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 $\text{10}$.     

Evaluation of process parameters of ultrasonic treatment of bacterial suspensions in a pilot scale water disinfection system

In this study, several process parameters that may contribute to the efficiency of ultrasound disinfection are examined on a pilot scale water disinfection system that mimics realistic circumstances as encountered in an industrial environment. The main parameters of sonication are: (i) power; (ii) duration of treatment; (iii) volume of the treated sample. The specific energy (E_s) is an indicator of the intensity of the ultrasound treatment because it incorporates the transferred power, the duration of sonication and the treated volume. In this study, the importance of this parameter for the disinfection efficiency was assessed through changes in volume of treated water, water flow rate and electrical power of the ultrasonic reactor. In addition, the influences of the initial bacterial concentration on the disinfection efficiency were examined. The disinfection efficiency of the ultrasonic technique was scored on a homogenous and on a mixed bacterial culture suspended in water with two different types of ultrasonic reactors (Telsonic and Bandelin). This study demonstrates that specific energy, treatment time of water with ultrasound and number of passages through the ultrasonic reactor are crucial influential parameters of ultrasonic disinfection of contaminated water in a pilot scale water disinfection system. The promising results obtained in this study on a pilot scale water disinfection system indicate the possible application of ultrasound technology to reduce bacterial contamination in recirculating process water to an acceptable low level. However, the energy demand of the ultrasound equipment is rather high and therefore it may be advantageous to apply ultrasound in combination with another treatment.     

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.     

Confusing cause and effect: energy-entropy compensation in the preferential solvation of a nonpolar solute in dimethyl sulfoxide/water mixtures

We performed molecular simulations to analyze the thermodynamics of methane solvation in dimethyl sulfoxide (DMSO)/water mixtures (298 K, 1 atm). Two contributions to the interaction thermodynamics are studied separately: (i) the introduction of solute-solvent interactions (primary contribution) and (ii) the solute-induced disruption of cohesive solvent-solvent interactions (secondary contribution). The energy and entropy changes of the secondary contribution always exactly cancel in the free energy (energy-entropy compensation), hence only the primary contribution is important for understanding changes of the free energy. We analyze the physical significance of the solute-solvent energy and solute-solvent entropy associated with the primary contribution and discuss how to obtain these quantities from experiments combining solvation thermodynamic and solvent equation of state data. We show that the secondary contribution dominates changes in the methane solvation entropy and enthalpy: below 30 mol % DMSO in the mixture, methane, because of more favorable dispersion interactions with DMSO molecules, preferentially attracts DMSO molecules, which, in response, release water molecules into the bulk, causing an increase in the entropy. This large energy-entropy compensating process easily causes a confusion in the cause for and the effect of preferred methane-DMSO interactions. Methane-DMSO dispersion interactions are the cause, and the entropy change is the effect. Procedures that infer thermodynamic driving forces from analyses of the solvation entropies and enthalpies should therefore be used with caution.