Force Spectroscopy of Metal-Crown Ether Multivalency: Effect of Local Environments on Energy Landscape and Sensing Kinetics.

Sandwich complexation involving alkali or alkaline-earth metals, multivalency, and effects associated with local environments is widely encountered in biological and synthetic systems yet the mechanic properties remain unexplored. Herein, AFM (atomic force microscopy)-based single-molecule force spectroscopy is employed to investigate a classical model of M(n+)[15C5]2, a metal cation hosted jointly by two 15-crown-5 moieties immobilized on both the substrate and the AFM tip. Factors reportedly promoting the recognition performance are examined. The rupture force required to break apart M(n+)[15C5]2 is found to be in the order of tens of pico-Newton, e.g., f(ß)=31 pN for K(+)[15C5]2. The presence of a second functional group, carboxylate, confers K(+)[15C5]2 with a longer lifetime (from 13 to 16 ms), faster association (from 0.4 to 1.3×10(6) M(-1) s(-1)), and slower dissociation (from 77 to 62 s(-1)). The effect of local environments is significant on association yet less critical on dissociation pathways.

Tactile-feedback stabilized molecular junctions for the measurement of molecular conductance.

Handling the (AFM) tip: The duration of stable molecular junctions was prolonged using a tactile feedback method in which the operator can sense the force of the AFM tip on the sample surface. The movement of the tip is adjusted accordingly, maintaining a more consistent current (i) and voltage (V), instead of having the tip move at a constant preset speed, as in the conventional setup.

Natural history and survival rate of familial amyloidosis with polyneuropathy: A nationwide databank.

OBJECTIVE: Hereditary amyloid transthyretin (ATTRv) amyloidosis with polyneuropathy, a rare autosomal-dominant disease, has gained attention in recent years owing to treatment improvements. However, epidemiological real-world mega database of nationwide natural history and survival rates, especially with the specific mutation of Ala97Ser, are limited. METHODS: Taiwan National Health Insurance Research Database contains data from over 23 million individuals; Among them, 175 ATTRv amyloidosis patients validated by rare disease registry were enrolled. Multivariable Cox proportional hazard analyses were applied to investigate the association between baseline characteristics and all-cause mortality. FINDINGS: From 2008 to 2020, the annual incidence and prevalence rates of specific mutations (Ala97Ser) leading to ATTRv amyloidosis with polyneuropathy were 0.04-1.14 and 0.04-4.79 per million in Taiwan, respectively. In Taiwan, these patients exhibited male predominance with a mean age at validation of 62.75 years. At the 5th year after validation, patients exhibited a survival rate of approximately 50%, with higher mortality in male patients (hazard ratio [HR]: 2.22, 95% confidence interval [CI]: 1.15-4.31) and patients older at validation (HR: 1.10, 95% CI: 1.06-1.15). The two most common departments in outpatient were neurology and family medicine, and neurology and cardiology in inpatient. The three most common causes of death registered were unspecified amyloidosis (30.6%), organ-limited amyloidosis (20.9%), and neuropathic heredofamilial amyloidosis (9.7%). INTERPRETATION: The annual prevalence rate of specific mutation (Ala97Ser)-dominant ATTRv amyloidosis with polyneuropathy in Taiwan is comparable to the mid- to high-prevalence country level of the research by Schmidt et al. The extraordinarily high mortality, especially among patients older at validation, may reflect the inadequate awareness and the necessity of early intervention with novel disease-modifying regimens.

Liposome-based immunostrip for the rapid detection of Salmonella.

Salmonellae are ubiquitous human pathogens, which pose a danger to the elderly and children. Due to the increased number of outbreaks of human illness associated with the consumption of contaminated products in the USA and many other countries, there is an urgent need to develop rapid assays to detect common food-borne pathogens. This study demonstrates the feasibility of using a detectable label comprising methyl blue (MB), a visible dye, entrapped inside liposomes. Immunoliposomes tagged with anti-Salmonella common structural antigens (CSA) antibody encapsulating MB dye were prepared and used as the signal amplifier for the development of a field-portable colorimetric immunoassay to detect Salmonellae. Tapping mode atomic force microscopy (TMAFM), a scanning probe technique, was utilized to demonstrate the presence of anti-Salmonella antibody at the thus-prepared liposome. A plastic-backed nitrocellulose strip with two immobilized zones formed the basis of a sandwich assay. The first zone was the antigen capture zone (AC zone), used in a sandwich (noncompetitive) assay format; the other was the biotin capture zone (BC zone), used as a quality control index for the strip assay. During the capillary migration of the wicking reagent containing 80 µL of immunoliposomes and 40 µL of the test sample (heat-killed S. typhimurium), sample pathogens with surface-bound immunoliposomes were captured at the AC zone, while the unbound immunoliposomes continued to migrate and bind to the anti-biotin antibodies coated on the BC zone. The color density of the AC zone was directly proportional to the number of Salmonella typhimurium in the test sample. The detection limit of the current assay with heat-killed Salmonella typhimurium was 1,680 cells. The cross-reactivity of the proposed immunoassay was also investigated, and pathogens including E. coli O157:H7 and Listeria genus specific caused no interference with the detection of Salmonella typhimurium.

The effect of molecular conformation on single molecule conductance: measurements of pi-conjugated oligoaryls by STM break junction.

Measurements of molecular break junction reveal quantitatively the correlation between the single-molecule conductance and the conformation of pi-conjugated molecules with 6-18 conjugated double bonds.

Steric zipper of the amyloid fibrils formed by residues 109-122 of the Syrian hamster prion protein.

We report the results of atomic force microscopy, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance, and molecular dynamics (MD) calculations for amyloid fibrils formed by residues 109-122 of the Syrian hamster prion protein (H1). Our data reveal that H1 fibrils contain no more than two beta-sheet layers. The peptide strands of H1 fibrils are antiparallel with the A117 residues aligned to form a linear chain in the direction of the fibril axis. The molecular structure of the H1 fibrils, which adopts the motif of steric zipper, is highly uniform in the region of the palindrome sequence AGAAAAGA. The closest distance between the two adjacent beta-sheet layers is found to be about 5 A. The structural features of the molecular model of H1 fibrils obtained by MD simulations are consistent with the experimental results. Overall, our solid-state NMR and MD simulation data indicate that a steric zipper, which was first observed in the crystals of fibril-forming peptides, can be formed in H1 fibrils near the region of the palindrome sequence.

A new generation of metal string complexes: structure, magnetism, spectroscopy, theoretical analysis, and single molecular conductance of an unusual mixed-valence linear [Ni5]8+ complex.

Two new linear pentanickel complexes [Ni5(bna)4(Cl)2][PF6]2 (1) and [Ni5(bna)4(Cl)2][PF6]4 (2; bna=binaphthyridylamide), were synthesized and structurally characterized. A derivative of 1, [Ni5(bna)4(NCS)2][NCS]2 (3), was also isolated for the purpose of the conductance experiments carried out in comparison with [Ni5(tpda)4(NCS)2] (4; tpda=tripyridyldiamide). The metal framework of complex 2 is a standard [Ni5]10+ core, isoelectronic with that of [Ni5(tpda)4Cl2] (5). Also as in 5, complex 2 has an antiferromagnetic ground state (J=-15.86 cm(-1)) resulting from a coupling between the terminal nickel atoms, both in high-spin sate (S=1). Complex 1 displays the first characterized linear nickel framework in which the usual sequence of NiII atoms has been reduced by two electrons. Each dinickel unit attached to the naphthyridyl moieties is assumed to undergo a one-electron reduction, whereas the central nickel formally remains NiII. DFT calculations suggest that the metal framework of the mixed-valence complex 1 should be described as intermediate between a localized picture corresponding to NiII-NiI-NiII-NiI-NiII and a fully delocalized model represented as (Ni2)3+-NiII-(Ni2)3+. Assuming the latter model, the ground state of 1 results from an antiferromagnetic coupling (J=-34.03 cm(-1)) between the two (Ni2)3+ fragments, considered each as a single magnetic centre (S=3/2). An intervalence charge-transfer band is observed in the NIR spectrum of 1 at 1186 nm, suggesting, in accordance with DFT calculations, that 1 should be assigned to Robin-Day class II of mixed-valent complexes. Scanning tunnelling microscopy (STM) methodology was used to assess the conductance of single molecules of 3 and 4. Compound 3 was found approximately 40% more conductive than 4, a result that could be assigned to the electron mobility induced by mixed-valency in the naphthyridyl fragments.