Does twist angle affect the properties of water confined inside twisted bilayer graphene?

Graphene nanoslit pores are used for nanofluidic devices, such as, in water desalination, ion-selective channels, ionic transistors, sensing, molecular sieving, blue energy harvesting, and protein sequencing. It is a strenuous task to prepare nanofluidic devices, because a small misalignment leads to a significant alteration in various properties of the devices. Here, we focus on the rotational misalignment between two parallel graphene sheets. Using molecular dynamics simulation, we probe the structure and dynamics of monolayer water confined inside graphene nanochannels for a range of commensurate twist angles. With SPC/E and TIP4P/2005 water models, our simulations reveal the independence of the equilibrium number density- n ∼ 13 nm-2 for SPC/E and n ∼ 11.5 nm-2 for TIP4P/2005- across twists. Based on the respective densities of the water models, the structure and dielectric constant are invariant of twist angles. The confined water structure at this density shows square ice ordering for SPC/E water only. TIP4P/2005 shows ordering at the vicinity of a critical density (n ∼ 12.5 nm-2). The average perpendicular dielectric constant of the confined water remains anomalously low (∼2 for SPC/E and ∼6 for TIP4P/2005) for the studied twist angles. We find that the friction coefficient of confined water molecules varies for small twist angles, while becoming independent for twists greater than 5.1°. Our results indicate that a small, angular misalignment will not impair the dielectric properties of monolayer water within a graphene slit-pore, but can significantly influence its dynamics.

Tunable lattice thermal conductivity of twisted bilayer MoS2.

We have studied the thermal conductivity (κ) of layered MoS2, a typical member of the transition metal dichalcogenide (TMDC) materials, using fully atomistic molecular dynamics simulations and Boltzmann transport equation (BTE) based first principles methods. We investigate the tuning of the thermal conductivity with the twist angle between two layers and found a decreasing trend of κ with the increase in the lattice constant of the moiré superlattice. The thermal conductivity at twist angle θ = 21.78° is found to be 72.03 W m-1 K-1 and for an angle of 2.87°, it reaches 54.48 W m-1 K-1, leading to a 32% reduction in the thermal conductivity. We use first principles calculations based on the BTE for phonons to give a microscopic origin of the decrease in thermal conductivity through anharmonic phonon scattering events and also reaffirm the MD simulation results for the monolayer and bilayer.

Donor-Site-Directed Rational Assembly of Heteroleptic cis-[Pd2 L2 L'2 ] Coordination Cages from Picolyl Ligands.

A donor-site engineering approach facilitates the formation of heteroleptic [Pd2 L2 L'2 ]4+ cage structures through a favored cis-'in2 /out2 ' spatial configuration of the methyl groups of 5- and 3-substituted bis-monodentate picolyl ligands with flat acridone and bent phenothiazine backbones. The heteroleptic cages were confirmed by ESI-MS and 2D NMR experiments as well as DFT calculations, which pointed toward a cis-configuration being energetically favored. This was further supported by the synthesis and X-ray structure of a previously unreported cis-[Pd(2-picoline)4 ]2+ complex. The formation of homoleptic structures, however, was met with considerable steric hindrance at the PdII centers, as observed by the formation of [Pd2 L3 (solvent)2 ]4+ and [Pd2 L2 (solvent)4 ]4+ species when only one type of acridone-based ligand was offered. In contrast, bent phenothiazine ligands with outside-pointing methyl groups showed the ability to form interpenetrated double-cages, as revealed by X-ray crystallography. The general route presented herein enables the assembly of uniform cis-[Pd2 L2 L'2 ]4+ coordination cages, thus furthering the possibility to increase structural and functional complexity in supramolecular systems.

Metal-mediated DNA assembly with ligand-based nucleosides.

Nucleic acids such as DNA are increasingly being applied in nanotechnology, as a result of their capability to self-assemble reversibly. The formal replacement of canonical base pairs by metal-mediated ones enables a site-specific introduction of metal-based functionality into these biomolecules, leading to the formation of predesigned metal arrays. This article offers an overview of structural aspects of metal-mediated base pairs, reviews recent advances in the field of metal-mediated base pairing and presents potential applications of the resulting metal-modified nucleic acids. It particularly focuses on recently developed metal-mediated base pairs with purine-derived nucleosides, gives an overview of metal-responsive systems relying on metal-mediated base pairs and summarizes various applications beyond metal-ion sensors.

Relative Strand Orientation in a DNA Duplex Controls the Nuclearity of a Metal-Mediated Base Pair.

1,N6 -Ethenoadenine (ϵA) and cytosine (C) are able to form two different metal-mediated base pairs. When the glycosidic bonds are arranged in a cisoid manner (i.e., in antiparallel-stranded DNA), the ϵA:C mispair binds one AgI ion, leading to a mononuclear ϵA-AgI -C base pair that contains a synergistic hydrogen bond. In contrast, a transoid orientation of the glycosidic bonds (as found in parallel-stranded DNA) results in the formation of a dinuclear metal-mediated base pair ϵA-AgI2 -C.

A Dinuclear Mercury(II)-Mediated Base Pair in DNA.

The first dinuclear metal-mediated base pair containing divalent metal ions has been prepared. A combination of the neutral bis(monodentate) purine derivative 1,N6 -ethenoadenine (ϵA), which preferentially binds two metal ions with a parallel alignment of the N-M bonds, and the canonical nucleobase thymine (T), which readily deprotonates in the presence of HgII and thereby partially compensates the charge accumulation due to the two closely spaced divalent metal ions, yields the dinuclear T-HgII2 -ϵA base pair. This metal-mediated base pair stabilizes the DNA oligonucleotide duplex as shown by an increase of 8 °C in its melting temperature. Formation of the base pair was demonstrated by temperature-dependent UV spectroscopy as well as by titration experiments monitored by UV and CD spectroscopy.

Retrospective comparison of functional and radiological outcome, between two contemporary high flexion knee designs.

INTRODUCTION: Patient satisfaction after total knee replacement (TKR) depends on the amount of pain relief and the functional activities achieved. An important criterion of good functional outcome is the amount of flexion achieved and whether the patient can manage high flexion activities. In order to increase the amount of safe flexion, various implant designs have been developed. This study aims to compare the outcome after TKR using two contemporary high flexion knee designs: Sigma CR150 High Flex Knee prosthesis (Depuy, Warsaw, Indiana) and NexGen High Flex Knee prosthesis (Zimmer, Warsaw, Indiana). MATERIAL: A retrospective study was conducted with 100 cases of each design and their functional and radiological outcome was assessed after two years of follow-up. RESULTS: The two groups had comparable results in terms of subjective satisfaction, range of motion achieved and radiological outcome. Depuy group fared better than Zimmer in terms of functional outcome (modified Oxford knee score). CONCLUSION: Depuy group was found to have fared better than Zimmer in terms of functional outcome. However, it is very difficult to rate one design above the other based on our small sample size and short duration of follow-up.

Metal-Mediated Assembly of 1,N(6)-Ethenoadenine: From Surfaces to DNA Duplexes.

The design of multinuclear metal complexes requires a match of the ligand-to-metal vectors and the preferred coordination geometries of the metal ions. Only a few ligands are known with a parallel orientation of N→M vectors that brings the metal ions into close proximity. We establish here the adenine derivative 1,N(6)-ethenoadenine (εA) as an ideal bis(monodentate) ligand. Scanning tunneling microscope images of alkylated εA on graphite surface clearly indicate that these ligands bind to Ag(I) ions. The molecular structures of [Ag2(1)2](ClO4)2 and [Ag2(2)2](ClO4)2 (1, 9-ethyl-1,N(6)-ethenoadenine; 2, 9-propyl-1,N(6)-propylenoadenine) confirm that dinuclear complexes with short Ag···Ag distances are formed (3.0256(3) and 2.984(1) Å, respectively). The structural motif can be extended to divalent metal ions, as was shown by determining the molecular structure of [Cu2(1)2(CHO2)2(OH2)2](NO3)2·2H2O with a Cu···Cu distance of 3.162(2) Å. Moreover, when introducing the 1,N(6)-ethenoadenine deoxyribonucleoside into parallel-stranded DNA duplexes, even dinuclear Ag(I)-mediated base pairs are formed, featuring the same transoid orientation of the glycosidic bonds as the model complexes. Hence, 1,N(6)-ethenoadenine and its derivatives are ideally suited as bis(monodentate) ligands with a parallel alignment of the N→M vectors for the construction of supramolecular metal complexes that require two metal ions at close distance.

Unprecedented dinuclear silver(I)-mediated base pair involving the DNA lesion 1,N(6)-ethenoadenine.

The DNA lesion 1,N(6)-ethenoadenine (εA) has been investigated with respect to its metal-binding properties. A synthetic DNA duplex comprising an εA : εA mispair readily forms doubly silver(I)-mediated base pairs εA-Ag(I)2-εA, representing the first example for a dinuclear metal-mediated homo base pair of a purine derivative. It also constitutes the first example for a Hoogsteen-type metal-mediated homo base pair within a B-DNA duplex.