Structural features of thiocarbamide derivatives of some lanthanide iodides

Data on the synthesis, IR spectroscopy, and single crystal XRD are presented for thiocarbamide compounds of the composition [Ln(H₂O)₉]I₃·2CS(NH₂)₂, where Ln = Dy (I) and Yb (II). The structural features of [Ln(H₂O)₉]I₃·2CS(NH₂)₂ (Ln = Pr, Nd, Eu, Gd, Dy, Ho, Er, and Yb) are discussed. The compounds of thiocarbamide with Pr, Nd, Eu, Gd, and Dy iodides are found to form the first isostructural series characterized by a continuous network structure, while with Ho, Er, and Yb iodides the second isostructural series with a layered type structure is formed.     

Fibre-optic fluorescing sensor for ammonia

The fluorescing sensor is based on the change in fluorescence intensity of a buffered pH indicator solution entrapped in silicone rubber. Exposure to ammonia increases the pH of the trapped solution; this increases the fluorescence intensity, which is monitored via an optical fibre bundle. Ammonium chloride in 0.001 M sodium hydroxide, or the indicators themselves, can serve as buffers. Effects of sensor preparation and buffer composition on response time, reversibility and sensitivity are discussed.     

Gold nanoparticle-fluorophore complex for conditionally fluorescing signal mediator

Fluorescent contrast agents with high specificity and sensitivity are valuable for accurate disease detection and diagnosis. Spherical gold nanoparticles (GNPs) can be smartly utilized for developing highly effective agents. The strong electromagnetic (plasmon) field on their surface can be very effective in influencing the electrons of fluorophores and, thus, manipulating the fluorescence output (i.e., either quenching or enhancement). Fluorescence quenching can be used for negative sensing, or for conditional de-quenching to increase the specificity. Fluorescence enhancement allows sensing to be more sensitive. The level of fluorescence alteration depends on the GNP size, the excitation and emission wavelengths and quantum yield of the fluorophore, and the distance between the GNP and the fluorophore. To understand the mechanisms of the fluorescence change by GNP, we have theoretically analyzed the parameters involved in the fluorescence alteration for commonly used fluorophores, with an emphasis on quenching. The results showed that the fluorescence of fluorophores with the excitation (Ex) and emission (Ex) wavelengths close to the GNP resonance peak tended to be significantly quenched by GNPs. For those fluorophores emitting fluorescence in red or near infrared, to achieve quenching, the distance between GNP and the fluorophore was required to be very short. In general, a shorter distance resulted in more quenching. Bigger GNPs require a shorter distance to achieve the same level of quenching. The fluorescence of a fluorophore with a lower quantum yield (especially the one with emission in far-red or near-infrared) is more difficult to be quenched by GNPs (requires very short distance). Instead, it can be enhanced. Based on the theoretical study, we have developed a near-infrared contrast agent, i.e., Cypate conjugated GNP via a short peptide spacer. Normally the fluorescence of Cypate was quenched. The spacer has a motif of a substrate for urokinase type plasminogen activator (uPA; cancer-secreting enzyme). This contrast agent emits fluorescence only in the presence of uPA, where the uPA cleaves the spacer. This design can be used in characterization of the cancer type and also in diagnosing other diseases with signature enzymes.     

Structural features of toxic chemicals for specific toxicity

We have studied the structural features of toxic chemicals from the RTECS database associated with specific toxicity. The frameworks, functional groups, and structure patterns of molecules are taken into account. Potential active frameworks, groups, and structure patterns for specific toxicity are gained by computational chemistry approaches. These structural features of toxic chemicals will be helpful in understanding activities of toxic chemicals and useful in predicting the toxicity of chemicals, especially in the early stage of drug design.     

Structural features of derivatives of 1,3- dihydropyrimidine- 2,4- diones in complexes with macrocyclic poly- and azapolyethers

The results of studies on the structure of organic complexes of the derivatives of 1,3-dihydropyrimidine-2,4-diones and their structural analogues with macrocyclic poly- and azapolyethers are generalized.     

Structural requirements for efficient cellular photoprotection by carotenoid derivatives

We have synthesized five carotenoid derivatives: (1) Girard's reagent P (GRP)-retinal from GRP and retinal; (2) GRP-carotenal from GRP and beta-apo-8'-carotenal; (3) Girard's reagent T (GRT)-carotenal from GRT and beta-apo-8'-carotenal; (4) (GRP2-canthaxanthin from 2 mol of GRP and 1 mol of canthaxanthin; and (5) dansyl hydrazine (DH)-carotenal from DH and beta-apo-8'-carotenal. The first three derivatives are cations, whereas the fourth is a dication and the fifth is a weak base. Using K562 cells, we compared the subcellular distribution of the synthetic carotenoid derivatives with two uncharged natural carotenoids, beta-carotene and beta-apo-8'-carotenal. The two natural carotenoids were present mainly within the cell membranes. The synthetic carotenoid derivatives were more broadly distributed among the cell organelles. The positively charged derivatives had relatively high concentrations in mitochondria, whereas DH-carotenal had a relatively high concentration in lysosomes. We also measured the amount of photoprotection provided by the synthetic and natural carotenoids for K562 cells labeled with a photosensitizer (hypericin, protoporphyrin IX or cis-di[4-sulfonatophenyl]diphenylporphine). In this model system, only carotenoid derivatives with a permanent positive charge provided significant photoprotection. Neither the two natural carotenoids nor DH-carotenal were effective photoprotectors.     

Structural features of zinc hydroxyfluoride

Zinc hydroxyfluoride (ZnOHF), obtained by coprecipitation of a zinc salt in aqueous HF, exhibits a variable stoichiometry Zn(OH)_2−xF_x, where x is tuneable from 0.63 to 0.87 by controlling the pH of the solution. The structure was determined from Rietveld refinements using X-ray powder diffraction data. Crystallizing with the orthorhombic symmetry (SG : Pna2₁), the ZnOHF-type structure exhibits two different anionic sites. A bond valence analysis shows that fluorine exclusively occupies the anionic site that has shorter contacts to zinc. This site is split into two partially occupied sites, one corresponding to the position of a fluoride ion and the other to the position of a hydroxide ion. Bond valence calculations show that the split site model gives a more accurate picture of the local coordination of the anions on this site.     

Structural characteristics of dibromoborylated benzene derivatives

The crystal structures of five dibromobenzene derivatives, namely dibromoborylbenzene, C₆H₅BBr₂, (I), 1‐dibromoboryl‐4‐(trimethylsilyl)benzene, C₉H₁₃BBr₂Si, (II), 4‐bromo‐1‐(dibromoboryl)benzene, C₆H₄BBr₃, (III), dibromo(dimethylamino)(phenyl)borane, C₈H₁₂BBr₂N, (IV), and dibromo(dimethylsulfanyl)[4‐(trimethylsilyl)phenyl]borane, C₁₁H₁₉BBr₂SSi, (V), have been determined. Compounds (I)–(IV) crystallize with one molecule in the asymmetric unit, but the molecule of (V) is located on a crystallographic mirror plane, implying twofold disorder of the central aromatic ring, the S atom and one of the methyl groups bonded to the S atom. In (I), (II) and (III), the B atom is three‐coordinated, and in (IV) and (V) it is four‐coordinated. The geometric parameters of the –BBr₂ group in these five structures agree well with those of comparable structures retrieved from the Cambridge Structural Database. The C—B and B—Br bond lengths in the molecules with a three‐coordinated B atom are significantly shorter than those in the molecules with a four‐coordinated B atom. In the compounds with a three‐coordinated B atom, the –BBr₂ group tends to be coplanar with the aromatic ring to which it is attached.     

Structural consequences of weak interactions in dispirooxindole derivatives

Spiro scaffolds are being increasingly utilized in drug discovery due to their inherent three‐dimensionality and structural variations, resulting in new synthetic routes to introduce spiro building blocks into more pharmaceutically active molecules. Multicomponent cascade reactions, involving the in situ generation of carbonyl ylides from α‐diazocarbonyl compounds and aldehydes, and 1,3‐dipolar cycloadditon with 3‐arylideneoxindoles gave a novel class of dispirooxindole derivatives, namely 1,1′′‐dibenzyl‐5′‐(4‐chlorophenyl)‐4′‐phenyl‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐2,2′′‐dione, C₄₄H₃₃ClN₂O₃, (I), 1′′‐acetyl‐1‐benzyl‐5′‐(4‐chlorophenyl)‐4′‐phenyl‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐2,2′′‐dione, C₃₉H₂₉ClN₂O₄, (II), 1′′‐acetyl‐1‐benzyl‐4′,5′‐diphenyl‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐2,2′′‐dione, C₃₉H₃₀N₂O₄, (III), and 1′′‐acetyl‐1‐benzyl‐4′,5′‐diphenyl‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐2,2′′‐dione acetonitrile hemisolvate, C₃₉H₃₀N₂O₄·0.5C₂H₃N, (IV). All four compounds exist as racemic mixtures of the SSSR and RRRS stereoisomers. In these structures, the two H atoms of the dihydrofuran ring and the two substituted oxindole rings are in a trans orientation, facilitating intramolecular C—H...O and π–π interactions. These weak interactions play a prominent role in the structural stability and aid the highly regio‐ and diastereoselective synthesis. In each of the four structures, the molecular assembly in the crystal is also governed by weak noncovalent interactions. Compound (IV) is the solvated analogue of (III) and the two compounds show similar structural features.     

Structural features of catalytically active oligoorganometallosiloxanes

Copper- and (copper, aluminum)-containing organosiloxanes were studied by spectroscopic methods. It was found that in organometallosiloxanes (OMS) with an increased content of copper (Si/Cu=1 ∶ 1) Cu atoms are rather uniformly distributed in the siloxane matrix. All compounds under study are complexes characterized byd-d-transitions in copper ions with a constant coordination number of the metal atom. The intensity of thed-d-transition band increases as the copper content increases. ESR studies demonstrated that in the compounds under consideration, a change from mononuclear paramegnetic centers to clusters, in which copper ions are linked by strong spin-exchange interactions, occurs as the copper content increases. The catalytic activity of the above-mentioned compounds in isomerization reactions of 3,4-dichlorobutene-1 was studied. It was found that copper atoms serve as catalytic centers. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1946–1949, October, 1998.     

Structural features of semi-synthetic galactomannan sulfates

The positions of sulfate groups in two specimens of sulfated galactomannan from Cyamopsis tetragonoloba seeds were established by analysis of ¹H and ¹³C NMR spectra. For the degree of substitution of 0.6, the signals of galactopyranose residues sulfated at position O(6) or simultaneously at positions O(2) and O(3) were the most intense. Minor signals were due to O(2)- or O(3)-monosubstituted and 2,3,4-tri-O-substituted galactose residues. The substitution of mannopyranose residues involved positions O(6) > O(2,3) > O(2) > O(3). At higher degree of substitution (1.0), the pattern of distribution of sulfate groups over various positions in the residues did not change, the molar content of 2,3-di-O-substituted galactopyranose residues being higher than the content of 6-O-monosubstituted residues. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1745–1749, August, 2008.     

Structural characteristics of some diphenyl oxide derivatives

Conclusions Data are given which question the reliability of the communication concerning the preparation of two conformational isomers of p-bromodiphenyl ether.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 143–145.     

Structural peculiarities of some diphenyl ether derivatives

Conclusions On bromination of diphenyl ether the first bromine atom enters into the hydrocarbon ring, and the second bromine atom enters into the ethereal ring. The same principle was found for the chloromethylation of diphenyl ether.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 142–144, January, 1969.     

Structural characteristics of fluoronitro derivatives of pentane

Division of the Institute of Chemical Physics, Academy of Sciences of the USSR. Translated from Zhurnal Struckturnoi Khimii, Vol. 31, No. 1, pp. 126–131, January–February, 1990.     

Structural analysis of polysaccharides and polysaccharide derivatives

The general strategies and methods applied in the analysis of the primary structure of polysaccharides and derivatives are shortly lined out. Methods involving complete degradation of the polysaccharide are discussed in more detail. Advantages of the reductive-cleavage method compared to classical methylation analysis are illustrated by giving some examples of application.     

Structural studies on penicillin derivatives. X. Chlorination of azetidinone derivatives

The allylic methyl group of several azetidinone derivatives can be cleanly chlorinated by a mechanism which appears to be that of an ene-reaction.     

Hydrazine: Structural features and conformational preference in nanotubes

Investigation of structural features and conformational transformations of the hydrazine molecule in open single walled carbon nanotubes using the hybrid DFT method PBE/3ζ revealed in most cases the contraction of the N–N bond length, decrease in its order, generation of a positive or negative charge on the encapsulated molecule and a substantial decrease in the rotation barrier about the N–N bond caused by stabilization of the local maximum (anti-form) apparently, due to attenuation of the hyperconjugation effect in the hydrazine molecule. In one of clusters this form becomes the global minimum on the potential energy surface.