The model single-stranded DNA binding protein of bacteriophage T4, gene 32 protein (gp32) has well-established roles in DNA replication, recombination, and repair. gp32 is a single-chain polypeptide consisting of three domains. Based on thermodynamics and kinetics measurements, we have proposed that gp32 can undergo a conformational change where the acidic C-terminal domain binds internally to or near the single-stranded (ss) DNA binding surface in the core (central) domain, blocking ssDNA interaction. To test this model, we have employed a variety of experimental approaches and gp32 variants to characterize this conformational change. Utilizing stopped-flow methods, the association kinetics of wild type and truncated forms of gp32 with ssDNA were measured. When the C-domain is present, the log-log plot of k vs. [NaCl] shows a positive slope, whereas when it is absent (*I protein), there is little rate change with salt concentration, as expected for this model.A gp32 variant lacking residues 292-296 within the C-domain, ΔPR201, displays kinetic properties intermediate between gp32 and *I. The single molecule force-induced DNA helix-destabilizing activitiesas well as the single- and double-stranded DNA affinities of ΔPR201 and gp32 truncated at residue 295 also fall between full-length protein and *I. Finally, chemical cross-linking of recombinant C-domain and gp32 lacking both N- and C-terminal domains is inhibited by increasing concentrations of a short single-stranded oligonucleotide, and the salt dependence of cross-linking mirrors that expected for the model. Taken together, these results provide the first evidence in support of this model that have been obtained through structural probes.

The selectivity of catalytic asymmetric transformations of bifunctional symmetrical substrates often depends on the linker between the two reactive sites. If the catalyst controls the selectivity of reactions at both sites, the rac product will be formed in high enantiomeric ratio (er) via asymmetric amplification. Substrate control may augment this selectivity (positive cooperativity) or detract from it (negative cooperativity). Here, we investigated the effect of linker length on the selectivity of catalytic asymmetric alkylation of the bis(secondary phosphines) PhHP(CH2)(n)PHPh (n = 2-6; 1a-e) with benzyl bromide using the base NaOSiMe3 and the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(CI). These reactions yielded the diastereomerically and enantiomerically enriched bis(tertiary phosphines) Ph(PhCH2)P(CH2)(n)P(CH2Ph)Ph (n = 2-6, 2a-e). Pt-catalyzed benzylation of the model phosphines PH(Ph)((CH2)(n)H) (n = 2-6; 4a-e) gave enantiomerically enriched P(CH2Ph)(Ph)((CH2)(n)H) (n = 2-6; 5a-e). The partially alkylated bis(phosphines) PhHP(CH2)(n)P(CH2Ph)Ph (n = 2, 3, 5; 3a,b,d) were prepared with different degrees of enantiomeric enrichment at the tertiary phosphine centers and then catalytically alkylated to give 2a,b,d. From the diastereoselectivity and enantioselectivity of the transformations 1 -> 2 and 3 -> 2, the selectivity of each individual alkylation step (1 -> 3R or 3S; 3R -> 2RR or 2RS; 3S -> 2SS or 2SR) could be determined as a function of linker length and compared to the selectivity of alkylation of the model monophosphines 4. The two alkylations of bis(secondary phosphines) 1b-e with longer linker lengths (n = 3-6) showed identical selectivity, within experimental error. This catalyst control resulted in asymmetric amplification of rac-2. In contrast, the selectivity of the first alkylation of ethano-bridged la was lower than that in 1b-e (negative cooperativity), but the selectivity of the second alkylation (of intermediate 3a) increased due to positive cooperativity. Possible mechanistic explanations for the observed dependence of selectivity on linker length are discussed.

The crystal and molecular structures of three new thiosemicarbazones, 2-[1-(2-hydroxy-5-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide monohydrate (1), 2-[1-(2-hydroxy-5-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide (2) and 2-[1-(2-hydroxy-4-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide acetonitrile solvate (3), are reported and confirmed by single crystal X-ray diffraction, NMR and UV-vis spectroscopic data. Compound (1), C11H15N3O2S·H2O, crystallizes in the monoclinic with space group P21/c, with cell parameters a = 8.2304(3) Å, b = 16.2787(6) Å, c = 9.9708(4) Å, and β = 103.355(4)°. Compound (2), C12H17N3O2S, crystallizes in the C2/c space group with cell parameters a = 23.3083(6) Å, b = 8.2956(2) Å, c = 13.5312(3) Å, β = 91.077(2)°. Compound (3), C11H15N3O2S·C2H3N, crystallizes in the triclinic P-1 space group with cell constants a = 8.9384(7) Å, b = 9.5167(8) Å, c = 10.0574(8) Å, α = 110.773(7)°, β = 92.413(6)°, and γ = 90.654(7)°. DFT B3LYP/6-31(G) geometry optimized molecular orbital calculations were also performed and frontier molecular orbitals of each compound are displayed. The correlations between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound have been proposed. Additionally, similar correlations observed among three closely related compounds, (4), 2-[1-(2-hydroxy-4-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide, (5), 2-[1-(2-hydroxy-6-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide acetonitrile monosolvate and (6), 2-[1-(2-hydroxy-6-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide, examining structural differences from the substitution of the methoxy group from the phenyl ring (4, 5, or 6 position) and the substitution of the terminal amine (methyl or ethyl) to their frontier molecular orbital surfaces and from their Density Functional Theory (DFT) molecular orbital energies provide further support for the suggested assignments of the title compounds.

In the title compound, C16H16N4OS, an intramolecular C—H...S hydrogen bond is observed. With the exception of the phenyl ring of the phenylpropylidene unit, the remainder of the molecule has an almost planar skeleton with an r.m.s. deviation of 0.121 (5) Å from the plane through the remaining 16 atoms. In the crystal O—H...N hydrogen bonds are observed between the terminal hydroxyimino groups, forming inverson dimers with R22(6) graph-set motifs. Additional C—H...N contacts stack the dimers along [100]. While no π—π interactions are present, weak C—H...O and O—H...Cg interactions are also observed and help stabilize the crystal packing.

Three new Schiff base derivatives of (2-amino-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl)-phenylmethanone, namely, C23H21NO3S (I), C24H22N2O5S (II) and C26H28N2O2S (III) have been synthesized and characterized by NMR, single-crystal X-ray diffraction and DFT molecular orbital calculations. Compound (I) crystallizes in the orthorhombic space group P212121, with Z = 4 in cells with a = 5.02536(8) Å, b = 17.5927(3) Å, c = 21.2134(4) Å, V = 1875.47(5) Å3 and displays weak C–H···O intermolecular interactions which contribute to crystal packing. Compound (II) crystallizes in the monoclinic space group P21/c, with Z = 4 in cells with a = 11.2263(2) Å, b = 19.7401(3) Å, c = 10.0202(2) Å, β = 108.565(2)°, V = 2105.00(8) Å3 and displays weak C–H···O intermolecular interactions forming zig-zag chains along the b axis and weak π–π stacking interactions which influence crystal packing. Compound (III) also crystallizes in the monoclinic space group P21/c, with Z = 4 in cells with a = 10.9599(2) Å, b = 11.9287(3) Å, c = 17.0626(4) Å, β = 97.680(2)°, V = 2210.71(8) Å3 and displays weak C–H···O intermolecular interactions which contribute to crystal packing. Additionally, the DFT frontier molecular orbitals of each compound are displayed and correlation between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound has been proposed.

Two new Schiff base derivatives of (2-amino-5-ethyl-thiophen-3-yl)-(2-chloro-phenyl)-methanone, namely C22H19N2O5SCl (I) and C20H15N2O3SCl (II), have been synthesized and characterized by means of NMR, single-crystal X-ray diffraction and density functional theory geometry optimization and molecular orbital calculations. Compound (I) crystallizes in the triclinic space group P-1, with a = 7.8235(6) Å, b = 10.3256(5) Å, c = 13.6678(9) Å, α = 82.597(5)°, β = 74.759(6)°, γ = 89.968(5)°, V = 1055.96(12) Å3 and Z = 2. Compound (II) also crystallizes in the triclinic space group P-1, with a = 8.0644(7) Å, b = 10.7984(9) Å, c = 10.8191(9) Å, α = 104.142(7)°, β = 92.660(7)°, γ = 93.292(7)°, V = 910.31(13) Å3 and Z = 2. Geometry optimization calculations for each compound support these observations. Both compounds display R 2 2 (10) ring motifs formed by weak C···H···O intermolecular interactions and contribute to crystal packing. Additionally, the frontier molecular orbitals of each complex are displayed and correlation between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra has been proposed.

The asymmetric unit of the title compound, C 12 H 17 N 3 O 2 S, contains two independent molecules, A and B . Both molecules are nearly planar with the dihedral angle between the mean planes of the thioamide group and benzene ring being 7.5 (1)° in A and 4.3 (2)° in B . In each molecule, the hydroxy group participates in intramolecular O—H...N hydrogen bonding, while the amino H atom is not involved in hydrogen bonding because of the steric hinderence caused by two neighboring methyl groups. In the crystal, the individual molecules are linked by weak C—H...O hydrogen bonds, forming A – A and B – B inversion dimers. The dimers are linked via C—H...π interactions which help stabilize the packing.

The crystal and molecular structures of the title compounds, phenyl quinoline-2-carboxylate and 2-methoxyphenyl quinoline-2-carboxylate, two new derivatives of quinolone-2-carboxylic acid, are reported and confirmed by single crystal X-ray diffraction and spectroscopic data. Compound (I), C16H11NO2, crystallizes in the monoclinic space group P21/c, with 8 molecules in the unit cell. The unit cell parameters are a = 14.7910(3) Å; b = 5.76446(12) Å; c = 28.4012(6) Å; β = 99.043(2)°; V = 2391.45(9) Å3. Compound (II), C17H13NO5, crystallizes in the monoclinic space group P21/n with 4 molecules in the unit cell. The unit cell parameters are a = 9.6095(3) Å; b = 10.8040(3) Å; c = 13.2427(4) Å; β = 102.012(3)°; V = 1344.76(7) Å3. Density functional theory (DFT) geometry optimized molecular orbital calculations were performed and frontier molecular orbitals of each compound are displayed. Correlation between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound has been proposed. Additionally, similar correlations observed among six closely related compounds examining small structural differences to their frontier molecular orbital surfaces and from their DFT molecular orbital energies, provide further support for the suggested assignments of the title compounds.

The asymmetric unit of the title compound, C12H17N3O2S, contains two independent mol-ecules, A and B. Both mol-ecules are nearly planar with the dihedral angle between the mean planes of the thio-amide group and benzene ring being 7.5 (1)° in A and 4.3 (2)° in B. In each mol-ecule, the hy-droxy group participates in intra-molecular O-H⋯N hydrogen bonding, while the amino H atom is not involved in hydrogen bonding because of the steric hinderence caused by two neighboring methyl groups. In the crystal, the individual molecules are linked by weak C-H⋯O hydrogen bonds, forming A-A and B-B inversion dimers. The dimers are linked via C-H⋯π inter-actions which help stabilize the packing.

In the title hydrated salt [systematic name: 1-(1,3-benzodioxol-5-ylmethyl)piperazin-1-ium 4-nitrobenzoate monohydrate], C 12 H 17 N 2 O 2 + ·C 7 H 4 NO 4 − ·H 2 O, the piperazinium ring of the cation adopts a slightly distorted chair conformation. The piperonyl and piperazine rings are rotated with respect to each other with an N—C—C—C torsion angle of 45.6 (2)°. In the anion, the nitro group is almost coplanar with the adjacent benzene ring, forming a dihedral angle of only 3.9 (4)°. In the crystal, the cations, anions and water molecules are linked through N—H...O and O—H...O hydrogen bonds into chains along the a axis. In addition, weaker intermolecular C—H...O interactions are also observed within the chains. The anions form centrosymmetric couples through π-stacking interactions, with an intercentroid distance of 3.681 (4) Å between the benzene rings.

In the title salt {systematic name: 1-[(1,3-benzodioxol-5-yl)methyl]piperazin-1-ium 4-chlorobenzoate}, C12H17N2O2+·C7H4ClO2−, the piperazine ring adopts a slightly disordered chair conformation. The dioxole ring is in a flattened envelope conformation with the methylene C atom forming the flap. The relative orientation of the piperonyl ring system and the piperazine rings is reflected in the N—C—C...;C torsion angle of 132.3 (1)°. In the anion, the mean plane of the carboxylate group is twisted from that of the benzene ring by 14.8 (9)°. In the crystal, the components are linked by N—H...O and weak C—H...O hydrogen bonds, forming chains along [010].

The title salt {systematic name: bis[1-(3-chlorophenyl)piperazinium 2,4,6-trinitrophenolate]–picric acid (2/1)}, 2C10H14ClN2+·2C6H5N3O7−·C6H6N3O7, crystallized with two independent 1-(3-chlorophenyl)piperazinium cations, two picrate anions and a picric acid molecule in the asymmetric unit. The six-membered piperazine ring in each cation adopts a slightly distorted chair conformation and contains a protonated N atom. In the picric acid molecule, the mean planes of the nitro groups in the ortho-, meta-, and para-positions are twisted from the benzene ring by 31.5 (3), 7.7 (1), and 3.8 (2)°, respectively. In the anions, the dihedral angles between the benzene ring and the ortho-, meta-, and para-nitro groups are 36.7 (1), 5.0 (6), 4.8 (2)°, and 34.4 (9), 15.3 (8), 4.5 (1)°, respectively. The nitro group in one anion is disordered and was modeled with two sites for one O atom with an occupancy ratio of 0.627 (7):0.373 (7). In the crystal, the picric acid molecule interacts with the picrate anion through a trifurcated O—H...O four-centre hydrogen bond involving an intramolecular O—H...O hydrogen bond and a weak C—H...O interaction. Weak intermolecular C—H...O interactions are responsible for the formation of cation–anion–cation trimers resulting in a chain along [010]. In addition, weak C—H...Cl and weak π–π interactions [centroid–centroid distances of 3.532 (3), 3.756 (4) and 3.705 (3) Å] are observed and contribute to the stability of the crystal packing.

In the title compound, C9H10N4OS, the dihedral angle between the benzene and 1H-1,2,4-triazole-5(4H)-thione rings is 67.51 (16)°. In the crystal, molecules are liked via N—H...O hydrogen bonds, forming chains along the c-axis direction. The chains are linked via O—H...S hydrogen bonds, forming corrugated layers lying parallel to the bc plane. The layers are linked via N—H...N and N—H...S hydrogen bonds, forming a three-dimensional network.

The title co-crystal, 3-(4-fluorophenyl)-1 H -pyrazole–5-(4-fluorophenyl)-1 H -pyrazole (1/1), C 9 H 7 FN 2 , crystallizes with four independent molecules ( A , B , C and D ) in the asymmetric unit exhibiting two tautomeric forms ( A and D ; B and C ) due to N—H proton exchange between the two N atoms of the pyrazole ring. The dihedral angles between the mean planes of the pyrazole and benzene rings are 15.6 (1), 19.8 (9), 14.0 (1) and 10.7 (7)° in molecules A , B , C and D , respectively. In the crystal, N—H...N hydrogen bonds link the four molecules in the asymmetric unit into a ring with an R 4 4 (12) motif. Furthermore, weak C—H...F interactions link the molecules into a three-dimensional network.

The title salt, 2C19H23FN3O3+·C2O42− {systematic name: bis-[4-(3-carboxy-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinolin-7-yl)-1-ethylpiperazin-1-ium] oxalate}, crystallizes with two independent monocations (A and B) and an oxalate dianion (C) in the asymmetric unit. The piperazinium ring in both the cations adopts a slightly disordered chair conformation. The dihedral angles between the mean planes of the cyclopropyl ring and the 10-membered quinoline ring are 50.6 (5)° (A) and 62.2 (5)° (B). In each of the cations, a single O—H...O intramolecular hydrogen bond is observed. In the crystal, the oxalate anions interact with the cations through N—H...O hydrogen bonds and weak C—H...O interactions, forming R22(8) graph-set ring motifs. Weak C—H...F interactions along with further C—H...O interactions are observed between the cations, forming zigzag chains along [001]. In addition, π–π stacking interactions are observed with centroid–centroid distances of 3.5089 (13), 3.5583 (13), 3.7900 (13) and 3.7991 (13) Å.

The title compound, C12H17N3OS, crystallizes with two independent molecules (A and B) in the asymmetric unit. The dihedral angle between the mean planes of the benzene ring and the hydrazinecarbothioamide group are 6.9 (4) and 37.2 (5)° in molecules A and B, respectively. An intramolecular O—H...N hydrogen bond is observed in each molecule. This serves to maintain an approximately planar conformation for molecule A, but leaves a significant twist between these two groups in molecule B. In the crystal, a weak N—H...S interaction is observed, forming inversion dimers among the B molecules and resulting in an R22(8) motif. These dimers are further interconnected by weak N—H...O and C—H...O intermolecular interactions, forming chains along [011].

The title compound, C12H18N4O2, crystallizes in the zwitterionic form with protonation at the N atom of the piperazine ring bearing the carboxylate group. The piperazine ring adopts a slightly distorted chair conformation. In the crystal, N—H...O hydrogen bonds are observed, forming chains along [010]. The packing is consolidated by C—H...O interactions, which generate a three-dimensional network.

In the cation of the title salt, C3H6N3+·C4H5O4−, the protonated pyrazolium ring is planar (r.m.s. deviation = 0.012 Å). An intramolecular C—H...O hydrogen bond occurs in the anion. In the crystal, N—H...O hydrogen bonds and a weak C—H...O interaction between the cations and anions form two sets of R22(8) graph-set ring motifs. Intermolecular O—H...O hydrogen bonds between these lead to a criss-cross pattern along the b axis. In addition to the classical hydrogen bonds, a weak C—H...π(pyrazolium) interaction is observed and contributes to crystal packing. All of these interactions link the molecules into a two-dimensional supramolecular framework parallel to (10-1).

In the title salt, C6H12N3+·C7H3N2O7−, the imidazole ring is planar, with a maximum deviation of 0.0013 (14) Å for the N attached to the propanaminium group. In the anion, a single intramolecular O—H...O hydrogen bond is observed. The mean planes of the nitro groups in the anion are twisted from the benzene ring mean plane making dihedral angles of 24.7 (9) and 3.9 (6)°. In the crystal, the ammonium H atoms form N—H...N and N—H...O hydrogen bonds, resulting in an infinite chain along [111]. In addition to the classical hydrogen bonds, weak C—H...O and π–π [centroid–centroid distance = 3.7124 (9) Å] interactions are also observed, which lead to the formation a three-dimensional supramolecular structure that links the chains into layers along the bc plane.