Peptide late-stage C(sp3)–H arylation by native asparagine assistance without exogenous directing groups

There is a strong demand for novel native peptide motifs for post-synthetic modifications of peptides without pre-installation and subsequent removal of directing groups. Herein, we report an efficient method for peptide late-stage C(sp³)–H arylations assisted by the unmodified side chain of asparagine (Asn) without any exogenous directing group. Thereby, site-selective arylations of C(sp³)–H bonds at the N-terminus of di-, tri-, and tetrapeptides have been achieved. Likewise, we have constructed a key building block for accessing agouti-related protein (AGRP) active loop analogues in a concise manner.

An efficient method for peptide late-stage C(sp³)-H arylations assisted by unmodified side chain of asparagine (Asn) without any exogenous directing group has been reported.     

Preparation of a molecularly imprinted polymer for the solid-phase extraction of scopolamine with hyoscyamine as a dummy template molecule

Molecularly imprinted polymers (MIPs) selective for scopolamine were produced using hyoscyamine (a close structural analogue) as template molecule. The produced polymers were used as media for solid-phase extraction, exhibiting selective binding properties for the analyte from biological samples. Human and calf urine and serum were processed on the MIP under various extraction protocols. The best performance was observed after loading the analyte in aqueous environment facilitating retention on the MIP by non-selective hydrophobic interactions. The MIPs were subsequently washed using an optimised solvent system to enable selective desorption of the analyte. Other related and non-related compounds were accessed to evaluate molecular recognition properties. Recoveries of up to 79% were achieved for the analyte of interest from biological samples.     

A statistical model of free-radical copolymerization/crosslinking reactions

A statistical model for network formation by the free-radical copolymerization and crosslinking reaction with small crosslinker content is used to obtain expressions for structural averages as a function of reaction parameters. The analysis accounts for reaction features that are characteristic of free-radical mechanisms and can be adapted to include cyclization, various modes of termination, and the gel effect. Profiles for structural averages such as the weight average molecular weight, the sol weight fraction, the molecular weight between crosslinks, and the number of elastically active network chains are obtained as functions of conversion.     

Enantioselective synthesis of an aziridinomitosane and selective functionalizations of a key intermediate

An enantioselective synthesis of mitosane core (-)-1 has been achieved. Key steps include a rapid assembly of a key eight-membered-ring intermediate employing ring-closing metathesis. Kinetic resolution of an advanced secondary alcohol was then accomplished by using a peptide-based asymmetric acyl transfer catalyst that was discovered from a parallel screen of catalyst candidates. Optically pure material was then converted to the mitosane core, which was the subject of additional studies on the selective modification to produce several substituted compounds containing a mitosane ring system.     

Preparations and spectroscopic studies of organotin complexes of diclofenac

The reactions of the potent and widely used anti-inflammatory drug diclofenac, HL, with diorganotin(IV) oxides were studied. The dimeric tetraorganodistannoxane complexes [Me(2)LSnOSnLMe(2)](2), [Bu(2)LSnOSnLBu(2)](2), [Ph(2)LSnOSnLPh(2)](2) and the dibutyltin complex [Bu(2)SnL(2)], have been prepared and structurally characterized in the solid state by means of vibrational and 119Sn M?ssbauer spectroscopy. Determination of lattice dynamics by temperature-dependent 119Sn M?ssbauer spectroscopy. From the variable-temperature M?ssbauer effect, the Debye temperature was determined. The complexes have been characterized in solution by NMR (1H and 13C) spectroscopy. Vibrational, M?ssbauer, and NMR data are discussed in terms of the proposed structures.     

New gas chromatographic instrumentation for studying the action of sulfur dioxide on marbles

Reversed-flow gas chromatography, which is a sub-technique of inverse gas chromatography, is an experimental arrangement simulating a simple model for the action of air pollutants on buildings and monuments, in laboratory scale. By using a commercial gas chromatograph and an appropriate mathematical analysis, kinetic parameters such as rate constants for adsorption k1, adsorption/desorption kR and surface reaction k2, as well as surface diffusion coefficients Dgamma, deposition velocities Vd and reaction probabilities gamma of SO2 on marble surfaces at different temperatures (303.15-353.15 K) in the presence or in the absence of protective materials (an acrylic copolymer, Paraloid B-72 or a siloxane, CTS Silo 111) were calculated. From the above mentioned physicochemical quantities the ability of the examined materials to minimize the dry deposition of SO2 on marble is carrying out and a possible mechanism for the interaction between SO2 and Paraloid B-72 was suggested. Both materials (CTS SILO 111 and Paraloid B-72) are good enough for protecting marble against SO2 at low temperatures (303.15-323.15), while at high temperatures (333.15-353.15), siloxane seems to protect marble better than acrylic copolymer.     

Polycondensation of mono- and difunctional derivatives of p-xylene

A new method for the production of polydimethylbenzylenes,$ \rlap{--} [{\rm C}_6 {\rm H}_4 ({\rm CH})_2 {\rm CH}_{\rm 2} \rlap{--} ]_n $, involves the polycondensation of the mono- and dichloromethyl and mono- and diacetoxymethyl derivatives of p-xylene via an acid-catalyzed reaction in anhydrous acetic acid. The reaction of the difunctional derivatives is slower than the reaction of the monofunctional ones, leading to linear, predominantly crystalline, high-melting polymers with molecular weights of 2000–3000. Polycondensation of both monomers under different feed ratios leads to polymers with the same structure, and the monofunctional monomers condense with themselves more favorably than with the difunctional ones. Thus a head-to-head structure is preferred, and crystalline polymers of high structural purity are obtained.     

Visualizing defects and pore connectivity within metal–organic frameworks by X-ray transmission tomography

Metal–Organic Frameworks (MOFs) have the potential to change the landscape of molecular separations in chemical processes owing to their ability of selectively binding molecules. Their molecular sorting properties generally rely on the micro- and meso-pore structure, as well as on the presence of coordinatively unsaturated sites that interact with the different chemical species present in the feed. In this work, we show a first-of-its-kind tomographic imaging of the crystal morphology of a metal–organic framework by means of transmission X-ray microscopy (TXM), including a detailed data reconstruction and processing approach. Corroboration with Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) images shows the potential of this strategy for further (non-destructively) assessing the inner architecture of MOF crystals. By doing this, we have unraveled the presence of large voids in the internal structure of a MIL-47(V) crystal, which are typically thought of as rather homogeneous lattices. This challenges the established opinion that hydrothermal syntheses yield relatively defect-free material and sheds further light on the internal morphology of crystals.

TXM-tomography unraveled large macropore defects within a MIL-47(V) MOF crystal. These pores do not seem to be well connected and they show a preferential orientation.     

Radon—Nikodym theorems for multimeasures and transition multimeasures

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Research supported by N. S. F. Grant DMS-8802688.     

Probability and expectation inequalities

Summary This paper introduces a mathematical framework within which a wide variety of known and new inequalities can be viewed from a common perspective. Probability and expectation inequalities of the following types are considered: (a)P(ZA) P(ZA) for some class of setsA, (b)k(Z)k(Z) for some class of functionsk, and (c)l(Z)k(Z) for some class of pairs of functionsl andk. It is shown, sometimes using explicit constructions ofZ andZ, that, in several cases, (a) (b) (c); included here are cases of normal and elliptically contoured distributions. A case where (a) (b) (c) is studied and is expressed in terms ofn monotone functions for (some of) which integral representations are obtained. Also, necessary and sufficient conditions for (c) are given.Research supported by the Air Force Office of Scientific Research under Grants AFOSR-75-2796 and AFOSR-80-0080Research supported by the National Science Foundation under Grants MCS78-01240 and MCS81-00748