Using transmittance electron microscopy, fluorescence and polarizing optical microscopy, optical spectroscopy, and fluorescent correlation spectroscopy, it was shown that CdSe/ZnS quantum dots coated ...with a specifically designed surfactant were readily dispersed in nematic liquid crystal (LC) to form stable colloids. The mixture of an alkyl phosphonate and a dendritic surfactant, where the constituent molecules contain promesogenic units, enabled the formation of thermodynamically stable colloids that were stable for at least 1 year. Stable colloids are formed due to minimization of the distortion of the LC ordering around the quantum dots.
While only one enantiomer of chiral biomolecules performs a biological function, access to both enantiomers (or enantiomorphs) proved to be advantageous for technology. Using dye covalent attachment ...to a DNA Holliday junction (HJ), we created two pairs of dimers of bis(chloroindolenine)squaraine dye that enabled strongly coupled molecular excitons of opposite chirality in solution. The exciton chirality inversion was achieved by interchanging single covalent linkers of unequal length tethering the dyes of each dimer to the HJ core. Dimers in each pair exhibited profound exciton-coupled circular dichroism (CD) couplets of opposite signs. Dimer geometries, modeled by simultaneous fitting absorption and CD spectra, were related in each pair as nonsuperimposable and nearly exact mirror images. The origin of observed exciton chirality inversion was explained in the view of isomerization of the stacked Holliday junction. This study will open new opportunities for creating excitonic DNA-based materials that rely on programmable system chirality.
Molecular aggregates exhibit emergent properties, including the collective sharing of electronic excitation energy known as exciton delocalization, that can be leveraged in applications such as ...quantum computing, optical information processing, and light harvesting. In a previous study, we found unexpectedly large excitonic interactions (quantified by the excitonic hopping parameter
J
m
,
n
) in DNA-templated aggregates of squaraine (SQ) dyes with hydrophilic-imparting sulfo and butylsulfo substituents. Here, we characterize DNA Holliday junction (DNA-HJ) templated aggregates of an expanded set of SQs and evaluate their optical properties in the context of structural heterogeneity. Specifically, we characterized the orientation of and
J
m
,
n
between dyes in dimer aggregates of non-chlorinated and chlorinated SQs. Three new chlorinated SQs that feature a varying number of butylsulfo substituents were synthesized and attached to a DNA-HJ
via
a covalent linker to form adjacent and transverse dimers. Various characteristics of the dye, including its hydrophilicity (in terms of log
P
o/w
) and surface area, and of the substituents, including their local bulkiness and electron withdrawing capacity, were quantified computationally. The orientation of and
J
m
,
n
between the dyes were estimated using a model based on Kühn-Renger-May theory to fit the absorption and circular dichroism spectra. The results suggested that adjacent dimer aggregates of all the non-chlorinated and of the most hydrophilic chlorinated SQ dyes exhibit heterogeneity; that is, they form a mixture of dimers subpopulations. A key finding of this work is that dyes with a higher hydrophilicity (lower log
P
o/w
) formed dimers with smaller
J
m
,
n
and large center-to-center dye distance (
R
m
,
n
). Also, the results revealed that the position of the dye in the DNA-HJ template, that is, adjacent or transverse, impacted
J
m
,
n
. Lastly, we found that
J
m
,
n
between symmetrically substituted dyes was reduced by increasing the local bulkiness of the substituent. This work provides insights into how to maintain strong excitonic coupling and identifies challenges associated with heterogeneity, which will help to improve control of these dye aggregates and move forward their potential application as quantum information systems.
Molecular aggregates exhibit collective sharing of electronic excitation energy known as exciton delocalization, that can be leveraged in applications such as quantum computing, optical information processing, and light harvesting.
Molecular (dye) aggregates are a materials platform of interest in light harvesting, organic optoelectronics, and nanoscale computing, including quantum information science (QIS). Strong excitonic ...interactions between dyes are key to their use in QIS; critically, properties of the individual dyes govern the extent of these interactions. In this work, the electronic structure and excited-state dynamics of a series of indolenine-based squaraine dyes incorporating dimethylamino (electron donating) and/or nitro (electron withdrawing) substituents, so-called asymmetric dyes, were characterized. The dyes were covalently tethered to DNA Holliday junctions to suppress aggregation and permit characterization of their monomer photophysics. A combination of density functional theory and steady-state absorption spectroscopy shows that the difference static dipole moment (Δd) successively increases with the addition of these substituents while simultaneously maintaining a large transition dipole moment (μ). Steady-state fluorescence and time-resolved absorption and fluorescence spectroscopies uncover a significant nonradiative decay pathway in the asymmetrically substituted dyes that drastically reduces their excited-state lifetime (τ). This work indicates that Δd can indeed be increased by functionalizing dyes with electron donating and withdrawing substituents and that, in certain classes of dyes such as these asymmetric squaraines, strategies may be needed to ensure long τ, e.g., by rigidifying the π-conjugated network.
Resolution of rac‐3,3,3‐trifluorolactic acid by diastereomeric salt formation was reinvestigated. The use of (S)‐1‐phenylethylamine gives coprecipitation of two diastereomeric phases, 1 ...(S)‐NH3CH(CH3)Ph(S)‐CF3CH(OH)COO and 2 (S)‐NH3CH(CH3)Ph(R)‐CF3CH(OH)COO·H2O. Pure phase 1 may be obtained using molecular sieves as desiccants. Resolution by (S,S)‐2‐amino‐1‐phenylpropan‐1,3‐diol gives monoclinic (S,S)‐NH3CH(CH2OH)CHOHPh (R)‐CF3CH(OH)‐COO 3 with minor (S)‐3,3,3‐trifluorolactate contamination, which is precluded in the recrystallized orthorhombic form 4. A new resolution using inexpensive phenylglycinol gives pure phase 5 (S)‐NH3CH(CH2OH)Ph (S)‐CF3CH(OH)COO in 76% yield, 94% ee in a single step, in preference to its (S)‐(R) diastereomer 6. Overall efficient resolution for both enantiomers of the trifluorolactic acid (each ca. 70% yield, 99% ee) may be achieved by various two‐step “tandem” crystallizations, involving direct addition of either water or a second base to the filtrate from the initial reaction.
Efficient resolution of 3,3,3‐trifluorolactic acid (each enantiomer ca. 70% yield and 99%ee) is achieved by two step "tandem" diastereomeric salt crystallizations, using bases such as 1‐phenylethylamine and phenylglycinol.
Novel homodimeric dyes based on the acridine orange (AO) chromophore were synthesized and investigated. The photophysical properties measured free in solution and on binding to double-stranded DNA ...(dsDNA) were compared to those of widely used nucleic acid labelling dyes, namely SYBR Green I (SG) and YOYO-1. All studied dyes demonstrated negligible intrinsic fluorescence and strong fluorescence enhancement upon binding to dsDNA with quantum yields 0.45–0.55. Contrary to SG and YOYO-1, the obtained dyes showed better resistance to high temperatures, light and oxidizing reagents. The inhibitory effect and the effect on DNA melting temperature in a real-time quantitative polymerase chain reaction (qPCR) for all studied dyes were investigated. In qPCR experiments, dimeric dyes composed of two AO moieties coupled by neutral linkers comprising 2,5- or 2,6-disubstituted five- or six-membered heterocyclic fragments were less inhibitory to qPCR than SG at a broader range of dye concentrations (i.e. 0.75–1.75 μM). Moreover, these dyes are nontoxic when used at concentrations well above the qPCR working concentration. The strong fluorescent signal without inhibiting the qPCR along with the promotion of the formation of specific amplification products make these dyes suitable for high-resolution melt curve analysis and routine qPCR at a broad range of concentrations.
Display omitted
•New dimeric dyes exhibit a strong fluorescence enhancement on binding to dsDNA along with good PCR instrument compatibility.•Obtained dyes are non-toxic and demonstrate high thermal, photolytic and hydrolytic stability.•Dyes 6a–6d are less inhibitory to qPCR than SYBR Green I at a broader range of dye concentrations (i.e. 0.75–1.75 μmol/L).
In order to enhance the phase stability of dispersions of magnetic nanoparticles (NPs) in a polymorphic liquid crystal, new ligands have been designed consisting of a terphenyl-based liquid ...crystalline core. The most stable dispersions were obtained with 7 nm super-paramagnetic Fe
3
O
4
NPs decorated with the new ligands in place of 10 nm ferromagnetic CoFe
2
O
4
spherical NPs.
Retro-aldol reactions in micellar media Vashchenko, Elena V.; Knyazeva, Irina V.; Krivoshey, Alexander I. ...
Monatshefte für Chemie,
11/2012, Letnik:
143, Številka:
11
Journal Article
Recenzirano
Convenient methods for retro-aldol reactions of
α
,
β
-unsaturated ketones in micellar media under acidic or basic conditions are proposed that enable obtaining optically pure (3
R
...)-methylcyclohexanone and (1
R
,4
R
)-4-methylmenthone in high yields.
Graphical abstract
Display omitted
•New chiral components of ferroelectric liquid crystals induce nano-scaled helix pitch.•New materials have large spontaneous polarization and wide SmC* temperature range.•Highest ...helical twisting power in chiral smectic liquid crystals is obtained so far.
Design and studying of derivatives of fluorinated and non-fluorinated p-terphenyl-containing symmetric tetraesters as chiral components (CCs) of ferroelectric liquid crystal (FLC) materials working in deformed helix FLC (DHFLC) mode are described. The tetraesters combine a lactate and alcoholic residues in chiral tails. The new CCs induce short helix pitch (as short as 78 nm) and large spontaneous polarization (PS > 100 nC/cm2) at moderate concentrations (as low as 12 mol. %) in a non-chiral biphenylpyrimidine host. We have studied the effects of the (S)-lactate linker, terminal alkyl chains and fluorine atoms on helix pitch and other useful properties of the chiral tilted smectic (SmC*) phase induced by these CCs in the biphenylpyrimidine host. Depending on positions of the fluorine atoms, the fluorination of the p-terphenyl core shows little effect or even reduces the helical twisting power (HTP) of the CCs. At the same time, modifications in the chiral tails can essentially enhance the HTP and other CC performance characteristics. Thus, the combination of the (S)-lactate linker with a (S)-alkan-2-olic residue results in high HTP (up to 85 μm−1) even without fluorine atoms in the chiral tails. Substitution of the (S)-alkan-2-olic residue with a fluorinated analogue, viz. (R)-1,1,1-trifluoroalkan-2-ol derivative, provides further increase of the HTP in the induced SmC* phase up to the highest known to date value of 101 μm−1.
The LDA-mediated reaction of 4-methyl-1-phenylquinolone and 3-methyl-2-(methylthio)benzothiazolium tosylate proceeds differently depending on the amount of LDA used. With about 1 eq. LDA, the known ...condensation reaction takes place, and the expected benzothiazolic derivative forms. However, when 2 eq. LDA or more is used, a new reaction occurs by an interaction of the condensation product with an excess of LDA and results in cleavage of the C–S bond in the benzothiazole moiety along with the formation of the other C–S bond in the quinolone moiety to give the 2-aminothienoquinolone derivative.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
