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Cyclisation of peptides by forming thioether (lanthionine), disulfide (cystine) or methylene thioacetal bridges between side chains is established as an important tool to stabilise a given structure, enhance metabolic stability and optimise both potency and selectivity. However, a systematic comparative study of the effects of differing bridging modalities on peptide conformation has not previously been carried out. In this paper, we have used the NMR deconvolution algorithm, NAMFIS, to determine the conformational ensembles, in aqueous solution, of three cyclic analogues of angiotensin(1–7), incorporating either disulfide, or non‐reducible thioether or methylene thioacetal bridges. We demonstrate that the major solution conformations are conserved between the different bridged peptides, but the distribution of conformations differs appreciably. This suggests that subtle differences in ring size and bridging structure can be exploited to fine‐tune the conformational properties of cyclic peptides, which may modulate their bioactivities. [ABSTRACT FROM AUTHOR]

The conformational preferences of N‐((6‐methylpyridin‐2‐yl)carbamothioyl)benzamide were studied in solution, the gas phase and the solid state via a combination of NMR, density functional theory (DFT) and single crystal X‐ray techniques. This acyl thiourea derivative can adopt two classes of low energy conformation, each stabilized by a different 6‐membered intramolecular hydrogen bond (IHB) pseudoring. Analysis in different solvents revealed that the conformational preference of this molecule is polarity dependent, with increasingly polar environments yielding a higher proportion of the minor conformer containing an NH⋅⋅⋅N IHB. The calculated barrier to interconversion is consistent with dynamic behaviour at room temperature, despite the propensity of 6‐membered IHB pseudorings to be static. This work demonstrates that introducing competitive IHB pathways can render static IHBs more dynamic and that such systems could have potential as chameleons in drug design. [ABSTRACT FROM AUTHOR]

Different molecular balances were designed previously to compare noncovalent interactions. However, some balances are difficult to synthesise and there is a need for developing a computational approach. In this work, we probe noncovalent interactions of π systems using DFT methods to assess their reliability in reproducing experimentally measured conformer populations. Based on our results, the PW6B95D3 functional performed best, followed by M11L and ωB97XD. Additionally, the simulation of the rotation of the hydroxyl group revealed stabilising OH⋯Alkyne and OH⋯Nitrile interactions that are difficult to identify experimentally. These methods were then applied to compare the strengths of sulfur⋯π interactions in molecules which have not been explored experimentally. Compared to the hydroxyl counterpart, the simulation of the thiol group rotation showed that the geometry of the conformer with the two sulfur lone pairs oriented towards the aromatic ring or the double bond is stabilised, suggesting that S(LP)⋯π interactions can be attractive in nature. The ability of sulfur to rearrange its electronic surrounding to form an attractive interaction with π systems, including those with either electron‐donating or withdrawing groups, was also confirmed. Overall, the results show a promising future for both qualitative and quantitative assessments of the strengths of noncovalent interactions using selected DFT techniques. [ABSTRACT FROM AUTHOR]

Solid-State (super 13)C NMR and (super 2)H NMR techniques are used to investigate structural and dynamic properties of hydrogen-bonded complexes or sheets, inclusion compound and pure crystalline phase of urea. Ribbons of urea molecules alternating with ribbons of alpha,omega-dicyanoalkane molecules are present within each sheet.

The synthetic approaches to ureidopyrimidinones possessing p-aminophenyl groups at C-6, and an alkyl or hydrophilic side chain at R(sub 2), as well as an azo-derivative, are described. The studies investigating the tautomeric distributions of the compounds prepared are also presented.

Herein we report a fundamental discovery on the use of tris(dialkylamino)phosphine reagents for peptide and protein modification. We discovered that C-terminal thiophosphonium species, which are uniquely stable, could be selectively and rapidly generated from their disulfide counterparts. In sharp and direct contrast, internal thiophosphonium species rapidly degrade to dehydroalanine. We demonstrate this remarkable chemoselectivity on a bis-cysteine model peptide, and the formation of a stable C-terminal-thiophosphonium adduct on an antibody fragment, as well as characterise the species in various small molecule/peptide studies. [ABSTRACT FROM AUTHOR]

Dynamic properties of the hydroxyl groups in a selectively deuterated sample of triphenylsilanol (Ph3SiOD) are studied using variable-temperature solid-state (super 2)H NMR spectroscopy. The crystal structure of triphenylsilanol contains eight crystallographically independent molecules, which are arranged in two tetrameric building units.

The spontaneous dissolution of 2D polytriazine imide (PTI) carbon nitrides in certain solvents diverges dramatically from the inherent insolubility of other 2D materials such as graphene. Here, the mechanism of dissolution and underlying factors which govern PTI solubility are probed, uncovering a complex and adaptable system. At high concentrations, multi-layered species are co-dissolved, and these solubilised stacks may be further exfoliated to few- or single-layer species with the addition of water. While the PTI sheets are fundamentally soluble, the presence of intercalated lithium salts increases yield and improves the degree of exfoliation, with lithium cations adsorbed on the solvated PTI layers. The tuneable degree of delamination modifies the solutions' photoluminescent properties, which may be trapped in a solid phase following vitrification of the solvent. [ABSTRACT FROM AUTHOR]

The palladium‐catalysed sp3 C−H arylation of a selection of saturated amine scaffolds was investigated using substituted picolinamide directing groups. On the bornylamine scaffold, highly selective monoarylation takes place using unsubstituted picolinamide or 3‐methylpicolinamide, whereas a double C−H arylation occurs with other substituents present, becoming a significant product with 3‐trifluoromethylpicolinamide. DFT calculations were used to help rationalise the effect of directing groups on the C−H palladation steps which were found experimentally to be irreversible. The substituted picolinamide directing groups were also examined on acyclic amine scaffolds and in many cases increased yields and selectivity could be obtained using methylpicolinamides. For a selection of other amine scaffolds, the yield of C−H arylation could be improved significantly using 3‐methylpicolinamide as the directing group and/or 3‐methylpentan‐3‐ol as the solvent [ABSTRACT FROM AUTHOR]

Herein we report a retro-Michael deconjugation pathway of thiol–pyridazinedione linked protein bioconjugates to provide a novel cleavable linker technology. We demonstrate that the novel pyridazinedione linker does not suffer from off-target modification with blood thiols (e.g., glutathione, human serum albumin (HSA)), which is in sharp contrast to an analogous maleimide linker. [ABSTRACT FROM AUTHOR]

The results of the ring conformational analysis of various L-prolines in water are reported. The prolines are found to have two distinct forms of zwitterionic L-proline.

A new quadruple hydrogen bonding module based on an ureido-substituted cytosine moiety is described. It was found that the cytosine module described is capable of forming strong quadruple hydrogen bonding and has potential for the construction of supramolecular arrays.

Herein, various molecular balances used for comparing the strengths of intramolecular noncovalent interactions are reviewed. Our overview indicates that considerable quantitative insight into the strength of noncovalent interactions can be gained through the careful design of molecular balances. Many exciting opportunities certainly exist for the design of further new balances to quantify and dissect the relative strengths of noncovalent interactions as a function of solvation and the importance of the many factors that contribute to overall molecular recognition. However, even simple model molecules can show a multiplicity of intramolecular noncovalent interactions acting in a combined fashion. It is therefore essential to undertake a detailed computational analysis to identify all possible noncovalent interactions present in a selected molecular balance prior to a quantitative experimental assessment of the strength of a particular noncovalent interaction. It is also argued that the words "torsion" and "molecular balance" seem to have become inextricably linked and, in consequence, even top pan and seesaw balances have been mistakenly referred to in these terms. [ABSTRACT FROM AUTHOR]

Investigates on the dynamic attributes of dioctanoyl peroxide guest molecules in the urea tunnel using the incoherent quasielastic neutron scattering (IQNS) and nuclear magnetic resonance (NMR). Benefits of the application of both techniques for monitoring motion at different time scales; Caliber of IQNS and NMR; Importance of both IQNS and NMR.

In this paper we outline how dihalohydration reactions of propargylic alcohols can be used to access a wide variety of useful halogenated building blocks. A novel procedure for dibromohydration of alkynes has been developed, and a selection of dichloro and dibromo diols and cyclic ethers were synthesized. The dihalohydration of homo‐propargylic alcohols provides a useful route to 3‐halofurans, which were shown to readily undergo cycloaddition reactions under mild conditions. Finally, a novel ring expansion of propargylic alcohols containing a cyclopropylalkyne provides access to halogenated alkenylcyclobutanes. [ABSTRACT FROM AUTHOR]

Abstract: The relative strength of noncovalent interactions between a thioether sulfur atom and various π systems in designed top pan molecular balances was determined by NMR spectroscopy. Compared to its oxygen counterpart, the sulfur atom displays a remarkable ability to interact with almost equal facility over the entire range of π systems studied, with the simple alkene emerging as the most powerful partner. With the exception of the O⋅⋅⋅heteroarene interaction, all noncovalent interactions of sulfur with π systems are favoured over oxygen. [ABSTRACT FROM AUTHOR]

The combustion of mercury(II) thiocyanate to form 'Pharaoh's serpents' is a spectacular reaction first described nearly two centuries ago. The large volume of distinctive yellow branches that grow from a tiny quantity of flaming reactants makes this an enchanting demonstration, often used to depict the magic of chemistry. In recent years several videos of this bizarre process have 'gone viral' online. Formally, the reaction should yield a carbon nitride with the ideal formula C3N4 along with HgS. However, since early characterization attempts there has been little further study of the materials produced. Herein we apply modern characterization techniques to reinvestigate the nature of the carbon nitride and its intimate relationship to the HgS produced. The HgS phase forms nanoparticles that decorate the surfaces of a C3N4 foam matrix. Both of these compounds are important wide-gap semiconductors and we propose that the 'Pharaoh's serpents reaction' could be used to produce a potentially important heterojunction nanocomposite materials that could be useful optoelectronic and photocatalytic applications. [ABSTRACT FROM AUTHOR]

ABSTRACT The use of biomass-sourced chemical feedstocks creates a conflict over land use between food and fuel/chemical production. Such conflict could be reduced by making use of the annual 1.3 Pg food waste resource. Oleic acid is available from seed oils such as pumpkin, grape, avocado and mango. Its esterification with diols 1,3-propanediol, resorcinol and orcinol was used to form diesters and the naturally occurring norspermidine was used to prepare a diamide, all under ambient conditions. These compounds were then epoxidized and polymerized. When esterification was followed by epoxidation and subsequent curing at elevated temperature with p-phenylenediamine or diethylenetriamine, hard insoluble resins were formed. When the sequence was changed such that the epoxidized oleic acid was first reacted with cis-1,2-cyclohexanedicarboxylic anhydride and then esterified with orcinol and resorcinol, insoluble crosslinked polymers were also obtained. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3159-3170 [ABSTRACT FROM AUTHOR]

Correction for 'Use of pyridazinediones as extracellular cleavable linkers through reversible cysteine conjugation' by Calise Bahou et al., Chem. Commun., 2019, 55, 14829–14832, https://doi.org/10.1039/C9CC08362F. [ABSTRACT FROM AUTHOR]

The Abraham solute hydrogen bond acidity parameter A can be derived both from physical methods, A(Gen) and NMR experiments, A(NMR) and results for a large number of hydroxylic solutes show that the two methods agreed very well. However for halophenols the values of A(NMR) were not consistent with the A(Gen) values. The values of A(NMR) suggest that there is no intra-molecular hydrogen bonding in any of the 2-halophenols. In contrast the values of A(Gen) indicate that there is no intra-molecular hydrogen bonding in 2-fluorophenol, but weak intra-molecular hydrogen bonding in 2-chloro, 2-bromo, and 2-iodo-phenol. In view of this uncertainty in the presence or absence of intra-molecular H-bonds in the 2-halophenols, a detailed investigation of the methods used in the literature is presented together with a novel NMR method to determine the ratio of cis and trans forms in these compounds. The experimental data is complemented by a detailed theoretical analysis of the structures and bonding in these molecules to assess the presence or absence of an intra-molecular H-bond. We conclude that there is weak hydrogen bonding in 2-chloro, 2-bromo and 2-iodophenol but very little in 2-fluorophenol. [ABSTRACT FROM AUTHOR]

Compounds that comprise the erythrina alkaloid class of natural products are based on a tetracyclic spiroamine framework and exhibit a range of biological activities on the central nervous system. Herein, we report a new and efficient total synthesis of this multiple-ring system based on an intramolecular acylal cyclisation (IAC) approach. Using this methodology, the tetracyclic core was rapidly assembled over a two-step domino process catalysed by a Lewis acid. The effect of heteroatoms, substituents and ring size on the IAC has also been investigated, and the broad application of this procedure is demonstrated by the synthesis of a library of derivatives in good yields with excellent regioselectivity. [ABSTRACT FROM AUTHOR]

A comparative study using NMR spectroscopy and designed top-pan molecular balances demonstrates that the noncovalent interaction of a hydroxy group with p-deficient pyrazine and quinoxaline units involves a lone pair-heteroarene interaction which is much stronger and solvent independent when measured relative to the classical p-facial hydrogen bond to a benzene ring. Alkyl fluorides also prefer the heteroarene rings over the benzene ring. The attractive interaction between a quinoxaline and a terminal alkyne is also stronger than the intramolecular hydrogen bond to an arene. [ABSTRACT FROM AUTHOR]

A comparative study of molecular balances by NMR spectroscopy indicates that noncovalent functional-group interactions with an arene dominate over those with an alkene, and that a π-facial intramolecular hydrogen bond from a hydroxy group to an arene is favored by approximately 1.2 kJ mol−1. The strongest interaction observed in this study was with the cyano group. Analysis of the series of groups CH2CH3, CHCH2, CCH, and CN shows a correlation between conformational free-energy differences and the calculated charge on the Cα atom of these substituents, which is indicative of the electrostatic nature of their π interactions. Changes in the free-energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter β. [ABSTRACT FROM AUTHOR]