Near-ambient pressure instrumentation: New directions for Surface Analysis with

XPS and related core-level spectroscopies

Sven L. M. SchroederRoyal Academy of Engineering Bragg Centenary Chairin Engineering Applications of Synchrotron Radiation

University of LeedsDiamond Light Source

Research Complex at Harwell

Near-ambient pressure (NAP) technology …

No need for samples to be ultra-high vacuum compatible

This opens core level electron spectroscopies to a wide range of new analytical applications….

Specs EnviroESCA - Versatile Operation

Liquids Volatile powders Single crystal facet Woven fabric

Samples are placed on

an analysis table with

XYZ positioning

no mounting on a

manipulator

high flexibility

• Whole devices

• In situ / operando

experiments

• Sample libraries

No requirement for ultra-high vacuum or charge neutralisation

Analyser

entrance coneAnalyser

entrance cone

Analyser entrance

coneAnalyser

entrance cone

Analysis

spot

Analysis

spot

Analysis

spot

Analysis

spot

Feasibility

experiments

Carried out with prototype

EnviroESCA system at

supplier’s site

April/May 2017

1 cm

1 cm 1 cm1 cm

Manufacturing of an Active Pharmaceutical Ingredient

• Formulation: fumarate salt ofAPI

• Normally of white appearance, but some batches yellow

• Specific surface area (gSSA)with low, medium, and highspecific energy inputs (SEI)

• Strong connection between colour and mechanical properties forthe material

• Mechanical milling of material with discoloured surfaces was verydifficult at laboratory scale, and not possible at plant scale

JS Stevens, SJ Byard, E Zlotnikov, SLM Schroeder, J Pharm Sci, 100 (2011) 942-948.

?

Origin of surface colour - conventional techniques provide no answer

• Two functional groups containing nitrogen in the API• One nitrogen group is protonated in the salt (white)• Yellow colour suggestive of free base of the API (no salt)• Validation difficult; conventional techniques tried

X-ray Powder Diffraction (XRPD) - slight evidence of amorphous material(halo)

Differential Scanning Calorimetry (DSC) - No second order events wereobserved to support XRPD result

High Performance Liquid Chromatography (HPLC) – no differences in chemicalpurity

Confocal Raman microscopy – no difference

Attenuated Total Reflection (ATR) IR – no difference

JS Stevens, SJ Byard, E Zlotnikov, SLM Schroeder, J Pharm Sci, 100 (2011) 942-948.

Origin of surface colour……analyse XPS N1s emission

• 58% of nitrogen present as NH+

• 49% of nitrogen present as NH+

Surface region is enriched in free base

JS Stevens, SJ Byard, E Zlotnikov, SLM Schroeder, J Pharm Sci, 100 (2011) 942-948.

As expected for the salt

Salt/Co-crystal Continuum

Acidity Constants of the Donor/Acceptor Groups

X HN+ XH----N

XH N

Co-crystal (DpKa < 0)Salt (DpKa > 3)

proton transferProtonation H-bond

theophylline + 5-sulfosalicylic acid theophylline + oxalic acid

??? 0 < DpKa < 3 ???

Example: Theophylline complexes

+ = 2:1 co-crystal

+ = 1:1 dihydrate salt

DpKa = 0.3

DpKa = 2.3

Theophylline Complexes

J. S. Stevens, S. J. Byard, S. L. M. Schroeder, Cryst. Growth Des. 2010, 10, 1435-1442.J. S. Stevens, S. J. Byard, S. L. M. Schroeder, J. Pharm. Sci., 2010, 11, 4453-4457J. S. Stevens, S. J. Byard, C. A. Muryn, S. L. M. Schroeder, J. Phys. Chem. B, 2010 , 14, 13961-13969

C=N

C=NH+

N1s chemical shift of +2.3 eV on protonation of the base - unequivocal

Isonicotinamide Complexes

J.S. Stevens, S.J. Byard, C.C. Seaton, G. Sadiq, R.J. Davey, S.L.M. Schroeder

Angew. Chem. Int. Ed. 50 (2011), 9916–9918

Physical Chemistry – Chemical Physics, 16 (2014) 1150-1160.

C=N

C=NH+

XPS identifies unequivocally whether protonation has occurred

Shift of +2.0 eV with hydrogen transfer to the base

Salt/Co-Crystal Continuum

Unequivocal N1s binding energy

separation between protonated

(HN+) and unprotonated nitrogen

of the base component

Correct and unequivocal assignment of all complexes – 9 salts, 9 co-crystals

Novel & reliable analytical tool for product development

Universal chemical shift of ~ +2 eV due to protonation

J.S. Stevens, S.J. Byard, C.C. Seaton, G. Sadiq, R.J. Davey, S.L.M. Schroeder

Angew. Chem. Int. Ed. 50 (2011), 9916–9918.

Physical Chemistry – Chemical Physics, 16 (2014) 1150-1160.

Salts

Co-crystals

15N solid state NMR

-140

-120

-100

-80

-60

-40

-20

0

20

40

-5 -3 -1 1 3 5 7 9 11 13 15 17 19

∆pK a

Dd

/ p

pm

Salt (amine)

Co-crystal

Protonated nitrogen identifiable

from the magnitude of change in

chemical shift (Dd)

Smaller shift for protonation of

amine compared to heterocyclic,

aromatic nitrogen

Larger shift for co-crystal with

formation of H-bond and

conformational/crystallographic

packing differences

CASTEP analysis permits

unequivocal assignments

Shifts of 50-100 ppm to low frequency with protonation of heterocyclic, aromatic

nitrogen

J.S. Stevens, S.J. Byard, C.C. Seaton, G. Sadiq, R.J. Davey, S.L.M. Schroeder, Physical

Chemistry – Chemical Physics, 16 (2014) 1150-1160.

Salts

Co-crystals

XPS and ssNMR synergy - accelerated development

example: biomaterials/devices - scaffolds for nerve growth (A)

Poly--caprolactone (PCL)

Identify successful peptide immobilisation

– surface technique

– elemental/chemical group sensitivity

RGD-based peptides elicit positive Schwann

cell response

Promote cell adhesion and proliferation

Strong + Biodegradable

Biocompatible

Low Schwann cell attachment / growth

A. C. del Luca, J. S. Stevens, S. L. M. Schroeder, J.-B.

Guilbaud, A. Saiani, S. Downes, G. Terenghi, J.

Biomed. Mater. Res. A, 2013, 101A, 491

Poly--caprolactone

(C6H10O2)n10 mm

10 mm

40-60 mm thickness

with pits

18 mm2 thin films

Nerve

biomedical materials and devices

RGD Neuropeptide Coatings

• Step I

Activation of polycaprolactone (PCL) film

Attachment of 2-chloroethylamine through

nucleophilic attack at carboxylic acid groups of

PCL, forming an amide bond

• Step II

Peptide immobilization

Attachment of RGDSC pentapeptide through

nucleophilic substitution between thiol (CSH)

of peptide and Cl

ClNH3

+Cl

OO

O

O

O NH

Cl

O NH

Cl

OH OH

O NH

S

Cys

Ser

Asp

Gly

Arg

O NH

S

Cys

Ser

Asp

Gly

Arg

RGDSC

PCL film

PCL film

PCL film

A.C. de Luca, J.S. Stevens, S.L.M. Schroeder, J.B. Guilbaud, A. Saiani, S. Downes & G. Terenghi

Journal of Biomedical Materials Research Part A 101A (2013) 491-501.

J. S. Stevens, A. C. de Luca, S. Downes, G. Terenghi, S. L. M. Schroeder,

Surface and Interface Analysis 46 (2014) 673-678.

PeptidesRGD: Arg-Gly-Asp RGDS: Arg-Gly-Asp-Ser

CC

CCOO/

CCOOH

NC=O

COO

CNH+

CN

NH

NH2

H2N

+

CN

CCOO/

CCOOH

NC=O

COO

CNH+/C

O

CC

NH

NH2

H2N

+

C 1s C 1s

N 1s N 1s

O=CN / O=CN /

CNH+

CNH+

NH

NH2

H2N

+NH

NH2

H2N

+

J. S. Stevens, A. C. de Luca, M. Pelendritis, G. Terenghi, S. Downes, S. L. M. Schroeder

Surface and Interface Analysis 45 (2013), 1238-1246.

Control of Surface Chemistry Using XPS

CCl

2p1/2

CCl

2p3/2

Cl

2p3/2

Cl

2p1/2

N 1s Cl 2p

S 2p

De Luca et al., J. Biomed. Mat. Res. A 101 (2013) 2.

DEB = 1.7 eV

C 1s

C 1s

N 1s

N 1sCombination with StoBe DFT calculations of core level binding energy shifts in monomeric gas phase molecules

JACS 130 (2008) 8150

DEB = 0

Aqueous Imidazolewith Emad Aziz, BerlinLiquids…

• Spectra insensitive to

concentration changes

• Strong self-association of

imidazole in solution?

Concentration

Dependence….

M Thomason, GA Hembury, B Sattelle, JS Stevens, E. F. Aziz & S. L. M. Schroeder

Faraday Discussions 179 (2015) 269-289

XPS of Para-aminobenzoic acid (PABA)

a-polymorph

Strong H-bonded COOH dimers and intermolecular NHO bonds

p-p stacking between offset aromatic rings

XPS identifies different chemical moieties

C 1s

J. S. Stevens, C. R. Seabourne, C. Jaye, D. A. Fischer, A. J. Scott

S. L. M. Schroeder, J. Phys. Chem B 118 (2014) 12121-12129.

b-polymorph

Orbitals: GAUSSIAN09 B3LPY/6-31G* DFT

a-PABA

p* resonances sensitive to

chemical environment and

unoccupied MOs

C K-edge

NEXAFS

C K-edge

Electronic and

chemical environment

J. S. Stevens, C. R. Seabourne, C. Jaye, D. A. Fischer, A. J. Scott, S. L. M.

Schroeder, J. Phys. Chem B 118 (2014) 12121-12129.

a-PABA

b-PABA

a-PABA

b-PABACN

XPS XANES

a-PABA

b-PABA

a-PABA

b-PABA

Variation in local environment –

electronic structure and bonding

NEXAFS Spectroscopy

Highest sensitivity for N spectra as only single

nitrogen atom and directly involved in H-

bonding

Polymorphism: a- and b-PABA C

O

N

a-PABA

b-PABA

AMBNAC07 / 08

a-PABA

Only single type of nitrogen, so

more sensitive probe of

electronic structure

Two oxygen environments

Electronic and

chemical environment

O K-edge N K-edge

NEXAFS

J. S. Stevens, C. R. Seabourne, C. Jaye, D. A. Fischer, A. J. Scott, S. L. M. Schroeder, J. Phys. Chem B 118 (2014) 12121-12129.

Solutions: pH dependence

Direct observation of alterations

for in situ solution species

b-

N K-edge

p* sensitive to protonation state

and solvation through unoccupied

MOs

Beam

Microjet

J. S. Stevens, A. Gainar, C. Jaye, E. Suljoti, J. Xiao, R. Golnak, E. F. Aziz & S. L. M. Schroeder

Chem. Eur. J. 21 (2015) 7256-7263

b-

N K-edgeProtonation state and bond length

Ionisation potential (IP) is a direct reflection of

the chemical state and electron density

a

b

Anionic

Cationic

s*CN energy relative to IP is dependent on C

N bond length (term value d = s*CN – IP)

J. S. Stevens, A. Gainar, C. Jaye, E. Suljoti, J. Xiao, R. Golnak, E. F. Aziz & S. L. M. Schroeder

Chem. Eur. J. 21 (2015) 7256-7263

pH dependence

RIXS at nitrogen edge excitation

energies for in situ solution species

Occupied states: RIXS – resonant

inelastic X-ray scattering

Essentially, high resolution X-ray emission

spectroscopy

Similarities in shape for pH 11 and methanol, with shift to lower energy for anionic form

Highest energy peaks (2p p→1s) absent for pH 1 cationic form as use of nitrogen lone pair in extra NH bond instead of delocalised into p MOs

N RIXS

RIXS of pH dependence: interpretation

Widening energy gap between

nitrogen-contributing orbitals for

anionic species

Larger nitrogen HOMO-LUMO gap

for anionic than non-ionic form

J. S. Stevens, A. Gainar, C. Jaye, E. Suljoti, J. Xiao, R. Golnak, E. F. Aziz & S. L. M. Schroeder

Chem. Eur. J. 21 (2015) 7256-7263

Amorphous Components

Surface Amorphous Phases - ‘Dynamic Vapour NEXAFS’Before Humidity Cycle

After Humidity Cycle

• C K-edge – High Surface

Sensitivity

• Micronised API looks like

amorphous API

100% Relative

Humidity Cycle

• Micronised API looks like

Crystalline API

• Recrystallisation of surface

amorphous component has

taken place

A. M. Booth, S. Braun, T. Lonsborough, J. Purton, S. Patel, S. L. M. Schroeder, Am. Inst. Phys. Proc, 882 (2007) 325-327.

Coatings

Presence of an XPS signal from an active pharmaceutical ingredient (API) under a PEG-coat

• Either a very thin coating was applied• Or the coating is present in patches on the surface• Or a physical mixture of the components• Or a more complicated heterogeneous product has been prepared

Patchy polymer coating

Closed-layer PEG coating with thickness below the sampling depth of XPS (1-2 nm)

?

NEXAFS of the Coated API: C K-edge

Coated samples look like the API – where is the PEG ?

C K-edge after Humidity Cycle

• Coated samples look like PEG

• Signal from API suppressed after high humidity

• PEG wets surface if given sufficient mobility through presence of water

DLCDiamond-Leeds

Collaboration

VERSOX - Versatile Soft X-ray

Spectroscopy Beamline

+ complementary Diamond

beamlines

funded by

CMAC @ RCaHContinuous

Manufacturing and

Crystallisation

Research Group

funded by

RAEng Bragg Centenary ChairEngineering Applications of Synchrotron Radiation

Funded by

(Bragg Centre)

VXSFVersatile X-ray

Spectroscopy Facility

XPS / EnviroESCA / XES /

HAXPES

Service and build user

community– industry &

academia

funded by

Facility

Location

Funders

Integrated NAP X-ray Core Level Spectroscopy Infrastructure