Restriction on molecular fluxionality by substitution: A case study for the 1,10-dicyanobullvalene.

We show herein that 1,10-dicyano substitution restricts the paragon fluxionality of bullvalene to just 14 isomers which isomerize along a single cycle. The restricted fluxionality of 1,10-dicyanobullvalene (DCB) is investigated by means of: (i) Bonding analyses of the isomer structures using the adaptive natural density partitioning (AdNDP). (ii) Quantum dynamical simulations of the isomerizations along the cyclic intrinsic reaction coordinate of the potential energy surface (PES). The PES possesses 14 equivalent potential wells supporting 14 isomers which are separated by 14 equivalent potential barriers supporting 14 transition states. Accordingly, at low temperatures, DCB appears as a hindered molecular rotor, without any delocalization of the wavefunction in the 14 potential wells, without any nuclear spin isomers, and with completely negligible tunneling. These results are compared and found to differ from those for molecular boron rotors. (iii) Born-Oppenheimer molecular dynamics (BOMD) simulations of thermally activated isomerizations. (iv) Calculations of the rate constants in the frame of transition state theory (TST) with reasonable agreement achieved with the BOMD results. (v) Simulations of the equilibration dynamics using rate equations for the isomerizations with TST rate coefficients. Accordingly, in the long-time limit, isomerizations of the 14 isomers, each with Cs symmetry, approach the "14 Cs → C7v" thermally averaged structure. This is a superposition of the 14 equally populated isomer structures with an overall C7v symmetry. By extrapolation, the results for DCB yield working hypotheses for so far un-explored properties e.g. for the equilibration dynamics of C10H10.

Time-dependent Extension of Grimme's Continuous Chirality Measure for Electronic Chirality Flips in Femto- and Attosecond Time Domains.

Grimme's Continuous Chirality Measure (CCM ) was developed for comparisons of the chirality of the electronic wave functions of molecules, typically in their ground states. For example, CCM=14.5, 1.2,  and 0.0 for alanine, hydrogen-peroxide, and for achiral molecules, respectively. Well-designed laser pulses can excite achiral molecules from the electronic ground state to time-dependent chiral superposition states, with chirality flips in the femto- or even attosecond (fs or as) time domains. Here we provide a time-dependent extension CCM(t) of Grimme's CCM for trailing the electronic chirality flips. As examples, we consider two laser driven electronic wavefunctions which represent flips between opposite electronic enantiomers of oriented NaK within 4.76 fs and 433 as. The corresponding  CCM(t) vary respectively from 14.5 or from 13.3 to 0.0, and back.

Distinguishing the responsive mechanisms of fluorescent probes to hydrogen peroxide, proteins, and DNA/RNA.

The responsive mechanisms of cationic quinolinium-vinyl-N,N-dimethylaniline boronate (QVD-B) derivative probes to hydrogen peroxide (H2O2), proteins and DNA/RNA are theoretically investigated in this study. The potential energy curves of QVD-B scanned on a dihedral angle (N+-C-CC) in the first singlet (S1) state exhibit large torsional energy barriers. Additionally, the energy of the lowest unoccupied molecular orbital (LUMO) of an acceptor moiety (-3.14 eV) is lower than that of a donor moiety (-1.13 eV) in QVD-B. This demonstrates that photoinduced electron transfer (PET) quenches the fluorescence of QVD-B, as opposed to the previous report of intramolecular single-bond rotation. After reacting with H2O2, the reaction product of quinoline-vinyl-N,N-dimethylaniline (QVD) turns off the PET pathway and turns on the fluorescence at 550 nm, which is consistent with the experimental results (580 nm). Among the possible configurations of QVD-B that forms with proteins and DNA, the calculated fluorescence values of corresponding twisted QVD-B-P (638 nm) and QVD-B-D (686 nm) are consistent with the experimental results (632 and 688 nm). The frontier molecular orbital and electron-hole analysis show that the charge transfer distance follows the order of QVD (1.88 Å) < QVD-B-P (4.49 Å) < QVD-B-D (6.39 Å), which induces the fluorescence red-shifts of QVD-B-P and QVD-B-D compared to that of QVD. The multi-detection mechanism of the fluorescent probe QVD-B is attributed to PET progress and different degrees of local charge transfer after photoexcitation.

Efficient Catalytic Degradation of Methyl Orange by Various ZnO-Doped Lignin-Based Carbons.

Herein, a series of ZnO-doped lignin-based carbons (LC/ZnO) were successfully prepared from different types of lignin and used for methyl orange (MO) photocatalytic degradation. The apparent morphology, internal structure, and photoelectric properties of prepared LC/ZnO composites and their effects on subsequent MO photocatalytic degradation were investigated by various characterization techniques. The results showed that the LC/ZnO composites that were prepared in this work mainly consisted of highly dispersed ZnO nanoparticles and lignin-based carbon nano-sheets, which were beneficial for subsequent photogenerated electrons and holes formation, dispersion, and migration. The MO could be significantly degraded with various ZnO-doped lignin-based carbons, especially over the LCSL/ZnO, and the maximum degradation rate was 96.9% within 30 min under the simulated 300w sunlight exposure. The experiments of free radical elimination showed that the photocatalytic degradation of MO over LC/ZnO were a result of the co-action of multiple free radicals, and h+ might play the predominant roles in MO degradation. In addition, the pH of the solution had little effect on MO degradation, and the MO could be effectively degraded even in an alkaline solution of pH = 12.0. The cycling experiments showed that the prepared LC/ZnO had a good stability for MO photodegradation, especially for LCSL/ZnO, even after 5 times recycling, and the degradation rate of MO only dropped from 97.0% to 93.0%. The research not only provided a fundamental theory for the efficient photocatalytic degradation of MO by LC/ZnO composites, but also offered a new insight into lignin valorization.

Crystalline-Dependent Discharge Process of Locally Enhanced Electrooxidation Activity on Ni2P.

The state-of-the-art transition-based electrocatalysts in alkaline media generally suffer from unavoidable surface reconstruction during oxygen evolution reaction measurements, leading to the collapse and loss of the crystalline matrix. Low potential discharge offers a gentle way for surface reconstruction and thus realizes the manipulation of the real active site. Nevertheless, the absence of a fundamental understanding focus on this discharge region renders the functional phase, either the crystalline or amorphous matrix, for the controllable reconstruction still undecidable. Herein, we report a scenario to employ different crystalline matrices as electrocatalysts for discharge region reconstruction. The representative low crystalline Ni2P (LC-Ni2P) possesses a relatively weak surface structure compared with highly crystalline or amorphous Ni2P (HC-Ni2P or A-Ni2P), which contributes abundant oxygen vacancies after the discharge process. The fast discharge behavior of LC-Ni2P leads to the uniform distribution of these vacancies and thus endows the inner interface with reactant activating functionality. A high increase in current density of 36.7% is achieved at 2.32 V (vs RHE) for the LC-Ni2P electrode. The understanding of the discharge behavior in this study, on different crystalline matrices, presents insights into the establishment of controllable surface reconstruction for an effective oxygen evolution reaction.

Design of BPEA-based derivatives with high singlet fission performance: a theoretical perspective.

The development of singlet fission (SF) is greatly hindered by the severe shortage of the types and numbers of SF materials. Here, essential energy conditions and SF-related competitive processes of a series of BPEA derivatives, which are a kind of new promising SF material, are investigated theoretically. Encouraging advantages and interesting laws of key energy conditions of those derivatives were found and potential BPEA derivatives were predicted. Those derivatives present mild exothermic SF processes with 0.3-0.4 eV free energies (ΔE(S1-2T1)) consistently. Their lowest triplet states (T1) are stable and totally enter into the ideal energy window (≥1.0 eV), which is beneficial for achieving the maximum efficiency of PCE. Their large ΔE(T2-2T1) can suppress the higher-state annihilation of T1 well. The E(S1) and ΔE(S1-2T1) of the derivatives are sensitive to both the slip patterns of the dimer and ending substituents. Terminal substituents with both strong electron-withdrawing and electron-donating abilities can lower E(S1), and decreases in the former are more obvious due to the larger intramolecular charge transfer. Interestingly, it is found firstly that the terminal substituent modulation effect on E(S1) and ΔE(S1-2T1) is more effective when large longitudinal slips are included in their stacking modes. The reason is that the direction of the transition dipole moments (µs1) is along X, and large longitudinal slips will bring about the approach of positive and negative charge centers of monomers, and lead to large Davydov splitting. By further evaluation of important radiation and non-radiation processes, it is predicted that the BPEA-based derivatives, which have rigid -Cl, -Br, or -CN terminals and include large longitudinal slips in their crystal packing, are expected to achieve excellent SF performances. Our work provides useful ideas for developing or optimizing acene-derivative SF materials with high efficiency.

Ultrafast laser induced charge migration with de- and re-coherences in polyatomic molecules: A general method with application to pyrene.

We develop a general method to study ultrafast laser induced charge migration in molecules, which includes both electronic and nuclear dynamics. The method can be applied to relatively large systems. A detailed analysis of charge migration in pyrene is performed. Decoherences and recoherences of charge migration in pyrene are found and explained in terms of nuclear motions.

Fabrication of Composite Gel Electrolyte and F-Doping Carbon/Silica Anode from Electro-Spun P(VDF-HFP)/Silica Composite Nanofiber Film for Advanced Lithium-Ion Batteries.

The aim of this work is to effectively combine the advantages of polymer and ceramic nanoparticles and improve the comprehensive performance of lithium-ion batteries (LIBs) diaphragm. A flexible film composed of electro-spun P(VDF-HFP) nanofibers covered by a layer of mesoporous silica (P(VDF-HFP)@SiO2) was synthesized via a sol-gel transcription method, then used as a scaffold to absorb organic electrolyte to make gel a electrolyte membrane (P(VDF-HFP)@SiO2-GE) for LIBs. The P(VDF-HFP)@SiO2-GE presents high electrolyte uptake (~1000 wt%), thermal stability (up to ~350 °C), ionic conductivity (~2.6 mS cm-1 at room temperature), and excellent compatibility with an active Li metal anode. Meanwhile, F-doping carbon/silica composite nanofibers (F-C@SiO2) were also produced by carbonizing the P(VDF-HFP)@SiO2 film under Ar and used to make an electrode. The assembled F-C@SiO2|P(VDF-HFP)@SiO2-GE|Li half-cell showed long-cycle stability and a higher discharge specific capacity (340 mAh g-1) than F-C@SiO2|Celgard 2325|Li half-cell (175 mAh g-1) at a current density of 0.2 A g-1 after 300 cycles, indicating a new way for designing and fabricating safer high-performance LIBs.

Dual-Channel Fluorescent Probe for the Simultaneous Monitoring of Peroxynitrite and Adenosine-5'-triphosphate in Cellular Applications.

Changes in adenosine triphosphate (ATP) and peroxynitrite (ONOO-) concentrations have been correlated in a number of diseases including ischemia-reperfusion injury and drug-induced liver injury. Herein, we report the development of a fluorescent probe ATP-LW, which enables the simultaneous detection of ONOO- and ATP. ONOO- selectively oxidizes the boronate pinacol ester of ATP-LW to afford the fluorescent 4-hydroxy-1,8-naphthalimide product NA-OH (λex = 450 nm, λem = 562 nm or λex = 488 nm, λem = 568 nm). In contrast, the binding of ATP to ATP-LW induces the spirolactam ring opening of rhodamine to afford a highly emissive product (λex = 520 nm, λem = 587 nm). Due to the differences in emission between the ONOO- and ATP products, ATP-LW allows ONOO- levels to be monitored in the green channel (λex = 488 nm, λem = 500-575 nm) and ATP concentrations in the red channel (λex = 514 nm, λem = 575-650 nm). The use of ATP-LW as a combined ONOO- and ATP probe was demonstrated using hepatocytes (HL-7702 cells) in cellular imaging experiments. Treatment of HL-7702 cells with oligomycin A (an inhibitor of ATP synthase) resulted in a reduction of signal intensity in the red channel and an increase in that of the green channel as expected for a reduction in ATP concentrations. Similar fluorescence changes were seen in the presence of SIN-1 (an exogenous ONOO- donor).

Stereostructure Dependence Phenomenon on the Self-Assembly of Ala-Ala-Ala Lipotripeptides.

A series of lipotripeptide stereoisomers based on alanine were synthesized, and their self-assembling behaviors were studied by means of circular dichroism spectra, ATR-IR, temperature-dependent 1H NMR, and X-ray diffraction patterns. In the mixed solvent of hexafluoroisopropanol/H2O (1/9, v/v), eight lipotripeptides were able to self-assembled into nanoflakes or nanoribbons driven by the hydrophobic association of alkyl chains, intermolecular hydrogen bonding among carboxyl groups at C-terminal and amide groups of alanine moieties in the peptide segment. It was found that the stacking chirality of carbonyl groups was determined by the chirality of alanine residue at C-terminal (i.e., "C-terminal determination" rule). Moreover, our research also highlighted the intermolecular hydrogen bonding on amide groups of each alanine residue, terminal carboxyl as well as the molecular packing structures can be subtly manipulated by changing the stereochemical sequence of peptide segment.

Dual-factor Synergistically Activated ESIPT-based Probe: Differential Fluorescence Signals to Simultaneously Detect α-Naphthyl Acetate and Acid α-Naphthyl Acetate Esterase.

α-Naphthyl acetate esterase (α-NAE) and acid α-naphthyl acetate esterase (ANAE), a class of special esterases, are important for lymphocyte typing and immunocompetence-monitoring. As such, the simultaneous detection of α-NAE and ANAE has become a target to effectively improve the accuracy in lymphocyte typing. Therefore, we developed a dual-factor synergistically activated ESIPT-based probe (HBT-NA) to detect α-NAE and ANAE sensitively, rapidly, and simultaneously in a differential manner. HBT-NA exhibits differential fluorescence signal outputs toward small changes of α-NAE and ANAE activities. HBT-NA displays a weak fluorescence signal at 392 nm over a pH range from 6.0 to 7.4. However, when it interacts with α-NAE (0-25 U) at pH = 7.4, the fluorescence intensity at 392 nm enhanced linearly within 60 s (F392 nm/F0392 nm = 0.042 Cα-NAE + 1.1, R2 = 0.99). Furthermore, HBT-NA emits ratiometric fluorescence signals (F505 nm/F392 nm) for ANAE (0-25 U) at pH = 6.0 within 2.0 min, exhibiting a good linear relationship (F505 nm/F392 nm = 0.83CANAE - 1.75, R2 = 0.99). The differential fluorescence signals can be used to simultaneously detect the activities of α-NAE and ANAE in solutions and complex living organisms. More importantly, based on the differential fluorescence signals toward α-NAE and ANAE, T lymphocytes and B lymphocytes could be successfully typed and differentiated among nontyped lymphocytes, facilitating the real-time evaluation of their immune functions using flow cytometry. Hence, HBT-NA could be used for the ultrasensitive detection of the enzyme activities of α-NAE and ANAE, the real-time precise typing of lymphocytes, and the monitoring of immunocompetence.

Visualizing and Isolating Iron-Reducing Microorganisms at the Single-Cell Level.

Iron-reducing microorganisms (FeRM) play key roles in many natural and engineering processes. Visualizing and isolating FeRM from multispecies samples are essential to understand the in situ location and geochemical role of FeRM. Here, we visualized FeRM by a "turn-on" Fe2+-specific fluorescent chemodosimeter (FSFC) with high sensitivity, selectivity, and stability. This FSFC could selectively identify and locate active FeRM from either pure culture, coculture of different bacteria, or sediment-containing samples. Fluorescent intensity of the FSFC could be used as an indicator of Fe2+ concentration in bacterial cultures. By combining the use of the FSFC with that of a single-cell sorter, we obtained three FSFC-labeled cells from an enriched consortium, and all of them were subsequently shown to be capable of iron reduction; two unlabeled cells were shown to have no iron-reducing capability, further confirming the feasibility of the FSFC.IMPORTANCE Visualization and isolation of FeRM from samples containing multiple species are commonly needed by researchers from different disciplines, such as environmental microbiology, environmental sciences, and geochemistry. However, no available method has been reported. In this study, we provide a method to visualize FeRM and evaluate their activity even at the single-cell level. When this approach is combined with use of a single-cell sorter, FeRM can also be isolated from samples containing multiple species. This method can be used as a powerful tool to uncover the in situ or ex situ role of FeRM and their interactions with ambient microbes or chemicals.

Coherent Interference Fringes of Two-Photon Photoluminescence in Individual Au Nanoparticles: The Critical Role of the Intermediate State.

The interaction between light and metal nanoparticles enables investigations of microscopic phenomena on nanometer length and ultrashort timescales, benefiting from strong confinement and enhancement of the optical field. However, the ultrafast dynamics of these nanoparticles are primarily investigated by multiphoton photoluminescence on picoseconds or photoemission on femtoseconds independently. Here, we presented two-photon photoluminescence (TPPL) measurements on individual Au nanobipyramids (AuNP) to reveal their ultrafast dynamics by double-pulse excitation on a global timescale ranging from subfemtosecond to tens of picoseconds. Two orders of magnitude photoluminescence enhancement, namely, coherent interference fringes, has been demonstrated. Power-dependent measurements uncovered the transform of the nonlinearity from 1 to 2 when the interpulse delay varied from tens of femtoseconds to tens of picoseconds. We proved that the real intermediate state plays a critical role in the observed phenomena, supported by numerical simulations with a three-state model. Our results provide insight into the role of intermediate states in the ultrafast dynamics of noble metal nanoparticles. The presence of the intermediate states in AuNP and the coherent control of state populations offer interesting perspectives for imaging, sensing, nanophotonics, and in particular, for preparing macroscopic superposition states at room temperature and low-power superresolution stimulated emission depletion microscopy.

The unified quantum mechanical structure of tubular molecular rotors with multiple equivalent global minimum structures: the 18*C2h → D9d case of La-[B2@B18]-La.

La-[B2@B18]-La demonstrates decisive changes of the properties of molecular rotors, from multiple (here 18) equivalent individual global minimum structures to a quantum mechanical unified structure. This affects their geometries, their symmetries (18*C2h → D9d), the generation of energy bands, and high-resolution spectroscopy.

Handedness Inversion of Chiral 3-Aminophenol Formaldehyde Resin Nanotubes Mediated by Metal Coordination.

Precise adjustment of microstructure and handedness of chiral nanomaterials is important to regulate their properties and performance. Herein, helical 3-aminophenol formaldehyde resin (APF) nanotubes and corresponding carbonaceous nanotubes with controllable handedness and optical activity were obtained via an external metal ion-mediated supramolecular co-templating method in an enantiomerically pure template system, in which an appropriate amount of Mn2+ (Co2+ or Ni2+ ) with moderate coordination abilities can reverse the spatial arrangement of the phenylglycine-based amphiphilic template molecules through metal coordination. Different stacking modes of coordination complexes in disparate metal ion systems lead to diverse helical senses (diameter and pitch) of the obtained helical APF. In addition, this coordination mode of metal intervention can be applied to other amine-based helical polymer synthesis systems, which paves the way for the design of high-quality chiral nanomaterials with satisfactory physical parameters and properties.

Correction to: Duganella rivus sp. nov., Duganella fentianensis sp. nov., Duganella qianjiadongensis sp. nov. and Massilia guangdongensis sp. nov., isolated from subtropical streams in China and reclassification of all species within genus Pseudoduganella.

In the published version of the article, the title should have read 'Duganella rivi sp. nov., Duganella fentianensis sp. nov., Duganella qianjiadongensis sp. nov. and Massilia guangdongensis sp. nov., isolated from subtropical streams in China and reclassification of all species within genus Pseudoduganella'.

Duganella rivus sp. nov., Duganella fentianensis sp. nov., Duganella qianjiadongensis sp. nov. and Massilia guangdongensis sp. nov., isolated from subtropical streams in China and reclassification of all species within genus Pseudoduganella.

Four Gram-stain-negative, catalase-positive, rod-shaped and motile strains (FT55WT, FT93WT, CY13WT and DS3T) were isolated from subtropical streams in China. Comparisons based on 16S rRNA gene sequences indicated that strains FT55WT, FT93WT and CY13WT take strain Pseudoduganella danionis E3/2T, and strain DS3T takes strain Pseudoduganella eburnea 10R5-21T as their closest neighbour, respectively. The genome sizes of strains FT55WT, FT93WT, CY13WT and DS3T were 6.15, 5.10, 5.31 and 5.72 Mbp with G+C contents of 61.7, 60.9, 60.6 and 64.0%, respectively. The reconstructed phylogenomic tree based on concatenated 92 core genes showed that strain FT55WT clusters closely with Duganella radicis KCTC 22382T and Duganella sacchari Sac-22T, strains FT93WT and CY13WT form a distinct clade with P. danionis DSM 103461T and this clade clusters with the clades of genus Duganella together, and strain DS3T forms a distinct clade with P. eburnea JCM 31587T and Pseudoduganella violaceinigra DSM 15887T and this clade clusters closely with the clades of genus Massilia, respectively. The calculated pairwise OrthoANIu values and digital DNA-DNA hybridization (DDH) values among strains FT55WT, FT93WT, CY13WT, DS3T and related strains were in the ranges of 75.6-94.2% and 20.6-56.2%, respectively. Q-8 was the sole respiratory quinone of these four strains. The major fatty acids were C16:1ω7c, C16:0 and C12:0. The polar lipids included phosphatidylglycerol, phosphatidylethanolamine and one unidentified phospholipid. Considering the similar fatty acids and polar lipids profiles of species within genus Pseudoduganella, Massilia and Duganella, there is currently no justification for assigning the species of genus Pseudoduganella into the Massilia and Duganella clades in the phylogenomic tree. It is reasonable to transfer P. violaceinigra and P. eburnea to the genus Massilia as Massilia violaceinigrum comb. nov. and Massilia eburnea comb. nov., and transfer P. danionis to the genus Duganella as Duganella danionis comb. nov. Considering phylogenomic analysis, OrthoANIu data, digital DDH data and a range of physiological and biochemical characteristics, strains FT55WT, FT93WT and CY13WT should be assigned to genus Duganella, and strain DS3T should be classified as a novel species within genus Massilia, for which the names Duganella rivus sp. nov. (type strain FT55WT = GDMCC 1.1675T = KACC 21467T), Duganella fentianensis sp. nov. (type strain FT93WT = GDMCC 1.1683T = KACC 21475T), Duganella qianjiadongensis sp. nov. (type strain CY13WT = GDMCC 1.1669T = KACC 21461T) and Massilia guangdongensis sp. nov. (type strain DS3T = GDMCC 1.1636T = KACC 21312T) are proposed.

Adaptive Responses of Shewanella decolorationis to Toxic Organic Extracellular Electron Acceptor Azo Dyes in Anaerobic Respiration.

Bacterial anaerobic respiration using an extracellular electron acceptor plays a predominant role in global biogeochemical cycles. However, the mechanisms of bacterial adaptation to the toxic organic pollutant as the extracellular electron acceptor during anaerobic respiration are not clear, which limits our ability to optimize the strategies for the bioremediation of a contaminated environment. Here, we report the physiological characteristics and the global gene expression of an ecologically successful bacterium, Shewanella decolorationis S12, when using a typical toxic organic pollutant, amaranth, as the extracellular electron acceptor. Our results revealed that filamentous shift (the cells stretched to fiber-like shapes as long as 18 µm) occurred under amaranth stress. Persistent stress led to a higher filamentous cell rate and decolorization ability in subcultural cells compared to parental strains. In addition, the expression of genes involved in cell division, the chemotaxis system, energy conservation, damage repair, and material transport in filamentous cells was significantly stimulated. The detailed roles of some genes with significantly elevated expressions in filamentous cells, such as the outer membrane porin genes ompA and ompW, the cytochrome c genes arpC and arpD, the global regulatory factor gene rpoS, and the methyl-accepting chemotaxis proteins genes SHD_2793 and SHD_0015, were identified by site-directed mutagenesis. Finally, a conceptual model was proposed to help deepen our insights into both the bacterial survival strategy when toxic organics were present and the mechanisms by which these toxic organics were biodegraded as the extracellular electron acceptors.IMPORTANCE Keeping toxic organic pollutants (TOPs) in tolerable levels is a huge challenge for bacteria in extremely unfavorable environments since TOPs could serve as energy substitutes but also as survival stresses when they are beyond some thresholds. This study focused on the underlying adaptive mechanisms of ecologically successful bacterium Shewanella decolorationis S12 when exposed to amaranth, a typical toxic organic pollutant, as the extracellular electron acceptor. Our results suggest that filamentous shift is a flexible and valid way to solve the dilemma between the energy resource and toxic stress. Filamentous cells regulate gene expression to enhance their degradation and detoxification capabilities, resulting in a strong viability. These novel adaptive responses to TOPs are believed to be an evolutionary achievement to succeed in harsh habitats and thus have great potential to be applied to environment engineering or synthetic biology if we could picture every unknown node in this pathway.

bola-Type Ala-Ala Dipeptides: Odd-Even Effect in Molecular Packing Structures.

A series of bola-type Ala-Ala dipeptides with different alkylene bridges (n = 10-15) were synthesized. In methanol, the molecules with even-numbered carbon bridges self-assembled into twisted nanoribbons, while those with odd-numbered carbon bridges self-assembled into straight belts. The morphology displays a pronounced odd-even dependence upon the number of carbons (n) in the connecting alkylene bridge. The circular dichroism spectra of the self-assemblies showed that molecules with even- and odd-numbered carbon bridges stacked in different structures. FT-IR spectra indicated that the dipeptides with even-numbered carbon bridges formed hydrogen bonds between the amide group and carboxyl ester group, while those with odd-numbered carbon bridges formed hydrogen bonds only between the amide groups. X-ray diffraction patterns revealed that molecules with odd- and even-numbered carbon bridges stacked in monoclinic and triclinic structures, respectively.

Timing the recoherences of attosecond electronic charge migration by quantum control of femtosecond nuclear dynamics: A case study for HCCI.

This work suggests an approach to a new target of laser control of charge migration in molecules or molecular ions. The target is motivated by the fact that nuclear motions can not only cause decoherence of charge migration, typically within few femtoseconds, but they may also enable the reappearance of charge migration after much longer times, typically several tens or even hundreds of femtoseconds. This phenomenon is called recoherence of charge migration, opposite to its decoherence. The details depend on the initiation of the original charge migration by an ultrashort strong intense pump laser pulse. It may reappear quasiperiodically, with reference period Tr. We show that a well-designed pump-dump laser pulse can enforce recoherences of charge migration at different target times Tc, for example, at Tc ≈ Tr/2. The approach is demonstrated by quantum dynamics simulations of the laser driven electronic and nuclear motions in the oriented linear cation HCCI+. First, the concept is explained in terms of a didactic one-dimensional (1D) model that accounts for the decisive CI stretch. The 1D results are then confirmed by a three-dimensional model for the complete set of the CH, CC, and CI stretches.