Angular momentum generation in nuclear fission

When a heavy atomic nucleus splits (fission), the resulting fragments are observed to emerge spinning¹; this phenomenon has been a mystery in nuclear physics for over 40 years^2,3. The internal generation of typically six or seven units of angular momentum in each fragment is particularly puzzling for systems that start with zero, or almost zero, spin. There are currently no experimental observations that enable decisive discrimination between the many competing theories for the mechanism that generates the angular momentum^4-12. Nevertheless, the consensus is that excitation of collective vibrational modes generates the intrinsic spin before the nucleus splits (pre-scission). Here we show that there is no significant correlation between the spins of the fragment partners, which leads us to conclude that angular momentum in fission is actually generated after the nucleus splits (post-scission). We present comprehensive data showing that the average spin is strongly mass-dependent, varying in saw-tooth distributions. We observe no notable dependence of fragment spin on the mass or charge of the partner nucleus, confirming the uncorrelated post-scission nature of the spin mechanism. To explain these observations, we propose that the collective motion of nucleons in the ruptured neck of the fissioning system generates two independent torques, analogous to the snapping of an elastic band. A parameterization based on occupation of angular momentum states according to statistical theory describes the full range of experimental data well. This insight into the role of spin in nuclear fission is not only important for the fundamental understanding and theoretical description of fission, but also has consequences for the γ-ray heating problem in nuclear reactors^13,14, for the study of the structure of neutron-rich isotopes^15,16, and for the synthesis and stability of super-heavy elements^17,18.

Fluorescent molecular rotors as sensors for the detection of thymidine phosphorylase

Three new fluorescent molecular rotors were synthesized with the aim of using them as sensors to dose thymidine phosphorylase, one of the target enzymes of 5-fluorouracil, a potent chemotherapic drug largely used in the treatment of many solid tumors, that acts by hindering the metabolism of pyrimidines. 5-Fluorouracil has a very narrowtherapeutic window, in fact, its optimal dosage is strictly related to the level of its target enzymes that vary significantly among patients, and it would be of the utmost importance to have an easy and fast method to detect and quantify them. The three molecular rotors developed as TP sensors differ in the length of the alkylic spacer joining the ligand unit, a thymine moiety, and the fluorescent molecular rotor, a [4-(1-dimethylamino)phenyl]-pyridinium bromide. Their ability to trigger an optical signal upon the interaction with thymidine phosphorylase was investigated by fluorescent measurements.

Large Impact of the Decay of Niobium Isomers on the Reactor ν[over ¯]_{e} Summation Calculations

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of ^{100gs,100m}Nb and ^{102gs,102m}Nb β decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

Functionalized lignin biomaterials for enhancing optical properties and cellular interactions of dyes

We report a library of functionalized lignins and demonstrate their utility as nanocontainers for organic dyes in biologically relevant applications. Kraft lignin was modified via S_N2 reaction at the phenolic -OH group utilizing a mild base, potassium carbonate, and various alkyl halides, several bearing additional functionalities, with dimethylsulfoxide as solvent. The resulting phenoxy ethers were characterized by ¹H-NMR and IR spectroscopy, as well as DLS and SEM to evaluate their morphology and supramolecular organization. Lignin modified with long-chain hydrocarbon tails was found to effectively encapsulate DiD, a cyanine dye, decrease aggregation, enhance optical transitions and exert a photoprotective effect. The dye-lignin assemblies were also examined as imaging agents, via confocal microscopy, and found to accumulate intracellularly with no leaching of the dye to hydrophobic subcellular components observed. Lignin functionalized with short chain carboxylic acids interacts with ligands directed at the norepinephrine transporter (NET), suggesting applications in sequestration of neuroactive compounds.

Synthesis and photophysical properties of a fluorescent cyanoquinoline probe for profiling ERBB2 kinase inhibitor response

A fluorescent probe targeting the ERBB2 receptor tyrosine was designed, synthesized and evaluated as reporter of ERBB2 dynamics in overexpressing BT474, i.e. Her2(+), cells. Two cyanoquinazoline (CQ) probes modeled after type-I (CQ1) or active state and type-II (CQ2) or inactive state inhibitors were designed and synthesized with extended π systems that impart binding-induced, turn-on fluorescence. Solution spectroscopy revealed that CQ1 exhibited attractive photophysical properties and displayed turn-on emission in the presence of purified, soluble ERBB2 kinase domain, while CQ2 was found to be non-emissive, likely due to quenching via a photoinduced electron transfer mechanism. Live cell imaging with CQ1 revealed that this probe targeted an intracellular population of ERBB2, which increased following treatment with type-I inhibitors, gefinitib and canertinib, but showed no response to type-II inhibitors. CQ1 thus provides a novel means of imaging the dynamic response of ERBB2(+) cells to kinase inhibitors.

Bioimaging with Macromolecular Probes Incorporating Multiple BODIPY Fluorophores

Seven macromolecular constructs incorporating multiple borondipyrromethene (BODIPY) fluorophores along a common poly(methacrylate) backbone with decyl and oligo(ethylene glycol) side chains were synthesized. The hydrophilic oligo(ethylene glycol) components impose solubility in aqueous environment on the overall assembly. The hydrophobic decyl chains effectively insulate the fluorophores from each other to prevent detrimental interchromophoric interactions and preserve their photophysical properties. As a result, the brightness of these multicomponent assemblies is approximately three times greater than that of a model BODIPY monomer. Such a high brightness level is maintained even after injection of the macromolecular probes in living nematodes, allowing their visualization with a significant improvement in signal-to-noise ratio, relative to the model monomer, and no cytotoxic or behavioral effects. The covalent scaffold of these macromolecular constructs also permits their subsequent conjugation to secondary antibodies. The covalent attachment of polymer and biomolecule does not hinder the targeting ability of the latter and the resulting bioconjugates can be exploited to stain the tubulin structure of model cells to enable their visualization with optimal signal-to-noise ratios. These results demonstrate that this particular structural design for the incorporation of multiple chromophores within the same covalent construct is a viable one to preserve the photophysical properties of the emissive species and enable the assembly of bioimaging probes with enhanced brightness.

Highlighting Cancer Cells with Halochromic Switches

Halochromic coumarin-oxazine prefluorophores and targeting folate ligands can be connected covalently to the side chains of amphiphilic polymers. The resulting macromolecular constructs assemble into nanoparticles in aqueous environments. The prefluorophores do not produce any detectable fluorescence at neutral pH, but are converted into fluorophores with intense visible emission at acidic pH. Protonation opens the oxazine heterocycle to shift bathochromically the coumarin absorption and activate fluorescence with a brightness per nanoparticle approaching 5 × 10⁵ M^-1 cm^-1. This value translates into a 170-fold enhancement relative to the isolated fluorophores dissolved in organic solvent. The folate ligands direct these multicomponent constructs into acidic intracellular compartments of folate-positive cells, where the prefluorophores switch to the corresponding fluorophores and produce fluorescence. The pH-induced activation of the signaling units ensures negligible background fluorescence from the extracellular matrix, which instead limits considerably the contrast accessible with model systems incorporating conventional nonactivatable fluorophores. Furthermore, no intracellular fluorescence can be detected when the very same measurements are performed with folate-negative cells. Nonetheless, control experiments demonstrate that the covalent connection of the prefluorophores to the polymer backbone of the amphiphilic constructs is essential to ensure selectivity. Model systems with prefluorophores noncovalently encapsulated cannot discriminate folate-positive from -negative cells. Thus, our structural design for the covalent integration of activatable signaling units and targeting ligands within the same nanostructured assembly together with the photophysical properties engineered into the emissive components offer the opportunity to highlight cancer cells selectively with high brightness and optimal contrast.

Fluorescent Kinase Probes Enabling Identification and Dynamic Imaging of HER2(+) Cells

The human epidermal growth factor receptor, EGFR/ERBB/HER, family of receptor tyrosine kinases is central to many signaling pathways and a validated chemotherapy target in multiple cancers. While EGFR/ERBB-targeted therapies, including monoclonal antibodies, e.g., trastuzumab, and small molecule kinase inhibitors, such as lapatinib, have been developed, rapid identification and classification of cancer cells is key to identifying the best treatment regime. We report ERBB2 (also HER2) targeting kinase probes that exhibit a "turn-on" emission response upon binding. These live cell compatible probes differentiate ERBB2(+) cells from low-level, ERBB2(-) cells by targeting the intracellular ATP-binding pocket of ERBB2 with therapeutic inhibitor-like specificity. Beyond kinase expression levels, probe signal is linked to the phosphotyrosine-correlated activation state of the ERBB2 population. Additionally, the rapid signaling capability of the probes can report changes in activation state in live cells providing a unique type of complementary information to immunohistochemical assays of receptor kinase populations.

A New Design Strategy and Diagnostic to Tailor the DNA-Binding Mechanism of Small Organic Molecules and Drugs

The classical model for DNA groove binding states that groove binding molecules should adopt a crescent shape that closely matches the helical groove of DNA. Here, we present a new design strategy that does not obey this classical model. The DNA-binding mechanism of small organic molecules was investigated by synthesizing and examining a series of novel compounds that bind with DNA. This study has led to the emergence of structure-property relationships for DNA-binding molecules and/or drugs, which reveals that the structure can be designed to either intercalate or groove bind with calf thymus dsDNA by modifying the electron acceptor properties of the central heterocyclic core. This suggests that the electron accepting abilities of the central core play a key role in the DNA-binding mechanism. These small molecules were characterized by steady-state and ultrafast nonlinear spectroscopies. Bioimaging experiments were performed in live cells to evaluate cellular uptake and localization of the novel small molecules. This report paves a new route for the design and development of small organic molecules, such as therapeutics, targeted at DNA as their performance and specificity is dependent on the DNA-binding mechanism.

Leukocyte Responsiveness to Exercise in Individuals Positive for Human Cytomegalovirus

Human cytomegalovirus (HCMV) infects 50% of adults in the United States. HCMV can become a cause for concern in individuals who have a compromised immune system, which may occur after high-intensity exercise. The purpose of this preliminary study was to characterize the lymphocyte, monocyte, and neutrophil responses to exercise in HCMV+individuals. Participants were either positive (HCMV +) or negative (HCMV-) for HCMV. Participants visited the laboratory on 3 separate occasions: HCMV screening, 100% VO2max test, and 80% VO2max run. Mixed-model factorial ANOVA procedures with repeated measures on sampling condition were performed on absolute and relative circulating lymphocytes, monocytes, and neutrophils. Significant main effects for time for both absolute and relative values were seen for all leukocyte subsets regardless of virus status. Significant differences for absolute and relative values were seen between sampling conditions for all leukocyte subsets. We report for the first time that HCMV status does not affect circulating neutrophil responses to high-intensity exercise, though exercise-induced neutrocytosis is seen during the post-exercise and 60 min post-exercise sampling conditions, regardless of HCMV status. There is no HCMV effect on circulating monocyte responses to exercise, though exercise-induced monocytosis was seen during the post-exercise sampling condition regardless of HCMV status.

In vitro/in vivo study of novel anti-cancer, biodegradable cross-linked tannic acid for fabrication of 5-fluorouracil-targeting drug delivery nano-device based on a molecular imprinted polymer

The structure of a 5-fluorouracil carrier and fluorescent image of an animal after injection under a magnetic field.

Binding-induced, turn-on fluorescence of the EGFR/ERBB kinase inhibitor, lapatinib

We report the photophysical properties, binding-induced turn-on emission, and fluorescence imaging of the cellular uptake and distribution of lapatinib, an EGFR/ERBB inhibitor. Lapatinib, a type II, i.e. inactive state, inhibitor that targets the ATP binding pocket of the EGFR family of receptor tyrosine kinases. DFT calculations predict that the 6-furanylquinazoline core of lapatinib should exhibit an excited state with charge transfer character and an S0 to S1 transition energy of 3.4 eV. Absorption confirms an optical transition in the near UV to violet, while fluorescence spectroscopy shows that photoemission is highly sensitive to solvent polarity. The hydrophobicity of lapatinib leads to fluorescent aggregates in solution, however, binding to the lipid-carrier protein, BSA or to the kinase domain of ERBB2, produces spectroscopically distinct photoemission. Confocal fluorescence microscopy imaging of lapatinib uptake in ERBB2-overexpressing MCF7 and BT474 cells reveals pools of intracellular inhibitor with emission profiles consistent with aggregated lapatinib.

Organic cation transporter 3 contributes to norepinephrine uptake into perivascular adipose tissue

Perivascular adipose tissue (PVAT) reduces vasoconstriction to norepinephrine (NE). A mechanism by which PVAT could function to reduce vascular contraction is by decreasing the amount of NE to which the vessel is exposed. PVATs from male Sprague-Dawley rats were used to test the hypothesis that PVAT has a NE uptake mechanism. NE was detected by HPLC in mesenteric PVAT and isolated adipocytes. Uptake of NE (10 μM) in mesenteric PVAT was reduced by the NE transporter (NET) inhibitor nisoxetine (1 μM, 73.68 ± 7.62%, all values reported as percentages of vehicle), the 5-hydroxytryptamine transporter (SERT) inhibitor citalopram (100 nM) with the organic cation transporter 3 (OCT3) inhibitor corticosterone (100 μM, 56.18 ± 5.21%), and the NET inhibitor desipramine (10 μM) with corticosterone (100 μM, 61.18 ± 6.82%). Aortic PVAT NE uptake was reduced by corticosterone (100 μM, 53.01 ± 10.96%). Confocal imaging of mesenteric PVAT stained with 4-[4-(dimethylamino)-styrl]-N-methylpyridinium iodide (ASP(+)), a fluorescent substrate of cationic transporters, detected ASP(+) uptake into adipocytes. ASP(+) (2 μM) uptake was reduced by citalopram (100 nM, 66.68 ± 6.43%), corticosterone (100 μM, 43.49 ± 10.17%), nisoxetine (100 nM, 84.12 ± 4.24%), citalopram with corticosterone (100 nM and 100 μM, respectively, 35.75 ± 4.21%), and desipramine with corticosterone (10 and 100 μM, respectively, 50.47 ± 5.78%). NET protein was not detected in mesenteric PVAT adipocytes. Expression of Slc22a3 (OCT3 gene) mRNA and protein in PVAT adipocytes was detected by RT-PCR and immunocytochemistry, respectively. These end points support the presence of a transporter-mediated NE uptake system within PVAT with a potential mediator being OCT3.

One probe, two-channel imaging of nuclear and cytosolic compartments with orange and red emissive dyes

Several new DNA-targeting probes that exhibit binding-induced 'turn on' fluorescence are presented. Two of the dyes, orange emissive 1, (E)-4-(4(-4-methylpiperazin-1-yl)phenyl)6-(4-(4-methylpi-perazin-1-yl)styryl)pyrimidin-2-ol), and red emissive 2, (E)-4-(4(-4-methyl-piperazin-1-yl)-phenyl)6-(4-(4-methylpiperazin-1-yl)styryl)-1,3-propanedionato-κO,κO']difluoroborane), are brightly fluorescent when bound to DNA, but are virtually non-fluorescent in aqueous solutions. Confocal fluorescence microscopy of live BT474, MCF7 and HEK293 cells demonstrates that both probes are cell permeable and rapidly accumulated intracellularly into cell nuclei and the cytosol. Taking advantage of their environmental sensitivity, these two pools of fluorophores are readily resolved into separate channels, and thus, a single dye allows two-color imaging of the nuclear and cytosolic compartments.

Emission tuning of fluorescent kinase inhibitors: conjugation length and substituent effects

Fluorescent N-phenyl-4-aminoquinazoline probes targeting the ATP-binding pocket of the ERBB family of receptor tyrosine kinases are reported. Extension of the aromatic quinazoline core with fluorophore “arms” through substitution at the 6- position of the quinazoline core with phenyl, styryl, and phenylbutadienyl moieties was predicted by means of TD-DFT calculations to produce probes with tunable photoexcitation energies and excited states possessing charge-transfer character. Optical spectroscopy identified several synthesized probes that are nonemissive in aqueous solutions and exhibit emission enhancements in solvents of low polarity, suggesting good performance as turn-on fluorophores. Ligand-induced ERBB2 phosphorylation assays demonstrate that despite chemical modification to the quinazoline core these probes still function as ERBB2 inhibitors in MCF7 cells. Two probes were found to exhibit ERBB2-induced fluorescence, demonstrating the utility of these probes as turn-on, fluoroescent kinase inhibitors.

Binding-induced fluorescence of serotonin transporter ligands: A spectroscopic and structural study of 4-(4-(dimethylamino)phenyl)-1-methylpyridinium (APP(+)) and APP(+) analogues

The binding-induced fluorescence of 4-(4-(dimethylamino)-phenyl)-1-methylpyridinium (APP(+)) and two new serotonin transporter (SERT)-binding fluorescent analogues, 1-butyl-4-[4-(1-dimethylamino)phenyl]-pyridinium bromide (BPP(+)) and 1-methyl-4-[4-(1-piperidinyl)phenyl]-pyridinium (PPP(+)), has been investigated. Optical spectroscopy reveals that these probes are highly sensitive to their chemical microenvironment, responding to variations in polarity with changes in transition energies and responding to changes in viscosity or rotational freedom with emission enhancements. Molecular docking calculations reveal that the probes are able to access the nonpolar and conformationally restrictive binding pocket of SERT. As a result, the probes exhibit previously not identified binding-induced turn-on emission that is spectroscopically distinct from dyes that have accumulated intracellularly. Thus, binding and transport dynamics of SERT ligands can be resolved both spatially and spectroscopically.

Abstract 307: The Presence of an Adrenergic System in Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is under recognized for its importance in blood pressure regulation. Visceral adipocytes reportedly contain catecholamines. Adipocytes in PVAT are directly adjacent to the blood vessels they surround and therefore the production, release and/or reuptake of catecholamines may significantly affect vascular tone. We hypothesize that an adrenergic system is present in PVAT. Glyoxylic acid staining revealed the presence of catecholamines in the cytosol of mesenteric PVAT adipocytes. Dopamine (DA), norepinephrine (NE) and epinephrine were quantified by HPLC in rat aortic PVAT, brown fat, mesenteric PVAT and retroperitoneal fat with NE being the most abundant at concentrations of 731.9, 815.0, 668.7 and 73.2 ng/g from each tissue, respectively. Two key enzymes in catecholamine synthesis; tyrosine hydroxylase and dopamine β-hydroxylase, were located to PVAT adipocytes by immunohistochemistry. The norepinephrine transporter (NET) was detected on mesenteric PVAT adipocytes by confocal microscopy using ASP+ (2μM), a fluorescent NET substrate. Uptake of ASP+ was blocked by the NET specific inhibitor nisoxetine (10μM) (see figure). These data show that PVAT contains all of the elements of an adrenergic system and may contribute to vascular and adipose function in health and disease.

Turn-on, fluorescent nuclear stains with live cell compatibility

DNA-binding, green and yellow fluorescent probes with excellent brightness and high on/off ratios are reported. The probes are membrane permeable, live-cell compatible, and optimally matched to 405 nm and 514 nm laser lines, making them attractive alternatives to UV-excited and blue emissive Hoechst 33342 and DAPI nuclear stains. Their electronic structure was investigated by optical spectroscopy supported by TD-DFT calculations. DNA binding is accompanied by 27- to 75-fold emission enhancements, and linear dichroism demonstrates that one dye is a groove binder while the other intercalates into DNA.

Observation of large scissors resonance strength in actinides

The orbital M1 scissors resonance has been measured for the first time in the quasicontinuum of actinides. Particle-γ coincidences are recorded with deuteron and (3)He-induced reactions on (232)Th. The residual nuclei (231,232,233)Th and (232,233) Pa show an unexpectedly strong integrated strength of B(M1)=11-15μ(n)(2) in the E(γ)=1.0-3.5 MeV region. The increased γ-decay probability in actinides due to scissors resonance is important for cross-section calculations for future fuel cycles of fast nuclear reactors and may also have an impact on stellar nucleosynthesis.

A fluorescent reporter of ATP binding-competent receptor kinases

ERBB receptor kinases play a crucial role in normal development and cancer malignancies. A broad range of modifications creates receptor subpopulations with distinct functional properties in live cells. Their apparent activation state, typically assayed by tyrosine phosphorylation of substrates, reflects a complex equilibrium of competing reactions. With the aim of developing optical tools to investigate ERBB populations and their state of activation, we have synthesized a fluorescent 'turn-on' probe, DMAQ, targeting the ERBB ATP binding pocket. Upon binding, probe emission increases due to the hydrophobic environment and restricted geometry of the ERBB2 kinase domain, facilitating the analysis of receptor states at low occupancy and without the removal of unbound probes. Cellular ERBB2 autophosphorylation is inhibited with saturation kinetics that correlate with the increase in probe fluorescence. Thus, DMAQ is an example of a new generation of 'turn-on' probes with potential applications in querying receptor kinase populations both in vitro and in live cells.

Probing the functional limits of the norepinephrine transporter with self-reporting, fluorescent stilbazolium dimers

A series of stilbazolium dimers were synthesized and investigated as sterically demanding ligands targeting the norepinephrine transporter (NET). The environmentally sensitive fluorescence of the dyes enables their use as self-reporting ligands; binding to and displacement from NET can be monitored by fluorescence microscopy.

Fluorescent reporters of monoamine transporter distribution and function

Serotonin is a monoamine serving as a chemical messenger in diverse brain regions, as well as in blood and various other organs. We synthesized six ethylamine functionalized fluorophores as fluorescent probes for serotonin. The one with best spectral properties and aqueous solubility, 6-amino-2-(2-aminoethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione, was studied in detail both in vivo and in vitro. It was shown to act as a ligand for serotonin transporter (SERT) without acute cerebral or cardiovascular toxicity or adverse effects. Fluorescent serotonin analogs can be used for direct visualization of SERT distribution and activity in live tissue.

Luminescent charge-transfer complexes: tuning emission in binary fluorophore mixtures

Charge-transfer (CT) complexes composed of a π-electron-poor naphthalene diimide (NDI) derivative combined with a series of π-electron-rich donors were investigated. Solutions of the CT complexes are nonemissive; however, solid-state complexes and aqueous suspensions display emission that is dependent on the energy of the HOMO of the electron donor. Crystallographic analysis of a pyrene-NDI complex reveals columnar packing and a high degree of frontier molecular orbital (FMO) overlap that likely contributes to the observed optical properties. The fluorescent CT particles are utilized as imaging agents; additional luminescent CT complexes may be realized by considering FMO energies and topologies.

Evidence of preferential pi-stacking: a study of intermolecular and intramolecular charge transfer complexes

Nine combinations of pi-electron donors and acceptors were examined by UV-vis, fluorescence and (1)H-NMR spectroscopy to identify pi-stacked charge transfer complexes in macromolecular and supramolecular constructs. The high association constant of pyrene and naphthalene diimide suggests a preferentially pi-stacking pair rationalized by frontier orbital congruence.

Photoreaction of the rutile TiO2(011) single-crystal surface: reaction with acetic acid

The reaction of acetic acid with stoichiometric and reduced rutile TiO(2)(011) single-crystal surfaces has been studied under dark and UV illumination conditions. The surface coverage after the dissociative adsorption of acetic acid with respect to Ti was found to be 0.55. Monitoring XPS Ti, O, and C lines revealed that the surface population decreased incrementally with temperature up to 650 K. The decrease in the slope of both the -CH(3)- and -COO- XPS peaks was not monotonic and followed two slopes in agreement with TPD results. The first channel involves the removal of surface acetates to acetic acid by recombinative desorption, and the second mainly involves dehydration to ketene. UV-light illumination was conducted at 300 K in the absence and presence of molecular oxygen at different pressures: in the 10(-6)-10(-9) Torr range. Acetate species were found to decrease with illumination time, and their decrease is seen to be dependent on the oxygen pressure. Plausible decomposition pathways are presented. Deliberately reducing the surface by electron bombardment prior to the adsorption of acetic acid did not affect the photoreaction rate within the experimental limits.

Polyfluorophore labels on DNA: dramatic sequence dependence of quenching

We describe studies carried out in the DNA context to test how a common fluorescence quencher, dabcyl, interacts with oligodeoxynucleoside fluorophores (ODFs)--a system of stacked, electronically interacting fluorophores built on a DNA scaffold. We tested twenty different tetrameric ODF sequences containing varied combinations and orderings of pyrene (Y), benzopyrene (B), perylene (E), dimethylaminostilbene (D), and spacer (S) monomers conjugated to the 3' end of a DNA oligomer. Hybridization of this probe sequence to a dabcyl-labeled complementary strand resulted in strong quenching of fluorescence in 85% of the twenty ODF sequences. The high efficiency of quenching was also established by their large Stern-Volmer constants (K(SV)) of between 2.1 x 10(4) and 4.3 x 10(5) M(-1), measured with a free dabcyl quencher. Interestingly, quenching of ODFs displayed strong sequence dependence. This was particularly evident in anagrams of ODF sequences; for example, the sequence BYDS had a K(SV) that was approximately two orders of magnitude greater than that of BSDY, which has the same dye composition. Other anagrams, for example EDSY and ESYD, also displayed different responses upon quenching by dabcyl. Analysis of spectra showed that apparent excimer and exciplex emission bands were quenched with much greater efficiency compared to monomer emission bands by at least an order of magnitude. This suggests an important role played by delocalized excited states of the pi stack of fluorophores in the amplified quenching of fluorescence.

Polyfluorophores on a DNA backbone: a multicolor set of labels excited at one wavelength

We recently described the assembly of fluorescent deoxyriboside monomers ("fluorosides") into DNA-like phosphodiester oligomers (oligodeoxyfluorosides or ODFs) in which hydrocarbon and heterocyclic aromatic fluorophores interact both physically and electronically. Here we report the identification of a multicolor set of water-soluble ODF dyes that display emission colors across the visible spectrum, and all of which can be simultaneously excited by long-wavelength UV light at 340-380 nm. Multispectral dye candidates were chosen from a library of 4096 tetramer ODFs constructed on PEG-polystyrene beads using a simple long-pass filter to observe all visible colors at the same time. We resynthesized and characterized a set of 23 ODFs containing one to four individual chromophores and included 2-3 spacer monomers to increase aqueous solubility and minimize aggregation. Emission maxima of this set range from 376 to 633 nm, yielding apparent colors from violet to red, all of which can be visualized directly. The spectra of virtually all ODFs in this set varied considerably from the simple combination of monomer components, revealing extensive electronic interactions between the presumably stacked monomers. In addition, comparisons of anagrams in the set (isomers having the same components in a different sequence) reveal the importance of nearest-neighbor interactions in the emissive behavior. Preliminary experiments with human tumor (HeLa) cells, observing two ODFs by laser confocal microscopy, showed that they can penetrate the outer cellular membrane, yielding cytoplasmic localization. In addition, a set of four distinctly colored ODFs was incubated with live zebrafish embryos, showing tissue penetration, apparent biostability, and no apparent toxicity. The results suggest that ODF dyes may be broadly useful as labels in biological systems, allowing the simultaneous tracking of multiple species by color, and allowing visualization in moving systems where classical fluorophores fail.

New designs for DNA bases: expanded DNAs and oligofluorosides

Properties and applications of two new classes of DNA base replacements are described. The first class is size-expanded DNA bases; these are benzo-homologous versions of A, C, T, G that yield base pairs 2.4 Angstroms larger than natural pairs. New studies have explored the ability of expanded DNA base pairs to be replicated by DNA polymerase enzymes. The second class of DNA-like molecules described here are "oligodeoxyfluorosides" (ODFs), which are deoxyribose-phosphate oligomers in which all nucleobases are replaced by hydrocarbon and heterocyclic fluorophores. These compounds have been prepared in large libraries and have been screened for unusual fluorescence and sensing properties.

Oligodeoxyfluorosides: Strong Sequence Dependence of Fluorescence Emission

We describe the properties of a series of oligomeric polyfluorophores assembled on the DNA backbone. The eleven oligomers (oligodeoxyfluorosides, ODFs), 4 to 7 monomers in length, were composed of only two fluorescent monomers and a spacer in va ried sequences, and were designed to test how fluorescent nucleobases can interact electronically to yield complexity in fluorescence emission. The monomer fluorophores were deoxyribosides of pyrene and perylene, which emit light in violet and blue wavele ngths respectively. The experiments show that simple variation of sequence and spacing can dramatically change fluorescence, yielding emission maxima ranging from 380 to 557 nm and visible colors from violet to orange-red. Fluorescence lifetimes data, excitation spectra, and absorption data point to a number of multi-fluorophore electronic interactions, including pyrene-pyrene and perylene-perylene excimers, pyrene-perylene exciplexes, as well as monomer dye emissions, contributing to the final spectral outcomes. Thus, two simple fluorophores can be readily combined to give emissions over much of the visible spectrum, all requiring only a single excitation. The results demonstrate that fluorescent nucleobases in oligomeric form can act cooperatively as electronic units, and that fluorophore sequence in such oligomers is as important as fluorophore composition in determining fluorescence properties.

Observation of a rotational band in the odd-Z transfermium nucleus 101251Md

A rotational band has been unambiguously observed in an odd-proton transfermium nucleus for the first time. An in-beam gamma-ray spectroscopic study of 101/251Md has been performed using the gamma-ray array JUROGAM combined with the gas-filled separator RITU and the focal plane device GREAT. The experimental results, compared to Hartree-Fock-Bogolyubov calculations, lead to the interpretation that the rotational band is built on the [521]1/2(-) Nilsson state.

Fluorescent DNA base replacements: Reporters and sensors for biological systems

We describe the design, synthesis, and properties of nucleoside monomers in which the DNA base is replaced by fluorescent hydrocarbons and heterocycles, and the assembly of these monomers into DNA-like molecules in which the all bases are fluorescent. As monomers, such molecules have useful applications as reporters in the DNA context. The use of fluorescent DNA bases, rather than more traditional fluorophores tethered to the DNA strand, gives a more predictable location and orientation, and yields a more direct response to changes that occur within the helix. In addition to uses as monomers, such compounds can be assembled into polychromophoric oligomers ("oligodeoxyfluorosides" or ODFs). ODFs are water soluble, discrete molecules and are easily arranged into specific sequences by use of a DNA synthesizer. They have displayed a number of properties not readily available in commercial fluorophores, including large Stokes shifts, tunable excitation and emission wavelengths, and sensing responses to physical changes or molecular species in solution. We describe an approach to assembling and screening large sets of oligofluorosides for rapid identification of molecules with desirable properties. Such compounds show promise for applications in biochemistry, biology, environmental and materials applications.

A hallmark of balancing selection is present at the promoter region of interleukin 10

As an anti-inflammatory mediator IL10 is beneficial in certain contexts and deleterious in others. As increased production of IL10 favours protection against inflammatory disease, whereas low production promotes elimination of foreign pathogens by the host, we investigated the possible influence of balancing selection at this locus. We began by resequencing 48 European and 48 African chromosomes across 2.2 kb of the IL10 promoter region, and compared this with four neighbouring gene regions: MK2, IL19, IL20 and IL24. Analysis of nucleotide diversity showed a positive Tajima's D-test for IL10 in Europeans, of borderline statistical significance (1.89, P=0.05). Analysis of F(st) values showed significant population divergence at MK2, IL19, IL20 and IL24 (P<0.01) but not at IL10. Taken together, these findings are consistent with the hypothesis that balancing selection has played a role in the evolution of polymorphisms in the IL10 promoter region.

Cruciforms as Functional Fluorophores: Response to Protons and Selected Metal Ions

The photophysics of dialkylamino- and/or pyridine-containing functional chromophores, 1,4-distyryl-2,5-bis(ethynylaryl)benzenes (cruciforms) was investigated; their fluorescence quantum yields and emissive lifetimes were determined. Depending upon their substituents, the frontier molecular orbitals (FMOs) of these cruciforms are either congruent, i.e., HOMO and LUMO occupy the same real space, or disjoint, i.e., the HOMO is located on one branch of the cruciform while the LUMO is located on the second one. Donor-acceptor substitution leads to a disjoint FMO pattern, while the parent 1,4-distyryl-2,5-bis(phenylethynyl)benzene shows congruent FMOs. The photophysics of the cruciforms was investigated upon addition of either an excess of trifluoroacetic acid or an excess of selected metal (Mg(2+), Ca(2+), Mn(2+), Zn(2+)) trifluoromethanesulfonate salts. Addition of either metal ions or protons led to analogous but not identical changes in the spectroscopic properties of the investigated cruciforms. The collected data suggest that the metals bind preferentially at the aniline nitrogen and not at the electron-rich arene. The spatially separated FMOs permit the independent manipulation of the HOMO and the LUMO of such cruciforms. If the branches contain metal-complexing moieties, metal binding leads to either a hypsochromic or a bathochromic shift in emission via interaction of the metal cations with either the HOMO or the LUMO.

Reduced Fluorescence Quenching of Cyclodextrin−Acetylene Dye Rotaxanes

An acetylene dye rotaxane with alpha-CD has been synthesized using the Heck-Cassar-Sonogashira-Hagihara-type reaction in aqueous solution. Free dye with tetracarboxylic acids is found to be highly sensitive to various metal ions, showing high Stern-Volmer constants, KSV. As CD encapsulation protects and stabilizes the threaded chromophore against an outside quencher, metal-insensitive biological tags are an obvious application for this class of molecules.

Supramolecular cruciforms

By self-assembling fluorescent pyridyl cruciforms with bis-Pd-pincer complexes, supramolecular assemblies with attractive optical properties were synthesized; these assemblies show potential as electro-optical materials.