Surface Preparation for Single-Molecule Chemistry

Abstract

Immobilization procedures, intended to enable prolonged observation of single molecules by fluorescence microscopy, may generate heterogeneous microenvironments, thus inducing heterogeneity in the molecular behavior. On that account, we propose a straightforward surface preparation procedure for studying chemical reactions on the single-molecule level. Sensor fluorophores were developed, which exhibit dual-emissive characteristics in a homogeneously catalyzed showcase reaction. These molecules undergo a shift of fluorescence wavelength of about 100 nm upon Pd(0)-induced deallylation in the Tsuji–Trost reaction, allowing for separate visualization of the starting material and product. Whereas a simultaneous immobilization of dye and inert silane leads to strongly polydisperse reaction kinetics, a consecutive immobilization routine with deposition of dye molecules as the last step provides substrates underlying the kinetics of ensemble experiments. Also, the found kinetics are unaffected by the chemical variation of inert silanes, nearly uniform, and therefore well reproducible. Additional parameters like photostability, signal-to-noise ratio, dye-molecule density, and spatial distribution of dye molecules are, as well, hardly affected by surface modification in the successive immobilization scheme.

Kinetics of Palladium(0)‐Allyl Interactions in the Tsuji‐Trost Reaction, derived from Single‐Molecule Fluorescence Microscopy

“…We synthesized pyrene‐based, reactive fluorophores 2 a , 2 b and 2 c from 1 a , 1 b and 1 c according to existing procedures (scheme ). The benzylated probes 3 a , 3 b and 3 c were synthesized in a similar fashion (SI pp.…”

“…: 4–7). Compounds 2 a , b and 3 a , b were used for kinetic experiments in cuvette whereas 2 c and 3 c were used for immobilization on quartz surfaces prior to SM visualization . All probes 2 a , 2 b , 3 a and 3 b were stable in ethanol at standard conditions in the time span of these experiments.…”

“…From these intermediates a consecutive dissociation step then is expected . With the aim of obtaining new insights into the mechanisms of leaving group release, we studied the interactions of Pd 0 with our recently introduced, dual‐emissive and immobilizable substrates: During this reaction, tetrakis(triphenylphosphine)‐palladium(0) (Pd 0 ) causes a strong bathochromic shift in substrate fluorescence (SI Figure S2).…”

Kinetic and spectroscopic responses of pH-sensitive nanoparticles: influence of the silica matrix

“…Following the same strategy, a compound similar to 5a, where 4 was converted with trimethoxy[3-(methylamino)propyl]silane aer treatment with chlorosulfonic acid, has been used for immobilization in single-molecule chemistry. 69 The uorescence excitation and emission spectra of 5a were measured at various pH values (ESI, Fig. S6 and Table S3 †), from which the pK a value of 6.06 AE 0.11 (ESI, Fig.…”

“…37 The sensitivity of our probe molecule is also of minor importance as single-molecule detection has been realized earlier. 69 Furthermore, the fairly high intensity change upon pH changes simplies the subsequent analyses and can be, at least partially, traced back to the smaller size as compared to other nanoparticle preparations. 31,[34][35][36]85 In addition, the particles consist of hardly toxic components and are smaller than most well-known nanoprobes.…”