Acceptor Carbonyl Group Research Articles

Design of High-Performance Inorganic-Organic Hybrid Nonlinear Optical Materials Using Superhalogen Al13 and Dianhydrides.

Novel inorganic-organic hybrid complexes Al13-X (X represents the dianhydrides PMDA, NTCDA, and PTCDA) are theoretically designed and studied using density functional theory (DFT) and time-dependent DFT. These conjugated dianhydrides containing four acceptor carbonyl groups are commonly used as electron acceptor materials. These compounds possess large binding energies, reflecting the sufficient binding of Al13 to the dianhydride molecule. The binding nature of the complexes is of charge transfer type, i.e., electrons are transferred from the aluminum cluster to the dianhydride. All of the aimed complexes have large mean polarizability (α0) and first hyperpolarizability (β0). The β0 values are explained on the basis of electronic transitions in crucial excited states using the TD-DFT method. Additionally, the hole-electron distribution was analyzed, revealing the nature of electronic excitation. Absorption spectra analysis shows that these complexes have an excellent infrared (IR) transparent region (1000-5000 nm). Therefore, these inorganic-organic hybrid complexes with high stability can be considered as potential candidates for new IR nonlinear optical molecules.

Mechano-responsive D–A luminogen based on bisarylic methanone derivative with brightly tricolored mechanochromic luminescence

A new luminogen PTZ-BZ-DBF bearing an electron donor phenothiazine unit and an electron acceptor carbonyl group is designed and synthesized. This molecule adopts highly twisted molecular conformation and exhibits intramolecular charge transfer (ICT), effective solid-state luminescence, and high contrast mechanofluorochromic (MFC) properties. The as-prepared powders show bright yellow-green fluorescence. Under conditions of external mechanical stimulation, the color changes to bright orange-red, and a red shift of 87 nm is observed in the emission spectral profile. Meanwhile, the solid-state luminescence efficiency increases from 20.5% to 28.5%. It is different from general MFC materials, when fumed using DCM vapor or annealed at 150 °C, the fluorescence peaks blue shift to approximately 560 nm, and the yellowish-emitting Y-powders are obtained. The ground solids and Y-powders can be converted to the as-prepared solid powders following the process of solvent recrystallization. Thus, tricolor switching is realized. The results obtained using the PXRD and DSC techniques indicate that the MFC phenomenon can be attributed to the process of crystalline-to-amorphous transition. The red shift of the PL spectra is attributed to the planar intramolecular charge transfer (PICT) process induced by conformational planarization in response to external forces.

Ultrafast nonadiabatic excited-state intramolecular proton transfer in 3-hydroxychromone: A surface hopping approach.

We employ the ab initio molecular dynamics within the surface hopping method to explore the excited-state intramolecular proton transfer taking place on the coupled "bright" S1 (ππ*) and "dark" S2 (nπ*) states of 3-hydroxychromone. The nonadiabatic population transfer between these states via an accessible conical intersection would open up multiple proton transfer pathways. Our findings reveal the keto tautomer formation via S1 on a timescale similar to the O-H in-plane vibrational period (<100fs). Structural analysis indicates that a few parameters of the five-membered proton transfer geometry that constitute the donor (hydroxyl) and acceptor (carbonyl) groups would be adequate to drive the enol to keto transformation. We also investigate the role of O-H in-plane and out-of-plane vibrational motions in the excited-state dynamics of 3-hydroxychromone.

Comparison of Drug Release and Adsorption under Supersaturating Conditions for Ordered Mesoporous Silica with Indomethacin or Indomethacin Methyl Ester.

Incomplete drug release from mesoporous silica systems has been observed in several studies. This work aims to increase the understanding of this phenomenon by investigating the mechanism of drug-silica interactions and adsorption behavior from supersaturated aqueous solutions of two similar drug molecules with different hydrogen bonding capabilities. Drug-silica interactions between indomethacin or its methyl ester and SBA-15 were investigated using spectroscopic techniques (infrared, fluorescence and X-ray photoelectron) and adsorption experiments. The results demonstrate that the predominant mechanism of interaction of both drugs with silica is hydrogen bonding between drug acceptor carbonyl groups with donor groups on the silica surface. The presence of a drug hydrogen bond donor group did not enhance drug adsorption. No evidence was obtained for drug adsorption through nonspecific hydrophobic interactions. Drug adsorption onto the silica surface was investigated under supersaturating conditions through the generation of adsorption isotherms. Similar adsorption isotherms were observed for each compound when the concentration scale was normalized to the drug amorphous solubility. In other words, the equilibrium between the drug adsorbed on the silica surface and free drug in solution was related to the drug activity in solution. The high tendency of the drug to adsorb when the solution is supersaturated was, in turn, found to limit the extent of drug release during dissolution under nonsink conditions. Thus, adsorption provides an explanation for incomplete drug release.

Heteroleptic palladium(II) complexes of dipyrrin-1,9-dione supported by intramolecular hydrogen bonding

The dipyrrin-1,9-dione framework, which is characteristic of the propentdyopent pigments deriving from heme metabolism, coordinates metal ions as monoanionic bidentate donors. The resulting analogs of dipyrrinato complexes undergo reversible ligand-based reductions, thus showcasing the ability of the dipyrrindione scaffold to act as an electron reservoir. Herein we report the synthesis and characterization of three heteroleptic palladium complexes of the redox-active dipyrrindione ligand. Primary amines were chosen as additional ligands so as to assemble complexes of planar geometries with complementary interligand hydrogen-bonding. Full chemical characterization confirms the hydrogen bonding interactions between the primary amine ligands and the acceptor carbonyl groups on the dipyrrolic ligand. The resulting heteroleptic compounds display reversible one-electron reduction events that are centered on the dipyrrindione ligand as revealed by voltammetry and spectroelectrochemistry data. Within these planar Pd(II) complexes, the propentdyopent motif therefore combines reversible ligand-based redox chemistry with interligand hydrogen bonding in the primary coordination sphere of the metal center.

Towards a Mechanistic Understanding of Factors Controlling the Stereoselectivity of Transketolase

AbstractA structural model for thiamine‐diphosphate (ThDP)‐dependent transketolase (TK) was developed to analyse the effect of amino acid exchanges on the stereoselectivity of this synthetically important class of enzymes. In this study the carboligation of 3‐hydroxypyruvate as a donor and propanal, as well as pentanal, was studied. Based on literature data and additional mutagenesis studies using E. coli TK, a four‐state model was developed to explain the stereoselectivity of TKs by the relative orientation of donor and acceptor substrates in the active site prior to C−C‐bond formation. To enable a functional comparison of relevant amino acids of TKs from different species, a standard numbering scheme was developed. Using this concept, H26, H261, and F434 were identified as the key residues which mediate stereoselectivity, where two main factors influenced the arrangement of ThDP‐bound donor and acceptor prior to carboligation: the relative orientation of the substrate side chains and the orientation of the acceptor carbonyl group towards the donor hydroxy group. This model provides a first framework to understand the structure‐function relationships of TKs with respect to their stereoselectivity.

Conformational studies of Gram-negative bacterial quorum sensing acyl homoserine lactone (AHL) molecules: The importance of the n → π* interaction

A 1H NMR study shows the presence of intermolecular hydrogen bonds for AHLs in CDCl3 solution. A detailed computational study of the structure of AHLs and the relative stability between the extended conformations (X) and those showing n → π* interactions (np) have been carried out by means of DFT calculations. Solvent effects have been shown to be very important when stabilising np conformations, particularly with polar solvents. This was shown by the shortening of C⋯O intramolecular distances and the increase in the relative energies favouring the np conformation with the dielectric constant of the solvent. The charge transfer between the O donor and the acceptor carbonyl group, assessed by second order perturbation energies, E(2), also shows an increase in the E(2) values with the dielectric constant of the solvent.

A Review on Perylene-3,4,9,10-Tetracarboxylic Acid Diimide Molecules

The aim of this article is to inform about perylene-3,4,9,10-tetracarboxylic acid dimide (PDI) derivatives. Also, it is to give short and simple information about optical properties and using fields. Perylene-3,4,9,10-tetracarboxylic acid dimide derivatives known as perylene diimides are material of highly conjugated molecule. PDIs exhibit strong absorptions within the range of 400-450 nm (B band) and 500-700 nm (Q band). Perylene diimide dyes show generally characteristic absorption peaks at 458, 490, 526 nm. These absorption peaks are matched by the corresponding emission peaks at 540, 576, 624 nm, respectively. It has donor core and acceptor carbonyl groups. Perylene dimide has good electron mobility, high fluorescence quantum yields, strong absorption in the visible region, photostability, thermal stability, good semi-conductivity. These properties benefit them application of electronic material. Applications of PDIs are in the field of photo-electronic material, dye lasers, organic light-emitting diodes, and chemosensing materials .

Effect of Donor-Acceptor Coupling on TICT Dynamics in the Excited States of Two Dimethylamine Substituted Chalcones.

Significant effect of coupling between the electron donor and acceptor groups in intramolecular charge transfer (ICT) dynamics has been demonstrated by comparing the photophysical properties of two isomeric N,N-dimethylaminochalcone derivatives (namely, DMAC-A and DMAC-B). In the case of the DMAC-B molecule, the distance between the donor (N,N-dimethylaniline or DMA) and the acceptor (carbonyl) groups is larger by one ethylene unit as compared to that in the case of DMAC-A. The excited singlet (S1) states of both the isomers have strong ICT character but their photophysical properties are remarkably different. In polar solvents, fluorescence quantum yields (and the lifetimes of the S1 state) of DMAC-A are more than 2 orders of magnitude lower (and shorter) than those of DMAC-B. Remarkable differences in the photophysical properties of these two isomers arise due to occurrence of the ultrafast twisting of the DMA group (or the TICT process) during the course of deactivation of the S1 state of the DMAC-A molecule, but not in the case of DMAC-B. In the later case, because of the presence of a large energy barrier along the twisting coordinate(s), TICT is not a feasible process, and hence, the S1 state of DMAC-B has the planar ICT structure. In the DMAC-A molecule, the strength of coupling between the donor and acceptor groups is relatively stronger because of a shorter distance between these groups. Femtosecond transient absorption spectroscopic measurements and DFT/TDDFT calculations have been adopted to establish the above aspects of the relaxation dynamics of the S1 states of these two isomeric chalcones.

Regulating Nucleation Kinetics through Molecular Interactions at the Polymer–Solute Interface

Heterogeneous nucleation is ubiquitous both in nature and in industrial practice; therefore, the ability to inhibit or enhance the kinetics of a crystallization process is essential in many scientific and technological areas. In order to better understand the role of surface functionality in regulating the nucleation rate, six commercially available polymers have been used as heteronucleants of acetaminophen (ACM) molecules: polydimethylsiloxane (PDMS) with siloxane functional groups Si–O–Si forming the backbone of silicones, partially fluorinated elastomer polyvinylidenedifluoride (PVDF), polystyrene (PS) having weak electron-donor phenyl rings, poly(n-buthyl methacrylate) (PnBMA) showing ester functionality, polyimide (PI) that includes both hydrogen-bond acceptor imide functionality and carbonyl groups, ethylene/acrylic acid (EAA) copolymer with carboxyl moiety. Experimental results from induction time statistics, van Oss–Chaudhury–Good model of surface energetics, and powder X-ray diffraction (PXRD) a...

An n→π* interaction reduces the electrophilicity of the acceptor carbonyl group

Carbonyl-carbonyl (C=O···C'=O') interactions are ubiquitous in both small and large molecular systems. This interaction involves delocalization of a lone pair (n) of a donor oxygen into the antibonding orbital (π*) of an acceptor carbonyl group. Analyses of high-resolution protein structures suggest that these carbonyl-carbonyl interactions prefer to occur in pairs, that is, one donor per acceptor. Here, the reluctance of the acceptor carbonyl group (C'=O') to engage in more than one n→π* electron delocalization is probed using imidazolidine-based model systems with one acceptor carbonyl group and two equivalent donor carbonyl groups. The data indicate that the electrophilicity of the acceptor carbonyl group is reduced when it engages in n→π* electron delocalization. This diminished electrophilicity discourages a second n→π* interaction with the acceptor carbonyl group.

Novel aminoimidazole derived proline organocatalysts for aldol reactions

A series of l-proline amides with 2-aminoimidazole have been synthesized and found to be highly efficient organocatalysts for aldol reactions when an appropriate acid was added to control and activate the acceptor carbonyl group. Under optimized reaction conditions, high yields (over 80%) and high selectivities (ee 98%, de 98/2) were obtained in intermolecular aldol reaction even with only 1 equiv of ketone. Likewise, these systems also can catalyze intramolecular aldol reactions with good results.

Heterolytic N–Cα Bond Cleavage in Electron Capture and Transfer Dissociation of Peptide Cations

Mass spectrometry techniques employing electron capture and electron transfer dissociation represent powerful approaches for the analysis of biological samples. Despite routine employment in analytical fields, the underlying physical processes dictating peptide fragmentation remain less understood. Among the most accepted mechanisms, the Cornell proposal of McLafferty postulates that the homolytic cleavage of N-C(α) bonds located in the peptide backbone occurs on the right (C-terminal) side of a hydrogen acceptor carbonyl group. Here, we illustrate that an alternative "enol" mechanism, based on a heterolytic N-C(α) bond cleavage located on the left (N-terminal) side of an acceptor carbonyl group, not only is thermodynamically viable but also often represents the energetically preferred cleavage route.

Simple, efficient and selective colorimetric sensors for naked eye detection of Hg2+, Cu2+ and Fe3+

Compounds 3 and 4 are all push–pull molecules containing both a donor 1,3-dithiole ring and an acceptor carbonyl group or thiocarboyl group, and their structures confer them with special spectroscopic properties. Their recognition behaviors towards metal ions were explored by UV-vis spectral analysis, and the results showed that combination of 3 and 4 could efficiently detect Hg2+, Cu2+ and Fe3+. The instant color changes induced by the addition of corresponding metal ions make them excellent naked eye sensors for the detection of heavy metal ions.

Fluorene Analogues of Prodan with Superior Fluorescence Brightness and Solvatochromism

In a search for environmentally sensitive (solvatochromic) dyes with superior properties, we extended the electronic conjugation of one of the best solvatochromic dyes, Prodan, by substituting its naphthalene core with fluorene. The newly synthesized fluorene derivatives bearing strong electron-donor (dialkylamino) and -acceptor (carbonyl) groups at the 2 and 7 positions showed red-shifted absorption (close to 400 nm), twice as large of a absorption coefficient (43 000 M−1 cm−1), and a manifold larger two-photon absorption cross section (∼400 GM) compared to Prodan. Studies in solvents revealed much stronger fluorescence solvatochromism of the new dyes, which is connected with their twice as large transition dipole moment (14.0 D). Similarly to Prodan, they exhibit high fluorescence quantum yields, while their photostability is largely improved. Thus, substitution of the naphthalene core in Prodan with fluorene resulted in new fluorophores with superior spectroscopic and solvatochromic properties. We expe...

Usnic Acid and the Intramolecular Hydrogen Bond. A Computational Experiment for the Organic Laboratory

A computational experiment is described for the organic chemistry laboratory that allows students to estimate the relative strengths of the intramolecular hydrogen bonds of usnic and isousnic acids, two related lichen secondary metabolites. Students first extract and purify usnic acid from common lichens and obtain 1H NMR and IR spectra. The 1H NMR spectrum reveals three downfield singlets at 11.1, 13.3, and 18.9 ppm, which correspond to three intramolecular hydrogen bonds. The IR spectrum additionally reveals three carbonyl stretching frequencies, which represent the hydrogen bond acceptors in usnic acid. The AM1 semi-empirical method is then employed to calculate (i) the heats of hydrogen bond formation, (ii) the atomic charges on the bridging hydrogens, (iii) the bond lengths of the acceptor carbonyl groups, and (iv) carbonyl IR stretching frequencies. The computed properties are then correlated to NMR and IR spectroscopic properties to reinforce fundamental concepts of the hydrogen bond.

2-(phenylaminomethylidene)cyclohexane-1,3-dione.

In the title compound, C(13)H(13)NO(2), there is polarization of pi-electron density from the amine N atom to the acceptor carbonyl groups: as a result, the molecule exists predominantly in an azomethino-1,3-diketone tautomeric form. There is crystallographic evidence that the phenyl ring, although roughly coplanar with the rest of the molecule, is deconjugated with the adjacent pi system of the molecule. The cyclohexane ring adopts an unsymmetrical half-chair conformation and converts between two inversion-related conformers. The molecule is stabilized by an intramolecular hydrogen bond, while the intermolecular packing is dominated by a number of short C-H.O contacts.

Engineering Crystalline Architecture with Supramolecular Tapes: Studies on Secondary Donor−Acceptor Interactions in Cocrystals of the Cyclic Dipeptide of Glycine

In this study, we examine the noncovalent interactions that occur between the cyclic dipeptide of glycine (GLYDKP) and a carboxylic acid guest. This study complements our earlier studies on the cyclic dipeptide of aspartic acid by exploring further the possibility of using hydrogen-bonded tapes comprised of molecules of GLYDKP, as a scaffold with which to control the location of guest molecules in a crystalline lattice. On the basis of the 11 cocrystals of GLYDKP reported herein, we conclude that guest molecules will be positioned between tapes of GLYDKP if the guest molecules meet the following criteria. First, the width of the guest molecule should be between 4.5 and 8.5 A. Second, interactions between adjacent guest molecules should be stronger than a van der Waals contact. Third, a hydrogen-bond donor (hydroxyl group) and a hydrogen-bond acceptor (carbonyl group) should be present in the structure of the guest with their separation no greater than two bonds between the carbon atom of the carbonyl grou...

5-(Tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based potent and selective CCK(1) receptor antagonists: structural modifications at the tryptophan domain.

Analogues of the previously reported potent and highly selective CCK(1) receptor antagonist (4aS, 5R)-2-benzyl-5-(N-Boc-tryptophyl)amino-1,3-dioxoperhydropyrido-[1, 2-c]pyrimidine (2a) were prepared to explore the structural requirements at the Boc-tryptophan domain for CCK(1) receptor affinity. Structural modifications of 2a involved the Trp side chain, its conformational freedom, the Boc group, and the carboxamide bond. Results of the CCK binding and in vitro functional activity evaluation showed three highly strict structural requirements: the type and orientation of the Trp side chain, the H-bonding acceptor carbonyl group of the carboxamide bond, and the presence of the Trp amino protection Boc. Replacement of this acid-labile group with 3, 3-dimethylbutyryl or tert-butylaminocarbonyl conferred acid stability to analogues 14a and 15a, which retained a high potency and selectivity in binding to CCK(1) receptors, as well as an in vivo antagonist activity against the acute pancreatitis induced by caerulein in rats. Oral administration of compounds 14a and 15a also produced a lasting antagonism to the hypomotility induced by CCK-8 in mice, suggesting a good bioavailability and metabolic stability.

Formation of a propellanone in the solvolysis of a 2-oxo bicyclic bridgehead compound

Methanolysis of 2-oxobicyclo[3.3.1]non-1-yl triflate gives the corresponding [3.3.1]-propellanone 2 in 15% yield. Primary factors involved in the reaction would be the marked electrophilicity of the destabilized 2-oxo bridgehead carbocation and stabilization of the cyclopropane ring of 2 by the π acceptor carbonyl group.