313.2 355.2457.3+MS, 30.9min #3019 02465x10Intens. 50 100 150 200 250 300 350 400 450 m/z 43.1 55.073.0 85.0 97.0114.0 131.0 143.0 153.0171.0 [600540]

43.1
55.173.1
85.1101.1
113.0
127.0
141.0 155.0
187.0213.2
229.2
313.2 355.2457.3+MS, 30.9min #3019
02465x10Intens.
50 100 150 200 250 300 350 400 450 m/z
43.1
55.073.0
85.0
97.0114.0
131.0
143.0
153.0171.0
186.1201.1213.2
229.1
244.1301.2
317.1457.3+MS, 32.1min #3164
01235x10Intens.
50 100 150 200 250 300 350 400 450 m/zResults and discussion
The recorded EI-MSspectra, along with thestructures ofanalyzed compounds, aregiven inFig.1a-1d.As
expected from literature, themolecular peak isextremely faint (sometimes itcanbeeven absent), andthemolecular
mass can bededuced from the[M-15]+peak which results from losing one methyl group from one ofthetwo
isopropylidene moieties, giving exceptionally stable carboxonium ions.Thus, thispeak canbefound atm/z429(octyl)
or457(decyl) forboth glucose andsorbose derivatives .Another feature easily spotted inthecase ofboth glucose
derivatives isthem/z101 peak, usually thebase peak fordiisopropylidenated mannofuranose, galactofuranose or
glucofuranose structures, resulting from thefavorable breaking ofC4/C5bond [1,2].
However, thebase peak foralltheanalyzed spectra appears tobeateither m/z185or213.Such high peak
intensity must involve theformation ofawellstabilized cation, andtheobvious candidate would bethebreaking ofthe
lateral chain close tothesugar unit, without retention oftheconnecting oxygen inthelinear cation formed .Still, only a
simple breaking could notaccount forthehigh peak intensity experimentally observed, thus thehypothesis ofa
neighboring group participation (NGP), orananchimeric assistance, wasproposed, which would imply theparticipation
oftheincluded ether oxygen atom andtheformation ofarelatively stable fivemember ring.Theproposed mechanism
isgiven inFig.2.
Tofurther verify ourassumption, wehave performed quantum chemical calculations using semi -empirical
methods ontheresulting cations, using forourstudy both theopen (linear) andthecyclic (anchimerically assisted)
forms .Thelowest energy states ofthelater correspond totheendo conformers withthelateral chain towards thenewly
formed fivemember ring, asillustrated inFig.3.
Thenewly formed dative bond isconfirmed byallcalculated parameters .First, theheat offormation dropped by
33kcal/mol forboth types ofcations, thus suggesting anincrease instability forthecyclic forms .Second, thedistance
between theformally charged carbon andtheether oxygen atom dropped toabout 1.47Å,similar tothelength ofa
usual C-Obond .Third, thecharges forthesame atoms dropped inintensity, asexpected when acharge transfer
occurs from donor toacceptor .Allthree parameters seem tobeindependent from thechain length .Allthese arguments
plead fortheformation ofanew C-Obond andalso ofarelatively stable fivemember cycle, namely tetrahydrofuran .
„Nanoscience in Chemistry, Physics, Biology and Mathematics”
–
NanoMathChem
2015
Cluj
, Romania, November 12
–
14, 2015
PM7 evidence of neighboring group participation in EI
–
MS fragmentation
of some long chain glycoderivatives
Mihai -Cosmin PASCARIU1,2,3, Mircea NICULESCU3,4, Nicolae DINC Ă5, Eugen ȘIȘU1, MihaiMEDELEANU4*
1“Victor Babeș” University of Medicine and Pharmacy of Timișoara, Faculty of Medicine, 2 Eftimie Murgu Sq., RO -300041, Timișoara , ROMANIA
2“Vasile Goldiș” Western University of Arad, Faculty of Pharmacy, 86 Liviu Rebreanu, RO -310045, Arad, ROMANIA
3“Chemeia Semper” Association, 6 Giuseppe Verdi, RO -300493, Timișoara, ROMANIA
4University Politehnica Timișoara, Faculty of Industrial Chemistry and Environmental Engineering, 6 Vasile Pârvan, 300223, Tim ișoara, ROMANIA
5“Aurel Vlaicu” University of Arad, “Faculty of Food Engineering, Tourism and Environmental Protection, 2 Elena Drăgoi, RO -31033 0, Arad, ROMANIA
* Corresponding author: mihai.medeleanu@upt.ro
Theelectron ionization mass spectra forsome long chain glycoderivatives were acquired inpositive ionmode .Some peaks withthem/zvalues connected tothelength ofthelateral chain show high
intensity, which could imply aneighboring group participation (NGP) inthedecomposition cations .Totestifsuch anintramolecular cyclization could befavored wehave performed PM7semi -empirical calculation
onthecorresponding ions, inboth cyclic (open) andacyclic (extended) variants .Both geometrical andenergetic parameters confirmed theformation ofacoordinative bond inthelateral chain between oneoxygen
atom (asdonor) andtheformally charged carbon atom (acceptor) .
Keywords : long chain glycoderivatives, computational chemistry, PM7 semi -empirical method, electron ionization mass spectrometry
Acknowledgement: This work was supported by the Romanian National Authority for Scientific Research (CNCS -UEFISCDI) through project PN -II-PCCA -2011-142.
References:
[1] Pascariu M.C., Șișu E., Ordodi V.L., Rusnac L.M. ,Spectral analysis of diisopropylidenated monosaccharides. Low energy EI -MS fragmentation study. Chem. Bull. “Politehnica” Univ. (Timișoara) , 2011 , 56(1), p. 6 -11.
[2] Rafailă M., Pascariu M.C., Gruia A., Penescu M., Purcarea V.L., Medeleanu M., Rusnac L.M., Davidescu C.M. (2013). GC -MS anal ysis of long chain mannofuranose derivatives as biocompatible surfactant precursors. Correlation between peak
intensities and stability of corresponding fragments. Farmacia (Bucharest) , 2013 ,61(1), p. 116 -126.
[3] Pascariu M.C., Sugar based surfactants (PhD thesis) , “Politehnica” Publishing House, Timișoara, 2011 .
[4] HyperChem™ Professional, Hypercube, Inc., 1115 NW 4th Street, Gainesville, Florida 32601, USA.
[5] J.J.P. Stewart ,Optimization of parameters for semiempirical methods VI: more modifications to the NDDO approximations and re -optimization of p arameters, J. Mol. Model. , 2013 , 19, p. 1-32, DOI: 10.1007/s00894 -012-1667 -x.Introduction
Four biocompatible and biodegradable surfactant precursors, based ondiisopropylidenated D-glucose and L-
sorbose andpossessing anoctyloxybutyl ordecyloxybutyl lateral chain, were analyzed using positive ionmode EI-MS.
Such compounds were expected togive similar spectra tothose oftheir parent sugar compounds, without along chain,
already described inacetal literature [1,2].However, thisgroup proved tohave asignificant effect ontheappearance of
themass spectra, anditslength could also beeasily confirmed from each spectrum using thebase peak .
Methods
The four compounds canbeobtained bybis-acetalation ofD-glucose/ L-sorbose with acetone inacidic media,
followed byeither 1,4-dibromobutane and1-octanol/ 1-decanol, ormesylated octyloxybutanol/decyloxybutanol, both of
these variants being conducted inalkaline organic media .Thesynthesis ofthese glycoderivatives was presented ina
previous work [3].The analyzed structures were drawn using HyperChem molecular modeling software [4]andwere
optimized with PM7semi -empirical method [5],with and without molecular mechanics pre-optimization .Force fields
used include MM+, AMBER 99,BIO+ (CHARMM 27)and OPLS, with their default parameters asimplemented in
HyperChem .The other computational parameters and also theconditions used intheGC-EI-MSanalyses are
thoroughly described inanother paper [2].
43.0
55.073.0
85.0101.0
113.0
127.0
141.0
155.0185.1
201.1
213.1285.1 327.2429.2+MS, 28.7min #2761
01234×10
50 100 150 200 250 300 350 400 450 m/z
43.0
55.073.0
85.0
91.097.0113.0
131.0
143.0
153.0171.0185.1
201.0
215.0229.0
244.1273.1
317.1429.2
439.0+MS, 29.6min #2873
0.00.51.01.52.02.54x10Intens.
50 100 150 200 250 300 350 400 450 m/z
Fig. 1a
Fig. 1b
Fig. 1c
Fig. 1d
Fig. 2Conclusions
Quantum chemical calculations successfully confirmed theanchimeric assistance proposed forexplaining thebase peak found in
EI-MSspectra ofthestudied glycoderivatives .This specific peak was also discovered having unusual high intensity (butnotnecessarily
being thebase peak) insimilar galactose, fructose andmannose derivatives, theresults pending publication infuture papers .
Fig. 3