The DNA bisintercalator triostin A is structurally based on a disulfide-bridged depsipeptide scaffold that provides preorganization of two quinoxaline units in 10.5 Å distance. Triostin A analogues are synthesized with nucleobase recognition units replacing the quinoxalines and containing two additional recognition units in between. Thus, four nucleobase recognition units are organized on a rigid template, well suited for DNA double strand interactions. The new tetra-nucleobase binders are synthesized as aza-TANDEM derivatives lacking the N-methylation of triostin A and based on a cyclopeptide backbone. Synthesis of two tetra-nucleobase aza-TANDEM derivatives is established, DNA interaction analyzed by microscale thermophoresis, cytotoxic activity studied and a nucleobase sequence dependent self-aggregation investigated by mass spectrometry. 相似文献
The spectral features appearing in mass spectra of random and block copolymers which display a drift in composition are discussed along with features appearing in mass spectra of terpolymers and tetrapolymers with sequence constraints. It is shown that previous models cannot account for these features. A new model is presented and a compact equation is derived which yields MS intensities. The prediction of the model is compared with some literature data, namely mass spectrometric data concerning a block copolymer sample containing units of alpha-methyl styrene and of methylmethacrylate which display a strong drift in composition, the molar fraction of methylmethacrylate units changing from 0.99 to 0.80 when passing from short to long macromolecular chains. The agreement between theory and experiment is good. A hyperbranched polymer obtained by condensing 4,4'-bis[p(acetoxy)phenyl] valeric acid (referred to as diphenolic acid, DPA) was then considered. The polymer turned out to be a copolymer with regular DPA units and modified DPA units (possessing a phenol group). The molar fraction of regular DPA units changes from 0.80 to 0.95 when passing from low masses to high masses. Copolymers with sequence constraints are considered, such as ABC copolymers in which AA cannot be found along the chain or ABCD copolymers in which A cannot follow A, B cannot follow B, etc. The novel method is applied to an exactly alternating copolymer with units of styrene (St) and maleic anhydride (MAH). The St-MAH sample turned out to be a complex mixture and the presence of a small amount of units of maleic acid (MAC) is detected. The abundance of MAC, estimated by the chain statistical method, is 5%. The method is applied to the copolymer obtained by reactive blending of poly(butylene terephthalate) and poly(bisphenolA carbonate). In this case, the theoretical spectra are generated and spectral features are discussed. 相似文献
A method based on use of NMR and infrared spectroscopy is described for the quantitative determination of the structural units generally occurring in polyalkenamers. The possibilities offered by both techniques are pointed out: in particular, the values found for the absorptivities of the infrared bands typical of unsaturated alkenamer units are extensively discussed. 相似文献
Summary: The thermodynamic equilibrium in a melt of homopolymer C mixed with clay modified by a diblock copolymer AB is considered in theory. It is assumed that mixing is carried out in two stages. At first, the diblock copolymer penetrates into the interlayers formed by long clay sheets. Then, the clay with adsorbed diblock copolymer chains is added to the homopolymer melt. It is shown that the first process is thermodynamically favorable only if the interlayer width exceeds some threshold value that depends mostly on the difference in the adsorption energy of units A and B. A spontaneous mixing at the second stage is possible only if the enthalpic interactions between homopolymer and copolymer units are not very unfavorable. If so, the formation of an intercalated state is expected for a homopolymer of length comparable to the copolymer length, while for a long homopolymer the anticipated equilibrium state is exfoliation. The spatial distribution of A, B, and C units across the interlayer has been studied for different parameters of the system. The most readily adsorbing units A occupy almost all clay surface. However, the layer of block A is considerably swelled by both B and C units. The mutual distribution of units B and C may vary from almost homogeneous to having rather sharp boundary depending on the value of the Flory‐Huggins parameter χBC. The formation of a pure homopolymer layer at the center of the interlayer indicates about a tendency to exfoliate.
Interlayer profiles of the fractions of units A, B, and C, respectively. 相似文献
The conformational behavior of a single comb-shaped macromolecule with associating groups in side chains was studied by means of Monte Carlo simulation. The side chains contain two types of units, type A representing nonfunctional units (main chain units are likewise classified with type A) and type B representing functional (attracting) units. As a result of an increase in attraction energy between associating groups, the transition of the macromolecule from coil to the globule state takes place. The coil-globule transition is accompanied by segregation of unlike units; as a result, the globule has a complex structure: the core of the globule is formed by attracting groups of side chains, and the envelope is formed from soluble units of both main and side chains. The dependence of the size and shape of the macromolecule on its structural parameters, such as the length of main and side chains and the graft density of side chains, and on the position of the functional groups in side chains was examined. Along with the single globule, conformations in which the attracting units of side chains formed several bead globules were observed. 相似文献
The International System of Units (SI) was first adopted in 1960, as the more recent implementation of the Metre Treaty signed in 1875. Basic features of the original SI are that (a) seven units are chosen as “base units”, all the others being “derived units”, and (b) the definitions of the base units should not create interdependence. This way, the SI conforms to the basic principle of the Metre Treaty that each signatory country can realise its choice of primary national standards of the very definitions of the units without needing to resort to calibrations obtained from another country, and without obligation to have them realised for all the units. A mismatch already occurs to some extent with respect to the above features in the present definitions of SI base units. This contribution, strictly based on metrological considerations, illustrates how the present proposal concerning new definitions for the base units, called “New SI”, would extend the mismatch. In this frame, also the meaning is discussed of the concepts of hierarchy and traceability in metrology. By outlining some of the consequences, a discussion is stimulated related to the status of base unit, to the meaning of calibration at the level of the standards of the unit definitions, and to the interdependence of countries’ standards. 相似文献
A number of alternating copolymers containing anthryl and aryl units in the polymer chain have been prepared by Friedel-Crafts arylation of the anthracene (polymer type B) or by condensation of 9,10-bis(chloromethyl) anthracene with opportune aromatic substrates (polymer type A). Polymers of type A were all found to contain 9,10-disubstituted anthracene units, but polymers of type B were found to contain 1,4-disubstituted anthracene units. Structure of the polymers were established through their NMR and ultraviolet spectra, and through analogy with appropriate model compounds. It has been found that the inclusion of anthracene units in the polymer chain yields higher melting and more soluble materials with respect to polybenzyls containing only aryl units. Anthracene units introduce, also, some interesting fluorescence characteristics in the polymers, which show intense emission at about 440 mμ. 相似文献
Results of molecular dynamics simulation studies of structural and dynamical properties of 12-, 13-, and 14-atom transition metal clusters are presented. The calculations are carried out using a Gupta-like potential expressed in reduced units. The transformation to absolute units involves two size-dependent parameters which effectively convert the potential into a size-dependent one. The minimum energy geometries of the clusters are obtained through the technique of simulated thermal quenching. A melting-like transition is observed as the energy of the clusters is increased. A novel element of the transition is that it may involve a premelting state. 相似文献
