Solid State Analysis of Metal-Containing Polymers Employing Mössbauer Spectroscopy, Solid State NMR...

Solid State Analysis of Metal-Containing Polymers EmployingMossbauer Spectroscopy, Solid State NMR and F EI TOFMALDI MS

Charles E. Carraher Jr. • Frank D. Blum • Manikantan B. Nair •

Girish Barot • Amitabh Battin • Tiziana Fiore • Claudia Pellerito •

Michelangelo Scopelliti • Anna Zhao • Michael R. Roner • Lorenzo Pellerito

Received: 18 December 2009 / Accepted: 9 February 2010 / Published online: 3 March 2010

� Springer Science+Business Media, LLC 2010

Abstract Polymers in general and metal-containing

polymers in particular are often sparingly soluble or

insoluble, in contrast to small molecules. Thus, special

significance is attached to characterization techniques that

can be applied to the materials as solids. Here, three

techniques are discussed that give structural information

gained from the solid material. Mossbauer spectroscopy is

a powerful technique that may give information on the

structure about the metal-containing moiety for about 44

different nuclei. Its use in describing the structure of the

product obtained from organotin dichlorides and the

unsymmetrical ciprofloxacin is presented along with the

reaction implications of the results. Solid state NMR is also

a useful tool in describing the structure of metal-containing

polymers and its use is briefly described. Finally, MALDI

MS can be used to gain structural information. For many

metals it is particularly useful because of the presence of

different isotopes that allow the identification of units

through comparison of these isotope abundances with ion

fragment clusters. Each of these tools can provide impor-

tant structural characterization information.

Keywords Mossbauer spectroscopy � Solid-state NMR �MALDI MS � F MALDI MS � Organotin polyethers �Antimony-containing polymers � Metallocene polymers

1 Introduction

Polymer solubility is a general problem and is especially

true with metal-containing polymers [1–3]. Because of this,

we and others have focused part of our effort on structural

C. E. Carraher Jr. (&) � G. Barot � A. Battin � A. Zhao

Department of Chemistry and Biochemistry, Florida Atlantic

University, Boca Raton, FL 33431, USA

e-mail: [email protected]

C. E. Carraher Jr. � G. Barot � A. Battin � A. Zhao

Florida Center for Environmental Studies, Palm Beach Gardens,

FL 33410, USA

F. D. Blum � M. B. Nair

Department of Chemistry and Materials Research Center,

Missouri University of Science and Technology, Rolla,

MO 65409-0010, USA

T. Fiore � C. Pellerito � M. Scopelliti � L. Pellerito

Dipartimento di Chimica Inorganica e Analitica ‘‘Stanislao

Cannizzaro’’, Universita degli Studi di Palermo, Viale delle

Scienze, Ed. 17, 90128 Palermo, Italy


C. Pellerito


M. Scopelliti


L. Pellerito


A. Zhao

Everglades Research and Education Center, University

of Florida, Belle Glade, FL 33430, USA

M. R. Roner

Department of Biology, University of Texas at Arlington,

Arlington, TX 76010, USA


Present Address:F. D. Blum

Department of Chemistry, Oklahoma State University,

Stillwater, OK 74078, USA

123

J Inorg Organomet Polym (2010) 20:570–585

DOI 10.1007/s10904-010-9336-y

analysis techniques that can be carried out on solid mate-

rials. Here, we will briefly describe some of these tech-

niques utilizing examples from our research. The

techniques that will be covered are Mossbauer spectros-

copy, MALDI MS, and solid state NMR.

2 Mossbauer Spectroscopy

Mossbauer spectroscopy is a powerful technique that gives

information on the electronic distribution and on structural

environment of about 44 different nuclei [4–12]. The use of

Mossbauer spectroscopy to assist in the structural deter-

mination of polymers has been practiced since the 1960s

with an early review dated in 1971 [13]. Its use as a

polymer analysis tool has been recently reviewed [14].

Pittman helped pioneer this area for polymers employing it

in describing a number of ferrocene-containing polymers,

where portions of the pendant ferrocenes were converted to

ferricenium units [15–17].

Mossbauer spectroscopy allows the structural analysis of

certain elements situated in complex structures. Briefly,

Mossbauer spectroscopy is a resonant absorption spec-

troscopy that is observed best in isotopes having long-

lived, low-lying excited nuclear energy states. The largest

recoil-free resonant cross-section is found for iron 57.

Recently, Mossbauer spectroscopy was used on Mars to

identify iron compounds that are present in the Martian

landscape. There are over 20,000 entries in SciFinder for

Mossbauer spectroscopy of which the two largest entries

are for iron and tin-containing compounds. Mossbauer

spectroscopy is an extremely powerful structural charac-

terization tool that has been greatly overlooked, probably

because often Mossbauer spectrometers must be dedicated

to a single element and measurements generally take hours

to weeks to complete. Even so, it has been helpful in our

work.

2.1 Experimental 119Sn Mossbauer Spectroscopy

The 119Sn Mossbauer spectra were measured at liquid

nitrogen temperature with a multichannel analyzer [TAKES

Mod. 269, Ponteranica, Bergamo (Italy)] and the following

Wissenschaftliche Elektronik system [MWE, Munchen

(Germany)]: a MR250 driving unit, a FG2 digital function

generator and a MA250 velocity transducer, moved at linear

velocity, constant acceleration, in a triangular waveform.

The organotin(IV) samples were maintained at liquid

nitrogen temperature in a model NDR-1258-MD Cryo

liquid nitrogen cryostat (Cryo Industries of America, Inc.,

Atkinson, NH, USA) with a Cryo sample holder. The

temperature was controlled at 77.3 ± 0.1 K with a model

ITC 502 temperature controller from Oxford Instruments

(Oxford, England). The multichannel calibration was per-

formed with an enriched iron foil [57Fe = 95.2%, thickness

0.06 mm, Dupont, MA (USA)], at room temperature, by

using a 57Co/Rh [10 mCi, Ritverc GmbH, St. Petersburg

(Russia)], while the zero point of the Doppler velocity scale

was determined, at room temperature, through absorption

spectra of natural CaSnO3 (119Sn = 0.5 mg/cm2) and a

Ca119SnO3 source [10 mCi, Ritverc GmbH, St. Petersburg

(Russia)]. The obtained 5 9 105 count spectra were refined

to obtain the isomer shift, d (mm s-1), and the nuclear

quadrupole splitting, |Dexp| (mm s-1).

2.2 Results Obtained with 119Sn Mossbauer

Spectroscopy

We have synthesized a number of organotin polymers

based on reactions between organotin dihalides and various

antibiotics [18–32]. These polymers have shown a good

ability to inhibit a variety of cancer cell lines, bacteria, and

viruses. One of these antibiotics is ciprofloxacin.

Ciprofloxacin is a broad spectrum antibiotic used to treat

both gram negative and gram positive bacterial infections. A

second generation fluoroquinolone, it is marketed worldwide

under over 300 different brand names. It kills bacteria by

interfering with the enzymes that cause DNA to rewind after

being copied resulting in DNA and protein synthesis being

stopped. We have synthesized a variety of products from the

reaction of ciprofloxacin with organotin dihalides, Fig. 1

[28, 29]. These products show a good ability to inhibit a

variety of cancer cell lines and some ability to inhibit various

viruses and a number of bacteria [30–32].

While the general repeat unit for R2Sn ciprofloxacinate is

given in Fig. 1, there are several structural variations that

involve the precise structure about the organotin moiety. The

organotin moiety can be connected through two oxygen

atoms, two nitrogen atoms, or one nitrogen atom and one

oxygen atom. The structures with two nitrogen and two

oxygen atoms are referred to as the symmetric structures, and

the structure containing one oxygen atom and one nitrogen

NN

N

F

O

O

O

Sn

R

OR

O

NSn

R

R

N

Fig. 1 Proposed general structure of the R2Sn-ciprofloxacinate

polymer

J Inorg Organomet Polym (2010) 20:570–585 571

123

atom connected to the organotin is referred to as the asym-

metric structure. These possibilities are shown below.

�O�Sn�O� �N�Sn�N� �N�Sn�O�

Further, the carbonyl group can be attached to the

oxygen by what is referred to as bridging and non-bridging.

The bridging structure forms a distorted octahedral

arrangement about the organotin moiety, whereas the non-

bridging structure forms a distorted tetrahedral structure.

Infrared and Mossbauer spectroscopy can be used to assign

these structures. Further, the bridging structures can be

either cis or trans. Mossbauer spectroscopy is capable of

distinguishing between these possibilities.

The analysis of the experimental spectra is given in

Fig. 2.

The structures of six coordinate R2SnCh2 species were

considered to be simple octahedral (HCh can be a variety

of bidentate, monoprotic chelating agents). Most early

studies interpreted results on the basis of simple trans or cis

structures [33–39]. It is true that some structures are trans

in solution [40, 41] and the solid state [42], and others are

certainly cis [43, 44]. In 1977, Kepert [45] reported that

many octahedral organometallic complexes, including

several tin complexes, are of neither regular trans nor

regular cis geometry, but that an intermediate geometry,

skew or trapezoidal bipyramidal, is more stable (skew

structures have C–Sn–C angles of 135–155 �C).

As a rule, R2SnCh2 complexes prefer a trans arrange-

ment where the ligand bite (distance between the two

coordinating atoms) is large and tend to become cis when

the bite is small [36]. For example, acetylacetonate (acac)-

type ligands form a six-member chelate-metal ring, and

trans configurations are expected. The calculated and

experimental C–Sn–C angles are 175–178� for the

benzoylacetonates and di benzoylmethanoates trans struc-

tures [46]. Both picolinates and tropolonates (trop) have

smaller bites than the acac family ligands and the structural

assignment is described as skew or cis-skew configurations

for R2Sn(trop)2 (119–143� for C–Sn–C angle) [46]. In the

quinolinolate group of these complexes, the oxinates, with

less steric crowding about the central atom, have structures

that are nearly cis (109–120�) [37].

Sn

O O

OOR RR1

R1

(1)

Sn

O O

O O

R R

R 1 R 1

(2)

The analysis of the Mossbauer spectra of the three

diorganotin(IV) ciprofloxacinate complexes allowed the

calculation of the Mossbauer parameters, isomer shifts, d,

and quadrupole splittings, |Dexp|, reported in Table 1. Each

complex showed a two doublets spectrum characteristic of

the occurrence of two different tin(IV) environments in the

organotin polymers. The values of Mossbauer parameters

are in the range found for other organotin(IV) derivatives.

49.0

59.0

69.0

79.0

89.0

99.0

1

10.1

6- 4- 2- 0 2 4 6

rela

tive

abso

rptio

n (%

)

mm/s

Fig. 2 Mossbauer spectrum of

the product of diethyltin

dichloride and ciprofloxacin

where ? denotes experimental

points. The bold line is the fitted

spectrum of the Et2Sn(IV)

ciprofloxacinate which gives

two doublets, the first

attributable to N–Sn–N

environment (long dashes), the

second to OCO–Sn–OCO (shortdashes)

572 J Inorg Organomet Polym (2010) 20:570–585

123

Because of the electron-withdrawing property, the isomer

shift, d, of the diphenyltin derivative is lower than that of

the dialkyltin(IV) compounds [47–50] (see Table 1).

The experimental |D1exp| values ranged from 1.61 for

Ph2Sn(IV)ciprofloxacin to 2.03 mm s-1 for Bu2Sn(IV)cip-

rofloxacin, while |D2exp| ranged from 2.04 to 2.66 mm s-1

for these organotinciprofloxacinates (Table 1).

The |D1exp| values are consistent with a R2SnN2 tetra-

hedral configuration (Fig. 3). The |D2exp| values are con-

sistent with a tetrahedral environment around the tin(IV)

atoms, presumably distorted towards a skew trapezoidal

trans-R2SnO4 configuration, with C–Sn–C angles �180�(Fig. 4).

Infrared spectroscopy is an assumed solid state analysis

technique that can be carried out on solids, liquids and

gases and so is not covered as a separate solid state analysis

technique. Even so, it is often employed in tandem with

other analysis techniques as well as being used as a stand-

alone tool. Here, we briefly describe its use in conjunction

with Mossbauer spectroscopy for analyzing the structure of

the ciprofloxacin polymers.

The infrared spectra for the diorganotin(IV) ciprofloxa-

cinate polymers are complicated by the presence of an

additional carbonyl, the ring ketone, assigned around

1,623 cm-1.

The strong peak at 1,708 cm-1 in the ciprofloxacin

spectrum, assigned to the carbonyl group of the carboxylic

acid, is missing in the spectrum of the products. A new

band is found in all of the polymer spectra at 1,578 cm-1.

This band is assigned to the asymmetric stretching for

bridged carboxylic groups. A new band is also found at

about 1,420 cm-1 for all of the polymer products assigned

to the symmetric carbonyl stretching. The ketone carbonyl

band is also present at about 1,620 cm-1 for all of the

polymer products.

The infrared spectrum is then consistent with the

organotin moiety present in a distorted octahedral structure

in the symmetric –O–Sn–O structure. The data is also

consistent with the structural assignments given by the

Mossbauer findings.

2.3 Reaction Implications

The most reasonable way for the symmetrical structures to

form about the organotin moiety is by the preferential initial

addition of one of the Lewis bases, either the nitrogen or

oxygen. The organotin polymer production occurs by means

of the coupling of these units and their subsequent growth.

We believe that the initial growth step in the polymer-

ization is the formation of the –O–Sn–O– group based on

the following. The reaction with model compounds (i.e.

compounds that are structurally similar antibiotics but

contain only one functional group) enrofloxacin in partic-

ular, occurs rapidly and in good yield. Here only the

enrofloxacin–Sn–enrofloxacin compound can form, 3.

N

O

O

N

O O Sn

N

N

N

N

F

F

CH 3

CH 3

O O

R

R

(3)

By comparison, reaction with the ester of ciprofloxacin,

where only the amine reacts with the organotin chloride,

gives a poor yield of the corresponding dimer, 4.

Table 1 Experimental Mossbauer parameters for diorganotin(IV)

ciprofloxacinate

Compound d1 |D1exp| Dtet d2 |D2exp|

Et2Sncipro2a 0.97 1.96 -1.82 1.08 2.29

Bu2Sncipro2a 0.98 2.03 -1.82 1.20 2.66

Ph2Sncipro2a 0.82 1.61 -1.61 0.92 2.04

Cipro = ciprofloxacinate, sample thickness ranged between 0.50 and

0.60 mg 119Sn cm-2; isomer shift, d ± 0.03, mm s-1, with respect to

BaSnO3; nuclear quadrupole splittings, |Dexp| ± 0.02, mm s-1

a The partial quadrupole splittings, mm s-1, used in the calculations

are: {Alk} = -1.37; {Ph} = -1.26; {N} = -0.564

Fig. 3 Tetrahedral configuration of tin connected to two nitrogens of

two ciprofloxacin-derived moieties


123

Sn N N

N

N

N

N

O

O

O

O

O

O R

R

F

F

C H 3

CH 3

(4)

Both products were formed employing reaction condi-

tions similar to those employed for the polymer synthesis.

As noted, the yield for the enrofloxacin was high whereas

the product yield for the ciprofloxacin ester was low, con-

sistent with the initial formation of the –O–Sn–O– product.

We are currently investigating the use of Mossbauer

spectroscopy to help solve other structures. For instance,

we have reported the synthesis of a number of metal-con-

taining materials that form what we call anomalous fibers.

This phenomenon has been known for about 40 years, but

the precise structures of the fibrous and non-fibrous prod-

ucts have not been fully investigated [14, 51, 52]. Pre-

liminary Mossbauer evidence indicates that the non-fibrous

materials contain only tetrahedral organotin compounds,

while the fibrous products are present in extremely strained

environments.

3 Solid State NMR Spectroscopy

We have synthesized a wide variety of organotin polye-

thers for the purpose of beginning to understand the

structure/property relationship with respect to their ability

to inhibit cancer growth [53–58].

One of these products was derived from the reaction of

dibutyltin dichloride and poly(ethylene glycol) (PEG

10,000; Fig. 5). This product shows a reasonable ability to

retard the growth of a number of cancer cell lines [56]. Of

specific interest is its ability to inhibit several pancreatic

cancer cell lines offering very high Chemotherapeutic

Index values [58]. This product is soluble so structural

studies and comparisons can be made that are not usually

available with metal-containing polymers. Here, we briefly

describe 13C NMR spectra for this product.

3.1 Experimental 13C-Nuclear Magnetic Resonance

(NMR)

Liquid state 13C NMR spectra were recorded on a Varian

Mercury 400 (100 MHz) spectrometer. Chemical shifts

were reported in ppm (from tetramethylsilane), with the

solvent resonance employed as the internal standard

(CDCl3 at 77.0 ppm) using a 5 mm tube. Samples were

prepared in the 5–20 mg/ml range in D2O and CDCl3.

Broadband proton decoupling was used.

The solid state NMR spectra were obtained on a Tecmag

Discovery spectrometer equipped with a DotyXC4 mm

CP-MAS probe (Doty Scientific, Columbia, SC) operating

at 100.7 MHz for 13C. Proton cross-polarization was used

followed by proton decoupling. The samples were spun at

approximately 9.6 kHz. A cross polarization (CP) time of

2.0 ms at a field strength of 66 kHz, and a 1 s recycle delay

was used. The number of scans used depended on the

sample, but ranged from 5,000 to 21,000. The chemical

shifts were set using an external standard of poly(methyl

methacrylate) in a separate experiment just before mea-

suring the samples of interest to this study.

3.2 Results from 13C NMR

In the 13C NMR (100 MHz, CDCl3) spectrum of Bu2SnCl2,

signals were found at d 26.8, 26.5, and 26.3 ppm attribut-

able to the three CH2 groups next to tin metal, and at

Fig. 4 Octahedral

configuration about tin


123

13.5 ppm associated with the CH3 group of the butyl

groups (Fig. 6). For PEG (Mw 10,000), the spectrum

(Fig. 7) showed one resonance at d 70.5 ppm, in addition

to the triplet from CDCl3. The polymer of Bu2SnCl2 and

PEG Mw 10,000 (Fig. 8) exhibited resonances at d57.9 ppm using solid state 13C NMR. This narrow reso-

nance was associated with the PEG-10,000 carbons and the

sharpness was likely due to the mobility of the PEG chains.

Resonances around 16.0 (broad) and at 1.9 ppm were due

to the Bu2Sn groups. These results are consistent with the

proposed structure.

Metal-containing polymers do not always yield high-

quality, high-resolution spectra. For example, the product

from nitro-p-phenylenediamine and titanocene dichloride

gives a solid state spectrum with poor resolution (broad

resonance), possibly because the product is paramagnetic.

This particular product offers entire or whole-chain elec-

tron delocalization and was doped with iodine, thereby

increasing the bulk conductivity 104–105 times [59]. The

terms entire chain electron delocalization or resonance are

employed to indicate that electron movement can occur

through the entire chain because of the presence of pi

electrons and vacant d orbitals on the metal.

4 F TOF MALDI MS

Mass spectrometry can be run on solids, but most EI MS

are limited to about 500 Da for useful ion fragmentation.

Many metal-containing compounds are not suitable for

general GC MS because of their lack of appreciable vola-

tility. Pyroprobe EI MS has been employed to good mea-

sure, giving useful spectra to about 500 Da. Years ago we

developed a version of pyroprobe MS employing the

thermogravimetric instrument to create the temperatures

needed to effect volatile fragments that were then analyzed

using EI MS [60]. This instrument, is now commercially

available from Finnigan as the model TSQ 70 quadrupole

MS. Again, the mass limit is about 500 Da. Today there

exists a number of MS approaches that exceed this range,

but the technique that allows the greatest mass range is

Fragmentation Matrix Assisted Laser Desorption/Ioniza-

tion Mass Spectrometry, MALDI MS.

In 1981, Barber et al. [61] and Liu et al. [62] independently

introduced the concept of employing matrix-assisted desorp-

tion/ionization where the absorption of the matrix is chosen to

coincide with the wavelength of the employed laser to assist in

the volatilization of materials. In 1988, Tanaka et al. [63], and

Hillenkamp and coworkers [64] employed the laser as the

energy source giving birth to matrix-assisted laser/desorption

mass spectroscopy, MALDI MS.

MALDI MS was developed for the analysis of nonvol-

atile samples and was heralded as an exciting new MS

technique for the identification of materials with special

use in the identification of polymers. Although it has ful-

filled this promise to only a limited extent, it has been an

immensely powerful tool in the hands of biochemists who

work with water-soluble products. Why has MALDI MS

been largely neglected by most synthetic polymer chem-

ists? The answer involves the lack of congruency between

the requirements of MALDI MS and most synthetic poly-

mers. In order for MALDI MS to be effective, the product

to be analyzed should be soluble in the same solvent,

typically water, that contains the matrix molecules allow-

ing intimate contact between the matrix and the product.

For some polymers, such as poly(ethylene glycol) that are

water soluble, good analysis is routine. For most other

polymers, only oligomeric materials have been success-

fully analyzed employing traditional MALDI MS. This

problem of analyzing samples that do not meet the solu-

bility requirement has been recognized by us and others.

Progress has been made to allow MALDI MS to become a

routine analysis tool [20, 57, 65–72].

There are several keys to obtaining a successful MALDI

MS spectrum. Briefly, these include sample preparation

and choice of matrix. It is best to experiment with different

sample preparations until one is identified that gives suit-

able spectra. For structurally similar compounds, once an

appropriate sample preparation is determined for one

compound, it should be suitable for the other compounds.

Sn

CH3

CH3

ClCl OHO

HSn

CH3

CH3

O

OO

R

R

n m

n+

Fig. 5 Synthetic outline of

organotin products from

reaction with poly(ethylene

glycol)


123

It is believed that the matrix performs several tasks.

First, it captures the incident laser radiation and, in the best

case scenario, acts to make the polymer volatile. Thus, it

absorbs the laser radiation without imparting excessive

internal energy to the analyte. Second, it assists in

‘‘securing’’ the sample or analyte through chelation of the

sample. Third, it contributes a proton thus charging the

analyte. Typical MALDI MS matrixes are pictured in

Fig. 9. All are polar and are ideal for polar molecules

such as many natural polymers including nucleic acids,

polysaccharides and proteins but not for most non-polar

synthetic polymers. Also, all contain acidic protons that

)1f( mpp00102030405060708

)1f( mpp0.510.020.52

Fig. 6 13C NMR spectra of

dibutyltin dichloride in CDCl3

ppm (f1)050100150200

Fig. 7 13C NMR spectra of

PEG-10,000 in CDCl3


123

can be somewhat easily extracted and added to the analyte,

creating a charged analyte molecule suitable for trans-

versing the instrumental pathway for analysis, 5.

RCOOH + M RCOO- + MH+ (5)

We have focused on the fragmentation of polymers

emphasizing those containing metal atoms. Thus far, we

have analyzed polymers containing tin [25, 57, 73], tita-

nium [73, 74], zirconium [73], hafnium [73], iron [66],

cobalt [74], arsenic [65, 66], antimony [69, 75], bismuth

[69, 75], vanadium [67], and niobium [68]. While we have

analyzed non-metal containing samples, there are several

positive aspects of employing metal-containing samples.

First, most metals exist with isotopes that are present in

sufficient amounts that will allow isotopic matching to

assist in identifying the presence of a particular metal. In

fact, we have routinely been able to analyze ion fragments

to 2,000 Da with good isotopic abundance matches. Sec-

ond, we are finding that most of the ion fragments are

created at heteroatom sites, especially metal moiety sites.

Thus, metal-containing samples have a built-in site that is

susceptible to fragmentation.

Following, we will describe examples illustrating the

use of MALDI MS to structurally characterize metal-con-

taining samples. Since the emphasis is on the fragmentation

of the polymer chains (rather than on analysis of whole or

total intact chains), we often refer to this emphasis as

Fragmentation MALDI MS or simply F MALDI MS. Even

so, we have been able to identify ion fragments and intact

chains to about 200 kDa, the limit thus far employed.

These high mass ion fragments are often sporadic in

appearance with some repeatable and others not; i.e. in

looking at the same material over a period of time some of

the high mass ion fragments continue to appear while

others appear in only some of the mass spectra. Thus, it is

best to simply note: (1) that the appearance of such ion

fragments is evidence that the materials’ molecular weight

is reasonable with suggested possible structures, and (2) to

emphasize the appearance of dimers, trimers, and higher

units since their appearance is predictable and can be

verified through isotopic abundance comparisons.

We reacted triphenylantimony dichloride with acyclovir

to obtain a product with an average molecular weight of

8 9 106 (6) [75]. Figure 10 contains the low-range

MALDI MS for the product of triphenylantimony and

acyclovir. Antimony has two natural occurring isotopes,

Sb-121 at 57% and Sb-123 at 43%. Table 2 contains

assignments for the fragments given in Fig. 10. U stands

for a unit here and throughout this discussion.

N

N H

N

N

NH

O

O

O Sb

R 1

R 1

(6)

The couplets had ratios of about 57/43 corresponding to

the natural abundance of antimony isotopes (Table 3) and

consistent with the presence of one antimony atom. Spectra

were found at higher masses that correspond to the pres-

ence of two, three, and four antimony atoms within

Fig. 8 Solid state 13C NMR

spectra of polymer of dibutyltin

dichloride and PEG-10,000


123

fragments that approximately correspond to dimer, trimer,

and tetramer-containing fragments (Table 4). In each case

the agreement was reasonable and consistent with the

number of antimony atoms assigned to the proposed

structure.

Dienestrol (4-[4-(hydroxyphenyl)hexa-2,4-dien-3-yl]phe-

nol, 7), is one of the most widely used sex hormones. It is

sold under a variety of trade names including Farmacyrol,

Lipamone, and Retalon-Oral.(7)

C H 3

CH 3

OH

O H

O

CH 3

O H

O

OH

O H

O OH

OH

OH OH OH

N

O

OH

O H

O

O H

O

CH 3

C H 3

O

OH

Ferulic Acid 2,5-Dihydroxybenzoic Acid Dithranol

4-Hydroxy-alpha-cyanocinnamic Acid Sinapinic Acid

Fig. 9 Structures of commonly

employed MALDI MS matrix

materials

1001.0820.6640.2459.8279.499.0

Mass (m/z)

0

2.8E+4

0

10

20

30

40

50

60

70

80

90

100

% In

ten

sity

]36972 ,6.924 = PB[1# cepS regayoV

7.924

7.134

6.234

4.251

5.641

6.4515.891

7.5055.0025.531

5.271 5.8424.0116.7725.741

4.501 5.622 6.3726.561 5.983 4.434 7.9054.031 6.402 0.732

Fig. 10 MALDI MS for the product of triphenylantimony dichloride and acyclovir


123

Dienestrol is widely used in hormone therapy, mainly

hormone replacement therapy or more precisely, estrogen

replacement therapy.

We synthesized metallocene polyethers from reaction of

dienestrol with the corresponding Group IVB metallocene

dichloride [25, 73, 74]. The repeat unit is given in 8. These

materials have shown the ability to inhibit a wide variety of

cancer cell lines [73].

CH 3

CH 3

O

O

R

Ti

R

(8)

MALDI MS was carried out on the products. Here we

will describe the results related to dienestrol itself and the

titanocene product. The MALDI MS for dienestrol was

obtained and three major ion fragments were found. The

most intense was at 265 (all ion fragments are given in m/z

or m/e = 1 in Daltons, Da) assigned to dienestrol. The next

intense at 212 was assigned to dienestrol minus 2 C2H4.

The third ion fragment was assigned to the matrix itself.

Table 5 contains the ion fragments and ion fragment

clusters found for the product of titanocene dichloride and

dienestrol in a range to 1,000 Da.

A number of abbreviations are employed to describe the

possible ion fragment structures. Some of these are described

in 9. Additional ones are U = one unit; 2U = two units,

D = dienestrol, and Ph = phenylene. Further, in Tables 5, 6

and 7 A represents the O-phenylene moiety, and B represents

the dienestrol unit minus the O-phenylene unit as shown in 9.

C H 3

CH 3

O

O

R

R A

B

(9)

There is some loss of the cyclopentadienyl, Cp, group.

This is not unexpected in light of other MS studies that show

that metallocene associated Cp groups are especially sensi-

tive to removal from the metallocene moieties [60, 74].

Table 2 Fragments derived from the product of triphenylantimony

dichloride and acyclovir employing alpha-cyano-4-hydroxycinnamic

acid as the matrix

m/e Assignment

136 Pu

198,200 SbPh

278,280 SbPh2

507,509 U-OCCOC

152,154 SbOC

248 Ac,Na

430,432 Ph3SbOCCOC

Pu purine moiety, Ph phenyl, U one unit, Ac acyclovir moiety

Table 3 Isotope abundance ratios for various single antimony-con-

taining fragments from Fig. 10

m/e 121 123

Natural abundance, % 57 43

SbPh 198 200

Found 57 43

SbPh2 278 280

Found 57 43

Ph3SbOCCOC 430 432

Found 52 48

U-OCCOC 507 509

Found 55 45

Ph phenyl, U one repeat unit

Table 4 Isotope abundance ratio for fragments containing multiple

antimony atoms for the product of triphenylantimony dichloride and

acyclovir

Two antimony-containing fragments

Calculated percentage 33 49 18

2U-COCCO, m/e 1,078 1,080 1,082

Found 36 46 18

2U-NPuCO, m/e 1,323 1,325 1,327

Found 35 48 17

Three antimony-containing fragments

Calculated percentage 19 42 31 8

3U, m/e 1,718 1,720 1,722 1,724

Found 15 47 30 8

Four antimony-containing fragments

Calculated percentage 11 32 36 18 3

4U-NPuOC, m/e 2,121 2,123 2,125 2,127 2,129

Found 11 31 38 16 4

Pu purine moiety, U unit so 4U is four units


123

Titanium has five isotopes. This allows isotopic abun-

dance matches to be made. Table 6 contains the isotopic

matches for two of these ion fragment clusters. The

abundance matches are reasonable and consistent with the

presence of one titanium atom in each ion fragment cluster.

While 2,5-dihydroxybenzoic acid, BA, has been rec-

ommended as a preferred matrix material for some poly-

meric materials, we found that, at low masses, some of the

major ion fragments were derived from reaction of the

metal-containing moiety with the matrix, BA (or other

matrix employed). This was also found for the current

products. For instance, the ion fragment at 507 is derived

from the solid state reaction between two Cp2Ti units and

the matrix 2,5-dihydroxybenzoic acid, BA. While there

were a few matrix-associated low mass ion fragments, the

proportion was small in comparison to the analogous or-

ganotin-containing polymers [26]. The organotin polymers

were particularly susceptible to dissociation when exposed

to UV radiation so that production of organotin species

appears to have been more prevalent in comparison to the

Group IVB metallocene-containing products studied here.

(The MALDI mass spectrophotometer employed an UV

laser for excitation.)

Table 7 contains the ion fragment clusters found in the

range of 10,000 to about 150,000, along with possible

assignments. These assignments are to be viewed as sug-

gestive only. This is particularly true because of the ready

removal of the Cp group. In other cases, such removals

occur at only the sites of bond scission so the loss of one or

two Cp groups is believed to be typical.

A number of these ion fragments may be entire chains

such as those at 17,068, 21,940, 22,219, 28,310, 49,238,

88,777, and 14,244 which is consistent with the ‘‘soft’’

nature of MALDI MS.

We also modeled the particular assignments as illus-

trated by the following. The product from reaction of

dibutyltin dichloride and 4,6-diamino-1-nitroso-pyrimidine

had the following repeat unit structure, 10, and its low

range MALDI MS is given in Fig. 11 [55]. Alpha-cyano-4-

hydroxycinnamic acid is the employed matrix here.

Table 5 Most abundant ion fragment clusters for the product from

titanocene dichloride and dienestrol; 100–1,000 Da

m/e (Proposed) assignment

129 CpTiO

266 D

313 U - A

551 U ? B - Cp

643 U ? Cp2TiO

193 Cp2TiO

289 D, Na

529 U ? A, O - Cp

573 U ? B

A and B are defined in 9

Cp cyclopentadiene moiety, U one unit, D dienestrol unit

Table 6 Isotopic abundance matches for ion fragment clusters cen-

tering about 529 and 551 Da

m/e % Nat

abundance

U ? A, O - Cp U ? B - Cp

m/e % Rel

abundance

m/e % Rel

abundance

46 11 527 11 549 12

47 10 528 10 550 11

48 100 529 100 551 100

49 7 530 7 552 8

50 7 531 5 553 7


Cp cyclopentadiene; U one repeat unit

Table 7 MALDI MS results for the mass range of 10,000–

150,000 Da for the product of titanocene dichloride and dienestrol

m/e (Possible) assignment

10,823 24U ? Cp2TiO

11,568 26U ? A - Cp

15,692 35U ? Cp2TiO

17,068 39U - Cp2Ti

22,219 50U ? A - OMe

28,863 65U ? Cp2Ti

38,381 87U - OPh

48,138 109U - OPh

49,569 112U ? O

56,959 129U - O

67,201 152U - Cp ? O

88,777 201U - A

116,850 264U ? A - Cp

141,309 319U ? Cp2TiO

11,172 25U ? B - Cp

13,070 30U - Cp2TiO

16,750 38U - Cp

21,940 50U - Cp2Ti

28,310 64U

32,027 72U ? Cp2Ti

44,590 101U - OPh

49,238 111U - A

56,009 127U - Cp2Ti

59,220 134U - Cp

84,377 191U - 2Cp ? O

94,899 214U ? D - O

130,742 296U - Cp2TiO

142,044 321U


U unit and prefixes denote the number of units so that 321U is 321

units, Ph phenyl, Cp cyclopentadiene, Me methyl


123

N H

N ON

NH NH

O

Sn C H 3

C H 3

R

R

(10)

There were four major mass fragment clusters with the

initial significant ion fragment cluster occurring about

565 Da. An expanded view of this ion fragment cluster is

given in Fig. 12.

This ion fragment cluster is tentatively assigned as

being associated with the structure given in 11; that is,

two organotin moieties connected to one 4,6-diamino-1-

nitrosopyrimidine.

N H

N O N

NH

SnH

CH 3

CH 3

NH

O

SnH C H 3

C H 3

(11)

This structure was modeled (Fig. 13) using a modeling

program that allowed the relative ion fragment intensities

to be calculated from the assigned structure (Matt Monroe;

jjor.chem.unc.edu). The calculated values are in reasonable

agreement with the ion fragment cluster about 565 Da and

are consistent with the assignment.

8.0964.9160.845ssaM ( z/m )

0

01

02

03

04

05

06

07

08

09

001

% In

ten

sity

V 1 ,3.816 = PB[1# cepS regayo 3

6603.816

6023.636

8303.716

7223.836

3413.916 7103.656

9813.5364413.0669672.565

5892.1260022.465 9192.226 3203.556

9412.845 5582.316 1582.1669803.3266682.0062803.665 7852.056

8073.106 6062.0863168.5267351.945 1023.3072622.1560132.575 0292.7273486.695 0623.3767107.845 5774.696

Fig. 11 MALDI MS for the

product of dibutyltin dichloride

and 4,6-diamino-1-nitroso-

pyrimidine

559.4556.0 562.8 566.2 569.6 573.0

Mass (m/z)

0

4608.2

0

10

20

30

40

50

60

70

80

90

100

% In

ten

sity

]29231 ,3.816 = PB[1# cepS regayoV9672.565

8882.365

0022.465

4303.4650482.165

2803.6655452.265

1092.965

2603.9551903.7552690.165 1302.8656205.6654933.655 4197.755 9580.565 3221.1754272.065 9900.8654834.655 0040.0757943.855 3960.6654206.465 6546.1759025.3658586.065 0178.165

7625.755 8296.855 0988.965

Fig. 12 Expanded view of the ion fragment cluster appearing at about 565 Da


123

The next major ion fragment cluster occurred at about

618 Da. An expanded view of this cluster is given in Fig. 14.

Its suggested structure is given in 12 and is the product

from reaction with the 2,5-dihydroxybenzoic acid matrix.

O O

OH

O

SnH

SnH

CH 3 CH 3

C H 3

C H 3

(12)

The corresponding model calculation is visually shown

in Fig. 15.

There is reasonable agreement between the model and

suggested structure.

As with other organotin polymers, there is a tendency to

react with the matrix at low masses (below 1,000 Da) where

the organotin moiety has broken free from the chain react-

ing with the matrix. This tendency is particularly found for

2,5-dihydroxybenzoic acid, the matrix material employed in

the current study. Thus, the ion fragment cluster centering

about 618 Da is then tentatively assigned the structure of two

dibutyltin moieties with one unit derived from the matrix

material 2,5-dihydroxybenzoic acid.

Other ion fragments are also associated with the matrix

material. These will be omitted because they only show the

presence of the organotin moiety. It is not surprising that

such ion fragments are formed since the organotin moiety

is reported to be particularly sensitive to degradation in the

presence of UV radiation and the particular MALDI MS

employed uses a UV source as the laser light source.

Further, 2,5-dihydroxybenzoic acid contains a carboxylic

acid group that is known to be active in condensations with

organotin units as well as the presence of two alcohol

groups that can also react with the organotin unit.


636 Da. The tentative structure assigned to this ion frag-

ment cluster 13 consists of two dibutyltin moieties con-

nected to one 4,6-diamino-1-nitrosopyrimidine unit with an

550.00 560.00 570.00 580.000.0

20.0

40.0

60.0

80.0

100.0

Fig. 13 Calculated ion fragment cluster from the proposed structure

containing one 4,6-diamino-1-nitrosopyrimidine unit and two dibu-

tyltin units, as pictured above, 11

0.7268.3266.0264.7162.4160.116 ssaM ( z/m )

0

1.3E+4

0

10

20

30

40

50

60

70

80

90

100

% In

ten

sity

]29231 ,3.816 = PB[1# cepS regayoV6603.816

6692.6168303.716 0903.026

3413.916

1213.5162882.416

5892.1269192.226 8803.426

5582.3167992.216 4356.816 9803.326

9824.4264599.616 0699.816 4099.1263656.026 3168.5262252.116 1300.5162785.216 6700.3266275.316 0749.716 4157.4265565.9162897.116

Fig. 14 Expanded MALDI MS for the ion fragment cluster occurring at about 618 Da

600.00 610.00 620.00 630.000.0

20.0

40.0

60.0

80.0

100.0

Fig. 15 Model of the structure given above in 12


123

additional NH2 group connected to one of the tin atoms.

The expanded MALDI MS for this is given in Fig. 16.

N H

N NH

NH

O

N O

Sn

SnH

CH 3

C H 3

C H 3

CH 3

NH 2

(13)

The calculated model for the tentatively assigned ion

fragment cluster formed from 13 is given in Fig. 17.


753 Da. Its expanded spectrum is given in Fig. 18.

The tentative structural assignment and modeling results

follow. Reasonable agreement exists between the observed

ion fragment cluster and the modeling results, Fig. 19. The

assigned structure is composed of two units, 14. The

sodium ion is derived from the matrix solvent.

N H

NH NH

Sn

SnH

NH

N

N H 2

O N

O N

O

O

CH 3

C H 3

C H 3

CH 3

Na +

(14)

From our investigation of a number of organotin poly-

amines, we determined that bond breakage occurred at the

hetero atom sites as pictured in 15. In fact, this preferred

hetero atom breakage was common for all of the polymers

studied.

N H

NH NH

Sn

Sn

NH

N

N H 2

O N

O N

O

O

CH 3

C H 3

C H 3

CH 3NH

N H

N H 2

O N

O

(15)

0.8466.3462.9368.4364.0360.626

Mass (m/z)

0

9.7E+3

0

10

20

30

40

50

60

70

80

90

100

% In

ten

sity

]29231 ,3.816 = PB[1# cepS regayoV6023.636

7223.8366513.436

9813.536 8403.0468113.736

7613.336 0482.2462013.936

7392.0365132.726

9082.4466923.626 4184.4360196.826 7190.936 7223.6460890.036 3667.3464790.1467778.3364595.1362173.726 3226.636 7594.6466379.8363278.436

Fig. 16 Expanded MALDI MS spectrum for the ion fragment cluster occurring at about 636 Da

620.00 630.00 640.00 650.000.0

20.0

40.0

60.0

80.0

100.0

Fig. 17 Calculated ion fragment cluster created from the tentatively

assigned structure 13 containing two dibutyltin moieties connected to

a 4,6-diamino-1-nitrosopyrimidine and NH moiety


123

5 Summary

In summary, valuable structural information can be

obtained from materials in the solid state. Contributions to

the overall structure can be gained using MALDI MS and

solid state NMR. A beneficial detailed analysis of the

environment about a metal for appropriate metal atoms was

gained by using Mossbauer spectroscopy. Each technique

can provide important structural information concerning

potentially significant materials that is not easily gained by

using other methods to study poorly soluble or insoluble

compounds.

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0.4678.9576.5574.1572.7470.347

Mass (m/z)

0

2.8312

0

10

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40

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]29231 ,3.816 = PB[1# cepS regayoV

3062.357

9692.157

9982.557

1262.657 6161.8573771.057

6969.0670583.9578264.947

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0897.2574176.7475089.447

Fig. 18 Expanded MALDI MS for the ion fragment cluster assigned to structure 14 occurring at about 753 Da

740.00 750.00 760.00 770.000.0

20.0

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Fig. 19 Calculated ion fragment cluster created from the tentatively

assigned structure containing two dibutyltin moieties connected to

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units


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123

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