Near-90° Switch in the Polar Axis of Dion-Jacobson Perovskites by Halide Substitution.

Ferroelectricity in two-dimensional hybrid (2D) organic-inorganic perovskites (HOIPs) can be engineered by tuning the chemical composition of the organic or inorganic components to lower the structural symmetry and order-disorder phase change. Less efforts are made toward understanding how the direction of the polar axis is affected by the chemical structure, which directly impacts the anisotropic charge order and nonlinear optical response. To date, the reported ferroelectric 2D Dion-Jacobson (DJ) [PbI4]2- perovskites exhibit exclusively out-of-plane polarization. Here, we discover that the polar axis in ferroelectric 2D Dion-Jacobson (DJ) perovskites can be tuned from the out-of-plane (OOP) to the in-plane (IP) direction by substituting the iodide with bromide in the lead halide layer. The spatial symmetry of the nonlinear optical response in bromide and iodide DJ perovskites was probed by polarized second harmonic generation (SHG). Density functional theory calculations revealed that the switching of the polar axis, synonymous with the change in the orientation of the sum of the dipole moments (DMs) of organic cations, is caused by the conformation change of organic cations induced by halide substitution.

Boosting Charge Transport in a 2D/3D Perovskite Heterostructure by Selecting an Ordered 2D Perovskite as the Passivator.

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA0.8 Cs0.2 PbI3 , we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (ϕµ), and carrier diffusion length (LD ) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of ≈1.3 µs, high ϕµ of ≈18.56 cm2  V-1 s-1 , and long LD of ≈7.85 µm is achieved in the 2D/3D films when passivated by 16.67 % para-fluoro-PEA2 PbI4 . This carrier diffusion length is comparable to that of some perovskite single crystals (>5 µm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.

Conformational Order of Alkyl Side Chain of Poly(3-alkylthiophene) Promotes Hole-Extraction Ability in Perovskite/Poly(3-alkylthiophene) Heterojunction.

Molecular structures of hole transport materials (HTMs) have significant impact on the optoelectronic properties of perovskite/HTM heterojunction. But the structure-property relationship in the heterojunction remains poorly understood. By using poly(3-alkylthiophene) (P3AT) as the HTM model, here we apply sum frequency generation vibrational spectroscopy to establish correlations among conformations of P3ATs, the hole extraction ability of P3ATs from the perovskite layer, and the charge mobility of P3ATs. It is revealed that with similar energy-level alignment, the conformational order of alkyl side chains in regioregular P3ATs can effectively regulate the hole extraction ability of P3ATs from perovskite layer by tuning reorganization energy. By contrast, the charge mobility of P3ATs strongly depends on the P3AT backbone's coplanarity. Our findings decouple the roles of the long-hidden conformational order of alkyl side chain and the polythiophene backbone's coplanarity on the performance of perovskite/HTM heterojunction, offering useful guidelines for boosting the performance of optoelectronic devices.

Conformational disorder of organic cations tunes the charge carrier mobility in two-dimensional organic-inorganic perovskites.

The chemical nature of the organic cations governs the optoelectronic properties of two-dimensional organic-inorganic perovskites. But its mechanism is not fully understood. Here, we apply femtosecond broadband sum frequency generation vibrational spectroscopy to investigate the molecular conformation of spacer organic cations in two-dimensional organic-inorganic perovskite films and establish a correlation among the conformation of the organic cations, the charge carrier mobility, and broadband emission. Our study indicates that both the mobility and broadband emission show strong dependence on the molecular conformational order of organic cations. The gauche defect and local chain distortion of organic cations are the structural origin of the in-plane mobility reduction and broad emission in two-dimensional organic-inorganic perovskites. Both of the interlayer distance and the conformational order of the organic cations affect the out-of-plane mobility. This work provides molecular-level understanding of the conformation of organic cations in optimizing the optoelectronic properties of two-dimensional organic-inorganic perovskites.

hTERT promoter methylation promotes small cell lung cancer progression and radiotherapy resistance.

Small cell lung cancer (SCLC) has been a devastating actuality in clinic and the molecular mechanisms underlying this disease remain unclear. The epigenetic alterations located in the promoter region of human telomerase reverse transcriptase (hTERT) have been demonstrated as one of the most prevalent non-coding genomic modifications in multiple cancers. However, alteration of hTERT promoter methylation in SCLC and the subsequently induced change in tumor cell behavior remains unclear. In this research, we hypothesized that abnormal methylation of hTERT promotor enhanced the progression of SCLC and the outcome of radiotherapy resistance. Quantitative real-time PCR and western blot assays were performed to evaluate the RNA and protein levels of hTERT and enhancer of zeste homolog 2 (EZH2), respectively. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to estimate the viability and X-ray sensitivity of H20 and H446 cell lines. Functionally, upregulation of hTERT promoted the proliferation and migration of H20 and H446 cells, and the high-level of methylation in the promoter region of hTERT induced by radiation caused radio-resistance in SCLC. Mechanically, methylation of hTERT promoter enhanced the progression and radio-resistance of SCLC through upregulating the expression of its downstream effector EZH2.

Ultrafast energy relaxation dynamics of amide I vibrations coupled with protein-bound water molecules.

The influence of hydration water on the vibrational energy relaxation in a protein holds the key to understand ultrafast protein dynamics, but its detection is a major challenge. Here, we report measurements on the ultrafast vibrational dynamics of amide I vibrations of proteins at the lipid membrane/H2O interface using femtosecond time-resolved sum frequency generation vibrational spectroscopy. We find that the relaxation time of the amide I mode shows a very strong dependence on the H2O exposure, but not on the D2O exposure. This observation indicates that the exposure of amide I bond to H2O opens up a resonant relaxation channel and facilitates direct resonant vibrational energy transfer from the amide I mode to the H2O bending mode. The protein backbone motions can thus be energetically coupled with protein-bound water molecules. Our findings highlight the influence of H2O on the ultrafast structure dynamics of proteins.

Directly monitoring the active sites of charge transfer in heterocycles in situ and in real time.

Coherent degenerate infrared-infrared-visible sum frequency generation vibrational spectroscopy provides a powerful label-free sensitive probe for charge transfer active sites in heterocyclic molecules in situ and in real time.

Influenza A M2 transmembrane domain tunes its conformational heterogeneity and structural plasticity in the lipid bilayer by forming loop structures.

We discovered for the first time that the influenza A virus M2TM tunes its conformational heterogeneity and structural plasticity to respond to environmental cues by undergoing a helix-to-loop transition, resolving controversies regarding the mechanism of proton conduction and plasticity of the M2TM in lipid bilayers.

Amide I SFG Spectral Line Width Probes the Lipid-Peptide and Peptide-Peptide Interactions at Cell Membrane In Situ and in Real Time.

The balance of lipid-peptide and peptide-peptide interactions at cell membrane is essential to a large variety of cellular processes. In this study, we have experimentally demonstrated for the first time that sum frequency generation vibrational spectroscopy can be used to probe the peptide-peptide and lipid-peptide interactions in cell membrane in situ and in real time by determination of the line width of amide I band of protein backbone. Using a "benchmark" model of α-helical WALP23, it is found that the dominated lipid-peptide interaction causes a narrow line width of the amide I band, whereas the peptide-peptide interaction can markedly broaden the line width. When WALP23 molecules insert into the lipid bilayer, a quite narrow line width of the amide I band is observed because of the lipid-peptide interaction. In contrast, when the peptide lies down on the bilayer surface, the line width of amide I band becomes very broad owing to the peptide-peptide interaction. In terms of the real-time change in the line width, the transition from peptide-peptide interaction to lipid-peptide interaction is monitored during the insertion of WALP23 into 1,2-dipalmitoyl- sn-glycero-3-phospho-(1'- rac-glycerol) (DPPG) lipid bilayer. The dephasing time of a pure α-helical WALP23 in 1-palmitoyl-2-oleoyl- sn-glycero-3-phospho-(1'- rac-glycerol) and DPPG bilayer is determined to be 2.2 and 0.64 ps, respectively. The peptide-peptide interaction can largely accelerate the dephasing time.

Self-supported chiral titanium cluster (SCTC) as a robust catalyst for the asymmetric cyanation of imines under batch and continuous flow at room temperature.

A robust heterogeneous self-supported chiral titanium cluster (SCTC) catalyst and its application in the enantioselective imine-cyanation/Strecker reaction is described under batch and continuous processes. One of the major hurdles in the asymmetric Strecker reaction is the lack of availability of efficient and reusable heterogeneous catalysts that work at room temperature. We exploited the readily hydrolyzable nature of titanium alkoxide to synthesize a self-supported chiral titanium cluster (SCTC) catalyst by the controlled hydrolysis of a preformed chiral titanium-alkoxide complex. The isolated SCTC catalysts were remarkably stable and showed up to 98 % enantioselectivity (ee) with complete conversion of the imine within 2 h for a wide variety of imines at room temperature. The heterogeneous catalysts were recyclable more than 10 times without any loss in activity or selectivity. The robustness, high performance, and recyclability of the catalyst enabled it to be used in a packed-bed reactor to carry out the cyanation under continuous flow. Up to 97 % ee and quantitative conversion with a throughput of 45 mg h(-1) were achieved under optimized flow conditions at room temperature in the case of benzhydryl imine. Furthermore, a three-component Strecker reaction was performed under continuous flow by using the corresponding aldehydes and amines instead of the preformed imines. A good product distribution was obtained for the formation of amino nitriles with ee values of up to 98 %. Synthetically useful ee values were also obtained for challenging α-branched aliphatic aldehyde by using the three-component continuous Strecker reaction.

Self-association of acetic acid in dilute deuterated chloroform. Wide-range spectral reconstructions and analysis using FTIR spectroscopy, BTEM, and DFT.

The binary solution of acetic acid in CDCl(3) was studied at room pressure on the interval T = 293-313 K with a series of acetic acid concentrations up to 0.16 M. In-situ Fourier transform infrared (FTIR) spectroscopy measurements on the interval of 400-3800 cm(-1) were utilized as the analytical method to monitor the spectral changes due to self-association of acetic acid. The band-target entropy minimization (BTEM) algorithm was employed to reconstruct the underlying pure component spectra. Analysis successfully provided two major spectral estimates of acetic acid, namely, the monomer (primarily in the form of monomer-CDCl(3) complex) and the centrosymmetric cyclic dimer. In addition, analysis provided one minor spectral estimate containing signals from both noncyclic dimers and higher aggregates. Also, spectral estimates were obtained for phosgene and water which were present at trace levels even though considerable precaution was taken to conduct the experiments under anhydrous and anaerobic conditions. Density functional theory (DFT) calculation was performed to assign the acetic acid structures corresponding to the BTEM spectral estimates. Since the structure of dilute acetic acid has been the subject of numerous studies, the present investigation helps to resolve some issues concerning the speciation of acetic acid at low concentrations in low polarity solvents. In particular, the present study provides for the first time, wide-range spectral reconstructions of the species present.

Concurrent synergism and inhibition in bimetallic catalysis: catalytic binuclear elimination, solute-solute interactions and a hetero-bimetallic hydrogen-bonded complex in rh-mo hydroformylations.

Hydroformylations of cyclopentene and 3,3-dimethylbut-1-ene were performed using both Rh(4)(CO)(12) and (eta(5)-C(5)H(5))Mo(CO)(3)H as precursors in n-hexane at 298 K. Both stoichiometric and catalytic hydroformylations were conducted as well as isotopic labeling experiments. Six organometallic pure component spectra were recovered from the high-pressure FTIR experiments, namely the known species Rh(4)(CO)(12), (eta(5)-C(5)H(5))Mo(CO)(3)H, RCORh(CO)(4), and the new heterobimetallic complexes RhMo(CO)(7)(eta(5)-C(5)H(5)), a weak hydrogen bonded species (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4), and a substituted RhMo(CO)(7-y)(eta(5)-C(5)H(5))L(y), where y = 1 or 2 and L = (pi-C(5)H(8)). The main findings were (1) catalytic binuclear elimination (CBER) occurs between (eta(5)-C(5)H(5))Mo(CO)(3)H and RCORh(CO)(4) resulting in aldehyde and RhMo(CO)(7)(eta(5)-C(5)H(5)), and this mechanism is responsible for ca. 10% of the product formation; (2) molecular hydrogen is readily activated by the new heterobimetallic complex(es); (3) FTIR and DFT spectroscopic evidence suggests that the weak hydrogen bonded species (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4) has an interaction of the type eta(5)-C(5)H(4)-H...O=C; and (4) independent physicochemical experiments for volumes of interaction confirm that significant solute-solute interactions are present. With respect to the efficiency of the catalytic cycle, the formation of a weak (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4) complex results in a significant decrease in the measured turnover frequency (TOF) and is the primary reason for the inhibition observed in the bimetallic catalytic hydroformylation. Such hydrogen bonding through the eta(5)-C(5)H(5) ring might have relevance to inhibition observed in other catalytic metallocene systems. The present catalytic system is an example of concurrent synergism and inhibition in bimetallic homogeneous catalysis.

The loss of CO from [Rh12(mu12-Sn)(CO)27]4-: synthesis, spectroscopic and structural characterization of the electron-deficient, icosahedral [Rh12(mu12-Sn)(CO)25]4- and [Rh12(mu12-Sn)(CO)26]4- tetra-anions.

Heating (80 degrees C) the electron-precise, Sn-centred, icosahedral cluster [Rh(12)Sn(CO)(27)](4-) under a nitrogen atmosphere affords in sequence the electron-deficient icosahedral [Rh(12)Sn(CO)(26)](4-) and [Rh(12)Sn(CO)(25)](4-) derivatives. The reaction is reversible in solution and the parent compound is quantitatively regenerated upon exposure to carbon monoxide. The reaction course has been unravelled via a combination of Band-target Entropy Minimization (BTEM) IR analysis and X-ray studies. While icosahedral clusters displaying electron counts formally exceeding 13 skeletal electron pairs (SEP) are known, [Rh(12)Sn(CO)(26)](4-) and [Rh(12)Sn(CO)(25)](4-) show for the first time that icosahedral clusters may also be stabilized with a deficiency of SEPs with respect to the requirement based on the cluster-borane analogy. In contrast to the behaviour of the electron-precise cluster [Rh(12)Sn(CO)(27)](4-), the electron-deficient cluster [Rh(12)Sn(CO)(25)](4-) undergoes reversible electrochemical reductions.

Combination of Raman microscopy, multiwell plate experimental designs, and BTEM analysis for high-throughput experimentation.

Both nonreactive and reactive multiwell plate experiments were combined with Raman microscopy and band-target entropy minimization (BTEM) analysis. The multicomponent nonreactive experiments showed that accurate pure component spectral estimation is possible without recourse to any spectral libraries. The multicomponent reactive experiments showed that, in addition to accurate pure component spectral estimation, concentration profiles can be obtained for quantitative purposes. In the present case, the solvent and time dependence of a cycloaddition reaction was addressed as the high-throughput experimentation issue. A total of 1152 experimental spectra were collected and analyzed. Two methods were used, namely, (A) each solvent set was individually analyzed and (B) the entire set of spectra, from 4 different solvents, were analyzed all together. Method B provided very satisfactory results. The present study with combined Raman-multiwell plate-BTEM analysis establishes proof of concept. The new approach appears to be applicable to other frequently conducted combinatorial/high-throughput experimentations. These include, but are not restricted to, chemo- and regioselective studies, solid-phase syntheses, etc.

Synchronicity of mononuclear and dinuclear events in homogeneous catalysis. Hydroformylation of cyclopentene using Rh4(CO)12 and HRe(CO)5 as precursors.

The combined application of two or more metals in homogeneous catalysis can lead to synergistic effects; however, the phenomenological basis for these observations often goes undetermined. The hetero-bimetallic catalytic binuclear elimination reaction, a system involving both mononuclear and dinuclear intermediates, has been repeatedly suggested as a possible mechanism. In the present contribution, the simultaneous application of Rh4(CO)12 and HRe(CO)5 as precursors in the hydroformylation reaction leads to a very strong synergistic rate effect. In situ spectroscopic measurements confirm the presence of both mononuclear and dinuclear intermediates such as RCORh(CO)4 and RhRe(CO)9 in the active system. Moreover, kinetic analysis confirms interconversion of these intermediates as well as their statistical correlation with organic product formation. Specifically, the rate of hydrogen activation by RhRe(CO)9 is exactly equal to the rate of aldehyde formation from binuclear elimination between HRe(CO)5 and RCORh(CO)4 at all reaction conditions studied. Thus the catalytic events involving mononuclear species and those involving dinuclear species are synchronized. In the present experiments, the new topology is orders of magnitude more efficient than the corresponding unicyclic rhodium system.

Biomechanical and magnetic resonance characteristics of a cartilage-like equivalent generated in a suspension culture.

OBJECTIVE: To generate a cartilage biomaterial using a suspension culture with biophysical properties similar to native articular cartilage. DESIGN: A novel cartilage tissue equivalent (CTE) using a no-scaffold, high-density suspension culture of neonatal porcine chondrocytes was formed on poly 2-hydroxyethyl methacrylate-treated plates for up to 16 weeks. Equilibrium aggregate modulus and hydraulic permeability were measured at 8 and 16 weeks using confined compression stress relaxation experiments. The CTE proteoglycan composition was characterized using sodium and T(1rho) magnetic resonance imaging methods after 8 weeks. RESULTS: The resultant CTE produces a biomaterial consistent with a hyaline cartilage phenotype in appearance and expression of type II collagen and aggrecan. The equilibrium aggregate modulus and permeability for the 8-week specimens were 41.6 (standard deviation (SD) 4.3) kPa and 2.85(-13) (SD 2.45(-13)) m(4)/Ns, respectively, and, for the 16-week specimens, 35.2 (SD 7.6) kPa and 2.67(-13) (SD 1.06(-13)) m(4)/Ns, respectively. Average sodium concentration of the 8-week CTE ranged from 260 to 278 mM and average T(1rho) relaxation times from 105 to 107 ms, indicating proteoglycan content similar to that of native articular cartilage. CONCLUSION: The high-density culture method produced a CTE with characteristics that approach those of native articular cartilage. The CTE mechanical properties are similar to those of the native cartilage. The CTE developed in this study represents a promising methodological advancement in cartilage tissue engineering and cartilage repair.

Human immunodeficiency virus type 1 can establish latent infection in resting CD4+ T cells in the absence of activating stimuli.

Resting CD4(+) T cells are the best-defined reservoir of latent human immunodeficiency virus type 1 (HIV-1) infection, but how the reservoir is formed is unclear. Understanding how the reservoir of latently infected cells forms is critical because it is a major barrier to curing HIV infection. The system described here may provide an in vitro model of latent HIV-1 infection in resting CD4(+) T cells. We demonstrated that HIV-1 integrates into the genomes of in vitro-inoculated resting CD4(+) T cells that have not received activating stimuli and have not entered cell cycle stage G(1b). A percentage of the resting CD4(+) T cells that contain integrated DNA produce virus upon stimulation, i.e., are latently infected. Our results show that latent HIV-1 infection occurs in unstimulated resting CD4(+) T cells and suggest a new route for HIV-1 reservoir formation.

Band-target entropy minimization. A robust algorithm for pure component spectral recovery. Application to complex randomized mixtures of six components.

A newly developed self-modeling curve resolution method, band-target entropy minimization (BTEM), is described. This method starts with the data decomposition of a set of spectroscopic mixture data using singular value decomposition. It is followed by the transformation of the orthonormal basis vectors/loading vectors into individual pure component spectra one at a time. The transformation is based in part on some seminal ideas borrowed from information entropy theory with the desire to maximize the simplicity of the recovered pure component spectrum. Thus, the proper estimate is obtained via minimization of the proposed information entropy function or via minimization of derivative and area of the spectral estimate. Nonnegativity constraints are also imposed on the recovered pure component spectral estimate and its corresponding concentrations. As its name suggests, in this method, one targets a spectral feature readily observed in loading vectors to retain, and then combinations of the loading vectors are searched to achieve the global minimum value of an appropriate objective function. The major advantage of this method is its one spectrum at a time approach and its capability of recovering minor components having low spectroscopic signals. To illustrate the application of BTEM, spectral resolution was performed on FT-IR measurements of very highly overlapping mixture spectra containing six organic species with a two-component background interference (air). BTEM estimates were also compared with the estimates obtained using other self-modeling curve resolution techniques, i.e., SIMPLISMA, IPCA, OPA-ALS, and SIMPLISMA-ALS.

The Rh4(CO)12-catalyzed hydroformylation of 3,3-dimethylbut-1-ene promoted with HMn(CO)5. Bimetallic catalytic binuclear elimination as an origin for synergism in homogeneous catalysis.

The bimetallic origins of catalytic synergism were studied using unmodified rhodium and manganese carbonyls as catalyst precursors during the low-temperature hydroformylation of 3,3-dimethylbut-1-ene to 4,4-dimethylpentanal in n-hexane solvent (T approximately 298 K, P(CO) = 1.0-4.0 MPa, P(H2) = 0.5-2.0 MPa). A dramatic increase in the catalytic rate was observed in the experiments conducted when both metals were used simultaneously. Detailed in-situ FTIR measurements indicated the observable presence of only homometallic complexes during catalysis, e.g., RCORh(CO)(4), Rh(4)(CO)(12), Rh(6)(CO)(16), HMn(CO)(5), and Mn(2)(CO)(10). The kinetics of product formation show a distinct linear-bilinear form in observables: k(1)[RCORh(CO)(4)][CO](-1)[H(2)] + k(2)[RCORh(CO)(4)][HMn(CO)(5)][CO](-1.5). The first term represents the classic unicyclic rhodium catalysis, while the second indicates a hydride attack on an acyl species. These spectroscopic and kinetic results strongly suggest that the origin of synergism is the presence of bimetallic catalytic binuclear elimination and not cluster catalysis. This appears to be the first detailed evidence for such a catalytic mechanism, and its implications for selectivity and nonlinear catalytic activity are accordingly discussed.