Molecular function improvement

As one can see, the SLG-MINDO/3 in general improves the description of molecular geometry as compared to the SCF-MINDO/3 method. Obvious deterioration takes place only for the ammonia molecule (particularly for the valence angle). However, in other cases, transition to the SLG wave function improves the values of the valence angles. This is seen in the example of the hydrogen peroxide molecule. 

A major basis for the advancement in macro-molecular functionality is our improving ability to control the macromolecular and supramolecular structures in great detail. Dense and cascade-type branching provided access to three-dimensional molecules, which do not interpenetrate but interact via their surfaces. Recent synthetic developments include microgels,15 17 dendrimers,18-26 and arborescent graft... 

Not only can molecular design improve the miscibility with other oils, it can also confer ILs with special functions, such as antioxidation and the ability to adapt to a broader temperature range. We synthesized three imidazolium-based ILs containing sterically hindered phenol groups with antioxidant functions and evaluated the tribological behaviors of these ILs as additives for PEG appfication in steeFsteel contacts on an Optimol SRV-IV oscillating reciprocating friction and wear tester, as well as on MRS-IJ four-ball testers [100]. The rotary bomb oxidation test (RBOT) test, thermal analysis, and Cu strip test results revealed that synthesized ILs possessed excellent antioxidation capability. 

Research and development efforts in the pharmaceutical and biotech industries depend critically on patent protection for commercially valuable biological molecules. In this context, patent laws broadly require clear disclosure of molecular function. Deriving this essential functional information is far from trivial [101]. Basic sequence homology studies are already a first step in these critical research efforts. Pattern-based approaches focusing on fundamental structural and functional motifs can valuably focus expensive and lengthy laboratory efforts. The power of these approaches will invariably increase with expansion and improvement of data repositories and associated analysis tools. The U.S. Patent and Trademark Office already welcomes these sorts of in silico studies as valuable adjunct evidence in support of a molecule s functional specification. 

Fig.11. The influence of the molecular weight on viscosity is shown as a function of the shear rate A raise in molecular weight improves the viscosity with low shear rates. In the case of fairly high shear rates vicosity and molecular weight become independent from each other (modified according to Bothner and Wik, 1989)...

The first point to remark is that methods that are to be incorporated in MD, and thus require frequent updates, must be both accurate and efficient. It is likely that only semi-empirical and density functional (DFT) methods are suitable for embedding. Semi-empirical methods include MO (molecular orbital) [90] and valence-bond methods [89], both being dependent on suitable parametrizations that can be validated by high-level ab initio QM. The quality of DFT has improved recently by refinements of the exchange density functional to such an extent that its accuracy rivals that of the best ab initio calculations [91]. DFT is quite suitable for embedding into a classical environment [92]. Therefore DFT is expected to have the best potential for future incorporation in embedded QM/MD. 

Inadequate availability of experimental data can considerably inhibit the development of improved energy functions for more accurate simulations of energetic, structural, and spectroscopic properties. This has led to the development of class II force fields such as CFF and the Merck Molecular Force Field (MMFF), which are both based primarily on quantum mechanical calculations of the energy surface. The purpose of MMFF, which has been developed by Thomas Halgren at Merck and Co., is to be able to handle all functional groups of interest in pharmaceutical design. 

ADF uses a STO basis set along with STO fit functions to improve the efficiency of calculating multicenter integrals. It uses a fragment orbital approach. This is, in essence, a set of localized orbitals that have been symmetry-adapted. This approach is designed to make it possible to analyze molecular properties in terms of functional groups. Frozen core calculations can also be performed. 

The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers (see Acrylic ester polymers), olefin polymers and copolymers, and styrene—butadiene copolymers. The degree of VI improvement from these materials is a function of the molecular weight distribution of the polymer. VI improvers are used in engine oils, automatic transmission fluids, multipurpose tractor fluids, hydrautic fluids, and gear lubricants. Their use permits the formulation of products that provide satisfactory lubrication over a much wider temperature range than is possible using mineral oils alone. 

Viscosity (Viscosity-Index) Improvers. Oils of high viscosity index (VI) can be attained by adding a few percent of ahnear polymer similar to those used for pour-point depressants. The most common are polyisobutylenes, polymethacrylates, and polyalkylstyrenes they are used in the molecular weight range of about 10,000 to 100,000 (18). A convenient measure for the viscosity-increasing efficiency of various polymers is the intrinsic viscosity Tj, as given by the function... 

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