Multiple Schedules Facilitate Rapid Noncontingent Reinforcement Schedule Thinning.

We evaluated a noncontingent reinforcement treatment that included initial brief exposures to signaled alternation of availability and nonavailability of reinforcement, followed by rapid schedule thinning. Results confirmed findings from previous research (typically with differential reinforcement schedules) that establishing stimulus control across multiple treatment components facilitated schedule thinning. We discuss both the clinical utility of this procedure and the utility of stimulus control for making interventions more practical for clinicians.

α-Methylstilbene Isomers: Relationship of Structure to Photophysics and Photochemistry.

Significant differences in the photochemical and photophysical behavior of trans-α-methylstilbene and trans-stilbene have been attributed to structural changes caused by the steric requirements of the methyl group. We present here the X-ray structures of cis- and trans-α-methylstilbene (c- and t-MeSt). This is the first X-ray structure of a cis-stilbene. Despite the pronounced departure from phenyl group coplanarity, the solid-state packing of t-MeSt resembles that of trans-stilbene in that both exhibit disorder with a bicycle pedal structural relationship, dynamic in t-St but static in t-MeSt. We compare the X-ray structures with calculated structures. We also compare our steady state and transient photochemical and spectroscopic results with predictions in a recent theoretical paper that anticipated some of our experiments. Deviations from planarity imposed by the methyl substitution account for the shorter lifetimes of the trans excited states. The rapid torsional relaxation of 1t-MeSt* to the twisted intermediate 1p*, ktp = 2.9 × 1012 s-1, observed using fs transient absorption spectroscopy, explains the sharp decrease in the fluorescence quantum yield of t-MeSt. We correct misconceptions that have appeared in the literature concerning the shape of the stilbene potential energy surface in S1. The nonplanarity due to methyl substitution leads to chirality issues that are relevant in biological molecules such as the protonated Schiff bases of retinal in the opsins.

Photochemistry and photophysics of cholesta-5,7,9(11)-trien-3ß-ol: a fluorescent analogue of cholesterol.

Cholesta-5,7,9(11)-trien-3ß-ol (9,11-dehydroprovitamin D3, CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. CTL is known to be photochemically active, but little consideration has been given to the formation efficiency and possible toxicity of its photoproducts. In degassed tetrahydrofuran (THF) solution, we isolated the photoproduct of CTL and of its 25-hydroxy derivative (HOCTL), and X-ray crystal structures were obtained for HOCTL and the photorearrangement product. The X-ray crystal structure and its 1H NMR spectrum confirm the product structure as a pentacyclic HOCTL isomer. In the presence of air in THF, endoperoxide formation via [2+4] addition of 1O2* across the B ring of CTL or HOCTL becomes the dominant photoreaction. The UV spectrum and decay kinetics of the triplet state of HOCTL, the precursor of 1O2*, are determined by transient absorption spectroscopy. We confirm the proposed structure of the endoperoxide by X-ray crystallography. Kinetics analysis of quantum yields provides rate constants for photophysical and photochemical events.

Evaluation of Instructions and Video Modeling to Train Parents to Implement a Structured Meal Procedure for Food Selectivity Among Children With Autism.

We evaluated written instructions plus video modeling-and when necessary, in vivo prompting and feedback-to teach 3 parents to implement a structured meal procedure to decrease food selectivity among their children with autism. In addition to data on correct parent implementation, we also collected data on child bite acceptance. Results showed that instructions and video modeling were effective to achieve the mastery criteria for 1 parent; the other 2 parents required in vivo prompts and feedback. Two of the children exhibited an increase in bite acceptance during the structured meal procedure.

Synthesis of 1-Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4-Cyano-1,2,3-triazoles.

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium(II)-catalyzed regiospecific azide-alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides.

Fluorescence of Hydroxyphenyl-Substituted "Click" Triazoles.

The structural and optical properties of hydroxyphenyl-substituted-1,2,3-triazole molecules ("click" triazoles) are described. "Click" triazoles are prepared from the copper(I)-catalyzed azide-alkyne cycloaddition reactions. The alkyne-derived C4 substituent of a "click" triazole engages in electronic conjugation more effectively with the triazolyl core than the azide-derived N1 substituent. Furthermore, triazolyl group exerts a stronger electron-withdrawing effect on the N1 than the C4 substituent. Therefore, the placement of an electron-donating group at either C4 or N1 position and the presence or the absence of an intramolecular hydrogen bond (HB) have profound influences on the optical properties of these compounds. The reported "click" triazoles have fluorescence quantum yields in the range of 0.1-0.3 and large apparent Stokes shifts (8000-13 000 cm-1) in all tested solvents. Deprotonation of "click" triazoles with a C4 hydroxyphenyl group increases their Stokes shifts; while the opposite (or quenching) occurs to the triazoles with an N1 hydroxyphenyl substituent. For the triazoles that contain intramolecular HBs, neither experimental nor computational results support a model of excited state intramolecular proton transfer (ESIPT). Rather, the excited state internal (or intramolecular) charge transfer (ICT) mechanism is more suitable to explain the fluorescence properties of the hydroxyphenyl-substituted "click" triazoles; specifically, the large Stokes shifts of these compounds.

Electronic Structure and Properties of Berkelium Iodates.

The reaction of 249Bk(OH)4 with iodate under hydrothermal conditions results in the formation of Bk(IO3)3 as the major product with trace amounts of Bk(IO3)4 also crystallizing from the reaction mixture. The structure of Bk(IO3)3 consists of nine-coordinate BkIII cations that are bridged by iodate anions to yield layers that are isomorphous with those found for AmIII, CfIII, and with lanthanides that possess similar ionic radii. Bk(IO3)4 was expected to adopt the same structure as M(IO3)4 (M = Ce, Np, Pu), but instead parallels the structural chemistry of the smaller ZrIV cation. BkIII-O and BkIV-O bond lengths are shorter than anticipated and provide further support for a postcurium break in the actinide series. Photoluminescence and absorption spectra collected from single crystals of Bk(IO3)4 show evidence for doping with BkIII in these crystals. In addition to luminescence from BkIII in the Bk(IO3)4 crystals, a broad-band absorption feature is initially present that is similar to features observed in systems with intervalence charge transfer. However, the high-specific activity of 249Bk (t1/2 = 320 d) causes oxidation of BkIII and only BkIV is present after a few days with concomitant loss of both the BkIII luminescence and the broadband feature. The electronic structure of Bk(IO3)3 and Bk(IO3)4 were examined using a range of computational methods that include density functional theory both on clusters and on periodic structures, relativistic ab initio wave function calculations that incorporate spin-orbit coupling (CASSCF), and by a full-model Hamiltonian with spin-orbit coupling and Slater-Condon parameters (CONDON). Some of these methods provide evidence for an asymmetric ground state present in BkIV that does not strictly adhere to Russel-Saunders coupling and Hund's Rule even though it possesses a half-filled 5f 7 shell. Multiple factors contribute to the asymmetry that include 5f electrons being present in microstates that are not solely spin up, spin-orbit coupling induced mixing of low-lying excited states with the ground state, and covalency in the BkIV-O bonds that distributes the 5f electrons onto the ligands. These factors are absent or diminished in other f7 ions such as GdIII or CmIII.

Cu(II)-Catalyzed Oxidative Formation of 5,5'-Bistriazoles.

Copper(II) acetate under aerobic conditions catalyzes the formation of 5,5'-bis(1,2,3-triazole)s (5,5'-bistriazoles) from organic azides and terminal alkynes. This reaction is an oxidative extension of the widely used copper-catalyzed azide-alkyne "click" cycloaddition. The inclusion of potassium carbonate as an additive and methanol or ethanol as the solvent, and in many instances an atmosphere of dioxygen, promote the oxidative reaction to afford 5,5'-bistriazole at the expense of 5-protio-1,2,3-triazole (5-protiotriazole). If needed, tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) as a ligand additive further accelerates the formation of 5,5'-bistriazoles. A convenient procedure to prepare TBTA is also reported to facilitate the adoption of this method for preparation of 5,5'-bistriazoles. Aromatic azide-derived 5,5'-bistriazoles possess rigid axially chiral structures with a broad distribution of dihedral angles, which may be explored as chiral ligands in enantioselective catalysis if decorated with proper functional groups.

Domino Fragmentations in Traceless Directing Groups of Radical Cascades: Evidence for the Formation of Alkoxy Radicals via C-O Scission.

Direct evidence for the formation of alkoxy radicals is reported in radical cascades using traceless directing groups. Despite the possibility of hydrogen abstraction in the fragmenting step, followed by loss of R-OH, ß-scission is preferred for the formation of alkoxy radicals. For the first time, the C-O radical was intermolecularly trapped using a silyl enol ether. Various C-X fragmenting groups were explored as possible traceless directing groups for the preparation of extended polyaromatics. Computational evidence shows that a combination of aromatization, steric and stereoelectronic effects assists the fragmentation to alkoxy radicals. Additionally, a new through-space interaction was discovered between O and Sn in the fragmentation as a specific transition state stabilizing effect.

On the Mechanism of Copper(I)-Catalyzed Azide-Alkyne Cycloaddition.

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction regiospecifically produces 1,4-disubstituted-1,2,3-triazole molecules. This heterocycle formation chemistry has high tolerance to reaction conditions and substrate structures. Therefore, it has been practiced not only within, but also far beyond the area of heterocyclic chemistry. Herein, the mechanistic understanding of CuAAC is summarized, with a particular emphasis on the significance of copper/azide interactions. Our analysis concludes that the formation of the azide/copper(I) acetylide complex in the early stage of the reaction dictates the reaction rate. The subsequent triazole ring-formation step is fast and consequently possibly kinetically invisible. Therefore, structures of substrates and copper catalysts, as well as other reaction variables that are conducive to the formation of the copper/alkyne/azide ternary complex predisposed for cycloaddition would result in highly efficient CuAAC reactions. Specifically, terminal alkynes with relatively low pKa values and an inclination to engage in π-backbonding with copper(I), azides with ancillary copper-binding ligands (aka chelating azides), and copper catalysts that resist aggregation, balance redox activity with Lewis acidity, and allow for dinuclear cooperative catalysis are favored in CuAAC reactions. Brief discussions on the mechanistic aspects of internal alkyne-involved CuAAC reactions are also included, based on the relatively limited data that are available at this point.

5-Arylvinyl-2,2'-bipyridyls: Bright "push-pull" dyes as components in fluorescent indicators for zinc ions.

This article reviews the zinc(II)-dependent photophysical properties of arylvinylbipyridines (AVBs), a class of fluoroionophores in which 2,2'-bipyridyl and an aryl moiety are electronically conjugated. Zinc(II) binding of an AVB may lead to an emission bathochromic shift of the fluoroionophore without diminishing its fluorescence quantum yield. This observation can be explained using the excited state model of electron donor-π bridge-electron acceptor "push-pull" fluorophores, in which the bipy moiety acts as an electron acceptor, and zinc(II)-coordination strengthens its electron affinity. The spectral sensitivity of bipy-containing fluoroionophores, such as AVBs, to zinc(II) can be exploited to prepare fluorescent indicators for this ion. In several cases, AVB moieties are incorporated in fluorescent heteroditopic ligands, so that the variation of zinc(II) concentration over a relatively large range can be correlated to fluorescence changes in either intensity or color. AVB fluoroionophores are also used to introduce an intramolecular Förster resonance energy transfer (FRET) strategy for creating zinc(II) indicators with high photostability and a narrow emission band, two desired characteristics of dyes used in fluorescence microscopy.

Photoisomerization of cis-1,2-di(1-Methyl-2-naphthyl)ethene at 77 K in Glassy Media.

cis-1,2-Di(1-methyl-2-naphthyl)ethene, c-1,1, undergoes photoisomerization in methylcyclohexane, isopentane and diethyl ether/isopentane/ethanol glasses at 77 K. On 313 nm excitation the fluorescence of c-1,1 is replaced by fluorescence from t-1,1. Singular value decomposition reveals that the spectral matrices behave as two component systems suggesting conversion of a stable c-1,1 conformer to a stable t-1,1 conformer. However, the fluorescence spectra are λexc dependent. Analysis of global spectral matrices shows that c-1,1 is a mixture of two conformers, each of which gives one of four known t-1,1 conformers. The λexc dependence of the c-1,1 fluorescence spectrum is barely discernible. Structure assignments to the resolved fluorescence spectra are based on the principle of least motion and on calculated geometries, energy differences and spectra of the conformers. The relative shift of the c-1,1 conformer spectra is consistent with the shift of the calculated absorption spectra. The calculated structure of the most stable conformer of c-1,1 agrees well with the X-ray crystal structure. Due to large deviations of the naphthyl groups from the ethenic plane in the conformers of both c- and t-1,1 isomers, minimal motion of these bulky substituents accomplishes cis → trans interconversion by rotation about the central bond.

LnV3Te3O15(OH)3·nH2O (Ln = Ce, Pr, Nd, Sm, Eu, Gd; n = 1-2): a new series of semiconductors with mixed-valent tellurium (IV,VI) oxoanions.

Six new lanthanide tellurium vanadates with the general formula LnV3Te3O15(OH)3·nH2O (LnVTeO) (Ln = Ce, Pr, Nd, Sm, Eu, and Gd; n = 2 for Ce and Pr; n = 1 for Nd, Sm, Eu, and Gd) have been prepared hydrothermally via the reactions of lanthanide nitrates, TeO2, and V2O5 at 230 °C. LnVTeO adopts a three-dimensional (3D) channel structure with a space group of P63/mmc. Surprisingly, two types of oxoanions: Te(IV)O3(2-) trigonal pyramids and Te(VI)O6(6-) octahedra, coexist in these compounds. Solid-state UV-vis-NIR absorption spectra for LnVTeO show approximate band gaps on the order of 1.9 eV, suggesting the wide band gap semiconducting nature of these materials. No magnetic phase transition was observed in any of the analogues, but a clear increase in the strength of short-range antiferromagnetic correlations was found with the shortening of distances between magnetically coupled Ln(3+) ions in LnVTeO.

Stabilization of cucurbituril/guest assemblies via long-range Coulombic and CH···O interactions.

Cucurbit[n]urils (CB[n], n = 6-8) interact strongly with metal-bound 4'-substituted terpyridine ligands (M = Fe(II) and Ir(III)) via CH···O hydrogen bonding, despite significant separation between the positive metallic cation and the carbonylated rim of CB[n], and the location of the latter in the second coordination sphere of the metal ion. While water has been shown to mediate interactions between cations and CB[n]s in some assemblies, mediation by organic ligands is unprecedented. The recognition process is driven by the contrasted combination of extremely favorable binding enthalpies (up to 20.2 kcal/mol) and very unfavorable entropic components (as low as -10.2 kcal/mol). Dynamic oligomers were prepared in the presence of CB[8], which acts as a "soft", noncovalent linker between metal/terpyridine complexes, and interconnects two 4'-substituents inside its cavity. Social self-sorting between CB[8] and metal/terpyridine complexes bearing 4'-(2-naphthyl) and 4'-(2,3,5,6-tetrafluorophenyl) substituents was also observed, and could afford well-organized oligomers with alternating Fe(II) and Ir(III) cations.

Anion-directed assembly of a non-interpenetrated square-grid metal-organic framework with nanoscale porosity.

A non-interpenetrated square grid metal-organic framework (MOF) comprised of octahedral Zn(II) ions and linear N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide (DPNDI) ligands was formed in the presence of noncoordinating perchlorate counterions that occupied the cavities of the porous network by forming CH···anion hydrogen bonds with DPNDI ligands, whereas a linear coordination polymer was obtained when Zn(II)-coordinated nitrate ions were present as counterions.

Integrated and passive 1,2,3-triazolyl groups in fluorescent indicators for zinc(II) ions: thermodynamic and kinetic evaluations.

In addition to being a covalent linker in molecular conjugation chemistry, the function of a 1,2,3-triazolyl moiety resulting from the copper(I)-catalyzed azide-alkyne cycloaddition reaction as a ligand for metal ions is receiving considerable attention. In this work, we characterize the thermodynamic and kinetic effects of incorporating a 1,2,3-triazolyl group in a multidentate ligand scaffold on metal coordination in the context of fluorescent zinc(II) indicator development. Ligands L14, BrL14, and FL14 (1,4-isomers) contain the 1,4-disubstituted-1,2,3-triazolyl group that is capable of binding with zinc(II) in conjunction with a di(2-picolylamino) (DPA) moiety within a multidentate ligand scaffold. Therefore, the 1,2,3-triazolyl in the 1,4-isomers is "integrated" in chelation. The 1,5-isomers L15, BrL15, and FL15 contain 1,2,3-triazolyls that are excluded from participating in zinc(II) coordination. These 1,2,3-triazolyls are "passive linkers". Zinc(II) complexes of 2:1 (ligand/metal) stoichiometry are identified in solution using (1)H NMR spectroscopy and isothermal titration calorimetry (ITC) and, in one case, characterized in the solid state. The 1:1 ligand/zinc(II) affinity ratio of L14 over L15, which is attributed to the affinity enhancement of a 1,2,3-triazolyl group to zinc(II) over that of the solvent acetonitrile, is quantified at 18 (-1.7 kcal/mol at 298 K) using an ITC experiment. Fluorescent ligands FL14 and FL15 are evaluated for their potential in zinc(II) sensing applications under pH neutral aqueous conditions. The 1,4-isomer FL14 binds zinc(II) both stronger and faster than the 1,5-isomer FL15. Visualization of free zinc(II) ion distribution in live HeLa cells is achieved using both FL14 and FL15. The superiority of FL14 in staining endogenous zinc(II) ions in live rat hippocampal slices is evident. In summation, this work is a fundamental study of 1,2,3-triazole coordination chemistry, with a demonstration of its utility in developing fluorescent indicators.

Fused polycyclic compounds via cycloaddition of 4-(1'-cyclohexenyl)-5-iodo-1,2,3-triazoles with 4-phenyl-1,2,4-triazoline-3,5-dione: the importance of a sacrificial iodide leaving group.

4-(1'-Cyclohexenyl)-5-iodo-1,2,3-triazole and 4-phenyl-1,2,4-triazoline-3,5-dione undergo a formal Diels-Alder reaction, which following an S(N)2' solvolysis process to displace the iodo group affords a fused polycyclic compound.

Elucidating the mechanism of multiferroicity in (NH4)3Cr(O2)4 and its tailoring by alkali metal substitution.

The antiferromagnetic Cr(V) peroxychromates, M(3)Cr(O(2))(4), M = K, Rb, and Cs, become ferroelectric when mixed with NH(4)(+), but the underlying mechanism is not understood. Our dielectric relaxation, Raman scattering, and high-frequency EPR measurements on the M(3-x)(NH(4))(x)Cr(O(2))(4) family clarify this mechanism. At 295 K, (NH(4))(3)Cr(O(2))(4) is tetragonal (I42m), with the NH(4)(+) ions occupying two distinctly different sites, N1 and N2. A ferroelectric transition at T(c1) = 250 K is revealed by λ-type anomalies in C(p) and dielectric constant, and lowering of symmetry to Cmc2(1). Below T(c1), the N1 sites lose their tetrahedral symmetry and thus polarization develops. Raman detection of translational modes involving the NH(4)(+) ions around 193 cm(-1) supports this model. EPR around T(c1) revealed that the [Cr(O(2))(4)](3-) ions reorient by about 10°. A minor peak at T(c2) ≈ 207 K is attributed to a short-range ordering that culminates in a long-range, structural order at T(c3) ≈ 137 K. At T(c3), the symmetry is lowered to P1 with significant changes in the cell parameters. Rb(+) and Cs(+) substitutions that block the N1 and N2 sites selectively show that T(c1) is related to the torsional motion of the N1 site, while T(c2) and T(c3) are governed by the motional slowing down of the N2 site. These data show that the multiferroic behavior of this family is governed by the rotational and translational dynamics of the NH(4)(+) ions and is tunable by their controlled substitutions. Relevance to other classes of possible multiferroics is pointed out.

Tricolor emission of a fluorescent heteroditopic ligand over a concentration gradient of zinc(II) ions.

The internal charge transfer (ICT) type fluoroionophore arylvinyl-bipy (bipy = 2,2'-bipyridyl) is covalently tethered to the spirolactam form of rhodamine to afford fluorescent heteroditopic ligand 4. Compound 4 can be excited in the visible region, the emission of which undergoes sequential bathochromic shifts over an increasing concentration gradient of Zn(ClO(4))(2) in acetonitrile. Coordination of Zn(2+) stabilizes the ICT excited state of the arylvinyl-bipy component of 4, leading to the first emission color shift from blue to green. At sufficiently high concentrations of Zn(ClO(4))(2), the nonfluorescent spirolactam component of 4 is transformed to the fluorescent rhodamine, which turns the emission color from green to orange via intramolecular fluorescence resonance energy transfer (FRET) from the Zn(2+)-bound arylvinyl-bipy fluorophore to rhodamine. While this work offers a new design of ratiometric chemosensors, in which sequential analyte-induced emission band shifts result in the sampling of multiple colors at different concentration ranges (i.e., from blue to green to orange as [Zn(2+)] increases in the current case), it also reveals the nuances of rhodamine spirolactam chemistry that have not been sufficiently addressed in the published literature. These issues include the ability of rhodamine spirolactam as a fluorescence quencher via electron transfer, and the slow kinetics of spirolactam ring-opening effected by Zn(2+) coordination under pH neutral aqueous conditions.

Synthesis of 5-iodo-1,4-disubstituted-1,2,3-triazoles mediated by in situ generated copper(I) catalyst and electrophilic triiodide ion.

Mixing copper(II) perchlorate and sodium iodide solutions results in copper(I) species and the electrophilic triiodide ions, which collectively mediate the cycloaddition reaction of organic azide and terminal alkyne to afford 5-iodo-1,4-disubstituted-1,2,3-triazoles. One molar equivalent of an amine additive is required for achieving a full conversion. Excessive addition of the amine compromises the selectivity for 5-iodo-1,2,3-triazole by promoting the formation of 5-proto-1,2,3-triazole. Based on preliminary kinetic and structural evidence, a mechanistic model is formulated in which a 5-iodo-1,2,3-triazole is formed via iodination of a copper(I) triazolide intermediate by the electrophilic triiodide ions (and possibly triethyliodoammonium ions). The experimental evidence explains the higher reactivity of the in situ generated copper(I) species and triiodide ion in the formation of 5-iodo-1,2,3-triazoles than that of the pure forms of copper(I) iodide and iodine.