Correcting for incomplete saturation and off-resonance effects in multiple-site saturation-transfer kinetic measurements

The effects of incomplete saturation and off-resonance irradiation on nuclear magnetic resonance saturation-transfer measurements of three-site chemical-exchange rates are discussed. A new method that uses double-saturation measurements is compared with two published methods, one that uses single-saturation measurements and one that uses a single-saturation measurement and a double-saturation measurement. Several formulas are compared for measuring the exchange rate constant k(DE) for exchange from a detected spin D to an exchanging spin E in the presence of exchange from spin D to a competing spin C. For each method, formulas are derived with corrections for incomplete saturation or off-resonance effects, with both corrections, and with neither correction. Exact formulas are available for three exchanging sites with incomplete saturation if there are no off-resonance effects. Off-resonance corrections are imperfect even with complete saturation.     

Effects of off-resonance irradiation, cross-relaxation, and chemical exchange on steady-state magnetization and effective spin-lattice relaxation times

In the presence of an off-resonance radiofrequency field, recovery of longitudinal magnetization to a steady state is not purely monoexponential. Under reasonable conditions with zero initial magnetization, recovery is nearly exponential and an effective relaxation rate constant R_1eff = 1/T_1eff can be obtained. Exact and approximate formulas for R_1eff and steady-state magnetization are derived from the Bloch equations for spins undergoing cross-relaxation and chemical exchange between two sites in the presence of an off-resonance radiofrequency field. The relaxation formulas require that the magnetization of one spin is constant, but not necessarily zero, while the other spin relaxes. Extension to three sites with one radiofrequency field is explained. The special cases of off-resonance effects alone and with cross-relaxation or chemical exchange, cross-relaxation alone, and chemical exchange alone are compared. The inaccuracy in saturation transfer measurements of exchange rate constants by published formulas is discussed for the creatine kinase reaction.     

A transportation mode selection model for a consolidation warehouse system

Summary This paper presents a transportation mode selection model for a consolidation warehouse system. It determines the transportation mode to be used by each plant or warehouse (point of origin) to ship its order to the company's consolidation point or central warehouse. The model considers the tradeoff between the total cost of transporting items and the maximum time until a complete order has reached the consolidation point. It brings to bare the effect of each possible mode on (1) buyer transportation cost, and (2) related buyer inventory costs. An algorithm is provided to determine the most preferable shipping plan. A prototypical example is presented to illustrate the use of the algorithm.

---

Zusammenfassung Es wird ein Liefersystem betrachtet, bei dem die bestellten Waren von verschiedenen Herstellern oder Lagerhäusern über eine gemeinsame Zentrale an den Kunden geliefert werden. Für den Transport der Waren von jedem Hersteller zur Zentrale sind verschiedene Transportarten wählbar, die unterschiedliche Transportkosten und Transportdauern verursachen. Die verschiedenen Transportdauern führen zu unterschiedlichen Lagerhaltungskosten beim Kunden. Es wird ein Modell angegeben, das die mit der gewählten Transportart verbundenen Transportkosten und Lagerhaltungskosten berücksichtigt. Ein Algorithmus zur Auswahl der günstigsten Transportart wird bereitgestellt. An einem kleinen Beispiel wird der Algorithmus erläutert.

     

On the stereospecificity of the structurally diagnostic m/z 84 ion in the mass spectra of gibberellins and kaurenes with a 15-hydroxy substituent

The presence of a 15-hydroxy substituent in naturally-occurring kaurenes and gibberellins gives rise to a structurally diagnostic ion at m/z84 (C₅H₈O) in their electron-impact mass spectra, which shifts to m/z156 for the TMS derivative, and is unaffected by differences in the A and B rings. Studies on a model tricyclic system have shown that this ion is more intense when the stereochemistry of the B/C ring junction is cis than when it is trans. In accordance with a previously proposed pathway for the formation of this ion, deuterium labelling confirms that there is a site-specific transfer of the β-hydrogen from the cis ring junction to the C₅ fragment ion, although a minor modification of the earlier mechanism is proposed.     

Photophysics of aminoxanthone derivatives and their application as binding probes for DNA

Xanthones with amino substituents were synthesized to diminish the photoreactivity of the xanthone chromophore with DNA, with the objective of using these molecules to study their binding dynamics with DNA. The aminoxanthones showed a strong solvatochromic effect on their singlet and triplet excited-state photophysics, where polar solvents led to a decrease of the energies for the excited states. Quenching of the triplet excited states by nitrite anions was used to determine the binding dynamics, and a residence time in the microsecond time domain was estimated for the bound 2-aminoxanthone with DNA. The quenching experiments performed showed that this methodology will not be applicable to study the binding dynamics of a wide variety of guests with DNA.