Geometry of multiple-spin systems as reflected in 13C-{1H} dipolar spectra measured at Lee-Goldburg cross-polarization

Theoretical calculation and analysis of (13)C-{(1)H} dipolar spectra of small-size spin clusters is presented. Dipolar spectra simulated using the time-independent average Hamiltonian are compared with the dipolar profiles obtained by 2D and 3D (1)H-(13)C correlation experiments employing Lee-Goldburg off-resonance cross-polarization (LG-CP). It is demonstrated that the structural parameters such as interatomic distances as well as mutual orientation of internuclear vectors can be derived from the dipolar profiles of simple spin clusters. Simplified analysis of the dipolar spectra based on isolated-like spin-pair approach can be used only if interacting spin cluster is reduced to the three-spin system in which the angle between both internuclear vectors ranges from 45 degrees to 135 degrees . For other local arrangements of spin systems the produced dipolar spectra must be analyzed with high caution. Contributions of all interacting spins to dipolar evolution of (13)C magnetization are mutually mixed and cannot be easily separated. However, simplification of the dipolar spectra is achieved by selective excitation. Enhanced selectivity of LG-CP transfer due to the initial (1)H chemical-shift-evolution period makes it possible to construct the dipolar spectra from (1)H-(13)C cross-peak intensities for every detected (1)H-(13)C spin-pair. Consequently, isolated-like spin pair evolution of the detected (1)H-(13)C coherence dominates to the resulting dipolar profile, while the influence of other interacting spins is suppressed. However, this suppression is not quite complete and analysis of the selective dipolar spectra based on isolated-like spin-pair approach cannot be used generally. Especially evolution of long-range (1)H-(13)C coherence is still significantly affected by spin states of other coupled hydrogen atoms.     

On the Discrepancy for Cartesian Products

Let B₂ denote the family of all circular discs in the plane.It is proved that the discrepancy for the family {B₁ x B₂ :B₁, B₂ B₂} in R⁴ is O(n^1/4+) for an arbitrarily small constant > 0, that is, it is essentially the same as that for thefamily B₂ itself. The result is established for the combinatorialdiscrepancy, and consequently it holds for the discrepancy withrespect to the Lebesgue measure as well. This answers a questionof Beck and Chen. More generally, we prove an upper bound forthe discrepancy for a family {^k_i=1A_i:A_iA_i, i = 1, 2, ..., k},where each A_i is a family in R^d_i, each of whose sets is describedby a bounded number of polynomial inequalities of bounded degree.The resulting discrepancy bound is determined by the ‘worst’of the families A_i, and it depends on the existence of certaindecompositions into constant-complexity cells for arrangementsof surfaces bounding the sets of A_i. The proof uses Beck's partialcoloring method and decomposition techniques developed for therange-searching problem in computational geometry.     

Polymerization of substituted acetylenes by various rhodium catalysts: Comparison of catalyst activity and effect of additives

This research deals with comparison of the activity of various Rh catalysts in the polymerization of monosubstituted acetylenes and the effect of various amines used in conjunction with [Rh(nbd)Cl]₂ in the polymerization of phenylacetylene. A zwitterionic Rh complex, Rh⁺(nbd)[(η⁶‐C₆H₅)B^?(C₆H₅)₃] ( 3 ), was able to polymerize phenylacetylene ( 5a ), t‐butylacetylene ( 5b ), N‐propargylhexanamide ( 5c ) and n‐hexyl propiolate ( 5d ), and displayed higher activity than the other catalysts examined, that is [Rh(nbd)Cl]₂ ( 1 ), [Rh(cod)(O‐o‐cresol)]₂ ( 2 ), and Rh‐vinyl complex ( 4 ). Monomers 5a and 5c polymerized virtually quantitatively or in fair yields with all these catalysts, while monomer 5b was polymerizable only with catalyts 3 and 4 . Monomer 5d did not polymerize in high yields with these Rh complexes. The catalytic activity tended to decrease in the order of 3 > 4 > 2 > 1 . Although polymerization of 5a did not proceed at all in toluene with [Rh(nbd)Cl]₂ alone, it smoothly polymerized in the presence of various amines as cocatalysts. The polymerization rate as well as the molecular weight of polymer depended on the basicity and steric bulkiness of amines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4530–4536, 2005     

No Helly Theorem for Stabbing Translates by Lines in R<Superscript>3</Superscript>

For each $n>2$ we construct a convex body $K\subset {\Bbb R}^3$ and a finite family ${\cal F}$ of disjoint translates of $K$ such that any $n-1$ members ${\cal F}$ admit a line transversal, but ${\cal F}$ has no line transversal.     

Loss of Hoogsteen pairing ability upon N1 adenine platinum binding

Chloroform- and Freon-soluble mixed thymine, adenine complexes trans-[Pt(MeNH(2))(2)(ChmT-N3)(ChmA-N1)]NO(3) (2) and trans-[Pt(MeNH(2))(2)(ChmT-N3)(TBDMS-ado-N1)]BF(4) (3) (ChmT = anion of 1-cyclohexylmethylthymine ChmTH, ChmA = 9-cyclohexylmethyladenine, TBDMS-ado = 2',3',5'-tri-tert-butyldimethylsilyladenosine) have been prepared and characterized to study their propensity to undergo Hoogsteen and/or reversed Hoogsteen pairing in solution with free ChmTH and free 3',5'-diacetyl-2'-deoxyuridine, respectively. No Hoogsteen or reversed Hoogsteen pairing between 2 and ChmT takes place in CDCl(3). In Freon, partial H bonding between N1 platinated TBDMS-ado and 3',5'-diacetyl-2'-deoxyuridine as well as its [3-(15)N] labeled analogue is unambiguously observed only below 150 K. Comparison of (1)J ((15)N-(1)H) coupling constants of 3',5'-diacetyl-2'-deoxyuridine involved in Hoogsteen pairing with free and N1 platinated adenine suggests that the interaction is inherently weaker in the case of platinated adenine. To better understand the complete absence of hydrogen bonding between the ChmA ligand in 2 and free ChmTH, ab initio calculations (gas phase, 0 K) have been carried out for Hoogsteen pairs involving adenine (A) and thymine (T), as well as simplified analogues of 2 and T, both in the presence and absence of counteranions. The data strongly suggest that reduction of the effective positive charge of the heavy metal ion Pt(2+) by counterions diminishes interaction energies. With regard to mixtures of 2 and ChmTH in chloroform, this implies that ion pair formation between the cation of 2 and NO(3)(-) may be responsible for the lack of any measurable Hoogsteen pairing in this solvent.     

Erbium-doped twin-core fibre narrow-band filter for fibre lasers

Theoretical analysis of a recently experimentally demonstrated erbium-doped twin-core (ErTCF) fibre saturable-absorber-based narrow-band tracking filter is presented. Basic qualitative characteristics of the filter are deduced from an analogy with an ideally inhomogeneously broadened saturable absorber while the effect of wide band saturation of absorption due to spatial overlap of individual spectral components of the radiation is studied in detail using a numerical model based on coupled mode theory, resolved in space and frequency. The effect of the input power, twin-core fibre length and laser operating wavelength on the spectral characteristics of the filter is investigated.     

Whole genome amplification induced bias in the detection of KRAS‐mutated cell populations during colorectal carcinoma tissue testing

Whole genome amplification replicates the entire DNA content of a sample and can thus help to circumvent material limitations when insufficient DNA is available for planned genetic analyses. However, there are conflicting data in the literature whether whole genome amplification introduces bias or reflects precisely the spectrum of starting DNA. We analyzed the origins of discrepancies in KRAS (Kirsten rat sarcoma viral oncogene homolog gene) mutation detection in six of ten samples amplified using the GenomePlex® Tissue Whole Genome Amplification kit 5 (WGA5; Sigma‐Aldrich, St. Louis, MO, USA) and KRAS StripAssay® (KRAS SA; ViennaLab Diagnostics, Vienna, Austria). We undertook reextraction, reamplification, retyping, authentication, reanalysis, and reinterpretation to determine whether the discrepancies originated during the preanalytical, analytical, and/or interpretative phase of genotyping. We conclude that a combination of glass slide/sample heterogeneity and biased amplification due to stochastic effects in the early phases of whole genome amplification (WGA) may have adversely affected the results obtained. Our findings are relevant for both forensic genetics testing and massively parallel sequencing using preamplification.     

Hapten Design and Development of Polarization Fluoroimmunoassay for Nonylphenol

Polyclonal antibodies to nonylphenol (NP), raised against two different haptenic derivatives were characterized by a rapid, homogeneous polarization fluoroimmunoassay (PFIA). The first hapten, ω-(4-hydroxyphenyl)nonanoic acid (NP9), was designed to mimic the linear NP isomer and contains hydroxyphenyl and linear alkyl chain moieties of the NP molecule. The second hapten, 4-aminophenol (4AP), contains the hydroxyphenyl moiety of NP molecule alone and thus potentially mimics various phenolic compounds with different side chain structures. A number of fluorescent labeled antigens (tracers) with various structures of the spacer arm between the antigen and the fluorescent dye was synthesized and used to optimize the competitor structure for NP-specific PFIA. The most sensitive assay with limit of detection (LOD) and IC₅₀ values of 8 and 53 mg L^–1, respectively, was obtained when anti-NP9 antibody and NP9-labeled antigen were used. Anti-NP9 resulted in more specific assay, where the cross-reactivity toward the relative phenolic compounds did not exceed 5%. Anti-4AP displayed substantial recognition of several bis-substituted phenols, including 2-amino-4-chlorophenol and 2,4-dinitrophenol.