Chemical Structure Modification

Novel nanoscale discotic liquid crystalline porphyrins 14 with partial alkyl chain perfluorination has been designed and synthesized in our group which exhibits exceptionally enhanced tendency to spontaneously self-assemble into homeotropically ordered nanostructures [107]. The defect-free homeotropically aligned fluorinated porphyrin thin films were fabricated and characterized. In the films thinner than 10 pm in glass cells, it shows strong tendency towards homeotropic 

Liquid crystalline triphenylene hexacarboxyUc esters 15 have been recently synthesized and the columnar phase has been observed to align homeotropically on different substrate surfaces [82]. The alignment behavior has been studied by polarizing optical microscopy and X-ray diffraction techniques. POM shows a dark view whereas optical microscopy image displayed a dendritic texture typical of columnar hexagonal assembly. The hexagonal columnar phase displays 

---

Fig. 4. Anticancer drugs paclitaxel and docetaxel. Both compounds can be obtained by chemical structure modification of baccatin III or 10-deacetyl baccatin III...

The extent of 1640 cm or 1675 cm band formation on the one hand, and phenylene peak intensity changes on the other, seem to be closely related, as one effect is never observed without the other. Further, there are connections with the availability of moisture during substrate storage, which increases the amount of adsorbed water and hydroxide on the surface that would react with the isocyanate groups. Therefore, urea or urea-like species (showing bands at 1695-1630 cm [30]) are the most reasonable candidates for these chemical structure modifications observed in the interphase on Al and - less intensely - on copper. 

Chemical structure modifications which enhance activity and refine specificity will be followed up using medicinal chemistry methods, relating structures of compounds to activity in certain assays. These exercises will result in the definition of a quantitative structure activity relationship (SAR) for the series of compounds active in the assays. 

In summary, the predictions of analytic PRISM theory [67] for the phase behavior of asymmetric thread polymer Uends display a ly rich dependence on the single chain structural asymn try variables, the interchain attractive potential asymmetries, the ratio of attractive and repulsi interaction potential length scales, a/d, and the thermodynamic state variaUes t) and < ). Moreover, these dependences are intimately coupled, which mathematically arises within the compressible PRISM theory from cross terms between the repulsive (athermal) and attractive potential contributions to the k = 0 direct correlations in the spinodal condition of Eq. (6.6). The nonuniversality and nonadditivity of the consequences of molecular structural and interaction potential asymmetries on phase stability can be viewed as a virtue in the sense that a great variety of phase behaviors are possible by rational chemical structure modification. Finally, the relationship between the analytic thread model predictions and numerical PRISM calculations for more realistic nonzero hard core diameter models remains to be fully established, but preliminary results suggest the thread model predictions are qualitatively reliable for thermal demixing [72,85]. 

Pandey L, Risko C, Norton JE, Bredas JL (2012) Donor-acceptor copolymers of relevance for organic photovoltaics a theoretical investigation of the impact of chemical structure modifications on the electronic and optical properties. Maaomolecules 45 6405... 

Scheme 4.2 Chemical structure modification from IIIA-IIIG to inj...

In general, increasing the temperature within the stability range of a single crystal structure modification leads to a smooth change in all three parameters of vibration spectra frequency, half-width and intensity. The dependency of the frequency (wave number) on the temperature is usually related to variations in bond lengths and force constants [370] the half-width of the band represents parameters of the particles Brownian motion [371] and the intensity of the bands is related to characteristics of the chemical bonds [372]. 

The optical properties can be tuned by variations of the chromophores (e.g. type of side-chains or length of chromophorc). The alkyl- and alkoxy-substituted polymers emit in the bluc-gnecn range of the visible spectrum with high photolu-inincsccncc quantum yields (0.4-0.8 in solution), while yellow or red emission is obtained by a further modification of the chemical structure of the chromophores. For example, cyano substitution on the vinylene moiety yields an orange emitter. 

Fig. 1 Chemical structures of backbone modifications used in therapeutic nucleic acid analogs. Shown are the unmodified DNA/RNA chemical structures in addition to a selection of first (PS), second (OMe, MOE), and third generation (PNA, LNA, MF) nucleic acid modifications...

Owing to multi-functionahty, physical properties such as solubihty and the glass transition temperature and chemical functionahty the hyperbranched (meth) acrylates can be controlled by the chemical modification of the functional groups. The modifications of the chain architecture and chemical structure by SCV(C)P of inimers and functional monomers, which may lead to a facile, one-pot synthesis of novel functionahzed hyperbranched polymers, is another attractive feature of the process. The procedure can be regarded as a convenient approach toward the preparation of the chemically sensitive interfaces. 

We alluded earlier to the variety of structural modifications which may he observed in sheet silicates. Clearly it is a matter of considerable in jortance to he able to determine if, for example, the aluminium content within a clay arises p a ely from octahedral substitution (as in montmorillonite) or whether there is some tetrahedral component (as in heidellite). a1 MASNMR readily provides the necessary answers. Figvire 1 illustrates the a1 spectrum for a synthetic heidellite material with Na as charge balancing cation. Aluminium in two distinct chemical environments is observed, with chemical shifts corresponding to octahedrally and tetrahedrally co-ordinated aluminium. 

Influencing the efficacy or potency of chemicals is a strategy used by the pharmaceutical industry as part of the drug discovery process that can be incorporated into designing safer industrial chemicals. Efficacy is the maximal effect, either therapeutic or toxic, that a chemical can achieve. Potency is a measure of the amount of a substance that is needed to attain a given response level. Opioid analgesics are examples of where structural modifications have been used to establish a relationship between structure and activity. ... 

---