rationalized also in the light of published data.

Elastin-like polypeptides in drug delivery

The use of recombinant elastin-like materials, or elastin-like recombinamers (ELRs), in drug-delivery applications is reviewed in this work. Although ELRs were initially used in similar ways to other, more conventional kinds of polymeric carriers, their unique properties soon gave rise to systems of unparalleled functionality and efficiency, with the stimuli responsiveness of ELRs and their ability to self-assemble readily allowing the creation of advanced systems. However, their recombinant nature is likely the most important factor that has driven the current breakthrough properties of ELR-based delivery systems. Recombinant technology allows an unprecedented degree of complexity in macromolecular design and synthesis. In addition, recombinant materials easily incorporate any functional domain present in natural proteins. Therefore, ELR-based delivery systems can exhibit complex interactions with both their drug load and the tissues and cells towards which this load is directed. Selected examples, ranging from highly functional nanocarriers to macrodepots, will be presented.

Formation of calcium phosphate nanostructures under the influence of self-assembling hybrid elastin-like-statherin recombinamers

The self-assembly properties of elastin-like-statherin recombinamers have great influence on calcium phosphate mineralization.

LCST Behavior is Manifested in a Single Molecule: Elastin-Like polypeptide (VPGVG)n

The physical origin of the lower critical solution temperature (LCST) behavior of a variety of fluids, including elastin-like polypeptides (ELPs), has been studied for the past few decades. As is the case for polymer solutions, LCST behavior of ELPs is invariably reported for large systems of molecules and is considered evidence for collective behavior. In contrast, we find evidence for properties changes associated with LCST behavior in a single molecule by performing long atomic-level molecular dynamics simulation on the ELP sequences (Val-Pro-Gly-Val-Gly)n for four different length peptides over a wide range of temperatures. We observe a sharp transition in the number of hydrogen bonds between peptide and water and in the number of water molecules within the first hydration shell as temperature rises; this is used to locate the transition temperature. The dependence of the transition temperatures of ELPs on their lengths agrees well with experiments in that both have the same power law exponents. Our simulations reveal that the tendency for pentamers (VPGVG) in ELPs of all lengths to lose H-bonds with water or to gain H-bonds with themselves as temperature rises is independent of the length of the chain in which they are embedded. Thus, the transition temperature of ELPs in pure water is determined by two factors: the hydrogen bonding tendency of the pentamers and the number of pentamers per ELP. Moreover, the hydrogen bonding tendency of pentamers depends only on their sequences, not on the ELP chain length.

Influence of amino acid specificities on the molecular and supramolecular organization of glycine-rich elastin-like polypeptides in water

Elastin-like polypeptides adopt complex supramolecular structures, showing either a hydrophobic or a hydrophilic surface, depending on their surrounding environment and the supporting substrate. The preferred organization is important in many situations ranging from biocompatibility to bio-function. Here we compare the n-repeat pentamer LeuGlyGlyValGly (n = 7) with the analogue ValGlyGlyValGly (n = 5), as water suspensions and as deposits on silicon substrates. These sequences contain the repeat XxxGlyGlyZzzGly (Xxx, Zzz = Val, Leu) motif belonging to the hydrophobic glycine-rich domain of elastin and represent a simplified model from which to obtain information on molecular interactions functional to elastin itself. The compounds studied differ only by the presence of the -CH(2)- spacer in the Leu moiety and thus the work was aimed at revealing the influence of this spacer element on self assembly. Both polypeptides were studied under identical conditions, using combined techniques, to identify differences in their conformational states both at molecular (CD, FTIR) and supramolecular (XPS, AFM) levels. By these means, together with a Congo Red spectroscopic assay of β-sheet formation in water, a clear correlation between amino acid sequences (sequence specificity) and their kinetics and ordering of aggregation has emerged. The novel outcomes of this work are from the supplementary measurements, made to augment the AFM and XPS studies, showing that the significant step in the self assembly of both polypeptides takes place in the liquid phase and from the finding that the substitution of Val by Leu in the first position of the pentapeptide effectively inhibits the formation of amyloidal fibers.

Recombinamers: combining molecular complexity with diverse bioactivities for advanced biomedical and biotechnological applications

The rapid development of polymer science has led to literally thousands of different monomers and an almost endless number of possibilities arising from their combination. The most promising strategy to date has been to consider natural products as macromolecules that provide the best option for obtaining functional materials. Proteins, with their high levels of complexity and functionality, are one of the best examples of this approach. In addition, the development of genetic engineering has permitted the design and highly controlled synthesis of proteinaceous materials with complex and advanced functionalities. Elastin-like recombinamers (ELRs) are presented herein as an example of an extraordinary convergence of different properties that is not found in any other synthetic polymer system. These materials are highly biocompatible, stimuli-responsive, show unusual self-assembly properties, and can incorporate bioactive domains and other functionalities along the polypeptide chain. These attributes are an important factor in the development of biomedical and biotechnological applications such as tissue engineering, drug delivery, purification of recombinant proteins, biosensors or stimuli-responsive surfaces.

Influence of the amino-acid sequence on the inverse temperature transition of elastin-like polymers

This work explores the dependence of the inverse temperature transition of elastin-like polymers (ELPs) on the amino-acid sequence, i.e., the amino-acid arrangement along the macromolecule and the resulting linear distribution of the physical properties (mainly polarity) derived from it. The hypothesis of this work is that, in addition to mean polarity and molecular mass, the given amino-acid sequence, or its equivalent--the way in which polarity is arranged along the molecule--is also relevant for determining the transition temperature and the latent heat of that transition. To test this hypothesis, a set of linear and di- and triblock ELP copolymers were designed and produced as recombinant proteins. The absolute sequence control provided by recombinant technologies allows the effect of the amino-acid arrangement to be isolated while keeping the molecular mass or mean polarity under strict control. The selected block copolymers were made of two different ELPs: one exhibiting temperature and pH responsiveness, and one exhibiting temperature responsiveness only. By changing the arrangement and length of the blocks while keeping other parameters, such as the molecular mass or mean polarity, constant, we were able to show that the sequence plays a key role in the smart behavior of ELPs.

Gels and microgels for nanotechnological applications

In recent years, "smart" materials have been the focus of considerable interest, from both fundamental and applied perspectives. Polymer gels are within this category; they respond to specific environmental stimuli by changing their size. Thus, the internal structure, the refractive index, and the mechanical properties of the polymer network change. They are considered super absorbent materials, as they can absorb solvent up to several hundred times their own weight. They respond rapidly to local environmental variations, an important fact in device miniaturization and microsensor developments. As size changes are accompanied by changes in internal dimensions, microgels have found application as carriers of therapeutic drugs and as diagnostic agents. They have also been used as microreactors, optically active materials, for template synthesis of nanoparticles or fabrication of artificial muscle. In this paper we review a set of application based on the special features associated to this systems. Basic concepts on the physical-chemistry of gel swelling is first described, followed by different applications covering drug delivery, composite materials using polymer gels to modulate optical or magnetic and electrical properties, molecular imprinting, gel-based biosensors and polymer sensors and actuators used in the field of artificial muscles.

A synthetic resilin is largely unstructured

Proresilin is the precursor protein for resilin, an extremely elastic, hydrated, cross-linked insoluble protein found in insects. We investigated the secondary-structure distribution in solution of a synthetic proresilin (AN16), based on 16 units of the consensus proresilin repeat from Anopheles gambiae. Raman spectroscopy was used to verify that the secondary-structure distributions in cross-linked AN16 resilin and in AN16 proresilin are similar, and hence that solution techniques (such as NMR and circular dichroism) may be used to gain information about the structure of the cross-linked solid. The synthetic proresilin AN16 is an intrinsically unstructured protein, displaying under native conditions many of the characteristics normally observed in denatured proteins. There are no apparent alpha-helical or beta-sheet features in the NMR spectra, and the majority of backbone protons and carbons exhibit chemical shifts characteristic of random-coil configurations. Relatively few peaks are observed in the nuclear Overhauser effect spectra, indicating that overall the protein is dynamic and unstructured. The radius of gyration of AN16 corresponds to the value expected for a denatured protein of similar chain length. This high degree of disorder is also consistent with observed circular dichroism and Raman spectra. The temperature dependences of the NH proton chemical shifts were also measured. Most values were indicative of protons exposed to water, although smaller dependences were observed for glycine and alanine within the Tyr-Gly-Ala-Pro sequence conserved in all resilins found to date, which is the site of dityrosine cross-link formation. This result implies that these residues are involved in hydrogen bonds, possibly to enable efficient self-association and subsequent cross-linking. The beta-spiral model for elastic proteins, where the protein is itself shaped like a spring, is not supported by the results for AN16. Both the random-network elastomer model and the sliding beta-turn model are consistent with the data. The results indicate a flat energy landscape for AN16, with very little energy required to switch between conformations. This ease of switching is likely to lead to the extremely low energy loss on deformation of resilin.

Nanobiotechnological approach to engineered biomaterial design: the example of elastin-like polymers

Today, the development of advanced biomaterials is still lacking an appropriate tailored engineering approach. Most of the biomaterials currently used have their origin in materials developed for other technological applications. This lack of adequate biomaterial design is probably due to the peculiar environment where those materials must operate. On the one hand, this environment is dominated by the immune rejection system. On the other hand, the functionality of natural biomolecules is based on complex topological physical-chemical function distributions at the nanometer level. This review presents arguments concerning the role of biotechnology and nanotechnology in the future development of new advanced biomaterials and the potential of these biomaterials as a way to achieve highly biofunctional and truly biocompatible biomaterials for hot areas, such as regenerative medicine and controlled release. Recombinant protein-polymers will be presented as an example of candidates for this new paradigm in biomaterial design and production.

Biofunctional design of elastin-like polymers for advanced applications in nanobiotechnology

Elastin-like recombinant protein polymers are a new family of polymers which are captivating the attention of a broad audience ranging from nanotechnologists to biomaterials and more basic scientists. This is due to the extraordinary confluence of different properties shown by this kind of material that are not found together in other polymer systems. Elastin-like polymers are extraordinarily biocompatible, acutely smart and show uncommon self-assembling capabilities. Additionally, they are highly versatile, since these properties can be tuned and expanded in many different ways by substituting the amino acids of the dominating repeating peptide or by inserting, in the polymer architecture, (bio)functional domains extracted from other natural proteins or de novo designs. Recently, the potential shown by elastin-like polymers has, in addition, been boosted and amplified by the use of recombinant DNA technologies. By this means, complex molecular designs and extreme control over the amino-acid sequence can be attained. Nowadays, the degree of complexity and control shown by the elastin-like protein polymers is well beyond the reach of even the most advanced polymer chemistry technologies. This will open new possibilities in obtaining synthetic advanced bio- and nanomaterials. This review explores the present development of elastin-like protein polymers, with a particular emphasis for biomedical uses, along with some future directions that this field will likely explore in the near future.

Thermoresponsive self-assembly of short elastin-like polypentapeptides and their poly(ethylene glycol) derivatives

Short polypeptides with four pentad repeats, (VPGVG)(4) and (VPAVG)(4), were synthesised by manual fluorenylmethoxycarbonyl/tert-butyl (Fmoc/t-Bu) solid phase peptide synthesis using a convergent approach. In the next step, the peptides were coupled via their N-terminus with activated semi-telechelic poly(ethylene glycol) O-(N-Fmoc-2-aminoethyl)-O'-(2-carboxyethyl)undeca(ethylene glycol) (Fmoc-PEG-COOH) to yield monodisperse Fmoc-PEG-peptide diblock copolymer. Both the presence of the terminal hydrophobic Fmoc group and the hydrophilic PEG chain in the copolymers were shown to play a crucial role in their self-associative behaviour, leading to reversible formation of supramolecular thermoresponsive assemblies. The peptides and their PEG derivatives were characterised by HPLC, NMR and MALDI-TOF MS. The associative behaviour of the peptides and their PEG derivatives was studied by dynamic light scattering, MAS NMR and phase contrast microscopy. [image: see text]

Effect of NaCl on the Exothermic and Endothermic Components of the Inverse Temperature Transition of a Model Elastin-like Polymer

TMDSC data have been employed to observe the effect of NaCl on the inverse temperature transition of the model elastin-like polymer (GVGVP)251. NaCl causes a decrease in Tt and an increase in DeltaH. The increase in enthalpy appears both in the enthalpy related with the folding of the polymer and in the contribution associated with disruption of the structured water of hydrophobic hydration. It has been suggested that the presence of NaCl may cause a better formation of water structures surrounding the apolar polymer chains.

Tailored recombinant elastin-like polymers for advanced biomedical and nano(bio)technological applications

The genetic engineering of protein-based polymers is a method that enables, in an easy way, the design of complex and highly functional macromolecules. As examples of this approach, different molecular designs are presented, with increasing degree of complexity, showing how the controlled increase in their complexity yields (multi)functional materials with more selected and sophisticated properties. The simplest designs show interesting properties already, but the adequate introduction of given chemical functions along the polymer chain provides an opportunity to expand the range of properties to enhanced smart behavior and self-assembly. Finally, examples are given where those molecular designs further incorporate selected bioactivities in order to develop materials for the most cutting edge applications in biomedicine and nano(bio)technology.

Biocompatibility of elastin-like polymer poly(VPAVG) microparticles:in vitro andin vivo studies

Poly(L-valine-L-proline-L-alanine-L-valine-L-glycine) (VPAVG) is a new kind of proteinaceous polymer belonging to the Elastin-like family. These polymers are based on the recurrence of certain short peptide monomers that are considered as "building blocks" in the natural elastin. This smart thermoresponsive polymer has the ability to self-associate at physiological temperature to form aggregates with about 60% in water. This ability can be harnessed to prepare microparticles loaded with an active substance. The aim of this report is to evaluate, from the results of the experiment conducted, the biocompatibility of microparticles prepared from poly(VPAVG). We have studied the cytotoxic effects of microparticles, edema formation after subcutaneous injection (1 and 2.5 mg) in rats (n = 6), and also intraocular tolerance after the intravitreal injection of 2.5 mg of poly(VPAVG) microparticles into pigmented rabbits (n = 12). The polymer did not induce any cytotoxicity or nonspecific depression of cellular respiration on macrophages under the range of polymer concentrations investigated in this study (20, 30, 40, and 60 mg/mL). We observed no inflammatory response to microparticles after subcutaneous injection in the hind-paw of rats, with no significant differences between the control group (PBS) and experimental groups. Anterior and posterior segment signs were evaluated after intraocular injection of poly(VPAVG) microparticles. Only a few eyes (2/11) of the experimental group presented inflammation signs at day 28 postinjection. Nevertheless, 45% (5/11) of the eyes receiving microparticles showed tractional retinal detachment. The results observed in this work suggested certain fibroblastic activity induced by poly(VPAVG) microparticles after their intraocular injection.

Nanopore Formation by Self-Assembly of the Model Genetically Engineered Elastin-like Polymer [(VPGVG)2(VPGEG)(VPGVG)2]15

The self-assembly characteristics of the model genetically engineered elastin-like polymer [(VPGVG)2(VPGEG)(VPGVG)2]15 have been studied in this work. An AFM study of the topology of polymer films deposited from acid and basic solutions on a hydrophobic silicon substrate has been carried out. Under acidic conditions, polymer deposition results in a flat surface with no particular topological features. However, from basic solutions, polymer deposition clearly shows an aperiodic pattern of nanopores ( approximately 70 nm width and separated about 150 nm). This dramatic dependence of film topology on pH is explained in terms of the different polarity of the free gamma-carboxyl group of the glutamic acid. In the carboxylate form, this moiety shows a markedly higher polarity than the rest of the polymer domains and the substrate itself. Under these conditions, the charged carboxylates impede hydrophobic contact with their surroundings, which is the predominant assembly pathway for this type of polymer. The charged domains, along with their hydration sphere, are then segregated from the hydrophobic surroundings giving rise to nanopores.

Probing the mechanism of aqueous two-phase system formation for alpha-elastin on-chip

The kinetics of formation of the aqueous two-phase system (ATPS) for alpha-elastin was studied by dark field microscopy in an on-chip linear temperature gradient. Scattering intensities of protein solutions were recorded as a function of temperature and time, simultaneously at several concentrations. It was found that the formation rate of the ATPS could be fit as a first-order process and that the apparent rate constant increased with protein concentration. The activation energy for the process was 9.5 +/- 0.5 kcal/mol, and this result was consistent with a coalescence mechanism. Experiments were also conducted with varying concentrations of sodium dodecyl sulfate, which shut off the coalescence mechanism forcing ATPS formation to proceed through Ostwald ripening. When this was done, the activation energy increased to 33 +/- 2 kcal/mol and the kinetics became consistent with a second-order process.

Smart Elastin-like Polymers

Elastin-like polymers are a new family of proteinaceous polymers. In these polymers converge a wide set of interesting properties that difficultly can be found together in other polymers. They are extremely biocompatible and show an acute smart and self-assembling behaviour. The increasing in complexity of the molecular design renders polymers showing combination of functionalities and complex performance. This is specially true nowadays where, taking into account their peptide nature, these polymers can be produced as recombinant proteins in genetically modified (micro)organisms. The absolute control and absence of randomness in the primary structure makes possible the realization of multifunctional polymers that can combine physical, chemical and biological functions in a desired fashion. It can be said that the molecular design is mainly limited by imagination and not by technique. This chapter is intended to show the molecular parameters that explain the smart behaviour finally observed and how the increase in complexity of the molecular designs leads to a richer behaviour of the polymer, as a way to show the enormous potential of this family in the development of advanced materials and systems for biomedicine and nanotechnology for the next decades.

Structure and dynamics of two elastin-like polypentapeptides studied by NMR spectroscopy

The structure and dynamics of two synthetic elastin-like polypentapeptides, poly(G(1)V(1)G(2)V(2)P) and poly(AV(1)GV(2)P), were studied in D(2)O and H(2)O at various temperatures by using (1)H, (2)H,(13)C, and (15)N NMR spectra, relaxations, and PGSE self-diffusivity measurement. Signal assignments were made using COSY, NOESY, HXCORR, HSQC, HMBC, and SSLR INEPT techniques. Temperature-induced conformation changes were studied using (3)J(NHCH) couplings, NOESY connectivity, chemical shifts, and signal intensities. Hydrodynamic radii were derived from self-diffusion coefficients measured by the pulsed-gradient spin-echo (PGSE) method. Selective hydration (hydrophilic or hydrophobic) was explored using NOESY and ROESY spectral methods and longitudinal and transverse (1)H relaxation of HOD and quadrupolar (2)H relaxation of D(2)O. Four different physical states were discerned in different temperature regions for both polymers: state I of a rather extended, statistically shaped and fully hydrated polymer below the critical temperature (approximately 299-300 K); state II, a relatively coiled and globular but disordered preaggregation state, developing in a rather narrow region, 300-303 K, in the case of poly(AV(1)GV(2)P) and in a broader region, overlapping with the next one, in poly(G(1)V(1)G(2)V(2)P); state III, a tightly coiled, more compact state in the region 303-313 K; and, finally, state IV, an aggregated (and eventually flocculating and sedimenting) state beyond 313 K. States II-IV coexist in varying proportions in the whole temperature range above 299 K. A structure characterized by a beta-turn stabilized by H-bonding between the Ala carbonyl and Val(2) NH groups of poly(AV(1)GV(2)P) was detected by NOESY just above the transition temperature. States II and III are progressively more stripped of their hydration sheath but retain some molecules of water confined and relatively immobilized in their coils.

Raman spectroscopy of secondary structure of elastinlike polymer poly(GVGVP)

Raman spectra of the elastinlike polypentapeptide poly(GVGVP) were measured in H(2)O and D(2)O as solutions and, after increasing the temperature, as suspensions and sediments. In addition, spectra of the polypentapeptide in the solutions of increasing concentration and in the solid state were also investigated by gradually evaporating the water. Significant changes in band frequencies, intensities, and shapes were found for selected Raman bands in the measured spectra, particularly for the C-H stretching, the glycine CH(2) wagging, and some amide vibrations. The C-H stretching vibrations are influenced predominantly by the presence of water, the glycine CH(2) wagging vibrations are associated with conformational transitions. Three possible types of poly(GVGVP)s in the presence of water were indicated: polymer chains in a relatively extended state in the solution, a beta-spiral structure in the suspension, and irregularly bent chains in the sediment.