Secondary Structure Of Gelatin Research Articles

Analysis of gelatin secondary structure in gelatin/keratin-based biomaterials

The possibility of using protein-based materials as cellular scaffold strongly depends on protein conformation, and several attempts have been made by researchers to obtain scaffold with morphology miming the extracellular matrix. It is widely recognized that the secondary structure of proteins affects the mechanical and biological properties of protein-based scaffolds. However, few studies have been published, and an exhaustive explanation is still missing. In this work the study of the gelatin structure in gelatin-based materials and the investigation of the possible correlations between structure, mechanical and biological features is reported.We have examined how the secondary structure of gelatin is affected (i) by the process used to obtain the biomaterials (solvent casting vs. electrospinning), (ii) by the concentration of cross linker (3-(Glycidyloxypropyl)trimethoxysilane) (GPTMS), and (iii) by the raw keratin extract added. Gelatin electrospun materials have shown a content of ordered structure higher than gelatin casted films, likely due to the random coil – α-helix transition occuring during electrospinning. GPTMS gives a decrease of ordered structures in gelatin casted films (random structure increasing from 20% to 60%), while it does not affect the percentage of ordered structure in electrospun samples. In the gelatin/keratin electrospun biomaterials, the presence of keratin produces a decrease of α-helix content from 31% to 2–15% and an increase of β-structures, promoting the conversion from antiparallel to parallel β-sheet. The structure of gelatin affects the mechanical performances of biomaterials. In gelatin/keratin electrospun biomaterials we have found a positive correlation between failure strain and helix conformation and a negative correlation with β-structures. Elastic modulus has opposite correlations. All gelatin-based biomaterials have been tested as scaffold for pre-osteoblastic cells showing good biocompatibility for both casted films and electrospun biomaterials.

Impact of the solvent properties on molecular interactions and phase behaviour of alginate-gelatin systems

Alginate-gelatin systems are used in a wide range of applications, e.g., foods, cosmetics, drugs, and medicine. To target the techno-functionalities of alginate-gelatin systems such as texture, stability, or appearance it is necessary to understand the structure formation of gel systems, which is influenced by the molecular interactions and the phase behaviour. Therefore, the aim of this study was to characterise the molecular interactions and phase behaviour of dilute alginate-gelatin systems. For this purpose, we analysed alginate, gelatin A and their mixtures at pH 7. First, we characterised the effect of the sodium chloride concentration on the single polymer solutions by measuring the critical overlap concentration, the zeta potential, intrinsic viscosity, the Huggins coefficient as well as the molecular weight and the second virial coefficient. To gain a better understanding of the molecular interactions between alginate and gelatin, we determined the Huggins coefficient and the interaction parameter by Wolf as a function of mixing ratio, NaCl and urea concentration. Additionally, we calculated the second cross-virial coefficient. Lastly, we characterised the influence of the interactions on the secondary structure of gelatin by Fourier-transform-infrared-spectroscopy. The attractive interactions between alginate and gelatin potentially enabling the formation of soluble complexes, were demonstrated as deviations from additivity of intrinsic viscosity and negative cross-virial coefficients. Interestingly, the Wolf interaction parameter was affected by the NaCl concentration and the mixing ratio, whereas the presence of urea showed no impact. This indicates that the attractive interactions of alginate and gelatin A at pH 7 is rather caused by electrostatic interactions than hydrogen bonds. The present study clarifies the relevance of hydrogen bonds and electrostatic interactions as well as the impact of mixing ratio and solvent properties on the phase behaviour of alginate-gelatin systems. The insights contribute to a better understanding of the structure formation of concentrated alginate-gelatin systems, levelling the path to specific modifications of functionality.

Preparation and characterization of active Cirish fructans-fish gelatin film: Physicochemical, antioxidant, and antimicrobial properties.

This study was aimed to evaluate the film-forming ability and characterization of ultrasonically extracted Cirish fructans (CF) and CF-cold-water fish gelatin (G) composite films. The film-forming solutions were prepared at different levels (CF100-0G, CF75-G25, CF50-G50, CF25-G75, and CF0-G100) and the corresponding data were analyzed based on one-way analysis of variance. The results indicated that CF addition led to an impressive increase in composite films thickness (69.38-86.45 μm), moisture content (16.05%-27.8%), surface hydrophobicity, tensile strength (5.73-17.89 MPa), elongation at break (0.83%-1.66%), Young's modulus (77.12-88.15 MPa), and Tg (38.83-47.4°C) which CF75-G25 had the highest values. Meanwhile, the solubility (77.12%-88.15%), WVP (1.89-2.86 × 10-10gm-1 s-1Pa-1), and oxygen permeability (1.53-3.26 × 1014 cm3m-1s-1Pa-1) of the composite films decreased. The FTIR spectra indicated the protein-polysaccharide interactions and revealed that the secondary structure of gelatin was shifted from triple-helix structure (1661 cm-1) toward α-helix structure (1650-1657 cm-1) when CF was incorporated. The microstructure observations indicated that unlike gelatin film, CF film exhibited the smooth and uniform surface without cracks and phase separation. It was found that CF films had high total phenolic content (6.73 mg GEA g-1) and showed DPPH radical scavenging activity (67.86%). On the other hand, it showed inherent antimicrobial activity against both gram-positive and gram-negative bacteria. The results indicated that CF and CF-cold fish gelatin have great potential as active films with improved physical, mechanical, and barrier properties.

Adding Humic Acids to Gelatin Hydrogels: A Way to Tune Gelation.

Exploring the chance to convert biowaste into a valuable resource, this study tests the potential role of humic acids (HA), a class of multifunctional compounds obtained by oxidative decomposition of biomass, as physical agents to improve gelatin’s mechanical and thermal properties. To this purpose, gelatin–HA aqueous samples were prepared at increasing HA content. HA/gelatin concentrations changed in the range 2.67–26.67 (wt/wt)%. Multiple techniques were employed to assess the influence of HA content on the gel properties and to unveil the underlying mechanisms. HAs increased gel strength up to a concentration of 13.33 (wt/wt)% and led to a weaker gel at higher concentrations. FT-IR and DSC results proved that HAs can establish noncovalent interactions through H-bonding with gelatin. Coagulation phenomena occur because of HA–gelatin interactions, and at concentrations greater than 13.33 (wt/wt)%, HAs established preferential bonds with water molecules, preventing them from coordinating with gelatin chains. These features were accompanied by a change in the secondary structure of gelatin, which lost the triple helix structure and exhibited an increase in the random coil conformation. Besides, higher HA weight content caused swelling phenomena due to HA water absorption, contributing to a weaker gel. The current findings may be useful to enable a better control of gelatin structures modified with composted biowaste, extending their exploitation for a large set of technological applications.

Polyelectrolyte Polysaccharide–Gelatin Complexes: Rheology and Structure

General features of rheological properties and structural peculiarities of polyelectrolyte polysaccharide–gelatin complexes were discussed in this paper. Experimental results were obtained for typical complexes, such as κ-carrageenan–gelatin, chitosan–gelatin and sodium alginate–gelatin complexes. A rheological method allows us to examine the physical state of a complex in aqueous phase and the kinetics of the sol–gel transition and temperature dependences of properties as a result of structural changes. The storage modulus below the gelation temperature is constant, which is a reflection of the solid-like state of a material. The gels of these complexes are usually viscoplastic media. The quantitative values of the rheological parameters depend on the ratio of the components in the complexes. The formation of the structure as a result of strong interactions of the components in the complexes was confirmed by UV and FTIR data and SEM analysis. Interaction with polysaccharides causes a change in the secondary structure of gelatin, i.e., the content of triple helices in an α-chain increases. The joint analysis of the structural and rheological characteristics suggests that the formation of additional junctions in the complex gel network results in increases in elasticity and hardening compared with those of the native gelatin.

Interactions between gelatin and sodium alginate: UV and FTIR studies

The interaction between macromolecular chains of gelatin and anionic polysaccharide sodium alginate during the formation of polyelectrolyte complexes was examined using UV and FTIR spectroscopy. It has been shown that in an aqueous phase, where the pH is slightly higher than the pI of gelatin, complexes are formed through hydrogen bonds as well as electrostatic interactions between two biopolymers. The complex formation is accompanied by a change in the secondary structure of gelatin. At a low weight (w/w) ratio of polysaccharide to gelatin (up to 0.2) a decrease in the share of collagen-like helices and an increase in the share of the random coil conformation of gelatin chains were reported. SEM was used to identify a fundamental distinction between the morphologies of the gelatin hydrogel and the mixed alginate–gelatin hydrogel with a low mass ratio of biopolymers. Spherical formations were found in the structure of the latter that were interpreted as aggregations of complexes.

Interactions of quercetin, curcumin, epigallocatechin gallate and folic acid with gelatin

Some small bioactive molecules from food show the potential health benefits, but with poor chemical stability and bioavailability. The interactions between small molecules and gelatin were investigated. Fluorescence experiments demonstrated that the bimolecular quenching constants (kq) of complexes (gelatin-quercetin, gelatin-curcumin, gelatin-epigallocatechin gallate, gelatin-folic acid) were 3.7 × 1012 L·mol−1·s−1, 1.4 × 1012 L·mol−1·s−1, 2.7 × 1012 L·mol−1·s−1 and 8.5 × 1012 L·mol−1·s−1, indicating that fluorescence quenching did not arise from a dynamical mechanism, but from gelatin-small molecules binding. Furthermore, the affinity with gelatin was ranked in the order of folic acid > quercetin > epigallocatechin gallate > curcumin. Fluorescence spectroscopy, ultraviolet and visible absorption spectroscopy, FTIR and circular dichroism showed that the interactions between small molecules and gelatin did not significantly alter the conformation and secondary structure of gelatin. Non-covalent interactions may result in the binding of gelatin with small molecules. The interactions were considered to be through two modes: (1) small molecules bound within the hydrophobic pockets of gelatin; (2) small molecules surrounded the gelatin molecule mainly through hydrogen bonds and hydrophobic interactions.

Increasing Elasticity through Changes in the Secondary Structure of Gelatin by Gelation in a Microsized Lipid Space.

Even though microgels are used in a wide variety of applications, determining their mechanical properties has been elusive because of the difficulties in analysis. In this study, we investigated the surface elasticity of a spherical microgel of gelatin prepared inside a lipid droplet by using micropipet aspiration. We found that gelation inside a microdroplet covered with lipid membranes increased Young’s modulus E toward a plateau value E* along with a decrease in gel size. In the case of 5.0 wt % gelatin gelled inside a microsized lipid space, the E* for small microgels with R ≤ 50 μm was 10-fold higher (35–39 kPa) than that for the bulk gel (∼3 kPa). Structural analysis using circular dichroism spectroscopy and a fluorescence indicator for ordered beta sheets demonstrated that the smaller microgels contained more beta sheets in the structure than the bulk gel. Our finding indicates that the confinement size of gelling polymers becomes a factor in the variation of elasticity of protein-based microgels via secondary structure changes.

Gelatin and amylopectin-based phase-separated hydrogels: An in-depth analysis of the swelling, mechanical, electrical and drug release properties

The current study delineates the development of gelatin–amylopectin-based phase-separated hydrogels for drug delivery applications. Gelatin and amylopectin were used as the representative protein and polysaccharide phases, respectively. The hydrogels were prepared by adding different proportions of amylopectin to gelatin solutions and subsequently cross-linking the mixture using glutaraldehyde. Microscopic analysis showed formation of phase-separated hydrogels. Secondary structure of gelatin was conserved within the hydrogels. The presence of amylopectin drastically reduced the rate of water absorption by the hydrogels. Viscoelastic analysis using stress relaxation study suggested an increase in the viscous component of the hydrogels with the increase in the amylopectin content. After incorporating amylopectin within the gelatin hydrogel, even though the bulk resistance remained unaltered, there was a corresponding variation in the capacitive elements of the equivalent electrical models. The release of the drug from the hydrogels was diffusion mediated. Suitable mathematical models were used for the analysis of the swelling (Peleg’s model), viscoelastic (Weichert model), electrical (RQQ model) and drug release (Korsmeyer–Peppas and Peppas–Sahlin models) properties. The drug retained its antimicrobial activity within the hydrogels. An analysis of the results suggested that the developed hydrogels may be explored as matrices for controlled drug delivery applications.

Effect of gelatin on micellization and microstructural behavior of amphiphilic amitriptyline hydrochloride drug solution: A detailed study

Herein we have investigated the dealings between amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) and gelatin interaction using different proposed techniques. AMT is used for the treatment of mental/mood problems such as depression. Gelatin interacts with this drug alike fashions to the interaction of polymers and surfactants i.e., critical aggregation concentration (cac) and polymer saturation point (psp) were together achieved significantly. AMT and gelatin interaction starts due to the highly surface active complex formation as disclosed by decreasing of surface tension of gelatin solution by adding of AMT. It was uncovered from results that cac decreases on increasing the gelatin concentrations, whereas psp increases which is a sign of the attraction between AMT and gelatin. Thermodynamic parameters were also evaluated and discussed in detail. Fluorescence measurements were used to find the values of average aggregation numbers (Nagg) and various other parameters like Stern–Volmer constant (Ksv) and micropolarity. The nuclear magnetic resonance (1H NMR) data suggested that AMT interacts with gelatin by the means of hydrophobic interaction. The 1H NMR experiments explain that the extent of chemical shifts (δ) and line width (lw) increases with the increase in gelatin concentration. Secondary structure of gelatin was also examined via circular dichroism (CD) technique at different concentration of AMT. CD results confirmed that with increasing drug concentration the random coil portion of gelatin enhances. Field emission scanning electron microscope (FESEM) provided clear pictures of (drug+gelatin) interaction.

A gelatin based antioxidant enriched biomaterial by grafting and saturation: Towards sustained drug delivery from antioxidant matrix

Proteins grafted with antioxidant molecules have drawn much attention due to their increased life time and biocompatibility. When protein macromolecules are cross linked chemically and physically with antioxidant molecules, they can act as antioxidant biomaterials as well as scaffolds to release the antioxidant molecules by diffusion. In our work, we have attempted to release catechin molecules from the matrix of glutathione grafted gelatin. Conjugation of glutathione and cross linkage was done by carbodiimide method to achieve smaller pores in the gelatin matrix and the characterization was performed by means of FTIR-ATR and calorimetric analyses. The glutathione grafted gelatin (GGSH) has been shown to have more thermal stability and pores with lesser radii than blank gelatin (bGEL). Free radical scavenging activity of GGSH was also found to be more than that of bGEL. Catechin was added to GGSH and bGEL by physical blending in order to achieve short term release of antioxidant molecules. CD spectra revealed that significant conformational changes occurred in secondary structure of gelatin upon interaction with catechin. Slower rate of catechin release from GGSH reflected the influence of cross linkage and physical interactive forces on the drug release properties. We conclude that the mixture of catechin with GGSH can be a potent antioxidant biomaterial releasing catechin at slower rate than the mixture of catechin with bGEL.

A study of interaction between antidepressant drug nortriptyline hydrochloride with gelatin

The effect of gelatin on the micellization behavior of amphiphilic drug nortriptyline hydrochloride (NOT) in aqueous as well as aqueous urea (250mM) solutions has been studied using conductimetric technique. NOT is indicated for the relief of symptoms of depression. It is a tricyclic antidepressant drug. The drug interacts with gelatin similar to the interaction of surfactants and polymers. The plots of specific conductivity versus concentration of drug were nonlinear with three different linear regions with two clear breaks. The first break point, i.e., critical aggregation concentration (cac), appeared well below the typical critical micelle concentration (cmc). The second break point is considered as polymer saturation point (psp) that is similar to cmc. The cac value decreases on increasing the gelatin concentration, whereas psp value increases for all fixed concentrations (%, w/v) of gelatin which is a clear signal of the interaction of the drug with gelatin. Free energies of aggregation (ΔGagg) and micellization (ΔGmic) were also evaluated. In the presence of urea the increase in the surface charge of the micelles was observed followed by halt of the aggregation. Effect of NOT (drug) on the secondary structure of gelatin in aqueous solutions was also examined using CD measurements. The measurements verified that the random coil content of gelatin increases with increasing the NOT concentration.

Interaction of gelatin with promethazine hydrochloride: Conductimetry, tensiometry and circular dichroism studies

The interaction of amphiphilic phenothiazine drug promethazine hydrochloride (PMT) with gelatin in aqueous as well as aqueous-electrolyte (50mM NaCl) solutions has been studied by using conductimetry, tensiometry and circular dichroism (CD) techniques. The drug interacts with gelatin similar to the interaction of surfactants and polymers. Hence, we have considered the gelatin–amphiphile interaction approach using conductimetry and tensiometry. The plots of specific conductivity versus concentration of drug were nonlinear with three different linear regions with two clear breaks. The critical aggregation concentration (cac), i.e., first break point, appeared well below the usual critical micelle concentration (cmc). Second break is regarded as polymer saturation point (psp) which is similar to cmc. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule (gelatin). The results further show that the cac decreases on increasing the gelatin concentration, while psp increases for all concentrations of gelatin which is a clear indication of the interaction between the drug and gelatin. By the use of degree of ionization, free energies of aggregation (ΔGagg) and micellization (ΔGmic) were also evaluated. As inorganic salts increase the ionic strength, the solubility of amphiphile (drug) is lowered by ionic screening effects, resulting in a greater tendency to aggregate at lower concentration. Therefore, both the cac and psp/cmc values decrease. Effect of PMT on the secondary structure of gelatin in aqueous solutions was also investigated using CD measurements. The measurements demonstrated that the random coil content of gelatin increases with increasing the drug concentration.

Complexation behavior of gelatin with amphiphilic drug imipramine hydrochloride as studied by conductimetry, surface tensiometry and circular dichroism studies

Herein we report our studies carried out on the interaction between IMP and gelatin in aqueous medium at 25 °C using conductimetry, surface tensiometry and circular dichroism (CD) techniques. Both surface tensiometry and conductimetry results indicate that the drug interacts with the gelatin in a surfactant-like manner, i.e., both critical aggregation (cac) and polymer saturation points (psp) were observed. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule. The decrease in cac on increasing gelatin concentration is an indication of the strong interaction between gelatin and IMP. However, at low concentration of gelatin the interaction was not much strong as exposed by surface tension study, i.e., the cac was not very clear (as with higher gelatin concentrations). As usual, the psp increased on increasing the gelatin concentration and was always higher than the critical micelle concentration of the drug in pure aqueous medium. Using CD measurements the influence of IMP on the secondary structure of gelatin in aqueous solutions was also investigated. CD studies (performed at very low drug concentrations) illustrated that the random coil content of gelatin increases with increasing drug concentration. Free energies of aggregation (Δ G agg) and micellization (Δ G mic) were computed with the help of degrees of micelle ionization obtained from the specific conductivity – [IMP] plots.

The influence of surfactants on the structure of transparent gelatin films

The interference image of cold-dried transparent gelatin films containing different surfactants was determined in the conoscopic ray of monochromatic light. From the results obtained the order of the structure of gelatin in the film was characterized. Unlike the ionic surfactants (sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide), which lead to a reduction of the ordered structure, the addition of nonionic and amphoteric surfactants [ethoxylized octylphenole and a technical C12/C14-dipoly(oxyethylene)ammoniopropane sulfonate] causes an increase of the ordered structure of gelatin. The results quantitatively agree with those found for the influence of surfactants on the secondary structure of gelatin in diluted gelatin solutions. The influence is independent of the gelatin/surfactant ratio and has been explained by gelatin/gelatin interaction competing with the gelatin/surfactant interaction if the gelatin concentration becomes sufficiently high.