Matrix Effects on Selective Chemical Sensing by Sol-Gel Entrapped Complexing Agents

Changes in the selectivity of molecular recognition systems on sol-gel entrapment are reported. Thermodynamic effects are exemplified by studies of the metal-ion complexing agent Eriochrome Cyanine R (ECR). In aqueous solution this binds strongly and selectively to Al3+, whereas in a TMOS-based sol-gel matrix it is selective for Cu3+. Thermodynamic effects, due to restricted translational freedom of water molecules or different solvent structure and isolation of ligands, can explain these observations. Effects of entrapment on molecular recognition by a large conformationally flexible molecule have been studied using a tris-terminated PAMAM dendrimer. The dendrimer conformation and its complexation with Cu2+ changes on entrapment, and binding of aromatic carboxylic acids such as ibuprofen can be detected by changes in visible absorption and surface plasmon resonance using spun films of the sol-gel composite. These effects show that in addition to providing a porous entrapment matrix of good optical quality, sol-gels may be used to alter the binding characteristics of the entrapped receptors.     

Novel approach to trans-fused carbobicycles

The combination of a silicon directed N-acyliminium ion cyclization reaction and a subsequent S_N2′ substitution of an imide nitrogen with lithium dimethyl cuprate constitutes a novel approach to functionalized transfused carbobicycles.     

Intramolecular reactions of acyclic n-acyliminium ions II allyl silanes as nucleophiles

Intramolecular reactions of acyclic N-acyliminium ions with allyl silanes, induced by protic or Lewis acid, lead to 3-vinylpyrrolidines or 3-vinylpiperidines.     

A study of operands in terms of maximal generalized orbits

An operand X of a monoid S is called saturated if every generalized orbit in X is contained in a union of others. Every operand has a natural decomposition as a union of an operand admitting an irredundant cover by maximal generalized orbits and of a saturated operand. There is a descending chain of suboperands of an operand which leads to the definition of the saturation length of an operand. S has no saturated operands if and only if S satisfies the ascending chain condition on orbits.     

Novel synthesis of aza-heterocycles

N-formyl aza-heterocycles $\text{15}$ – $\text{24}$ can be prepared by RaNi desulfirization of thiazolidine derived polycyclics $\text{5}$ – $\text{14}$ which in turn are obtained by intramolecular thiono α-acyliminium cyclisations of π-nucleophiles.     

α-acyliminium ion synthesis of elaeokanine B

Elaeokanine B has been synthesized utilizing the acid-catalyzed cyclisation of hydroxylactam $\text{9}$ as key step in the formation of the chloride $\text{10}$.     

A new enantiomerization mechanism for tripodal penta-coordinate Zn(II)(nta) complexes. Theoretical clarification of the observed 1H NMR spectrum

Based on DFT calculations (RB3LYP/LANL2DZp), the unexpected single-line 1H NMR spectrum of Zn(II)(nta), nta = 2,2',2'-nitrilotriacetate, can be ascribed to a non-dissociative enantiomerization process (deltadeltadelta<=>lambdalambdalambda) from C3viaC3v to C3 symmetry. The energy barrier is rather low and depends to a lesser extent on the nature of the co-ligand in [Zn(nta)X]2- (X: H-, CH3- NH2-, OCH3-, F-, Cl-, Br-, I-) and [Zn(nta)Y]- (Y: NCH, CO, N2, O(CH3)2), but more so on the overall charge of the complex. The energy barrier for enantiomerization of [Zn(nta)X]2- is between 5.7 and 6.7 kcal mol-1, and for [Zn(nta)Y]- between 2.2 and 3.1 kcal mol-1.     

Engineering Polymer Informatics: Towards the Computer‐Aided Design of Polymers

The computer‐aided design of polymers is one of the holy grails of modern chemical informatics and of significant interest for a number of communities in polymer science. This paper outlines a vision for the in silico design of polymers and presents an information model based on modern semantic web technologies, thus laying the foundations for achieving the vision.