Synthesis, structure, and biological activity of mixed-ligand platinum(II) complexes with aminonitroxides

Mixed-ligand platinum complexescis-Pt^II(R⁶NH₂)(NH₃)X₂ andcis-Pt^II(R⁵NH₂)(NH₃)X₂ (R⁶ is 2,2,6,6-tetramethyl-4-piperidyl-1-oxyl and R⁵ is 2,2,5,5-tetramethyl-3-pyrrolidinyl-1-oxyl) were synthesized by either the reaction of aminonitroxides RNH₂ with Na[Pt^II(NH₃)Cl₂I] generatedin situ (for X₂=ClI) or by replacement of the iodo-chloro ligands incis-Pt¹¹(RNH₂)(NH₃)ClI by dichloro and oxalato ligands. The complexes obtained were characterized by elemental analysis and by IR, UV, and ESR spectra. Forcis-Pt¹¹(R⁵NH₂)(NH₃)Cl₂, crystal and molecular structures were determined by X-ray diffraction analysis. Cisplatin accelerates autooxidation of methyl linoleate and the platinum nitroxide complexes synthesized exhibit antioxidant properties. The rate of isolated DNA binding with the new complexes is almost as high as that for cisplatin.cis-Pt¹¹(R⁶NH₂)(NH₃)Cl₂ exhibits the highest antitumor activity. The high antitumor activity of platinum nitroxide complexes shows that the possible “radical component” is not a crucial factor in the cytotoxic action of cisplatin. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1624–1630, September, 2000.     

Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

 The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH₂) _n NH₃] _x M _y X _z , [R(CH₂) _n NH(CH₃)₂] _x M _y X _z , [R(CH₂) _n S(CH₃)₂] _x M _y X _z , [R(CH₂) _n SC(NH₂)₂] _x M _y X _z , and [R(CH₂) _n SeC(NH₂)₂] _x M _y X _z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X = I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties.     

Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

Summary.  The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH₂) _n NH₃] _x M _y X _z , [R(CH₂) _n NH(CH₃)₂] _x M _y X _z , [R(CH₂) _n S(CH₃)₂] _x M _y X _z , [R(CH₂) _n SC(NH₂)₂] _x M _y X _z , and [R(CH₂) _n SeC(NH₂)₂] _x M _y X _z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X = I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties. Received June 23, 2000. Accepted August 1, 2000     

Syntheses and crystal structures of NH4Ag2(AsS2)3 and (NH4)5Ag16(AsS4)7 with a discussion of (NH4)Sx polyhedra

Summary The atomic arrangements within the structures of NH₄Ag₂(AsS₂)₃ [a=9.557(2),b=7.414(2),c=16.29(1) Å; =91.30(5)°; space group P2₁/n;R(F)=0.042] and (NH₄)₅Ag₁₆(AsS₄)₇ [a=64.49(6),b=6.471(2),c=12.806(4) Å; =95.47(5)°; space group Cc;R(F)=0.073] were determined from single crystal X-ray data. In these two compounds the coordination spheres of the Ag atoms are quite different. In NH₄Ag₂(AsS₂)₃, the Ag atoms exhibit a [2+2]- and a [3+1]-coordination to S atoms up to 3.3 Å and with Ag atom neighbours at 2.93 Å and 3.05 Å respectively. In (NH₄)₅Ag₁₆(AsS₄)₇, the Ag atoms are — with one exception- [4] coordinated (Ag-S<3.3 Å) and the distances to further Ag atom neighbours are greater than 3.1 Å. NH₄Ag₂(AsS₂)₃ represents an ordered cyclo-thioarsenate(III) with three-membered As₃S₆ rings, (NH₄)₅Ag₁₆(AsS₄)₇ a neso-thioarsenate(V) with two split Ag atom positions. Both compounds were synthesized under moderate hydrothermal conditions.

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Synthesen und Kristallstrukturen von NH₄Ag₂(AsS₂)₃ und (NH₄)₅Ag₁₆(AsS₄)₇ mit einer Diskussion über (NH₄)S_x Polyeder

Zusammenfassung Die Atomanordnungen in den Strukturen von NH₄Ag₂(AsS₂)₃ [a=9.557(2),b=7.414(2),c=16.29(1) Å; =91.30(5)°; Raumgruppe P2₁/n;R(F)=0.042] und (NH₄)₅Ag₁₆(AsS₄)₇ [a=64.49(6),b=6.471(2),c=12.806(4) Å; =95.47(5)°; Raumgruppe Cc;R(F)=0.073] wurden anhand von röntgenographischen Einkristalldaten bestimmt. In diesen beiden Verbindungen sind die Koordinationsverhältnisse um die Ag-Atome sehr unterschiedlich. In NH₄Ag₂(AsS₂)₃ besitzen die Ag-Atome bis 3.3 Å eine [2+2]- und [3+1]-Koordination durch S-Atome mit weiteren Ag-Atomen bei 2.93 Å und 3.05 Å. In (NH₄)₅Ag₁₆(AsS₄)₇ sind die Ag-Atome mit einer Ausnahme [4]-koordiniert (Ag-S < 3.3 Å), und die Abstände zu weiteren Ag-Atomen sind größer als 3.1 Å. NH₄Ag₂(AsS₂)₃ stellt ein geordnetes Cyclothioarsenat(III) mit dreigliedrigen As₃S₆-Ringen dar, (NH₄)₅Ag₁₆(AsS₄)₇ ein Nesothioarsenat (V) mit zwei aufgespaltenen Ag-Positionen. Beide Verbindungen wurden unter mäßigen Hydrothermalbedingungen synthetisiert.

     

Banana‐shaped molecules with 4,6‐dichlorinated central core: effect of lateral substituents and terminal chains on the formation of antiferroelectric smectic mesophases

Six banana‐shaped compounds with a central core based on a 4,6‐dichloro‐1,3‐phenylene group were synthesized by varying the terminal chains (R = OC₁₀H₂₁ or OC₁₁H₂₁) and the lateral substituents (X = H, F or Cl). Their mesophases were characterized by a combination of differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X‐ray diffractometry. Mesomorphic properties of the banana‐shaped mesogens with an olefinic group (R = OC₁₁H₂₁) as a terminal chain are sensitive to lateral halogen substituents as much as those of the analogues with a saturated group (R = OC₁₀H₂₁). The compounds with X = F showed an antiferroelectric switchable smectic phase, which has been designated a B₂ phase. The compounds without a lateral halogen substituent only formed a nematic phase, while the compounds with X = Cl did not exhibit a mesophase in the melt.     

The compounds KAs4O6 X (X=Cl,Br, I) and NH4As4O6 X (X=Br,I): Hydrothermal syntheses and structure determinations

The crystal structures of five isotypic hexagonal compounds with general formulaMAs₄O₆ X [M=K, NH₄;X=Cl, Br, I; space group: P622;Z=1] were determined from 370 single crystal X-ray data and refined toR values <0.05. The structure type is characterized by neutral charged [As₂O₃] sheets arranged parallel (00.1). The As atoms of neighbouring two sheets point to each other and the sheets are combined by interlayeredM andX atoms, respectively. TheM atoms are coordinated to twelve oxygen atoms, theX atoms are coordinated to twelve arsenic atoms. In both cases the coordination polyhedron is a hexagonal prism. The compounds were synthesized by thermal treatments of cubic As₂O₃ and potassium or ammonium haloids in a saturated aqueous solution of potassium acetate resp. ammonia [500 K, saturation vapour pressure].

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Die Verbindungen KAs₄O₆ X (X=Cl, Br, I) und NH₄As₄O₆ X (X=Br, I): Hydrothermalsynthese und Strukturbestimmung

Zusammenfassung Die Kristallstrukturen der fünf isotypen hexagonalen Verbindungen mit der allgemeinen FormelMAs₄O₆ X [M=K, NH₄;X=Cl, Br, I; Raumgruppe: P622;Z=1] wurden anhand von 370 Einkristall-Röntgendaten bestimmt und aufR-Werte <0.05 verfeinert. Der Strukturtyp ist ausgezeichnet durch neutrale [As₂O₃]-Schichten, die parallel (00.1) angeordnet sind. Die As-Atome zweier benachbarter Schichten weisen jeweils aufeinander zu, und die Schichten selbst werden durch zwischengelagerteM- bzw.X-Atome verbunden. DieM-Atome werden jeweils von zwölf O-Atomen, dieX-Atome von zwölf As-Atomen umgeben. Das Koordinationspolyeder ist in beiden Fällen ein hexagonales Primsa. Die einzelnen Verbindungen wurden unter Hydrothermalbedingungen aus kubischem As₂O₃ und dem jeweiligen Kalium- oder Ammoniumhalogenid in einer gesättigten wäßrigen Lösung von Kaliumacetat bzw. Ammoniak synthetisiert (500 K, Sättigungsdampfdruck).

     

Crystal and moleclar structures of 5-allyl-25-methoxy-26,27,28-tribenzoylcalix[4]arene

The crystal and molecular structures of 5-allyl-25-methoxy-26,27,28-tribenzoylcalix[4]arene, an unsymmetrically substituted macrocycle, are reported. The space group is orthorhombic,P2₁2₁2₁, witha=13.4181(6),b=16.6652(10) andc=18.9936(14) Å andZ=4. Refinement by least-squares calculations converged with aR=0.060 for 4018 observed reflections. The molecule assumes a 1,3 alternate conformation with 2 benzoate rings and the disordered allyl side chain on one side and the third benzoate ring and the methoxy group on the opposite side of the mean plane of the methylene bridging groups. The four phenyl rings that comprise the macrocycle are approximately parallel in pairs; the members of a pair are 5.6 Å apart. The carbonyl oxygen atoms of the 3 benzoate groups are oriented away from the center of the cavity while the ester oxygen atoms and the methoxy oxygen atom are oriented toward the cavity center. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82033 (26 pages).     

Conformational analysis of carbonyl and thiocarbonyl ethyl esters: The HC(X) (X,Y = O or S) internal rotation

The internal rotation in the HC(?X)YCH₂CH₃ (X, Y = O or S) series of molecules was studied by the ab initio SCF-MO method using 3-21G and 3-21G + d(ζ = 0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-by-sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the ? CH₂CH₃ and the HC(?X)Y (X, Y = O or S) fragments are also discussed. © 1992 by John Wiley & Sons, Inc.     

Preparation, structures, and properties of niobium chalcogenide halides, NbX2Y2 (X = S, Se; Y = Cl, Br, I)

The preparation of the compounds NbX₂Y₂ (X = S, Se; Y = Cl, Br, I). including that of large single crystals, by chemical transport techniques is reported. Most of these compounds exist in a triclinic low-temperature form and a monoclinic high-temperature form. The crystal structures of triclinic low-temperature NbSe₂Cl₂ and monoclinic NbS₂Cl₂ are reported; both structures consist of cage-shaped units of Nb₂X₄ which are linked together by the Cl atoms to form sheets parallel to the a, b planes. Both the Nb and the X atoms are present in pairs which indicates that the compounds can be formulated as Nb⁴⁺₂(X₂)²⁻₂₂Y⁻₄, in agreement with XPS spectra. The presence of Nb⁴⁺ in pairs explains the observed diamagnetic and semiconducting properties of NbX₂Y₂. The preparation and some properties of MoS₂Cl₂ (orthorhombic) are also given.     

Optimization of process variables and corrosion properties of a multi layer silica sol gel coating on AZ91D using the Box–Behnken design

Anti-corrosion silica coating was prepared via the sol–gel method for AZ91D magnesium alloy using tetraethoxysilane and methyltriethoxysilane as precursors. Silica coating was deposited on fluorinated magnesium alloy substrates by dip coating. The surface morphology of the silica coating was characterized by scanning electron microscope (SEM). The corrosion properties were studied by electrochemical impedance measurements and polarisation technique in 3.5 wt% Sodium chloride solution. The results showed an improvement in the corrosion performance from these coatings. A three-factor, three-level design of experiment (DOE) with response surface methodology including a Box–Behnken design was run to evaluate the main and interaction effects of several independent formulation variables, which included precursor ratios MTES/TEOS (X₁), sintering temperature (X₃) and sol dilution (X₂) which measured the volume of the diluted sol divided by the initial volume of sol. The dependent variables included the corrosion current derived from the polarisation curve (i_cor = Y₁) and the coating resistance derived from the Nyquist curve (R_coat = Y₂). Optimizations were predicted to yield Y₁ and Y₂ values of 1.57018E–7A cm⁻² and 14279 Ω cm², when X₁, X₂, and X₃ were 3.36, 1.52 and 222, respectively.     

Carbon-13 chemical shifts of 3-substituted thietanes,thietane 1-oxides and thietane 1,1-dioxides

Carbon-13 chemical shifts of the α- and β-carbon atoms for 12 thietane 1,1-dixides, 9 thietane 1-oxides and 7 thietanes with a variety of 3-substituents [H, CH(CO₂Et)₂, SEt, Br, SPh, Ph, Cl, NMe₂, OH, OSiMe₃, OAc, OEt] are correlated according to the nature of the sulfur atom (Y=sulfone, sulfoxide, sulfide) and the nature of the 3-substituent (X) by the equations δ_α= a_Y+b_X and δ_β=a_X+b_Y, where a and b are parameters characteristic of X and Y. One-bond coupling constants [J(CH)] are reported for 21 compounds. The chemical shifts for the α- and the β-carbon atoms of the sulfones show the ‘fore-membered ring sulfone effect’ (α-carbon unusually deshielded, β-carbon unusually shielded), but the α-carbon-hydrogen coupling constants are similar to those of the sulfoxides and sulfides; the β-carbon-hydrogen coupling constants are sensitive to the nature of the substituent (X) but no special β-effect is observed. Comparison of the chemical shifts of the α-methylene carbon atoms of 3-phenyl-, 3-(β-naphthyl)- and 3-(α-thienyl)-thietes with those of the coresponding sulfones also reveals the ‘four-membered ring sulfone effect’ cis- and trans-3-Substituted thietane 1-oxides may be distinguished by the greater downfield shift for the β-carbon atom in the trans-isomer.     

The Glaserite-like Structure of Double Sodium and Iron Phosphate Na3Fe(PO4)2

The double sodium and iron phosphate Na₃Fe(PO₄)₂ was synthesized and studied by the XRD method, the second harmonic generation technique, and Mössbauer and IR spectroscopy. The compound crystallizes into a monoclinic system (space group C2/c) with unit cell parameters a=9.0736(2) Å, b=5.0344(1) Å, c=13.8732(3) Å, β=91.435(2)° and is found to be related to the K₃Na(SO₄)₂ structure type. The crystal structure was determined by Rietveld analysis (R_wp=5.86, R_I=2.03). Iron cations occupy the M (Na) position while sodium cations occupy the X (K) and Y (K) positions of the glaserite-like structure. Mössbauer spectroscopy shows the presence of high-spin Fe³⁺ in octahedral coordination.     

Structural Diversity and Magnetic Properties of Hybrid Ruthenium Halide Perovskites and Related Compounds

There has been a great deal of recent interest in extended compounds containing Ru³⁺ and Ru⁴⁺ in light of their range of unusual physical properties. Many of these properties are displayed in compounds with the perovskite and related structures. Here we report an array of structurally diverse hybrid ruthenium halide perovskites and related compounds: MA₂RuX₆ (X=Cl or Br), MA₂MRuX₆ (M=Na, K or Ag; X=Cl or Br) and MA₃Ru₂X₉ (X=Br) based upon the use of methylammonium (MA=CH₃NH₃⁺) on the perovskite A site. The compounds MA₂RuX₆ with Ru⁴⁺ crystallize in the trigonal space group and can be described as vacancy‐ordered double‐perovskites. The ordered compounds MA₂MRuX₆ with M⁺ and Ru³⁺ crystallize in a structure related to BaNiO₃ with alternating MX₆ and RuX₆ face‐shared octahedra forming linear chains in the trigonal space group. The compound MA₃Ru₂Br₉ crystallizes in the orthorhombic Cmcm space group and displays pairs of face‐sharing octahedra forming isolated Ru₂Br₉ moieties with very short Ru–Ru contacts of 2.789 Å. The structural details, including the role of hydrogen bonding and dimensionality, as well as the optical and magnetic properties of these compounds are described. The magnetic behavior of all three classes of compounds is influenced by spin–orbit coupling and their temperature‐dependent behavior has been compared with the predictions of the appropriate Kotani models.     

Backbone modified small bite-angle diphosphines: Synthesis and molecular structures of [M(CO)4{X2PC(RR)PX2}] (M = Mo, W; X = Ph, Cy; R = H, Me, Et, Pr, allyl, R = Me, allyl)

A range of new small bite-angle diphosphine complexes, [M(CO)₄{X₂PC(R¹R²)PX₂}] (M = Mo, W; X = Ph, Cy; R¹ = H, Me, Et, Pr, allyl, R² = Me, allyl), have been prepared via elaboration of the methylene backbones in [M(CO)₄(X₂PCH₂PX₂)] as a result of successive deprotonation and alkyl halide addition. When X = Ph it proved possible to replace both methylene protons but for X = Cy only one substitution proved possible. This is likely due to the electron-releasing nature of the cyclohexyl groups but may also be due to steric constraints. Attempts to prepare the bis(allyl) substituted complex [Mo(CO)₄{Ph₂PC(allyl)₂PPh₂}] were only moderately successful. The crystal structures of nine of these complexes are presented.     

Rheological studies of aqueous alkylpolyglucoside surfactant solutions

Alkylpolyglucosides (C _Y G _X ) are industrial products of mixtures consisting of a hydrocarbon chain with Y carbon atoms linked to X sugar residues. Based on detailed analytical investigation of technical grade alkylpolyglucosides (C_8–10G _X , C_12–14G _X and C_8–16G _X )/water systems using high-performance liquid chromatography in combination with a special kind of mass spectroscopy their rheological behaviour is discussed and compared to the rheological behaviour of pure alkyl monoglycosides (C₈G₁ and C₁₀G₁) in water. The rheological properties that exhibit a dependence on the alkyl chain length, Y, and the degree of polymerisation, X, are investigated by rotation and oscillation experiments over an extended concentration range. The Maxwell model fits the frequency dependence of the dynamic functions fairly well. The viscosity shows an Arrhenius-like dependence on temperature. A comparison is drawn between the monoglucosides and the polyglucosides, which shows that the rheological properties are more sensitive to the a change in chain length than in the degree of polymerisation. Phase transitions, especially liquid-crystalline to isotropic solutions, phase split into two coexisting liquid phases, and could be followed using visual observation and rheology. Depending on the difference in the rheological properties of the corresponding phases, viscoelastic measurements showed these transitions clearly. Additionally, the changes in viscosities were measured after addition of a second surfactant. Received: 4 January 1999 Accepted in revised form: 12 April 1999     

Quantum-Chemical Estimation of the Stability and Reactivity of Diphosphonium Salts

For a series of diphosphonium salts containing two positively charged covalently bonded phosphorus atoms, X_{/sub> n} Y_3-n P⁺P⁺X _n Y_3-n (X = alkyl substituent, Y = amino group, n = 0-3), the stability, reactivity, and P-P bond strength were evaluated by various physicochemical methods. The P-P bond energy is appreciably influenced by both steric factors and donor properties of the substituents. The calculations confirmed that transformations of diphosphonium salts can involve cleavage of both P-P and P-N (or P-C) bonds.     

Approximate transferability in alkanenitriles

The atomic and bond properties of a series of alkanenitriles were calculated in order to analyze the transferability of the CN, methyl, and methylene groups. The calculations were carried out using the atoms in molecules (AIM) theory on RHF/6‐31++G**// RHF/6‐31G** wave functions obtained for compounds CN–R (R ranging from H to C₁₁H₂₃). Linear correlations between L(Ω) and N(Ω) were used to establish N(CH₂) and N(CH₃) nearly transferable values. Average values and maximum differences to the mean value of several properties were used for classifying the CN group. It shows a transferable behavior along the CN–R series for R>Et. The methyl group presents specific properties when R<Pr. The methylene groups can be classified considering both their position with respect to the end of the chain and the position with respect to the CN group. The atomic energy displays a dependence on the molecular size. Although this behavior does not allow to consider this property as transferable, both the ab initio total electronic molecular energies and the experimental heats of formation can be fitted, by linear regression analysis, as a function of the number of methylene groups. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Asymmetrische Hg(II)-Komplexe mit Organothiolato- bzw. Organoselenolato-und Triazenato-Liganden

The mixed mercury complexes (2XC₆H₄)₂N₃HgY (X=CH₃, F, Cl, Br, I;Y=SC₂H₅, SC₆H₅, SeC₆H₅) have been prepared. Both the Hg–S and Hg–Se bonds and, in contrast to other mixed triazenato-mercury compounds, the triazenato-mercury bonds have been shown to be kinetically labile on the NMR time scale by means of⁷⁷Se and¹⁹⁹Hg NMR spectroscopy. Evidence has been obtained for the presence of (2XC₆H₄)₂N₃HgY together with HgY ₂ and [(2XC₆H₄)₂N₃]₂Hg in solution.

     

Evidence for Cluster Orbital Formation in CsSn2X5 Compounds (X=Cl, Br)

The formation of cluster orbitals in CsSn₂Br₅ is discussed and related more generally to tetragonal compounds of the type AB₂X₅ (A=monovalent cation; B=Sn, Pb; X=Cl, Br, I). The crystal structures of CsSn₂Cl₅ and CsSn₂Br₅ have been solved by single-crystal X-ray diffraction. These compounds are isostructural with each other and a range of AB₂X₅ structural analogues. In many AB₂X₅ compounds where B is a subvalent main group metal a tetragonal cell is observed with space group I4/mcm. The structures of CsSn₂Br₅ and CsSn₂Cl₅ are layered with polymeric sheets of [Sn₂X₅]ⁿ⁻_n separated by the Cs⁺ cations. Stereochemical considerations suggest that stabilization of this structural form, rather than the more ionic NH₄Pb₂Cl₅ or NaSn₂Cl₅ structures, is through interaction of the “nonbonding” valence electron pairs on tin with low-lying empty d-orbitals on neighboring X atoms. Electronic structure calculations based on the structural data confirm the likelihood of cluster orbital formation. Crystal data: CsSn₂Cl₅, tetragonal, I4/mcm, a=8.153(1) Å, c=14.882(4) Å, Z=4, R₁=0.0215, wR₂=0.0503 [I>2σ(I)], R₁=0.0393, wR₂=0.0536 (all data); CsSn₂Br₅, tetragonal, I4/mcm, a=8.483(6) Å, c=15.28(2) Å, Z=4, R₁=0.0607, wR₂=0.1411 [(I>2σ(I)], R₁=0.1579, wR₂=0.1677 (all data).     

The Cα?C internal rotation in α-alkyl substituted carbonyls and thiocarbonyls: CH(CH3)2C(X)YH (X,Y O or S)

The C_α? C internal rotation in 2-methylpropionic, 2-methylthiopropionic (thiol and thion forms) and 2-methyldithiopropionic acids was studied by the ab initio SCF-MO method using 3-21G and 3-21G + d(0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-by-sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the α-methyl substituents and the C(?X)Y (X, Y? O or S) fragment are also discussed.