Molecular resolution

Tang S L, McGhie A J and Suna A 1993 Molecular-resolution imaging of insulating macromolecules with the scanning tunnelling microscope via a nontunnelling, electric-field-induced mechanism Phys. Rev. B 47 3850... 

Lai R, Kim FI, Garavito R M and Arnsdorf M F 1993 Imaging of reconstituted biological channels at molecular resolution by atomic force microscopy Am. J. Physiol. 265 C851... 

In the 1970s, computers on a chip (microprocessors) appeared. Electron microscopes neared molecular resolution. By the end of the decade, transistors could be made the size of a human cell (10 microns). 

The resolution of infra-red densitometry (IR-D) is on the other hand more in the region of some micrometers even with the use of IR-microscopes. The interface is also viewed from the side (Fig. 4d) and the density profile is obtained mostly between deuterated and protonated polymers. The strength of specific IR-bands is monitored during a scan across the interface to yield a concentration profile of species. While in the initial experiments on polyethylene diffusion the resolution was of the order of 60 pm [69] it has been improved e.g. in polystyrene diffusion experiments [70] to 10 pm by the application of a Fourier transform-IR-microscope. This technique is nicely suited to measure profiles on a micrometer scale as well as interdiffusion coefficients of polymers but it is far from reaching molecular resolution. 

Thus, for the investigation of buried polymer interfaces, several techniques with molecular resolution are also available. Recently NMR spin diffusion experiments [92] have also been applied to the analysis of a transition zone in polymer blends or crystals and even the diffusion and mobility of chains within this layer may be analyzed. There are still several other techniques used, such as radioactive tracer detection, forced Rayleigh scattering or fluorescence quenching, which also yield valuable information on specific aspects of buried interfaces. They all depend very critically on sample preparation and quality, and we will discuss this important aspect in the next section. 

In the analysis of polymer surfaces and interfaces there has been tremendous progress in recent years. This is to a large extent due to the development of surface- and interface-sensitive analytical techniques which previously had not been applied to polymers. It is thus possible to achieve molecular resolution both for the free polymer surface and for buried interfaces between polymers. In addition, suitable sample preparation techniques are available and extremely homogeneous and smooth polymer thin films can be prepared. They may be put together to investigate the interface between polymers. 

Scanning force microscopy (SFM) is the only tool that allows one to image S-layer protein monolayers on solid supports at molecular resolution (Fig. lb and c) [22-25]. In particular, SFM in contact mode under water with loading forces in the range of <500 pN leads to an image resolution in the subnanometer range (0.5-1.0 nm). 

Fukuma, T., Kobayashi, K., Matsushige, K., and Yamada, H. (2005). True molecular resolution in liquid by frequency-modulation atomic force microscopy. Appl. Phys. Lett. 86, 193108. 

Liquid interfaces are widely found in nature as a substrate for chemical reactions. This is rather obvious in biology, but even in the diluted stratospheric conditions, many reactions occur at interfaces like the surface of ice crystallites. The number of techniques available to carry out these studies is, however, limited and this is particularly true in optics, since linear optical methods do not possess the ultimate molecular resolution. This resolution is inherent to nonlinear optical processes of even order. For liquid-liquid systems, optics turns out to be rather powerful owing to the possibility of nondestructive y investigating buried interfaces. Furthermore, it appears that planar interfaces are not the only config-... 

Chirality at surfaces can be manifested in a number of forms including the intrinsic chirality of the surface structure and even the induction of chirality via the adsorption of achiral molecules onto achiral surfaces. The ability of STM to probe surfaces on a local scale with atomic/molecular resolution has revolutionized the understanding of these phenomena. Surfaces that are globally chiral either due to their intrinsic structure or due to the adsorption of chiral molecules have been shown by STM to establish control over the adsorption behavior of prochiral species. This could have profound consequences for the understanding of the origin of homochirality in life on Earth and in the development of new generations of heterogeneous chiral catalysts that may, finally, make a substantial impact on the pharmaceutical industry. 

PS-P2VP copolymers with a miktoarm starlike architecture deposited onto mica or Si wafers have been investigated by Kiryi et al. [116]. These authors studied, using AFM with molecular resolution, single-molecule conforma-... 

In contrast to solid dendrimers [71, 84, 88], molecular resolution was not achieved for a closed film of the carbosilane dendrimers. However, one could extract structural information about the molecular conformation from the film thickness and wetting edges on a solid substrate and from surface pressure/area... 

MD simulations of model membrane systems have provided a unique view of lipid interactions at a molecular level of resolution [21], Due to the inherent fluidity and heterogeneity in lipid membranes, computer simulation is an attractive tool. MD simulations allow us to obtain structural, dynamic, and energetic information about model lipid membranes. Comparing calculated structural properties from our simulations to experimental values, such as areas and volumes per lipid, and electron density profiles, allows validation of our models. With molecular resolution, we are able to probe lipid-lipid interactions at a level difficult to achieve experimentally. 

Kawata, Y, Xu, C., and Denk, W. 1999. Feasibility of molecular-resolution fluorescence nearfield microscopy using multi-photon absorption and field enhancement near a sharp tip. J. Appl. Phys. 85 1294-1301. 

Leenheer, J. A., Rostad, C. E., Gates, P. M., Furlong, E. T., and Ferrer, I. (2001). Molecular resolution and fragmentation of fulvic acid by electrospray ionization/multistage tandem mass spectrometry. Anal. Chem. 73,1461-1471. 

Complete monolayers adsorbed on surfaces can also be observed by STM.139 The separation of monolayer components in self-assembled monolayers on gold was unknown and unexpected before multicomponent films were examined using STM.140 Having the ability to resolve components with molecular resolution,107 this field has since advanced rapidly to exploit intermolecular interactions to produce desired patterns.141 Such advances in other important materials could easily be driven by this ability to observe their structures and functions with atomic resolution. Other environments—liquid, gas, elevated and reduced temperature—... 

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