The emergence offlexible organic crystals changed the perception of molecu-lar crystals that were regarded as brittle entities over a long period of time,and sparked a great interest in exploring mechanically compliant organic crystalline materials toward next-generation smart materials during the past decade.Schiff base compounds are considered to be one of the most promising candidates forflexible organic crystals owing to their easy synthesis,high yield,stimuli respon-siveness and good mechanical properties.This paper gives an overview of the recent development of Schiff baseflexible organic crystals(including elastic organic crystals,plastic organic crystals,andflexible organic crystals integrating elastic-ity and plasticity)from serendipitous discovery to design strategies and versatile applications such as stimuli responses,optical waveguides,optoelectronic devices,biomimetic soft robots,and organic photonic integrated circuits.Notably,atomic force microscopy-micromanipulation technique has been utilized to bring the mul-tifunctional applications offlexible organic crystals from the macroscopic level to the microscopic world.Since understanding mechanicalflexibility at the molec-ular level through crystal engineering can assist us to trace down the structural origin of mechanical properties,we focus on the packing structures of various Schiff baseflexible organic crystals driven by non-covalent intermolecular inter-actions and their close correlation with mechanical behaviors.We hope that the information given here will help in the design of novelflexible organic crys-tals combined with other unique properties,and promote further research into the area of mechanically compliant organic crystalline materials toward multifunctional applications.
Rhodopsin is a seven-helical transmembrane protein with a retinal chromophore covalently bound to a conserved lysine in helix G via a retinal protonated Schiff base(RPSB).Microbial rhodopsins absorb light through chromophore and play a fundamental role in optogenetics.Numerous microbial rhodopsins have been discovered,contributing to diverse functions and colors.Solid-state NMR spectroscopy has been instrumental in elucidating the conformation of chromophores and the three-dimensional structure of microbial rhodopsins.This review focuses on the 15N chemical shift values of RPSB and summarizes recent progress in the field.We displayed the correlation between the 15N isotropic chemical shift values of RPSB and the maximum absorption wavelength of rhodopsin using solid-state NMR spectroscopy.
The efficient photo-response mechanism is one of the key factors in the commercialization of dye-sensitized solar cells in a bid to satisfy renewable energy demands. Progress in green technology has put solar energy on the front burner as a provider of clean and affordable energy for a sustainable society. We report the synthesis of a novel Schiff base with optical transparency in the visible and near IR region of the solar spectrum that can find application in the DSSCs photo-response mechanism. The synthesized crystal exhibited features that could handle some of the shortcomings of dye-sensitized solar cells which include wide band solar spectrum absorption and capability for swift charge transfer within the photoelectrodes. The synthesized Schiff base was characterized using x-ray diffractometer, UV/Visible spectrometer, Frontier transmission infrared spectrometer and conductometer. XRD data revealed the grown crystal to have an average crystallite size of 2.08 nm with average microstrain value of about 269.43. The FT-IR recorded transmission wave ѵ (CO) at 1207.7 cm−1 while dominant wave occurred at ѵ1654.9 and ѵ1592.3 cm−1 relating to ѵ (CN) stretching and ѵ (NH) bending respectively were observed. The IR spectrum revealed the bonding species and a probable molecular structure of 2,6-bis(benzyloxy)pyridine. The UV/Visible spectra convoluted to maximum peak within the near IR region suggesting that 2,6-bis(benzyloxy)pyridine can absorb both the visible and near IR region while its electrical conductivity was determined to be 4.58 µS/cm. The obtained result of the present study revealed promising characteristics of a photosensitizer that can find application in the photo-response mechanism of DSSCs.
BACKGROUND The Alcian blue(AB)and periodic acid Schiff(PAS)stains are representative mucus markers in gastric signet ring cell carcinoma(SRCC).They are low-cost special staining methods used to detect acidic mucus and neutral mucus,respectively.However,the clinical importance of the special combined AB and PAS stain is unclear.AIM To investigate AB expression,PAS expression and the AB-to-PAS(A/P)ratio in gastric SRCC patients and to assess patient prognosis.METHODS Paraffin-embedded sections from 83 patients with gastric SRCC were stained with AB and PAS,and signet ring cell positivity was assessed quantitatively.Immuno-histochemical staining for Ki67,protein 53(P53)and human epidermal growth factor receptor 2(HER2)was performed simultaneously.The cancer-specific survival(CSS)rate was estimated via Kaplan-Meier analysis.Cox proportional hazards models were used for univariate and multivariate survival analyses.RESULTS Kaplan-Meier survival analysis revealed that the 3-year CSS rate was significantly greater in the high-PAS-expression subgroup than in the low-PAS-expression subgroup(P<0.001).The 3-year CSS rate in the A/P≤0.5 group was significantly greater than that in the A/P>0.5 group(P=0.042).Univariate Cox regression analysis revealed that the factors affecting prognosis included tumor diameter,lymph node metastasis,vessel carcinoma embolus,tumor stage,the A/P ratio and the expression of Ki67,P53 and the PAS.Cox multivariate regression analysis confirmed that low PAS expression[hazard ratio(HR)=3.809,95%confidence interval(CI):1.563-9.283,P=0.003]and large tumor diameter(HR=2.761,95%CI:1.086-7.020,P=0.033)were independent risk factors for poor prognosis.CONCLUSION A/P>0.5 is potentially a risk factor for prognosis,and low PAS expression is an independent risk factor in the prognosis of gastric SRCC.PAS expression and the A/P ratio could help in predicting the clinical prognosis of patients with SRCC.
Two new dinuclear lanthanidecomplexes,namely[Ln_(2)(dbm)_(2)(HL)_(2)(CH_(3)OH)_(2)]·4CH_(3)OH[Ln=Tb(1)and Dy(2),Hdbm=dibenzoylmethane]have been synthesized using prepared multidentate Schiff base ligand H_(3)L(hydroxy‑acetic acid(4‑diethylamino‑2‑hydroxy‑benzylidene)‑hydrazide)with good biological activity.Structure characterizations show that the complex comprises two Ln3+ions,two dbm-ions,two HL^(2-)ligands,two CH_(3)OH molecules,and four free methanol molecules.Each Ln^(3+)ion is eight‑coordinated.The two central Lnions are bridged by twoμ_(2)‑O atoms leading to a parallelogram[Ln2O2]core.The interaction between the compounds(H_(3)L,1,and 2)and the calf thymus DNA(CT‑DNA)has been further confirmed by UV‑Vis spectrometry,fluorescence titration,and cyclic voltammetry.The results showed that both 1 and 2 could undergo insertion with CT‑DNA.CCDC:2343005,1;2343006,2.
A general protocol for the synthesis ofα,β-dehydroamino acids and their peptides was developed.Proline efficiently catalyzed an aldol condensation reaction of a glycine Schiff base with a variety of aldehydes.The hydroxy group on the benzophenone imine was crucial for high Z/E selectivity and further transimination for protecting group-freeα,β-dehydroamino esters.Peptide elongation of both the C-and N-terminals highlighted the usefulness of our present protocol.
While enol-keto tautomerism has attracted great interest in Schiff bases and related compounds in solution and crystal states,the self-assembly of energy-unfavored keto form were scarcely investigated.Here,we report a keto-form directed self-assembly of a naphthalene-attached enantiomeric N-salicylideneanil analog L/DGG-Nap accompanied with a significantly amplified circularly polarized luminescence(CPL).It was found that LGG-Nap exists as a mixture of enol and keto form in monomer at a diluted toluene solution.The increment of the concentrations leads to the formation of predominated keto form,which subsequently triggers the self-assembly.Cryo-transmission electron microscopy(Cryo-TEM)revealed that a hierarchical assembly process happened upon increasing the concentration of LGG-Nap in toluene.Individual nanofibers formed at 1×10-4 mol/L and transferred into helical nanofiber bundles in 5×10-3 mol/L.Interestingly,while these is nearly no circular dichroism(CD)or CPL in the monomeric solution,the assembly showed strong CD and CPL.Remarkably,the dissymmetry factor(glum)was significantly amplified from zero in solution through the 0.005 in individual nanofiber to 0.1 in nanofiber bundles.This work demonstrates that the enol-keto tautomerism can be broken and trigger the self-assembly upon increasing the concentration,which can subsequently direct the chiral self-assembly and significantly amplify the dissymmetry factor of assembled CPL materials.
Yimeng SunYuqian JiangJian JiangTiesheng LiMinghua Liu
Covalent organic frameworks(COFs)after undergoing the superlithiation process promise high-capacity anodes while suffering from sluggish reaction kinetics and low electrochemical utilization of redox-active sites.Herein,integrating carbon nanotubes(CNTs)with imine-linked covalent organic frameworks(COFs)was rationally executed by in-situ Schiff-base condensation between 1,1′-biphenyl]-3,3′,5,5′-tetracarbaldehyde and 1,4-diaminobenzene in the presence of CNTs to produce core–shell heterostructured composites(CNT@COF).Accordingly,the redox-active shell of COF nanoparticles around one-dimensional conductive CNTs synergistically creates robust three-dimensional hybrid architectures with high specific surface area,thus promoting electron transport and affording abundant active functional groups accessible for electrochemical utilization throughout the whole electrode.Remarkably,upon the full activation with a superlithiation process,the as-fabricated CNT@COF anode achieves a specific capacity of 2324 mAh g^(−1),which is the highest specific capacity among organic electrode materials reported so far.Meanwhile,the superior rate capability and excellent cycling stability are also obtained.The redox reaction mechanisms for the COF moiety were further revealed by Fourier-transform infrared spectroscopy in conjunction with X-ray photoelectron spectroscopy,involving the reversible redox reactions between lithium ions and C=N groups and gradual electrochemical activation of the unsaturated C=C bonds within COFs.
Nan JiangMengpei QiYalong JiangYin FanShiwei JinYingkui Yang
