Global structure of forked DNA in solution revealed by high-resolution single-molecule FRET

Branched DNA structures play critical roles in DNA replication, repair, and recombination in addition to being key building blocks for DNA nanotechnology. Here we combine single-molecule multiparameter fluorescence detection and molecular dynamics simulations to give a general approach to global structure determination of branched DNA in solution. We reveal an open, planar structure of a forked DNA molecule with three duplex arms and demonstrate an ion-induced conformational change. This structure will serve as a benchmark for DNA-protein interaction studies.     

Laser Optogalvanic Analysis in a Radiofrequency Plasma: Detection of Iodine Atoms and Molecules

The optogalvanic effect (OGE) may be used to detect specific species in a plasma (ions, atoms, radicals, or molecules) by selective laser excitation of the plasma. The plasma itself is merely the reservoir of electronically excited, ionized, and atomized species. Compared with conventional ICP-AES, OGE has many advantages: no external detector, zero background, no interferences, and greater versatility. Since the photoacoustic (PA) and ionization rate change (IRC) components of the OGE signal can be separated, optogalvanic spectroscopy can exhibit a further selectivity based on this discriminatory ability. The OGE method has been applied to iodine analysis. By careful selection of the operating conditions, pure atomic and pure molecular iodine signals constitute the PA and IRC profiles, respectively. The best detection limit, in a somewhat primitive experiment, is 10⁻⁷μg/ml of I₂, which is comparable to laser-induced fluorescence. This detection limit can be improved by at least three orders of magnitude by optimizing the experimental conditions.     

Molecular Rydberg transitions: The lowest-energy Rydberg transitions of s-type in CH3X and CD3X,X = Cl,Br, and I

The absorption spectra associated with transitions to the lowest-energy s-type Rydberg states of CH₃X and CD₃X, X = Cl, Br, and I, have been measured and analyzed. The spectra of the bromides and iodides consist, individually, of four electronic origins of s-excitation type. The vibrational frequency of a given normal mode is more or less identical in all four excited states of any one molecule; and the excited state/ground state ratios of the frequencies of any given normal vibrational mode are essentially identical for all four molecules (i.e., for 16 states, four for each of two bromides and two iodides). The spectra of the chlorides are amenable to a number of different vibronic analyses, none of them unique; these analyses are discussed.     

The electronic spectroscopy of oxamides

The electronic emission and absorption spectra of various oxamides for which the dihedral angles vary from 0° to 180° have been studied experimentally and computationally. The interpretation of the computational data proceeds along a composite-molecule point of view in which the electronic states of oxamide are related to those of component amides. By this means, we have identified the lower-energy excited singlet states of various trans-planar, cis-planar, and twisted oxamides and have determined their dependence on the dihedral angle between the two carbonyl groups. The phosphorescence characteristics of the oxamides are not unambiguously interpretable. Nonetheless, if oxamide be viewed as a member of the large set of isoelectronic α-dicarbonyls and if our singlet state assignments be accepted, we find it possible to rationalize the phosphorescence characteristics of oxamides in terms of vibronic mixing of ${}^3\text{Γ}{}_{\mathrm{n\pi }}{}^1$ and ${}^3\text{Γ}{}_{\mathrm{\pi \pi }}{}^1$ state.     

Electronic spectroscopy of highly polar aromatics. XI. Luminescence of the cyanoanilines

The absorption and emission spectra of the three isomeric cyanoanilines have been investigated. Quantum yields and decay lifetimes are reported for both fluorescence and phosphorescence processes. It is shown that the lowest energy absorption band of p-cyanoaniline consists of two distinct electronic transitions of the ¹π^*←¹π type, whereas, in the o- and m-cyanoanilines, the lowest energy absorption band consists of a single electronic transition of the ¹π^*←¹π type. These conditions are consistent with absorption data, emission data and kinetic analyses. The largest ?_P/?_F ratio is exhibited by the p-cyanoaniline and this observation is rationalized.     

Synthesis of vinylsilanes by palladium-catalyzed reaction of trimethylsilylallyl acetates with nucleophiles

Treatment of 1-trimethylsilylallyl and 3-trimethylsilylallyl acetates with nucleophiles (active methylene compounds and enamines) in the presence of a catalytic amount of Pd(PPh₃)₄ affords vinylsilane derivatives selectively.     

Isolation and synthesis of pygmanilines,phenylurea derivatives from the Northeastern Atlantic lichen Lichina pygmaea

A library of 864 extracts prepared from Irish marine organisms was screened in the search for novel antioxidants. Chemical investigation of the most promising extract obtained from the common lichen Lichina pygmaea led to the isolation of five resorcinol derivatives. An unusual urea moiety was found embedded in two of these compounds, pygmanilines A (1) and B (2) and their structures were confirmed by one-step chemical syntheses.     

Experimental Determination of Carrier Mobilities in Organic Molecular Crystals

The measurement of carrier mobilities in organic molecular crystals enables one to understand the basic mechanisms of charge-transport in these systems. This, in turn, has direct bearing on electronic conduction in biologically important molecules such as 5-carotene, chlorophyll, nucleic acids, etc. However, because of many inherent difficulties (for example: low quantum–efficiency of carrier–generation; severe trapping effects; development of space-charge regions; electrode crystal contact and other barrier phenomena; etc.) progress toward better understanding remains limited. In view of these difficulties, it is not surprising that the first successful determination of drift mobilities in atypical molecular crystal, namely anthracene, was not completed until 1960 when LeBlanc' and Kepler independently measured mobilities using a method now known as the “pulse photocurrent technique”. Despite this apparent initial success, no consistent approach or the general application of such methods to organic materials has evolved. As a result, the list of organic molecular crystals for which reliable mobility data exists is quite small.     

Assessment of numeracy in sports and exercise science students at an Australian university

The effect of high school study of mathematics on numeracy performance of sports and exercise science (SES) students is not clear. To investigate this further, we tested the numeracy skills of 401 students enrolled in a Bachelor of Health Sciences degree in SES using a multiple-choice survey consisting of four background questions and 39 numeracy test questions. Background questions (5-point scale) focused on highest level of mathematics studied at high school, self-perception of mathematics proficiency, perceived importance of mathematics to SES and likelihood of seeking help with mathematics. Numeracy questions focused on rational number, ratios and rates, basic algebra and graph interpretation. Numeracy performance was based on answers to these questions (1 mark each) and represented by the total score (maximum = 39). Students from first (n = 212), second (n = 78) and third (n = 111) years of the SES degree completed the test. The distribution of numeracy test scores for the entire cohort was negatively skewed with a median (IQR) score of 27(11). We observed statistically significant associations between test scores and the highest level of mathematics studied (P < 0.05), being lowest in students who studied Year 10 Mathematics (20 (9)), intermediate in students who studied Year 12 General Mathematics (26 (8)) and highest in two groups of students who studied higher-level Year 12 Mathematics (31 (9), 31 (6)). There were statistically significant associations between test scores and level of self-perception of mathematics proficiency and also likelihood of seeking help with mathematics (P < 0.05) but not with perceived importance of mathematics to SES. These findings reveal that the level of mathematics studied in high school is a critical factor determining the level of numeracy performance in SES students.     

Characterization of nitrogen-doped ZnO thin films grown by plasma-assisted pulsed laser deposition on sapphire substrates

The crystalline, optical and electrical properties of N-doped ZnO thin films were measured using X-ray diffraction, photoluminescence and Hall effect apparatus, respectively. The samples were grown using pulsed laser deposition on sapphire substrates coated priorly with ZnO buffer layers. For the purpose of acceptor doping, an electron cyclotron resonance (ECR) plasma source operated as a low-energy ion source was used for nitrogen incorporation in the samples. The X-ray diffraction analyses indicated some deterioration of the ZnO thin film with nitrogen incorporation. Temperature-dependent Van der Pauw measurements showed consistent p-type behavior over the measured temperature range of 200–450 K, with typical room temperature hole concentrations and mobilities of 5×10¹⁵ cm⁻³ and 7 cm²/V s, respectively. Low temperature photoluminescence spectra consisted of a broad emission band centered around 3.2 eV. This emission is characterized by the absence of the green deep-defect band and the presence of a band around 3.32 eV.