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International audience; We present theoretical and experimental demonstrations of the electro-optic activity in crystalline molecular thin films with octupolar D-3h symmetry. Applying a longitudinal electric field modulation within the molecular plane, we analyze the induced refractive index change relative to the orientation of the octupoles in their plane, and show that a maximum value is reached when one octupolar branch lies along the direction of the modulating field. These characteristics, as well as their electric field dependence, are drastically different from more traditional one-dimensional symmetry samples, bringing additional advantages related to electro-optic coupling possibilities.

Reactions of (E)-O-arylbenzaldoximes in which the O-aryl group is 2,4-dinitrophenyl (1a-d) and picryl (2a-d) nvith secondary amines in acetonitrile have been studied kinetically. The reactions proceeded via competing E2 and S N Ar mechanisms. For eliminations from 1a-d promoted by R 2 NH in MeCN, the transition state was changed toward E1cb-like by a more electron-withdrawing β-aryl substituent and a stronger base. On the other hand, the transition states for eliminations from 2a-d and for the S N Ar reactions of all substrates were relatively insensitive to the variation of either β-aryl substituent or base strength. The yield of S N Ar product increased with base concentration, electron-withdrawing ability of the O-aryl group, and base strength

Two-photon microscopy (TPM) has become an indispensible tool in biology and medicine owing to the capability of imaging the intact tissue for a long period of time. To make it a versatile tool in biology, a variety of two-photon probes for specific applications are needed. In this context, many research groups are developing two-photon probes for various applications. In this Focus Review, we summarize recent results on model studies and selected examples of two-photon probes that can detect intracellular free metal ions in live cells and tissues to provide a guideline for the design of useful two-photon probes for various in vivo imaging applications.

Elimination reactions of N-(arylsulfonoxy)-N-alkylbenzylamines 1-5 with MeONa−MeOH have been studied kinetically. The elimination reactions are regiospecific, producing only corresponding benzylidenalkylamines. The rate equation for the reactions is k obs =k 0 +k 2 [MeONa], indicating that the reactions proceed by competing solvolytic- and base-promoted pathways. The relative rates of elimination for the k 2 and k 0 pathways are 1, 0.67, 0.53, 0.35, and 0.27 for R=Me, Et, i-Pr, s-Bu, and t-Bu and 1, 4.1, 5.1, and 8.7 for R=Et, i-Pr, s-Bu and t-Bu, respectively. For MeONa-promoted elimination from 1-5, Hammett p and k H /k D decrease but ρ 1g and |β 1g | increase with a bulkier alkyl substituent

Reactions of (E)-O-arylbenzaldoximes 1-3 with MeONa-MeOH have been studied kinetically. The reactions proceed via competing E2 and S N Ar reactions, in which the first step is rate-determining. Although the reactions were strongly influenced by the electronic effect of the β- and O-aryl substituents, they were insensitive to the steric effect of the O-aryl group, except that the S N Ar reaction was retarded by the CF 3 group of 2. For eliminations from 1-3 promoted by MeONa-MeOH, the k H /k D value increased and the Hammett p value decreased with better leaving groups

Reactions of PhCH2CH(OTs)R [R = Me (1), Et (2), Pri(3), Bus(4), But(5)] with MeONa in MeOH have been studied. The reactions produce both conjugated and unconjugated alkenes. The yields of the conjugated alkenes are nearly the same for 1–4, while the E/Z ratios depend strongly upon the α-alkyl group. The rates of eliminations forming the conjugated E alkenes are decreased by a bulkier alkyl group as indicated by the relative rate of 1, 0.8, 0.7, 0.6, 0.2 for 1, 2, 3, 4, 5, respectively. On the other hand, the relative rates for the formation of the unconjugated alkenes are 1, 1.7, 2.8, 1.9 for 1, 2, 3, 4 respectively, indicating that the rate increases with the double bond stabilizing ability of the alkyl groups and decreases with their steric effect. From these results, the relative steric effect of the α- and β-alkyl groups in alkene-forming elimination is assessed.

The first evaluation of the β for 2-[2-(p-diethylaminophenyl)vinyl]furan derivatives is reported in comparison with the corresponding thiophene derivative.

Elimination reactions of (E)-2,4-dinitrobenzaldehyde O-aryloximes 1−3 promoted by EtO-, PhC(CH3)NO-/PhC(CH3)NOH, and CF3CH2O-/CF3CH2OH buffers in ethanol have been studied kinetically. The reactions produced 2,4-dinitrobenzonitrile and aryloxides as the only products. The observed second-order kinetics, Bronsted β = 0.55−0.75, |βlg| = 0.39−0.48 are consistent with the E2 mechanism. The Bronsted β decreased as the leaving group was made more nucleofugic and the |βlg| increased with a weaker base. The result can be described by a positive interaction coefficient, pxy = ∂β/∂pK1g = ∂β1g/∂pKBH > 0, which provides additional support for the E2 mechanism.

Elimination reactions of (Z)-thiophene- and (Z)-furan-2-carbaldehyde O-benzoyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and kH/kD values, and an E2 mechanism is evident. The relative rates of elimination from (Z)-ArCHNOC(O)C6H4Y are 1/1.1/0.6 for Ar = phenyl/thienyl/furyl, respectively. For reactions of 1 with DBU in MeCN, kH/kD = 8.2 ± 0.1, Hammett ρ = 1.22 ± 0.19, β1g = −0.43 ± 0.01, ΔH⧧ = 5.9 ± 0.1 kcal/mol, and ΔS⧧ = −28.5 ± 0.3 eu have been determined. The corresponding values for 2 are kH/kD = 8.8 ± 0.2, ρ = 1.87 ± 0.05, β1g = −0.55 ± 0.10, ΔH⧧ = 6.5 ± 0.1 kcal/mol, and ΔS⧧ = −29.0 ± 1.5 eu. The kH/kD, Hammett ρ, and |β1g| values increase as the β-aryl group is changed in the order phenyl < thienyl < furyl. The results indicate that the transition state structure for the nitrile-forming elimination changes slightly toward product-like with the change of the β-aryl group.

We report a two-photon fluorescent probe (AHg1) that can be excited by 780 nm femto-second pulses, shows high photostability and negligible toxicity, and can visualize the site of Hg(2+) accumulation, but can also estimate trace amounts of mercury ions in fresh fish organs by two-photon microscopy.

Reactions of (E)-O-arylbenzaldoximes 1-3 with MeONa-MeOH have been studied kinetically. The reactions proceed via competing E2 and S N Ar reactions, in which the first step is rate-determining. Although the reactions were strongly influenced by the electronic effect of the β- and O-aryl substituents, they were insensitive to the steric effect of the O-aryl group, except that the S N Ar reaction was retarded by the CF 3 group of 2. For eliminations from 1-3 promoted by MeONa-MeOH, the k H /k D value increased and the Hammett p value decreased with better leaving groups

Crystallization of amorphous silicon (a-Si) by Ni–silicide mediated crystallization (SMC) has been studied in an electric field with Ni area density between 3.3×1013 and 5.7×1014 atoms/cm2 on the a-Si. The needlelike crystallites of ∼1000 A in width and several micron length grow in the 〈111〉 directions with the 〈011〉 normal to the film surface when Ni area density was between 5.1×1013 and 2.9×1014 atoms/cm2. However, dendritic crystallites have been found in the a-Si matrix without complete crystallization of the a-Si when the Ni area density was 3.3×1013 atoms/cm2. The field-effect mobility of the thin-film transistor using the SMC poly-Si was 60–112 cm2/V s when the average Ni bulk density in the poly-Si was around 3.0×1018 atoms/cm3, and it decreases with increasing Ni density.

Electric field enhanced silicide mediated crystallization (SMC) was introduced for low-temperature polycrystalline silicon thin-film transistors (TFTs) on glass substrates. The amorphous silicon (a-Si) film having an average Ni thickness of 0.15 /spl Aring/, was completely crystallized at a temperature of 480/spl deg/C within 30 min in the presence of an electric field of 40 V/cm. The poly-Si is composed of needlelike crystallites with a few /spl mu/m length and about 50 nm width. The poly-Si TFT using the SMC exhibited a field effect mobility of 86 cm/sup 2//Vs, a threshold voltage of -0.6 V, and a subthreshold slope of 0.6 V/dec.

Sodium ion plays critical roles in many physiological and pathological processes such as nerve conduction, muscle and heart contraction; it modulates the electrolyte level, cation transport, and cell volume. [1] To understand these functions, a number of one-photon (OP) fluorescent probes have been developed, with SBFI and Sodium Green (SG) being commercially available (Figure 1). [2] A disadvantage of these probes is that they are bulky and suffer from difficulties in loading into live cells. The second problem, which is common for most OP probes, is their short excitation wavelength ( 500 μm), localized excitation, and prolonged observation time. [3] Using TPM, one can image intact tissue for a long period of time with minimum interference from tissue preparation artifacts that can extend more than 70 μm into the tissue slice. However, there is no report on the TP probe for Na+ that is capable of imaging [Na + ]i deep inside living tissues. To address both of these problems, we designed a two photon (TP) probe (ANa1) derived from 2acetyl-6-(dimethylamino)naphthalene (acedan) as the TP fluorophore and 1,7-diaza-15-crown-5 as the Na + ion receptor by considering the following requirements (Figure 1); (i) small MW for cell permeability; (ii) high selectivity for Na + ions; (iii) significant TP cross section for bright TPM image; (iv) large spectral shifts in different environments for discrimination between the cytosolic and membrane-bound probes; and (v) high photostability. Herein, we report that ANa1 is capable of detecting intracellular free Na + ions in live cells and tissues at >100 μm depth for a long period of

Optical imaging with fluorescence microscopy is a vital tool in the study of living systems. The most common method for cell imaging, one-photon microscopy (OPM), uses a single photon of higher energy to excite the fluorophore. However, two-photon microscopy (TPM), which uses two photons of lower energy as the excitation source, is growing in popularity among biologists because of several distinct advantages. Using TPM, researchers can image intact tissue for a long period of time with minimum interference from tissue preparation artifacts, self-absorption, autofluorescence, photobleaching, and photodamage. However, to make TPM a more versatile tool in biology, researchers need a wider variety of two-photon probes for specific applications. In this Account, we describe a series of two-photon probes that we developed that can visualize the distribution of intracellular metal ions, acidic vesicles, and lipid rafts in living cells and tissues. The development of these probes requires a significant two-photon cross section for the bright image and receptors (sensing moieties) that triggers the emission of the two-photon excited fluorescence upon binding with the ions or membrane in the living system. These probes also must be sensitive to the polarity of the environment to allow selective detection of cytosolic and membrane-bound probes. In addition, they need to be cell-permeable, water-soluble for the staining of cells and tissues, and highly photostable for long-term imaging. The resulting probes-AMg1 (Mg(2+)), ACa1-ACa3 (Ca(2+)), AZn1 and AZn2 (Zn(2+)), AH1, AH2, and AL1 (acidic vesicles), and CL2 (membrane)-use 2-acetyl-6-aminonaphthalene as the fluorophore and receptors for the target ions or membrane. All of these two-photon turn-on probes can detect the intracellular free metal ions, acidic vesicles, and lipid rafts at 100-300 microm depth in live tissues. Moreover, with ACa1-AM, we could simultaneously visualize the spontaneous Ca(2+) waves in the somas of neurons and astrocytes at approximately 120 microm depth in fresh hypothalamic slices for more than 1000 s without appreciable decay. Furthermore, AL1 could visualize the transport of the acidic vesicles between cell body and axon terminal along the axon in fresh rat hippocampal slices at approximately 120 microm depth.

A two-photon fluorescent probe (ACaL) is reported that can be excited by 780 nm fs pulses, shows high photostability and negligible toxicity, and can visualize near-membrane Ca2+ in live cells and deep inside live tissues by two-photon microscopy.

The development of two-photon materials has been growing very fast during the last decade due to the potential applications in optical limiting, 3D microfabrication, and multiphoton microscopy. In this article, the structure–two-photon absorption property relationships of dipolar, quadrupolar, and octupolar molecules as well as the derivatives of triphenylamine, [2.2]paracyclophanes, multi-annulenes, and porphyrins are briefly reviewed to provide a guideline for the design of efficient two-photon materials.

International audience; We present a polarimetric two-photon microscopy technique to quantitatively image the local static molecular orientational behavior in lipid and cell membranes. This approach, based on a tunable excitation polarization state complemented by a polarized readout, is easily implementable and does not require hypotheses on the molecular angular distribution such as its mean orientation, which is a main limitation in traditional fluorescence anisotropy measurements. The method is applied to the investigation of the molecular angular distribution in giant unilamellar vesicles formed by liquid-ordered and liquid-disordered micro-domains, and in COS-7 cell membranes. The highest order contrast between ordered and disordered domains is obtained for dyes locating within the membrane acyl chains.

Wireless sensor networks are evolving from relatively undemanding applications to applications which have stronger requirements. The coordination of distributed entities and events requires time synchronization. Although a number of methods have been studied for WSNs, some applications require high precision time synchronization. Precision time synchronization enables a variety of extensions of applications. The IEEE 1588 precision time protocol (PTP) provides a standard method to synchronize devices in a network with sub-microsecond precision. This paper deals with precision time synchronization using IEEE 1588 over wireless sensor networks. Precision time synchronization using IEEE 1588 provides compatibility between heterogeneous systems in WSNs. This paper also presents experiments and performance evaluation of precision time synchronization in WSNs. Our result established a method for nodes in a network to maintain their clocks to within a 200 nanosecond offset from the reference clock of a master node.

Novel methyl metacrylate (MMA) and maleimide copolymers P1 and P2 containing 5-[5‘-(p-diethylaminostyryl)furfurylidene]-N,N‘-diethylthiobarbituric acid in the side chain have been synthesized and their electro-optic properties were determined. Copolymers P1 and P2 exhibited the maximum r33 values of 45.1 and 23.3 pm/V at 1.3 μm with poling fields of 0.6 and 0.4 MV/cm, respectively. The r33 values of the copolymers P1 and P2 retained 80% and 90% of the original values, respectively, after heating at 80 °C for 50 h.

A series of pyrene derivatives having 4-(N,N-dimethylamino)phenylethynyl groups as the substituent (1-5) have been synthesized and their two-photon absorption properties were investigated. Comparison of two-photon cross section (delta(max)) with related compounds reveals that pyrene is as efficient a pi-center as anthracene in two-photon materials. Moreover, the two-photon cross section (delta(max)) increased with the number of substituents reaching at the maximum value of 1150 GM for the tetra-substituted derivative (5). Furthermore, the two-photon action cross section (Phi delta(max)) of 5 is comparable to that the most efficient two-photon materials. This result provides a useful guideline to the design of efficient two-photon materials bearing pyrene as a pi-center.

We report a new two-photon fluorescence turn-on probe 6-[(E)-3-oxo-1-dodecenyl]-2-[N-methyl-N-(carboxymethyl)amino]naphthalene (CL2) that is designed specifically for visualizing lipid rafts in living cells and tissues. This probe emits much brighter two-photon excited fluorescence in lipid rafts than in non-raft domains and allows direct visualization of the lipid rafts in the live cells and pyramidal neuron layer of the CA1 region at a depth of 100-250 mum in live tissues using two-photon microscopy.

2-Acetyl-6-(dimethylamino)naphthalene-derived two-photon fluorescent Ca2+ probes (ACa1-ACa3) are reported. They can be excited by a 780 nm laser beam, show 23-50-fold enhancement in one- and two-photon excited fluorescence in response to Ca2+, emit fourfold stronger two-photon excited fluorescence than Oregon Green 488 BAPTA-1 upon complexation with Ca2+, and can selectively detect intracellular free Ca2+ ions in live cells and living tissues with minimum interference from other metal ions and membrane-bound probes. Moreover, these probes are capable of monitoring calcium waves at a depth of 120-170 microm in live tissues for 1100-4000 s using two-photon microscopy with no artifacts of photobleaching.

A series of 2,6-bis(p-dihexylaminostyryl)anthracence derivatives having phenyl, styryl, and phenylethynyl groups at 9,10-positions (1-4) have been synthesized and their two-photon cross-sections were determined. Overall, the wavelengths of the longest wavelength absorption band and emission spectra increase with increase in the conjugation length and the electron withdrawing ability of the 9,10-substituents. All compounds show two-photon cross sections in the range of 740-3940 GM at 780-960 nm, which increase significantly by the donor and acceptor groups at 9,10-positions. In addition, Ph and phenylethynyl groups are better when compared to the styryl group at the 9,10-positions in terms of the two-photon action cross section. From a practical perspective, 1a, 2a-c, and 4b showed significant two-photon action cross-section and are most useful for applications that use two-photon excited fluorescence.

1,3-Alternate calix[4]arene-based fluorescent chemosensors bearing two-photon absorbing chromophores have been synthesized, and their sensing behaviors toward metal ions were investigated via absorption band shifts as well as one- and two-photon fluorescence changes. Free ligands absorb the light at 461 nm and weakly emit their fluorescence at 600 nm when excited by UV-vis radiation at 461 nm, but no two-photon excited fluorescence is emitted by excitation at 780 nm. Addition of an Al(3+) or Pb(2+) ion to a solution of the ligand causes a blue-shifted absorption and enhanced fluorescence due to a declined resonance energy transfer (RET) upon excitation by one- and two-photon processes. Addition of a Pb(2+) ion to a solution of 1.K(+) results in a higher fluorescence intensity than the original 1.Pb(2+) complex regardless of one- or two-photon excitation, due to the allosteric effect induced by the complexation of K(+) with a crown loop.

The Kin.46 ribozyme catalyzes transfer of the gamma (thio)phosphoryl group of ATP (or ATPγS) to the ribozyme's 5′ hydroxyl. Single-turnover catalytic activities of topologically rearranged versions of Kin.46 were studied to gain insight into its overall tertiary architecture. The distal ends of stems P3 and P4 were tethered through a single-stranded connection domain that altered the interhelical connectivity. The shortest linkers interfered with catalysis, while seven or more nucleotides (nt) in the linker allowed near-normal catalytic rates, suggesting that a distance of roughly 25–35 Å optimally separates the termini of these helices. Activity was maximal when the tether contained 15 nt, at which point the kcat (0.016 min−1) and Km (1.2 mM) values were identical to those of a nontethered control. The presence of the tether alters Mg2+ dependence, in that Mg2+ binding appears to be more cooperative in the tethered ribozyme (Hill coefficient 1.4–1.8 versus 0.8 for the nontethered ribozyme). Binding affinity for the ATPγS substrate increases at elevated concentrations of Mg2+, particularly for the tethered ribozyme. The tethered ribozyme displays significantly enhanced thermal stability, with a maximum initial velocity (0.126 min−1) at 60°C, whereas the nontethered ribozyme has a lower maximum initial velocity (0.051 min−1) at 50°C. The tether also significantly reduces the apparent entropy of activation. Both of these effects can be understood in terms of stabilization of the ribozyme in a conformation that is on-path with respect to catalysis, and in terms of facilitating formation of the allosteric activation helix P4.

Initiation factor 1 (IF1) is an essential protein in Escherichia coli involved in the initiation step of protein synthesis. The protein level of IF1 increases when E. coli cells are subjected to cold shock, however, it remains unclear as to how this increase occurs. The infA gene encoding IF1 contains two promoters, the distal P1 and the proximal P2 promoter. In this study, we found that infA mRNA was greatly increased, and that this increase resulted from transcriptional activation of P1, not P2, during cold shock although stability of transcripts from both promoters concomitantly increased.

A series of donor-pi-donor derivatives containing phenyl, naphthyl, and anthryl groups as the pi-center and heterocyclic rings as the conjugation bridge have been synthesized and their one- and two-photon spectroscopic properties and photostability were determined. These compounds show bathochromic shifts in the absorption and emission spectra, larger two-photon cross-section, and enhanced photostability in comparison to their open-chain analogues. In addition, a convenient method for the qualitative photostability measurement is proposed.

[Structure: see text] Anthracene derivatives with a variety of donor-acceptor substituents have been synthesized and shown to exhibit large two-photon cross sections over a wide range of wavelengths.

To gain insight into the mechanism by which the sequence at the rne-dependent site of substrate RNA affects the substrate specificity of Escherichia coli RNase E, we performed kinetic analysis of the cleavage of precursorMl RNA molecules containing various sequences at the rne-dependent site by the N-terminal catalytic half of RNase E (NTH-RNase E). NTH-RNase E displayed higher K m and k c a t values for more specific substrates. The retention of single strandedness at the rne-dependent site was essential for cleavage efficiency. Moreover, the loss of single-strandedness was accompanied by a decrease in both the K m and k c a t values.

A two-photon sensor for the metal ions derived from azacrown ether as the receptor is reported. The sensor emits strong two-photon fluorescence when excited by 800 nm laser photons. Moreover, the binding constants measured by the one- and two-photon fluorescence are similar. This result may be useful for the design of efficient two-photon fluorescence probes for biological substrates.

[structure: see text] Triphenylamine derivatives have been synthesized and shown to exhibit large two-photon cross-sections at a wide range of wavelengths and the largest value measured by fs Z-scan experiment. Moreover, a linear relationship is noted between the two-photon cross-sections measured by ns fluorescence and fs Z-scan methods.

E-mail: brcho@cju.ac.krReceived September 6, 2012, Accepted September 26, 2012Key Words : Guanine-rich RNA, RNA aptamer, RNase T1, Nuclease S1, RNase V1 RNA structure has sometimes been analyzed by bio-physical method such as NMR (nuclear magnetic resonance),which has not been popular because the RNA with smallsize only is available and a large amount of RNA is requiredfor the structural analysis with NMR.

Elimination reactions of (4'-ClC6H4)2CHCO2C6H3-2-X-4-NO2 promoted by R2NH-R2NH2+ in 70 mol% MeCN (aq.) have been studied kinetically. The reactions are second-order and exhibit Brönsted beta = 0.44-0.86 and /beta(lg)/ = 0.41-0.71. The Brönsted beta decreased with a poorer leaving group and /beta(lg)/ increased with a weaker base. The results are consistent with an E2 mechanism. When X=H, the reaction proceeded by the concurrent E2 and Elcb mechanism.

Synthesis and physical properties of novel multibranched two-photon materials are reported. The compound with three units of 4-(p-diphenylaminostyryl)-2,5-dicyanostyryl moieties attached to the central triphenylamine core exhibits a very large two-photon absorption cross-section.

Octupolar oligomers containing 2-12 molecules of 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives have been synthesized and their nonlinear optical and two-photon absorption (TPA) properties were determined. The beta(0) values are in the range of (85-1219) x 10(-30) esu and increase monotonically with the increasing number of the octupolar units within the molecule. The two-photon-induced fluorescence excitation spectra are quite similar to the single-photon absorption spectra except that the wavelength is doubled, indicating that the one- and two-photon allowed excited states are the same. The peak TPA cross-section values (delta(max)) measured with nanosecond pulses by the two-photon-induced fluorescence method are in the range (3010-62, 930) x 10(-50) cm(4)s photon(-1). The delta(max) increases as the number of the octupolar units in the molecules increases. A linear relationship is observed between delta(max) and beta, and this delta-beta relationship serves as a useful design strategy for the synthesis of novel octupolar oligomers and polymers with large TPA and beta.

Sixteen lipophilic N-(X)sulfonyl carbamoyl lariat ethers with polyether ring sizes of 12-crown-4, 14-crown-4, 15-crown-5, and 18-crown-6 are utilized for competitive alkali metal cation extractions from aqueous solutions into chloroform. Variation of the electron-withdrawing properties of X in the series of methyl, phenyl, 4-nitrophenyl, and trifluoromethyl allows the influence of the acidity of the C(O)NHSO2X group in the side arm upon extraction efficiency and selectivity to be assessed. With X = trifluoromethyl, effective alkali metal cation extractions from acidic, neutral, and basic aqueous solutions are achieved. When the crown ether rings are 14-crown-4, 15-crown-5, and 18-crown-6, selectivities for Li+, Na+, and K+, respectively, are observed. Results are compared with those reported for analogous lariat ether carboxylic acids and phosphonic acid monoethyl esters.