Bifunctional Thiol Research Articles

A hybrid methacrylate‐norbornene‐thiol photopolymerization system with tunable physical and mechanical properties

AbstractPhotopolymerization of a hybrid methacrylate‐norbornene‐thiol system is used for the solvent‐free synthesis of polymers with tunable physical and mechanical properties. We demonstrate competitive adhesive performance of this system by examining factors such as thiol:ene ratio, thiol functionality, and the incorporation of a methacrylate as a hard monomer. Firstly, ethylene glycol dicyclopentenyl ether methacrylate (EGDEMA) and the di‐functional thiol ethylene bis(3‐mercapto propionate) (EBM) are photopolymerized to produce crosslinked networks with high conversion (up to 100%), high gel content (up to 77%), and low Tg (−2.5 to −13.5°C). Rheological studies found these formulations satisfied the Dahlquist criteria for pressure‐sensitive adhesives (PSAs) with the best adhesive/cohesive performance at thiol:ene ratios = 0.5–0.75. Secondly, a tetra‐functional thiol (PEMP) is crosslinked with EGDEMA photochemically, yielding elastomeric polymer films made to high conversion (up to 100%), with comparatively higher Tg (9–17°C), and higher gel content (up to 100%). Finally, isobornyl methacrylate (IBOMA) is incorporated as a hard monomer and crosslinked with a bifunctional thiol to produce thermoplastic polymers with negligible gel content and variable Tg (−12 to 41°C), suitable for application as temporary adhesives. These findings propose the use of the hybrid system in one‐step solventless formulations for UV curable adhesives, depending on component selection.

Noble Metal Nanoparticles Networks Stabilized by Rod‐Like Organometallic Bifunctional Thiols

AbstractRod‐like organometallic dithiol containing square‐planar Pt(II) centers, i. e., trans,trans‐[(H3COCS)Pt(PBu3)2(C≡C−C6H4−C6H4−C≡C)(PBu3)2Pt(SCOCH3)] was used as bifunctional stabilizing agent for the synthesis of Pd‐, Au‐, and AgNPs (MNPs). All the MNPs showed diameters of about 4 nm, which can be controlled by carefully modulating the synthesis parameters. Covalent MNPs stabilization occurred through a single S bridge between Pt(II) and the noble metal nanocluster surfaces, leading to a network of regularly spaced NPs with the formation of dyads, as supported by SR‐XPS data and by TEM imaging analysis. The chemical nature of NPs systems was also confirmed by EDS and NMR. Comparison between SR‐XPS data of MNPs and self‐assembled monolayers and multilayers of pristine rod‐like dithiols deposited onto polycrystalline gold surfaces revealed an electronic interaction between Pt(II) centers and biphenyl moieties of adjacent ligands, stabilizing the organic structure of the network. The possibility to obtain networks of regularly spaced MNPs opens outstanding perspectives in optoelectronics.

Thiol‐Functionalized Palladium Nanoparticles Networks: Synthesis, Characterization, and Room Temperature (Toxic) Vapor Detection

AbstractThe preparation of three different functionalized palladium nanoparticles (PdNPs) systems for room temperature BTX (benzene, toluene, p‐xylene) sensing detection and their morphostructural characterization is described. PdNPs are prepared through a two‐phase water/toluene wet chemical reduction method in the presence of bifunctional organic thiols as stabilizing agents suitable for the formation of covalently linked PdNPs networks: p‐terphenyl‐4,4″‐dithiol (PdNPs‐TR), biphenyl‐4,4′‐dithiol (PdNPs‐BP), or with 9,9‐didodecyl‐2,7‐bis(acetylthio)fluorene (PdNPs‐FL). Comparing the hydrodynamic diameter values, TR and BP ligands help to obtain networks consisting of spherical NPs of about 2 nm, in which each bifunctional ligand act as a bridge between PdNPs. In contrast, PdNPs‐FL show a population centered at <2RH> = 45 ± 5 nm. To perform preliminary gas sensing measurements, PdNPs networks are cast deposited on interdigitated electrodes to study their resistive response toward volatile organic compounds (VOCs) such as benzene (0–5%), toluene (0–1.7%), and p‐xylene (0–0.4%) (BTX) and common interfering gases (H2S, NH3, SO2, and relative humidity, RH). PdNPs‐FL show enhanced response to BTX with an appreciable response also toward H2S and RH. PdNPs‐TR exhibit a better ability to discriminate benzene gas with a negligible response after H2S exposure. Moreover, all the PdNPs systems show little to no response to NH3 and SO2 gases, offering an interesting perspective in practical sensing applications.

Thiol‐ene emulsion step polymerization in a photochemical stirred tank reactor: Molecular weight, cyclization, and fragmentation

AbstractUnlike many step polymerizations, the polymerization of bifunctional thiol and alkene monomers can be carried in emulsion to prepare a range of sulfur‐containing polymer particles differing markedly from conventional emulsion chain polymers. This study examines how the change of polymerization mechanism affects polymer molecular weight, structure and composition. A 2,2′‐dimercaptodiethyl sulfide/diallyl phthalate emulsion is photopolymerized in a photochemical stirred‐tank reactor equipped with Light‐emitting diodes (LEDs) to yield a 30% solids content latex with a high weight‐average molecular weight (100 kDa) and a broad molecular weight distribution (Đ = 8.5). Intramolecular cyclization occurs during polymerization by the addition of a thiyl radical to the unsaturated end group of the same molecule. Irreversible ring‐closure takes place to produce “dead” cyclic oligomers in the early stage of the reaction, whereas chain‐growth continues at high conversion. Consequently, the particles are composed of high molecular weight linear chains and a fraction of stable oligomer cycles, showing a broad and bimodal molecular weight distribution. The linear poly(thioether) chains include occasionally disulfide units due to thiyl radical recombination. The reversibility of disulfide bonds causes a decrease of molecular weight during storage. The addition of radical inhibitor to the latex stops fragmentation of SS bonds.

Synthesis and In Vitro Evaluation of Gold Nanoparticles Functionalized with Thiol Ligands for Robust Radiolabeling with 99mTc.

Radiolabeled gold nanoparticles (AuNPs) have been widely used for cancer diagnosis and therapy over recent decades. In this study, we focused on the development and in vitro evaluation of four new Au nanoconjugates radiolabeled with technetium-99m (99mTc) via thiol-bearing ligands attached to the NP surface. More specifically, AuNPs of two different sizes (2 nm and 20 nm, referred to as Au(2) and Au(20), respectively) were functionalized with two bifunctional thiol ligands (referred to as L1H and L2H). The shape, size, and morphology of both bare and ligand-bearing AuNPs were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. In vitro cytotoxicity was assessed in 4T1 murine mammary cancer cells. The AuNPs were successfully radiolabeled with 99mTc-carbonyls at high radiochemical purity (>95%) and showed excellent in vitro stability in competition studies with cysteine and histidine. Moreover, lipophilicity studies were performed in order to determine the lipophilicity of the radiolabeled conjugates, while a hemolysis assay was performed to investigate the biocompatibility of the bare and functionalized AuNPs. We have shown that the functionalized AuNPs developed in this study lead to stable radiolabeled nanoconstructs with the potential to be applied in multimodality imaging or for in vivo tracking of drug-carrying AuNPs.

Phosphatidylinositol-4,5-Biphosphate (PI(4,5)P2) Is Required for Rapid Endocytosis in Chromaffin Cells.

Objective Phosphoinositides play a regulatory role in clathrin-mediated endocytosis. However, their involvement in clathrin-independent endocytosis termed rapid endocytosis (RE), which is the mode of vesicle recycling during neurotransmitter release by transient fusion (known as kiss-and-run), has not been investigated. Here, we used patch-clamp recording of whole-cell membrane capacitance in adrenal chromaffin cells (ACC) to monitor changes of RE kinetics in response to pharmacological alteration of phosphatidylinositol-4,5-biphosphate (PI(4,5)P2) level by phenylarsine oxide (PAO) or antibody against phosphatidylinositol 4-kinase (AbPI4K). Results We found that PAO and AbPI4K significantly abrogated RE kinetics. Infusion of PI(4,5)P2 through the patch pipette potentiated RE kinetics and reversed PAO- and AbPI4K-induced blockade of RE. Similarly, the application of the bifunctional thiol dithiothreitol (DTT) to PAO-treated cells completely prevented the inhibitory effect of PAO on RE. These findings indicate that PI(4,5)P2 is implicated in the signaling (mechanistic) process of RE in ACC.

2H-Azirines as Potential Bifunctional Chemical Linkers of Cysteine Residues in Bioconjugate Technology.

2H-Azirine-2-caboxamides have been designed to perform as a new type of bifunctional thiol linker under very mild reaction conditions. The cleavage of a C-N double bond of 2H-azirine furnishes an amino amide functional group in situ through a thiol addition and ring-opening process. It works with a broad scope of thiols and 2H-azirines in the absence of any catalysts at room temperature. Cysteine-containing peptides have also been demonstrated to work efficiently in a completely water solution.

Synthesis of gold and silver nanoparticles functionalized with organic dithiols

In this work commercially available bifunctional organic dithiols, 4,4′-dithiol-biphenyl (BI), 4,4′-dithiolterphenyl (TR) and the on purpose prepared precursor of 4,4′-dithiol-trans-stilbene (ST), have been used for the stabilization of gold and silver nanoparticles (AuNPs and AgNPs). The bifunctional thiols have been chosen with different conjugation length, to prepare interconnected system of nanoparticles in order to achieve a tuning of their optical properties. The obtained AuNPs and AgNPs have been characterized by means of UV–vis spectroscopy to investigate the presence and shift of the Surface Plasmon Resonance (SPR); Field Effect Scanning Electron Microscopy (FESEM) allowed to achieve information on the NP’s morphology and size. Furthermore, the X-ray Photoelectron spectroscopy (XPS) measurements have been carried out to obtain structural information. AuNPs and AgNPs with mean size in the range 5–20nm appeared at regular distances in FESEM images and XPS analysis revealed the presence of physisorbed and chemisorbed thiols. In particular AgNPs showed a lower quantity of physisorbed thiol and an higher tendency to form interconnected networks, also suggested by UV–vis data, with a strong red shift of the SPR band up to 550nm. ST dithiol showed high tendency in the formation either of AuNPs and AgNPs networks as highlight by the pronounced redshift of the Surface Plasmon Resonance absorption wavelength as revealed by XPS characterization, where no physisorbed thiol was observed, indicating that all the sulphur atoms are involved in the functionalization of the nanoparticles metal surface.

Electron microscopy reveals a soluble hybrid network of individual nanocrystals self-anchored by bifunctional thiol fluorescent bridges.

Today, nanochemistry research of hybrid materials growth in liquid media represents a new challenge for tailoring specific nano-sized materials directly related to the hybrid electron-optical properties. Distinctive assumptions about the origin, the growth, and the functionalization of hybrid nanoparticles have recently been proposed by scientific research to attend the different aspects of observable behaviors. Therefore, appropriate morpho-structural observation of the hybrid nanoparticles is the most important factor for controlling the chemical and physical properties. Here, we report how the gold nanocrystals (Au-NCs) structurally covered by an outer layer material of 9,9-didodecyl-2,7-bisthiofluorene (FL) bifunctional stabilizer evolve into a self-organized 2D-network as a function of different nano-structural features. Detailed morpho-structural investigation of this hybrid material through electron microscopy techniques has been performed from the atomic-scale to hundreds of nanometers. The experimental information gathered allowed us to figure out the evolution growth of the gold-FL nanoparticles (AuFL-NPs) from the early stage of the gold-organic nucleation to the final assembled bi-dimensional network. The reported results represent a valuable background toward the full comprehension of growth mechanisms of organic-inorganic materials responsible for the final chemical and physical properties.

Facile and Efficient Synthesis of Carbosiloxane Dendrimers via Orthogonal Click Chemistry Between Thiol and Ene.

A combination of a thiol-Michael addition reaction and a free radical mediated thiol-ene reaction is employed as a facile and efficient approach to carbosiloxane dendrimer synthesis. For the first time, carbosiloxane dendrimers are constructed rapidly by an orthogonal click strategy without protection/deprotection procedures. The chemoselectivity of these two thiol-ene click reactions leads to a design of a new monomer containing both electron-deficient carbon-carbon double bonds and unconjugated carbon-carbon double bonds. Siloxane bonds are introduced as the linker between these two kinds of carbon-carbon double bonds. Starting from a bifunctional thiol core, the dendrimers are constructed by iterative thiol-ene click reactions under different but both mild reaction conditions. After simple purification steps the fifth dendrimer with 54 peripheral functional groups is obtained with an excellent overall yield in a single day. Furthermore, a strong blue glow is observed when the dendrimer is excited by a UV lamp.

Enhanced adsorption of trivalent arsenic from water by functionalized diatom silica shells.

The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

Reactions of (+)-Camphene with Dithiols

Electrophilic addition of thiols to camphene is known characteristically to follow various pathways and to produce both adducts that retain the starting camphene structure against Markovnikov’s rule or according to it and isomerization products that most frequently have the bornane structure [1–6]. We studied previously the BF3 Et2O-catalyzed addition of a series of thiols to (+)-camphene. Terpene sulfides with the camphene or bornane structure were formed according to Markovnikov’s rule for aromatic and heteroaromatic thiols whereas the reactions with other thiols went against the rule and retained the starting structure [7]. In continuation of research on the electrophilic addition of S-containing reagents to (+)-camphene (1), we studied its reaction with bifunctional thiols such as 1,2-ethanedithiol and bis(2-mercaptoethyl)sulfide under various conditions by varying the catalyst (BF3 Et2O or ZnCl2) and substrate:reagent ratio (Scheme 1).

Green chemistry of carbon nanomaterials.

The global trend of looking for more ecologically friendly, "green" techniques manifested itself in the chemistry of carbon nanomaterials. The main principles of green chemistry emphasize how important it is to avoid the use, or at least to reduce the consumption, of organic solvents for a chemical process. And it is precisely this aspect that was systematically addressed and emphasized by our research group since the very beginning of our work on the chemistry of carbon nanomaterials in early 2000s. The present review focuses on the results obtained to date on solvent-free techniques for (mainly covalent) functionalization of fullerene C60, single-walled and multi-walled carbon nanotubes (SWNTs and MWNTs, respectively), as well as nanodiamonds (NDs). We designed a series of simple and fast functionalization protocols based on thermally activated reactions with chemical compounds stable and volatile at 150-200 degrees C under reduced pressure, when not only the reactions take place at a high rate, but also excess reagents are spontaneously removed from the functionalized material, thus making its purification unnecessary. The main two classes of reagents are organic amines and thiols, including bifunctional ones, which can be used in conjunction with different forms of nanocarbons. The resulting chemical processes comprise nucleophilic addition of amines and thiols to fullerene C60 and to defect sites of pristine MWNTs, as well as direct amidation of carboxylic groups of oxidized nanotubes (mainly SWNTs) and ND. In the case of bifunctional amines and thiols, reactions of the second functional group can give rise to cross-linking effects, or be employed for further derivatization steps.

Network assembly of gold nanoparticles linked through fluorenyl dithiol bridges

Gold nanoparticles stabilized by two novel bifunctional fluorenyl thiols, generated in situ from 9,9-didodecyl-2,7-bis(acetylthio)fluorene (1) and 9,9-didodecyl-2,7-bis(acetylthiophenylethynyl)fluorene (2), exhibit bridged structures which self-assemble in parallel lines.

Silver nanoparticles linked by a Pt-containing organometallic dithiol bridge: study of local structure and interface by XAFS and SR-XPS.

Silver nanoparticles (AgNPs) functionalized with an organometallic bifunctional thiol containing Pt(ii) centers, generated in situ from trans-trans-[thioacetyl-bistributylphosphine-diethynylbiphenyl-diplatinum(ii)], were synthesized with different sulphur/metal molar ratios (i.e. AgNPs-1 and AgNPs-2) with the aim to obtain nanosystems of different mean size and self-organization behaviour. AgNPs spontaneously self-assemble, giving rise to 2D networks, as previously assessed. In this work a deeper insight into the chemico-physical properties of these AgNPs is proposed by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and X-ray absorption fine structure spectroscopy (XAFS) techniques. The results are discussed in order to probe the interaction at the interface between a noble metal and a thiol ligand at the atomic level and the aim of this study is to shed light on the chemical structure and self-organization details of nanosystems. The nature of the chemical interaction between the dithiol ligand and the Ag atoms on the nanoparticle surface was investigated by combining SR-XPS (S2p, Ag3d core levels) and XAS (S and Ag K-edges) analysis. UV-visible absorption and emission measurements were also carried out on all samples and compared with TD-DFT calculations so as to get a better understanding of their optical behavior and establish the nature of the excitation and emission processes.

Degradable thiol-acrylate hydrogels as tunable matrices for three-dimensional hepatic culture

A degradable poly(ethylene glycol)-diacrylate (PEGDA) hydrogel system was developed using simple macromer formulations and visible light initiated thiol-acrylate photopolymerization. In addition to PEGDA, other components in this gelation system include eosin-Y as a photo-sensitizer, bi-functional thiol (dithiothreitol, DTT) as a dual-purpose co-initiator and cross-linker, and N-vinylpyrrolidone (NVP) as a co-monomer. Gelation was achieved through a mixed-mode step-chain growth polymerization mechanism under bright visible light exposure. Increasing photo-sensitizer or NVP concentrations accelerated photo-crosslinking and increased final gel stiffness. Increasing bi-functional thiol content in the prepolymer solution only increased gel stiffness to some degree. As the concentration of thiol surpassed certain range, thiol-mediated chain-transfer events caused thiol-acrylate gels to form with lower degree of cross-linking. Pendant peptide, such as integrin ligand RGDS, was more effectively immobilized in the network via a thiol-acrylate reaction (using thiol-bearing peptide Ac-CRGDS. Underline indicates cross-linkable motif) than through homo-polymerization of acrylated peptide (e.g., acryl-RGDS). The incorporation of pendant peptide comes with the expense of a lower degree of gel cross-linking, which was rectified by increasing co-monomer NVP content. Without the use of any readily degradable macromer, these visible light initiated mixed-mode cross-linked hydrogels degraded hydrolytically due to the formation of thiol-ether-ester bonds following thiol-acrylate reactions. An exponential growth relationship was identified between the hydrolytic degradation rate and bifunctional thiol content in the prepolymer solution. Finally, we evaluated the cytocompatibility of these mixed-mode cross-linked degradable hydrogels using in situ encapsulation of hepatocellular carcinoma Huh7 cells. Encapsulated Huh7 cells remained alive and proliferated as time to form cell clusters. The addition of NVP at a higher concentration (0.3%) did not affect Huh7 cell viability but resulted in reduction of cell metabolic activity, which was accompanied by an elevated urea secretion from the encapsulated cells.

Specific behavior of the p-aminothiophenol – Silver sol system in their Ultra-Violet–Visible (UV–Visible) and Surface Enhanced Raman (SERS) spectra

The UV–Visible and Surface Enhanced Raman Spectroscopy (SERS) behavior of silver sol (a typical SERS agent) were studied in the presence of different bifunctional thiols such as p-aminothiophenol, p-mercaptobenzoic acid, p-nitrothiophenol, p-aminothiophenol hydrochloride, and 2-mercaptoethylamine hydrochloride in diluted aqueous solution. Our results confirm that the p-aminothiophenol induced aggregation of citrate stabilized silver colloid originates from its electrostatic nature, as well as the azo-bridge formation cannot be the reason of the observed time dependent UV–Visible spectra. Based on our parallel SERS and electrospray ionization mass spectrometry measurements, we have concluded that certain amount of oxidized form of the probe molecule has to be present for the so-called b2-mode enhancement in the SERS spectrum of p-aminothiophenol. Our findings seem to support the idea that the azo-bridge formation is responsible for the b2-mode enhancement in the SERS spectrum of p-aminothiophenol.

Synthesis and structural characterization of cyclic indium thiolate complexes and their utility as initiators for the ring-opening polymerization of cyclic esters

We have synthesized indium complexes incorporating bifunctional thiolate ligands and examined their utility as initiators for the ring-opening polymerization of rac-lactide and ε-caprolactone. The facile reaction of Me3In with the corresponding bifunctional thiols in diethyl ether or thf resulted in the formation of [MeIn(SCH2C(O)OMe)2]2 (5), [MeIn(SCH2CH2NMe2)2] (6) or [Me2In(SCH2C(O)OMe)] (7). The solid-state structure of 5 is dimeric via short intermolecular In⋯S interactions, yielding an asymmetric In2S2 core. One pendant and one chelating methyl thioglycolate ligand gives a distorted trigonal bipyramidal S3OC bonding environment for indium. Compound 6 shows a bicyclic monomeric structure with a distorted trigonal bipyramidal S2N2C bonding environment for indium. Compound 5 polymerized bulk rac-lactide rapidly with high conversion, but yielded broad PDIs and low MWs. Solution polymerizations using one equivalent of benzyl alcohol per metal centre were reasonably well controlled at 70 °C, though molecular weights were lower than theoretical values. Compound 6 was also an efficient mediator of bulk rac-lactide polymerization when initiated by benzyl alcohol, reaching >90% conversion in 15 min. Molecular weights were in excellent agreement with the theoretical values and the PDIs were narrow. Solution polymerizations utilizing 6 in conjunction with benzyl alcohol were much slower than the analogous reactions using 5. Compound 5 was less efficient at controlling the ROP of ε-caprolactone versus rac-lactide, while 6 was inactive towards ε-caprolactone under a variety of conditions. This work represents the first study of indium thiolate complexes for the ROP of cyclic esters, and contains rare examples of structurally characterized organoindium bis(thiolate) compounds, the first to be prepared via the hydrocarbon elimination reaction.

Mechanism-Based Small Molecule Cross-Linkers of HECT E3 Ubiquitin Ligase–Substrate Pairs

Here we report the discovery that bifunctional thiol- and amine-reactive electrophiles serve as mechanism-based covalent cross-linkers for HECT E3 ubiquitin ligase-substrate pairs. We demonstrate that these chemical cross-linkers covalently cross-link the catalytic Cys residue of the yeast HECT E3 ubiquitin ligase Rsp5 with the Lys of the ubiquitination site in the model substrate Sic60-GFP. This work represents the first example of a mechanism-based covalent cross-link of HECT E3-substrate pairs that converts transiently interacting HECT E3-substrate pairs into stable, covalently cross-linked protein complexes, thereby facilitating their subsequent isolation, identification, and study.

Bioconjugation of trypsin onto gold nanoparticles: Effect of surface chemistry on bioactivity

The systematic study of activity, long-time stability and auto-digestion of trypsin immobilized onto gold nanoparticles (GNPs) is described in this paper and compared to trypsin in-solution. Thereby, the influence of GNP's size and immobilization chemistry by various linkers differing in lipophilicity/hydrophilicity and spacer lengths was investigated with regard to the bioactivity of the conjugated enzyme. GNPs with different sizes were prepared by reduction and simultaneous stabilization with trisodium citrate and characterized by UV/vis spectra, dynamic light scattering (DLS), ζ-potential measurements and transmission electron microscopy (TEM). GNPs were derivatized by self-assembling of bifunctional thiol reagents on the nanoparticle (NP) surface via dative thiol-gold bond yielding a carboxylic acid functionalized surface. Trypsin was either attached directly via hydrophobic and ionic interactions onto the citrate stabilized GNPs or immobilized via EDC/NHS bioconjugation onto the carboxylic functionalized GNPs, respectively. The amount of bound trypsin was quantified by measuring the absorbance at 280nm. The activity of bound enzyme and its Michaelis Menten kinetic parameter Km and vmax were measured by the standard chromogenic substrate Nα-Benzoyl-DL-arginine 4-nitroanilide hydrochloride (BApNA). Finally, digestion of a standard protein mixture with the trypsin-conjugated NPs followed by analysis with LC–ESI-MS and successful MASCOT search demonstrated the applicability of the new heterogenous nano-structured biocatalyst. It could be shown that the amount of immobilized trypsin and its activity can be increased by a factor of 6 using a long hydrophilic spacer with simultaneous reduced auto-digestion and reduced digestion time. The applicability of the new trypsin bioreactor was proven by digestion of casein and identification of α- as well as κ-casein by subsequent MASCOT search.