Application of the randomly optimized RDSQC experiment for the elucidation of an unknown compound

The application of the randomly optimized RDSQC (Randomly optimized Direct correlation Single Quantum Coherence) experiment for the detection of direct correlations facilitated the characterization of an unknown compound. The expected structure consisted of purely aliphatic moieties. The actual, identified compound contained the desired structure plus an adenosine functionality with two protons whose direct proton‐carbon couplings were over 200 Hz. Application of a 130 Hz optimized direct heteronuclear GHSQC experiment afforded no correlations for the adenine responses. The RDSQC experiment allowed for the simultaneous optimization of multiple couplings in a range of 130 to 220 Hz producing a direct correlation spectrum with all the expected responses.     

Direct optical detection in bioanalysis: an update

In biomolecular interaction analysis, direct optical detection is attracting increasing interest in academia and industry. Therefore, a previous review has been updated. Optical principles are given in brief, focussing especially on modern and frequently used techniques. Commercialized methods are listed with some specific applications. In addition, some of the many applications found in the literature are listed; others which have been reviewed elsewhere are cited. Overall, the growing interest in direct optical monitoring of biomolecular interaction is demonstrated and future trends are outlined. Because optical methods is a very wide field, the paper concentrates on the currently most common methods, microrefractometry and microreflectivity.     

Toward an artificial aldolase

A new functional polymer where proline is bonded to polystyrene through a 1,2,3-triazole linker depicts characteristics targeted for an artificial aldolase. In spite of the hydrophobicity of the polymer backbone, the resin swells in water with building of an aqueous microenvironment. This property, arising from the formation of a hydrogen-bond network connecting the proline and 1,2,3-triazole fragments, is translated into a very high catalytic activity and enantioselectivity toward direct aldol reactions in water.     

A three-electrode direct current plasma as compared to an inductively coupled argon plasma

Summary A direct comparison of some analytical properties of a three-electrode direct current plasma and an inductively coupled argon plasma in the case of pneumatic nebulization of aqueous solutions was performed. The measurements were carried out under similar conditions using a 3.4-m spectrograph. The spectra to be compared were recorded on photographic plates in the spectral range from 250 nm to 430 nm. Strong molecular band systems of OH, NH, and N ₂ ⁺ were observed in the case of the direct current plasma. Detection limits for 27 spectral lines of 20 elements were determined for both sources yielding a slight advantage in favour of the inductively coupled plasma. The effect of sodium upon line and background intensities was investigated and found to be generally higher in the direct current plasma.

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Ein Drei-Elektroden-Gleichstromplasma im Vergleich zu einem induktiv gekoppelten Argonplasma

     

Addressing an instability in unrestricted density functional theory direct dynamics simulations

In Density Functional Theory (DFT) direct dynamics simulations with Unrestricted Hartree Fock (UHF) theory, triplet instability often emerges when numerically integrating a classical trajectory. A broken symmetry initial guess for the wave function is often used to obtain the unrestricted DFT potential energy surface (PES), but this is found to be often insufficient for direct dynamics simulations. An algorithm is described for obtaining smooth transitions between the open-shell and the closed-shell regions of the unrestricted PES, and thus stable trajectories, for direct dynamics simulations of dioxetane and its •O CH₂-CH₂ O• singlet diradical. © 2018 Wiley Periodicals, Inc.     

TBHP-mediated oxidative thiolation of an sp3 C-H bond adjacent to a nitrogen atom in an amide

The first example of molecular sieve-promoted TBHP-mediated direct oxidative thiolation of an sp(3) C-H bond adjacent to a nitrogen atom with disulfides under metal-free conditions, which allows for preparation of numerous S,N-containing compounds, is presented. Moreover, diverse benzothiazoles and a fipronil analog can be synthesized through this strategy.     

Redox-neutral synthesis of beta-amino aldehydes from imines by an alkynylation/hydration sequence

N-Protected beta-amino aldehydes have been prepared starting from imines through a sequence involving a Zn-mediated direct alkynylation followed by a Ru-catalyzed anti-Markovnikov alkyne hydration. The rate and the efficiency of the latter reaction are enhanced by the use of microwave irradiation. The possibility to carry out a one-pot Ru-catalyzed hydration/oxidation process from a terminal alkyne to a carboxylic acid was demonstrated, which provided direct access to a N-protected beta-amino acid from the corresponding terminal alkyne.     

Error in an approximate wave function and an error minimization scheme

An estimate of error in an approximate wave function for a stationary state is put forward that does not require any information about the exact state. The measure is sensitive and direct. Parameters embedded in a trial wave function can be varied to minimize this error as well, leading to a variational principle. Such a scheme works nicely for bound states and the more so for Siegert states, for which the standard energy minimization principle does not apply. Pilot calculations on the anharmonic oscillator system and the radial Stark effect in the hydrogen atom reveal the worth of the endeavor. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

A Designed Amide as an Aldol Donor in the Direct Catalytic Asymmetric Aldol Reaction

The direct catalytic asymmetric aldol reaction offers efficient access to β‐hydroxy carbonyl entities. Described is a robust direct catalytic asymmetric aldol reaction of α‐sulfanyl 7‐azaindolinylamide, thus affording both aromatic and aliphatic β‐hydroxy amides with high ee values. The design of this transformation features a cooperative interplay of a soft and a hard Lewis acid, which together facilitate the challenging chemoselective enolization by a hard Brønsted base.     

Effect of an external periodic field on the rate of chemical reactions

The rates of direct and concert passages of nuclei through a potential barrier in an external periodic field were determined within a generalized Slater model of thermal dissociation of multiatomic molecules. The external field accelerated direct and — to a much greater degree — concert passages. The curves of the efficiency of the concert mechanism of the chemical reaction as a function of the field amplitude were estimated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 127–132, March–April, 1993.     

Electrospraying: an in-situ polymerisation route for fabricating high macroporous scaffolds

This paper reports a direct jet-based polymerisation by polycondensation approach to forming a self-supporting scaffold structure. The processing technique is electrospraying, which is also known as electrohydrodynamic atomization. A specially formulated ethanolic siloxane sol derived from alkoxysilanes was synthesised and electrosprayed using a ring-shaped ground electrode configuration. The medium was seen to electrospray in the stable cone-jet mode, which later gave rise to the growing or forming of “fir-tree” like structures. The materials were characterised using microscopy, solid state NMR, FTIR, XRD and DSC. Hence this paper explains the direct controlled polycondensation from the siloxane sol and further presents the basis by which these scaffolds take shape.     

Signal Generation at an Electrochemical Immunosensor via the Direct Oxidation of an Electroactive Label

In this paper, we report the development of an electrochemical immunosensor with a direct signal generation scheme. To achieve this, ferrocenecarboxylic acid was conjugated as an electroactive label to an immunocomplex immobilized on an electrochemically pretreated glassy carbon electrode. The pregnancy hormone and tumor marker, human chorionic gonadotrophin (hCG), was employed as a model analyte. Direct oxidation of ferrocenecarboxylic acid facilitated a signal generation scheme for the quantification of hCG at the immunosensor. Evaluation of the immunosensor performance has yielded statistically acceptable agreement in hCG levels present in several human serum samples compared to those reported by a Sydney hospital.     

Using an aluminum-selective electrode in continuous flow analysis

The possibility of using an ion-selective electrode containing 1,2-dihydroxyanthraquinone for direct determinations based on complexation reaction in continuous flow analysis was studied. A procedure allows aluminum to be determined in a flow with a throughput of 180 sample/h with a satisfactory precision and accuracy (RSD = 0.84%).     

Vergleichende Untersuchungen an polarographischen Analysenverfahren

The universal voltammetric instrument, described in part I of this series, is used for comparative studies on the most important polarographic methods, direct current, derivative pulse, simple and phase-sensitive alternating current, double-tone, and harmonic-wave polarography. In general the peak-heights of these methods are influenced in the same measure by the composition of base electrolyte. In single cases characteristic differences are observed.     

Isomers of C20: an energy profile III

Semiempirical calculations, at the PM3 level provided within the Winmopac v2.0 software package, are used to geometrically optimize and determine the absolute energies (heats of formation) of a variety of C(20) isomers that are predicted to exist in and around the ring and cage isomers. Using the optimized Cartesian coordinates for the ring and the cage isomers, a saddle-point calculation was performed. The resulting energy profile, consisting of a series of peaks and valleys, is used as a starting point for the identification and location of fifteen additional isomers of C(20) that are predicted to be energetically stable, both via geometry optimizations and force constant analysis. These additional isomers were subsequently determined to lie adjacent to one another on the potential surface and establish a step-wise transformation between the ring and the cage. Transition-state optimization of the Cartesian coordinates at the saddle point between adjacent isomers was performed to quantify the energy of the transition state. The step-wise process from one isomer to another, which extends out over the three-dimensional surface, is predicted to require approximately 15% less energy than that of the direct, two-dimensional transformation predicted in the bowl-cage profile. However, the net atomic rearrangement for the step-wise process is about four times greater than that of the direct process. Although less in energy, the amount of atomic rearrangement in the step-wise process would make the occurrence of such a route prohibitive. Utilizing the direct distance separating the three primary isomers (ring, bowl, cage), the method of triangulation is performed to quantitatively position other C(20) structures on the potential surface, relative to the ring, bowl, and cage isomers.     

Continuous-Flow Photocatalysis for the Direct C-H Trifluoromethylation of Heterocycles with an Organic Photoredox Catalyst

Photocatalysis for direct C−H trifluoromethylation represents an ideal way to synthesize trifluoromethyl-containing chemical compounds, but the conventional batch processes are inefficient with limited light penetration and indispensably irradiated for a long while. Herein, we report a continuous-flow protocol for photocatalytic direct C−H trifluoromethylation of heterocycles in the presence of an organic photoredox catalyst: 2,4,6-tris(diphenylamino)-3,5-difluorobenzonitrile (3DPA2FBN). In this approach, benefiting from the merger of organic photoredox catalysis and continuous-flow techniques, a variety of trifluoromethylated heterocycles were rapidly synthesized up to 85 % yield with 80 min residence time under metal- and oxidant-free reaction conditions.     

Bifunctional copper catalysts for an atom efficient ether synthesis

A direct etherification of aromatic ketones and aliphatic alcohols into the corresponding asymmetrical ethers by the use of a bifunctional heterogeneous copper catalyst is described. The reaction protocol reveals to be versatile and convenient respect to the traditional ether synthesis for both environmental and practical concerns.     

Formamide as an Ammonia Synthon in Amination of Acid Chlorides

The use of formamide as a convenient source of ammonia has been explored for the direct transformation of acid chlorides to primary amides. Various aliphatic, alicyclic aromatic, and heterocyclic acid chlorides are converted to the corresponding carboxamides in good yields (75–94%).     

Structure sensitivity of methanol electrooxidation pathways on platinum: an on-line electrochemical mass spectrometry study

By monitoring the mass fractions of CO(2) (m/z 44) and methylformate (m/z 60, formed from CH(3)OH + HCOOH) with on-line electrochemical mass spectrometry (OLEMS), the selectivity and structure sensitivity of the methanol oxidation pathways were investigated on the basal planes--Pt(111), Pt(110), and Pt(100)--and the stepped Pt electrodes--Pt(554) and Pt(553)--in sulfuric and perchloric acid electrolytes. The maximum reactivity of the MeOH oxidation reaction on Pt(111), Pt(110), and Pt(100) increases in the order Pt(111) < Pt(110) < Pt(100). Mass spectrometry results indicate that the direct oxidation pathway through soluble intermediates plays a pronounced role on Pt(110) and Pt(111), while, on Pt(100), the indirect pathway through adsorbed carbon monoxide is predominant. In 0.5 M H(2)SO(4), introducing steps in the (111) plane increases the total reaction rate, while the relative importance of the direct pathway decreases considerably. In 0.5 M HClO(4), however, introducing steps increases both the total reaction rate and the selectivity toward the direct oxidation pathway. Anion (sulfate) adsorption on (111) leads to a more prominent role of the direct pathway, but, on all the other surfaces, (bi)sulfate seems to block the formation of soluble intermediates. For both electrolytes, increasing the step density results in more methylformate being formed relative to the amount of CO(2) detected, indicating that the [110] steps themselves catalyze the direct oxidation pathway. A detailed reaction scheme for the methanol oxidation mechanism is suggested based on the literature and the results obtained here.     

Synthesis of ordered mesoporous carbons with channel structure from an organic-organic nanocomposite

Mesoporous carbons with ordered channel structure (COU-1) have been successfully fabricated via a direct carbonization of an organic-organic nanocomposite.