Simultaneous presence of two charges or two spins in a linear polyene

Summary In this work we examine the ease of finding simultaneously two charges or two spins in various AO positions of a linear neutral polyene such as octatetraene. By applying the general multi-electron population analysis on a correlated wave function we calculate contributions from various ionic and covalent (in a probabilistic sense) resonance structures as well as electron-pair distributions with parallel and anti-parallel spins; the initial wave function used is a PPP + (quasi-total) CI wave function. Based on the second and fourth order anticommutation relations (and independently of the level of the MO wave function used) we show existing relationships between the quantities considered, as well as their constant behaviour. Covalent structures depend strongly on the parity and distance between the AO positions, while ionic ones arequasi-constant along the polyene. It is also shown that when the AO positions considered are non-vicinal, (+) and (–) charges appearmutually independent and the -electron conjugation has, rather surprisingly, no effect on them.     

Konformative Beweglichkeit Flexibler Ringsysteme—X. Untersuchungen mit Hilfe der Protonenresonanz-Spektroskopie. Substituentenabhängigkeit der Ringinversion bei 1.3-Dioxanen, 1.3-Dithianen und 1.3-Oxathianen

Activation energies E_α and free enthalpies of activation ΔG? were determined by NMR for the ring inversions of nineteen 1.3-dioxanes, 1.3-dithianes and 1.3-oxathianes and their methyl-substituted derivatives. The rate constant k of the chair to chair-inversion of these rings depend on the number and positions of the substituents. In substituted 1.3-dioxanes k is lower than in 1.3-dioxane itself if two geminal CH₃-groups are situated in position 5. However, k becomes higher when the geminal CH₃-groups are in positions 2 or 4. The rate constants are particularly high for 4.4.6.6-tetramethyl-1.3-dioxane. A similar dependence of k on substituents has been observed in the oxathianes, while with 1.3-dithianes only a small influence is noticed. The effect of the methyl substituents in positions 2 or 4 in 1.3-dioxanes can be explained by assuming that the chair conformation is deformed by 1.3-interactions. In 1.3-dithianes such 1.3-interactions are expected to be smaller because of the larger C? S bond length. For 1.3-oxathianes the dependence of k on the substituents is more difficult to understand since these molecules are not symmetrical.     

Reliable Functionalization of 5,6-Fused Bicyclic N-Heterocycles Pyrazolopyrimidines and Imidazopyridazines via Zinc and Magnesium Organometallics

DFT-calculations allow prediction of the reactivity of uncommon N-heterocyclic scaffolds of pyrazolo[1,5-a]pyrimidines and imidazo[1,2-b]pyridazines and considerably facilitate their functionalization. The derivatization of these N-heterocycles was realized using Grignard reagents for nucleophilic additions to 5-chloropyrazolo[1,5-a]pyrimidines and TMP₂Zn ⋅ 2 MgCl₂ ⋅ 2 LiCl allowed regioselective zincations. In the case of 6-chloroimidazo[1,2-b]pyridazine, bases such as TMP₂Zn ⋅ MgCl₂ ⋅ 2 LiCl, in the presence or absence of BF₃ ⋅ OEt₂, led to regioselective metalations at positions 3 or 8. Subsequent functionalizations were achieved with TMPMgCl ⋅ LiCl, producing various polysubstituted derivatives (up to penta-substitution). X-ray analysis confirmed the regioselectivity for key functional heterocycles.     

Dyad algebra and multiplication of graphs. II. Undirected graphs

In paper I abstract vectors |e>, their adjoints <e|, dyads such as |e><e|, and abstract linear operators were related to graphs which are in general directed. With an Hermitian operator one gets equivalence classes of undirected graphs with or without loops and multi-lines. The present paper II gives rules for the multiplication of such graphs based on their underlying dyad algebra. The results may be used in the evaluation of the outcome of successive applications of operators for observables as in the case of the powers of a one-electron Hamiltonian in the method of moments, or in using projection operators, electron density, and the like.     

Structural features of diastereomeric oxazolidin-2-ones

Model diastereomeric oxazolidinones containing various substituents at positions 3 and 5 were synthesized. Several individual diastereomers bearing methyl groups at positions 4 and 5 in cis-and trans orientations were isolated. The TLC and ¹H NMR spectroscopic data suggest that diastereomers, particularly those containing the aryl substituent at position 5, are substantially different in the physical and spectral properties. The configurations of some diastereomers were established by X-ray diffraction and NOESY spectroscopy. For these compounds, the reliable assignment of the characteristic ¹H NMR signals of individual groups was made, which provided evidence for the cis or trans orientation of the methyl groups at positions 4 and 5. The scope of the method as applied to the determination of the cis and trans isomers from their ¹H NMR spectra is discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 133–139, January, 2007.     

Two-level QSAR network (2L-QSAR) for peptide inhibitor design based on amino acid properties and sequence positions

In the design of peptide inhibitors the huge possible variety of the peptide sequences is of high concern. In collaboration with the fast accumulation of the peptide experimental data and database, a statistical method is suggested for peptide inhibitor design. In the two-level peptide prediction network (2L-QSAR) one level is the physicochemical properties of amino acids and the other level is the peptide sequence position. The activity contributions of amino acids are the functions of physicochemical properties and the sequence positions. In the prediction equation two weight coefficient sets {a_k} and {b_l} are assigned to the physicochemical properties and to the sequence positions, respectively. After the two coefficient sets are optimized based on the experimental data of known peptide inhibitors using the iterative double least square (IDLS) procedure, the coefficients are used to evaluate the bioactivities of new designed peptide inhibitors. The two-level prediction network can be applied to the peptide inhibitor design that may aim for different target proteins, or different positions of a protein. A notable advantage of the two-level statistical algorithm is that there is no need for host protein structural information. It may also provide useful insight into the amino acid properties and the roles of sequence positions.     

ABC–ABC-Type Directly meso–meso Linked Porphyrin Dimers

Covalently linked porphyrin oligomers are attractive because of their extended π-conjugated systems. Among various porphyrin oligomers, directly meso–meso linked porphyrin oligomers exhibit unique photophysical properties due to their strong exciton couplings derived from the alternative orthogonal geometry of the porphyrins. Although their structural and electronic properties can be greatly altered by substituents at meso positions, it is still difficult to introduce different substituents at the meso positions. Thus, it is a challenge to develop general synthetic methodologies for functional porphyrin dimers and oligomers with different substituents at the meso positions. Herein, a general synthetic strategy for ABC–ABC-type directly meso–meso linked porphyrin dimers by stepwise functionalization starting from 10,15,20-meso-free 5-substituted porphyrin as building block is established. A meso-ABC–ABC-type meso–meso-linked donor–π-acceptor-type porphyrin dimer was prepared and exhibited the highest power conversion efficiency (7.91 %) ever reported for dye-sensitized solar cells based on dimeric orthogonal donor–π-acceptor-type organic sensitizers. This synthetic strategy will provide useful guidance for the rational design of functional porphyrin dimers and oligomers for diverse applications.     

Bio-based vinylphenol family: Synthesis via decarboxylation of naturally occurring cinnamic acids and living radical polymerization for functionalized polystyrenes

A series of bio-based vinylphenols or hydroxystyrenes is prepared by simple decarboxylation of various naturally occurring cinnamic acids such as o-, m-, and p-coumaric; caffeic; ferulic; and sinapinic acids, which possess hydroxy groups and other substituents at different positions on the aromatic ring. After protection of the phenolic moieties with trialkylsilyl groups, reversible addition–fragmentation chain-transfer polymerization is accomplished with cumyl dithiobenzoate to afford various bio-based hydroxyl-protected polystyrenes with controlled molecular weights and narrow molecular weight distributions. Subsequent deprotection of the silyl groups under mild conditions results in a series of well-defined functionalized polystyrenes possessing different numbers (mono-, di-, tri-) of hydroxy groups at different positions (o, m, p). The obtained functionalized polystyrenes show unique thermal properties depending on the substituents, and those with phenol and catechol groups serve as reducing agents for silver ions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 91–100     

Convenient Synthesis of Alkenyl‐, Alkynyl‐, and Allenyl‐Substituted Imidazo[1,2‐a]pyridines via Palladium‐Catalyzed Cross‐Coupling Reactions

A systematic study on the Stille and Sonogashira cross‐coupling of iodinated imidazo[1,2‐a]pyridines was performed, permitting the preparation of various vinyl‐, ethynyl‐, and allenyl‐substituted derivatives. These methods are particularly valuable, given their experimental simplicity and high degree of flexibility with regard to functional groups that can be introduced in positions 3, 6, or 8 of the imidazo[1,2‐a]pyridine core. Effects concerning different substitution positions and the nature of the 2‐substituent under various reaction conditions are reported in detail for the above types of unsaturated groups introduced.     

Phenylimido Complexes of Technetium and Rhenium with Maleonitriledithiolate

[Tc(NPh)Cl₃(PPh₃)₂] or [Re(NPh)Cl₃(PPh₃)₂] react with two equivalents of Na₂mnt (mnt^2– = 1,2‐dicyanoethene‐1,2‐dithiolate) with formation of anionic complexes of the composition [M(NPh)(mnt)₂]^–. The products can be isolated as large red blocks of their AsPh₄⁺ salts. The complex anions contain square‐pyramidal coordinated metal atoms with the phenylimido ligands in apical positions. The M–N–C bonds are almost linear. A similar phenylimido complex with an additional amino group was synthesized from [Re(NC₆H₄‐4‐NH₂)Cl₃(PPh₃)₂]. The presence of such substituents may allow coupling of the metal complexes to biomolecules such as peptides, proteins, or sugars, provided the M=N bonds are sufficiently stable against hydrolysis.     

Ab initioMODPOT/VRDDO/MERGE calculations on energetic compounds. IV. Nitrocubanes: Mononitro to octanitro quantum chemical calculations and electrostatic molecular potential contour maps

Ab initio MODPOT /VRDDO /MERGE calculations have been carried out for all the different position isomers of nitrocubane from mononitrocubane through octanitrocubane for a perfect symmetrical cubic cubane skeleton and for mononitrocubane through septanitrocubane for the almost cubic experimentally determined cubane skeleton. These calculations were carried out with our own rapid efficient ab initio programs which also incorporate a number of desirable computational strategies for calculations on large molecules. The skeletal total overlap population of the cubane skeleton (a theoretical index we showed years ago to be sensitive and predictive of stability of energetic molecular frameworks) indicates that successive nitration seems to increase the stability of the cubane skeleton. Successive nitration also seems to increase the total overlap population of the C? NO₂ bond. There are subtle differences depending on the exact positional isomer for a constant number of nitro groups—but the overall trend is definite. We have also generated electrostatic molecular potential contour (EMPC ) maps around these nitrocubanes. These maps are indicative of preferred positions of electrophilic and nucleophilic attack as a function of the number of nitro groups or their positions. These EMPC maps can also indicate, to a first approximation, a limit on how close these molecules may be able to approach each other in a crystal.     

Studies on iron(III) and manganese(III) derivatives of new meso-aryl substituted and brominated porphyrins

A series of Fe^III and Mn^III porphyrins with various tolyl and naphthyl substituents at the meso positions, and their perbromoderivatives with Br substituents at the -pyrrole positions, have been synthesised and investigated. As seen in the case of the free-base porphyrins, both Fe^III and Mn^III derivatives of the Br-substituted porphyrins also exhibit pronounced red-shifts in both B and Q bands compared to their nonbrominated analogues. This is attributed to the electron-withdrawing ability of eight Br substituents at -pyrrole positions and is also due to distortion brought about in the -framework by the bulky substituents including those at the meso positions. The naphthyl groups seem to be making mesomeric contributions for both nonbrominated and brominated porphyrins of these metal ions as is evident from the higher wavelength absorption of the B band as compared to the tolyl derivatives. While the meso-substituent do not exhibit any isomer dependent change on the electronic properties of Fe^III porphyrins, they show a noticeable effect in the Mn^III derivatives. During the metallation of meso-tetratolylporphyrins by Fe^III ions -oxo dimeric compounds are formed, while the naphthyl porphyrins and the bromoderivatives do not form such dimeric species. The presence of bulky groups at the meso positions and heavy bromines on the -pyrrole positions can be considered to prevent the formation of catalytically inert -oxo dimers.     

The mass spectra of some aliphatic and alicyclic sulphoxides and sulphones

Characteristic fragmentation processes of aliphatic sulphoxides and sulphones such as loss of hydroxyl, ‘alkene’ and/or ‘alkenyl’ are associated with hydrogen migrations to oxygen. A study of the mass spectra of di-n-butyl sulphoxide and sulphone, the saturated five-, six- and seven-membered ring sulphoxides and sulphones and their site-specifically deuterated analogues shows that these hydrogen migrations are nonspecific. Apparently steric factors play an important role in determining the relative contributions of initial hydrogen transfer from the various positions. The sites of abstraction probably determine the extent of competition between consecutive or concerted loss of hydroxyl, carbon-sulphur fission or other processes (e.g. McLafferty rearrangement). Apart from the McLafferty rearrangement only the loss of hydroxyl from sulphones shows a strong dependence on the site of initial hydrogen abstraction: γ-hydrogen is lost preferentially, yielding a cyclized [M ? OH] ion.     

Preparation and properties of low-cost cotton nanocomposite fabrics with in situ-generated copper nanoparticles by simple hydrothermal method

In this work, copper nanoparticles were in situ generated in cotton fabrics by simple hydrothermal method. These low-cost nanocomposite fabrics were characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, thermogravimetric analysis, and antibacterial tests. The presence of spherical nanoparticles was visualized by SEM analysis. FTIR spectra did not show any differences between the peak positions of cotton fabrics and their nanocomposites. The crystallinity of cotton nanocomposites was enhanced by the copper nanoparticles. The cotton nanocomposite fabrics exhibited good antibacterial activity against Escherichia coli bacteria and hence can be considered for medical applications such as wound dressing, surgical aprons, hospital bed materials, etc.     

Synthesis and polymerization of 1- and 2-cyano-1,3-butadienes

1-Cyano-1,3-butadiene and 2-cyano-1,3-butadiene were prepared and designated 1-cyanoprene and 2-cyanoprene, respectively. These compounds, and their intermediates, were characterized by their infrared and proton magnetic resonance spectra. Their polymerizations with lithium or aluminum alkyl catalysts are described. The synthesis of these monomers involves a thermal cracking process (400–500°C). The yield of monomer by this process depends on the positions of the cyano and acetoxy groups in the butene intermediate; if the cyano and the acetoxy groups are attached to the same allylic carbon, a low monomer yield is obtained. The polymers of 1-cyanoprene are the results of 1,4-enchainment (cis and trans) and are amorphous; the polymers of 2-cyanoprene may involve 1,4-enchainment but are partially crystalline. Both of these polymers are thermoplastic.     

Kristallographische Gruppe-Untergruppe-Beziehungen und ihre Anwendung in der Kristallchemie

Crystallographic Group-subgroup Relations and their Use in Crystal Chemistry Family trees of crystallographic group-subgroup relations are especially suited to display relationships among crystal structure types. Starting from an aristotype, a simple, highly symmetrical structure type, more and more complicated structures are obtained by reducing the space group symmetry. In doing so, it is important to keep trace of how the occupied Wyckoff positions develop from a space group to its subgroups and which coordinate transformations and origin shifts occur. The neccessary information can by obtained from the new volume A1 of International Tables for Crystallography. Possible error sources are demonstrated with the aid of examples. When a Wyckoff position is split into different symmetry-independent Wyckoff positions, substitution derivatives become possible. If the position does not split, its site symmetry must be reduced, thus rendering possible distorted derivative structures. Such distortions are of special importance in phase transitions, as shown with the examples K₂[TeBr₆], (NO)₂[TiCl₆] and SrCu₂(BO₃)₂. Phase transitions involving a symmetry reduction are likely to produce twinned crystals. This can be the cause of errors in crystal structure determinations, as shown with the example of CaMnF₅. The possible ways to occupy voids in sphere packings can be followed and calculated systematically, including the possibility to predict crystal structures. Sometimes the indices of the symmetry reduction take values that seem curious, such as 13 for CZr₆I₁₂ and 37 for PtCl₃. The systematic application is also possible to molecular packings, such as to the modifications of P₄S₃. Tetraphenylphosphonium salts often crystallize in the space group P4/n or its subgroups, retaining pseudotetragonal symmetry even in monoclinic and triclinic structures.     

Cyclic and non cyclic aliphatic–aromatic polyesters derived from biomass: Study of structures by MALDI-ToF and NMR

New polyesters were prepared by polycondensation in solution of 1,4:3,6 dianhydrohexitols with various aliphatic–aromatic acid dichlorides which differ by their chain length (m = 6,8,10). They are obtained with yields in the range of between 89% and 95%. In order to obtain these polymers within optimum conditions, a systematic study was conducted on the effect of the parameters involved in the reaction, such as the alkyl chain length of acid dichlorides and the endo or exo positions of hydroxyl function of diols. The resulting polyesters were characterized by different analytical techniques such as NMR (¹H and ¹³C), FT-IR spectrometry, SEC measurements and MALDI-ToF mass spectrometry. Under optimized conditions a high molar fraction of cyclic polyesters was formed.The differential scanning calorimetry (DSC) measurements revealed an amorphous character with glass transition temperatures in the range of 27–45 °C. The polymers are obtained with inherent viscosities in the range of 0.11–0.25 dL/g with a polydispersity index between 1.75 and 1.99.     

sym-Triazine Derivatives. 2. Synthesis, Properties, and Structure of 2-Oxo-1,2-dihydro-sym-triazines

Previously unreported 2-oxo-1,2-dihydro-sym-triazines have been prepared and their alkylation reactions have been studied. It was found that, independently of the structure and nature of the substituent in positions 4 and 6 of the triazine ring or the structure of the alkyl halide used, the reaction occurs regioselectively at the oxygen atom. The stereostructure of the 2-oxo-1,2-dihydro-sym-triazines was investigated by X-ray analysis and it was shown that they exist as dimers in the crystalline state.     

Clickable functionalization of liposomes with the gH625 peptide from Herpes simplex virus type I for intracellular drug delivery

Liposomes externally modified with the nineteen residues gH625 peptide, previously identified as a membrane‐perturbing domain in the gH glycoprotein of Herpes simplex virus type I, have been prepared in order to improve the intracellular uptake of an encapsulated drug. An easy and versatile synthetic strategy, based on click chemistry, has been used to bind, in a controlled way, several copies of the hydrophobic gH625 peptide on the external surface of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPG)‐based liposomes. Electron paramagnetic resonance studies, on liposomes derivatized with gH625 peptides, which are modified with the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐4‐amino‐4‐carboxylic acid (TOAC) spin label in several peptide positions, confirm the positioning of the coupled peptides on the liposome external surface, whereas dynamic light scattering measurements indicate an increase of the diameter of the liposomes of approximately 30 % after peptide introduction. Liposomes have been loaded with the cytotoxic drug doxorubicin and their ability to penetrate inside cells has been evaluated by confocal microscopy experiments. Results suggest that liposomes functionalized with gH625 may act as promising intracellular targeting carriers for efficient delivery of drugs, such as chemotherapeutic agents, into tumor cells.     

Synthesis of Polysubstituted Symmetrical BODIPYs via Fischer Carbene Complexes: Theoretical,Photophysical and Electrochemical Evaluation

A series of new symmetrical highly substituted BODIPYs 6 a – l was synthesized through a prefunctionalization approach in 35 %–89 % yields from the pyrrole core. This strategy allowed modulation of the substituents at the different positions based on the choice of Fischer's alkynyl carbenes, oxazolones and aldehydes used as precursors. The substituent variation at positions 2, 6, 3 and 5 had the greatest effect on the modulation of their photophysical properties such as absorption (λ_abs) and emission (λ_em) wavelengths, extinction coefficient (ϵ), quantum yields (ϕ), Stokes shifts (Δν), fluorescence decay, radiative (k_rad) and non-radiative (k_nr) constants and the CIE 1931 coordinates. Theoretical calculations allowed to corroborate the effect of the substituents of meso-position on the modification of the dihedral angles. Cyclic voltammetry studies revealed that the BODIPY series presents similar redox potential behavior, being electrochemically active even in successive cycles, which suggests that transport by diffusion is the dominant process.