Dynamic molecular recognition in the generation of a new crystal-engineering motif: a unique case study of a dicarboxylic acid with a ditopic receptor favouring a polymeric over a dimeric hydrogen-bonded supramolecular complex

A new crystal-engineering motif has been developed where a ditopic receptor 1 shows a novel syn-syn hydrogen-bonded polymeric supramolecular complex (Fig. 4b) (instead of a 1:1 dimeric syn-syn or polymeric syn-anti complex) giving rise to a hydrogen-bonded stair-like polymeric ribbon structure between the binding groups of the receptor pyridine amide and the carboxyl groups of the guest substrate.     

Forces between a stiff and a soft surface

The contact between a sphere and a planar half space, one being rigid and the other elastic (or between two elastic spheres), can be described by the JKR theory of Johnson, Kendall and Roberts (Proc. R. Soc. Lond. A 1971, 324, 301). One assumption of JKR theory is that the characteristic length scale L ≈ w/E is much smaller than the radius R of the sphere; where w is the work of adhesion and E is the Young's modulus of the soft, elastic body. Relative deformations for a mechanical contact increase with increasing L and decreasing particle size R. Experiments show that up to at least L/R = 0.2, JKR theory predicts the correct dependencies between the contact radius, the indentation and the load. However, when R ≫ L is no longer satisfied, the change in total free surface area due to deformation needs to be considered. Then, elastocapillary effects start playing a significant role. In addition to discussing theory and experiments of pure solid contacts, the effect of elastic deformation on capillary and hydrodynamic forces is discussed. Finally, we consider the interaction of hollow capsules as one example of a deformable body that is still formed from a stiff material.     

Heat transfer from a transferred-arc plasma to a cylindrical enclosure

Hear-transfer rates from an axially enclosed transferred arc to a surrounding water-cooled cylindrical sleeve, 15 cm high, were measured. The arc (argon or nitrogen) was struck between a movable cathode within the sleeve and a bath of molten copper below the sleeve, serving as anode. The distance from the bottom of the sleeve to the surface of the molten copper (L _o) was constant. Variables studied were the diameterD of the sleeve (5, 7.5. and 10 cm), the length of the arc within the sleeveL (5, 10, and 15 cm), the currentI (200, 250, and 300 A) and a tangential flow of gas or vortex within the sleeve (0, ?0, and 50 liters/min). The total power transferred to the sleeve,P _s was measured caloronetrically and was the sure ofP _r the effective power radiated by the arc of lengthL within the sleeve.P _a, the power radiated into the sleeve from the arc of length L_o below the sleeve, andP _o , the power radiated from the melt surface (a constant of small value), minusP _a , the power lost by convection from the sleeve (negligible, except for a strong vortex). BothP _r andP _o were found to be equal to the product of the Joule heat released within their respective arc lengths, IV_gL and IV_g0L₀ (where V_g and V_g0 are the voltage gradients), and dimenonless efliciency factors, η_r and η₀. which are functions ofL/D andL ₀ /D, respectively, for each gas, regardless of the geometry of the sleeve, the current, and the strength of the vortex.     

Facile access to a benzoazepinoquinazolinone via a free radical cyclization

An efficient synthetic protocol based on a free-radical cascade reaction via 6-exo-trig and 7-endo-trig cyclization processes is described for a new substituted benzoazepinoquinazolinone system which could in principle be used to form the cyclopropanequinone system found in duocarmycins.     

Synthesis and isolation of a monoamine having a thermodynamically stabilized pseudo-chirotopic nitrogen

We have synthesized a tricyclic monoamine, (1S,4R)-(E)-7,3′-heptenylene-2,3:5,6-dibenzo-7-azabicyclo[2.2.1]heptane (1), by applying a ring-closing metathesis reaction in the key step of the synthetic route and by using preparative chiral HPLC for the separation. The X-ray crystallographic analysis of its salt with (1R)-camphor-10-sulfonic acid showed that the geometry and absolute configuration are (E) and (1S,4R), respectively. The theoretical calculations revealed that the inversion of the nitrogen atom at the 7-position of (1S,4R)-(E)-1 thus isolated takes place through a very slow process and that the configuration of the N(7) is highly biased to (R), indicating that (1S,4R)-(E)-1 is a thermodynamically controlled N-pseudo-chirotopic compound ((1S,4R,7R): (1S,4R,7S) = 99.68:0.32 at 120 °C).     

Motion of a laser-cooled three-level ion in a harmonic trap

The relative stabilities of eight-atom Si clusters were calculated with the semiempirical MO method SINDO1. With the aid of the group theoretical concept of kernels and epikernels, stationary points ofD _{2d, C 2v} andC _s symmetry on the potential energy surface near the unstable cube were found. Apart from these stationary points which adopt epikernel symmetries, aD _4d stationary point not derivable from group theory is possible in configuration space. The cubic array with eight equivalent atoms can be classified as a diradical.     

Synthesis of a vinylchlorine-containing 1,3-diol from a marine cyanophyte

Using epoxy chiral building blocks readily derived from d-gluconolactone as the source of the stereogenic centers, both (6R,8R)- and (6R,8S)-isomers of (E)-1-chlorotridec-1-ene-6,8-diol were synthesized. The vinylchloro unit was installed onto the substrate carbon chain in an approximately 9:1 (E)/(Z) ratio via a condensation of CrCl₂/CHCl₃ with a terminal aldehyde. A tosylation protocol featuring addition of H₂O was also developed for a highly polar tetraol. The synthetic products allowed for re-acquisition of the NMR spectra of better quality and revealed some delicate yet unignorable discrepancies in the ¹³C NMR for the natural isomer obtained by synthesis and that isolated some 30 years ago from the marine cyanophyte. The puzzling discrepancies were eventually shown to be caused by deuteration of the hydroxyl groups.     

Optimisation of a key cross-coupling reaction towards the synthesis of a promising antileishmanial compound

During the course of a research program aimed at identifying novel antileishmanial compounds, a multi-gram synthesis of N-(trans-4-((4-methoxy-3-((R)-3-methylmorpholino)-1H-pyrazolo[3,4-d]pyrimidin-6-yl)amino)cyclohexyl)-2-methylpropane-1-sulfonamide ((R)-1) was required. This letter describes optimisation of the reaction conditions and protecting group strategy for a key Buchwald-Hartwig coupling, delivering the required quantities of (R)-1, as well as further compounds in the series.     

Hybridization and correlation in a model calculation of a two-electron bond

The paper presents a quantitative examination of some aspects of the molecular two-electron problem, using a calculation for a two-electron homonuclear bond based on a restricted set of one 2s and one 2p orbital per nucleus. The single-determinant approximations with pure 2s STO's and with hybrid AO's are considered, as well as “partial” configuration mixing (CI) over MO's involving one hybrid per atom and “complete” CI over the whole four-orbital basis. The calculations simulate an exact calculation as regards hybridization and (left-right) correlation effects. These are studied, for the lowest state, at various distances, introducing the axial electron density as a means for interpreting quantitatively the various effects. The importance of orthogonalizing the 2s AO's to the corresponding 1s AO's and the MO's used to the MO formed by 1s AO's is reviewed, pending further numerical analysis.     

Scattering by a hard sphere in a laser field

We consider the scattering of electrons by a hard sphere in the presence of a strong laser field. If the electrons are nonrelativistic and if the radiation field is treated as a monochromatic plane wave in the dipole approximation, the solution of our problem can be expressed in terms of well-known functions. The crux for finding this solution lies in the fact that in the potential-free region (V = 0) a space-translated solution can be written down and expressed in spherical polar coordinates. For this solution it is relatively easy to derive the matching equations on the surface of the scattering sphere of radiusR, whereV = ∞ and Ψ(R) = 0.     

Equation of state for hydrofluorocarbon refrigerant mixtures of HFC-125/143a,HFC-125/134a,HFC-134a/143a and HFC-125/134a/143a

Equations of state (EOSs) in the form of dimensionless Helmholtz free energy have been developed for the binary hydrofluorocarbon (HFC) refrigerant mixtures HFC-125/143a, HFC-125/134a, HFC-134a/143a and for the ternary refrigerant mixture HFC-125/134a/143a in the present work. These EOSs are effective in the temperature and pressure ranges where the experimental measurements covered, i.e., 200 K⩽T⩽413 K, P⩽35 MPa for HFC-125/143a and HFC-125/134a; 243 K⩽T⩽413 K, P⩽17 MPa for HFC-134a/143a and HFC-125/134a/143a. Experimental measurements in both single-phase and two-phase regions are represented by the present EOSs within their estimated uncertainties.     

Desymmetrisation of a meso-N-hydroxyimide via a chiral Lossen reaction

N-[(1S)-10-Camphorsulphonyloxy]norborn-5-ene-endo-2,3-dicarboximide 2 underwent a Lossen type reaction with dicyclohexylmethylamine to furnish endo-2-methoxycarbonyl-endo-3-(methoxycarbonylamino)norborn-5-ene 3, in 84% yield and 33% e.e. (by NMR).     

Transform of a thermogram into a thermogenesis curve by the use of the frequency transfer function of a calorimeter

In calorimeter experiments, we obtain the thermogram y = y(t), temperature variation y(t) as a function of time t, when thermal reaction occurs in the calorimeter reaction cell. For thermokinetic studies, we need to know the calorific power generated in the cell, due to the thermal reaction, as a function of time. By use of the frequency transfer function of the calorimeter, we can calculate numerically the calorific power at any time from numerical analysis of the thermogram without any assumption of analytical form of the transfer function.The method is composed of three steps. (1) Experimental determination of the frequency transfer function G of the calorimeter from numerical analysis of the thermogram which is obtained by applying a constant calorific power in the calorimeter cell. (2) Numerical Laplace transform L[y] = Y of the thermogram which is recorded when the thermal reaction under investigation occurs in the cell. (3) Numerical determination of the calorific power, evolved by the thermal reaction in the cell, by numerical inverse Laplace transform of Y/G.This method is examined in two ways. First, simulation by numerical calculation on a mathematical model calorimeter is done and the accuracy of the method is assured. Second, experiments and numerical analysis on the heat-flow (conduction) type of calorimeter are performed to test the availability of the method.     

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: with a comment

This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)^1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)^1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm⁻³ and η value from 0.01 to 0.22 g cm⁻¹ s⁻¹, respectively), the slope of the plot of ΔF versus (ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.     

Vertical excitation as a transient phenomenon

For a particular model with two electronic states, each with two vibrations, the dipole correlation function governing electronic absorption is e ^?iωOt cosγt with spectrum ω ₀±γ. The function starts as e ^?iωOt (γ?ω ₀), with Fourier transform peaking around ω ₀ instead of ω ₀±γ, and this is associated with vertical excitation. After a time t～2/γ the spectrum goes over into the normal one. As a generalization, a procedure is outlined for characterizing the state reached first after interaction with light is initiated. Finally it is suggested that one can understand aspects of internal conversion by analogy with the case of vertical excitation.     

Musanahol: a new aureonitol-related metabolite from a Chaetomium sp.

Two antibacterial furano-polyenes, (−)-musanahol (1) and 3-epi-aureonitol (5), and a fatty acid, linoleic acid (8) were isolated from the laboratory cultures of a Chaetomium sp. accessed from tomato fruits, and grown on YMG medium (yeast extract, glucose, malt extract and water) at pH 5.8-6.0. The structure of compound 1, a new furano-polyene, was elucidated by spectroscopic methods that include extensive 2D NMR experiments, double resonance experiments, Mosher's method and PM3 calculations. (−)-Musanahol (1) and 3-epi-aureonitol (5) were present in the culture filtrate of the fungus. 3-epi-Aureonitol (5) completely inhibited the growth of Streptococcus pyogenes at 15.63 μg/mL and Escherichia coli, Staphylococcus aureus, Salmonella choleraesuis and Corynebacterium diphtheriae at 31.25 μg/mL, whereas (−)-musanahol (1) lacked the antimicrobial potency of compound 5 in spite of the similarities in their structures. Linoleic acid (8) was isolated from the mycelia of the fungus; it inhibited the growth of S. aureus and Bacillus subtilis at a minimum concentration of 15.62 μg/mL.     

An efficient catalytic method for the synthesis of 2,7-dialkyl-2,3a,5a,7,8a,10a-hexaazaperhydropyrenes

An efficient method for the synthesis of 2,7-dialkyl-2,3a,5a,7,8a,10a-hexaazaperhydropyrenes in high yields (up to 95%) via the intermolecular cyclization of 1,4,5,8-tetraazadecalin with N,N-bis(methoxymethyl)-N-alkylamines in the presence of SmCl₃·6H₂O as the catalyst has been developed.     

Broad-band spectroscopy of a vanadyl porphyrin: a model electronuclear spin qudit

We explore how to encode more than a qubit in vanadyl porphyrin molecules hosting a S = 1/2 electronic spin coupled to a I = 7/2 nuclear spin. The spin Hamiltonian and its parameters, as well as the spin dynamics, have been determined via a combination of electron paramagnetic resonance, heat capacity, magnetization and on-chip magnetic spectroscopy experiments performed on single crystals. We find low temperature spin coherence times of micro-seconds and spin relaxation times longer than a second. For sufficiently strong magnetic fields (B > 0.1 T, corresponding to resonance frequencies of 9–10 GHz) these properties make vanadyl porphyrin molecules suitable qubit realizations. The presence of multiple equispaced nuclear spin levels then merely provides 8 alternatives to define the ‘1’ and ‘0’ basis states. For lower magnetic fields (B < 0.1 T), and lower frequencies (<2 GHz), we find spectroscopic signatures of a sizeable electronuclear entanglement. This effect generates a larger set of allowed transitions between different electronuclear spin states and removes their degeneracies. Under these conditions, we show that each molecule fulfills the conditions to act as a universal 4-qubit processor or, equivalently, as a d = 16 qudit. These findings widen the catalogue of chemically designed systems able to implement non-trivial quantum functionalities, such as quantum simulations and, especially, quantum error correction at the molecular level.

We show that a sizeable electronuclear entanglement of the S = 1/2 and I = 7/2 spins of a vanadyl porphyrin provides the conditions to act as a universal 4-qubit processor, and thus implement quantum error correction at the molecular level.     

Representation of one-dimensional motion in a morse potential by a quadratic hamiltonian

A representation of the algebraic hamiltonian for the anharmonic Morse oscillator as a quadratic form, H = T1ω($\text{1}\text{2}$P² + $\text{1}\text{2}$Q²), where P and Q are operators is derived. The commutator of P and Q is an operator that tends to i (times the identity operator) in the harmonic limit. Coherent states and anharmonic normal modes for a linear triatomic molecule are discussed as potential applications.