Biomedical subjects

V M Lynch

Publications and source records attributed to V M Lynch.

At least 37 records · Page 2Linked to original sources

PubMed1991

Structure of a novel bisindole derivative.

(3aR-[3a alpha,4 beta,5a beta,9[1R,3R(2S),5R,7aS,-12aS],10bR,13a alpha])-Methyl-4-(acetyloxy)-3a-ethyl-3a,4,5,5a,6,11,12,13a-oct ahy dro-9- [1,2,3,4,6,7,7a,- 12-octahydro-3-(2-hydroxy-2-hydroxymethylbutyl)- 1-(methoxycarbonyl)indolizino[1,2-b]indol-7a-yl]-5- hydroxy-8-methoxy-6-methyl-1H-indolizino[8,1-c,d]- carbazole-5-carboxylate methanol hydrate solvate, C46H60N4O10.CH3OH.H2O, Mr = 879 x 06, monoclinic, P2(1), a = 8 x 2878 (8), b = 31 x 018 (4), c = 9 x 2267 (7) A, beta = 105 x 211 (7) degrees, V = 2288 x 8 (4) A3, Z = 2, Dx = 1 x 28 g cm-3, mu = 0 x 8580 cm-1, Mo K alpha radiation, lambda = 0 x 7107 A, F(000) = 944, T = 198 K, R = 0 x 0382 for 2931 reflections [Fo greater than or equal to 4 sigma(Fo)]. A very short intramolecular hydrogen-bonding interaction is observed between the hydroxyl group and N9 of the vindoline portion of the molecule. The relevant parameters are: O3--H3O...N9, O...N 2 x 598 (4), H...N 1 x 68 (5) A, O--H...N 164 (5) degrees. Molecules related by the 2(1) screw operation are hydrogen bonded into columns parallel to b.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbazoles↗

PubMed1991

Determination of the absolute configuration of a novel dipeptide isostere.

(1R-[1 alpha(1R*,2R*,3S*),2 beta,5 alpha])-2-(4-Morpholinocarbonyl)- 3-phenylcyclopropane 2-(1-methyl-ethyl)-5-methylcyclohexyl ester, C25H35NO4, Mr = 413 x 56, orthorhombic, P2(1)2(1)2(1), a = 9 x 359 (2), b = 10 x 1172 (14), c = 24 x 710 (4) A, V = 2339 x 8 (6) A3, Z = 4, Dx = 1 x 17 g cm-3, mu = 0 x 7332 cm-1, Mo K alpha radiation, lambda = 0 x 7107 A, F(000) = 896, T = 198 K, R = 0 x 0475 for 2460 reflections [Fo greater than or equal to 4 sigma(Fo)]. The assignment of the absolute configuration was based on internal comparison to the (-)-menthol moiety. The morpholenyl and cyclohexyl rings are in the chair conformation. The amide group is essentially planar [max. deviation 0.025 (2) A for N19] resulting in a close non-bonded contact between the amide oxygen, O18, and H24a of 2 x 24 (4) A.

Dipeptides↗

PubMed1991

Structure of a fully protected seco-erythronolide B acid derivative.

(3S,4R,5S,6R,7R,9R,10S,11S,12S,13S,- 14R)-14-Benzyloxymethoxy-10,12-O-carbonyl-4-N- imidazolylcarbonyl-6,7-O-isopropylidene-3,5,7,9,11,- 13-hexamethylhexadec-1-ene-4,6,7,10,12,14-hexol, C38H56N2O9, Mr = 684.87, monoclinic, P2(1), a = 8.7302 (12), b = 15.597 (2), c = 14.463 (2) A, beta = 104.797 (10) degrees, V = 1904.1 (4) A3, Z = 2, Dx (198 K) = 1.19 g cm-3, mu = 0.7893 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 740, T = 198 K, R = 0.0301 for 3141 reflections [Fo greater than or equal to 4 sigma (Fo)]. The crystal structure was undertaken to determine the stereochemistry of the title compound. The molecule is folded on itself in such a way that the portion of the molecule from the phenyl ring at C44 and extending to C28 forms nearly a single turn of a right-handed screw. Large deviations from ideality for several Csp3-Csp3 bond angles are observed that are presumably due to intramolecular steric effects. The largest deviations are: C3-C4-C5 117.8 (2), C5-C6-C7 121.2 (2), C7-C8-C9 115.3 (2), C9-C10-C11 116.2 (2), C11-C12-C13 117.2 (2), C14-C15-C16 115.5 (3) degrees.

Imidazoles↗

PubMed1991

Structure of aqua-hexakis(mu 2-benzoato)-bis(methanol)-mu 3-oxo-triiron(III) benzoate ethanol methanol solvate.

[Fe3(O)(C7H5O2)6(CH3OH)2(H2O)]-[C7H5O2]-C2H5OH-CH3OH (1/1/1), Mr = 1191.56, triclinic, P1-, a = 11.591 (3), b = 13.308 (2), c = 20.154 (3) A, alpha = 96.910 (12), beta = 96.95 (2), gamma = 114.10 (2) degrees, V = 2767.1 (9) A3, Z = 2, Dx = 1.43 g cm-3, mu = 8.471 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 1234, T = 198 K, R = 0.0522 for 6252 reflections [Fo greater than or equal to 4 sigma (Fo)]. The complex has nearly D3h symmetry with two coordinated CH3OH molecules and one coordinated H2O molecule. The coordination around the Fe atoms is essentially octahedral. Each Fe atom lies slightly out of the plane of the O atoms of the bridging benzoates and is directed towards the mu 3-O atom. The average Fe--O distances are 1.907 (2) A for the mu 3-O atom and 2.010 (1) A for the benzoate O atoms.

Benzoates↗

PubMed1991

Structure of a key intermediate in the asymmetric synthesis of (+)-KDO.

Methyl 3-deoxy-7,8-O-(1-methylethylidene)- 1-O-(phenylmethyl)-alpha-D-manno-2-octalopyranoside cyclic carbonate, (1), C20H26O8, Mr = 394.42, orthorhombic, P2(1)2(1)2(1), a = 10.667 (3), b = 10.7972 (14), c = 16.509 (5) A, V = 1901.4 (8) A3, Z = 4, Dx = 1.38 g cm-3, mu = 0.9960 cm-1, lambda(Mo K alpha) = 0.7107 A, F(000) = 840, T = 298 K, R = 0.0355 for 2248 reflections, Fo greater than or equal to 4[sigma (Fo)]. The X-ray structure was undertaken to confirm the stereochemistry of the substituents on the six-membered pyranose ring. The two rings are cis-fused with ring junction torsion angles of -18.7 (3) degrees for C2-C3-C8-C9 and -18.2 (2) degrees for O4-C3-C8-O7. The six-membered ring assumes a slightly distorted twist conformation while the fused five-membered ring is in the half-chair conformation. The isopropylidene moiety is in the envelope conformation.

Deoxy Sugars↗

PubMed1991

The structure of a key intermediate in the total synthesis of dendrobine.

(1R*,4R*,5S*,8R*,11S*)-3,11-Dimethyl-5-hydroxy-6-isopropyl-3-azatricy clo[6.2.1.0(4,11)]undec-6-en-2-one, C15H23NO2, Mr = 249.35, monoclinic, P2(1)/c, a = 7.782(2), b = 23.119(4), c = 7.932(2) A, beta = 101.53 (2)degrees, V = 1398.1(5) A3, Z = 4, Dx = 1.184 g cm-3, Mo K alpha, gamma = 0.7107 A, mu = 0.7259 cm-1, F(000) = 544, T = 298 K, R = 0.0464 for 1887 reflections (F0 greater than or equal to 4[sigma (F0)]). The molecules are H-bonded into infinite columns parallel to c involving the hydroxyl group and the carbonyl O atom [O15...O13(x,y,z-1) 2.756(2); H15...O13 1.84(3) A; O-H...O 173(3) degrees]. The bonds from the bridgehead atom of the tricyclic ring to other ring atoms appear to be elongated [av. 1.549(2) A] compared to the other Csp3-Csp3 bonds in the molecule.

Alkaloids↗

PubMed1991

Structure of a key intermediate in the synthesis of (-)-5-carboxytetrahydroalstonine and (-)-tetrahydroalstonine.

Methyl [4aS*-(4 alpha,4a beta,7 beta,13b beta,14a beta)]-7,8,13,13b,14,14a- hexahydro-4-methyl-5-oxo-4H-indolo-[2,3-a]pyrano[3,4-g]qu inolizine-7-carboxylate acetone solvate, C22H22N2O4.C3H6O, Mr = 424.50, triclinic, P1, a = 9.9955(13), b = 10.8523(14), c = 11.9352(14) A, alpha = 63.189(9), beta = 72.286(9), gamma = 72.901(10) degrees, V = 1081.8(2) A3, Z = 2, Dx = 1.30 g cm-3(198K), mu = 0.8554 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 452, T = 198 K, R = 0.0435 for 3842 reflections, FO greater than or equal to 4 sigma (FO). The acetone solvent is hydrogen bonded to the indole NH group with relevant parameters: N13...O1A 2.982(2), H13...O1A 2.10(2) A, N--H...O 164(2) degrees. The conformation at the C and D ring junction is quasi-cis [relevant torsion angles are C7--N6--C13B--C13A 9.4(2) degrees and C5--N6--C13B--C14 46.7(2) degrees] while the conformation at the D and E ring junction is cis [relevant torsion angles are 37.8(2) degrees for C5--C4A--C14A--C14 and 41.3(2) degrees for C4--C4A--C14A--C1].

Molecular Structure↗

PubMed1991

Structure of (+/-)-(1R,6S)-1-benzyloxy-8,11,11-trimethyl-6-phenylthiobicyclo [5.3.1 ]undec-7-en-3-one.

C27H32O2S, Mr = 420.61, monoclinic, P2(1)/c, a = 8.4756(13), b = 14.710(2), c = 18.425(3) A, beta = 99.575(13) degrees, V = 2265.2(6) A3, Z = 4, Dx = 1.23 g cm-3, mu = 1.5567 cm-1, Mo K alpha, lambda = 0.7107 A, F(000) = 904, T = 298 K, R = 0.0630 for 2942 reflections [Fo greater than or equal to 6 sigma (Fo)]. The cyclooctane portion of the [5.3.1] ring system assumes the boat-chair conformation while the cyclohexene portion has the boat conformation. As has been observed in other [5.3.1]undecene systems, ring strain appears to cause a distortion of the geometry of the bridgehead alkene. The bond length C7--C8 [1.343(5) A] is long for an isolated C--C double bond. The Csp2--Csp3 bond lengths at C7 are asymmetric with C7--C6 being 1.498(5) A while C7--C11 is 1.535(5) A. The maximum deviation from ideality for the torsion angles around the double bond is 16.2(4) degrees (absolute value). This twist in the alkene group is reflected in the non-planarity of the group [max. deviation 0.193(6) A for C9] and in the dihedral angle between the nearly planar portions (C6, C7, C8, C11 and C7, C8, C9, C15), which is 9.4(2) degrees.

Bridged Bicyclo Compounds↗

PubMed1991

The structure of (+-)-21-oxoisopteropodine.

Methyl (1'S*,3S*,4a'S*,5a'S*,10a'R*)- 3',4a',5a',6',7',8',10',10a'-octahydro-2-hydroxy-1'-methyl-10'- oxospiro[3H-indole-3,6'-[1'H]pyrano[3,4-f]indolizine-4'-carb oxylate, (1), C21H22N2O5, Mr = 382.42, monoclinic, P21/c, a = 12.920 (4), b = 10.342 c = 15.192 (8) A, beta = 105.68 (3) degrees, V = 1954.4 (14) A3, Z = 4, D chi = 1.30 g cm-3 (298 K), mu = 0.8738 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 808, T = 298 K, R = 0.0800 for 1000 reflections, F zero greater than or equal to 4 sigma(F zero). The indole NH group is hydrogen bonded to the amide oxygen, O15' (related by chi, 0.5 -y, -0.5 + z), of the indolizine moiety with relevant parameters: N...O 2.79 (2)A, H...O 2.02 (15) A, N-H...O 145 (14) degrees. A close, non-bonded contact of 2.28 (8) A is also observed between O15' and H7'A (related by -chi, 0.5 + y, 1.5 - z).

Chemical Phenomena↗

PubMed1990

The structure of (4R,7R)-4,10,11,11-tetramethyl-5- oxobicyclo[5.3.1]undec-1(10)-en-4-carbaldehyde.

C16H24O2, Mr = 248.36, orthorhombic, P2(1)2(1)2(1), a = 9.0745 (9), b = 12.1499 (15), c = 12.8820 (10) A, V = 1420.3 (3) A3, Z = 4, Dx = 1.16 g cm-3, mu = 0.6946 cm-1, Mo K alpha, lambda = 0.7107 A, F(000) = 544, T = 298 K, R = 0.0624 for 1238 reflections where Fo greater than or equal to 4[sigma (Fo)]. The cyclooctane ring is in the usual boat-chair conformation. The bridgehead atom of the alkene group, C7, has one short [C7--C6 1.485 (6) A] and one long [C7--C11, 1.541 (6) A] Csp2--Csp3 bond. The alkene group is presumably distorted due to ring strain. The six C atoms comprising the group are non-planar [max. dev. 0.114 (7) A for C9]. The two nearly planar fragments (C6, C7, C8, C11 and C7, C8, C9, C18) are twisted by 8.9 (3) degrees.

Aldehydes↗

PubMed1990

Structure of (+/-)-(1R,4S,6S*)-1-benzyloxy-4,8,11,11-tetramethyl-6- phenylthio-bicyclo[5.3.1]undec-7-en-3-one.

C28H34O2S, Mr = 434.64, triclinic, P1, a = 8.9868 (7), b = 11.2933 (11), c = 12.3497 (6) A, alpha = 80.937 (6), beta = 73.108 (5), gamma = 87.405 (7) degrees, V = 1184.32 (15) A3, Z = 2, Dx = 1.22 g cm-3, mu = 1.509 cm-1, Mo K alpha radiation, lambda = 0.7107 A, F(000) = 468, T = 298 K, R = 0.0583 for 6924 reflections [Fo greater than or equal to 4 sigma(Fo)]. The cyclooctane portion of the [5.3.1] ring system is in the boat-chair conformation while the cyclohexene portion assumes the boat conformation. The carbonyl group and the alkene group are nearly parallel in the molecule with a dihedral angle of 14.9 (1) degree between planes through the two groups. Ring strain appears to cause distortion in the alkene functionality. The bond length [C7-C8 1.343 (2) A] is long for an isolated C-C double bond. The torsion angles deviate between 3.7 (2) and 18.39 (14) degrees (absolute values) from ideality. This twist in the alkene group is reflected in the non-planarity of the group [max. deviation -0.177 (2) A for C9] and in the dihedral angle between the nearly planar portions (C6,C7,C8,C11 and C7,C8,C9,C16) which is 12.1 (1) degrees.

Bridged Bicyclo Compounds↗

PubMed1990

Structure of (+/-)-(1S,3S)-3-hydroxy-8,11,11-trimethyl-9-oxobicyclo[5.3.1]undec-7- en-1-yl benzoate.

C21H26O4, Mr = 342.43, monoclinic, P2(1)/n, a = 7.211 (2), b = 19.521 (6), c = 12.674 (3) A, beta = 95.04 (2) degrees, V = 1777.2 (8) A3, Z = 4, Dx = 1.28 g cm-3, Mo K alpha radiation, lambda = 0.7107 A, mu = 0.8152 cm-1, F(000) = 736, T = 163 K, R = 0.0632 for 3754 reflections [Fo greater than or equal to 4 sigma(Fo)]. The molecules exist as hydrogen-bonded dimers [O14-H14...O16 (related by -x, 1-y, 1-z), O14...O16 2.775 (2), H14...O16 1.93 (2) A, O14-H14...O16 175 (2) degrees] which stack in columns along b. Distortion at the bridgehead double bond is observed. Deviations from ideal values for the torsion angles around the double bond, C7-C8, are as large as 17.8 (2) degrees. The dihedral angle between planes through C6-C7-C8-C11 and C7-C8-C9-C15, the planar portions of the alkene moiety, is 13.4 (9) degrees. The Csp2--Csp3 bond lengths involving C7 are asymmetric with C7-C6 1.501 (2) and C7-C11 1.538 (2) A. The bond length C7-C8 is elongated [1.352 (3) A] for a C-C double bond. The enone system is also non-planar [max. deviation -0.404 (2) A for C10].

Bridged Bicyclo Compounds↗

PubMed1990

Structure of the ABC ring subunit of 3-hydroxy-2-oxodendrobine.

(1S*, 4S*, 5R*, 6S* ,8S*, 11R*)-5,6-Epoxy-1-hydroxy-6-isopropyl-3,11- dimethyl-3-azatricyclo-[6.2.1.0(4,11)]undecan-2-one, C15H23NO3, Mr = 265.35, triclinic, P1, a = 7.2170 (6), b = 8.5578 (10), c = 12.4342 (14) A, alpha = 97.017 (9), beta = 91.733 (8), gamma = 109.799 (8) degree, V = 715.04 (13) A3, Z = 2, D chi = 1.23 g cm-3 (298 K), lambda(Mo K alpha) = 0.7107 A, mu = 0.7949 cm-1, F(000) = 288, T = 298 K, R = 0.0482 for 2464 reflections. The molecules exist as hydrogen-bonded dimers in the crystal involving the hydroxyl group and the carbonyl O atom [O13...O14 (related by 2 - x, - y, - z) 2.719 (2) A; H13...O14 1.90 (2) A; O13--H13...O14 165 (2) degrees]. The bonds from the bridgehead atom of the tricyclic ring to other ring atoms appears to be elongated [av. 1.557 (1) A] compared to the other Csp3--Csp3 bonds in the molecule. The lactam ring is essentially planar [maximum deviation is 0.010 (3) A for N3].

Bridged-Ring Compounds↗

PubMed1990

Dendrobine support studies. The structure of a novel 3-azatricyclo[6.2.1.0(4,11)]-undecane derivative.

(1S*, 4R*, 8S*, 11R*)-3-Diphenylmethyl-11-methyl-3- azatricyclo[6.2.1.0(4,11)]undec-5-en-2-one, C24H25NO, Mr = 343.47, monoclinic, P2(1), a = 10.248 (3), b = 8.859 (2), c = 10.344 (2) A, beta = 99.816 (14) degrees, V = 925.4 (3) A3, Z = 2, D chi = 1.23 g cm-1 (163 K), lambda(Mo K alpha) = 0.7107 A, mu = 0.6927 cm-1, F(000) = 368, T = 163 K, R = 0.0423 for 2569 reflections. The compound is spontaneously resolved upon crystallization. The N atom appears to be sp2 hybridized [N is 0.0901 (13) A from plane through three ligand atoms] and in conjugation with the carbonyl group [short N--C bond 1.351 (2) A]. The tricyclic ring system is concave. Ring strain appears to affect C--C bond lengths of the central atom of the 3-ring system. The average C--C bond length for this atom to other ring atoms is 1.551 (2) while the average for all other sp3 C--sp3 C bonds is 1.530 (2) A.

Alkaloids↗

PubMed1990

Structures of two diastereomers of the tetrahydrobenzothiophene moiety of breynolide.

(1) (+/-)-3-Triisopropylsiloxy-2,3,3a,7a-tetrahydrobenzo[b]thiophen -5(4H)-one 1,1-dioxide, C17H30O4SSi, Mr = 358.57, triclinic, P1, a = 7.4383 (14), b = 8.1000 (15), c = 16.895 (3) A, alpha = 80.202 (14), beta = 88.800 (15), gamma = 76.231 (14) degrees, V = 974.0 (3) A3, Z = 2, Dx = 1.22 g cm-3, Mo K alpha, lambda = 0.7107 A, mu = 2.339 cm-1, F(000) = 388, T = 298 K, R = 0.0436 for 3086 reflections [F0 greater than or equal to 4 sigma(F0)]. (2) (+/-)-3-tert-Butyldiphenylsiloxy-2,3,3a,7a-tetrahydrobenzo[b]th iophen- 5(4H)-one 1,1-dioxide, C24H28O4SSi, Mr = 440.63, triclinic, P1, a = 9.113 (2), b = 11.020 (2), c = 12.551 (3) A, alpha = 74.01 (2), beta = 70.83 (2), gamma = 88.70 (2) degrees, V = 1141.4 (4) A3, Z = 2, Dx = 1.28 g cm-3, Mo K alpha, lambda = 0.7107 A, mu = 2.125 cm-1, F(000) = 468, T = 298 K, R = 0.0424 for 4262 reflections [F0 greater than or equal to 4 sigma(F0)]. The two rings are cis-fused with the cyclohexenone ring in the sofa conformation and the tetrahydrothiophene ring in the half-chair conformation for both (1) and (2). However, the bulky siloxy groups assume different orientations in the two compounds. In (1), the triisopropylsiloxy group is equatorial and close intramolecular contacts between H2A and H4B [2.29 (3) A], O11 and C4 [2.934 (3) A] and O9 and C7 [2.979 (3) A] are observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗

PubMed1989

Structure of a functionalized tetrahydrobenzothiophene.

(+-)-4-(tert-Butyldimethylsiloxy)-3a,4,7,7a-tetrahydrobenzo[b] thiophen -3(2H)-one 1,1-dioxide, C14H24O4SSi, Mr = 316.49, monoclinic, P2(1)/n, a = 7.1431 (7), b = 19.643 (2), c = 12.528 (1) A, beta = 104.810 (8) degrees, V = 1699.4-(3) A3, Z = 4, Dx = 1.24 g cm-3, Mo K alpha radiation, lambda = 0.71073 A, mu = 2.597 cm-1, F(000) = 680, T = 298 K, R = 0.0566 for 2733 reflections [Fo greater than or equal to 4o-(fo)]. The two rings are cisfused with the cyclohexene ring in the half-chair conformation while the thiophene moiety has the envelope conformation. The endocyclic bond angles of the cyclohexene ring are enlarged, especially at the bridgehead C atoms, C3a and C7a, which have angles 116.0 (2) and 116.8 (2)o, respectively. There are several close intramolecular contacts: C3...O11 2.614 (3), O10...O11 3.137 (3), O10...C7 3.073 (4) A. Adjacent molecules related by 1-x, 1-y, 2-z stack so that the carbonyl O and C atoms of one molecule lie directly over the carbonyl C and O atoms of the second molecule. The C...O distance is 3.023 (3) A in this intermolecular interaction.

Organosilicon Compounds↗

PubMed1989

Structure of a protected C(1)-C(10) subunit of C(2)-epi-erythronolides A and B.

1-[5-(2-Hydroxy-1,3-dimethyl-4-pentenyl)-2,2,4-trimethyl-1,3- dioxolan-4-yl]-2-methyl-3-pentanone, C19H34O4, Mr = 326.48, monocline, P2i, a = 11.409 (3), b = 7.889 (2), c = 11.690 (3) A, beta = 109.24 (2) degrees, V = 993.4 (4) A3, Z = 2, Dx = 1.09 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 0.6963 cm-1, F(000) = 360, T = 194 K, R = 0.0595 for 1496 reflections [Fo greater than or equal to 4 sigma(Fo)]. Molecules stack into columns parallel to the screw axis. Molecules are hydrogen bonded within each column. A hydrogen bond involving the hydroxyl group of one molecule and the carbonyl O of a second molecule (related by - x, -1/2 + y, - z) with an O...O distance of 2.859 (7) A, an H...O distance of 2.01 (7) A and an O--H...O angle of 164 (6) degrees is observed.

Chemical Phenomena↗

PubMed1989

Structure of a protected C(1)-C(10) subunit of erythronolides A and B.

C19H34O4, Mr = 326.48, orthorhombic, P2(1)2(1)2(1), a = 7.949 (2), b = 14.880 (5), c = 17.047 (5) A, V = 2016 (1) A3, Z = 4, Dx = 1.08 g cm-3, mu = 0.6861 cm-1, lambda(Mo K alpha) = 0.71069 A, F(000) = 720, T = 163 K, R = 0.0644 for 1476 reflections [Fo greater than or equal to 4 sigma (Fo)]. There is an intermolecular H bond involving the hydroxyl group and the carbonyl O (related by 1/2 + x, 3/2 - y, 1 - z) with an O...O distance of 2.838 (5) A, an H...O distance of 2.06 (5) A and an O-H...O angle of 172 (6) degrees. There are no such intramolecular contacts.

Crystallography↗