The synthesis of carboxymethyl derivatives of purines and pyrimidines and their condensation with naturally occurring macromolecules

1-Carboxymethylthymine, 1-carboxymethylcytosine and 9-carboxymethyladenine were obtained by the direct carboxymethylation of the appropriate bases. In addition a small amount of 3-carboxymethyladenine was obtained. 9-Carboxymethylhypoxanthine was obtained by deamination of 9-carboxymethyladenine. 1-Carboxymethyluracil, 1-carboxymethylthymine and 9-carboxymethyl-hypoxanthine were each condensed with protamine and with dextran to give water-soluble, base-substituted polymers. The 1-carboxymethylthymine-dextran showed a slow decrease in optical density at 268 nm in 2 × SSC at 20°, of 30%. This did not occur in 7M urea. 1-Carboxymethylthymine-dextran gave an additional hypochromic effect with polyadenylic acid in 2 × SSC at 4° or 14° of 13% and 9% respectively. The ratio of thymine: adenine residues at the point of maximum hypochromicity was 3:1. The other dextran derivatives did not show similar hypochromic effects. The 1-carboxy-methylthymine-protamine gave a precipitate with polyadenylic acid probably due to electrostatic interaction.     

Mechanistic analogies amongst carbohydrate modifying enzymes

Carbohydrates are known to play essential roles in a myriad of biological processes. The enormous complexity of the various oligosaccharide structures found in biology is derived from a rational orchestration of the enzymatic formation and breakdown of glycosidic linkages achieved by glycosyltransferases, glycosidases and phosphorylases. A detailed understanding of the chemical mechanisms by which these classes of enzymes function not only provides a rational basis for their engineering and application in both the development and synthesis of new classes of therapeutic agents, but also provides insight into the role of convergence in the natural evolution of enzyme function.     

A plasticity model for powder compaction processes incorporating particle deformation and rearrangement

This paper develops a mechanistic model of granular materials that can be used with a commercial finite element package (ABAQUS). The model draws on the ideas of critical state soil mechanics and combines them with the theory of envelopes to develop an elasto-plastic model with a non-associated flow rule. The model incorporates both local deformation at the granule contacts, and rearrangement of the granules so that jointly they account for any bulk deformation. The mechanics of the model closely reflect the physicality of the material behaviour and the model parameters are closely linked (although not simplistically identical) to the characteristics of the granules. This not only gives an insight into the material behaviour, but also enables the model to be used to facilitate design of the material, its processing properties and, hence, component development. The model is used to simulate drained triaxial tests, settlement of a powder in a bin, and some examples of die pressing. Simulations are compared with experimental data and with predictions obtained using other models.     

Laser Mass Spectrometry of Organophosphorus Pesticides and Related Compounds

Abstract

Laser mass spectra obtained for 20 organophosphorus (OP) compounds were systematically evaluated for groups containing analogous structural features. Variations in fragmentation can be understood based on simple organic reactions. While detailed mechanistic interpretations of the laser mass spectra (LMS) were not possible, the qualitative features in the LMS obtained from five compounds, not in the original set, could be predicted based on the characteristics of the other OP compounds studied. The success of the prediction lends credence to the qualitative models developed for rationalizing the LMS. A specific feature in the LMS of aromatic thionophosphates is a thiono-thiolo rearrangement. Detailed investigation into the phenomena involved comparison of LMS obtained from aromatic thionophosphates with spectra from electron impact, chemical ionization, field desorption, and secondary ion mass spectrometry. These results led to the conclusion that the rearrangement in laser mass spectrometry must occur during volatilization while the molecule/ion is in the “cloud” present immediately above the laser impact area.     

The Distribution of the Bit Error Rate for an M Branch Antenna with N Interferers

Given an antenna with M branches, the bit error rate (BER) and mean squared error (MSE) for choosing the antenna weights (to approximately cancel M???1 interferers), are given by $$ \mathit{BER} \approx C \;\exp \left(-\alpha-\alpha Z_N\right) \mbox{ and } \mathit{MSE}=1/\left(1+Z_N\right), $$ where Z _N is the signal-to-interference plus noise ratio and C, α are some fixed parameters. So, obtaining the distribution of Z _N allows one to obtain the distribution of the MSE and to approximate that of the BER. Three cases are presented:

• the case of fixed powers for the interferers, say Q ₁, ..., Q _N , and for the wanted signal, say Q ₀;
• the case of fixed power for the wanted signal and random powers for the interferers;
• the case of random powers for both the wanted signal and the interferers.

We assume that Q ₀,...,Q _N are independent with different distributions. We show that to magnitude 1/N, the distribution of Z is just that of Q ₀ g _M /T, where g _M is a gamma random variable with mean M and T is the average of the total interferer power: $$ T = \mathbb{E} \ \left\{ \sum\limits_{j=1}^N Q_j\right\}. $$ We also show how to obtain an expansion in powers of 1/N for the distribution of $\mathit{TZ}$ about that of Q ₀ g _M . For example, to get the distribution of $\mathit{TZ}$ up to magnitude 1/N ², one requires only the means of Q ₁,...,Q _N and $Q_1^2,\ldots,Q_N^2$ and the distribution of Q ₀.     

Polymerization (Polycondensation) of Alkanes over Fluosulfonic Acid and Antimony Pentafluoride

Several low molecular weight alkanes have been polymerized (polycondensed) over HSO₃ F-SbF₅ to yield a highly branched oily oligomer with a molecular weight range from the molecular weight of the monomer to around 700. The order of reactivity for butane and lower molecular alkanes is isobutane > n-butane > propane > ethane > methane. The reactivity is explained by the ease of attack of an acid proton derived from the acid on the alkane sigma bonds as well as the relative stability of the resulting cation formed. A cationic mechanism for this reaction is proposed.