1

Integrated Writing Guide

Abstract

The rate of hydrolysis of sucrose by

beta-fructofuranosidase from

Saccharomyces cerevisiae was measured by

polarimetry. Experiments were performed

at 300 K, 310 K, and 320 K. The enzyme

catalyzed activation energy was 29.2 ± 0.2

kJ/mol. The rate constant at 300 K was

found to be 0.065 ± 0.001 min-1

. The

activation energy was comparable to the

activation energy for beta-

fructofuranosidases isolated from plant

sources.

The abstract should be a concise (short) and

specific summary of the report that allows

readers to decide whether they want to read

the report. It should include purpose,

methods, scope, results, and conclusions. A

technical document is not a mystery novel.

Give a very brief version of your conclusions

right away and support them later. For more

information, see the ACS Style Guide1, pp.

21-22.

• purpose

• method

• numerical results with error limits and

correct units

• conclusion

• clear

• concise

• no major conceptual errors

• no grammar errors

1 The ACS Style Guide: Effective communication of

scientific information, 3rd

ed.; Coghill, A.M, Garson,

L.R., Eds.; Oxford University Press: New York,

2006.

2

Introduction

The introduction must accomplish two

objectives: it must give the purpose of the

report and acquaint the reader with the

experiment. This should set the background

and the context of your experiment.

Primarily, you will be trying to explain what

you were trying to do and why it is

significant. Describe what others have done

in this area and cite the relevant references.

Ask your instructor if you need help

searching for literature articles. The

introduction should also provide whatever

background theory or formulas the reader

needs to know to understand your paper.

You may have to define the terms used in

stating the subject and provide background

such as theory or history of the subject.

Much of this information will be in the lab

manual, but the instructor will usually

expect you to show your own

comprehension of the problem by describing

it in your own words. For more

information, see the ACS Style Guide, pp.

22-23.

Plants and yeasts use -D-

fructofuranosidases (EC 3.2.1.26) to catalyze

the hydrolysis of the disaccharide sucrose into

the two monosaccharides, fructose and

glucose. Because sucrose rotates plane-

polarized light to the right, while an equimolar

solution of glucose and fructose rotates plane-

polarized light to the left, -fructofuranosidase

is commonly called invertase. Similarly, the

mixture of glucose and fructose is called invert

sugar. Invertase is used in the confectionary

industry, because invert sugar is less prone

than sucrose to form grainy crystals.1

Invertases can be isolated from plants2 and

from yeasts.3 The kinetics of these enzymes

under various conditions are of interest because

they can be so used.4 Invertase activity in

fruits and vegetables contributes to spoilage in

stored food.4

The rate of reaction for the invertase-

catalyzed hydrolysis of sucrose can be

measured by following changes in optical

rotation of an aqueous solution of sucrose and

invertase. When sucrose is hydrolyzed to a

mixture of glucose and fructose, the optical

rotation changes from clockwise (+) to counter

clockwise (-).

• background

• at least 4 literature references to prior

work

• equations

• significance of topic

• purpose

• clear

• no major conceptual errors

• no grammar errors

3

The optical rotation is monitored with an optical polarimeter and then used to

calculate the amount of sucrose left unhydrolyzed. The angle of rotation is determined at

the beginning of the experiment (a0) and at equilibrium (aeq). The algebraic difference

(a0 - aeq ) is a measure of the original sucrose concentration. The concentration of water

during the reaction remains essentially constant, since it is present in large excess.

All equations should be given a reference

number, so that you may refer to them later

in the text. Center equations, and format

them neatly. Introduce all variables in the

text the first time you use them in an

equation, so that the reader can interpret the

equation correctly. If you need help editing

equations, ask your lab instructor for help.

For more information, see the ACS Style

Guide, pp. 218-222.

The reaction is known to be first order in

sucrose, so the concentration of sucrose as a

function of time follows the relationship

lnCt

C0= kt (1)

where C0 is the initial concentration of sucrose,

Ct is the sucrose concentration at time t after

the addition of invertase, and k is the first order

rate constant for the reaction. Since Ct is

proportional to (at - aeq) and C0 is proportional

to (a0 -aeq), wheret

a is defined as the rotation

angle at time t, equation 1 can be re-written as

follows:

• Numbered sequentially

• Properly formatted

• All variables introduced in text

• Grammar

Any figures used should be

labeled with a reference number

and a caption. The captions

should consist of complete

sentences, and give the reader

enough information to

understand the figure without

going back to the main body of

the text. Figures should be neatly

drawn and centered on the page.

If you need to draw chemical

structures your lab instructor will

help you find the necessary

software. For more information,

see the ACS Style Guide, p. 365

and pp. 375-383.

O

OHOH

OH

O

OH OH

OH OH

O

OH

OH

OH OH

O

OHOH

OHOH

OH

O

OH

invertase

+

Figure 1. Invertase catalyzes the hydrolysis of sucrose

into glucose and fructose. Sucrose has a positive specific

rotation ([ ]D = 66.5°), while the equimolar mixture of

glucose and fructose that results from hydrolysis has a

negative specific rotation ([ ]D = -22.0°) .

• Captions in complete

sentences

• Numbered sequentially

• Neat, centered

4

ktaa

aa

eq

eqt=

0

ln (2)

This implies that the rate constant k can be determined from a plot of ( )eqt

aaln versus

time. The rate constant k depends on the absolute temperature T according to the

Arrhenius Equation:

k = AeEaRT (3)

where Ea is the activation energy. Thus if the rate constant is determined at several

different temperatures, the activation energy can be determined via a modification of

equation (3) by plotting ln(k) versus 1/T.

lnk = lnAEaRT

(4)

Once the plot is constructed the slope can be used to calculate the activation energy as

follows.

Ea = -R•slope (5)

The data treatment consists of determining the rate constants for the invertase-catalyzed

hydrolysis of sucrose at three different temperatures followed by determining the

activation energy from an Arrhenius plot (ln(k) versus 1/T).

5

Methods and Materials

Start with a description of the chemicals you

used. Include the source, grade, and method

you used to purify them. If you used

chemicals as supplied without further

purification, say so. A diagram of

instrumentation used in the experiment can be

helpful. Be complete, accurate, and precise.

Do not give details that are common

knowledge in the field, but do provide

information of particular interest, such as the

brand name and model or a complicated

apparatus or unusual equipment (for example,

Oscilloscope – Tectronix Model 561B-CRO-

158, Serial #123456789).

For the experimental procedure, you

should use clear paragraph organization to

list all steps in the correct order. Be

complete. You should provide enough

information so that another researcher in

your field could use your description to

replicate the experiment. State what you

really did and what actually happened, not

what was supposed to happen or what the

textbook said. If you deviated from the

given procedure, describe the changes you

made and explain how the affected your

outcome. For more information, see the

ACS Style Guide, pp. 22-23.

Sucrose (Sigma-Aldrich, #47289) and

invertase (from baker’s yeast, Sigma-Aldrich,

#I9274) were used as received and all solutions

were made with distilled water. Optical rotation

was measured at a wavelength of 589 nm using a

digital polarimeter (Jasco, DIP-360) and a quartz

cell with a 10 cm path length. The concentration

of the sucrose solution used in each experiment

was 50 g/L. The invertase solution was prepared

in an acetate buffer with a pH of 5.0 at a

concentration of 0.04 g/L. Temperature was

controlled with a refrigerated circulating water

bath (VWR, 1140) connected to the polarimeter

cell. All solutions were placed in the

temperature bath prior to mixing for thermal

equilibration.

Experiments were conducted at 300K,

310K, and 320K using the same procedure.

First the polarimeter cell was filled with sucrose

solution (~10 mL) and the optical rotation was

measured producing a0. Next, 5 mL of sucrose

solution was removed and 5 mL of the invertase

solution was added. After the addition of

invertase the optical rotation was measured

every 5 minutes until the measured value

approached the equilibrium value (aeq). The

equilibrium optical rotation (aeq) was measured

at t = 60 minutes for each temperature.

• source and grade of chemicals

• chemical purification/sample prep

• make and model of instrument(s)

• diagram of apparatus if needed

• complete

• clear

• no grammar errors

• past tense narrative format (not a list)

6

Results

State your actual, not expected, results.

Although results are usually presented

quantitatively, you should always introduce

each block of information with simple, clear

language. Do not rely upon figures, graphs and

tables exclusively to convey essential

information. Merely supplying the equations

or diagrams and expecting the reader to

interpret them without guidance from you is

not sufficient. You should describe all

significant results in words, clearly and simply.

Refer to the raw data only to point out trends

and identify special features. For more

information, see the ACS Style Guide, pp. 23.

Figures 2 through 4 show the change in

ln(at - aeq) as a function of time for 300K,

310K, and 320K respectively. As described

above by Equation 2, the slope of the graph of

ln(at -aeq) versus time will be equal to the

negative of the rate constant. The rate

constants for each temperature are indicated in

each figure and will be used to determine the

activation energy for the catalyzed reaction via

an Arrhenius Plot. Errors in the rate constants

were determined by a linear regression using

Excel. The linearity of each graph is quite

good, R2 values greater than 0.99 in each case,

which confirms the reaction is first order with

respect to the sucrose concentration. Further,

as expected the rate constants increase with

increasing temperature.

• All results presented

• Results explained

On all graphs, label both axes

and include the units of any

physical quantity. If you

have fit a curve to the data,

state the equation and the

values for the parameters in

the caption. Also, scale the

axes so the data occupies the

entire graph; don’t crowd the

data into one corner or side of

the graph. For more

information, see the ACS

Style Guide, pp. 344-360.

• axis labeled and units

• regression equation(s)

• Scaling

Figure 2: The optical rotation of sucrose is graphed versus time for hydrolysis at 300K.

The data were fit to Eq. 2, resulting in k = 0.065 ± 0.001 min-1

.

7

Figure 3: The optical rotation of sucrose is graphed versus time for hydrolysis at

310K.The data were fit to Eq. 2, resulting in k = 0.095 ± 0.002 min-1

.

Figure 4: The optical rotation of sucrose is graphed versus time for hydrolysis at 320K.

The data were fit to Eq. 2, resulting in k = 0.135 ± 0.006 min-1

.

The data obtained from Figures 2 through 4 is shown in Table 1 along with the

calculated values lnk and 1/T. Errors in the calculated values were determined by using

the propagation equations shown in Appendix A. The data in Table 1 was used to

8

construct an Arrhenius Plot (lnk versus 1/T) and to determine the activation energy for

the reaction.

Tables should be labeled and

given a reference number.

All Tables should be labeled

with titles, such as “Table 1.

Mass of Chloride Samples”.

Tables should be neatly

formatted and centered on the

page. Rule of thumb: If there

are more than ten rows or

columns, consider moving the

table to an appendix. For

more information, see the

ACS Style Guide, pp. 369-

374.

Table 1: Rate Constant Data For Different Temperatures

T ± error

(K)

k ± error

(min-1) lnk± error 1/T •10

-3± error

(K-1

)

300 ± 1 0.065 ± 0.001 -2.73 ± 0.02 3.33 ± 0.01

310 ± 1 0.095 ± 0.002 -2.35 ± 0.02 3.22 ± 0.01

320 ± 1 0.135 ± 0.006 -2.00 ± 0.04 3.13 ± 0.01

• Titled

• Proper units

• Error values

• Numbered

sequentially

• Neat, centered

9

Figure 5 shows the Arrhenius Plot obtained from the data in Table 1. As described in the

introduction the activation energy can be determined from the slope of a plot of lnk

versus 1/T via Equations 4 and 5.

Figure 5: Arrhenius plot for the hydrolysis of sucrose resulted in an activation energy of

29.3±0.2 kJ/mol.

10

Discussion

This section is the single most important part

of your report. Here, you have the opportunity

to of show that you understand the experiment

beyond the simple level of completing it. You

must explain, analyze, and interpret your

results. Be especially careful to account for

any errors or problems. You must not only

report the proper information, but also provide

evidence that you understand the material that

you are presenting.

The underlying question for this section is

“What is the significance of the results?” More

particularly focus your attention on questions

like these:

• What results were expected? What

results were obtained? If there are

any discrepancies, how can you

account for them?

• Do any of your results have particular

technical or theoretical interest?

• How do your results relate to your

experimental objective(s)?

• How do your results compare to those

obtained in similar investigations?

• What are the strengths and limitations

of your experimental design?

• If you encountered difficulties in the

experiment, what were their sources?

How might they be avoided in future

experiments?

For more information, see the ACS Style

Guide, p. 23.

As shown in Figure 5 the activation

energy for the invertase-catalyzed hydrolysis

of sucrose is 29.2 +/- 0.2 kJ/mol. This value is

a measure of the energy barrier that the

reactants (sucrose, water, and invertase) must

overcome before products can be formed. The

uncertainty in the activation energy was

determined by a linear regression using Excel.

It is important to note that the R2 value for the

Arrhenius Plot is 1, which indicates excellent

agreement with the Arrhenius equation. In

addition, since a linear regression of the data

was used to determine the uncertainty in the

activation energy the value obtained is quite

small and may underestimate the error in the

experiment. A significant source of error was

temperature drift in the water bath, which was

approximately 1 °C.

The rate constants for the hydrolysis of

sucrose are summarized in Table 2.

Table 2: Rate Constants

The activation energy as determined from

the slope of the plot in Figure 5 is: Ea = 29.2

+/- 0.2 kJ/mol. Reference (1) gives a value of

31.4 kJ/mole for the value of Ea and thus the

actual error in our measured Ea value is [(31.4

– 29.2)/31.4]x100% = 7 %. However, the

actual value of 31.4 kJ/mol does not fall within

the uncertainty of our reported value, 29.2 +/-

0.2 kJ/mol. The fortuitous good fit exhibited in

the Arrhenius Plot led to underestimation of

the error in the experiment.

Temperature

(K)

Rate Constant

(min-1

)

300 0.065 ± 0.001

310 0.095 ± 0.002

320 0.135 ± 0.006

• sources of error

• clear

• concise

• no major conceptual errors

• no grammar errors

• comparison of literature value

• future work suggested

Note on combining sections:

The results and discussion sections can be combined in various ways.

Use whatever combination is most appropriate for your situation.

11

Conclusion

Draw conclusions from the results and

discussion that answer the question, ”So

what?” Then go on to explain your

conclusions. In this section, you may also

criticize the lab experiment and make

recommendations for improvement. For

more information, see the ACS Style Guide,

p. 23.

Repetition of the experiment over a wider

temperature range may lead to a better estimate

of the activation energy.

• significance of your result

• improvements suggested

• clear

• concise

• no major conceptual errors

• no grammar errors

12

References

In your references section, include only

those papers that you have read and cited in

your report. Be sure that the citation

numbers match those in your report, and use

a consistent format. It is useful to have a

journal article at hand so that you may

duplicate the format. Journals differ in their

format styles, so if you are unsure of which

one to use, ask your lab instructor. For more

information, see the ACS Style Guide, pp. 7-

8 and 287-339.

1. “New and modified invertases and their

applications.” In: Topics in Enzyme and

Fermentation Biotechnology, A. Wiseman,

Editor, Chapter 6, Wiley & Sons, New York

(1979), pp. 267–284.

2. Huang, Y. H.; Picha, D. H.; Johnson, C. E.;

J. Agric. Food Chem.; 1998; 46(8); 3158-3161.

3. Rubio, M.; Runco, R.; and Navarro, A.

Phytochemistry, Volume 61, Issue 6,

November 2002, pp 605-609 27.2536 kJ/mol

• Numbered as in report

• Correctly formatted

4. Picha, D. H.; Kilili, A. W.; Johnson, C. E.; J. Agric. Food Chem.; 1999; 47(12); pp.

4927-4931.

13

Appendix A: Error Propagation

Introduction

Appendices may include raw data, calculations,

graphs, and other quantitative materials that were

part of the experiment but not detailed in any of

the above sections. Refer to each appendix at

the appropriate point in your report. For

example, at the end of your results section, you

might have the note, “See Appendix A: Raw

Data Tables.”

The uncertainty in reading a is estimated to

be about ± 0.02˚ and is based on the

fluctuations in the readout of the digital

polarimeter. The uncertainty in the

temperature at which reaction rates were

measured is about ±1˚C and is based on the

observed temperature drift during each

experiment. Uncertainties in time

measurements were 4 seconds and were

estimated as the amount of time required to

record the rotation and time simultaneously.

The errors in (at – aeq) and ln(at – aeq) were

calculated by propagating the error from the

optical rotation using the equations shown in

below.

• raw data

• calculation spreadsheets

• error equations that you used

(A1) ( ) 2•=aeqat

(A2) ( )( )

eqt

aa

aaaa

eqt

eqt=

ln

(A3) Errors in the rate constants were determined from a linear regression

performed in Excel using ln(at - aeq) versus time data.

(A4) lnk =kk

(A5) 1/ T =T

T2

(A6) The error in the slope obtained from the Arrhenius plot was determined

from a linear regression performed in Excel using lnk versus 1/T data.

(A7) Ea = R• slope

14

Appendix B: Raw Data

Tables 1 through 3 give the values of t (the measured optical rotation), ( t - ), and

ln( t - ) measured as a function of reaction time.

Table B1: Optical Rotation as a Function of Time for the Hydrolysis of Sucrose at 300K

Time (min) error at (deg) error at – aeq (deg) error ln(at – aeq) error

0 0.07 22.52 0.02 26.02 0.03 3.259 0.001

5 0.07 14.54 0.02 18.04 0.03 2.893 0.002

10 0.07 10.51 0.02 14.01 0.03 2.640 0.002

15 0.07 6.52 0.02 10.02 0.03 2.305 0.003

20 0.07 3.41 0.02 6.91 0.03 1.933 0.004

25 0.07 1.53 0.02 5.03 0.03 1.615 0.006

30 0.07 0.51 0.02 4.01 0.03 1.389 0.007

35 0.07 -0.99 0.02 2.51 0.03 0.92 0.01

40 0.07 -1.72 0.02 1.78 0.03 0.58 0.02

45 0.07 -2.03 0.02 1.47 0.03 0.39 0.02

-3.5 0.02 0.00

Table B2: Optical Rotation as a Function of Time for the Hydrolysis of Sucrose at 310K

Time (min) error at (deg) error at - aeq (deg) error ln(at – aeq) error

0 0.07 22.00 0.02 25.50 0.03 3.239 0.001

5 0.07 11.97 0.02 15.47 0.03 2.739 0.002

10 0.07 5.95 0.02 9.45 0.03 2.246 0.003

15 0.07 3.00 0.02 6.50 0.03 1.872 0.005

20 0.07 0.25 0.02 3.75 0.03 1.322 0.008

25 0.07 -1.04 0.02 2.46 0.03 0.90 0.01

30 0.07 -2.12 0.02 1.38 0.03 0.32 0.02

-3.50 0.02 0.00

Table B3: Optical Rotation as a Function of Time for the Hydrolysis of Sucrose at 320K

Time (min) error at (deg) error at – aeq (deg) error ln(at – aeq) error

0 0.07 22.20 0.02 25.70 0.03 3.247 0.001

5 0.07 8.90 0.02 12.40 0.03 2.518 0.002

10 0.07 3.48 0.02 6.98 0.03 1.943 0.004

15 0.07 0.32 0.02 3.82 0.03 1.340 0.008

20 0.07 -1.92 0.02 1.58 0.03 0.46 0.02

-3.50 0.02 0.00