Surface Structure, Adsorption, and Thermal Desorption Behaviors of Methaneselenolate Monolayers on Au(111) from Dimethyl Diselenides

To understand the effect of headgroups (i.e., sulfur and selenium) on surface structure, adsorption states, and thermal desorption behaviors of self-assembled monolayers (SAMs) on Au(111), we examined methanethiolate (CH₃–S, MS) and metheneselenolate (CH₃–Se, MSe) monolayers formed from dimethyl disulfide (DMDS) and dimethyl diselenide (DMDSe) molecules by ambient vapor-phase deposition. Scanning tunneling microscopy imaging revealed that DMDS molecules on Au(111) after a 1 h deposition form MS monolayers containing a disordered phase and an ordered row phase with an inter-row spacing of 1.51 nm, whereas DMDSe molecules form long-range-ordered MSe monolayers with a (√3 × 3√3)<i>R</i>30° structure. X-ray photoelectron spectroscopy measurements showed that MS or MSe monolayers chemisorbed on Au(111) were formed via S–S bond cleavage of DMDS or Se–Se bond cleavage of DMDSe. On the other hand, we monitored three main desorption fragments for MS and MSe monolayers using TDS monomers (CH₃S⁺, CH₃Se⁺), parent mass species (CH₃SH⁺, CH₃SeH⁺), and dimers (CH₃S–SCH₃⁺, CH₃Se–SeCH₃⁺). Interestingly, we found that thermal desorption behaviors of MSe monolayers were markedly different from those of MS monolayers. All desorption peaks for MSe monolayers were observed at a higher temperature compared with MS monolayers, suggesting that the adsorption affinity of selenium atoms for the Au(111) surface is stronger than that of sulfur atoms. In addition, the desorption intensity of dimer fragments for MSe monolayers was much lower than for MS monolayers, indicating that selenolate SAMs on Au(111) did not undergo their dimerization efficiently during thermal heating compared with thiolate SAMs. Our results provide new insight into understanding the surface structure and thermal desorption behavior of MSe monolayers on Au(111) surface by comparing those of MS monolayers

Size Evolution of Protein-Protected Gold Clusters in Solution: A Combined SAXS–MS Investigation

We report a combined small-angle X-ray scattering (SAXS) and mass spectrometric (MS) study of the growth of gold clusters within proteins, in the solution state. Two different proteins, namely, lysozyme (Lyz) and bovine serum albumin (BSA), were used for this study. SAXS study of clusters grown in Lyz shows the presence of a 0.8 nm gold core, which is in agreement with the Au₁₀ cluster observed in MS. Dynamic light scattering suggests the size of the cluster core to be 1.2 nm. For BSA, however, a bigger core size was observed, comparable to the Au₃₃ core obtained in MS. Concentration- and time-dependent data do not show much change in the core size in both SAXS and MS investigations. When metal–protein adducts were incubated for longer time in solution, nanoparticles were formed and protein size decreased, possibly due to the fragmentation of the latter during nanoparticle formation. The data are in agreement with dynamic light scattering studies. This work helps to directly visualize cluster growth within protein templates in solution

Correction to “Size Evolution of Protein-Protected Gold Clusters in Solution: A Combined SAXS-MS Investigation”

Correction to “Size Evolution of Protein-Protected Gold Clusters in Solution: A Combined SAXS-MS Investigation

Chromogenic Tubular Polydiacetylenes from Topochemical Polymerization of Self-Assembled Macrocyclic Diacetylenes

Tubular materials formed by self-assembly of small organic molecules find great utility in chemical and material science. Conventional tubular structures often lack stability because noncovalent molecular interactions are responsible for their conformational integrities. Herein we report the development of covalently linked chromogenic organic nanotubes which are prepared by using topochemical polymerization of self-assembled macrocyclic diacetylenes (MCDAs). Crystal structures of five MCDAs having different diameters were elucidated, and four of these substances were transformed to tubular polydiacetylenes (PDA) by UV-induced polymerization. Surprisingly, MCDA-1 was found to self-assemble in stacks with a tilt angle of 62.1°, which significantly deviates from the optimal value for polymerization of 45°. This observation suggests that geometric parameters derived using linear diacetylene (DA) models might not be strictly applicable to polymerization of MCDA systems. Blue-phase PDAs obtained by polymerization of MCDA-1 and MCDA-3 have different thermochromic and solvatochromic properties, which enable them to be utilized for colorimetric differentiation of aromatic solvents including isomeric xylenes. The observations made and information obtained in this study should enhance the understanding and design of stimulus-responsive rigid organic nanotubes