Photoinduced Cleavage and Hydrolysis of <i>o</i>‐Nitrobenzyl Linker and Covalent Linker Immobilization in Gelatin Methacryloyl Hydrogels

Rebers

Macro Chemistry & Physics

et al. 2019

Self Cite

Cross‐linkable gelatin methacryloyl (GM) is widely used for the generation of artificial extracellular matrix in tissue engineering. However, so far, isoelectric points (IEPs) of highly methacryloylated GM derivatives are limited to IEPs below 7 due to the consumption of amino groups in the modification reaction. In this contribution, the synthesis of a new GM derivative, gelatin methacryloyl‐aminoethyl (GME), with an IEP above 7 similar to the gelatin type A (GA) starting material is reported, together with a high degree of methacryloylation. GME is obtained by reacting GM with ethylenediamine (EDA). The impact of the EDA functionalization on the properties of GM and GME derivatives is characterized thoroughly via 1H‐NMR, 1H‐13C‐HSQC‐NMR, IEP, solution viscosity, gel point, and physico‐chemical properties of resulting hydrogels. The second functionalization step results in amino group concentrations similar to GA and with that in an IEP of 9.9. The data suggest that amino functionalization with EDA prevents physical cross‐linking in the same way as described before for acetyl functionalization. Therefore, GME hydrogels are less stiff than GM hydrogels from GMs with a comparable amount of methacrylic functions. With GME, a gelatin derivative is available that is positively charged at neutral pH without being limited to low methacryl modifications.

Section: Introductionmentioning

confidence: 99%

Expanding the Range of Available Isoelectric Points of Highly Methacryloylated Gelatin

Rebers

Macro Chemistry & Physics

et al. 2019

Self Cite

“…At all pH values tested, p HP‐t‐showed faster hydrolysis than p HP‐ac. Rather fast hydrolysis of esters neighboring an oligo(ethylene glycol) moiety were reported before by Claaßen et al . and can presumably be explained by the negative inductive effect of the tri(ethylene glycol) residue, resulting in a better carboxylate leaving group.…”

Section: Resultsmentioning

confidence: 53%

“…At all pH values tested, pHP-t-showed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 faster hydrolysis than pHP-ac. Rather fast hydrolysis of esters neighboring an oligo(ethylene glycol) moiety were reported before by Claaßen et al [22] and can presumably be explained by the negative inductive effect of the tri(ethylene glycol) residue, resulting in a better carboxylate leaving group. The influence of the leaving group on pHP-based compounds can also be found in the literature: On the one hand, quantitative stabilities were reported for pHP esters and other pHP derivatives like pHPadenosine triphosphate (ATP) in TRIS buffer at pH 7 after 24 h. [1g,23] On the other hand, pHP esters similar to pHP-t showed reduced stability.…”

Section: Stability In Solutionmentioning

confidence: 54%

Coumarin‐4‐ylmethyl‐ and p‐Hydroxyphenacyl‐Based Photoacid Generators with High Solubility in Aqueous Media: Synthesis, Stability and Photolysis

et al. 2020

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(Coumarin‐4‐yl)methyl (c4m) and p‐hydroxyphenacyl (pHP)‐based compounds are well known for their highly efficient photoreactions, but often show limited solubility in aqueous media. To circumvent this, we synthesized and characterized the two new c4m and pHP‐based photoacid generators (PAGs), 7‐[bis(carboxymethyl)amino]‐4‐(acetoxymethyl)coumarin (c4m‐ac) and p‐hydroxyphenacyl‐2,5,8,11‐tetraoxatridecan‐13‐oate (pHP‐t), and determined their solubilities, stabilities and photolysis in aqueous media. The two compounds showed high solubilities in water of 2.77 mmol L−1±0.07 mmol L−1 (c4m‐ac) and 124.66 mmol L−1±2.1 mmol L−1 (pHP‐t). In basic conditions at pH 9, solubility increased for c4m‐ac to 646.46 mmol L−1±0.63 mmol L−1, for pHP‐t it decreased to 34.68 mmol L−1±0.62 mmol L−1. Photochemical properties of the two PAGs, such as the absorption maxima, the maximum molar absorption coefficients and the quantum yields, were found to be strongly pH‐dependent. Both PAGs showed high stabilities s24h ≥95 % in water for 24 h, but decreasing stability with increasing pH value due to hydrolysis. The present study contributes to a clearer insight into the synthesis, solubilities, stabilities, and photolysis of c4m and pHP‐based PAGs for further photochemical applications when high PAG concentrations are required, such as in polymeric foaming.

“…[31][32][33] Because of their wellknown photolysis mechanism and adjustable chemical structure, they can serve as photocages [34] or photolabile linkers. [31][32][33] Because of their wellknown photolysis mechanism and adjustable chemical structure, they can serve as photocages [34] or photolabile linkers.…”

Section: Molecular Mechanismsmentioning

confidence: 99%

Design and Applications of Photoresponsive Hydrogels

2019

materials with diverse applications in var ious fields due to their tunable chemistry structure and physical properties as well as excellent biocompatibility. [2][3][4][5] Hydrogel research has evolved from static mate rials to smart ones, whose structures and property show responsiveness to external stimuli, including temperature, pH, light, electric or magnetic fields, and the pres ence of enzymes or ion concentrations. [6][7][8][9][10][11] This unprecedented level of control over material properties has driven both med ical and industrial fields into the realm of possibility: controlled drug delivery, [12] chemical sensors, [13] soft actuators or robotics, [14][15][16] or scaffolds for dynamic 3D cell culture. [17] Photoresponsiveness is attractive due to the inherent advan tages of light as stimulus. Light is non invasive and allows remote manipulation of materials without requiring additional reagents, thus, with limited byproducts. Modulation of irradiation parameters, such as light intensity and irradiation time, permits the pre cise control of irradiation dosage, thereby, the degree of photo reactions. Spatial control can be achieved in both 2D and 3D, and temporal control is possible by simply turning the respec tive light source on or off. Wavelengthselective photo chemical reactions can be used for orthogonal photomediation of hydrogel properties. [18] Photoresponsive hydrogels, as externally tunable materials, strongly contribute to the field of soft smart materials in regard to the abovementioned applications. [19] In this review, we elaborate on the design and the emerging appli cations of photoresponsive hydrogels. A comprehensive review about utilizing light for the formation of hydrogels is given by Mi and coworkers. [20] First, we discuss responsive modes and photochemical mechanisms of photoresponsive hydrogels. Fol lowing this, we highlight their applications for dynamic cell environments, smart biointerfaces, controlled drug delivery, photodriven actuators, and lighthealing materials. The review concludes with an outlook on the challenges and potential future approaches for photo responsive hydrogels. Light as Stimulus for Hydrogels Macroscopic Hydrogel PhotoresponsesThe interaction of light with photoresponsive hydrogels can result in different responses, some of which are observable with the bare eye. Those include hydrogel formation or degradation, network contraction or expansion, and chemical modifications in the network, which then have an immediate consequence on Hydrogels are the most relevant biochemical scaffold due to their tunable properties, inherent biocompatibility, and similarity with tissue and cell environments. Over the past decade, hydrogels have developed from static materials to "smart" responsive materials adapting to various stimuli, such as pH, temperature, chemical, electrical, or light. Light stimulation is particularly interesting for many applications because of the capability of contact-free remote manipulation of biomaterial properties and inherent spatial and t...