Sequential Oxygenation of Bis(β-diketiminate) on a Selective Diruthenium Platform

This article demonstrated the redox-noninnocent phenylene-linked bis(β-diketiminate) (L2-)-bridged first example of isomeric diruthenium(III)-acac species (acac = acetylacetonate) and its ability to activate dioxygen. The coordination of deprotonated L2- to the {Ru(acac)2} in bis(bidentate) mode led to isomeric {(acac)2RuIII}2(μ-L2-) (S = 1, 1-trans/1-cis, green). 1 displayed Ru(III)-based anisotropic EPR in CH3CN but without the resolution of the forbidden (ΔMs = 2) g1/2 signal at 77 K. 1-cis, however, slowly transformed to the energetically favored 1-trans form. 1 underwent two-step oxygenation at the Cβ sites of L2- to form the β-diketiminate/α-ketodiimine (L'-)-bridged mixed valent (acac)2RuIII(μ-L'-)RuII(acac)2 (2, S = 1/2, pink) followed by bis(α-ketodiimine) (L″)-bridged isovalent (acac)2RuII(μ-L″)RuII(acac)2 (3, S = 0, red). The role of O2 toward 1 → 2/3 was corroborated by 18O2 labeling experiment. Redox steps of 1-3 varied as a function of isomeric identity, bridge, and metal oxidation state. The calculated MOs and Mulliken spin densities attributed to the noninnocence of L2-, L'-, and L″ in the respective complexes. Spectrophotometric monitoring of 1 → 2 revealed pseudo-first-order rate constants (105k s-1) of 1.8 (303 K), 3.5 (313 K), 7.7 (323 K), and 17.0 (333 K) and ΔH⧧/ΔS⧧/ΔG⧧ of 14.3 kcal mol-1/-33.1 cal mol-1 K-1/24.2 kcal mol-1 (298 K), respectively. Moreover, characterization of the short-lived blue intermediate obtained during the conversion of 1 → 2/3 upon exposure to O2 supported its valence tautomeric form (VT1, RuIII-L2--RuIII ↔ RuIII-L•--RuII, S = 1), which in effect facilitated oxygen activation at the ligand backbone.

Metal-ligand synergy driven functionalisation of alkylene linked bis(aldimine) on a diruthenium(II) platform. Cyclisation versus oxygenation

This article addresses the impact of metal-ligand redox cooperativity on the functionalisation of coordinated ligands. It demonstrates the structure-reactivity correlation of bis(aldimine) derived bis-bidentate L (Py-CHN-(CH2)n-NCH-Py, with n = 2 (L1), 3 (L2), 4 (L3)) as a function of the conformation (syn/anti) of its alkylene linker as well as the overall structural form (cis/trans) of (acac)2RuII(μ-L)RuII(acac)2 complex moieties (1-5) possessing an electron-rich acetylacetonate (acac) co-ligand. A systematic variation of the bridging alkylene unit of L in RuII/RuII-derived 1-5 led to the following reactivity/redox events, which were validated through structural, spectroscopic, electrochemical and theoretical evaluations: (i) Cyclisation of the ethylene linked (syn conformation) bis-aldimine unit of L1 via C-C coupling yielded pyrazine bridged (acac)2RuII(μ-L1')RuII(acac)2, 1a, while the corresponding anti-form (ethylene linker) of the metal-bound L1 in 2 ((acac)2RuII(μ-L1)RuII(acac)2) led to oxygenation at the ligand backbone (bis-aldimine (L) → bis(carboxamido) (L'')) via O2 activation to generate RuIIIRuIII-derived (acac)2RuIII(μ-L1''2-)RuIII(acac)2 (2a). (ii) Consequently, propylene and butylene linked L2 and L3 bridged between two {Ru(acac)2} units in 3 and 4/5 underwent oxygenation of L to L'' to yield diruthenium(III) complexes 3a and 4a/5a, respectively. (iii) In contrast, analogous L bridged oxidised [(acac)2RuIII(μ-L)RuIII(acac)2](ClO4)2 ([2](ClO4)2-[5](ClO4)2) and [{(PPh3)2(CO)(H)RuII}2(μ-L)](ClO4)2 ([6](ClO4)2-[8](ClO4)2) involving electron poor co-ligands failed to undergo the oxygenation of L irrespective of its n value, reemphasising the effective role of redox interplay between RuII and L particularly in the presence of an electron-rich acac co-ligand in the functionalisation of the latter in 1a-5a.

The isomer-sensitive electrochemical HER of ruthenium(II)-hydrido complexes involving redox-active azoheteroaromatics

The article deals with the development of isomeric ruthenium(II)-hydrido complexes [RuII(H)(L1)(PPh3)2(CO)]ClO4 ([1a]ClO4-[1b]ClO4)/[RuII(H)(L2)(PPh3)2(CO)]ClO4 ([2a]ClO4-[2b]ClO4) involving azo coupled L1 [L1: (E)-1,2-bis(1-methyl-1H-pyrazol-3-yl)diazene]/L2 [L2: (E)-1,2-bis(4-iodo-1-methyl-1H-pyrazol-3-yl)diazene], respectively. Structural evaluation of the complexes affirmed the syn conformation of the coordinated/uncoordinated pyrazole groups of L and its unperturbed neutral azo (NN) state. Isomeric forms in [1a]ClO4/[1b]ClO4 or [2a]ClO4/[2b]ClO4 differed with respect to the cis and trans orientations of the coordinated CO and N(azo) donor of L, respectively. It also demonstrated the formation of intermolecular hydrogen-bonded dimeric or 1D-polymeric chains in [1a]ClO4/[2b]ClO4 or [1b]ClO4, respectively. Successive two-electron reductions of the complexes varied to an appreciable extent as a function of the heterocycles connected to L. The involvement of the azo function of L towards the reductions ([NN]0 → [NN]˙- → [NN]2-) was supported by the DFT calculated MOs and Mulliken spin density at the paramagnetic state, which was further validated by the radical EPR profile of the first reduced (S = 1/2) state. Isomeric [1a]ClO4/[1b]ClO4 or [2a]ClO4/[2b]ClO4 immobilised on the carbon cloth support underwent various electrochemical acidic HERs (hydrogen evolution reactions) with TOF/10-1 s-1: [1a]ClO4 (0.83) > [1b]ClO4 (0.68) > [2a]ClO4 (0.50) > [2b]ClO4 (0.37).

Donor-acceptor bridge 2,5-bis(2-oxido-phenyl)thiazolo-[5,4-d]thiazole derived diruthenium and diosmium systems. Structural and competitive electronic events as a function of metal ion, bridge and ancillary ligand

The article deals with the structural and electronic forms of hitherto unexplored L^2- (H₂L = 2,5-bis(2-hydroxyphenyl)thiazolo-[5,4-d]thiazole) bridged analogous diruthenium [{(AL1/AL2)₂ Ru^II}₂(μ-L^2-)]²⁺ [1](ClO₄)₂/[2](ClO₄)₂ and diosmium [{(AL1/AL2)₂Os^II}₂(μ-L^2-)]²⁺ [3](PF₆)₂/[4](ClO₄)₂ complexes as a function of moderate-to-strongly π-accepting ancillary ligands: AL1 = 2,2'-bipyridine (bpy) and AL2 = 2-phenylazopyridine (pap). Structural elucidation of the complexes established an anti-oriented bridge (L^2-) linked to the metal units through its N,O^-/O^-,N-donor sets, which led to two six-membered chelates in each case. It also highlighted the twisting of the phenolato functions of L^2- with respect to the central thiazolothiazole (TzTz) unit and the unreduced state of the azo function of AL2 and multiple non-covalent π⋯π/CH⋯π interactions within the molecules in the nearby asymmetric units. The potential of the multiple redox steps of the complexes varied as a function of Ru versus Os and AL1 versus AL2. A collective consideration of experimental and DFT calculations revealed largely bridge- and metal-based first and second oxidative steps, which could be attributed to the electronic forms [(AL1/AL2)₂M^II(μ-L˙^-)M^II(AL1/AL2)₂]³⁺ ↔ [(AL1/AL2)₂M^II(μ-L^2-) M^III(AL1/AL2)₂]³⁺ and [(AL1/AL2)₂M^2.5(μ-L˙^-) M^2.5(AL1/AL2)₂]⁴⁺ for 1³⁺-4³⁺ and 1⁴⁺-4⁴⁺, respectively, implying the noninnocence of L^2-, which was enhanced on moving from bpy to pap and from Os to Ru. Reductions of 1²⁺-4²⁺ were, however, centred around the ancillary ligand (AL1/AL2), in spite of the π-accepting feature of the TzTz core of L, implying the weaker π-acceptor form of the latter with special reference to the former. Involvement of the primarily metal (with minor contribution of the bridge, L) and ancillary ligand (AL) based orbitals in the second oxidised and first reduced steps could also be corroborated by the metal-based anisotropic and free radical EPR spectral signatures, respectively. 1²⁺-4²⁺ displayed multiple moderately-intense-to-intense charge-transfer absorption bands in the visible-to-UV region, which originated from mixed metal/ligand and intra/inter-ligand charge-transfer transitions.

Inner-Sphere Electron Transfer Induced Reversible Electron Reservoir Feature of Azoheteroarene Bridged Diruthenium Frameworks

This article demonstrates the stabilization of ground- and redox-induced metal-to-ligand charge transfer excited states on coordination of azo-coupled bmpd(L4) [bmpd = (E)-1,2-bis(1-methyl-1H-pyrazol-3-yl)diazene; L4 = -N═N-] to the electron-rich {Ru(acac)₂} (acac = acetylacetonate) unit in mononuclear Ru^II(acac)₂(L4) (1) and diastereomeric dinuclear (acac)₂Ru^2.5(μ-L4^•-)Ru^2.5(acac)₂ [rac, ΔΔ/ΛΛ (2a)/meso, ΔΛ (2b)] complexes, respectively. It also develops further one-step intramolecular electron transfer induced L4^•- bridged isovalent higher analogue [(acac)₂Ru^III(μ-L4^•-)Ru^III(acac)₂]ClO₄ in diastereomeric forms, rac-[2a]ClO₄/meso-[2b]ClO₄. On the contrary, under identical reaction conditions electronically and sterically permuted bimpd [L5, (E)-1,2-bis(4-iodo-1-methyl-1H-pyrazol-3-yl)diazene)] delivered mononuclear Ru^II(acac)₂(L5) (3) as an exclusive product. Further, the generation of unprecedented heterotrinuclear complex [(acac)₂Ru^II(μ-L4)Ag^I(μ-L4)Ru^II(acac)₂]ClO₄ ([4]ClO₄) involving unreduced L4 via the reaction of 1 and AgClO₄ revealed the absence of any inner-sphere electron transfer (IET) as in precursor 1, which in turn reaffirmed an IET (at the interface of electron-rich Ru(acac)₂ and acceptor L4) mediated stabilization of 2. Structural authentication of the complexes with special reference to the tunable azo distance (N═N, N-N^•-, N-N^2-) of L and their spectro-electrochemical events in accessible redox states including the reversible electron reservoir feature of 2 → 2⁺/2⁺ → 2 were evaluated in conjunction with density functional theory/time-dependent density functional theory calculations. The varying extent of IET as a function of heteroaromatics appended to the azo group of L (L1 = abpy = 2,2'-azobipyridine, L2 = abbt = 2,2'-azobis(benzothiazole), L3 = abim = azobis(1-methylbenzimidazole), L4 and L5, Schemes 1 & 2) in the Ru(acac)₂-derived respective molecular setup has been addressed.

On the Question of S-S Bond Cleavage of 2,2'-Dithiodipyridine on Selective Ru and Os Platforms. MLCT or Hydride or Solvent Mediated Event

This article deals with the S-S bond scission of the model substrate 2,2'-dithiodipyridine (DTDP) in the presence of a selective set of metal precursors: Ru^II(acac)₂, [Ru^IICl₂(PPh₃)₃], [Ru^IIHCl(CO)(PPh₃)₃], [Ru^II(H)₂(CO)(PPh₃)₃], [Ru^II(bpy)₂Cl₂], [Ru^II(pap)₂Cl₂], [Os^II(bpy)₂Cl₂], and [Os^II(pap)₂Cl₂] (acac, acetylacetonate; bpy, 2,2'-bipyridine; pap, 2-phenylazopyridine). This led to the eventual formation of the corresponding mononuclear complexes containing the cleaved pyridine-2-thiolate unit in 1-4/[5]ClO₄-[8]ClO₄. The formation of the complexes was ascertained by their single-crystal X-ray structures, which also established sterically constrained four-membered chelate (average N1-M-S1 angle of 67.89°) originated from the in situ-generated pyridine-2-thiolate unit. Ruthenium(III)-derived one-electron paramagnetic complexes 1-2 (S = 1/2, magnetic moment/B.M. = 1.82 (1)/1.81(2)) exhibited metal-based anisotropic electron paramagnetic resonance (EPR) (Δg: 1/2 = 0.64/0.93, ⟨g⟩: 1/2 = 2.173/2.189) and a broad ¹H nuclear magnetic resonance (NMR) signature due to the contact shift effect. The spectroelectrochemical and electronic structural aspects of the complexes were analyzed experimentally in combination with theoretical calculations of density functional theory (DFT and TD-DFT). The unperturbed feature of DTDP even in refluxing ethanol over a period of 10 h can be attributed to the active participation of the metal fragments in facilitating S-S bond cleavage in 1-4/[5]ClO₄-[8]ClO₄. It also revealed the following three probable pathways toward S-S bond cleavage of DTDP as a function of metal precursors: (i) the metal-to-ligand charge-transfer (MLCT) (Ru^II → σ* of DTDP)-driven metal oxidation (Ru^II → Ru^III) process in the case of relatively electron-rich metal fragments {Ru^II(acac)₂} or Ru^IICl₂ in 1 or 2, respectively; (ii) metal hydride-assisted formation of 3 or 4 with the concomitant generation of H₂; and (iii) S-S bond reduction with the simultaneous oxidation of the solvent benzyl alcohol to benzaldehyde.

P-466 Decellularization of whole organ human cervix: Physio and biochemical aspects of decellularized extracellular matrix

Study question

Can the whole organ-cervix be decellularized while maintaining its fiber ultrastructure and extracellular matrix (ECM) functionality?

Summary answer

Cervix after decellularization could maintain the physical properties, ECM was found to be intact and functional.

What is known already

ECM-rich bioscaffolds are obtained from the process that utilizes the decellularization of tissues and organs. Cervical bioengineering is needed for clinical cervicovaginal reconstruction and tissue constructs can help women with cervical abnormalities.

Study design, size, duration

Human cervices were obtained from hysterectomized samples from 3 women undergoing surgery for complete hysterectomy during January 2021 to December 2021

Participants/materials, setting, methods

Human cervices were obtained from hysterectomized samples from 3 women undergoing surgery and were subjected to whole organ decellularization. Various physical, chemical methods were employed to remove cellular remnants for a period of 10 days via perfusion of ionic and detergent solutions. Validation of complete decellularization was done via hematoxylin and eosin (H&E) staining, DNA quantification. ECM functionality was observed.

Main results and the role of chance

Well-organized ECM was obtained. Effective complete decellularization was dictated and verified by cervical tissue density, histopathological studies, DNA quantification and biochemical tests. H&E staining reflected the absence of any nuclear material in the endocervical and ectocervical tissues. Tissue microarchitecture and descending uterine artery were intact and could be helpful in the nutrient and gas exchange. DNA was found to be around 70 ng/mg tissue weight. Cell-free tissue-derived scaffolds were obtained along with a combination of growth factors and proteins.

Limitations, reasons for caution

Acellular cervical scaffold as a whole organ with vasculature intact for site-specific transplantation is a bigger question and still unaddressed.

Wider implications of the findings

Our study creates numerous prospects for in-vitro and in-vivo whole cervix tissue engineering. Site-specific tissue holds a promising avenue for the reconstruction of cervical abnormalities.

Trial registration number

Not applicable

Diosmium compounds containing bis(imidazole)-p-quinone bridging ligands

The doubly deprotonated bridging ligand L₁^2- derived from 2,6-bis(2-pyridyl)-1,5-dihydro-1',4'-benzoquinono[2',3'-d:5',6'-d']diimidazole H₂L₁ forms coordination compounds with two bis(2,2'-bipyridine)osmium(II) complex fragments in anti ([1](ClO₄)₂) and syn configurations ([2](ClO₄)₂) of {(μ-L₁)[Os(bpy)₂]₂}(ClO₄)₂, as evident from crystal structure analyses. Exchange of the metal-coordinating 2-pyridyl functions in the bridge through non-coordinating 4-tolyl substituents (L₁^2- → L₂^2-) leads to [3](ClO₄)₂ which involves chelation of the [Os(bpy)₂]²⁺ groups through imidazole-N and carbonyl-O atoms of the central p-quinone function. In addition to identification, the compounds were subjected to electrochemical (CV, DPV) and spectroelectrochemical (UV-vis-NIR, EPR) analyses of electron transfer, the results being supported by results from TD-DFT calculations. Essential differences between [1ⁿ⁺]/[2ⁿ⁺] and [3ⁿ⁺] systems were found regarding variable but mostly metal centred oxidation, the two processes separated much more for [3ⁿ⁺]. The first reduction is bpy ([1⁺], [2⁺]) or quinone ligand centred ([3⁺]). Electronic structures and electron transfer behaviour are thus highly sensitive to differences of configuration and coordination.

Redox induced oxidative C-C coupling of non-innocent bis(heterocyclo)methanides

Redox driven C-C bond formation has gained recent attention over the traditional sequence of oxidative addition, insertion and reductive elimination reactions. In this regard, the transient radical mediated diverse reactivity profile of bis(heterocyclo)methanes (H-BHM: HL1-HL4) has been demonstrated as a function of varying metal ions and ligand backbones. It highlighted the following events: (a) redox induced homocoupling of deprotonated HL1 and HL4 on coordination to M(OAc)₂ precursors (M = Cu^II, Zn^II, Pd^II, Ag^I), including the effective role of molecular oxygen in the transformation process; (b) steric inhibition of C-C coupling of HL1 or HL4 on inserting the substituent at the bridged methylene centre (Ph in HL2 or CH₃ in HL3); (c) competitive C-C coupling versus oxygenation of free HL1 with varying concentrations of Pd^II(OAc)₂ as the ease of oxygenation over dimerisation of the deprotonated HL1 was corroborated by the DFT calculated lower activation barrier and greater thermodynamic stability of the former; and (d) redox non-innocence of BHMs on a coordinatively inert ruthenium platform, which in turn favored the involvement of a radical pathway for the aforestated coupling or oxygenation process. A combined structural, spectroscopic and DFT calculated transition state analysis demonstrated the mechanistic outline for the metal assisted oxidative coupling of BHMs.

Redox induced S-S bond cleavage of 2,2'-dithiobisbenzothiazole - leading to a [2Ru-2S] core analogous to [2Fe-2S] cluster

Facile reduction of 2,2'-dithiobisbenzothiazole by the mediation of metal-to-ligand charge transfer or by internal reducing equivalent is demonstrated. It leads to various binding modes of thiolates (κ¹, κ², μ) in a series of mononuclear and dinuclear ruthenium complexes. The dinuclear complex exhibited electron transfer processes similar to a [2Fe-2S] cluster.

Pancreatic cancer prognosis is predicted by an ATAC-array technology for assessing chromatin accessibility

Unlike other malignancies, therapeutic options in pancreatic ductal adenocarcinoma (PDAC) are largely limited to cytotoxic chemotherapy without the benefit of molecular markers predicting response. Here we report tumor-cell-intrinsic chromatin accessibility patterns of treatment-naïve surgically resected PDAC tumors that were subsequently treated with (Gem)/Abraxane adjuvant chemotherapy. By ATAC-seq analyses of EpCAM+ PDAC malignant epithelial cells sorted from 54 freshly resected human tumors, we show here the discovery of a signature of 1092 chromatin loci displaying differential accessibility between patients with disease free survival (DFS) < 1 year and patients with DFS > 1 year. Analyzing transcription factor (TF) binding motifs within these loci, we identify two TFs (ZKSCAN1 and HNF1b) displaying differential nuclear localization between patients with short vs. long DFS. We further develop a chromatin accessibility microarray methodology termed "ATAC-array", an easy-to-use platform obviating the time and cost of next generation sequencing. Applying this methodology to the original ATAC-seq libraries as well as independent libraries generated from patient-derived organoids, we validate ATAC-array technology in both the original ATAC-seq cohort as well as in an independent validation cohort. We conclude that PDAC prognosis can be predicted by ATAC-array, which represents a low-cost, clinically feasible technology for assessing chromatin accessibility profiles.

Blood clotting and traumatic injury with shock mediates complement-dependent neutrophil priming for extracellular ROS, ROS-dependent organ injury and coagulopathy

Polymorphonuclear (PMN) leucocytes participate in acute inflammatory pathologies such as acute respiratory distress syndrome (ARDS) following traumatic injury and shock, which also activates the coagulation system systemically. Trauma can prime the PMN nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex for an enhanced respiratory burst, but the relative role of various priming agents in this process remains incompletely understood. We therefore set out to identify mediators of PMN priming during coagulation and trauma-shock and determine whether PMN reactive oxygen species (ROS) generated in this manner could influence organ injury and coagulation. Initial experiments demonstrated that PMN are primed for predominantly extracellular ROS production by products of coagulation, which was abrogated by CD88/C5a receptor(C5aR) inhibition. The importance of this was highlighted further by demonstrating that known PMN priming agents result in fractionally different amounts of extracellular versus intracellular ROS release depending on the agent used. Plasma from trauma patients in haemodynamic shock (n = 10) also primed PMN for extracellular ROS in a C5a-dependent manner, which correlated with both complement alternative pathway activation and thrombin generation. Furthermore, PMN primed by preincubation with products of blood coagulation directly caused loss of endothelial barrier function in vitro that was abrogated by C5aR blockade or NADPH oxidase inhibition. Finally, we show in a murine model of trauma-shock that p47phox knock-out (KO) mice with PMN incapable of generating ROS were protected from inflammatory end-organ injury and activated protein C-mediated coagulopathy. In summary, we demonstrate that trauma-shock and coagulation primes PMN for predominantly extracellular ROS production in a C5a-dependent manner that contributes to endothelial barrier loss and organ injury, and potentially enhances traumatic coagulopathy.

Optimized weak measurements of Goos-Hänchen and Imbert-Fedorov shifts in partial reflection

The spatial and the angular variants of the Imbert-Federov (IF) beam shifts and the angular Goos-Hänchen (GH) shift contribute in a complex interrelated way to the resultant beam shift in partial reflection at planar dielectric interfaces. Here, we show that the two variants of the IF effects can be decoupled and separately observed by weak value amplification and subsequent conversion of spatial ↔angular nature of the beam shifts using appropriate pre and post selection of polarization states. Such optimized weak measurement schemes also enable one to nullify one effect (either the GH or the IF) and exclusively observe the other. We experimentally demonstrate this and illustrate various other intriguing manifestations of optimized weak measurements in elliptical and / or linear polarization basis. We also present a Poincare sphere based analysis on conversion / retention of the angular or spatial nature of the shifts with pre and post selection of states in weak measurement. The demonstrated ability to amplify, controllably decouple or combine the beam shifts via weak measurements may prove to be valuable for understanding the different physical contributions of the effects and for their applications in sensing and precision metrology.

Catalyst free growth of ZnO nanowires on graphene and graphene oxide and its enhanced photoluminescence and photoresponse

We demonstrate the graphene assisted catalyst free growth of ZnO nanowires (NWs) on chemical vapor deposited (CVD) and chemically processed graphene buffer layers at a relatively low growth temperature (580 °C) in the presence and absence of ZnO seed layers. In the case of CVD graphene covered with rapid thermal annealed ZnO buffer layer, the growth of vertically aligned ZnO NWs takes place, while the direct growth on CVD graphene, chemically derived graphene (graphene oxide and graphene quantum dots) without ZnO seed layer resulted in randomly oriented sparse ZnO NWs. Growth mechanism was studied from high resolution transmission electron microscopy and Raman spectroscopy of the hybrid structure. Further, we demonstrate strong UV, visible photoluminescence (PL) and enhanced photoconductivity (PC) from the CVD graphene-ZnO NWs hybrids as compared to the ZnO NWs grown without the graphene buffer layer. The evolution of crystalinity in ZnO NWs grown with ZnO seed layer and graphene buffer layer is correlated with the Gaussian line shape of UV and visible PL. This is further supported by the strong Raman mode at 438 cm(-1) significant for the wurtzite phase of the ZnO NWs grown on different graphene substrates. The effect of the thickness of ZnO seed layers and the role of graphene buffer layers on the aligned growth of ZnO NWs and its enhanced PC are investigated systematically. Our results demonstrate the catalyst free growth and superior performance of graphene-ZnO NW hybrid UV photodetectors as compared to the bare ZnO NW based photodetectors.

Topological defect transformation and structural transition of two-dimensional colloidal crystals across the nematic to smectic-A phase transition

We observe that topological defects in nematic colloids are strongly influenced by the elasticity and onset of smectic layering across the nematic (N) to smectic-A (SmA) phase transition. When approaching the SmA phase from above, the nematic hyperbolic hedgehog defect that accompanies a spherical colloidal inclusion is transformed into a focal conic line in the SmA phase. This phase transformation has a strong influence on the pairwise colloidal interaction and is responsible for a structural transition of two-dimensional colloidal crystals. The pretransitional behavior of the point defect is supported by Landau-de Gennes Q-tensor modeling accounting for the increasing elastic anisotropy.

Strong memory effect at room temperature in nanostructured granular alloy Co0.3Cu0.7

Non-interacting magnetic CoCu nanoparticles with a blocking temperature distribution show strong magnetic memory effect even at room temperature.

Flipping growth orientation of nanographitic structures by plasma enhanced chemical vapor deposition

Nanographitic structures (NGSs) with a multitude of morphological features are grown on SiO₂/Si substrates by electron cyclotron resonance-plasma enhanced chemical vapor deposition (ECR-PECVD).

Influence of boron addition to Ti-13Zr-13Nb alloy on MG63 osteoblast cell viability and protein adsorption

Cell proliferation, cell morphology and protein adsorption on near β-type Ti-13Zr-13Nb (TZN) alloy and Ti-13Zr-13Nb-0.5B (TZNB) composite have been investigated and compared to evaluate the effect of boron addition which has been added to the Ti alloy to improve their poor tribological properties by forming in situ TiB precipitates. MG63 cell proliferation on substrates with different chemistry but the same topography was compared. The MTT assay test showed that the cell viability on the TZN alloy was higher than the boron containing TZNB composite after 36 h of incubation and the difference was pronounced after 7 days. However, both the materials showed substantially higher cell attachment than the control (polystyrene). For the same period of incubation in fetal bovine serum (FBS), the amount of protein adsorbed on the surface of boron free TZN samples was higher than that in the case of boron containing TZNB composite. The presence of boron in the TZN alloy influenced protein adsorption and cell response and they are lower in TZNB than in TZN as a result of the associated difference in chemical characteristics.

Laser-driven microflow-induced bistable orientation of a nematic liquid crystal in perfluoropolymer-treated unrubbed cells

We demonstrate laser-driven microflow-induced orientational change (homeotropic to planar) in a dye-doped nematic liquid crystal. The homeotropic to planar director alignment is achieved in unrubbed cells in the thermal hysteresis range of a discontinuous anchoring reorientation transition due to the local heating by light absorption in dye-doped sample. Various bistable patterns were recorded in the cell by a programmable laser tweezers. The width of the patterns depend on the scanning speed of the tightly focussed laser beam and the minimum width obtained is approximately equal to 0.57μm which is about 35 times smaller than the earlier report in the rubbed cells. We show that the motion of the microbeam spot causes local flow as a result the liquid crystal director is aligned along that direction.

UV induced zener diode characteristic in a single n-ZnO/p++-Si nanoheterojunction

Rectification is observed in a single n-ZnO/p++-Si nanoheterojunction using ultra high vacuum compatible scanning tunneling microscope. The nanohetrojunctions have been grown using catalyst free vapor-solid growth of ZnO nanorods on p++-Si substarte. A high rectification ratio approximately 100 at 2 V is observed in the current voltage measurements. Temperature dependent study in these nanohetero-junctions showed activation energy for carrier conduction approximately 66 meV, which is primarily associated to the presence of heterojunction induced interface states. Role of ultra violet excitation on these finite sized (approximately 500 nm) nanoheterojunction is also studied with photo-generated electron-hole pairs. A Zener breakdown is observed in this photo-excitation process. Increase in the concentration of minority carriers and corresponding decrease in barrier width and height at the junction have been identified for the observed tunneling behavior under UV illumination. The large carrier concentration in the finite sized device with large diffusion length of electron (approximately 2 microm) is made responsible for the observed voltage regulation.

Viscoelasticity of ambient-temperature nematic binary mixtures of bent-core and rodlike molecules

We report measurements of the temperature variations of physical parameters in ambient-temperature nematic liquid crystal mixtures of bent-core (BC) and rodlike molecules (5CB): birefringence Δn; static dielectric constants ε(||) and ε(⊥); splay K(11) and bend K(33) elastic constants; rotational viscosity γ(1); and diffusion coefficients D(||) and D(⊥) of a microsphere. Both Δn and ε(||) decreases rapidly with increasing BC concentration, whereas ε(⊥) remains almost constant. At a shifted temperature (e.g., T-T(NI)=-10 °C), K(11) increases by ~50% and K(33) decreases by ~80% compared to pure 5CB when the BC concentration is increased to ~43 mol % in the mixture. Viscosities parallel and perpendicular to the director, η(||), η(⊥), which are nearly equal to the Miesowicz viscosities η(2) and η(3), respectively, were obtained by D(||) and D(⊥) using the Stokes-Einstein relation. Both the viscosities at room temperature increase by 60 and 50 times, respectively, whereas γ(1) increases by 180 times (at ~43 mol %) compared to the corresponding values of pure 5CB. The stiffening of K(11) and exorbitantly large enhancement in all the viscosities at a higher mol % of BC indicate that the viscoelastic properties are highly impacted by the presence of smectic clusters of BC molecules that results from the restricted free rotation of the molecules along the bow axis in the nematic phase. A possible attachment model of smectic type clusters of BC molecules surrounding the microparticle is presented.

Effect of electric field on the rheological and dielectric properties of a liquid crystal exhibiting nematic-to-smectic-A phase transition

We report simultaneous measurements of shear viscosity (η) and dielectric constant (ε) of octyloxy cyanobiphenyl (8OCB) in the nematic (N) and smectic-A (SmA) phases as functions of temperature and electric field. With increasing electric field η increases in the N phase whereas it decreases in the SmA phase and saturates beyond a particular field in both the phases. The flow curves in the intermediate-field range show two Newtonian regimes in the N phase. The temperature-dependent behavior of η and ε at zero or at small electric field suggests the occurrence of several structures that results from precessional motion of the director along the neutral direction as reported in similar other system. We show that the precessional motions are gradually suppressed with increasing electric field and the effective viscosity resembles with the Miesowicz viscosity η1 at high enough electric field. In the intermediate field range the temperature-dependent η exhibits anomalous behavior across the N-SmA phase transition which is attributed to the large contribution of Leslie coefficient α1.

Calorimetric study of the effect of bent-shaped dopant molecules on the critical behavior at the nematic-smectic-Ad phase transition

We report results of calorimetric studies for the binary mixture of rodlike host n-alkyloxy-cyanobiphenyl (nOCB, n=8,9) and bent-shaped guest 1,3-phenylene-bis[4-(3-methylbenzoyloxy)]-4'-n-dodecylbiphenyl-4'-carboxylate (BC12). The effect of bent-shaped dopant molecules on the critical behavior associated with the nematic-smectic-A(d) phase transition has been studied in detail. The transition temperature for the nematic-smectic-A(d) phase sharply decreases as the increase of the mole fraction of the dopant concentration (denoted X for the BC12/9OCB mixture and Y for the BC12/8OCB mixture). The dependence of the critical exponent α on X and Y is well explained in terms of the McMillan ratio. A nearly tricritical exponent has been obtained for the X=0.01 mixture. X=0.02-0.03 mixtures, pure 8OCB, and Y=0.01-0.03 mixtures exhibit nonuniversal behaviors with effective exponents lying between the 3D-XY and tricritical exponents. The heat capacity anomaly for Y=0.05 has been well described with the 3D-XY exponent. The critical amplitude ratio A(-)/A(+) is close to 1 and insensitive to the dopant concentration. No Fisher renormalization of the critical exponent has been observed even for nearly tricritical compositions, which indicates the smallness of the concentration plays a decisive role rather than the steepness of the N-SmA(d) phase boundary.

Splay-bend elasticity of a nematic liquid crystal with T-shaped molecules

We measured the splay (K11) and bend (K33) elastic constants in the nematic phase of a liquid crystal with T-shaped molecules. We find that the ratio, K33/K11 ≃1 in the entire nematic range except very close to the nematic to Sm-A (SN) transition. Both K33 and K11 show pretransitional divergence as the SN transition is approached from higher temperature. The ratio, K33/K11 suggests that the length (L) to effective width (D) ratio (i.e., L/D ) is significantly smaller due to the presence of long and flexible lateral group, compared to that of rigid rodlike molecules. It is argued that apart from the extra contribution to the elasticity the long and flexible lateral group also has a significant contribution to the suppression of the splay fluctuations in the onset of smectic short-range fluctuation. The structure of the Sm-A phase is investigated by using small angle x-ray diffraction, and a possible arrangement of the molecules in the Sm-A layer is proposed.

Critical behavior at transitions from uniaxial to biaxial phases in a smectic liquid-crystal mixture

We report results of calorimetric and optical investigations of binary mixtures of rodlike and bent-shaped molecules. We find that the observed critical heat anomaly associated with the smectic-A2 to biaxial smectic-A2b transition is well described with a Fisher-renormalized form of the usual scaling expression. The effect of renormalization is large in this system in part because of the moderately steep slope of the phase boundary (dT(c)/ dX∼100 K, where X is the mole fraction of the bent-core molecules) and in part because of the proximity to the tricritical point. The magnitude of heat anomaly at the smectic-A2-smectic-A2b transition showed a drastic decrease as X becomes smaller. Moreover, the nematic-smectic-A2 transitions investigated turned out to be always first order and the transition enthalpy showed only weak dependence on the concentration X. The results imply that the energy fluctuations around the smectic-A2-smectic-A2b transition are very sensitive to the underlying ordering of the smectic-A2 background.

Phonon confinement in stressed silicon nanocluster

Confined acoustic and optical phonons in Si nanoclusters embedded in sapphire, synthesized using ion-beam implantation are investigated using Raman spectroscopy. The l=0 and l=2 confined acoustic phonons, found at low Raman shift, are analyzed using complex frequency model and the size of the nanoparticles are estimated as 4 and 6 nm. For the confined optical phonon, in contrast to expected red shift, the Raman line shape shows a substantial blue shift, which is attributed to size dependent compressive stress in the nanoparticles. The calculated Raman line shape for the stressed nanoparticles fits well to data. The sizes of Si nanoparticles obtained using complex frequency model are consistent with the size estimated from the fitting of confined optical phonon line shapes and those found from X-ray diffraction and TEM.

Hedgehog inhibition prolongs survival in a genetically engineered mouse model of pancreatic cancer

BACKGROUND AND AIMS

Pancreatic cancer is among the most dismal of human malignancies. Current therapeutic strategies are virtually ineffective in controlling advanced, metastatic disease. Recent evidence suggests that the Hedgehog signalling pathway is aberrantly reactivated in the majority of pancreatic cancers, and that Hedgehog blockade has the potential to prevent disease progression and metastatic spread.

METHODS

Here it is shown that the Hedgehog pathway is activated in the Pdx1-Cre;LsL-Kras(G12D);Ink4a/Arf(lox/lox) transgenic mouse model of pancreatic cancer. The effect of Hedgehog pathway inhibition on survival was determined by continuous application of the small molecule cyclopamine, a smoothened antagonist. Microarray analysis was performed on non-malignant human pancreatic ductal cells overexpressing Gli1 in order to screen for downstream Hedgehog target genes likely to be involved in pancreatic cancer progression.

RESULTS

Hedgehog inhibition with cyclopamine significantly prolonged median survival in the transgenic mouse model used here (67 vs 61 days; p = 0.026). In vitro data indicated that Hedgehog activation might at least in part be ascribed to oncogenic Kras signalling. Microarray analysis identified 26 potential Hedgehog target genes that had previously been found to be overexpressed in pancreatic cancer. Five of them, BIRC3, COL11A1, NNMT, PLAU and TGM2, had been described as upregulated in more than one global gene expression analysis before.

CONCLUSION

This study provides another line of evidence that Hedgehog signalling is a valid target for the development of novel therapeutics for pancreatic cancer that might be worth evaluating soon in a clinical setting.

Mechanism of bright red emission in Si nanoclusters

A bright photoluminescence around 1.7 eV is observed for post-annealed samples of 1 MeV Si(2+) implanted in an SiO(2) matrix. A super-linear power dependence of photoluminescence intensity accompanied by pulse shortening under continuous wave laser excitation is recorded without any spectral narrowing. An emission process comprised of an initial non-radiative recombination (time constant ∼280-315 ps) of excited carriers in the defect states in SiO(2) matrices to the conduction band minima of nc-Si, followed by a slower process of radiative recombination in the direct band transition for nc-Si along with a non-radiative Auger recombination (time constant ∼2.67 ns) is proposed.

Effect of high electric fields on the nematic to isotropic transition in a material exhibiting large negative dielectric anisotropy

We report the experimental high electric field phase diagram of a nematic liquid crystal which exhibits a large negative dielectric anisotropy. We measure simultaneously the birefringence (Deltan) and the dielectric constant (epsilon( perpendicular)) at various applied fields as functions of the local temperature of an aligned sample. We also measure the higher harmonics of the electrical response of the medium. The following experimental results are noted: (i) enhancement of orientational order parameter S in the nematic phase due to both the Kerr effect and quenching of director fluctuations; (ii) enhancement in the paranematic to nematic transition temperature (T(PN)) with field; (iii) divergence of the order parameter susceptibility beyond the tricritical point as measured by third harmonic electrical signal; (iv) a small second harmonic electrical signal which also diverges near T(PN), indicating the presence of polarised domains. Our measurements show that DeltaT(PN)(= T(PN)(E)-T(NI)(0)) varies linearly with |E| whereas the Landau de Gennes theory predicts a dependence on E(2). It is argued that the quenching of director fluctuations by the field makes the dominant contribution to all the observations, including the thermodynamics of the transition.

Aberrant methylation of the Human Hedgehog interacting protein (HHIP) gene in pancreatic neoplasms

Hedgehog pathway overactivity has been implicated in the development of a variety of human cancers. The Human Hedgehog interacting protein (HHIP), a negative regulator of hedgehog signaling, has been shown to be underexpressed in pancreatic cancers. In this study we determined if the HHIP gene is a target for genetic and epigenetic alterations. While no mutations of HHIP were identified, we found complete methylation of the HHIP promoter CpG island in three pancreatic cancer cell lines, and partial hypermethylation in 13/17 (80%) pancreatic cancer cell lines, 35/75 (46%) primary pancreatic cancers and 14/18 (78%) pancreatic cancer xenografts, but no methylation in 13 normal pancreata. In pancreatic cancer cell lines, complete methylation was associated with absent or reduced HHIP expression by real-time RT-PCR. HHIP expression could be restored in methylated cell lines using epigenetic modifier drugs. Restoring the expression of HHIP in pancreatic cancer cells by 5-aza-2'-deoxycytidine led to a decrease in Gli reporter activity, consistent with downregulation of Hedgehog signaling. These results indicate in some pancreatic adenocarcinomas that HHIP is epigenetically inactivated by promoter methylation, and its silencing could contribute to the increased Hedgehog signaling observed in pancreatic neoplasms.

A subgroup of microsatellite stable colorectal cancers has elevated mutation rates and different responses to alkylating and oxidising agents

An early step in the carcinogenesis of hereditary non-polyposis colorectal cancer (HNPCC) and some sporadic colorectal cancers (CRCs) is the acquisition of a ‘mutator phenotype’ resulting from defects in DNA mismatch repair (MMR) genes, which normally maintain genomic stability. This mutator phenotype causes an approximately 100–1000-fold increase in base substitutions and small insertion/deletion mutations thereby driving carcinogenesis. It also causes genome-wide microsatellite instability (MSI) due to the inability to repair mutations within these small, hard to replicate, repetitive DNA elements. In contrast, less is known about the role of mutator phenotypes in microsatellite stable (MSS) CRC. In this report, we have measured the mutation rates in 11 MSS CRC cell lines to obtain an estimate of the prevalence of mutator phenotypes in MSS carcinogenesis. Of the 11 cell lines, three of them (27%) possess spontaneous hypoxanthine phosphoribosyltransferase mutation rates approximately 10–100-fold above background. When challenged with alkylating and oxidising agents, the degree of survival and apoptotic responses are different, indicating that these cell lines may represent more than one mutator phenotype. These data demonstrate that a significant portion of MSS CRC cell lines has increased mutation rates and that this may play a role in MSS CRC carcinogenesis.

Blue luminescence of Au nanoclusters embedded in silica matrix

Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO(2) matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar(+) irradiation on Au [40 nm]/SiO(2) at various fluences and subsequent annealing at high temperature. The blue bands above approximately 3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blueshift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals formalism with generalized gradient approximation for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states for different strain values in order to explain the blueshift of approximately 0.1 eV with decreasing cluster size around L-symmetry point.

Banana-shaped mesogens: observation of a direct transition from the antiferroelectric B2 to nematic phase

The synthesis and characterisation of the first banana-shaped mesogens which exhibit a direct transition from the antiferroelectric B2 phase to the nematic phase are reported.

Immunohistochemical localization of insulin-like growth factors I and II at the primary implantation site in the Rhesus monkey

There are various cellular mediators which can affect the process of blastocyst implantation by regulating the proliferation and differentiation of conceptus and maternal endometrial cells. Insulin-like growth factors I (IGF-I) and II (IGF-II) are potent mitogenic and differentiation-promoting growth factors. However, the role of IGF peptides at implantation in primate species is not well understood. The objective of the present study was to immunohistochemically localize IGF-I and IGF-II peptides in trophoblast cells and maternal endometrial cells during lacunar and villous stages of placentation in the Rhesus monkey. Female animals (n = 10) were laparotomized on estimated days 13-16 after fertilization to collect primary implantation sites which were subjected to immunohistochemical staining for IGF-I and IGF-II peptides. Cell-type specificity for IGF-I and IGF-II was evident with a very low level of IGF-I peptide immunolocalized in trophoblast cells lining lacunae, and primary and secondary villi, while moderate to high amounts of IGF-II peptide were detected in lamellar syncytiotrophoblast cells lining lacunae, early villi and cell columns, as well as in migrating trophoblast cells in the extravillous compartment and in endovascular trophoblast cells. The observed presence of IGF-II peptide in differentiated lamellar syncytiotrophoblast cells during the very early stages of implantation and placentation in the Rhesus monkey may be important in their transition to this differentiated cell population. Maternal endometrial cells showed similar distribution profiles for IGF-I and IGF-II. In conclusion, we report differential distribution of IGF-I and IGF-II peptides in trophoblast cell populations at the feto-maternal interface during lacunar and villous stages of gestation in the Rhesus monkey.

Expression of vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) in conceptus and endometrium during implantation in the rhesus monkey

The aim of this study was to analyse the expression of transcripts and proteins for vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF) in different compartments of the early conceptus at primary implantation sites during lacunar (n = 6), early villous (n = 9) and villous placenta (n = 6) stages of gestation in the rhesus monkey. During the lacunar stage, VEGF expression was observed in the cytotrophoblast cells lining the extraembryonic cavity, but these cells did not express PlGF. With further development, cytotrophoblast cells lining villi, forming columns, and constituting anchoring villi, expressed both VEGF and PlGF during early villous and villous placenta stages. In addition, chorion, amnion and villous stromal cells expressed both VEGF and PlGF proteins and mRNA. During the lacunar stage, all epithelial cells in maternal endometrium generally expressed VEGF, while PlGF expression was observed in the plaque epithelium only. As gestation advanced, the expression of VEGF and PlGF from plaque cells decreased, and in surface and glandular epithelium the expression of VEGF increased, while the expression of PlGF remained unaltered. Decidual stromal cells expressed VEGF and PlGF only at low levels during the lacunar stage, while the expression of both increased during the early villous and the villous placenta stages of implantation. It appears from the present study that the expression of VEGF and PlGF are regulated in a temporal and spatial manner during early stages of implantation and that their concerted actions in placental and maternal compartments play a critical role in the evolving pregnancy in the rhesus monkey.