Microscopic study of polymorphism of a photographic coupler

Polymorphism and polymorphic transformation of a photographic coupler have been examined using hot stage optical microscopy (HSOM). Two different polymorphs, metastable needle-like crystals and stable cubic-like crystals, were identified on heating. A solid-state transformation was found to occur from the metastable form to the stable form. Both polymorphs can precipitate from coupler solutions. The needle-like crystals appear in all cases examined; the cubic-like crystals precipitate only with higher concentrations and lower cooling rates. The solution-mediated transformation occurs in an organic solvent through dissolution of the metastable polymorph and growth of the stable polymorph. The growth rate of the stable polymorph is dependent on temperature as well as concentration. The activation energy of the growth is estimated for coupler solutions with different concentrations.     

A method for identification of interfering signals in EPR dating of tooth enamel

In this paper, a method for identifying interfering EPR signals in fossil tooth enamel is presented. This method consists of optimizing EPR parameters to enhance spectral resolution of the fossil signals followed by a g-factor and intensity normalized subtraction of a high-dosed, modern tooth enamel sample spectrum. By scanning the modern tooth enamel sample with the same parameters as the fossil sample, the difference spectrum of the fossil and modern irradiated tooth enamel samples can resolve numerous hyperfine and other interfering signals. This method was successfully applied to a fossil sample studied elsewhere (Grün, R., 1998a. Ancient TL 16, 51–55; Grün, R., Clapp, R., 1996. Ancient TL 14, 1–5; Martin Jonas, 1997. Ph.D. Thesis, Cambridge University; Jonas, M., Grün, R., 1997. Radiat. Meas. 27, 49–58; Vanhaelewyn et al., 2000. Appl. Radiat. Isot. 52, 1317–1326). This sample has shown discrepancies in dose estimations obtained from the power absorption curve versus those obtained from the first derivative spectra (Grün, R., 1998b. Radiat. Meas. 29, 177–193). The reason for this, and other discrepancies, are accounted for by the signals resolved using the method presented here.     

Some comments on the mechanism of the preparation of (Et4N)2B10H10 by thermolysis of Et4NBH4

The volatile intermediate Et₃NBH₃ was isolated during the thermolysis of Et₄NBH₄ at 185°C for 16 hr under dynamic vacuum. The rate of decomposition of Et₄NBH₄ was studied. Separate thermolyses of Et₄NBH₄ (or Et₃NBH₃) with closo B₉H₉^2?nido B₉H^?₁₂, or arachno B₉H₁₄^? did not produce B₁₀H₁₀^2? as the major product. These results are inconsistent with the “build-up” mechanism previously proposed for the thermolytic convertion of BH ₄^? to B₁₀H₁₀^2? and a new mechanism is required.     

Bands on trees

Communicated by D. R. Brown     

An approximate lower tolerance bound for the three-parameter Weibull applied to lumber property characterization

We investigate a large sample approach for obtaining tolerance bounds where the underlying population is a three-parameter Weibull distribution. Accurate tolerance bounds could play an important role in the development of lumber standards. Properties of the maximum likelihood based approach are compared with those of the standard nonparametric tolerance procedure. The asymptotic normal approximation to the tolerance bound was found to be inadequate for most of the cases considered.     

Stereoselectivity in Reactions of Metal Complexes. Part XV. Structure and stability of chiral cobalt(III) complexes with pentadentate ligands

The syntheses and characterization of four new linear pentadentate ligands and their Co^III complexes are described: N,N′-[(pyridine-2,6-diy)bis(methylene)]bis[sarcosine] (sarmp), N,N′-[(pyridine-2,6-diyl)bis(methylene)]bis[(R)- or (S)-proline] ((R,R)- or (S,S)-promp), N,N′-[(pyridine-2,6-diyl)bis(methylene)]bis[N-(methyl)-(R)- or (S)-alanine] ((R,R)- or (S,S)-malmp); 2,2′-[pyridine-2,6-diyl]bis[(S)- or rac-N-(acetic acid)pyrrolidine] ((S,S)- or rac-bapap). The complexes were characterized and, with but one exception, complex formation is stereospecific: Δ-exo-(R,R) (or Λ-exo-(S,S)) for promp and Λ-(R,R) (or Δ-(S,S)) for bapap. The exception is [Co((R,R)- or (S,S)-malmp)H₂O]ClO₄ for which two forms are obtained, to which Λ-endo-(R,R) (or Δ-endo-(S,S)) and, tentatively, Δ-unsymmetric-(R,R)- (or Λ-unsymmetric-(S,S)-) configurations are assigned. X-Ray crystal structures are presented for the complexes [Co(sarmp)H₂O]ClO₄, [Co((S,S)-promp)H₂O]ClO₄, [Co(rac-bapap)H₂O]ClO₄ and endo-[Co(rac-malmp)H₂O]ClO₄. Ligand acid dissociation and Co^II and Fe^II complex-formation constants are reported.     

Sub-picomole colorimetric single nucleotide polymorphism discrimination using oligonucleotide-nanoparticle conjugates

Oligonucleotide-gold nanoparticle conjugates are employed to demonstrate selective colorimetric discrimination of a cystic fibrosis-related genetic mutation in a model oligonucleotide system. Specifically, three strand oligonucleotide complexes are employed, wherein two probe oligonucleotide-gold nanoparticle conjugates are linked together by a third target oligonucleotide strand bearing the chosen CF-related mutation. By monitoring the solution optical absorption behaviour of the complexes as a function of temperature, melting profiles may be accurately acquired and reproducibly compared. Following this method, fully complementary sequences are successfully distinguished from mismatched sequences, with single base mismatch resolution, for the V232D mutation. To extend the detection sensitivity of this oligonucleotide-nanoparticle conjugate assay, a novel and compact LED-based optical monitoring system capable of sub-picomole level colorimetric SNP discrimination is also demonstrated.     

Rapid cloning and expression of a fungal polyketide synthase gene involved in squalestatin biosynthesis

PCR primers designed to selectively amplify the unique C-methyltransferase domain of fungal polyketide synthases were used to selectively clone a polyketide synthase gene involved in the biosynthesis of the squalene synthase inhibitor squalestatin S1 , heterologous expression of which led to the biosynthesis of the squalestatin side-chain.     

Using Earth’s Field NMR to Study Brine Content in Antarctic Sea Ice: Comparison with Salinity and Temperature Estimates

We report on the use in Antarctica of a portable nuclear magnetic resonance spectrometer which utilizes the Earth’s magnetic field. We obtain estimates of brine content, in samples of sea ice extracted at different depths from the annual ice of McMurdo Sound, in the vicinity of Cape Evans, Ross Island. These measurements are correlated with estimates of brine content obtained from temperature and salinity measurements at each depth, using a knowledge of the phase diagram.