Noncritical detection of tunable CO2 laser radiation into the green by upconversion in silver thio-gallate

Tangential near-noncritical phase matching is reported for upconversion in silver thiogallate (AgGaS₂) using a dye laser as pump. A large acceptance angle for noncollinearity as desirable from a device view point is realised. Weak temperature tunability is also exploited to realise noncriticality.     

Retarded Van der Waals potential between a conducting plane and a polarizable particle

The method of zero point energy is used to obtain the retarded Van der Waals potential between a perfectly conducting plane and a particle possessing both electric and magnetic polarizability. As a special case, the force between a conducting plane and a conducting sphere is obtained.     

Berry's phase,density matrices and incompatible observables

Adiabatically time-varying parameter-dependent cyclic Hamiltonians are known to generate Berry's phase in state vectors in addition to the usual dynamical phase. Using the standard algorithm for collapse into a mixture following a quantum measurement process, we investigate the general nature of measurements in which the effects of Berry's phase, introduced at some intermediate stage of the measurement process, persist in the final collapsed density matrix. We find that it is possible to construct a sequence of a preparation followed by a measurement of an observable incompatible with the prepared state, where the collapsed density operator carries intermediate changes of phase in pure states; hence unitary time evolution alone is not essential for the observation of geometrical phases. This result confirms similar suggestions made by other investigators.     

Solid-phase extraction for the decontamination of alkali metal, alkaline Earth metal, and ammonium salts from heavy metal ions

Salicylaldoxime-immobilized silica gel was characterized and used as a potential sorbent for heavy metal ions, viz. Cu(II), Ni(II), Co(II), and Zn(II). The experimental conditions were optimized both in batch and column processes to achieve the maximum efficiency. Kinetic and thermodynamic parameters as well as isotherm constants were evaluated to test the feasibility of the process. The role of various metal ions and different anions were tested in order to monitor the process in case of real samples. The alkali metal, alkaline earth metal, and ammonium salts do not have any effect on the said process. This differential behavior can be effectively used for the decontamination of alkali metal, alkaline earth metal, and ammonium salts from Cu(II), Ni(II), Co(II), and Zn(II) ions via solid phase extraction following AAS measurement. The purification of the salts was confirmed by voltammetric experiment.     

A model calculation on the transport of excitation energy in a molecular crystal

We report a model calculation of the transport of a local (site) excitation in a doped molecular crystal containing one impurity. We do not consider the impurity as a direct trap for electronic excitations (zero trap depth) but assume that exciton-phonon interaction is exclusively given by the coupling of excitons with the vibrational displacement of the impurity. The dynamical problem is solved by using a time-dependent effective potential consisting of equilibrium average exciton-phonon interaction and fluctuations around this average. Two correlation functions are computed using the slow phonon limit and assuming that the temperature of the system is 300 K. Transmission of the excitation energy over a distance of eight spacings takes place, electronically, within a few picoseconds. With the exciton-phonon interaction switched on, calculated correlation functions diminish very rapidly with increasing time, indicating that an irreversible transfer of excitonic energy to the thermal bath takes place. Thus transmission of the excitation energy over such a distance (and without a high rate of trapping) is not an efficient process.     

Transport of excitation energy in a three-dimensional doped molecular crystal

We report here a theoretical formulation of the transport of excitation energy in a three-dimensional molecular crystal containing one impurity. The excitation is assumed to be localized in the jth site at time t, and the expression for the probability of finding the excitation at some other site j′ at a later time t′ is derived. The probability is given by the correlation function $ \left\langle {\hat P_j (t)\hat P_j (0)} \right\rangle $, where $ \left\langle {\hat P_m } \right\rangle $ represents the site projection operator, |m〉 〈m|. In our derivation we neglect the interaction among excitons of different bands, account for the presence of the impurity by adding a small perturbation term to the pure crystal Hamiltonian, and calculate the exciton solutions through first order. We consider a general impurity; that is, the trap depth is nonvanishing and may even be complex. The exciton–phonon interaction is taken to be linear in lattice displacement vectors; we assume that the short time behavior of $ \left\langle {\hat X} \right\rangle _{{\rm phonon}} $ gives the dominant contribution to the physical property X being studied and solve the dynamical problem by using a time-dependent effective potential consisting of fluctuations around the equilibrium average exciton–phonon interaction. Several limiting cases are briefly discussed.     

Regioselective Barbier reactions of 2-bromomethylcyclohexenone

Although the addition of crotyl or prenyl organometallic reagents has certainly found application in organic synthesis, the use of other non-symmetric allylic organometallic reagents has not received much attention. In part this is due to potential problems in controlling the regioselectivity of the addition products. We have noted that the tin and zinc reagents derived from 2-bromomethylcyclohexenone afford the complementary α and γ addition products, respectively. These conditions work for the reaction with a range of aldehydes, affording the products in good to modest yield.     

Supported aqueous-phase enzymatic catalysis in organic media

The use of partially hydrated porous silica particles has been studied as a support for cofactor-dependent enzymatic catalysis in organic solvents. At an optimal pore hydration corresponding to 70% pore volume, horse liver alcohol dehydrogenase catalyzes the oxidation and reduction of alcohols and aldehydes, respectively, with rates sixfold higher than with nonporous glass beads as the enzymatic support and with cofactor recycling numbers in excess of 10⁵. Thus, supported aqueous-phase enzymatic catalysis makes highly effective use of the enzyme and cofactor by coimmobilization and by providing a high interfacial area for reactions in organic media.     

Enantiomeric cannabidiol derivatives: synthesis and binding to cannabinoid receptors

(-)-Cannabidiol (CBD) is a major, non psychotropic constituent of cannabis. It has been shown to cause numerous physiological effects of therapeutic importance. We have reported that CBD derivatives in both enantiomeric series are of pharmaceutical interest. Here we describe the syntheses of the major CBD metabolites, (-)-7-hydroxy-CBD and (-)-CBD-7-oic acid and their dimethylheptyl (DMH) homologs, as well as of the corresponding compounds in the enantiomeric (+)-CBD series. The starting materials were the respective CBD enantiomers and their DMH homologs. The binding of these compounds to the CB(1) and CB(2) cannabinoid receptors are compared. Surprisingly, contrary to the compounds in the (-) series, which do not bind to the receptors, most of the derivatives in the (+) series bind to the CB(1) receptor in the low nanomole range. Some of these compounds also bind weakly to the CB(2) receptor.