How Taxol stabilises microtubule structure

The structure of tubulin shows paclitaxel (Taxol(R)) binding to a pocket in beta tubulin on the microtubule's inner surface, which counteracts the effects of GTP hydrolysis occurring on the other side of the monomer.     

Avermectin-milbemycin studies. 4. An expedient two-step preparation of p-hydroxybenzoates

Dianions derived from a variety of 1,3-diketones react with $\text{Z}$-ethyl-3-bromopropenoate to afford unsaturated diketoesters which upon treatment with base undergo facile cyclization-dehydration to p-hydroxybenzoates.     

A change of variable for the perturbation parameter in rayleigh–Schrödinger perturbation theory

The Feenberg–Goldhammer change of scale, whereby the H₀ in perturbation theory is replaced by (1/μ)H₀ with μ a scaling parameter, is shown to be equivalent to a change of variable for the perturbation parameter. A more general change of variable is shown to lead to a perturbation series with perturbation energies E₃, …, E_2n+1 equal to zero. The resulting energy through (2n + 1)th order has the same form as that found from the Brillouin–Wigner series by different methods.     

Electron densities from the Brueckner Doubles method

Summary The concept of the Brueckner orbital is examined, following a resurgence of interest in wavefunctions constructed from them. The distinction between Self Consistent Field, Natural and Brueckner orbitals are discussed. Total electron densities are calculated for several examples, and correlation densities are studied. It is found that the Brueckner orbitals are more localised than SCF orbitals. The total electron density constructed from the Brueckner reference determinant with Brueckner orbitals gives qualitatively similar pictures as other correlated methods. Brueckner orbitals are found to show dissociation well.     

Single-nucleotide-specific PNA-peptide ligation on synthetic and PCR DNA templates

DNA-directed chemical synthesis has matured into a useful tool with applications such as fabrication of defined (nano)molecular architectures, evolution of amplifiable small-molecule libraries, and nucleic acid detection. Most commonly, chemical methods were used to join oligonucleotides under the control of a DNA or RNA template. The full potential of chemical ligation reactions can be uncovered when nonnatural oligonucleotide analogues that can provide new opportunities such as increased stability, DNA affinity, hybridization selectivity, and/or ease and accuracy of detection are employed. It is shown that peptide nucleic acid (PNA) conjugates, nonionic biostable DNA analogues, allowed the fashioning of highly chemoselective and sequence-selective peptide ligation methods. In particular, PNA-mediated native chemical ligations proceed with sequence selectivities and ligation rates that reach those of ligase-catalyzed oligodeoxynucleotide reactions. Usually, sequence-specific ligations can only be achieved by employing short-length probes, which show DNA affinities that are too low to allow stable binding to target segments in large, double-stranded DNA. It is demonstrated that the PNA-based ligation chemistry allowed the development of a homogeneous system in which rapid single-base mutation analyses can be performed even on double-stranded PCR DNA templates.     

Total synthesis of (+)-dactylolide

[reaction: see text] The total synthesis of the new cytotoxic marine macrolide (+)-dactylolide (1) has been achieved in nine steps from known vinyl bromide (-)-AB. In addition, (+)-zampanolide (2) has been converted to (+)-dactylolide (1) via thermolysis.     

Interpreting Social Accounting Matrix (SAM) as an Information Channel

Information theory, and the concept of information channel, allows us to calculate the mutual information between the source (input) and the receiver (output), both represented by probability distributions over their possible states. In this paper, we use the theory behind the information channel to provide an enhanced interpretation to a Social Accounting Matrix (SAM), a square matrix whose columns and rows present the expenditure and receipt accounts of economic actors. Under our interpretation, the SAM’s coefficients, which, conceptually, can be viewed as a Markov chain, can be interpreted as an information channel, allowing us to optimize the desired level of aggregation within the SAM. In addition, the developed information measures can describe accurately the evolution of a SAM over time. Interpreting the SAM matrix as an ergodic chain could show the effect of a shock on the economy after several periods or economic cycles. Under our new framework, finding the power limit of the matrix allows one to check (and confirm) whether the matrix is well-constructed (irreducible and aperiodic), and obtain new optimization functions to balance the SAM matrix. In addition to the theory, we also provide two empirical examples that support our channel concept and help to understand the associated measures.     

Bond properties using a modern version of the Drude model

Using a mixture of classical and quantum mechanics, Drude model formulas for the polarizability and magnetic susceptibility of an atom or molecule and the dispersion coefficient for intermolecular forces between atoms and molecules are obtained both when the same frequency of oscillation is used for all the electrons and when different frequencies are used. The latter case allows us to discuss bond properties. The frequencies involved can be determined in a nonempirical way when it is recognized that the Frost model can be regarded as giving an ab initio quantitative justification for the Drude model. © 1996 John Wiley & Sons, Inc.