Visualization of π-hole in molecules by means of Kelvin probe force microscopy.

Submolecular charge distribution significantly affects the physical-chemical properties of molecules and their mutual interaction. One example is the presence of a π-electron-deficient cavity in halogen-substituted polyaromatic hydrocarbon compounds, the so-called π-holes, the existence of which was predicted theoretically, but the direct experimental observation is still missing. Here we present the resolution of the π-hole on a single molecule using the Kelvin probe force microscopy, which supports the theoretical prediction of its existence. In addition, experimental measurements supported by theoretical calculations show the importance of π-holes in the process of adsorption of molecules on solid-state surfaces. This study expands our understanding of the π-hole systems and, at the same time, opens up possibilities for studying the influence of submolecular charge distribution on the chemical properties of molecules and their mutual interaction.

Probing Charges on the Atomic Scale by Means of Atomic Force Microscopy.

Kelvin probe force spectroscopy was used to characterize the charge distribution of individual molecules with polar bonds. Whereas this technique represents the charge distribution with moderate resolution for large tip-molecule separations, it fails for short distances. Here, we introduce a novel local force spectroscopy technique which allows one to better disentangle electrostatic from other contributions in the force signal. It enables one to obtain charge-related maps at even closer tip-sample distances, where the lateral resolution is further enhanced. This enhanced resolution allows one to resolve contrast variations along individual polar bonds.

Atomic structure affects the directional dependence of friction.

Friction between two objects can be understood by the making, stretching, and breaking of thousands of atomic-scale asperities. We have probed single atoms in a nonisotropic surface [the H-terminated Si(100) surface] with a lateral force microscope operating in noncontact mode. We show that these forces are measurably different, depending upon the direction. Experimentally, these differences are observable in both the line profiles and the maximum stiffnesses. Density functional theory calculations show a concerted motion of the whole Si dimer during the tip-sample interaction. These results demonstrate that on an asperity-by-asperity basis, the surface atomic structure plays a strong role in the directional dependence of friction.

Reversal of atomic contrast in scanning probe microscopy on (111) metal surfaces.

We study the origin of atomic contrast on Cu(111) and Pt(111) surfaces probed by a non-contact atomic force microscope and scanning tunnelling microscope. First-principles simulations of the interaction between the atoms of the scanning tip and those of the probed surface show a dependence of the resulting contrast on the tip-sample distance and reveal a close relation between contrast changes and relaxation of atomic positions in both the tip and the sample. Contrast reversion around the distance where the short-range attractive atomic force reaches its maximum is predicted for both types of microscopies. We also demonstrate a relation between the maximal attractive force in a F-z atomic force spectroscopy and the chemical identity of the apex atom on the imaging tip.

In situ upregulation of IL-10 reflects the activity of human glomerulonephritides.

A reciprocal regulation between the expression of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10, demonstrated in monocytes and mesangial cells, provides a rationale for new therapeutic approaches in glomerulonephritis (GN). Administration of IL-10 to mice with antibody-mediated GN attenuated the severity of glomerular lesions. Recently, however, it has been shown that the genetically determined predominance of Th1 or Th2 cytokines results in different glomerular responses to the same planted antigen, but in an equally severe impairment of renal function. We looked for the expression of IL-10 and TNF-alpha in 111 renal biopsy specimens with proliferative and nonproliferative forms of GN and in 10 control kidneys, by means of immunocytochemistry, in situ hybridization, or reverse-transcriptase polymerase chain reaction (RT-PCR). Six patients had acute endocapillary GN (AGN), 10 patients had pauci-immune GN due to microscopic polyangiitis (MP), 48 patients had immunoglobulin-A (IgA)-GN, 18 patients had idiopathic membranous GN (IMGN), 12 patients had minimal change disease (MCD), and 13 patients had focal segmental glomerulosclerosis (FSGS) and four other forms of GN. Antibodies against monocytes (CD14) and macrophages (CD68) were applied to attribute the expression of TNF-alpha and IL-10 to resident renal or infiltrating cells. We show that mRNAs for TNF-alpha and IL-10 are detected by RT-PCR and in situ hybridization in the normal kidney. A constitutive expression of TNF-alpha protein is observed in mesangial cells, smooth muscle cells in renal arteries, and in the interstitium. A trace immunoreactivity for IL-10 is restricted to arterial smooth muscle cells, distal tubular epithelial cells, and some interstitial cells. Upregulation of both cytokines is found in glomerular diseases. The expression of TNF-alpha increases in mesangial areas in MCD, IMGN stages I/II, and IgA-GN with minor glomerular abnormalities, that is, under conditions with a generally well-preserved glomerular structure. Conversely, marked glomerular proliferation in IgA-GN and, particularly, acute vascular lesions in MP, are accompanied by a significant upregulation of IL-10 (at the mRNA and protein level). Patients with nephrotic-range proteinuria show a significant increase in tubulointerstitial expression of IL-10, whereas the immunoreactivity for TNF-alpha reflects the extent of interstitial fibrosis. Thus, our results confirm previous suggestions that proinflammatory and antiinflammatory cytokines are produced in situ by resident renal cells and contribute to the natural course of human GN.