We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers of L-cysteine deposited under ultrahigh vacuum conditions on Au(110). The analysis of core level shifts allowed us to distinguish unambiguously the states of the first-layer molecules from those of molecules belonging to the second layer. The first-layer molecules strongly interact with the metal through their sulfur headgroup. The multipeaked structure of the N 1s, O 1s, and C 1s core levels is interpreted in terms of different molecular moieties. The neutral acidic fraction (HSCH2CH(NH2)COOH) is abundant at low coverage likely associated with isolated molecules or dimers. The zwitterionic phase (HSCH2CH(NH3+)COO-) is largely dominant as the coverage approaches the monolayer limit and is related to the formation of ordered self-assembled molecular structures indicated by electron diffraction patterns. The occurrence of a small amount of cationic molecules (HSCH2CH(NH3+)COOH) is also discussed. The second-layer molecules mainly display zwitterionic character and are weakly adsorbed. Mild annealing up to 100 degrees C leads to the desorption of the second-layer molecules leaving electronic states of the first layer unaltered.
The increasing demand for heterogeneous materials prompts the interest for the physics and chemistry of organic-inorganic interfaces. Within this field of interest we have investigated the electronic states of L-cysteine (Cys) adsorbed on Au(111) from aqueous solution with synchrotron-based, high resolution X-ray photoemission spectroscopy. The analysis of the S 2p core level region in pristine samples prepared with purified Cys indicates that Cys adsorbs on gold as a thiolate. The absence of a signal related to physisorbed sulfur indicates that Cys forms a monomolecular layer. The high resolution allowed us to resolve two components in the C 1s spectral region related to carboxyl. The comparative analysis of C 1s, N 1s and O 1s core level regions indicates the presence of the neutral and ionic form for both the carboxyl and the amine groups. From the quantitative analysis of the C 1s and N 1s data we can infer that the zwitterionic form is the prevalent one, with a ratio of zwitterionic to neutral molecules of 3 : 1. This value is quite different from that in the deposition solution. Prolonged exposure to the X-ray beam and thermal annealing induce the formation of atomic sulfur through S-C bond breaking and molecular fragment desorption. This response to X-ray irradiation differs from the results recently reported on long chain alkanethiols.
We have investigated the optical response of thiolate self-assembled monolayers (SAMs) deposited from the liquid phase on well characterized, (111)-textured gold films based on the use of in situ and ex situ optical spectroscopic ellipsometry. We considered SAMs formed by several molecules with thiol functionality, focusing on the octadecanethiol (C 18 ) SAM model system. We were able to show the tiny spectroscopic variations induced by the monolayer thick films with great reproducibility and high signal-to-noise ratio. We identified spectral features related to the alkyl chain and to the S-Au interface, providing a reliable spectral "fingerprint" of the formation of densely packed thiolate layers. By comparing data with simulations based on several effective models developed within the framework of Fresnel approach, we identified the main optical features related to the thiolate interface and in particular an absorption band whose spectral weight increases regularly from 500 nm toward the IR limit. We also obtained reliable estimations of the SAM thickness. The interface absorption properties have been tentatively assigned to a modification of the nearly free electron behavior, related to nanoscale morphological modifications following the formation of Au-thiolate moieties.
Dialysis-related amyloidosis is characterized by the deposition of insoluble fibrils of  2 -microglobulin ( 2 -m) in the musculoskeletal system. Atomic force microscopy inspection of ex vivo amyloid material reveals the presence of bundles of fibrils often associated to collagen fibrils. Aggregation experiments were undertaken in vitro with the aim of reproducing the physiopathological fibrillation process. To this purpose, atomic force microscopy, fluorescence techniques, and NMR were employed. We found that in temperature and pH conditions similar to those occurring in periarticular tissues in the presence of flogistic processes,  2 -m fibrillogenesis takes place in the presence of fibrillar collagen, whereas no fibrils are obtained without collagen. Moreover, the morphology of  2 -m fibrils obtained in vitro in the presence of collagen is extremely similar to that observed in the ex vivo sample. This result indicates that collagen plays a crucial role in  2 -m amyloid deposition under physiopathological conditions and suggests an explanation for the strict specificity of dialysis-related amyloidosis for the tissues of the skeletal system. We hypothesize that positively charged regions along the collagen fiber could play a direct role in  2 -m fibrillogenesis. This hypothesis is sustained by aggregation experiments performed by replacing collagen with a poly-L-lysine-coated mica surface. As shown by NMR measurements, no similar process occurs when poly-L-lysine is dissolved in solution with  2 -m. Overall, the findings are consistent with the estimates resulting from a simplified collagen model whereby electrostatic effects can lead to high local concentrations of oppositely charged species, such as  2 -m, that decay on moving away from the fiber surface.The deposition of  2 -microglobulin ( 2 -m) 2 into amyloid fibrils is the hallmark of dialysis-related amyloidosis (DRA), a disease arising as a complication of long-term hemodialysis.  2 -m is a 99-residue protein (molecular mass 11.7 kDa) that represents the light chain of the major histocompatibility complex class I (MHCI), an integral membrane protein involved in the immune response. As a result of normal MHCI catabolism,  2 -m is released in the serum from the cell surface and carried to the kidney for clearance. In the presence of kidney failure, the concentration of free circulating  2 -m can increase by up to 50-fold; the persistent increase in  2 -m concentration results in amyloid deposition, preferentially localized in the musculoskeletal system. The accumulation of  2 -m deposits has been shown to cause arthralgias, destructive osteoarthropathies, and carpal tunnel syndrome (1). Although a high concentration of  2 -m is a necessary condition for the onset of the disease, there is not a strict correlation between the disease severity and  2 -m levels (2), suggesting that other factors might be involved in  2 -m amyloid deposition.The aggregation process of  2 -m has been the object of extensive investigation for many years. Severa...
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