Selective Interactions of O-Methylated Flavonoid Natural Products with Human Monoamine Oxidase-A and -B

A set of structurally related O-methylated flavonoid natural products isolated from Senecio roseiflorus (1), Polygonum senegalense (2 and 3), Bhaphia macrocalyx (4), Gardenia ternifolia (5), and Psiadia punctulata (6) plant species were characterized for their interaction with human monoamine oxidases (MAO-A and -B) in vitro. Compounds 1, 2, and 5 showed selective inhibition of MAO-A, while 4 and 6 showed selective inhibition of MAO-B. Compound 3 showed ~2-fold selectivity towards inhibition of MAO-A. Binding of compounds 1–3 and 5 with MAO-A, and compounds 3 and 6 with MAO-B was reversible and not time-independent. The analysis of enzyme-inhibition kinetics suggested a reversible-competitive mechanism for inhibition of MAO-A by 1 and 3, while a partially-reversible mixed-type inhibition by 5. Similarly, enzyme inhibition-kinetics analysis with compounds 3, 4, and 6, suggested a competitive reversible inhibition of MAO-B. The molecular docking study suggested that 1 selectively interacts with the active-site of human MAO-A near N5 of FAD. The calculated binding free energies of the O-methylated flavonoids (1 and 4–6) and chalcones (2 and 3) to MAO-A matched closely with the trend in the experimental IC_50′s. Analysis of the binding free-energies suggested better interaction of 4 and 6 with MAO-B than with MAO-A. The natural O-methylated flavonoid (1) with highly potent inhibition (IC₅₀ 33 nM; Ki 37.9 nM) and >292 fold selectivity against human MAO-A (vs. MAO-B) provides a new drug lead for the treatment of neurological disorders.     

Ultrasound Promoted and Ionic Liquid Catalyzed Cyclocondensation Reaction for the Synthesis of 4(3H)-Quinazolinones

4(3H)‐Quinazolinones were synthesized in high yields by one‐pot three‐component condensation of anthranilic acid, carboxylic acid and aniline in the presence of ionic liquid such as 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF₄) as catalyst under solvent free and neutral conditions.     

Shape and eccentricity effects in adhesive contacts of rodlike particles

The effects of shape and eccentricity on adhesion and detachment behavior of long, rodlike particles in contact with a half-space are analyzed using contact mechanics. The particles are considered to have cross sections that are squarish, oblate, or prolate rather than circular. Such cross sections are represented very generally by using superellipses. The contact mechanics model allows deduction of closed-form expressions for the contact pressure, load-contact size relation, detachment load, and detachment contact size. It is found that even relatively small deviations in shape from a cylinder have a significant influence on the detachment load. Eccentricity also affects the adhesive behavior, but to a lesser extent, with oblate shapes requiring larger separation loads than prolate shapes. The load-contact size solution reduces to that for a right-circular, cylindrical rod when the appropriate limit is taken. The detachment behavior of right-circular cylinders is also found to be mimicked by an entire family of rod shapes with different cross sections.     

Gold-catalyzed 1,2-difunctionalizations of aminoalkynes using only N- and O-containing oxidants

We report two viable routes for the 1,2-difunctionalization of aminoalkynes using only oxidants. In the presence of a gold catalyst, nitrones enable the oxoamination of aminoalkynes 1 to form 2-aminoamides 2. With a suitable gold catalyst, nitrosobenzenes implement an alkyne/nitroso metathesis of the same substrates to give 2-oxoiminylamides 3. These two novel oxidations also provide 1,2-aminoalcohols with opposite regioselectivity via NaBH(4) reduction in situ.     

Thermally controlled cyclic insertion/ejection of dopant ions and reversible zinc blende/wurtzite phase changes in ZnS nanostructures

We report a reversible phase transformation of platelet-shaped ZnS nanostructures between wurtzite (WZ) and zinc blende (ZB) phases by reversible insertion/ejection of dopant Mn(II) ions induced by a thermocyclic process. In a reaction flask loaded with WZ ZnS platelets and Mn molecular precursors, during heating Mn ions are incorporated and change the phase of the host nanostructures to ZB; during cooling Mn ions are spontaneously ejected, returning the host nanoplatelets to the original WZ phase. These reversible changes are monitored for several cycles with PL, EPR, XRD, and HRTEM. Interestingly, the (0001) WZ platelets transform to (110) ZB following a nucleation and growth process triggered by a local increase/depletion of the Mn(2+) concentration in the nanocrystals.     

Solvent-Free Green Synthesis of Azines and Their Conversion to 2,5-Disubstituted-1,3,4-thiadiazoles

A solvent-free, clean, and efficient method has been developed for the synthesis of 2,5-disubstituted-1,3,4-thiadiazoles via azines. This approach exploits the synthetic potential of clean reactions and offers many advantages such as excellent product yields, easy isolation of products, and ecofriendly benign reaction conditions. The newly synthesized compounds were analyzed by infrared, ¹H NMR, ¹³C NMR, and elemental analysis.     

Review of non-reactive and reactive wetting of liquids on surfaces

Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems.     

Efficient and color-tunable Mn-doped ZnSe nanocrystal emitters: control of optical performance via greener synthetic chemistry

Formation of Mn-doped ZnSe quantum dots (Mn:ZnSe d-dots) using nucleation-doping strategy was studied systematically and optimized through greener approaches. The resulting d-dots were with high ( approximately 50%) photoluminescence (PL) quantum yield (QY), which was achieved by the controlled formation of small-sized MnSe nanoclusters as the core and a diffused interface between the nanocluster core and the ZnSe overcoating layers. Synthesis of the d-dots under high temperatures (240-300 degrees C) was achieved by varying the structure of the metal carboxylate precursors, concentration of the inhibitors, free fatty acid, and concentration of the activation reagents, fatty amines. Highly emissive d-dots synthesized under desired conditions were found to be extremely stable upon thermal treatment up to the boiling point of the solvent (about 300 degrees C), which was quantitatively studied using in situ measurements. The PL peak of the d-dots was controllably tuned in a surprisingly large optical window, from 565 to 610 nm. These highly emissive and stable d-dots possess characteristics of practical emissive materials, especially for applications requiring high power, high concentration of emitters, and under tough conditions.     

Modulated Binary–Ternary Dual Semiconductor Heterostructures

A generic modular synthetic strategy for the fabrication of a series of binary‐ternary group II‐VI and group I‐III‐VI coupled semiconductor nano‐heterostructures is reported. Using Ag₂Se nanocrystals first as a catalyst and then as sacrificial seeds, four dual semiconductor heterostructures were designed with similar shapes: CdSe‐AgInSe₂, CdSe‐AgGaSe₂, ZnSe‐AgInSe₂, and ZnSe‐AgGaSe₂. Among these, dispersive type‐II heterostructures are further explored for photocatalytic hydrogen evolution from water and these are observed to be superior catalysts than the binary or ternary semi‐conductors. Details of the chemistry of this modular synthesis have been studied and the photophysical processes involved in catalysis are investigated.     

Pharmacokinetic studies of a novel trioxane antimalarial (99/411) in rats and monkeys using LC–MS/MS

The pharmacokinetic profile of 99/411, a novel anti‐malarial drug, was established in rats (12 mg/kg of body weight) and monkeys (20 mg/kg of body weight). Following oral administration, the presence of 99/411 was rapidly determined in rat plasma, tissues, urine, feces and monkey plasma using a validated LC–MS/MS method. The tissue distribution studies in rats indicated that the drug was partially distributed in all major tissues and plasma, and peak concentration levels were achieved within 0.5–4 h. Area under the curve in different rat tissues and plasma was found in order of blood > lung > intestine > heart > muscle > brain > kidney > spleen > liver. The total recoveries (within 86 h) of 99/411 were <0.0017% and <0.08% in urine and feces, respectively. The peak plasma concentration was 3499 ng/mL in rats after ~2 h of oral administration and 697–767 ng/mL in monkeys after ~6 h of oral administration. No plasma accumulation was observed in both male and female monkeys, even after multiple dosing. The preclinical pharmacokinetic profile and tissue distribution data are expected to assist in future clinical explorations of 99/411 as a promising anti‐malarial agent.