Studies on nonlinear optical materials: structure of diphenylmethyl (Z)-1-(1-methylthio-2-nitrovinyl)tetrahydropyrrole-2-carboxylate

C21H22N2045, M r = 398.5, orthorhombic, P212~21, a = 9.799 (1), b = 11.853 (1), c = 17.316(2)/~, V=2011.4A 3, Z=4, Dm=l.320, Dx=1.314Mgm -3, CuKa, A=1.5418A, Iz= 1.63 ram-1, F(000) = 840.0, T = 293 K, R = 0.055 for 1735 significant reflections. In the 1-methylthio-2- nitrovinyl moiety the C--C bond, 1.368 (7)A, is significantly longer than in ethylene, 1.336 (2)/~. The second harmonic generation (SHG) efficiency of this compound is only 0.25 of the urea standard. The correlation between the molecular packing and SHG is discussed.

Quinoxaline: Z `=1 form

A new Z' = 1 crystal structure of quinoxaline (or 1,4-diazanaphthalene), C8H6N2, with one-fifth the volume of the earlier known Z' = 5 structure was obtained by means of an in situ cryocrystallization technique.

Hydrochalcogenation of Symmetrical and Unsymmetrical Buta-1,3-diynes with Diaryl Dichalcogenides: Facile Entry to (Z)-1-(Organylchalcogeno)but-1-en-3-yne Derivatives

This work describes an efficient and stereoselective method for the hydrothiolation and -selenation of buta-1,3-diyne derivatives using diaryl disulfides or diselenides, respectively. In the presence of rongalite (HOCH2SO2Na) and potassium carbonate, buta-1,3-diynes undergo stereoselective addition of the thiolate or selenide anion generated in situ from diaryl disulfides or diselenides to afford the corresponding (Z)-1-sulfanyl-or (Z)-1-selanylalk-1-en-3-yne derivatives, respectively. The reaction of buta-1,3-diynes with diaryl disulfides or diselenides at higher temperature (70 degrees C) gave a mixture of monothiolation/selenation and bisthiolation/selenation products in moderate to good yields.

Structure of tri-1-naphthylborane-benzene (1/1) complex, c30h21b.c6h6

M r= 470.46, rhombohedral, R3, a =8.710(4)A, a=91.10(3) o, V= 660.4 (9) A 3, Z= 1,D m= 1.170 (flotation in KI solution), D x=1.183 Mg m -a, Mo Kct, 2 = 0.7107/~,, /t =0.033 mm -1, F(000) - 248.0, T= 293 K, R -- 4.6%(481 unique reflections). The molecule has C a symmetry and is propeller shaped, the angle of twist about the B-C bond being 41.5 (7) °. The space group being chiral, this is yet another example of spontaneous resolution. The results of a thermal-motion analysis are discussed.

Peptide mimics for structural features in proteins. Crystal structures of three heptapeptide helices with a C-terminal 6-->1 hydrogen bond.

The crystal structure determination of three heptapeptides containing alpha-aminoisobutyryl (Aib) residues as a means of helix stabilization provides a high-resolution characterization of 6-->1 hydrogen-bonded conformations, reminiscent of helix-terminating structural features in proteins. The crystal parameters for the three peptides, Boc-Val-Aib-X-Aib-Ala-Aib-Y-OMe, where X and Y are Phe, Leu (I), Leu, Phe (II) and Leu, Leu (III) are: (I) space group P1, Z = 1, a = 9.903 A, b = 10.709 A, c = 11.969 A, alpha = 102.94 degrees, beta = 103.41 degrees, gamma = 92.72 degrees, R = 4.55%; (II) space group P21, Z = 2, a = 10.052 A, b = 17.653 A, c = 13.510 A, beta = 108.45 degrees, R = 4.49%; (III) space group P1, Z = 2 (two independent molecules IIIa and IIIb in the asymmetric unit), a = 10.833 A, b = 13.850 A, c = 16.928 A, alpha = 99.77 degrees, beta = 105.90 degrees, gamma = 90.64 degrees, R = 8.54%. In all cases the helices form 3(10)/alpha-helical (or 3(10)helical) structures, with helical columns formed by head-to-tail hydrogen bonding. The helices assemble in an all-parallel motif in crystals I and III and in an antiparallel motif in II. In the four crystallographically characterized molecules, I, II, IIIa and IIIb, Aib(6) adopts a left-handed helical (hL) conformation with positive phi, psi values, resulting in 6-->1 hydrogen-bond formation between Aib(2) CO and Leu(7)/Phe(7) NH groups. In addition a 4-->1 hydrogen bond is seen between Aib(3) CO and Aib(6) NH groups. This pattern of hydrogen bonding is often observed at the C-terminus of helices proteins, with the terminal pi-type turn being formed by four residues adopting the hRhRhRhL conformation.

Syntheses and structural studies of new bicyclic 1,3-diphenyl-1,3,2.lambda.3,4.lambda.3-diazadiphosphetidines

Reactions of cis-[(C6H5N)PC1]z(1 ) with the difunctional reagents HO(CH2)20H,H (CH3)N(CHz)zN(CH3)HH, (CH3)N(CH& OH, and HO(CHz)30Hi n the presence of triethylamine yield the new bicyclic 1,3,2X3,4h3-diazadiphosphetidines[( C6H5- N)PIZ[-O(CHZ)Zo-l (2), [(C6H5N)PlZ[-(CH3)N(CHZ)ZN(CH3)-l (319 [(C6H~N)PlZ~-(CH3)N(cHZ)20 (4), and [(C6H5 N)P],[-Q(CH2),0-] (5), respectively. The products have been characterized by elemental analyses and IR and NMR spectroscopic data. The structures of 4 and 5 have been determined by single-crystal X-ray analysis. Crystal data for 4: monoclinic, P2,/c, a = 9.823 (2) A, b = 8.608 (1) A, c = 18.423 (3) A, i3 = 90.55 (1)O, Z = 4. Crystal data for 5 monoclinic, P2,/c, a = 9.727 (2) A, b = 8.064 (2) A, c = 19.702 (4) A, @ =I 91.31 (l)', 2 = 4. The structures have been solved by direct methods and refined to R = 0.028 for 4 and R = 0.050 for 5. Compound 4 is the first example of an aminoalkoxy-l,3,2X3,4X3-diazadiphosphetidine. The PzNz ring is slightly puckered in both 4 and 5 and the puckering occurs in a manner opposite to that observed for cis-[(RN)PX],structures.

X-ray studies on crystalline complexes involving amino acids and peptides. XXI. Structure of a (1:1) complex between L-phenylalanine and D-valine

CsHllNO2.C9HilNO2, Mr = 282.3, P1, a = 5.245 (1), b = 5.424 (1), c = 14.414 (2) A, a = 97.86 (1), fl = 93-69 (2), y = 70-48 (2) °, V= 356 A 3, Z = 1, O m = 1-32 (2), Dx = 1.32 g cm-3, h(Mo Ka) = 0-7107 A, g = 5-9 cm-1, F(000) = 158, T= 298 K, R=0.035 for 1518 observed reflections with I>2tr(I). The molecules aggregate in double layers, one ayer made up of L-phenylalanine molecules and the other of D-valine molecules. Each double layer is stabilized by interactions involving main-chain atoms of both types of molecules. The interactions include hydrogen bonds which give rise to two head-to-tail sequences. The arrangement of molecules in the complex is almost the same as that in the structure of DL-valine (and DL-leucine and DL-isoleucine) except for the change in the side chain of L molecules. The molecules in crystals containing an equal number of L and O hydrophobic amino-acid molecules thus appear to aggregate in a similar fashion, irrespective of the precise details of the side chain.

1, 2-Bis (diphenylphosphino) etane bridged dinuclear copper (I) complexes: Investigations of solid state and solution structures by CP/MAS31P NMR spectroscopy, X-ray crystallography, IR spectroscopy and solution 31P NMR and 63Cu NMR spectroscopy

Three different complexes of copper (I) with bridging 1, 2-bis(diphenylphosphino)ethane (dppe), namely [Cu2 (mu-dppe) (CH3CN)6] (ClO4)2 (1), [Cu2 (mu-dppe)2 (CH3 CN)2] (ClO4)2 (2), and [Cu2 (mu-dppe) (dppe)2 (CH3CN)2] (ClO4)2 (3) have been prepared. The structure of [Cu2 (mu-dppe) (dPPe)2 (CH3CH)2] (ClO4)2 has been determined by X-ray crystallography. It crystallizes in the space group PT with a=12.984(6) angstrom, b=13.180(6) angstrom, c=14.001(3) angstrom, alpha=105.23(3), beta=105.60(2), gamma=112.53 (4), V=1944 (3) angstrom3, and Z=1. The structure was refined by least-squares method with R=0.0365; R(w)=0.0451 for 6321 reflections with F0 greater-than-or-equal-to 3 sigma (F0). The CP/MAS P-31 and IR spectra of the complexes have been analysed in the light of available crystallographic data. IR spectroscopy is particularly helpful in identifying the presence of chelating dppe. P-31 chemical shifts observed in solid state are very different from those observed in solution, and change significantly with slight changes in structure. In solution, complex 1 remains undissociated but complexes 2 and 3 undergo extensive dissociation. With a combination of room temperature H-1, Cu-63, and variable temperature P-31 NMR spectra, it is possible to understand the various processes occurring in solution.

Halogen Bonding and Chalcogen Bonding in 4,7-Dibromo-5, 6-dinitro-2,1,3-benzothiadiazole

An organic solid, 4,7-dibromo-5,6-dinitro-2,1,3-benzothiadiazole, has been designed to serve as an illustrative example to quantitatively evaluate the relative merits of halogen and chalcogen bonding in terms of charge density features. The compound displays two polymorphic modifications, one crystallizing in a non-centrosymmetric space group (Z' = 1) and the other in a centrosymmetric space group with two molecules in the asymmetric unit (Z' = 2). Topological analysis based on QTAIM clearly brings out the dominance of the chalcogen bond over the halogen bond along with an indication that halogen bonds are more directional compared to chalcogen bonds. The cohesive energies calculated with the absence of both strong and weak hydrogen bonds as well as stacking interaction are indicative of the stabilities associated with the polymorphic forms.

LISA as a dark energy probe

Recently, it has been shown that the inclusion of higher signal harmonics in the inspiral signals of binary supermassive black holes (SMBH) leads to dramatic improvements in the parameter estimation with Laser Interferometer Space Antenna (LISA). In particular, the angular resolution becomes good enough to identify the host galaxy or galaxy cluster, in which case the redshift can be determined by electromagnetic means. The gravitational wave signal also provides the luminosity distance with high accuracy, and the relationship between this and the redshift depends sensitively on the cosmological parameters, such as the equation-of-state parameter w = p(DE)/rho(DE) of dark energy. Using binary SMBH events at z < 1 with appropriate masses and orientations, one would be able to constrain w to within a few per cent. We show that, if the measured sky location is folded into the error analysis, the uncertainty on w goes down by an additional factor of 2-3, leaving weak lensing as the only limiting factor in using LISA as a dark energy probe.

Parallel packing of alpha-helices in crystals of the zervamicin IIA analog Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe.2H2O.

An apolar synthetic analog of the first 10 residues at the NH2-terminal end of zervamicin IIA crystallizes in the triclinic space group P1 with cell dimensions a = 10.206 +/- 0.002 A, b = 12.244 +/- 0.002 A, c = 15.049 +/- 0.002 A, alpha = 93.94 +/- 0.01 degrees, beta = 95.10 +/- 0.01 degrees, gamma = 104.56 +/- 0.01 degrees, Z = 1, C60H97N11O13 X 2H2O. Despite the relatively few alpha-aminoisobutyric acid residues, the peptide maintains a helical form. The first intrahelical hydrogen bond is of the 3(10) type between N(3) and O(0), followed by five alpha-helix-type hydrogen bonds. Solution 1H NMR studies in chloroform also favor a helical conformation, with seven solvent-shielded NH groups. Continuous columns are formed by head-to-tail hydrogen bonds between the helical molecules along the helix axis. The absence of polar side chains precludes any lateral hydrogen bonds. Since the peptide crystallizes with one molecule in a triclinic space group, aggregation of the helical columns must necessarily be parallel rather than antiparallel. The packing of the columns is rather inefficient, as indicated by very few good van der Waals' contacts and the occurrence of voids between the molecules.

N-Urethane-Protected Amino Alkyl Isothiocyanates: Synthesis, Isolation, Characterization, and Application to the Synthesis of Thioureidopeptides

Synthetically useful N-Fmoc amino-alkyl isothiocyanates have been described, starting from protected amino acids. These compounds have been synthesized in excellent yields by thiocarbonylation of the monoprotected 1,2-diamines with CS2/TEA/p-TsCl, isolated as stable solids, and completely characterized. The procedure has been extended to the synthesis of amino alkyl isothiocyanates from Boc- and Z-protected amino acids as well. The utility of these isothiocyanates for peptidomimetics synthesis has been demonstrated by employing them in the preparation of a series of dithioureidopeptide esters. Boc-Gly-OH and Boc-Phe-OH derived isothiocyanates 9a and 9c have been obtained as single crystals and their structures solved through X-ray diffraction. They belong to the orthorhombic crystal system, and have a single molecule in the asymmetric unit (Z′ = 1). 9a crystallizes in the centrosymmetric space group Pbca, while 9c crystallizes in the noncentrosymmetric space group P212121.

Crystal and molecular structures of alkali- and alkaline-earth-metal complexes of N,N-dimethylformamide

Structures of lithium, sodium, magnesium, and calcium complexes of NJ-dimethylformamide (DMF) have been investigated by X-ray crystallography. Complexes with the formulas LiCl.DMF.1/2H20, NaC104.2DMF, CaC12.2DMF.2H20, and Mg(C104)2.6DMF crystallized in space groups P2]/c, P2/c, Pi, and Ella, respectively, with the following cell dimensions: Li complex, a = 13.022 (7) A, b = 5.978 (4) A, c = 17.028 (10) A, = 105.48 (4)O, Z = 8; Na complex, a = 9.297 (4)A, b = 10.203 (3) A, c = 13.510 (6) A, /3 = 110.08 (4)O, Z = 4; Ca complex, a = 6.293 (4) A, b = 6.944 (2) A, c = 8.853(5) A, a = 110.15 (3)O, /3 = 105.60 (6)", y = 95.34 (5)", Z = 1; Mg complex, a = 20.686 (11) A, b = 10.962 (18) A,c = 14.885 (9) A, /3 = 91.45 (5)O, Z = 4. Lithium is tetrahedrally coordinated while the other three cations are octahedrally coordinated; the observed metal-oxygen distances are within the ranges generally found in oxygen donor complexes of these metals. The lithium and sodium complexes are polymeric, with the amide and the anion forming bridging groups between neighboring cations. The carbonyl distances become longer in the complexes accompanied by a proportionate decrease in the length of the central C-N bond of the amide; the N-C bond of the dimethylamino group also shows some changes in the complexes. The cations do not deviate significantly from the lone-pair direction of the amide carbonyl and remain in the amide plane. Infrared spectra of the complexes reflect the observed changes in the amide bond distances.

Quench dynamics and defect production in the Kitaev and extended Kitaev models

We study quench dynamics and defect production in the Kitaev and the extended Kitaev models. For the Kitaev model in one dimension, we show that in the limit of slow quench rate, the defect density n∼1/√τ, where 1/τ is the quench rate. We also compute the defect correlation function by providing an exact calculation of all independent nonzero spin correlation functions of the model. In two dimensions, where the quench dynamics takes the system across a critical line, we elaborate on the results of earlier work [K. Sengupta, D. Sen, and S. Mondal, Phys. Rev. Lett. 100, 077204 (2008)] to discuss the unconventional scaling of the defect density with the quench rate. In this context, we outline a general proof that for a d-dimensional quantum model, where the quench takes the system through a d−m dimensional gapless (critical) surface characterized by correlation length exponent ν and dynamical critical exponent z, the defect density n∼1/τmν/(zν+1). We also discuss the variation of the shape and spatial extent of the defect correlation function with both the rate of quench and the model parameters and compute the entropy generated during such a quenching process. Finally, we study the defect scaling law, entropy generation and defect correlation function of the two-dimensional extended Kitaev model.

Monoclinic polymorph of Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe(anhydrous). Parallel packing of 3(10)-/alpha-helices and a transition of helix type

The structures of two crystal forms of Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe have been determined. The triclinic form (P1, Z = 1) from DMSO/H2O crystallizes as a dihydrate (Karle, Sukumar & Balaram (1986) Proc, Natl, Acad. Sci. USA 83, 9284-9288). The monoclinic form (P2(1), Z = 2) crystallized from dioxane is anhydrous. The conformation of the peptide is essentially the same in both crystal system, but small changes in conformational angles are associated with a shift of the helix from a predominantly alpha-type to a predominantly 3(10)-type. The r.m.s. deviation of 33 atoms in the backbone and C beta positions of residues 2-8 is only 0.29 A between molecules in the two polymorphs. In both space groups, the helical molecules pack in a parallel fashion, rather than antiparallel. The only intermolecular hydrogen bonding is head-to-tail between helices. There are no lateral hydrogen bonds. In the P2(1) cell, a = 9.422(2) A, b = 36.392(11) A, c = 10.548(2) A, beta = 111.31(2) degrees and V = 3369.3 A for 2 molecules of C60H97N11O13 per cell.