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We report the experimental charge density of HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid], which is a common buffering agent. The structure was refined using the Hansen–Coppens formalism. The ability of the HEPES molecule to form stable intermolecular interactions and intermolecular hydrogen bonds in the crystal structure is discussed in terms of its buffering properties. The protonation mode observed in the crystal structure is different from that expected in solution, suggesting that additional factors must be taken into consideration in order to explain the solution properties of the compound. As ordered HEPES molecules are found in the active sites of proteins in several protein crystal structures, our results will allow for quantitative analysis of the electrostatic potential of the interacting surfaces of those proteins.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768110023025/pi5006sup1.cif
Contains datablock HEPES_XD

fcf

Structure factor file (CIF format) https://doi.org/10.1107/S0108768110023025/pi5006HEPES_XDsup2.fcf
Contains datablock HEPES_XD

pdf

Portable Document Format (PDF) file https://doi.org/10.1107/S0108768110023025/pi5006sup3.pdf
Density maps, probability and scale plots, and extra tables

CCDC reference: 788865

Computing details top

Data collection: Bruker APEX2 software; cell refinement: Bruker APEX2 software; data reduction: SAINT intergration software, Bruker AXS SORTAV, R. H. Blessing, Acta Cryst., 1995, A51, 33; program(s) used to solve structure: SHELXS97, G. M. Sheldrick, Acta. Cryst., 2008, A64, 112; program(s) used to refine structure: SHELXS97, G. M. Sheldrick, Acta. Cryst., 2008, A64, 112 XD2006, A. Volkov et al., 2006.

4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid top
Crystal data top
C8H18N2O4SDx = 1.475 Mg m3
Mr = 238.31Melting point: not measured K
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 2838 reflections
a = 8.3222 (2) Åθ = 2.9–52.5°
b = 9.5441 (2) ŵ = 0.30 mm1
c = 27.0123 (6) ÅT = 100 K
V = 2145.53 (8) Å3Unspecified, colourless
Z = 80.30 × 0.17 × 0.17 mm
F(000) = 1024
Data collection top
Bruker APEXII
diffractometer
14200 independent reflections
Radiation source: TXS rotating anode9205 reflections with I > 2σ(I)
Multi-layer optics monochromatorRint = 0.072
ω scansθmax = 55.9°, θmin = 1.5°
Absorption correction: multi-scan
R. H. Blessing, Acta Cryst., 1995, A51, 33
h = 1919
Tmin = 0.917, Tmax = 0.960k = 2221
183825 measured reflectionsl = 5962
Refinement top
Refinement on F2677 parameters
Least-squares matrix: full0 restraints
R[F2 > 2σ(F2)] = 0.023 w2 = 1/[s2(Fo2)]
wR(F2) = 0.048(Δ/σ)max = 0.00001
S = 1.17Δρmax = 0.25 e Å3
7812 reflectionsΔρmin = 0.30 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
S(1)0.449780 (11)0.223422 (10)1.055875 (3)0.01
O(1)0.30720 (5)0.13200 (5)1.055766 (19)0.012
O(2)0.59722 (6)0.14391 (7)1.06091 (2)0.016
O(3)0.43272 (9)0.33901 (7)1.09030 (2)0.019
O(4)0.72733 (6)0.16471 (6)0.716346 (19)0.013
N(2)0.52318 (5)0.30072 (4)0.802790 (14)0.009
N(1)0.53180 (5)0.24798 (4)0.908675 (14)0.009
C(3)0.56020 (6)0.13469 (5)0.871532 (15)0.011
C(6)0.49765 (5)0.41283 (5)0.839221 (16)0.011
C(1)0.45499 (6)0.30079 (5)0.995804 (15)0.011
C(4)0.42546 (5)0.35749 (5)0.886742 (16)0.011
C(5)0.63117 (5)0.19602 (5)0.824642 (15)0.011
C(2)0.46764 (6)0.18862 (5)0.956043 (15)0.012
C(8)0.59956 (5)0.26244 (6)0.713531 (17)0.013
C(7)0.58938 (6)0.36237 (5)0.757307 (16)0.012
H(3A)0.4469190.0806520.8643450.028
H(3B)0.642960.0586260.8877180.028
H(6A)0.4154870.4911040.8241020.032
H(6B)0.6130990.4602560.8486180.029
H(1A)0.3464220.3641660.9920710.028
H(1B)0.5617190.3673370.9954290.028
H(4A)0.4161010.4432020.9133670.029
H(4B)0.3088860.3092460.8794150.028
H(5A)0.7486250.2409370.833180.027
H(5B)0.6542730.111720.7982490.028
H(2A)0.5509990.1061050.9672120.026
H(2B)0.3515340.1428640.9463780.026
H(8A)0.4869650.204280.7105870.029
H(8B)0.6092460.3266570.6802070.028
H(7A)0.707640.4084160.7637970.028
H(7B)0.5104880.4490870.747070.029
H(1)0.638980.2903380.9176640.025
H(2)0.8244140.2184710.7112420.025
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S(1)0.00968 (3)0.01103 (4)0.00846 (3)0.00038 (2)0.00048 (2)0.00017 (3)
O(1)0.00951 (12)0.01311 (15)0.01465 (14)0.00087 (11)0.00130 (12)0.00194 (14)
O(2)0.00963 (14)0.0210 (2)0.01650 (18)0.00171 (13)0.00220 (12)0.00327 (16)
O(3)0.0288 (2)0.01575 (19)0.01223 (16)0.00268 (18)0.00419 (16)0.00476 (15)
O(4)0.01210 (15)0.01339 (17)0.01423 (15)0.00048 (12)0.00226 (12)0.00140 (13)
N(2)0.00958 (11)0.00963 (12)0.00840 (11)0.00021 (9)0.00006 (9)0.00060 (10)
N(1)0.00938 (12)0.01020 (12)0.00841 (11)0.00011 (9)0.00008 (9)0.00036 (10)
C(3)0.01479 (15)0.00986 (14)0.00972 (12)0.00141 (12)0.00014 (11)0.00051 (10)
C(6)0.01423 (15)0.00929 (14)0.01041 (13)0.00152 (11)0.00185 (11)0.00060 (11)
C(1)0.01314 (14)0.01088 (14)0.01011 (12)0.00022 (12)0.00178 (11)0.00050 (10)
C(4)0.01139 (14)0.01207 (15)0.01018 (13)0.00218 (11)0.00151 (10)0.00056 (11)
C(5)0.01170 (13)0.01144 (14)0.00948 (12)0.00260 (11)0.00042 (10)0.00033 (11)
C(2)0.01512 (15)0.01111 (14)0.00912 (12)0.00148 (12)0.00103 (11)0.00029 (11)
C(8)0.01250 (14)0.01720 (18)0.00999 (13)0.00089 (12)0.00011 (11)0.00119 (13)
C(7)0.01335 (14)0.01115 (15)0.01013 (13)0.00023 (12)0.00162 (11)0.00100 (11)
H(3A)0.0255720.0302590.0267080.0097180.0009060.004404
H(3B)0.0329070.0273120.0251910.0130690.0004240.003757
H(6A)0.0390820.0296340.0262230.0161390.0031310.00651
H(6B)0.0296140.0306550.0265010.0086640.0019060.003725
H(1A)0.0278840.02940.0261260.0117510.0017990.00096
H(1B)0.028680.0305050.0256050.0129120.0022680.001975
H(4A)0.0446690.0205530.0226780.005970.003810.003587
H(4B)0.0202270.0351960.0290170.0023480.0029150.005006
H(5A)0.0190750.0336460.0282490.0052030.0036330.00281
H(5B)0.038960.0218140.0220560.0048170.0032980.005119
H(2A)0.0278030.0254170.025340.0108490.0001180.003624
H(2B)0.0197060.0327660.0252980.0076630.001210.002361
H(8A)0.0214880.0341180.0318250.0090220.0009180.004314
H(8B)0.0330640.0298610.0197050.0016590.0033810.005762
H(7A)0.023150.0337830.0256960.0089890.0006010.002515
H(7B)0.033950.0284450.0258750.0124440.0016530.004883
H(1)0.0174330.028960.0278770.0049810.0003230.006657
H(2)0.0194230.0280280.0266690.0002950.0024180.001149
Geometric parameters (Å, º) top
S(1)—O(1)1.4729 (4)C(6)—H(6B)1.0920
S(1)—O(2)1.4491 (5)C(1)—C(2)1.5201 (6)
S(1)—O(3)1.4497 (6)C(1)—H(1A)1.0920
S(1)—C(1)1.7833 (4)C(1)—H(1B)1.0920
O(4)—C(8)1.4164 (7)C(4)—H(4A)1.0920
O(4)—H(2)0.9670C(4)—H(4B)1.0920
N(2)—C(6)1.4691 (6)C(5)—H(5A)1.0920
N(2)—C(5)1.4679 (6)C(5)—H(5B)1.0920
N(2)—C(7)1.4694 (6)C(2)—H(2A)1.0920
N(1)—H(1)1.0090C(2)—H(2B)1.0920
C(3)—C(5)1.5152 (6)C(8)—C(7)1.5216 (6)
C(3)—H(3A)1.0920C(8)—H(8A)1.0920
C(3)—H(3B)1.0920C(8)—H(8B)1.0920
C(6)—C(4)1.5125 (6)C(7)—H(7A)1.0920
C(6)—H(6A)1.0920C(7)—H(7B)1.0920
O(1)—S(1)—O(2)111.85 (3)C(6)—C(4)—H(4A)109.01
O(1)—S(1)—O(3)111.91 (3)C(6)—C(4)—H(4B)110.26
O(1)—S(1)—C(1)105.25 (2)H(4A)—C(4)—H(4B)111.83
O(2)—S(1)—O(3)114.92 (4)N(2)—C(5)—C(3)111.13 (3)
O(2)—S(1)—C(1)106.35 (3)N(2)—C(5)—H(5A)111.45
O(3)—S(1)—C(1)105.72 (3)N(2)—C(5)—H(5B)110.29
C(8)—O(4)—H(2)105.68C(3)—C(5)—H(5A)108.91
C(6)—N(2)—C(5)108.36 (3)C(3)—C(5)—H(5B)109.26
C(6)—N(2)—C(7)108.82 (4)H(5A)—C(5)—H(5B)105.64
C(5)—N(2)—C(7)112.29 (3)C(1)—C(2)—H(2A)110.90
C(5)—C(3)—H(3A)111.74C(1)—C(2)—H(2B)112.91
C(5)—C(3)—H(3B)110.22H(2A)—C(2)—H(2B)109.87
H(3A)—C(3)—H(3B)107.56O(4)—C(8)—C(7)114.38 (4)
N(2)—C(6)—C(4)111.82 (4)O(4)—C(8)—H(8A)108.26
N(2)—C(6)—H(6A)109.77O(4)—C(8)—H(8B)111.00
N(2)—C(6)—H(6B)109.29C(7)—C(8)—H(8A)109.11
C(4)—C(6)—H(6A)107.91C(7)—C(8)—H(8B)107.03
C(4)—C(6)—H(6B)107.27H(8A)—C(8)—H(8B)106.77
H(6A)—C(6)—H(6B)110.75N(2)—C(7)—C(8)114.81 (4)
S(1)—C(1)—C(2)110.67 (3)N(2)—C(7)—H(7A)111.40
S(1)—C(1)—H(1A)107.05N(2)—C(7)—H(7B)106.85
S(1)—C(1)—H(1B)105.61C(8)—C(7)—H(7A)109.08
C(2)—C(1)—H(1A)112.47C(8)—C(7)—H(7B)108.17
C(2)—C(1)—H(1B)110.29H(7A)—C(7)—H(7B)106.11
H(1A)—C(1)—H(1B)110.48
 

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