Pairs Of Functional Groups Research Articles

Comparative Study of Bis-Schiff Case Containing Conjugated Oligomers Based on Phosphate and Silane Moieties: Investigation of Photophysical and Thermal Properties.

Oligo(azomethine)s bearing phosphate and silane moieties were the subject of an investigation within this study. The initial stage involved the synthesis of two Schiff base monomers, denoted as SCH-1 and SCH-2 (SCHs), each possessing a pair of hydroxyl functional groups. This was achieved through a loss of water between the aldehyde and diamine precursors. Subsequently, the Schiff base entities were subjected to oligomerization through HCl-mediated elimination due to the interaction between the hydroxyl groups of the Schiff bases and the chlorine moieties of dichlorodiethylsilane (Si) or phenyl dichlorophosphate (P). This procedure yielded distinct P-oligo(azomethine) (P1-P, P2-P) and Si-oligo(azomethine) (P1-Si and P2-Si) structures corresponding to each precursor. The molecular structures of the synthesized Schiff base monomers and oligo(azomethine)s were elucidated employing Fourier transform infrared, 1H NMR, and 13C NMR techniques. Thermal properties of the resulting products were assessed by utilizing thermogravimetric analysis (TG-DTG/DTA and DSC) techniques. Scanning electron microscopy (SEM) was employed to acquire high-resolution images and detailed surface information on the samples. Additionally, X-ray diffraction was employed to analyze the phase properties of the solid samples. Furthermore, the optical band gap (E g) values of the resulting P-oligo(azomethine)s and Si-oligo(azomethine)s were determined utilizing UV-vis spectrophotometer. The relatively low band gap values exhibited by the synthesized oligo(azomethine)s were indicative of their potential suitability as semiconductive materials in the realm of electronic and optoelectronic device fabrication. Photoluminescence (PL) measurements disclosed a green emission profile upon excitation by blue light. The oligo(azomethine)s incorporating methoxy groups demonstrated a red shift in comparison to their counterparts with methyl groups. Remarkably, no discernible fluctuations in fluorescence were observed over a 3600 s interval under consistent conditions. This observation underscored the inherent stability of the PL emission across the spectral range of exciting light. Thermal analyses unveiled high thermal stability of the synthesized oligo(azomethine)s, sustaining their structural integrity up to 220 °C. The char % of P-oligo(azomethine)s and Si-oligo(azomethine)s were observed to fall within the range of 29.45-55.47% at 1000 °C. SEM images revealed the absence of pores on the surface of P2-Si, which exhibited the highest limiting oxygen index and thermal heat release index (T HRI) values.

Efficient and Stable Mesoporous CsSnI3 Perovskite Solar Cells via Imidazolium‐Based Ionic Liquid Additive

Inorganic tin halide perovskite compound with its eco‐friendly property has attracted tremendous attention of researchers in the field of lead‐free perovskite solar cells. However, the trap‐assisted nonradiative recombination caused by deep‐level defects originating from surface undercoordinated Sn2+ cations significantly deteriorates the CsSnI3 device's performance. Herein, adding low concentrations of an ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EMIMAc) shows promise in controlling deep‐level defects in CsSnI3 perovskites. Both experimental observation and theoretical simulation reveal that EMIMAc can have strong electrostatic attraction and coordination interaction with the surface undercoordinated Sn2+ through the lone electron pairs of carboxyl functional groups and the donated π electrons from electron‐rich imidazole moieties, leading to a reduced deep‐level defect density and a restrained nonradiative recombination. Consequently, the processed CsSnI3 perovskite solar cells based on a printable fluorine‐doped tin oxide/compact‐TiO2/mesoporous‐TiO2/Al2O3/NiO/carbon framework achieve a power conversion efficiency as high as 8.54%, which is the champion efficiency among all the reported CsSnI3 mesoporous perovskite solar cells up to now. In addition, the unencapsulated devices have shown an impressive long‐term stability with only ≈6% efficiency degradation after over 2000 h aging under nitrogen atmosphere.

Boronic Acid Pairs for Sequential Bioconjugation.

Boronic acids can play diverse roles when applied in biological environments, and employing boronic acid structures in tandem could provide new tools for multifunctional probes. This Letter describes a pair of boronic acid functional groups, 2-nitro-arylboronic acid (NAB) and (E)-alkenylboronic acid (EAB), that enable sequential cross-coupling through stepwise nickel- and copper-catalyzed processes. The selective coupling of NAB groups enables the preparation of stapled peptides, protein-protein conjugates, and other bioconjugates.

Catalytic reductive desymmetrization of malonic esters.

Desymmetrization of fully substituted carbons with a pair of enantiotopic functional groups is a practical strategy for the synthesis of quaternary stereocentres, as it divides the tasks of enantioselection and C-C bond formation. The use of disubstituted malonic esters as the substrate of desymmetrization is particularly attractive, given their easy and modular preparation, as well as the high synthetic values of the chiral monoester products. Here, we report that a dinuclear zinc complex with a tetradentate ligand can selectively hydrosilylate one of the carbonyls of malonic esters to give α-quaternary β-hydroxyesters, providing a promising alternative to the desymmetric hydrolysis using carboxylesterases. The asymmetric reduction features excellent enantiocontrol that can differentiate sterically similar substituents and high chemoselectivity towards the diester motif of substrates. Together with the versatile preparation of malonic ester substrates and post-reduction derivatization, the desymmetric reduction has enabled the synthesis of a diverse array of quaternary stereocentres with distinct structural features.

IsoStar Program Suite for Studies of Noncovalent Interactions in Crystals of Chemical Compounds

Both Cambridge Crystallographic Data Centre (CCDC) and Protein Data Bank (PDB) provide unique opportunities for finding information about the structures of chemical and biochemical compounds in the solid state. The IsoStar—a knowledge-based library of intermolecular interactions—is a very powerful tool for automatic analysis of a large amount of data from these databases. The IsoStar program suite could help chemists in understanding of probability of occurrence (frequencies) and spatial characteristics (directionalities) of noncovalent contacts (including hydrogen, halogen, and chalcogen bonds, as well as interactions involving π-systems) between pairs of chemical functional groups; this web application may also be useful for crystal engineers, crystallographers, medicinal chemists, and researchers in fields of computational chemistry and molecular modeling.

Homogeneous Glycoconjugate Produced by Combined Unnatural Amino Acid Incorporation and Click-Chemistry for Vaccine Purposes.

Genetic code expansion is a powerful tool to introduce unnatural amino acids (UAAs) into proteins to modify their characteristics, to study or create new protein functions or to have access to protein conjugates. Stop codon suppression, in particular amber codon suppression, has emerged as the most popular method to genetically introduce UAAs at defined positions. This methodology is herein applied to the preparation of a carrier protein containing an UAA harboring a bioorthogonal functional group. This reactive handle can next be used to specifically and efficiently graft a synthetic oligosaccharide hapten to provide a homogeneous glycoconjugate vaccine. The protocol is limited to the synthesis of glycoconjugates in a 1:1 carbohydrate hapten/carrier protein ratio but amenable to numerous pairs of biorthogonal functional groups. Glycococonjugate vaccine homogeneity is an important criterion to ensure complete physico-chemical characterization, thereby, satisfying more and more demanding drug regulatory agency recommendations, a criterion which is unmet by classical conjugation strategies. Moreover, this protocol makes it possible to finely tune the structure of the actual conjugate vaccine, giving rise to tools to address structure-immunogenicity relationships.

Difunctionalization of Cyclopropyl Amines with N-Iodosuccinimide (NIS) or in Situ Formed Cyanogen Iodide (ICN).

We report herein a 1,3-difunctionalization of cyclopropylamines that serve as a π nucleophile in a two-electron (2e) SN2-like ring opening pathway. N-Iodosuccinimide (NIS) or in situ generated cyanogen iodide (ICN) is employed as electrophilic iodinating reagents in conjunction with TMSCN or succinimide to furnish multiple pairs of functional groups disposed in a 1,3-manner. This 2e ring opening manifold overcomes the constraint of our previously reported 1e protocol as demonstrated by successful activation of monocyclic tertiary cyclopropylamines.

Recent Advances in Bioorthogonal Click Chemistry for Efficient Synthesis of Radiotracers and Radiopharmaceuticals

In recent years, several catalyst-free site-specific reactions have been investigated for the efficient conjugation of biomolecules, nanomaterials, and living cells. Representative functional group pairs for these reactions include the following: (1) azide and cyclooctyne for strain-promoted cycloaddition reaction, (2) tetrazine and trans-alkene for inverse-electron-demand-Diels–Alder reaction, and (3) electrophilic heterocycles and cysteine for rapid condensation/addition reaction. Due to their excellent specificities and high reaction rates, these conjugation methods have been utilized for the labeling of radioisotopes (e.g., radiohalogens, radiometals) to various target molecules. The radiolabeled products prepared by these methods have been applied to preclinical research, such as in vivo molecular imaging, pharmacokinetic studies, and radiation therapy of cancer cells. In this review, we explain the basics of these chemical reactions and introduce their recent applications in the field of radiopharmacy and chemical biology. In addition, we discuss the significance, current challenges, and prospects of using bioorthogonal conjugation reactions.

Deformation modeling of polyamide 6 and the effect of water content using molecular dynamics simulation

Polyamide 6 (PA6) shows significant water absorbability and hygroscopicity, which affect its mechanical properties such as Young’s modulus and yield strength, as water content enhances deformability. This study aims to investigate the effect of water molecules on the deformation behavior of PA6 and to elucidate the deformation mechanism at a molecular level. By using excluded volume map sampling method, we explored the possible incursion sites for water molecule absorption in the computational material cell. Using molecular dynamic simulations, we created the computational cell of PA6, and we applied mechanical loadings with and without the water molecule to determine the effect of water molecules on the deformation behavior. To investigate the fundamental reasons why water molecules enhance the deformability of PA6, we calculated the non-bonded potential energy of a pair of amide functional groups with and without the water molecule. The results reveal that water molecules decrease the interaction energy of the amide group, leading to macroscopic deformation. This study clarified the effect of water molecules on the deformation behavior of PA6, and it may be useful for predicting the mechanical deformation of PA6.

Discovery of a pathway for terminal-alkyne amino acid biosynthesis.

Living systems can generate an enormous range of cellular functions, from mechanical infrastructure and signalling networks to enzymatic catalysis and information storage, using a notably limited set of chemical functional groups. This observation is especially notable when compared to the breadth of functional groups used as the basis for similar functions in synthetically derived small molecules and materials. The relatively small cross-section between biological and synthetic reactivity space forms the foundation for the development of bioorthogonal chemistry, in which the absence of a pair of reactive functional groups within the cell allows for a selective in situ reaction1-4. However, biologically 'rare' functional groups, such as the fluoro5, chloro6,7, bromo7,8, phosphonate9, enediyne10,11, cyano12, diazo13, alkene14 and alkyne15-17 groups, continue to be discovered in natural products made by plants, fungi and microorganisms, whichoffers a potential route to genetically encode the endogenous biosynthesis of bioorthogonal reagents within living organisms. In particular, the terminal alkyne has found broad utility via the Cu(I)-catalysed azide-alkyne cycloaddition 'click' reaction18. Here we report the discovery and characterization of a unique pathway to produce a terminal alkyne-containing amino acid in the bacterium Streptomyces cattleya. We found that L-lysine undergoes an unexpected reaction sequence that includes halogenation, oxidative C-C bond cleavage and triple bond formation through a putative allene intermediate. This pathway offers the potential for de novo cellular production of halo-, alkene- and alkyne-labelled proteins and natural products from glucose for a variety of downstream applications.

Click Chemistry in the Development of Contrast Agents for Magnetic Resonance Imaging.

Click chemistry provides fast, convenient, versatile, and reliable chemical reactions that take place between pairs of functional groups of small molecules that can be purified without chromatographic methods. Due to the fast kinetics and low or no elimination of byproducts, click chemistry is a promising approach that is rapidly gaining acceptance in drug discovery, radiochemistry, bioconjugation, and nanoscience applications. Increasing use of click chemistry in synthetic procedures or as a bioconjugation technique in diagnostic imaging is occurring because click reactions are fast, provide a quantitative yield, and produce a minimal amount of nontoxic byproducts. This review summarizes the recent application of click chemistry in magnetic resonance imaging and discusses the directions for applying novel click reactions and strategies for further improving magnetic resonance imaging performance.

Synthesis and characterization of bifunctional surfaces with tunable functional group pairs

Grafting of pairs of functional groups onto a silica surface was demonstrated by tethering both terminals of an organochlorosilane precursor molecule, Cl2(CH3)Si(CH2)4(CO)(OSi(i-Pr)2)(CH2)2Si(CH3)Cl2, that possess a cleavable silyl ester bond, onto a silica surface. Hydrolytic cleavage of the silyl ester bond of the grafted molecule resulted in the generation of organized pairs of carboxylic acid and organosilanol groups. This organosilanol moiety was easily transformed into other functional groups through condensation reactions to form, together with the neighboring acid group, pairs such as carboxylic acid/secondary amine, carboxylic acid/pyridine, and carboxylic acid/phosphine. In the case of carboxylic acid/amine pairing, there was evidence of the formation of amide. A sample grafted with amine–carboxylic acid pairs was three times more active (per free amine) than a sample without such pairs for the nitroaldol condensation of 4-nitrobenzaldehyde and nitromethane.

Big data reduction by fitting mathematical functions: A search for appropriate functions to fit Ramachandran surfaces

The potential energy surface associated with internal rotation of a pair of geminal functional groups was studied using electron structure calculations. The functional groups were attached to a methylene carbon and were chosen as saturated hydrocarbons, unsaturated hydrocarbons and heteroatom containing moieties like amide bonds in various orientations. For the majority of the studied compounds extended Fourier expansions, augmented with Gaussian functions were needed to achieve accuracy within a few kJ/mol. The present letter aims to take the first steps of a bottom up solution for protein folding by finding the functions of small peptide residues.

Chemical Assignment of Symmetry-Adapted Perturbation Theory Interaction Energy Components: The Functional-Group SAPT Partition.

Recently, we introduced an effective atom-pairwise partition of the many-body symmetry-adapted perturbation theory (SAPT) interaction energy decomposition, producing a method known as atomic SAPT (A-SAPT) [Parrish, R. M.; Sherrill, C. D. J. Chem. Phys. 2014, 141, 044115]. A-SAPT provides ab initio atom-pair potentials for force field development and also automatic visualizations of the spatial contributions of noncovalent interactions, but often has difficulty producing chemically useful partitions of the electrostatic energy, due to the buildup of oscillating partial charges on adjacent functional groups. In this work, we substitute chemical functional groups in place of atoms as the relevant local quasiparticles in the partition, resulting in a functional-group-pairwise partition denoted as functional-group SAPT (F-SAPT). F-SAPT assigns integral sets of local occupied electronic orbitals and protons to chemical functional groups and linking σ bonds. Link-bond contributions can be further assigned to chemical functional groups to simplify the analysis. This approach yields a SAPT partition between pairs of functional groups with integral charge (usually neutral), preventing oscillations in the electrostatic partition. F-SAPT qualitatively matches chemical intuition and the cut-and-cap fragmentation technique but additionally yields the quantitative many-body SAPT interaction energy. The conceptual simplicity, chemical utility, and computational efficiency of F-SAPT is demonstrated in the context of phenol dimer, proflavine(+)-DNA intercalation, and a cucurbituril host-guest inclusion complex.

The finite-size effect on the transport properties in edge-modified graphene nanoribbon-based molecular devices

The size-dependence on the electronic and transport properties of the molecular devices of the edge-modified graphene nanoribbon (GNR) slices is investigated using density-functional theory and Green's function theory. Two edge-modifying functional group pairs are considered. Energy gap is found in all the GNR slices. The gap shows an exponential decrease with increasing the slice size of two vertical orientations in the two edge terminated cases, respectively. The tunneling probability and the number of conducting channel decreases with increasing the GNR-slices size in the junctions. The results indicate that the acceptor-donor pair edge modulation can improve the quantum conductance and decrease the finite-size effect on the transmission capability of the GNR slice-based molecular devices.

Metal-Free Sequential [3 + 2]-Dipolar Cycloadditions using Cyclooctynes and 1,3-Dipoles of Different Reactivity

Although metal-free cycloadditions of cyclooctynes and azides to give stable 1,2,3-triazoles have found wide utility in chemical biology and material sciences, there is an urgent need for faster and more versatile bioorthogonal reactions. We have found that nitrile oxides and diazocarbonyl derivatives undergo facile 1,3-dipolar cycloadditions with cyclooctynes. Cycloadditions with diazocarbonyl derivatives exhibited similar kinetics as compared to azides, whereas the reaction rates of cycloadditions with nitrile oxides were much faster. Nitrile oxides could conveniently be prepared by direct oxidation of the corresponding oximes with BAIB, and these conditions made it possible to perform oxime formation, oxidation, and cycloaddition as a one-pot procedure. The methodology was employed to functionalize the anomeric center of carbohydrates with various tags. Furthermore, oximes and azides provide an orthogonal pair of functional groups for sequential metal-free click reactions, and this feature makes it possible to multifunctionalize biomolecules and materials by a simple synthetic procedure that does not require toxic metal catalysts.

Transport properties of graphene nanoribbon‐based molecular devices

The electronic and transport properties of an edge-modified prototype graphene nanoribbon (GNR) slice are investigated using density functional theory and Green's function theory. Two decorating functional group pairs are considered, such as hydrogen-hydrogen and NH(2)-NO(2) with NO(2) and NH(2) serving as a donor and an acceptor, respectively. The molecular junctions consist of carbon-based GNR slices sandwiched between Au electrodes. Nonlinear I-V curves and quantum conductance have been found in all the junctions. With increasing the source-drain bias, the enhancement of conductance is quantized. Several key factors determining the transport properties such as the electron transmission probabilities, the density of states, and the component of Frontier molecular orbitals have been discussed in detail. It has been shown that the transport properties are sensitive to the edge type of carbon atoms. We have also found that the accepter-donor functional pairs can cause orders of magnitude changes of the conductance in the junctions.

Near-IR electromer emission from new ambipolar carbazole containing phosphorescent dendrimer based organic light emitting diode

The solution process is more suitable for large-sized OLED in terms of small material usage and no need for fine mask patterning technique. Among soluble materials, dendrimers are acknowledged as a new class of emissive OLED materials that can carry both the emissive chromophore and the charge transporting moiety simultaneously. Here, we report on a new Ir(III)-based dendrimer and an efficient single emission layer OLED device by spin-coating the dendrimer itself on PEDOT:PSS polymer. This dendrimer carries a pair of carbazole functional groups on the pyridine side and a fluorinated phenyl on the other side of the Ir(ppy) 3 ligand. The latter functional group acts as an electron transporting material and the former as a host and hole-transporting material. The dendrimer device has a green emission at 540 nm with current efficiency as high as 25 Cd/A. Interestingly, we have found that the two neighboring carbazole form the electromer under the applied electrical current and, thus, that the EL device shows new near-IR emission over 720 nm.

Heterobifunctional isotope‐labeled amine‐reactive photo‐cross‐linker for structural investigation of proteins by matrix‐assisted laser desorption/ionization tandem time‐of‐flight and electrospray ionization LTQ‐Orbitrap mass spectrometry

Chemical cross-linking combined with a subsequent enzymatic digestion and mass spectrometric analysis of the created cross-linked products presents an alternative approach to assess low-resolution protein structures. By covalently connecting pairs of functional groups within a protein or a protein complex a set of structurally defined interactions is built up. We synthesized the heterobifunctional amine-reactive photo-cross-linker N-succinimidyl p-benzoyldihydrocinnamate as a non-deuterated (SBC) and doubly deuterated derivative (SBDC). Applying a 1:1 mixture of SBC and SBDC for cross-linking experiments aided the identification of cross-linked amino acids in the mass spectra based on the characteristic isotope patterns of fragment ions. The cross-linker was applied to the calcium-binding protein calmodulin with a subsequent analysis of cross-linked products by nano-high-performance liquid chromatography matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (nano-HPLC/MALDI-TOF/TOF-MS) and nano-HPLC/nano-electrospray ionization (ESI)-LTQ-Orbitrap-MS.

Higher-Order Genomic Organization of Cellular Functions in Yeast

Previous studies have shown that the distribution of genes in prokaryotes and eukaryotic genomes is not random. Using the thousands of cellular functions that appear in the Gene Ontology (GO) project, we exhaustively studied the relation between functionality and genomic localization of genes across 16 organisms with rich GO ontologies (one prokaryote and 15 eukaryotes). Overall, we found that the genomic distribution of cellular functions tends to be more similar in organisms that have higher evolutionary proximity. At the primary level, which measures localization of functionally related genes, the prokaryote Escherichia coli exhibits the highest level of organization, as one would expect given its operon-based genomic organization. However, examining a higher level of genomic organization by analyzing the co-localization of pairs of different functional gene groups, we surprisingly find that the eukaryote yeast Saccharomyces cerevisiae is markedly more organized than E. coli. A network-based analysis further supports this notion and suggests that the eukaryotic genomic architecture is more organized than previously thought. See online Supplementary Material at (www.liebertonline.com).