Muon spin relaxation measurements of CsC60, RbC60, KC60

Muon spin relaxation (μ⁺SR) measurements of CsC₆₀ and RbC₆₀ have revealed magnetic ordering at 20 K and 15 K respectively, with static internal fields at the muon site of \sim7 G for both samples. No magnetic ordering is seen in KC₆₀ down to 2.5 K. An apparent small increase in muon spin relaxation which had been seen at 70 K in RbC₆₀ is ascribed to an extrinsic effect, originating in muons which stopped in the aluminum sample holder. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimal economic growth with foreign trade and a learning industry

Ryder (Ref. 1) has developed a simple two-sector macroeconomic model incorporatinglearning by doing as a determinant of the growth of productivity-enhancing experience and its effect on foreign trade. In this paper, optimal foreign trade and capital allocation policies are determined, in the context of the above model, for ranges of the international trade price not considered by Ryder. An extension of Ryder's model to include a dual trade price structure is briefly discussed. A specific numerical example is used to ascertain the configuration of the various features occurring in the extremal fields at different price levels.     

Operation of a conducting PRIZ

The construction and operation of a PRIZ spatial light modulator is reported using semi-transparent electrodes and no insulating layers. Qualitative observations of the dynamic properties of such conducting devices are found to be similar to those reported in the Soviet literature with several exceptions. The devices demonstrated dynamic detection, memory, and oscillatory instability as well as the typical directional filtering and dc suppression of the standard PRIZ which uses insulating layers. This is the first report of a non-Soviet built device of this type.     

Magnetic dilution in the geometrically frustrated SrCr(9p)Ga(12-9p)O19 and the role of local dynamics: A muon spin relaxation study

We investigate the spin dynamics of SrCr(9p)Ga(12-9p)O19 for p below and above the percolation threshold p(c) using muon spin relaxation. Our major findings are as follows: (i) At T-->0 the relaxation rate is T independent and approximately p(3), (ii) the slowing down of spin fluctuation is activated with an energy U, which is also a linear function of p(3) and lim U as p-->0 = 8 K; this energy scale could stem only from a single ion anisotropy, and (iii) the p dependence of the dynamical properties is identical below and above p(c), indicating that they are controlled by local excitation.     

Synthesis and biochemical characterisation of fluorinated analogues of pepstatin A and grassystatin A

Pepstatin A and grassystatin A are natural, statine-containing peptides that act as inhibitors of aspartic protease enzymes. In this work, stereoselective fluorination is investigated as a strategy for enhancing the pharmacodynamic and pharmacokinetic properties of these lead compounds. Fluorination is found to modestly affect the protease inhibitory potency, leading to the identification of two highly active new inhibitors of the cancer-associated protease, cathepsin D. However, no dramatic changes are observed in terms of target selectivity, lipophilicity, membrane permeability or metabolic stability.     

Strong,Self‐Healable,and Recyclable Visible‐Light‐Responsive Hydrogel Actuators

The most pressing challenges for light‐driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine‐functionalized anthracene group, which red‐shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double‐crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self‐healing, and fast visible‐light‐driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.     

Modular Chemoenzymatic Synthesis of Terpenes and their Analogues

Non‐natural terpenoids offer potential as pharmaceuticals and agrochemicals. However, their chemical syntheses are often long, complex, and not easily amenable to large‐scale production. Herein, we report a modular chemoenzymatic approach to synthesize terpene analogues from diphosphorylated precursors produced in quantitative yields. Through the addition of prenyl transferases, farnesyl diphosphates, (2E,6E)‐FDP and (2Z,6Z)‐FDP, were isolated in greater than 80 % yields. The synthesis of 14,15‐dimethyl‐FDP, 12‐methyl‐FDP, 12‐hydroxy‐FDP, homo‐FDP, and 15‐methyl‐FDP was also achieved. These modified diphosphates were used with terpene synthases to produce the unnatural sesquiterpenoid semiochemicals (S)‐14,15‐dimethylgermacrene D and (S)‐12‐methylgermacrene D as well as dihydroartemisinic aldehyde. This approach is applicable to the synthesis of many non‐natural terpenoids, offering a scalable route free from repeated chain extensions and capricious chemical phosphorylation reactions.     

Enantioselective Syntheses of Strychnos and Chelidonium Alkaloids through Regio‐ and Stereocontrolled Cooperative Catalysis

We describe enantioselective syntheses of strychnos and chelidonium alkaloids. In the first case, indole acetic acid esters were established as excellent partner nucleophiles for enantioselective cooperative isothiourea/Pd catalyzed α‐alkylation. This provides products containing indole‐bearing stereocenters in high yield and with excellent levels of enantioinduction in a manner that is notably independent of the N‐substituent. This led to concise syntheses of (?)‐akuammicine and (?)‐strychnine. In the second case, the poor performance of ortho‐substituted cinnamyl electrophiles in the enantioselective cooperative isothiourea/Ir catalyzed α‐alkylation was overcome by appropriate substituent choice, leading to enantioselective syntheses of (+)‐chelidonine, (+)‐norchelidonine, and (+)‐chelamine.     

Fingerprint vibrational spectra of protonated methyl esters of amino acids in the gas phase

Infrared spectra of the protonated monomers of glycine, alanine, valine, and leucine methyl esters are presented. These protonated species are generated in the gas phase via matrix assisted laser desorption ionization (MALDI) within the cell of a Fourier transform ion cyclotron resonance spectrometer (FTICR) where they are subsequently mass selected as the only species trapped in the FTICR cell. Alternatively, they have also been generated by electrospray ionization and transferred to a Paul ion-trap mass spectrometer where they are similarly isolated. In both cases IR spectra are then derived from the frequency dependence of the infrared multiple photon dissociation (IRMPD) in the mid-infrared region (1000-2200 cm(-1)), using the free electron laser facility Centre de Laser Infrarouge d'Orsay (CLIO). IR bands are assigned by comparison with the calculated vibrational spectra of the lowest energy isomers using density functional theory (DFT) calculations. There is in general good agreement between experimental IRMPD spectra and calculated IR absorption spectra for the lowest energy conformer which provides evidence for conformational preferences. The two different approaches to ion generation and trapping yield IRMPD spectra that are in excellent agreement.